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An investigation into the Use of Fischer Tropsch wastewater as an organic source in the treatment of acid mine drainage (AMD) using dissimilatory sulfate reduction
(2024) Magowo, Webster
Acid mine drainage (AMD) and Fischer Tropsch wastewater (FTWW) are two major pollutants associated with coal mining and usage, as such these pollutants are likely to be found in proximity to each other in coal mining regions. AMD is characterized by high sulfate and dissolved ion concentrations with little to negligible organic content, while FTWW has a very high organic content made mainly from alcohols and short chain fatty acids (SCFA). FTWW has very high COD of up to 30 000 mg/L. Sulfate reducing bacteria (SRB) can use organic substrates to reduce sulfate to sulfide in the process generating alkalinity. The hydrogen sulfide reacts with dissolved metals to form metal sulfide precipitates, while the alkalinity attenuates pH. This means SRB can be used to remove organic pollutants from FTWW and dissolved metals and sulfates from AMD. This study sought to use FTWW as the carbon source and electron donor for biological sulfate reduction in a fixed bed bench scale bioreactor treating AMD. Batch and continuous flow reactors including single stage and two stage continuous sulfate-reducing bioreactors were evaluated in this investigation. The reactors were assessed on their ability to remove COD from the FTWW, sulfate and dissolved iron from AMD. Considerable success was observed in batch reactors, with up to 99 % of iron removed from AMD, sulfate removals was at 95 %, while more than 99 % COD was removed from the effluent. Fed batch and continuous reactors were not as successful as the treatment efficiency dropped with time due possibly to the accumulation of inhibitory substances such as hydrogen sulfide and metal sulfide precipitates. The two-stage continuous bioreactor performed better compared to the single stage continuous reactor. All the reactors however maintained the pH above 7.0 against an influent pH of 2.0. Lower temperatures during winter reduced the performance of the bioreactors as the pH of the effluent dropped to below 6.0. There was a a large amount of residual sulfate, iron and COD in the reactors operated in winter than in those operated in summer. Another 2-stage bioreactor system consisting of a sulfate reducing bioreactor connected in series to a sulfate oxidising bioreactor was operated for converting the hydrogen sulfide produced in the sulfidogenic bioreactor to sulfur. Micro aerobic conditions were applied by pumping limiting amounts of oxygen into the sulfur oxidising reactor to allow for the oxidation of sulfide to elemental sulfur. Up to 92 % of sulfate was removed in the silfidogenic reactor with the subsequent production of an average 116mg/L/d of hydrogen sulfide during the operational period. The hydrogen sulfide was converted to sulfur in the oxidising reactor with 97 % sulfur recovery. An average102 mg/L/d sulfur was produced in the sulfur oxidising reactor. The results indicate the potential in using FTWW as a cost-effective electron and carbon source for biological sulfate reduction allowing for the co-treatment of AMD and FTWW.
Design of an acid mine drainage remediation process using by-products from the steel manufacturing and sugar processing industries
(2024) Naidu, Tamlyn Sasha
Acid mine drainage (AMD) and basic oxygen furnace (BOF) steel slag are waste products from the mining and steel refining processes that are produced in large volumes throughout the world. Although both substances possess useful characteristics, they are largely treated as wastes, and dumped or disposed of in waterways and landfills, causing detrimental environmental and health issues. Treatment schemes that have aimed to address the occurrence or presence of AMD, in particular, are limited due to (i) the high cost of remediation (when compared to the relatively low cost of water), and (ii) variation in AMD characteristics which makes a standard/uniform treatment approach difficult to achieve. The technology explored within this dissertation has the potential to combat both challenges: (i) the cost of the treatment scheme would be substantially lower due to very little envisioned operational involvement, as well as the cost of reagents being kept low (through the use of waste and by products, and through potential valorisation of these wastes); (ii) the technology is aimed to be deployed at the source of production – individual mining sites – in a modular manner, allowing for alteration of treatment schemes to combat a wide variety of AMD strengths and qualities. BOF slag and AMD combined in an optimized process allowed for the rise in pH of the AMD to neutral levels, as well as the removal of substantial amounts of metals and sulfates. Following this initial physical and chemical treatment, the partially treated AMD stream was then suitable for biological treatment using by-products from the sugar industry, allowing for further removal of sulfate, bringing the water closer to discharge and even drinking water limits: at a laboratory scale, sulfate was shown to reach levels of below 200 mg/L and levels of below 10 mg/L were reached for Al, Fe, Mg and Mn. Operation of a pilot-scale plant treating 200-1000 L/day demonstrated Al, Fe, Mn and SO4 2- removals of 97%, 87%, 100%, and 87% respectively – showing that treatment occurred even in fluctuating AMD conditions. The configuration of the treatment scheme that yielded the best results was suggested for the final design and included a modular system in which BOF slag was used to increase the pH of the system before bacteria sugarcane derivatives were used to polish the sulfate leftover in the stream to below 400 mg/L. The system which was proposed, designed and tested in this study was successful in treating AMD. It proved to be able to serve as a precursor to multiple other treatment regimes (reverse osmosis, membrane filtration, ionic exchange), or as a stand-alone system to service smaller, isolated areas that aim to reuse the AMD affected water in processes or for irrigation.
