WO2009009322A1

WO2009009322A1 - Integrated facility for producing alcohol using homoacidogenic fermentation

Info

Publication number: WO2009009322A1
Application number: PCT/US2008/068569
Authority: WO
Inventors: David James Shcreck; Norman Louis Balmer
Original assignee: Best Energies, Inc.
Priority date: 2007-07-06
Filing date: 2008-06-27
Publication date: 2009-01-15

Abstract

Esters are hydro genated to provide product alcohols such as ethanol. In one aspect, the hydrogenation is conducted to substantially completely react the hydrogen and provide a hydrogenation product containing product alcohol and unreacted ester which is recycled. In another aspect, hydrogen for the hydrogenation is provided by pyrolysis of biomass and hydrogen separation operation, and the rate of hydrogen supply from the pyrolysis to the hydrogenation is controlled by adjusting the purity of hydrogen from the hydrogen separation operation.

Description

INTEGRATED FACILITY FOR PRODUCING ALCOHOL USING HOMOACIDOGENIC FERMENTATION

FIELD OF THE INVENTION

[0001] This invention pertains to improved processes for the production of alcohol, especially ethanol, by homoacidogenic fermentation of carbohydrates and hydrogenation of esters of the fermentation product. The processes of this invention enable the high yield of product alcohol based upon fermentable feedstock.

BACKGROUND TO THE INVENTION [0002] An interest exists in producing ethanol from biomass as fuel ethanol, either as an additive to or a replacement for liquid transportation fuels or as chemical feedstock. Ethanol can be synthesized from biomass by various processes, including through fermentation. The direct fermentation of a sugar as the biomass with yeast results in the inherent generation of carbon dioxide and results in usually less than 65, and often less than 50, percent of the sugar being converted to ethanol. This relatively low yield of ethanol per unit of fermentable biomass places a higher demand on raw material, which is typically corn and places a greater disruption on the use of arable land.

[0003] Another process for making ethanol is the indirect process in which homoacidogenic fermentation results in the production of acetic acid. In this type of fermentation process, virtually all the fermentable biomass is converted. While the acid is not readily hydrogenated to ethanol, the indirect process involves generating an ester and then hydrogenating the ester to ethanol. The advantage is that the sugars can be converted to acetic acid in nearly 100 percent yield.

[0004] The acetic acid causes the fermentation medium to become acidic and thus can be deleterious to the microorganism for the fermentation. Conventionally, the acetic acid is neutralized during the fermentation (base neutralization route), and recovered. The acid form is regenerated, e.g., by contact with mineral acid, and then esterified with a primary alcohol. An alternative approach is disclosed in copending patent application [Atty. Docket: GEIN- 109-PCT], filed on even date herewith and incorporated by reference in its entirety, in which the acetic acid is esterified with primary alcohol in the presence of the fermentation medium and is passed into a water-immiscible phase. This later process is referred to as the direct, or insitu, esterification route. [0005] Homoacidogenic fermentation is well known. See, for instance, U.S. Patent

Nos. 4,371,619; 4, 506,012; 4,935,360 and 6,509,180. U.S. Patent Nos. 6,509,180 and 7,074,603 disclose corn dry milling to provide the sugars for fermentation to produce acetic acid for conversion to ethanol. [0006] Although the yield of fermentation product per unit of fermentable biomass is substantially greater for the indirect process than for direct fermentation to ethanol, hydrogen is required for the hydrogenation to make ethanol from the ester. Moreover, conventional hydrogenation, especially in the liquid phase, is conducted at high pressure to assure complete conversion of the ester. SUMMARY OF THE INVENTION

[0007] By this invention, energy efficient, homoacidogenic processes to provide alcohol such as ethanol, propanol and butanol are provided.

[0008] One broad aspect of the invention pertains to the continuous hydrogenation of ester of acid from homoacidogenic fermentation wherein the hydrogenation conditions provide for substantially complete consumption of hydrogen. One advantage of this aspect of the invention is that a hydrogen stripper and hydrogen compressor need not be used, saving both capital and energy costs. While this total consumption of hydrogen will result in only a portion of the ester being hydrogenated, the product alcohol can readily be removed by distillation from the unreacted ester. The energy consumption and capital costs associated with recycling a liquid stream to the hydrogenation step are much less than those entailed in compressing and recycling hydrogen gas. A further advantage of this broad aspect of the invention is that with the focus on total consumption of hydrogen rather than essentially complete hydrogenation of ester, hydrogen need not be required to be at the high hydrogenation pressures heretofore used to assure dispersion of hydrogen throughout the volume of ester. Accordingly, savings in compression costs for feed hydrogen can be achieved.

[0009] The processes of this aspect of the invention for producing ethanol may desirably comprise: a. contacting an acetic ester with hydrogen under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising ethanol wherein the molar ratio of hydrogen to acetic ester is sufficiently less than 1 :1 so that the hydrogenation product contains less than about 0.01 mole percent hydrogen; b. subjecting to hydrogenation product to distillation to provide a lower boiling fraction comprising ethanol and a higher boiling fraction comprising unreacted acetic ester; and c. recycling at least a portion of the higher boiling fraction to step (a). [0010] Often the molar ratio of hydrogen to ester is less than about 0.9:1, say, about 0.1 :1 to 0.8:1, and sometimes between about 0.2:1 and 0.7:1. The hydrogenation may be conducted in the vapor, liquid or mixed phases. Preferably the ester is substantially in the liquid phase. The hydrogenation conditions typically comprise the presence of hydrogenation catalyst, a temperature of between about 150°C and 300⁰C and a pressure between about 300 and 5000 kPa absolute. Preferably the hydrogenation reaction menstruum is highly agitated, most preferably by high shear mixing. See, for instance, WO 02/089966, herein incorporated by reference in its entirety, for one type of apparatus for high shear mixing. The contact time between the hydrogen and liquid phase can vary widely depending upon the type of reaction system used and the extent of conversion of the ester to alkanol. The apparatus may include one or more contact stages to facilitate contact between hydrogen and ester in the liquid phase. If desired, one or more final reaction stages may be used where residual hydrogen in the liquid menstruum can continue to react. In these stages, a longer reaction time may be used. The reaction time can thus vary substantially depending upon the percentage of hydrogen fed is sought to be reacted. Hence, the reaction time can vary from 1 or 2 seconds to 24 or more hours. As stated above, the unreacted ester can be recycled, or if desired, passed to one or more additional hydrogenation reaction stages. [0011] The alcohol portion of the ester comprises hydrocarbon of at least 2, preferably at least 3, say 3 to 30, say, 8 to 24, carbon atoms. The most preferred esters, e.g., methyl esters, acetic esters, propyl esters or butyl esters, are those having an alcohol portion that is substantially immiscible with water. [0012] A preferred process for making alcohol product comprises: a. subjecting an aqueous menstruum containing carbohydrate to homoacidogenic fermentation conditions to provide an organic acid corresponding to the alcohol product, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. esterifying at least a portion of said organic acid with esterifying alcohol, preferably comprising a primary alcohol, having a greater number of carbon atoms than the organic acid to provide an ester product; c. hydrogenating the ester product under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising alcohol product wherein the molar ratio of hydrogen to ester product is sufficiently less than 1 :1 that the hydrogenation product contains less than about 0.01 mole percent hydrogen; d. subjecting to hydrogenation product to distillation to provide a lower boiling fraction comprising alcohol product and a higher boiling fraction comprising unreacted ester product and esterifying alcohol; and e. recycling at least a portion, often at least about 10 mass percent, and sometimes from about 50 mass percent to essentially all, of the higher boiling fraction to step (b). [0013] The alcohol product is often at least one of ethanol, propanol and butanol.

In some instances, the organic acid in step (a) is neutralized with base to form a salt, and the base is then reacidified to provide the organic acid which is then esterifϊed in step (b). [0014] The homoacido genie fermentation and esterification can occur in the same zone, or a portion of the fermentation menstruum can be withdrawn, subjected to esterification with the water-immiscible phase removed, and the menstruum recycled to the fermentation zone.

[0015] The catalyst for the esterification can be heterogeneous or homogeneous and may be in the aqueous phase, water-immiscible phase, or both. Thus, the esterification catalyst may be solid esterification catalyst, dissolved catalyst or even an esterase capable of converting organic acid to ester.

