A novel approach to geologic CO₂ sequestration is the surface dissolution method. This method involves lifting native brine from an aquifer, dissolution of CO₂ into the brine using pressurized mixing and injection of the CO₂ saturated brine back into the aquifer. This approach has several advantages over the conventional approach, including minimization of the risk of buoyancy driven leakage and dramatic reduction in the extent of pressure elevation in the storage structure. The mass transfer coefficient for the CO₂/brine two-phase system and associated transport calculations allow efficient design of the surface equipment required to dissolve CO₂ under pressure. This data was not previously available in the literature. Original experimental data on the rate of dissolution of CO₂ into Na-Ca-Cl brines across a range of temperatures and wet CO₂ densities are presented. From this data, the intrinsic mass transfer coefficient between CO₂-rich and aqueous phases has been calculated. The statistically significant variation in the mass transfer coefficient was evaluated and compared with the variation caused by the experimental method. An empirical correlation was developed that demonstrates that the mass transfer coefficient is a function of the NaCl salinity, temperature and wet CO₂ density. For the conditions tested, the value of the coefficient is in the range of 0.015 to 0.056 cm/s. Greater temperature and smaller NaCl salinity increases the mass transfer coefficient. There is an interaction effect between temperature and wet CO₂ density, which increases or decreases the mass transfer coefficient depending on the value of each. CaCl₂ salinity does not have a statistically significant effect on the mass transfer coefficient. The transport calculations demonstrate that wellhead co-injection of CO₂ and brine is feasible, providing the same technical outcome at lower cost. For example, assuming a 2000 ft deep well and typical aquifer injection conditions, complete dissolution of the bulk COv phase can be achieved at 670 ft for bubbles of 0.16 cm initial radius. Using a horizontal pipe or mixing tank was also shown to be feasible. Gas entrainment was shown to provide a marked reduction in size of mixing apparatus required. / text

Carbon dioxide serves as co-substrate in the production of succinic acid by Actinobacillus succinogenes. The transient concentration of dissolved CO2 in the broth (CCO2) controls the uptake of CO2 in the cell. Based on CCO2 , three distinct regimes could be identified in which the behaviour of the organism differed with CCO2 availability. When CCO2 was higher than 8.4 mM (44.4% saturated at an atmospheric pressure of 86 kPa), there was no evidence of CO2 limiting succinic acid productivity and flux to succinic acid remained constant. When CCO2 decreased below 8.4 mM a decrease in the succinic acid production and glucose consumption rates was observed to 28.01% and 19.89% of their original value respectively, at the lowest CCO2 value investigated. Below a CCO2 of 4 mM (21.16% saturated at an atmospheric pressure of 86 kPa), the productivity continued to decrease along with a shift in the total carbon flux from the succinic acid-producing pathway (C4-pathway) to the by-product-producing pathway (C3-pathway). The fraction of total carbon flux directed to the C4-pathway decreased from 0.48 to 0.33 at the lowest CCO2 value investigated. Although the by-product acetic acid concentration decreased to 88% of the original value, formic acid remained relatively stable and the ethanol concentration increased from an average of 0.26 g.L-1 to 1 g.L-1. The organism starts producing ethanol in order to satisfy the redox balance when the C4-pathway becomes less active. It was calculated that the flux shift to the C3-pathway does not favour ATP production. The organism is, however, still viable at the very low ATP production rates found at very low values of CCO2. Since succinic acid production is not limited at relatively low values of CCO2 (44.4% saturation), adequate CO2 supply to the fermenter can be achieved without major CO2 sparging which is beneficial from an industrial processing perspective. / Dissertation (MEng)--University of Pretoria, 2016. / Chemical Engineering / MEng / Unrestricted

The literature on stream reaeration was reviewed. A recirculating loop open channel system was desiqned and experiments were performed to study the effects of average stream velocity and temperature on the mass transfercoefficient for oxyqen dissolution into "clean" water. The applicability of the apparatus to the study of the effects of surfactants was also investigated. The velocity ranged from 0.1 to 0.9 ft/sec and the temperature from 5,0 to 25.o0c. The results indicated that the mass transfer coefficient varies approximately linearly with average stream velocity and that the temperature coefficient is a variable which depends on mixinq condHions. Furthermore, it was found that the temperature dependency of the mass transfer coefficient could be expressed as either a linear or power function. Correlations expressing the mass transfer coefficient in terms of easily measurable stream parameters. were developed and compared to those found in the recent literature / Thesis / Master of Engineering (ME)

