Catalytic Transfer Hydrogenation Of Lactic Acid And Its Derivatives To Produce1,2-propanediol

As one of the most important chemical products and owing to its excellent hygroscopicity and low toxicity,1,2-propanediol has been widely applied in pharmaceutical and chemical industries. Nowadays1,2-propanediol is still produced by the hydration of propylene oxide, a method that is not only energy consumptive but also under harsh conditions. Therefore, the development of an environmental friendly process for the preparation of1,2-propanediol has attracted great attention. As one of the widely used platform compounds, lactic acid can be produced through the fermentation of a series of renewable resources such as carbohydrates and biomass streams. It is significant if1,2-propanediol could be produced from renewable lactic acid instead of unrenewable petroleum products.Using a high pressure reactor together with the XRD and TEM catalyst characterization instruments, the catalytic transfer hydrogenation (CTH) of lactic acid and its derivatives for preparation of1,2-propanediol has been studied systematically. The Ni and Cu based catalysts were used in the catalytic transfer hydrogenation reaction. The effect of the preparation method, support and promoter of those catalysts and the reaction conditions on catalytic activity for the CTH reaction has been investigated. Because lactic acid can react with Ni and Cu, and leads to catalyst deactivation, the yield of1,2-propanediol in the catalytic transfer hydrogenation of lactic acid is very low if Ni or Cu based catalyst are used. On the other hand, in the catalytic transfer hydrogenation of ethyl lactate they give a relatively high catalytic activity.Three different Ni based catalysts:Ni/TiO2, Ni-B and Raney-Ni were studied in the catalytic transfer hydrogenation of ethyl lactate. The selectivity of1,2-propanediol was57.3%,73.0%and60.4%, respectively for those three catalysts. In comparison with the Ni base catalysts, the Cu based ones generally show a better catalytic activity for the catalytic transfer hydrogenation and a higher selectivity of1,2-propanediol. The Cu/SiO2, Cu/Al2O3and Cu-Cr/Al2O3with10wt%load of catalysts gave a1,2-propanediol selectivity of59.3%,64.4%and77.6%, respectively, in the catalytic transfer hydrogenation of ethyl lactate. Under the optimized experimental conditions a100%conversion of ethyl lactate was realized and a1,2-propanediol selectivity of89.7%was achieved.In addition, based on the GS MASS analysis of the catalytic transfer hydrogenation reaction products and a thermodynamic analysis, a possible reaction mechanism was proposed and discussed.