Chemical and Biomolecular Engineering - Theses
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ItemPromoted Direct Air Capture of Carbon Dioxide by Synergistic Water Harvesting( 2023-10)Adsorption-based direct air capture (DAC) of carbon dioxide has been widely recognized as a necessary measure to contain atmospheric CO2 concentrations. Chemisorbents like solid amines are effective in capturing ppm level CO2. However, because of the large heat of adsorption, the regeneration of solid amines requires high energy consumption and a significant driving force, compromising the economic viability and productivity of DAC. A vapor-promoted desorption (VPD) process was developed to recover the CO2 adsorbed on solid amines by in situ vapor purge using water harvested from the atmosphere synergistically. A double-layered adsorption configuration, sequentially packed with solid amines and water adsorbents, was used to perform direct air capture based on the VPD process. The desorption of CO2 was substantially enhanced in the presence of concentrated water vapors at around 100 degrees Celsius, resulting in the concurrent production of 97.7% purity CO2 and fresh water at ambient pressure. CO2 working capacities of 1.0 mmol/g could be achieved using a commercial amine-grafted resin. Furthermore, a solar-heating DAC prototype was demonstrated to power the regeneration, recovering over 98% of the adsorbed CO2 while consuming 10.4 MJ/kgCO2 thermal energy. PEI-impregnated sorbents have been extensively studied for DAC due to their high atmospheric CO2 adsorption capacities. However, efficient recovery of the adsorbed CO2 from PEI has received limited attention. The developed VPD process was employed to effectively regenerate PEI-impregnated sorbents, producing fresh water and 98% pure CO2 with a remarkable working capacity of 1.61 mmol/g at 105 degrees Celsius. The high CO2 working capacity was realized through a reduction in CO2 partial pressure inside the column caused by the increase of water vapor pressure. The in situ vapor purge allowed for the recovery of more than 95% of the CO2 adsorbed on PEI, with an energy consumption of only 8.9 MJ/kgCO2 for sorbent regeneration. While the VPD process has demonstrated excellent performance in regenerating PEI-impregnated sorbents, a significant concern arises from amine deactivation at high regeneration temperatures. To address this issue, a vapor-promoted temperature vacuum swing adsorption (VPTVSA) process was developed, reducing the temperature required for the in situ vapor purge. This VPTVSA process regenerated PEI-impregnated sorbents at temperatures as low as 60 degrees Celsius, producing 99% purity CO2 with a stable working capacity of 1.10-1.13 mmol/g over 45 cycles. The minimum work required for adsorbent regeneration was only 1.62 MJ/kgCO2, over 37% lower than temperature-vacuum swing desorption. This low-temperature regeneration process not only reduces the exergy demand but also has the potential to extend the lifespan of numerous low-cost PEI-impregnated sorbents, contributing to a reduction in the overall cost of DAC.
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ItemMastering Precision Control of Nanocomposite Structures for Ultrathin Membranes( 2023-11)The increasing levels of carbon dioxide (CO2) emissions and their significant role in climate change make it one of the most urgent global challenges. To combat this issue, membrane-based gas separation technologies present a promising solution by removing CO2 from flue gas streams before entering the atmosphere and have a high potential for integration into existing industrial processes. Among these technologies, ultrathin film composite (UTFC) membranes are preferred due to their ability to process large volumes of gases. However, the technology faces challenges due to low partial pressures of CO2 in flu gases. Essential design objectives include developing mature fabrication techniques that enable the formation of membranes with high-performing materials, and enhancing CO2 separation performance. Research into improving the performance of UTFC membranes involves understanding the design of nanocomposite structure and its construction with controlled chemistries. The membrane gutter layer typically uses polydimethylsiloxane (PDMS), due to its high CO2 permeability, enhancing overall gas permeance of the subsequent selective layer. However, the CO2 permeance reported in literature is significantly lower than the theoretical performance due to challenges during fabrication process. Ultimately, a gutter-layer-free UTFC membrane is desired to advance CO2 capture technology in terms of membrane performance and manufacturing process. However, this has been challenging due to limitations in the geometric design of gas pathways on highly porous substrate and incompatibility between the substrate and selective layers. Ideally, materials with exceptional separation performance would be chosen for the selective layer however some materials have challenges limiting their use. For example, poly (1,3-dioxolane) (PDXL) has shown a greater CO2 affinity and an outstanding CO2/N2 selectivity of 70, but it has not been used as a UTFC membrane due to compatibility issues with the gutter layer and the associated risk of delamination during fabrication. The aim of this thesis are to develop gutter layers with CO2 permeance close to theoretical values; to produce UTFC membranes with superior separation performance using the developed gutter layer; and to ultimately develop a gutter-layer-free UTFC membranes. In an initial