[0016] In another broad aspect of the invention, a pyrolysis of biomass is used to provide hydrogen for hydrogenating an acetic ester to make ethanol and to provide combustible gases for heating the pyrolysis kiln. In these processes, a hydrogen separation operation is used to provide a stream having a higher hydrogen concentration. The rate of hydrogen supply for the hydrogenation is controlled, at least in part, by changing the hydrogen purity of the hydrogen product produced by the hydrogen separation operation. Thus a continuous process can be provided that is able to provide the desired amount of hydrogen to the hydrogenation even with changes in the biomass to the pyrolysis kiln. As the biomass feed is variable in terms of composition and moisture content, and as the feed rates of biomass are difficult to maintain constant due to size and density variations, the ability to readily control the flow of hydrogen to the hydrogenation greatly facilitates the use of pyrolysis as a source of hydrogen. Further, the pyrolysis enables biomass that might otherwise decay to carbon dioxide, to be effectively used for producing a biofuel. Moreover, the char from pyrolysis can find use for soil additives which enhance the retention of nitrogen as well as have increased stability as compared to the biomass itself. [0017] Continuous processes of this aspect of the invention for making ethanol may desirably comprise: a. contacting an acetic ester with hydrogen under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising ethanol; b. pyrolyzing biomass feed to provide pyrolysis gases comprising hydrogen and carbon monoxide, said pyrolysis being under pyrolysis conditions comprising a substantial absence of molecular oxygen and elevated temperatures, said elevated temperatures being provided at least in part by indirect heat exchange with gases from the combustion of fuel comprising carbon monoxide and hydrogen; c. subjecting at least a portion of the pyrolysis gases to a hydrogen separation operation to provide a fraction containing an increased concentration of hydrogen and a fraction containing hydrogen and an increased concentration of carbon monoxide; d. providing said fraction containing an increased concentration of hydrogen to step (a) for the hydrogenation, and e. providing said fraction containing carbon monoxide to step (b) as at least a portion of the fuel, wherein the rate of hydrogen supply by step (d) is controlled by changing the purity of the hydrogen in said fraction containing an increased concentration of hydrogen. [0018] The hydrogen separation operation preferably comprises at least one of membrane separation and sorption, especially thermal swing and pressure swing sorption. For the membrane separation, the hydrogen purity can be changed through by-passing none to a portion of the pyrolysis gases on a retentate side of the membrane separator to the fraction containing hydrogen. For the sorption, the hydrogen purity can be changed through changing cycle times. [0019] The pyrolysis is typically at a temperature of between at least about 225°C, say between about 250°C and 600°C, and often between about 300°C and 450 or 550⁰C. If desired the pyrolysis gases may be subjected to water gas shift to increase the molar ratio of hydrogen to carbon monoxide. The water gas shift may occur prior to, during or after the hydrogen separation operation. [0020] The hydrogenation may be conducted in the vapor, liquid or mixed phases. Preferably the acetic ester is substantially in the liquid phase. The molar ratio of hydrogen to acetic ester may be such that substantially all the hydrogen is consumed during the hydrogenation. In which case, the molar ratio of hydrogen to acetic ester is less than about 0.9:1, say, about 0.1 :1 to 0.8:1, and sometimes between about 0.2:1 and 0.7:1, and the pressure can be between about 300 and 5000 kPa absolute. However, it is contemplated that in accordance with this aspect of the invention the molar ratio of hydrogen to acetic ester can be substantially higher with a recycle of unreacted hydrogen. In this case, the molar ratio of hydrogen to acetic ester is often in the range of about least about 1.1 :1, and more frequently at least about 2:1, preferably 2:1 to 8:1, and higher pressures are used to enhance conversion of the acetic ester to alcohol and ethanol, e.g., a pressure of at least about 3 MPa, say, 3 to 50 MPa (absolute). The hydrogenation conditions typically comprise the presence of hydrogenation catalyst and a temperature of between about 150⁰C and 300⁰C. Preferably the hydrogenation reaction menstruum is highly agitated, most preferably by high turbulence mixing. [0021] The alcohol portion of acetic ester comprises hydrocarbon of at least 2, preferably at least 3, say 3 to 30, say, 8 to 24, carbon atoms. The most preferred acetates are those having an alcohol portion that is substantially immiscible with water. [0022] A preferred process comprises: a. subjecting an aqueous menstruum containing carbohydrate to homoacidogenic fermentation conditions to provide an organic acid corresponding to the alcohol, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. esterifying at least a portion of said organic acid with esterifying alcohol, preferably comprising primary alcohol, having a greater number of carbon atoms than the organic acid; c. hydrogenating the ester product under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising product alcohol; d. subjecting the hydrogenation product to distillation to provide a lower boiling fraction comprising product alcohol and a higher boiling fraction comprising unreacted ester product and esterifying alcohol; and e. recycling at least a portion of the higher boiling fraction to step (b); f. pyrolyzing biomass feed to provide pyrolysis gases comprising hydrogen and carbon monoxide, said pyrolysis being under pyrolysis conditions comprising a substantial absence of molecular oxygen and elevated temperatures, said elevated temperatures being provided at least in part by indirect heat exchange with gases from the combustion of fuel comprising carbon monoxide and hydrogen; g. subjecting at least a portion of the pyrolysis gases to a hydrogen separation operation to provide a fraction containing an increased concentration of hydrogen and a fraction containing hydrogen and an increased concentration of carbon monoxide; h. providing said fraction containing an increased concentration of hydrogen to step (c) for the hydrogenation, and i. providing said fraction containing carbon monoxide to step (f) as at least a portion of the fuel, wherein the rate of hydrogen supply by step (h) is controlled by changing the purity of the hydrogen in said fraction containing an increased concentration of hydrogen. [0023] In some instances, the organic acid in step (a) is neutralized with base to form a salt, and the base is then reacidified to provide the organic acid which is then esterified in step (b).

[0024] The homoacidogenic fermentation and esterification can occur in the same zone, or a portion of the fermentation menstruum can be withdrawn, subjected to esterification with the water-immiscible phase removed, and the menstruum recycled to the fermentation zone.

[0025] The catalyst for the esterification can be heterogeneous or homogeneous and may be in the aqueous phase, water-immiscible phase, or both. Thus, the esterification catalyst may be solid esterification catalyst, dissolved catalyst or even an esterase capable of converting organic acid to ester.

[0026] The carbohydrate for step (a) can be derived from any suitable biomass. In preferred aspects of this invention, the carbohydrate comprises sugars from corn or sugar cane, and the biomass for the pyrolysis of step (f) comprises portions of the corn plant, e.g., corn stover, or sugar cane plant not used for the homoacidogenic fermentation. Preferably the pyrolysis of step (f) provides char and the char is used for soil enhancement. [0027] Those skilled in the art and guided by the teachings herein provided will appreciate that a process or selected process steps referred to herein as being "continuous" or being conducted in a "continuous" manner may require a period of time and/or operation to, respectively, arrive at or shut down from a desired state of operation. In particular, such processing may involve a "ramping up" to arrive at a sought operation and/or a "ramping down" from such operation, such as in the event of process shut down. For instance, the concentration of acetic acid in the aqueous menstruum may be allowed to build-up during an initial operational phase prior to initiating esterification. Similarly, esterification may proceed before introducing any additional water-immiscible phase. The addition of alcohol to provide the esterification product may also change with time, yet still have a continuous operation. If desired, the addition rates of alcohol and of any water-immiscible solvent may be constant through the duration of the continuous period of the process. [0028] Those skilled in the art and guided by the teachings herein provided will also appreciate that a continuous process or processing step in accordance with the invention may in practice generally have a duration that is limited or restricted such as by the viability of microorganisms employed in such process or processing step, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic description of an apparatus for synthesizing ethanol in accordance with processes of this invention.

[0030] Figure 2 is a schematic description of another type of apparatus for synthesizing ethanol in accordance with processes of this invention.

[0031] Figure 3 is a schematic description of yet a further type of apparatus for synthesizing ethanol in accordance with processes of this invention

DETAILED DESCRIPTION Homoacidogenic fermentation and esterification [0032] The homoacidogenic fermentation processes of this invention are suitable for the production of a wide variety of organic acids, including diacids, especially those having from 1 to 5, especially one to 3, carbon atoms. The acids may or may not be substituted, e.g., with hydroxyl or lower alkoxy moieties. Exemplary acids include, but are not limited to formic acid, acetylfomic acid, acetic acid, hydroxyacetic acid, methoxyacetic acid, propionic acid, hydroxypropionic acid, and butyric acid. The following discussion will refer to acetic acid and ethanol product for sake of ease of understanding, however, the broad scope of the invention is not intended to be so limited.

