Doctoral Degrees (Chemical Engineering)

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A framework for modelling the interactions between biochemical reactions and inorganic ionic reactions in aqueous systems.
(2022) Brouckaert, Christopher John.; Lokhat, David.
Bio‐processes interact with the aqueous environment in which they take place. Integrated bio‐process and three‐phase (aqueous–gas–solid) multiple strong and weak acid/base system models are being developed for a range of wastewater treatment applications, including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant‐wide wastewater treatment systems. In order to model, measure and control such integrated systems, a thorough understanding of the interaction between the bio‐processes and aqueous‐phase multiple strong and weak acid/bases is required. This thesis is based on a series of five papers that were published in Water SA during 2021 and 2022. Chapter 2 (Part 1 of the series) sets out a conceptual framework and a methodology for deriving bioprocess stoichiometric equations. It also introduces the relationship between alkalinity changes in bioprocesses and the underlying reaction stoichiometry, which is a key theme of the series. Chapter 3 (part 2 of the series) presents the stoichiometric equations of the major biological processes and shows how their structure can be analysed to provide insight into how bioprocesses interact with the aqueous environment. Such insight is essential for confident, effective and reliable use of model development protocols and algorithms. Where aqueous ionic chemistry is combined with biological chemistry in a bioprocess model, it is advantageous to deal with the very fast ionic reactions in an equilibrium sub‐model. Chapter 4 (part 5 of the series) presents details of how of such an equilibrium speciation sub‐model can be implemented, based on well‐known open‐source aqueous chemistry models. Specific characteristics of the speciation calculations which can be exploited to reduce the computational burden are highlighted. The approach is illustrated using the ionic equilibrium sub‐model of a plant‐wide wastewater treatment model as an example. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. The links between the modelling and measurement frameworks, which use summary measures such as chemical oxygen demand (COD) and alkalinity, are described in parts 3 and 4 of the series, which are included as appendices to the thesis. An additional paper, presenting case study on modelling an auto‐thermal aerobic bio‐reactor, is included as a third appendix, as it demonstrates the application of some of the principles developed in the series of papers.
Carbon dioxide encapsulation in methane hydrates.
(2022) Ndlovu, Phakamile.; Naidoo, Paramespri.; Babaee, Saeideh.; Moodley, Kuveneshan.
Coal mining and petroleum refining processes face extreme pressure under climate change and global warming threats. Hence alternative sustainable and renewable energy sources must be made available for the rising energy demands. Natural gas found in permafrost and seabed areas in the form of gas hydrates possess vast amounts of low-carbon methane gas, which can replace fossil-based energy sources. The capture and storage of carbon dioxide gas in natural gas hydrate beds with the release of methane gas is a sustainable route under intense research. This study investigates the methane-carbon dioxide (CH4-CO2) replacement reaction mechanisms and the improvement of the process using different techniques, namely, additives, secondary gas, and thermal stimulation. Firstly, the gas hydrate dissociation measurements for the former gases utilized in the study were performed. This was followed by kinetic measurements with nanoparticles (aluminum oxide, copper oxide, and graphene nanoplatelets) and chemical additives (zinc oxide powder, graphite powder, and magnesium nitrate hexahydrate crystals) in the presence of sodium dodecyl sulfate (SDS) to affect kinetic or thermodynamic improvement in hydrate formation. The kinetic parameters investigated were induction time, hydrate storage capacity, water consumed in hydrate formation, fugacity of the gaseous phase, and the ratio of gas consumed to moles of water. Graphene nanoplatelets were selected for replacement reaction based on promising results obtained from the kinetic studies. The CH4-CO2 replacement process was performed in a 52 cm3 equilibrium cell using deionized water and nanoparticles. Also, a new experimental setup with a 300 cm3 reaction vessel was designed and assembled for CH4-CO2 replacement in the presence of synthetic silica sand. The results from kinetic studies showed an improvement in the hydrate formation kinetics due to the presence of nanoparticles. The CO2 hydrate formation kinetics obtained a maximum storage capacity of 51 (v/v), with 1.2 wt.% graphene nanoplatelets which also produced a maximum water conversion of 25%. When nanoparticles were added, the induction time for CO2 hydrate in deionized water was reduced from 9 minutes to less than one minute. Graphite powder with a concentration of 1.2 wt.% had the highest rate of gas uptake of 0.0024 (mol of gas/ mol of water. min). In CH4 kinetics, the induction time was reduced from 18 minutes with deionized water to less than one minute due to addition of nanoparticles. A maximum storage capacity of 28.5 (v/v), water-to-hydrate conversion of 13.09%, rate of gas uptake of 0.0089 (mol of gas/ mol of water. min), and gas consumption of 0.0238 moles were obtained with 0.1 wt.% CuO + 0.05 wt.% SDS. Also, CH4-CO2 replacement measurements showed that an 80 mol% N2/20 mol% CO2 gas mixture yielded a CH4 replacement efficiency of 17.04% at a temperature of 274.77 K and pressure of 5.34 MPa. The highest amount of CO2 sequestrated was 57.03%, and 28.77% was the highest CH4 replacement efficiency. These results were obtained using pressurized CO2 with application of thermal stimulation at a temperature of 275.90 K and pressure of 5.66 MPa. In the replacement reaction with silica sand, the maximum amount of CH4 replaced was 37.49% with the pressurized CO2 at a pressure of 7.01 MPa and temperature of 276.43 K. Applying thermal stimulation and adding secondary gas (N2) improved CO2 sequestration from 51.73% to 76.63%. These outcomes are vital in applying hydrates in gas storage and CO2 sequestration.
Removal of wastewater contaminants by adsorption using iron on carbon foam.
(2022) Khumalo, Siphesihle Praise-God.; Lokhat, David.
