Chemical and Biomolecular Engineering - Research Publications
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ItemAssessment of Membrane Performance for Post-Combustion CO2 Capture(AMER CHEMICAL SOC, 2022-01-12)This work investigates the separation performance of a commercial carbonized polyimide hollow fiber membrane module for post-combustion CO2 capture applications. In particular, the resilience to water and sulfur and nitrogen oxides (SOx and NOx) as gas impurities was examined. The membrane exhibited a CO2 permeance of 660 Gas Permeance Units (GPU) and a CO2/N2 permselectivity of 20 at 50 °C when the permeate side was controlled at 0.2 bar absolute pressure. With an increase in water vapor in the feed stream, this CO2 permeance decreased slightly, while the CO2/N2 selectivity increased slightly, due to the combination of competitive sorption and concentration polarization. The water vapor permeance was high, which made accurate measurement difficult due to the concentration polarization but a value of 1090 ± 200 GPU was recorded. The membrane was then examined under three mixed gas conditions (i.e. SO2/CO2/O2/N2, NO/CO2/N2, and NO/NO2/N2) for a time frame of 30 days. The permeances of SO2, O2, NO, and NO2 were 650 ± 50, 155 ± 5, 125 ± 10, and 70 ± 5 GPU at 30 °C, respectively. All of these minor components had a marginal impact on the membrane separation performance during the testing period, indicating strong commercial potential. The higher permeance of SO2 and NO relative to nitrogen meant that these penetrants were concentrated in the permeate stream, which might lead to issues with downstream corrosion in a humid environment. Conversely, the permeance of NO2 was low.
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ItemThe impact of water, BTEX compounds and ethylene glycol on the performance of perfluoro(butenyl vinyl ether) based membranes for CO2 capture from natural gas(ELSEVIER, 2022-07-15)Glassy perfluoropolymers offer a remarkable resistance towards many species that can alter the separation performance of conventional polymeric membranes. In this study, the performance of Cytop® and CyclAFlor™ random copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) are studied for the first time for carbon dioxide capture in the presence of impurities that are common in raw natural gas. Water vapor sorption isotherms were S-shaped for both polymers, indicating the formation of water clusters. The water permeability decreased with vapor activity in both perfluoropolymers as the formation of these clusters decreased water diffusivity. The presence of the water clusters, however, had no impact on the performance of Cytop® and poly(50%PBVE-co-50%PDD) for CO2/CH4 separation. Typical concave sorption isotherms were obtained for toluene and xylene in poly(50%PBVE-co-50%PDD), while convex isotherms were observed in Cytop®. It was speculated that this change in isotherm shape may have been due to the small number of larger free volume elements within Cytop®, as observed in x-ray diffraction analysis. Neither toluene nor xylene had a significant impact on CO2 and CH4 permeabilities in Cytop®, while a gradual decrease in both permeabilities was noted for poly(50%PBVE-co-50%PDD) as the vapor activity increased, due to either competitive sorption or pore blocking. Finally, liquid glycol carryover caused no change on the performance of Cytop® membranes, while a slight drop in the CO2/CH4 separation factor for poly(50%PBVE-co-50%PDD) was observed.
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ItemInternal polymeric coating materials for preventing pipeline hydrogen embrittlement and a theoretical model of hydrogen diffusion through coated steel(PERGAMON-ELSEVIER SCIENCE LTD, 2022-08-26)This work develops a theoretical analysis of the coating permeability necessary for use as internal coatings of transmission pipelines to prevent hydrogen embrittlement. Internal coating materials suitable to be applied in situ on existing steel pipelines are also evaluated. Twelve different commercially available coatings; crosslinked poly (vinyl alcohol) (PVA), poly (vinyl chloride) and bisphenol A diglycidyl ether (DGEBA)/polyetheramine (D-400) epoxy coatings prepared in-house were tested. Films fabricated from two commercial epoxies had hydrogen permeability of 0.40 Barrer and 0.35 Barrer respectively, which show potential as coating materials. A hydrogen permeability of 0.0084 Barrer was achieved with a crosslinked poly (vinyl alcohol) coating, indicating that this material shows the highest potential of all coatings tested. Unsteady-state hydrogen diffusion through coated steel was then modeled to evaluate the effect of the coating film in reducing hydrogen embrittlement. The result shows that with a 2 mm PVA coating, hydrogen permeation inside the coating will take seven years to reach equilibrium and the final hydrogen concentration on the steel surface will be 44% lower than that without a coating. Greater protection can be provided if coatings can be developed with lower hydrogen permeability.
