BIOFUEL COMPOSITIONS AND METHODS BASED ON CO-PROCESSING AROMATIC-RICH AND AROMATIC-LEAN COMPONENTS

Abstract

Biofuel compositions obtained by the simultaneous hydroprocessing of at least two distinct hydroprocessing feedstocks, either or both of which are derived from biomass, are disclosed. The co-processing of these feedstocks can result in an upgraded product having suitable characteristics, in terms of composition (e.g., quantities of compounds such as aromatic hydrocarbons, present in relatively large amounts) and in terms of quality (e.g., quantities of compounds such as oxygenates, present in relatively small amounts) for use as a hydroprocessed biofuel such as hydroprocessed aviation biofuel.

Description

FIELD OF THE INVENTION

The present invention relates to the hydroprocessing of both aromatic-rich and aromatic-lean components, either or both of which are derived from biomass, as well as hydroprocessed biofuels (e.g., aviation fuel) made from this co-processing. The present invention also relates to such hydroprocessing methods, utilizing hydrogen generated from biomass-derived C₄⁻ byproducts, in order to further reduce the carbon footprint of the biofuel.

DESCRIPTION OF RELATED ART

Environmental concerns over fossil fuel greenhouse gas (GHG) emissions have led to an increasing emphasis on renewable energy sources. Wood and other forms of biomass including agricultural and forestry residues are examples of some of the main types of renewable feedstocks being considered for the production of liquid fuels. Energy from biomass based on energy crops such as short rotation forestry, for example, can contribute significantly towards the objectives of the Kyoto Agreement in reducing GHG emissions.

Gasification is a known process for the conversion of a wide range of carbonaceous materials, such as coal and natural gas, into a gaseous mixture containing carbon monoxide and hydrogen, referred to as synthesis gas or syngas. The process involves contacting the raw material in a gasification reactor with a controlled amount of oxygen and/or steam to achieve partial oxidation but not complete combustion. Representative processes for coal gasification to syngas are described, for example, in WO 2006/070018; U.S. Pat. No. 4,836,146; and WO 2004/005438. In the case of biomass gasification, in which the source of carbon is renewable, the incomplete combustion generally results in a mixture called producer gas, which includes small amounts of methane in addition to the CO and H₂. See, for example, Rajvanshi, A. K., “Biomass Gasification,” Ch. 4 of ALTERNATIVE ENERGY IN AGRICULTURE, Vol. II, CRC Press, 1986, pp. 83-102. Other known routes for the production of syngas from biomass include “hydro-gasification” (gasification in the presence of hydrogen), to generate methane, followed by steam reforming, pyrolytic reforming, or steam pyrolysis of the methane. Representative processes are described, for example in U.S. Pat. No. 7,619,012; US Publication 2005/0256212; and US Publication 2005/0032920.

Once syngas is obtained, the Fischer-Tropsch (F-T) process can be used for the further synthesis, from this feed, of paraffinic hydrocarbons having from one carbon atom (methane) to 200 carbon atoms or even more. In particular, the syngas is fed to an F-T reactor where it is converted over a suitable catalyst at elevated temperature and pressure into these hydrocarbons. The F-T process is described, for example, in WO 02/02489, WO 01/76736, WO 02/07882, EP 0 510 771 and EP 0 450 861. The combination of biomass gasification and F-T synthesis therefore provides a Biomass to Liquid (BTL) pathway for producing renewable fuel components.

In addition to BTL, pyrolysis is an alternative route for obtaining liquid fuels, including transportation fuel and heating oil, from biomass feedstocks. Pyrolysis refers to thermal decomposition in the substantial absence of oxygen (or in the presence of significantly less oxygen than required for complete combustion). Initial attempts to obtain useful oils from biomass pyrolysis yielded predominantly an equilibrium product slate (i.e., the products of “slow pyrolysis”). In addition to the desired liquid product, roughly equal proportions of non-reactive solids (char and ash) and non-condensable gases were obtained as unwanted byproducts. More recently, however, significantly improved yields of primary, non-equilibrium liquids and gases (including valuable chemicals, chemical intermediates, petrochemicals, and fuels) have been obtained from carbonaceous feedstocks through fast (rapid or flash) pyrolysis, accompanied by a reduction in undesirable, slow pyrolysis products.

The development of fuel compositions, and particularly those useful as transportation fuels, which are derived at least partly from renewable feedstocks such as biomass, is an ongoing objective of major industrial importance. Of significant interest are compositions, or fractions useful for blending into compositions, having characteristics (e.g., energy content, distillation curve, and density) that are representative of their counterpart petroleum derived compositions or blending fractions, used for the same intended purpose (e.g., as aviation fuel). Of further interest are methods for producing such compositions and fractions in a manner that exploits processing synergies and/or economies of scale, thereby resulting in the lowest possible carbon footprint, based on a lifecycle assessment of their GHG emissions.

SUMMARY OF THE INVENTION

The present invention is associated with the discovery of fuel compositions exhibiting reduced greenhouse gas (GHG) emissions, based on a lifecycle assessment (LCA) from the time of cultivation of feedstocks (in the case of plant materials) required for the compositions, up to and including the ultimate combustion of the fuel composition by the end user. The compositions are prepared by co-processing at least two distinct hydroprocessing feedstocks, either or both of which are derived from biomass. Advantageously, co-processing results in an upgraded, hydroprocessed product (or an upgraded, hydroprocessed biofuel as a hydroprocessed product fraction) having suitable characteristics, in terms of composition (e.g., quantities of compounds such as aromatic hydrocarbons, present in relatively large or minimally required amounts) and in terms of quality (e.g., quantities of thermally unstable compounds such as oxygenates, present in relatively small amounts) for use as a fuel composition or component thereof.

