Glycerol valorization through production of di-glyceryl butyl ether with sulfonic acid functionalized KIT-6 catalyst

In this work, the etherification of glycerol with n-butanol catalyzed by sulfonic acid functionalized on KIT-6 mesoporous silica (SO3H-KIT-6) was investigated for the production of valuable fuel additives. The SO3H-KIT6 catalyst was synthesized by co-condensation with different molar ratios of tetraethoxysilane and 3-mercaptopropyl(methyl)di-methoxy silane. The etherification reaction was systematically examined to determine the optimal reaction temperature, reaction time, catalyst loading, and glycerol to n-butanol ratio under autogenous pressure. The maximum glycerol conversion and di-glyceryl n-butyl ether (di-GNBE) selectivity were 59.09 and 51.50%, respectively, when the SO3H-KIT-6 catalyst with the highest acidity was applied. Interestingly, the presence of a methyl group on the catalyst surface prevented glycerol adsorption during the reaction process, leading to the inhibition of undesired product formation. The SO3H-KIT-6 catalyst could be reused up to three times, with only a 13% decrease in glycerol conversion being found. Moreover, the superior performance of the SO3H-KIT-6 catalyst for di-GNBE production was also demonstrated compared with conventional solid acid catalysts including HZSM-5, H-beta zeolite, Amberlyst-35, and Amberlyst-36.