[0033] Carbohydrates are compounds containing carbon, oxygen and hydrogen that contains a succharose unit or its first reaction product and in which the ratio of hydrogen to oxygen is the same as in water. Any suitable carbohydrate-containing feedstock may be used in the processes of this invention that is converted to acetic acid by the chosen microorganism for the fermentation. Examples of carbohydrate-containing feedstocks are cellulosic materials such as derived from wood, grasses, cotton, corn stover, and the like, especially hemicellulosic materials; starches and sugars including, but not limited to, xylose, sucrose, dextrose, fructose, lactose, maltose, cellobiose, gum Arabic, tragacanth, and the like. The sugars may be derived from various sources such as sugar cane, sugar beet, milk, milo, grapes, sorghum, maple syrup, corn, and the like.

[0034] The carbohydrate-containing feedstocks may be used directly, but most often are pretreated to recover other useful components therefrom or to convert the carbohydrate into a form more suitable for fermentation. Examples of pretreatment include milling; extraction; fermentation to an intermediate such as hydroxypropionic acid thereof or acetylformic acid, especially where a lower molecular weight acid is sought; enzyme hydrolysis and chemical treatment such as hydrolysis. Particularly advantageous sources of carbohydrate-containing feedstocks are sugar cane, sugar beets, wheat and corn. The corn may be dry milled or wet milled to recover other useful products. If desired, the feedstock may be pretreated to remove oils, if present, e.g., glycerides, or proteins. [0035] The fermentation is preferably an anaerobic fermentation and is conducted in an aqueous menstruum in the presence of nutrients and growth factors for the microorganism. Numerous microorganisms are known for homoacidogenic fermentation. Representative acidogenic microorganisms are those of the Acetobacterium, Clostridium, Lactobacillius, and Peptostreptococcus species, such as Clostridium thermoaceticum, Acetogenium kivui, Acetobacterium woodii, Clostridium formicoaceticum, Lactobacillius casei, Lactobacillius delbruckii, Lactobacillius heiveticus, Lactobacillius acidophilus, Lactobacillius amylovorus, Lactobacillius leichmanii, Lactobacillius bulgaricus. Lactobacillius amylovorus, Lactobacillius pentosus, Propionibacterium shermanii, Clostridium butyricu, Clostridium tyrobutylicum, Propionibacterium acidipropionic, and Clostridium thermobutyricum.

[0036] The conditions of the fermentation can fall within a broad range depending upon the microorganism used and the fermentor design. Generally, the concentration of carbohydrate to water is in the range of about 2 to 50, preferably 3 to 20, and most often between about 3 and 10, mass percent. Amino acids and trace metals and other components may need to be provided, if not contained in the feedstock, to assure a sufficient nutrient medium for the microorganisms. Buffers may also be present. The temperature of the fermentation is often within the range of about 25° to 75°C, say, about 40° to 70⁰C. The fermentation may be conducted in batch or continuous or semi-continuous modes. Advantageously, the fermentation vessel is agitated, e.g., by stirring, pumped recycle or vibration. The microorganism may be dispersed in the fermentation menstruum or growing on a solid support such as activated carbon, pumice stone and corn cob granules. The fermentation may occur in a single stage, or two or more sequential fermentation stages may be used. [0037] The conversion of the carbohydrate to acetic acid or salt is usually at least about 90, preferably at least about 95, and sometimes in excess of 98, percent. Typically the fermentation liquid contains between about 2 and 7, most frequently between about 3 and 6, mass percent acid (calculated as the acid). [0038] The pH of the fermentation menstruum is typically maintained at a suitable level for the growth of the microorganisms. Usually the pH is within the range of about 2 to 7, say, 3 or 4 to 7. The pH selected will depend, in part, upon the tolerance and productivity of the microorganism for the homoacidogenic fermentation. The fermentation menstruum can have a lower pH with more acid-tolerant microorganisms.

Base neutralization route

[0039] In the base neutralization route, this pH range is maintained by the use of buffers, and is often adjusted by using ammonia, ammonium hydroxide, amines (preferably primary, secondary and tertiary), inorganic base such as hydroxides, carbonates and oxides of alkali and alkaline earth metals such as sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide and calcium carbonate.

[0040] Upon completion of the fermentation, the liquid menstruum is preferably separated from solids. The separation may be by one or more of centrifugation and filtration. Filtration is preferably sufficient to remove unreacted carbohydrate and proteins. The liquid menstruum having solids removed therefrom, is then further processed to convert the acetic acid or salts into ethanol. Preferred feed alcohols comprise primary alcohols and may contain secondary and tertiary alcohols. As these secondary and teriary alcohols have a slower reaction rate, the amount contained in preferred alcohol feeds should not be so great as to unduly adversely affect the process. In general, of the alcohol feedstock, at least 50, and preferably at least about 80, mole percent of the alcohol is primary alcohol. The alcohol may be methanol or ethanol or may be higher molecular weight alcohols depending upon the process option selected.

[0041] For the esterification to proceed, acetate salts are preferably converted to the free acid and water is removed to assist in driving the esterification reaction toward the ester. Usually the acetate salts are treated with acid to provide acetic acid which is esterified with alcohol. The acidification can be done with any suitable acid, especially one where a precipitate is formed to facilitate its removal. Thus, the selection of the base for the pH adjustment during the fermentation and the acid for acidification of the acetate salt is such that a precipitate will form. Calcium oxide, hydroxide and carbonate are the preferred bases for addition to the fermentation medium and sulfuric acid and carbon dioxide are the preferred components for acidifying the acetate salt. Alternatively, the acetate salt may be converted to an ammonium salt which can be esterified directly. [0042] Several process options exist for conducting the esterification. For instance, water removed from the acetic acid prior to or during the esterification to drive toward completion of the esterification reaction. One preferred mode of operation is to subject the liquid menstruum to reverse osmosis or pervaporation using a membrane to concentrate the acetic acid or salts prior to esterification. Suitable reverse osmosis and pervaporation processes and apparatus are well known. Often at least about 10, say, 20 to 60 to 80, mass percent of the water in the liquid menstruum can be removed by reverse osmosis or pervaporation. [0043] In another alternative, U.S. Patent Nos. 6,509,180 and 7,074,603 propose the use of a reactive distillation for esterification. In this process, the liquid from the fermentation menstruum which contains calcium acetate and about 95 percent water is contacted in the reactive distillation column with carbon dioxide and an excess of ethanol. An azeotrope of ethanol, ethyl acetate and water is taken as an overhead. The patentees state that the azeotrope boils at about 7O⁰C. A water, ethanol and calcium carbonate mixture constitutes the bottoms stream. The azeotrope must be broken to obtain the ethyl acetate for hydrogenation to ethanol. The patentees suggest doing this by the addition of water for a phase separation. Although the process has the advantage of not having to distill the water from the ethyl acetate, which represents an energy savings, the presence of water in such large concentrations, hinders the rate of esterification. [0044] Another option is disclosed in copending patent application [Atty. Docket:

GEIN-108-PCT], filed on even date herewith and incorporated by reference in its entirety. In this option, a simultaneous extraction and esterification in the presence of water is used. In this preferred mode of operation, a substantially water-insoluble, liquid phase is in contact with the liquid menstruum. The substantially water-insoluble, liquid phase comprises the alcohol for the esterification or is a liquid in which the alcohol is soluble. Preferably, the alcohols have at least 3 or 4 carbon atoms, and preferably at least about at least about 6, preferably at least about 8, and most conveniently between about 8 and 24, carbon atoms. Acetic acid, having solubility in the substantially water-insoluble liquid phase, reacts at the phase interface or therein to form the ester. The ester is also soluble in this liquid phase. As the reaction proceeds, more acetic acid is drawn from the aqueous phase and reacted. Accordingly, a significant portion of the acetic acid contained in the feed to the esterification step can be consumed. That remaining in the aqueous phase can be recycled, preferably to a reverse osmosis or pevaporation unit operation to remove a portion of the water and reintroduced into the esterification step.

