Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Gandida albicans strain 105 from a normal human and strain 582 (from the American type Culture Collection) were used for studying the effect in vitro of pH, various amounts of carbon dioxide, nitrogen, and composition of media on filamentation in this yeast-like organism. The yeast phase of the organism was maintained on a glucose, glycine, yeast extract (GGY) medium (1%; 1%; 0.5%) at 37°C. The experiments were conducted on both solid and liquid media. All cultures were incubated at 37°C. for 48 hours. The two strains of c. albicans, although similar to one another in their yeast forms, behaved differently toward the environmental conditions used; strain 582 responded more readily to the factors inducing filament formation than did strain 105. Increasing the pH above 6.5 to 7.0, 7.5 and 8.0 induced maximum filamentation in strain 582, whereas no filaments were produced by strain 105. All the aerobic cultures on solid GGY medium showed alkalinity and were positive for ammonia at the end of the incubation period. In liquid media, no alkalinity was observed at any pH values. Presence of 75% carbon dioxide in the atmosphere increased filamentation in strain 582 to a maximum degree, and induced mycelial formation in strain 105. With 94% or 95% carbon dioxide, growth and filamentation decreased in both strains. None of the CO2 cultures showed alkalinity at the end of the incubation period. Moreover, all the CO2 cultures were negative for ammonia. Growth under nitrogen (9J%) was less than that of the aerobic cultures. However, colonies appeared larger in size. Nitrogen stimulated filamentation in strain 105 only at a pH of 8.0, whereas strain 582 formed a maximum amount of filaments at pH values of 7.0 to 8.0. All the solid cultures under nitrogen showed alkalinity, while the liquid cultures were acid at all pH values. The occurrence of deamination in a medium without glucose in both strains of C. albicans showed that this organism was able to use glycine its source of both nitrogen and carbon. However, only a sparse growth was obtained in a medium lacking glucose. Strain 105 did not form filaments in such a medium, while strain 582 did so. Since more filaments were produced by the latter strain when a fresh subculture on a GGY medium was transferred to a medium without glucose, it was concluded that possibly glucose is required for both growth and filamentation. Comparative studies of the effect of a medium containing mannose with a glucose medium showed the two sugars behaved similarly with regard to fermentation and filament induction in both strains or c. albicans. Under conditions where glucose induced filamentation (e.g., with C02 or N2), mannose also induced filamentation. The decreased growth in the presence of oleic or stearic acid in a concentration of 40 micrograms per liter was attributed to the toxic effect of the fatty acids. Moreover, it was noted that the two acids had different effects on filamentation in the two strains. Oleic acid in a solid GGY medium induced hyphal formation in strain 105 only under nitrogen; without glucose, oleic acid did not bring about filamentation under any of the atmospheric conditions tested. In liquid media, oleic acid induced filamentation for strain 105 only when glucose was omitted. With strain 562, oleic acid promoted filamentation in both liquid and solid media with or without glucose, except for solid cultures incubated under nitrogen in the absence or glucose. Stearic acid did not stimulate filamentation in strain 105 under any conditions, but did increase hypha! formation in strain 582. In the presence of stearic acid, maximum filamentation occurred in aerobic cultures wnen glucose was absent. Although maximum filamentation occurred with an increase in the pH of the medium under aerobic conditions, in the presence of 75% C02, under nitrogen or in the presence of stearic acid in a medium without glucose, yeast cells were also present, indicating that this Y to f transformation was not complete. / 2999-01-01

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: See item for full text / AFRIKAANSE OPSOMMING: Sien item vir volteks