The dyes in textile effluents have a deleterious impact on water bodies and impede photosynthesis by decreasing sunlight penetration. This work examined the adsorption capacity of an iron oxide sorbent immobilised on carbon foam generated from natural sources for to remove organic methylene blue dye from water. In this investigation, the carbon precursor and iron oxide precursor were combined in a single tank and carbonised. The carbon foam created had a self-assembled structure with flour as a basic constituent. This study examined the thermal and mechanical properties of carbon-based foam created from an inexpensive, green, and template-free carbonisation technique using natural grain and pyrolytic char. In addition, the adsorption capability of an iron oxide sorbent immobilised on natural carbon foam to remove organic methylene blue dye from water and the adsorption of phenol was investigated. The preparation method for iron-based nanoparticles substantially impacts particle shape and size, size distribution, active sites, and subsequent applications. As the number of nanoparticles grew, the dye adsorption increased due to the increased number of active sites. At high temperatures, the molecules of the pigment worked together more efficiently, making it simpler to eliminate. The possible application of magnetic nanopowder for phenol adsorption mobilised on natural grain carbon foam from an aqueous solution was also examined. Priority pollutants with high toxicity, even at low concentrations, are phenolic chemicals. A magnetic nanopowder was synthesised by dissolving an iron sponge in nitric acid to form iron nitrate, which was then added to a natural grain mixture consisting primarily of flour. Investigating the effect of starting concentration under constant adsorbent dosage revealed that absorbance values rose with increasing concentration. In each of these tests, the amount of phenol adsorbed increased as the original concentration rose. In addition, absorption increased when the carbon foam iron level increased. Using an equation relating to a pseudo first-order chemical reaction, a kinetic investigation determined that the phenol adsorption data sufficiently covered all carbon foam samples evaluated. The Freundlich, Langmuir, and Temkin equations were evaluated for modelling equilibrium adsorption isotherms, and it was determined that the Temkin model satisfactorily fit the experimental data. Sorbents with 0, 6 and 15 wt iron were produced. Transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) techniques were utilised to analyse the physical characteristics and surface morphology of the synthesised carbon foam. In batch testing, the adsorption capacities were examined by identifying the effects of a rise in iron content, sorbent dosage, contact time, and dye concentration. Breakthrough curves were obtained by adjusting the height of the sorbent bed and varying the flowrate of the dye solution. A higher bed height equates to a bigger amount of adsorbent. With increasing bed height, the breakthrough and equilibrium adsorption capabilities were shown to rise. When the flow rate is high, the dye solution leaves the column before equilibrium, resulting in shorter breakthrough and saturation durations. Higher bed heights and lower flow rates resulted in excellent dye removal in the flow through the system. Breakthrough time increases as iron content rises. The 15 wt.% iron sample had more adsorption capabilities than the 6 wt.% iron sample, but the 0 wt.% iron control sample exhibited minimum adsorption properties. This investigation was best represented by the pseudo-first order kinetic model (R2 > 0.96), while the Freundlich isotherm best describes the adsorption equilibrium (R2 > 0.99). The results show that an iron oxide sorbent immobilised on natural carbon foam effectively removes blue methylene dye. Variable amounts of iron, nitric acid and magnetite were added to each sample. Additionally, aqueous solutions with varying amounts of methylene blue dye were produced. Based on the change in Gibbs free energy, all samples demonstrated exothermic adsorption except for the magnetite sample, which displayed endothermic adsorption. As the temperature increases, the viscosity of the dye mixture reduces, allowing more adsorbate to flow through the outer boundary layer and internal pores of the adsorbent. In the adsorption of methylene blue onto iron supported by carbon foam, intraparticle diffusion was not the single rate-limiting step for all samples; rather, the adsorption rate was limited by a multistep elementary reaction mechanism in which numerous processes happened simultaneously. The pseudo-second order kinetic model best describes this experiment (R2 > 0.96), while the Freundlich isotherm best describes the adsorption equilibrium (R2 > 0.999). According to the results, an iron oxide sorbent immobilised on natural carbon foam effectively eliminates methylene dye.
Characterization and analysis of keratinous material from waste chicken feathers as protein ingredient for animal feed.
(2022) Kekana, Lizzy Mpho.; Sithole, Bishop Bruce.; Govinden, Roshini.
Keratin is one of the most abundant proteins, which is derived from wool, feathers, nails, hair, and other sources. Chicken feathers are a well-known keratin waste by-product, produced in large quantities by poultry slaughterhouses. Their disposal is expensive, and includes incineration of the waste thus contributing to greenhouse gases; or disposal in landfills, also leading to environmental pollution or they can be recycled into low-quality feeds for animals. Research is done worldwide for the beneficiation of waste chicken feathers into commercial products; these include cosmetics, pharmaceutical products, and biomedical products, and it is also useful in the production of animal feed. The focus of this research was to characterize and analyze keratinous hydrolysates formed from waste chicken feathers using enzymatic and chemical hydrolysis for their suitable applications in different industries. The novelty of this project is based on looking at analytical techniques of the keratinous hydrolysate produced from newly formed keratinolytic microorganisms and newly optimized chemical methods from the waste chicken feathers. Different fungal and bacterial strains were tested for the degradation of waste chicken feathers. The quality and quantity of the hydrolysate formed were determined by using a combination of analytical techniques, where the characterization is done via proximate and ultimate analysis. We used Fourier Transform Infrared Spectroscopy (FTIR), which showed the presence of the keratinous structure, which is known to have high protein content. Thermogravimetric Analysis (TGA), showed that a thermally stable hydrolysates were obtained, which is known to be formed by the hydrophobic hydrolysate, which is best for animal feed. CHNS analysis showed evidence that we have high protein content in the hydrolysate. Bradford assay revealed different quantities of the hydrolysate while Sodium Dodecyl Sulphate–Poly-Acrylamide Gel Electrophoresis (SDS-PAGE), showed mostly medium to low molecular weight, due to the presence of amino acids and small peptide chain. A low Ash Content was obtained which means a cleaner fraction of keratin. The hydrolysate formed from the enzymatic hydrolysis contains a mixture of amino acids and peptides. These peptides and essential amino acids formed are known to play a special role in various biological activities. The hydrolysates formed from different degradation methods were also compared, focusing on the qualities and quantities formed from enzymatic and chemical hydrolysis. While looking at all the characterization techniques, enzymatic was the best and suitable for animal feed due to the obtained keratin structure, which is more soluble, contains high protein content, has low molecular weights, and has a cleaner fraction of keratin. Future work will be based on obtaining a peptide chain using Liquid Chromatography with tandem Mass Spectrometry (LC-MS/MS), then testing the hydrolysates for bioactivities.
Decentralised sanitation to fill the gap in urban wastewater treatment within the eThekwini Municipality: a focus on tertiary treatment in vertical down-flow constructed wetlands.
(2022) Arumugam, Preyan.; Pocock, Jonathan.; Brouckaert, Christopher John.