[0045] The substantially water-insoluble, liquid phase may include any suitable organic material that is liquid under the conditions of the esterification. See, for instance, copending patent application [Atty. Docket: GEIN-109-PCT], filed on even date herewith. Suitable organic liquids include hydrocarbons having at least 4 carbon atoms, such as butanes, hexanes, octanes, petroleum fractions including kerosenes, white oils, naphthas, aromatics including benzene, toluene, xylene, naphthalenes and mixtures thereof; and preferably the alcohol to be used for the esterification. The composition of the organic layer introduced into the esterification medium is preferably at least about 5, say, between about 10 and essentially 100 mass percent of the alcohol feed. The esterifying alcohol is provided in a molar ratio to acetic acid of at least 0.5:1, preferably at least about 1.5:1, and sometimes as high as 100:1 or 200:1 or more. [0046] Regardless of the option selected, esterification conditions typically comprise the use of elevated temperature and the presence of esterification catalyst. The pressure for esterification is not critical but should be sufficient to maintain the acetic acid and alcohol in the liquid state. Usually the pressure is between about 50 kPa absolute to about 10 MPa absolute. Temperatures for esterification are often in the range of about 50°C to 300°C, say, about 7O⁰C to 250⁰C. The catalyst may be heterogeneous or homogeneous. Where an organic phase is provided to the reaction medium or forms therein, it is preferred that the esterification be conducted under conditions that provide high surface area interfaces such as by high turblence mixing and ultrasonic agitation. High turbulence mixing can be by stirring or by reactor design, such as the presence of vanes, tortuous microtubes, and the like to physically disperse the phases. Additives, such as emulsifiers may also find utility.

[0047] The catalyst may be heterogeneous or homogeneous. Where an organic layer is provided or is formed in the reaction medium, catalyst is preferably contained in the organic layer or at least is such that it is active at the interface between the organic layer and the aqueous medium. Typical esterification catalysts are acidic and include acids such as carbonic acid, hydrochloric acid, sulfuric acid, sulfonic acid, especially toluene sulfonic acid, acidic molecular sieves, ion exchange resins, especially Nafion™ resins, and esterases. Preferred catalysts are solid catalysts and those highly soluble in the water-immiscible, liquid phase, especially the alcohol, such as alkylbenzene sulfonates, e.g., toluene sulfonate (preferably p-toluene sulfonate), nonylbenzene sulfonates, and the like. Another preferred catalyst are esterases. Esterases are typically present in the aqueous menstruum as opposed to the water-immiscible liquid phase. The catalyst is provided in a catalytically effective amount. The catalyst is provided in an amount of at least about 0.005, say, 0.01 to 20, mass percent based upon the mass of acetic acid. The duration of the esterification should be sufficient to convert at least about 50, and preferably at least about 70, say 75 to 98 or essentially all the acetic acid to ester. Unreacted acetic acid may be recovered from the aqueous stream by any suitable means including distillation, membrane separation, sorption, extraction, and the like. Where an organic phase exists and contains acetic acid, the unreacted acetic acid can be removed from the ester, e.g., by distillation, or more preferably remain in the organic phase and be recycled with the higher alcohol after the hydrogenation and recovery of ethanol. [0048] The reactor design and configuration may vary widely. As stated above, the reactor may be a reactive distillation unit or may be a high shear mixing vessel of various types. The esterification process may proceed in a single reactor or two or more sequentially positioned reactors may be used. Where more than one reactor is used, one or more of liquid menstruum or alcohol may be added between sequential reactor stages. [0049] The esterification product is withdrawn from the esterification zone and hydrogenated to provide ethanol and the alcohol. The manner in which the esterification product is recovered will, in part, be determined by the nature of the esterification process. Thus, where a reactive distillation is used, the higher boiling fraction will comprise esterification product. If solids are present, they can be separated and the remaining liquid subjected to hydrogenation to make ethanol. For esterification operations where the acetate ester is in an organic phase, the organic phase may be separated by phase separation.

Direct esterification route

[0050] In the direct esterification route, or in situ esterification route, acetic acid is esterified in the presence of the fermentation medium. Thus, no salt of the acetic acid need be formed as conversion of the acid to ester can prevent deleteriously high acidity being built up in the fermentation medium. The direct esterification process is disclosed in copending patent application [Atty. Docket: GEIN- 109-PCT], filed on even date herewith. [0051] Preferably the alcohols for the esterifi cation have sufficient carbons that at least the formed ester is substantially water insoluble. Thus often the alcohol has at least 3 or 4 carbon atoms, and preferably at least about at least about 6, preferably at least about 8, and most conveniently between about 8 and 24, carbon atoms. Preferred feed alcohols comprise primary alcohols and may contain secondary and tertiary alcohols. As these secondary and teriary alcohols have a slower reaction rate, the amount contained in the preferred alcohol feed should not be so great as to unduly adversely affect the process. In general, of the alcohol feedstock, at least 50, and preferably at least about 80, mole percent of the alcohol is primary alcohol. The primary alcohol used should be relatively non-toxic in the concentrations present to the microorganisms used for the fermentation. Hence aliphatic alcohols are generally used. Primary alcohols include propanol, isopropanol, butanol, isobutanol, pentanol, methylpentanol, hexanol, lauryl alcohol, cetyl alcohol, and the like. [0052] The esterification is conducted in the presence of the aqueous fermentation menstruum and in the presence of a substantially water-immiscible, liquid phase in which the ester is soluble. The substantially water-insoluble, liquid phase is any suitable organic material that is liquid under the conditions of the esterification. The substantially water-insoluble, liquid phase comprises the alcohol for the esterification or is a liquid in which the alcohol is soluble. Suitable organic liquids are substantially non-toxic to the microorganisms for fermentation and include hydrocarbons having at least 4 carbon atoms, such as butanes, hexanes, octanes, dodecanes, petroleum fractions including kerosenes, white oils, and naphthas, high molecular weight esters and alcohols such as biodiesel, and mixtures thereof. Preferably the primary alcohol to be used for the esterification comprises at least a portion of the water-immiscible phase. [0053] The volume ratio of the water-immiscible phase to the aqueous fermentation menstruum with which it contacts may vary widely and will depend upon the apparatus and conditions used. For instance, where the fermentation and esterification are only conducted in the same zone, the volume ratio may range from 5:100 to 50:100 or more. Where a slip stream of fermentation media is taken and contacted with the water-immiscible phase, it is feasible to have a volume ratio of 20: 1 or more. The alcohol is provided in a molar ratio to acid of at least 0.5:1, preferably at least about 1.5:1, and sometimes as high as 100:1 or 200:1 or more. [0054] Esterification conditions typically comprise the use of elevated temperature and the presence of esterification catalyst. The pressure for esterification is not critical but should be sufficient to maintain the acid and alcohol in the liquid state. Advantageously, the esterification is conducted under substantially the same conditions as the fermentation. However, where a slip stream is taken from the fermentation of contact with the water-immiscible phase, different conditions may be used, but preferably not such that any material damage will be done to the microorganism. Usually the pressure is between about 50 kPa absolute to about 10 MPa absolute. Temperatures for esterification are often in the range of about 50⁰C to 300⁰C, say, about 70⁰C to 250⁰C. [0055] The catalyst may be heterogeneous or homogeneous. Where an organic layer is provided or is formed in the reaction medium, catalyst is preferably contained in the organic layer or at least is such that it is active at the interface between the organic layer and the aqueous medium. Typical esterification catalysts are acidic, and hence preferably reside mostly in the water-immiscible phase to avoid deleteriously affecting the microorganism, hi one embodiment of the invention, a slip stream from the fermentation zone is taken and most of the solids removed by filtration or centrifugation. The solids can be returned to the fermentation vessel and the nascent liquid, which will contain little, if any, of the microorganism, can be subjected to more acidic conditions. Catalysts for esterification include acids such as carbonic acid, hydrochloric acid, sulfuric acid, sulfonic acid, especially toluene sulfonic acid, acidic molecular sieves, ion exchange resins, especially Nafion™ resins, and esterases. Preferred catalysts are solid catalysts and those highly soluble in the water-immiscible, liquid phase, especially the alcohol, such as alkylbenzene sulfonates, e.g., toluene sulfonate (preferably p-toluene sulfonate), nonylbenzene sulfonic acid, and the like. Another preferred catalyst are esterases. Esterases are typically present in the aqueous menstruum as opposed to the water-immiscible liquid phase. One preferred mode of operation with esterases and other catalysts preferentially located in the aqueous medium, is to use a water miscible alcohol that converts to a water-immiscible ester, e.g., n-butanol. The catalyst is provided in a catalytically effective amount. The catalyst is provided in an amount of at least about 0.005, say, 0.01 to 20, mass percent based upon the mass of acid.

