A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. 10 February, 2017. / Climate change due to the ever-increasing emission of anthropogenic greenhouse gases arising from the use of fossil fuels for power generation and most industrial processes is now a global challenge. It is therefore imperative to develop strategies or modern technologies that could mitigate the effect of global warming due to the emission of CO2. Carbon capture and storage (CCS) is a viable option that could ensure the sustainable use of cheap fossil fuels for energy generation with less CO2 emission. Amongst existing CCS technologies, absorption technology using monoethanolamine (MEA) is very mature and widely embraced globally. However, the absorption technology has a lot of challenges such as, low CO2 loading, high energy requirement for solvent regeneration, corrosive nature etc. On this note, the adsorption technology using solid sorbents is being considered for CO2 capture due to its competitive advantages such as flexibility, low energy requirement for sorbent regeneration, non-corrosive nature etc. On the other hand, adsorbents have a very vital role to play in adsorption technology and there is need to understand the behaviour of adsorbents for CO2 capture under different operating conditions in order to adapt them for wider applications. On this note, the study contained in this dissertation investigated the adsorption behaviour of a novel polymer-based adsorbent (polyaspartamide) during post-combustion CO2 capture using experimental study and mathematical modelling approach. Polyaspartamide is an amine-rich polymer widely used in drug delivery. In addition, its rich amine content increases its affinity for CO2. Its porosity, thermal stability and large surface area make it a promising material for CO2 capture. In view of this, polyaspartamide was used as the adsorbent for post-combustion CO2 capture in this study. This dissertation investigated the kinetic behaviour, the diffusion mechanism and rate limiting steps (mass transfer limitation) controlling the CO2 adsorption behaviour of this adsorbent. Furthermore, effect of impurities such as moisture and other operating variables such as temperature, pressure, inlet gas flow rate etc. on the CO2 adsorption behaviour of polyaspartamide was also investigated. Existing mathematical models were used to understand the kinetics and diffusion limitation of this adsorbent during CO2 capture. Popularly used gas-solid adsorption models namely; Bohart- Adams and Thomas model were applied in describing the breakthrough curves in order to ascertain the equilibrium concentration and breakthrough time for CO2 to be adsorbed onto polyaspartamide. Lagergren’s pseudo 1st and 2nd order models as well as the Avrami kinetic models were used to describe the kinetic behaviour of polyaspartamide during post-combustion CO2 capture. Parameter estimations needed for the design and optimization of a CO2 adsorption system using polyaspartamide were obtained and presented in this study. The Boyd’s film diffusion model comprising of the interparticle and intra-particle diffusion models were used to investigate the effect of mass transfer limitations during the adsorption of CO2 onto polyaspartamide. Data obtained from continuous CO2 adsorption experiments were used to validate the models in this study. The experiments were conducted using a laboratory-sized packed-bed adsorption column at isothermal conditions. The packed bed was attached to an ABB CO2 analyser (model: ABB-AO2020) where concentrations of CO2 at various operating conditions were obtained. The results obtained in this study show that temperature, pressure and gas flow rate had an effect on the adsorption behaviour of polyaspartamide (PAA) during CO2 capture. Polyaspartamide exhibited a CO2 capture efficiency of 97.62 % at the lowest temperature of 303 K and pressure of 2 bar. The amount of CO2 adsorbed on polyaspartamide increased as the operating pressure increased and a decrease in the adsorption temperature resulted in increased amount of CO2 adsorbed by polyaspartamide. The amounts of CO2 adsorbed on polyaspartamide were 5.9, 4.8 and 4.1 mol CO2/kg adsorbent for adsorption temperatures of 303, 318 and 333 K, respectively. The maximum amount of CO2 adsorbed by polyaspartamide at different flow rates of 1.0, 1.5 and 2.5 ml/s of the feed gas were 7.84, 6.5 and 5.9 mmol CO2/g of adsorbent. This shows that higher flow rates resulted in decreased amount of CO2 adsorbed by polyaspartamide because of low residence time which eventually resulted in poor