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 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.