Chemical and Biomolecular Engineering - Theses
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ItemThe structural-functional relationship of polymer-surfactant complexes relevant to personal care product( 2020)Polymer-surfactant (PS) mixtures are widely used to control both solution and surface properties. The link between the molecular structure of polymers and surfactants and their associative behaviours is of great interest and it is not very well understood. The examination using several different methods in the colloidal systems is to link the function of PS complexes to their microstructure from different aspects. My thesis aims to investigate how oppositely charged PS complexes can affect the interaction and the adhesive force of drops to surfaces and link these attributes to the target functions of a formulation, including shelf life stability and drop deposition or adhesion of an emulsion formulated chemical products, for example, personal care products. This was achieved by using both novel microscopic methods to quantify adhesion interactions and probe the adsorption and microstructure of PS complexes coated on drops and model surfaces as well as correlating these data to macroscopic methods for bulk solution properties. In this work, cellulose based cationic polymer and anionic surfactants, sodium lauryl (or dodecyl) sulphate surfactants were used based on current key ingredients in personal care product formulation. We have studied when drops will stick to surfaces in the presence of PS complexes by systematically varying the components of PS complexes (e.g. polymer type, surfactant concentration and type, and electrolyte concentration) and correlating the observed drop adhesion to hydrophobic surfaces with the phase diagrams of PS complexes. This observed that polydispersity in anionic surfactant headgroup can drive different drop adhesion, which motivated studies on surfactants in the absence of polymer to see how polydispersity of head group affects the micellization of the surfactant by measuring their critical micelle concentration (cmc) as a function of polydispersity degree and added electrolyte as well as the shape and dimension of the micelle using small angle neutron scattering (SANS). These measurements demonstrated that by controlling the degree of polydispersity in surfactant headgroup, the micelle character and their interaction with polymer can be possibility predicted. The measurements of drop adhesion were then compared to the adsorption of the PS complexes in order to explain how the structure of PS complexes on different surfaces can affect drop adhesion. The adsorption of PS complexes onto model surfaces that have more complexity, relevant to skin, hair or textiles were studied by measuring the adsorbed PS layer thickness using AFM imaging as well as force measurements in combination with measures of the adsorbed amount using QCM-D. By combing the observation of the layer thickness and adsorbed mass of PS complexes upon surfactant and electrolyte dilutions, and the effect from surface character, more insights of the mechanism of the structure change of PS complexes is understood.
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ItemCarbon dioxide separation from natural gas: evaluation of adsorbents and influence of process variables( 2018)The use of natural gas in place of coal offers a method to effectively reduce greenhouse gas emissions. Adsorption processes, specifically, pressure swing adsorption (PSA), offers an energy efficient method to perform bulk removal of CO2 from high pressure sour natural gas. A selection of zeolitic imidazolate frameworks (ZIFs) were chosen and evaluated using PSA process simulation. ZIFs -8, -14 and -71 were synthesised and gas adsorption isotherms measured. Using these isotherms, process simulation over a range of feed conditions from 15 %mol to 35 %mol CO2 at 100 bar(a) and 303 K, process performance metrics including CO2 and CH4 purity and recovery were observed. Considering CH4 is the saleable product, it was decided that its purity target of 98 %mol could not be compromised, and was thus set as a requirement. Using a 9 step, 3 bed PSA cycle, ZIF-14 was not able to meet this CH4 purity requirement; however, ZIF-8 and ZIF-71 were able to meet it while achieving CO2 purities of 24 – 45 %mol with good recovery (89 – 96 %mol), and CH4 recoveries of 48 – 34 %mol. A thorough investigation of the adsorption properties and thermodynamics of the ZIF adsorbents was also carried out. It was known that ZIF-8 demonstrated a structural transition upon adsorption; based on this work, it is quite likely that such transitions are also taking place in ZIF-14 and ZIF-71, however, definitive experimental evidence of this is required such as in-situ X-ray diffraction. Some artefacts seen in the adsorption isotherms of ZIF-71 were found to correlate with the adsorbate liquid phase surface tension. It was also found that these ZIF adsorbents deteriorated over time, contrary to existing claims in the literature. During the thermodynamic analysis, it was found that temperature invariant properties such as the differential enthalpy of adsorption were affected by temperature, and this was attributed to the structural transition. It was also found that the adsorbed phase was not ‘liquid like’ at low loadings, but was at higher loadings. A published method (osmotic potential) was used in evaluating the thermodynamics of the structural transition, and it was found that this method was inconsistent and inconvenient when multiple isotherms are used. An alternative method based on van ‘t Hoff plots was proposed and better results were observed, however, further application of this method is required to confirm its general applicability. In order to form a more general view on the topic, the literature was reviewed for high pressure adsorption isotherms of CO2 and