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Abstract A highly efficient biocatalytic carbonic anhydrase (CA)-polydopamine (PDA)/polyethylenimine (PEI)-polyvinylidene fluoride (PVDF) (referred to as CA-m-PVDF) composite membrane was fabricated for CO 2 conversion and capture in the gas-liquid membrane contactor (GLMC) process. The co-deposition of PDA/PEI with amino functional groups was employed to amine-functionalize a PVDF substrate as support for subsequent in-situ CA immobilization by cross-linking with glutaraldehyde. This enhances the enzyme stability and prolongs its lifespan, thus facilitates CO 2 hydration efficiency in the GLMC process. In this work, different immobilization CA protocols were compared based on the CA activity and activity recovery. For biocatalytic CA-m-PVDF membranes, the best activity of 498 U m−2 (membrane) and a corresponding activity recovery of 31.5% were achieved (m(5 h)-PVDF as support, 0.67 (v/v)% GLU as cross-linking agent, 600 μg mL−1 CA solution, pH 8.0, temperature at 25 °C, and 24 h reaction time). By using water as absorbent with a liquid velocity of 0.25 m s−1 in a bench-scale GLMC setup, a high-efficiency CO 2 absorption flux of 2.5 × 10−3 mol m−2 s−1 was obtained, which was ~165% higher than that of the non-biocatalytic m-PVDF membrane. The long-term stability test showed a good enzyme activity for CO 2 hydration capacity for the CA-m-PVDF membranes during 40 days of test duration. Overall, the results achieved in this work may provide promising insights into enzyme immobilization on polymeric supports for the development of high-efficiency biocatalytic membranes for CO 2 capture in GLMC applications. Highlights • A highly efficient biocatalytic composite membrane was fabricated for CO 2 conversion and capture. • PDA/PEI with amino functional groups was co-deposited to amine-functionalize a PVDF substrate. • Subsequent in-situ carbonic anhydrase (CA) immobilization was conducted by cross-linking. • The resultant membrane shows a high CO 2 absorption flux of 2.5 × 10-3 mol m-2 s-1 in the gas-liquid membrane contactor. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work is to study in detail the sorption of binary gas mixtures containing methane into polymers suitable for membrane separations. A novel measuring procedure has been developed and validated by performing mixed gas sorption tests on the n-C4/CH4 mixture in films of poly(1-trimethylsilyl-1-propyne) (PTMSP), for which literature data are available. Then, individual uptakes of CH4 and CO2 from binary gas mixtures were measured at 35°C and up to 35bar in PTMSP, in the whole gas composition range. The experiments were conducted on a pressure-decay apparatus equipped with a gas chromatographic device. The novel experimental procedure was set up in order to obtain data either at constant partial pressure of one gas, as done by previous authors, or at constant gas composition and variable total pressure. The latter protocol allows to mimic more closely the real membrane separation processes, where only the total pressure of the mixture can be varied arbitrarily. It was observed that the presence of CH4 does not alter significantly the sorption of CO2 and of n-C4 in PTMSP, while the mixed gas solubility of CH4 is lower than the pure gas value at the same CH4 fugacity. In particular, the CH4 solubility coefficient, as well as the mixed gas solubility selectivity are univocal functions of CO2 fugacity (or concentration) and are otherwise independent of the gas phase composition. The real CO2/CH4 solubility-selectivity of PTMSP is similar to the ideal value at low CO2 fugacity but it becomes significantly higher, up to 4.5 times, at 25bar of CO2 fugacity. A quantitative rule can be drawn using data of several binary gas mixtures in glassy polymers, based on which the ratio between actual mixed gas and pure ideal solubility selectivity of CO2 over CH4 is a single, monotonously increasing function of the ratio between the concentration of the two components, c(CO2)/c(CH4), which becomes higher than unity as c(CO2)>c(CH4). In other words, the competition effects depress more significantly the less abundant penetrant in the polymer, that is usually CH4. [Copyright &y& Elsevier]