Aspects of the invention relate to the use hydroprocessing to simultaneously upgrade (i) a hydroprocessing feedstock that is rich in cyclic compounds, for example a crude or refined pyrolysis oil or tall oil, together with (ii) a hydroprocessing feedstock that is lean in aromatic compounds, for example the highly paraffinic product obtained from gasification and Fischer-Tropsch (F-T) synthesis. In component (i), namely the “aromatic-rich” component, the cyclic compounds are effectively precursors to aromatic compounds formed in the hydroprocessing. Both pyrolysis oil and component (ii), namely the “aromatic-lean” component, such as an F-T synthesis product, may be derived from biomass. Particular embodiments of the invention are therefore directed to hydroprocessing methods, or methods for making fuel compositions, in which both the aromatic-rich component and the aromatic-lean component are derived from biomass, or otherwise such methods in which the aromatic lean component is derived from tall oil (e.g., tall oil rosin acids) and the aromatic-lean component is derived from biomass.

Pyrolysis oil, either in its crude form (i.e., raw pyrolysis oil) or treated to remove solid contaminants and soluble metallic compounds, typically contains a high oxygen content and a low energy content, relative to petroleum derived liquid fuel fractions. Other properties of pyrolysis oil render it generally unusable, in any appreciable proportion, as a component of a transportation fuel composition. Likewise, the products of Biomass to Liquid (BTL) pathways described above, which include the products of gasification followed by F-T synthesis, are generally of significantly lower quality, compared to their counterpart, paraffin-rich petroleum derived products used for fuel blending. This quality deficit results from the presence of oxygenates and possibly olefins, with amounts of these non-paraffin impurities depending on the F-T catalyst and processing conditions used. Moreover, the high overall paraffin content characteristic of products obtained from this reaction renders them unsuitable, even in the absence of their oxygenate and olefin impurities, for use in current commercial applications such as aviation fuel, unless blended with aromatic hydrocarbons.

Hydroprocessing of both aromatic-rich and aromatic-lean components advantageously provides simultaneous upgrading of at least these two components, which, optionally followed by fractionation of the resulting, hydroprocessed product, can provide a hydroprocessed biofuel meeting applicable composition and quality standards. In addition, the oxygenate content of the aromatic-rich component, which is generally significantly higher than that of the aromatic-lean component (e.g., derived from F-T synthesis), is diluted during hydroprocessing. This further simplifies the overall process, by reducing adiabatic temperature rise and the corresponding production of undesirable coke precursors. According to embodiments of the invention, a biofuel that does not require further blending with aromatic hydrocarbons, such as an on-spec aviation biofuel, is obtained after hydroprocessing and fractionation.

Embodiments of the invention therefore relate to novel production methods for fuel compositions that are at least partially, but often completely, derived from renewable carbon sources. These sources include an aromatic-rich biomass derived component and an aromatic-lean component that may likewise be biomass derived (e.g., from the BTL pathway, combining gasification and F-T synthesis, as described above). Representative methods comprise contacting these components with hydrogen together in a common hydroprocessing reactor to achieve efficiencies and other advantages, as discussed herein, compared to separately upgrading these components. Following fractionation of the hydroprocessed product, the resulting hydroprocessed biofuel (e.g., a hydroprocessed aviation biofuel, having a significant quantity of aromatic hydrocarbons) may be used in neat form (e.g., as an aviation fuel) or otherwise blended, for example, with conventional petroleum derived blending stocks. Whether or not the hydroprocessed biofuel is blended, the carbon footprint of the resulting neat biofuel or blended biofuel can be reduced.

Other embodiments of the invention relate to production methods for hydroprocessed biofuel exhibiting a GHG emission, based on a Life Cycle Assessment (LCA), which is further reduced by virtue of using a biomass-derived source of hydrogen for the hydroprocessing step. In particular, byproducts (e.g., light hydrocarbons) of hydroprocessing, F-T synthesis, and/or pyrolysis can be converted, according to an overall hydroprocessed biofuel production process, in an integrated hydrogen generation unit. For example, a catalytic steam reformer may be integrated with one or more of a catalytic hydroprocessing unit, a F-T synthesis unit, and/or a Rapid Thermal Processing (RTP) pyrolysis unit. Therefore, at least a portion of the byproducts of any one or more of these operations may be converted to hydrogen (e.g., by catalytic steam reforming), thereby generating at least a portion of the hydrogen required for hydroprocessing. Importantly, the generation of hydrogen in this manner (i.e., from byproducts obtained from the processing of feedstocks comprising renewable carbon) beneficially reduces the amount of hydrogen that must be obtained from external fossil sources (imported), thereby further lowering the lifecycle GHG emission value of the resulting hydroprocessed biofuel. According to other embodiments in which gasification and F-T synthesis are used to provide the aromatic-lean component, a portion of the syngas from gasification can be purified and used as a renewable source of hydrogen for hydroprocessing.

Representative production methods include (i) the pyrolysis of a first biomass feedstock to raw pyrolysis oil, to provide the aromatic-rich component and also (ii) the gasification of a second biomass feedstock, followed by F-T synthesis, to provide the aromatic-lean component. Alternatively, the aromatic-rich component may be obtained from other naturally occurring sources without pyrolysis, such as from tall oil or oils derived from aromatic foliage such as eucalyptols. The first and second biomass feedstocks may comprise the same or different types of biomass, and, according to particular embodiments, both components are derived from second generation (e.g., lignocellulosic) biomass feedstocks. The aromatic-rich and/or aromatic-lean components may optionally be obtained after separation from (e.g., by fractionation), and/or pretreatment of, the raw pyrolysis oil and/or the F-T synthesis product, respectively, prior to hydroprocessing. In any event, the subsequent hydroprocessing of the aromatic-rich and aromatic-lean components beneficially reduces their total oxygen content and increases their total heating value.

The methods can further comprise separating an effluent or product of hydroprocessing (e.g., a hydrotreating or hydrocracking reactor effluent), for example, by fractionation and/or absorption, to provide the hydroprocessed biofuel as a hydroprocessed product fraction (e.g., a hydroprocessed aviation biofuel, a hydroprocessed gasoline biofuel, etc.) comprising hydrocarbons having normal boiling points characteristic of their counterpart petroleum derived fractions used for the same application. It is also possible to blend such petroleum derived fractions, in a subsequent blending step, to provide the fuel compositions having a reduced carbon footprint (i.e., exhibiting reduced GHG emissions based on their LCA), by virtue of at least part of the carbon content of the compositions being renewable.