South Africa’s bulk sanitation infrastructure is failing, and there is an urgent need to look at other appropriate sanitation solutions. Moreover, there is no data on the proportion of population with access to safely managed sanitation services, an indicator for the United Nation’s Sustainable Development Goal (SDG) 6.2.1a. In a safely managed sanitation service, the user is provided with an improved facility, not shared with other households, and the excreta is safely disposed in situ or transported and treated off-site. In the city of eThekwini, informal settlements spring up faster than services can be delivered, severely impacting on public health, the environment, and the social well-being of these communities. The eThekwini Municipality sees the benefits of decentralised sanitation solutions for in situ informal settlement housing upgrades, but the selected system needs to produce fully compliant effluent with the Department of Water and Sanitation’s (DWS) Revised General Authorisation (GA) limits for safe discharge to a water resource. Since 2010, a modular-designed demonstration-scale decentralised wastewater treatment system (DEWATS) for raw domestic wastewater from 84 households has been in operation in eThekwini. The DEWATS operates with no electricity or chemicals for treatment, but was designed according to European best practice, and not according to the community served (such as influent characterisation and hydraulic loading). This study evaluated the applicability of vertical downflow constructed wetlands (VFCWs) as the tertiary treatment module in DEWATS in four design configurations, to determine an appropriate design that can be applied for the formal housing upgrades where safe discharge of the final effluent is required. These designs, all receiving anaerobically treated domestic wastewater from the demonstration-scale DEWATS and operating in the field, were: 1. A single-stage demonstration-scale VFCW (design 1) compared to its hybrid configuration with a horizontal flow CW (HFCW) (design 2). 2. VFCWs with extended filter depths (1 m) consisting of 2-3 mm coarse sand media (at pilot-scale) (design 3). 3. Two-stage VFCWs (at pilot-scale, operating under field conditions) (design 4): a. First stage: 0.5 m filter depth consisting of 2-3 mm coarse sand media. b. Second stage: 0.6 m filter depth with 0.5-2 mm fine to coarse sand media. Neither design was able to produce fully compliant effluent for safe discharge to a water resource. Depth had no impact on the treatment efficiency of the pilot-scale single-stage VFCWs; although the design with a two-stage VFCW, adapted from the Austrian design, did achieve higher total nitrogen removal compared to single-stage VFCWs with/without extended filter depths. Overall, design 2 with the demonstration-scale hybrid CW design (VFCWHFCW) produced the highest quality effluent. However, nitrate-N removal was limited in the HFCW due to low residence times, mixed aggregate media, high dissolved oxygen (DO) concentrations and lack of available carbon as an energy source for denitrification. A plantbased carbon source from dried plant material of the invasive Giant reed, Arundo donax L., was used to augment the carbon availability for denitrifying bacteria within the HFCW. However, it is surmised that the DO concentration above 0.5 mg L-1 limited NO3-N removal. It is recommended that the DEWATS design with the hybrid CW system be redesigned according to the raw wastewater characterisation and media gradation within both CWs to ensure sufficient residence times, natural aeration in the VFCW, limited diffusion of oxygen into the HFCW, and increased availability of biodegradable chemical oxygen demand carbon for denitrification. Moreover, if the upgraded households are installed with urine diversion flushing toilets, then the nutrient load to the DEWATS will be reduced, potentially resulting in fully compliant effluent. Consequently, DEWATS will then be considered a safely managed sanitation service, allowing South Africa to track their progress against SDG 6.2.1a.
Phase equilibria studies on chemical mixtures encountered in the natural gas industry.
(2022) Zvawanda, Paul.; Naidoo, Paramespri.; Nelson, Wayne Michael.; Moodley, Kuveneshan.
Natural gas processing involves removing impurities from the gas streams. These impurities include carbon dioxide, nitrogen, hydrogen sulphide, water vapour, mercury, and others. These impurities must be eliminated from the gas streams, often using solvents, to meet sales specifications, enhance calorific value, lessen corrosion and blockages in pipelines due to hydrate formation and to allow for cryogenic gas processing. Solvents such as methanol and the lower molecular weight glycols have the most suitable characteristics to be employed as hydrate inhibitors, whilst 2,2′-[Ethane-1,2-diylbis(oxy)] di(ethan-1-ol) (triethylene glycol (TEG)) is mostly used in dehydration plants. In this study, phase equilibria data for mixtures of six chemical species commonly encountered in the processing of natural gas were studied. Phase equilibrium measurements were performed using a combined static (synthetic or analytic) apparatus. The apparatus comprises a horizontal cylindrical sapphire tube fitted with a movable piston that can be used to adjust the cell volume, thereby fixing/controlling the pressure in the process. A mobile Rapid Online Sampler Injector (ROLSI™) was fitted to the equilibrium cell for sampling both the vapour and the liquid phases. Vapour- liquid equilibrium (TPxy) data were measured and modelled for the following test systems, carbon dioxide + n-hexane and carbon dioxide + n-decane over a temperature range of 313.15 to 319.23 K. Bubble point (TPx) data were measured and modelled for the following test systems: carbon dioxide + methanol; carbon dioxide + TEG; methane + methanol; methane + TEG; carbon dioxide + aqueous TEG systems over a temperature range of 298.10 to 323.15 K. Generally, good agreement was observed between the reported literature data and the experimental data measured in this work, thus validating the experimental techniques used. New TPx data were measured and modelled for seven novel systems of this study, namely: methane + propane + methanol; methane + propane + TEG; methane + methanol + TEG; carbon dioxide + methanol + TEG; methane + propane + methanol + TEG; methane + propane + methanol + water + TEG; methane + propane + carbon dioxide + methanol + water + TEG over a temperature range of 283.15 to 323.15 K and in selected composition regions. The composition ranges and conditions are typical of those found in gas pipelines and gas dehydration units. The experimental data were modelled in Aspen Plus V11-12 using appropriate thermodynamic models, i.e., Peng Robinson (PR), Soave-Redlich-Kwong (SRK), Peng Robinson Wong Sandler (PRWS), Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), and the Cubic Plus Association (CPA) models. The maximum absolute average relative deviation (AARD) in pressure on all the modelled data were 4.89%, 8.67%, 7.39%, 9.63% and 19.7% for the PRWS, SRK, CPA, PR, and PCSAFT models, respectively, indicating that the PRWS model best described most of the systems. The measured data contributes to the information required for the process design, control and monitoring of methanol and/or TEG in gas conditioning systems. Furthermore, the data helps refine thermodynamic models that can predict phase behaviour in multicomponent systems in applications mentioned earlier, including gas hydrate inhibition, subsea gas processing, carbon capture, and storage.
A comprehensive investigation of existing sanitation helminth enumeration methods with the aim of producing an international standard.
(2022) Naidoo, Danica.; Archer, Colleen Edith.
TeHelminth testing in faecal sludge should be consistent so data are comparable. New faecal sludge treatments for on-site toilet technologies are constantly being developed in order for municipalities in developing countries to supply dignified alternatives to sewered systems that waste large amounts of potable water and require pumping to wastewater treatment works for centralised treatment. In order to ensure that these new, onsite toilet technologies adequately sanitise the faecal matter, helminth eggs are spiked into these systems to test inactivation according to the ISO-30500 standard for non-sewered sanitation systems (NSSS). A sensitive, standard helminth isolation and enumeration method, accredited to the ISO-17025 international standard for testing and calibration laboratories, is therefore required for application in laboratories globally. Internationally, laboratories and groups have used variations of the standard United States Environmental Protection Agency (USEPA) Method (2003), the Mexican Standard for Wastewater Analysis (2012), the Bailenger Method (1996) and the Pollution Research Group (PRG) Helminth Method (2017) previously used by the Water, Sanitation and Hygiene Research and Development Centre (WRDC) for helminth testing, and formed the foundation of this study. Conventional helminth methods can be broken down into five steps: washing and sedimentation of samples to separate eggs from larger particles, flotation using density gradients to separate eggs from heavier particles, centrifugation after both washing and flotation, extraction, that involves the use of a buffer and solvent combination to further separate organic material from eggs, and microscopic analysis. Some methods also include incubation that allows for egg-viability assessment. Every reagent used in these helminth methods was tested on Ascaris suum eggs for varying time intervals; ammonium bicarbonate and 7X® (a brand of ionic surfactant) performed best in terms of egg development and viability. Washing samples under pressure and no pressure were compared and the former produced the best egg recovery. Different flotation solutions were tested at different specific gravities, and zinc sulphate at specific gravity of 1.3 recovered the most eggs. Centrifugation speeds and times were tested after the washing and flotation steps, and 3000 rpm for 10 minutes and 2000 rpm for 15 minutes produced optimal egg recovery, respectively. Different extraction combinations were tested, and it was discovered that eggs were lost in this step. It was therefore recommended that extraction be removed from the method. Different wash solutions were then tested against various sample types to determine which resulted in the highest percentage egg recovery and which solutions facilitated easier microscopic analysis. Based on data from each experiment, a final SOP was produced for the new WRDC Helminth Method, that accommodates different sample types and egg viability assessment post incubation.st method.
