HK1114642B - Methods and systems for biomass conversion to carboxylic acids and alcohols - Google Patents

Description

Methods and systems for converting biomass to carboxylic acids and alcohols

Technical Field

The present invention relates to a process for the conversion of biomass to useful materials such as carboxylic acids and primary alcohols, which process comprises an integrated pretreatment, fermentation, dewatering and treatment process. More particularly, the present invention relates to methods applied to lignocellulosic biomass.

Background

Large amounts of biomass, particularly lignocellulosic biomass, have not been utilized or effectively utilized in agricultural and industrial processes. Disposal of such biomass is often difficult or costly. Therefore, processes for producing useful chemicals from such biomass are valuable.

Organic acids are important commercial chemicals. Historically, organic acids have been prepared from animal fat or vegetable oil sources, or from petroleum sources that are essentially non-aqueous systems. In recent years, organic acids have been identified as the most attractive products to be produced from biomass by fermentation. Alcohols are also important industrial chemicals that can be produced by fermentation of biomass. However, extraction of organic acids and alcohols from fully fermented products is not easy and is often inefficient in energy, water and reactant chemical utilization.

Summary of The Invention

The present invention provides methods, processes and apparatus for converting biomass to carboxylic acids and/or primary alcohols.

According to one embodiment, the present invention provides a system for converting biomass. The system includes a pretreatment/fermentation subsystem operable to pretreat the biomass with lime or quicklime and air to produce a treated biomass and to ferment the treated biomass with an inoculum (inoculum) to produce a carboxylate-containing fermentation broth. 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-generating (acid-spraying) subsystem operable to mix the concentrated product with a low molecular weight tertiary amine or ammonia, generate a low molecular weight tertiary amine or ammonia carboxylate product from the carboxylate, 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, form a high molecular weight tertiary amine carboxylate product, thermally break the amine-carboxylate bonds in the high molecular weight tertiary amine carboxylate product, and produce a mixed carboxylic acid product.

In a more specific embodiment, the system further includes a hydrogenation subsystem operable to combine the combined carboxylic acid product with a high molecular weight alcohol to form an ester, convert the ester to a mixture of alcohols with a hydrogenation catalyst, and separate the mixture of alcohols from the high molecular weight alcohol.

According to another embodiment, the present invention provides a method of making a fermentation product. The method comprises the following steps: treating the biomass pile with lime or quicklime, water, inoculum and air to produce a fermentation broth; acidifying the fermentation broth with a high molecular weight carboxylic acid to produce an acidified fermentation broth; stripping the fermentation broth in a stripping column to produce a stripped fermentation broth; concentrating the stripped fermentation broth in an evaporator to produce a 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 a low molecular weight tertiary amine or aminocarboxylate 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 the acid/amine bond to produce a free carboxylic acid product; and recovering the free carboxylic acid product.

In a more specific embodiment, the method further comprises: mixing the carboxylic acid product with a high molecular weight alcohol to form 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 Drawings

The invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:

FIG. 1 shows 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 generation system according to an embodiment of the present invention;

FIG. 4 shows a hydrogenation system according to an embodiment of the present invention.

Detailed Description

The present invention relates to systems, methods and apparatus for biomass conversion, particularly lignocellulosic biomass conversion to carboxylic acids and alcohols, particularly primary alcohols.

Referring now to fig. 1, a pretreatment and filtration system 10 is provided in which a pile of biomass 12 may be mixed with lime or quicklime (calcium carbonate or calcium oxide) and carbon dioxide (not shown) and deposited on top of a pit 14 filled with gravel 16. Pit 14 may also be lined with liner 18. The pile of biomass 12 may contain any kind of biomass. In selected embodiments, the biomass pile may comprise lignocellulosic biomass, such as processed sugar cane or sorghum stalks or corn stover. The porous drain pipe 20 may be buried in gravel 16. The biomass pile 12 may be covered with a cover 22 to prevent rain and debris from falling, particularly when the system 10 is outdoors. The pump 24 may circulate water 34 from the pit 14 to the top of the pile of biomass 12. As the water 34 circulates through the stack 12, it flows through the heat exchanger 26, which may regulate the temperature. Cooling water or heat source 28 may also be circulated through heat exchanger 26.