Development of a tool for determining and evaluating the most optimal reaction pathway systems: converting carbon dioxide to methanol and dimethyl ether
(2024) Jugmohan, Jaimee
An integral cog in the design of new chemical plants is the identification of promising, feasible reaction pathways, thereby necessitating that an extensive amount of resources be focused on this developmental stage. Despite the substantially expanded quantity of reaction pathway possibilities in the chemical and fuel industries, it is exceedingly difficult to build an economically and environmentally sound manufacturing processes. Additionally, this task has proven to be time consuming. Novel catalytic pathways that exhibit feasibilities at laboratory scale, may not hold true when scaled to an industrial level, leaving potential plant application with much uncertainty. One of the major concerns, is the cost of unit operations required to achieve the reaction and separation conditions, as well as the separation units needed in achieving a marketable purity of the desired product. To increase feasibility, products from a single reactive system can be treated as an intermediate, thereby producing a secondary product with greater economic value. Whilst this is not guaranteed, the possibility cannot be negated. This would involve employing two reactive systems consecutively, in a chemical plant, potentially optimizing the economic and environmental gains of the overall process system. The Automated Systematic Synthesis Framework tool (ASSF tool) presented herein, is a novel, rapid screening tool which bridges the gap between the scale up of laboratory systems, process design, and economic and environmental analysis, by (1) providing generic design structures, cost and environmental implications associated with the scale up of a reactive system, (2) systematically searching for, and identifying, the possibility of pairing reactive systems as consecutive reaction mechanisms in a chemical plant, attempting to increase overall feasibility of the process structure. This, however, does not imply that the ASSF tool is able to identify new reaction pathways, but rather uses existing reaction pathways in the inputted database to look at extending the boundaries of the chemical plant to incorporate a secondary and/or tertiary reactive system. This search space reduction-based strategy aids in identifying promising reactive systems, and their likely bottlenecks, prior to the utilization of extensive time and design resources. The potential and novelty in the ASSF tool are demonstrated through its application to a case study focused on the production of methanol (MeOH) and dimethyl ether (DME) via carbon dioxide (CO2) hydrogenation. Existing engineering software systems require prior training, and an in depth understanding of multiple engineering concepts, including widely utilized platforms such as Aspen ® Plus. One of the novel aspects of the ASSF tool, however, lies in its generic design and level of detail required to analyse a reactive system, only needing the balanced stoichiometric equation and its operating conditions. Once entered as a database, the ASSF tool searches for potential reaction pathway combinations. Each reactive system undergoes a basic, generic process design, costing the unit operations required in, and leading up to, the reaction and separation systems. These plant structures are then analysed using economic and environmental criteria, with the final, reduced search space being ranked in order of its expected industrial feasibility. It is important to note, however, that the ASSF tool is not designed to replace existing engineering design and simulation software systems, such as Aspen ® Plus. Instead, the ASSF tool is a novel, precursory platform with the ability of automatically narrowing large reaction pathway search spaces in a fraction of the time than would be needed if individually simulated in the existing software platforms. Once the search space has been reduced and ranked, as per the ASSF tool, the user can focus their design resources on the intricate design of those potentially feasible reactive systems, necessitating the use of extensive engineering software. Additionally, the simple interface of the ASSF tool allows it to be utilized without prior training, providing reliable results with limited/streamlined inputs. To ensure reliability of the results obtained from the ASSF tool, the code was validated and verified against data published when using existing simulation platforms, i.e., CHEMCAD ® and WEcoMP, noting minor deviations (< 6%) in capital costs. This is within the ± 30% range for preliminary design procedures. Previously a reaction pathway database (RPD) developed and analysed by Jugmohan, et al. (2020) noted an analysis period of 10 months, owing to the manual design and transfer of data between four intricate software platforms. The use of the ASSF tool on the same RPD results in a complete analysis in under 5 hours, concluding an identical final search space of 5 potentially feasible reactive systems – using economic and environmental criteria as the crux of this feasibility. This reiterates the use and uniqueness of the ASSF tool in identifying promising reactive systems at the early onset of the design process, allowing for future design and research resources to be more focus driven. Whilst not designed for the purpose of analysing experimental data, the ASSF tool can be expanded to provide a quick, preliminary analysis of experimental data, determining the economic practicality of attaining operating conditions in a scaled up industrial setting. When practical, the ASSF tool provides the user with an indicative range of operating conditions likely to provide the greatest chance of success in future experimental work and scale up ventures, allowing for research resources to be concentrated within this narrow scope.
