Kinetic analysis of isobutane/butene alkylation over ultrastable H-Y zeolite

Michael F. Simpson, James Wei, Sankaran Sundaresan

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Abstract

The alkylation of isobutane with trans-2-butene over ultrastable Y-type zeolites has been studied. It is well-known that this reaction is accompanied by a rapid deactivation of the catalyst. The objective of our study is to elucidate the route to catalyst deactivation so that the means of mitigating this problem can be identified. Using the initial reaction rate data, evidence has been found for a Brönsted acid mechanism. Under liquid-phase conditions, the reaction has been found to be severely diffusion limited. Using a kinetic model that accounts for the effect of diffusion, it was found that alkylation over this catalyst suffers from slow hydride transfer relative to olefin addition. This gives rise to a rapid formation of C12+ carbocations. The formation of these cations has been tied to catalyst deactivation, using a mathematical model for the reaction. On the basis of the insight gained from the experiments and modeling work, optimal reactor and catalyst design issues are examined. It is inferred from the reaction mechanism and confirmed experimentally that alkylation under pulsed flow conditions yields higher trimethylpentane/dimethylhexane ratios and slower rates of deactivation. It is suggested that the cause of the slow rate of hydride transfer is steric hindrance. Strategies for relieving this steric hindrance are proposed.

Original languageEnglish (US)
Pages (from-to)3861-3873
Number of pages13
JournalIndustrial and Engineering Chemistry Research
Volume35
Issue number11
DOIs
StatePublished - Nov 1996

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering

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