Chemical and Biomolecular Engineering - Theses
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ItemNo Preview AvailableMolecular Insights into Nanoengineered Metal–Phenolic Networks( 2023-06)Coordination assembly has garnered significant attention in designing advanced materials with well-defined geometry and functions for diverse applications across various fields. Metal–phenolic networks (MPNs) are supramolecular coordination network materials composed of metal ions and natural phenolic ligands. The distinctive combination of hybrid physicochemical properties and versatile coating ability have endowed MPNs with widespread potential in biomedical, environmental, and agricultural applications. However, despite recent advancements, regulating coordination chemistry in MPNs through different coordination modes remains largely unexplored and a challenge. A comprehensive understanding of this aspect and the associated knowledge is expected to significantly boost the development of MPNs with unique morphologies and properties for a wide range of fields. This thesis aims to expand the realm of MPNs by engineering their coordination modes and kinetic at the nanoscale, thereby imparting materials with controllable properties or emerging functions for various targeting applications. Firstly, the dynamic and selective coordination modes of MPNs were experimentally and computationally investigated using flavonoids with monotopic, ditopic, and multitopic chelating sites. The dominating coordination modes in MPNs could be adjusted from metal–catechol to metal–maltol by simply changing the assembly pH, leading to distinct crosslinked coordination networks and tunable physiochemical properties (e.g., selective permeability and pH-dependent degradability) for desired applications. Secondly, flexible MPNs featuring guest-responsive behavior were achieved by introducing intermolecular competitive coordination between MPNs and external guest molecules (e.g., glucose). Upon exposure to glucose molecules, glucose partially replaced flavonoids in MPNs due to the comparable intermolecular coordination of metal ions to flavonoid ligands and glucose. This led to the re-conformation of metal-organic networks and changes in their physiochemical properties, as demonstrated experimentally and computationally. The resulting cargo-loaded MPNs could be responsive to external guest stimuli, showcasing promising potential in smart drug delivery. Thirdly, a library of MPN nanoparticles with different compositions was fabricated by controlling the coordination kinetics of metal-phenolic complexes. The formation kinetics and physiochemical properties of MPN nanoparticles were systematically controlled by employing various strategies, including adjusting the incubation time, precursor types and concentrations, and the assembly pH. Moreover, various functional components (e.g., enzyme and drug) were incorporated with MPN to fabricate functional nanoparticles for desired biomedical applications, including cell targeting and drug delivery. These studies expand the understanding of the coordination chemistry of MPNs and provide a guideline for the rational design of metal-organic materials for broader applications.
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ItemNo Preview AvailableThermal Decomposition Mechanisms and Kinetics for Regulated and Emerging Per- and Polyfluoroalkyl Substances (PFAS) through Computational Chemistry( 2022-08)Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are highly regulated and extensively documented anthropogenic compounds, belonging to the family of per- and polyfluoroalkyl substances (PFAS). Owing to their useful physicochemical properties, they were widely used as commodity chemicals in various products, from fabric protectors to firefighting foams. Concerns over their adverse health effects led to the phasing out of PFOS and PFOA, and hexafluoropropylene oxide dimer acid (GenX) was introduced as an alternative. However, it poses a similar threat to humans and wildlife as its predecessors. Commercially, thermal treatment is often used to remediate PFAS-contaminated soil and other media, yet little is known about the exact degradation mechanism at elevated temperatures. In this thesis, we investigated the thermal decomposition mechanisms and kinetics of PFOS, PFOA, GenX, and other related PFAS, including perfluoro-alkyl lactones, perfluorinated alcohols, perfluorinated aldehydes, and perfluorinated alkylene oxides. We utilised computational chemistry and reaction rate theory modelling to determine reaction mechanisms and kinetics. We discovered that the decomposition of these compounds commences at the functional headgroup, and the final degradation products include SO2, CO, CO2, HF, COF2, and CF2. We developed a detailed chemical kinetic model, comprising a large number of reactions, indicating that the acid headgroup in PFAS can be efficiently destroyed in incinerators operating at relatively modest temperatures. The new insights provided by this research into the exact decomposition mechanism and kinetics of the tested PFAS will be utilised to enhance remediation technologies that are currently under active development.