Fischer–Tropsch synthesis: application of clinoptilolite (natural zeolite) as catalyst support
(2024) Chikati, Roick
In this study, clinoptilolite (a naturally occurring zeolite) was used as catalyst support in Fischer Tropsch Synthesis. Prior to its use, raw clinoptilolite was crushed sieved to yield different particle sizes (-212 to +150 µm; -150 to +106 µm; -106 to +75 µm; -75 to +53 µm; -53 to +38 µm; -38 to +25 µm; and less than -25 µm). Seven 10% wt cobalt catalyst supported on different size classes of clinoptilolite were prepared using the incipient wetness impregnation method. A thorough investigation was done on the characteristics of cobalt supported on clinoptilolite particles of different sizes using TPR, XRD, XRF, BET and SEM techniques. It has been demonstrated that these techniques provide insight on the effect of the support particle size, and this could be used as a quality control tool to evaluate the efficacy of the preparation method. Temperature-programmed reduction (TPR) was used to examine the non-isothermal reduction of cobalt oxide using 5% hydrogen in argon at three distinct heating rates (5, 10, 15 o C/min). When using the Kissinger model, it was discovered that the activation energy (Ea), varied from 102.45 to 254.01 kJ/mol, depending on the support particle size of the catalyst. The lowest activation energy being achieved with a support particle size in the 212 to 150 µm range. Reducing the catalyst reduction temperature has significance in FTS, since it drastically reduces the sum of money spent on the energy input required for reduction. XRD, XRF and SEM confirmed the phases making up the catalyst, loading of the catalyst and the particle size distribution respectively. It is worth noting that though differences exist between different size classes, no clear trend was obtained for any of the BET parameters. For this study, three size classes were investigated as the support for an FT catalyst: -75 to +53 µm; -53 to +38 µm; less than 25 µm. Using a fixed bed reactor at 220 o C and 10.85 bar(abs), the maximum CO conversion obtained was 44.97% when using the -53 to +38 µm size class (-78 to +53 µm size class giving 32.06 %, and < 25 µm µm giving 31.29% Co conversion). At the conditions studied, methane selectivity ranged between 14.95 and 16.97% for the support class size studied, while C2-C4 selectivity ranged between 14.55 and 19.01%, and C5+ selectivity ranged between 66.04 and 70.29%. The acquired product selectivity results are similar to those reported in the literature, which validates the use of this support. Statistical analysis done on the FT results obtained, one-way analysis of variance (ANOVA) and post-hoc Bonferroni adjustment indicated that utilization of different support size classes had an effect on CO conversion. An innovative data simulation technique based on response surface methodology (RSM) was used as part of the design of experiments (DOE) to thoroughly investigate the effect of the various operating FTS conditions for both cobalt and Iron based catalyst. These discoveries might be have valuable implications for the design of a catalyst that can be used in the coal/biomass to liquid process
Hydrothermal (CO) treatment of coal discards and sewage sludge for production of advanced materials
(2024) Kahilu, Gentil Mwengula
The disposal of coal discards (CD) and sewage sludge (SS) is a substantial problem to waste management in coal beneficiation and wastewater treatment plants (WWT). This work investigates essential aspects for contributing to the reduction of environmental effects, with a particular emphasis on the hydrothermal carbonization (HTC) technology for the synergetic treatment of CD and SS to produce value-added carbonaceous materials (CM). When compared to the individual treatment of CD and SS, the Co-hydrothermal carbonization (Co-HTC) method improved the physicochemical attributes of the produced hydrochars (HCs). The produced HCs could be suitable for a wide range of potential applications i.e., soil amendment, WWT, production of activated carbon (AC). The findings of this thesis indicate that profitable commodities may be made from the aforementioned waste materials, lowering the cost of waste disposal and ecological damage while also providing new green jobs. South Africa, as one of the world's top coal producers, creates approximately 60 million tons of coal waste each year, which is typically stockpiled in the form of a discard dump and slurry ponds. The environmental risk and public health risk posed by the presence of these wastes represent a significant impediment to the socioeconomic growth of the coal mining sector. As a result, waste coal management is advised to devise innovative approaches for the reuse and recovery of coal waste. In this thesis, the HTC and co-HTC of CD and CD-SS blend respectively has been experimentally performed for the upgrading of the fuel properties and adsorbent characteristics of the raw material utilized proving the ability of HTC to produce high-quality HCs from CD alone or in conjunction with SS as precursors for decontamination of polluted waters and energy storage. The absorbent properties of the obtained HCs were evaluated in this study on the removal of nonbiodegradable pharmaceutical products dissolved in recycled water. The Co-HTC-derived hydrochar (HCB) had a high SBET of 20.35 m2 /g and pore volume of 0.38 cm3 /g, leading to significant adsorptive reductions of nevirapine (NEV) and lamivudine (LAM) (97.19% and 93.32%, respectively). The HC from coal tailing (HCT) and HC from coal slurry (HCS) displayed high NEV and LAM adsorption iii capacities (50 mg g-1 , 42 mg g-1 and 52 mg g-1 , 41 mg g-1 ) respectively despite being less effective than HCB (53.8 mg g-1 , 42.8 mg g-1 ). In addition, the use of spent adsorption residues for energy storage applications was investigated further. The results revealed that the textural structure of the produced ACs electrode from the spent residues has a significant impact on the electric conductivity qualities. The produced ACs exhibited roughly rectangular cyclic voltammetry shape, good reversibility and stability as observed from the ideal electrical double-layer capacitors (EDLCs). These findings showed that spent adsorption residues are an effective CM precursor for the production of excellent EDLCs for current densities ranging from 1 A/g to 5 A/g in energy storage applications. Furthermore, the synthesis of AC from the obtained HCs for adsorptive hydrogen storage was conducted. The hydrogen adsorption characteristics of the produced ACs were evaluated at 77 K and 293 K and 40 bars. The results indicate that the values of hydrogen adsorbed onto the ACs were approximatively 6.12wt%, 6.8wt% and 6.57 wt% for AC-HCT, AC-HCS and AC-HCB respectively at 35 bars implying that they could be used for hydrogen storage, sustainable carbon emissions management and provide viable pathways for cost-effective energy and material circular economies for both WWTPSs and the mining industry.