Treatment and beneficiation of Kraft mill sludge to hydrogen and methane for bioenergy production.
(2021) Rorke, Daneal Carmine Solange.; Sithole, Bishop Bruce.; Gueguim Kana, Evariste Bosco.
The key drivers behind research into renewable and sustainable practices are escalating global energy demands and financial instability linked to the depletion of fossil fuel-derived energy resources. Additional drivers include the environmental ramifications of continued fossil fuel usage and unsustainable industrial waste disposal methods. As the fifth-largest global coal producer, South Africa is heavily dependent on coal for its energy needs, accounting for approximately 80% of its greenhouse gas (GHG) emissions in 2015. Efforts to decarbonise the economy and promote low-carbon technologies have thus been on the rise. Examples include implementing a carbon tax, sectoral GHG emission targets, carbon budgets and phasing out inefficient fossil fuel incentives. The South African pulp and paper industry plays an essential role in the economy by contributing 4% and 25% to the country’s manufacturing and agricultural GDP, respectively. In 2019, 4.1 million tonnes of pulp and paper products were produced in South Africa. As a water-intensive industry, advanced water treatment and recycling technologies are implemented, generating significant solid waste volumes as paper mill sludge (PMS) of up to 100 tonnes per 550 tonnes of pulp produced. The industry relies heavily on landfilling as its primary waste disposal method, with up to 69% of the generated PMS being landfilled. Due to the environmental concerns of landfilling, such as GHG emissions, leaching of toxic compounds into the surrounding land and water and limited land space availability, environmental regulations have become stricter, impeding the future applicability of landfilling. Biorefineries have gained significant interest as an approach to utilise biomass such as industrial wastes efficiently. Fuels, chemicals, energy and heat can be produced from industrial waste streams, adding value to what many industries consider a financial and environmental burden. Therefore, the beneficiation of PMS can contribute to the circular economy by serving as a low-cost, abundantly available feedstock for sustainable energy generation. The bioproduction of hydrogen and methane from PMS as alternative energy carriers offers a sustainable approach to energy production. Hydrogen is a CO2-neutral energy source with a high energy content that can be converted to electricity in fuel cells, producing only water when combusted. In comparison, methane exhibits an octane rating higher than gasoline and produces less CO2 than fossil fuels upon combustion. Furthermore, the application of biohythane, an advanced fuel mixture of hydrogen and methane, shows great potential to reduce GHG emissions and improve engine combustion yield in the automotive industry. Unfortunately, the presence of process rejects, ash, and residual lignin in PMS waste streams further contributes to its recalcitrance to microbial degradation, which leads to low product yields and high process times, thus significantly hampering the applicability of its beneficiation. Therefore, this study aimed to develop economic beneficiation strategies to enhance the amenability of PMS to microbial digestion and improve subsequent process efficiency of hydrogen and methane production. A combined mixture and factorial Response Surface Methodology (RSM) design was used to develop a novel pretreatment protocol using green liquor dregs (GLD), a waste generated by the pulp and paper industry, to improve the enzymatic hydrolysis of PMS. Optimised process conditions of 56% GLD: 44% PMS, 4.5% Tween-80, 60 min heating time, and a solid-to-liquid ratio (S:L) of 9.5% gave a maximal reducing sugar release of 16.38 g/L. Elemental analysis of each phase of the pretreatment protocol also showed a significant reduction in the concentrations of heavy metals; aluminium (81.39%), chromium (74.05%), cobalt (83.66%), nickel (88.06%), cadmium (88.89%), tin (83.82%) and lead (75.24%), and the complete removal of mercury. This is the first account of the utilisation of GLD as a pretreatment agent for PMS. Thereafter, the use of pharmaceutical wastewater (PW) as a supplementary nitrogen source to balance the system’s carbon-to-nitrogen ratio (C/N) in the optimisation of simultaneous saccharification and fermentation (SSF) hydrogen production from pretreated PMS was assessed, using a Box-Behnken design. The investigated process parameters included nitrogen source, enzyme dosage, substrate concentration, and pH. Using PW as the nitrogen source gave a 2.26 and 39.38% increase in the optimised hydrogen yield, compared to yeast extract and ammonium nitrate, respectively. A maximum hydrogen yield of 33.56 mL/g volatile solids (VS)added was obtained. Kinetic studies using the modified Gompertz model produced comparable data between PW and yeast extract, displaying a 3.26 h difference in process lag time. Furthermore, the maximum potential hydrogen production rate (Rm) obtained using PW was 9.22 mL/h, exhibiting an 8.73% increase compared to ammonium nitrate. The feasibility of using the effluent generated from the optimised processes for a two-stage anaerobic digestion (TSAD) system for methane production was then determined and compared to conventional single-stage anaerobic digestion (SSAD) of pretreated PMS. A low methane yield of 4.79 mL/gVSadded was obtained using SSAD. A significant improvement in the methane yield was observed using TSAD, reaching 30.88 mL/gVSadded. However, re-adjustment of the effluent’s C/N to 25 increased the process duration from 10 days to 17 days and negatively impacted the methane yield, resulting in an 8.16% reduction. In addition, a significant variation in process kinetics was observed between PW and yeast extract in the SSAD system, illustrated by production rates (Rm) of 0.29 mL/h for PW and 1.29 mL/h for yeast extract. The TSAD system exhibited enhanced stability for both nitrogen sources, exhibited by PW and yeast extract supplemented processes giving maximum potential gas production volumes (Gm), maximum potential gas production rates (Rm) and lag times (tL) of 113.28 and 104.93 mL, 1.28 and 1.40 mL/h and 4.25 and 1.71 h, respectively. Although C/N adjustment showed higher Gm values of 119.70 and 135.89 mL for PW and yeast extract, respectively, production rates were significantly reduced (0.50 mL/h). Compositional analysis of the resultant digestate showed a high VS content and C/N ratio, and an approximate NPK ratio of 2.3:1:2 from SSAD, whereas TSAD digestate exhibited an NPK ratio of 4.8:1:2, presenting almost double the nitrogen content. A high electrical conductivity (EC) value of 18.50 mS/cm observed in the digestate of TSAD was indicative of high sodium levels from PW, illustrating that, if the effluent C/N is adjusted to 25, the digestate of TSAD would require dilution before use as a soil amendment. To the author’s best knowledge, this is the first study describing the optimal beneficiation of PMS from the South African pulp and paper industry by pretreatment and subsequent two-stage anaerobic digestion for the production of hydrogen and methane. This study demonstrated the potential of PMS as a feedstock for bioenergy production, as well as the effects of supplementing its nitrogen deficiency with a secondary waste stream such as PW on process efficiency. Incorporating industrial wastes such as GLD and PW as alternatives to reagents such as NaOH and yeast extract to supplement fermentation processes can contribute to the circular economy concept by recycling waste streams. This improves the economic feasibility of PMS beneficiation and creates a sustainable energy solution to the disposal of PMS. This study has generated; one paper that has been published in a high impact, peer-reviewed journal, two papers that have been submitted for publication, and one more paper that is currently being prepared for submission to a peer-reviewed journal.