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ItemRational design of novel adsorbents for nitrogen rejection in natural gas( 2023-05)Natural gas is an important energy resource that plays a critical role in meeting the global energy consumption. It is a clean-burning fuel that emits fewer pollutants than other fossil fuels, making it a more environmentally friendly alternative for power generation, heating, and transportation. Natural gas is also an important feedstock for the chemical industry, as it is used to produce a wide range of chemicals and materials. In addition, natural gas is abundant and widely available, making it a reliable and cost-effective source of energy. Due to its many advantages, natural gas is expected to continue to be an essential part of the global energy mix for many years to come. Rejecting nitrogen (N2) in natural gas is essential because it reduces its heating value, making it less efficient as a fuel. Separating nitrogen from methane (CH4), the main component of natural gas, is difficult because the two gases have similar physicochemical properties, and traditional separation methods such as distillation are energy-intensive and expensive. While an adsorption technology based on the selective adsorption of nitrogen (the minor component in natural gas) could minimize the process operating cost, the lack of proper N2-selective adsorbent material with high selectivity and capacity is the biggest drawback for this purpose. Among numerous available adsorbent materials, few have been identified to be N2-selective at equilibrium. Accordingly, the main objective of this thesis is to apply both computational and experimental techniques to discover N2-selective adsorbents and evaluate them for N2 rejection in natural gas. In chapter 3, cyclohexane-chair, toluene, benzene, and nine different polycyclic aromatic hydrocarbon molecules (PAH), along with their Li-doped complexes, are screened to compare their ease of Li doping and binding energy with N2/CH4 through a first-principle computational study. Lithium possesses the unique ability to undergo a gradual reaction with N2 gas at normal atmospheric conditions. In the 1990s, lithium metal emerged in the gas separation area and was patented to separate N2 from crude argon. However, lithium pellets are far too slow in the reaction kinetics due to the lack of surface area, normally taking many hours for a 1 mm diameter lithium pellet to be completely consumed by N2 gas, which is obviously impractical in an adsorption process. Here the aim of this chapter was to design a high-performance N2-selective material featuring Li atoms scattered in the aromatic nucleus under mild conditions. One strategy is to make Li metal react more adequately in a more decentralized system. Earlier work demonstrated that hydrogen adsorption capacity increased on aromatic-supported lithium. Accordingly, the PAH molecules were selected as the base surface for lithium doping. The results demonstrated that aromaticity is the key factor for lithium doping due to the delocalized p bond. Furthermore, it was concluded that the extent of electron delocalization plays a major role in the stability of Li-doped PAH complexes. However, considering a specific PAH, it was found that for those sites with minor differences in the degree of electron delocalization, the role of the symmetrical structure in the stability of the Li-doped PAH complex is dominant compared with the effect of aromaticity. The interaction energies obtained for N2 with Li-doped adsorbents showed that Li doping significantly increases the gas adsorption energies, resulting in considerable N2 selectivities. This was achieved through the incorporation of Li metal on the aromatic substrate, where Li bridges the aromatic molecule p bond and N2 LUMO. In particular, Li-doped phenanthrene and chrysene showed the highest N2/CH4 selectivities of 119.7 and 80.8, respectively. These results indicated the high potential of Li-doped phenanthrene and chrysene for N2 removal from natural gas. Chapter 4 presents the computational investigations conducted on a specific type of zeolite called KZSM-25, which possesses the most extensive unit cell compared to other zeolites. This unique zeolite demonstrates the capability to selectively trap N2 gas over CH4, exhibiting an exceptional selectivity of up to 34. Previously, a novel mechanism was discovered for molecular separation, namely, the molecular “trapdoor” effect, in some small-pore zeolites with eight-membered rings (8MRs) windows. In the context of the trapdoor mechanism, zeolites exhibit a temperature-controlled adsorption phenomenon where the ability of gas molecules to access the internal pores of the crystal depends on the thermal oscillation of specific cations known as "door-keepers" in relation to the gases. This thermal oscillation leads to the opening or closing of gates at different temperatures, allowing for the admission or rejection of molecules. By differentiating the gate-opening temperature for each molecule, it becomes possible to develop a novel approach to separate specific gas pairs by manipulating the working temperature. However, existing small-pore zeolites face challenges in effectively differentiating N2 from CH4 due to their similar gate-opening temperatures and relatively low working temperatures. Recently, a new small-pore zeolite called ZSM-25, with a low Si/Al ratio, has been introduced to enable efficient separation of N2 over CH4. This is achieved by incorporating the "door-keeping" cation in the 8MRs (eight-membered rings) of the zeolite structure. In this chapter, molecular dynamics (MD) simulations and ab initio density functional theory (DFT) calculations are employed to investigate the temperature-dependent gas admission behavior and elucidate the atomistic-level N2/CH4 separation mechanism within the ZSM-25 unit cell. The extent of vibration of the K cation plays a crucial role in regulating the access to the cage, thereby influencing the adsorption uptake of the material. The theoretical findings align with experimental observations, confirming that the incorporation of cations into