Further embodiments of the invention relate to methods of preparing fuel compositions. Representative methods comprise blending a hydroprocessed product fraction, and particularly a hydroprocessed biofuel made according to methods described herein, with a petroleum derived component. Representative amounts of the hydroprocessed product fraction (e.g., a hydroprocessed aviation biofuel) and petroleum derived components are also described herein.

These and other embodiments and aspects relating to the present invention are apparent from the following Detailed Description.

DETAILED DESCRIPTION

Representative methods for making a fuel composition, according to embodiments of the invention, comprise contacting an aromatic-rich biomass derived component and an aromatic-lean component with hydrogen under catalytic hydroprocessing conditions effective to deoxygenate and upgrade both of these components simultaneously and provide a hydroprocessed biofuel meeting industry specifications. The simultaneous co-processing results in efficiencies and other advantages as described above. Preferably both the aromatic-rich component and the aromatic-lean component are derived from biomass to provide a hydroprocessed biofuel having a carbon content that is all or substantially all derived from renewable carbon. The carbon footprint of the biofuel is thereby greatly reduced according to U.S. government greenhouse gas (GHG) emission accounting practices, in which emissions associated with the combustion of biomass derived fuels are not reported in the lifecycle assessment (LCA) of the GHG emission value, since biomass is renewed over a very short time frame compared to petroleum derived components. Of particular interest with respect to the biofuel compositions described herein are aviation (e.g., jet) fuels.

Biomass suitable as a renewable carbon source for the aromatic-rich component, for example a pyrolysis oil obtained using Rapid Thermal Processing (RTP), can be any plant material, or mixture of plant materials, including a hardwood (e.g., whitewood), a softwood, or a hardwood or softwood bark. Energy crops, or otherwise agricultural residues (e.g., logging residues) or other types of plant wastes or plant-derived wastes, may also be used as plant materials. Specific exemplary plant materials include corn fiber, corn stover, and sugar cane bagasse, in addition to “on-purpose” energy crops such as switchgrass, miscanthus, and algae. Short rotation forestry products, as energy crops, include alder, ash, southern beech, birch, eucalyptus, poplar, willow, paper mulberry, Australian blackwood, sycamore, and varieties of paulownia elongate. Other examples of suitable biomass include organic waste materials, such as waste paper and construction, demolition, and municipal wastes. In general, the pyrolysis derived component (e.g., pyrolysis derived gasoline) may be obtained from any feedstock comprising lignocellulosic biomass. Because the biomass feedstocks are composed of the same building blocks, namely cellulose, hemi-cellulose, and lignin, pyrolysis conditions are relatively similar in the production of raw pyrolysis oils from these various feedstocks.

These same types of biomass may also be independently selected as a renewable carbon source for the aromatic-lean component, for example obtained according to a Biomass to Liquid (BTL) pathway involving Fischer-Tropsch (F-T) synthesis as discussed above. Other types of biomass include waste plastic, rubber, manure, and biosolids from waste water (sewage) treatment, which may also be employed as feedstocks in the methods described herein.

Aromatic-Rich Component

The “aromatic-rich” component is derived from biomass and comprises a significant quantity, for example generally from about 5% to about 85%, and often from about 10% to about 75%, by weight of cyclic compounds, including cyclic organic oxygenates. The term “cyclic organic oxygenates” is meant to include compounds in which oxygen is incorporated into a ring structure (e.g., a pyran ring), as well as compounds (e.g., phenol) having a ring structure with oxygen being incorporated outside the ring structure. In either case, the ring structure may have from 3 to 8 ring members, be fused to other ring structures, and may be completely saturated (e.g., naphthenic), completely unsaturated (e.g., aromatic), or partially unsaturated. After hydroprocessing, these cyclic compounds, including cyclic organic oxygenates, can contribute to the total aromatics content of the hydroprocessed biofuel. These cyclic compounds are preferably obtained from natural sources, such as lignocellulosic biomass, as described above, that has been pyrolyzed to depolymerize and fragment the cyclic building blocks of cellulose, hemicellulose, and lignin. According to representative embodiments of the invention, the aromatic-rich component is derived from biomass subjected to pyrolysis in an oxygen depleted environment, for example using Rapid Thermal Processing (RTP).

Fast pyrolysis refers generally to technologies involving rapid heat transfer to the biomass feedstock, which is maintained at a relatively high temperature for a very short time. The temperature of the primary pyrolysis products is then rapidly reduced before chemical equilibrium is achieved. The fast cooling therefore prevents the valuable reaction intermediates, formed by depolymerization and fragmentation of the biomass building blocks, namely cellulose, hemicellulose, and lignin, from degrading to non-reactive, low-value final products. A number of fast pyrolysis processes are described in U.S. Pat. No. 5,961,786; Canadian Patent Application 536,549; and by Bridgwater, A. V., “Biomass Fast Pyrolysis,” Review paper BIBLID: 0354-9836, 8 (2004), 2, 21-49. Fast pyrolysis processes include Rapid Thermal Processing (RTP), in which an inert or catalytic solid particulate is used to carry and transfer heat to the feedstock. RTP has been commercialized and operated with very favorable yields (55-80% by weight, depending on the biomass feedstock) of raw pyrolysis oil. The pyrolysis oil, as an aromatic-rich component, whether or not subjected to pretreating prior to hydroprocessing as described above, is normally characterized by a relatively high content of cyclic compounds, which is generally from about 10% to about 90%, and typically from about 20% to about 80%, by weight. These cyclic compounds are precursors to aromatic hydrocarbons obtained through their further reaction in the hydroprocessing step, which also beneficially decreases the oxygenate content and increases the heating value of the pyrolysis oil, as discussed in greater detail below.

