PRODUCTION OF ALCOHOL BLEND USABLE IN FLEXIBLE FUEL VEHICLES VIA FISCHER-TROPSCH SYNTHESIS FIELD OF THE INVENTION

Abstract

Alternative fuel compositions, blends of the alternative fuel compositions and gasoline, and methods for their preparation and use are disclosed. The alternative fuel compositions ideally include ethanol, isopropyl alcohol, and one or more of sec-butanol and t-butanol, and ideally include no more than 3% methanol, and no more than 15% C5 or higher alcohols. The fuel compositions can be prepared using Fischer-Tropsch synthesis to convert syngas to a product stream comprising C2-4 olefins, and hydrolyzing these olefins. The process facilitates isolation of C2-4 alkanes, because the boiling point difference of these alkanes is significantly lower than that of the C2-4 alcohols. Ideally, the compositions provide more energy per unit volume than E85, even without the addition of gasoline, although the compositions can be blended with gasoline in any desired ratio. The resulting alternative fuel can be derived, at least in part, from renewable resources, in that the syngas can be derived from renewable resources, and a significant portion of the molecule is derived from the water used to hydrolyze the olefins. The alternative fuel compositions, and blends thereof with gasoline, can help reduce U.S. dependence on foreign crude oil.

Description

This application is a continuation-in-part of PCT application No. PCT/US07/069,635, filed May 24, 2007, which claims priority to U.S. Provisional Application No. 60/896,099, filed Mar. 21, 2007.

The present invention relates to alternative fuel compositions which comprise ethanol, isopropyl alcohol, and secondary-butanol and/or t-butanol, as well as blends of these compositions with gasoline.

BACKGROUND OF THE INVENTION

Gasoline is derived from crude oil, which is a non-renewable resource of finite supply. Extensive research effort is now being directed toward replacing some or all petroleum-based transportation fuels with gasoline/ethanol blends such as E85 (85% ethanol and 15% gasoline by volume). E85 suffers from a significant loss (roughly 20%) in energy per unit volume relative to gasoline. However, flexible fuel vehicles can run efficiently on these fuels, and the high oxygenate content makes them very clean burning fuels.

Because ethanol suffers from relatively low energy content per unit volume, there have been significant efforts to develop n-butanol as an alternative energy source. N-butanol provides sufficient power to run a normal gasoline engine.

However, the use of n-butanol as a viable energy source is not without its problems. Much like ethanol oxidizes to acetic acid, n-butanol oxidizes to butyric acid, which has a very strong and offensive odor. Also, there is a finite amount of feedstock to produce fermentable materials such as n-butanol. That is, sugar can be fermented, but it is difficult and expensive to convert lignocellulosic materials to the component parts, such as lignin, cellulose, and hemicellulose, and to then depolymerize the cellulose and/or hemicellulose to the component sugars. Further, fermentation produces a significant amount of carbon dioxide.

Fischer-Tropsch synthesis has been used to convert coal and natural gas, available domestically, into distillate fuels. More recently, biomass, including lignin, sugars, cellulose, and the like, has been converted to syngas for use in Fischer-Tropsch synthesis. When catalysts with high chain growth probabilities are used, the products are primarily paraffin wax and water. The paraffin wax is typically hydrocracked to form fuel products.

When catalysts with low chain growth probabilities are used, the products tend to include a carbon dioxide, unreacted syngas, and low molecular weight (C_2-4) paraffins and olefins, in addition to some products in the gasoline and diesel ranges. Because of the relatively lower yield, many companies using Fischer-Tropsch synthesis have opted to produce paraffin wax, and hydrocrack the wax, rather than producing relatively low molecular weight hydrocarbons (along with carbon dioxide, methane, and unreacted syngas). It would be desirable to provide a source of alternative fuels that overcomes at least some of the limitations associated with fermentation, that is, the significant production of carbon dioxide, the difficulty in obtaining fermentable sugars in high yield from lignocellulosic materials, the low energy per unit volume associated with ethanol, and/or the oxidation of butanol to butyric acid. It would further be advantageous to provide alternative gasoline-containing compositions that include ethanol, but which overcome the limitations of current gasoline/ethanol blends. The present invention provides such alternative fuels and gasoline-containing blends, processes for preparing the fuels, and methods of using the fuels.

SUMMARY OF THE INVENTION

Alternative fuel compositions, blends of the alternative fuel compositions and gasoline, and methods for their preparation and use are disclosed. The alternative fuel compositions comprise ethanol, n-propyl and/or isopropyl alcohol, and n-butanol, sec-butanol and/or t-butanol.

Ideally, methanol is substantially absent from the composition. By substantially absent is meant less than 10% by volume, ideally less than 5% by volume, and, more ideally, less than 1% by volume.

In one embodiment, the fuel compositions are prepared by first conducting Fischer-Tropsch synthesis using a catalyst with low chain growth possibilities to produce a product stream which comprises C_2-4 olefins, and subjecting the olefins to hydrationhydration conditions, which add water across the double bonds. The hydrationhydration is typically done with an acid catalyst, and the resulting C₃ and C₄ alcohols are therefore primarily secondary or tertiary alcohols.

Fischer-Tropsch chemistry performed using an iron catalyst, or other catalyst with low chain growth probabilities, tends to provide a variety of gaseous and liquid products, including unreacted synthesis gas, methane, and C_2-4 hydrocarbons (a mixture of olefins and paraffins). Typically, about 75% of the C_2-8 products from Fischer-Tropsch synthesis are normal alpha-olefins (NAOs), and the gases are typically separated from the liquid products (see, for example, U.S. Pat. No. 6,849,774, the contents of which are hereby incorporated by reference).

The methane and other light paraffins can be recycled through an upstream synthesis gas generator, but the light olefins must be separated from the light paraffins in order to do this. The olefins and paraffins have very similar boiling points. Prior art approaches for separating the olefins from the paraffins involve relatively expensive cryogenic distillation. However, the processes described herein convert the olefins to alcohols, optionally in the presence of the methane and paraffins. Since the alcohols have significantly higher boiling points than the paraffins, this enables facile separation of olefins (when converted to the resulting alcohols) from paraffins. The other light paraffins (i.e., C₂-₄ paraffins) can be used, for example, to heat houses, in barbecue grills, and/or to run automobiles, such as cars or buses, that run on liquid propane gas.