Investigating the effect of counter-current precipitation of cobalt hydroxide on its quality and MgO consumption rate
(2024) Tshibob, Nawej Bob
In this work, a different configuration for precipitating cobalt hydroxide is investigated and presented in order to enhance the cobalt hydroxide quality and maximize the utilization of magnesium oxide. The proposed configuration includes a precipitation step in presence of sodium sulphate using magnesium oxide to recover cobalt from cobalt-bearing solution, followed by a cobalt hydroxide washing step to fully utilize the excess or residual magnesium oxide using acidic cobalt-bearing solution. The results of precipitation experiments showed that using 4g/L of sulphate ions at 25°C, a magnesia dosage of 1.10g of MgO/g Co, and precipitation duration of 4 hours, approximately 99% of cobalt can be recovered in the precipitation step while leaving 87% of the manganese in solution. The equilibrium pH at precipitation stage was 8.42. The washing experiments' findings demonstrated that the cobalt hydroxide quality could be significantly improved by using an acidic cobalt sulphate solution as the washing solution, with cobalt upgrading of approximately 8% at 45°C, a washing solution volume of 350ml, and a washing time of 4 hours. The equilibrium pH at washing stage was 7.36. The ability of cobalt sulphate solution to lower or remove the excess or undissolved magnesium oxide which enhances the upgrading of cobalt hydroxide while maximizing the MgO usage was demonstrated. A reduction in magnesium oxide consumption rate of roughly 18% was evaluated as the effect of washing
Kripke completeness of predicate modal logics
(2024) Bowditch, Zachary
Kripke semantics is well-known for predicate and propositional modal logic. While the study of Kripke semantics has produced numerous completeness results for propositional modal logics, there are substantially fewer examples of Kripke complete predicate modal logics. This is dually attributable to inadequacies of predicate Kripke semantics as well as to the inherent technical difficulties that accompany domains in semantics of predicate logic. There is presently little literature in the area of Kripke completeness for predicate modal logics, which motivates a comprehensive survey of existing results, recent innovations as well as an investigation into what insights are required to produce more general results. The study of canonicity - the property of a modal logic where it is validated by its canonical frame - has led to wide coverage of Kripke completeness results in propositional modal logic. Canonicity, however, does not always persist for predicate extensions of propositional modal logics. We survey a number of propositional and predicate modal logics, both canonical and non-canonical, demonstrating techniques which show Kripke completeness for these logics, and discuss the extent to which the canonical model technique is useful to this end.
Natural gas to methanol process flowsheet improvement via integration of ITM oxygen technology
(2024) Fankomo, Phumzile
Current industrial gas-to-liquids (GTL) processes suffer high energy penalties and associated carbon emissions caused by inefficient energy utilization and recovery. With the increasing demand for methanol and stricter regulations requiring reduced carbon intensity, there is a need to improve efficiencies of the existing process. This study analysed the existing large-scale natural gas to methanol flow sheet and investigated development of a new and improved flow sheet. In a conventional natural gas to methanol process, the air compressors in the cryogenic air separation unit (ASU) as well as the syngas compressor in the methanol synthesis unit are the most energy intensive and contribute significantly to the energy cost of large-scale syngas manufacture. The conventional autothermal reformer (ATR) process contributes the largest exergy losses as a result of the large temperature driving force used in the syngas cooler. The novel ion transport membrane (ITM) oxygen technology has the potential to replace the cryogenic air separation and reduce the large power demands associated with oxygen production. Its high temperature operation makes it suitable for process integration with syngas production. Integration of this ITM oxygen technology into a natural gas to methanol flow sheet was investigated. The pinch analysis method was used to evaluate flow sheet minimum energy requirements and identify opportunities for process heat integration to reduce utility requirements. Exergy analysis was conducted to identify areas of large exergy destruction and opportunities for improvement and, to quantify and compare exergy losses of the flow sheet cases. Power cycles were integrated to efficiently recover and convert process heat to power. Performance of the power cycles was measured by the cycles’ thermal efficiencies. The overall plant and process efficiency as well as the specific iv gas efficiency were evaluated to assess and compare energy efficiency of the process flow sheet cases. Replacing the cryogenic ASU with ITM and integrating ITM oxygen into the ATR process is a more efficient method to recover the high temperature syngas heat with reduced exergy losses. The ITM oxygen unit integrated with power cycles resulted in 47% more power production compared to the conventional case A. The exergy analysis results showed a decrease in overall exergy losses by 26% in this new flow sheet. The ITM oxygen power cycle was found to produce enough power to drive its own compressors and with excess power of 28 MW, whereas the cryogenic ASU in the conventional case has a power demand of 33 MW. This work shows that lower cost production of oxygen may be the feasible solution to reduce the high costs of large-scale syngas manufacture. The ITM oxygen presents such opportunities by substituting the energy intensive cryogenic ASU and combining oxygen, syngas and power production into a single thermally integrated unit. The methanol loop was found to have sufficient process heat for combined heat and power production. The Rankine medium pressure (MP) steam cycle produced enough power to drive the syngas compressor. Configuring the methanol process into a power production cycle results in an increase in the flow sheet excess power production by 68% compared to the conventional case. However, reduced methanol production rate caused by lower flash pressures as well as reduced process heat for feed preheat are the main challenges to consider. The specific gas efficiency improved by 6% while carbon dioxide emissions decreased by 40%. The overall thermal efficiencies of the cases were not optimized as this was not part of the study objectives. A further study can be conducted to investigate improving the thermal efficiencies of the power cycles in each case by performing a sensitivity analysis to impact parameters such as turbine and compressor inlet temperature and v pressure ratio. The specific parameters to assess can be determined from the airstandard model equation for a Brayton power cycle. The thermal efficiency improvement can result in higher power production and reduced equipment duties which is a benefit to both capital and operating costs.