High atmospheric concentrations of CO2 contribute to adverse effects that impact human health and the climate. The need to reduce CO2 is evident, and climate stabilization will require a combination of mitigation, utilization, and even negative emission technologies. Thus, one key approach will be to transform abundant CO2 into a useful feedstock for processes that not only produce value-added products but also match the scale necessary to impact anthropogenic emissions. The tandem CO2 reduction and light alkane transformation reactions over specialized bifunctional catalysts have the potential to produce olefins or synthesis gas by efficiently utilizing the C2-C4 components in shale gas while reducing a greenhouse gas. The reactions of CO2 with light alkanes may occur through two distinct pathways, oxidative dehydrogenation (CO2 + CnH2n+2 → CnH2n + CO + H2O, CO2-ODH) and dry reforming (nCO2 + CnH2n+2 → 2nCO + (n+1)H2, DR). The two reactions can occur simultaneously at temperatures ≥823 K with considerable conversions. Until recently, there has been little understanding regarding the identification of bimetallic catalytic systems that either selectively cleave the C-H bonds to produce olefins or effectively break all the C-C and C-H bonds to produce dry reforming products. In this work, we discuss a combined approach of flow reactor experiments, in situ characterization, and density functional theory (DFT) calculations to help create a design platform for catalysts that are inherently active and selective for the reactions of CO2 and light alkanes. Particularly, it was of interest to use propane as CO2 reduction feedstock due to its increasing abundance and highly marketable respective olefin. Through the combined approach, non-precious Fe3Ni1 and precious Ni3Pt1 supported on CeO2 were identified as promising catalysts for the CO2-ODH and DR of propane, respectively. In situ X-ray absorption spectroscopy measurements revealed the oxidation states of metals under reaction conditions and DFT calculations were utilized to identify the most favorable reaction pathways over the two types of catalysts. While both the CO2-ODH and DR reactions of alkanes produce valuable molecules, the separation of gas phase products is challenging. Therefore, it was highly desirable to develop a tandem reaction scheme in which the reaction of CO2 and alkanes can produce liquid products. Another potential chemistry with increased similarity to the operating conditions of CO2-ODH, is the tandem reactions of CO2-assisted oxidative dehydrogenation and aromatization of light alkanes (CO2-ODA). In this process, alkanes are transformed directly into aromatics without the need for expensive naphtha while increasing the consumption of CO2 per mol of value-added product and facilitating downstream separation because of the production of liquid aromatics. One critical change upon the introduction of CO2 to the dehydrogenation/aromatization pathway is the formation of water. The presence of water under reaction conditions has been shown to be problematic for zeolites as it causes changes in the framework. Phosphorous modification at an optimal loading improved the hydrothermal stability of Ga/ZSM-5, reduced coke formation on the catalyst surface, and allowed for the formation of more liquid aromatics through the CO2-ODAE reaction pathway compared to the direct dehydrogenation and aromatization reaction. With the aid of DFT calculations, the mechanisms for the production of aromatics from ethane were identified, providing insight on the effect of Ga modification on ethylene formation over ZSM-5 as well as the role of CO2 on the aromatization of ethylene. Future efforts should be geared toward enhancing aromatics yield through the design of hydrothermal stable zeolite-based materials with bimetallic active centers that are capable of activating CO2.

Australia is recognising that carbon capture and storage (CCS) may be a feasible pathway for addressing increasing levels of CO2 emissions. This thesis presents a preliminary economic assessment and comparison of the capture costs for different Australian CO2 emission sources. The capture technologies evaluated include solvent absorption, pressure swing adsorption (PSA), gas separation membranes and low temperature separation. The capture cost estimated for hydrogen production, IGCC power plants and natural gas processing is less than A$30/tonne CO2 avoided. CO2 capture cost for iron production ranges from A$30 to A$40 per tonne CO2 avoided. Higher costs of A$40 to over A$80 per tonne CO2 avoided were estimated for flue gas streams from pulverised coal and NGCC power plants, oil refineries and cement facilities, and IDGCC synthesis gas. Based on 2004 and 2005 EU ETS carbon prices (A$30 to A$45 per tonne CO2 avoided), the cost of capture using current commercially available absorption technology may deter wide-scale implementation of CCS, in particular for combustion processes. A sensitivity analysis was undertaken to explore the opportunities for reducing costs. The high cost for capture using solvent absorption is dependent on the energy needed for solvent regeneration and the high capital costs. Cost reductions can be achieved by using new low regeneration energy solvents coupled with recycling the waste heat from the absorption process back to the steam cycle, and using low cost ???fit-for-purpose??? equipment. For membrane and PSA technologies, the capture costs are dominated by the flue gas and post-capture compressors. Operating the permeate or desorption stream under vacuum conditions provides significant cost reductions. Improvements in membrane and adsorbent characteristics such as the adsorbent loading or membrane permeability, CO2 selectivity, and lower prices for the membrane or adsorbent material provide further cost benefits. For low partial pressure CO2 streams, capture using low temperature ???anti-sublimation??? separation can be an alternative option. Low costs could be achieved by operating under low pressures and integrating with external sources of waste heat. Applying the cost reductions achievable with technology and process improvements reduces the capture and CCS costs to a level less than current carbon prices, making CCS an attractive mitigation option.

