WO2009009320A1 - Improved indirect process for producing ethanol - Google Patents

Improved indirect process for producing ethanol Download PDF

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Publication number
WO2009009320A1
WO2009009320A1 PCT/US2008/068543 US2008068543W WO2009009320A1 WO 2009009320 A1 WO2009009320 A1 WO 2009009320A1 US 2008068543 W US2008068543 W US 2008068543W WO 2009009320 A1 WO2009009320 A1 WO 2009009320A1
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process
alcohol
step
water
acetic acid
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PCT/US2008/068543
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French (fr)
Inventor
David James Schreck
Norman Louis Balmer
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Best Energies Inc.
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Priority to US60/958,620 priority
Application filed by Best Energies Inc. filed Critical Best Energies Inc.
Publication of WO2009009320A1 publication Critical patent/WO2009009320A1/en

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    • CCHEMISTRY; METALLURGY
    • C12BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12PFERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00Preparation of oxygen-containing organic compounds
    • C12P7/40Preparation of oxygen-containing organic compounds containing a carboxyl group including Peroxycarboxylic acids
    • C12P7/54Acetic acid
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07CACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/74Separation; Purification; Use of additives, e.g. for stabilisation
    • C07C29/88Separation; Purification; Use of additives, e.g. for stabilisation by treatment giving rise to a chemical modification of at least one compound
    • C07C29/92Separation; Purification; Use of additives, e.g. for stabilisation by treatment giving rise to a chemical modification of at least one compound by a consecutive conversion and reconstruction
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00Technologies for the production of fuel of non-fossil origin
    • Y02E50/10Biofuels
    • Y02E50/17Grain bio-ethanol

Abstract

Ethanol is produced by an indirect route involving fermentation of carbohydrate under homoacidogenic conditions to form acetic acid; esterifying the acid with primary alcohol containing at least 4 carbons and hydrogenating the ester to form ethanol and to recover primary alcohol for recycle. The processes of this invention enable water separations without formation of water azeotropes and further enable water separations by phase separations thereby resulting in energy efficiencies.

Description

IMPROVED INDIRECT PROCESS FOR PRODUCING ETHANOL

FIELD OF THE INVENTION

[0001] This invention pertains to improved processes for the indirect production of ethanol by the fermentation of carbohydrates, and particularly to such processes that yield acetic acid or salt thereof in the fermentation. The processes can reduce utility costs while still providing a high yield of ethanol.

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. An important consideration in any process for the synthesis of alternative fuels is the energy ratio. The energy ratio is the ratio of the energy produced divided by the energy consumed in making the alternative fuel. Also, important is the conversion of the biomass to fuel ethanol. [0003] 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 sometimes less than 50, percent of the sugar being converted to ethanol. [0004] Another process for making ethanol is the indirect process in which the fermentation results in the production of acetic acid. The acid is not readily hydrogenated and thus is converted into an ester and then hydrogenated. The advantage is that the sugars can be converted to acetic acid in nearly 100 percent yield. This 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.

[0005] Although the yield of fermentation product per unit of sugar being fermented is substantially greater for the indirect process than for direct fermentation to ethanol, consideration must still be given to the energy consumption per unit volume of ethanol produced. The indirect process involves three key process steps. First is the fermentation. The fermentation menstruum provides a relatively dilute solution in water, often less than about 5 mass percent. And to even reach this level, the acetic acid fermentation product is neutralized. Hence not only must solids be removed, but also distillation or solvent extraction is used to remove water or esterification product to allow the esterification to proceed. Then the esterification product is hydrogenated and the product ethanol must be obtained. Not only does the indirect process pose additional steps but also the associated unit operations represent consumption of energy, thus lowering the energy ratio.

[0006] 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 70°C. 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.

SUMMARY OF THE INVENTION [0007] By this invention, processes are provided that enable a high yield of ethanol at a desirable energy ratio using the indirect process. Pn accordance with this invention, the acetic ester is formed using esterifying alcohol having a higher boiling point than water and which does not form an azeotrope with water, acetic acid or the ester of the alcohol. Suitable alcohols have at least three, and preferably at least four carbons, and most preferably, the alcohol is a substantially water insoluble primary alcohol, e.g., at least about 5, preferably at least about 8, and most conveniently between about 8 and 24, carbons. The acetic ester preferably does not form an azeotrope with water. Most preferably, the acetic ester is water immiscible.

