Abstract:
The disclosure includes a method, process and apparatus for the conversion of biomass to carboxylic acids and/or primary alcohols. The system may include a pretreatment/fermentation subsystem operable to produce a fermentation broth containing carboxylic acid salts from biomass, such as lignocellulosic biomass. The system may also include a dewatering subsystem operable to remove excess water from the fermentation broth to produce a concentrated product. The system may also includes an acid springing subsystem operable to produce a mixed carboxylic acid product. The system may also include a hydrogenation subsystem operable to produce an alcohol mixture, such as a mixture containing primary alcohols. Methods of operating this system or other systems to obtain a carboxylic acid or alcohol mixture are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 60/580,291 filed Jun. 16, 2004. 
    
    
     TECHNICAL FIELD 
     The present invention relates to methods of converting biomass to useful substances, such as carboxylic acids and primary alcohols, through an integrated pretreatment, fermentation, dewatering and treatment process. More specifically it may relate to a method applied to lignocellulosic biomass. 
     BACKGROUND 
     A great deal of biomass, particularly lignocellulosic biomass, remains unused or inefficiently used during agricultural and industrial processes. Disposal of this biomass is often difficult or costly. Therefore, methods of using this biomass to produce useful chemicals are quite valuable. 
     Organic acids are important chemicals of commerce. Historically, organic acids were produced from animal fat or vegetable oil sources or from petroleum sources in substantially nonaqueous systems. More recently, organic acids have been identified as among the most attractive products for manufacture from biomass by fermentation. Alcohols are also important industrial chemicals that may be produced by fermentation of biomass. However, extraction of organic acids and alcohols from the overall fermentation product is not easy and is often inefficient in the use of energy, water and reactant chemicals. 
     SUMMARY OF THE INVENTION 
     The present invention includes a method, process and apparatus for the conversion of biomass to carboxylic acids and/or primary alcohols. 
     According to one embodiment, the invention includes a system for the conversion of biomass. The system includes a pretreatment/fermentation subsystem operable to pretreat biomass with lime or quick lime and air to produce treated biomass and ferment the treated biomass with an inoculum to produce a fermentation broth containing carboxylic acid salts. The system also includes a dewatering subsystem operable to remove excess water from the fermentation broth to produce a concentrated product. Finally, the system includes an acid springing subsystem operable to combine the concentrated product with a low-molecular-weight tertiary amine or ammonia to produce a low-molecular-weight tertiary amine or ammonia carboxylate product from the carboxylic acid salts, replace the low-molecular-weight tertiary amine or ammonia in the low-molecular-weight tertiary amine or ammonia carboxylate product with a high-molecular-weight tertiary amine to form a high-molecular-weight tertiary amine carboxylate product, and thermally break the amine-carboxylate bonds in the high-molecular-weight tertiary amine carboxylate product to produce a mixed carboxylic acid product. 
     In a more specific embodiment the system may also include a hydrogenation subsystem operable to combine the mixed carboxylic acid produce with a high-molecular-weight alcohol to form an ester, convert the ester to an alcohol mixture using a hydrogenation catalyst, and separate the alcohol mixture from the high-molecular-weight alcohol. 
     According to another embodiment, the invention includes a method of obtaining a fermentation product. The method may include: treating a pile of biomass with lime or quick lime, water, an inoculum and air to produce a fermentation broth; acidifying the fermentation broth with a high-molecular-weight carboxyllic acid to produce acidified fermentation broth; stripping the fermentation broth in a stripping column to produce stripped fermentation broth; concentrating the stripped fermentation broth in an evaporator to produce concentrated product; mixing the concentrated product with a low-molecular-weight tertiary amine or ammonia and carbon dioxide to produce a low-molecular-weight tertiary amine or ammonia carboxylate; exchanging the low-molecular-weight tertiary amine or ammonia carboxylate with a high-molecular-weight tertiary amine to produce a high-molecular-weight tertiary amine carboxylate; heating the high-molecular-weight tertiary amine carboxylate to a temperature sufficient to break acid/amine bonds to produce a free carboxylic acid product; and recovering the free carboxylic acid product. 