There are several ways to produce the alcohols that make up the alcohol blends described herein. The alcohols can be produced by olefin hydration, by fermentation, by hydroformylation of the C_2-4 olefin products of Fischer-Tropsch synthesis, and by conducting Fischer-Tropsch synthesis in a way that maximizes alcohol formation. That is, normal straight chain alcohols can be formed during Fischer-Tropsch synthesis under certain conditions, and if they do not dehydrate under the Fischer-Tropsch conditions, they can be isolated (often in yields approximating 60%).

As there is an abundant supply of methane, coal, biomass, and other feedstocks (renewable biomass, municipal solid waste, etc.) which can be converted to syngas, the chemistry described herein can be combined with one or more products resulting from fermentation chemistry, such as ethanol and/or n-butanol, to produce a variety of alcoholic fuel mixtures that can be used alone, or in combination with gasoline.

Ideally, the alcoholic mixture produced using the processes described herein includes sufficient C₃ and C₄ alcohols, and, optionally, C_5-8 alcohols, such that the alcohol blend has approximately the same, and, ideally, more, energy per unit volume than E85, even without the addition of gasoline. That is, butanols (n-butanol, sec-butanol, and t-butanol) have approximately the same energy per unit volume as gasoline. So, a mixture comprising ethanol, isopropyl alcohol, and sec-butanol and/or t-butanol, where the butanols are present in at least 15% by volume, will have at least the same energy per unit volume as E85. Since isopropyl alcohol has energy per unit volume between that of ethanol and butanol, the presence of isopropyl alcohol in combination with the sec-butanol and/or t-butanol also results in at least equivalent energy per unit volume to E85, even if the butanol content is less than at least 15% by volume.

The alcohol blends can further be combined with conventional gasoline, thereby increasing the energy per unit volume.

In one embodiment, the composition comprises between about 5 and 45% by volume of sec-butanol and/or t-butanol, between about 5 and about 45% isopropyl alcohol, between about 5 and about 80% by volume ethanol, and between about 0 and about 25% C_5-8 alcohols. Blends of this alcoholic composition with gasoline, where the ratio of the alcoholic composition to gasoline range from 1:99 to 99:1, are also disclosed.

The alternative fuel can also be a gasoline/alcohol blend, where the alcohol comprises a) ethanol b) n-propanol and/or isopropyl alcohol, and c) n-butanol, sec-butanol, or t-butanol, where the alcohols are present in amounts up to about 95 percent by volume of the gasoline/alcohol blend.

In one aspect of this embodiment, gasoline is blended with between about 5 and about 85 percent by volume of the alcoholic mixtures described herein, and between about 5 and 85 percent by volume of gasoline. The olefins can be derived, in whole or in part, by Fischer-Tropsch synthesis on syngas formed using, for example, coal, glycerol, ethanol, methanol, methane, lignin, cellulose, hemicellulose, black liquor, or biomass (including corn stover, switchgrass, bagasse, sawdust, recycled paper, and the like) as a starting material. The olefin hydration can be run at substantially quantitative yields, and adds significantly to the total weight of the product. That is, assuming a roughly C₃ average molecular weight for the olefins, with a molecular weight of around 44 g/mole, addition of water to the double bond adds 18 g/mole, or around 29%, to the molecular weight.

Thus, fuel products that burn in flexible fuel vehicles can be obtained in significant yields from Fischer-Tropsch reactors, using relatively inexpensive iron-containing catalysts, without the need for a hydrocracker (such as is used to crack Fischer-Tropsch wax). Product yields are improved, relative to the volume of the olefins produced, by the addition of water across the double bond. Further, the resulting product is more stable than the olefins, which are otherwise prone to polymerization or other further reactions. The separation of C_2-4 alkanes from C_2-4 alcohols is significantly easier than the separation of C_2-4 alkanes from C_2-4 olefins. Further, the cost of setting up the plant is significantly reduced by using a combination of relatively inexpensive Fischer-Tropsch catalysts and conditions, and relatively inexpensive (compared with a hydrocracker) olefin hydration reactor. The amount of water present in the hydration reaction is significantly less than that present in a fermentation plant, so distillation costs are relatively lower.

The fuel compositions described herein can be blended with biofuels such as ethanol and “biobutanol” (n-butanol derived by fermentation) to maximize the yield of alternative fuels that run on flexible fuel vehicles. Unlike biobutanol, olefin hydration tends to form secondary and/or tertiary alcohols, which do not oxidize to corrosive and odiferous carboxylic acids such as butyric acid. Unlike E85, which requires gasoline to work in a flexible fuel vehicle, the presence of higher molecular weight alcohols means that the fuel can work in flexible fuel vehicles without adding any gasoline. Also, the presence of higher molecular weight alcohols means that the fuel can be used in conventional gasoline engines at higher concentrations than ethanol (i.e., at concentrations greater than 5% by volume, ideally up to or greater than 10% by volume).

The resulting alternative fuel can be derived, at least in part, from renewable resources, in that the syngas can be derived from renewable resources, and a significant portion of the molecule comes from the water used to hydrolyze the olefins. The alternative fuel compositions, and blends thereof with gasoline, can help reduce U.S. dependence on foreign crude oil.

DETAILED DESCRIPTION

An alternative fuel composition that comprises C_2-4 alcohols, ideally with at least a portion of the C₃ and C₄ alcohols being secondary or tertiary alcohols, are disclosed. Blends of the fuel composition with gasoline, and methods of making and using the composition and blends thereof, are also disclosed.

In some embodiments, the processes described herein are integrated processes. As used herein, the term “integrated process” refers to a process which involves a sequence of steps, some of which may be parallel to other steps in the process, but which are interrelated or somehow dependent upon either earlier or later steps in the total process.

The Following Definitions Will Further Define the Invention:

The term “alkyl”, as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic hydrocarbon of C_1-6, and specifically includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl.

The term “olefin” refers to an unsaturated straight, branched or cyclic hydrocarbon of C_2-10, and specifically includes ethylene, propylene, butylene, isobutylene, pentene, cyclopentene, isopentene, hexene, cyclohexene, 3-methylpentene, 2,2-dimethylbutene, 2,3-dimethylbutene, 1-heptene, 2-heptene, 3-heptene, 1-octene, 2-octene, 3-octene, 4-octene, 1-nonene, 2-nonene, 3-nonene, A-nonene, 1-decene, 2-decene, 3-decene, 4-decene, and 5-decene. Ethylene, propylene and isobutylene can be preferred due to their relatively low cost, and C₂-₈ olefins can be preferred as they are produced as the major products in Fischer-Tropsch synthesis when an iron catalyst is used.

Highly substituted olefins can be preferred, because they can stabilize a carbocation intermediate more readily than unsubstituted olefins, and thus facilitate olefin hydration to form alcohols.

