Optimization of in situ hydrogenolysis of glycerol to propylene glycol and ethanol

Alternative ways of converting crude glycerol from biodiesel production to value-added products are in high demand to solve the issue of increasing glycerol surplus. Propylene glycol (PG) and ethanol are examples of valuable chemicals that had been successfully produced from glycerol through in situ hydrogenolysis in our previous studies. This study aimed to determine the optimum conditions for maximizing the yields of PG and ethanol through in situ hydrogenolysis of glycerol. Depending on the targeted products, the optimum process conditions, obtained through statistical analysis and experimentally confirmed with a high PG yield of 47.2%mol, were 220°C, 51 min and 1.0:1.0 water to glycerol mass ratios (WGMR). However, the complex reactions involved in the production of ethanol lead to inconclusive results for the optimization. The key to maximizing the PG yield from in situ hydrogenolysis of glycerol is to operate the system at mild reaction temperatures (e.g., 220°C) at which the further conversion of PG to ethanol is slowed. Meanwhile, a 1:1 mixture of water and glycerol minimizes the side reactions and improves the PG formation. The ethanol production alone from glycerol does not seem economically justified for large scale production due to its low yield. However, co-production of PG and ethanol might be a viable solution.