CH4. These adsorbents, in addition to the ZIF adsorbents synthesised in this work, and a family of zeolite-Y adsorbents for which adsorption isotherms were measured for, were evaluated for process performance using a simple PSA model. It was found that ZIF-71 was most often the best performing adsorbent over the range of conditions investigated. The adsorbents were evaluated over a range of process conditions such that the output could be used as an adsorbent screening method. Feed temperature, pressure, and desorption pressure were all varied for feed compositions of 10 %mol and 30 %mol CO2. This finding implied that ZIF-71 should be investigated further for high pressure CO2/CH4 separations, with the belief that a more advanced PSA cycle could be developed or used to give better performance than was found earlier in this work. It was originally thought that the bed void fraction would be a significant limitation for high pressure separations. It was found, however, that the void fraction of the adsorbent bed did not have as great an influence as was imagined, although minor gains in CO2 purity and CH4 recovery could be found. Finally, a range of model adsorbents/isotherms were made in order to uncover the key adsorbent properties that result in good process performance. It was found that adsorbents with either a moderate loading, low heat of adsorption and low selectivity or low loading, moderate heat of adsorption and high selectivity yielded the best results. The unexpected outcome of this finding was that these characteristics align very well with ZIF-71. A range of future work was also recommended. ZIF-71 should be investigated further in different PSA cycles, and high pressure binary adsorption data should also be measured to investigate the true effects of multicomponent adsorption as they are currently unknown. A series of experiments were also suggested to confirm findings regarding the adsorption properties of the ZIF adsorbents, including in-situ X-ray diffraction for the suspected structural transitions of ZIF-14 and ZIF-71, and isotherm measurements using a wider variety of adsorbates regarding the suggested surface tension related phenomenon in ZIF-71. A selection of adsorbent development tasks were also recommended including, post-synthesis modification of the ZIF adsorbents in an effort to tune adsorption properties, further investigation into an adsorbent called ZSM-25 for which adsorption properties are not well known at the time of writing, and a hierarchical LTA-FAU adsorbent was also suggested. Regarding the separation process, it was speculated that a hybrid PSA-membrane based separation process may offer enhanced process performance, with the PSA system helping to overcome issues such as membrane plasticisation and the membrane system increasing the attainable CO2 purity and CH4 recovery.
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ItemSimplified computational models for adsorbent screening and cycle design for cyclic adsorption cycles for post-combustion CO2 capture applications( 2014)Cyclic adsorption processes are a promising technology for CO2 capture from large emissions point sources. Thousands of adsorption materials have been developed for CO2 capture, but there is no accepted method of determining which adsorbents are truly promising for use in an industrial process. Detailed adsorption simulation software is available, but it requires significant computational time and expert users. Therefore, most researchers resort to crude isotherm analysis when evaluating materials, which can be misleading in many cases. In order to rapidly screen adsorbent materials, we have developed a novel simple pressure/vacuum swing adsorption (PSA/VSA) model which can be solved in less than one second using MATLAB while still approximating experimental data. We have used this model to rapidly screen different classes of adsorbents for post-combustion CO2 capture, determine the ideal operating conditions, and identify optimal adsorbent properties. Our study suggests that zeolite 13X is still the best material available for post-combustion CO2 capture from dry flue gas. However, purity, recovery, and specific power results can be much improved if materials are developed with ideal, yet reasonably achievable, properties. Our results also showed that thermal effects and selectivity are much more important to VSA performance than is CO2 adsorption capacity and that the ideal CO2 heat of adsorption for this process is between 35KJ/mol and 45KJ/mol. Temperature swing adsorption (TSA) has also gained much attention recently as a CO2 capture technology because of its low energy penalty. The main drawback of TSA is long cycle times which can take several hours to complete. In order the overcome this challenge, we have developed a hot product purge TSA cycle using structured supported amine adsorbents which can be used to capture CO2 at high throughput with purities and recoveries over 90%. We analyzed several configurations of this cycle in attempt to reduce the associated thermal energy requirement. We also found the ideal adsorbent isotherm parameters for this process from a range of feasible adsorbent capacities, heats of adsorption, and entropies of adsorption. Using these ideal isotherms, we were able to simulate a process with a thermal energy requirement as low as 2.9 GJ/ton CO2 for a 90°C feed and 2.3 GJ/ton CO2 for a 30°C feed. We also performed a case study on the integration of our process into a Victorian brown coal-fired power station based on thermal efficiency data from the Loy Yang B power station. Our calculations suggest that for this process, the parasitic energy can be as low as .5GJ/ton CO2 which is much lower than that which can be achieved using VSA. We also estimated the bed size factor for this process to be approximately 500 kg/TPD CO2 which is on the same order of magnitude as VSA.