Numerical investigation of selective withdrawal of brine from salt cavern with entrainment of the light phase oil
(2024) Moropane, Isaac Sekontshe
This paper presents a numerical simulation of selective withdrawal of brine from salt cavern with entrainment of crude oil. Selective withdrawal is the siphoning of one layer of fluid from two immiscible fluids and avoiding the entrainment of other fluid. A trial of three incline siphons (60o , 75o and 90o ) were utilized and each passing through 2.54 cm silicon oil layer and face down below the liquid-liquid interface drawing water upwards. The siphons had a submergence depth of 2.54 cm below the liquid-liquid interface. The simulation was done using the software Ansys Academic, Student 2021 R1. The flow was simulated using two dimensions CFD. The volume of Fluid model and Pressure-based solver were adopted for this simulation. The turbulence model used in the CFD was standard k-epsilon. Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm was adopted for pressure velocity coupling. The results showed that, for avoiding oil entrainment, 90o siphon is better followed by 60o inclined, whereas the 75o inclined was the worse. The results obtained from CFD simulation were validated using experimental data and found to agree. The paper's findings can be useful for Petroleum Engineers to reduce oil entrainment in selective withdrawal from salt caverns in the Strategic Petroleum Reserve (SPR). By predicting the transition from selective withdrawal to oil entrainment, an improved design can optimize the withdrawal process. The design can be enhanced by adjusting the withdrawal rate, pressure, and siphon orientation to minimize the transition from selective withdrawal to oil entrainment. The consequences of oil in the brine system necessitate the separation of oil from the brine, the transfer of oil entrainment back into the salt caverns, and clean-up to avoid environmental contamination. This process of separating and cleaning oil from brine in a brine pond is more time-consuming and expensive.
On the adsorption of Cu2+ and Zn2+ from wastewater using water hyacinth: the mathematical modelling approach
(2024) Eltahhan, Nashwa Tarek
Several industries utilize heavy metals in their industrial processes, eventually discharging them in their wastewater. Water contamination by heavy metals is a major environmental problem due to their acute toxicity and their accumulation in food chains. Therefore, intensive research has been carried out lately on the feasibility of water hyacinth as low cost adsorbent for the removal of heavy metals from wastewater. One of the present research objectives was to examine the potential of raw South African water hyacinth for the removal of Cu2+ and Zn2+ from a synthetic wastewater. The research work is divided into three core phases. In Phase I, batch equilibrium experiments were carried out to compare the performance of water hyacinth from the different countries, Egypt and South Africa, in the removal of copper and zinc from water solutions. The effect of several operating parameters on the uptake of Cu2+ and Zn2+ was tested. The tested parameters were the pH of the solution, contact time, water hyacinth dose and initial Cu2+ and Zn2+ concentration. The percent removal of Cu2+ and Zn2+ was found to increase with increasing the pH, contact time, and water hyacinth dose up to the point of equilibrium. However, it decreased with the increase in the initial concentration of Cu2+ and Zn2+. Langmuir and Freundlich isotherm models were used for the evaluation of the equilibrium experimental data. The correlation coefficients for Langmuir isotherm were 0.84 and 0.82 for copper and zinc adsorbed by Egyptian water hyacinth, respectively, and 0.98 for both copper and zinc adsorbed by South African water hyacinth. The correlation coefficients for Freundlich isotherm were 0.99 and 0.98 for copper and zinc adsorbed by Egyptian water hyacinth, respectively, and 0.94 and 0.98 for copper and zinc adsorbed by South African water hyacinth, respectively. Phase II was carried out to investigate the optimum operating conditions using Response Surface Methodology (RSM) design and General Algebraic Modeling System (GAMS). Here, optimization of an adsorption case study with conflicting optimal solutions based on singleobjective Response Surface Methodology (RSM) design was facilitated with the implementation of BARON solver based on General Algebraic Modeling System (GAMS) with identical variables, levels, and model equations. RSM suggested optimum settings of which the validation is quite expensive and onerous, whereas GAMS suggested a single optimum setting which makes it more economically viable, especially for large scale systems. Phase III was the final stage of the experimental part. It was conducted using fixed-bed column tests (continuous flow). The more promising water hyacinth which is the South African water hyacinth was used at that phase to define the impact of a number of parameters, namely the influent heavy metal concentration, bed depth, and the flowrate. The service time of the columns to breakthrough and to exhaustion was found to increase with the increase in the bed depth of the packed water hyacinth. However, it decreased with the increase in the initial Cu2+ and Zn2+ concentrations and the flowrate of the solution. Generic equations were used to describe the adsorption mechanism of the water hyacinth used to remove Cu2+ and Zn2+ from wastewater and validate the proposed generic model against experimental data. The results indicate the suitability of the generic models for copper and zinc removal using water hyacinth. The data obtained was used to scale up the adsorption column, and the economic feasibility was then demonstrated. Assuming 80% efficiency, the scale up column for copper can run for one day and requires 19.44 hr to treat 3.69 m3 of contaminated water using 22 kg of water hyacinth as adsorbent. On the other hand, the scale up column for zinc can run for one day and requires 19.44 hr to treat 3.44 m3 of contaminated water using 22 kg of water hyacinth as adsorbent. The production cost of the adsorption column was estimated at US$36,434.
