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In situ monitoring of isomerization/oligomerization of butenes over H-ferrierite catalyst

Lucia Marina Petkovic, University of Nebraska - Lincoln

Abstract

This dissertation presents a study of the surface reactions that accompany the isomerization of butenes on a ferrierite (H-FER) catalyst by means of a packed-bed configured oscillating balance reactor (OBR). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and continuous mass spectrometric monitoring of the OBR product were used to discriminate between oligomerization and true coke formation. Both 1-butene and isobutene were contacted with the H-FER catalysts. For the n-butene-to-isobutene case, the modeling of the surface deposition process of high molecular weight species indicates that H-FER undergoes site blockage, followed by a pore blockage phase that sets in after c.a. 70% the total uptake is achieved. Before reaching saturation uptake, a significant fraction of selective sites for isobutene formation are lost suggesting that such sites are unlikely to exist exclusively at the pore mouths of H-FER, as proposed earlier by other research groups. For the isobutene adsorption/reaction case, the zeolite surface becomes covered with oligomeric hydrocarbons within the first few minutes on stream. There are a number of differences between the isobutene isomerization reaction and the n-butenes-to-isobutene transformation. The kinetically controlled regimes of these two reactions are roughly 70 K apart and the difference in apparent activation energies suggests that the two reactions are likely to proceed via different kinetic pathways. DRIFTS and mass spectrometric results revealed that the production of octenes and/or higher oligomers goes through a maximum at short times on stream (i.e., before the zeolite pores reach saturation uptakes). This is consistent with the idea that bimolecular processes dominate the catalysis of fresh H-FER. A higher degree of branching in the oligomeric species formed by acid-catalyzed polymerization of isobutene, relative to those from 1-butene, causes a smaller coke precursors critical uptake required to effect the site to pore blockage transition. The aging of such branched chains is slower than those resulting from a 1-butene feed. The impact of intrazeolitic oligomeric hydrocarbons on both its own formation rate and the skeletal isomerization process is also discussed.

Subject Area

Chemical engineering|Organic chemistry

Recommended Citation

Petkovic, Lucia Marina, "In situ monitoring of isomerization/oligomerization of butenes over H-ferrierite catalyst" (1999). ETD collection for University of Nebraska-Lincoln. AAI9929221.
https://digitalcommons.unl.edu/dissertations/AAI9929221

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