Browsing by Author "Ruben G. Carbonell, Committee Member"

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Characterization of Phase Equilibrium associated with Heterogeneous Polymerizations in Supercritical Carbon Dioxide
(2004-10-23) Kennedy, Karen Alyce; George W. Roberts, Committee Co-Chair; Douglas J. Kiserow, Committee Member; Richard J. Spontak, Committee Member; Joseph M. DeSimone, Committee Co-Chair; Ruben G. Carbonell, Committee Member
This thesis details research to understand the phase equilibrium associated with heterogeneous polymerizations in supercritical carbon dioxide (scCO2), particularly the polymerization of vinylidene fluoride (VF2) in scCO2. Knowledge of the equilibrium between the supercritical fluid and polymer phases may be applied to understanding the mechanisms involved in heterogeneous polymerizations in scCO2. Several experimental systems were developed and/or utilized for measuring the phase equilibrium. These included a system for measuring the swelling of solid polymer particles in the presence of scCO2, a system for measuring the mass sorption and diffusion of supercritical fluids into the polymer phase, and a system for measuring the partitioning of reactant species between the polymer and supercritical fluid phases. The sorption and swelling of poly(vinylidene fluoride) (PVDF) was measured at conditions similar to those of the polymerizations. The Sanchez-Lacombe equation of state was applied to modeling the binary and ternary phase equilibria for the VF2-CO2-PVDF system. Carbon dioxide exhibits a favorable interaction with PVDF that is enhanced at increasing fluid densities. Additionally, the monomer exhibits a favorable interaction with PVDF that improves the mass sorption into the polymer phase and expands the tunability of the fluid to change the polymer properties. The impact of the phase equilibrium on the precipitation polymerization of vinylidene fluoride in scCO2 is discussed. The bimodal molecular weight distribution of PVDF synthesized in CO2 could be due, in part, to the sorption of VF2 into the polymer phase and the plasticization of the polymer to facilitate propagation of the polymer chains to high molecular weights within the polymer particles. This dissertation provides a foundation for understanding the impact of the phase equilibrium on heterogeneous polymerizations in supercritical carbon dioxide. It provides techniques for identifying and improving conditions for polymerizations in supercritical carbon dioxide and optimizing CO2-based processes of a heterogeneous nature.
Deposition of Metal and Metal Oxide Thin Films from Metal Organic Precursors in Supercritical Carbon Dioxide Solution
(2005-04-22) Barua, Dipak; Ruben G. Carbonell, Committee Member; Gregory N. Parsons, Committee Chair; Carlton Osburn, Committee Member
Thin films of metals and metal-oxides are deposited in batch (Chemical Fluid Deposition) and cyclic (Atomic Layer Deposition) processes from metal organic precursors in supercritical carbon dioxide solutions. New materials have been introduced in the deposition processes. Deposited films are analyzed in details in order to evaluate their quality and chemical composition. Analyzing techniques, X-ray photoelectron spectroscopy (XPS), ellipsometry, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and auger electron spectroscopy (AES) are adopted to characterize the films. Capacitance-voltage measurements are performed to prove the device quality deposition of metal oxide films. The process establishes a new approach in metal oxide deposition, and controllable growth of metal and metal oxide films in supercritical carbon dioxide.
Heterogeneous Catalytic Hydrogenation of Polymers Facilitated by Supercritical Carbon Dioxide
(2005-07-26) Xu, Dawei; Peter K Kilpatrick, Committee Member; David R Buchanan, Committee Member; Saad A Khan, Committee Member; Douglas J. Kiserow, Committee Member; George W Roberts, Committee Chair; Ruben G. Carbonell, Committee Member
The heterogeneous catalytic hydrogenation of polystyrene (PS) in decahydronaphthalene (DHN) was studied in a batch reactor using 5%Pd/BaSO4 as the catalyst. The effects of temperature and H2 pressure were investigated over the ranges from 90 to 180C and 250 to 1000 psig. At high H2 pressure, the rate of PS hydrogenation was approximately first order with respect to aromatic ring concentration, with an apparent activation energy of 59.6 kJ/mol. For the hydrogenation of 3wt% PS solution at 150C and with agitation above 2000 rpm, the resistance to gas-liquid mass transfer was negligible. Calculations indicated that influences of liquid-solid mass transfer and pore diffusion were minimal during hydrogenation of PS solutions at concentrations of 3wt% or less. The resistance to mass transport became severe in the hydrogenation of PS solutions at concentrations of 4.5wt% or higher. Precipitation of PS from different solvents under high pressure CO2 was investigated. DHN was selected as the solvent for PS hydrogenation in the presence of supercritical CO2 (scCO2) due to the high precipitation pressure and the saturated structure of DHN. It was found that H2 solubility in CO2-swollen DHN was substantially higher than in pure DHN at a constant H2 pressure. Deactivation of 5%Pd/BaSO4 was observed during PS hydrogenation in CO2-swollen DHN above 150C. The analysis of the gas phase showed that about 50 ppm CO was formed at 150C, which could poison the catalyst. It was found that 65%Ni/Al2O3/SiO2 could effectively convert CO to CH4. Therefore, the bimetallic catalyst system (5%Pd/BaSO4 plus 3wt% 65%Ni/Al2O3/SiO2) showed improved resistance to CO poisoning during PS hydrogenation in CO2-swollen DHN. The irreversible adsorption of PS on the surface of catalyst was found to lead to a lower hydrogenation rate. The adsorption of PS from DHN onto solid catalyst was studied. At equilibrium, the amount of adsorbed PS increased with increasing temperature. The presence of high pressure CO2 significantly reduced the adsorption of PS. Assuming PS adsorption to be irreversible, a kinetic model of PS adsorption was developed and was demonstrated to be consistent with the experimental results at temperatures from 25 to 150C.