[0056] It is preferred that the esterification be conducted under conditions that provide high surface area interfaces such as by high turbulence mixing and ultrasonic agitation. High turbulence mixing can be by stirring or by reactor design, such as the presence of vanes, tortuous microtubes, and the like to physically disperse the phases. Desirably, the high turbulence mixing is not so vigorous that undue lysing of the fermentation microorganism occurs. [0057] Preferably, the duration of the esterification is sufficient to convert at least about 20, and preferably at least about 30, mass percent of the acid to ester. It is not essential to convert a high percentage of the acid to ester as the unreacted acid can be recycled to the fermentation menstruum. Rather, the rate of removal of acid needs to be sufficient to maintain the desired pH. Often, the organic acid has some solubility in the water-immiscible phase. Hence not only will the pH be controlled by conversion of the acid to an ester, but also by acid being dissolved in the water-immiscible phase. Advantageously, the processes of this invention, regardless of the conversion to ester, facilitate a low energy separation of water from the sought ester product. [0058] At least periodically, and preferably continuously, a portion of the water- immiscible phase is withdrawn for recovery of the sought organic, whether it be acid, the ester or a subsequent synthesis product such as an alcohol, amine, aldehyde or the like. Any suitable technique may be used for further processing. For instance, to generate the acid, the water-immiscible phase may be contacted with ion exchange resin and hydrolyzed to generate the acid and alcohol. A particularly useful application of the processes of this invention is to generate alcohol such as ethanol, propanol, and the like from the ester. The ester is much more readily hydrogenated to provide the alcohol than is the acid. Since the homoacidogenic fermentation is nearly 100 percent efficient to the production of acid, high conversions to alcohol can be achieved while minimizing the discharge of carbon dioxide. [0059] The manner in which water-immiscible phase containing the esterification product is recovered will, in part, be determined by the nature of the esterification process. Often phase separation will be adequate.

Hydrogenation

[0060] The hydrogenation may be conducted in the liquid or vapor phase. Due to the high boiling point of the esters, the hydrogenation is preferably conducted in the liquid phase or an ebulating or trickle bed where the liquid is mixed with gaseous hydrogen. Hydrogenation conditions include the presence of hydrogen at elevated temperatures and pressures in the presence of a catalytically-effective amount of selective hydrogenation catalyst. The hydrogenation should not be so severe that neither the product alcohol such as ethanol nor the primary alcohol is converted to hydrocarbons.

[0061] A number of options exist for the hydrogenation. One mode of hydrogenation is to conduct the hydrogenation to substantially consume the introduced hydrogen, albeit at a loss of conversion. In this mode, the reaction medium containing ester can be recycled. The advantages of this mode of hydrogenation are that lower hydrogen partial pressures, and hence lower reaction pressures can be used, saving costs in hydrogen compression and in eliminating the need for a stripping column to recover unreacted hydrogen. Although the per-pass conversion of ester to alcohol may be low, pumping costs for liquids are relatively inexpensive. In this mode, the hydrogenation may be conducted at between about 300 and 5000 kPa absolute with between about 0.1 and 0.9, say, 0.2 and 0.7, moles of hydrogen per mole of ester.

[0062] Another mode of hydrogenation is the conventional, higher pressure hydrogenation where high conversion of ester to alcohols is achieved on a per pass basis. Typically in this mode, the hydrogenation is conducted at a pressure of at least about 3 MPa, say, 3 to 50 MPa (absolute). Typically at least about 1.1, and more frequently at least about 2, preferably 2 to 8, moles of hydrogen are provided per mole of ester. [0063] In either mode of hydrogenation, the temperature is often in the range of about 150⁰C to 300⁰C. Hydrogenation catalysts comprise a hydrogenation metal component which may be one or more metals selected from noble metals and base metals. The noble metal can desirably be a platinum-group metal is selected from platinum, palladium, rhodium, ruthenium, osmium, iridium and mixtures thereof. The base metal can desirably be selected from the group consisting of rhenium, chromium, tin, germanium, lead, cobalt, nickel, iron, indium, gallium, zinc, uranium, dysprosium, thallium, and mixtures thereof. A promoter or modifier may also be used in the catalyst formulation. Such promoters or modifiers are one or more of base metals, IUPAC groups 1, 2, 5, 6, 7, 11, 12, 13, 14, 15, 16 and 17. The catalyst may be supported or unsupported. Supports include carbonaceous supports and refractory oxides such as silicas, aluminas, silica-aluminas including molecular sieves, and the like. Raney nickel, nickel, rhenium, nickel and rhenium mixtures, iridium, and copper chromite are examples of hydrogenation catalysts. [0064] The sought product alcohol, such as ethanol, can be recovered during or subsequent to the hydrogenation by distillation from the higher, primary alcohol and any unreacted ester, acetic acid and any other organic material used to form the water-immiscible phase. At least a portion of the water-immiscible phase can be recycled to the fermentation. If desired, another portion can be recycled to the hydrogenation operation.

[0065] The hydrogenation may also convert glycerides present to the corresponding alcohols and glycerin. The alcohols can be recycled as alcohol for the esterification. A purge stream may be taken to maintain steady state operation in a continuous process. This purge can be used as biofuel after suitable processing to remove undesirable components, e.g., glycerin to provide a biodiesel product.

Pyrolysis

[0066] Regardless of whether the hydrogenation is operated in a total hydrogen consumption mode or in a hydrogen excess mode, the indirect processes for making alcohol require hydrogen for the hydrogenation. Hydrogen can be provided by a number of sources including from a hydrogen plant, which is often associated with a petroleum refinery; by reforming methane or other hydrocarbons including from an on-site hydrogen generator; or by pyrolysis ofbiomass. [0067] The pyrolysis ofbiomass is particularly attractive due to the ability to locate the pyrolysis units proximate to the ethanol production facility and due to the available source of biomass including the non-fermentable portions of the biomass used for the indirect ethanol process. Further, pyrolysis provides a char co-product that can beneficially be used as a soil enhancer. Frequently where corn is used for the source of the fermentable biomass, a portion of the corn stover, usually at least a third, is left in the fields as a soil enhancer. The stover, however, rapidly degrades and carbon dioxide is emitted to the atmosphere. Char has the advantage of not contributing to the same extent as such corn stover to the emission of global warming gases. Moreover, char enhances the efficacy of fertilizer as well as providing desirable mineral nutrients. Accordingly, pyrolysis is a particularly preferred source of hydrogen for the indirect ethanol process. [0068] The biomass feed for pyrolysis can, as stated above, be derived from the plants from which the fermentable biomass is obtained, e.g., corn stover and sugar cane plant. In addition or alternatively other sources ofbiomass can be used including wood and wood products including paper and cardboard, carbonaceous refuse including animal manures and trash. Generally biomass feeds that can generate undue amounts of adverse gases such as hydrogen chloride are avoided.

[0069] If necessary, the biomass for pyrolysis is dried prior to being pyrolyzed. Often the desired moisture content of the pyrolysis feed is below about 25 mass percent. Any suitable means for drying can be used such as sun drying, oven heating and passing a drier gas over the biomass. In some instances, a suitably dry feed can be obtained by mixing a moister feed, e.g., cattle manure, with a drier feed, e.g., corn stover or saw dust, to obtain an adequately dry pyrolysis feed. The drying may occur in a single stage, or more frequently in two or more stages, the latter of which use the spent heating gases for the pyrolysis kiln as the drying medium.

[0070] The pyrolysis is conducted in a substantially molecular oxygen-free environment in a kiln. The amount of oxygen in the kiln is commonly less than about 1 , more preferably less than about 0.1 , mole percent of the gaseous environment in the kiln. The kiln is heated to effect the pyrolysis reactions. Generally the heat is provided by one or more external burners although supplemental internal combustion can be used to facilitate providing heat to the biomass undergoing pyrolysis. The amount of heat provided is sufficient to provide a maximum gas temperature within the kiln of at least about 225°C, say between about 250⁰C and 600°C, and often between about 300⁰C and 450⁰C. The pressure is not critical for the pyrolysis. Usually at least a slightly positive pressure is maintained in the kiln to prevent air from entering the kiln. Typically the pressure in the kiln is from about 5 to 1000 kPa (gauge).

[0071] The residence time of the biomass in the kiln can vary within a wide time span depending upon the other kiln conditions such as temperature and the type of biomass being used. Typically the average residence time of solids is between about 1 and 500, say 3 and 120, minutes. Advantageously, the residence time is sufficient to provide a char having little, if any, hydrocarbon present, frequently less than about 5, preferably less than about 0.5, mass percent. The char product can be used as a soil supplement or gasified in the presence of steam to make additional hydrogen and carbon monoxide. [0072] The pyrolysis kiln may be of any suitable design. Kilns typically have a generally cylindrical configuration with biomass feed entering one end and char and pyrolysis gases exiting the other. The kiln may rotate, in which case it preferably has internal baffles, to provide mixing and more uniform heating of the biomass undergoing pyrolysis. Alternatively, the kiln may have a stationary shell and contain paddles or other agitators to mix the biomass undergoing pyrolysis. A further kiln design is a fluid bed or riser bed. The heat for the pyrolysis is provided by burners. Any suitable fuel for the burners can be used, including, but not limited to, solids such as coal, char, peat, etc.; liquids such as kerosene, fuel oil, waste organic streams such as glycerin, etc.; and gases such as natural gas, propane, butane, and preferably carbon monoxide and hydrogen contained in the pyrolysis gases from the kiln. [0073] The pyrolysis gases from the kiln contain carbon monoxide and hydrogen and often also contain condensable carbonaceous components, i.e., higher molecular weight hydrocarbons, aldehydes, carboxylic acids, and the like, some of which may also by capable of polymerization. These condensable components may be removed by any convenient means including but not limited to one or more of chemical reaction such as reforming and/or thermal cracking in the presence of oxygen and steam; sorption with a solid or liquid sorbent; cooling to effect condensation; and the like.

