Influence of Process Variables on the Continuous Alkylation of Isobutane with 2-Butene on Superacid Sulfated Zirconia Catalysts

Two sulfated zirconia catalysts have been prepared by impregnation of zirconium hydroxide with H2SO4 0.3 N and 1 N. Both samples showed superacid sites as shown by a desorption temperature peak in the NH3 TPD at ca. 813 K. The activity and selectivity of these catalysts have been studied for the alkylation of isobutane with trans-2-butene in a computer-controlled continuous fixed bed reactor coupled with a sampling system which allows to make differential analysis of the products from very short reaction times. In this way, the influence of the main process variables, i.e., time on stream, reaction temperature, olefin WHSV, and isoparaffin/olefin ratio, on the 2-butene conversion and product distribution has been investigated. Cracking of larger carbocations and alkylation of isobutane with 2-butene to give trimethylpentanes were the predominant reactions occurring on the superacid catalyst in the initial stages of the reaction. The alkylation/cracking ratio increased when decreasing reaction temperature. A fast catalyst decay with time on stream was also observed, and this was accompanied by an increase in the oligomerization of butene.