Valorization of glycerol by ultrasound-assisted acetalization to solketal

Abstract Conversion of glycerol into high-value chemical products is a compelling process in the biomass conversion and biorefinery industry. In this study, a novel approach was employed to investigate ultrasound-assisted solketal synthesis using glycerol and acetone as raw material and sulfated zirconia as catalyst. Effect of six factors, including reactant ratio (1:2 -1:6), catalyst dosage (0.5-1.5 wt%), ultrasound voltage (180-220 V), tip depth (0.5-1.5 cm), time of reaction (10-20 min) and temperature of reaction (30°-50°C) on glycerol conversion were studied. The significant factors obtained from Box-Behnken Design (BBD) were in the order of reactant ratio > ultrasonic voltage > catalyst dosing for fixed tip depth, temperature, and time of 1 cm, 50°C and 15 min, respectively. Then, the reaction was carried out at the optimum reactant ratio (glycerol: acetone) 1:6, ultrasonic voltage 200 V, catalyst dosing 0.5 wt.%. The conversion of glycerol was estimated from the results of ultrasonic velocity measurement, and the same was later cross-verified by TLC and GC-MS analysis. Further acidity of the catalyst (Zr-S-400) was increased by increasing acid concentration (0.5M, 0.7M and 1M H2SO4) and Zr-S-0.5, Zr-S-0.7, and Zr-S-1 catalysts were synthesized. Catalysts were characterized by FESEM, EDAX, XRD, BET and Ammonia TPD. At the optimum condition of the reaction, a high glycerol conversion (94%) with solketal selectivity (93.9%) and isomer (0.1%) was achieved using Zr-S-1 as the catalyst. The sulfated zirconia catalyst demonstrated remarkable reusability, maintaining consistent glycerol conversion and solketal selectivity over 4 consecutive cycles.