Porous asymmetric composite membranes (ACMs) have attracted intensive attentions in energy-efficient gas separations. However, fabricating ACMs with defect-free interface and enhanced selectivity without sacrificing permeability remains great challenge. Herein, a major step towards this goal is proposed by employing an efficient co-weaving strategy to regulate interfacial microstructure of ACMs with bilayer geometry on porous substrates. The double layers are constructed by in-situ growing zeolitic imidazolate frameworks-8 (ZIF-8) on the surface of amidoxime-functionalized polymer of intrinsic microporosity-1 (AO-PIM-1) layer (denoted as AO-PIM-1@ZIF-8). The pre -designed amidoxime groups on the AO-PIM-1 backbone provide abundant coordinate sites for Zn (ΙΙ) ions, offering advantages for building a continuous membrane. Consequently, the obtained AO-PIM-1@ZIF-8 membrane demonstrates remarkable performance in H 2 /CO 2 separations, with the H 2 /CO 2 selectivity of 11.97 and the H 2 permeability of up to 5688 Barrer at 298 K and 1 bar. Both the H 2 permeability and H 2 /CO 2 selectivity exceed most of reported ACMs, and far surpassed Robeson's 2008 upper bound by taking advantage of the molecular sieving effect of interfacial layer formed by co-weaving of AO-PIM-1 chains with ZIF-8. This is contributed either by position-space renormalisation for AO-PIM-1 chains or pore space partition in ZIF-8 at the interface. The study reports herein offer an alternative route to develop high-performance composite membranes for improved gas separations. [Display omitted] • Two continuous composite membranes were prepared using a simple fabrication method. • Co-weaving strategy was used to eliminate the interfacial defects. • H 2 /CO 2 separations of the as-made membrane far exceeded Robeson's 2008 upper bound. • This performance was from the molecular sieving effect of the interfacial layer. [ABSTRACT FROM AUTHOR]

Abstract: Current artificial lungs and respiratory assist devices designed for carbon dioxide removal (CO2R) are limited in their efficiency due to the relatively small partial pressure difference across gas exchange membranes. To offset this underlying diffusional challenge, bioactive hollow fiber membranes (HFMs) increase the carbon dioxide diffusional gradient through the immobilized enzyme carbonic anhydrase (CA), which converts bicarbonate to CO2 directly at the HFM surface. In this study, we tested the impact of CA-immobilization on HFM CO2 removal efficiency and thromboresistance in blood. Fiber surface modification with radio frequency glow discharge (RFGD) introduced hydroxyl groups, which were activated by 1M CNBr while 1.5M TEA was added drop wise over the activation time course, then incubation with a CA solution covalently linked the enzyme to the surface. The bioactive HFMs were then potted in a model gas exchange device (0.0084m2) and tested in a recirculation loop with a CO2 inlet of 50mmHg under steady blood flow. Using an esterase activity assay, CNBr chemistry with TEA resulted in 0.99U of enzyme activity, a 3.3 fold increase in immobilized CA activity compared to our previous method. These bioactive HFMs demonstrated 108mL/min/m2 CO2 removal rate, marking a 36% increase compared to unmodified HFMs (p <0.001). Thromboresistance of CA-modified HFMs was assessed in terms of adherent platelets on surfaces by using lactate dehydrogenase (LDH) assay as well as scanning electron microscopy (SEM) analysis. Results indicated HFMs with CA modification had 95% less platelet deposition compared to unmodified HFM (p <0.01). Overall these findings revealed increased CO2 removal can be realized through bioactive HFMs, enabling a next generation of more efficient CO2 removal intravascular and paracorporeal respiratory assist devices. [Copyright &y& Elsevier]

Abstract: Nowadays, many industrial gas absorption processes are carried out in harsh environment conditions such as high temperatures and pressures. Therefore, in order to replace these conventional methods with new membrane technologies, several studies and investigations must be established to gain valuable knowledge on the transport mechanism under real operating conditions. In this work, a comprehensive 2-D mathematical model was developed for the physical and chemical absorption of CO2 from natural gas at high pressure up to 50bar using membrane contactors. Although, pseudo-wetting conditions could be ignored at low pressure operations, it was found to be an important factor at high pressures even for hydrophobic membranes such as PTFE. Using chemical solvents such as MEA solutions enhanced the removal of CO2, however, the surface tension of the solvent decreased with increasing concentrations which resulted in higher percent wetting of the membrane. The effect of membrane properties such as porosity and tortuosity was negligible on the physical absorption of CO2 using water as the absorbent solvent. However, this effect was more dominant on the chemical absorption using MEA. The model predictions agreed very well with the experimental data as the percent removal of CO2 increased with increasing pressure for both physical and chemical absorption. [ABSTRACT FROM AUTHOR]