ZSM-25 offers a promising approach for achieving efficient N2-selective adsorption over CH4. Chapter 5 reports a microporous zeolite called NaZSM-25 capable of adsorbing N2 over CH4 with an exceptional selectivity of 47 at room temperature. While clinoptilolite, titanosilicate, and trapdoor KZSM-25 are exceptional N2-selective materials, trapdoor zeolite has higher equilibrium selectivity toward N2, as proved in the previous chapter. In this chapter, NaZSM-25 zeolite is reported with exceptionally high N2/CH4 selectivity at room temperature, outperforming all previously known N2-selective adsorbents. MD and DFT calculations were used to investigate the gas adsorption and diffusion mechanism of this zeolite. CH4 was blocked in the experimental temperature range of 273-323 K showing minor external surface adsorption. MD simulations were used to estimate the self-diffusion coefficient of N2 (3.5e-10 m2/s) and CH4 (= 0 m2/s) in NaZSM-25 with Si/Al ratio of 4.33 representing the same Na density in the sample. Ab initio DFT calculation results also supported the CH4 diffusion limitation because of the change in the 8MR pore opening caused by Na. Diffusion energy barriers of 63 and 96 (kJ/mol) were found for N2 and CH4, respectively through DFT calculations. The much higher energy barrier of CH4 revealed that diffusion is the controlling mechanism in the gas adsorption of the NaZSM-25. This zeolite showed outstanding N2/CH4 selectivity, fair N2 capacity, and high thermal stability all of which make it an ideal adsorbent for N2 rejection in natural gas to avoid energy-intensive cryogenic distillation. Incorporating the presented material into industrial adsorption processes can potentially offer access to natural gas reservoirs that are otherwise not viable due to high N2 impurity content. In Chapter 6, 1425 alkali metal-exchanged zeolites are screened to identify the candidates with the best potential for the separation of N2 from CH4. Zeolites are the most common adsorbents for gas separations and are manufactured over 4.2 million metric tons every year. Approximately 254 zeolite topologies have been reported and numerous in silico structures have been predicted. It is both time-consuming and expensive to experimentally test all known zeolites for the separation of CH4 and N2. High-throughput molecular simulations can be utilized to screen the adsorption performance of a large number of nanoporous frameworks. The result of these simulations is the identification of a manageably limited number of the best materials that could be tested experimentally. In this chapter, molecular simulations are used to evaluate materials within the database for the separation of N2 and CH4. The extra framework cations considered were lithium, sodium, potassium, rubidium, and cesium. Zeolites with silicon over aluminum ratios of 3, 5, 10, 25, and 50 were also generated. The Grand canonical Monte Carlo (GCMC) simulation was performed to identify the best candidates for selective adsorption of N2 over CH4. The effect of the alkali metal type and Si/Al ratio on the performance of each framework was investigated. The K cation showed the highest affinity toward N2 adsorption, while the smaller Li cation had the highest gas uptake. In addition, lower Si/Al ratios were favorable for N2/CH4 selectivity. Seven different zeolites showing equilibrium adsorption selectivity toward N2 were reported. These results are significantly important as there are few zeolites capable of adsorbing N2 over CH4. Accordingly, all exceptional zeolites reported in this chapter are worth to be investigated experimentally. Notably, Li-RRO-3 was found to have the highest N2 capacity among all zeolites while showing equilibrium selectivity toward N2. The reasons for the high N2 uptake of Li-RRO-3 were found to be the exposure of all Li cations to the gas molecules as well as the lack of blocked pores. The selective adsorption of N2 over CH4 on Li-RRO-3 was revealed by DFT studies, which showed a higher adsorptive affinity of N2. Li-RRO-3 is a promising adsorbent candidate for adsorption-based technology to separate N2 and CH4 gas mixtures. The outcome of the thesis indicates the feasibility of adsorption-based technology for the separation of N2 and CH4. Four different types of adsorbents were discovered to show N2 selectivity. Lithium-doped PAHs and Li-RRO-3 are predicted to be potential candidates and require further experimental studies. NaZSM-25 and KZSM-25 have been proven to exhibit the highest selectivity toward N2 among all adsorbent materials and they could be used to design a pressure swing adsorption (PSA) process for N2 rejection in natural gas.
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ItemMembrane ultrafiltration of skim milk and its application to cream cheese manufacture( 2023-02)Cream cheese is an important export product for Australia; cream cheese production and consumption also continue to increase in many countries. The traditional manufacture of cream cheese generates a large volume of acid whey (~65–70%, w/w) that is often treated as wastewater, animal feed or fertilizer and can have a negative impact on the environment. Membrane ultrafiltration (UF) can be used to pre-concentrate the milk used in cream cheese production to improve the retention of whey proteins, increase productivity and reduce the generation of acid whey. The effect of UF concentration on the properties of milk and subsequent effects on the acid-coagulated gels and resulting cream cheese were investigated in this thesis. The thesis commences with a literature review of cream cheese manufacture and membrane filtration in Chapter 2. The fundamental and physico-chemical properties of cream cheese acid gels made from the addition of UF milk are then reported in Chapter 3. It was hypothesised that UF addition would impact the properties of both the milk and acid gels formed during the early stages of cream cheese production. Skim milk was concentrated to a volumetric concentration factor (VCF) of 2.5 or 5 by UF and the milk samples were standardized to a protein-to-fat ratio of ~0.23 to achieve a milk composition typical of