Study Of Catalytic Transfer Hydrogenolysis Of Glycerol To Propylene Glycol

With the development of biodiesel production in recent years, large amounts of glycerol are available as a reaction by-product. Finding new outlets for glycerol consisting of high value-added products has gained more and more attention. In this paper, we have systematically investigated the effect of different reaction conditions and Ni-based catalysts on the conversion of glycerol and the selectivity of1,2-PDO and1,3-PDO in glycerol catalytic transfer hydrogenolysis.Firstly, the influence of the temperature, catalyst amount and molar ratio of raw material on the reaction has been studied over Raney Ni catalyst in aqueous media with methanol as the hydrogen donor. Then, we quantify the significance level of the reaction conditions and got the optimal combination of the reaction conditions which we have studied in the single factor experiment by orthogonal experimental and variance analysis.Secondly, the performance of Ni/γ-Al2O3as catalysts for the catalytic transfer hydrogenolysis of glycerol has been studied in comparison with that of the Raney Ni. Ni/γ-Al2O3catalyst was prepared by equal volume impregnation method using nickel nitrate as precursor and γ-Al2O3as the supports. We have found that the composition in the liquid product obtained by using Ni/γ-Al2O3was quite different from that by using Raney Ni. The target product was mainly1,3-propanediol with little1,2-propylene glycol. At240℃, a30.5%conversion of glycerol was achieved after12hour reaction with the initial molar ratio of raw material nglycerol:nmethanol:nwater=0.45:0.51:1, and the selectivity of1,3-propanediol was up to73.7%.Finally, the mechanism of glycerol catalytic transfer hydrogenolysis was proposed. There are two coherent reactions in this glycerol catalytic transfer hydrogenolysis, which are the methanol reforming for hydrogen generation and the transfer hydrogenolysis of glycerol. In general, the Raney Ni catalyst is active in the cleavage of the primary hydroxyl group in preference to the secondary one and results in forming1,2-propylene glycol as the main product. On the contrary, the cleavage of the secondary hydroxyl group was advantageous by using Ni/γ-Al2O3catalyst and produced mainly the1,3-propanediol.