Glycerol transformation to value added C3 diols: reaction mechanism, kinetic, and engineering aspects

Glycerol can serve as a starting material for the production of a variety of chemicals currently formed via fossil-based routes. The selective hydro-deoxygenation to C-3-diols is one of the most attractive methods for glycerol upgrading. 1,2- and 1,3-Propanediols which are the target products of this reaction are high added value chemicals with a wide range of applications. The reaction mechanisms for both routes (1,2- and 1,3-diols) are presented and analyzed including the strategies followed for mechanistic understanding. 1,2-Propanediol is proposed to be formed via two mechanisms namely dehydration-hydrogenation and dehydrogenation-dehydration-hydrogenation. The selective conversion of glycerol to 1,3-propanediol is suggested to proceed through dehydration-hydrogenation and direct hydrogenolysis mechanisms. The reaction mechanism depends on various factors such as the catalyst formulation, acid and basic character of the system and the H-2 origin. A section focusing on engineering issues describes and compares the reaction mode ie batch-continuous and liquid-gas phase operation. The different reaction configurations have an impact mainly on product distribution and catalyst stability, which is greatly improved when continuous operation is applied. In addition, the impact of reaction temperature, hydrogen pressure, glycerol concentration as well as the reaction kinetics are also discussed. The approach of operating under inert conditions with H-2 generated in situ seems to be a very promising concept for process intensification. (C) 2014 John Wiley & Sons, Ltd.