KIT-6 sulfonic catalysts for glycerolisis reaction. Influence of the preparation method

Abstract

In this work, the KIT-6 silica support functionalized with different contents of sulfonic groups (10 and 15 % S/Si) was employed to prepare mesoporous acid catalysts. Catalysts with modified properties were obtained introducing the functional groups by co-condensation or grafting methods.The catalytic activity was studied in the glicerolysis of soybean derived fatty acids, for the obtention of mono-, di- and triglycerides using a batch reactor. Vacuum was applied to eliminate water from the system and shift the equilibrium to the products. The effect of the catalytic formulation was studied modifying the synthesis method and the sulfonic content. Additionally, a comprehensive study was conducted regarding the distribution of products and by-products. The effect of reaction temperature, molar ratio of reactants (free fatty acids: glycerol) and catalyst concentration on conversion and selectivity was analyzed. The solids were studied by numerous characterization techniques. It was found that the KIT-6 catalysts functionalized with sulfonic groups synthesized by grafting retained the original structure of KIT-6, as opposed to those modified by co-condensation. However, all the catalysts provided adequate catalytic activities in glycerolysis with relatively high conversions of 90 % in 3 h of reaction, indicating that these materials have potential for a more environmentally friendly process. In addition to the reversible esterification, secondary reactionsoccurred that decrease the selectivity to the desired products, which could be attributed to the presence of insaturations in the carbonaceous chain of the fatty acids used. Additionally, the recyclability of the catalysts was evaluated; demonstrating sustained catalytic activity for up to three cycles.