Dissertations

2017

Isabella Ndlovu, “An evaluation of a microchannel reactor for the production of hydrogen from formic acid”, Master dissertation, Promoters: Raymond Everson, Steven Chiuta, Hein Neomagus, Henrietta Langmi, Jianwei Ren and Dmitri Bessarabov, Faculty of Engineering, North-West University, 2017.

This dissertation evaluates the performance of a microchannel reactor for the decomposition of vaporised formic acid as a promising technology for the production of hydrogen for proton exchange membrane fuel cell applications. Accordingly, a combined experimental and modelling approach was used to evaluate the microchannel reactor coated with a gold supported on alumina (1.15 wt. % Au/Al2O3) catalyst. For the experimental evaluation, two sets of experiments were carried out where pure formic acid (99.99 %) and dilute formic acid (50 vol. %) were taken as the feed to the reactor respectively. The first set of the experimental evaluation involved measuring key performance parameters such as, formic acid conversion, formic acid residual concentration, selectivity to hydrogen and hydrogen yield at different temperatures of 250 – 350°C and formic acid (99.99 %) vapour flowrates of 12 – 48ml/min. Overall, the reactor performed well in decomposing pure formic acid (99.99 %), achieving conversions (98 to 99 %) close to equilibrium at 350 oC and all studied vapour formic acid flowrates of 12- 48 ml/min. The highest hydrogen production rate (0.04mol.h-1) was measured at the highest formic acid flowrate of 48 ml/min when the reactor was operated at 350 oC. At all studied temperatures however, both dehydrogenation (HCOOH → H2 +CO2) and dehydration (HCOOH → H2O+CO) reactions occurred and the dehydrogenation reaction was found to be dominant. The dehydration reaction was mostly favoured at high temperatures and carbon dioxide concentrations ranged between 4 – 15 % while the corresponding selectivity towards H2 production ranged between 0.7 and 0.88.  Effort was made to improve the H2 yields in the second set of the experiments through decomposing a mixture of formic acid and water (50/50 vol. %) thereby promoting the occurrence of the forward water gas shift reaction. Under these conditions, carbon monoxide concentrations decreased to a range of 2 – 7 % while selectivity towards hydrogen production increased to a range of 0.84 – 0.94. Overall, the reactor was found stable at a continuous period of 144 hours after running for approximately 1 200 hours. A computational fluid dynamic model was developed for concentrated formic acid (99.99 %) experiments aimed at describing reaction-coupled transport phenomena relating to velocity, mass and temperature profiles within the microchannel reactor. Kinetic rate expressions that best described the experimental results were successfully estimated using a model-based parameter optimisation and refinement on Comsol Multiphysics™ 4.3b. Validation of the model against the experimental results showed that the developed model was an acceptable fit to the experimental conversions and hydrogen yields especially at temperatures higher than 250 oC. Overall, this dissertation highlights the first steps in the development and use of microchannel reactors in promoting formic acid as a future hydrogen storage medium for portable and distributed fuel cell applications.

2016

Nicolaas Engelbrecht, “Carbon dioxide methanation in a catalytic microchannel reactor”, Master dissertation, Promoters: Raymond Everson, Steven Chiuta, Hein Neomagus and Dmitri Bessarabov, Faculty of Engineering, North-West University, 2016.

