Research Grants/Fellowships/SBIR

2000 Progress Report: Federal Demonstration Partnership (FDP) solid-catalyzed reactions in supercritical reaction media

EPA Grant Number: R826034
Title: Federal Demonstration Partnership (FDP) solid-catalyzed reactions in supercritical reaction media
Investigators: Subramaniam, Bala
Institution: University of Kansas
EPA Project Officer: Karn, Barbara
Project Period: October 1, 1998 through September 30, 2001 (Extended to May 20, 2003)
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $125,000
RFA: Technology for a Sustainable Environment (1998) RFA Text |  Recipients Lists
Research Category: Nanotechnology , Sustainability , Pollution Prevention/Sustainable Development



The objectives of the research project are to: (1) develop a solid-acid catalyzed 1-butene/isobutane and skeletal isomerization process with enhanced catalyst activity and product selectivity; and (2) demonstrate the safe operation (characterized by stable catalyst activity and excellent temperature control) of solid catalyzed hydrogenations in supercritical CO2-based reaction media.

Progress Summary:

  • Steady C8 alkylates production activity during experimental runs lasting up to 2 days was demonstrated during the alkylation of isobutene with 1-butene over silica-supported Nafion? catalyst particles suspended in a CO2-based supercritical reaction mixture in a slurry reactor. At a butene space velocity of 0.05 h-1, 368 K (1.1 Tc), molar feed I/O ratio of 5 with 70 mole percent CO2 in feed, pressure-tuning studies revealed that while the butene conversion was relatively insensitive to pressure at 80 percent between 80 (~ 1.1 Pc) and 167 bar (~ 2.3 Pc), the C8 alkylates selectivity decreased fourfold from approximately 30 percent at 80 bar to 7 percent at 167 bar. The overall C8 selectivity decreased from approximately 60 percent to 30 percent in the same pressure range with heavier (C12 and higher) products being formed in denser supercritical reaction mixtures. The pressure-tuning studies clearly show that milder supercritical pressures provide the optimum combination of liquid-like densities and gas-like transport properties to desorb the C8 products and transport them out of the catalyst pores before they are transformed to heavier products. We currently are performing modeling studies to better understand the pressure-tuning effects. Such an understanding should aid in rational process design and development.

    The demonstration of extended butene conversion (80 percent) and C8 selectivity (~74 percent, with the alkylates constituting approximately 40 percent of the total C8 compounds) at a relatively mild pressure (80 bar at 568 K), low I/O ratio (5), and reasonable CO2 dilution (70 percent) is a significant advance over previous efforts. Our results clearly indicate that with rational design of catalyst, tailoring parameters such as acidity and pore structure, it should be possible to further enhance the C8 alkylates selectivity. Thus, CO2-based supercritical reaction mixtures offer an excellent opportunity in general for developing environmentally benign alternatives to conventional processes that employ mineral acids.

  • The Pd/C hydrogenation of cyclohexene to cyclohexane was performed in a fixed-bed reactor employing supercritical carbon dioxide (scCO2) to solubilize the reaction mixture consisting of the reactants (cyclohexane and hydrogen) and the product (cyclohexane) in a single supercritical phase surrounding the solid catalyst. The reaction was performed at a near critical temperature of 343 K and at a pressure of 13.6 MPa that was verified experimentally to permit operation in a single phase. For an olefin space velocity of 20 h-1, excellent temperature control around the set point (343 K) and stable catalyst activity were demonstrated at cyclohexene conversion exceeding 80 percent throughout a 22 h run. This indicates that the near-critical reaction medium (possibly aided by the reactor material) has sufficient heat capacity to effectively remove the heat of reaction. Total cyclohexane selectivity was observed with its productivity being nearly 6.0x104 kg/kgcat/h. Gradual catalyst deactivation (2 percent loss in cyclohexene conversion per hour) occurred with the as-received cyclohexene feed that typically contains 180 ppm organic peroxides. When these peroxides were mitigated to 6 ppm or less by pretreating the cyclohexene feed in an alumina trap, the catalyst activity was stable with minimal changes in surface area or pore volume. Based on prior studies in our laboratory, it has been well established that organic peroxides can catalyze the formation of olefinic oligomers that adsorb strongly on the catalyst surface and cause deactivation by fouling. No CO was detected in the reactor effluent during any of the continuous runs, and no H2 was observed during the post-run depressurization step, indicating that neither the reverse water-gas shift activity between CO2 and H2 nor the formation of Pd formate complexes is significant enough at our operating conditions to deactivate the Pd sites.

    The equipment infrastructure and the insights provided by the foregoing results on how to operate an exothermic reaction in scCO2 with tight temperature control and stable catalyst activity pave the way for systematic fundamental investigations of fixed-bed hydrogenations of functional groups on supported catalysts. Clearly, such investigations are essential for rational design and scaleup of scCO2-based hydrogenations.

  • Future Activities:

    Specific activities include: (1) the development of experimental and modeling tools that aid in the rational analysis, design, and operation of continuous sc phase reactors; (2) the optimization of the scCO2-based, fixed-bed hydrogenations on supported catalysts aimed at maximizing the selectivity of the desired product?this optimization will be based on systematic experimental and modeling studies that take into account the phase behavior of the reaction mixture, the intrinsic hydrogenation kinetics, temperature control, and catalyst deactivation issues; and (3) the optimization of the scCO2-based solid-acid alkylation process developed in our laboratory, aimed at demonstrating C8 alkylates selectivity that are comparable to those obtained with mineral acids. This optimization will be achieved via rational design of solid-acid catalysts (with controlled pore size and acid site density/accessibility) complemented by modeling studies based on a reliable knowledge of the intrinsic kinetics.

    Journal Articles on this Report : 3 Displayed | Download in RIS Format

    Other project views: All 26 publications 7 publications in selected types All 6 journal articles
    Type Citation Project Document Sources
    Journal Article Arunajatesan V, Subramaniam B, Hutchenson KW, Herkes FE. Fixed-bed hydrogenation of organic compounds in supercritical carbon dioxide. Chemical Engineering Science 2001;56(4):1363-1369.
    abstract available   full text available
    R826034 (2000)
    R826034 (2001)
  • Full-text: Science Direct - Full Text HTML
  • Abstract: Science Direct - Abstract
  • Other: ScienceDirect - Full Text PDF
  • Journal Article Lyon CJ, Subramaniam B, Pereira CJ. Extended alkylate production on SiO2-supported Nafion at supercritical conditions.. Studies In Surface Sciences. 2001;139:221-228. R826034 (2000)
    not available
    Journal Article Subramaniam B. Enhancing the stability of porous catalysts with supercritical reaction media. Applied Catalysis A: General 2001;212(1-2):199-213.
    abstract available   full text available
    R826034 (2000)
    R826034 (2001)
  • Abstract: Science Direct - Abstract
  • Supplemental Keywords:

    supercritical carbon dioxide, acid catalyst, hydrogenation, 1-butene/isobutane alkylation., RFA, Industry Sectors, Scientific Discipline, Sustainable Industry/Business, Chemical Engineering, cleaner production/pollution prevention, Environmental Chemistry, Manufacturing - NAIC 31-33, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, Accommodation and Food Services - NAIC 72, Federal Demostration Program, aldehydes, cleaner production, sustainable development, waste minimization, waste reduction, environmentally conscious manufacturing, Federal Demonstration Partnership, solid-catalyzed reactions, catalysts, green process systems, alkylation reaction, isomerization, pollution prevention, source reduction, supercritical reaction media, catalysis, green chemistry

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    Progress and Final Reports:
    Original Abstract
    2001 Progress Report