mass transfer between the adsorbent and adsorbate. Under dry conditions, the adsorption capacity of polyaspartamide was 365.4 mg CO2/g adsorbent and 354.1 mgCO2/g adsorbent under wet conditions. Therefore, the presence of moisture had a negligible effect on the adsorption behaviour of polyaspartamide. This is very common with most amine-rich polymer-based adsorbents. This could be attributed to the fact that CO2 reacts with moisture to form carbonic acid, thereby enhancing the CO2 adsorption capacity of the material. In conclusion, this study confirmed that the adsorption of CO2 onto polyaspartamide is favoured at low temperatures and high operating pressures. The adsorption of CO2 onto polyaspartamide was governed by film diffusion according to the outcome of the Boyd’s film diffusion model. It was also confirmed that intra-particle diffusion was the rate-limiting step controlling the adsorption of CO2 onto polyaspartamide. According to the results from the kinetic study, it can be inferred that lower temperatures had an incremental effect on the kinetic behaviour of polyaspartamide, external mass transfer governed the CO2 adsorption process and the adsorption of CO2 onto polyaspartamide was confirmed to be a physicochemical process (both physisorption and chemisorption). / MT2017

O uso de microalgas e cianobactérias para a produção de biocombustíveis e outros produtos e matérias-primas de interesse comercial tem sido amplamente divulgado como uma tecnologia sustentável bastante promissora, em função das elevadas produtividades areais, potencial para fixação de CO2, uso de terras não adequadas para cultivo e possibilidade de utilizar fontes alternativas de nutrientes, tais como água salobra ou efluentes agroindustriais. A produção comercial de cianobactérias em tanques abertos em formato de pista foi estudada combinando-se a modelagem matemática do crescimento nos tanques com a avaliação técnica, econômica e de sustentabilidade do processo. Construiu-se um macromodelo para a simulação dos tanques, que permitiu determinar o impacto de variáveis ambientais como, por exemplo, temperatura e luminosidade, e otimizar condições de operação e coleta. A análise econômica detalhada demonstrou o impacto dos custos de capital, operação e consumo de energia pelo processo, também destacando a importância da receita de produtos de alto valor agregado para a viabilidade do sistema, com base na tecnologia atual. Os valores de transformidade e índices de sustentabilidade e carga ambiental, obtidos através da análise emergética, são comparáveis com outros processos para obtenção de biocombustíveis de segunda geração, mas os elevados custos de construção e operação e grande consumo de energia nas etapas de coleta e extração representam ainda grandes desafios à sua sustentabilidade. A análise de sensibilidade para as principais variáveis de processo e estudos de caso para melhorias e modelos de negócio alternativos permitiram priorizar áreas para pesquisa futura com base no impacto econômico e ambiental. / The use of microalgae and cyanobacteria for the production of biofuels and other substances of commercial interest has been widely advertised as an extremely promising sustainable technology, due to the high areal productivity, potential for fixation of CO2, possibility of using non-arable land and alternative sources of nutrients such as brackish water and agricultural and industrial effluents. The commercial production of cyanobacteria in open raceway ponds was studied through the combination of a mathematical model for the algal growth with technical, economical and sustainability evaluations. A macromodel was developed to simulate the ponds, and it was used to assess the impact of environmental variables, such as light and temperature, and to optimize the process conditions for operation and harvesting. A detailed economic analysis demonstrated the impact of capital, operation costs and energy consumption, also highlighting the importance of revenue from high value products to process viability, considering the current technology. The transformity, emergy sustainability and environmental loading indices obtained by emergy analysis are comparable to other second generation biofuels, but the high construction and operation costs and energy consumption by the harvesting and extraction steps still represent major challenges to sustainability. The sensitivity analysis and evaluation of both technology improvements and alternative business models enabled the prioritization of future research areas, based on economic and environmental impact.

