Browsing by Subject "carbon dioxide"
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Item Advances in Synthesis of Co- and Ter- Polycarbonates and Polyesters from Non-Petroleum Feedstocks and Kinetic Studies of Ligand Substitution from Manganese Half-Sandwich Complexes(2012-07-16) Poland, Ross RiversThis dissertation is written in two parts. The first pertains to polycarbonate and polyester synthesis using relatively benign processes. The synthesis of polycarbonates from the coupling of CO2 and epoxides catalyzed by transition metal catalysts has long been studied in the DJD group. The benefits of this process are that it utilizes comparatively benign reagents, can be performed using no extraneous solvent, and is 100% atom efficient. A method potentially useful for achieving more desirable polycarbonate properties is to produce an epoxide A/epoxide B/CO2 terpolymer, thus allowing more fine "tuning" of properties to what one may desire while simultaneously influencing relative epoxide reactivity to potentially increase catalytic turnovers. Specifically, the coupling of propylene oxide and cyclohexene oxide with CO2 to yield a random copolymer with tunable properties has been studied via a Fineman-Ross analysis. Propylene oxide was found to be incorporated into the resultant polymer chain with anywhere from 4-10 times the preference of cylcohexene oxide. Although it has been reported as early as 1969, the copolymerization of epoxides and cyclic anhydrides catalyzed by transition metal complexes to yield polyesters via a chain-growth mechanism has recently gained much attention. This robust method of polyester synthesis can utilize rather inexpensive reagents to synthesize an array of polyester products which have a wide range of Tg values (-30 degrees C ? 90 degreesC), achievable through simple monomer selection. The second part of this dissertation deals with the kinetic study of ligand substitution from manganese carbonyl metal fragments. Some time ago it was postulated that complexes of the (Cp)M(CO)2L variety undergo ligand substitution via a associative mechanism allowed by a haptotropic eta5-eta3 shift in the eta5 ligand. Through kinetic studies and theoretical modeling, an approximate activation energy barrier of ~34 kJ/mol has been calculated for the ring slip of (2,5-dimethylpyrrole)Mn to occur. Additionally, further kinetic studies were performed in which Tp, a ligand electronically similar to Cp, was compared to MnCp complexes.Item Application of Polymer Gels as Conformance Control Agents for Carbon Dioxide for Floods in Carbonate Reservoirs(2012-10-15) Al Ali, Ali 1986-With the production from mature oil fields declining, the increasing demand of oil urges towards more effective recovery of the available resources. Currently, the CO2 Floods are the second most applied EOR processes in the world behind steam injection. With more than 30 years of experience gained from CO2 flooding, successful projects have showed incremental oil recovery ranging from 7 to 15 % of the oil initially in place. Despite all of the anticipated success of CO2 floods, its viscosity nature is in heterogeneous and naturally fractured reservoirs is challenging; CO2 will flow preferentially through the easiest paths resulting in early breakthrough and extraction ineffectiveness leaving zones of oil intact. This research aims at investigating gel treatments and viscosified water-alternating-gas CO2 mobility control techniques. A set of experiments have been conducted to verify the effectiveness and practicality of the proposed mobility control approaches. Our research employed an imaging technique integrating an X-Ray CT scanner with a CT friendly aluminum coreflood cell. With the integrated systems, we were able to obtain real time images when processed provide qualitative and qualitative evaluations to the coreflood. The research studies included preliminary studies of CO2 and water injection performance in fractured and unfractured cores. These experiments provided a base performance to which the performances of the mobility control attempts were compared. We have applied the same methodology in evaluation of the experimental results to both conformance control gel treatments and viscosified water-alternating-gas CO2 mobility control. The gel conformance control studies showed encouraging results in minimizing the effect of heterogeneities directing the injected CO2 to extract more oil from the low permeability zones; the gel strength was evaluated in terms of breakdown and leakoff utilizing the production data aided with CT imaging analysis. The viscosified water coupled with CO2 investigations showed great promising results proving the superiority over neat CO2 injection. This research serves as a preliminary understanding to the applicability of tested mobility control approaches providing a base to future studies in this category of research.Item Conversion of CO2 to Polycarbonates and Other Materials: Insights through Computational Chemistry(2014-09-25) Yeung, Andrew DThe use of carbon dioxide as a chemical feedstock for the copolymerization with epoxides to give polycarbonates, and for coupling with hydrocarbons to give carboxylic acids, was probed using computational chemistry. Metal-free systems were modeled at high levels using composite methods that give ?chemical accuracy?, whereas metal-bound systems were studied using density functional theory, benchmarked to these high-accuracy results for confidence. The thermodynamics of polymer vs. cyclic carbonate formation was calculated, and polymer is the exothermic product, whereas cyclic carbonate is the entropic product. The barriers for the metal-free carbonate and alkoxide backbiting reactions were also determined, carbonate backbiting having a higher barrier than alkoxide backbiting. The base degradation of polymers to epoxide co-monomers, and the acid- and base-catalyzed degradation of glycerol carbonate to glycidol were investigated too. Poly(cyclopentene carbonate) preferentially degrades to epoxide co-monomer instead of cyclic carbonate due to angle strain for alkoxide