Browsing by Subject "High pressure chemistry"
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Item Membrane based separations of carbon dioxide and phenol under supercritical conditions(2004) Damle, Shilpa C.; Johnston,Keith P.; Koros, William J.Polyimide membranes have been implemented in a variety of applications due to their attractive productivities, selectivities, and processing characteristics. Their use in high pressure carbon dioxide environments has not been well investigated; however, increasing industrial interest in using supercritical CO2 in place of organic solvents as a processing agent makes this study important. Many potential end uses of CO2 as an industrial solvent will require purification of contaminated high pressure CO2 streams with further recycling of the CO2 to prevent significant emission into the atmosphere. Well designed membranes, which selectively partition the organic solutes into the material and transfer it out of the effluent stream, leaving the CO2 at high pressure, offer a low cost and high productivity alternative to de-pressurization. The focus of this project is to study the effects of high pressure carbon dioxide on the properties of polyimide materials and to successfully separate the organic solute, phenol, from CO2. Investigation of the transport properties of 6FDA-based polyimide materials in the presence of pure carbon dioxide at high pressures showed interesting permeability trends, in which the permeabilities exhibited a maximum after which they declined with further increases in pressure. These ìconditionedî polymers showed decreased chain spacing and swelling effects as compared to untested samples, indicating a possible lattice collapse of the material. It seems that the competition between the CO2 induced swelling tendency is at some point balanced by the tendency for a non-equilibrium high free volume polymer to relax to its equilibrium state. The permeability maximum occurs when the two effects are equal, after the volume contraction is dominant. By modeling transport through the membrane starting with Fickís law, and taking into account convective contributions to transport, an unconventional approach, termed ìSorp-Vectionî, to describing mixed gas transport through a membrane was developed. This model predicted a high separation efficiency of 79 for the organic solute, phenol, in a glassy polymer, 6FDA-DAM. Experimental separation efficiencies of 40 ñ 44 were obtained for this polymer, which represent 59% of the efficiency predicted via modeling. These experimental results provide a proof of concept of bulk flow based separations of phenol from CO2. These experiments verify that (1) the separation of phenol from carbon dioxide is possible using glassy materials, (2) these separation factors are large enough for industrial viability, and (3) bulk flow effects are working to enhance the separation effectiveness.Item Methanol production by direct oxidation of methane in a plasma reactor(Texas Tech University, 1998-08) Mooday, RickMethanol is one of the most widely-produced chemicals in the world. It is a key raw material in the production of many chemicals in the petrochemical industry. Methanol also has vast potential for expanded applications as a fuel. It is currently produced by an energy intensive and expensive two step process. An economically feasible one step process could significantly reduce methanol production cost, saving millions of dollars. A methane-to-methanol process, built at remotely located methane reserves, would convert methane into a different energy form that is much easier to transport. This would make methane a much more attractive and valuable energy source. The purpose of this investigation was to evaluate the feasibility of producing methanol by direct oxidation of methane using a plasma reactor. The chemistry of methane oxidation is well understood and free radicals play a central role in methane oxidation reactions. Low pressure experiments by other researchers indicated that methanol can be produced by direct oxidation of methane in plasma reactors. However, the viability of a plasma-based methanol production process depends on its ability to convert large quantities of methane. This work was directed at plasma reactor operation near atmospheric pressure to increase the amount of material processed. The focus of this mvestigation was the design and construction of an experimental apparatus which could achieve methanol synthesis in a plasma reactor by direct oxidation of methane at atmospheric pressure. A microwave source provided the energy to generate the plasma. The system was designed to study the effects of reactant concentration and flow configurations on methanol production. Since high levels of methanol selectivity are the primary consideration in direct synthesis of methanol from methane, improvements in methanol selectivity were desired. The objective of the four experimental phases was to investigate reactor operating conditions and improve methanol production and selectivity. Methanol production at atmospheric pressure was demonstrated in this plasma system and steady improvements in methanol selectivity were achieved as the investigation proceeded. Experiments showed that high concentrations of water and low concentrations of oxygen improved methanol selectivity. In the last experimental phase, oxygen was divided into both reactant streams, but this approach did not improve methanol production. It was observed that higher methanol selectivities were obtained only at low methane conversions. As in other plasma studies, methanol production did not approach what would be required for commercial feasibility.