O uso de microalgas e cianobactérias para a produção de biocombustíveis e outros produtos e matérias-primas de interesse comercial tem sido amplamente divulgado como uma tecnologia sustentável bastante promissora, em função das elevadas produtividades areais, potencial para fixação de CO2, uso de terras não adequadas para cultivo e possibilidade de utilizar fontes alternativas de nutrientes, tais como água salobra ou efluentes agroindustriais. A produção comercial de cianobactérias em tanques abertos em formato de pista foi estudada combinando-se a modelagem matemática do crescimento nos tanques com a avaliação técnica, econômica e de sustentabilidade do processo. Construiu-se um macromodelo para a simulação dos tanques, que permitiu determinar o impacto de variáveis ambientais como, por exemplo, temperatura e luminosidade, e otimizar condições de operação e coleta. A análise econômica detalhada demonstrou o impacto dos custos de capital, operação e consumo de energia pelo processo, também destacando a importância da receita de produtos de alto valor agregado para a viabilidade do sistema, com base na tecnologia atual. Os valores de transformidade e índices de sustentabilidade e carga ambiental, obtidos através da análise emergética, são comparáveis com outros processos para obtenção de biocombustíveis de segunda geração, mas os elevados custos de construção e operação e grande consumo de energia nas etapas de coleta e extração representam ainda grandes desafios à sua sustentabilidade. A análise de sensibilidade para as principais variáveis de processo e estudos de caso para melhorias e modelos de negócio alternativos permitiram priorizar áreas para pesquisa futura com base no impacto econômico e ambiental. / The use of microalgae and cyanobacteria for the production of biofuels and other substances of commercial interest has been widely advertised as an extremely promising sustainable technology, due to the high areal productivity, potential for fixation of CO2, possibility of using non-arable land and alternative sources of nutrients such as brackish water and agricultural and industrial effluents. The commercial production of cyanobacteria in open raceway ponds was studied through the combination of a mathematical model for the algal growth with technical, economical and sustainability evaluations. A macromodel was developed to simulate the ponds, and it was used to assess the impact of environmental variables, such as light and temperature, and to optimize the process conditions for operation and harvesting. A detailed economic analysis demonstrated the impact of capital, operation costs and energy consumption, also highlighting the importance of revenue from high value products to process viability, considering the current technology. The transformity, emergy sustainability and environmental loading indices obtained by emergy analysis are comparable to other second generation biofuels, but the high construction and operation costs and energy consumption by the harvesting and extraction steps still represent major challenges to sustainability. The sensitivity analysis and evaluation of both technology improvements and alternative business models enabled the prioritization of future research areas, based on economic and environmental impact.

The aim of this study was to determine a carbon and water footprint for a beverage manufacturing company. The carbon footprint etermination was conducted on Scope 1 and Scope 2. The water footprint was determined on the blue water and grey water. The beverage production volumes of the beverage manufacturing company were used to determine both the carbon and the water footprint. The theoretical background to this study was based on both local and international beverage companies and the outcome for the carbon and water footprint was benchmarked against the local and international companies. The objectives of this study were achieved by calculating a carbon and water footprint for the beverage company. The carbon footprint unit of measure is g CO2e / litre produced and the water footprint is litre water/litre produced. The unit of measure for pollutant grey water footprint is measured in milligram. Based on the results achieved in this study, commendations for carbon and water footprint reductions were made to the beverage company. Reduction targets for production year 2020 were also recommended based on the implementation of the reduction plans. / Environmental Sciences / M. Sc. (Environmental Management)

This dissertation combines methods from engineering, operations research, and economics to analyze how emerging residential energy technologies can be effectively used to reduce both energy costs and carbon emissions. Our most important finding is that air-source heat pumps can be used to reduce both energy costs and carbon emissions in four out of the five major climate regions studied, but that electric retail rate reform is needed to provide customers with appropriate incentives. In cold climates, it may be advantageous to use heat pumps in tandem with fossil fuel-powered furnaces; in warmer regions, furnaces can be cost-effectively abandoned altogether. We do not find that distributed rooftop solar panels or distributed battery storage are effective tools for reducing the cost of energy services. Rather, in our simulations, customers adopt these technologies in response to poor price signaling by electric utilities. By reforming electric retail rates so that the prices paid by consumers better reflect the cost of energy services, utilities can promote the adoption of technologies that reduce both aggregate costs and carbon emissions.