that used for full fat cream cheese production. The UF cheese milk had a similar particle size distribution to the unconcentrated cheese milk after homogenization but increased viscosity and a slower rate of acidification, which could be improved by increasing starter culture concentration. The acid gels formed with the addition of UF retentate contained more protein and fat, resulting in a higher storage modulus, firmness and viscosity. A denser microstructure was observed in the acid gels formed with UF retentate and quantitative two- or three-dimensional analysis of confocal images found a greater volume percentage of protein and fat, decreased porosity and increased coalescence of fat. The mobility of water, as assessed by proton Nuclear Magnetic Resonance (1H NMR), was reduced in the dense UF gel networks. These insights improve our understanding of acid gel formation and can be used by manufacturers to optimize processing conditions for the use of concentrated milk and subsequent handling of firmer gels in industrial-scale cream cheese production. Chapter 3 demonstrated how calcium content increases in VCF2.5 and VCF5 retentate to ~260 mg/100 mL and ~480 mg/100 mL respectively, significantly higher than the concentration of ~120 mg/100 mL in the skim milk. The elevated calcium content that occurs in the milk concentrate after ultrafiltration is regarded as a potential cause for the defects reported in some UF-based dairy products, such as fresh cheese. In Chapter 4, to reduce calcium concentration in the UF preparations, skim milk was treated with 1% (w/v) or 2% (w/v) cation exchange resin and the treated milk then concentrated by UF to a VCF of 2.5 or 5. It was hypothesised that the removal of calcium from skim milk by cation resin would affect the properties of milk proteins as well, as the ultrafiltration process. The calcium content in the resin-treated skim milk, as well as the resulting retentates (VCF2.5 and VCF5), decreased by 20–30% compared with the non-resin treated controls. As a result of decalcification, the casein micelles partially solubilized and dissociated, which led to an increase in the soluble protein content and a lower relative turbidity for these milk samples. The decalcification of the skim milk feed also decreased the permeation flux during UF and led to a decrease in the gel concentration (or maximum concentration factor) from ~30% (w/w) solids (~6.5 fold concentration) for the control skim milk to ~24% (w/w) solids (~5.4 fold concentration) for 2% (w/v) resin treated skim milk. The average diameter of particles in skim milk was found to increase from ~160 nm to ~180 nm after calcium reduction, while the ultrafiltration process led to a decrease in particle size for the resin-treated milk samples. The zeta-potential of the calcium reduced UF retentates did not change but surface hydrophobicity increased. Analysis of the milk solids indicated that calcium depletion increased the hydration of the milk proteins to 3.3 g water per g dry pellet (2% resin, w/v), compared to the 2.2 g water per g dry pellet for the non-resin treated controls. The increase in milk protein hydration also contributed to a higher milk viscosity. Differential scanning calorimetry (DSC) showed calcium reduction decreased the denaturation temperature of alpha-lactalbumin and beta-lactoglobulin by ~3 and ~1 Celsius degree respectively. Overall, the work in Chapter 4 provides a route to produce calcium-reduced milk concentrate with potential in retentate-based dairy products with tailored functionality. The impacts of UF retentate addition and calcium reduction on the properties of the final cream cheese were then evaluated in Chapter 5. It was hypothesised that the properties of cream cheese made from UF retentate would significantly differ from those of the control cheese made from unconcentrated milk and the reduction of calcium by ion exchange would also affect the properties of cream cheese. In this work, cream cheese was made from UF concentrated milk (2.5- and 5-fold), treated with or without 2% (w/w) cation resin and the properties compared with a control cream cheese made from unconcentrated milk. The UF cheeses did not differ in protein, fat and moisture content from the control but had a higher calcium concentration if not treated with resin (~150 mg/100 g and ~230 mg/100 g for cheese made from non-calcium reduced VCF2.5 and VCF5 retentate respectively vs ~90 mg/100 g for cheese made from unconcentrated skim milk). The microstructure of the cheese made with UF without calcium reduction was more heterogeneous and porous than the control, consistent with a decreased hardness and thermal stability, providing new insights into the link between UF cream cheese microstructure and functional properties. The calcium reduction of ~20% induced by 2% (w/w) cation resin treatment prior to UF to VCF2.5 or VCF5 did not significantly affect the texture properties of the cheese formed compared to the non-resin treated counterparts but led to an increase in the size of the corpuscular structures found within the UF cheese. The concentration of free amino acids and peptides was highest in the cheese made with added UF retentate and decreased in the samples with reduced calcium, although not as low as the concentration in the control cream cheese, illustrating the potential to tune this property. This study improves our understanding of UF-produced cream cheese with differing calcium content and this knowledge may benefit future scale-up to industrial production. In conclusion, the work from this thesis broadly explored the impact of processing conditions including the concentration factor of milk, starter culture concentration and calcium concentration on the properties of the milk, acid gels and the final cream cheese product. These findings illustrate how milk solids concentration and calcium concentration can be systematically used to alter intermediate and final product properties and may be beneficial for industrial manufacturers to further optimize cream cheese production at different manufacturing stages when using concentrated milk to reduce acid whey production.