Incomplete oxidation on the anode side of a solid oxide fuel cell (SOFC) leaves a considerable amount of unused fuel (e.g., H 2 and CO) in the anode exhaust. In order to enhance fuel utilization, CO 2 -selective membranes can be employed to remove the CO 2 in the anode exhaust before returning the recovered fuel to the SOFC. In this study, two membrane processes have been designed for integration with a SOFC system, one with an air sweep (SOFC-MB air) and the other with a vacuum (SOFC-MB vac), on the permeate side. The transport properties of developed membranes were applied to the processes, and techno-economic analysis (TEA) was carried out to estimate the CO 2 removal cost of each process. The parameters investigated were the anode exhaust recycle percentage, stack fuel utilization of the SOFC, power output, as well as the area and transport properties of the membranes. Notably, at 100% anode exhaust recycle, the system fuel utilization can be boosted to >99% for both processes. By tuning the stack fuel utilization, a steam-to-carbon ratio above 1.5 is achievable. It was found that the SOFC-MB vac process can achieve a lower CO 2 removal cost than the SOFC-MB air process. For the SOFC-MB vac process, by considering the value of the recovered fuel, the CO 2 removal cost not only can be fully rebated by the recovered fuel value, but also there is a profit of about $38 per tonne of CO 2 captured. Moreover, by taking into account a CO 2 sale price of $40/tonne for enhanced oil recovery, a profit of about $66 per tonne of CO 2 captured may be achieved. Furthermore, more cost reduction or profit is attainable by developing membranes with higher CO 2 permeances. In addition, a zero-carbon electricity generation can be achieved by the SOFC-MB vac process. Image 1 • Membrane processes were designed for removing CO2 from SOFC anode exhaust recycle •System fuel utilization >99% is achievable with complete anode exhaust recycle •Vacuum-assisted membrane process is more cost-effective than using air sweep •CO2 removal cost is better than being fully rebated by considering fuel saving •Anode exhaust recycle of 100% enables zero-carbon electricity generation [ABSTRACT FROM AUTHOR]

Carbon hollow fiber membranes (CHFMs) were fabricated based on cellulose hollow fiber precursors spun from a cellulose/ionic liquid system. By a thermal treatment on the precursors using a preheating process before carbonization, the micropores of the prepared CHFMs were tightened and thus resulting in highly selective carbon molecular sieve (CMS) membranes. By increasing the drying temperature from RT to 140 °C, the cellulose hollow fiber precursors show a substantial shrinkage, which results in a reduction of average pore size of the derived CHFMs from 6 to 4.9 Å. Although the narrowed micropore size causes the decrease of gas diffusion coefficient, stronger resistance to the larger gas molecules, such as CH 4 , eventually results in an ultra-high CO 2 /CH 4 ideal selectivity of 917 tested at 2 bar for CHFM-140C due to the simultaneously enhanced diffusion and sorption selectivity. The CHFM-140C was further tested with a 10 mol%CO 2 /90 mol%CH 4 mixed gas at 60 °C and feed pressure ranging from 10 to 50 bar. The obtained remarkable CO 2 /CH 4 separation factor of 131 at 50 bar and good stability make these carbon membranes great potential candidates for CO 2 removal from high-pressure natural gas. • Highly CO 2 selective CMS membranes made from cellulose precursors. • CMS membranes present ultra-high CO 2 /CH 4 selectivity of 917 at 2 bar. • CO 2 /CH 4 mixed gas testing up to 50 bar shows potential for natural gas sweetening. [ABSTRACT FROM AUTHOR]

Thermally induced decarboxylation cross-linking of carboxylic acid bearing polyimides has been recently introduced to create cross-linked polymer membranes with enhanced gas permeability. The main focus has been on the cross-linking of high permeability/low selectivity 6FDA copolymers with a relatively low amount of carboxylic acid groups. In contrast, decarboxylation cross-linking was applied in this work on a low permeability/high selectivity polymer with a large amount of –COOH groups (pure 6FDA-DABA). 6FDA-DABA membranes were thermally treated at different temperatures (100 °C, 180 °C, 250 °C, 350 °C and 400 °C and tested for CO 2 /CH 4 and CO 2 /N 2 separation and thoroughly characterized by ATR-FTIR, TGA-MS, DSC, EDX, XRD, density measurements, fluorescence spectroscopy and gas sorption measurements. Two counteracting mechanisms defined the overall performance of the cured membranes. Physical tightening of the membrane significantly enhanced the CO 2 /CH 4 separation factor with increasing annealing temperature due to an improved polymer chain packing efficiency, which was confirmed by fluorescence spectroscopy and membrane density experiments. In contrast, cross-linking through decarboxylation occurred from 330 °C onward and induced a more open polymer structure for 6FDA-DABA-350 and 6FDA-DABA-400. Consequently, the more open polymer structure resulted in an increase in permeability of all gases. For 6FDA-DABA-350, a synergy was observed between the dilation effect of cross-linking and the tightening effect, causing a simultaneous, strong improvement of both separation factor (+100%) and permeability (+40%). As a result, the membrane performance crossed the 2018 mixed-gas upper bound and scored very close to the 2008 Robeson upper bound. Moreover, the cross-linked 6FDA-DABA-350 showed an increased resistance to CO 2 -induced plasticization thanks to covalent cross-linking. • 6FDA-DABA membranes were thermally treated at different temperatures and thoroughly characterized. • Two counteracting mechanisms defined membrane performance: decarboxylation cross-linking and physical tightening. • Decarboxylation cross-linking at 350 and 400 °C caused a more open polymer structure and an increase in gas permeability. • Physical tightening, due to enhanced stacking efficiency, resulted in an increased separation factor. • 6FDA-DABA-350 profits from both effects, leading to an increased separation factor (+100%) and permeability (+40%). [ABSTRACT FROM AUTHOR]