High efficiency organosolv saccharification process

In a process for the production of carbohydrate hydrolysates as sugars and lignin from comminuted cellulosic material which can contain lignin by treating the material in a pressure vessel with a solvent mixture of acetone and water containing a small amount of an acidic compound at elevated temperatures to solubilize any lignin and to form reducing sugars in a liquor, the improvement which comprises:

• (a) providing mixtures of acetone and water containing greater than 70 volume percent acetone and the catalytic acid compound as the solvent mixture in the pressure vessel at the elevated temperatures with the cellulosic material;
• (b) repeatedly treating the cellulosic material in the solvent mixture for limited periods of time at the elevated temperatures until the cellulosic material is at least partially dissolved and such that at least 90 percent of the solubilized sugars from the cellulosic material are recovered without degradation to non-sugars wherein the carbohydrates in the cellulosic material are dissolved and hydrolyzed partially or substantially completely;
• (c) continuously removing the liquor from the pressure vessel;
• (d) rapidly cooling the liquor by controlled flash evaporation of acetone to form a residual aqueous solution after each treatment, wherein the cellulosic material is treated in the pressure vessel using successive amounts of the solvent mixture thereby defining successive stages of treatment at the elevated temperatures, wherein less than 50 percent of the cellulosic material is dissolved in each stage and wherein in each stage the cellulosic material is treated for a limited period of time in the pressure vessel and then the withdrawn liquor is rapidly cooled when removed from the pressure vessel so as to achieve the sugar recovery.