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ItemDeposition Behaviour of Coated Particles and Capsules( 2023-01)Particle deposition is a key phenomenon for processes involving colloidal transport in a wide range of industrial applications. Despite the number of deposition studies involving homogeneous particles, a significant gap lies in understanding the deposition of coated particles, capsules, balloons, or, more broadly, composite particle systems. One of the probable reasons for the limited number of investigations is the complexity involved with the surface force interactions, notably the effects from retarded van der Waals interactions, essential in the deposition of composite colloids. Therefore, this thesis aims to establish a critical connection between the surface force interactions associated with the composite colloids and the modification of existing simulation models for predicting the deposition behaviour of flowing particles in a microfluidic channel. Since the surface interaction is sensitive to the size and shapes of colloids, a successful attempt has been made to develop a template-directed nanolithographic approach for making anisotropic particles of varying sizes and shapes. A combination of thermal scanning probe lithography and reactive ion etching allows the fabrication of templates of uniform cross-sections with precise resolutions. E-beam evaporation was then employed for depositing nanometer-thick films in the templates. A template wash technique was used for particle release, followed by filtration to collect the particles in a solvent. The coefficient of variation of the lateral dimension of triangular prismatic particles was found to be 0.2% by an AFM particle analysis, confirming the low polydispersity index of the fabricated particles. Further, stair-like particles from a three-dimensional template were also made following the same method. This generalised technique showed excellent flexibility in choosing the shapes and sizes of the anisotropic particles with a minimum dimension of ~50 nm. Prior to exploring the deposition dynamics of composite colloids, a systematic analysis to determine the significance of surface forces in the deposition process was crucial. Although the previously developed Brownian dynamics models established a comprehensive understanding of the deposition of polystyrene in a microfluidic channel by including advection, diffusion, and surface forces, the model lagged in the precision of colloidal interaction calculation between the particles and the surface. Since the van der Waals interaction is subjected to the retardation effect, the model overestimated the attraction force between the particles and the surface by assuming Hamaker as a constant. Further, their model also neglected the screening effect of ions for calculating the van der Waals force in an electrolyte solution. Since this thesis is particularly interested in investigating the deposition behaviour of composite colloids, considering the effect of retardation from both the core and coating materials and the screening effect of ions in the electrolyte solution is necessary for evaluating the retarded van der Waals interaction in the system. Utilising the Lifshitz theory, the effect of retardation was included in the Hamaker function to calculate the retarded van der Waals force between the coated particles and surface and incorporate it into existing simulation frameworks. The results from the adapted deposition model showed that both the geometry of the coating and the contrast between the material properties of core and coating materials played a crucial role in evaluating the significance of retarded van der Waals interaction in the deposition model. Motivated by the relevance in sunscreen products, the deposition behaviours of titania particles coated with silica and alumina were explored in varying system conditions. The prediction results by the adapted model revealed that the deposition of titania-silica composite particles was governed by diffusion or surface forces depending on the electrolyte concentration in the solution. In the solution of low ionic strength, where the net surface force between the composite particles and the glass surface was repulsive in nature, the deposition was ‘unfavourable’, and the colloidal force close to the surface controlled the kinetics. In the absence of a net repulsive barrier between particles and the surface in solutions of high electrolyte concentration, i.e., in ‘favourable’ conditions, Brownian diffusion of composite particles dominated the deposition process. For titania-alumina particles, the deposition was enhanced due to the presence of attractive double-layer interaction in the system. As the ionic strength increased, the deposition of titania-alumina particles decreased. The extensive analysis enabled us to answer why, when and where the composite particle deposit while flowing in a microfluidic channel. Further extending the understanding of the deposition of composite particles, the attachment of air-filled polymeric capsules was investigated in varying solution conditions. The presence of long-range van der Waals repulsion between the air balloons and the surface in an aqueous medium significantly reduced the deposition efficiency when compared with the composite particle systems. A deposition phase diagram was provided to indicate the deposition behaviour and the governing factors based on the parameters, such as ionic strength, colloid size, nature of total surface force, and relative surface charges between colloids and the surface. Finally, a new experimental technique for studying deposition was developed by integrating resonance imaging microscopy with microfluidics. Thus, the efficiency of the adapted deposition model in an ‘unfavourable’ condition was validated by comparing the predicted deposition of silica-polydopamine composite particles with experimental measurements. The prediction by the model was in excellent agreement with the measured deposition dynamics for the initial stage of deposition. Further development of the model is achievable by including the interparticle interactions, which are critical for the advanced stages of deposition.
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ItemHierarchical structure function relationships in biopolymer systems( 2023-03)Biopolymer networks are assemblies of biopolymer chains that form into a coherent self-supporting structure and on the macro-scale appear as gels. These biopolymers often assemble in a very specific manner exhibiting various structures at different length scales. Thus, a structural hierarchy exists. This work investigates whey protein isolate as a model biopolymer system to establish the relationship between the 3D microstructure and the mechanics of the network. The molecular, aggregate, and micro through to macroscopic assemblies of these materials leads to their complex physical and rheological properties. The structure at multiple length scales has been examined using a range of techniques including but not limited to x-ray scattering, circular dichroism, and microscopy. The rheological properties of the gels and aggregate suspensions resulting from preparation methods incorporating heating, pH adjustment and shear is reported. Particular attention focuses on the application of shear forces during gelation and the effects on the microstructure, aggregation behaviour, particle sizes, and rheological properties of the resulting protein suspensions and gels produced during heating has been investigated. Models have been proposed to explain the results. A key finding from this work relates to the role of effective concentration, resulting from an interplay between nominal concentration and pH, in determining the outcome during biopolymer microparticulation. The use of small-scale perturbations to augment gel rheology was also examined with effects such as strain hardening being introduced into otherwise non-strain hardening gels. This research brings new insights to structural design principles and opens avenues to control the mechanics of gelled systems and the sizes of aggregates resulting from microparticulation.