Gas-phase epoxidation of hexafluoropropene over supported copper oxide catalysts: mechanism and kinetics.
(2021) Ndlovu, Lindelani Archie.; Lokhat, David.; Ramjugernath, Deresh.
Abstract available in PDF.
Bioethanol production from excess food crops in Nigeria: process design, optimization, and techno-economic analysis.
(2021) Awoyale, Adeolu Abiodun.; Lokhat, David.
The global drive for diversification of energy sources, particularly by focusing less on non-renewable fossil fuels and harnessing renewable energy resources like bioethanol, has motivated this research work. Before the last 10 years, bioethanol meant for use as fuel was produced from carbohydrate-rich crops such as cassava, yam, maize, millet, rice amongst others. Because the production of bioethanol from these food crops has been envisaged to jeopardize food security, the focus has been shifted to the production of bioethanol from the residues left behind after processing the food crops. These residues can be classified as lignocellulosic biomass. The major concentration of this study is the production of bioethanol from residues of food crops, namely, corn cobs, rice husks, sugarcane bagasse, cassava peels, and yam peels. The biomass used in this research were sourced from different locations in Nigeria, where they are found in abundance at certain seasons yearly. In the course of the work, the biomass were sieved into two mesh sizes of 300 and 425 microns, and also some of the biomass as well as all the five biomass were all mixed and firstly characterized to evaluate the effects of particle size as well as hybridized biomass mixtures on the end products and production efficiency of bioethanol. The effects of the adopted pretreatments in this study on the biomass were also investigated, as such, three types of pretreatments were adopted in this study namely; combined hydrothermal and acid pretreatment, combined hydrothermal and alkaline pre-treatment, and hydrothermal only pretreatment. The results of the characterization of the different biomass, including the hybridized biomass after pretreatment showed the pore features for hybridized corn cobs and rice husks biomass have the maximum specific surface area and pore volume of 1837 m2/g and 0.5570 cc/g respectively. Also, the values of the cellulose content improved slightly with the pretreatment and the value of the lignin content decreased considerably. The cellulose values range from 34.2 to 36.5 wt% for the acid, alkali and hot water pretreated hybridized biomass. Releases from the pretreatment process to air, soil, and water were measured with SimaPro. The environmental impact categories accessed include global warming potential (GWP)/climate change, and acidification (AP). With a mean value of 15.82 kg CO2 (eq), the alkaline pretreatment using sodium hydroxide shows the highest release of GHG emissions, while acid pretreatment employing dilute sulphuric acid generated a mean value of 8.68 kg CO2. Hybridized feedstocks of cassava peels plus yam peels, and corn cobs plus rice husks biomass, were optimized using the Response Surface Methodology (RSM) centred on the statistical design of experiments (DOE) of the Box-Behnken design (BBD), in the production of bioethanol. The BBD was harnessed using a 3-level, 3-factor process variables using pH, time, and particle size. The bioethanol yield from the two hybridized biomass feedstocks was predicted by the developed quadratic polynomial models from BBD. The hybridized rice husks plus corn cobs biomass with a maximum bioethanol yield of 160 ml/1500 g biomass gave a better prospect for bioethanol production when compared with hybridized cassava peels plus yam peels biomass with a maximum bioethanol yield of 125 ml/1500 g biomass. This reinforces the finding that hybridizing the feedstocks enhances the capacity for better bioethanol yield after fermentation. The economic analysis of the produced bioethanol gave a price of 0.41 USD/l, which is a good deal as it compares favorably well with the 0.45 USD/l price of ethanol in the Nigerian open market.
Evaluation of forward osmosis technology for the treatment of selected concentrated brines.
(2021) Sitabule, Namadzavho Enos.; Buckley, Christopher Andrew.
Abstract available in PDF.
Cellulose nanocrystals: plant design for up-scaled production and applications in green construction materials.
(2021) Roopchund, Rishen.; Andrew, Jerome Edward.; Sithole, Bishop Bruce.
Two main problems were addressed in this project. Firstly, upscaling technologies from the laboratory scale to industrial scale is difficult in the absence of pilot scale facilities. This research entailed the development of upscaling protocols for large scale production of cellulose nanocrystals (CNC) from sawdust waste biomass to meet increasing end-user demands at the Biorefinery Industry Development Facility (BIDF). Secondly, despite CNC having excellent properties for potential applications in high performance products and materials, CNC applications are still in their infancy, thus needing the demonstration of high impact applications. To propose potential solutions to these problems, the purpose of this research was to firstly design up-scaled CNC production plants with production capacities ranging from 1 kg/day to 1000 kg/day. These upscaling protocols will ease the difficulty of upscaling the CNC production from the laboratory scale to industrial scale without pilot scale facilities. The second research purpose was to demonstrate the application of CNC in novel green construction materials. The widespread use of ordinary Portland cement (OPC) in the construction industry, and the current landfilling of fly ash are environmentally-degrading. Hence, the CNC-enhanced novel green construction materials used fly ash as a precursor to potentially replace OPC in the construction industry. Furthermore, a database of the mechanical, electrical, thermal, and microstructural properties of the novel green construction material was produced to guide further research and optimizations. Additionally, a universal iterative empirical framework was produced to develop novel green construction materials, whose properties can be customized per the requirements of the target application. Based on the two main research purposes, the dissertation was divided into two parts: Part A dealt with the up-scaled CNC production process design, and Part B dealt with the application of CNC in the development of novel green construction materials. Regarding the research design and methodology, the Project Life Cycle Management framework commonly applied in Industry, in conjunction with literary design standards and guidelines, were used in the process design. Software simulations were also used for certain aspects of the process design. The CNC production process design included a de-mineralization (process) water plant and an acid recovery plant. The equipment sizing and degree of automation were different for each production scale. For the development of the novel green construction material, meta-analyses coupled with statistical experimental design were used to optimize the experimental trials. The mechanical and electrical test results were used to generate three-dimensional response plots of the CNC effects, thus forming the property database. CNC was found to improve the strength, density, and corrosion resistance (dictated by the electrical resistivity) of the fly ash-based geopolymer construction materials produced at small quantities (optimally 1.7% by volume) when cured for 48 hours with sample rotation. The geopolymer exhibited endothermic properties based on the heat flow analysis, implying its suitability in thermal resistance applications. Furthermore, higher CNC concentrations were found to induce thermal stability during thermal variations in the curing and elevated temperature exposure. Overall, the application of CNC in green construction materials and the empirical framework for the custom development of green construction materials showed substantial potential, thus holding the ability to improve the commercial viability of novel green construction materials to improve their competition against OPC. The study concluded that the up-scaling protocols developed for CNC production from sawdust waste biomass can be applied in the absence of pilot scale facilities. Furthermore, this study demonstrated that CNC can be applied to develop high performance green construction materials. Only small quantities of CNC (less than 0.5% concentration) were required to improve the thermal and mechanical properties of the novel green construction materials. These small CNC concentrations yielded compressive strengths of up to 8000 kPa and generally reduced the mass loss of samples when exposed to elevated temperatures up to 7%. The broader implication of this project is that the implementation of the desired up-scaled CNC production plant can create employment and boost the economy while providing a steady supply of CNC to meet the growing end-user requirements. Furthermore, the two environmental issues of unsustainable industrial waste disposal and unsustainable OPC building materials can be solved by applying suitable industrial waste materials to produce novel green construction materials as alternatives to OPC using the empirical framework provided in this work.