     In a more specific embodiment, the method may also include: combining the carboxylic acid produce with a high-molecular-weight alcohol to from an ester; hydrogenating the ester to form an alcohol product; separating the high-molecular-weight alcohol from the alcohol product; and recovering the alcohol product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be better understood through reference to the following detailed description, taken in conjunction with the drawings, in which: 
         FIG. 1  illustrates a pretreatment and fermentation system, according to an embodiment of the present invention; 
         FIG. 2  illustrates a dewatering system, according to an embodiment of the present invention; 
         FIG. 3  illustrates an acid springing system, according to an embodiment of the present invention; 
         FIG. 4  illustrates a hydrogenation system, according to an embodiment of the present invention; 
         FIG. 5  illustrates a biomass converting system, according to an embodiment of the present invention; and 
         FIG. 6  illustrates a flow diagram of a method for producing carboxylic acids and alcohols, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to systems, methods, and devices for the conversion of biomass, particularly lignocellulosic biomass, to carboxylic acids and alcohols, particularly primary alcohols. 
     Referring now to  FIG. 1 , pretreatment and filtration system  10  may be provided in which biomass pile  12  may be blended with lime or quick lime (calcium carbonate or calcium oxide) and carbon dioxide (not shown) and piled on top of pit  14  filled with gravel  16 . Pit  14  may also be lined with liner  18 . Biomass pile  12  may include any sort of biomass. In selected embodiments it may include lignocellulosic biomass, such as processed sugarcane or sorghum stalks or corn stover. Perforated drain pipe  20  may be embedded in gravel  16 . Biomass pile  12  may be covered by cover  22  to keep out rain and debris, particularly if system  10  is outside. Pump  24  may circulate water  34  from pit  14  to the top of biomass pile  12 . As water  34  circulates through pile  12 , it may flow through heat exchanger  26 , which may regulate the temperature. Cooling water or heat source  28  may also circulate through heat exchanger  26 . 
     During approximately the first month after biomass pile  12  is assembled, air  38  may be blown through pile  12  using blower  30 . To remove carbon dioxide from the air, it may be bubbled through lime water slurry  32 . Oxygen-rich air  28  may also be supplied. The combined effect of lime plus air  28  in pile  12  removes lignin from the biomass, rendering it more digestible. Further, the lime removes acetyl groups from hemicellulose, which also helps digestibility. Once the lime is exhausted, the pH drops to near neutral, at which point a mixed-culture inoculum may be added. 
     The inoculum may be derived from any source, but in many embodiments it may be derived from soil. Organisms derived from organic-rich soil in marine environments appear to be particularly well-suited for use with embodiments of the present invention. Such organisms are able to be productive in high-salt environments. For example, the inoculum may include a salt-tolerant microorganism. 
     After inoculation, the organisms digest the biomass and convert it to carboxylic acids. These acids react with the calcium carbonate or calcium oxiode in pile  12 , producing calcium carboxylate salts or other calcium salts that are dissolved in the water that circulates through the pile. This aqueous solution, called fermentation broth  36  may be harvested and sent for further processing. 
     Referring now to  FIG. 2 , fermentation broth  36  may be dewatered in dewatering system  40 . Fermentation broth  26  may be pumped through heat exchanger  42 , which preheats the broth. Preheated fermentation broth  36  may then be acidified with high-molecular-weight carboxylic acid  46  (e.g. caproic, valeric, hepotanoic acids). Acidified fermentation broth  36  may be sent to stripping column  44  where steam  80  strips out dissolved carbon dioxide, a noncondensible gas that may interferes with evaporator  58  and cause calcium carbonate scaling on heat exchanger  56 . Preferably, stripper  44  may operate at 1 atm, or higher, which allows exiting steam  86  to be used for heat elsewhere in the process. Further, if heat exchanger  42  becomes fouled by dissolved calcium carbonate, the pressure in stripper  44  may be reduced, which lowers the temperature of steam exiting heat exchanger  42  and may reduce fouling. However, if stripper  44  is operated at a reduced pressure, a vacuum pump (not shown) may be needed to remove the noncondensible gases from fermentation broth  36 . 
     Steam-stripped, acidified fermentation broth  36  may then be sent to mixer  48  where the pH may be raised to between approximately 11 and 12 through the addition of lime  50  from reservoir  78 , which causes scum  54  to precipitate. Scum  54  may then be removed in solids separator  52 . This degassed, descummed fermentation broth  36  may be further heated in heat exchanger  56 , after which it may enter evaporator  58 . Compressor  60  may evaporate water from the low-pressure chamber of evaporator  58 . The heat of condensation released in the high-pressure chamber of evaporator  58  may provide the heat of evaporation needed in the low-pressure chamber. The energy needed to drive the evaporation process may be provided by an engine. 