According to other embodiments, cyclic compounds are obtained from rosin acids of tall oil. Tall oil refers to a resinous yellow-black oily liquid, which is namely an acidified byproduct of the kraft or sulfate processing of pine wood. Tall oil, prior to refining, is normally a mixture of rosin acids, fatty acids, sterols, high-molecular weight alcohols, and other alkyl chain materials. Distillation of crude tall oil may be used to recover a tall oil fraction that is enriched in the rosin acids, for use as an aromatic-rich component as described herein. The aromatic-rich component may therefore comprise tall oil either in its crude form or distilled (e.g., by vacuum distillation) to remove pitch (i.e., depitched tall oil) or otherwise distilled to concentrate the rosin acids, which are primarily abietic acid and dehydroabietic acid but include other cyclic carboxylic acids. As discussed above, the aromatic-rich component may in general be obtained after separation from (e.g., by fractionation), and/or pretreatment of, a raw pyrolysis oil or crude tall oil, prior to hydroprocessing. In the former case, raw pyrolysis oil is often subjected to pretreatment such as filtration to remove solids and/or ion exchange to remove soluble metals, prior to hydroprocessing.

Importantly, the aromatic-rich component can be hydroprocessed to provide cyclic hydrocarbons, including aromatic hydrocarbons in an amount governed by the equilibrium between homologous naphthenic and aromatic ring structures under hydroprocessing conditions of temperature and hydrogen partial pressure, as described herein. According to preferred embodiments, the aromatic-rich component is present in the combined hydroprocessing feedstock (including both the aromatic-rich and aromatic-lean components) in a quantity effective to obtain a hydroprocessed biofuel or hydroprocessed biofuel fraction (e.g., a hydroprocessed aviation biofuel) comprising aromatic hydrocarbons generally in an amount of at least 2% by volume (e.g., from about 2% to about 25% by volume), typically in an amount of at least 3% by volume (e.g., from about 3% to about 20% by volume), and often in an amount of at least 8% by volume (e.g., from about 8% to about 15% by volume). Due to the nature of the cyclic compounds of the aromatic-rich component, when derived from biomass, the aromatic hydrocarbons in the resulting hydroprocessed product or hydroprocessed biofuel fraction of this product (e.g., hydroprocessed aviation biofuel) generally include only minor amounts of benzene and toluene. In representative embodiments, such hydroprocessed biofuel fractions comprise generally less than about 3% by weight, and typically less than about 2% by weight, of benzene and toluene combined.

Aromatic-Lean Component

The aromatic-lean component generally comprises non-cyclic, and predominantly straight-chain paraffinic and olefinic hydrocarbons, for example in an amount of generally from about 50% to about 98%, and typically from about 75% to about 97%, by weight. The amount of cyclic compounds in the aromatic-lean component is generally less than about 3%, and often less than about 1%, by weight. A representative aromatic-lean component is obtained from a combination of gasification, for example of a biomass feedstock, to provide syngas, followed by F-T synthesis to provide the mixture of non-cyclic paraffinic and olefinic hydrocarbons, in proportions governed substantially by the catalyst system used. In general, a representative aromatic-lean component is the product of a BTL pathway as discussed above. Like the aromatic-rich component, the aromatic-lean component may also generally be obtained after further processing steps, which in this case include separation from (e.g., by fractionation), and/or pretreatment of, a BTL product or other Fischer-Tropsch synthesis product, prior to hydroprocessing. For example, the normally liquid phase product of this synthesis may be separated from normally gas phase by-products such as light hydrocarbons, as well as from other by-products, such as water, according to known methods.

F-T synthesis of liquid fuel refers to a process for converting syngas, namely a mixture of CO and H₂, into hydrocarbons of advancing molecular weight according to the reaction:

n(CO+2H₂)→(—CH₂—)_n+nH₂O+heat.

Products of the F-T synthesis reaction may therefore range from methane to heavy paraffin waxes. Normally, the production of methane is minimized and a substantial portion of the hydrocarbons produced have a carbon chain length of a least 5 carbon atoms. Therefore, C₅⁺ hydrocarbons are present in the F-T reaction product in an amount generally of at least about 60% (e.g., from about 60% to about 99%), and typically at least about 70% (e.g., from about 70% to about 95%) by weight. These amounts are also representative of those in the aromatic-lean product, even following conventional removal of light hydrocarbon (e.g., methane and ethane) byproducts and water as described above.

F-T synthesis is carried out in the presence of an appropriate catalyst and generally at elevated temperatures, for example from about 125° C. (257° F.) to about 350° C. (662° F.), and typically from about 175° C. (347° F.) to about 275° C. (527° F.). Suitable absolute pressures are generally from about 0.5 MPa (75 psig) to 15 MPa (2200 psig), and typically from about 0.7 MPa (100 psig) to about 3.5 MPa (500 psig). The F-T synthesis may be carried out in a multi-tubular reactor, a slurry phase regime or an ebullating bed regime, wherein the catalyst particles are kept in suspension by an upward superficial gas and/or liquid velocity.

Representative catalysts for the F-T synthesis of hydrocarbons comprise, as the catalytically active component, a metal from Group VIII of the periodic table, which is typically selected from ruthenium, iron, cobalt, nickel and mixtures thereof. The catalytically active metal or combination of metals is normally disposed on a carrier, which may be a porous inorganic refractory oxide, such as alumina, silica, titania, zirconia or mixtures thereof. The amount of catalytically active metal may range generally from about 1% to about 50% by weight, and typically from about 2% to about 30% by weight. The catalytically active metal may be present in the catalyst in combination with one or more metal promoters or co-catalysts. These promoters may be metals or metal oxides, for example the oxides of metals selected from Groups IIA, IIIB, IVB, VB, VIIB and/or VIII of the Periodic Table, or oxides of the lanthanides and/or the actinides. Particular representative F-T catalysts comprise iron or cobalt as the catalytically active metal and further comprise a promoter selected from the group consisting of zirconium, manganese, and vanadium. Iron-containing F-T catalysts are preferred for syngas feeds having a low H₂ content, such as those derived from biomass, as this metal also promotes the water-gas shift reaction to increase H₂ availability. Other representative metal promoters include rhenium, platinum, and palladium. Reference to groups of the Periodic Table are based on the “previous IUPAC form” as described in the Handbook of Chemistry and Physics (CPC Press), 68^th Ed. As discussed above, the particular catalyst system chosen, including the types and amounts of metal(s) and promoters, as well as the type of carrier, has a significant impact on the relative quantity of olefins obtained in the F-T synthesis, relative to paraffins.