Valorisation of waste chicken feathers: regeneration of keratin fibre into tubular nanofibres via electrospinning.
(2021) Khumalo, Mduduzi Blessing.; Ramjugernath, Deresh.; Sithole, Bishop Bruce.
The poultry industry generates billions of kilograms of chicken feathers as a by-product during chicken meat processing. A large proportion of the produced feathers is disposed of by landfilling, burial or incineration, but this causes environmental concerns due to greenhouse gas emissions and land pollution. Thus beneficiation of feathers into high-value materials is desirable. In the past few decades, there has been an influx of research on fabrication of nanofibres for applications in the health care sector. This is due to nanofibrous materials' unique properties, including high surface area to volume ratio, porosity and flexibility. These properties are vitally important in the clinical health care sector as they allow nanofibres to mimic the native extracellular matrix of most human tissues and organs, including peripheral nerves. This work aimed to valorise waste chicken feathers by extracting keratin and converting it into keratin nanofibres tubes for potential application as nerve regeneration conduits. The first step was the development of a process for extraction of keratin from chicken feathers. The method was optimised by Response Surface Methodology to obtain the best extraction conditions that included sodium bisulphite, sodium dodecyl sulphate, urea, temperature and time as independent factors that affect the yield of keratin. The process was statistically analysed to evaluate the effects of each factor and the factors' interactions on the extraction. Through scientific evidence, this work discovered that temperature is the most significant factor in the extraction process, followed by reaction time, the concentration of sodium bisulphite, and concentration of sodium dodecyl sulphate. The optimisation analysis produced a new model that predicts keratin yield (up to 67.23%) from the keratin extraction process. The second step was studying electrospinnability of the extracted keratin to generate tubular keratin nanofibres for possible use as nerve conduits in nerve regeneration. The results showed that pure keratin could not be electrospun to keratin nanofibres; however, keratin blended with polyvinyl alcohol (PVA) was spun to novel keratin nanofibres tubes. As far as the author's knowledge, this is the first time that this has been demonstrated. Analysis of the nanofibres' thermal stability, chemical properties, and morphological properties showed that the increase in keratin content in keratin/PVA mixtures increases the thermal stability of keratin/PVA nanofibres conduits, and causes a decrease in nanofibres diameters and porosity. The distribution of the nanofibers diameters also narrows as keratin content increase. Nano dimensions of the fibres were confirmed by scanning electron microscopy. These results imply a possible breakthrough in plausible applications of chicken feathers keratin into the nerve regeneration space as nerve repair conduits. This innovation will benefit the clinical health care sector in saving patients' livelihood and promoting a rapid utilisation of waste chicken feathers, resulting in a cleaner and safer environment.
Beneficiation of kraft pulp millwaste: using green liquor dregs in treatment of acid mine drainage as a new disposal solution in South Africa.
(2020) Sebogodi, Keolebogile Revelation.; Sithole, Bishop Bruce.; Johakimu, Jonas Kalebe.
Globally, water scarcity, depletion of non-renewable natural resources, handling and management of industrial wastes are not only significant environmental and economic burdens but also impact human and environmental health. In South Africa, the mining industry is essential to the country and a significant contributor to the GDP of the country. Two major ones are gold and coal mining. Unfortunately, the industries generate large amounts of acid mine drainage (AMD) that originate from the mining activities. The AMD is formed when the 3% pyrite mineral found in the mine effluent dams and voids of gold and coal mines is oxidised upon exposure to water and oxygen resulting in the formation of sulphuric acid which dissolves and leaches surrounding rock and soil matter thus introducing toxic metals into the aquatic waters and biota thus negatively impacting human, animal, and environmental health. Currently, this acidic discharge is neutralised by the use of alkaline reagents such as CaO, Ca(OH)2, NaOH, and CaCO3. However, these chemicals are expensive or are not sustainably resourced in the case of the widely used calcium carbonate. Possible landfilled, industrial, carbonic wastes such as the green liquor dregs (GLDs), from Kraft pulp mills, could be used as sustainable alternatives for the CaCO3 and its derivatives in pre-treating AMD. These wastes streams are produced at the rate of 7-15 kg/ton of dry pulp. In South Africa, this translates to ~100 000 tons of GLDs that are produced and landfilled annually. However, this is an environmentally challenging and not cost-effective practice. Thus, this study entailed characterising GLDs produced in South Africa, evaluating them for the potential of neutralisation of AMD, and optimising the neutralisation process variables. This is the first time that this type of study has been conducted in South Africa. Furthermore, the neutralisation of the coalfields AMD with GLDs has not yet reported in the literature and this is the first time the optimisation of AMD treatment by GLDs is being studied. The study entailed statistically designed experiments that employed a Box-Behnken Design and Response Surface Methodology to optimise the variables involved in the neutralisation process. The results indicate that although characteristics of GLDs from different mills differ they all are effective in neutralisation of AMD from gold or coal mines and their neutralisation potential is similar to that of calcium carbonate. Nevertheless, the SEM/EDX, ICP-AES/ICP-MS, XRF, and XRD analysis on the sludge that emanated from either of the neutralisation processes showed that the neutralisation of AMD using GLDs is effective and enables precipitation, co-precipitation, or adsorption of the different metals from the AMD. The pH of AMD could be raised to optimum pH process value and reduce the acidity at a low dosage, thus offering a competitive advantage over commercial CaCO3. Thus, using GLDs for neutralisation of AMD can be an effective symbiotic process that can benefit two industries in managing their waste discharges: the Kraft pulp industry and the mining industries. The results obtained from the optimisation of the variables (neutralising reagent dosage, process time, and stirring speed) involved in the neutralisation process showed that the reagent dosage was the most significant variable while the stirring speed was the least significant one. The models for all the GLDs and reference materials were proven to be significant because all of them had a p-value of <0, 000001 and their R2 and Adjusted R2 were close to 1.
Investigation and optimization of intensified separation processes: treatment of aqueous organic mixtures using reactive extraction and emulsion liquid membrane techniques.
(2020) Inyang, Victoria Malachy.; Lokhat, David.
