Selective Conversion of Glycerol to Propylene Glycol Over Fixed Bed RaneyA® Cu Catalysts

Net propylene glycol (1,2 propanediol) yields of up to 94% at 100% glycerol conversion have been achieved over a fixed bed Raney(A (R)) Cu catalyst in trickle bed mode, at relatively low total pressure, 14 bar (200 psig), and minimal feedstock dilution (20 wt% water). The main identified byproducts are ethylene glycol and ethanol (each < 2%), with methanol and 1,3 diol both < 1%. The other key operating parameters for high yields are a narrow optimum in temperature (near 205 A degrees C), and a high H-2/liquid flow ratio, about 375/0.05 by volume. The effects of chromium promotion have also been studied for effects on side reactions and rates. Our evidence points to initial dehydrogenation as the rate-limiting step in a likely three step mechanism.