Life Cycle Assessment of Chemical Processes and Products
(2007-10-28) Li, Yong; Ruben G. Carbonell, Committee Member; Perry L. Grady, Committee Member; Christine S. Grant, Committee Co-Chair; David F. Ollis, Committee Member; Michael R. Overcash, Committee Co-Chair
In this study, environmental assessment of carbon dioxide application in soybean oil and bitumen production has been investigated using life cycle approach. In soybean oil production, the initial life cycle comparison finds that the lab scale CO2 system is not as good in life cycle impacts as the hexane system. However, reasonable engineering improvements of typical scale-up practices will make the CO2 technology better than hexane and eliminate the hexane emissions. Utilization of membrane techniques to separate the small molecular CO2 from the soybean oil hydrocarbon appears to be a much better R&D direction for development. In bitumen production, we find extraction step consumes more energy than other steps in the life cycle of bitumen production. Hot water extraction requires more energy than carbon dioxide extraction because of the heating demand of large water flow in the process. Furthermore, Three carpet products: polyvinyl chloride (PVC) backed tile, styrene butadiene latex (SBL) backed broadloom, and polyurethane (PU) backed broadloom, are studied and compared using a life cycle approach. We find that the supply chains of carpet products play very important roles in the life cycle environmental performance of carpet products. Nylon fibers, as the economically significant component in carpet products, are also environmentally significant in the life cycles of carpet products. Our results show that SBL broadloom has the least global warming impact, HH cancer impact, and HH noncancer impact.
Nanoscale Engineering Materials with Supercritical Fluid and Atomic Layer Deposition
(2009-08-04) Peng, Qing; Gregory N. Parsons, Committee Chair; Jan Genzer, Committee Member; Ruben G. Carbonell, Committee Member; Saad A. Khan, Committee Member
With the development of material science and technology, modification of substrates, which have random geometry and high aspect ratio three dimensional (3D) complex structures, with desired functional, reactive and stable coatings becomes important and challenging. The ability to fabricate mono- or multi-layers of functional materials with precisely controlled dimensions, finely tuned composition and molecular structures, attracts significant interests in materials science and is the key to construct such devices and structures at nano- and micro- scale with desired properties. In this study, supercritical carbon dioxide (scCO2) has been studied as an alternative route for modifying substrates due to the unique gas-like (low viscosity, high diffusivity and zero surface tension) and liquid-like properties (high density). 1) The reaction kinetics of metal oxides thin film deposition from pyrolysis of metal organics in scCO2 was studied in detail. This method was demonstrated as a powerful technique to coat oxides, including Al2O3, Ga2O3 and others, into 3D high aspect ratio complex structure of carbon nanotubes (CNTs) forest. 2) The low temperature scCO2 based hydrogenolysis process was developed as a useful way to functionalize aligned CNTs forest with dense Nickel nanoparticles. On the second part of this work, atomic layer deposition (ALD) /molecular layer deposition (MLD), as a vapor phase, stepwise and self-limiting vacuum based deposition process, was demonstrated as a powerful way to form highly conformal and uniform film onto substrates, even into highly complex 3D complex structures. In this study, 4) Metal oxide ALD is applied onto 3D electrospun polymer microfiber mats template to illustrate an effective and robust strategy to fabricate long and uniform metal oxide microtubes with precisely controllable wall thickness. Designer tubes of various sizes and different materials were demonstrated by using this method. 5) By further extending this technique, complex coaxial Al2O3/ZnO/Al2O3 multilayed microtubular structure is fabricated, which provides an unique platform to study the solid state reaction and diffusion process (Kirkendall Effect) between Al2O3 shells and the confined middle ZnO layers by annealing the samples at 700 Ã‹Å¡C. 6) The extension of ALD-MLD process of polyamides, zinc hybrid, aminosilane self assembly monolayers were studied by various techniques to illustrate the surface reaction mechanism.
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 â€œsalt-and-pepperâ€ 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.