I. Alcohols

The alcohols described herein are a blend comprising, and in one embodiment, consisting essentially of, C_2-4 alcohols. Higher molecular weight alcohols can also be present. Methanol can be present, but since it has a relatively low energy per unit volume, is not a preferred component, and is ideally substantially absent (i.e., less than about 3% by volume, preferably less than about 1% by volume) from the composition. Cs₊ alcohols can be present, although it is preferred that the alcohols not exceed C₁₀ (i.e., that less than 5% of the composition is C₁₀₊). More ideally, the amount of C_2-4 alcohols is between about 60 and about 80 percent of the alcohols, and even more ideally, is greater than 90 percent of the alcohols, by volume.

In one embodiment, alcohols are present in a fuel composition comprising a mixture of ethanol, isopropanol, and one or more alcohols selected from the group consisting of sec-butanol and t-butanol. The composition can further comprise n-propanol. Ideally, the composition comprises less than 10% of alcohols with a molecular weight greater than butanol, and comprises at least 15%, preferably at least 25%, more preferably, at least 30% sec-butanol and/or t-butanol by volume. The energy content of the fuel composition meets or exceeds that of ASTM D5798-99 (Standard Specification for Fuel Ethanol for Automotive Spark-ignition Engines).

In one aspect of this embodiment, the composition is preferably substantially devoid (i.e., less than 3%) of each of n-butanol and methanol, and in another aspect, the composition includes less than 5% n-butanol.

As discussed in more detail below, the composition can be produced by converting syngas to a C₂-₄ olefin-containing product stream using Fisher-Tropsch synthesis, and subjecting all or a portion of the C_2-4 olefins to olefin hydration.

It is not required that the C₃₊ alcohols be secondary or tertiary alcohols, but these can be preferred, as it can be desired to minimize the ability of the alcohols to oxidize to carboxylic acids, which acids can be undesirable due to their corrosiveness and/or odor. Any alcohol that provides a fuel composition with sufficient energy for use in gasoline or flexible fuel engines can be used to prepare either the fuel compositions. Suitable alcohols for use in the present invention include, but are not limited to, saturated straight, branched, or cyclic alcohols of C_1-6, and specifically include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, cyclopentanol, isopentanol, neopentanol, hexanol, isohexanol, cyclohexanol, 3-methylpentanol, 2,2-dimethylbutanol, and 2,3-dimethylbutanol.

Ethanol is generally available commercially in a denatured form, for example, grade 3 A, which contains minor amounts of methanol and water. The ethanol can be that which is produced commercially from addition of water across the double bond in ethylene, and/or by fermentation of grains. It can be preferred that any alcohol used in the present invention contains less than five percent water, preferably less than approximately one percent water. However, unlike E85, where the presence of water in the ethanol results in product separation, it is possible to keep a certain amount of water (i.e., less than around 10%, ideally less than around 5%, more ideally, less than around 2%, and most ideally, less than around 1%) in the composition without resulting in product separation, because water is soluble in the alcohol blend. The water, at these levels, is not believed to result in substantially decreased performance, and, in some embodiments, may actually increase performance and/or reduce certain emissions.

Ideally, the alcohol blends include at least 15%, more ideally, at least 20%, still more ideally, at least 25%, and even more ideally, more than 30% by volume of secondary and/or tertiary butanol. Ideally, the alcohol blends include at least 15%, more ideally, at least 20%, still more ideally, at least 25%, and even more ideally, more than 30% by volume of isopropanol.

The alcohols can be derived from a variety of sources. In one embodiment, the alcohols are derived in a two step process, where the first step is Fischer-Tropsch synthesis to produce a mainly olefinic fraction rich in C2-4 olefins, and the second step is hydration of the C2-4 olefins to form C2-4 alcohols. The C2-4 olefins can be, but need not be, isolated before the olefin hydration. When they are isolated, they can be co-isolated with the C₂-₄ paraffins (i.e., separating the C2-4 fraction from any methane/unreacted syngas/carbon dioxide, water, and C5₊ fractions).

Before Fischer-Tropsch synthesis is performed, a suitable raw material must be converted to syngas, and the syngas is typically desulfurized to avoid poisoning the catalyst. In one embodiment, this raw material comprises biomass, such as corn stover, bagasse, switchgrass, algae, wood, sawdust, or waste streams derived from biomass, including the crude glycerol from biodiesel synthesis and hemicellulose, lignin or black liquor derived from cellulose and/or paper production. In this embodiment, biomass and waste streams can be converted to useful fuel and other products, rather than being sent to a landfill or, in the case of black liquor, often dumped into water supplies. In this embodiment, the process can be compatible with cellulosic ethanol production. That is, cellulosic ethanol will require the separation of cellulose from lignin and, optionally, hemicellulose. Delignification generates black liquor, which can be converted to syngas, and, ultimately, to a C_2-4 alcohol-containing feedstock. The hemicellulose can be depolymerized and, often inefficiently, fermented to alcohol, or also used as a feedstock to produce the C2-4 alcohols described herein. The cellulosic ethanol can then be combined with the C₂-₄ alcohols described herein, if desired. However, since the process can be optimized to use pure biomass as a starting material, and the C2-4 alcohols produced have a higher energy per unit volume than ethanol, without generating around 40% carbon dioxide by weight of biomass (the amount produced by bacteria or yeast in consuming the biomass to generate ethanol), while using the lignin, cellulose, and hemicellulose to generate these alcohols, it may be desirable to avoid ethanol production via fermentation altogether in favor of the approach described herein.

After the Fischer-Tropsch synthesis and, ideally after olefin hydration, are performed, any C₁-₄ saturated hydrocarbons can be isolated (though these can be isolated earlier, if desired). All or part of any C₅-₁₅ hydrocarbons that are produced can also be isolated and used, for example, in gasoline production. These products can be isolated, for example, by distillation.

Unreacted syngas can be burned on-site to provide energy to run the plant, recycled through the process to improve yields, or used to generate electricity, as desired. The alcohols can be blended with gasoline in any desired ratio, provided the energy per unit volume meets or exceeds that of E85. Since E85 includes predominantly ethanol and gasoline, and the alcohols produced according to the methods described herein can have an average carbon number of 3 or more, the energy content of the alcoholic mixture should meet or exceed that of E85 even without the addition of any gasoline. Thus, all that is required to produce commercial quantities of a fuel with performance rivaling or exceeding that of E85 is a source of material that can form syngas (biomass, coal, waste streams and/or methane), water, a syngas generator, a Fischer-Tropsch catalyst bed, an olefin hydration reactor, and a distillation apparatus. No hydrocracking is required, which significantly lowers the cost of setting up the plant, relative to a conventional Fischer-Tropsch facility that initially produces Fischer-Tropsch wax.