Optimization of biodiesel production from castor seed oil as an alternative fuel in sub-Saharan African countries
(2024) Lumu, Tshibaka
Biodiesel-fuelled diesel motors offer a unique chance to address two general issues confronting our worldwide society: energy utilization and global warming. Biodiesel from utilized vegetable oil is simple and has numerous natural advantages. To generate a good fuel for use in diesel motors, these triglycerides are typically transformed into individual mono-alkyl esters by base-catalysed transesterification with short-chain alcohol, normally methanol. Initially, the transesterification reactions of castor oil with methanol were studied by employing sulphuric acid as a catalyst in an ultrasound reactor. The castor oil and the methyl ester products were characterised by diverse analytical techniques such as gas chromatography (GC-MS). The impacts of diverse reaction variables (reaction temperature, methanol to oil ratio, reaction time, catalyst amount) on FAME yield were studied. The optimum reaction conditions of the diverse process systems were established. The optimum operating conditions for methyl esters production using ultrasound reaction, with the castor oil was established as follows: In the presence of sulphuric acid: reaction time of 40 min at 50 ºC with methanol to oil ratio of 6:1 as well as 0.5 H2SO4 wt. % of oil; in the presence of unsupported castor shell catalyst: reaction time of 40 min at 50 ºC with methanol to oil ratio of 9:1 and 1 unsupported castor shell (UCS) wt.% of oil; in the presence of Co/TiO2: reaction time 40 min at 50 ºC with methanol to oil ratio of 9:1 plus 1 Co/TiO2 wt.% of oil. The transesterification reaction in the presence of sulphuric acid led to higher yields of methyl esters (90%) compared to methyl ester yields (85 and 83 %) for Co/TiO2 and UCS, respectively. The utilization of homogeneous catalysts presents several inconveniences; nevertheless, heterogeneous catalysts are exciting because their use could lead to biodiesel production in a low-cost manner. Therefore, a solid base catalyst (UCS) was prepared from a castor shell (supplied by the Mpumalanga caster plant) and Co/TiO2 was prepared by the incipient wetness impregnation method. Numerous analytical techniques were applied for characterization purposes. EDS results showed that the UCS predominantly contained some elements such as calcium, oxygen, and potassium, and Co/TiO2 contained titanium, followed by cobalt. The high amount of calcium (Ca), carbon (C), and oxygen (O) in the UCS was beneficial because their combination probably leads to the formation of CaO or CaCO3, which could increase the activity of the UCS catalyst. The presence of CaO and CaCO3 was confirmed by Fourier- transform infrared. The XRD characterization of the castor shell reveal the presence of CaCO3 peaks only, while XRD characterization of Co/TiO2 indicated that the diffraction peaks at ca. 2θ = 31, 59, and 65° were observed only in the 10% Co/TiO2 catalyst data (pattern a) and can be ascribed to Co3O4 resulting from the decomposition of Co (NO3)2.6H2O during catalyst calcination in air. The BET described the specific surface area and pore volume distribution for 10% Co/TiO2 catalyst, blank support TiO2, and UCS catalyst. The assessment indicated that the specific surface and volume distribution for the Co/TiO2 catalyst where the used blank supporter TiO2 acting as a catalyst. The volume distribution and surface area for Co/TiO2 were greater due to the heating treatment of the catalyst system, which removed all the volatile materials. This increased the activity of the catalyst.
The development of whisker and cubic boron nitride reinforced titanium carbide ceramic matrix composites
(2024) Petersen, Shaheeda
TiC as the matrix in ceramic matrix composites (CMC’s) is limited due to its poor fracture toughness. In order to increase their use in interrupted cutting applications, it is necessary to improve their fracture toughness and hardness. The purpose of this study was to improve the fracture toughness of TiC without causing a decrease in its other mechanical properties by adding SiC whiskers to the starting TiC powder before Spark Plasma Sintering (SPS). To improve the hardness cBN was also added as a secondary hard phase prior to sintering. The reinforced powders where then sintered at temperatures between 1550°C and 1650°C, under pressures of 50-70 MPa and hold times between 5-20 minutes. The resulting materials were then characterized by density, hardness, fracture toughness, biaxial strength, sliding wear testing and scanning electron microscopy. Analysis of the hardness and fracture toughness of the sintered TiC matrix compacts with/without SiO2 concluded that the sintered sample with the highest hardness was found to be 90TiC-8Al2O3-2Y2O3 SPS’d at 1625°C, 70MPa and the sintered sample with the highest fracture toughness was determined to be 90TiC-8Al2O3-2Y2O3 SPS’d at 1625°C, 50MPa. From the XRD results we observed that the SPS material with the highest fracture toughness had formed YAP instead of YAG during sintering. The 77.8TiC-6.9Al2O3-1.7Y2O3-14 (20 vol.%) SiCw composition had the greatest ultimate fracture strength of 152.67 GPa and a Weibull modulus of 26.973 which is higher than unreinforced engineering ceramics but similar to other CMC’s reinforced with ceramic fibres. Out of all the compositions tested the 78.6TiC-3.5Al2O3-5.6Y2O3- 4.9SiO2-7.5 (10 vol.%) cBN removed the most material and had the lowest frictional coefficient making it suitable for use as a cutting blade.