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ItemThe influence of propane and n-butane on the structure and separation performance of cellulose acetate membranes(Elsevier BV, 2021-11-15)This work presents the impact of propane and n-butane on the CO2/CH4 separation performance of both cellulose diacetate (CDA) and cellulose triacetate (CTA) membranes by exposing both pristine membranes to either propane (400 kPa) or n-butane (200 kPa) at room temperature (22 ± 2 °C) for 4 weeks. The propane and n-butane sorption isotherms in both membranes were anomalous at 35 °C. X-ray diffraction (XRD) results indicated that the crystalline nature of both polymers was altered by this exposure, although dynamic scanning calorimetry (DSC) did not detect a significant change in the overall crystallinity. Positron Annihilation Lifetime Spectroscopy (PALS) revealed that the average pore size of the CTA polymer and the number of free volume elements of both membranes also increased, even though the sorption uptake was less than 2 wt%. CO2 and CH4 permeabilities at 35 °C were essentially unaffected by the propane or n-butane exposure, indicating that while the crystalline regions of the polymer were affected, plasticization of the glassy amorphous region did not occur. There was a slight decrease in CH4 permeability for the CDA membrane after n-butane exposure, consistent with a slight decline in the CH4 solubility at this feed pressure. The propane and n-butane permeabilities were 0.029 Barrer at 300 kPa and 0.019 Barrer at 125 kPa for the fresh CTA membrane, but these fell significantly after long term exposure to these gases, possibly due to penetrant clustering.
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ItemRecovery of Sevoflurane Anesthetic Gas Using an Organosilica Membrane in Conjunction with a Scavenging System(AMER CHEMICAL SOC, 2021-03-02)Approximately 95% of the anesthetic gas administered to a patient is exhaled and ultimately released into the atmosphere. Most anesthetic gases have high global warming potential and so this approach adds significantly to the global greenhouse gas footprint. In this work, we develop a feasible means to capture such an anesthetic gas (sevoflurane) before it is released to the hospital scavenging system so that it is retained within the anesthetic circuit. Sevoflurane is retained using a microporous 1,2-bis(triethoxysilyl)ethane (BTESE) membrane prepared by a sol-gel method. The use of a ceramic membrane facilitates sanitization at high temperatures. A rapid thermal processing (RTP) technique is employed to reduce production time and to create a looser organosilica network, resulting in higher gas permeances, compared with the membrane synthesized from conventional thermal processing. The RTP membrane shows a slight decline in gas permeance when used with a dry mixture of CO2/N2/sevoflurane. This permeance falls again under 20% relative humidity feed conditions but the CO2/sevoflurane selectivity increases. The membrane performance shows little variation when the relative humidity is further increased. These promising results demonstrate that this microporous BTESE membrane has great potential for the recovery of sevoflurane in an anesthetic application.
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ItemEfficient degumming of crude canola oil using ultrafiltration membranes and bio derived solvents(Elsevier BV, 2020-01-01)Vegetable oils derived from rapeseed and its genetic variant canola, are conventionally extracted from oilseeds by means of an organic solvent, typically hexane. Concerns regarding the toxicity of hexane have meant safer and more environmentally friendly solvents such as terpenes are becoming attractive. In this research, the degumming of canola oil/terpene mixtures using ultrafiltration is considered as a critical step in such an extraction process. Polysulfone (PSF) and polyethersulfone (PES) membranes were found to be ineffective in this application, as the oil appeared to cause swelling of the membrane structure. This meant that the original flux could not be restored after cleaning. Conversely, a ceramic membrane (MWCO 5 kDa) provided stable behaviour over several cycles of operation when cleaned with pure solvent at high cross velocity at 40 °C. This membrane showed high phospholipid retention (95 ± 2%), although some oil was also retained (16 ± 3%). Cymene emerged as the most attractive of the three terpenes tested, with higher permeate flux and phospholipid rejection than limonene or pinene.
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ItemModelling of methane and n-butane sorption, diffusion and permeation in polydimethylsiloxane using PC-SAFT(Elsevier Inc., 2020-03-01)Published sorption, diffusion and permeation data for methane and n-butane in polydimethylsiloxane (PDMS) from −20 to 50 °C was simulated using a perturbed chain statistical association theory (PC-SAFT) based model. The use of a temperature-dependent interaction parameter within the PC-SAFT model allowed the pure gas sorption data to be very well represented. The mixed gas sorption results were fully predictable from these pure gas parameters, without the introduction of any additional parameters, and agreed well with the experimental data. The model was also able to model the dilation behavior of PDMS under various gas compositions, making it possible to analyse gas sorption properties using pure gas sorption data only. A diffusion model coupled with the PC-SAFT model was capable of fitting both pure and mixed gas permeation data well by applying an exponential expression to account for such dilation in the diffusivity term. Only two parameters (i.e. infinite dilution mobility coefficient L0 and plasticization factor β) were used and no coupling effect between the two penetrants was needed. The activation energies of L0 were 11.7 and 13.4 kJ mol−1 for methane and n-butane. Moreover, the model was also able to calculate the concentration profiles of the penetrants across the membrane thickness. For n-butane, the mass concentration profile changed from linear to non-linear when the feed pressure increased from 4 to 11 atm for 8 mol% n-butane at 25 °C. Conversely, methane showed a linear concentration profile under both conditions.