(442g) Investigation of Liquid Phase 1,2-Propanediol Dehydration Using Zeolite Catalysts

To reduce the dependence of our society in oil, significant effort is devoted to the production of fuels and chemicals from biomass derived sources. Glycerol, which is a major byproduct of biodiesel production, can be selectively reduced to 1,2 propanediol (propylene glycol) and 1,3 propanediol. The dehydration of these low carbon content polyols results in the formation of a number of ketones, aldehydes, or linear or cyclic ethers, which are raw materials for the production of fine chemicals. However, selective dehydration is challenging due to the presence of different of hydroxyl groups with similar reactivity, and due to a complex reaction network (combination of reactions in parallel and in series).

Several zeolite catalysts on the liquid phase dehydration of 1,2 have been studied and compared to of Amberlyst-15. 1,2-diol dehydration using Amberlyst-15 leads to high selectivity to the formation of cis- and trans- 2-ethyl-4methyl-1,3-dioxolane, which is formed via an acetal reaction of propanal with 1,2-propanediol.  This result indicates that Amberlyst-15 catalyzes the dehydration of the secondary OH group of the polyol to form propanal. On the other hand, it has been found that zeolites catalyze the dehydration of either the primary and secondary OH group of 1,2-propanediol as well as etherification reactions. When the primary OH group is eliminated acetone is formed, which can further react with the diol to form 2,2,4-trimethyl-1,3-dioxolane. Etherification reactions lead primarily to the formation di-propylene glycol and tri-propylene glycol. By adjusting the pore size of the zeolite and the strength of its acid sites, it is possible to selectively remove the primary or the secondary OH group of 1,2 propanediol and obtain selective elimination of the primary OH group.  The effect of the catalyst properties on the reaction path selectivity and the product distribution will be presented. Furthermore, the experimental results will be compared with ab-initio calculations that provide further insight into the reaction mechanisms and help guide the catalyst design.