Application of nano size ZSM-48 zeolite framework for toluene methylation to p-xylene

Abstract

Methylation of toluene with methanol to p-xylene over conventional HZSM-5 zeolites is accompanied by various unwanted reactions. Narrowing of pores and lowering of acidity of HZSM-5 zeolites to maximize p-xylene have resulted into trade-off between p-xylene selectivity and toluene conversion. ZSM-48 zeolites, owing to narrower pores and lower acidity than ZSM-5, can be useful for direct utilization for toluene methylation. Further, such zeolites with reduced crystal sizes can shorten the pore retention time for small and highly reactive methanol and eliminate diffusion limitations to toluene and p-xylene molecules respectively to avoid methanol overuse in side reactions and to improve catalytic activity for toluene methylation. Envisaging above advantages, objective of the present work is to synthesize nano size ZSM-48 zeolite and demonstrate combined role of its narrow pore, less acidity and small crystals in maximization of p-xylene in toluene methylation reaction. Morphology and crystal information for prepared ZSM-48 are obtained from Field Emission Scanning Electron Microscopy and High Resolution Transmission Electron Microscopy. Results revealed 44% p-xylene selectivity and 26% toluene conversion at 400 °C, improved methanol utilization and remarkable catalyst stability with no sign of drop in catalyst activity for 120 h time on stream study.