Chemical and Biomolecular Engineering - Theses
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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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ItemAmmonia removal from Sirofloc treated sewage using natural zeolite from Australia( 1996)A high-rate process for the removal of ammonia from sewage was investigated. Of the existing high-rate processes, ion-exchange with an ammonium-selective zeolite has shown considerable advantages. The recent commercial mining of a natural Australian zeolite, clinoptilolite, encouraged the investigation of its application to wastewater treatment for ammonia removal. The applicability of the mineral, for continuous ammonia removal from sewage, depends on its chemical and physical properties. For Australian zeolite, these factors, and thus the potential usefulness of this mineral for wastewater treatment, were largely unknown prior to this study. The study endeavoured to determine the most viable way in which to use Australian natural zeolite in this process, with the most critical part being the economical regeneration of the zeolite. (From Abstract)