Pulsed gas-phase alkylation of isobutane/2-butene over sulfated zirconia Original Research Article

A pulsed-feed alkylation study of gas-phase 2-butene with isobutane was conducted over sulfated zirconia (SZ) to determine the effect of temperature and feed composition on the dominant reactions and deactivation mechanisms. For all conditions, high initial conversion of 2-butene to C5 was observed, which is attributed to alkylation followed by rapid cracking on the strongest acid sites. These sites deactivated quickly, and then the steady-state catalyst behavior was observed to be different at different temperatures. During alkylation at 50°C, the catalyst deactivated after 40 pulses, which is attributed to the build-up of trimethylpentane (TMP) products that do not readily desorb from the catalyst surface at this temperature, and was verified when pulses of pure 2,3,4-TMP over SZ produced similar cracking results. At 100°C, the adsorbed alkylation and/or oligomerization products were very selectively cracked to form 2-butene, resulting in a net dehydrogenation of isobutane to 2-butene. At temperatures in the 150–250°C range, the product selection was dominated by high cracking rates, but the catalytic activity remained stable with nearly complete conversion of 2-butene at the highest temperatures. It was also found that the deactivated catalyst at 50°C could be regenerated by simply heating to 150°C, which apparently removed the adsorbed hydrocarbons by either volatilization or cracking.