During the approximately 1 month after the heap 12 of biomass is collected, air 38 is blown through the heap 12 with the blower 30. To remove carbon dioxide from the air, air may be bubbled through the lime water slurry 32. Oxygen-enriched air 28 may also be fed. The combined effect of lime plus air 28 in the pile 12 removes lignin from the biomass, making the biomass more digestible. In addition, lime removes acetyl groups from hemicellulose, which also contributes to digestibility. After the lime is consumed, the pH drops to near neutral, at which point the mixed culture inoculum may be added.

The inoculum may be derived from any source, but in many embodiments, is derived from fecal soil (soil). Organisms derived from soil rich in organic matter in marine environments appear to be particularly suitable for use in embodiments of the present invention. These organisms can multiply in high salt environments. For example, the inoculum may comprise salt tolerant microorganisms.

After inoculation, the organism digests the biomass and converts it into carboxylic acids. These acids react with calcium carbonate or calcium oxide within the biomass pile 12 to form calcium carboxylate or other calcium salts that are soluble in the water circulating through the pile. This aqueous solution, referred to as fermentation broth 36, may be collected and subjected to further processing.

Referring to fig. 2, fermentation broth 36 may be dewatered in dewatering system 40. Fermentation broth 26 is pumped through heat exchanger 42 to preheat the broth. The preheated fermentation broth 36 is then acidified with a high molecular weight carboxylic acid 46 (e.g., hexanoic acid, pentanoic acid, heptanoic acid). Acidified fermentation broth 36 is fed to stripping column 44 where steam 80 strips out dissolved carbon dioxide, a non-condensable gas that can interfere with the operation of evaporator 58 and foul calcium carbonate on heat exchanger 56. Stripper 44 is preferably operated at 1 atmosphere or higher, which allows the vented steam 86 to be used for heating elsewhere in the process. In addition, if the heat exchanger 42 becomes fouled with dissolved calcium carbonate, the pressure in the stripper 44 drops, lowering the temperature of the steam exiting the heat exchanger 42 and possibly reducing fouling. However, if stripper 44 is operated at reduced pressure, a vacuum pump (not shown) may be required to remove non-condensable gases from fermentation broth 36.

The steam-stripped and acidified fermentation broth 36 may then be fed to a mixer 48, where the pH is raised to about 11-12 by adding lime 50 from a storage tank 78, which may precipitate scum 54. The dross 54 is then removed in a solids separator 52. This degassed, descummed fermentation broth 36 may be further heated in heat exchanger 56 before entering evaporator 58. The compressor 60 may evaporate water from the low pressure chamber of the evaporator 58. The heat of condensation released in the high pressure chamber of the evaporator 58 provides the heat required for evaporation in the low pressure chamber. The energy required to drive the evaporation process may be provided by the engine.

In the embodiment shown in fig. 2, a combined cycle engine may be used, which may improve energy efficiency. The gas turbine 88 may provide shaft power to the compressor 60. The gas turbine may use fuel 74. Exhaust gas 72 from the gas turbine 88 may be directed to the boiler 62, which generates high pressure steam that drives the steam turbine 64. The heat exchanger 66 is capable of condensing the low pressure steam discharged from the steam turbine 64. Cooling water 76 may be used to facilitate such cooling. The high pressure portion of distilled water 82 from evaporator 58 may be condensed in heat exchangers 56 and 42 and returned to pretreatment/fermentation system 10. The concentrated product 68 may be cooled in heat exchangers 56 and 42 and sent to an acid generation system 90. The liquid turbine 70 is capable of extracting some work (work) from the high pressure liquid exiting the evaporator 58.

