COOKING FUEL COMPOSITIONS AND USES THEREOF
The present invention provides useful cooking and/or heating fuel compositions which may be produced substantially from renewable resources, such as biomass, to provide green fuel compositions, methods, and systems. The fuel compositions include gases stored under pressure, liquids, and gels/gelled waxes. Gases and liquids can include dimethyl ether and one or more C2 or larger alcohols, or can include dimethyl ether and one or more C2 or larger hydrocarbons. Gels and gelled waxes can include dimethyl ether and/or one or more C1-4 alcohols and wax or a gel. Methods of making these fuel compositions, particularly from biomass-derived syngas, are also described. Various applications and methods of using the fuel compositions, such as portable cylinder fuels for camping, are disclosed. Additionally, principles of burner design for these fuel compositions are disclosed herein.
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This patent application is a continuation-in-part of and claims priority under 35 U.S.C. 120 to U.S. Ser. No. 13/655,450, filed Oct. 19, 2012, which it turn is a continuation of and claims priority under 35 U.S.C. 120 to U.S. Ser. No. 13/291,107, filed Nov. 8, 2011, which in turn claims priority under 35 U.S.C. 120 from U.S. Provisional Patent Application Nos. 61/410,965; 61/410,967; and 61/410,968, each filed Nov. 8, 2010, and the disclosures of which are hereby incorporated by reference herein for all purposes.
FIELD OF THE INVENTIONThis invention generally relates to the field of cooking fuel compositions, including compositions that include dimethyl ether, as well as apparatus to store and combust such fuel compositions.
BACKGROUND OF THE INVENTIONSynthesis gas (hereinafter referred to as syngas) is a mixture of hydrogen (H2) and carbon monoxide (CO). Syngas can be produced, in principle, from virtually any material containing carbon. Carbonaceous materials commonly include fossil resources such as natural gas, petroleum, coal, and lignite; and renewable resources such as lignocellulosic biomass and various carbon-rich waste materials. It is preferable to utilize a renewable resource to produce syngas because of the rising economic, environmental, and social costs associated with fossil resources.
Syngas is a platform intermediate in the chemical and biorefining industries and has a vast number of uses. Syngas can be converted into alkanes, olefins, oxygenates, and alcohols. These chemicals can be blended into, or used directly as, diesel fuel, gasoline, and other liquid fuels. Syngas can be converted to liquid fuels, for example, by methanol synthesis, mixed-alcohol synthesis, Fischer-Tropsch chemistry, and syngas fermentation to ethanol. Syngas can also be directly combusted to produce heat and power.
Syngas can also be converted to dimethyl ether (DME), either directly from syngas or through a methanol intermediate. DME is an oxygenated molecule (CH3—O—CH3) that is non-toxic, non-carcinogenic, non-corrosive, and clean-burning (little or no soot formation). The energy content of DME, on a weight basis, is over 40% higher than that of methanol. DME has a high cetane number (about 60) and is a known replacement for diesel fuel. In addition to its uses as a fuel, DME can also be used as a propellant.
The market for DME fuels has been slow to develop, particularly in the United States. There is no current infrastructure in place to deploy DME as a liquid-transportation fuel for vehicles. Additionally, pure DME is typically a vapor at ambient conditions, so DME fuel would need to be pressurized in a vehicle tank to provide a sufficient quantity of DME in a single fill. Pure DME needs to be under about 5 bar pressure to be liquefied at room temperature.
On the other hand, there is an existing market for distributing and utilizing cylinder fuels for residential use, such as for cooking and heating; and for portable use, such as during camping, hiking, and the like. The rise in popularity of light-weight equipment for extended backpacking, and the increasing restrictions on campfires in wilderness areas, have made small cooking and heating devices popular. There is also a need for cooking and heating fuels in developing countries. Many of these countries have historically used biomass, but in several countries, supplies are growing scares, and this can contribute to soil erosion and the growth of deserts.
In view of the beneficial fuel properties of DME, while recognizing certain thermodynamic limitations of DME, what are needed are new fuel compositions that contain DME, methods of making the fuel compositions, methods of using the fuel compositions, apparatus for making and using the fuel compositions, and systems relating to the foregoing. Preferably, these new fuel compositions are produced substantially from renewable resources, such as biomass, to provide green fuel compositions, methods, and systems.
SUMMARY OF THE INVENTIONIn one embodiment, the present invention provides a fuel composition comprising dimethyl ether and a C2 or larger alcohol. For example, the alcohol may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, and/or tert-butanol.
In another embodiment, the invention provides a fuel composition comprising dimethyl ether and a C2 or larger hydrocarbon. For example, the hydrocarbon may be selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, and/or 1,3-butadiene.
In yet another embodiment, the invention also provides methods of producing a fuel composition. In one aspect of this embodiment, the method involves:
(a) converting a first amount of syngas into dimethyl ether;
(b) providing a C2 or larger alcohol, or mixture thereof;
(c) combining at least a portion of the dimethyl ether with the alcohol, thereby producing a fuel composition,
wherein the alcohol is in a concentration of at least 1 wt %.
In one aspect of this embodiment, the C2 or larger alcohol or mixture thereof is derived from either a) converting syngas to olefins, including predominantly C2-4 olefins, and hydrating the olefins to form a mixture of alcohols, or b) converting syngas to methanol, converting the methanol to olefins, and hydrating the olefins to form a mixture of alcohols. In this aspect, the entire fuel composition can be derived from syngas, and, accordingly, can be derived from local feedstocks. Such local feedstocks include, without limitation, one or more of wood and other sources of biomass, coal, natural gas, digester gas (a gas which is primarily methane (CH4) and carbon dioxide (CO2), and which is produced by the breakdown of organic matter, in the absence of oxygen, by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops), stranded gas, and/or municipal solid waste/refuse derived fuel.
In another aspect of this embodiment, the method involves:
(a) converting a first amount of syngas into dimethyl ether;
(b) providing a C2 or larger hydrocarbon or mixture thereof; and
(c) combining at least a portion of the dimethyl ether with the hydrocarbon, thereby producing a fuel composition,
wherein the dimethyl ether is in a concentration of at least 10 wt %.
In one aspect of this embodiment, the C2 or larger hydrocarbon or mixture thereof is derived from either a) converting syngas to olefins, including predominantly C2-4 olefins. In this aspect, the entire fuel composition can be derived from syngas, and, accordingly, can be derived from local feedstocks. Such local feedstocks include wood and other sources of biomass, coal, natural gas, digester gas, and/or municipal solid waste/refuse derived fuel.
In another embodiment, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing the mixture and an oxidant to a burner under suitable conditions for combustion of at least a portion of the mixture.
In one aspect of this embodiment, the C2 or larger alcohol or mixture thereof is derived from either a) converting syngas to olefins, including predominantly C2-4 olefins, and hydrating the olefins to form a mixture of alcohols, or b) converting syngas to methanol, converting the methanol to olefins, and hydrating the olefins to form a mixture of alcohols, or the C2 or larger hydrocarbon or mixture thereof is derived from either a) converting syngas to olefins, including predominantly C2-4 olefins. In this aspect, the entire fuel composition can be derived from syngas, and, accordingly, can be derived from local feedstocks. Such local feedstocks include wood and other sources of biomass, coal, natural gas, digester gas, and/or municipal solid waste/refuse derived fuel.
In one aspect of this embodiment, the method involves introducing the mixture and an oxidant to a catalyst surface under suitable conditions for catalytic, flameless oxidation of at least a portion of the mixture.
In another embodiment, the invention provides a method of using a mixture comprising (i) dimethyl ether, (ii) a hydrocarbon or alcohol having at least two carbon atoms, and (iii) water, the method comprising introducing the mixture and an oxidant to a fuel cell under suitable conditions for oxidation of at least a portion of the dimethyl ether and/or at least a portion of the hydrocarbon or alcohol, to generate electrical power.
In one aspect of this embodiment, the C2 or larger alcohol or mixture thereof is derived from either a) converting syngas to olefins, including predominantly C2-4 olefins, and hydrating the olefins to form a mixture of alcohols, or b) converting syngas to methanol, converting the methanol to olefins, and hydrating the olefins to form a mixture of alcohols.
In yet other embodiments, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing a primary fluid and the mixture, as a propellant for the primary fluid, to a container or chamber.
In certain embodiments, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing the mixture, as a refrigerant, to a refrigeration cycle.
The present invention also provides apparatus, systems, and kits. For example, in some embodiments, a system of the invention includes:
(a) a container adapted for containing a mixture comprising dimethyl ether, and a hydrocarbon or alcohol;
(b) a burner adapted for receiving the mixture from the container, and for receiving an oxidant, to oxidize at least a portion of the mixture, thereby generating heat and/or light; and
(c) a heating and/or lighting region for conveying the heat and/or light to a user.
In still further embodiments, wax, such as paraffin wax, is combined with one or more of dimethyl ether, methanol, ethanol, isopropanol, secondary butanol, and isobutanol, to form a waxy material to be used for cooking. The material can be placed, for example, into a container, optionally including a wick, so that it can be burned underneath a cooking implement, such as a chafing dish. The material can be formed, for example, by melting wax, preferably paraffin wax, ideally at a relatively high heat, which is then reduced to a relatively low heat once the wax has melted. To the molten wax is added dimethyl ether, a C1, C2, C3, and/or C4 alcohol, or any mixture thereof, in a ratio of between around 5 and 25 percent by volume.
In still further embodiments, a gelled-alcohol cooking fuel can be prepared. In one aspect of this embodiment, solid calcium carbonate is mixed with vinegar until no more carbon dioxide evolves, and the mixture is heated until around half of the water is evaporated. The mixture can then optionally be filtered to remove any excess calcium carbonate. Then, around 20-40% by volume of the original volume of vinegar of dimethyl ether, a C1, C2, C3, and/or C4 alcohol, or any mixture thereof, is added, with stirring. Upon cooling, the resulting gel can be used as a cooking fuel.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTIONThis description will enable one skilled in the art to make and use the invention, and it describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.
As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. As used herein, a “composition,” “blend,” or “mixture” are all intended to be used interchangeably.
Unless otherwise indicated, all numbers expressing parameters, conditions, concentrations, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending at least upon a specific analytical technique.
I. Fuel CompositionsSome aspects of the present invention are premised on the realization that DME fuels can be improved by the addition of certain other chemicals to the DME. The improvements may relate to the resulting chemical properties of the fuel blend, the economics of the selection of fuels in the blend, environmental benefits associated with the source of the fuels selected for the blend, or various consumer benefits associated with the blend.
In some variations, a fuel composition comprises dimethyl ether and a C2 or larger alcohol (“C2+ alcohol”), or mixture thereof. As intended herein, an “alcohol” means any hydrocarbon with at least one hydroxyl group bonded to a carbon atom. Alcohols include primary, secondary or tertiary alcohols, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl group. The C2+ alcohol may be linear, branched, cyclic, or aromatic, and may contain carbon-carbon double or triple bonds. As is known, the number of structural isomers increases significantly as the carbon number of the alcohol increases.
