Sustainable production of acrolein: investigation of solid acid-base catalysts for gas-phase dehydration of glycerol

Synthesis of acrolein by catalytic gas-phase dehydration of biomass-derivate glycerol was studied over various solid catalysts with a wide range of acid -base properties. The catalyst acidity and basicity were measured, respectively, by n-butylamine and benzoic acid titration methods using Hammett indicators. The most effective acid strength for the selective dehydration of glycerol to form acrolein appeared between -8.2 <= H-0 <= -3.0, with which acrolein was produced at a selectivity of 60-70 mol%. The catalysts having very strong acid sites ( H-0 <= -8.2) effected a lower acrolein selectivity (40-50 mol%) due to more severe coke deposition in the reaction. Solid acids holding medium strong and weak acid sites (-3.0 <= H-0 <= + 6.8) were found to be not selective for the acrolein production, the acrolein selectivity being less than 30 mol%. The mass specific catalytic rate for the acrolein production showed a general trend to increase with the fractional acidity at -8.2 <= H-0 <= -3.0. The catalytic data also suggest that Bronsted acid sites were advantageous over Lewis acid sites in catalyzing the selective synthesis of acrolein from glycerol dehydration. Solid base catalysts were shown not to be effective for acrolein production.