The application of intensified processes of reactive extraction and emulsion liquid membrane technique for the separation of various low molecular weight carboxylic acids (propionic acid, malic acid and butyric acid) from very dilute aqueous solution was undertaken. The aqueous phase feed concentration ranges of the different carboxylic acids for reactive extraction [propionic, butyric (0.4-1 kmol/m3), malic (0.1-1kmol/m3) acids] and emulsion liquid membrane (propionic and malic acid (0.05 – 0.1 k mol/m3) were chosen to simulate the actual aqueous waste streams and fermentation conditions encountered in industry. Trioctylamine extractant in 1-decanol as active diluent was used as the extractant (organic) phase to perform the experiment. The effect of different process variables on the extraction efficiency expressed in terms of distribution coefficient (KD) and degree of extraction (%E) was systematically determined. Three independent process variables were chosen, including temperature (298.15-313.15 K for propionic acid and malic acid and 298.15-318.15 K for butyric acid), initial organic acid concentration in the aqueous phase and trioctylamine composition (10-30 %) in the organic phase for the reactive extraction technique. The interactive effects and optimum values of these process design variables were determined using response surface methodology (RSM) for the reactive extraction process. The statistical design analysis demonstrated that the acid concentration and trioctylamine composition had significant effect while temperature had an insignificant effect on the response value as well as interactive and quadratic effect on the response. The optimum solution led to an experimentally determined extraction efficiency of 89.79% for propionic acid, 93.25% for malic acid and 96.45% for butyric acid. The extraction efficiency in the emulsion liquid membrane process is dependent on the studied parameters such as initial acid concentration, sodium carbonate concentration, trioctylamine concentration, treat ratio and extraction time. The formulation of the liquid membrane consists of trioctylamine as carrier, 1-decanol as modifier, sorbitan monooleate (Span 80) as surfactants in heptane and sodium carbonate (Na2CO3) as a stripping agent. Response surface methodology (RSM) and artificial neural network (ANN) was employed for experimental design, optimization, construction and interpretation of response/output surface plots so as to show the effect of input variables on extraction efficiency in addition to the combined effects between variables. The optimum solution achieved by RSM led to an experimentally determined extraction efficiency of 92.28% and 85.91% in the propionic and malic acid extraction respectively by (emulsion liquid membrane) ELM process. The intrinsic kinetic studies of reactive extraction were determined for propionic and malic acid extraction using dilute solutions of the acids with concentration range of 0.2 to 0.6 kmol/m3 and trioctylamine (10%v/v) in 1 decanol as extractant at 303.15 K. The kinetic process parameters such as reaction order, mass transfer coefficient and rate constant were evaluated using the experimental data. From the results obtained, the reaction was found to be an instantaneous second-order chemical reaction occurring in the organic diffusion film. The values of the rate constants were found to be 0.430 m3/mol s and 0.332 m3/mol s respectively for propionic acid and malic acid while the mass transfer coefficient, km was also obtained for propionic acid (9 x 10-6 m/s) and malic acid (3x10-6 m/s). From the results obtained, these intensified technique represents an effective method for the recovery of low concentrations of carboxylic acids from aqueous waste streams and fermentation broths, with emulsion liquid membrane offering significantproperties/characteristics like small quantity of organic phase and extractant, very fast extraction time, increased solute transfer rate and selectivity through the membrane, high selectivity and applicability in specie removal from very low to high concentrations and governed by a non-equilibrium mass transfer. It is therefore worth investing in this process or alternatively a hybrid of both reactive extraction and emulsion liquid membrane processes.
Beneficiation of chicken feathers and sawdust waste biomass: extraction of keratin and cellulose nanocrystals for use as binders in particleboard production.
(2020) Fagbemi, Olajumoke Deborah.; Sithole, Bishop Bruce.
The wood industry consumes large quantities of synthesis adhesives accounting for more than 65% by volume of the adhesives used worldwide. Synthetic adhesives are formaldehyde-based and that cause environmental pollution and affect human health. Hence, there is a growing interest in bio-adhesives sourced from natural sources: plant and animal, these could be a suitable replacement for environmental toxic formaldehyde-based binders. In addressing the problems mentioned above, from both economic and environmental points of view, this study focused on the beneficiation of waste chicken feathers generated by poultry slaughterhouses and waste sawdust from the sawmilling industry into binders to replace fossil-based binders and explore their use in the production of wood panel particleboards. The linear and interactive effect of process condition on the extraction efficiency of keratin protein were modelled and optimized. To the best of the author’s understanding, the work presented here is first for South Africa as a country. Extraction processes with varying key process parameters were experimentally assessed for protein and keratin yield. The novel extraction procedure used a hybrid of two reducing agents; sodium hydroxide and sodium bisulphite, under mild concentrations to minimize the keratin protein structure's degradation. The extraction variables, optimised using Response Surface Methodology, were temperature (87°C), extraction time (111 minutes), sodium hydroxide (1.78%), and sodium bisulphite (0.5%). Analysis of the protein hydrolysate content showed the elemental composition of 13.85% N, 47.25% C, 6.90% H and 2.8% S, and a molecular weight range between 15 and 3 kDa; ideal characteristics for bio-binder applications. Keratin and cellulose nanocrystals were each evaluated separately as bio-adhesives for particleboard production. The efficiency of the formulated bio-adhesives and the mechanical strength performances of their fabricated particleboards were also assessed. Results showed that keratin on its own did not display significant binding properties; however, these were significantly improved by adding the citric acid-based polyamide-epichlorohydrin cross-linking agent. The fabricated particleboard's mechanical strength performance met the 1-L-1 grade specification of the American National Standards Institute. Moreover, the beneficiation of extracted keratin protein hydrolysate from waste chicken feather with incorporated cellulose nanocrystals for bio-adhesive formulation and particleboard fabrication was investigated. The FTIR spectra confirmed the covalent bonding between the azetidinium of the citric acid-based polyamide-epichlorohydrin cross-linking and the hydroxyl groups of the keratin protein hydrolysate. The mechanical strength performance of the fabricated particleboard met the specification for the 1-L-1 grade of the American National Standards Institute (A208.1). 6, 5 and 1184, 34 MPa, were the respective values obtained for modulus of rupture and modulus of elasticity of the panels made with keratin-based adhesive. Additionally, the keratin-based adhesive incorporated with cellulose nanocrystals as a filler enhanced the static bending and bonding strength properties of the formulated bio-adhesive. Furthermore, the valorisation of wood sawdust into cellulose nanocrystals (CNC) for application as a binder in the manufacture of particleboard was also carried out. The cellulose nanocrystal extracted from wood sawdust using acid hydrolysis and an oxidizing agent, incorporated with crosslinking agents, viz., CNC-glyoxal, CNC-hexamine, CNC-polyamide-epichlorohydrin, and CNC-polyethylene to make cross-linked bio-binders. X-ray diffraction (XRD) indicated high crystallinity index (78%) of the CNC and typical nano dimensions of 2.1–10 nm for diameter and 150-350 nm for length as revealed by the transmission electron microscope (TEM). Thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) showed high thermal stability (250 – 400 ℃) of the CNC. Significant mechanical strength performances of the particleboard panels were evident in the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the CNC-binder fabricated particleboard. The panels met grade 1-L-1 specification of the American National Standards Institute A208.1. Similarly, the incorporation of cross-linking agents enhanced the static bending and bonding strength properties of the formulated CNC-binders. Hence, the research conducted in this thesis demonstrated the potential of bio-binders produced from waste biomass, viz., chicken feathers and sawdust to replace fossil-based binder.
