(73b) Catalytic Glycerol Conversion

Methanol to Gasoline (MTG) is a well known process for the conversion of methanol to hydrocarbons and water developed by Mobil long ago. The hydrocarbons obtained in this reaction are alkanes in the gasoline boiling range (C4-C10) but with substantial amounts of aromatics. Zeolites A, Erionite, and HZSM-5 have been used as catalysts for MTG. The widely accepted reaction scheme includes three main sequential steps: (1) dehydration of methanol to dimethyl ether; (2) dehydration of dimethyl ether to olefins; and (3) transformation of olefins to paraffins and aromatics. Similarly, Gayubo et al. reported the successful transformation of other alcohols and oxygenates, such as, propanol, butanol, acetone, and butanone to higher paraffins and olefins over HZSM-5 catalyst. The proposed reaction scheme involves the dehydration of oxygenates to corresponding olefins and paraffins as the first step, followed by oligomerization. In parallel, deoxygenation reactions over oxides have been a subject of recent studies. For example, Pestman et al. have investigated the mechanism of organic acid deoxygenation on oxides such as ZnO and TiO2. The deoxygenation preceded two steps, including a lattice oxygen atom removal by hydrogen and the deoxygenation by refilling the oxygen vacancy. Based on these previous studies, the conversion of glycerol (an oxygenate containing three hydroxyl groups) by two alternative paths under various pressure and temperature conditions has been investigated. The first one is the direct conversion of glycerol over various acidic zeolites, specifically HZSM-5, HZSM-11, HZSM22, HY, HMOR, and H-OMEGA. The second approach utilizes two consecutive catalytic beds, one with Pd/ZnO among others for deoxygenation of glycerol and one with the acidic zeolites for dehydration and oligomerization.