Further, because the ethanol is present in lower concentrations than that in E85, the hygroscopic nature of ethanol is of a lesser concern. That is, the higher the concentration of C3₊ alcohols in the fuel composition, the more easy it is to ship and store the fuel composition. In some embodiments, it can be possible to ship the fuel composition in a conventional pipeline, and/or store the composition without the retrofitting required to store E85.

In one embodiment, some or all of the ethanol, propanol and/or isopropyl alcohol, and n-butanol can be produced by fermentation. In another embodiment, 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.

II. 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, municipal solid waste, 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 C_20-50 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 (C_2-8) olefins and a relatively low proportion of high molecular weight (C₃₀₊) waxes. Optimized conditions for producing predominantly C_2-4 olefins are known to those of skill in the art. For example, conditions using an ammonia/iron catalyst are described, for tropsch.org/primary documents/presentations/recent research/recent rcport.htm, the contents of which are hereby incorporated by reference, and which are described in detail below.

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 C_2-4 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%.

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 C_2-4 range, one would obtain yields of around 40% hydrocarbons in the C_2-4 range and around 40% in the gasoline/diesel ranges, which could be separated before the olefin hydration occurs. Of the roughly 40% product (olefins and alkanes) in the C₂-₄ range, about 75% (30% overall) will be olefinic. By hydrating 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 could 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 the higher boiling point alcohols (which are then easily separated from the (C₂-₄ alkanes), and able to be used as an alternative fuel itself, around 39% of a blend of alcohols that can be used directly to fuel a flexible fuel vehicle, or which can be blended with gasoline to fuel flexible fuel vehicles or conventional gasoline engines, depending on the relative amounts of each and the corresponding energy per unit volume, and around 40% by weight of hydrocarbons in the C_5-20 range, which can be isolated separately from the C_2-4 alcohols and used as jet, diesel, or gasoline, depending on the desired use and downstream process steps, such as cyclization, hydrotreatment and isomerization (collectively referred to herein as catalytic reforming).

At least some of the hydrocarbons in the C_5-20 range can be used to produce gasoline, for example, by isomerizing and then hydrotreating/hydro finishing hydrocarbons in the C_5-10, ideally in the C₆-₈ range. These hydrocarbons can then optionally be blended with the alcoholic blend and used in conventional gasoline or flexible fuel engines, as appropriate depending on the energy per unit volume. Assuming all of the hydrocarbons (LPG and hydrocarbons in the C_5-20 range) were used in fuel compositions, this would provide approximately 90% conversion of syngas to fuel compositions (LPG, alcohol blends that have the same or more energy per unit volume than E85, gasoline, jet, and diesel fuel), all without expensive hydrocracking.

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%.

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 affect 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., “LG. 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.

III. 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.

N-butanol has approximately the same energy per unit volume as gasoline, but is prone to oxidation to form butyric acid. However, hydration of 1-butene or 2-butenes produces secondary and/or tertiary butanol, not n-butanol. The oxidation product of sec-butanol is methyl ethyl ketone, and t-butanol is not very prone to oxidation (except when combusted). Therefore, at least one problem associated with the use of butanol (i.e., the oxidation to butyric acid and the resulting unpleasant odor) is not present with the fuel compositions described herein.

Dehydrogenation of the C_2-4 Paraffin Fraction

In one embodiment, all or part of the C_2-4 paraffins may be dehydrogenated to mono-olefins, and hydrolyzed 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.

Alternative Means for Forming Alcohols (the Oxo Process)

Alpha and internal-olefins can be hydroformylated in a process commonly 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 80 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 hydro formulation 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 C_3-5 alcohol stream, such as a composition including between about 60 and about 90%, or consisting essentially of, C_3-5 alcohols, can be obtained. Because this product will have a C₄ average molecular weight, it will have energy per unit volume approximately equal to that of gasoline, and can run in a conventional gasoline engine without the need for modification (i.e., no need for a flexible fuel engine). This is advantageous over hydroformylation of higher olefins, since it produces a fuel product that can run in a conventional engine, and the boiling points of the alcohols are not too high for such use.

Following the OXO reaction, and distillation of alcohols away from paraffins, the alcohol blends can be used as described herein.

IV. Blends of Gasoline and the Alcohol-Containing Compositions

The alcohol-containing compositions described herein can be blended with gasoline to increase the energy per unit volume. The amount of alcohol that can be present in the gasoline/alcohol blends can vary. The alcohols can be the only components present in the fuel composition, along with the optional presence of conventional fuel additives. The ratio of gasoline to the alcohol composition can range from 1:99 to 99:1 by volume, although it can be preferred that the amount of gasoline present is less than around 15% by volume because the energy content will meet or exceed that of E85. That said, given the size of the gasoline market, it may be desirable to use as little as 1-10% of the alcohol composition in gasoline/alcohol blends. In one embodiment, the amount of the alcohol composition is between about 1 and 20 percent by volume, and more ideally, about 15 to 20 percent by volume. In another embodiment, the amount of alcohol composition is between about 75 and 85 percent by volume, and more ideally, about 15 to 20 percent by volume.

The alternative fuel composition described herein can be prepared by mixing gasoline with the alcohol blends described herein, in any suitable manner, and in any desired ratio.

In one embodiment, the gasoline is present in a range of about 75 to 85 percent, with between about 5 and about 20 percent of the alcohol blends described herein, each by volume, with the balance being other additives as described above.

Optimum selection of an appropriate ratio of gasoline and the alcohol blends described herein will depend on a variety of factors, including the season (i.e., winter, summer, spring and fall), altitude, type of alcohols, and type of gasoline. When used to form a gasoline/alcohols blend, one can identify a sufficient quantity of alcohols to provide adequate performance, such as adequate energy per unit volume, by simply adding the alcohol composition and measuring the energy per unit volume until the desired level is reached. Those of skill in the art can readily measure the energy content of the fuel compositions described herein. Alcohols with higher molecular weights (i.e., C_3-4 and higher) have higher energy per unit volume than ethanol, are not as hygroscopic as ethanol, and do not have the same vapor pressure problems as ethanol.

When it is desired to increase the fuel economy of a fuel composition, such as a gasoline/alcohol composition, one can add sufficient gasoline to improve the fuel economy to a desired level. In one embodiment of this aspect, at least a portion of the ethanol and/or butanol are derived from renewable resources.

