Monoglyceride synthesis by glycerolysis of methyl oleate on MgO: catalytic and theoretical investigation of the active site

CRISTIÁN FERRETTI; SILVIA A. FUENTE; RICARDO M. FERULLO; NORBERTO J. CASTELLANI; CARLOS APESTEGUÍA; ISABEL DI COSIMO

Detroit

Encuentro; 22nd North American Meeting of the North American Catalysis Society; 2011

North American Catalysis Society

During biodiesel synthesis by oil or fat transesterification, glycerol (Gly) is obtained as the main co-product, representing 10 % of the biodiesel production. Nowadays, glycerol surplus is becoming a matter of environmental and economic concern and conversion of Gly into high value-added chemicals or fuels is needed. Monoglyceride (MG) synthesis by glycerolysis of fatty acid methyl esters (FAME is an interesting option to transform this biomass-derived compound into fine chemicals. In this work, the glycerolysis of oleic acid (C18:1) methyl ester was studied using MgO. The chemical nature of the base site for promoting the MG synthesis was investigated using several characterization techniques and Density Functional Theory (DFT) calculations. Glyceryl monooleate (MG) yields as high as 70% can be obtained at 493 K on MgO treated at different Tcalc with 30% DG and no TG formation. The initial catalytic activity of MgO for the glycerolysis reaction was affected by Tcalc (Figure 4) in a similar way to the base sites indicating that the reaction mainly takes place on strong base sites, such as the coordinatively unsaturated oxygen anions present in corners or edges. Preliminary DFT calculations reveal that Gly chemisorbs non dissociatively on terrace sites whereas dissociative chemisorption of the O-H bond occurs on strong base sites. The O-H bond breaking is a necessary step of the glycerolysis reaction mechanism. Gly chemisorption through the primary OH groups is favored over that of the secondary OH, in line with the catalytic results showing that the major MG isomer is alpha MG. Besides, calculations suggest that Gly adsorbs more strongly than FAME on MgO. Results suggest that the reaction is preferentially promoted by low-coordination oxygen anions where Gly primary OH groups dissociate.