The Alkylation of Naphthalene over One-Dimensional Fourteen-Membered Ring Zeolites. The Influence of Zeolite Structure and Alkylating Agent on the Selectivity for Dialkylnaphthalenes

Abstract

Abstract The alkylation, i.e., isopropylation, s-butylation, and t-butylation, of naphthalene (NP) was examined over one-dimensional fourteen-membered (14-MR) zeolites: CIT-5 (CFI), UTD-1 (DON), and SSZ-53 (SFH), and compared to the results over H-mordenite (MOR) to elucidate how zeolite structure and alkylating agent play roles in the shape-selective catalysis. The β,β-selectivities (for β,β-dialkylnaphthalene (2,6- and 2,7-dialkylnaphthalenes, β,β-DAN)) and the 2,6-selectivities (for 2,6-DAN) were varied with the types of zeolite and of alkylating agent. MOR gave high β,β-selectivities in the all alkylations in the range of 150–300 °C. However, the 14-MR zeolites, CFI, DON, and SFH, gave much lower β,β-selectivities in the isopropylation: bulky and less stable α,β- and α,α-diisopropylnaphthalenes (α,β-DIPN: 1,3-, 1,5-, and 1,7-DIPN); α,α-DIPN (1,4- and 1,5-DIPN) were predominantly obtained under kinetic control at low temperatures, and stable and less bulky β,β-DIPN were formed under thermodynamic control at high temperatures. The β,β-selectivities were higher than 95% over CFI in the s-butylation, and increased from 50–60% at 150 °C to 75% at 300 °C over DON and SFH, respectively. They were almost 100% in the t-butylation over all zeolites. The alkylation over MOR occurred with high 2,6-selectivities in the range of 150–250 °C: 60% for the isopropylation, 80% for the s-butylation, and 95% for the t-butylation. CFI, DON, and SFH gave the 2,6-selectivities in the range of 5–30% in the isopropylation, 65%, 55%, and 50%, respectively, in the s-butylation, and higher than 80% in the t-butylation. These different features are explained by the discrimination of the least bulky DAN isomers from the other isomers by steric restriction with the zeolite channels at the transition states: β,β-DAN from the DAN isomers, and 2,6-DAN from β,β-DAN. The bulkiness of alkylating agent also enhances the discrimination of the isomers, particularly, between 2,6- and 2,7-DAN. The β,β- and 2,6-selectivities are synergistically governed by the zeolite channel and the bulkiness of alkylating agents.