WO2008086115A2

WO2008086115A2 - Hydrolyzation of cellulose using carbonic acid

Info

Publication number: WO2008086115A2
Application number: PCT/US2008/050142
Authority: WO
Inventors: James L. Lucas
Original assignee: Colusa Biomass Energy Corporation
Priority date: 2007-01-03
Filing date: 2008-01-03
Publication date: 2008-07-17
Also published as: WO2008086115A3

Abstract

The present invention provides methods for hydrolyzing cellulose using carbonic acid, wherein the carbonic acid is produced by introducing carbon dioxide gas into a solution containing the cellulose. The carbon dioxide gas may be a recycled stream from a fermentation system that is used to ferment sugars generated by the hydrolysis of the cellulose. The hydrolysis of hemicellulose may be performed concurrently also using carbonic acid that is produced by introducing carbon dioxide gas into a solution containing the hemicellulose. The resulting sugar solutions may be combined for fermentation and the production of ethanol.

Description

Hydrolyzation of Cellulose Using Carbonic Acid

BACKGROUND

[0001] This invention relates to a method for hydrolyzing cellulose. In particular, this invention relates to a method of using carbonic acid as a catalyst for the hydrolyzation of cellulose to its glucosans monomers, which may be fermented to produce ethanol fuel.

[0002] During recent years, alternative fuels have attracted considerable interest.

This is particularly true of fuels based on renewable sources such as wood, straw, and other types of plant biomass, including a variety of wood and biomass waste. For example, rice straw, which, along with rice hulls, are the by-products of producing rice grain, has limited uses and, therefore, is readily attainable for use in producing ethanol fuels. Also peat, even though not renewable, may be used in a manner similar to these types of renewable sources. [0003] In many cases, a first step in producing ethanol fuels is extracting and hydrolyzing hemicellulose and cellulose from plant biomass. The use of a weak solution of a strong acid or the use of strong acid alone to extract and hydro lyze hemicellulose and cellulose from plant biomass is well known in the art. In addition, the use of enzymatic hydrolysis has also been used. The hydrolyzation of hemicellulose and cellulose produces five- and six-carbon sugars, as well as other simple sugars. These sugars are then treated with a weak solution of a strong acid such as sulfuric acid before being fermented to produce ethanol. However, a need still exists for an alternative method for hydrolzying cellulose. [0004] The following references are incorporated by reference herein to the extent they supplement, explain, provide background for, or teach methodology technology, and compositions employed herein:

[0005] Hagg, W.O., Rodewald, P.G. and Weisz, P.B., U.S. Pat No 4,300,009, Nov.

10, 1981, which discloses a method of converting biological materials to liquid fuels; [0006] Montencourt, B. S. and Eveleigh, D. E., Proceedings of Second Annual

Symposium on Fuels from Biomass, Vol. II, p 613. Renssseleaer, which describes strains of bacteria and fungi having cellulose hydrolytic capabilities; and [0007] Humphrey, A. E. and E. J. Nolan Report to the Office of Technology

Assessment, Biological Production of Liquid Fuels and Chemical Feedstocks, Govt. Printing Office, which also describes production of alternative fuels. SUMMARY

[0008] One embodiment of the invention provides for a method for hydro lyzing cellulose using carbonic acid by placing plant biomass solids comprising cellulose in a pressure vessel, adding water, heating the water to between about 60 ⁰C and about 150 ⁰C, agitating the solid- water mixture while adding carbon dioxide gas to a pressure of between about 40 pounds per square inch gauge (psig) and about 80 psig with continued agitation for between about 20 minutes and about 60 minutes, withdrawing the liquid water mixture separating the liquid from the remaining solids, and withdrawing a stream of glucose that can be fermented to produce ethanol in a fermentation system. In another embodiment of the invention, carbon dioxide gas may be introduced to the pressure vessel as a recycled stream from the fermentation system.

