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1. Hollow fiber gas membrane-based removal and recovery of ammonia from water in three different scales and types of modules

   https://doi.org/https://doi.org/10.1016/j.seppur.2019.04.074  

   Philip A. Aligwe, Kamalesh K. (April 2019, Separation and purification technology)

   Ammonia present in many industrial process streams and effluent streams is beginning to be recovered by means of microporous hydrophobic hollow fiber-based membrane contactor devices with gas-filled pores; the process is often characterized as supported gas membrane (SGM) process. Ammonium sulfate is usually obtained in a sulfuric acid stream on the other side of the membrane. It is useful to develop a quantitative basis for the extent of ammonia removal in such devices. Unlike deoxygenation of aqueous streams in such devices, membrane resistance is quite important for ammonia transport. Ammonia transport modeling in such devices is hampered by the complexity of feed liquid flow in the shell side of commercially used devices and lack of information on membrane resistance where membrane tortuosity introduces considerable uncertainty. The approach adopted here involves studying ammonia transport with the feed solution flowing through the hollow fiber bore where the fluid mechanics is simpler than shell-side flows. Comparison of model-based predictions of overall mass transfer coefficient (ko) with experimentally observed values allows estimation of the membrane mass transfer coefficient (km). One can use such estimates of km to model the observed ammonia transport in small crossflow devices and develop an empirical guidance of the dependences of the shell side mass transfer correlations. Guided by such information and deoxygenation SGM literature, a model was developed for large modules used for ammonia recovery via SGM. Model predictions of performances of the large modules are likely to be useful for various process considerations including the effect of temperature and feed flow rate variations on ammonia removal. 

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2. A two hollow-fiber-set membrane module for air gap membrane distillation with high thermal efficiency

   https://doi.org/10.1016/j.desal.2025.118683  

   Liu, Fangzhou; Qing, Weihua; Zhu, Guangyu; Ma, Qingquan; Chau, John; Sirkar, Kamalesh K; Zhang, Wen (February 2025, Desalination)

   An air gap membrane distillation (AGMD) module was developed by incorporating a poly(etheretherketone) (PEEK) hollow fiber membrane (HFM) having a nonporous wall. This PEEK HFM was placed inside a polyvinylidene fluoride (PVDF) hydrophobic porous wall HFM with a larger bore diameter. The outside diameter (OD) of PVDF HFM is 925 μm, small enough to be capable of achieving a high surface area packing density of 1297 m2/m3. The air gap thickness was very small, 121 μm. Hot brine flowed on the outside of the PVDF HFM; the colder liquid was passed through the lumen of the PEEK-based condenser hollow fibers. Water vapor condensed in the air gap formed between the inner surface of the porous PVDF HFM and the outer surface of the nonporous condenser PEEK fiber. With 85o C hot brine flowing at 40 mL•min􀀀1 and 5o C coolant flowing at 8 mL•min􀀀1, the water vapor flux was 9.05 kg/m2•h with a salt rejection of 98.7 %. Simulation by COMSOL Multiphysics predicted water flux and interfacial temperature of HFM, which supported the experimental observations. Moreover, the influence of module geometry, membrane characteristics and internal flow configuration on permeate flux, thermal efficiency, gained output ratio (GOR), and temperature and concentration polarization were evaluated. Principal component analysis (PCA) was used to illustrate the interconnections among various parameters and their respective contributions to water flux and other performance indicators. Air gap thickness had the strongest influence on temperature polarization. 

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3. Antifouling UV-treated GO/PES hollow fiber membranes in a membrane bioreactor (MBR)

   https://doi.org/10.1039/c9ew00217k  

   Fathizadeh, Mahdi; Xu, Weiwei L.; Shen, Margaret; Jeng, Emily; Zhou, Fanglei; Dong, Qiaobei; Behera, Dinesh; Song, Zhuonan; Wang, Lei; Shakouri, Abolfazl; et al (June 2019, Environmental Science: Water Research & Technology)

   Single layer graphene oxide (SLGO) was studied as a novel coating material to drastically improve the antifouling performance of polyether sulfone (PES) hollow fiber (HF) membranes in membrane bioreactor (MBR) application. By selectively modifying the membrane surface, only a small amount of SLGO coating (6.2 mg m −2 ) was needed to achieve acceptable membrane performance. The UV treatment of the SLGO coating further assisted in improving the antifouling properties of the as-prepared PES HF membranes. By comparing the transmembrane pressure of pristine PES HF and PES_GO 6.20_ UV X (X = 0–1.5 h) membranes in a MBR for wastewater treatment at a fixed water flux, the PES_GO 6.20_ UV 1.0 membrane coated with 1 h UV-treated SLGO was demonstrated to substantially relieve the bio-fouling problem. To understand the influence of SLGO modification on membrane performance, FESEM, ATR-FTIR, and AFM analyses were conducted to characterize the as-prepared membranes, and the SLGO deposition mechanism was also proposed in this study. 

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4. Hollow fiber membrane supported metal organic framework-based packed bed for gas/vapor adsorption

   https://doi.org/10.1016/j.cej.2022.140228  

   Song, Yufeng; Sirkar, Kamalesh K. (February 2023, Chemical Engineering Journal)
5. Composite Hollow Fiber Membrane Reactor Containing Immobilized Organocatalysts and Palladium for Sustainable Chemical Transformation

   Rownaghi, Ali (May 2023, North American Membrane Society 2023)

   Catalytically active asymmetric membranes were developed by crosslinking a polydimethylsiloxane (PDMS) thin layer onto a porous polyamide‐imide hollow fiber (PAIHF) support, followed by grafting of aminosilane with hydroxyl derived-PDMS/PAIHF, and finally palladium nanoparticles (PdNPs) immobilization using salicylic aldehyde. Aminosilane and salicylic aldehyde linkers were used to permanently immobilize PdNPs onto the PDMS surface through metal coordination chelation, which prevented their agglomeration and leaching from the catalytic membrane reactor (CMR) module. The obtained CMRs were used as a heterogeneous catalyst and continuous-flow membrane reactor for hydrogenation of 4-nitrophenol, aldol and nitroaldol condensation, Heck coupling, CO2 cycloaddition and hydroxyalkylation of aniline, and tandem reactions of glucose and fructose to 5-hydroxymethylfurfural (HMF). Our findings also revealed that the turnover frequency (TOF) and selectivity can be tuned and controlled by adjusting the chemistry and degree of cross-linkers, reaction solvents, and flow rates. Even though our polymeric hollow fiber microreactors showed relatively good performance at temperatures up to 150 °C, some amount of active spices (e.g., Pd nanoparticles) leached out from the microreactor due to polymer swelling, plasticization, and pore shrinkage during flow reaction, especially when exposed to polar aprotic solvents and aromatics, and deteriorated the stability of the immobilized catalysts. 

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