Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

Abstract

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO2/Al2O3 = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively.