Isobutane alkylation with butenes in gas phase

This article studies the isobutane alkylation with butenes using solid acid catalysts in order to analyze the reaction in the gas phase, at temperatures higher than those typically used in the liquid phase. Y zeolite and mordenite exchanged with lanthanum are used as catalysts. As the reaction temperature is increased, the cracking rate also increases; consequently, at short reaction times, a very low concentration of trimethylpentanes and other C8 products in the liquid fraction can be observed. After an induction period in which coke deposition occurs decreasing the cracking rate, these compounds appear in the product. The length of this induction period changes as a function of the reaction temperature. Based on these results, we tested a process in which the reaction temperature is increased during the run, carrying out the reaction in the gas phase at atmospheric pressure. Using this procedure, we found that the production of trimethylpentanes is largely increased. This is because as the catalyst deactivates due to coke deposition at a given temperature, consequently losing activity for hydrogen transfer, the increase in temperature accelerates the gasification of coke residues, thus cleaning the surface. For this reason, a higher amount of coke is found in catalysts used at higher temperatures, since under these conditions coke precursors are gasified thus avoiding pore mouth plugging, and making possible a more efficient use of the internal surface. (C) 2010 Elsevier B.V. All rights reserved.