The syngas used for F-T synthesis may be obtained from a wide variety of carbonaceous feedstocks through gasification (e.g., non-catalytic partial oxidation). Preferably, the syngas is obtained from gasification of biomass, although other suitable gasification feedstocks that do not necessarily include renewable carbon may also be used. If the product of F-T synthesis is not derived from any renewable carbon, then the renewable carbon of the resulting hydroprocessed biofuel may be only that portion of the total carbon that is obtained from the aromatic-rich component. Carbonaceous feedstocks that are capable of being gasified to a mixture of hydrogen and carbon monoxide include coal (e.g., anthracite, brown coal, bitumous coal, sub-bitumous coal, lignite, and petroleum coke), bituminous oils, mineral crude oil or fractions (e.g., resids) thereof, and methane containing feedstocks (e.g., refinery gas, coal bed gas, associated gas, and natural gas). Processes for converting such feedstocks to syngas are described, for example, in “Gasification” by C. Higman and M van der Burgt, Elsevier Science (USA), 2003, ISBN 0-7506-7707-4, Ch. 4 and 5. If desired, the H₂:CO molar ratio obtained via gasification may be adapted for the specific Fischer-Tropsch catalyst and process. In case of syngas formed by gasification, this molar ratio is generally less than about 1, for example in the range from about 0.3 to about 0.9. It is possible to use such H₂:CO molar ratios in the Fischer-Tropsch synthesis, but more satisfactory results may be obtained by increasing this ratio, for example by performing a water-gas shift reaction or by adding hydrogen to the syngas mixture. According to preferred embodiments, the H₂:CO ratio in the syngas is at least about 1.5, for example in the range from about 1.6 to about 1.9.

Hydroprocessing

When the aromatic-lean component is a product of a BTL pathway involving gasification of biomass and Fischer-Tropsch synthesis as discussed above, this component is essentially free of sulfur and aromatic hydrocarbons. However, this component also generally contains oxygenates (e.g., aliphatic alcohols), such that the total oxygen content of the aromatic-lean component is typically in the range from about 0.25% to about 10%, and often from about 0.5% to about 5%. Furthermore, reactive olefins may be present in the aromatic-lean component in widely varying amounts, depending on the particular F-T synthesis catalyst system, process, and conditions used.

The raw pyrolysis oil obtained from a feedstock comprising biomass, as described above, contains generally from about 20% to about 50%, and often from about 30 to about 40%, by weight of total oxygen, for example in the form of both (i) organic oxygenates, such as hydroxyaldehydes, hydroxyketones, sugars, carboxylic acids, and phenolic oligomers, and (ii) dissolved water. For this reason, although a pourable and transportable liquid fuel, the raw pyrolysis oil has only about 55-60% of the energy content of crude oil-based fuel oils. Representative values of the energy content are in the range from about 19.0 MJ/liter (69,800 BTU/gal) to about 25.0 MJ/liter (91,800 BTU/gal). Moreover, this raw product is often corrosive and exhibits chemical instability due to the presence of highly unsaturated compounds such as olefins (including diolefins) and alkenylaromatics. Hydroprocessing of this pyrolysis oil is therefore beneficial in terms of reducing its oxygen content and increasing its stability, thereby rendering the hydroprocessed product more suitable for blending in fuels, such as gasoline, meeting all applicable specifications. As discussed above, the term “pyrolysis oil,” as it applies to a feedstock to the hydroprocessing step, refers to the raw pyrolysis oil obtained directly from pyrolysis (e.g., RTP) or otherwise refers to this raw pyrolysis oil after having undergone pretreatment such as filtration to remove solids and/or ion exchange to remove soluble metals, prior to the hydroprocessing step.

As discussed above, the aromatic-lean component is preferably obtained from BTL pathways.

These also include combined coal to liquid/biomass to liquid (CTL/BTL) pathways, involving coal gasification, in which biomass is added to the CTL unit to improve the carbon footprint of the syngas used as a feed to F-T synthesis. For any BTL pathway involving gasification of biomass followed by Fischer-Tropsch synthesis, the aromatic-lean component contains predominantly paraffinic or olefinic hydrocarbons, depending on the Fischer-Tropsch catalyst system used. In either case, however, oxygenates are present as impurities (e.g., as aliphatic alcohols) in these hydrocarbons. Upgrading of the aromatic-lean component through hydroprocessing, which normally involves hydrotreating to remove oxygenates and other heteroatom-containing impurities, and possibly hydrocracking to reduce average molecular weight, is therefore beneficial for providing a desired fuel such as synthetic paraffinic kerosene (SPK). This hydroprocessed biofuel, however, cannot meet aviation fuel ASTM specifications (e.g., both density and aromatic content) without the addition of aromatic hydrocarbons.

Likewise, naturally derived oils rich in cyclic compounds (and therefore useful as the aromatic-rich component in compositions and methods of the present invention), including pyrolysis oil, crude tall oil, and depitched tall oil, have a high oxygenate content. In the case of tall oil, for example, rosin acids (all multi-ring organic acids) are present in significant concentrations. Deoxygenation of these oxygenated cyclic compounds under hydroprocessing conditions beneficially yields aromatic hydrocarbons. In combination with oxygen removal, ring saturation and/or ring opening of at least one ring (but not all rings) of the multi-ring compounds leads to the formation of napthenic and/or alkylated cyclic hydrocarbons, respectively. Importantly, the naphthenic/aromatic hydrocarbon equilibrium under the particular hydroprocessing conditions used, may be used to govern the relative proportions of these species and thereby meet desired specifications for a particular application, for example the content of aromatic hydrocarbons in the hydroprocessed aviation biofuel.

Aspects of the invention are therefore associated with the operational synergies that may be obtained by co-processing both the aromatic-rich and aromatic-lean components to not only achieve similar objectives (e.g., oxygenate removal) but also produce a hydroprocessed biofuel that meets a number of important product specifications, for example minimum aromatic content and maximum total oxygen content in the case of jet fuel. According to some embodiments, blending of the hydroprocessed biofuel with petroleum derived aviation fuel and/or further processing, is not required to achieve an “on-spec” fuel.

