Carbon dioxide emissions per year have risen exponentially. It is widely known the contribution of CO2 to global warming phenomena, so storage/utilisation of carbon dioxide has become a topical issue and an emerging research area. Despite the fact that utilization of CO2 waste would not solve the problem of the huge quantities going to the atmosphere every year as only less than 1% of it could be reused for the industry, recycled carbon dioxide presents itself as a possible cheap and accessible chemical feedstock. The challenge on recycling CO2 is to minimize energy and cost efficiency of any suitable reaction. On previous investigations the electrochemical synthesis of 5-membered cyclic carbonate from epoxides was accomplished under mild conditions and optimized (1 atm CO2 pressure, 60 mA constant current and 50 °C heating). In order to understand the mechanism of this electrochemical process a deep investigation on the variables of the synthesis of cyclic carbonates was carried out and is presented in this thesis. The variables studied include electrochemical system conditions (application of current through Cu/Mg electrodes, electrodes connected on a closed circuit system with no current, an open circuit system where electrodes were there was no connection between them, and reactions without electrodes), temperature of reaction, solvent screening, catalysts, epoxide substituents, concentration of species and ratio of reactants. As a result of the variables optimization, a new, cheap, simple and relatively fast method (5 to 24 hours of reaction time) for cyclic carboxylation of epoxides with CO2 at atmospheric pressure in acetonitrile in the presence of ammonium salt (TBAI) at mild temperatures (50-75 °C) has been developed and improved. The concentration of the reactants, especially of the epoxide, was found to be the most important factor on the success of the reaction. The new reaction conditions also allow converting epoxides to carbonates without the help of any cocatalyst or electrochemical system obtaining excellent yields (50-100%) with the important saving on cost and energy of co-catalyst synthesis and recovery. Chlorostyrene oxide (1 M) reacted almost completely (94%) after 24 hours with TBAI (1 M), in 1 mL of acetonitrile at 75 °C and 1 atm pressure of CO2. Epoxide carboxylation under neat conditions was feasible, producing 44% of chlorostyrene carbonate from chlorostyrene oxide in the presence of TBAI at 75 °C and 1 atm pressure of CO2.

This research work presents the thermodynamic analysis of hydrogen production using steam methane reforming process at different conditions. The model is developed using HSC 4.1 software and spreadsheet. Methane is chosen to represent the carbonaceous fuel and steam methane reforming process (once through and cyclic) for hydrogen production is analyzed based on 1st law and 2nd law of thermodynamics i.e., energetic and exergetic efficiencies. The mass, energy and exergy analysis of each step is done. The optimal condition for production of maximum hydrogen is found using CO2 removal agent and O2 transfer compound. The efficiency is calculated as a function of steam content, temperature and amount of CO2 removal agent and O2 transfer compound. The pressure is kept constant at one atmosphere. Operating temperature, CaO loading, Fe2O3 loading and H2O content is determined from the once through process. It is found that the maximum H2 production is with the cyclic process. Maximum H2 produced in cyclic process with CaO & Fe2O3 loadings is 99.2%. Also CO2 content is comparatively lower in cyclic process. Theoretical efficiencies can be used to compare with the available data which will help to minimize the losses in the process. The results can be used as a baseline for the design of H2 production technology. The main aim of this research is to develop a thermodynamic protocol for evaluating hydrogen production processes.