[0009] Another embodiment of the invention provides a method for hydro lyzing cellulose and hemicellulose by extracting hemicellulose from plant biomass solids comprising cellulose and hemicellulose to produce extracted hemicellulose; hydrolyzing the extracted hemicellulose using carbonic acid, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the extracted hemicellulose; and hydrolyzing the cellulose in the plant biomass solids using carbonic acid, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the cellulose. [0010] Another embodiment of the present invention provides a method for producing ethanol from plant biomass solids by extracting hemicellulose from plant biomass solids comprising cellulose and hemicellulose to produce a first solution comprising hemicellulose and a second solution comprising cellulose; hydrolyzing the hemicellulose in the first solution using carbonic acid to produce a third solution comprising sugars, wherein the carbonic acid is generated by introducing carbon dioxide gas into the first solution containing the hemicellulose; hydrolyzing the cellulose in the second solution using carbonic acid to produce a fourth solution comprising sugars, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the cellulose; and fermenting the third and fourth solutions comprising sugars to produce ethanol. [0011] In other embodiments, the methods described herein may be combined with techniques for separating silica and lignin from the cellulose, such as those described in U.S. Patent No. 5,735,916 entitled Process for Production of Lignin Fuel, Ethyl Alcohol,

Cellulose, Silica/Silicates, and Cellulose Derivatives from Plant Biomass, which is hereby incorporated by reference herein, including ultrafiltration. In these embodiments, the silica and lignin may then be further separated from each other.

[0012] The present invention provides methods for economically generating alternative fuels, such as ethanol as a engine fuel, from plant biomass, particularly since the production of alternative fuels has generally centered around aromatic compounds, which is relatively expensive. The present invention allows for increased efficiency by using carbonic acid to catalyze the hydrolysis of cellulose, wherein the carbonic acid is generated by introducing a carbon dioxide gas stream into a vessel containing the cellulose. In addition, hemicellulose may also be concurrently hydrolyzed using carbonic acid that is generated by introducing a carbon dioxide gas stream into a vessel containing the hemicellulose. Carbon dioxide from a fermentation system that ferments the sugars produced by the hydrolysis of the cellulose and hemicellulose may be recycled and used as the carbon dioxide gas stream for the hydrolysis of either or both of the cellulose and the hemicellulose.

DETAILED DESCRIPTION OF THE INVENTION [0013] Reference will now be made in detail to various embodiments of the present invention. To provide a thorough understanding of the present invention, numerous specific details of preferred embodiments are set forth including material types, dimensions, and procedures. Practitioners having ordinary skill in the art will understand that the embodiments of the present invention may be practiced without many of these details. [0014] Increased efficiency in ethanol production may be achieved by using carbonic acid to extract and hydro lyze cellulose and concurrently hemicellulose. Cellulose and hemicellulose may be extracted from plant biomass, such as straw or wood. Rice straw is one example of a plant biomass that can be used in the various embodiments of the present invention. Accordingly, the plant biomass is first harvested for use. [0015] In some embodiments, the plant biomass is first ground. The plant biomass may be placed in a hammermill or ball mill and ground. The plant biomass may be ground to between about 40 and 60 mesh, preferably between about 45 and 55 mesh, and more preferably to about 50 mesh. [0016] In some embodiments, hemicellulose may be first extracted from the plant biomass. The hemicellulose may be removed and hydrolyzed to produce five-carbon sugars, such as xylose. In one embodiment the hemicellulose may be removed by heating the plant biomass in a solution of carbonic acid. The carbonic acid is generated by feeding a gas stream comprising carbon dioxide into the solution containing the hemicellulose. In some embodiments, the carbon dioxide gas stream comprises carbon dioxide produced in a fermentation system used to ferment the sugars produced from the hydrolysis. In other words, the carbon dioxide from the fermentation is recycled and used in the hydrolysis. [0017] The plant biomass remaining after extracting the hemicellulose may be treated with NaOH and centrifuged to extract silica and lignin leaving a cellulose fraction. The cellulose fraction may then be hydrolyzed to produce six-carbon sugars, such as glucose, using carbonic acid that is generated by feeding a gas stream comprising carbon dioxide into the solution. In some embodiments, the carbon dioxide gas stream comprises carbon dioxide produced in a fermentation system used to ferment the sugars produced from the hydrolysis. In other words, the carbon dioxide from the fermentation is recycled and used in the hydrolysis. It should be appreciated that the recycled carbon dioxide gas stream may be used for both the hydrolysis of the hemicellulose as well as the cellulose. It should also be appreciated that the extraction of silica and lignin is performed such that these are in solution and may be further separated using techniques such as those described in U.S. Patent No. 5,735,916 entitled Process for Production of Lignin Fuel, Ethyl Alcohol, Cellulose,

Silica/Silicates, and Cellulose Derivatives from Plant Biomass, which is hereby incorporated by reference herein, including ultrafiltration. It should also be appreciated that the solutions resulting from the hydrolysis of the hemicellulose and the cellulose containing various sugars may be combined prior to fermentation and then fermented together. Alternatively, each of these solutions may be fermented separately.

[0018] In some embodiments, the hydrolysis of hemicellulose and cellulose is performed in a pressure vessel. Preferably, the pressure vessel should be capable of withstanding pressures up to about 100 psig and temperatures up to about 150 ⁰C. Water may also be added to the vessel. The water may be heated to between about 60 ⁰C and about 150 ⁰C. In some embodiments, the water may be heated to between about 110 ⁰C and about 130

⁰C.

[0019] In some embodiments, the weight ratio of water to plant biomass can be between about 65:35 and about 30:70. In other embodiments, the weight ratio of water to plant biomass can be between about 55:45 and about 40:60. In other embodiments, the weight ratio of water to plant biomass can be between about 50:50 and about 45:55. The weight ratio of water to plant biomass may be adjusted to produce the maximum recovery of five-carbon sugars from hemicellulose and six-carbon sugars from cellulose. [0020] In some embodiments, after adding water to the pressure vessel, carbon dioxide gas may be introduced to the vessel. The purity of the carbon dioxide gas may vary between 100% and 75%. In some embodiments, the carbon dioxide gas may contain water vapor and air; this may occur if the carbon dioxide is recycled from a fermentation system as described below. When introduced to the pressure vessel containing the water and plant biomass mixture, the carbon dioxide gas may generate carbonic acid. The hydrogen ion produced by the carbonic acid may act as a catalyst for the hydro lyzation of both five-carbon and six-carbon sugars. [0021] Preferably, the carbon dioxide gas is bubbled through the water and plant biomass mixture through a device used to disperse gas into a liquid solution. The carbon dioxide gas may be pressurized to match the internal pressure of the pressure vessel. Carbon dioxide gas may be introduced until pressure in the vessel reaches between about 40 psig and about 80 psig. In some embodiments, the carbon dioxide gas may be introduced until pressure in the vessel reaches between about 55 psig and about 65 psig. In one embodiment, the carbon dioxide gas may be introduced until the pressure in the vessel reaches about 60 psig and the temperature of the water in the vessel is about 120 ⁰C. [0022] As noted, in some embodiments, the source of the carbon dioxide may be carbon dioxide produced from a fermentation system. In this case, the carbon dioxide may be recycled from the fermentation process back to the pressure vessel containing the plant biomass. The fermentation of reducing sugars may produce carbon dioxide as a by-product. The carbon dioxide gas from a fermentation process may also contain air and water vapor. In some embodiments, the carbon dioxide gas may be captured at atmospheric pressure from the fermentation system. In some embodiments, the water may be pressurized before it is introduced to the pressure vessel. The captured gas may be sent to the pressure vessel and bubbled through the water and plant biomass as described above.

[0023] In some embodiments, the water and plant biomass mixture in the vessel may be agitated while the carbon dioxide gas is introduced. Agitation may ensure circulation of a hydrogen ion catalyst to provide maximum contact with the water and plant biomass mixture. Agitation may continue after the carbon dioxide gas is introduced for between about 20 minutes and about 60 minutes. Methods of agitation may include a bladed agitator inside the pressure vessel. In some embodiments, a bladed agitator may revolve at about 20 rpm. [0024] After the carbon dioxide is added to the vessel, the liquid mixture may be withdrawn from the vessel, thus separating the liquid from the remaining solids. In some embodiments, the liquid may comprise glucose and/or five-carbon sugars. In those embodiments where the liquid comprises five-carbon sugars and/or six-carbon sugars, the liquid may be sent to a fermentation system where it can be converted to ethanol. [0025] In some embodiments, five-carbon sugars and/or six-carbon sugars may be sent to a fermentation system. Bacteria may be added to the sugars in the fermentation system. The bacteria may be genetically engineered bacteria. After fermentation, the solution leaving the fermentation system may contain ethanol. The solution may then be sent to a distillation unit where the ethanol may be distilled to 100% (200 proof). As described above, carbon dioxide from the fermentation system may be recycled back to the pressure vessel containing the plant biomass.