study, a novel approach involving precision control of the pre-crosslinking process was employed to produce PDMS gutter layer based UTFC membranes with excellent CO2 permeances that are significantly close to the theoretical potential. This newly developed technique demonstrated exceptional repeatability, with a measurement of 98.4 % based on 1,300 membrane samples. In addition, the importance of this super-permeable gutter layer was demonstrated by the addition of a PolyActive as a selective layer. This resulting UTFC membrane achieved a superior CO2 permeance. Secondly, UTFC membranes using PDXL as the selective layer were creasted for the first time. These membranes incorporated the exceptional PDMS gutter layer membranes developed in the first study. In this work, a novel macrocrosslinker, poly(1,3-dioxolane) dimethacrylate (PDXLMA), was synthesized and employed as a selective layer precursor. Furthermore, a modified version of the CAPATRP process used to form a PDXL selective layer to prevent potential delamination of the selective layer from the gutter layer. The resulting PDXL-based UTFC membrane exhibited outstanding CO2/N2 selectivity, preserving PDXL’s inherent properties throughout the fabrication process with enhanced chemical and mechanical strength. Lastly, a series of MOF@PDXL nanoparticles with core-shell structures with different PDXL layer thicknesses were developed enabling the formation of a gutter-layer-free UTFC membrane. These membranes formed using a straightforward drop spreading technique. This approach resulted in UTFC membranes that exhibit exceptional gas separation performance. The findings outlined in this thesis demonstrates a significant step forward in moving UTFC membrane technology towards feasible commercial-scale implementation. The innovative methodologies devised in this research can readily be incorporated into the existing setups of laboratories and industries. Furthermore, the development of a method to produce two-layered UTFC membranes is anticipated to make a substantial contribution to the evolution of membrane technology.
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ItemRetrofitting pipelines by in situ coating( 2024-01)Global energy demand is on the rise, urging a shift toward sustainable solutions. Hydrogen stands out as a clean, efficient energy source that could significantly reduce emissions. However, challenges persist in its storage and transportation. Using current natural gas pipelines for hydrogen transport is cost-effective but raises concerns about potential steel degradation due to hydrogen's ability to permeate steel. Hydrogen embrittlement threatens the safety and reliability of these pipelines. Addressing hydrogen embrittlement effects on steel infrastructure is crucial to maintain the safety and reliability of hydrogen transportation via pipelines. Internal coatings on pipelines can hinder the contact between hydrogen gas and the pipeline steels, thus preventing embrittlement. Nonetheless, the limitations of buried pipelines pose constraints on coating selection. Space restrictions and extensive pipeline distances limit the use of thermal or chemical treatments. Optimal coating materials need to be liquid or solution-based and not reliant on expensive materials to enable widespread usage. Considering these limitations, utilizing polymers for internal steel pipe coatings emerges as a promising solution. Polymer materials are cost-effective and easy to process, showing effectiveness in gas barriers and pipeline coatings. This thesis focuses on developing internal polymeric coatings for existing pipelines to prevent hydrogen embrittlement during transportation. Numerous commercially available pipeline coating materials have been studied for their gas permeability, particularly concerning oxygen. However, none of these studies have documented the permeability of hydrogen thus far. The thesis examined the hydrogen permeability of various coating materials, including poly (vinyl chloride), poly (vinyl alcohol) (PVA), crosslinked PVA and bisphenol A diglycidyl ether (DGEBA)/polyetheramine (D-400) films, and twelve commercial coatings. Notably, among these materials, two commercial two-part epoxy coatings exhibited promising results with hydrogen permeability of 0.40 and 0.35 Barrer respectively which are still too high for adequate protection, necessitating further enhancements. Glutaraldehyde crosslinked PVA exhibited the lowest permeability at 0.0084 Barrer, indicating strong potential as a coating. The level of hydrogen concentration within steel that can trigger embrittlement, however, remains unclear. Therefore, this thesis developed a mathematical model to evaluate unsteady state hydrogen diffusion through coated steel. The results suggested that a 2 mm thick crosslinked PVA film could extend the time to reach diffusion equilibrium from eight days to seven years, with a 44% decrease in final hydrogen concentration on the steel surface. Besides low hydrogen permeability, the material needs to be shear-thinning to be applied in situ onto underground pipelines. The thesis demonstrated the development of poly (ethylene glycol) diglycidyl ether (PEGDGE) and PVA crosslinked polymer coatings with ultralow hydrogen permeability and appropriate shear-thinning properties for on-site application. The material reached a hydrogen permeability of 0.01 Barrer, which is two magnitudes lower than most commercial coatings. The work found that alkali catalyst (KOH) concentration variations do not affect film permeability but promote the shear-thinning