Green synthesis of spherical mesoporous SBA-16 and its supported Fe2O3- ZrO2 catalyst for selective acetalization of glycerol to dioxolane as biofuel additive

Abstract

Acid catalyzed acetalization of glycerol to fuel additive is an important valorization for the available surplus glycerol arising due to ever increasing biodiesel production. For this reaction, mesoporous spherical SBA-16 was synthesized first time from bamboo leaf ash derived sodium silicate (BLASS) and impregnated with 10 wt% each of Fe and Zr, characterized by XRD, N2 adsorption-desorption, SEM-EDX, TEM, NH3 TPD, XPS and evaluated for the acetalization of glycerol with furfural. The crystalline and pore structure of SBA-16 (BLASS) support were not altered by the impregnated Fe and Zr which formed α-Fe2O3 and monoclinic ZrO2 respectively on its surface. Fe2O3 and ZrO2 impregnated spherical SBA−16 (BLASS) gave higher glycerol conversion and dioxalane selectivity compared to the same impregnated on shapeless SBA-16, synthesized from tetraethyl orthosilicate (TEOS), confirmed the positive influence of spherical morphology. Further it retained the activity and selectivity for five recycles. Prolonged reaction time transformed kinetically favored dioxolane to thermodynamically stable dioxane based on which plausible reaction mechanism was proposed. Optimum temperature, glycerol: furfural feed molar ratio, amount of catalyst and reaction time were found to be 100 °C, 1:1, 3.6 wt% of glycerol and 3 h respectively for the maximum glycerol conversion with the highest dioxolane selectivity. Glycerol conversion and dioxolane selectivity for acetalization of glycerol with para substituted benzaldehydes were less than benzaldehyde due to steric effect. Dioxalane selectivity decreased with increase in size of aldehydes due to inductive effect while the cyclic ketones were more reactive for the acetalization of glycerol.