The work reported in this dissertation demonstrated the practicality of a catalytic microchannel reactor for CO2 methanation implemented via the Sabatier reaction for potential power-to-gas applications. A combined experimental and computational fluid dynamic (CFD) modelling approach was used to evaluate the microchannel reactor washcoated with an 8.5 wt.% Ru/Al2O3 catalyst. For the experiments, a stoichiometric feed ratio (1:4) of CO2 and H2 was used. The reactor was evaluated for CO2 methanation at different reaction temperatures (250‒400°C), pressures (atmospheric, 5 bar and 10 bar), and gas hourly space velocities (32.6–97.8 NL.gcat-1.h-1). The highest CO2 conversion of 96.8% was achieved for the lowest space velocity (32.6 NL.gcat-1.h-1) and conditions corresponding to 375°C and 10 bar. The CH4 production was however maximised operating the reactor at conditions corresponding to high space velocity (97.8 NL.gcat-1.h-1), high temperature (400°C) and at 5 bar. At this operating point the reactor showed 83.4% CO2 conversion, 83.5% CH4 yield and high CH4 productivity (16.9 NL.gcat-1.h-1). The microchannel reactor demonstrated good long-term performance and no observable catalyst deactivation even after start-stop and continuous cycles, thereby proving its ability to handle dynamic operation required for power-to-gas applications. A CFD model was developed and used to interpret the experimental reactor performance, as well as provide fundamental insight into the reaction-coupled transport phenomena within the reactor. Most importantly, global kinetic rate expressions were developed using model-based parameter estimation. Results from the CFD model corresponded with good agreement to the experimental reactor performance in terms of CO2 conversion and CH4 yield over a wide range of operating parameters. The model also provided velocity and concentration distributions to better understand the transport principles established within the reactor. Overall, the results presented in this dissertation pinpointed the important aspects of realising CO2 methanation at the micro-scale and could provide a platform for future studies using microchannel reactors for power-to-gas applications.

Wikus Kirsten, “Characterisation pf proton exchange membranes using high-pressure gas membrane rupture test”, Master dissertation, Promotors: Hein Neomagus and Dmitri Bessarabov, Faculty of Engineering, North-West University, 2016.

A biaxial tensile testing method was proposed to characterise the viscoelastic properties that affect the mechanical durability of proton exchange membranes. It served as a good representation of the operational environment found within electrochemical hydrogen energy systems, replicating stresses induced on the constrained membranes. The highpressure membrane rupture test was used to determine the Young’s modulus of Nafion® membranes at three temperatures (20 ℃, 50 ℃ and 80 ℃) and four relative humidity levels (35 %, 50 %, 70 % and 90 %). The results showed that the Young’s modulus decreases with increased temperature and RH with the change in temperature having a significantly larger effect. Nafion® 1110 membrane samples were found to have a higher rupture pressure at sub-zero temperatures than at the studied temperature larger than 0 ℃. It was also shown that the properties of the membrane remain constant for the two temperatures.  Nafion® 1110 membranes were subjected to ion exchange with cations (Na+, Mg2+ and Fe3+). An increase in the Young’s modulus was observed with the presence of foreign cations as a result of reduced moisture uptake. Reinforced membranes were ruptured at 90 % RH and 50 ℃ with the rupture pressures compared to Nafion® membranes with similar thicknesses at the same environmental conditions. The rupture pressure of the reinforced membranes showed a nearly 100 % increase in strength compared to that of the Nafion® membranes. It is therefore clear that the e-PTFE layer of the reinforced membranes strongly improves the mechanical strength of the specimen. Unhydrolyzed perfluorinated membranes were partially hydrolysed for up to 46 hours to investigate the effect of the equivalent weight of the membrane specimen on the mechanical strength. These tests showed that the equivalent weight of the specimens decreased as the hydrolysis time increased, which in turn resulted in an increase of the rupture pressure of the specimen at 50 % RH and 50 ℃.

Gerhardus Human, “Power management and sizing optimisation of renewable energy hydrogen systems”, PhD Thesis, Promotors: George van Schoor and Kenny Uren, Faculty of Engineering, North-West University, 2016.

An integrated sizing and control optimisation strategy for renewable energy hydrogen production systems is developed. The aim was to provide insight into the design of these systems which comprise complex non-linear components and intermittent renewable energy sources, in this case wind and sun. A multi-objective strength Pareto evolutionary algorithm to optimise a simulated system model that he developed and configured for three different geographic sites is implemented. A reduced fuzzy rule base was derived for each site, resulting in reduced complexity and allowing ease of rule interpretation. The unique contributions are the insight into the relationship between system design and performance parameters, and also the process followed to generate Pareto optimal solutions.