[0026] In some embodiments, rice straw may be used as a source of plant biomass. In one embodiment, the rice straw may be heated in carbonated water for 1.0 hour at 60 ⁰C to remove the hemicellulose. The hemicellulose may then be hydro lyzed to produce five- carbon sugars in a vessel as described above. The remaining solids may be treated with 1.0 M NaOH solution to solubilize silica and lignin. A centrifuge may then be used to extract the lignin/silica solution from the remaining cellulose solids. The recovered cellulose may be added to a pressure vessel with water and hydrolyzed with carbonic acid as described above. [0027] The following examples illustrate various aspects of the present invention.

These examples are not to be construed as limiting the scope of the present invention or any of its embodiments.

EXAMPLES

[0028] In one example, 3 L of de-ionized water was added to a pressure vessel. 50Og

+ O.Olg of rice straw was also added to the pressure vessel. The pressure vessel was then sealed, and carbon dioxide gas was bubbled through the water and rice straw mixture until the pressure reached about 50 psig. The heat in the pressure vessel was adjusted to about 80 ⁰C. The mixture in the vessel was agitated using a stirring bar. These conditions produced a hydrogen ion concentration that produced hydrolysis of the cellulose. [0029] A sample of 215.88 g of cellulose extracted from rice straw was placed in a

300 ml of carbonated water. The mixture was placed in a canning cooker, sealed, and brought to a pressure of 20 psig by heating to 100 ⁰C. The mixture was stirred continually for one hour with a magnetic bar. [0030] The remaining solids were dried overnight and weighed. The remaining dried solids weighed 88.23 g showing a 41% hydrolysis of the cellulose. It was noted at the time that increasing the time, pressure, and temperature could result in a higher hydrolyzation of the cellulose to its glucosans.

[0031] Various embodiments of the invention have been described above. The descriptions are intended to be illustrative of various embodiments of the present invention and are not intended to be limiting. It will be apparent to one of skill in the art that modifications may be made to the invention as described without departing from the scope of the present invention.

Claims

CLAIMSWhat is claimed is:

1. A method of hydro lyzing cellulose, comprising: placing plant biomass solids comprising cellulose in a pressure vessel; adding water to the pressure vessel; heating the water; introducing carbon dioxide gas into the water in the pressure vessel; agitating the water; and separating liquid and remaining solids present in the pressure vessel.

2. The method of claim 1 , wherein the water is heated to between about 60 ⁰C and about 120 ⁰C.

3. The method of claim 1, wherein the carbon dioxide gas is introduced to the water in the pressure vessel until pressure in the vessel reaches between about 40 psig and about 60 psig.

4. The method of claim 1 , wherein the water is agitated for between about 20 minutes to about 60 minutes after the carbon dioxide is introduced to the water in the pressure vessel.

5. The method of claim 1 , wherein glucose is withdrawn from the liquid and remaining solids in the pressure vessel.

6. A method for hydro lyzing cellulose and hemicellulose, comprising: extracting hemicellulose from plant biomass solids comprising cellulose and hemicellulose to produce extracted hemicellulose; hydrolyzing the extracted hemicellulose using carbonic acid, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the extracted hemicellulose; and hydrolyzing the cellulose in the plant biomass solids using carbonic acid, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the cellulose.

7. A method for producing ethanol from plant biomass solids, comprising: extracting hemicellulose from plant biomass solids comprising cellulose and hemicellulose to produce a first solution comprising hemicellulose and a second solution comprising cellulose; hydrolyzing the hemicellulose in the first solution using carbonic acid to produce a third solution comprising sugars, wherein the carbonic acid is generated by introducing carbon dioxide gas into the first solution containing the hemicellulose; hydrolyzing the cellulose in the second solution using carbonic acid to produce a fourth solution comprising sugars, wherein the carbonic acid is generated by introducing carbon dioxide gas into a liquid containing the cellulose; and fermenting the third and fourth solutions comprising sugars to produce ethanol.

8. The method of claim 7, further comprising: extracting silica and lignin from the second solution using a strong base.

9. The method of claim 8, further comprising: separating the silica and the lignin.

10. The method of claim 7, wherein the fermenting produces an ethanol solution, and further comprising distilling the ethanol solution to its azeotrope.