Atmospheric carbon dioxide (CO₂) concentrations have increased rapidly in recent decades due to the burning of fossil fuels, deforestation, and other industrial practices. The excessive accumulation of CO₂ in the atmosphere leads to global warming, ocean acidification, and other environmental imbalances, which may ultimately have wider societal implications. One potential solution to closing the carbon cycle is utilizing CO₂, rather than fossil fuels, as the carbon source for fuels and chemicals production. This lowers atmospheric CO₂ levels while simultaneously providing an economic incentive for capturing and converting CO₂ into more valuable products. This dissertation includes studies on three hybrid catalytic reactor systems coupling electrochemistry, thermochemistry, and plasma chemistry for the conversion of CO₂ into value-added oxygenates, such as methanol and C3 oxygenates (propanal and 1-propanol). First, a tandem two-stage system is described where CO₂ is electrochemically reduced into syngas followed by the thermochemical methanol synthesis reaction. The work here specifically focuses on the electrochemical CO₂ reduction reaction to produce syngas with tunable H₂/CO ratios. Using a combination of electrochemical experiments, in-situ characterization, and density functional theory calculations, palladium-, gold-, and silver-modified transition metal carbides and nitrides were found to be promising catalysts for enhancing electrochemical activity while reducing the overall precious metal loading. Second, another tandem two-stage system is demonstrated where CO₂ is electrochemically reduced into ethylene and syngas followed by the thermochemical hydroformylation reaction to produce propanal and 1-propanol. The CO₂ electrolyzer was evaluated with Cu catalysts containing different oxidation states and with modifications to the gas diffusion layer hydrophobicity, while the hydroformylation reactor was tested over a Rh₁Co₃/MCM-41 catalyst. The tandem configuration achieved a C₃ oxygenate selectivity of ~18%, representing over a 4-fold improvement compared to direct electrochemical CO₂ conversion to 1-propanol in flow cells. Third, a hybrid plasma-catalytic system is investigated where CO₂ and ethane are directly converted into multi-carbon oxygenates in a one-step process under ambient conditions. Oxygenate selectivity was enhanced at lower plasma powers and higher CO₂ to C₂H₆ ratios, and the addition of a Rh₁Co₃/MCM-41 catalyst increased the oxygenate selectivity at early timescales. Plasma chemical kinetic modeling, isotopically-labeled CO₂ experiments, and in-situ spectroscopy were also used to probe the reaction pathways, revealing that alcohol formation occurred via the oxidation of ethane-derived activated species rather than a CO₂ hydrogenation pathway. It is critical to assess whether the proposed CO₂ conversion strategies consume more CO₂ than they emit. A comparative analysis of the energy costs and net CO₂ emissions is conducted for various reaction schemes, including four hybrid pathways (thermocatalytic-thermocatalytic, plasma-thermocatalytic, electrocatalytic-thermocatalytic, and electrocatalytic-electrocatalytic) for converting CO₂ into C₃ oxygenates. The hybrid processes can achieve a net reduction in CO₂ provided that low-carbon energy sources are used, however further catalyst improvements and engineering optimizations are necessary. Hybrid catalytic systems can provide an alternative approach to traditional processes, and these concepts can be extended to other chemical reactions and products, thereby opening new opportunities for innovative CO₂ utilization technologies.