[0074] If desired, the ratio of carbon monoxide to hydrogen can be shifted through a water gas shift to convert carbon monoxide to hydrogen and carbon dioxide. [0075] The pyrolysis and the hydrogenation can be integrated through the use of one or more of membrane and sorption, herein referred to as hydrogen separation operation. In this aspect of the invention, the pyrolysis gases are separated into a fraction richer in hydrogen, at least a portion of which is provided to the hydrogenation, and a fraction richer in carbon monoxide, which is provided as at least a portion of the fuel for the burners for the pyrolysis kiln. As the heating value of carbon monoxide is greater than that of hydrogen, not only do these aspects of the invention enhance the use of the pyrolysis gases for each of the intended uses, but also, a facilitated control system is provided.

[0076] In the control systems of the invention, the efficiency of the hydrogen separation operation provides a desired supply of hydrogen for the hydrogenation with the balance being used to supply heat to the pyrolysis kiln. Thus, where more hydrogen is required for the hydrogenation, or alternatively, the rate of hydrogen being provided by directly or indirectly (through a water gas shift) the biomass is decreased, the hydrogen purity in the separation operation product stream is decreased with a concomitant increase in absolute hydrogen flow rate. Similarly, where a lesser hydrogen rate is required or the rate of hydrogen production from the pyrolysis increases, the hydrogen purity of the separation operation product stream is increased.

[0077] For membrane separation, hydrogen purity in the separation operation product stream can be changed by a by-pass from the retentate side. A portion of the feed to the membrane separator or a portion of the retentate can be passed to the effluent from the permeate side. Hence, additional hydrogen is supplied to that contained in the permeate. For sorption systems such as pressure swing sorption and thermal swing sorption, the volume of hydrogen contained in the product gas is increased by increasing cycle times. Because the frequency of the blow-down and purge cycle steps is reduced, the rate of hydrogen is increased.

[0078] Both membrane and sorption can be used. However, for the sake of economy, pressure swing sorption is preferred. Where very large swings in hydrogen requirements for hydrogenation occur, or for purposes of start-up of the pyrolysis kiln, it may be desired to by-pass pyrolysis gases directly to the burners for the pyrolysis kiln.

[0079] The drawings are provided to facilitate an understanding of the invention but are not in limitation of the invention.

[0080] With respect to Figure 1, an apparatus 100 is provided for the indirect process to make ethanol wherein the esterification occurs in the same zone as the fermentation to make the acid. As shown, a carbohydrate feedstock is passed via line 102 to fermentation vessel 104. The feedstock, for purposes of this discussion is an aqueous solution of corn sugars. Also fed to fermentation vessel 104 are nutrients via line 106. In fermentation vessel 104 acetic acid is generated by microorganisms. The fermentation vessel also contains a water-immiscible phase comprising higher, primary alcohol. The fermentation vessel is agitated to not only admix the components of the aqueous fermentation menstruum but also to provide contact area with the water-immiscible phase for consuming acetic acid by esterification.

[0081] The fermentation menstruum is withdrawn from fermentation vessel 104 and passed via line 110 to separator 112. A purge of the fermentation menstruum can be periodically or continuously discharged via line 108. As shown, the purge is taken at the bottom of fermentation vessel 104 and thus will contain little of the water-immiscible phase. [0082] Separator 112 may be any convenient separation device to separate the aqueous fermentation menstruum from the water-immiscible phase. Because the apparatus recycles water-immiscible phase to the fermentation vessel, the separator need not be highly efficient. Nevertheless, it is desired to minimize the amount of water in the water-immiscible layer. As shown, separator 112 is a phase separator and aqueous phase is withdrawn via line 114 and can be recycled to fermentation vessel 104. [0083] The organic layer in separator 112 will contain the acetic ester, unreacted higher alcohol, ethyl acetate from transesterification between product alcohol, and acetic acid. This layer is passed via line 116 to hydrogenation reactor 118 containing solid hydrogenation catalyst, e.g., Raney nickel catalyst. Hydrogen is introduced into hydrogenation reactor 118 via line 120. In hydrogenation reactor 118, ethanol and higher alcohol are formed. The amount of hydrogen provided is sufficiently low that it is essentially completely consumed. The reaction product, which is ethanol, higher alcohol, unreacted acetate ester, acetic acid and any additional organic material used to form the water-immiscible phase, is passed via line 122 to stripper 150.

[0084] Stripper 150 serves to remove hydrogen and lights from the reaction product. Often, the stripping is conducted at about the pressure of the hydrogenation reaction. Hydrogen and lights exit stripper 150 via line 152. The liquid phase from stripper 150 is passed via line 154 to distillation column 124. [0085] In distillation column 124, ethanol is stripped and a higher boiling fraction containing acetic acid, ethyl acetate, acetate ester of the higher alcohol, the higher alcohol and any organic material used to provide the water-immiscible phase is obtained. The lower boiling fraction, which is ethanol, from distillation column is recovered via line 126 as product ethanol. To the extent that water is present, it is below that which forms an azeo trope with water.

[0086] The higher boiling fraction is recycled via line 128 to hydrogenation reactor

118. A portion of the higher boiling fraction is passed to fermentation vessel 104 via line 130. Make-up esterification catalyst, e.g., toluene sulfonic acid, can be provided via line 132. [0087] Apparatus 100 includes an integrated hydrogen production unit.

Carbonaceous materials are passed via line 156 to pyrolysis kiln 158. Suitable carbonaceous material are those containing carbon and hydrogen, preferably carbohydrate-containing materials such as corn stover, wood, and other plant-derived matter, waste process streams such as glycerin from biodiesel production, waste products such as carbonaceous house and municipal waste, manure, and the like. Pyrolysis kiln 158 is operated to convert carbonaceous materials to carbon monoxide and hydrogen and generate char. Char is withdrawn via line 160 and can be used in any suitable manner, e.g., returning to the soil. Not only will the char contain minerals and provide beneficial effects on the soil such as enhancing fertilizer retention and water, but also the carbon in the char is relatively inert to oxidation and thus represents a capture of carbon. Stover and other carbonaceous materials contained in a corn plant are subject to decomposition over time to carbon dioxide. Thus, the processes of this invention can serve to reduce greenhouse gases.

[0088] The gases from the pyrolysis, which contain carbon monoxide and hydrogen, are passed via line 162 to membrane separator 164. As shown, a portion of the pyrolysis gases can be directly provided to burners for providing heat to the pyrolysis kiln. Often, the gases are treated to remove condensable and reactively unstable components prior to contact with the membrane to prevent fouling. Membrane separator 164 is a preferred mode of operation and need not be used. Membrane separator serves to provide a carbon monoxide-enriched retentate which is passed via line 170 to burners 172 to provide heat for the pyrolysis. Additional fuel for the burners, if needed, can be supplied via line 186. Carbon monoxide has a higher heat of combustion per gram-mole than does hydrogen.

[0089] Any suitable membrane may be used. The membranes may be of any suitable configuration including flat, spiral wound and hollow fiber. The permeator may be designed to provide flow patterns of the permeator feed fraction and the retentate co-current, cross-current or counter-current. The variety of membrane materials range from metallic membranes such as vanadium, tantalum, niobium, and palladium and allows of such elements to organic membranes such as polysulfone, polyamide, polyimide, polycarbonate, polyketone, and the like membranes. The hydrogen purity in the permeate will depend in part upon the membrane selected. In general, the metallic membranes provide a higher hydrogen purity. Typically the metallic membranes use elevated temperatures, e.g., from about 200° to 700°C or more, to achieve attractive permeation rates. If polymeric membranes are to be used, the temperature should be sufficiently low that no undue damage to the membrane occurs, e.g., to 175°C or less. A partial pressure driving force is used to effect permeation of hydrogen through the membrane. Accordingly, a pressure differential is maintained across the membrane. Often the pressure differential is at least about 200, preferably at least about 300, kPa, and sometimes in the range of 300 to 200O kPa.