     In the embodiment shown in  FIG. 2 , a combined cycle engine may be used, which increases energy efficiency. Gas turbine  88  may provide shaft power to compressor  60 . Gas turbine may use fuel  74 . Exhaust gas  72  from gas turbine  88  may be directed to boiler  62 , which may produce high-pressure steam that may drives steam turbine  64 . Heat exchanger  66  may condense the low-pressure steam exiting steam turbine  64 . Cooling water  76  may be used to facilitate this cooling. Distilled water  82  from the high-pressure section of evaporator  58  may be cooled in heat exchangers  56  and  42 , and may be returned to pretreatment/fermentation system  10 . Concentrated product  68  may be cooled in heat exchangers  56  and  42 , and sent to acid springing system  90 . Liquid turbine  70  may recapture some work from the high-pressure liquids that exit evaporator  58 . 
     Pumps  84  may be included at various points in the system to facilitate fluid flow. 
     Referring now to  FIG. 3 , concentrated product  68  may next be sent to acid springing system  90 . In mixer  92 , concentrated product  68  from dewatering system  40  may be mixed with carbon dioxide  94  and low-molecular-weight tertiary amine  96 , such as triethyl amine. The carboxylate reacts with low-molecular-weight tertiary amine  96  to form a soluble salt. The calcium reacts with carbon dioxide  94  to form insoluble calcium carbonate  98 , which may be recovered using solids separator  100 . Calcium carbonate  98  may then be washed with distilled water to remove adhering product and steam stripped in vessel  102  to ensure that all low-molecular-weight tertiary amine  96  is removed from calcium carbonate  98 . Calcium carbonate  98  may then be sent to pretreatment/fermentation system  10  to act as a buffer or to a lime kiln (not shown) to be converted to lime. 
     Aqueous solution  104  contains dissolved low-molecular-weight tertiary amine carboxylate. It may then be preheated in heat exchanger  106  and sent to evaporator  108 , where most of the water may be removed using the same vapor-compression technology used in dewatering system  40 . Specifically, turbine  130  may provide energy to compressor  132 . Waste fluid exiting evaporator  108  may be sent to column  134  where it may be combined with lime  136  and steam  138  to provide additional product stream to mixer  92  and water  140  to pretreatment/fermentation system  10 . 
     The concentrated low-molecular-weight tertiary amine carboxylate solution  104  may then be sent to column  110  where high-molecular-weight tertiary amine  112 , such as trioctyl amine or triethanol amine, may be added. Low-molecular-weight tertiary amine  96  may be replaced and exit the top of column  110 , while high-molecular-weight tertiary amine carboxylate solution  104  may exit the bottom of column  110 . 
     The high-molecular-weight tertiary amine carboxylate solution  104  may then be preheated in heat exchanger  114  and sent to column  116 . In column  116 , the temperature may be high enough to break chemical bonds, allowing the more volatile carboxylic acids  146  to exit the top of column  116 . The less volatile high-molecular-weight tertiary amine  112  may exit the bottom of the column and may be recycled to column  110 . 
     Any salts  120  that are in high-molecular-weight tertiary amine  112  may be removed using a solids separator  118 . Recovered salts  120  may be washed with volatile solvent  122 , such as triethyl amine, to remove high-molecular-weight tertiary amine  112  in separator  118 . Solvent  122  may be separated from the recovered high-molecular-weight tertiary amine in distillation column  124 . Salts  120  may then be steam stripped in stripper  126  to remove volatile solvent  122  and form solids  144 . 
     System  90  may contain various heat exchangers  140  that may be used to recycle process heat. Various fluids may pass through these heat exchangers, such as cooling waters  142 , steam  148 , and fuel  150 . In one heat exchanger  140 , steam  86  from dewatering system  40  may be used as a heat source then collected in condenser  152  where carbon dioxide  154  may be separated from water  156 , which may be returned to fermentation/pretreatment system  10 . 
     Pumps  158  may also be included at various points in the system to facilitate fluid flow. 