behaviour with shorter reaction times. Higher PVA to PEGDGE ratios enhance polymer crystallinity, reducing permeability but have a negative impact on the rheology. The molecular weight of reactants was also investigated. PVA with higher molecular weight reduces permeability and promotes shear-thinning. PEGDGE with higher molecular weight increases permeability but enhances shear-thinning properties with quicker reaction times. During hydrogen embrittlement processes, hydrogen molecules first dissociate into hydrogen radicals and then penetrate steel. Hence, in addition to barrier coatings for hydrogen embrittlement protection, this thesis also investigated a novel approach in hydrogen radical scavenging coatings. Polydopamine (PDA) was chosen here as the scavenging material. PDA films were fabricated on cellophane supporting films by dopamine self-polymerization. A microwave-assisted plasma chemical vapor deposition system generated hydrogen radicals which reacted with the PDA films. X-ray photoelectron spectroscopy analyzed the change in the composition and chemical structure of PDA and indicated its reactions with hydrogen radicals occur mainly within catechol and quinone groups in the PDA structure, reducing oxygen atoms and altering group proportions. Molecular dynamic simulations affirmed experimental findings, confirming that the hydrogen radicals indeed react with the quinone and catechol moieties present in PDA. The study in this thesis underscores the potential of PDA as a coating for scavenging hydrogen radicals on steel piping, thereby mitigating the risk of hydrogen embrittlement. In summary, this thesis delves into the hydrogen barrier properties of various coatings, employing mathematical models to assess their effectiveness. Additionally, it investigates novel coating materials, focusing on their hydrogen permeability and rheological properties. A novel insight into hydrogen radical scavenging materials for hydrogen embrittlement protection and the scavenging mechanisms, are also presented through both experiments and molecular dynamic simulation.
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ItemEnzyme-responsive nanomaterials for the delivery of antimicrobial peptides( 2023-10)The rate of resistance to antibiotics that are commonly used in the clinic is escalating rapidly, surpassing the introduction of new antimicrobial drugs. To address this problem, alternative strategies are being explored, such as the re-evaluation of antibiotics, that have not yet gained widespread clinical application. Antimicrobial peptides (AMPs) represent one of those antibiotics, offering remarkable antimicrobial efficacy against various pathogens. However, in clinical settings, AMPs are typically considered a last-resort option due to their off-target effects and poor stability in-vivo resulting from their cationic and amphiphilic peptide nature. Therefore, most of current strategies addressing these limitations focus primarily on the control and shielding of the cationic charge and the amphiphilic nature of AMPs. These can potentially be achieved through encapsulation of AMPs inside stimuli-responsive polyelectrolyte complexes (PECs) by combining the cationic drug with anionic polyelectrolytes. Stimuli-responsive polymers can be employed as encapsulation materials in PECs to design systems that activate drug release in response to specific changes encountered during microbial infection, such as variations in pH, enzyme activity, or temperature. The overarching aim of this Thesis was to explore the creation of PECs capable of encapsulating the clinically approved antimicrobial peptide, Polymyxin B and its subsequent enzyme-induced release. In Chapters 2 and 3, the aims were: Firstly, to synthesize anionic and helical polymers incorporating enzyme-degradable peptide side chains (Aim 1.1), followed by evaluation of the degradation properties of these polymers in response to the enzyme released by gram-negative bacterium Pseudomonas aeruginosa (Aim 1.2). In Chapter 4, the first objective (Aim 1.3) was to assemble Polymyxin B and the anionic enzyme-degradable polymers into PECs. The next objective (Aim 1.4 ) involved investigating the P. aeruginosa-induced drug release from these PECs, while Aim 1.5 focused on assessing the antimicrobial activity of the developed PECs against P. aeruginosa strains. Chapter 1 provides a review of the current developments in the field of the stimuli- responsive delivery of AMPs using polyelectrolyte complexes. Chapters 2 and 3 discuss the synthesis of polymers with poly(methacrylamide) and poly(acetylene) backbones respectively coupled to enzyme-degradable peptide side chains. Of the synthesized materials, two poly(methacrylamide) polymers from Chapter 2 were found to be the most effective in terms of degradation by the enzyme released by P.aeruginosa, while none of the synthesized acetylene-containing peptides from Chapter 3 polymerized. Subsequently, the poly(methacrylamide) polymer with the highest multivalency was used to form PECs with Polymyxin B in Chapter 4. Eight different formulations of PECs were created, with one being the most optimized in terms of encapsulation efficacy and physiological stability. The stability of the particles was further improved by the addition of Tannic Acid, which acted as a protective coating and a cross-linker. The Thesis then evaluated the ability of the PECs to release Polymyxin B under enzymatic degradation. Finally, the preliminary evaluation of the antimicrobial activity of the PECs against various P.aeruginosa strains were presented.
