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The purpose of the investigation was the design and development of an oxygen carrier system for oxygenation of liver cells (hepatocytes) in a bio-artificial liver support system. Acute liver failure is a devastating condition with higher than 80% mortality. Currently the only successful treatment is orthotopic liver transplantation. The high mortality rate could be reduced if a system could be developed that could bridge the patient either until recovery (due to the liver’s well-known regeneration ability) or until transplantation. Such a system requires a bioreactor with a high density of cultured cells. Sufficient oxygen delivery to the cells is critical to ensure efficient cell function. The CSIR and University of Pretoria (UP) have designed and developed a novel bio-artificial liver support system (BALSS) that utilizes perfluorooctyl bromide (PFOB) as artificial oxygen carrier. As the PFOB is not miscible with water, it needs to be emulsified. To enable the use of the PFOB emulsion in the UP-CSIR BALSS, a study was carried out to investigate relevant aspects relating to the PFOB emulsion, i.e. the formulation, manufacturing procedure, stability, rheology and mass transfer characteristics. The study results are reported in this dissertation, including a proposed mass transfer model for describing oxygen mass transfer to and from the PFOB emulsions. Emulsion stability can be improved through control of the droplet size and size distribution, limiting Ostwald ripening, and control of zeta potential of the dispersed phase droplets. PFOB emulsions with dispersed phase (PFOB) volume fractions between 0.4 and 0.5 and Sauter mean droplet diameter between 100 and 200 nm were found to be optimal for oxygen mass transfer in cell culture systems. The PFOB emulsion in the UP-CSIR BALSS can be concentrated and recirculated using ultrafiltration. Quantitative recovery of PFOB from its emulsions can be carried out using distillation with orthophosphoric acid. Experimental overall mass transfer coefficients for membrane oxygenators obtained without PFOB compared well with literature reported values of 2.5x10-5 m/s by Goerke et al. (2002) and 1 – 3x10-5 m/s by Schneider et al. (1995) for similar systems. The addition of 0.2 v/v PFOB leads to an increase in the membrane oxygenator mass transfer coefficient by a factor of about 30, and an increase in oxygen carrying capacity by a factor of about 4.5. It was also shown that suitable PFOB emulsions can have a significant impact on the growth and function of hepatocytes in a BALSS. / Thesis (PhD (Chemical Engineering))--University of Pretoria, 2005. / Chemical Engineering / unrestricted

Traditional chemical looping technologies utilize solid oxygen carriers and has some disadvantages, especially when solid fuels like coal are used. In this work, a novel chemical looping process using gaseous metal oxide as oxygen carrier was proposed. The reaction of activated charcoal with gas-phase MoO3 was studied for the first time. The experiments were conducted isothermally at different temperatures in a fixed-bed reactor. The apparent activation energy of the reaction was calculated and suitable kinetic models were determined. The results and analysis showed that the proposed concept has potential in both coal chemical looping combustion and gasification process. To further investigate the mechanism of carbon oxidation by gas-phase MoO3, the adsorption of a gaseous (MoO3)3 cluster on a graphene ribbon and subsequent generation of COx was studied by density functional theory (DFT) method and compared with experimental results. The (MoO3)n -graphene complexes show interesting magnetic properties and potentials for nanodevices. A comprehensive analysis of plausible reaction mechanisms of CO and CO2 generation was conducted. Multiple routes to CO and CO2 formation were identified. The (MoO3)3 cluster shows negative catalytic effect for CO formation but does not increase the energy barrier for CO2 formation, indicating CO2 is the primary product. Mechanism of the homogenous MoO3 - CO reaction was studied and showed relatively low energy barriers. The DFT result accounts for key experimental observations of activation energy and product selectivity. The combined theoretical and experimental approach contributes to the understanding of the mechanism of reactions between carbon and metal oxide clusters. To gain a better understanding of the MoO2 oxidation process, the adsorption and dissociation of O2 on MoO2 surface were studied by DFT method. The results show that O2 molecules prefer to be adsorbed on the five-coordinated Mo top sites. Density of states analysis shows strong hybridization of Mo 4d orbitals and O 2p orbitals in the Mo-O bond. Clean MoO2 slab and slabs with O2 adsorption are metallic conductors, while the surface with high O atom coverage is reconstructed and becomes a semiconductor. Surface Mo atoms without adsorbed O or O2 are spin-polarized. The oxygen adsorption shows ability to reduce the spin of surface Mo atoms. The adsorption energy of O2 and O atoms decreases as coverage increases. The transition states of O2 dissociation were located. The energy barriers for O2 dissociation on five-coordinated and four-coordinated Mo top sites are 0.227 eV and 0.281 eV, respectively.

