Kinetic studies on high-pressure methylation of 2-methylnaphthalene over MTW-type zeolite with different crystal sizes

•MTW-type zeolites (Si/Al = 100) with different crystal sizes were prepared.•2-Methylnaphthalene methylation was carried out over the MTW-type zeolites.•Under high-pressure conditions, the amount of coke loaded could be decreased.•Kinetics for methylation of 2-methylnaphthalene were evaluated.•Crystal size required to achieve the reaction-limiting condition was below 240 nm.

Methylation of 2-methylnaphthalene (2-MN) under high-pressure reaction conditions over MTW-type zeolites (Si/Al = 100) was carried out using a batch-type reactor. Compared with macro-sized MTW-type zeolites, nano-sized MTW-type zeolites exhibited higher 2-MN conversion and dimethylnaphthalene (DMN) selectivity. In addition, coke formation on the catalyst could be suppressed due to improvement of the produced DMN solubility by increasing the bulk phase pressure, which enabled kinetic analysis of 2-MN methylation over MTW-type zeolites. Kinetics analysis of 2-MN methylation over MTW-type zeolites with different crystal sizes was successfully carried out, and reaction rate constants and activation energies for methylation and isomerization of 2-MN over MTW-type zeolites were obtained. The apparent reaction rate constants of 2-MN methylation were improved by decreasing MTW-type zeolite crystal size due to decrease in diffusion resistance. Moreover, the effectiveness factors for methylation of 2-MN were estimated based on the rate constants of 2-MN methylation and crystal sizes of the MTW-type zeolites. As a result, it was revealed that the crystal size of MTW-type zeolite (Si/Al = 100) required for methylation of 2-MN to achieve the reaction-limiting condition was below 240 nm.