PULSED GAS-PHASE ALKYLATION OF ISOBUTANE 2-BUTENE OVER SULFATED ZIRCONIA/

A pulsed-feed alkylation study of gas-phase 2-butene with isobutane wa s conducted over sulfated zirconia (SZ) to determine the effect of tem perature and feed composition on the dominant reactions and deactivati on mechanisms. For all conditions, high initial conversion of 2-butene to C-5 was observed, which is attributed to alkylation followed by ra pid cracking on the strongest acid sites. These sites deactivated quic kly, and then the steady-state catalyst behavior was observed to be di fferent at different temperatures. During alkylation at 50 degrees C, the catalyst deactivated after 40 pulses, which is attributed to the b uild-up of trimethylpentane (TMP) products that do not readily desorb from the catalyst surface at this temperature, and was verified when p ulses of pure 2,3,4-TMP over SZ produced similar cracking results. At 100 degrees C, the adsorbed alkylation and/or oligomerization products were very selectively cracked to form 2-butene, resulting in a net de hydrogenation of isobutane to 2-butene. At temperatures in the 150-250 degrees C range, the product selection was dominated by high cracking rates, but the catalytic activity remained stable with nearly complet e conversion of 2-butene at the highest temperatures. It was also foun d that the deactivated catalyst at 50 degrees C could be regenerated b y simply heating to 150 degrees C, which apparently removed the adsorb ed hydrocarbons by either volatilization or cracking. (C) 1998 Elsevie r Science B.V.