In some embodiments, the fuel composition comprises an alcohol selected from C2 to C12 alcohols, such as C2, C3, C4, C5, or C6 alcohols. For example, the alcohol may be selected from ethanol, 1-propanol (also known as n-propanol), 2-propanol (also known as isopropyl alcohol), 1-butanol (also known as n-butanol), 2-butanol (also known as sec-butanol), isobutanol, or tert-butanol.
The concentration of the alcohol may vary within the fuel composition. Generally speaking, the alcohol concentration may be selected to optimize one or more fuel properties, and/or for economic reasons. Fuel properties may relate, for example, to energy content (lower heating value or higher heating value), vapor pressure, boiling point, autoignition temperature, flash point, or gel point. Fuel properties for adjustment or optimization may also relate to solution thermodynamics, such as the ability to maintain a single phase wherein the alcohol and DME are co-solvents.
In some embodiments, the fuel composition comprises the C2+ alcohol in a concentration of at least 1 wt %, or at least 10 wt %, such as about 15, 20, 25, 30, 35, 40, or 45 wt %. In certain embodiments, the C2+ alcohol is present in a concentration of at least 50 wt %.
For example, a fuel composition may consist essentially of 50 wt % DME and 50 wt % isobutanol. As used herein, the phrase “consist essentially of” is intended to refer to fuel species present in the fuel composition, and excludes any additives. As another example, a fuel composition may consist essentially of 80 wt % DME and 20 wt % ethanol, or 35 wt % DME and 65 wt % 2-propanol.
Certain fuel compositions may include additional alcohols, which may be selected from any alcohols (including methanol). In some embodiments, the additional alcohol(s) are selected from methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol.
In some variations, a fuel composition comprises dimethyl ether and a C2 or larger hydrocarbon (“C2+ hydrocarbon”), such as a C2 to C10 hydrocarbon. As intended herein, a “hydrocarbon” means any organic molecule consisting of carbon and hydrogen. Hydrocarbons include saturated hydrocarbons (alkanes), which may be linear or branched; unsaturated hydrocarbons having one or more double bonds (alkenes, or olefins) or triple bonds (alkanes) between carbon atoms; cycloalkanes containing one or more carbon rings to which hydrogen atoms are attached; and aromatic hydrocarbons, also known as arenes, that have at least one aromatic ring. Depending primarily on the molecular weight, hydrocarbons can be gases, liquids, waxes, oligomers, or polymers.
In some embodiments, the fuel composition comprises ethane and/or ethylene. In some embodiments, the fuel composition comprises one or more C3 hydrocarbons selected from propane, propylene, propyne, or propadiene. In these or other embodiments, the fuel composition comprises one or more C4 hydrocarbons selected from n-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene.
In some embodiments, the fuel composition comprises a C5 to C10 hydrocarbon, such as n-pentane, cyclohexane, or isooctane. In certain embodiments, the fuel composition does not include C3 hydrocarbons, C4 hydrocarbons, or both C3 and C4 hydrocarbons. Some fuel compositions do not include liquefied petroleum gas.
The concentration of the hydrocarbon may vary within the fuel composition. Generally speaking, the hydrocarbon concentration may be selected to optimize one or more fuel properties, and/or for economic reasons. Fuel properties may relate, for example, to energy content (lower heating value or higher heating value), vapor pressure, boiling point, autoignition temperature, flash point, or gel point.
In some embodiments, the fuel composition comprises DME in a concentration of at least 10 wt %. DME may be present in a concentration of at least 20 wt %, such as about 25, 30, 35, 40, 45, 50 wt % or more, in various embodiments. In these or other embodiments, the fuel composition may include one or more hydrocarbons in a hydrocarbon concentration from about 10 wt % to about 80 wt %, such as about 20, 30, 40, 50, 60, or 70 wt %.
For example, a fuel composition may consist essentially of 50 wt % DME and 50 wt % isobutane. As another example, a fuel composition may consist essentially of 70 wt % DME and 30 wt % ethane, or 25 wt % DME and 75 wt % 1,3-butadiene.
Some embodiments include two, three, four, five, or more unique hydrocarbon species in a fuel mixture with DME. These additional hydrocarbons may be selected from methane, ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene, for example. When additional hydrocarbons are employed, the relative proportions of the hydrocarbons within the blend with DME may vary.
Certain embodiments provide a fuel composition comprising DME, a C2+ hydrocarbon, and a C2+ alcohol. The alcohol may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. When a fuel composition includes a hydrocarbon and an alcohol, each of the hydrocarbon and alcohol may be present (independently) in a concentration of at least 1 wt %, such as at least 10 wt %, along with DME and any other components that may be in the mixture.
Some fuel compositions of the invention further include water, either as unintentional moisture or as an intended concentration of water in the fuel mixture. In some embodiments, water is present in an amount from about 0.01 wt % to about 10 wt %, such as from about 0.1 wt % to about 1 wt %.
The fuel compositions of the invention may include any number of additional fuel components or fuel additives. For example, the fuel compositions may include various stabilizers, lubricants, and/or the additives. In preferred embodiments, the selected fuel composition with DME and either (or both) of C2+ alcohols or C2+ hydrocarbons is relatively stable without the need for an additional fuel stabilizer.
In some embodiments, the fuel composition further comprises at least one fuel additive to adjust the color or appearance of the mixture. For example, colorants or dyes may be added to the composition to impart a certain color, such as green or blue, to distinguish the fuel in the market.
In some embodiments, the fuel composition further comprises at least one fuel additive to adjust the scent or aroma of the mixture. For example, a pine fragrance oil or derivatives of pinene (e.g., catalytically oxidized pinene) may be utilized to impart a pine scent to the fuel compositions.
Additionally, various unintentional impurities may be present in any fuel compositions provided herein. Impurities include solids (e.g., dust and dirt particles, or metals), liquids (e.g., water, degradation products, or reaction products from fuel species), or vapors (e.g., air or carbon dioxide). These impurities may be introduced during the initial production of the mixture, or during storage, distribution, or consumer use.
II. Methods of Producing Components of the Fuel CompositionsMethods for producing the various components of the fuel compositions are described in detail below.
Syngas Production
Many of the processes described herein involve producing syngas. The method used to produce syngas is not particularly limited. Carbon-containing feedstocks may be converted to syngas by gasification, for example. Gasification requires an oxidant, commonly air, high-purity oxygen, steam, or some mixture of these gases. Common gasifier configurations include fixed-bed updraft, fixed-bed downdraft, bubbling fluidized bed, and circulating fluidized bed.
Syngas can also be produced by pyrolysis, devolatilization, steam reforming, and partial oxidation of one or more feedstocks recited herein. In some embodiments, syngas is produced according to methods described in Klepper et al., “Methods and apparatus for producing syngas,” U.S. patent application Ser. No. 12/166,167 (filed Jul. 1, 2008), the assignee of which is the same as the assignee of the present application. U.S. patent application Ser. No. 12/166,167 is incorporated by reference herein in its entirety.
The syngas may be produced from a wide range of feedstocks of various types, sizes, and moisture contents. “Biomass,” for the purposes of the present invention, is any material not derived from fossil resources and comprising at least carbon, hydrogen, and oxygen. Biomass includes, for example, plant and plant-derived material, vegetation, agricultural waste, forestry waste, wood waste, paper waste, animal-derived waste, poultry-derived waste, and municipal solid waste. Other exemplary feedstocks include cellulose, carbohydrates, biochar, and charcoal.
In various embodiments of the invention utilizing biomass to produce syngas, the biomass feedstock may include one or more materials selected from: timber harvesting residues, softwood chips, hardwood chips, tree branches, tree stumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover, wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus, animal manure, municipal garbage, municipal sewage, commercial waste, grape pumice, almond shells, pecan shells, coconut shells, coffee grounds, grass pellets, hay pellets, wood pellets, cardboard, paper, plastic, and cloth.
The syngas may alternatively, or additionally, be produced from carbon-containing feedstocks other than biomass, such as a fossil fuel (e.g., coal or petroleum coke), or any mixtures of biomass and fossil fuels. Any method, apparatus, or system described herein can be used with any carbonaceous feedstock. Also, various mixtures may be utilized, such as mixtures of biomass and coal.
Selection of a particular feedstock or mixture of feedstocks is not regarded as technically critical, but is carried out in a manner that tends to favor an economical process and business system, preferably including consideration of the net renewable carbon content in the resulting fuel compositions. In various embodiments of this invention, the fuel composition preferably includes at least 20%, more preferably at least 50%, such as 80%, 95%, or even more, renewable carbon content.
In some embodiments, syngas is produced or otherwise provided in a biorefinery. The syngas may be divided into a plurality of streams and fed to several unit operations. Biorefinery optimization may be carried out to adjust the splits to the different units, for economic reasons. At least a portion of the syngas, in the context of the present invention, is converted to liquid fuels.
The syngas may alternatively, or additionally, be provided by a third party for conversion into DME and optionally into hydrocarbons and/or alcohols. Syngas may be received from a third party via pipeline, portable tanks or cylinders, trucks, rail, or by any other known means of transporting syngas.
Variations of the present invention relate to methods of making certain fuel compositions. In some variations, a method of producing a fuel composition comprises: (a) converting a first amount of syngas (CO and H2) into DME; (b) providing a C2 or larger alcohol; (c) combining at least a portion of the DME with the alcohol, thereby producing a fuel composition with an alcohol in a concentration of at least 1 wt %, such as about 5, 10, 20, 30, 40, 50 wt % or higher.
The alcohol is a linear or branched C2 to C6 alcohol, in some embodiments, such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. Additional alcohols, including methanol, may further be included in the fuel composition.
Dimethyl Ether (DME) Production
Step (a) above produces DME from syngas. There are several methods known in the art to convert syngas to DME. One option is to employ a two-step process, wherein syngas is first converted to methanol, and then the methanol is dehydrated to DME (two moles of methanol convert to one mole of DME plus one mole of water). Typically, fixed-bed reactors are employed for the methanol synthesis and dehydration reactions, but other types reactors may be used. Catalysts for converting syngas to methanol are known, such as catalysts that include a mixture of copper, zinc oxide, and alumina. Catalysts for dehydrating methanol to DME include solid-acid catalysts, such as various forms of alumina and silica.
Another option for step (a) is to employ a one-step route, wherein syngas is directly converted, catalytically, into DME. A fixed-bed or slurry reactor may be employed, for example. Although there are potential cost and yield advantages with the one-step route, management of heat and recycle streams is regarded as more complex compared to the two-step route. Reference is made to Peng et al., “Single-Step Syngas-to-Dimethyl Ether Processes for Optimal Productivity, Minimal Emissions, and Natural Gas-Derived Syngas,” Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999, incorporated by reference for its teachings regarding syngas conversion to DME.
