Multi-stage aldoses to polyols process

Abstract

Aldoses such as glucose solution are catalytically hydrogenated in a multiple-stage fixed-bed reaction process to produce glycerol and other polyol products. The feedstream pH to each reactor is controlled to between about 7 and 14 by adding an alkaline promotor material such as calcium hydroxide. First-stage reaction zone conditions are 130.degree.-180.degree. C. temperature, 500-2000 psig hydrogen partial pressure, and feedstream liquid space velocity is within range of 0.5-3.5 V.sub.f /Hr/V.sub.c. The first reactor uses a high activity nickel catalyst to produce at least about 98 W % conversion to alditol such as sorbitol solution. The resulting alditols such as 15-40 W % sorbitol solution in water is catalytically hydrocracked in a second-stage fixed-bed reaction zone preferably using a high-activity nickel catalyst to produce at least about 30 W % conversion to glycerol and glycols products. Second-stage reaction zone conditions are 420.degree.-520.degree. F. temperature, 1200-2000 psig hydrogen partial pressure, and liquid hourly space velocity of 1.5 to 3.0. The reaction products are separated in a recovery step, and unconverted heavy alditol feed can be diluted and recycled to the second-stage reaction zone for further hydrogenolysis to produce 40-90 W % glycerol product. Sorbitol conversion is maintained preferably at between about 30-70 W % and a purge stream containing unconverted sugars is passed to a third-stage catalytic reaction zone for further conversion to alditols and polyols.