Process for the acid hydrolysis of carbohydrate polymers and the continuous fermentation of the sugars obtained therefrom to provide ethanol

A process for the acid hydrolysis of carbohydrate polymer and the continuous fermentation of the fermentable sugars therefrom to provide ethanol which comprises:

• (a) substantially uniformly mixing a pressurized acidified aqueous slurry of carbohydrate polymer particles with relatively high pressure stream;
• (b) passing the acidified carbohydrate polymer slurry through a conduit under substantially steady state temperature and pressure for a period sufficient to convert at least about 60% by weight of the carbohydrate polymer to fermentable sugar but without appreciable conversion of carbohydrate polymer to non-fermentable products;
• (c) reducing the pressure of the hydrolyzed carbohydrate polymer slurry to a level at which undesirable reactions of the fermentable sugar present in solution therein cannot readily occur;
• and
• (d) continuously fermenting the fermentable sugar, previously adjusted to a pH suitable for carrying out fermentation, with or without partial hydrolysate therein having been previously further saccharified, in a series of fermentation vessels in which the ethanol content of the fermentation medium is progressively increased in each fermentation vessel as the fermentable sugar is consumed therein, the fermentation employing at least two different strains of ethanol-producing yeast, one of which provides a high rate of ethanol production in a fermentation medium containing a relatively low concentration of ethanol and a relatively high concentration of sugar and the other of which provides a high rate of ethanol production in a fermentation medium containing a relatively high concentration of ethanol and a relatively low concentration of fermentable sugar.