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-12-08Bitstream added on 2014-06-13T18:40:02Z : No. of bitstreams: 1 arceferrufino_gla_me_guara.pdf: 1056072 bytes, checksum: 1cac7a1cd9ce6c0468bceb4898770311 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O dióxido de carbono (CO2) é um importante gás de efeito estufa. No entanto, um aumento gradual ameaça substancialmente o clima. Um dos principais desafios do planejamento ambiental é identificar um modelo que vincule todos os fatores do ciclo de carbono, ou seja, oceano – ecossistema terrestre – emissão antropogênica – atmosfera. Princípios básicos de Termodinâmica podem ser aplicados em uma modelagem estatística com bases em séries históricas para obter concentrações de CO2 na atmosfera, possibilitando a construção de cenários para uma melhor tomada de decisões. Por este motivo, foi desenvolvido no trabalho um modelo que interliga todos os fatores do ciclo de carbono, focalizando em quatro zonas térmicas ou climáticas (Boreal, Temperada, Tropical, Polar), para cálculos de armazenamento de CO2 atmosférico. Os resultados mostram que no ano 2100 se atingirá uma concentração de CO2 quatro vezes maior do que antes do período pré-industrial. A zona temperada emite quase a metade de dióxido de carbono à atmosfera na atualidade; para o ano 2100, essa emissão aumentará a quinze vezes mais que a zona tropical. A China será responsável em uma proporção de vinte quatro a onze com relação aos Estados Unidos. A estabilização das concentrações de CO2 na atmosfera será obtida quando as emissões de dióxido de carbono antropogênico tiverem uma diminuição de mais do que trinta e quatro por cento para o ano 2100 na zona temperada. / Carbon dioxide (CO2) is the most important greenhouse gas. A gradual increase on its atmospheric concentration threatens significantly the climate. One of the main challenges of environment planning is to identify a model that connects all factors that determine the carbon cycle, that is, ocean – terrestrial ecosystem – anthropogenic emissions – atmosphere. Basic thermodynamic principles can be applied in a statistical modeling with historic time series to obtain atmospheric CO2 concentration, creating the possibility of construction of scenarios that will help decision making. A model that links all carbon cycle factors was developed in this dissertation work, focusing in four thermal of climatic zones (Boreal, Temperate, Tropical, and Polar) for calculations of atmospheric CO2 storage. Results show that in 2100, the atmospheric CO2 concentration will reach a value four times higher than that of the pre-industrial period. The temperate zone already emits almost half of the carbon dioxide to the atmosphere; by 2100, this emission will increase 15 times more than that corresponding to the tropical zone. China will be responsible for emissions in a proportion of 24 to 11 in comparison to that of the United States. Stabilization of CO2 concentrations in the atmosphere will be obtained when the anthropogenic carbon dioxide emissions attain a decrease of at least 34% in 2100 in the temperate zone.

Made available in DSpace on 2018-08-01T21:58:47Z (GMT). No. of bitstreams: 1 tese_10597_Dissertação Tamires FINAL 08042017.pdf: 3045708 bytes, checksum: 346790de110160baf3a5382b4013c028 (MD5) Previous issue date: 2017-02-20 / O petróleo ainda continua sendo a maior fonte de energia não renovável do planeta. No seu estado bruto tem pouca utilidade. No entanto, seus derivados apresentam alto valor econômico. Nas etapas de processamento primário do petróleo alguns compostos de ocorrência natural são indesejáveis, como os ácidos naftênicos, resinas, asfaltenos, compostos sulfurados e metálicos. O poder corrosivo dos ácidos naftênicos preocupa as indústrias petrolíferas devido ao prejuízo causado nas tubulações e refinarias. Estudos recentes indicam que uma parcela desses ácidos quando submetidos a elevadas temperaturas (>280°C) pode sofrer reações de descarboxilação e degradação térmica, originando dióxido de carbono (CO2) e ácidos de cadeias menores como produtos de degradação. Os ácidos de cadeias menores juntamente com os ácidos naftênicos que se mantiveram preservados são corrosivos e o CO2 ao entrar em contato com água forma o ácido carbônico (H2CO3), podendo contribuir nas taxas de corrosão nos equipamentos do refino. Assim, o presente trabalho consistiu no desenvolvimento de uma metodologia para quantificação online do CO2 liberado no processo de destilação de petróleo. A metodologia desenvolvida foi baseada na técnica de microcromatografia gasosa. Os dados quantitativos de concentração de CO2 gerados pela microcromatografia foram relacionados com os valores de temperaturas de destilação, obtendo-se assim uma variação na concentração de CO2 de acordo com a temperatura de destilação do óleo. Com os resultados obtidos observou-se que para todos os petróleos destilados houve uma tendência na formação do gás CO2 partir de temperaturas superiores a 200°C. Na tentativa de elucidar a possível origem deste gás, supôs um mecanismo de descarboxilação para tais ácidos