The specific source of syngas, including the feedstock type and the syngas-generation method (discussed below), may influence the selection of the DME production method. For direct synthesis, it may be desirable for the syngas to have a H2/CO ratio of about 1. In a two-step route through methanol, syngas with a H2/CO ratio of about 2 is generally preferred, for stoichiometric conversion of syngas to methanol.
Methods of Forming Alcohols
Step (b) which provides an alcohol may include receiving some or all of the alcohol for use in the method. That is, an alcohol may be purchased or otherwise acquired (e.g., in a trade) by the person or entity carrying out the method of making the fuel composition.
In other embodiments, step (b) includes converting a second amount of syngas into an alcohol. The syngas to produce the alcohol may be from the same source of syngas as that used to produce the DME, or it may be from a different feedstock within the same plant, or from a different source or location.
Step (b) may provide an alcohol via catalytic conversion of the second amount of syngas into an alcohol. For example, an alcohol-synthesis catalyst can be employed to produce mixed alcohols, such as C2 to C5 alcohols, from syngas. Suitable catalysts may include, but are not limited to, those disclosed in co-pending and commonly assigned U.S. patent application Ser. No. 12/166,167. Exemplary catalysts for syngas conversion to alcohols include Co, Mo, Cu, Zn, Rh, Ti, Fe, Ir, ZnO/Cr2O3, Cu/ZnO, CuO/CoO, Co/S, Mo/S, Co/Mo/S, Ni/S, Ni/Mo/S, Ni/Co/Mo/S, Rh/Ti, Rh/Mn, Rh/Ti/Fe/Ir, and mixtures thereof. The addition of basic promoters (e.g., K, Li, Na, Rb, Cs, and Fr) increases the activity and selectivity of some of these catalysts for C2+ alcohols.
Alternatively, or additionally, step (b) may include biological conversion of syngas into an alcohol, preferably a C2 to C4 alcohol, by syngas fermentation with a suitable microorganism. Bioconversion of CO or H2/CO2 to ethanol or butanol is well known. For example, syngas biochemical pathways and energetics of such bioconversions are summarized by Das and Ljungdahl, “Electron Transport System in Acetogens” and by Drake and Kusel, “Diverse Physiologic Potential of Acetogens,” appearing respectively as Chapters 14 and 13 of Biochemistry and Physiology of Anaerobic Bacteria, L. G. Ljungdahl eds., Springer (2003).
Any suitable microorganisms may be utilized that have the ability to convert CO, H2, or CO2, individually or in combination with each other or with other components that are typically present in syngas. Anaerobic bacteria, such as those from the genus Clostridium, have been demonstrated to produce ethanol from CO, H2, or CO2 via the acetyl CoA biochemical pathway. Generally speaking, microorganisms suitable for syngas fermentation to C2+ alcohols may be selected from genera including Clostridium, Moorella, Carboxydothermus, Acetogenium, Acetobacterium, Butyribacterium, Peptostreptococcus, and Geobacter. Microorganism species suitable for syngas fermentation may be selected from Clostridium ljungdahli, Clostridium autoethanogenum, Clostridium ragsdalei, Clostridium carboxidivorans, Butyribacterium methylotrophicum, Eurobacterium limosum, and genetically engineered, mutated, or evolved variations thereof.
In preferred embodiments, the first amount of syngas (for making the DME) is generated from a biomass feedstock. In some embodiments wherein the alcohol is produced from syngas conversion as part of the method, the second amount of syngas is also generated from a biomass feedstock. The first and second amounts of syngas are optionally generated from a common biomass feedstock at a single location, or at co-located manufacturing sites.
The resulting fuel composition preferably includes at least 20%, more preferably at least 50%, such as 80%, 95%, or even more, renewable carbon content. By “renewable carbon” it is meant that the carbon atoms in the fuel mixture are derived from a renewable feedstock, such as (but by no means limited to) lignocellulosic biomass.
In some embodiments, an alcohol is produced from one or more sugars contained in a biomass feedstock. Cellulosic biomass contains C5 sugars, such as xylose and arabinose, and C6 sugars, such as glucose, galactose, and mannose, which may be recovered from the biomass, such as by acid or enzymatic hydrolysis of the cellulose and hemicellulose chains, to form the sugar monomers. The C5 and C6 sugars may then be converted to alcohols by fermentation, using well-known techniques and microorganisms (including natural or modified bacteria or yeast).
When more than one alcohol is included in the fuel composition with DME, the different alcohols may be produced or provided from different techniques or sources. For example, a first alcohol could be ethanol produced from syngas fermentation while a second alcohol could be methanol produced from syngas catalytic conversion. Or, a first alcohol could be isobutanol provided by (and received from) a third party while a second alcohol could be ethanol produced from glucose fermentation, the glucose being derived from the same type of feedstock as that used to generate the syngas for DME synthesis.
In other variations of the invention, a method of producing a fuel composition comprises: (a) converting a first amount of syngas into DME; (b) providing a C2 or larger hydrocarbon; and (c) combining at least a portion of the DME with the hydrocarbon, thereby producing a fuel composition with DME in a concentration of at least 10 wt %, such as about 15, 20, 30, 40, 50 wt % or higher. In some embodiments, the concentration of the hydrocarbon is from about 10 wt % to about 80 wt %, such as about 15, 20, 30, 40, or 50 wt %.
The hydrocarbon is a C2 to C4 hydrocarbon, in some embodiments, such as ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene. Additional hydrocarbons, including methane, may further be included in the fuel composition. In some embodiments, the hydrocarbon is a C5 to C10 hydrocarbon, such as n-pentane, cyclohexane, or isooctane. An additional hydrocarbon, including methane, may further be included.
Step (b) which provides a hydrocarbon may include receiving some or all of the hydrocarbon for use in the method. That is, a hydrocarbon may be purchased or otherwise acquired (e.g., in a trade) by the person or entity carrying out the method of making the fuel composition.
In other embodiments, step (b) includes converting a second amount of syngas into a C2+ hydrocarbon. The syngas to produce the hydrocarbon may be from the same source of syngas as that used to produce the DME, or it may be from a different feedstock within the same plant, or from a different source or location.
Step (b) may include catalytic conversion of the second amount of syngas into a hydrocarbon. For example, the well-known Fischer-Tropsch process can be employed to produce hydrocarbons, such as C5+ hydrocarbons, from syngas. Catalysts known to be active for Fischer-Tropsch chemistry include, but are not limited to, cobalt, iron, nickel, and ruthenium. In addition to the active metal, these catalysts typically contain a number of promoters, such as potassium and/or copper. Fischer-Tropsch catalysts are usually supported on high-surface-area supports such as silica, alumina, or zeolites.
When branched C4 hydrocarbons are specifically desired, syngas may be converted into isobutane and/or isobutylene by isosynthesis of syngas. The isosynthesis reactions can convert syngas to isobutane and isobutylene under relatively extreme reaction conditions, using a thorium-based or zirconium-based catalyst, for example. Isosynthesis is selective to iso-C4 hydrocarbons and only trace amounts of oxygenates are typically formed. The specific catalyst and conditions may be selected to adjust the ratio of isobutane to isobutylene. Various promoters may improve the activity and selectivity.
In preferred embodiments, the first amount of syngas (for making the DME) is generated from a biomass feedstock. In some embodiments wherein the hydrocarbon is produced from syngas conversion as part of the method, the second amount of syngas is also generated from a biomass feedstock. The first and second amounts of syngas are optionally generated from a common biomass feedstock at a single location, or at co-located manufacturing sites.
In some embodiments, a C2 to C10 hydrocarbon is produced from one or more sugars contained in a biomass feedstock. Cellulosic biomass contains C5 sugars, such as xylose and arabinose, and C6 sugars, such as glucose, galactose, and mannose, which may be recovered from the biomass, such as by acid or enzymatic hydrolysis of the cellulose and hemicellulose chains, to form the sugar monomers. The C5 and C6 sugars may then be converted to hydrocarbons by known catalytic techniques, including catalytic hydrotreating and catalytic condensation processes, such as base-catalyzed condensation, acid-catalyzed dehydration, and alkylation reactions.
When more than one hydrocarbon is included in the fuel composition with DME, the different hydrocarbons may be produced or provided from different techniques or sources. For example, a first hydrocarbon could be n-hexane produced from catalytic conversion of syngas while a second hydrocarbon could be methane produced from biomass gasification. Or, a first hydrocarbon could be isobutane produced from syngas isosynthesis while a second hydrocarbon could be propane provided by (and received from) a third party.
In these methods, step (c) may include calculating and optionally adjusting, by varying the fuel composition, one or more properties selected from lower heating value, higher heating value, vapor pressure, boiling point, autoignition temperature, flash point, or gel point.
Formation of Olefins Via Fischer-Tropsch Olefin Synthesis, and Optional Olefin Hydration
In one embodiment, the olefins and/or paraffins used in the cooking fuel embodiments described above that include olefins and/or paraffins can be produced via Fischer-Tropsch Synthesis.
In another embodiment, the alcohols used in the cooking fuel embodiments can include alcohols derived from hydrating the olefins produced via Fischer-Tropsch Synthesis. These processes are discussed below.
However, in other embodiments, some or all of the olefins that can be hydrogenated to form the alcohols can be derived from sources other than Fischer-Tropsch Synthesis (i.e., they can be formed in hydrocracking reactors, isolated from crude oil distillation, and the like). That said, production of olefins via Fischer-Tropsch synthesis, and the production of alcohols from olefins via olefin hydration, is a preferred way to prepare the alcohol blends described herein. These processes are described in more detail below.
Fischer-Tropsch Synthesis
The use of Fischer-Tropsch synthesis to form relatively low molecular weight olefins is well known. A brief discussion of Fischer-Tropsch synthesis is provided below.
i. Synthesis Gas (Syngas) Production
It is known in the art to convert a variety of feedstocks, such as coal, methane, methanol, ethanol, glycerol, biomass such as corn stover, switchgrass, sugar cane bagasse, sawdust, and the like, black liquor, and lignin to synthesis gas (see, for example, [http://www.biocap.ca/files/biodiesel/dalai.pdf]). The water-gas-shift reaction plays an important role in the conversion of certain of these feedstocks to hydrogen via steam gasification and pyrolysis. Catalytic steam gasification can give high yields of syngas at relatively low temperatures.
Biomass can be converted to syngas using a variety of known methods, including thermal gasification, thermal pyrolysis and steam reforming, and/or hydrogasification, each of which can produce syngas yields of 70-75% or more.