Angelique Janse van Rensburg, “Multi-scale model of a valve-regulated lead-acid battery with electromotive force characterization to investigate irreversible sulphation”, PhD Thesis, Promotors: George van Schoor and Pieter Andries van Vuuren, Faculty of Engineering, North-West University, 2016.-

Operating modes that cause irreversible sulphation (IS) in a lead-acid battery were investigated using a multi-scale electrochemical model. Experimental data from a valve-regulated lead-acid battery with an immobile electrolyte were used in a novel concentration-based method for electromotive force (EMF) characterization. The EMF curve was used for model calibration during parametric analysis of the multi-scale model. Variance-based sensitivity analysis confirmed that the parameters for electrode kinetics have the most significant effect on the simulated voltage. After verification and experimental validation of the multi-scale model, it was used to simulate partial state-of-charge (SOC) operation. It was found that the available active surface area suffers irreversible decreases due to minor errors in SOC indication. Additionally, the internal resistance during the initial voltage drop increases from one discharge to the next. It was concluded that IS cannot be prevented satisfactorily using SOC information because SOC is not indicative of a specific damage mechanism.

Tshiamo Segakweng, “Hydrogen physisorptive storage in metal-organic frameworks (MOFs)”, MSc, Dissertation, Study leaders: Philip Crousea, Jianwei Renb, Henrietta Langmi, University of Pretoria, bHySA Infrastructure CSIR.

The overall aim of this study was to evaluate the potential offered by MOFs for hydrogen storage. Three types of MOFs were studied namely: Zn-based MOF (MOF-5); Zr-based MOF (UiO-66); and Cr-based MOF (MIL-101). The study investigated the optimisation of the three different MOFs for hydrogen storage by gaining an understanding of their optimal synthesis conditions. It was shown that a simple variation in the synthesis of the MOFs was able to have a significant effect on the hydrogen storage properties of the MOFs, and enable a fast and reproducible synthesis method. The synthesised MOFs were characterised and their hydrogen adsorption capacity measured. Hydrogen uptake was found to be related to the quality of the MOF crystals and also directly related to the surface area, pore volume and/or pore size of the particular MOF.

2015

Steven Chiuta, “Experimental and modelling evaluation of an ammonia-fuelled microchannel reactor for hydrogen generation”, PhD., dissertation, Study Leaders: Raymond Everson; Hein Neomagus; Dmitri Bessarabov, Faculty of Natural Science, North-West University.

Ammonia decomposition was assessed as a fuel processing technology for producing hydrogen on-demand for fuel cell applications. An experimental study of an ammonia-fuelled microchanel reactor was undertaken, and the performance data subsequently used to develop and validate a mathematical model for the effective design of microchannel reactors for ammonia decomposition. The work described in the thesis was motivated by the need for a convenient and efficient method of providing hydrogen for a proton-exchange membrane fuel cell (PEMFC) in portable and distributed power applications.

Andries Krüger, “Evaluation of process parameters and membranes for SO2 electrolysis”, PhD., dissertation, Study Leader: Henning Kriega and Dmitri Bessarabovb, Faculty of Natural Science, Chemical Resource Beneficiationa, Faculty of Engineeringb, North-West University.

The use of the SO2 electrolyser was evaluated for the production of both hydrogen gas and sulfuric acid.  Various operating parameters were investigated for the SO2 electrolyser which included cell temperature, catalyst loading, membrane thickness and MEA manufacturing procedure.  Using the optimised operating conditions the performance of the SO2 electrolyser was evaluated using electrochemical impedance spectroscopy (EIS) to separate the kinetic and membrane resistance while the mass transport limitations could be quantified.  The impact of H2S presence in the SO2 feed was also investigated using cyclic voltammetry and CO stripping to determine the electrochemical surface area (ECSA).  The results obtained showed that the SO2 electrolyser could possibly be applied in a mining environment.  To further increase the electrolyser efficiency various PBI based membranes were also evaluated for application in the SO2 electrolyser environment.