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Made available in DSpace on 2014-12-17T15:41:57Z (GMT). No. of bitstreams: 1 VitorRMM_DISSERT.pdf: 2544703 bytes, checksum: 4453e8b3e10e994e669daf77efdaa72b (MD5) Previous issue date: 2012-08-04 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Perovskites oxides win importance by its properties and commercials applications, they have a high thermal stability, have conductive properties, electrical, catalytic, electro catalytic, optical and magnetic, and are thermally stable. Because of these properties, are being widely studied as carriers of oxygen in the process of power generation with CO2 capture. In this work, the base carrier system La1-xMexNiO3 (Me = Ca and Sr) were synthesized by the method via the combustion reaction assisted by microwave. were synthesized from the combustion reaction method by microwave process. This method control the synthesi`s conditions to obtain materials with specific characteristics. The carriers calcined at 800 ? C/2h were analyzed by thermal analysis (TG-DTA), to verify its thermal stability, X-ray diffraction (XRD) to verify the phase formation, with subsequent refinement by the Rietveld method, to quantify the percentage of phases formed, the surface area by BET method was determined, scanning electron microscopy (SEM) was obtained to evaluate the material morphology and temperature programmed reduction (TPR) was done to observe the metallic phase of the nickel. After all proposed characterization and analysis of their results can be inferred to these oxides, key features so that they can be applied as carriers for combustion reactions in chemical cycles. The final products showed perovskite-type structures K2NiF4 (main) and ABO3. / ?xidos com estrutura tipo perovsquita destacam-se por suas diversas propriedades e aplica??es comerciais, pois possuem alta estabilidade t?rmica, apresentam propriedades condutoras, el?tricas, catal?ticas, eletrocatal?ticas, ?pticas e magn?ticas, al?m de serem termicamente est?veis. Devido a estas propriedades, est?o sendo amplamente estudados como carreadores de oxig?nio em processos de gera??o de energia com captura de CO2. Neste trabalho, carreadores a base do sistema La1-xMexNiO3 ( Me = Ca e Sr) foram sintetizados a partir do m?todo via rea??o de combust?o assistida por microondas. Este m?todo controla as condi??es de s?ntese para obten??o de materiais com caracter?sticas espec?ficas. Os carreadores calcinados a 800?C/2h foram analisados atrav?s de an?lise t?rmica (TG-DTA), para verifica??o de sua estabilidade t?rmica; difra??o de raios-X (DRX), para verifica??o das fases formadas, com posterior refinamento atrav?s do m?todo de Rietveld, para quantificar o percentual das fases formadas; ?rea superficial pelo m?todo BET; microscopia eletr?nica de varredura (MEV) e redu??o ? temperatura programada (TPR). Ap?s toda caracteriza??o proposta e an?lise dos seus resultados pode-se inferir a esses ?xidos, caracter?sticas fundamentais para que os mesmos possam ser aplicados como carreadores em rea??es de combust?o por ciclos qu?micos. Os carreadores de oxig?nio obtidos possuem estruturas perovsquitas do tipo K2NiF4 (principal) e ABO3.

Chemical looping combustion (CLC) is a technique for separating pure carbon dioxide from the combustion of fuels. The oxygen to burn the fuel comes from the lattice oxygen contained in solid particles of an inorganic oxide (the 'oxygen carrier'), instead of from oxygen in the air. Thus only CO2 and water leave the combustor, or fuel reactor. Next, the water is condensed, leaving pure CO2. The oxygen carrier is regenerated by oxidising it in air in a second reactor, called the air reactor. Accordingly, a stream of pure carbon dioxide can be produced, uncontaminated with gases such as nitrogen, normally present when the fuel burns in air. This intrinsic separation with CLC enables CO2 to be separated more efficiently than with other techniques, such as post-combustion scrubbing of carbon dioxide from stack gases with amine-based solvents. The design of a CLC system and its performance within an electricity system represents a multi-scale problem, ranging from the behaviour of single particles of oxygen carrier within a reactor to how a CLC-based power plant would perform in an electricity grid. To date, these scales have been studied in isolation, with little regard for the vital interactions and dependences amongst them. This Dissertation addresses this problem by considering CLC holistically for the first time, using a multi-scale approach. A stochastic model was developed, combining the particle-and reactor-scales of CLC. It included an appropriate particle model and can be coupled to a detailed reactor model. The combination represented a significant change from existing approaches, uniquely accounting for all the important factors affecting the assemblage of particles performing in the CLC reactors. It was used to determine the regimes of operation in which CLC is sensitive to factors such as the manner in which the particles are reacting, the residence time distribution of particles in the two reactors, the particle size distribution and the reaction history of particles. To demonstrate that the approach could simulate specific configurations of CLC, as well as a general system, the model was compared with results from experiments in which CLC with methane was conducted in a laboratory-scale circulating fluidised bed. The long-term performance of oxygen carrier materials is important, because, in an industrial process, they would be expected to function satisfactorily for many thousands of hours of operation. Long-term experiments were conducted to evaluate the resistance of different oxygen carrier materials to physical and chemical attrition. The evolution of their chemical kinetics was also determined. The results were used to evaluate the impact of different oxygen carrier materials in a fuel reactor at industrial-scale. Finally, a theoretical approach was developed to simulate how a fleet of CLC-based power plants would perform within the UK's national grid. By understanding how different parameters such as capital cost, operating cost and measures of efficiency, compared with other methods of generation offering carbon reduction, desirable design modifications and needs for improvement for CLC were identified by utilising the theoretical and experimental work conducted at the particle- and reactor-scales.

