Role of Si/Al ratio in the Valorization of Glycerol to a Fuel Additive, Solketal over HZSM-5 Catalysts

Abstract Valorization of glycerol, a by-product of bio-diesel production is an inevitable process for its economic viability. The study on various zeolites showed HZSM-5 to be an effective and stable catalyst in the conversion of glycerol to solketal which motivated the present study in order to understand the role of Si/Al ratio on its catalytic activity. HZSM-5 catalysts with Si/Al ratios of 12:1, 30:1, 80:1 and 150:1 that have been modified to acidic form from ammonical form. All these catalysts were characterized by BET-SA, XRD, SEM-EDAX, FT-IR, Raman, XPS, TPD of NH3 and Py adsorbed IR studies. The catalytic activity towards selective acetalization of glycerol to solketal was evaluated by varying the parameters viz., temperature, mole ratio of glycerol:acetone, catalyst amount and time on stream in order to understand the significance of Si/Al ratio of HZSM-5 catalysts. The optimized conditions of reaction parameters indicated a 100 mg catalyst, mole ratio of glycerol:acetone = 1:10, at 80 oC, ambient pressure and the lowest ratio of Si/Al = 12:1 of HZSM-5 to show higher activity (~ 14.5 mmol h-1gcat-1) over its counterparts attributed to higher acidity as indicated from TPD of NH3 and Ex-situ py-IR studies.