The work undertaken involved the exploration of CO2 electroreduction systems, focussing heavily upon electrocatalysis utilising an array of electrochemical, spectroelectrochemical and spectroscopic techniques. The identification and characterisation of a relatively inexpensive and simple electrocatalyst for CO2 reduction was achieved, with the optimisation and development undertaken in such a manner that not just the electrocatalytic species, but also the entire electrochemical system was investigated, in order to determine and better understand the roles played by the various components. The complex of interest, Mo(CO)4bpy, represents the first molybdenum based molecular electrocatalyst reported to be active toward CO2 reduction, despite the prominence of Mo in enzymes with analogous function. The electrochemical characterisation of the complex in the both the presence and absence of CO2 was undertaken, yielding valuable information on the redox behaviour of the complex within the non-aqueous system in which it was employed and highlighting previously unreported features such as a third reduction and new reoxidation attributed to the reoxidation of a tricarbonyl anionic species. Non-aqueous solvents were chosen as they provide greater CO2 solubility than water with portions of the investigation undertaken in tetrahydrofuran, THF, then moving to the less widely used N-methylpyrrolidone, NMP. NMP is significantly less volatile than THF and has a large negative electrochemical window so is ideal for looking at reduction processes and, importantly, is also used as a commercial CO2 scrubbing solvent. Upon addition of CO2 to the Mo(CO)4bpy system there was an observable lowering of the overpotential by over 300 mV, and significant increase in CO2 associated current when compared to that for ‘direct’ CO2 reduction within the same system, at the reduction potential associated with the first reduction of the tetracarbonyl bipyridyl species. The confirmation of the anionic radical as the active species was attained through DFT calculation and EPR spectroelectrochemistry. Under inert gas the spectrum rapidly generated upon application of the first reduction potential is consistent with the expected response for the radical anionic [Mo(CO)4bpy] •−. When the system is saturated with CO2 this radical is no longer detectable. This supports the idea that the unpaired electron is transferred from the [Mo(CO)4bpy]•− to the CO2 molecule and also suggests that this transfer is rapid as no adduct is detectable via EPR even at reduced temperature (240 K). This is in keeping with the rate constants calculated from the voltammetric measurements made. The stability and activity toward CO2 reduction exhibited by Mo(CO)4bpy displayed a strong dependence on working electrode material, with gold proving optimal, indicative of adsorption being significant in the process. Optimisation of both the catalyst structure and the solvent and electrolyte system were also explored, as well as the (somewhat less directly related) comparison of various sources of diffusivity data.

No description available.