[0008] In the broad aspects, processes of this invention for producing ethanol may desirably comprise: a. subjecting a carbohydrate-containing feed to homoacidogenic fermentation conditions to provide a fermentation product comprising at least one of acetic acid and salt thereof, said conditions comprising the presence of nutrients and an acid- producing microorganism; b. contacting acetic acid from step (a) with esterifying alcohol having at least 3 carbon atoms under esterification conditions to provide an esterification product, preferably a substantially water-immiscible esterification product, comprising acetate of said alcohol; c. separating water from said esterification product; d. hydrogenating said esterification product to provide ethanol and said esterifying alcohol; and e. recycling at least a portion, preferably at least about 80, and more preferable from about 90 to essentially 100, mass percent, of said esterifying alcohol from step (d) to step (b).

[0009] Within the broad aspects of processes of this invention, at least a portion of the water can be removed from the acetic acid prior to the esterification, or alternatively or in addition, water can be removed during the esterification, e.g., by a reactive distillation process, or, especially when using substantially water insoluble alcohols, by phase separation. Any acetic acid in the separated water phase can be recycled. [0010] 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. [0011] 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

[0012] Figure 1 is a schematic depiction of an apparatus for synthesizing ethanol in accordance with processes of this invention using base neutralization of acetic acid in the fermentation.

[0013] Figure 2 is a schematic depiction of an apparatus for synthesizing ethanol in accordance with processes of this invention using direct esterification.

DETAILED DESCRIPTION [0014] 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. Numerous microorganisms are known for homoacidogenic fermentation especially acetogenic microorganisms, see for instance, Acetogenisis, Chapman & Hall, 1994. Representative microorganisms are those of the Acetobacterium, Clostridium, Lactobacillius, and Peptostreptococcus species, such as Clostridium thermoaceticum, Acetogenium kivui, Acetobacterium woodii, Clostridium formicoaceticum, Lactobacillius casei, and Lactobacillius delbruckii.

[0015] Carbohydrates are compounds containing carbon, oxygen and hydrogen that contain a saccharose 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.

[0016] 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. [0017] 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 70°C. 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.

[0018] 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).

[0019] 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

[0020] 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. [0021] 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.

[0022] 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 esterifϊed 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 esterifϊed directly. [0023] 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. [0024] Regardless of whether or not the liquid menstuum is concentrated using reverse osmosis or pervaporation, water can be removed by distillation prior to esterification or during esterification through distillation, including reactive distillation. Water has a lower boiling point than acetic acid or acetic esters of alcohols having at least 3 or 4 carbons. As no ethanol is present, no azeotrope is formed, thereby facilitating the retention of acetic acid in the higher boiling fraction.

[0025] A preferred alternative is a simultaneous extraction and esterification in the presence of water. 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. 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.

[0026] 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 and incorporated by reference in its entirety. 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 primary 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 primary 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. [0027] 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 700C 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 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. Additives, such as emulsifiers may also find utility. [0028] 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. [0029] 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. [0030] 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

[0031] 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. [0032] The esterification with esterifying alcohol 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.

[0033] 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 primary 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.

[0034] 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.

[0035] 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. In 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 Nafϊon™ 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.

[0036] 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. [0037] Preferably, the duration of the esterification should be 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.

[0038] 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.

[0039] 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

[0040] 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. The hydrogen may be obtained from any suitable source. One convenient source is through the pyrolysis of biomass. One preferred source of biomass is the discarded portion of the crop providing the fermentable carbohydrate. Copending patent application [Atty. Docket: GEIN-110-P CT], filed on even date herewith and incorporated by reference in its entirety, discloses an integrated pyrolysis and indirect alcohol production process.

[0041] A number of options exist for the hydro genation. 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.

[0042] 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.

[0043] In either mode of hydrogenation, the temperature is often in the range of about 1500C to 300°C. 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, indium, and copper chromite are examples of hydrogenation catalysts.

[0044] 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. [0045] 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. [0046] The drawings are provided to facilitate an understanding of the invention but are not in limitation of the invention.

[0047] With respect to Figure 1, an apparatus 100 is provided for the indirect process to make ethanol. 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 and calcium carbonate for adjusting the pH of the fermentation menstruum via line 108. Make-up base, which may be provided as an aqueous calcium hydroxide slurry or solution is provided via line 108 A. In fermentation vessel 104 acetic acid is generated by microorganisms and at least a portion of the acetic acid is neutralized with calcium carbonate to calcium acetate. Carbon dioxide is generated during the neutralization and may be exhausted from fermentation vessel 104.