[0090] If metallic membranes are used to provide a highly pure permeate, the permeate, which is withdrawn via line 166 from permeator 164, can be directly provided to hydro genation reactor 118. Alternatively, the permeate in line 166 can be passed to water gas shift reactor 168 for the purpose of converting carbon monoxide and water to hydrogen and carbon dioxide, and thereby increase the amount of hydrogen available for the hydrogenation operation.

[0091] As shown, line 174 passes a portion of the retentate, which contains carbon monoxide, to water gas shift reactor 168. The amount of retentate passed into line 174 can be such that either the amount of retentate to burner 172 is sufficient to maintain the desired heat production for the pyrolysis or to assure a desired rate of hydrogen production for the hydrogenation through both recovery of hydrogen in the retentate and by conversion of carbon monoxide in the water gas shift. Where no permeator is used, the gases in line 162 can be split, with a portion going to burner 172 via line 170 and another portion going to water gas shift reactor 168. In either situation, a control mechanism is provided to facilitate operation of the integrated pyrolysis and ethanol production facility.

[0092] Water is provided via line 176 to water gas shift reactor 168. The water gas shift is conducted in the presence of a shift catalyst. The shift reaction is an equilibrium reaction, and higher concentrations of hydrogen can be achieved at lower temperatures. Typical water gas shift catalysts include copper oxide, or copper supported on other transition metal oxides such as zirconia, ferric oxide or chromic oxide, and optionally including a promoter such as copper or iron suicide, zinc supported on transition metal oxides or refractory supports such as silica, alumina, zirconia, etc., or a noble metal such as platinum, rhenium, palladium, rhodium or gold on a suitable support such as silica, alumina, zirconia, carbon and the like. Any number of water gas shift reaction zones may be employed to reduce the carbon monoxide level in the hydrogen product, the preferred processes of this invention using pressure swing adsorption for hydrogen purification use only a high temperature shift at high temperature shift conditions comprising temperatures between about 15O⁰C and about 450⁰C. A water gas shift product is provided that contains an increased concentration of hydrogen and a decreased concentration of carbon monoxide. It is likely that the water gas shift product will contain, in addition to water and carbon dioxide, nitrogen. [0093] As shown, the water gas shift product is passed via line 178 to pressure swing adsorber system (PSA system) 180. Usually the PSA systems operate at lower temperature than do the water gas shift reactors. Typically, the water gas shift product is cooled, e.g., to about 20⁰C to 80⁰C, to condense out water and to provide the stream at a suitable pressure for the PSA system. [0094] Pressure swing adsorption provides a product stream having a higher concentration of hydrogen which is passed via line 120 to hydrogenation reactor 118. The PSA system can provide considerable flexibility. For instance, by changing cycle times, the percent recovery of hydrogen can be altered as well as the concentration of hydrogen in the product. Often, the pressure swing adsorption provides a hydrogen product stream of at least about 90, preferably at least 95, volume percent although higher and lower concentrations may be useful. Preferably, PSA system 180 is operated to recover at least about 60, and more preferably at least about 75 or 80, mole percent of the hydrogen contained in the feed to the system. [0095] Any suitable adsorbent or combination of adsorbents may be used for the pressure swing adsorption. The particular adsorbents and combinations of adsorbents used will, in part, depend upon the components of the feed to the pressure swing adsorber, the sought compositions in the purified hydrogen product and the geometry and type of pressure swing adsorber used. Adsorbents include molecular sieves including zeolites, metal oxide or metal salt, and activated carbon. Particularly advantageous sorbents include a combination of sorbents with the first portion of the bed being composed of activated carbon which is particularly effective for water and carbon dioxide removal followed by one or more molecular sieves such as NaY, 5A, lithium or barium exchanged X, silicalite and ZSM-5. The sorbents may be of any suitable particle size given the constraints of pressure drop and bed lifting for an up-flow fixed bed. [0096] The pressure swing adsorber may be of any suitable design including rotary and multiple bed. The purging of the bed may be by vacuum, but most conveniently for simplicity, the purge is above ambient atmospheric pressure. A preferred pressure swing adsorption system for low maintenance operation uses at least four fixed beds. By sequencing the beds through adsorption and regeneration steps, a continuous flow of purified hydrogen stream can be achieved without undue loss of hydrogen. With at least four beds, one bed at a given time will be adsorbing, another will be providing purge, another will be undergoing purging and another will be undergoing repressurization. Preferably, at least one, and more preferably two or three, pressure equalization steps are used to increase hydrogen recovery.

[0097] The operation of the pressure swing adsorber will also be influenced by the cycle time and the ratio of the pressures for the swing. The sorption may be at 500 to 1500 KPa, the purge usually occurs within about 100, preferably within about 50, say, 10 to 50, KPa above ambient atmospheric pressure. The cycle times are selected to provide the hydrogen product of a desired purity. For a given pressure swing adsorber system, as the cycle times become shorter, the purity achievable increases, but also, less hydrogen is recovered. Thus, the cycle times and adsorber sizing can be selected for a given unit based upon the hydrogen specification and sought recovery.

[0098] PSA system 180 provides a purge, which contains unrecovered hydrogen. If desired, this purge may be passed via line 182 to burner 172 for the pyrolysis kiln 158. [0099] PSA system can be used for an additional control of the integrated process.

The amount of hydrogen generated by the pyrolysis may change depending upon type and rate of feed and upon pyrolysis conditions. Cycle times of PSA system 180 can be changed to assure adequate supply of fresh hydrogen for the hydrogenation in hydrogenation reactor 118. Where ample hydrogen is being produced, the cycle times may shorten so as to provide a purge having a higher hydrogen concentration and thus more heating value for burner 172. Where less hydrogen is being produced by pyrolysis kiln 158, the cycle times may lengthen to provide a greater recovery of hydrogen in the PSA product stream.

[00100] If desired, a portion of the overhead in line 152 from stripper 150 may be passed via line 184 to PSA system 180 to remove any light end contaminants that may be contained in the overhead and thus maintain a steady state operation. [00101] As can be seen, the processes of this invention provide for an indirect process for producing ethanol in an energy efficient manner.

[00102] In Figure 2, apparatus 200 is adapted to produce ethanol by the indirect process using two esterification stages. As shown, a carbohydrate feedstock is passed via line 202 to fermentation vessel 204. The feedstock, for purposes of this discussion is an aqueous solution of corn sugars. Also fed to fermentation vessel 204 are nutrients via line 206. In fermentation vessel 204 acetic acid is generated by microorganisms. The fermentation vessel also contains a water-immiscible phase comprising higher, primary alcohol. The fermentation vessel is agitated to not only admix the components of the aqueous fermentation menstruum but also to provide contact area with the water-immiscible phase for consuming acetic acid by esterification.

[00103] Fermentation vessel 204 contains annular tube 208 having sparger 210 in a lower portion. Sparger 210 is adapted to introduce water-immiscible phase, containing primary alcohol and transesterification catalyst, which rises in annular section 208, carrying with it a co-current flow of aqueous fermentation menstruum. The aqueous fermentation menstruum then passes on the outside of annular tube 208 to the bottom of fermentation vessel 204 to form a cyclic pattern. Acetic acid is absorbed in the water-immiscible phase as well as reacted to form an ester. Coalescer 212 in an upper portion of fermentation vessel 204 serves to facilitate phase separation and a water-immiscible phase is withdrawn from fermentation vessel 204 via line 214 and passed to esterification reactor 216. Since the aqueous fermentation menstruum has been separated, the esterification conditions in esterification reactor 216 may be selected based upon desired conversion without regard to effect on the microorganism. [00104] The esterification product is passed from esterification reactor 216 to hydrogenation reactor 220 via line 218. Hydro genation reactor 220 is a conventional, high pressure hydrogenator designed to achieve high conversion of the ester to product alcohol, ethanol, and the higher molecular weight primary alcohol. The hydrogenation product exits via line 222 and is passed to flash stripper 224 for removal of hydrogen which is returned to hydrogenation reactor 220 via line 226. Make-up hydrogen is provided via line 228. Make-up hydrogen can be provided by the integrated pyrolysis unit as described in connection with Figure 1.

[00105] The liquid from flash stripper 224 is passed via line 230 to distillation column 232 where a product ethanol stream is provided via line 234 and a water-immiscible bottoms stream is recycled via line 236 to sparger 210. Make-up catalyst can be provided via line 238. [00106] Fermentation vessel 204 is provided with line 240 for purging aqueous fermentation menstruum.