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ItemNitrogen Removal from Wastewater Treatment Using Filamentous Algae( 2023-09)Nitrogen removal from wastewater using freshwater filamentous algae has advantages over conventional bacterially-dominant systems, especially for reducing greenhouse gas emissions. Further, filamentous algae provide easier harvesting compared to microalgal processes. However, there are large research gaps that must be addressed before this technology can be implemented at large scale. This thesis aims to understand how filamentous algae can be utilised in wastewater treatment for nitrogen removal alongside traditional treatment processes, with key research objectives being to understand the ammonia tolerance and organic carbon uptake of filamentous algae, and physical design parameters and practical considerations needed for implementation in outdoor conditions. Key experimental methods specific to the study of filamentous algae were also developed in the thesis. The ammonia tolerance of four filamentous algae species from the Oedogonium, Tribonema, Spirogyra and Cladophora genera was investigated, by cultivation under different combinations of pH, temperature and ammonia concentrations. At 60 mg-N/L initial TAN, the critical pH range was found to be approximately 8.0–8.6, 7.5–8.3 and 7.5–8.0 for Tribonema, Oedogonium and Spirogyra respectively. The critical threshold calculated based on the initial amount of free NH3 was 1.5–3 mg-N/L for Tribonema and Oedogonium and approximately 1 mg-N/L for Spirogyra. Although Oedogonium cultivated with TAN at pH 7.5 and 15 degree Celsius showed stable growth and capability to utilise TAN under controlled conditions, it was concluded that the use of filamentous algae for downstream wastewater treatment rather than direct TAN removal may be a more practical option. In terms of organic carbon utilisation, the filamentous alga Tribonema was found to have increased productivity and enhanced photosynthesis by direct utilisation of glucose. In contrast, acetate could only be indirectly utilised in the presence of bacteria, whereas ethanol could not be utilised under any conditions. Despite the positive results with respect to glucose utilisation, it was also found that bacteria can easily outcompete Tribonema in terms of organic carbon utilisation, implying that the algae-bacteria interactions require further understanding and optimisation especially for the complex outdoor environments. It was therefore concluded that Tribonema is more suitable for treatment of wastewater with low organic carbon concentrations, such as secondary-treated wastewater effluent. The performance of filamentous algae in real wastewater was also investigated during a series of outdoor trials. The effects of key parameters that require consideration for scale-up were investigated, including aeration, wastewater strength, weather, tank setup and operations, and the filamentous algae’s adaptability to strong wastewater. Overall, Tribonema was found to be able to remove nitrogen from diluted anaerobically treated wastewater at the Western Treatment Plant (Melbourne) under outdoor conditions, with the use of undiluted wastewater also possible following a lengthy adaptation period for the algae. However, the nitrogen recovery rate into the algal biomass was relatively low compared to the overall nitrogen removal rate required. Therefore, it was concluded that applying filamentous algal systems to remove nitrogen from partially treated wastewater containing reduced nitrogen levels is a more practical option, since the operation under low wastewater toxicity improves the robustness of the system without compromising nitrogen recovery and CO2 capture by filamentous algae. Combining the findings from all chapters, it was concluded that filamentous algae can be used for nitrogen recovery and CO2 capture in partially-treated, low-strength wastewater, with Tribonema identified to be the most suitable algal genera among the four isolated candidates. Despite the promising results presented in this thesis, more future studies focusing on the variations and complexity of large industrial scale operations need to be performed before the process can be implemented.
