Isobutane alkylation with solid catalysts based on beta zeolite

Abstract

The isobutane alkylation with butenes is a reaction in which the substitution of mineral acids, such as sulphuric and hydrofluoric acids, by solid acid catalysts is highly desirable. Solid catalysts with good activity and selectivity for this reaction have been previously reported. However, bad stability is a major drawback in most cases. In this work, catalysts based on beta zeolite, exchanged with lanthanum were studied. It was found that these catalysts have lower activity than the Y zeolite both, in the protonic form, or with lanthanum in replacement of protons. EDX analyses showed that lanthanum is practically fully removed from the zeolite structure during an exchange with ammonium nitrate, even though the catalyst was precalcined. The total acidity as measured by pyridine temperature-programmed desorption is similar in the beta and the Y zeolites. However, the former zeolite has stronger acid sites, and because of this, the deactivation process occurs faster. Pulses of 1-butene at different temperatures can be used as a technique to predict the catalytic behavior of acid catalysts in the alkylation reaction. Using this technique, it was possible to determine that the beta zeolite is deactivated during the alkylation reaction by pore mouth plugging. The addition of platinum to the beta zeolite is useful in order to regenerate the catalyst using hydrogen at 80 °C, although long times are needed to accomplish this regeneration.