This thesis aims to provide different aspects to make the Direct Air Capture Dual Function Materials (DAC-DFM) project more applicable in commercialization and large-scale deployment to directly address the global warming problem caused by anthropogenic CO₂. Dual function materials are comprised of nano dispersed alkaline sorbents and a methanation catalyst to capture CO₂ from ambient air and convert it to CH₄ upon the addition of green H₂. Two sub-projects named “Ru thrifting project” and “hydrophobicity/surface modification project” were performed to study the potential optimization and tradeoff when modifying the DFM components. The major accomplishment in this thesis has been the thrifting of Ru from its original value of 5% to 1% and finally 0.25% with no sacrifice in stability but with some decrease in capacity for CO₂ capture and methanation. Given the Ru unit price (around 14 USD/g, flexible market, in March 2024), this approach would greatly reduce the overall production cost. In the hydrophobicity/surface modification project, Al₂O₃ the high surface area carrier for the DFM components, was treated using 3 different methods (high temperature calcination, acid treatment, and metal oxide doping). The goal of this study was to reduce the surface water uptake in the Al₂O₃ from humidity, present in ambient air, by increasing hydrophobicity to reduce the energy evaporation cost during temperature swing in the DFM CO₂ desorption/methanation process. Samples treated after these 3 methods showed a significant decrease in water uptake. ZrO₂ doped Na₂CO₃-Al₂O₃ sample showed a low H₂O uptake and the highest CO₂ adsorption, twice that of the CO₂ capacity of the Na₂CO₃-Al₂O₃ samples treated by calcination and acid. Such hydrophobicity study would be used to further optimize the components of DFM to meet requirements in real world applications. Future outlook for DFMs is also briefly discussed with focuses on (1) using pre-heated H₂ to increase the temperature of inner DFM coatings for increased energy efficiency, (2) increased CO₂ capture, utilization, and conversion to CH₄, as well as (3) practical acceptance of DAC hubs and CO₂ taxes/credits. A new approach of moisture swing DAC sorbents as an alternate technology to the thermal swing DFM is suggested as a future project. With loaded CO₃²⁻ on both organic ion exchange particles/membranes and inorganic silica-based granules, the CO₂ adsorption/desorption effect can be controlled by the moisture level (relative humidity) from ambient air in the inlet sample chamber.

The aim of this study was to determine a carbon and water footprint for a beverage manufacturing company. The carbon footprint determination was conducted on Scope 1 and Scope 2. The water footprint was determined on the blue water and grey water. The beverage production volumes of the beverage manufacturing company were used to determine both the carbon and the water footprint. The theoretical background to this study was based on both local and international beverage companies and the outcome for the carbon and water footprint was benchmarked against the local and international companies. The objectives of this study were achieved by calculating a carbon and water footprint for the beverage company. The carbon footprint unit of measure is g CO2e / litre produced and the water footprint is litre water/litre produced. The unit of measure for pollutant grey water footprint is measured in milligram. Based on the results achieved in this study, recommendations for carbon and water footprint reductions were made to the beverage company. Reduction targets for production year 2020 were also recommended based on the implementation of the reduction plans. / Environmental Sciences / M. Sc. (Environmental Science)

Thesis (MDF)--Stellenbosch University, 2012. / In recent years there has been a growth in literature from multiple disciplines on the potential effects of climate change and a corresponding growth in literature on potential mitigation and adaptation response strategies, including multiple means of shifting to a low-carbon future. Multiple assessment techniques have been developed to understand the potential vulnerability to, and impacts of climate change. At the same time, there is a lack of methodology to understand the potential vulnerability to, and impacts of, responses to climate change on a micro level. This research report describes the development of a reference framework to be used to monitor the vulnerability of the Cape Town International Airport to changes in carbon pricing and/or a shift to a low-carbon future. A theoretical approach was taken, which reviews existing techniques and proposes an integrated framework approach which was then applied to the case study of Cape Town International Airport. Existing literature on what is understood by a low carbon future shows that there is uncertainty about what mitigation and adaptation approaches will be adopted on various scales, and, similarly, uncertainty on what this means for a low carbon economy. Existing scenario development, vulnerability assessment, risk assessment and impact assessment methodologies were then reviewed, revealing a dearth of integrated approaches and an emphasis on the direct impacts of climate change, with a lack of attention to the impacts of responses to climate change. Finally, an overview of what are considered key driving forces in airport feasibility is provided in order to identify potential areas of vulnerability that require attention in any assessment of an airports’ vulnerability to different futures. Building on the various methodologies reviewed, and the understanding of key airport drivers, a reference framework is developed with special focus on the Cape Town International Airport and its current financial structure and planning framework. The final section of the paper discusses preliminary findings as illustrative of the approach, concluding that the framework can be applied via multidisciplinary collaboration, but that further work would be required both internally and externally in order to better manage uncertainties.