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1. Supported gas membrane-based ammonia removal and recovery for a pH-dependent sink: Effect of water vapor transport

   https://doi.org/10.1016/j.memsci.2020.118308  

   Aligwe, Philip; Sirkar, Kamalesh K; Canlas, Christian J; Cheng, Wu-Cheng (November 2020, Journal of membrane science)

   null (Ed.)

   Sometimes NH₃ is stripped from process/effluent streams through hydrophobic porous hollow-fiber-membranes (HFMs) via a supported-gas-membrane (SGM) process and recovered in concentrated H₂SO₄ solution as (NH₄)₂SO₄. To recover relatively purified (NH₄)₂SO₄, one can avoid excess H₂SO₄ with a more dilute H₂SO₄ strip solution. Neglect of strip-side mass-transfer resistance for low-pH strip H₂SO₄ solutions is not desirable with higher-pH H₂SO₄ strip solutions. Small hollow-fiber membrane modules (HFMMs) were used with a higher-pH H₂SO₄ strip solution. Mass transfer was successfully modeled using reaction-enhanced mass transport in higher-pH H₂SO₄ solution. Employing larger-scale crossflow HFMMs, time-dependent ammonia removal from a large tank having ammonia-containing process effluent was modeled for batch recirculation operation. The larger-scale modules employ shell-side feed liquid in crossflow with an overall countercurrent flow pattern and acid flow in the tube side. Modeling ammonia transport without water vapor transfer can cause substantial errors in batch recirculation method. Water vapor transport was considered here for low-pH and high-pH H₂SO₄ strip solutions for ammonia-containing feed in a large tank. Model results describe literature-based experimentally observed mass transfer behavior in industrial-treatment systems well. Model calculations were also made for continuous ammonia recovery from industrial effluents by a number of series-connected HFMMs without any batch recirculation. 

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2. Modeling flux in tangential flow filtration using a reverse asymmetric membrane for Chinese hamster ovary cell clarification

   https://doi.org/10.1002/btpr.3115  

   Zhang, Da; Patel, Parag; Strauss, Daniel; Qian, Xianghong; Wickramasinghe, S_Ranil (January 2021, Biotechnology Progress)

   Abstract Tangential flow filtration is advantageous for bioreactor clarification as the permeate stream could be introduced directly to the subsequent product capture step. However, membrane fouling coupled with high product rejection has limited its use. Here, the performance of a reverse asymmetric hollow fiber membrane where the more open pore structure faces the feed stream and the barrier layer faces the permeate stream has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of Chinese hamster ovary cell feed streams has been investigated under conditions that could be expected in fed batch operations. The performance of the reverse asymmetric membrane is compared to that of symmetric hollow fiber membranes with nominal pore sizes of 0.2 and 0.65 μm. Laser scanning confocal microscopy was used to observe the locations of particle entrapment. The throughput of the reverse asymmetric membrane is significantly greater than the symmetric membranes. The membrane stabilizes an internal high permeability cake that acts like a depth filter. This stabilized cake can remove particulate matter that would foul the barrier layer if it faced the feed stream. An empirical model has been developed to describe the variation of flux and transmembrane pressure drop during filtration using reverse asymmetric membranes. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor clarification. 

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3. A Hybrid Catalytic Hydrogenation/Membrane Distillation Process for Nitrogen Recovery from Nitrate-Contaminated Waste Ion Exchange Brine

   https://doi.org/10.1016/j.watres.2020.115688  

   Huo, X.; Vanneste, J.; Cath, T.Y.; Strathmann, T.J. (January 2020, Water research)

   Ion exchange is widely used to treat nitrate-contaminated groundwater, but high salt usage for resin regeneration and management of waste brine residuals increase treatment costs and add environmental burdens. Development of palladium-based catalytic nitrate treatment systems for brine treatment and reuse has showed promising activity for nitrate reduction and selectivity towards the N2 over the alternative product ammonia, but this strategy overlooks the potential value of nitrogen resources. Here, we evaluated a hybrid catalytic hydrogenation/membrane distillation process for nitrogen resource recovery during treatment and reuse of nitrate-contaminated waste ion exchange brines. In the first step of the hybrid process, a Ru/C catalyst with high selectivity towards ammonia was found to be effective for nitrate hydrogenation under conditions representative of waste brines, including expected salt buildup that would occur with repeated brine reuse cycles. The apparent rate constants normalized to metal mass (0.30 ± 0.03 mM min−1 gRu−1 under baseline condition) were comparable to the state-of-the-art bimetallic Pd catalyst. In the second stage of the hybrid process, membrane distillation was applied to recover the ammonia product from the brine matrix, capturing nitrogen as ammonium sulfate, a commercial fertilizer product. Solution pH significantly influenced the rate of ammonia mass transfer through the gas-permeable membrane by controlling the fraction of free ammonia species (NH3) present in the solution. The rate of ammonia recovery was not affected by increasing salt levels in the brine, indicating the feasibility of membrane distillation for recovering ammonia over repeated reuse cycles. Finally, high rates of nitrate hydrogenation (apparent rate constant 1.80 ± 0.04 mM min−1 gRu−1) and ammonia recovery (overall mass transfer coefficient 0.20 m h−1) with the hybrid treatment process were demonstrated when treating a real waste ion exchange brine obtained from a drinking water utility. These findings introduce an innovative strategy for recycling waste ion exchange brine while simultaneously recovering potentially valuable nitrogen resources when treating contaminated groundwater. 

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4. Porous Organic Cages-Stabilized Carbon Molecular Sieve for Efficient Gas Separation

   Sharif, Usman; Kowey, Isha; Rownaghi, Ali (November 2023, 2023 AIChE Annual Meeting)

   Here we present results of gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the thermal and chemical imidization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C3H8, C3H6, CO2, and H2) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C3H8, C3H6 adsorption capacities reached 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO2, CH4, CO, N2 and H2 adsorption capacities of 1.48, 0.84, 0.33, 0.11, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane was formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary H2/CO2, CH4/CO2 and C3H6/C3H8 feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes. 

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5. Carbon Molecular Sieve-derived POC/Mixed-Matrix Membranes for Gas Separation

   kowey, Isha; Rownaghi, Ali (May 2023, North American Membrane Society 2023)

   Membrane-based separations offer the potential for the lowest energy demand requirements of all separation options. Among all nanoporous membranes, the carbon molecular sieves (CMS), metal-organic frameworks (MOFs), and mixed-matrix membranes (MMMs) with angstrom level molecular discrimination properties makes them appealing for separating a wide spectrum of gas-pairs. Here we present results of gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the iridization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C2H6, C2H4, C3H8, C3H6 adsorption capacities reached to 42.61, 2.56, 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO2, CH4, CO, N2 and H2 adsorption capacities of 1.48, 0.84, 0.33, 0.11, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane were formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary H2/CO2, CH4/CO2 and C3H6/C3H8 feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes. 

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