Catalytic hydrogenolysis of alditols to produce polyols

Abstract

Alditols such as 15-40 W % sorbitol solution in water are catalytically hydrocracked in a fixed bed catalytic reaction process using an active nickel catalyst to produce at least about 30 W % conversion to glycerol and glycol products. The feedstream pH is controlled to between 7 and 14 by adding a basic promotor material such as calcium hydroxide to prevent damage to the catalyst. Useful reaction zone conditions are 400.degree.-500.degree. F. temperature, 1200-2000 psig hydrogen partial pressure, and liquid hourly space velocity of 1.5 to 3.0. To maintain desired catalyst activity and product yields, the catalyst is regenerated to provide catalyst age within the range of 20-200 hours. The reaction products are separated in distillation steps at successively lower pressures, and unconverted alditol feed is recycled to the reaction zone for further hydrogenolysis to produce 80-95 W % glycerol product. Sorbitol conversion is maintained preferably at between about 30-70 W % by catalyst regeneration following 20 to 200 hours use, comprising washing to remove deposits and heating with hydrogen at 500.degree.-600.degree. F. temperature. Countercurrent flow of feed and hydrogen in the reaction zone can be used if desired, particularly for achieving higher conversion of alditol feed to glycerol products.