In the technologically driven information age, the consumption of power is as vital to daily life as food and shelter. The generation of that power comes from a variety of sources of which coal is the predominant provider of electrical energy. Coal combustion is a well-known technology and the United States possesses the most abundant coal deposits on Earth, however, the drawback accompanying this process is the significant emissions which are released during combustion. Over the years, much effort has gone into reducing the emissions of majority constituent elements CO2, CO, NOx, SOx, etc. but it is only in the last decade or so that much attention has been given to the trace metals present within coal. Most of the work into examining these trace metals has been upon Hg and how it speciates within the flue gas in order to determine the most effective means of removal. In this study, the trace metals arsenic (As) and selenium (Se) will be investigated in a similar manner to evaluate the speciation of these elements. While previous experimental work has been performed in this area, it has been limited to thermodynamic studies which determine the speciation after equilibrium has been reached, this ignores the fact the residence times within the flue are often only several minutes during which time rapid quenching is taking place. This study takes a different approach by examining the speciation using computational chemistry which affords the advantage of being able to perform a kinetic study which is more useful in creating a flue gas model. Using ab initio the properties of various As and Se species can be evaluated compared to existing experimental data for validation. After which, a number of reactions may be selected and the structure of the transition state for each identified. Once the properties of the transition structure are known, the appropriate kinetic model, be it Transition State Theory, RRKM Theory, etc. can be applied and the rate constant determined. It is by the determination of these rate constants that the kinetic model of the flue gas can be improved and a more accurate depiction of the speciation of these race metals created.

A Research Report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering (MSc 50/50) School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa November, 2016 / The global focus on cleaner air has seen sulphur removal processes’ gaining popularity and adsorptive desulphurisation has been identified as an effective alternative. Adsorptive desulphurisation was used to simulate and evaluate the performance of the polymer supported imidation agent (Sodium N-chloro-polystyrene sulphonamide) as an adsorbent in the desulphurisation of diesel fuel. This study involved the development of a mathematical model for the adsorption process of sulphur on the polymer supported imidation agent, based on the mass balance on a continuous fixed bed column and pseudo second order kinetics. The developed model was solved using numerical methods, and the simulation of the process carried out varying different parameters; the inlet sulphur concentration, the adsorption column bed height and the particle size (radius) of the adsorbent. The simulation showed that the adsorption capacity of the studied adsorbent increased with increase in the inlet sulphur concentration; an increase in the adsorption bed height and a decrease in the adsorbent particle size. Validation of the simulation done was carried out by comparing the simulation data with experimental data. The proposed model fit experimental data and can be used to predict the inlet concentration conditions, bed height and particle size of the adsorbent. The overall research enhances the understanding of the adsorptive desulphurisation of diesel fuel using the polymer supported imidation agent and the mathematical modelling of the process. / MT2017

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis.

Includes summary. Includes bibliographies.

Improvement of the efficiency of carbon dioxide (CO2) separation from flue gases has been identified as a high-priority research area to reduce the total energy cost of carbon capture and sequestration technologies in coal-fired power plants. Efficient CO2 removal from flue gases by adsorption systems requires the design of novel sorbents capable of capturing, concentrating and recovering CO2 on a cost-effective basis. The preparation of a novel aminosilane-functionalized cellulosic polymer sorbent by grafting of aminosilanes showed promising performance for CO2 separation and capture. A strategy for the introduction of N-(2-aminoethyl)-3-aminoisobutyldimethylmethoxysilane functionalities into cellulose acetate backbone by anhydrous grafting is described in this study. The dry sorption capacity of the aminosilane-functionalized cellulosic polymer reached 27 cc (STP) CO2/ cc sorbent at 1 atm and 39 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. Exposure to water vapor slightly increased the sorption capacity of the sorbent, suggesting its potential for rapid cyclic adsorption processes under humid feed conditions. In addition, a strategy for the preparation of a cellulose acetate-titanium(IV) oxide sorbent by the reaction of cellulose acetate with titanium tetrachloride is presented. The organic-metal hybrid sorbent presented a sorption capacity of 14 cc (STP) CO2/ cc sorbent at 1 atm and 49 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. The novel CO2 sorbents were characterized in terms of chemical composition, density changes, molecular structure, thermal stability, and surface morphology.

The use of novel hyperbranched aminosilica (HAS) materials created through the ring-opening polymerization of aziridine from mesoporous silica supports was proposed for the adsorption of CO2 from dilute sources. The limits of the adsorptive performance of these adsorbents were investigated via the preparation of sets of materials with a range of aminopolymer loadings on several different silica supports with different pore space characteristics. Relationships were determined between the materials' amine loadings and the CO2 adsorption performance. Adsorbents with substantial remaining pore volume displayed universal adsorption kinetics when normalized by amine loading. However, materials with blocked pores displayed substantially slower adsorption kinetics due to hindered mass transfer. In both humid and dry conditions, the HAS adsorbent was found to have a surprisingly large CO2 capacity in light of the 250-fold reduction in CO2 partial pressure from 10% CO2 (flue gas application) to 400 ppm CO2 (air capture application). Finally, a new series of linear aminosilicas was created through the reaction of existing aminosilicas with N-protected-aziridines. Specifically, reaction of aminosilane-functionalized silicas with N-methylaziridine resulted in the linear growth of methylaminoethyl groups, effectively increasing the amine loading of the adsorbent by a stoichiometric amount of an additional amine per attached silane.

Originally presented as the author's Thesis--Technische Hochschule Aachen, 2008. / Includes bibliographical references.

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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Jones, Christopher; Committee Member: Koros, William; Committee Member: Lyon, Andrew; Committee Member: Nair, Sankar; Committee Member: Weck, Marcus. Part of the SMARTech Electronic Thesis and Dissertation Collection.