Observations, modeling and optimization of yield, selectivity and activity duping dehydrogenation of isobutane and propane in a Pd membrane reactor

Moshe Sheintuch*, Ralph M. Dessau

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

Dehydrogenation of isobutane and propane was carried out in a membrane reactor made of a Pd/Ru (or Pd/Ag) tube packed with a supported Pt catalyst. The shell side was swept by a stream of nitrogen or its mixture with hydrogen. Significant gains in yield were achieved by separating the hydrogen through the selective Pd membrane: up to 76% butene at 500°C (compared with 32% in equilibrium) and 70% propene at 550°C (23% at equ.). The attained yields, however, were limited at low feed rates by suppressed catalyst activity in the absence of hydrogen. To avoid low activity and fast aging, hydrogen concentration should be kept at about 2% by adjusting the shell or tube flow rates. Fast deactivation was observed with high ratios of shell to tube flow rates. The degree of cracking and of isomerisation increases with conversion. Temperature should be kept below 500°C, during butane dehydrogenation, to avoid cracking and fast aging. Yields under high pressures (18 psi for isobutane and 100 psi for propane) were similar to those obtained under atmospheric conditions. Operation under pressure may be advantageous as high purity hydrogen can be produced. The yield dependence on feed rate and on hydrogen shell-side pressure were adequately described (at 500°C) by a simple model, that incorporates a three-parameter rate expression, that accounts for the accelerating role of hydrogen pressure. The degree of cracking and isomerisation were adequately described by a single-parameter rate expression which assumes that the main and side reactions occur on the same sites. The model was optimized to determine the feed and shell flow rates which maximize the yield. The optimization suggests that, in the present design, the yield cannot be improved significantly beyond 90%, but that almost complete conversion could be achieved when the reactor profile of hydrogen pressure is optimized.

Original languageEnglish
Pages (from-to)535-547
Number of pages13
JournalChemical Engineering Science
Volume51
Issue number4
DOIs
StatePublished - 1996
Externally publishedYes

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