backbiting. Conversely, glycerol carbonate only yields glycidol instead of the isomeric 3-hydroxyoxetane because formation of the latter has a higher barrier. The (salen)Cr(III)- and (salen)Co(III)-catalyzed copolymerization reactions were studied for a variety of epoxides, and the overall displacement of a polymeric carbonate by an epoxide, followed by ring-opening, was found to be rate limiting. Chromium(III)-catalyzed systems have higher free energy barriers than cobalt(III) systems due to enthalpy, which explains why such polymerization reactions have to be run at higher temperatures. The metal-bound polymer carbonate and alkoxide backbiting reactions generally have higher barriers than when unbound, due to the terminal oxygen atoms? reduced nucleophilicity. The carboxylation of metal-hydride and metal-carbon bonds was studied for a series of trans-ML2XY complexes, and thermodynamics of carboxylation of the M-X bond are influenced by M, L, and Y, in decreasing order. Similar cis-complexes did not exhibit as clear trends. Examination of these complexes indicated that the three steps for the overall conversion of hydrocarbons to carboxylic acids (oxidative addition of hydrocarbon, carboxylation, and reductive elimination of the carboxylic acid) must be optimized in parallel for the successful direct synthesis of carboxylic acids.Item DEVELOPMENT AND MECHANISTIC STUDIES OF THE CHROMIUM TETRAMETHYLTETRAAZAANNULENE CATALYST SYSTEM FOR THE COPOLYMERIZATION OF CARBON DIOXIDE AND EPOXIDES(2010-07-14) Fitch, ShawnA prominent goal of scientists is to develop products and processes to meet the ever-growing needs of society. Today's needs include products that are economical, specialized, and made through processes with minimal impact on the environment. One such product that serves an important and widespread need is poly(bisphenol A carbonate) for its physical properties and ease of synthesis and processing. However, this polymer does not meet the growing need of being environmentally benign as production involves carcinogenic, chlorinated solvents and toxic monomers that can leach out from the polymer product. An answer to this new demand is the development of a different process for the production of polycarbonate plastics utilizing carbon dioxide and epoxides. Carbon dioxide is an attractive monomer that is cheap and nontoxic, and its utilization signifies an important contribution to counteract global greenhouse emissions. The stability of carbon dioxide has posed a significant and complex challenge towards its utilization. Epoxides are attractive since they are synthesized from a wide variety of olefins, both naturally occurring and those derived from petroleum. The exploration of catalysts to facilitate the coupling of epoxides to carbon dioxide to afford polycarbonates has been under investigation in the Darensbourg lab for fifteen years, and has lead to the development of several successful systems such as zinc bisphenoxides and chromium salens. This dissertation focuses on the development of another successful catalyst system, chromium tetramethyltetraazaannulene, and further elucidation of the mechanism by which polycarbonates are formed. Herein, aspects of the copolymerization process using this system will be discussed in detail, such as cocatalyst and pressure dependence, catalyst derivatization, and kinetic and mechanistic investigations. The end result of these investigations is the development of the most active chromium-based catalyst for the copolymerization of cyclohexene oxide and carbon dioxide and a better understanding of how the copolymer product is produced.Item Synthesis, reactivity, and coordination chemistry relevant to the copolymerization of CO2 and epoxides by first row transition metal schiff base complexes(2009-05-15) Frantz, Eric BenjaminExcepting agricultural based products, which themselves require a great deal of energy to produce, our supply of natural resources such as minerals, metal ore, fresh water, coal, oil and natural gas are all limited in supply. The depletion of these substances is imminent and this knowledge weighs heavily on humankind. The utilization of CO2 for the production of polycarbonates is one attempt at exploiting a profoundly abundant and renewable resource. The importance of research in this and similar fields justifies the detailed study of the chemicals and procedures involved with this chemistry. This current work concentrates on the fundamental study of transition metal Schiff base complexes that have shown a great deal of promise in their ability to catalyze the copolymerization of CO2 and epoxide to form aliphatic polycarbonates. A new chromium(III) Schiff base complex has been synthesized and evaluated for its ability to catalyze the formation of polymer. The ligand employed bears an N2O2 coordination sphere identical to the widely utilized chromium(III) and cobalt(III) salen catalysts. This complex was shown to be active towards the copolymerization of CO2 and cyclohexene oxide. Although the activity was less than that seen with chromium(III) salen complex, the study demonstrates that new ligand systems are available beyond salen and deserve further attention. A class of manganese(III) Schiff base complexes was also synthesized and evaluated as catalysts. Although crystallographic data has shown that these complexes are structural analogs to chromium(III) salens, the difference in metal center leads to a nearly complete elimination of catalytic activity. Such a marked difference has been taken advantage of by using this very low activity to study the ring-opening of epoxide in the initial step of the copolymerization both mechanistically and kinetically. It has also been utilized in an evaluation of the coordination chemistry of the polymerization process. This has led to some valuable conclusions about the nature and role of the metal center that previously have not been studied. Manganese(III) salen complexes were also synthesized and evaluated in an effort to compare these important ligands to other Schiff bases and confirm the findings mentioned above.