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ItemDevelopment of new pressure swing adsorption (PSA) cycles( 2023-03)Pressure swing adsorption (PSA) is an adsorption-based process, which has been widely used and studied for gas mixture separation due to its low investment and operating cost and high automation. Numerous novel concepts based on basic features of traditional PSA cycles, such as simulated moving bed (SMB)-PSA, dual reflux (DR)-PSA and layered PSA, have been demonstrated for targeting specific separation requirements and obtaining better separation performance. Dual reflux pressure swing adsorption (DR-PSA), as a state-of-the-art process, uses a lateral feed inlet and both light and heavy reflux strategy while keeping the basic features of conventional PSA cycles, achieving the separation performance beyond the so-called separation limitations constrained by pressure ratio. However, there are still some typical problems of DR-PSA to be solved. The main objectives of this study are to develop new cycles to overcome some key problems of the DR-PSA process. This study is divided into three main sections, 1) parametric study of a dynamic-feed DR-PSA process for capturing dilute methane (CH4) from nitrogen (N2) gas; 2) development of a triple-reflux pressure swing adsorption (TR-PSA) for separating methane-nitrogen-helium ternary gas mixtures; 3) development of the dual reflux vacuum swing adsorption (DR-VSA) process for enrichment of low-grade CH4 which falls into the explosion range and demonstration of a new dual-objective optimization method. In the first section, it can be concluded that the dynamic-feed strategy can practically solve the mixing problem caused by the lateral feed inlet of the DR-PSA process and the performance of dynamic-feed DR-PSA elevates with the number of feed inlet positions along the column. Parametric studies are conducted based on three key operating parameters, heavy to feed flow ratio, light reflux flowrate and feed/purge step time, indicating that the dynamic-feed DR-PSA can always obtain both higher purity and recovery over the traditional DR-PSA process under same operating conditions; a typical comparison of separation results between two cycles is 53.5% vs. 47.5% for purity and 81.1% vs. 72.2% for recovery, respectively. In the second section, a triple-reflux (TR)-PSA process is demonstrated to separate a ternary gas mixture composing of 10% helium (He), 20% CH4 and 70% N2 via a single-stage process. The TR-PSA process can enrich 10% He up to 45.3 % with a recovery of 91.3% while achieving 60.0 % purity and 90.4% recovery for CH4 and 95.8 % purity and 68.9% recovery for N2 with a work duty of 49.6 kJ mol-1 (feed). The TR-PSA process can obtain slightly better product purity and recovery of He (45.3% purity with a recovery of 91.3 %) than the 2-stage DR-PSA process (purity is 44.8% and recovery is 89.7%) while leading to a mild decline in CH4 purity and recovery (1.4% and 1.7%, respectively) compared to the two-stage DR-PSA. TR-PSA process only requires a cycle work of 49.6 kJ/mol (feed), which is significantly (30%) lower than the specific work of the 2-stage DR-PSA process (64.3 kJ/mol (feed)) due to the use of one compressor in TR-PSA versus two in the 2-stage DR-PSA system. In the last section, vacuum swing adsorption (VSA) is integrated with the dual reflux strategy as the DR-VSA cycle which can be operated within a pressure range lower than the atmospheric pressure and avoid the usage of a compressor. Two types of DR-VSA cycles (A- or B-type cycle indicates that pressure reversal step is carried out through the heavy or light end, respectively) have been studied for enriching low-grade CH4 (CH4 molar fraction is between 5–20%) gas using activated carbon (AC) or ionic liquidic zeolites (ILZ). The optimal configuration is A-type cycle packing with ILZ adsorbents, which can enrich 20% CH4 to a purity of 80.2% with 95.5% recovery and a specific energy consumption of 180.8 kJ/(mol CH4 captured). The final optimal results achieve a good balance between purity and recovery by adopting the new optimization method which uses a dual convergence algorithm to iteratively vary operating conditions and a multiplicative score function to evaluate the separation performance of each case.
