Browsing by Author "Douglas J. Kiserow, Committee Co-Chair"

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    Polystyrene Hydrogenation in Supercritical CO2-Decahydronaphthalene Using Porous Catalysts
    (2010-06-28) Dong, Laura Beth; George W. Roberts, Committee Chair; Douglas J. Kiserow, Committee Co-Chair; Alan E. Tonelli, Committee Member; Ruben G. Carbonell, Committee Member
    The heterogeneous hydrogenation of polystyrene (PS) was studied in a slurry batch reactor. Mixtures of supercritical carbon dioxide (scCO2) and decahydronaphthalene (DHN) were used as the solvent for the polymer. Several palladium-based porous catalysts were identified for PS hydrogenation at 150oC. Relatively high degrees of hydrogenation were obtained with monometallic palladium catalysts for the reaction conducted in neat DHN. However, when either palladium catalyst was used in scCO2-DHN, hydrogenation ceased within 15 minutes of CO2 addition to the reactor. Carbon monoxide (CO) formed via the reverse water-gas shift (RWGS) reaction and poisoned hydrogenation sites. Physical mixtures consisting of a hydrogenation catalyst and a methanation catalyst were effective in reducing CO levels. However, when the “salt-and-pepper†catalyst was used, aromatic ring hydrogenation levels in scCO2-DHN were consistently lower than those obtained in neat DHN. A bimetallic catalyst in which the hydrogenation and methanation functions are located on the same support was successfully used to reduce CO levels and to hydrogenate PS in scCO2-DHN. The success of the bimetallic catalyst in hydrogenating PS in scCO2-DHN over the salt-and-pepper approach was attributed to the differences in internal mass transfer resistances for PS hydrogenation and the RWGS reaction. Polymer size effects on heterogeneous PS hydrogenation were determined by varying polymer molecular weight and by using CO2 to tune polymer coil size in DHN. The ability to tune polymer coil size by varying CO2 concentration was demonstrated in high pressure dynamic light scattering experiments. The improvements in reaction rate in either neat or CO2-expanded DHN were found to be directly related to increases in PS diffusivity and decreases in polymer coil diameter, both of which are functions of polymer molecular weight and solvent quality.
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    Transport Properties of Polystyrene Solutions Swollen with Carbon Dioxide
    (2005-01-16) Whittier, Rachel Elizabeth; John H. vanZanten, Committee Member; Douglas J. Kiserow, Committee Co-Chair; George W. Roberts, Committee Co-Chair
    The viscosity and diffusion coefficient of polystyrene (PS) in decahydronaphthalene (DHN) were measured in the presence of CO₂ to investigate the effect of CO₂ on the transport properties of polymers in solution. The viscosity of 1-15 wt% PS in DHN was measured, using a moving piston viscometer. The effects of CO₂ pressure (0 to 3000 psi), polymer concentration (1-15 wt%), temperature (33-150°C), and molecular weight (126 to 412 kDa) on viscosity were investigated. Viscosity measurements of PS in DHN showed the viscosity increase with increasing concentration was described by the Martin equation. Addition of 30-40 wt% CO₂ resulted in the maximum viscosity reduction for all temperatures, polymer concentrations, and molecular weights. Viscosity reduction was greatest for high molecular weight polymer, high polymer concentrations, and low temperatures. At the highest CO₂ pressures, the viscosity of all polymer solutions converged to approximately 1-3 cp. The viscosity of PS/DHN/SF₆ was also measured. The viscosity reduction with SF₆ was approximately the same as that with CO₂. In addition, the diffusion coefficient of 0.5- 1.25 wt% 412,000 M[subscript n] PS in DHN was measured from 25-150°C. The diffusion coefficient results were extrapolated to zero concentration to determine the infinite dilution diffusion coefficient, D₀. The hydrodynamic radius was calculated from D₀. The hydrodynamic radius increased with temperature, indicating an increase in solvent quality of DHN with increasing temperature. Upon addition of CO₂ to 0.75-1 wt% 412,000 M[subscript n] PS in DHN, the diffusion coefficient increased, approximately doubling in value. The decrease in viscosity and increase in diffusion coefficient with CO₂ show that CO₂ is effective as a facilitator of improved transport.