[0048] The fermentation menstruum is withdrawn from fermentation vessel 104 and passed via line 110 to solids separator 112. As shown, solids separator has several components: first, a centrifuge yielding fermentation solids that are exhausted via line 114; second, an acidification of the acetate salt with carbon dioxide supplied via line 116; and third, a filtration separation, which may be a series of membrane separations from micro to nano-sized, to remove calcium carbonate, unreacted sugars, and other higher weight organics from the liquid containing acetic acid. A solids phase from the filtration separation, which contains calcium carbonate, is recycled to fermentation vessel 104 via line 108.

[0049] The filtered liquid from solids separator 112 is passed via line 118 to reverse osmosis unit 120 for removal of a portion of the water which exits via line 122. This water can be recycled to the fermentation vessel 104 if desired. A more concentrated aqueous acetic acid stream is passed from reverse osmosis unit 120 via line 124 to esterification reactor 126. In esterification reactor 126, which comprises a high turbulence mixer, a highly dispersed two phase mixture is held under esterification conditions including the presence of toluene sulfonic acid catalyst. The organic phase is provided by a higher molecular weight, primary alcohol, which for purposes of this discussion is a Cj6 to C20 alcohol derived by the hydro genation of biodiesel and is introduced from line 158A. If desired, an additional water-insoluble organic liquid such as kerosene or mineral oil can supplement the higher alcohol. In esterification reactor 126, acetic acid and the higher alcohol are reacted to form an ester. The reaction product is sent via line 128 to phase separator 130.

[0050] In phase separator 130, an aqueous phase is formed that is removed and passed through line 132 to reverse osmosis unit 120. This lower layer will contain, in addition to water, unreacted acetic acid. A portion of the stream in line 132 may be purged or, as shown in the drawing, passed via line 134 to distillation column 136 to remove water via line 138 and recover acetic acid as the bottoms fraction which fraction can be passed via line 140 to esterification reactor 126.

[0051] The organic layer in phase separator 130 will contain the acetic ester, unreacted higher alcohol, ethyl acetate from transesterification between product alcohol, and acetic acid. This layer is passed via line 142 to hydrogenation reactor 144 containing solid hydrogenation catalyst, e.g., Raney nickel catalyst. Hydrogen is introduced into hydrogenation reactor 144 via line 156. In hydrogenation reactor 144, ethanol and higher alcohol are formed. The reaction product is passed via line 146 to flash stripper 148. The liquid from flash stripper 148 which is ethanol, higher alcohol, unreacted acetate ester, ethyl acetate, acetic acid and any additional organic material used to form the water-insoluble phase, is passed via line 150 to distillation column 152. The gas fraction in stripper 148 is passed via line 154 to hydrogen header 156 for recycle to hydrogenation reactor 144. [0052] In distillation column 152, ethanol is stripped and a higher boiling fraction containing acetic acid, acetate ester of the higher alcohol, the higher alcohol and any organic material used to provide the water-insoluble phase is obtained. This higher boiling fraction is recycled via line 158 to esterifi cation reactor 126. Make-up higher alcohol and organic material, if used, can be provided via line 158 A.

[0053] The lower boiling fraction from distillation column 152 is passed via line

160 to condenser 162. The gas phase, which is primarily hydrogen, can be passed from condenser 162 to hydrogen header 156. Make-up hydrogen is provided via line 156A. The liquid phase in condenser 162 is ethanol and is removed via line 164 for product storage. [0054] Figure 2 depicts an embodiment of the invention wherein a slip stream from the fermentation vessel is subjected to esterifi cation, hi apparatus 200, 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. A slip stream is withdrawn via line 208 and contains the aqueous fermentation menstruum including acetic acid and microorganism, and is passed to solids separator 210.