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / Global climate change is among the major challenges the world is facing today, and can be attributed to enhanced concentrations of Greenhouse Gases (GHG), such as carbon dioxide (CO2), in the atmosphere. Therefore, there is an urgent need to mitigate CO2 emissions, and carbon capture and storage (CCS) is amongst the possible options to reduce CO2 emissions. Against this background, this work investigated the synthesis and performance evaluation of Polyaspartamide (PAA) adsorbent for CO2 capture. In particular, the effect of the presence of water-soluble amines in the amine-grafted poly-succinimide (PSI) (referred to as Polyaspartamide (PAA) adsorbent), was investigated. Methyl Amine (MA) and Mono-Ethanol Amine (MEA) were employed as water-soluble amines and the effect of changes in their concentration on CO2 adsorption capacity was investigated as well. Water-soluble amines were incorporated to allow water solubility of the adsorbent paving the way for freeze-drying to improve the geometric structure (surface area, pore volume and pore size) of the adsorbent. Initially, the PSI was loaded with Ethylenediamine (EDA), forming PSI-EDA. The water-soluble amines were grafted to PSI-EDA, with the EDA added to improve the chemical surface of the adsorbent for CO2 capture. NMR and FTIR analyses were performed and confirmed the presence of MA and MEA amine groups in the PAA, thereby indicating the presence of the grafted amines on the backbone polymer. BET analysis was performed and reported the pore volume, pore size and surface area of the freeze-dried material. It was observed that the physical properties did not change significantly after the freeze-drying compared to literature where freeze-drying was not employed. An increase in adsorption capacity with an increase in MA and MEA concentrations in MA-PAA and MEA-PAA samples was observed. At low amine concentrations (20% amine and 80% EDA grafted), MEA-PAA was observed to exhibit higher adsorption capacity compared to the MA-PAA samples. At high amine (100% amine grafted) concentrations, MA-PAA samples displayed higher adsorption capacity. Three runs were performed on each sample and the results obtained were reproducible. The best adsorption capacity obtained was 44.5 g CO2/kg Ads. Further work was then performed to understand the effects of operating variables on CO2 adsorption as well as the interactive effect using the Response Surface Methodology approach. The experiments were done by use of CO2 adsorption equipment attached to an ABB gas analyzer. A central composite design of experiment method with a total of 20 experiments was employed to investigate three factors, namely, temperature, pressure and gas flow rate. Six regression models were drawn up and mean error values computed by use of Matlab, followed by response surfaces as well as contours, showing the influence of the operating variables on the adsorption capacity as well as interaction of the factors were then drawn up. The results obtained displayed that each of the factors investigated, temperature, pressure and gas flowrate had an incremental effect on the adsorption capacity of PAA, that is, as each factor was increased, the adsorption capacity increased up to a point where no more increase occurred. Adsorption was seen to increase for both an increase in gas flowrate and adsorption pressure to a maximum, thereafter it starts to decrease. A similar trend was observed for the interaction between temperature and pressure. However, the interaction between gas flowrate and temperature was such that, initially as the temperature and the gas flowrate increase, the adsorption capacity increases to a maximum, thereafter, the temperature seizes to have an effect on the adsorption capacity with a combined effect of decreasing temperature and increasing gas flowrate resulting in a further increase in adsorption capacity. It was confirmed that the operating variables as well as the flow regime have an effect on the CO2 adsorption capacity of the novel material. The highest adsorption capacity was obtained in the pressure range 0.5 bar to 1.7 bar coinciding with the temperature range of 10 oC to 45 oC. The interaction of gas flowrate and adsorption pressure was such that the highest adsorption capacity is in the range 0.8 bar to 1.5 bar which coincides with the gas flowrate range from 35 ml / min to 60 ml / min. In conclusion, the best adsorption capacity of 44.5 g / kg via the TGA and 70.4 g / kg via the CO2 adsorption equipment was obtained from 100 % MA grafted PSI. / GR2016