The effect of petrographically determined parameters on carbonaceous reductant reactivity in the production of high-carbon ferromanganese
(2024) Soqinase, Sanda
In pyrometallurgical processes, metal oxides are reduced from slag through carbothermic reduction. The carbonaceous reductant reactivity to slag is of industrial interest as it provides information such as the rate at which MnO dissolves in the slag, which ultimately influences the manganese yield in the alloy. However, knowledge is limited on the effectiveness of organic composition of the reductants when heated and its contribution that gives rise to the differences of the reductant reactivities of the chosen reductants. This study compares the effect of organic composition of coal on the reductant reactivity to slag. The objectives of the study are (1) To determine empirically reductant reactivity to slag (2) To determine petrographically the intrinsic organic properties of the bituminous coal and anthracite as reductants (3) To compare the fundamental properties and characteristics of bituminous coal and anthracite The study examined two medium-rank C bituminous coals—labelled coal 1 and coal 2—and anthracite. It investigated the effect of petrographic characteristics on carbonaceous reductant reactivity to slag. The reductant reactivity towards slag tests were conducted in a gas-tight muffle furnace at 1500°C applicable to the chosen three carbonaceous materials. Analytical techniques, such as SEM-EDS, were applied to measure the extent of MnO reduction (and SiO2 to a lesser extent) from the slag. It was expected for MnO and SiO2 from slag to be partially reduced to form Mn and Si in the alloy phase. Other analytical techniques were applied, such as proximate analyses, which indicated the differences and similarities between the chosen carbonaceous reductants as the fundamental basis for evaluating coal for technological use. The maceral data revealed coal 2 consisted of a greater proportion of reactive macerals than coal 1 and anthracite. The anthracite sample, consisting of the highest inert maceral proportions, had the least mass loss.
The influence of imidazolium-based ionic liquids on the spontaneous combustion characteristic of hydrothermal hydrochars and hydrochar/coal blends
(2024) Matsobane, Ethel Tsholofelo
Spontaneous combustion is a major problem facing South African coal mines. It is caused by the build-up of heat during oxidation, which eventually leads to the temperature of the coal reaching the point of ignition. The adverse effects of spontaneous combustion, such as the release of large toxic gases into the environment and the loss of valuable materials, called for a solution to the problem and for further new fuels to be explored. Biomass, hydrochar and hydrochar/coal blends have been proposed as alternative energy sources to coal to reduce greenhouse gas emissions. However, given that the new fuels are derived from biomass, which is highly reactive, there is a need to investigate their susceptibility to spontaneous combustion and preventative measures thereof. This study assessed the factors that contribute to the spontaneous combustion of 100% coal discard, 100% biomass, 100% hydrochar, 25% hydrochar + 75% discard coal, 50% hydrochar + 50% discard coal and 75% hydrochar + 25% discard coal through their characteristics. The thermogravimetric analysis (TGA) and the Wits-Ehac apparatus were used to predict the spontaneous combustion susceptibility of the fuels. Those that were found to be highly susceptible to spontaneous combustion from the six were treated with three imidazolium-based ionic liquids, 1-butyl-3-methyl-imidazolium hydrogen sulphate [Bmim+HSO4 − ] (IL-A), 1- ethyl-3-methyl-imidazolium hydrogen sulphate [Emim+HSO4 − ] (IL-B) and 1-Butyl-3-methylimidazolium acetate [Bmim+OAc−] (IL-C), to inhibit their spontaneous combustion characteristic. The physicochemical analysis results for the samples revealed an increase in the energy characteristic of the hydrochar produced from 100% biomass. In addition, the 100% discard coal was found to have low energy characteristics, however, the quality improved when it was blended with 100% hydrochar at different ratios. 100% biomass was found to have the highest moisture content, volatile matter and oxygen content at 8.01%, 60.52% and 37.67%, respectively. Additionally, the sample was also found to have the lowest ash content, fixed carbon, and total carbon at 2.92%, 19.54% and 44.60%, respectively. As a result, 100% biomass is highly susceptible to spontaneous combustion compared to other fuels. The Fourier Transform Infrared Spectroscopy (FTIR) analysis results revealed that all samples had a transmittance of the C=O stretch, which is known to promote spontaneous combustion. The fingerprint region of the FTIR spectra of the samples showed that the 100% discard coal had the highest mineral content, which tends to inhibit spontaneous combustion. Whereas 100% iii biomass had the lowest mineral content in comparison to other fuels, making it more susceptible to spontaneous combustion. The TGA results showed that 100% biomass is highly reactive with a 𝑇𝐺𝑠𝑝𝑐 index of 0.1457 %/ ˚C.min, while 100% discard coal was found to be non-reactive with a 𝑇𝐺𝑠𝑝𝑐 index of 0.0135 %/ ˚C.min. The remaining fuels were classified as low reactive given that their 𝑇𝐺𝑠𝑝𝑐 index was between 0.02 and 0.03 %/ ˚C.min. A significant correlation was seen between the TGA susceptibility data and the physiochemical properties of the samples. The Wits-Ehac results showed that the 100% biomass had the lowest spontaneous combustion susceptibility index of 3.49, while the 50% hydrochar/50% discard coal blend was found to have the highest spontaneous combustion susceptibility index of 4.79. The remaining fuel was classified as medium risk as their Wits-Ehac values ranged from 3 to 5. No correlation was found between the TGA and Wits-Ehac spontaneous combustion results, as the Wits-Ehac results showed some inconsistencies, especially for samples derived from 100% biomass. In addition, the Wits-Ehac results were inconsistent with the characterisation results from the samples. The three imidazolium-based ionic liquids were used to treat 100% biomass to inhibit its spontaneous combustion characteristic, as it was the only sample that was highly susceptible to spontaneous combustion. The TGA results from the treated biomass showed that 1-butyl-3- methyl-imidazolium hydrogen sulfate [Bmim+HSO4 − ] (IL-A) and 1-ethyl-3-methylimidazolium hydrogen sulfate [Emim+HSO4 − ] (IL-B) reduced the 𝑇𝐺𝑠𝑝𝑐 index of 100% biomass from 0.1457 %/ ˚C.min to 0.0839 and 0.0576 %/ ˚C.min, respectively at a lower heating rate. The two imidazolium-based ionic liquids were found to be inefficient in inhibiting the spontaneous combustion of 100% biomass, as the samples were still classified as highly reactive after treatment. 1-Butyl-3-methyl-imidazolium acetate [Bmim+OAc−] (IL-C) showed the best inhibitory effects given that the 𝑇𝐺𝑠𝑝𝑐 index of 100% was reduced to 0.0207 %/ ˚C.min, and the sample was classified as low reactive after treatment. The results of the physicochemical analysis showed that after IL-C treatment, the physicochemical properties, textural properties and microstructure of the 100% biomass improved significantly