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ItemFormation and Destruction of Environmental Contaminants in High Temperature Processes( 2022)This thesis deals with the high temperature processes with the potential to generate environmental contaminants which adversely affect wildlife and human health. Identification of decomposition pathways and kinetics of reactions at moderate to elevated temperatures are required to avoid or limit the formation of contaminants. The text emphasizes both degradation chemistry and process design aspects as individual steps to form an efficient process. Safe and efficient implementation of a thermal process is highly dependent on understanding the chemistry of the process. Chapter 1 provides a brief overview of different high temperature processes with the potential for the formation and destruction of environmental contaminants ranging from industrial scale to personal devices. Waste-to-energy plants, water sludge and contaminated soil treatment, and chemical stockpile destruction facilities are industrial-scale processes that can be designed to use thermal methods for man-made chemical destruction. On a smaller scale, vaping devices are another group of thermal processes which can form a low concentration of contaminants but these chemicals directly inhaled by humans can be a serious threat to human health. Chapter 2 covers detailed chemical kinetic modeling of the two most regulated compounds of per- and poly-fluoroalkyl substances (PFAS) family namely perfluorooctane sulfonic acid (PFOS), and perfluorooctanoic acid (PFOA). A high amount of these forever chemicals can be found in solid waste material feeding to waste-to-energy plants. Also, these compounds can be presented in a lower concentration in wastewater sludge and contaminated soil due to their environmental persistence and wide array of applications. Kinetic modeling of perfluorinated sulfonamides, an emerging compound of PFAS family, is detailed in Chapter 3. To examine the effectiveness of thermal processes for the disposal of phosphorus chemical stockpiles a preliminary study using theoretical methods is crucial to be applied due to hazardous safety issues linked to their laboratory use. Thermochemical properties of less toxic simulant compounds, such as triethyl phosphate (TEP) and diethyl-methyl phosphonate (DEMP), and their decomposition intermediates along with their kinetic rate coefficients were calculated to modify the developed kinetic models for combustion and pyrolysis processes (Chapter 4). Glyphosate as the world’s widespread weed killer is another phosphorous compound classified as “probably carcinogenic to humans” and has the potential to be fully banned in the future. The thermal decomposition mechanism of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) were presented in Chapter 5. In chapter 6, the biomolecular degradation of AMPA through a reaction with OH radicals in the atmosphere was studied. This reaction is of importance in high-temperature processes due to the presence of OH radicals. Chapter 7 focused on identifying the pyrolysis chemistry of triclosan and its chlorinated derivatives and then developing a chemical kinetic model to predict their pyrolysis products. This compound belongs to the family of pharmaceuticals and personal care products (PPCPs) and ended in biosolids from wastewater treatment as biosolids are used to fuel waste-to-energy plants. High temperature chemistry can be important even in a condition with a trace amount of target compound in the reaction chamber. In the vaping process, the decomposition products are directly inhaled into the human lung, and the presence of a low concentration (ppm) of an acutely toxic compound can be lethal. Vaping of vitamin E acetate (VEA) under dry hit vaping conditions was examined to predict toxic ketene formation potential (Chapter 8). This chapter presents the concentration of VEA decomposition reaction products versus vaping temperature. Chapter 9 focused on identifying the high-temperature chemistry of ethyl ester flavor additives and simulated vaping process in a plug flow reactor to find the concentration of vaping products in the inhaled stream.
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ItemRecycling of Lithium-ion Batteries by Solvent Extraction( 2022)The increasing demand for lithium-ion batteries (LiBs) is putting a strain on the critical metal supply chain. Moreover, a significant proportion of spent LiBs are disposed of in landfills. The linear LiB value chain has a massive environmental footprint, making it imperative to create a circular economy for LiBs by recycling spent LiBs to manufacture new batteries. Among the recycling processes, extractive hydrometallurgy is a promising technology for recovering valuable metals from black mass leachate. The purpose of this study is to establish a theoretical foundation for developing a cost-effective and robust solvent extraction process that can prepare mixed valuable metals LiB cathode resynthesis. A thermodynamic model, which assumes solvent extraction as a heterogeneous polynuclear complexation, was developed first. The model, namely equilibrium status iterations (ESI), required experimental data from mixed metal chloride solution to regress parameters related to the stoichiometric ratio and equilibrium constants. The ESI was used to describe the performance of solvent extraction of lithium, nickel, cobalt, and manganese under varying operating conditions. The experimental equilibria suggested that the solvent containing Cyanex 272 as the extractant, TBP (tributyl phosphate) as the modifier, and kerosene as the diluent was suitable for extracting lithium, cobalt, manganese, and nickel, however with low selectivity of cobalt and manganese. To reduce the separation cost, it was proposed not to separate the valuable metals during the recycling process as these would be mixed in the downstream cathode synthesis. To obtain the essential mass balance data for process design, synthetic leachate was prepared to capture all potential metals in practice, including lithium, cobalt, manganese, nickel, aluminium, copper, and iron. The experimental data confirmed ESI could predict the equilibria of solvent extraction of synthetic solution with seven metal ions in a sodium chloride solution. ESI was further applied to scale up the process, using a three-stage counter current mixer-settler to increase the lithium extraction yield, and a three-step stripping process to produce streams with different compositions. As a key novelty of this study, metals were not separated and purified individually. Instead, the solvent extraction process provided streams with mixed compositions, stoichiometrically aligned to manufacture cathode active material precursors. This novel approach saved significant costs compared to conventional solvent extraction processes, making it a recommended process in this study.