The effective mass transfer area (a [subscript e]), liquid film mass transfer coefficient (k [subscript L]), and gas film mass transfer coefficient (k [subscript G]) of eleven structured packings and three random packings were measured consistently in a 0.428 m packed column. Absorption of CO₂ with 0.1 gmol/L NaOH with 3.05 m packing was used to measure a [subscript e], while air stripping of toluene from water with 1.83 m packing was used to measure k [subscript L], and absorption of SO₂ with 0.1 gmol/L NaOH with 0.51 m packing was used to measure k [subscript G]. The experiments were conducted with liquid load changing from 2.5 to 75 m³/(m²*h) and gas flow rate from 0.6 to 2.3 m/s. Packings with surface area from 125 to 500 m²/m³ and corrugation angle from 45 to 70 degree were tested to explore the effect of packing geometries on mass transfer. The effective area increases with packing surface area and liquid flow rate, and is independent of gas velocity. The packing corrugation angle has an insignificant effect on mass transfer area. The ratio of effective area to surface area decreases as surface area increases due to the limit of packing wettability. A correlation has been developed to predict the mass transfer area with an average deviation of 11%. [Mathematical equation]. The liquid film mass transfer coefficient is only a function of liquid velocity with a power of 0.74, while the gas film mass transfer coefficient is only a function of gas velocity with a power of 0.58. Both k [subscript L] and k [subscript G] increase with packing surface area, and decrease with corrugation angle. A new concept, Mixing Point Density, was introduced to account for effect of the packing geometry on k[subscript L] and k [subscript G]. Mixing Point Density represents the frequency at which liquid film is refreshed and gas is mixed. The mixing point density can be calculated by either packing characteristic length or by surface area and corrugation angle: [mathematical equation]. The dimensionless k [subscript L] and k [subscript G] models can then be developed based on the effects of liquid/gas velocity, mixing point density, packing surface area: [mathematical equation] [mathematical equation]. Mi is the dimensionless form of Mixing Point Density (M), which is M divided by a [subscript P]³. Because Mi is only a function of corrugation angle (θ), it is a convenient transformation to represent the effect of θ on mass transfer parameters. An economic analysis of the absorber was conducted for a 250 MW coal-fired power plant. The optimum operating condition is between 50 to 80 % of flooding, and the optimum design is to use packing with 200 to 250 m²/m³ surface area and high corrugation angle (60 to 70 degree). The minimum total cost ranges from $4.04 to $5.83 per tonne CO₂ removed with 8 m PZ.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

To screen amine solvents for application in CO2 capture from coal-fired power plants, the equilibrium CO2 partial pressure and liquid film mass transfer coefficient were characterized for CO2-loaded and highly concentrated aqueous amines at 40 – 100 °C over a range of CO2 loading with a Wetted Wall Column (WWC). The acyclic amines tested were ethylenediamine, 1,2-diaminopropane, diglycolamine®, methyldiethanolamine (MDEA)/Piperazine (PZ), 3-(methylamino)propylamine, 2-amino-2-methyl-1-propanol and 2-amino-2-methyl-1-propanol/PZ. The cyclic amines tested were piperazine derivatives including proline, 2-piperidineethanol, N-(2-hydroxyethyl)piperazine, 1-(2-aminoethyl)piperazine, N-methylpiperazine (NMPZ), 2-methylpiperazine (2MPZ), 2,5-trans-dimethylpiperazine, 2MPZ/PZ, and PZ/NMPZ/1,4-dimethylpiperazine (1,4-DMPZ). The cyclic CO2 capacity and heat of CO2 absorption were estimated with a semi-empirical vapor-liquid-equilibrium model. 5 m MDEA/5 m PZ, 8 m 2MPZ, 4 m 2MPZ/4 m PZ and 3.75 m PZ/3.75 m NMPZ/0.5 m 1,4-DMPZ were identified as promising solvent candidates for their large CO2 capacity, fast mass transfer rate and moderately high heat of absorption. The speciation in 8 m 2MPZ and 4 m 2MPZ / 4 m PZ at 40 °C at varied CO2 loading was investigated using quantitative 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. In 8 m 2MPZ at 40 °C over the CO2 loading range of 0 – 0.37 mol CO2/mol alkalinity, more than 75% of the dissolved CO2 exists in the form of unhindered 2MPZ monocarbamate, and the rest is in the form of bicarbonate and dicarbamate; 19% - 56% of 2MPZ is converted to 2MPZ carbamate at 0.1 - 0.37 mol CO2/mol alkalinity. A rigorous thermodynamic model was developed for 8 m 2MPZ in the framework of the Electrolyte Nonrandom Two-Liquid (ENRTL) model. At 40 °C, the reaction stoichiometry for 2MPZ and CO2 is around 2 at lean loading but diminishes to 0 at rich loading. Bicarbonate becomes the major product at CO2 loading greater than 0.35 mol/mol alkalinity. The predicted heat of CO2 absorption is 75 kJ/mol at 140 °C and decreases with temperature when CO2 loading is above 0.25. The mass transfer rate data for 8 m 2MPZ was represented with a rate-based WWC model created in Aspen Plus®. The reaction rate was described with termolecular mechanism on an activity basis. With minor CO2 loading adjustment and regression of pre-exponential kinetic constants and diffusion activation energy, a majority of the measured CO2 fluxes in the WWC experiments were fitted by the model within ±20% over 40 – 100 °C and 0.1 – 0.37 mol CO2/mol alkalinity. The diffusion activation energy for 8 m 2MPZ at the rich loading is about 28 kJ/mol. The activity-based reaction rate constant at 40 °C for 2MPZ carbamate formation catalyzed by 2MPZ is 1.94×1010 kmol/m3•s. The calculated liquid film mass transfer coefficients are in close agreement with the experimental values. The liquid film mass transfer rate is dependent on the diffusion coefficients of amine and CO2 to the same extent at lean loading and 40 °C. The sum of the powers for the two diffusivities is approximately equal to 0.5 over the loading range of 0 – 0.4 mol CO2/mol alkalinity. The sum of the powers for the dependence of the liquid film mass transfer coefficient on the carbamate formation rate constants (k2MPZ-2MPZ and k2MPZCOO--2MPZ) approaches 0.5 at very lean loading at low temperature, but it decreases as CO2 loading and temperature is increased. At 100 °C, the physical liquid film mass transfer coefficient is the most important factor that determines the liquid mass transfer rate. The pseudo-first order region shifts to higher range of physical liquid film transfer coefficient as temperature increases. / text