     Referring now to  FIG. 4 , mixed carboxylic acids  146  from acid springing system  90  may be sent to hydrogenation system  170 . Mixed acids  146  may be placed in column  172  and combined with high-molecular-weight alcohol  174  such as heptanol. Carboxylic acids  146  react with alcohol  174  to form ester  176  and water  178 . Water  178  may be separated in column  172  and sent to heat exchanger  180  then returned to column  172  or used elsewhere in systems  10 ,  40 ,  90  or  170 . Ester  176  may be sent to hydrogenation reactor  182  which contains a suitable hydrogenation catalyst, such as a Raney nickel. In reactor  182 , hydrogen  200  is added and ester  176  is converted to alcohol. Solids may be separated from alcohol  184  using solids separator  186 . Alcohol mixture  184  may be sent column  188  which may recover high-molecular-weight alcohol  174  from the bottom and alcohol product  190  from the top. Alcohol product  190  may be a primary alcohol. 
     System  170  may contain various heat exchangers  192  that may be used to recycle process heat. Various fluids may pass through these heat exchangers, such as cooling waters  194  and steam  196 . Pumps  198  may also be included at various points in the system to facilitate fluid flow. 
     Alternative systems to recover carboxylic acids without production of alcohol are known in the art any may be used in place of the hydrogenation system of  FIG. 4 . 
     Referring now to  FIG. 5 , system  300  may include as subsystems  302  pretreatment/fermentation system  10 , dewatering system  40 , acid sprining system  90  and optionally also hydrogenation system  170 . System  300  may reuse process heat, water, lime, carbon dioxide and other materials among different subsystems  302 . 
     In an alternative embodiment not explicitly shown, ammonia may be used in place of low-molecular-weight tertiary amine  96  in acid sprining system  90 . Further, if the ammonia is supplied earlier, the a reaction between calcium carboxylate, carbon dioxide and ammonia may occur prior to entry into dewatering system  40 . In this embodiment, an aqueous solution of ammonia carboxylate may be evaporated in dewatering system  40  rather than calcium carboxylate. This may help prevent scaling in heat exchangers or system  40  because ammonium salts have a lesser tendency to scale than calcium salts. Ammonia is also cheap and lost ammonia may be diverted to pretreatment/fermentation system  10  where it may serve as a nitrogen source. However, ammonia may react with carboxylic acids to form amides, which may not be a desired byproduct. 
     Embodiments of the invention may include all processes involved in the operation of the above-described systems. Referring now to  FIG. 6 , the invention may include an integrated method for producing carboxylic acids and alcohols. The method may include treating pile of biomass  12  with lime or quick lime, water  34 , an inoculum and air in step  400  to produce fermentation broth  36 . In step  410 , fermentation broth  36  may be acidified with high-molecular-weight carboxylic acid  46  then, in step  420 , stripped in stripping column  44 . In step  430 , the product may be concentrated in evaporator  58  to produce concentrated product  68 . Concentrated product  68  may be mixed with carbon dioxide  94  and low-molecular-weight tertiary amine  96  in step  440  to form a low-molecular weight tertiary amine carboxylate. This carboxylate may be exchanged with high-molecular-weight tertiary amine  112  in column  110  in step  450  to produce a high-molecular-weight tertiary amine carboxylate. The high-molecular-weight tertiary amine carboxlate may be heated in column  116  to a temperature high enough to break the acid to amine bonds in step  460 . This produces carboxylic acids  146  which may be recovered in step  470 . In some embodiments, carboxylic acids  146  may be combined with high-molecular-weight alcohol  174  to form ester  176  in step  480 . In step  490 , ester  176  may be hydrogenated in chamber  182  to form alcohol product  190 . In step  500 , high-molecular-weight alcohol  174  and alcohol product  190  may be separated in column  188 . Alcohol product  190  may be a primary alcohol. 
     In an alternative embodiment, ammonia may be used in place of low-molecular-weight tertiary amine  96 . Ammonia may be added immediately after step  400 . 
     Various methods, systems and apparati useful in the present invention may also be described in U.S. Pat. No. 6,043,392, issued Mar. 28, 2000, U.S. Pat. No. 5,986,133, issued Nov. 16, 1999, U.S. Pat. No. 6,478,965, issued Nov. 12, 2002, U.S. Pat. No. 6,395,926, issued May 28, 2002, U.S. Pat. No. 5,962,307, issued Oct. 5, 1999, and WO 04/041995, published May 21, 2004, and their US and foreign counterpart applications and patents. All of the above patents and applications are incorporated by reference herein.