Effect of dealumination of zeolite catalysts on methylation of 2-methylnaphthalene in a high-pressure fixed-bed flow reactor

Catalytic performances of various dealuminated zeolite catalysts such as H-mordenite (HM), H-beta (Hβ), USY and HMCM-22, for methylation of 2-methylnaphthalene (2-MN) were investigated in a high-pressure fixed-bed flow reactor. Methanol and 1,2,4-trimethylbenzene (TMB) were used as solvents and methylating agents. Dealumination of HM substantially improved 2-MN conversion, 2,6-dimethylnaphthalene (2,6-DMN) selectivity and stability. HM after the steam treatment at 550 °C followed by acid leaching exhibited a high and a steady conversion of 40% with the very high 2,6-/2,7-DMN ratio of 2.4 for 5 h of time on stream. In contrast, the untreated HM showed a severe deactivation, with a conversion of 8.4% and the 2,6-/2,7-DMN ratio of 1.4. On the other hand, Hβ showed very high and nearly steady conversion, but with reduced selectivity for 2,6-DMN; USY showed initially high conversion but the value decreased and there was no selectivity for 2,6-DMN; and HMCM-22 showed low but steady conversion with low selectivity for 2,6-DMN for 5 h of time on stream. No promotion effect by dealumination on the conversion, stability, or selectivity was observed over Hβ, USY or HMCM-22. These distinguishing characteristics of these catalysts are discussed based on the differences in their porosity and acidity.