Hydroprocessing which includes hydrotreating (e.g., hydrodeoxygenation) and optionally hydrocracking reactions, involves contacting the combined, aromatic-rich and aromatic-lean components with hydrogen and in the presence of a suitable hydroprocessing catalyst, generally under conditions sufficient to convert a large proportion of the organic oxygenates in the combined hydroprocessing feedstock to CO, CO₂ and water that are easily separated from the hydroprocessed product. The hydrogen may be present in one or more streams, as discussed in greater detail below. The hydrogen may be substantially pure (e.g., as makeup or fresh hydrogen) or relatively impure (e.g., as recycle hydrogen), as long as sufficient hydrogen partial pressure is maintained in the reaction environment to achieve the desired performance (e.g., conversion, catalyst stability, and product aromatic content).

According to particular embodiments of the invention, the aromatic-rich and aromatic-lean components may be mixed or combined prior to the resulting mixture being contacted with any hydrogen. In other embodiments, one component may be contacted with hydrogen upstream of contacting with the other component (which may similarly have been contacted with a separate hydrogen stream). Optionally, streams containing the aromatic-rich and aromatic-lean components (either or both of which having been previously contacted with hydrogen) may be combined and optionally contacted with hydrogen, for example as a separate hydrogen stream. According to yet further embodiments, streams containing portions of the aromatic-rich and/or aromatic-lean components (any of which, any combination of which, or all of which having been previously contacted with hydrogen) may be combined and the combined streams optionally contacted further with hydrogen. The important consideration is that, at some point in the hydroprocessing, the aromatic-rich and aromatic-lean components are in the presence of the same hydroprocessing catalyst and conditions, thereby gaining efficiencies and other advantages associated with co-processing, as described above.

Typical hydroprocessing conditions, under which the aromatic-rich and aromatic-lean components are co-processed, include an average catalyst bed temperature from about 40° C. (104° F.) to about 538° C. (1000° F.), often from about 150° C. (302° F.) to about 426° C. (800° F.), and a hydrogen partial pressure from about 3.5 MPa (500 psig) to about 21 MPa (3000 psig), often from about 6.2 MPa (800 psig) to about 10.5 MPa (1500 psig). In addition to pressure and temperature, the residence times of the aromatic-rich and aromatic-lean components in the presence of hydroprocessing catalyst (e.g., disposed in one or more catalyst beds or zones) can also be adjusted to increase or decrease the reaction severity and consequently the quality of the resulting hydroprocessed biofuel. With all other variables unchanged, lower residence times are associated with lower reaction severity. The inverse of the residence time is closely related to a variable known as the Liquid Hourly Space Velocity (LHSV, expressed in units of hr⁻¹), which is the volumetric liquid flow rate over the catalyst bed divided by the bed volume and represents the equivalent number of catalyst bed volumes of liquid processed per hour. Therefore, increasing the LHSV or hydroprocessing feedstock flow rate, processed over a given quantity of catalyst, directionally decreases residence time and the conversion of undesirable compounds present in this oil, such as organic oxygenate compounds. A typical range of LHSV for mild hydrotreating according to the present invention is from about 0.1 hr⁻¹ to about 10 hr⁻¹, often from about 0.5 hr to about 3 hr ⁻¹. The quantity of hydrogen used may be based on the stoichiometric amount needed to convert organic oxygenates to hydrocarbons and H₂O. In representative embodiments, hydroprocessing is carried out in the presence of hydrogen in amount ranging from about 90% to about 600% of this stoichiometric amount.

The hydroprocessing catalyst may be present in the form of a fixed bed of particles comprising a catalytically active metal disposed on a support, with suitable metals and supports being described below. Otherwise the catalyst, either supported or otherwise unsupported (e.g., in the form of fine particles of a compound containing the catalytically active metal), may be used in a back-mixed bed, such as in the case of a slurry reactor. Homogeneous systems operating with catalysts that are soluble in the reactants and products may also be used. Catalytic hydroprocessing conditions will vary depending on the quality of the hydroprocessed biofuel desired, with higher severity operations directionally resulting in greater conversion of organic oxygenates and other undesirable compounds (e.g., reactive olefins and diolefins) by hydrogenation.

Suitable hydroprocessing catalysts include those comprising of at least one Group VIII metal, such as iron, cobalt, and nickel (e.g., cobalt and/or nickel) and at least one Group VI metal, such as molybdenum and tungsten, on a high surface area support material such as a refractory inorganic oxide (e.g., silica, alumina, titania, and/or zirconia). A carbon support may also be used. A representative hydroprocessing catalyst therefore comprises a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum, and mixtures thereof (e.g., a mixture of cobalt and molybdenum), deposited on any of these support materials, or combinations of support materials. The choice of support material may be influenced, in some cases, by the need for corrosion resistance in view of the presence of aqueous acids, for example in the aromatic-rich component (e.g., pyrolysis oil) as a feedstock to hydroprocessing.

The Group VIII metal is typically present in the hydroprocessing catalyst in an amount ranging from about 2 to about 20 weight percent, and normally from about 4 to about 12 weight percent, based on the volatile-free catalyst weight. The Group VI metal is typically present in an amount ranging from about 1 to about 25 weight percent, and normally from about 2 to about 25 weight percent, also based on the volatile-free catalyst weight. A volatile-free catalyst sample may be obtained by subjecting the catalyst to drying at 200-350° C. (392-662° F.) under an inert gas purge or vacuum for a period of time (e.g., 2 hours), so that water and other volatile components are driven from the catalyst.

Other suitable hydroprocessing catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum. It is within the scope of the invention to use more than one type of hydroprocessing catalyst in the same or a different reaction vessel. Two or more hydroprocessing catalyst beds of the same or different catalyst and one or more quench points may also be utilized in a reaction vessel or vessels to provide the hydroprocessed biofuel.

After hydroprocessing, the resulting hydroprocessed biofuel has an oxygen content that is generally reduced from about 90% to about 100% (i.e., complete or substantially complete oxygen removal), relative to the oxygen present in the feedstock to hydroprocessing, for example the oxygen present in the combined aromatic-rich and aromatic-lean components, optionally after any pretreatment prior to hydroprocessing. Importantly, the heating value, on a mass basis, of the hydroprocessed biofuel is simultaneously increased, typically by a factor ranging from about 1.5 to about 3, compared to that of the feedstock to hydroprocessing. Fractionation or other separation methods may be used to separate various fractions of the hydroprocessed product (or total hydroprocessing effluent), which includes the hydroprocessed biofuel such as a hydroprocessed aviation biofuel. These fractions or hydroprocessed biofuels, in addition to having been fractionated may also be obtained after other treatments including catalytic reaction (e.g., for further oxygen removal) and/or adsorption. The separated, hydroprocessed biofuel fraction may then, according to some embodiments, be blended with comparable petroleum derived fractions and possibly other suitable additives.