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ItemCompatibility of Plastic Piping with Future Fuels( 2023-10)The future fuels, methanol, ammonia (NH3) and dimethyl ether (DME), have gained significant attention as a substitute for conventional fossil fuels, owing to their high volumetric energy density and the ability to be synthesised from hydrogen. Utilising existing natural gas infrastructure to transport these future fuels would offer notable advantages from both economic and operational standpoints. However, these future fuels are highly condensable, and have strong interactions with HDPE (high-density polyethylene) pipelines and associated elastomers that may lead to high leakage and material failure. Hence, this thesis investigated the compatibility of commercial HDPE piping samples and common elastomers used in natural gas distribution pipelines with methanol, NH3 and DME. Methanol compatibility was investigated for HDPE, as well as poly(styrene-co-butadiene) (SBR) and poly(acrylonitrile-co-butadiene) (NBR) as the base elastomer material, with the inert polytetrafluoroethylene (PTFE) as the comparison gasket material. Commercial elastomers that incorporated additives were also studied to evaluate the interaction and impact of methanol when additives were present. Methanol solubility and diffusion in those polymeric materials, as well as changes to the mechanical properties, were determined through sorption measurements. Methanol exhibited higher solubility and diffusivity in HDPE than methane, thereby raising concerns about potential inventory losses in practice. Only minor changes in mechanical properties were observed upon exposure of HDPE to methanol, indicating that HDPE pipelines can safely transport methanol. In contrast, the two base elastomers -SBR and especially the more polar NBR- showed orders of magnitude higher solubility of methanol than methane, attributed to methanol’s high condensability and its similar polarity with these elastomers. In comparison, the inert gasket material PTFE was unaffected by exposure to methanol. Commercial elastomers demonstrated significant leaching of additives and mass change after methanol exposure. Subsequent mechanical testing revealed that the methanol significantly impacted the performance of the elastomers by reducing yield strain and therefore lowering flexibility, a key characteristic of elastomers. The compatibility of HDPE and associated elastomers -SBR and NBR- were investigated with gas phase NH3 and DME. A constant volume variable pressure (CVVP) method was employed for measuring transport properties. Both future fuel penetrants exhibited much higher solubility in these materials than methane, especially in the elastomers, due to the similar polar nature between these fuels and elastomers. The permeability of NH3 in HDPE was independent of pressure, while DME permeability displayed significant pressure dependence, which was also associated with a notable loss of structural integrity. DME caused swelling within HDPE, leading to a significantly higher permeability than methane. Over time, the strong interactions reduced the permeability to 52% of its initial value through a process known as anti-plasticisation. This outcome revealed that NH3 can be safely transported within HDPE pipes, but DME cannot be safely transported. DME significantly affected the elastomers, with an almost 70% decline in permeability observed for NBR systems, attributed to the combination of densification of the polymer structure and anti-plasticisation by the penetrant fuel. This indicated that elastomers undergo significant morphology change as a result of exposure to DME and therefore have a higher likelihood of failure when exposed to this fuel. Ammonia-resistant elastomers with low permeance already exist but are based on expensive fluorinated polymers, such as PTFE, which have several health and environmental impacts associated with their fabrication. Hence, methodologies to decrease the NH3 permeance in a common and cost-effective elastomer were developed here. Three kinds of additives were incorporated into the elastomer NBR, deploying three different approaches: increasing the basicity of the elastomer environment; chemically reacting with NH3 to limit transport; and incorporating barrier additives to prevent diffusion. Additives utilised included organic molecules, polymers, metal oxide, metal hydrides, metal organic frames and nanocomposites. The mechanical properties were also assessed, as these are fundamental to an elastomer’s role. The creation of a basic environment through amines, especially putrescine, resulted in NH3 permeability losses of 50%. Chemical additives lowered the permeability from 10% to 20% with limited impact on the tensile properties. The most significant decrease was observed for the addition of 3% graphene oxide to NBR, with NH3 permeability decreasing by 80%, but a negative consequence was the production of a more rigid material. As a result of this investigation, NH3 permeability can be significantly reduced in inexpensive NBR elastomers through tailored additives. This represents a relatively straightforward approach to future-proof natural gas infrastructure for NH3 transportation. This thesis has demonstrated the compatibility of transporting the future fuels methanol and NH3 through pipeline material HDPE, as well as the lack of compatibility for DME transportation. Importantly, the polar nature between elastomers and future fuels results in strong interactions and high sorption, leading to higher permeability than observed for methane, which places a greater safety risk on using these materials with these future fuels.
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ItemSynthetic peptides and polymers for self assembly and the control of surface forces(University of Melbourne, 2009)
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ItemLiving and conventional polymerizations for the development of precision polymers and functional materials(University of Melbourne, 2009)
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ItemNanoengineered capsules for the delivery of nucleic acids(University of Melbourne, 2009)
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ItemCore cross-linked star polymers and their multistar analogues : advancements in their versatility and commercial viability(University of Melbourne, 2009)