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

A transferência de oxigênio é um fator limitante para grande parte dos cultivos em biorreatores que operam com organismos estritamente aeróbios devido à baixa solubilidade do oxigênio em meios de cultivo. A introdução de meios não convencionais, como polidimetilsiloxanos (PDMS), em biorreatores pode ser vista como uma melhoria para o ajuste desses processos. Este trabalho propõe uma investigação do emprego de polidimetilsiloxano fluido e emulsificado, usados como carreadores de oxigênio, em meios de cultivo na produção de lipases de Staphylococcus warneri EX17, cepa capaz de utilizar glicerol residual como substrato, visando melhorar a disponibilidade de oxigênio e aperfeiçoar a produtividade. Inicialmente, foram realizados estudos para selecionar o uso de glicerol residual, oriundo da síntese química de biodiesel como fonte de carbono. A atividade lipolítica foi semelhante com glicerol comercial e residual. Após a seleção do glicerol foram realizados experimentos em incubadora rotatória horizontal nas condições previamente otimizadas em trabalhos anteriores do grupo, adicionando PDMS. Dois tipos de PDMS foram testados, fluido e emulsificado. A produção de lipase foi significativamente maior no meio contendo PDMS. Assim, ferramentas de planejamento experimental, delineamento composto central (DCC) foram utilizadas para verificar a influencia do PDMS no coeficiente de transferência de oxigênio kLa em meio de cultivo produtor de lipase livre de células. O kLa aumentou significativamente no meio de cultivo contendo PDMS. Dois novos planejamentos foram desenhados, para otimizar a produção de lipase em meio de cultivo com células. Um para PDMS fluido e outro para PDMS emulsificado. No meio contendo PDMS fluido, a atividade lipolítica foi cinco vezes maior, enquanto que no meio contendo silicone emulsificado a atividade lipolítica foi três vezes maior. Este estudo demonstrou que a lipase de S. warneri EX17 pode ser produzida utilizando glicerol residual como fonte de carbono, e polidimetilsiloxanos como carreadores de oxigênio aumentando a transferência de oxigênio no meio e elevando a produção da enzima, que apresenta diversas possibilidades de aplicação, principalmente na indústria de alimentos. / The oxygen transfer is a limiting factor in many bioreactors cultivations, in which strictly aerobic organisms are grown due to the low solubility of oxygen in culture media. The introduction of unconventional media, such as polydimethylsiloxanes (PDMS) in bioreactors can be seen as a potential improvement for these processes. This work proposes an investigation of the use of polydimethylsiloxane in its two forms, fluid and emulsified, used as carriers of oxygen in culture media for the lipase production of Staphylococcus warneri EX17, strain capable of using glycerol as substrate, to improve the oxygen availability and improve enzyme productivity. Initially, studies were performed to select the use of residual glycerol, derived from the chemical synthesis of biodiesel as a source of carbon. The lipase activity was similar in both commercial and residual glycerol. Experiments were performed on orbital shaker, using conditions previously optimized in another work of the group, but with the addition of PDMS. Two types of PDMS were tested, the fluid and the emulsified. The lipase production was significantly higher in medium containing PDMS. Experimental design and central composite design (CCD) were used to evaluate the influence of PDMS on the oxygen transfer coefficient kLa in culture medium free of lipase-producing cells. The kLa increased significantly in the medium containing PDMS. Two new experimental plannings were designed to optimize the production of lipase in culture medium with cells. In the medium containing the PDMS fluid lipase activity was five times higher than medium without the oxygen carrier, while in the medium containing the emulsified silicone lipase activity was three times higher. This study showed that the lipase from S. warneri EX17 can be produced using residual glycerol as carbon source and that polydimethylsiloxanes works as interesting carrier of oxygen by increasing oxygen transfer rates, improving enzyme production, which has several possible applications, especially in the food industry.