This project aims at investigating the effect of CO2 enrichment on the growth and gas exchange of C3, C3-C4 and C4 Panicum grasses. Potted plants were grown in soil under well watered conditions, in artificially lit environmentally controlled cabinets or naturally lit greenhouses at varying levels of CO2 enrichment. CO2 enrichment enhanced the dry weight of C3 and C4 Panicum species under optimal light and N supplies, but had no effect on the total leaf N or TNC concentrations. The high-CO2 induced photosynthetic reaction in the C3 species was accompanied by a reduced Rubisco concentration and was related to the conservation of the relative growth rate of the plant. Elevated CO2 had no effect on the photosynthetic capacity of the C4 species, but enhanced its CO2 assimilation rates under high light and N supplies. The effect of elevated CO2 on the leaf and stem anatomy reflected increased carbon supply at high CO2 in the C3 grass, and reduced transpiratory demand at high CO2 in C4 grasses. Consequently, it is clear that both C3 and C4 grasses are likely to be more productive under rising atmospheric CO2 concentrations. / Doctor of Philosophy (PhD)

We have successfully investigated the use of CO2 as a miscibility switch to create an environment in which we can run a homogeneously catalyzed reaction while maintaining a heterogeneous separation. We explored the use of this technique with fluorous biphasic systems, a fluorous solid support, and aqueous biphasic systems. In the case of the fluorous systems, CO2 was added to induce solubility of the fluorous catalyst. When the reaction was completed, CO2 was vented and the system returned to a biphasic state, making the separation easy. For the aqueous biphasic systems, the organic phase is chosen such that it is fully miscible with water at ambient conditions. Examples include acetonitrile, THF, and dioxane. The addition of CO2 reduces the polarity of the solvent and causes a phase split. The recovery of the water-soluble catalyst is once again heterogeneous. The application to aqueous biphasic systems is the most exciting studied. Aqueous biphasic systems are used industrially in the hydroformylation of propylene. With our technique, these systems can be extended to more hydrophobic substrates. We have shown a rate increase of 65 fold and 99% product recovery at modest pressures for the hydroformylation of 1-octene. These aqueous biphasic systems also show much promise in the arena of enzyme catalyzed reactions. We can create an environment in which the enzyme kinetics will no longer be mass transfer limited.

No description available.

No description available.

Climate change has exacerbated environmental degradation processes, causing an imbalance in the natural concentrations in atmospheric greenhouse gases. This has resulted in a myriad of socio–economic effects which have focused global attention on methodologies to reduce these effects, such as carbon sequestration. To achieve long term sustainability and success, community involvement in the technical and social aspects of carbon sequestration projects is necessary and must be acknowledged. One such mitigation methodology which incorporates the ideals of community proactive participation is carbon sink reforestation projects. This study is based on a community perspective of a carbon sink reforestation project, carried out in KwaZulu-Natal, South Africa. The study provides a holistic perspective of the concept of carbon sequestration drawing together technical aspects of carbon sequestration reforestation projects and the inclusion of the role of communities. The methodology comprised of questionnaires with industry experts and a local community, following a thematic data analysis. The current perception from industry is that the South African government lacks significant technology, capacity and finance to effectively manage national forest carbon sequestration regimes. Project participants expressed the view that these types of projects provided a sense of belonging and hope and articulated their gratitude for the environmental knowledge they gained from the project experience. Technical and social aspects of such projects such as carbon calculations and participatory rural appraisal techniques enhance a country’s ability for successful implementation of such projects. Findings reveal a need for technology, capacity building and finance; and the effects participation in these projects has on individuals. This is followed by recommendations and a ‘How To Guide’ developed by the researcher. This guide intends to enhance the collaboration of the technical aspects and involvement of communities throughout the project implementation process. Carbon regimes in this century will continue to grow in size and complexity. Stakeholder participation will be a strong factor in the success or failure of carbon sequestration reforestation projects. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Abstract available in pdf file.