Previous studies on dwarf bean plants have found a very limited growth response to CO₂ enrichment (Jolliffe and Ehret, 1985; Ehret and Jolliffe, 1985b). There was no increase in leaf area, and leaf injury was observed after about three weeks of CO₂ enrichment (Ehret and Jolliffe, 1985a). Although dry weight was increased, the increase may be limited due to restricted carbon utilization (e.g. no increases in leaf area). In this study, non-photosynthetic limitations, such as the partitioning of dry matter among plant parts, the partitioning of carbon among photosynthetic end products, and the interactive effects of nutrient and carbon supply on growth, that may contribute to the observed growth responses were investigated. Bean plants responded to CO₂ enrichment by increasing their total dry weights. This weight increase was caused by higher growth rate, at least at early growth stages, and higher unit leaf rate. The dry weight increase was mainly in the leaves, and was not evenly distributed among all plant parts. Leaf expansion and branching were not enhanced by CO₂ enrichment. The differential effects of CO₂ enrichment on growth of different parts caused significant increases in specific leaf weight and shoot root ratio, and a decrease in leaf area ratio. These results indicated that the bean plants used in this study have a limited ability to utilize the extra carbon that was fixed under CO₂ enrichment. There were small increases in glucose, fructose, and sucrose concentrations early in the CO₂ treatments. These increases became much larger after three weeks of CO₂ enrichment. The timing of the higher increases in leaf soluble sugars coincided with the timing of increases in stem and roots dry weight. There was also a large increase in starch concentration shortly after plants were transfered to CO₂ enriched condition. The higher starch concentration accounted for the majority of the weight increase in CO₂ enriched leaves, and this starch level was maintained for several days after plants were switched back to ambient CO₂ levels. A ¹⁴C study on the partitioning of carbon between leaf pools showed that carbon transfer out of the storage pool under CO₂ enrichment was limited. CO₂ enrichment had no effects on leaf protein and amino acid concentrations. No difference, or slight increases, were found in inorganic nutrient concentrations per unit leaf area. Plants grown under CO₂ enrichment, however, show a higher loss of nutrients (especially N and K) from older shoot parts (primary leaves and older trifoliates) to younger parts. High NO₃ ̄ supply increased plant dry weight and leaf area under both CO₂ enriched and ambient conditions. The dry weight increases of the stem and roots caused by CO₂ enrichment, however, were much higher and earlier for high NO₃ ̄treated plants. Furthermore, lower leaf starch concentration was also observed for those CO₂ enriched high NO₃ ̄ treated plants. High NO₃ ̄ supply also increased the leaf nutrient concentrations (N, K, Mg, Ca). Increased uptake of nutrients for high NO₃ ̄ treated plants may be partly contributed by the enhanced root growth. In addition to the growth responses, foliar abnormalities developed gradually in beans under CO₂ enrichment. Chlorosis, assessed by a loss in total chlorophyll concentration, was observed in the primary leaves after about three weeks of CO₂ enrichment. The disorder eventually appeared in the oldest trifoliate leaves after more prolonged CO₂ enrichment. The onset of leaf injury was correlated with the timing of the increases in leaf soluble sugars and the redistribution of nutrient elements from the older shoot parts to the younger parts. High NO₃ ̄ supply delayed the development of leaf injury induced by high CO₂. Results in the present studies indicate that growth responses of dwarf bean plants to CO₂ enrichment were affected by the limited carbon partitioning, and the restriction of starch degradation was indicated to be the probable cause. A higher carbon input under CO₂ enrichment may create a higher demand for inorganic elements. Effects of nutrient supply (NO₃ ̄) on growth responses and leaf injury of CO₂ enriched plants suggested that an imbalance between carbon and nutrient input could be partly related to the limited growth responses of dwarf bean plants to CO₂ enrichment. / Land and Food Systems, Faculty of / Graduate

No description available.

This thesis work focused on polymer modification of silicon surface to improve its resistance to protein adsorption. Surface modification was achieved through surface-initiated atom transfer radical polymerization (SI-ATRP) grafting of poly(N,N-dimethyl amino) ethyl methacrylate (PDMAEMA). Since PDMAEMA is CO2-responsive, CO2 cleaning of the modified surface was also investigated. SI-ATRP was chosen to graft PDMAEMA brushes on silicon surface for high graft densities and its good control of polymer molecular weight and polydispersity. Surface characterization of PDMAEMA-modified silicon surfaces included hydrophilicity, layer thickness and surface chemical elemental composition. Protein adsorption experiments were carried out to evaluate the protein resistance of the modified surfaces. Albumin adsorption from single protein solution, as well as from human plasma, decreased significantly after PDMAEMA grafting, and the adsorbed amount decreased with increasing polymer chain length. The maximum decrease in adsorption of 90% relative to the unmodified silicon, was reached at a graft layer thickness of 40 nm (measured in the dry state). Protein resistance in plasma showed PDMAEMA -modified silicon provided significant resistance to most of the tested proteins. Compared to the PEO-modified surface, the PDMAEMA surface showed much greater resistance to albumin adsorption, but, surprisingly, it adsorbed relatively large amounts of vitronectin and prothrombin. Vitronectin may have been degraded in contact with PDMAEMA-modified surface. Also, it was the only surface out of the four, which adsorbed significant amounts of prothrombin. These unexpected observations indicate further investigation will be required to fully assess the protein-resistant properties of these PDMAEMA surfaces. CO2-induced protein desorption was also studied. Cleaning experiments were performed by bubbling CO2 into vials containing the protein-adsorbed PDMAEMA-modified surface after 2 h protein solution exposure. Radiolabelling of albumin showed that the CO2 cleaning effectiveness was related with the PDMAEMA thickness. It was found that a surface with graft thickness 20 nm (dry) responded more strongly to CO2 than one with 15 nm thickness. Western blotting results confirmed that CO2 contributed to protein desorption from the PDMAEMA surface. / Thesis / Master of Applied Science (MASc)

No description available.