The pump 84 may be located at various locations in the system to facilitate fluid flow.

Referring to fig. 3, the concentrated product 68 may then be sent to an acid generation system 90. In mixer 92, concentrated product 68 from dewatering system 40 may be mixed with carbon dioxide 94 and a low molecular weight tertiary amine 96, such as triethylamine. The carboxylate reacts with low molecular weight tertiary amine 96 to form a soluble salt. The calcium reacts with the carbon dioxide 94 to form insoluble calcium carbonate 98, which may be recovered using a solids separator 100. The calcium carbonate 98 may then be washed with distilled water to remove adherent products and steam stripped in vessel 102 to ensure that all of the low molecular weight tertiary amine 96 is removed from the calcium carbonate 98. The calcium carbonate 98 is then fed to the pretreatment/fermentation system 10 for use as a buffer or to a lime kiln (not shown) for conversion to lime.

The aqueous solution 104 contains dissolved low molecular weight tertiary amine carboxylate. The solution is then preheated in heat exchanger 106 and sent to evaporator 108 where most of the water is removed using the same vapor-compression technique as dewatering system 40. Specifically, the turbine 130 provides energy to the compressor 132. The waste stream from the evaporator 108 is sent to a column 134 where it is mixed with lime 136 and steam 138 to provide another product stream to the mixer 92 and water 140 to the pretreatment/fermentation system 10.

The concentrated solution 104 of low molecular weight tertiary amine carboxylate is then fed to a column 110 where a high molecular weight tertiary amine 112, such as trioctylamine or triethanolamine, may be added. Low molecular weight tertiary amine 96 can be replaced and withdrawn from the top of column 110 while high molecular weight tertiary amine carboxylate solution 104 can be withdrawn from the bottom of column 110.

High molecular weight tertiary amine carboxylate solution 104 may then be preheated in heat exchanger 114 and fed to column 116. Within column 116, the temperature can be high enough to break chemical bonds, allowing more volatile carboxylic acid 146 to exit the top of column 116. The low volatility, high molecular weight tertiary amine 112 can be withdrawn from the bottom of the column and can be recycled to column 110.

Using a solids separator 118, any salts 120 in the high molecular weight tertiary amine 112 may be removed. The recovered salt 120 may be washed with a volatile solvent 122, such as triethylamine, to remove the high molecular weight tertiary amine 112 from the separator 118. In distillation column 124, solvent 122 is separated from the recovered high molecular weight tertiary amine. The salt 120 is then steam stripped in a stripper 126 to remove the volatile solvent 122 to form a solid 144.

The system 90 may include various heat exchangers 140 for circulating process heat. Different fluids may pass through these heat exchangers, such as cooling water 142, steam 148, and fuel 150. In one heat exchanger 140, steam 86 from the dewatering system 40 is used as a heat source and then collected in a condenser 152 where carbon dioxide 154 is separated from water 156 and returned to the fermentation/pretreatment system 10.

The pump 158 may also be located at various locations in the system to facilitate fluid flow.

Referring to fig. 4, the mixed carboxylic acid 146 from the acid generation system 90 is fed to a hydrogenation system 170. The mixed acid 146 is placed in column 172 and mixed with a high molecular weight alcohol 174, such as heptanol. Carboxylic acid 146 reacts with alcohol 174 to form ester 176 and water 178. Water 178 is separated in column 172 and sent to heat exchanger 180 and then returned to column 172 or used elsewhere in system 10, 40, 90 or 170. Ester 176 may be fed to hydrogenation reactor 182, which contains a suitable hydrogenation catalyst, such as Raney nickel. In reactor 182, hydrogen 200 is passed to convert ester 176 to an alcohol. Solids are separated from alcohol 184 using a solids separator 186. Alcohol mixture 184 is fed to column 188 from which high molecular weight alcohol 174 is recovered from the bottom and alcohol product is recovered from the top. The alcohol product 190 may be a primary alcohol.