The fuel composition can be formed by mixing/blending the gasoline and the alcohols. Means for mixing these components are well known to those of skill in the art. During blending, it can be advantageous to remove aliquots of the fuel composition and measure various properties, such as vapor pressure and energy content, to ensure that the mixture/blend has the desired properties.

The resulting fuel compositions and/or blends can be used at least in flexible fuel vehicles, and, ideally, in standard gasoline engines (depending on how much gasoline is present).

V. Optional Additional Components

The fuel compositions can optionally, but preferably, include one or more additives, such as lubricants, emulsifiers, wetting agents, densifiers, fluid-loss additives, corrosion inhibitors, oxidation inhibitors, friction modifiers, demulsifiers, anti-wear agents, anti-foaming agents, detergents, rust inhibitors and the like. Other hydrocarbons, such as those described in U.S. Pat. No. 5,096,883 and/or U.S. Pat. No. 5,189,012, the contents of which are hereby incorporated by reference, can be blended with the fuel, provided that the final blend has the necessary octane/cetane values, pour, cloud and freeze points, kinematic viscosity, flash point, and toxicity properties. The total amount of additives is preferably between 50-100 ppm by weight for 4-stroke engine fuel, and for 2-stroke engine fuel, additional lubricant oil may be added.

Engine performance additives can be added to improve engine performance. Fuel and/or crankcase lubricant can form deposits in the nozzle area of injectors—the area exposed to high cylinder temperatures. Injector cleanliness additives can be added to minimize these problems. Ashless polymeric detergent additives can be added to clean up fuel injector deposits and/or keep injectors clean. These additives include a polar group that bonds to deposits and deposit precursors and a non-polar group that dissolves in the fuel. Detergent additives are typically used in the concentration range of 50 ppm to 300 ppm. Examples of detergents and metal rust inhibitors include the metal salts of sulfonic acids, alkylphenols, sulfurized alkylphenols, alkyl salicylates, naphthenates and other oil soluble mono and dicarboxylic acids such as tetrapropyl succinic anhydride. Neutral or highly basic metal salts such as highly basic alkaline earth metal sulfonates (especially calcium and magnesium salts) are frequently used as such detergents. Also useful is nonylphenol sulfide. Similar materials made by reacting an alkylphenol with commercial sulfur dichlorides. Suitable alkylphenol sulfides can also be prepared by reacting alkylphenols with elemental sulfur. Also suitable as detergents are neutral and basic salts of phenols, generally known as phenates, wherein the phenol is generally an alkyl substituted phenolic group, where the substituent is an aliphatic hydrocarbon group having about 4 to 400 carbon atoms. Lubricity additives can also be added. Lubricity additives are typically fatty acids and/or fatty esters. Examples of suitable lubricants include polyol esters of C12-28 acids. The fatty acids are typically used in the concentration range of 10 ppm to 50 ppm, and the esters are typically used in the range of 50 ppm to 250 ppm.

Some organometallic compounds, for example, barium organometallics, act as combustion catalysts, and can be used as smoke suppressants. Adding these compounds to fuel can reduce the black smoke emissions that result from incomplete combustion. Smoke suppressants based on other metals, e.g., iron, cerium, or platinum, can also be used. Anti-foaming additives such as organosilicone compounds can be used, typically at concentrations of 10 ppm or less. Examples of anti-foaming agents include polysiloxanes such as silicone oil and polydimethyl siloxane; acrylate polymers are also suitable.

Drag reducing additives can also be added to increase the volume of the product that can be delivered. Drag reducing additives are typically used in concentrations below 15 ppm. Antioxidants can be added to the distillate fuel to neutralize or minimize degradation chemistry. Suitable antioxidants include, for example, hindered phenols and certain amines, such as phenylenediamine. They are typically used in the concentration range of 10 ppm to 80 ppm. Examples of antioxidants include those described in U.S. Pat. No. 5,200,101, the contents of which are hereby incorporated by reference. The '101 patent discloses certain amine/hindered phenol, acid anhydride and thiol ester-derived products.

Acid-base reactions are another mode of fuel instability. Stabilizers such as strongly basic amines can be added, typically in the concentration range of 50 ppm to 150 ppm, to counteract these effects.

Metal deactivators can be used to tie up (chelate) various metal impurities, neutralizing their catalytic effects on fuel performance. They are typically used in the concentration range of 1 ppm to 15 ppm.

Multi-component fuel stabilizer packages may contain a dispersant. Dispersants are typically used in the concentration range of 15 ppm to 100 ppm.

Biocides can be used when contamination by microorganisms reaches problem levels. Preferred biocides dissolve in both the fuel and water and can attack the microbes in both phases. Biocides are typically used in the concentration range of 200 ppm to 600 ppm.

Demulsifiers are surfactants that break up emulsions and allow fuel and water phases to separate. Demulsifiers typically are used in the concentration range of 5 ppm to 30 ppm.

Dispersants are well known in the lubricating oil field and include high molecular weight alkyl succinimides being the reaction products of oil soluble polyisobutylene succinic anhydride with ethylene amines such as tetraethylene pentamine and borated salts thereof.

Corrosion inhibitors are compounds that attach to metal surfaces and form a barrier that prevents attack by corrosive agents. They typically are used in the concentration range of 5 ppm to 15 ppm. Examples of suitable corrosion inhibitors include phosphosulfurized hydrocarbons and the products obtained by reacting a phosphosulfurized hydrocarbon with an alkaline earth metal oxide or hydroxide.

Examples of oxidation inhibitors include antioxidants such as alkaline earth metal salts of alkylphenol thioesters having preferably C_5-12 alkyl side chain such as calcium nonylphenol sulfide, barium t-octylphenol sulfide, dioctylphenylamine as well as sulfurized or phosphosulfurized hydrocarbons. Additional examples include oil soluble antioxidant copper compounds such as copper salts of C_10-18 oil soluble fatty acids.

Examples of friction modifiers include fatty acid esters and amides, glycerol esters of dimerized fatty acids and succinate esters or metal salts thereof. Pour point depressants such as C_8-18 dialkyl fumarate vinyl acetate copolymers, polymethacrylates and wax naphthalene are well known to those of skill in the art.

Examples of anti-wear agents include zinc dialkyldithiophosphate, zinc diary diphosphate, and sulfurized isobutylene. Additional additives are described in U.S. Pat. No. 5,898,023 to Francisco, et al., the contents of which are hereby incorporated by reference.

