Enhanced efficiency ethanol and sugar conversion processes

A process for producing ethanol by the fermentation of biomass containing carbohydrate comprising:

• a. hydrolyzing an admixture of water, enzyme and biomass under hydrolyzing conditions sufficient to convert carbohydrate by enzymatic hydrolysis and provide a hydrolysate containing pentose and hexose;
• b. subjecting at least a portion of the hydrolysate of step (a) to fermentation conditions sufficient to convert at least a portion of the hexose to ethanol to provide an ethanol-containing fermentation broth containing solids and pentose, said fermentation conditions comprising the presence of microorganism capable of converting hexose to ethanol, and said ethanol-containing fermentation broth containing solids;
• c. fractionating by distillation at least a portion of the ethanol-containing fermentation broth of step (b) to provide an ethanol product fraction and a whole stillage containing water, solids and unfermented sugars comprising pentose;
• d. separating at least a portion of the whole stillage of step (c) to provide a thin stillage containing pentose and having an essential absence of solids and to provide a solids-containing fraction;
• e. contacting under fermentation conditions in a fermentation zone at least a portion of the thin stillage of step (d) with biocatalyst said biocatalyst comprising:
• 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 a Hydration Expansion Volume (HEV), which is calculated in volume percent, of about 1000 or more, and
• ii. a population of microorganisms capable of converting pentose to ethanol substantially irreversibly retained in the interior of the solid structure, said population of microorganisms being in a concentration of about 60 grams per liter or more based upon the volume defined by the exterior of the solid structure when fully hydrated, to provide a treated thin stillage having a reduced pentose content and substantially no solids;
• f. withdrawing the treated thin stillage from the fermentation zone of step (e) while retaining the biocatalyst in the fermentation zone;
• g. evaporating water and ethanol from at least a portion of the treated thin stillage of step (f) to provide a concentrated solubles product and vapor;
• and
• h. passing at least a portion of the evaporated water and ethanol of step (g) to step (a).