The resulting syngas can be used in Fischer-Tropsch Synthesis. The syngas can be converted to a range of hydrocarbon products, collectively referred to as syncrude, via Fischer-Tropsch synthesis. Alternatively, low molecular weight olefins can be formed, which can be used directly in the glycerol ether synthesis. One advantage of the process described herein is that, unlike Fischer-Tropsch wax, which uses none of the oxygen in the syngas, the C2-4 alcohol-containing product stream includes oxygen atoms, thus improving the overall product yield. Another advantage is that, unlike the known processes for producing fuel products by hydrocracking Fischer-Tropsch wax, the instant process does not require a hydrocracker, but rather, only a means for adding water across the double bond of the olefins produced during the Fischer-Tropsch synthesis. Thus, with higher product yields and lower capitalization costs, the process offers benefits over traditional Fischer-Tropsch synthesis.
ii. Fischer-Tropsch Chemistry
Fischer-Tropsch chemistry tends to provide a wide range of products, from methane and other light hydrocarbons, to heavy wax. Syntroleum (a term used to define hydrocarbons in the diesel range formed by Fischer-Tropsch synthesis) is typically formed from the wax/heavy fraction obtained during Fischer-Tropsch Synthesis using a cobalt catalyst, or other catalyst with high chain growth probabilities, followed by hydrocracking of the wax. Low molecular weight olefins are typically obtained from the light gas/naphtha heavy fraction obtained via Fischer-Tropsch chemistry using iron catalysts, or other catalysts with low chain growth probabilities. Because the desired alcohols are predominantly in the C2-4 range, production of C2-4 olefins is more desired than production of Fischer-Tropsch wax. Therefore, catalysts with low chain growth probabilities are preferred.
Syngas is converted to liquid hydrocarbons by contact with a Fischer-Tropsch catalyst under reactive conditions. Depending on the quality of the syngas, it may be desirable to purify the syngas prior to the Fischer-Tropsch reactor to remove carbon dioxide produced during the syngas reaction, and any sulfur compounds, if they have not already been removed. This can be accomplished by contacting the syngas with a mildly alkaline solution (e.g., aqueous potassium carbonate) in a packed column. This process can also be used to remove carbon dioxide from the product stream.
In general, Fischer-Tropsch catalysts contain a Group VIII transition metal on a metal oxide support. The catalyst may also contain a noble metal promoter(s) and/or crystalline molecular sieves. Pragmatically, the two transition metals that are most commonly used in commercial Fischer-Tropsch processes are cobalt or iron. Ruthenium is also an effective Fischer-Tropsch catalyst but is more expensive than cobalt or iron. Where a noble metal is used, platinum and palladium are generally preferred. Suitable metal oxide supports or matrices which can be used include alumina, titania, silica, magnesium oxide, silica-alumina, and the like, and mixtures thereof.
Although Fischer-Tropsch processes produce a hydrocarbon product having a wide range of molecular sizes, the selectivity of the process toward a given molecular size range as the primary product can be controlled to some extent by the particular catalyst used. When forming syntroleum, it is preferred to produce C20-50 paraffins as the primary product, and therefore, it is preferred to use a cobalt catalyst, although iron catalysts may also be used.
The Fischer-Tropsch reaction is typically conducted at temperatures between about 300° F. and 700° F. (149° C. to 371° C.), preferably, between about 400° F. and 550° F. (204° C. to 228° C.). The pressures are typically between about 10 and 500 psia (0.7 to 34 bars), preferably between about 30 and 300 psia (2 to 21 bars). The catalyst space velocities are typically between about from 100 and 10,000 cc/g/hr, preferably between about 300 and 3,000 cc/g/hr.
The reaction can be conducted in a variety of reactors for example, fixed bed reactors containing one or more catalyst beds, slurry reactors, fluidized bed reactors, or a combination of different type reactors. Fischer-Tropsch processes which employ particulate fluidized beds in slurry bubble column reactors are described in, for example, U.S. Pat. Nos. 5,348,982; 5,157,054; 5,252,613; 5,866,621; 5,811,468; and 5,382,748, the contents of which are hereby incorporated by reference.
Low molecular weight fractions can be obtained using conditions in which chain growth probabilities are relatively low to moderate, and the product of the reaction includes a relatively high proportion of low molecular weight (C2-8) olefins and a relatively low proportion of high molecular weight (C30+) waxes. The waxes can be used to form the alcohol/wax mixtures and/or dimethyl ether/wax mixtures described herein.
Optimized conditions for conducting Fischer-Tropsch Synthesis to produce predominantly C2-4 olefins are known to those of skill in the art.
Iron/Ammonia Catalysts in Fixed/Fluidized Beds
In commercial fixed-bed reaction vessels, it is believed that the space velocity cannot be increased much beyond 100 vol. per hour without overheating the catalyst, although this limitation tends not to apply to small-scale laboratory reactors. One representative set of Fischer-Tropsch conditions can be adapted from the laboratory conditions outlined below. These conditions are only one example of a set of suitable conditions, and are not intended to be limiting in any respect.
On a relatively small scale, catalyst beds and reaction conditions involving the use of a thick-walled steel tube, 10 mm internal diameter, with a catalyst capacity of 100 ml, embedded in an electrically heated aluminum block, 6 cm. in diameter, and a commercial, fused-iron, synthetic-ammonia catalyst crushed and screened to 7/14 B.S. Test Sieves, which is reduced before use at 450° C. for 24 hours in pure hydrogen at a space velocity of 2,000 per hour, can be employed.
Synthesis gas with an H2:CO ratio of 2:1, containing 5 percent inert constituents and not more than 0.1 g total sulfur per 100 m3 as raw material, can be used to maintain carbon monoxide conversion of about 95 percent. Increasing the pressure from 10 to 20 and from 20 to 25 atm can have a marked beneficial effect, as indicated by the reduction in temperature required to maintain conversion at a fixed space velocity and by the increase in space velocity permissible at fixed temperature without fall in conversion. The CO conversion can be maintained at about 95 percent at space velocities up to 1,000 vol. per vol. catalyst per hour. The average velocity over duration of the experiment (128 days of synthesis) was approximately 500 per hour, and the average CO conversion, 95 percent.
The reaction pressures can range from 10-25 atms. gauge, and the temperature can range from between about 208 and about 318° C., ideally between about 260 and about 300° C. The H2:CO ratio in the synthesis gas can ideally range from about 2.03:1 to about 2.31:1, and the synthesis gas space velocity, vol./vol. catalyst/hr, can range from about 366 to about 1050. The recycle ratio, vol. residual gas vol. syn. gas, can range from about 1.33 to about 7.1. The CO conversion, as a weight percent, can range from about 78.1 to about 99.5, with most results being around 90% or more. The percent conversion of CO to CO2, as a percent of the total, can range from nil to about 29 percent, though it is typically less than around 6%. The percentage of CO converted to CH4 can range from about 10-28%, though is typically less than about 11-15%. The percentage CO converted to higher hydrocarbons, as a percent of total, is typically in the range of from about 70 to about 80%.
At space velocities, vol/vol. catalyst/hr. of 1000, pressures of 20 atm gauge, and temperatures of 300-318° C., a fixed bed reactor may convert about 95% of the carbon monoxide to products, whereas a fluidized bed may convert around 99+ percent of the carbon monoxide. Methane can be produced in lower quantities in a fixed bed, relative to a fluidized bed. Both fixed and fluidized bed reactors tend to produce around 77 to around 80% higher hydrocarbons, of which around 56 and around 75% by weight are C2-4 hydrocarbons, respectively. The fractions in the 30-200° C. boiling point range are around 34 and 18%, and in the 200-300° C. boiling point range are around 6 and 4.5%, respectively.
Particularly good results may be obtained using residual gas recirculation. By repressing the formation of carbon dioxide by water-gas-shift reaction and increasing the H2:CO utilization ratio, one can increase the proportion of carbon monoxide converted to hydrocarbons higher than methane. The catalyst may deteriorate somewhat in activity over time, and need replacement or regeneration as appropriate.
Using these conditions, one can obtain a product stream where more than half the higher hydrocarbons produced are in the C2-4 range, with an average carbon number of around 3.3 and an olefin content of around 75 percent.
Thus, these conditions, or conditions similar to these, would theoretically result in a yield of 80% based on syngas of hydrocarbons greater than methane. Since more than half of the higher hydrocarbons would be in the C2-4 range, one would obtain yields of around 40% hydrocarbons in the C2-4 range and around 40% in the gasoline/diesel ranges, which could be separated before the olefin hydrolysis occurs. Of the roughly 40% product (olefins and alkanes) in the C2-4 range, about 75% (30% overall) will be olefinic. By hydrolyzing the about 30% yield of olefins to alcohols, the yield goes up to around 39% overall yield of alcohols (assuming a roughly C3 average molecular weight of the olefins).
If these yields are met, one can theoretically obtain a mixture of products from Fischer-Tropsch synthesis, by volume, roughly as follows:
Around 5% syngas or less and around 15% methane or less, both of which can theoretically be recycled and reused,
around 10% LPG (i.e., C2-4 alkanes), ideally isolated in an easier fashion than in conventional Fischer-Tropsch synthesis when the C2-4 olefins are hydrated to form alcohols which have significantly higher boiling point alcohols, and which are then easily separated from the C2-4 alkanes. The C2-4 alkanes can be used in those embodiments of the cooking fuel described above which include such alkanes and dimethyl ether, or used as a stand-alone fuel source for cooking
The boiling ranges and olefin contents of the liquid products obtained using this particular set of catalysts and reaction conditions are set forth below. The products were low-boiling and highly unsaturated, and did not change markedly in composition with change in reaction conditions.
Regardless of whether a fixed bed or fluidized bed is used, the amount of products boiling below 200° C. typically range from about 63 to about 76%, the amount of products boiling between 200 and 300° C. typically ranged from about 13 to about 19%, and the amount of products boiling above 300° C. typically range from about 10 to about 20%. The olefin content of the fraction boiling below 200 typically ranges from about 65 to about 75%.
Separation of Olefins from Paraffins
In one embodiment, the olefins and paraffins prepared as described above are used together to form components of the cooking fuels described herein. However, in other embodiments, it can be advantageous to separate olefins from paraffins. This can be performed, for example, by hydrating the olefins, as described elsewhere herein. This can also be performed, for example, by oligomerizing all or a portion of the olefins. The oligomers have significantly higher boiling points than the alcohols, so are easily separated by distillation. The paraffins can be isolated and combined with the other components described herein to form cooking fuels.
Direct Alcohol Synthesis from Fischer-Tropsch Synthesis
Previous efforts at producing alcohols higher than methanol or ethanol using syngas have been largely unsuccessful, due to catalyst instability and/or low syngas conversion. It is believed that no prior art has suggested higher alcohol compositions predominantly (i.e., greater than about 60%, and, more ideally, greater than about 80% by volume of the alcohols) in the C2-4 range, for use in flexible fuel vehicles or as fuel blends with gasoline. Further, these methods tend to produce linear rather than branched alcohols.
When iron catalysts are used at 10 or 20 atms pressure, appreciable amounts of alcohols can be produced. When a synthetic ammonia iron catalyst is used at relatively low temperatures (190° to 220° C.) with a high gas velocity, straight chain primary alcohols can comprise around 60 percent of the liquid products. These can be isolated and used to prepare alternative fuel compositions, alone or in combination with gasoline.