VI. Use of the Fuel Compositions and Other Products

The C_2-4 alcohols can be used to fuel flexible fuel vehicles, alone or in combination with gasoline and/or gasoline additives as described herein, or in conventional gasoline engines when combined with gasoline at a ratio of about 5-25% of the fuel additives to 75-95% of the C2-4 alcohols.

The C₂-₄ alcohols can also be used to fuel solid oxide fuel cells, and produce significantly more electrical energy, per volume of alcohol feedstock, than methanol or ethanol. Thus, using crop wastes, one can generate fuels that can run flexible fuel vehicles and also provide electrical power. Solid oxide fuel cells and other fuel cells typically require fuel sources that are soluble in water, and above four carbons, alcohols tend not to be very soluble in water, so the C_2-4 alcohol product provides about as much energy per unit volume as possible to these fuel cells.

The higher molecular weight hydrocarbons (i.e., C_5-10 are typically a combination of olefins and paraffins. They can be isomerized, cyclized, dimerized or hydrotreated as desired to yield fuel in the gasoline, jet and/or diesel range.

The C_2-4 hydrocarbons can be used for any use conventional LPG is used, including powering certain alternative fuel vehicles, for example, taxis and buses, heating houses, generating electricity, drying crops, and as a fuel for barbecues.

Any methane that is formed can be recycled through the syngas generator, or used for any conventional use for methane, including heating homes and producing methanol.

The water from the Fischer-Trospch step may include alcohols and other oxygenated products, which can be isolated and combined with the remainder of the alcohol products, or the water can be passed through a fuel cell to generate electricity.

VII. Miscellaneous

Representative catalyst and conditions for conducting Fischer-Tropsch synthesis to yield, primarily, C_2-4 olefins are described in M. Janardanarao, Ind. Eng. Chem. Res. 29 (1990) 1735-1753.

Based on Janardanarao, it is believed that the optimum conditions for reacting syngas over a F-T catalyst to maximize selectivity to low molecular weight (i.e., C_2∝) olefins are as follows. Iron-manganese catalysts tend to produce a relatively large C_2-4 hydrocarbon fraction, suppress methane production, and have high syngas conversion. Reaction conditions used by Buessemeier et al., (1976) (Buessemeier, C. D. Frohning and B. Cornils, Hydrocarbon Processing, (November 1976) 105-112) converted syngas to a product mixture that, after accounting for water and carbon dioxide, included approximately 70.2% C_2-4 olefins (Table 1).

TABLE 1
Conversion of syngas to C2-4 products using a Fe catalyst at relatively
low temperature and pressure (Buessemeier et al., 1976).
	Catalyst	Fe/Mn/ZnO/K2O;
		100/100/10/4
	Temp	320°	C.
	Pressure	10	ATM
	H2/CO Ratio	1
	Space Velocity (hr−1)	500
	CO Conversion	86
	Methane	9.6%
	Ethylene	31.3%
	Propylene	22.2%
	Butylene	17.4%
	C2-4 paraffins	15.7%
	C5+ products	3.8%

Janardanarao also tested a variety of other catalysts and conditions that may provide fall-back positions for catalyst optimization. In addition, Tihay et al., (2000) (Tihay et. al. Fe—Co based metal/spinel to produce light olefins from syngas. Catalysis Today 58 (2000) 263-269) demonstrated that Co—Fe catalysts efficiently produce light hydrocarbons (C_1-4), where the C_2-4 fraction is greater than 70% olefinic.

Lower pressures also increase C_2-4 yield (Audier et al. C1 Molecule Chemistry (1984), 1(1), 33-48), while minimizing deactivation of both Fe- and Co-based catalysts (Kokuun et al., Erdoel & Kohle, Erdgas, Petrochemie (1985), 38(7), 299-301; Hutchings et al., Topics in Catalysis (1995), 2(1-4) 163-72.). These reduced operating pressures should also reduce production costs and allow for the potential to recycle unreacted syngas.

In addition to converting syngas to olefins, and olefins to alcohols, a comparable product mixture can be obtained by converting syngas to methanol, methanol to C_2-4 olefins, and C_2-4 olefins to alcohols. This approach can be particularly favorable when using methane as a feedstock, as it provides a syngas with a relatively high proportion of hydrogen relative to carbon monoxide, and can be converted in near quantitative yields to methanol. Representative conditions for converting syngas to methanol are found, for example, in Lee, Sunggyu., and Sardesai, Abhay. “Liquid Phase Methanol and Dimethyl Ether Synthesis from Syngas.” Topics in Catalysis, Vol. 32, No. 3-4, 2005.

Representative conditions for converting methanol to olefins are described, for example, in U.S. Pat. No. 4,499,327 to Kaiser, which discloses making olefins from methanol using a variety of SAPO molecular sieve catalysts. The advantage of using SAPO based catalysts, particularly SAPO-34 based catalysts, is that such catalysts produce a substantially large amount of ethylene and propylene relative to oxygenated hydrocarbons. U.S. Pat. No. 6,518,475 to Xu discloses increasing the ethylene selectivity in the conversion of methanol to olefins by contacting a silicoaluminophosphate molecular sieve catalyst with methanol containing from about 1% to about 15% by weight acetone, and separating the ethylene and propylene from the resulting olefinic product. The presence of acetone purportedly increases the amount of ethylene produced relative to that when pure methanol is used as the feed.

Once the methanol is converted to olefins, the olefin hydration conditions described herein can be used to form a mixed alcohol product essentially free of methanol. In this embodiment, one can take advantage of the relatively high yields associated with syngas to methanol conversion, while still producing a high-energy mixed alcohol product.

In another embodiment, the catalyst is not entirely selective for olefin hydration, and also converts a portion of the alcohols to ethers. Representative conditions are disclosed, for example, in U.S. Pat. No. 5,231,233. Thus, one can convert ethylene to diethyl ether and ethanol, propylene to i-propanol (IPA) and dipropyl ether (DIPE), and the like. All or part of the olefins can alternatively be oligomerized to higher hydrocarbons, using an oligomerization process such as the Mobil olefins to gasoline process (MOG), a vapor phase process carried out at high temperature with feedstreams introduced as gases.

In still a further embodiment, one can use an olefin hydration catalyst that is selective for one olefin over another. That is, one can selectively hydrate propylene and/or butylene, leaving ethylene as a gas. Thus, the high energy i-propyl alcohol and s-butanol can be recovered, and high value ethylene recovered as a co-product and used, for example, to produce polyethylene. If a catalyst selective for ethylene hydration is used, then pure propylene and/or butylene can be isolated. Such catalysts are well known to those of skill in the art, and the selectivity is typically a function of the pore size of the catalysts.

