Deposit formation and deactivation of zeolite LaX in isobutane/2-butene alkylation

Isobutane/2-butene alkylation is an important refining process for the production of branched alkanes. Although zeolites are easier to handle than the commercial catalysts, H₂SO₄ and HF, rapid deactivation has prevented their industrial application so far. A La-exchanged zeolite X was used for isobutane/2-butene alkylation. The reaction was stopped after different times on stream and the spent catalysts were analyzed by physicochemical techniques. Three stages of the alkylation reaction were identified. In the first stage carbenium ions were formed on Bronsted acid sites and complete olefin conversion was observed. The carbon content remained constant during the second stage. However, a transformation of the chemical structure of the deposits was observed leading to a decrease of the acid site concentration and pore volume in this stage. In the final stage, the conversion dropped sharply. Deactivation was attributed to pore mouth plugging and rapid polymerization of the olefins outside of the zeolite pores. This is an abstract of a paper presented at the 231st ACS National Meeting (Atlanta, GA 3/26-30/2006).