In addition to a hydroprocessed aviation or jet fuel, other fractions that may be recovered from separation (e.g., fractionation) of the hydroprocessed product include a hydroprocessed gasoline biofuel, a hydroprocessed kerosene biofuel, and/or a hydroprocessed diesel biofuel, as fractions having successively higher boiling point ranges. Likewise, lower boiling point range components may also be recovered by fractionation. These include, for example, a hydroprocessed renewable analogue of liquefied petroleum gas (LPG). After hydroprocessing and fractionation, the hydroprocessed biofuel fractions described above, including hydroprocessed aviation biofuel, comprise predominantly hydrocarbons, typically at least about 90% hydrocarbons (e.g., from about 90% to about 99.9% hydrocarbons) by weight, and often at least about 97% hydrocarbons (e.g., from about 97% to about 99.5% hydrocarbons) by weight.

A hydroprocessed aviation biofuel may therefore be separated from the hydrocarbon-containing products of hydroprocessing, based on boiling point or relative volatility, in a distillation column capable of carrying out a suitable number of theoretical stages of equilibrium contacting between rising vapor and falling liquid. According to representative embodiments, the hydroprocessed aviation biofuel will have an initial boiling point temperature characteristic of C₅ hydrocarbons, for example from about 30° C. (86° F.) to about 40° C. (104° F.) and a distillation end point temperature generally from about 138° C. (280° F.) to about 300° C. (572° F.), and typically from about 145° C. (293° F.) to about 288° C. (550° F.). These boiling point temperatures, which are also characteristic of petroleum derived aviation fuel fractions, are measured according to ASTM D86.

A hydroprocessed aviation biofuel component or other hydroprocessed biofuel fraction, therefore, may be separated by fractionation from lower boiling hydrocarbons contained in a more volatile component (e.g., a hydroprocessed analogue of LPG) and/or higher boiling hydrocarbons contained in a less volatile component (e.g., a hydroprocessed kerosene biofuel and/or a hydroprocessed diesel biofuel). According to preferred embodiments, the separated, lower boiling hydrocarbons comprise C₄ hydrocarbons (e.g., butanes and butenes) as well as lower boiling compounds, such that these lower boiling hydrocarbons may be referred to a C₄⁻ hydrocarbons. To further reduce the GHG emission value, based on LCA, of the hydroprocessed aviation biofuel or other hydroprocessed biofuel fraction(s), at least a portion of these biomass-derived C₄⁻ hydrocarbons are advantageously used to generate at least a portion of the hydrogen required for contacting with the aromatic-rich and/or aromatic-lean components during the hydroprocessing.

The conversion of the lower boiling hydrocarbons, contained in a less valuable, hydroprocessed biofuel fraction, to hydrogen, can reduce or even eliminate the need for an external source of hydrogen. This external hydrogen, if derived from fossil fuel, would otherwise add to the carbon footprint associated with the production of the hydroprocessed biofuel described herein, thereby increasing the GHG emissions based on LCA. Integrated hydrogen production is therefore beneficial in minimizing the GHG emissions exhibited by any of the hydroprocessed biofuel fraction(s) associated with the present invention. According to particular embodiments, the C₄⁻¹ hydrocarbons are catalytically reformed in the presence of steam. Representative steam reforming catalysts include alumina supported nickel oxide.

Whether or not integrated hydrogen production is used, the oxygen content remaining in the hydroprocessed aviation biofuel or other hydroprocessed biofuel fraction(s) described above is a function of the severity of the hydroprocessing operation, with higher severity resulting in a higher conversion of organic oxygenates to CO, CO₂, and water, which may be easily removed. While a reduction in organic oxygenates directionally increases heating value, this improvement in the quality of a hydroprocessed biofuel fraction is achieved at the expense of increased energy required for the hydroprocessing operation. Optimization of the organic oxygen content is therefore possible, depending on the particular biomass used as feedstock, the particular fuel (or fuel blend) composition, and its intended end use (e.g., for land transport, in the case of gasoline or diesel fuels that allow more than trace quantities of oxygenates).

Representative hydroprocessed biofuel fractions, other than hydroprocessed aviation biofuel, generally contain from about 0.001% to about 5%, typically from about 0.02% to about 4%, and often from about 0.05% to about 3%, by weight of organic oxygenates that are relatively refractory under hydroprocessing conditions. These ranges also apply to cyclic organic oxygenates (e.g., phenol and alkylated phenols), which normally account for most or substantially all of the organic oxygenates of a given hydroprocessed biofuel fraction(s). In view of these amounts of cyclic organic oxygenates a given hydroprocessed biofuel fraction, representative fuel compositions (e.g., containing one or more petroleum derived fractions) that are blended with such a hydroprocessed biofuel fraction will generally contain from about 0.0005% to about 2.5%, typically from about 0.01% to about 2%, and often from about 0.025% to about 1.5%, by weight of cyclic organic oxygenates. According to other embodiments, these ranges may be representative of the total phenol content, including alkylated phenols, in the fuel composition. In the case of hydroprocessed aviation biofuel, the total organic oxygen content remaining after hydroprocessing, fractionation, and optionally additional treatments as described above, is generally less than 0.5% by weight to meet ASTM thermal stability test specifications for aviation fuel. Preferably, the total organic oxygen content of the aviation biofuel is less than about 500 parts per million (ppm) by weight and more preferably less than about 300 ppm by weight. The hydrocarbon content of such aviation biofuels is therefore generally at least about 99.5% by weight, and the aromatic hydrocarbon content is as discussed above.

