Alkylation reactions over ion-exchanged molecular sieve zeolite catalysts. Part 3.—Alkylation of toluene and benzene with ethanol: consideration of the effects of initial coke formation on para selectivity

Abstract

The ethylation of toluene and benzene with ethanol at 423 K over a wide range of exchanged NaNH₄Y catalysts and also over a NH₄Y-91.5 sample calcined at 11 different temperatures between 523 and 875 K has been studied. Alkylation with ethanol was found not to lead to rapid catalyst deactivation or to excessive polysubstitution. The effect of such reaction variables as reaction temperature and contact time were studied in detail over an NH₄Y-87.2 sample. The selectivity for m-ethyltoluene formation remained constant at ca. 20% of the ethyltoluene product mixture irrespective of the catalyst studied, the calcination temperature used or the reaction conditions. However, the amount of the para isomer formed varied from 20 to 65% of the product mixture and its selectivity occurred at the expense of the ortho isomer. The selectivity of the catalysts was found to be a function of (i) the length of time on stream, (ii) the degree of cation exchange, (iii) calcination temperature, (iv) reaction temperature and (v) the contact time. It was found that altering the above reaction variables also varied the extent of coking of the catalysts as evidenced by the coloration changes of the catalysts. The inceased selectivity for para formation is related to configurational diffusion of the aromatic in zeolite pores of a restricted size brought about by coke deposition. Thus para selectivity in these catalysts can be regulated by controlling the extent of ammonium exchange.