Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
1999-11-03
2001-07-10
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C435S165000
Reexamination Certificate
active
06258175
ABSTRACT:
BACKGROUND OF THE INVENTION
Throughout the world there is increasing interest in converting renewable lignocellulose material to usable products such as ethanol. Conversion of wood to ethanol has been practiced during wartime due to a shortage of liquid fuels. Reported in Ind. & Eng. Chem. Vol. 38 No. 9, page 890 (1946). Because of high pressures, high temperatures, low yields and consumption of chemicals the conversion was found to be uneconomical for peacetime use. Present day interest in hydrolysis of Biomass, often termed lignocellulose material, is to provide an alternative fuel source to avoid dependence on unreliable imported petroleum crude oil for liquid fuels. Biomass often contains hemicellulose and lignins accompanying the cellulose contained in the lignocellulose material. Biomass is a term used to describe renewable material containing cellulose. For example, paper, pulp, wood waste, sawdust, municipal solid waste (MSW) and agricultural wastes, all are herein refereed to as lignocellulose material. The hemicellulose and amorphous cellulose of a lignocellulose material is easily hydrolyzed to form sugars for fermentation in a process called pre-hydrolysis which leaves a residue containing lignins and un-hydrolyzed crystalline cellulose. Pre-hydrolysis consists of the reaction of water with a lignocellulose material in the presence of a catalyst, usually sulfuric acid. The residue from pre-hydrolysis contains lignins, un-hydrolyzed hemicellulose and un-hydrolyzed cellulose and is consequently a lignocellulose material.
It is well known that a high concentration of sulfuric acid will hydrolyze cellulose and hemicellulose at low temperatures to produce sugars for fermentation.
A state of the art process being developed by workers at the University of Arkansas is reported in FY 1997 BIOCHEMICAL conversion/ALCOHOL FUELS PROGRAM, Annual Report page 85. It employs high concentration of sulfuric acid to convert corn stover to sugars. Described is a scheme to separate sugars contained in the concentrated sulfuric acid using a heavy boiling solvent to dissolve the sulfuric acid and a low boiling solvent to dissolve the heavy boiling solvent. They also reported that this method has a loss of solvents and a loss of sulfuric acid, which is neutralized with lime. Reported in the above named report, on page A-15, is a plan by TVA to develop a high concentration of sulfuric acid process. The current focus of TVA is to develop an inexpensive process for recovering the high concentration of sulfuric acid. Thus recovery of the sulfuric acid is reported as an unsolved problem. The problem with these methods is the failure to cost effectively recover concentrated sulfuric acid. Consequently it is believed that no satisfactory recovery method has yet been developed.
The present interest is related to concentrated sulfuric acid used to produce fermentable sugars contained in a lignocellulose material and the separation of sulfuric acid from sugars formed. Solids, substantially free from sulfuric acid, contain precipitated fermentable sugars. The fermentable sugars are then dissolved by a broth from fermentation. The dissolved fermentable sugars are then fermented in a fermentation vessel to form a fermentation broth. The concentrated sulfuric acid, separated from the fermentable sugars, is recycled to produce additional fermentable sugars.
Thus many of the limitations and disadvantages of the prior art to recover sulfuric acid employed to produce fermentable sugars will be obviated.
Therefore an object of this invention is to employ concentrated sulfuric acid to produce fermentable sugars from a lignocellulose material.
Another object of this invention is to economically separate sulfuric acid from lignins and sugars formed from a lignocellulose material and to supply concentrated sulfuric acid for recycle.
An additional object of this invention is to ferment sugars formed from a lignocellulose material contained in sterilized ethanol extracted solids.
A further object of this invention is to produce lignins substantially free of sugars and sulfuric acid formed from a lignocellulose material.
Still another object of this invention is to produce a yield of hydrolysis of cellulose and hemicellulose nearing 100%.
Yet another object of this invention is to operate the method in a closed environment.
Additionally another object of this invention is to operate and accomplish low energy consumption.
With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.
BRIEF DESCRIPTION OF THE INVENTION
The present invention, in its broadest aspect, will establish a method to convert lignocellulose materials, imploying concentrated sulfuric acid, into fermentable sugars from cellulose and hemicellulose contained in lignocellulose materials and to separate water insoluble solids also contained in the lignocellulose materials. Key features are:
Substantially freeing fermentable sugars from the concentrated sulfuric acid and recycling to reuse recovered concentrated sulfuric acid.
Hemicellulose accompanying cellulose in a lignocellulose material and will be converted to fermentable sugars.
Recycling to reuse ethanol essential to the method and withdrawal of water insoluble solids substantially free of sugars and chemicals integral to the method.
In this invention, concentrated sulfuric acid is recycled for employment in dissolving cellulose and hemicellulose contained in lignocellulose materials followed by hydrolyzing dissolved cellulose and hemicellulose in place to form fermentable sugars in concentrated sulfuric acid. An extractate containing ethanol and sulfuric acid is combined with concentrated sulfuric acid containing sugars to solidify sugars and inert water insoluble solids to form a solution of ethanol and sulfuric acid containing solidified sugars and water insoluble solids. After parting the solids from the solution, the solids are extracted by ethanol to produce sulfuric acid free solids and an extractate for foregoing employment. The ethanol extracted fermentable sugars from the extracted solids are dissolved in a fermentation broth to produce a broth containing water insoluble solids. Upon separation, the dissolved fermentable sugars containing ethanol and water insoluble solids are separated into water insoluble solids and the broth of dissolved fermentable sugars containing ethanol. The dissolved fermentable sugars, contained in the broth, are then fermented to produce additional fermentation broth. Additionally, separated water insoluble solids are extracted with an aqueous solution to form an aqueous extractate for separate fermentation followed by distillation stripping of the separate fermentation broth for substantial removal of ethanol in the overhead and to produce a bottoms of an aqueous solution for the previous extraction
The extracted water insoluble solids, including lignins, are substantially free of ethanol, sugars and sulfuric acid. pH of the fermentation broth will be controlled at an established predetermined level and maintained by feedback from the fermentation broth by addition of calcium carbonate or ammonia or sulfuric acid. Nutrient composition and activity of microorganisms required for fermentation in the fermentation broth is controlled at an established predetermined level.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of this invention embodies mixing together concentrated sulfuric acid with a lignocellulose material containing cellulose followed by hydrolysis in place to form fermentable sugars. This will depolymerize the cellulose and hemicellulose accompanying the cellulose to provide fermentable sugars and water insoluble solids. The invention embodies adding an extractate from a previous counter flow ethanol extraction containing ethanol which is soluble in concentrated sulfuric acid but substantially insoluble in the fermentable sugars to form solids containing a precipitate of the fermentable sugars and water inso
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