Catalytic Transfer Hydrogenolysis Of Glycerol To Propylene Glycol

The rapid growth of biodiesel production in recent years led to an oversupply of glycerol. An efficient use of the glycerol to produce high value-added products is significant for improving the economic benefits of the biodiesel production. The 1,2-PDO is an important raw material used widely in the chemical industries and its demand is very large. Currently it is produced by the hydration of propylene oxide or transesterification of propylene carbonate, which are both from petrochemical industries. As for as the sustainable development was concerned, it is of significance to explore the economic way to produce 1,2-PDO from the renewable glycerol.In this paper, supported catalysts for the transfer hydrogenolysis of glycerol to 1,2-PDO in liquid phase have been studied in a stainless steel autoclave with methanol and formic acid, respectively, as the hydrogen donor. The effect of different reaction conditions such as metal loading and temperature etc. in the catalytic transfer hydrogenation has been systematically investigated.The Cu and Ni catalysts supported over γ-Al2O3 were prepared by incipient impregnation method. For both catalysts, a relatively large amount of acetol was found in the products. It is shown that the transfer hydrogenolysis of glycerol to 1,2-PDO consists of two steps:first the dehydration of glycerol to acetol and then the transfer hydrogenation of acetol to 1,2-PDO. Further, the results indicated that Cu has a good catalytic activity for the dehydration of glycerol but relatively weak for the transfer hydrogenation. Ni, on the contrary, is weak for dehydration but good for the catalytic transfer hydrogenation.A series of Ni-Cu bimetallic catalysts were prepared. The effect of the Ni/Cu ratio, the total metal loading, support of the catalysts, and glycerol concentration, reaction time, hydrogen donor on the catalytic performance has been investigated. First the results show that the best Ni/Cu ratio is 3:2. Then, it indicated that 15%glycerol concentration and 16 hours reaction time has the optimal experimental result. Further, after anylysing the results of different total metal loadings of the catalysts under methanol and formic acid, respectively, it reveals that the catalyst has the best catalytic activity both using the two hydrogen donors when the total metal loading is 25wt%, and also the results with formic acid as hydrogen donor are better than methanol. Finally, the effect of supports has been studied with formic acid as hydrogen donor, it demonstrates the best support is γ-Al2O3. By using 15Ni-10Cu/γ-Al2O3 catalyst, a glycerol conversion rate of 85.2% and the 1,2-PDO selectivity of 80.4% were achieved after 16 hours reaction at 220℃.In addition, the mechanism of the transfer hydrogenolysis of glycerol to 1,2-PDO was proposed based on the analysis of the experimental results.