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ItemThe performance of perfluoro(butenyl vinyl ether) based polymeric membranes in gas and vapor separation( 2023)Amorphous perfluoropolymers have gained attention recently as a membrane material for gas separation because of their wide range of interesting features. They are chemically inert, thermally stable, have high gas permeability and display superior separation performance for several gas pairs including He/H2, He/CH4, N2/CH4 and CO2/CH4. They also have high resilience against plasticisation by condensable compounds such as water vapor and BTEX components (Benzene, toluene, ethylbenzene, and xylenes) due to the unfavorable interactions between their polymer matrix and these hydrogen containing molecules. Amorphous perfluoropolymers are thus promising membrane materials for CO2 capture from natural gas. CyclAFlorTM copolymers are amorphous perfluoropolymers in commercial use for optical fibers, but they have never been tested for gas separation. The gas separation performance of these perfluoropolymers was thus assessed in this thesis. The permeability of a series of pure gases was measured in CyclAFlorTM with two different monomer ratios at 35 C and higher temperatures below their glass transition temperatures. The permeability of these gases was also measured in Cytop for comparison. Permeability coefficients were found to be independent of pressure, while they followed Arrhenius behavior with temperature with a positive activation energy of permeation for all studied gases. The CyclAFlorTM copolymer with low FFV (Poly(88%PBVE-co-12%PDD)) showed separation performance close to that of Cytop for all gas pairs, while the one with high FFV (Poly(50%PBVE-co-50%PDD)) showed an interesting combination of high permeability and selectivity for several gas pairs compared to Teflon AF 1600. CyclAFlorTM copolymers operate in the vicinity of 2008 Upper Bound (UB) for several gas pairs including He/CH4, N2/CH4, N2/CH4 and He/N2. Cytop tested in the present study operates closer to the UB for several gas pairs than the performance reported in literature due to the greater removal of residual solvent. CyclAFlorTM and Cytop exhibited CO2/CH4 separation performance under mixed conditions comparable to the performance recorded with pure gases. The interesting separation performance of CyclAFlorTM and Cytop then led to a need to understand more about their superior performance compared to Teflon AFs and HyflonADs. The sorption of CO2 and CH4 were thus measured gravimetrically in Cytop and poly(50%PBVE-co-50%PDD) at different temperatures and pressures. The Non-Equilibrium Lattice Fluid (NELF) model and dual mode of sorption (DMS) model were then used to model the sorption isotherms in Cytop and poly(50%PBVE-co-50%PDD), respectively. The sorption data was consistent with the polymer fractional free volume (FFV), and the unfavorable interactions between methane and perfluoropolymers were confirmed. Both Cytop and poly(50%PBVE-co-50%PDD) showed CO2/CH4 solubility selectivity higher than other commercial perfluoropolymers. Gas diffusivity was then calculated using two different approaches for comparison: the transport model developed by Minelli and Sarti; and molecular dynamics (MD) simulations. The transport model confirmed the higher CO2/CH4 diffusivity selectivity of both polymers than Teflon AF 1600. The diffusion coefficients predicted by MD were overestimated relative to the transport model data, particularly for large penetrants (i.e. O2, N2 and CH4). The presence of condensable impurities such as water vapor, BTEX compounds and liquid glycol carryover can impact the performance of polymeric membranes. Therefore, the effect of water, toluene and xylene vapors on CO2/CH4 separation performance of Cytop and poly(50%PBVE-co-50%PDD) was studied over a wide range of vapor activities at 35 C with 10% CO2 in CH4 mixture at 9 bar. The sorption of these penetrants was also studied. Water vapor had no impact on the separation performance of Cytop and poly(50%PBVE-co-50%PDD) because of the low concentration of water vapor and the high FFV of these perfluoropolymers. Water permeability showed a decreasing trend with activity due to the formed water clusters, particularly at high activities. Toluene and xylene had no significant impact on the separation performance of Cytop, while both condensable penetrants caused a slight and gradual drop in CO2 and CH4 permeability with activity because of competitive sorption or/and pore blocking. Interestingly, convex sorption isotherms were noted with toluene and xylene in Cytop, while concave ones were obtained in poly(50%PBVE-co-50%PDD). This was attributed to the limited accessibility of toluene and xylene molecules to the Langmuir cavities in Cytop, unlike poly(50%PBVE-co-50%PDD). Liquid glycols carryover also had no impact on Cytop, while a slight plasticisation of poly(50%PBVE-co-50%PDD) was noted. High CO2 partial pressure (~ 7 bar) seemed to have no impact on the performance of Poly(50%PBVE-co-50%PDD), while a slight plasticisation was experienced with Cytop (3% increase in CO2 permeability). Overall, the thesis demonstrates that PBVE based perfluoropolymers are outstanding membrane materials for He/CH4, N2/CH4 and CO2/CH4 separation, with promising performance in the presence of a wide range of process stream impurities.