[00107] Figure 3 depicts an embodiment of the invention wherein a slip stream from the fermentation vessel is subjected to esterifi cation. In apparatus 300, a carbohydrate feedstock is passed via line 302 to fermentation vessel 304. The feedstock, for purposes of this discussion is an aqueous solution of corn sugars. Also fed to fermentation vessel 304 are nutrients via line 306. In fermentation vessel 304 acetic acid is generated by microorganisms. A slip stream is withdrawn via line 308 and contains the aqueous fermentation menstruum including acetic acid and microorganism, and is passed to solids separator 310.

[00108] Solids separator 310 serves to provide a concentrated, solid-containing phase which is rich in the microorganism. Solids separator may be a filtration device, or even more conveniently, a centrifuge. The concentrated, solids-containing phase, is passed via line 312 for recycle to fermentation vessel 304. The aqueous phase having a reduced concentration of solids is passed from solids separator 310 via line 314 to esterifi cation reactor 316. Esterifi cation reactor 316 is operated as a liquid-liquid extraction vessel for contact between aqueous fermentation menstruum containing acetic acid and water-immiscible, liquid phase containing primary alcohol. Packing 318 is provided in esterification reactor 316 to enhance contact between the phases and on the packing is supported acidic esterification catalyst (Nafion™ resin). An aqueous phase is withdrawn from esterification reactor 316 via line 320 for recycle to fermentation vessel 304. A purge of aqueous fermentation menstruum can be taken via line 322.

[00109] The water-immiscible phase from esterification vessel 316 contains ester and is passed via line 324 to phase separator 326. Phase separator 326 serves to remove aqueous menstruum entrained in the water-immiscible phase, and the remove aqueous menstruum is withdrawn via line 328 and may be recycled, if desired, to fermentation vessel 304. Line 330 serves to direct the water-immiscible phase provided by phase separator 326 to hydrogenation reactor 332 for hydrogenation of ester to product alcohol, ethanol, and primary alcohol. Hydrogen is provided by line 334 to hydrogenation reactor 332. Hydrogen can be provided by the integrated pyrolysis unit as described in connection with Figure 1. The apparatus in Figure 3 operates on a total consumption mode of hydrogen. The hydrogenation product is passed via line 336 to distillation column 338. Ethanol product is stripped and is directed via line 340. The higher boiling fraction, which contains primary alcohol and ester, is passed via line 342 to esteriflcation reactor 316 as the water-immiscible liquid. A portion of this stream can, if desired, be directed via line 344 to line 330 for recycle to hydrogenation reactor 332. The stripped ethanol in line 340 can be directed to condenser 346. Hydrogen and non-condensables are removed via line 348 and ethanol is directed to product storage via line 350.

Claims

IT IS CLAIMED:

1. A continuous process for the hydrogenation of acetic ester comprising: a. contacting the acetic ester with hydrogen under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising ethanol wherein the molar ratio of hydrogen to acetic ester is sufficiently less than 1 :1 that the hydrogenation product contains less than about 0.01 mole percent hydrogen; b. subjecting to hydrogenation product to distillation to provide a lower boiling fraction comprising ethanol and a higher boiling fraction comprising unreacted acetic ester; and c. recycling at least a portion of the higher boiling fraction to step (a).

2. The process of claim 1 wherein the molar ratio of hydrogen to acetic ester is less than about 0.9:1.

3. The process of claim 1 herein the hydrogenation conditions comprise the presence of hydrogenation catalyst, a temperature of between about 150⁰C and 300°C and a pressure between about 300 and 5000 kPa absolute.

4. The process of claim 1 wherein the alcohol portion of acetic ester comprises hydrocarbon of at 3 to 30 carbon atoms.

5. A continuous, indirect process for making alcohol product comprising: a. subjecting an aqueous menstruum containing carbohydrate to homoacidogenic fermentation conditions to provide an organic acid corresponding to the alcohol product, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. esterifying at least a portion of said organic acid with esterifying alcohol having a greater number of carbon atoms than the organic acid to provide an ester product; c. hydrogenating the ester product under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising alcohol product wherein the molar ratio of hydrogen to ester product is sufficiently less than 1 :1 that the hydrogenation product contains less than about 0.01 mole percent hydrogen; d. subjecting the hydrogenation product to distillation to provide a lower boiling fraction comprising alcohol product and a higher boiling fraction comprising unreacted ester product and esterifying alcohol from the alcohol portion of the ester product; and e. recycling at least a portion of the higher boiling fraction to step (b).

6. The process of claim 5 wherein from about 50 mass percent to essentially all of the higher boiling fraction from step (d) is recycled to step (e).

7. The process of claim 5 wherein the organic acid in step (a) is neutralized with base to form a salt, and the base is then reacidified to provide the organic acid which is then esterified in step (b).

8. The process of claim 5 wherein the esterification occurs in the presence of the aqueous menstruum of step (a).

9. The process of claim 5 wherein the alcohol product is ethanol and primary alcohol has 3 to 30 carbon atoms.

10. A continuous process for making ethanol comprising: a. contacting an acetic ester with hydrogen under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising ethanol; b. pyrolyzing biomass feed to provide pyrolysis gases comprising hydrogen and carbon monoxide, said pyrolysis being under pyrolysis conditions comprising a substantial absence of molecular oxygen and elevated temperatures, said elevated temperatures being provided at least in part by indirect heat exchange with gases from the combustion of fuel comprising carbon monoxide and hydrogen; c. subjecting at least a portion of the pyrolysis gases to a hydrogen separation operation to provide a fraction containing an increased concentration of hydrogen and a fraction containing hydrogen and an increased concentration of carbon monoxide; d. providing said fraction containing an increased concentration of hydrogen to step (a) for the hydrogenation, and e. providing said fraction containing carbon monoxide to step (b) as at least a portion of the fuel, wherein the rate of hydrogen supply by step (d) is controlled by changing the purity of the hydrogen in said fraction containing an increased concentration of hydrogen.

11. The process of claim 10 wherein the hydrogen separation operation preferably comprises membrane separation.

12. The process of claim 10 wherein the hydrogen separation operation comprises sorption.

13. The process of claim 12 wherein the sorption comprises pressure swing sorption.

14. The process of claim 10 wherein the pyrolysis is at a temperature between about 300°C and 450⁰C.

15. The process of claim 10 wherein at least a portion of the pyrolysis gases are subjected to water gas shift.

16. The process of claim 10 wherein the hydrogenation conditions comprise a molar ratio of hydrogen to acetic ester between about 2:1 to 8:1, and pressures 3 to 50 MPa (absolute), and a temperature of between about 150⁰C and 300⁰C

17. The process of claim 10 wherein the alcohol portion of acetic ester comprises hydrocarbon of 3 to 30 carbon atoms.

18. A continuous, integrated pyrolysis and indirect fermentation process to provide a product alcohol comprising: a. subjecting an aqueous menstruum containing carbohydrate to homoacidogenic fermentation conditions to provide an organic acid corresponding to the alcohol, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. esterifying at least a portion of said organic acid with esterifying alcohol having a greater number of carbon atoms than the organic acid; c. hydrogenating the ester product under hydrogenation conditions comprising the presence of hydrogenation catalyst to provide a hydrogenation product comprising product alcohol; d. subjecting the hydrogenation product to distillation to provide a lower boiling fraction comprising product alcohol and a higher boiling fraction comprising unreacted ester product and esterifying alcohol; and e. recycling at least a portion of the higher boiling fraction to step (b); f. pyrolyzing biomass feed to provide pyrolysis gases comprising hydrogen and carbon monoxide, said pyrolysis being under pyrolysis conditions comprising a substantial absence of molecular oxygen and elevated temperatures, said elevated temperatures being provided at least in part by indirect heat exchange with gases from the combustion of fuel comprising carbon monoxide and hydrogen; g. subjecting at least a portion of the pyrolysis gases to a hydrogen separation operation to provide a fraction containing an increased concentration of hydrogen and a fraction containing hydrogen and an increased concentration of carbon monoxide; h. providing said fraction containing an increased concentration of hydrogen to step (c) for the hydrogenation, and i. providing said fraction containing carbon monoxide to step (f) as at least a portion of the fuel, wherein the rate of hydrogen supply by step (h) is controlled by changing the purity of the hydrogen in said fraction containing an increased concentration of hydrogen.

19. The process of claim 18 wherein the product alcohol is ethanol.

20. The process of claim 18 wherein the carbohydrate comprises sugars from at least one of corn and sugar cane, and the biomass for the pyrolysis of step (f) comprises corn stover or at least a portion of sugar cane plant not used for fermentation.