Thermodynamics and kinetics of gas-hydrate based concentration for enhancing energysaving in the fruit juice industry
(2024) Nkosi, Nkululeko
The constant rise in energy costs is one of the major challenges confronting the fruit juice industry. As a result, it is in the industry's interest to find environmentally friendly measures that reduce energy consumption while cost-effectively maintaining product quality. In this industry, multi-effect evaporation is used as a traditional technique to reduce the water content of fruit juices. Because of the need for steam, this process is highly energy-intensive. An alternative technology based on renewable energy resources is required to reduce the industry's energy demand while increasing revenues and contributing to the UN's 2050 net-zero carbon emission targets. It is in this context that hydrate-based technology has emerged as a promising approach to meeting the food industry's energy demands and product quality challenges. It is a technology with the potential to contribute to sustainability while also establishing itself as a viable alternative to current juice concentration processes. This study aimed to investigate gas hydrate-based concentration as an energy-saving process in the fruit-juice energy. However, the rationale and economical design of this hydrate-based fruit juice concentration process would require the knowledge of the equilibrium hydrate forming conditions and their formation kinetics. For this reason, measurements of hydrate phase dissociation conditions and hydrate formation kinetics were conducted experimentally. The isochoric pressure-search experimental method used a newly developed static high-pressure stainless-steel equilibrium cell to measure the hydrate-vapour-liquid phase equilibrium data. Experimental measurements on hydrate phase equilibrium conditions on a known test system were conducted to test the validity and reliability of the experimental apparatus, calibrations, and method used. This includes gas hydrate dissociation points (P and T) for the CO2 + H2O test system. The experimental method and measurements were accurate and reliable, as shown by the agreement between the results and the literature measured within the acceptable uncertainty. Subsequently, novel systems measured include experimental hydrate phase equilibrium conditions of three systems involving juices (System 1: CO2 + grape juice; System 2: CO2 + pineapple juice; System 3: CO2 + bitter melon juice) at varying juice water cuts from (88.5 to 98.3 ± 2.53) wt.% were generated. In the experimental dissociation conditions reported for the hydrate phase, the temperatures and pressures ranged from 272.6 to 282.3 K and from 1.17 to 3.85 MPa. Based on the hydrate phase equilibrium measurements undertaken in this study, it was discovered that the juice systems under consideration have considerable inhibitory effects on hydrate formation. The results showed that reducing the water cut from (98.3 to 88.5 ± 2.53) wt.% could shift the hydrate phase equilibrium conditions toward higher pressures and lower temperatures. A further study examined the effect of different driving forces (temperature, pressure and subcooling) and juice water cuts on hydrate formation kinetics using a novel experimental kinetic measurement of the binary CO2 and grape/pineapple or bitter melon juice mixture. The kinetics of hydrate formation is fundamentally affected by the interaction between hydrate and dissolved. Insights into the potential commercialisation of hydrate-based technology can be gained through such measurements. Considering this fact, the conclusions of this comprehensive study, including measurements of hydrate phase dissociation conditions and kinetic experiments of hydrate formation, were crucial for calculating the optimum conditions of the proposed fruit juice concentration process. Also included in this research was the optimisation of dissociation conditions and kinetic data from three (3) different juice systems forming carbon dioxide hydrates. This was done to close the gap between the measured data and its applicability. A historical data design using response surface methodology (RSM) was used to determine optimal conditions from prediction models for the dissociation and formation of hydrates in the presence of pineapple, grape, and bitter melon juices. An examination of the effects of the RSM input variables, such as the system temperature T = (274.15 to 276.15) K, the juice concentration (88.5 to 97.4) wt.%, and the pressure P = (3.0 to 4.2) MPa, on the dehydration ratio (DHR) and apparent kinetic rate constant (Kapp) is presented in this study. Lastly, this study evaluated the feasibility of fruit juice concentration technology via hydrate formation as opposed to the multi-effect evaporation method. A preliminary analysis of the estimated energy consumption at optimum conditions for the hydrate-based concentration process was conducted for comparison purposes. The analysis suggests that hydrate separation technology requires between 4864.04 to 5006.66 kJ of cooling per stage to concentrate fruit juices. Comparatively to a multi-effect evaporator, this cooling process requires 48 to 52 % less energy. While these findings may seem promising, it is still necessary to determine the size and quality of crystals before hydrate-based concentration technology is implemented in the fruit juice industry. As such, methods for accurately determining the final concentration of the solution must be developed.

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