Hierarchical faujasite zeolite-supported heteropoly acid catalyst for acetalization of crude-glycerol to fuel additives

Abstract

Glycerol acetalization in the presence of aldehydes/ketals and acid catalysts leads to production of fuel-additives, which could improve clean fuel ignition, promote combustion process, and reduce fuel gelling in the engine. In this study, hierarchical faujasite zeolite-supported heteropoly acid catalysts (HR/Y) were prepared followed by impregnation of 10, 20 and 30wt% phosphotungstic acid (HPW). The synthesized catalysts (HR/Y-Wx) were characterized using XRD, FTIR, FESEM, EDX, TEM, NH3-TPD and N2 physisorption analyses. The impregnated hierarchical zeolites along with NaY zeolite were used as catalysts in crude-glycerol acetalization to produce a fuel additive, 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane (solketal). The catalysts possessed high thermal stability, large specific surface area, large pore diameter (mesoporous structure) and strong acidic sites. The highest solketal yield of 97.85% at 100% crude-glycerol conversion was obtained over the HR/Y-W20 catalyst. Optimization studies revealed that the best solketal yield of 97.87% at complete reaction conversion could be achieved at 40°C with 10wt% catalyst weight and 10/1MR of AC/Gl in 2h. The synthesized catalyst even maintained its activity after 30h reaction time due to its mesoporous structure and strong acidity. The impact of real impurities (e.g. water, methanol, and NaCl) on catalyst activity was evaluated and the results revealed that crude-glycerol acetalization over HR/Y-W20 acid catalyst was promising for solketal production with >86% solketal yield at >97% glycerol conversion in the presence of high concentrations of impurities (15wt% water, 10wt% methanol, and 15wt% NaCl). Results confirmed that the prepared HR/Y-W20 catalyst can be a potential candidate for future large scale research and development.