SYNTHESIS OF HIGHLY THERMAL STABLE ZEOLITE BETA CATALYST FOR SELECTIVE CONVERSION OF GLYCEROL TO SOLKETAL

Abstract

Highly thermal stable zeolite beta was successfully synthesized from fumed silica mixed with sodium aluminate and sodium hydroxide using crystalline nanoseeds instead of the organic template to encourage formation of the zeolite beta crystals. The starting gel with a composition of SiO2:0.027Al2O3:0.36Na2O:35H2O was hydrothermal crystallized in an autoclave under autogenous pressure. The effects of crystallization temperature, crystallization time, and calcined nanoseed amounts on the properties of zeolite beta products were studied. The zeolite beta products were characterized by XRD, FESEM, nitrogen adsorption, 27Al-MAS-NMR and ICP-MS techniques. The increase in temperatures and crystallization time leads to formation of zeolites Na-P1 and mordenite as impurities. The increase in seed amounts from 0.17 to 0.83 wt% to the starting gel resulted in high crystallinity zeolite beta with smaller average particle sizes from 620 nm x 840 nm to 140 nm x 150 nm, and shorter optimal crystallization time from 5 to 2 days, respectively. Their BET surface areas were approximately 600 m2/g. The intensities of the XRD parent peak of zeolite beta products were slightly decreased upon calcination at 550 °C indicating the high stability of the samples prepared by the nanoseed-assisted method. The absence of the non-framework peak in 27Al-MAS-NMR spectra indicated no dealumination after calcination. The zeolite catalysts contained SiO2/Al2O3 ratios in a range of 8.8-10.0. The catalytic activities of zeolite beta samples were investigated for acetalization of glycerol with acetone using dimethylformamide as solvent. The glycerol conversions and solketal yields were not influenced by nanoseed amounts used in the catalyst synthesis because all tested catalysts were selected from the optimal conditions of synthesis resulting in similar properties. Upon varying several parameters, the highest glycerol conversion of 35% with 93% selectivity to solketal were achieved after 150 minutes. The used catalyst was regenerated by calcinations and maintained similar activity.