Those of skill in the art can also provide other suitable conditions for maximizing alcohol production directly from other catalysts. For example, molybdenum sulfide and other catalysts have been proposed for use in preparing higher alcohols, although with extremely poor syngas conversion and low catalyst lifetimes.
While this can advantageously provide alternative fuel compositions, the alcohols are primary alcohols, not secondary or tertiary alcohols, and may not be preferred due to their potential to oxidize and form corrosive and odiferous carboxylic acids.
Representative Reaction Conditions
In one embodiment, a fixed-bed reactor is used, and the catalyst is a commercial, fused-iron, synthetic-ammonia catalyst crushed and screened to 7/14 B.S. Test Sieves. Before use for synthesis, the catalyst can be reduced, for example, at 450° C., for a sufficient period of time, for example, for 24 hours, in a hydrogen atmosphere, ideally using pure hydrogen, at a space velocity of around 2,000 per hour. In one embodiment, the synthesis gas (H2:CO=2:1) includes no more than 5 percent by volume of inert constituents and relatively low sulfur concentrations, to avoid poisoning the catalyst.
The pressure, recirculation of residual gas, reaction temperature, and synthesis gas space velocity all have an effect on the product yield and distribution. Ideally, the temperature and other factors are adjusted to maintain a constant carbon monoxide conversion of greater than about 85%, ideally, greater than about 95 percent. The exact values for these factors will be expected to vary depending on the nature of the reactor, that is, the reactor size, cooling conditions, type of catalyst, and the like. Those of skill in the art will readily understand how to optimize the reaction conditions to achieve a desired product distribution.
At least one author has observed that an increase in pressure from 10 to 20 and from 20 to 25 atmospheres reduced the temperature required to maintain conversion at a fixed space velocity, or the increase in space velocity permissible at a fixed temperature, without fall in carbon monoxide conversion.
Ideally, residual gases are recirculated. By repressing the formation of carbon dioxide by water-gas-shift reaction, and increasing the H2:CO utilization ratio, one can increase the amount of carbon monoxide converted to hydrocarbons (higher than methane), ideally to greater than 65%, more ideally, greater than 75%, and even more ideally, to around 80 percent.
Using a temperature range between about 280 and 330 C, more than half the higher hydrocarbons produced were in the C2 to C4 range, with roughly 75% of the hydrocarbons being olefins.
The same Fischer-Tropsch catalysts can be used in fixed and fluidized beds. The synthesis gas used can be of a similar composition to that use in a fixed-bed, however, to minimize wax and carbon formation, the H2:CO ratio can be increased (i.e., to around 2.35:1). It may be desirable to use relatively high recycle ratios in order to maintain the catalyst in a fluid condition without using excessively high synthesis-gas rates.
It is believed that the catalyst is more active in the fluidized powder form than in the fixed bed. It is also believed that by using a high recycle ratio, one can eliminate or reduce carbon dioxide formation, and increase H2/CO utilization. One can obtain a higher proportion of C2-C4 hydrocarbons in a fluidized bed relative to a fixed bed.
When iron catalysts are used in the synthesis at 10 or 20 atmospheres pressure, appreciable amounts of alcohols can be produced. Thus, when a synthetic ammonia iron catalyst is used at relatively low temperatures (190° to 220° C.) and with a high gas velocity (Holroyd, R., “I.G. Farbenindustrie A.G., Leuna,” C.I.O.S. Report File No. XXXII, 107 and Reichl, E. H. (U.S. Naval Technical Mission in Europe), “The synthesis of Hydrocarbons and Chemicals from CO and Hydrocarbon: B.I.O.S. Miscellaneous Report No. 60, the contents of each of which are hereby incorporated by reference), straight chain primary alcohols constitute 60 percent of the liquid products.
When a synthetic ammonia iron catalyst is used at relatively high temperatures (280° to 330° C.), the alcohol content of the products is low, but the olefin content very high. The olefins can be hydrogenated using an acid catalyst, forming iso-alcohols rather than normal alcohols.
Olefin Hydration
Olefin hydration is well known. In one embodiment, the olefins are a mixture of olefins, in unpurified form, obtained by the cracking of crude oil, and in another embodiment, from Fischer-Tropsch synthesis. Since mixtures of alcohols are the desired end product, it is unnecessary to use pure olefins.
Any acid catalyst that is suitable for performing etherifications can be used, in any effective amount and any effective concentration. Examples of suitable acids include, but are not limited to, hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, and solid catalysts such as Dowex 50™. Strong acids are preferred catalysts. The most preferred acid catalyst is sulfuric acid.
The catalytic hydration of olefins to provide alcohols is a well-established art. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,162,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,849; and, 3,989,762, 4,214,107, and 4,499,313, the contents of each of which are hereby incorporated by reference.
Olefin hydration using zeolite catalysts is known. As disclosed in U.S. Pat. No. 4,214,107, lower olefins, in particular, propylene, are catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., HZSM-5 type zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product.
U.S. Pat. No. 4,499,313 discloses hydrating an olefin to the corresponding alcohol in the presence of hydrogen-type mordenite or hydrogen-type zeolite Y, each having a silica-alumina molar ratio of 20 to 500. The use of such a catalyst is said to result in higher yields of alcohol than olefin hydration processes which employ conventional solid acid catalysts. Use of the catalyst is also said to offer the advantage over ion-exchange type olefin hydration catalysts of not being restricted by the hydration temperature. Reaction conditions employed in the process include a temperature of from 50-300° C., preferably 100-250° C., a pressure of 5 to 200 kg/cm2 to maintain liquid phase or gas-liquid multi-phase conditions and a mole ratio of water to olefin of from 1 to 20. The reaction time can be 20 minutes to 20 hours when operating batchwise and the liquid hourly space velocity (LHSV) is usually 0.1 to 10 in the case of continuous operation.
European Patent Application 210,793 describes an olefin hydration process employing a medium pore zeolite as hydration catalyst. Specific catalysts mentioned are Theta-1, said to be preferred, ferrierite, ZSM-22, ZSM-23 and NU-10.
Dehydrogenation of the C2-4 Paraffin Fraction
In one embodiment, all or part of the C2-4 paraffins may be dehydrogenated to mono-olefins, and hydrated to form additional alcohols. All or part of the hydrogen thus produced can be recycled into the process, for example, to increase the hydrogen/carbon monoxide ratio in the syngas. A well-known dehydrogenation process is the UOP Pacol™ process. Syntroleum has demonstrated the feasibility of dehydrogenation of paraffins to mono-olefins. Thus, suitable dehydrogenation processes are well known and need not be described in more detail herein.
Forming Alcohols Via Hydroformylation
Alpha and internal-olefins can be hydroformylated, a process which adds a carbon monoxide to an olefin, and then reduces the resulting carbonyl to an alcohol. One representative process is known as the “OXO” process. The OXO process to make alcohols is described in detail in Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, Volume 1, pp. 903 8 (1991), the contents of which are hereby incorporated by reference. The first step generally follows the following equation:
R—CH═CH+CO/H2—→R—CH2-CH2—CH═O
The hydroformylation product can then be hydrogenated to form alcohols either in the step illustrated above, or in a second step, illustrated by the equation below:
R—CH2—CH2—CH═O+H2—→R—CH2—CH2—CH—OH
The OXO process is characterized mainly by a certain ratio of normal product to isomeric product and the pressure of the reaction. A conventional OXO process employs a Co-hydrocarbonyl catalyst at pressures from about 3000 psig to about 5000 psig, temperatures from about 110 to about 180° C., and a ratio of CO:H2 of about 1:1. The OXO process is a two-step process, wherein first the aldehyde is formed and separated, and second the aldehyde is hydrogenated to alcohols or oxidized to acids.
A process employed by Shell functions at around 400 psig and uses a cobalt catalyst liganded with a tributyl phosphine instead of one of the carbonyl ligands. This process typically requires a ratio of CO:H2 of around 1:2, and generates an alcohol product in a single step.
A commercially available process, licensed by Davy Process Technology, uses an Rh catalyst with a triphenyl phosphine ligand in a two-stage low-pressure process (about 300 psig) with 1:1 CO:H2. Both the Davy Process Technology and Shell processes produce products with high linearity, the ratio of linear product to branched product being at least about 10:1.
Another feature of the OXO process is that it converts alpha-olefins much more readily than internal olefins and occurs in an isomerizing atmosphere. Thus, even internal olefins are partially converted into linear alcohols. The Shell process converts 75% of feed internal olefins to primary alcohols, while Davy process reportedly converts even more. Although normally a synthesis gas without diluents is used, a synthesis gas from the Syntroleum ATR containing from about 10 to about 60% N2 can be used. Because hydroformulation adds a —COH group to an olefin, the lightest of the produced alcohols will boil higher than the heaviest of the contained olefins, thus making the separation relatively facile.
Also, in this embodiment, when using a predominantly C2-4 olefin feedstock, a predominantly C3-5 alcohol stream, such as a composition including between about 60 and about 90%, or consisting essentially of, C3-5 alcohols, can be obtained.
Following the OXO reaction, and distillation of alcohols away from paraffins, the alcohol blends can be used as described herein.
Direct Conversion of Syngas to Mixtures of Methanol and Ethanol
Syngas can be directly converted to a mixture of methanol and ethanol, which mixture tends to also include at least minor amounts of C3-4 alcohols. This mixture can be used in any of the embodiments described herein in which methanol, ethanol, or a mixture of alcohols including these alcohols can be used. Representative catalysts and conditions are described, for example, in U.S. Pat. No. 7,923,405.
The catalysts for converting syngas into products comprising at least one C1-C4 alcohol include cobalt and molybdenum, and often include sulfur. In some embodiments, at least some of the cobalt and some of the sulfur are present as a cobalt-sulfur association, and wherein the molar ratio of sulfur to cobalt (S:Co) in the association is at least 1.2, the molar ratio S:Co calculated after assigning some of the sulfur to molybdenum by assuming all molybdenum is present in the composition as MoS2.
In some embodiments, the molar ratio S:Co is at least 1.5, at least 2.0, or between about 2.0 and about 4.0. The molar ratio S:Co can be calculated after assigning some of the sulfur to molybdenum by assuming all molybdenum is present in the composition as MoS2, and after subtracting any elemental sulfur present. Optionally, S:Co can further be calculated after subtracting any sulfur that is soluble in 3 N HCl.
In some embodiments, the cobalt in the catalyst is present in an amount between about 3-21 wt %, such as about 10-16 wt %, of the composition. In some embodiments, the molybdenum is present in an amount between about 33-56 wt % of the composition. The molar ratio of the molybdenum to the cobalt can be from about 1.5 to about 8, such as about 2.
