Liquid phase selective alkylation of naphthalene with t-butanol over large pore zeolites

Abstract

Liquid phase alkylation of naphthalene with t-butanol has been studied using HY and H-beta zeolites with varying silicon to aluminum ratios. Over both series of zeolites,2-( t-butyl)naphthalene (2-TBN) was observed as only monoalkylated product. Up to 84%2,6-di( t-butyl)naphthalene (2,6-DTBN) selectivity with β,β′-selectivity (2,6-+2,7-) 98–99% and2,6-/2,7- ratios from 5.6 to 5.9 were obtained on silica rich HY zeolites HY(20) and HY(6) under mild reaction conditions (160°C, 2 h reaction). H-beta zeolites show selective effect only for the formation of 2-TBN. For the different zeolites, the activity order isHY(20)≈HY(6)>H-beta(26)≈H-beta(13)>HY(2.5), while the selectivity to 2,6-DTBN stands in the orderHY(20)≈HY(6)>HY(2.5)>H-beta(26)≈H-beta(13). Kinetic parameters (temperature, t-butanol/naphthalene ratio) influencing the reaction were investigated using HY zeolites. Higher temperatures than 160°C cause a decrease in 2,6-DTBN selectivity due to secondary reactions; large t-butanol/naphthalene ratio results in lower activity, possibly caused by counter diffusion effect. The results show that alkylation of naphthalene with t-butanol should be much practical attractive not only because of the high activity, 2,6-DTBN selectivity and relatively mild reaction conditions but also due to an easy separation of the desired product (2,6-DTBN) from the reaction mixtures by crystallization.