The system 170 may include various heat exchangers 192 for circulating process heat. Various fluids are passed through these heat exchangers, such as cooling water 194 and steam 196. A pump 198 may also be in various locations in the system to facilitate fluid flow.

Another system known in the art for recovering carboxylic acid, but without producing alcohol, may be used in place of the hydrogenation system in figure 4.

Referring to fig. 5, system 300 may include pretreatment/fermentation system 10, dewatering system 40, acid production system 90, and optionally hydrogenation system 170 as subsystems 302. The system 300 reuses process heat, water, lime, carbon dioxide, and other substances in different subsystems 302.

In another embodiment not explicitly shown, ammonia may be used in place of low molecular weight tertiary amine 96 in acid generation system 90. Further, if ammonia is supplied more easily, the reaction between calcium carboxylate, carbon dioxide, and ammonia may be performed prior to entering dehydration system 40. In this embodiment, an aqueous solution of an aminocarboxylate, rather than an aqueous solution of calcium carboxylate, is evaporated in dewatering system 40. This will help prevent fouling in the heat exchanger or system 40 because ammonium salts are less likely to foul than calcium salts. Ammonia is also inexpensive, and the ammonia that is released can be diverted to the pretreatment/fermentation system 10 for use as a nitrogen source. However, ammonia may react with carboxylic acids to form amides, which are not desired by-products.

Embodiments of the present invention include all of the processes involved in the operation of the system described above. Referring to fig. 6, the present invention provides an integrated process for the production of carboxylic acids and alcohols. The method includes treating a pile of biomass 12 with lime or quicklime, water 34, an inoculum, and air to produce a fermentation broth 36 at step 400. Fermentation broth 36 may be acidified with high molecular weight carboxylic acid 46 at step 410 and then stripped in stripper 44 at step 420. At step 430, the product is 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. At step 450, this carboxylate salt is exchanged with high molecular weight tertiary amine 112 in column 110. In step 460, the high molecular weight tertiary amine carboxylate is heated in column 116 to a temperature high enough to break the acid to amine bond. This step produces carboxylic acid 146, which can be recovered at step 470. In certain embodiments, carboxylic acid 146 is mixed with high molecular weight alcohol 174 to form ester 176 at step 480. At step 490, ester 176 can be hydrogenated in chamber 182 to form alcohol product 190. At step 500, high molecular weight alcohol 174 and alcohol product 190 may be separated in column 188. The alcohol product 190 may be a primary alcohol.

In another embodiment, ammonia may be used in place of low molecular weight tertiary amine 96. Ammonia is added immediately after step 400.

Various methods, systems and devices that can be used with the present invention are also described in U.S. patent 6,043,392 issued on 28/3/2000, U.S. patent 5,986,133 issued on 16/11/1999, U.S. patent 6,478,965 issued on 12/11/2002, U.S. patent 6,395,926 issued on 28/5/2002, 5,962,307 issued on 5/10/1999, and WO04/041995 published on 21/2004, as well as their U.S. and foreign family applications and patents. All of the above patents and applications are incorporated herein by reference.

Claims (21)

1. A system for converting biomass, the system comprising:

a pretreatment/fermentation subsystem for:

pretreating the biomass with lime or quicklime and air to produce a treated biomass;

fermenting the treated biomass with an inoculum to produce a fermentation broth comprising a carboxylic acid salt;

a dewatering subsystem for:

acidifying the fermentation broth with a high molecular weight carboxylic acid to form an acidified fermentation broth;

stripping the acidified fermentation broth to produce a stripped fermentation broth; and

removing excess water from the stripped fermentation broth to produce a concentrated product;

an acid generation subsystem for:

mixing 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 carboxylate;

replacing 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;

thermally cleaving the amine-carboxylate bonds in the carboxylate product of the high molecular weight tertiary amine to produce a mixed carboxylic acid product.

2. The system of claim 1, further comprising a hydrogenation subsystem for:

mixing the mixed carboxylic acid product with a high molecular weight alcohol to form an ester;

converting the ester to an alcohol mixture with a hydrogenation catalyst;

separating the alcohol mixture from the high molecular weight alcohol.

3. The system of claim 1, wherein the biomass comprises lignocellulosic biomass.

4. The system of claim 1, wherein the pretreatment/fermentation subsystem further comprises:

a pit having:

a lining material;

gravel placed on the lining; and

a porous drain pipe buried in the gravel;

a pile of biomass located at the top of the pit;

a lid that covers over the pile of biomass; and

a pump for circulating water from the pit to the top of the pile of biomass.

5. The system of claim 4, wherein the pretreatment/fermentation subsystem further comprises:

a blower for circulating air through the pile of biomass;

a lime water slurry for removing carbon dioxide from air.

6. The system of claim 1, wherein the inoculum comprises salt-tolerant microorganisms.

7. The system of claim 1, wherein the dewatering subsystem further comprises:

a high molecular weight carboxylic acid added to the fermentation broth to produce an acidified fermentation broth;

an evaporator for concentrating the acidified fermentation broth.

8. The system of claim 7, wherein the high molecular weight carboxylic acid comprises hexanoic acid, pentanoic acid, or heptanoic acid.

9. The system of claim 1, wherein the acid generation subsystem further comprises:

a mixer for mixing the concentrated product with the low molecular weight tertiary amine or ammonia and carbon dioxide;

a column for exchanging 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;

a column for thermally cleaving amine-carboxylate bonds in a carboxylate product of the high molecular weight tertiary amine to produce a mixed carboxylic acid product.

10. The system of claim 1, wherein the low molecular weight tertiary amine comprises triethylamine.

11. The system of claim 1, wherein the high molecular weight tertiary amine comprises trioctylamine or triethanolamine.

12. The system of claim 2, wherein the hydrogenation subsystem further comprises:

a column for mixing the mixed carboxylic acid product with a high molecular weight alcohol to form an ester;

a hydrogenation reactor for converting the ester to an alcohol mixture with a hydrogenation catalyst;

a column for separating the alcohol mixture from the high molecular weight alcohol.

13. The system of claim 2, wherein the high molecular weight alcohol comprises heptanol.

14. The system of claim 2, wherein the alcohol mixture comprises primarily primary alcohols.

15. The system of claim 1, further comprising a system for circulating process heat within at least one subsystem or from one subsystem to another subsystem.

16. The system of claim 1, further comprising a system for circulating water within at least one subsystem or circulating water from one subsystem to another subsystem.

17. The system of claim 1, further comprising a system for circulating lime or quicklime within at least one subsystem or from one subsystem to another.

18. A method of making a fermentation product, the method comprising:

treating the biomass pile with lime or quicklime, water, inoculum and air to produce a fermentation broth;

acidifying said fermentation broth with a high molecular weight carboxylic acid to produce an acidified fermentation broth;

stripping the fermentation broth in a stripping column to produce a stripped fermentation broth;

concentrating the stripped fermentation broth in an evaporator to produce a concentrated product;

mixing the concentrated product with a low molecular weight tertiary amine or ammonia and carbon dioxide to produce a carboxylic acid salt of the low molecular weight tertiary amine or ammonia;

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 said high molecular weight tertiary amine carboxylate to a temperature sufficient to break the acid/amine bond to produce a free carboxylic acid product;

recovering the free carboxylic acid product.

19. The method of claim 18, further comprising:

mixing the carboxylic acid product with a high molecular weight alcohol to form an ester;

hydrogenating the ester to form an alcohol product;

separating the high molecular weight alcohol from the alcohol product;

recovering the alcohol product.

20. The method of claim 18, wherein the biomass comprises lignocellulosic biomass.

21. The method of claim 20, wherein the alcohol product comprises primarily primary alcohols.