The sulfur can be present in a total amount of at least 40 wt % of the composition, such as about 42-44 wt %. The sulfur can include elemental sulfur in an amount of at least 100 ppm, such as about 150-5000 ppm or about 300-1000 ppm of the composition. In some embodiments, at least 0.02% or 0.05% of the sulfur is capable of leaching into chloroform at 55° C. In certain embodiments, between about 0.02% and about 0.1% of the sulfur is capable of leaching into chloroform at 55° C.
In some embodiments, less than about 8%, preferably less than 3%, of the cobalt is capable of leaching into a 3N HCl solution at 90° C. In certain embodiments, substantially no cobalt is capable of leaching into a 3N HCl solution at 90° C. In some embodiments, less than about 0.5%, preferably less than 0.3%, of the molybdenum is capable of leaching into a 3N HCl solution at 90° C. In certain embodiments, substantially no molybdenum is capable of leaching into a 3N HCl solution at 90° C.
The catalyst compositions, the compositions of the invention can further comprise one or more base promoters selected from the group consisting of potassium, rubidium, cesium, barium, strontium, scandium, yttrium, lanthanum, cerium, and any combinations thereof.
One exemplary catalyst composition for converting syngas into at least some ethanol, comprises 13-15 wt % total cobalt, 40-45 wt % total molybdenum, at least 40 wt % total sulfur, and an effective amount of a base promoter, wherein (i) the total sulfur includes between 250-750 ppm elemental sulfur; (ii) at least some of the total cobalt and some of the total sulfur are present as a cobalt-sulfur association having a molar ratio of sulfur to cobalt (S:Co) of at least 2.0, the molar ratio S:Co calculated assuming all molybdenum is present as MoS2, and after subtracting sulfur that is capable of leaching into chloroform or 3N HCl at 25° C.; (iii) less than about 3% of the total cobalt is capable of leaching into a 3N HCl solution at 90° C.; and (iv) less than about 0.5% of the total molybdenum is capable of leaching into a 3N HCl solution at 90° C.
The catalysts can be used in methods for converting syngas to alcohols. The methods involve
(a) providing a reactor;
(b) providing a catalyst as described above, or other suitable catalyst for direct syngas to alcohols conversions, which typically comprise cobalt, molybdenum, sulfur, and a base promoter, wherein at least some of the cobalt and some of the sulfur are present as a cobalt-sulfur association having a first molar ratio of sulfur to cobalt, calculated by assuming all molybdenum is present as MoS2;
(c) activating the first catalyst composition by contact with a stream comprising syngas, under suitable conditions for catalyst activation, thereby producing a second catalyst composition having a second molar ratio of sulfur to cobalt; and
(d) flowing syngas into the reactor at conditions effective to produce at least one C1-C4 alcohol,
wherein the second molar ratio of sulfur to cobalt is lower than the first molar ratio of sulfur to cobalt.
In some of these methods, the first molar ratio of sulfur to cobalt is at least 1.2. In some embodiments, the second molar ratio of sulfur to cobalt is 1.5 or less, such as 0.5 or less. In certain embodiments, the first molar ratio of sulfur to cobalt is at least 2 and the second molar ratio of sulfur to cobalt is 1.4 or less.
The activating step (c) can be performed within the reactor provided in step (a).
Additional sulfur, or a compound containing sulfur, can optionally be injected into the reactor in an amount that is sufficient to maintain at least some of the cobalt in a sulfided state, and is further sufficient to maintain the molybdenum in a completely sulfided state. The additional sulfur injected in step (c) of this fifth aspect can be contained in one or more compounds selected from the group consisting of elemental sulfur, hydrogen sulfide, dimethyl disulfide, methylthiol, ethylthiol, cysteine, cystine, methionine, potassium disulfide, cesium disulfide, and sodium disulfide.
In some embodiments, conditions effective for producing alcohols from syngas include a feed hydrogen/carbon monoxide molar ratio (H2/CO) from about 0.2-4.0, preferably about 0.5-2.0, and more preferably about 0.5-1.5. These ratios are indicative of certain embodiments and are not limiting. It is possible to operate at feed H2/CO ratios less than 0.2 as well as greater than 4, including 5, 10, or even higher. It is well-known that high H2/CO ratios can be obtained with extensive steam reforming and/or water-gas shift in operations prior to the syngas-to-alcohol reactor.
In embodiments wherein H2/CO ratios close to 1:1 are desired for alcohol synthesis, partial oxidation of the carbonaceous feedstock can be utilized. In the absence of other reactions, partial oxidation tends to produce H2/CO ratios close to unity, depending on the stoichiometry of the feedstock.
When, as in certain embodiments, relatively low H2/CO ratios are desired, the reverse water-gas shift reaction (H2+CO2→H2O+CO) can potentially be utilized to consume hydrogen and thus lower H2/CO. In some embodiments, CO2 produced during alcohol synthesis or elsewhere, can be recycled to the reformer to decrease the H2/CO ratio entering the alcohol-synthesis reactor. Other chemistry and separation approaches can be taken to adjust the H2/CO ratios prior to converting syngas to alcohols, as will be appreciated. For example, certain commercial membrane systems are known to be capable of selectively separating H2 from syngas, thereby lowering the H2/CO ratio.
In some embodiments, conditions effective for producing alcohols from syngas include reactor temperatures from about 200-400° C., preferably about 250-350° C.; and reactor pressures from about 20-500 atm, preferably about 50-200 atm or higher. Generally, productivity increases with increasing reactor pressure. Temperatures and pressures outside of these ranges can be employed.
Production of Alcohols by Converting Syngas to Methanol, Methanol to Olefins, and Olefins to Alcohols
In still further embodiments of the invention, the alcohols include predominantly ethanol and isopropanol, with some amounts of secondary butanol or isobutanol and lesser amounts of higher alcohols, are produced by converting syngas to methanol, converting the methanol to olefins, and, optionally after separating the olefins via distillation, converting one or more of the olefins to one or more alcohols. Representative conditions for syngas to methanol conversion are well known and need not be described here. Similarly, methanol to olefin synthesis is also well-known. Suitable catalysts and conditions are described, for example, in U.S. Pat. No. 8,354,563.
In some embodiments, the method comprises:
(a) converting syngas into methanol in the presence of a methanol-synthesis catalyst;
(b) converting at least some of the methanol from step (a) into a composition including ethylene and propylene in the presence of a methanol-to-olefins catalyst; and
(c) hydrating at least some of the ethylene into ethanol and at least some of the propylene into 2-propanol.
In some embodiments, the syngas is derived from biomass. The syngas can be derived, however, from any carbon-containing source.
The methanol-to-olefins catalyst can comprise an aluminosilicate zeolite such as one selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, and ZSM-48.
The methanol-to-olefins catalyst can comprise a silicoaluminophosphate such as one selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, and SAPO-56. SAPO-34 is a preferred methanol-to-olefins catalyst.
In some embodiments, the silicoaluminophosphate further includes one or more transition metals, such as (but not limited to) one or more transition metals is selected from the group consisting of Mn, Ni, and Co. Nickel is a preferred transition metal, and a preferred methanol-to-olefins catalyst is Ni-SAPO-34. In some embodiments, the ratio of silicon to the transition metal is selected from about 1 to about 500, such as about 10 to about 200.
In preferred embodiments, step (c) is conducted in the presence of one or more olefin-hydration catalysts, such as one or more olefin-hydration catalysts selected from zeolites, supported acids, acidic resins, and heteropoly acids. One or more olefin-hydration catalysts includes sulfuric acid.
Preferably, one or more olefin-hydration catalysts includes a catalyst selected for ethylene hydration, such as phosphoric acid. Preferably, one or more olefin-hydration catalysts includes a catalyst selected for propylene hydration.
In some embodiments, in step (c), the hydrating of ethylene and propylene is conducted substantially simultaneously. In certain embodiments, the method further includes separating the ethylene from the propylene generated in step (b) and then separately hydrating the ethylene and the propylene during step (c).
In some embodiments, in step (c), hydrating of the propylene is substantially conducted prior to hydrating of the ethylene. In some embodiments, hydrating is conducted in a first reaction zone for converting propylene into 2-propanol and a second reaction zone for converting ethylene into ethanol. Step (b) can further generate butenes which can be hydrated to 2-butanol during step (c).
The first reaction zone can be located in a first reactor and the second reaction zone can be located in a second reactor. Or, both of the reaction zones can be located in a single reactor.
In some embodiments, the temperature within the first reaction zone is lower than the temperature within the second reaction zone. For example, the temperature within the first reaction zone can be selected from about 125-200° C. and the temperature within the second reaction zone can be independently selected from about 200-250° C.
In some embodiments, at least a portion of water produced from reactions during step (b) is used for the hydrating during step (c). In certain embodiments, all or substantially all of the water produced during step (b) is fed for the hydrating during step (c).
In some embodiments, during step (c), one or more dialkyl ethers are generated, and wherein the method further comprises removing at least a portion of the dialkyl ethers during or after step (c). Any ethers that are formed can be used in one or more of the cooking fuel embodiments described herein.
Un-hydrated olefins can be separated from the alcohols by distillation, or, additionally, or alternatively, unhydrated olefins can be separated from alcohols by absorbing the alcohols into water or dimethyl ether. In some embodiments, ethanol and/or the 2-propanol are separated (e.g., distilled) from water. In certain embodiments, ethanol is separated from the 2-propanol.
Some variations of the invention provide a method for producing ethanol and 2-propanol from biomass, the method comprising:
(a) producing syngas from biomass;
(b) converting at least some of the syngas into methanol in the presence of a methanol-synthesis catalyst;
(c) converting at least some of the methanol from step (b) into a composition including ethylene and propylene in the presence of SAPO-34 or Ni-SAPO-34; and
(d) catalytically hydrating ethylene into ethanol and propylene into 2-propanol,
wherein the hydrating is conducted in a first reaction zone for converting propylene into 2-propanol and a second reaction zone for converting ethylene into ethanol, and wherein the temperature in the second reaction zone is higher than the temperature in the first reaction zone.
In one aspect of this embodiment, one or more olefins is separated from one or more alcohols, by:
(a) providing a feed stream comprising one or more olefins and one or more alcohols;
(b) contacting the feed stream with dimethyl ether, under effective conditions for absorption of at least one of the alcohols into the dimethyl ether, to generate a solution of dimethyl ether and the at least one alcohol; and
(c) removing dimethyl ether from the solution from step (b), to generate a purified alcohol stream comprising the at least one alcohol.
The one or more olefins can include ethylene, propylene, or another olefin. The one or more alcohols can include ethanol, 2-propanol, or another alcohol. In some embodiments, during step (b), ethanol and 2-propanol absorb into the dimethyl ether and wherein ethylene and propylene do not substantially absorb into the dimethyl ether. In step (c) can include evaporation of dimethyl ether. The olefins can be derived from methanol, and the alcohols can be generated from hydration of the olefins. The dimethyl ether can be derived from the methanol, which can be the same source of methanol as that for generating the olefins.
