Browsing by Author "Bosman, Catharine Elizabeth"

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    Single and binary component adsorption of 1-alcohols from an alkane using various activated alumina adsorbents
    (Stellenbosch : Stellenbosch University, 2019-12) Bosman, Catharine Elizabeth; Schwarz, C. E.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: During surfactant production, an alcohol-alkane stream is produced which requires separation. Adsorption has been shown to be a technically viable process for the removal of single 1-alcohol contaminants from an alkane stream; however, little knowledge exists on the binary 1-alcohol adsorption. The aim of this study was to gain knowledge on the single and binary component adsorption of 1-alcohol contaminants from a n-alkane solvent using activated alumina adsorbents. The objectives of the study included: (i) the measurement and investigation of single and binary component adsorption data; (ii) the modelling of the equilibrium adsorption isotherms; and, (iii) the modelling of the adsorption kinetics of these systems. Investigation of the experimental data included comparing the adsorption abilities of three activated alumina adsorbents (Activated Alumina F220, Selexsorb CDx® and Selexsorb CD®); investigating the effect of temperature, initial adsorbate concentration and alcohol carbon chain length on the adsorption of 1-alcohols (1-hexanol, 1-octanol and 1-decanol) from n-decane; a comparison of single and binary 1-alcoholadsorption; and, an investigation of interaction in the binary 1-alcohol systems. Adsorption data was measured using a bench-scale batch adsorption system. The experimental procedure entailed immersing beakers containing alcohol-alkane solutions (1-alcohol concentration < 3.3 mass%) and adsorbent in a water bath, maintained at a specified temperature (25oC or 45oC), and measuring the alcohol concentration over time. When comparing the adsorbents, Selexsorb CDx® and Selexsorb CD® were found to exhibit slightly greater adsorbent loadings than Activated Alumina F220 for most systems, with overall equilibrium adsorbent loadings of approximately 110 to 130 mg/g for the single component systems and slightly more, 128 to 150 mg/g, for the binary component systems. Overall, increased temperature exhibited a corresponding increase in adsorbent loading. Adsorbent loading was found to increase with increasing initial alcohol concentration up to a concentration of approximately 1 to 1.2 mass% after which the equilibrium adsorbent loadings remained relatively constant. The alcohol carbon chain length had minimal effect on adsorption, with some cases exhibiting an increased rate of adsorption for the shorter chain alcohols. When comparing the adsorption of a 1-alcohol in a single and binary component system (with the specific 1-alcohol having an equal initial concentration in both systems), the adsorbent loading of the 1-alcohol in thebinary component system was notably poorer than in the corresponding single component system. Consequently, antagonistic/competitive behaviour was found to be predominant in the initial adsorbate concentration range of 1 to 1.5 mass%. For the single and binary component systems, the Redlich-Peterson (R2 > 0.96) and Extended Freundlich models (R2 > 0.85 for most systems) were found to provide the best correlation of the equilibrium data, respectively. The binary component isotherm models, however, provided poor correlation of the data. The single and binary component adsorption kinetics were found to be very similar with the pseudo-second-order model providing a good correlation of the kinetic data (R2 > 0.96 for most systems). The Intra-particle diffusion model was almost equally well suited to the data. Ultimately, the adsorption of single and binary 1-alcohols from n-decane using activated alumina adsorbents was found to be a technically viable process, with adsorption proposed to be dominated by weak chemisorption, and competitive adsorption slightly favouring shorter carbon chain alcohols.
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    A thermosiphon photobioreactor for photofermentative hydrogen production by Rhodopseudomonas palustris.
    (Stellenbosch : Stellenbosch University, 2023-03) Bosman, Catharine Elizabeth; Pott, Robert William M.; Bradshaw, Steven Martin; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Hydrogen has widely been identified as a commodity chemical. Currently, however, hydrogen is primarily produced through non-renewable methods. Biological hydrogen production through microbial photofermentation offers an environmentally friendly and potentially economically feasible alternative. Although this technology is promising, the costs associated with photofermentation systems need to be reduced and hydrogen productivity increased, to make the technology a competitive alternative to non-renewable hydrogen production methods. This can potentially be realised through cost-reduction strategies in combination with bioremediation – purifying wastewater whilst simultaneously producing a valuable chemical. This work applied a combination of techniques to develop and evaluate a novel thermosiphon photobioreactor (TPBR) for photofermentative hydrogen production, using Rhodopseudomonas palustris (R. palustris). The TPBR implements the thermosiphon effect to passively circulate biomass – the first and currently the only photobioreactor with the potential of operating without any external energy inputs. The TPBR was successfully implemented for photofermentative hydrogen production using R. palustris, achieving maximum hydrogen production rates of up to 0.310 mol·m−3 ·h−1 in the growing state. The effects of light intensity, temperature and biomass concentration on hydrogen production and passive circulation of biomass were investigated. The effects of biomass concentration were found to be most pronounced (0.4 to 1.2 g·L−1 ), while light intensities of 400 to 600 W·m−2 and an internal operating temperature of 31 to 44 °C were found to be suitable for hydrogen production. Exploring the effects of geometry, two novel TPBR designs were proposed – a tubular loop TPBR and a flat-plate TPBR. Using computational fluid dynamics (CFD) simulations, these designs were characterized in terms of fluid flow patterns, temperature profiles and radiation fields. Both TPBR designs showed potential for hydrogen production, achieving temperature gradients sufficient to ensure adequate circulation and velocities to maintain biomass in suspension. CFD simulations indicated light distribution as a possible area for improvement in the existing TPBR. Consequently, a reflector system was developed and implemented for the enhancement of light distribution and hydrogen production in the experimental TPBR – achieving a more uniform light field and an associated 48% increase in hydrogen production. Evaluating the feasibility of outdoor operation, the effects of diurnal light cycles and the emission spectrum of light were investigated. R. palustris was able to produce hydrogen under a sunlight-mimicking light emission spectrum achieving maximum hydrogen production rates of 0.790 mol·m−3 ·h−1 , albeit slightly lower as compared to under near-infrared light where it reached production rates up to 0.891 mol·m−3 ·h−1 . Hydrogen production was found to cease during dark periods in the diurnal light cycles; however, continuing again in the presence of light and achieving maximum Stellenbosch University https://scholar.sun.ac.za iii hydrogen production rates of ~0.015 mol·m−3 ·h−1 . This demonstrated promising potential towards outdoor operation of the TPBR, circumventing the requirement for external energy inputs. This dissertation has successfully demonstrated the application of a novel thermosiphon photobioreactor for photofermentative hydrogen production with minimal external energy input. The research comprised determination of suitable operating conditions for hydrogen production, a CFD modelling method for the design of PBRs, two novel TPBR designs and characterization thereof, a light distribution strategy for the enhancement of hydrogen productivity in PBRs, and insight into the passive circulation of biomass in a TPBR and the behaviour of R. palustris under simulated outdoor conditions. Collectively, this research provides knowledge not only improving the TPBR, but which could also be extended to other systems in the biohydrogen field.