Application of Supercritical Fluids to Solid Acid Catalyst Alkylation and

Chapter 13

Application of Supercritical Fluids to Solid Acid Catalyst Alkylation and Regeneration

Downloaded by INDIANA UNIV BLOOMINGTON on May 9, 2015 | http://pubs.acs.org Publication Date: April 12, 2007 | doi: 10.1021/bk-2007-0959.ch013

Lucia M . Petkovic, Daniel M . Ginosar*, David N. Thompson, and Kyle C. Burch Chemistry Department, Idaho National Laboratory, P.O. Box 1625, MS 2208, Idaho Falls, ID 83415-2208

Supercritical fluid (SCF) regeneration is a promising alternative method for regenerating solid catalysts deactivated by carbonaceous deposits. The unique solvent and transport properties of SCFs such as solvent strength similar to liquids and transport properties similar to gases make them highly suitable for extraction of fouling materials from porous heterogeneous catalysts. A brief review of the research work performed at the Idaho National Laboratory (INL) on the application of supercritical fluids to both isobutane/butene alkylation reaction and solid acid catalyst regeneration is presented in this contribution.

© 2007 American Chemical Society

In Ultraclean Transportation Fuels; Ogunsola, O., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

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170 Alkylation processes are utilized in the petroleum refining industry to produce a low vapor pressure, high-octane gasoline blend stock through the reaction of high vapor pressure isoalkanes and alkenes. The product ("alkylate") is desired not only because of its high octane rating, blending properties, and environmental advantages, but also because it is considered to be an essential factor in meeting the growing demand of reformulated gasoline in the US (/). Industrial processes use concentrated mineral acids to catalyze the alkylation reaction. This poses serious safety and environmental risks arising from the transport and storage of the concentrated liquid acids and the need to dispose of acid-oil sludges. Solid acid catalysts could be used as a safer and more environmentally acceptable alternative to liquid acids, however there are significant technical barriers to overcome before this can be realized. A major limitation to the use of the solid acid catalysts is their deactivation due to the formation and deposition of carbonaceous deposits. Current industrial methods to regenerate solid acid catalysts involve oxidation or hydrogénation. However, oxidation may alter catalyst structure; hydrogénation requires the presence of noble metals on the catalyst and a hydrogen supply infrastructure. All these factors significantly increase capital and operating costs. Many of the technical challenges surrounding isoparaffin-olefin alkylation processes (2) and the application of solid acid catalysts (5) have been reviewed. Supercritical fluid regeneration is a promising alternative method for regenerating solid catalysts deactivated by carbonaceous deposits. The unique solvent and transport properties of SCFs such as solvent strength similar to liquids and transport properties similar to gases make them highly suitable for extraction of fouling materials from porous heterogeneous catalysts. A review on the application of supercritical fluids in heterogeneous catalysis is available in the literature (4). In this article, a review of the research work performed at the Idaho National Laboratory (INL) on the application of supercritical fluids to both isobutane/butene alkylation reaction and solid acid catalyst regeneration is presented. The first section summarizes the exploration of isobutane/trans-2butene alkylation over six solid acid catalysts in the liquid (L), modified liquid (ML), near-critical liquid (NC-L), and supercritical (SC) regions through the addition of a cosolvent to the reaction feed mixture. The second section includes the work on the application of different fluids and fluid phases to regenerate a completely deactivated acidic ultrastable Y (USY) zeolite catalyst and the particular case of application of SC isobutane. The third section includes the research performed to explore two criteria to end the alkylation reaction and initiate SCF regeneration on a partially deactivated USY zeolite catalyst and the automated reaction/SCF regeneration application utilizing both synthetic feed and commercial refinery isoparaffin/olefin blends. The fourth section investigates the chemistry of the SC isobutane regeneration process.

In Ultraclean Transportation Fuels; Ogunsola, O., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

171


Application of SCF to the Isobutane/Butene Alkylation Reaction Initial experiments performed at the INL compared different catalysts, fluids, and operating conditions to determine the effect of SCF on solid acid catalyst alkylation (J). Three sets of studies were performed: a catalyst comparison using six different catalysts (i.e., two zeolites, two sulfated metal oxides, and two Nafion catalysts) with methane as a cosolvent; an exploration of the effect of varying methane addition on alkylation using a USY zeolite catalyst; and a study of the effect of seven cosolvents (i.e., three hydrocarbons, two fluorocarbons, carbon dioxide, and sulfur hexafluoride) at L, ML, NC-L, and SCF conditions on the USY catalyst performance. The six catalysts selected represented a variety of acidities and porosities to provide a wide range of properties. Seven different cosolvents were chosen to explore differing solvent strengths and transport properties and hence covered a wide range of densities, molecular weights, and dipole moments. A l l experiments were conducted in a plug-flow reactor system and the reaction was allowed to proceed until the concentration of trimethylpentanes (TMPs) in the outlet stream decreased to zero, indicating catalyst deactivation. In general, the light hydrocarbons and trifluoromethane were the best among the different cosolvents analyzed. Catalysts that presented higher acidities (i.e., Pt/USY and USY catalysts) produced at least 4 times greater yields of C + and TMP and demonstrated greater longevity than the other catalyst. However, operation under NC and SCF conditions was detrimental to catalyst longevity and product selectivity as compared to operation under liquid conditions. The application of different fluids and phases to regenerate a completely deactivated acidic USY catalyst and a more detailed analysis of the SC isobutane regeneration were undertaken next and are summarized in the following section. 5

Regeneration of a Completely Deactivated USY Catalyst Application of Different Fluids and Fluid Phases Activity recovery of a completely deactivated USY zeolite catalyst that initially was deactivated during the liquid phase isobutane/butene alkylation reaction was examined in a continuous plug-flow regeneration system employing a series of C -C alkanes (

Application of Supercritical Fluids to Solid Acid Catalyst Alkylation and

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