In step (b), the molar ratio of ethylene to propylene can be greater than about 2, 5, or 10 in various embodiments.
The alcohols produced using these methods can be used in the cooking fuels described herein, including being blended into wax, or mixed with a gelling formulation.
Regardless of how the components are formed, they can be mixed using conventional mixing techniques to form the desired cooking compositions.
In any of these methods, an optional step includes introducing one or more additives selected from fuel stabilizers, lubricants, colorants, odorants, or any other fuel or chemical additives. Additives may contribute functionally, ornamentally, or some combination of these, to the fuel composition.
III. Wax-Containing or Gelled Cooking CompositionsIn some embodiments, the cooking fuel composition is in the form of a solid or gel.
In one embodiment, the compositions comprise wax and one or more C3-6 alcohols. In one aspect of this embodiment, the one or more C3-6 alcohols are present in a concentration of at between 5 and 25 percent by weight.
The alcohols can include isopropyl alcohol and secondary butanol or isobutanol. The mixture of alcohols formed as described above, whether by converting syngas to olefins, and olefins to alcohols, or syngas to methanol, methanol to olefins, and olefins to alcohols, can be combined with wax to form this type of cooking fuel composition.
In one aspect of this embodiment, the composition includes less than one percent by weight of methanol. However, in another aspect of this embodiment, the composition further comprises one or more of methanol, ethanol, and dimethyl ether. The one or more of methanol, ethanol, and dimethyl ether can be present, for example, in a concentration of between 5 and 25 percent by weight.
In another embodiment, the cooking fuel composition is in the form of a gel, wherein the gel comprises a crosslinked calcium compound or other suitable cross-linked formulation and one or more C3-6 alcohols. Any type of gel that is commonly used to form cooking fuel can be used.
In one aspect of this embodiment, the one or more C3-6 alcohols are present in between around 30 and 50 percent by weight of the composition.
The alcohols can include isopropyl alcohol and secondary butanol or isobutanol. The mixture of alcohols formed as described above, whether by converting syngas to olefins, and olefins to alcohols, or syngas to methanol, methanol to olefins, and olefins to alcohols, can be combined with wax to form this type of cooking fuel composition.
In one aspect of this embodiment, the composition includes less than one percent by weight of methanol. However, in another aspect of this embodiment, the composition further comprises one or more of methanol, ethanol, and dimethyl ether. The one or more of methanol, ethanol, and dimethyl ether can be present, for example, in a concentration of between 5 and 25 percent by weight.
The wax-containing compositions can be prepared, for example, by melting a wax, which can be, but need not be, paraffin wax, and adding the alcohols, and, optionally, dimethyl ether, to the molten wax with stirring.
The gelled compositions are typically prepared by first reacting calcium ions with an anion, such as a carboxylate anion, in an aqueous solution. A portion of the water, for example, between 30 and 60 percent, and, more typically, around 50 percent, can then be removed by distillation. The alcohol or mixture of alcohols can then be added to the concentrated solution, and the resulting solution allowed to cool and form a gel.
In either case, it may be preferable to place the gel or wax compositions in a container while they are still in the molten state, rather than trying to fill the container when they are cooled. Means for filling containers with wax-based cooking fuel compositions are well known in the art, and are not repeated here.
IV. Use of the Cooking CompositionsAdditional variations of this invention relate to methods of using certain fuel compositions, and to commercial applications and systems for such compositions. In some variations, a method of using a mixture comprising (i) DME and (ii) a hydrocarbon or alcohol, includes introducing the mixture and an oxidant to a burner under suitable conditions for combustion of at least a portion of the mixture.
The hydrocarbon or alcohol may be selected from molecules having at least two carbon atoms, in some embodiments, including any of the compositions described herein. For example, a hydrocarbon, if present, may be selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, and 1,3-butadiene. An alcohol, if present, may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. The mixture may include both a hydrocarbon and an alcohol. The oxidant will typically be air, although other oxidants such as oxygen or oxygen-enriched air, may be employed as well.
In some embodiments, the combustion is intended primarily to provide a source of heat. The heat may be utilized for raising a local temperature for a user, such as for warming up a room or a piece of equipment (e.g., a heating mantle). Or, the heat may be utilized for heating up or cooking a liquid or solid substance for consumption, or other purposes. The burner may be adapted for a stationary cooking stove or a portable camping stove, for example.
In some embodiments, the combustion is intended primarily to provide a source of light. The light may be utilized for lighting up a room, a trail, or a camping site, for example. The burner may be adapted, in some embodiments, for a camping lantern or similar device intended to provide light (and optionally, heat). Because DME flames are usually blue, the addition of one or more hydrocarbons or alcohols into the fuel mixture may cause the flame to contain colors having more usable light (e.g., white, yellow, or orange light) when light output is desired.
In some embodiments, the combustion is intended primarily to provide a source of power (i.e., usable energy over a period of time). The power may be utilized in various stationary or portable applications, and may be utilized in both consumer and industrial settings. For example, the combustion of the fuel mixture may provide power for a hand-held pump or a personal water-purification device for camping. In a different example, the burner may be adapted for a vehicle combustion chamber, wherein the composition is used as a transportation fuel or fuel additive.
Other variations are premised on the realization that flameless oxidation may be achieved with a suitable catalyst capable of oxidizing the fuel mixture in the presence of an oxidant. In some variations, a method of using a mixture comprising (i) DME and (ii) a hydrocarbon or alcohol, includes introducing the mixture and an oxidant to a catalyst surface under suitable conditions for catalytic, flameless oxidation of at least a portion of the mixture.
The catalytic oxidation may provide a source of heat, such as for a cooking stove or camping stove, and/or a source of light, such as for a camping lantern. Many known catalysts are suitable for catalytic complete oxidation, such as (but not limited to) Pt, Pd, Rh, Re, Fe, and Sn, with various supports and promoters. The oxidation catalyst can take the form of a powder, pellets, granules, beads, extrudates, and so on. When a catalyst support is optionally employed, the support may assume any physical form such as pellets, spheres, monolithic channels, etc. The oxidation catalyst may be provided in various reactor configurations, such as in a microchannel reactor.
Still other variations provide a method of using a mixture comprising (i) dimethyl ether, (ii) a hydrocarbon or alcohol, and (iii) water, the method comprising introducing the mixture and an oxidant to a fuel cell under suitable conditions for oxidation of at least a portion of the DME and/or at least a portion of the hydrocarbon or alcohol, to generate electrical power.
The electrical power from the fuel cell may be utilized in various stationary or portable applications, and may be useful in consumer, industrial, and transportation applications.
Preferably, both the DME and hydrocarbon (or alcohol, when an alcohol is used) are oxidized in the fuel cell. The oxidation kinetics for particular fuel species in a fuel cell may vary due to different mass-transfer rates across membranes (or to/from solid-oxide surfaces), as well as due to different reaction rates at catalyst surfaces. Fuel compositions for fuel cells may be optimized in view of particular fuel cell configurations and systems that employ the fuel cells.
Additional aspects of the present invention are premised on the realization that DME as a propellant or refrigerant can be improved by the addition of certain other chemicals to the DME. The improvements may relate to the resulting chemical properties of the blend, to the economics of the selection of molecules in the blend, or to environmental benefits associated with the source of the materials selected for the blend.
In some variations, a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol, includes introducing a primary fluid and the mixture, as a propellant for the primary fluid, to a container or chamber. The primary fluid may be a fuel or fuel blend, such as diesel or biodiesel fuel. Or, the primary fluid may be a chemical or chemical blend for consumer use, such as an aerosol product.
In other variations, a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol, includes introducing the mixture, as a refrigerant, to a refrigeration cycle. The refrigeration cycle may be adapted for a refrigerator, a freezer, an air conditioner, a heat pump, or a cryogenic apparatus, for example.
Any of these disclosed methods may further include the step of actually providing the mixture for the purpose of using the mixture in an intended manner. The methods, however, do not require that the fuel mixtures be provided by the same person or entity that provides the rest of the components, such as the burner. For example, a fuel mixture may initially be provided in a small cylinder (or canister), with the intent that the cylinder be later refilled, or later replaced with a new cylinder filled with fuel, for repeating the methods of the invention any number of times.
V. Systems for Storing and Using the CompositionsStill other variations of the invention relate to systems, which may include methods and/or apparatus for using DME-based fuel compositions. Some variations provide a system comprising: (a) a container adapted for containing a mixture comprising dimethyl ether and a hydrocarbon or an alcohol; (b) a burner adapted for receiving the mixture from the container, and for receiving an oxidant, to oxidize at least a portion of the mixture, thereby generating heat and/or light; and (c) a heating and/or lighting region for conveying the heat and/or light to a user.
The container may be a rigid container, such as (but not limited to) a cylinder, a tank, or a tube. The container may be fabricated from a metal or metal alloy, such as steel, or from a ceramic, plastic, or other material. The container may be a flexible container, fabricated for example from a polymer. In some embodiments, the container is removable from the system, so that it can be refilled or replaced. In certain embodiments, the container is not readily removed from the system but rather is configured to be refilled, in place, with an additional amount of the fuel mixture. The container may or may not be initially filled with a fuel mixture.
The system includes a burner that may be configured to create a controlled combustion flame, or may be configured with a catalyst to create a flameless oxidation reaction. In principle, a burner could be designed with a catalytic surface or region, so that a portion of the fuel mixture is oxidized in surface reactions while the remainder of the fuel mixture is combusted in a flame front. Such a design could help control the quality of the flame, or could be used to adjust the relative outputs of heat, light, and power, for example.
The heating and/or lighting region for conveying the heat and/or light to a user may take on a wide variety of shapes, sizes, and materials of construction. Heat may be transferred from the burner to a user (or to an object to be heated) through a metal panel, a metal ring, a heat exchanger, or simply through open air, for example. Light may be transferred from the burner to a user through an open window or region of space, a glass panel, or a light reflector, for example.
In some embodiments, the system forms (or is part of) a cooking stove. In certain embodiments, the system forms a camping stove, a camping lantern, or another device for providing an energy source during camping, hiking, backpacking, long-distance cycling, or other outdoor activities.
The system components, and in particular the burner (as will be further discussed below), may be designed or optimized for specific fuels and mixtures, or may instead be designed for greater fuel flexibility. Preferably, the burner is specifically suitable for combustion of mixtures that contain DME, of various concentrations as described herein.
In particular embodiments, the burner is selected, designed, engineered, or adjusted to be suitable for one or more hydrocarbons selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene; and/or for one or more alcohols selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol.
A system of the invention may be provided in some form of “kit” which here means any type of package, box, or other means of collecting or storing the components of the system. The kit should include at least a fuel container, a burner, and a heating and/or lighting part or region for conveying heat and/or light to a user. In preferred embodiments, the system includes user instructions that describe the intended use(s) and safety aspects. The user instructions may be in the form of a physical manual, or may be provided by directing a user to a web site, for example. The kit may also include various other items, such as a spare cylinder, spare burner parts, optional components to adjust relative heat, light, or power output, a list of fuel suppliers, environmental, health, and safety information, and marketing material.