It is particularly desirable, from an environmental standpoint, to use biomass as a feedstock to produce syngas. However, it is difficult to obtain sufficient feedstock in one place to produce sufficient syngas to carry out Fischer-Tropsch synthesis in conventional reactors, which typically involve scales of 100 million gallons/year or more. One approach to getting sufficient biomass to one place is to subject the biomass to a pre-treatment step, such as torrefaction (M. J. Prins et al., More efficient biomass gasification via torrefaction. Energy 31 (2006) 3458-3470). Another approach is to have the feedstock sent to a large facility, for example, by train or truck. Another approach is to take advantage of existing infrastructure and use municipal solid waste (landfill waste) as a feedstock. Yet another approach is to use a series of relatively small reactors, which would allow one to efficiently and effectively use local feedstocks and produce a fuel that can, ideally, be sold locally as well.

Velocys, Inc. has developed micro-fluidic reactors for use in Fischer-Tropsch synthesis. Representative reactors are described, for example, in U.S. Pat. No. 7,084,180. Using micro-fluidic reactors (“microchannel reactors”) equipped with a suitable catalyst that selects for C_2-4 olefin production, as described above, one can convert a syngas composition comprising H₂ and CO to a product mixture predominantly comprising C_2-4 carbons, which product mixture is predominantly olefinic. In this embodiment, the process involves flowing the syngas through a microchannel reactor in contact with a Fischer-Tropsch catalyst selective for C_2-4 olefins, to convert the syngas to an intermediate olefin product. The microchannel reactors include a plurality of process microchannels, or, in one embodiment, a single process microchannel, containing the catalyst. Heat is transferred from the process microchannels to a heat exchanger, and the intermediate product can either be removed from the microchannel reactor, or flowed through another set of process microchannels (or a single microchannel) containing olefin hydration catalysts. Ideally, the process can be used to produce at least about 0.5 gram of C_2-4 olefins, or, if coupled to the olefin hydration step, at least about 0.5 grams of C_2-4 alcohols, per gram of catalyst per hour;. Ideally, the selectivity to methane in the product is less than about 25%, more ideally, less than about 15%, most ideally, less than about 10%.

In one embodiment, the heat exchanger includes a plurality of heat exchange channels adjacent to the process microchannels. In one embodiment, the heat exchange channels are microchannels.

In one embodiment, the present invention relates to a catalyst selective for C_2-4 olefin synthesis, the catalyst comprising iron and other metals, as well as a catalyst support, such as alumina.

In one aspect of this embodiment, the microchannel reactor includes at least one process microchannel, the process microchannel having an entrance and an exit; and at least one heat exchange zone adjacent to the process microchannel, the heat exchange zone comprising a plurality of heat exchange channels. The heat exchange channels can extend lengthwise at right angles relative to the lengthwise direction of the process microchannels. The heat exchange zones can extend lengthwise in the same direction as the process microchannels, and can be positioned near the process microchannel entrance. The length of the heat exchange zone is ideally less than the length of the process microchannel. The width of the process microchannel at or near the process microchannel exit is ideally greater than the width of the process microchannel at or near the process microchannel entrance. In one embodiment, the at least one heat exchange zone includes a first heat exchange zone and a second heat exchange zone, where the length of the second heat exchange zone being less than the length of the first heat exchange zone.

The products formed using this reactor, and using catalysts and reaction conditions favorable for producing a C_2-4 olefin intermediate, or a C_2-4 mixed alcohol product, tend to boil below about 350° C. The products can be separated into a tail gas fraction (e.g., tail gases through middle distillates), and a condensate fraction (a C_5-20 and higher fraction) using, for example, a high pressure and/or lower temperature vapor-liquid separator, or low pressure separators or a combination of separators. The product mixture can include water, carbon dioxide, unreacted syngas, methane, C_2-4 olefins, C_2-4 paraffins, and small amount of heavy (C₅₊) products, including hydrocarbons in the distillate fuel ranges, including the jet or diesel fuel ranges. Methane and unreacted syngas can be separated from other products using means well known to those of skill in the art, for example, using a demethanizer column appropriately sized for use with the microchannel reactor.

In one aspect of this embodiment, the process microchannels are characterized by having a bulk flow path. The term “bulk flow path” refers to an open path (contiguous bulk flow region) within the process microchannels. A contiguous bulk flow region allows rapid fluid flow through the microchannels without large pressure drops. The flow of fluid in the bulk flow region can be laminar. Bulk flow regions within each process microchannel can have a cross-sectional area of about 0.05 to about 10,000 mm², and in one embodiment, about 0.05 to about 5000 mm², and in another embodiment, about 0.1 to about 2500 mm². The bulk flow regions can include from about 5% to about 95%, and in one embodiment, include from about 30% to about 80%, of the cross-section of the process microchannels.

The contact time of the reactants with the catalyst within the process microchannels typically ranges up to about 2000 milliseconds (ms), and in one embodiment, from about 10 ms to about 1000 ms, and in another embodiment, from about 20 ms to about 500 ms. In one embodiment, the contact time may range up to about 300 ms, and in another embodiment, from about 20 to about 300 ms, and in a further embodiment from about 50 to about 150 ms.

The space velocity (or gas hourly space velocity (GHSV)) for the flow of the reactant composition and product through the process microchannels is typically at least about 1000 hr⁻¹ (normal liters of feed/hour/liter of volume within the process microchannels) or at least about 800 ml feed/(g catalyst) (hr). The space velocity typically ranges from about 1000 to about 1,000,000 hr⁻¹, or from about 800 to about 800,000 ml feed/(g catalyst) (hr). In one embodiment, the space velocity ranges from about 10,000 to about 100,000 hr⁻¹, or about 8,000 to about 80,000 ml feed/(g catalyst) (hr).

The temperature of the reactant composition entering the process microchannels typically ranges from about 150° C. to about 400° C., and in one embodiment is between about 180° C. to about 350° C., and in another embodiment, is from about 180° C. to about 325° C.

The temperature of the reactant composition and product within the process microchannels may range from about 200° C. to about 400° C., and in one embodiment is from about 220° C. to about 370° C.

The temperature of the product exiting the process microchannels typically ranges from about 200° C. to about 400° C., and in one embodiment is from about 320° C. to about 370° C.