 2014

Marcelle Potgieter, “A comparative study between Pt and Rh for the electro-oxidation of aqueous SO2 and other model electrochemical reactions”, M.Sc., Thesis, Study Leaders: Cobus Kriek; Vijay Ramani, Faculty of Natural Science, North-West University.

Adri Calitz, “A comparative study between Pt and Pd for the electro-oxidation of aqueous SO2 and other model electrochemical reactions”, M.Sc., Thesis, Study Leaders: Cobus Kriek; Vijay Ramani, Faculty of Natural Science, North-West University.

Francois Stander, “Evaluation of an advanced fixed bed reactor for sulphur trioxide conversion to sulphur dioxide using supported platinum catalysts”, PhD., Dissertation, Study Leaders: Ray Everson; Hein Neomagus, Faculty of Engineering, North-West University.

2013

Bongibethu Hlabano-Moyo, “Seperation of SO2/O2 using membrane techynology”, M.Eng., Thesis, Study Leaders: Percy van der Gryp; Dmitri Bessarabov; Henning Krieg, Faculty of Engineering, North-West University

Anzel Falch, “Synthesis, characterisation and potential employment of Pt-modified TiO2 photocatalysts towards laser induced H2 production”, M.Sc., Thesis, Study Leaders: Cobus Kriek; Vijay Ramani, Faculty of Natural Science, North-West University.

Christiaan Martinson, “Characterisation of a proton exchange membrane electrolyser using the current interrupt method”, M.Eng., Thesis, Study Leaders: Kenny Uren; George van Schoor; Dmitri Bessarabov, Faculty of Engineering, North-West University.

Jan-Hendrik van der Merwe, “Characterisation of proton exchange membrane electrolyser using electrochemical impedance spectroscopy”, M.Eng., Thesis, Study Leaders: Kenny Uren; George van Schoor; Dmitri Bessarabov, Faculty of Engineering, North-West University.

Rudolph Petrus Louw, “Design optimisation and costing analysis of a renewable hydrogen system”, M.Eng., Thesis, Study Leader: Willie Venter, Faculty of Engineering, North-West University.

Martinus (Gerhard) de Klerk, “Development of a simulation model for a small scale renewable energy system”, M.Eng., Thesis, Study Leader: Willie Venter, Faculty of Engineering, North-West University.

Richard Sutherland, “Performance of different proton exchange membrane water electrolyser components”, M.Eng., Thesis, Study Leaders: Henning Krieg; Percy vd Gryp; Dmitri Bessarabov, Faculty of Engineering, North-West University.

Sammy Rabie, “SO2 and O2 separation by using ionic liquid absorption”, M.Eng., Thesis, Study Leader: Marco le Roux, Faculty of Engineering, North-West University.

 2012

Boitumelo Mogwase, “An electrochemical study of the oxidation of platinum employing ozone as oxidant and chloride as complexing agent”, M.Sc., Thesis, Study Leader: Cobus Kriek, Faculty of Natural Science, North-West University.

Andries Kruger, “SO2 electrolyser development for hydrogen production with the hybrid sulfur process”, M.Sc., Thesis, Study Leader: Henning Krieg, Faculty of Natural Science, North-West University.

Hugo Opperman, “A theoretical and experimental approach to SO2 permeation through Nafion and a novel sFS-PBI membrane”, M.Sc., Thesis, Study Leader: Henning Krieg, Faculty of Natural Science, North-West University.

Hannes Schoeman, “H2SO4 stability of PBI blend membranes for SO2 electrolysis”, M.Sc., Thesis, Study Leader: Henning Krieg, Faculty of Natural Science, North-West University.