This invention also contemplates apparatus configured for a consumer or user to carry out any of the disclosed methods. In some variations, the design of the burner portion of the apparatus will generally follow certain principles as will now be further described. This disclosure incorporates by reference the following textbook, in its entirety: Turns, “An Introduction to Combustion: Concepts and Applications,” McGraw-Hill, Inc., pp. 1-565, 1996.
Fuel compositions will dictate, in part, the possible burner designs. While it may be preferred to design a burner that has wide fuel flexibility, it also may be preferred to design burners for specific, intended fuel compositions, such as the fuel compositions disclosed herein. Additionally, the intended uses of the apparatus should be considered when selecting or designing a burner. In some embodiments, an apparatus is designed in respect of certain properties or characteristics that may depend on the fuel composition as well as on physical dimensions, materials, or equipment constraints. Such properties may include, for example, average or maximum temperature or heat output, average or maximum light output, and equipment-specific flammability limits.
Some burner embodiments employ laminar jet flames, wherein the fuel stream is partially premixed with air. A primary concern in the design of a burner utilizing laminar jet flames is flame geometry, with short flames being typically preferred. In a jet flame, fuel flows along the flame axis and diffuses outward, while the oxidant (e.g., air) diffuses radially inward. The flame surface is nominally defined to be the locus of points where the fuel and oxidant meet in stoichiometric proportions for combustion, i.e., an equivalence ratio of one. The products formed at the flame surface (at least CO2 and H2O) diffuse radially inward and outward.
The flame geometry will depend on the physical burner geometry. Burner geometries may be, for example, circular, square, slot, or curved slot. For a given burner geometry, there will be a relationship between the fuel flow rate and the flame length. The quantity of heat (or light) desired, and/or the rate of heating, should be considered when designing for a fuel flow rate or range of flow rates. The flame length may be of secondary importance, although safety aspects should be considered in any design.
Burners may be designed to run slightly lean, slightly rich, or at or near the stoichiometric combustion ratio. Various equivalence ratios may be implemented. The “equivalence ratio” is defined as the ratio of the fuel-to-oxidant ratio to the stoichiometric fuel-to-oxidant ratio. Thus, equivalence ratios greater than one mean that the system is fuel-rich, and ratios less than one indicate the system is fuel-lean, and oxidant-rich.
In some embodiments, the apparatus is designed to premix some air with the fuel before it burns as a laminar jet diffusion flame. This primary aeration, which may be for example between about 20% and 80% of the stoichiometric air requirement, shortens the flames and helps prevents soot from forming. DME is known to have low soot potential, but other components (e.g., C2+ alcohols or hydrocarbons) may not have this attribute. Therefore, attention should be paid in the burner design to controlling soot formation.
The formation and destruction of soot is an important feature in some embodiments of the invention. The incandescent soot within the flame is the primary source of the luminosity of the flame. Because DME burns so cleanly, the flame tends to be blue. For lighting applications (e.g., camping lanterns), blue flames may be a less preferable source of light than orange, yellow, or red flames. In this context, the addition of a hydrocarbon or alcohol to DME allows for the creation of a light source that may be more appealing to a user. Note, however, that the invention is not limited to any particular color of light generated by combustion of the fuel mixtures. In certain embodiments, colors such as blue or green may be desired.
Fuel/oxidant flow regimes may be, for example, momentum-controlled, buoyancy-controlled, or transitional. To determine whether a flame is momentum- or buoyancy-controlled, the flame “Froude number” may be evaluated. The Froude number physically represents the ratio of initial jet momentum flow to the buoyant force experienced by the flame. Thus, a Froude number well in excess of one indicates momentum control, while a Froude number much less than one indicates buoyancy control.
In preferred burner designs, a stable flame is anchored at a desired location and is resistant to flashback, liftoff, and blowoff over the burner's operating range. To hold and stabilize a flame, the design principle is that the local flame speed (whether laminar or turbulent) should substantially match the local mean flow velocity. Design features that may follow this principle include low-velocity bypass ports, refractory burner tiles, flameholders, swirl or jet-induced recirculating flows, or a rapid increase in flow area.
Fuels with high diffusivities are more prone to flashback, whereby the flame propagates upstream, back toward the fuel source. DME has a high diffusivity, and is therefore susceptible to flashback. DME blends with hydrocarbons and alcohols may be optimized specifically to reduce or avoid flashback for a particular burner design. One way to reduce flashback is to design for high flame-propagation speeds.
Flame-propagation speeds may be designed to be relatively high by including a pump or compressor, for either or both of the fuel or oxidant. For example, an electrical air pump may be utilized to pump air through a fuel source, thereby pushing the fuel to the burner, optionally with a metering valve. Or, a small hand pump may be utilized to pump fuel and/or air to the burner. In preferred embodiments, a fuel cylinder of sufficient pressure is employed to drive the fuel to the burner at sufficient velocities.
Generally speaking, burners may be designed for a liquid fuel supply, a vapor fuel supply, or a combination of these. A combination burner, in this context, may refer to a dual design where either a liquid or a vapor may be fed. A combination burner may also mean that a multiphase fuel can be introduced.
Thermodynamically, in a flame, any liquid fuel must first vaporize and heat up before it can combust. Thus, if the fuel is a liquid, a heater may be included to vaporize the fuel before it reaches the flame, and preferably before premixing with the oxidant. For example, an electrical heating element or a small burner (which may operate with the same or a different fuel supply) may be included.
In some embodiments, the vapor pressure of the fuel is sufficiently high such that vaporized fuel is continually fed to the burner. It is also possible, when the fuel is a liquid, to introduce it to the burner using a spray, mist, or droplet injection, such that the liquid is quickly vaporized within the flame itself. A liquid spray or liquid mist may include some amount of vapor, as will be appreciated, dictated by complex mass and heat transfer within a vaporizing drop or particle.
The range of fuel compositions described in the present invention include mixtures that are vapor at room temperature (or typical outdoor temperatures), and some mixtures that are liquid at these temperatures. When the fuel is normally a vapor, it is preferably filled into a pressurized container so that it is present in liquid form (some vapor will usually also be present). Additionally, certain compositions described herein may be present in a multiphase solution, which may be a vapor and a liquid, or even two liquid phases.
Some burners further include a flame igniter. It is possible, but typically not preferable, to ignite a flame with a match or separate flame initiated by a user. A piezoelectric device may be included to cause ignition. Such a device utilizes the mechanical work done by the user in depressing a button to create an electric spark. Other flame igniters may be employed, such as direct or indirect solar-powered igniters.
Various means of controlling the apparatus, and burner, may be included. For example, features may be included to control the fuel flow or pressure, the oxidant flow, the flame output, the temperature of a heating region, and so on. Some form of automating the length of time for burning may be included, such as when a user may not be present to shut down the device.
Many of the aforementioned design principles for laminar flames will also apply for turbulent flows. Turbulent flames are common in larger devices including internal combustion engines, gas turbines, furnaces, and boilers. Such applications often involve—and allow the budget for—highly complicated design features.
For example, engineered fuel injectors may be employed to efficiently deliver fuel mixtures to burners or combustion chambers. Some embodiments include nozzles, i.e. mechanical devices designed to control the direction or characteristics of a fluid flow as it enters an enclosed chamber or pipe via an orifice. Nozzles are capable of reducing the fuel droplet size to generate a fine spray. Nozzles may be selected from atomizer nozzles, swirl nozzles which inject the liquid tangentially, etc. In some embodiments, screens, ceramic filters, or molecular sieves are included to help form small droplets.
In this detailed description, reference has been made to multiple embodiments of the invention and non-limiting examples relating to how the invention can be understood and practiced. Other embodiments that do not provide all of the features and advantages set forth herein may be utilized, without departing from the spirit and scope of the present invention. This invention incorporates routine experimentation and optimization of the methods and systems described herein. Such modifications and variations are considered to be within the scope of the invention defined by the claims.
All publications, patents, and patent applications cited in this specification are herein incorporated by reference in their entirety as if each publication, patent, or patent application were specifically and individually put forth herein.
Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially. For example, an integrated process may be employed wherein syngas is converted to DME as well as hydrocarbons and/or alcohols in the same reactor(s).
Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the appended claims, it is the intent that this patent will cover those variations as well. The present invention shall only be limited by what is claimed.
Claims
1. A cooking fuel composition comprising dimethyl ether and one or more C2 to C6 alcohols.
2. The composition of claim 2, wherein said alcohol is selected from the group consisting of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, and combinations thereof.
3. The composition of claim 1, said composition comprising said alcohol in a concentration of at least 10 wt %.
4. The composition of claim 3, said composition comprising said alcohol in a concentration of at least 50 wt %.
5. The composition of claim 1, further comprising methanol.
6. A composition comprising dimethyl ether one or more C2 to C10 hydrocarbons.
7. The composition of claim 6, said composition comprising ethane, ethylene, propane, propylene, butane, and butylenes.
8. The composition of claim 7, said composition further comprising one or more C5 to C10 hydrocarbons.
9. The composition of claim 6, wherein the dimethyl ether is present in a concentration of at least 10 wt %.
10. The composition of claim 6, wherein the dimethyl ether is present in a concentration of at least 50 wt %.
11. A cooking fuel composition comprising wax and one or more C3-6 alcohols.
12. The composition of claim 11, wherein composition includes less than one percent by weight of methanol.
13. The composition of claim 11, wherein the composition comprises isopropyl alcohol and secondary butanol or isobutanol.
14. The composition of claim 11, wherein the one or more C3-6 alcohols are present in a concentration of at between 5 and 25 percent by weight.
15. The composition of claim 11, further comprising one or more of methanol, ethanol, and dimethyl ether.
16. The composition of claim 15, wherein the one or more of methanol, ethanol, and dimethyl ether is present in a concentration of between 5 and 25 percent by weight.
17. A cooking fuel composition in the form of a gel, wherein the gel comprises a crosslinked calcium compound and one or more C3-6 alcohols.
18. The composition of claim 17, wherein the one or more C3-6 alcohols are present in between around 30 and 50 percent by weight of the composition.
19. The composition of claim 17, further comprising one or more of methanol, ethanol, and dimethyl ether.
20. The composition of claim 19, wherein the one or more of methanol, ethanol, and dimethyl ether is present in a concentration of between 5 and 25 percent by weight.
Type: Application
Filed: Jul 24, 2013
Publication Date: Nov 28, 2013
Applicant: Maverick Biofuels, Inc. (Chapel Hill, NC)
Inventors: Ronald C. STITES (Brighton, CO), David ALDOUS (Denver, CO), David S. BRADIN (Chapel Hill, NC), Eric CUMMING (Raleigh, NC)
Application Number: 13/949,360
International Classification: C10L 7/04 (20060101);
