Chinese Journal of Catalysis ›› 2019, Vol. 40 ›› Issue (11): 1766-1777.DOI: 10.1016/S1872-2067(19)63426-1

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Ethene and butene oligomerization over isostructural H-SAPO-5 and H-SSZ-24: Kinetics and mechanism

Christian Ahoba-Sam, Marius Westgard Erichsen, Unni Olsbye   

  1. SMN Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, N-0315 Oslo, Norway. aCurrent address:Matriks AS, Gaustadallèen 21, 0349 Oslo, Norway
  • Received:2019-06-17 Revised:2019-06-20 Online:2019-11-18 Published:2019-09-06
  • Contact: Unni Olsbye

Abstract: Brønsted-acidic zeolite and zeotype materials are potential catalysts for the conversion of ethene to higher alkenes. In this study, two materials with AFI structure but different acid strength, H-SAPO-5 and H-SSZ-24, were subject to studies of ethene, cis-2-butene and ethene-butene mixture conversion under conditions where C3-C5 alkene formation is thermodynamically favoured over higher hydrocarbons (673-823 K, 1 atm). Ethene and cis-2-butene partial pressures were varied in the range 9-60 and 0.9-8.1 kPa, respectively, and contact times were varied in the range 3.78-756 and 0.573-76.4 s.μmol H+/cm3 over H-SAPO-5 and H-SSZ-24, respectively. Less than 1% conversion of ethene and less than 10% conversion of butene was obtained in the range of conditions used for elucidation of rate parameters.
The ethene conversion rates were more than an order of magnitude higher over the more acidic H-SSZ-24 than over H-SAPO-5 (6.5 vs. 0.3 mmol/mol H+.s at 748 K, Pethene=33 kPa), with corre-sponding lower reaction order in ethene (1.5 vs. 2.0 at 673 K) and lower apparent activation energy (52 vs. 80 kJ/mol at 698-823 K). Propene selectivity was substantially higher over H-SSZ-24 than over H-SAPO-5 (68% vs. 36% at 0.5% ethene conversion). A similar difference in apparent reaction rates was observed for cis-2-butene conversion over the two catalysts, and for co-feeds of ethene and cis-2-butene. However, the cis-2-butene conversion to C3-C5 alkenes was found to be severely influenced by thermodynamic limitations, impeding a detailed kinetic analysis, and leading predominantly to isobutene formation at the highest temperatures.

Key words: Ethene oligomerization, Butene oligomerization, Kinetics, Zeolite, Acid strength, H-SAPO-5, H-SSZ-24