Application of a BPH zeolite for the transesterification of glycerol to glycerol carbonate: effect of morphology, cation type and reaction conditions

Abstract

Valorization of glycerol (Gly) to high-value chemicals is the key to unlocking economic and sustainable biodiesel production. The transesterification of Gly with dimethyl carbonate (DMC) to glycerol carbonate (GC) requires a catalyst with high basicity and uniform pore size for high product selectivity. BPH-type zeolite (Linde Q) nanosheets are promising catalysts for overcoming diffusion transport limitations inside the pore network and inhibiting the formation of glycidol as a side product. As-prepared BPH nanosheets (nano-sized CsBPH_AP, 192 nm size) and micron-sized BPH (micron-sized KBPH_AP, 600 nm size) were prepared by hydrothermal treatment with different Si/Al ratios. With a morphology-dependent reaction, the nano-sized CsBPH_AP demonstrates superior performance in the transesterification of Gly to GC as compared to micron-sized KBPH_AP. Ion-exchange of the nano-sized CsBPH_AP and micron-sized BPH_AP, with potassium and cesium precursors respectively, to afford nano-sized K-CsBPH_IE and micron-sized Cs-KBPH_IE resulted in similar thermal properties but different basicity and catalytic activity compared to the parent samples; higher basicity resulted in better catalytic performance. The nano-sized CsBPH_AP with a catalyst loading of 6 wt% shows good catalytic performance over four runs under optimized reaction conditions at 120 °C for 3 h and the Gly : DMC molar ratio of 1 : 5. This study reveals the crucial effect of catalyst morphology and size on the conversion of Gly to GC.