The hydroprocessed aviation biofuel or other hydroprocessed biofuel fraction(s) as described above, also advantageously share a number of important characteristics with their petroleum derived counterpart components. In terms of energy content, these fractions may have a lower heating value generally from about 42 MJ/kg (18,100 BTU/lb) to about 46 MJ/kg (19,800 BTU/lb) and typically from about 43 MJ/kg (18,500 BTU/lb) to about 45 MJ/kg (19,400 BTU/lb). While these hydroprocessed biofuel fractions can meet various standards required of their petroleum derived counterparts, their carbon footprint is greatly reduced according to U.S. government GHG emission accounting practices, in which emissions associated with the combustion of biomass derived fuels are not reported in the GHG emission value based on LCA, as discussed above. According to particular embodiments of the invention, in which the hydroprocessed biofuel or other hydroprocessed biofuel fraction(s) is derived completely from biomass and/or other renewable carbon sources, the lifecycle greenhouse gas emission value of such biofuel fraction(s), based on CO₂ equivalents, is/are generally from about 5 g CO₂-eq./MJ (11.6 lb CO₂ eq/mmBTU) to about 50 g CO₂-eq./MJ (116.3 lb CO₂-eq./mmBTU), typically from about 15 g CO₂-eq./MJ (34.9 lb CO₂ eq./mmBTU) to about 35 g CO₂-eq./MJ (81.3 lb CO₂-eq/mmBTU), and often from about 20 g CO₂-eq./MJ (46.5 lb CO₂-eq./mmBTU) to about 30 g CO₂-eq./MJ (69.8 lb CO₂-eq/mmBTU), as measured according to guidelines set forth by the Intergovernmental Panel on Climate Change (IPCC) and the U.S. federal government. LCA values of emissions in terms of CO₂ equivalents, from raw material cultivation (in the case of plant materials) or raw material extraction (in the case of fossil fuels) through fuel combustion, can be calculated using SimaPro 7.1 software and IPCC GWP 100a methodologies.

According to representative fuel compositions associated with the present invention, the hydroprocessed aviation biofuel or other hydroprocessed biofuel fraction as described above may be blended with a petroleum derived aviation fuel or other petroleum derived fraction that is present in the resulting fuel composition in an amount from about 30% to about 98% by weight. According to particular fuel compositions, (i) generally from 1 to about 99%, and typically from 1 to about 30%, of the hydroprocessed biofuel fraction by weight is blended with (ii) generally from about 1% to about 99%, and typically from about 70% to about 99% of a petroleum derived fraction by weight.

Overall, aspects of the invention are directed to methods of making fuel compositions comprising contacting, with hydrogen, a feedstock to a hydroprocessing step. The feedstock comprises both aromatic-rich and aromatic-lean components, either or both of which may be derived from biomass. According to some embodiments, for example, the aromatic-rich component may be derived from fossil fuels and the aromatic-lean component may be derived from biomass. Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes could be made in these methods, as well as compositions made by these methods, without departing from the scope of the present invention. Mechanisms used to explain theoretical or observed phenomena or results, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims.

Claims

1. A method for making a fuel composition, the method comprising contacting an aromatic-rich biomass derived component and an aromatic-lean component with hydrogen under catalytic hydroprocessing conditions to provide a hydroprocessed biofuel.

2. The method of claim 1, wherein the aromatic-lean component is obtained from a combination of gasification and Fischer-Tropsch synthesis.

3. The method of claim 2, wherein the aromatic-lean component comprises olefinic hydrocarbons and oxygenated compounds.

4. The method of claim 1, wherein the aromatic-lean component is derived from biomass and the aromatic-rich component is derived from either biomass or tall oil.

5. The method of claim 4, wherein the aromatic-lean component is derived from biomass independently selected from the group consisting of hardwood, softwood, hardwood bark, softwood bark, corn fiber, corn stover, sugar cane bagasse, switchgrass, miscanthus, algae, waste paper, construction waste, demolition waste, municipal waste, and mixtures thereof.

6. The method of claim 1, wherein the catalytic hydroprocessing conditions result in both hydrotreating and hydrocracking reactions.

7. The method of claim 1, wherein the aromatic-rich biomass derived component is obtained from pyrolysis.

8. The method of claim 1, wherein the aromatic-rich biomass derived component comprises tall oil rosin acids or eucalyptols.

9. The method of claim 8, wherein the aromatic-rich biomass derived component is crude tall oil or depitched tall oil.

10. The method of claim 1, wherein the aromatic-rich biomass derived component comprises from about 10% to about 50% of oxygen by weight.

11. The method of claim 1, wherein the hydroprocessed biofuel is a hydroprocessed aviation biofuel recovered from fractionation of a hydroprocessed product of the contacting of the aromatic-rich biomass derived component and the aromatic-lean component with hydrogen.

12. The method of claim 11, wherein fractionation separates the hydroprocessed aviation biofuel fraction from lower boiling hydrocarbons and higher boiling hydrocarbons present in the hydroprocessed product.

13. The method of claim 12, wherein the lower boiling hydrocarbons comprise C4−1 hydrocarbons.

14. The method of claim 13, further comprising generating, from at least a portion of the C4−1 hydrocarbons, at least a portion of the hydrogen for contacting with the aromatic-rich biomass derived component and the aromatic-lean component.

15. The method of claim 14, further comprising catalytically reforming at least the portion of the C4−1 hydrocarbons in the presence of steam to generate at least the portion of the hydrogen for contacting with the aromatic-rich biomass derived component and the aromatic-lean component.

16. The method of claim 11, further comprising blending the hydroprocessed aviation biofuel fraction with from about 1% to 99% by weight of a petroleum derived aviation fuel.

17. A fuel composition comprising a hydroprocessed aviation biofuel obtained from hydroprocessing an aromatic-rich biomass derived component and an aromatic-lean component.

18. The fuel composition of claim 17, wherein the hydroprocessed aviation biofuel fraction comprises less than about 500 part per million (ppm) of total organic oxygen by weight.

19. The fuel composition of claim 17, wherein the hydroprocessed aviation biofuel fraction comprises at least about 99.5% hydrocarbons by weight.

20. The fuel composition of claim 17, wherein the hydroprocessed aviation biofuel fraction comprises at least about 3% aromatic hydrocarbons by volume.