[0055] Solids separator 210 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 212 for recycle to fermentation vessel 204. The aqueous phase having a reduced concentration of solids is passed from solids separator 210 via line 214 to esterifi cation reactor 216. Esterification reactor 216 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 218 is provided in esterification reactor 216 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 216 via line 220 for recycle to fermentation vessel 204. A purge of aqueous fermentation menstruum can be taken via line 222. [0056] The water-immiscible phase from esterification vessel 216 contains ester and is passed via line 224 to phase separator 226. Phase separator 226 serves to remove aqueous menstruum entrained in the water-immiscible phase, and the removed aqueous menstruum is withdrawn via line 228 and may be recycled, if desired, to fermentation vessel 204. Line 230 serves to direct the water-immiscible phase provided by phase separator 226 to hydrogenation reactor 232 for hydrogenation of ester to product alcohol, ethanol, and primary alcohol. Hydrogen is provided by line 234 to hydrogenation reactor 232. Hydrogen can be provided by the integrated pyrolysis unit. The apparatus in this Figure 2 operates on a total consumption mode of hydrogen. The hydrogenation product is passed via line 236 to distillation column 238. Ethanol product is stripped via line 240. The higher boiling fraction, which contains primary alcohol and ester, is passed via line 242 to esterifϊcation reactor 216 as the water-immiscible liquid. A portion of this stream can, if desired, be directed via line 244 to line 230 for recycle to hydrogenation reactor 232. The stripped ethanol in line 240 can be directed to condenser 246. Any hydrogen and non-condensables are removed via line 248 and ethanol is directed to product storage via line 250. [0057] As can be seen, the processes of this invention provide for an indirect process for producing ethanol in an energy efficient manner.

Claims

IT IS CLAIMED:
1. A process for producing ethanol comprising: a. subjecting a carbohydrate-containing feed to homoacidogenic fermentation conditions to provide a fermentation product comprising at least one of acetic acid and salt thereof, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. contacting acetic acid from step (a) with esterifying alcohol having at least 3 carbon atoms under esterification conditions to provide an esterifϊcation product comprising acetate of said alcohol, wherein neither of the esterifying alcohol or esterification product forms an azeotrope with water; c. separating water from said esterification product; d. hydrogenating said esterification product to provide ethanol and said esterifying alcohol; and e. recycling at least a portion of said esterifying alcohol from step (d) to step (b).
2. The process of claim 1 wherein the esterification product is water immiscible.
3. The process of claim 1 wherein the alcohol comprises primary alcohol that is substantially insoluble in water.
4. The process of claim 3 wherein the primary alcohol has between about 8 and 24 carbon atoms.
5. The process of claim 4 wherein the primary alcohol is derived from biodiesel.
6. The process of claim 1 wherein the separation of step (c) is by distillation.
7. The process of claim 1 wherein the separation of step (c) is by phase separation and acetic acid is contained in the separated water, at least a portion of which acetic acid is recycled to step (b).
8. The process of claim 1 wherein acetic acid in step (a) is neutralized by reaction with base, and reacidified prior to step (b).
9. The process of claim 8 wherein the base comprises at least one of calcium oxide, calcium hydroxide and calcium carbonate and the reacidification is by contact with carbon dioxide.
10. A process for producing ethanol comprising: a. subjecting a carbohydrate-containing feed to homoacido genie fermentation conditions to provide a fermentation product comprising at least one of acetic acid and salt thereof, said conditions comprising the presence of nutrients and an acid-producing microorganism; b. contacting the fermentation product with esterifying alcohol under esterification conditions to provide a substantially water-insoluble esterification product comprising acetate of said alcohol; c. phase separating water and an organic phase from said esterification product; d. hydrogenating said the organic phase from the esterification product to provide ethanol and said esterifying alcohol; and e. recycling at least a portion of said esterifying alcohol from step (d) to step (b).
11. The process of claim 10 wherein an organic material is provided to step (b) to assist in providing a water-insoluble phase.
12. The process of claim 10 wherein the organic material is recycled with the esterifying alcohol in step (e) to step (b).
13. The process of claim 10 wherein the esterifying alcohol comprises primary alcohol.
14. The process of claim 13 wherein the esterifying alcohol is substantially water-immiscible.
15. The process of claim 14 wherein the primary alcohol has between about 8 and 24 carbon atoms.
16. The process of claim 15 wherein the primary alcohol is derived from biodiesel or glyceride.
17. The process of claim 10 wherein acetic acid is contained in the separated water, at least a portion of which acetic acid is recycled to step (b).
18. The process of claim 10 wherein acetic acid in step (a) is neutralized by reaction with base, and reacidified prior to step (b).
19. The process of claim 18 wherein the base comprises at least one of calcium oxide, calcium hydroxide and calcium carbonate and the reacidification is by contact with carbon dioxide.
PCT/US2008/068543 2007-07-06 2008-06-27 Improved indirect process for producing ethanol WO2009009320A1 (en)

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