According to IPCC reports, the greenhouse gas CO2 is responsible for global climate change. Studies show that CO2 concentration reached a level of 400 ppm in 2013, or 40 % above pre-industrial levels. The contribution of CO2 from industrial activity to increasing global CO2 concentrations is widely accepted and points to the need to reduce the emission of this greenhouse gas.One possible combustion technology that shows promise for reducing CO2 emissions is chemical looping combustion (CLC). It is an oxy-fuel technology, but has the advantages of in situ oxygen separation, low NOx emissions and low cost of CO2 emission abatement; it entails the use of an oxygen carrier (OC) to provide oxygen for combusting fuels. OC development is an important task in CLC. Iron based OCs have attracted most research attention in recent years, mainly due to their inexpensive and non-toxic nature. Bi-metal oxide OCs usually impart better CLC performance than mono-metal oxide OCs, one example of which is the introduction of CeO2 as a partially reducible material capable of generating oxygen vacancies that lead to oxygen storage and transfer. In this study, CeO2 was used as an additive to a Fe2O3-based OC and its effect on physical properties, such as morphology, surface area and mechanical strength, was analyzed in detail. The reactivity of OCs is studied using TGA-MS and a bench scale CLC setup. The results show that the reduction reaction at the surface is independent of whether CeO2 is present or not, but after the surface oxygen had been consumed, the OC with CeO2 provided faster oxygen transfer rates from the bulk to the surface to produce better average reaction rates. The OCs after reduction and oxidation were analyzed using XRD and Raman spectroscopy; based on these analytical data, a model for the promoting role of CeO2 is discussed. Furthermore, the reaction kinetics of the OCs were also studied using shrinking core model, the kinetics parameters were obtained and compared. Scale-up of laboratory-scale CLC reactors is another important task necessary to develop an understanding of the potential and efficiencies of CLC. In this study, scaling laws were used as a guide to design and then build two different-sized CLC reactors. Testing of the reactors involved a focus on chemical similarities. Comparisons of the performance of both reactors showed good consistency, thereby validating the scale modeling method and the scale laws for CLC reactors.

Background: Previously, we had shown that elevation of cerebral perfusion pressure, using pressors, improved short-term outcomes after traumatic brain injury and hemorrhagic shock in swine. The current study evaluates outcomes after resuscitation with diaspirin cross-linked hemoglobin (DCLHb)-a hemoglobin-based oxygen carrier with pressor activity-in the same swine model of traumatic brain injury and hemorrhagic shock. Methods: Anesthetized and ventilated swine received traumatic brain injury via cortical fluid percussion (6-8 atm) followed by 45% blood volume hemorrhage. One hour later, animals were randomized to either a control group (SAL) resuscitated with normal saline equal to three times shed blood volume or to one of two experimental groups resuscitated with DCLHb. The two experimental groups consisted of a low-dose group, resuscitated with 250 mL of DCLHb (Hb1), and a high-dose group, resuscitated with 500 mL of DCLHb (Hb2). Animals were observed for 210 minutes postresuscitation. Outcomes evaluated were cerebral oxygenation by measuring partial pressure and saturation of oxygen in cerebrovenous blood; cerebral function by evaluating the preservation and magnitude of cerebrovascular carbon dioxide reactivity; and brain structural damage by semiquantitatively assessing beta amyloid precursor protein positive axons. Results: Postresuscitation, cerebral perfusion pressure was higher in the DCLHb groups (p < 0.05, Hb1 and Hb2 vs. SAL), and intracranial pressure was lower in the Hb2 group (p < 0.05 vs. SAL). Cerebrovenous oxygen level was similar in all groups (p > 0.05). At baseline, 5% carbon dioxide evoked a 16 ± 1% increase in cerebrovenous oxygen saturation, indicating vasodilatation. At 210 minutes, this response was nearly absent in SAL (4 ± 4%) (p < 0.05 vs. baseline) and Hb1 (1 ± 5%), but was partially preserved in Hb2 (9 ± 5%). There was no intergroup difference in beta amyloid precursor protein positive axons. Five of 20 SAL and 0 of 13 DCLHb animals developed brain death (flat electroencephalogram) (p = 0.05, SAL vs. DCLhb). Postresuscitation, DCLHb animals maintained higher mean pulmonary arterial pressure (28 ± 1 mm Hg, SAL; 42 ± mm Hg, Hb1; 45 ± 1 mm Hg, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL) and lower cardiac output (3.9 ± 1.6 L/min, SAL; 2.6 ± 0.1 L/min, Hb1; 2.7 ± 0.1 L/min, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL). Three Hb2 animals died as a result of cardiac failure, and one SAL animal died as a result of irreversible shock. Conclusion: In this swine model of traumatic brain injury and hemorrhagic shock, resuscitation with DCLHb maintained a higher cerebral perfusion pressure. Low-dose DCLHb (minimal increase in oxygen carriage) failed to significantly improve short-term outcome. With high-dose DCLHb (significant improvement in oxygen carriage), intracranial pressure was lower and cerebrovascular carbon dioxide reactivity was partially preserved; however, this was at the cost of poorer cardiac performance secondary to high afterload.

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