Boitshoko Modingwane, “Investigation of Pt supported on carbon, ZrO2, Ta2O5 and Nb2O5 as electrolycatalysts for the electro-oxidation of SO2“, M.Sc., Thesis, Study Leader: Cobus Kriek, Faculty of Natural Science, North-West University.

HME Dreyer, “A comparison of catalyst application techniques for membrane electrode SO2 depolarised electrolysers”, M.Eng., Thesis, Study Leader: Johan Markgraaf, Faculty of Engineering, North-West University.

JH Hodgman, “The feasibility and application of multi-layer vacuum insulation for cryogenic hydrogen storage”, M.Eng., Thesis, Study Leader: Johan Markgraaf, Faculty of Engineering, North-West University.

Herman Retief, “A review of hydrogen storage for vehicular application and the determination of the effect of extraction boil-off”, M.Eng., Thesis, Study Leader: Johan Markgraaf, Faculty of Engineering, North-West University.

Morne Coetzee, “Upscaling of a sulfur dioxide depolarized electrolyser”, M.Eng., Thesis, Study Leader: Johan Markgraaf, Faculty of Engineering, North-West University.

Marco van Rhyn, “Recuperation of H2SO4 in the hybrid sulfur process using prevaporation”, M.Eng., Thesis, Study Leaders: Marco le Roux; Percy vd Gryp, Faculty of Engineering, North-West University.

Dian Kemp, “Technical evaluation of the copper chloride water splitting cycle”, M.Eng., Thesis, Study Leader: Ennis Blom, Faculty of Engineering, North-West University.

Marizanne Gouws, “Evaluation of the reduction of CO2 emissions from a coal-to-liquids utilities plant by incorporating PBMR energy”, M.Eng., Thesis, Study Leader: Ennis Blom, Faculty of Engineering, North-West University.

Liberty Mapamba, “Simulation of the copper-chloride thermochemical cycle”, M.Eng., Thesis, Study Leaders: Percy vd Gryp; Mike Dry, Faculty of Engineering, North-West University.

2011

Bothwell Nyoni, “Simulation of the sulphur iodine thermochemical cycle.”, M.Eng. (Chemical Enbgineering) Thesis, Study Leaders: Percy van der Gryp; Mike Dry, Faculty of Engineering, North-West University.

The demand for energy is increasing throughout the world, and fossil fuel resources are diminishing. At the same time, the use of fossil fuels is slowly being reduced because it pollutes the environment. Research into alternative energy sources becomes necessary and important. An alternative fuel should not only replace fossil fuels but also address the environmental challenges posed by the use of fossil fuels. Hydrogen is an environmentally friendly substance considering that its product of combustion is water. Hydrogen is perceived to be a major contender to replace fossil fuels. Although hydrogen is not an energy source, it is an energy storage medium and a carrier which can be converted into electrical energy by an electrochemical process such as in fuel cell technology. Current hydrogen production methods, such as steam reforming, derive hydrogen from fossil fuels. As such, these methods still have a negative impact on the environment. Hydrogen can also be produced using thermochemical cycles which avoid the use of fossil fuels. The production of hydrogen through thermochemical cycles is expected to compete with the existing hydrogen production technologies. The sulphur iodine (SI) thermochemical cycle has been identified as a high-efficiency approach to produce hydrogen using either nuclear or solar power. A sound foundation is required to enable future construction and operation of thermochemical cycles. The foundation should consist of laboratory to pilot scale evaluation of the process. The activities involved are experimental verification of reactions, process modelling, conceptual design and pilot plant runs. Based on experimental and pilot plant data presented from previous research, this study presents the simulation of the sulphur iodine thermochemical cycle as applied to the South African context. A conceptual design is presented for the sulphur iodine thermochemical cycle with the aid of a process simulator. The low heating value (LHV) energy efficiency is 18% and an energy efficiency of 24% was achieved. The estimated hydrogen production cost was evaluated at $18/kg.

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