Enhanced efficiency ethanol and sugar conversion processes

Abstract

Overlay processes are disclosed for making ethanol that not only increase ethanol conversion but do so in a cost effective manner with a reduction in energy requirements per unit of ethanol production. The processes can provide, if desired, higher organic compound as a co-product with ethanol.

It is claimed: 
     
         1 . A process for producing ethanol by the fermentation of biomass containing carbohydrate comprising:
 (a) contacting a solids-containing feedstock comprising fermentable sugars in an aqueous fermentation medium in a batch fermentor and under fermentation conditions including the presence of a microorganism capable of bioconverting sugars to ethanol, to convert a portion of the sugars to ethanol and provide a fermentation broth comprising ethanol, unconverted sugars, solids and water wherein the concentration of ethanol in the aqueous fermentation medium does not exceed that which is unduly deleterious to the microorganism;   (b) during or after step (a) separating at least a portion of the fermentation broth from step (a) to provide a clear liquor containing ethanol, unconverted sugars and water and a concentrated solids fraction comprising ethanol, unconverted sugars, solids and water;   (c) fractionating by distillation at least a portion of the concentrated solids fraction to provide an ethanol product fraction and a whole stillage bottoms fraction;   (d) contacting at least a portion of the clear liquor with biocatalyst under metabolic conditions to bioconvert at least a portion of the fermentable sugars in the clear liquor to at least one organic product and provide a first product stream comprising said at least one organic product and water, wherein said biocatalyst comprises
 i. a solid structure of hydrated hydrophilic polymer defining an interior structure having a plurality of interconnected major cavities having a smallest dimension of between about 5 and 100 microns and an HEV of at least about 1000 and 
 ii. a population of microorganisms capable of converting sugars to at least one organic product substantially irreversibly retained in the interior of the solid structure, said population of microorganisms being in a concentration of at least about 60 grams per liter based upon the volume defined by the exterior of the solid structure when fully hydrated, and 
   wherein the first product stream has a substantial absence of solids; and   (e) recovering at least one organic product from the first product stream.   
     
     
         2 . The process of  claim 1  wherein the organic product of step (d) is ethanol. 
     
     
         3 . The process of  claim 2  wherein the first product stream is passed to step (c). 
     
     
         4 . The process of  claim 3  wherein the first product stream has a higher ethanol concentration than the fermentation broth of step (a). 
     
     
         5 . The process of  claim 4  wherein step (d) is a continuous fermentation. 
     
     
         6 . The process of  claim 5  wherein between about 20 and 80 percent of the water in the fermentation broth is contained in the clear liquor. 
     
     
         7 . The process of  claim 5  wherein the biocatalyst of step (d) comprises biocatalyst capable of converting pentose to ethanol. 
     
     
         8 . The process of  claim 1  wherein the organic product is an organic product other than ethanol. 
     
     
         9 . The process of  claim 8  wherein the organic product is at least one of acetic acid, propionic acid, butyric acid, propanol, propanediol, butanol, butanediol, succinic acid, and lactic acid. 
     
     
         10 . A process for the bioconversion of sugars to ethanol and bio-product comprising:
 (a) separating a process stream containing fermentable sugars and solids in an aqueous medium to provide a clear liquor containing fermentable sugars and water and a concentrated solids fraction comprising fermentable sugars, solids and water;   (b) contacting at least a portion of the clear liquor with biocatalyst under conversion conditions to bioconvert at least a portion of the fermentable sugars in the clear liquor to at least one organic product and provide a first product stream comprising said at least one organic product and water, wherein said biocatalyst comprises:
 i. a solid structure of hydrated hydrophilic polymer defining an interior structure having a plurality of interconnected major cavities having a smallest dimension of between about 5 and 100 microns and an HEV of at least about 1000 and 
 ii. a population of microorganisms capable of converting sugars to at least one organic product substantially irreversibly retained in the interior of the solid structure, said population of microorganisms being in a concentration of at least about 60 grams per liter based upon the volume defined by the exterior of the solid structure when fully hydrated, and wherein the first product stream has a substantial absence of solids; 
   (c) recovering at least one organic product from the first product stream and providing a water-containing lean stream;   (d) combining at least a portion of the lean stream from step (c) with the concentrated solids fraction of step (a) to provide a combined stream comprising solids, fermentable sugars, and water;   (e) subjecting the combined stream of step (d) fermentation conditions sufficient to convert at least a portion of the fermentable sugars to ethanol to provide an ethanol-containing fermentation broth, said fermentation conditions comprising the presence of microorganism capable of bioconverting sugars to ethanol; and   (f) fractionating by distillation at least a portion of the ethanol-containing fermentation broth to provide an ethanol product fraction and a whole stillage containing water and solids.   
     
