On the impact of co-feeding aromatics and olefins for the methanol-to-olefins reaction on HZSM-5

Xianyong Sun, Sebastian Mueller, Hui Shi, Gary L. Haller, Maricruz Sanchez-Sanchez, Andre C. Van Veen, Johannes A. Lercher

Research output: Contribution to journalArticlepeer-review

134 Scopus citations

Abstract

The impact of adding various aromatic molecules (benzene, toluene, and xylenes) or olefins (ethene, propene, 1-butene, 1-pentene, and 1-hexene) to methanol over a HZSM-5 catalyst on activity and selectivity was systematically studied. Addition of a low concentration of aromatic molecules (16-32 C%), which are free of diffusion constraints, significantly enhanced the aromatics-based catalytic cycle and greatly suppressed the olefin-based cycle. This led to enhanced methane and ethene formation and methylation of aromatic rings at the expense of propene and C4+ higher olefins. The ratio of propene to ethene is controlled by the concentration of the aromatic molecules added. Co-feeding the same molar concentration of benzene, toluene and p-xylene influenced the methanol conversion to a nearly identical extent, as none of them experience transport constraints and the methylation rapidly equilibrates the aromatic molecules retained in the pores. In stark contrast, addition of small concentrations (10-40 C%) of C3-6 olefins with 100 C% methanol does not selectively suppress the catalytic cycle based on aromatic molecules. This led to unchanged selectivities to ethene and higher olefins (C3+). Within the C3+ fraction, the selectivity to propene decreased and the selectivity to butenes were enhanced with increasing concentration of the co-fed olefin. Because of the relatively fast rates in methylation and cracking of C3-6 olefins in the olefin-based cycle, the product distributions at high methanol conversion were identical when co-feeding C3-6 olefins with the same carbon concentrations. This work provides further insights into the two distinct catalytic cycles operating for the methanol conversion to produce ethene and propene over HZSM-5 catalysts.

Original languageEnglish
Pages (from-to)21-31
Number of pages11
JournalJournal of Catalysis
Volume314
DOIs
StatePublished - May 2014

Keywords

  • Co-feeding
  • Hydrocarbon pool
  • Methanol-to-olefins
  • Selectivity

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