The pressure within the process microchannels is typically between about 5 and 50 atmospheres, more typically, 10 to about 50 atmospheres, and in one embodiment from about 10 to about 30 atmospheres, and in one embodiment from about 10 to about 25 atmospheres, and in one embodiment from about 15 to about 25 atmospheres.

The pressure drop of the reactants and/or products as they flow through the process microchannels can range up to about 10 atmospheres per meter of length of the process microchannel (atm/m), and in one embodiment, up to about atm/m, and in one embodiment up to about 3 atm/m.

The reactant composition entering the process microchannels is typically in the form of a vapor, while the product exiting the process microchannels may be in the form of a vapor, a liquid, or a mixture of vapor and liquid. The Reynolds Number for the flow of vapor through the process microchannels is typically in the range of about 10 to about 4000, and in one embodiment about 100 to about 2000. The Reynolds Number for the flow of liquid through the process microchannels is typically about 10 to about 4000, and in one embodiment about 100 to about 2000.

The heat exchange fluid entering the heat exchange channels may be at a temperature of about 150° C. to about 400° C., and in one embodiment about 150° C. to about 370° C. The heat exchange fluid exiting the heat exchange channels may be at a temperature in the range of about 220° C. to about 370° C., and in one embodiment about 230° C. to about 350° C. The residence time of the heat exchange fluid in the heat exchange channels typically ranges from about 50 to about 5000 ms, and in one embodiment, about 100 to about 1000 ms. The pressure drop for the heat exchange fluid as it flows through the heat exchange channels may range up to about 10 atm/m, and in one embodiment from about 1 to about 10 atm/m, and in one embodiment from about 2 to about 5 atm/m. The heat exchange fluid may be in the form of a vapor, a liquid, or a mixture of vapor and liquid. The Reynolds Number for the flow of vapor through the heat exchange channels is typically from about 10 to about 4000, and in one embodiment about 100 to about 2000. The Reynolds Number for the flow of liquid through heat exchange channels may be from about 10 to about 4000, and in one embodiment about 100 to about 2000.

The conversion of CO is ideally at least about 40% or higher per cycle, and in one embodiment about 50% or higher, and in one embodiment about 55% or higher, and in one embodiment about 60% or higher, and in one embodiment about 65% or higher, and in one embodiment about 70% or higher. The term “cycle” is used herein to refer to a single pass of the reactants through the process microchannels.

The selectivity to methane in the product is typically about 25% or less, and in one embodiment about 20% or less, and in one embodiment about 15% or less, and in one embodiment about 12% or less, and in one embodiment about 10% or less.

The yield of product is ideally about 25% or higher per cycle, and in one embodiment about 30% or higher, and in one embodiment about 40% or higher per cycle.

In one embodiment, the conversion of CO is at least about 50%, the selectivity to methane is about 15% or less, and the yield of product is at least about 35% per cycle.

Using the microchannel reactors described herein, one can efficiently control the heat generated from the exothermic Fischer-Tropsch reaction, and, with appropriate use of heat exchangers, ideally transfer this heat energy to, and use the energy in, the olefin hydration step. Ideally, using the microfluidic approach, whereas water and olefins will separate in a large scale Fischer-Tropsch reactor, and may need to be separately added to the olefin hydration step, they may remain in close enough proximity in the microchannel reactor to be simultaneously passed through the olefin hydration catalyst(s). In this embodiment, it may be possible to carry out the entire synthesis, and only isolate products, such as unreacted syngas, methane, C_2-4 paraffins, and the desired C_2-4 alcohols, as the products exit the microchannel reactor.

All patents and publications disclosed herein are hereby incorporated by reference in their entirety and for all purposes. Modifications and variations of the present invention, related to an alternative fuel composition, and blends of the alternative fuel composition with gasoline, will be obvious to those skilled in the art from the foregoing detailed description of the invention.

Claims

1. An alternative fuel composition, comprising a mixture of: a) ethanol, b) isopropanol, and c) one or more alcohols selected from the group consisting of sec-butanol and t-butanol.

2. The composition of claim 1, wherein the composition further comprises gasoline.

3. The composition of claim 1, wherein the composition comprises less than 10% of alcohols with a molecular weight greater than butanol.

4. The composition of claim 1, wherein the composition comprises at least 15% sec-butanol and/or t-butanol by volume.

5. The composition of claim 1, wherein the energy content of the fuel composition meets or exceeds that of ASTM D5798-99 (Standard Specification for Fuel Ethanol for Automotive Spark-ignition Engines).

6. The composition of claim 1, wherein the composition is comprises less than 3% of each of n-butanol and methanol.

7. The composition of claim 1, wherein the alcohols are produced by converting syngas to a C2-4 olefin-containing product stream using Fisher-Tropsch synthesis, and subjecting all or a portion of the C2-4 olefins to olefin hydration.

8. A method for forming an alternative fuel composition comprising a mixture of: a) ethanol, b) isopropanol, and c) one or more alcohols selected from the group consisting of sec-butanol, and t-butanol, comprising the steps of:

i) converting syngas to a C2-4 olefin-containing product stream via Fisher-Tropsch synthesis, and/or

ii) subjecting all or a portion of the C2-4 olefins to olefin hydration

9. The method of claim 8, wherein a C2-4 olefin-rich stream is isolated before being converted to alcohols.

10. The method of claim 8, wherein the composition comprises less than 10% of alcohols with a molecular weight greater than butanol.

11. The method of claim 8, wherein the composition comprises at least 15% sec-butanol and/or t-butanol by volume.

12. The method of claim 8, wherein the energy content of the alcohol fuel composition meets or exceeds that of ASTM (D5798-99 Standard Specification for Fuel Ethanol for Automotive Spark-ignition Engines).

13. The method of claim 8, wherein the olefin hydration is performed on a composition comprising C2-4 alkanes and C2-4 olefins.

14. The method of claim 8, wherein all or part of the C2-4 alkanes are isolated following the olefin hydration.

15. The method of claim 8, wherein all or part of the C2-4 alkanes are dehydrogenated to form hydrogen and additional C2-4 olefins.

16. The method of claim 15, wherein the composition comprises less than 3% of each of n-butanol and methanol.

17. The method of claim 8, wherein the syngas is derived from cellulosic biomass.

18. The fuel composition of claim 1, further comprising gasoline.

19. The composition of claim 18, wherein the composition comprises between about 75 and about 95 percent by volume of gasoline and between about 5 and about 25 percent by volume of the composition of claim 1.

20. An alternative fuel composition, consisting essentially of a mixture of:

a) ethanol, b) isopropanol, and c) one or more alcohols selected from the group consisting of sec-butanol and t-butanol.