     
         11 . The process of  claim 10  wherein the bio-product of step (b) is at least one of acetic acid, propionic acid, butyric acid, propanol, propanediol, butanol, butanediol, succinic acid, and lactic acid. 
     
     
         12 . The process of  claim 10  wherein step (b) is a continuous fermentation. 
     
     
         13 . A process for the production of ethanol and other bioproduct from an aqueous fermentation broth comprising ethanol and containing solids comprising:
 (a) passing an aqueous, ethanol-containing fermentation broth, which broth also contains solids, to a distillation zone;   (b) fractionating by distillation said fermentation broth in said distillation zone to provide a lower-boiling, ethanol-rich stream and a higher boiling, aqueous stream which also contains solids;   (c) withdrawing from said distillation zone a side stream comprising ethanol and water and having a substantial absence of solids;   (d) subjecting the withdrawn side stream to fermentation conditions in at least one fermentation zone including the presence of at least one biocatalyst capable of bioconverting ethanol or ethanol metabolite to another organic product to provide a bioconversion effluent comprising the another organic product, ethanol, and water, and preferably having a substantial absence of solids, wherein:
 (i) said biocatalyst comprises:
 A. a solid structure of hydrated hydrophilic polymer defining an interior structure having a plurality of interconnected major cavities having a smallest dimension of between about 5 and 100 microns and an HEV of at least about 1000 and 
 B. a population of microorganisms capable of converting ethanol or ethanol metabolite substantially irreversibly retained in the interior of the solid structure, said population of microorganisms being in a concentration of at least about 60 grams per liter based upon the volume defined by the exterior of the solid structure when fully hydrated, 
 
 (ii) said biocatalyst is retained in said at least one fermentation zone, 
 (iii) said withdrawn side stream is passed continuously through said at least one fermentation zone and said bioconversion effluent is withdrawn continuously from said at least one fermentation zone; and 
   (iv) said withdrawn side stream has an ethanol concentration below that which adversely affects the biocatalyst in the porous matrices, preferably said side stream having an ethanol concentration of less than about 25 mass percent;   (e) recovering at least a portion of another organic product from said bioconversion effluent; and   (f) passing at least a portion of the ethanol and water in the bioconversion effluent to the distillation zone.   
     
     
         14 . The process of  claim 13  wherein the bioconversion effluent has a substantial absence of solids. 
     
     
         15 . The process of  claim 13  wherein the other bioproduct is at least one of acetic acid, ethylene glycol, propionic acid, n-propanol, i-propanol, propanediol, hydroxypropionic acid, n-butanol, i-butanol, butanediol, hexanol, lactic acid, and succinic acid. 
     
     
         16 . The process of  claim 13  wherein the fermentation zone contains at least two different biocatalysts, at least one of which is adapted to bioconvert ethanol to at least one ethanol fermentation product and at least one of which is adapted to bioconvert at least one ethanol fermentation product to another organic product. 
     
     
         17 . The process of  claim 16  wherein the ethanol fermentation product comprises one or more of acetaldehyde, acetic acid or salt thereof, pyruvic acid or salt thereof, acetyladenylate, and acetyl CoA.