Extraction of sulphur compounds from model fuels with use of ionic liquids.
(2020) Durski, Marcin Hubert.; Naidoo, Paramespri.; Ramjugernath, Deresh.; Domańska-Żelazna, Urszula Maria.
One of the most promising applications of ionic liquids in the modern chemical industry is its use as extractants in separation methods, primarily extraction and extractive distillation. Sulphur emissions are regulated widely by governments and international organisations, to ensure the lowest possible emission of sulphur oxides to the atmosphere, with many stipulations that the amount of sulphur compounds in the fuel must not exceed 10 ppm. This study focused on the screening of the potential extractants for the desulphurisation of the fuels by performing experimental measurements for five different ionic liquids via two-phase separation techniques, namely, gas-liquid chromatography (GLC) and liquid-liquid extraction (LLE) measurements. The 1-butyl-1-methypyrrolidinium dicyanamide [BMPYR][DCA] was used as a solvent in a packed column during gas-liquid chromatography measurements of the retention times which allowed for the calculation of activity coefficients at infinite dilution. This technique was used to ensure coverage of the whole spectrum of the experimental methods and thermodynamic principles for assessing the suitability of ILs for the intended purpose. Four ionic liquids: dihydroxyimidazolium bis{(trifluoromethyl)sulphonyl}imide [OHOHIM][NTf2], 1-butyl-3-methylimidazolium trifluoromethanesulphonate [BMIM][OTf], 1-butyl-1-methylpiperidinium dicyanamide [BMPIP][DCA] and tri-iso-butylmethylphosphonium tosylate [P-i4,i4,i4,1][TOS], were were assessed via liquid-liquid equilibria measurements for suitability as extractants. Ternary LLE measurements for the systems {IL+thiophene+hydrocarbon} were performed, and the selectivity (S), distribution ratio (β) and performance index (PI) of the ILs investigated in this work was compared to ILs reported in the literature. The LLE tielines were modelled using the Non-Random Two Liquid (NRTL) model, which showed a satisfactory correlation of the experimental data, with a maximum absolute average deviation of 0.01 in the mole fractions. The most promising IL determined in this study is [BMIM][OTf] with PI equal to 54.8 and 193 for octane and hexadecane systems, respectively. This conforms with the findings in literature as imidazolium ILs with relatively short alkyl substituents as reported to be the most promising extractants in terms of performance index (PI). The least promising results were obtained for [BMPIP][DCA]. Dicyanamide anion was not strongly represented in LLE literature, yet PIs calculated using activity coefficients data for ILs with this anion provided justification for further investigations. The recommendation from this work is that laboratory-scale extraction measurements be performed to assess the viability and reuse of this IL.
Development of a computationally efficient monolith reactor simulator: CFD-hybrid model analysis of methane oxidation monolith catalysed systems.
(2020) Khama, Mopeli Ishmael.; Rawatlal, Randhir.
The optimisation of complex geometries such as that of monolith reactors can be supported by computation and simulation. However, complex boundaries such as those found in multi-channel monoliths render such simulations of extremely high computational expense. Adding to the computational expense is the strong coupling among reaction kinetics, heat and mass transfer limitations in these channels. This severely limits the possibilities for geometric optimisation. In the first step toward developing a fast-solving hybrid simulation, a detailed CFD simulation was used to obtain the unsteady state, spatial temperature and concentration (and hence reaction rate) profiles for a range of input conditions. The results of the CFD simulation were then accepted as the benchmark to which faster-solving models were measured against to be considered as viable descriptions. A modified plug flow with effectiveness factor correction for wall mass-transfer was developed and evaluated as the first step towards the development of a multi-channel model. However, the modified plug model is only applicable to single channel monoliths and cannot account for heat transfer across high-density multi-channel beds. For multichannel simulations, the modified plug flow model is embedded into a hybrid-model framework. The hybrid model is based on the principle that, due to the high density of channels in a monolith, there will exist an equivalent homogeneous cylindrical model that approximates the behaviour of a bundle of channels acting as axial heat sources. This model entails the coupling of analytical solutions to single channel mass and momentum transfer with heat transfer across the single-shell extra-multi-channel space. Due to the application of effectiveness-factor type approaches, it is shown that the model can be represented by algebraic models that accurately represent the partial differential equations (PDEs) that describe monolith reactors. A close agreement between both temperature and species mole fraction profiles predicted from the modified plug flow model and a detailed CFD model was found with R2 values of 0.994 for temperature. The time needed to find a converged solution for plug flow model on an Intel(R) Core(TM) i5-5300U CPU @ 2.30GHz workstation was found to be 53 seconds in comparison to 1.3 hours taken by a CFD model. The hybrid model was itself validated against the CFD multichannel model. The hybrid model axial temperature and species concentration profiles at various radial positions were found to be in a close agreement with CFD simulations, with relative error found to be in the 0.35 % range. The clock time on an Intel(R) Core(TM) i5-5300U CPU @ 2.30GHz workstation was found to be 38 hours for a CFD multi-channel simulation which when compared with the 53 seconds clock time of the hybrid model implies the suitability of hybridisation for the application to geometric optimisation in the design of monolith reactors. The hybrid-model is developed to facilitate geometric optimization with the view of reducing hot spot formation, pressure drop and manufacturing costs. This is because monolith reactors applied in catalytic partial oxidation of methane are coated with precious metal catalysts, significantly contributing to capital costs. By isolating regions of high catalytic activity, it becomes possible to reduce the amount of precious metal coating required to achieve high conversion. The fast-solving hybrid model was used in the economic analysis of the catalytic partial oxidation of methane to syngas. Due to the low computational expense of the hybrid model, it was possible to investigate a wide range of design geometry and operating condition .It is shown that, for methane oxidation over a Platinum gauze catalyst, the channel diameter could be optimised to the 0.8 mm level resulting in the highest syngas revenue (R 65754.14 /day). The distribution of the catalytic material on the monolithic walls was found to influence the reactor performance hence the process profitability. The non-uniform distribution was found to significantly reduce the cost of fabrication while maintaining a high syngas productivity. In general, a method is proposed to optimise design and operation of catalytic monolith reactors through the application of fast-solving models.
Purification of nitrogen trifluoride (nf3) via physical separation.
(2020) Hassanalizadeh, Rasoul.; Ramjugernath, Deresh.; Naidoo, Paramespri.; Nelson, Wayne Michael.
Abstract available in the PDF.
Analysis of non-Newtonian behavior of crude oil: experimental study annumerical modeling using computational fluid dynamics (CFD) technique.
(2020) Mohammadi, Amirabbas.; Mkhize, Ntandoyenkosi Malusi.
Abstract available in the PDF.

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