Process for the production of ethanol and solvents from lignocellulosic biomass with recycling of an ethanolic liquor obtained from the fermentation of pentoses

Embodiments provided here relate to second generation processes for the production of alcohols or solvents, wherein the lignocellulosic or cellulosic biomass undergoes a pre-treatment before being converted into ethanol after an enzymatic hydrolysis and fermentation. The glucidic polymers of the pre-treated plant material are hydrolysed by cellulases. The alcoholigenic microorganisms used for the ethanolic fermentation principally use hexoses, for example, glucose and mannose. The alcohols of the liquor, with or without separation of the suspended material are extracted by distillation. The stillage, containing pentoses which have not been used, are fermented into an ex-pentose ethanolic liquor and at least a portion of the liquor is recycled upstream of the enzymatic hydrolysis. The enzymatic hydrolysis and the ethanolic fermentation are thus carried out separately or simultaneously in the presence of a portion of the ethanolic liquor, which mixture does not interfere with the performance of the enzymes and microorganisms.