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Highlights • Simultaneous production of pure water and salt crystal by S-VMDC. • Stirring and aeration are conducive to improve heat transfer in boundary layer. • Bulk crystallization plays dominated role with turbulent intensification. • The CSD of crystals can be regulated by selecting an optimal operation condition. Abstract The feasibility of simultaneous pure water production and salt crystal recovery from highly concentration NaCl solution was evaluated by utilizing a submerged vacuum membrane distillation crystallization (S-VMDC) system with different turbulent intensification modes. The effect of intensification mode including stirring and aeration on membrane distillation performance and crystallization behavior was investigated systematically. An iterative method was used to evaluate the heat transfer enhancement effect. The results indicated that both stirring and aeration had positive influence on permeate flux due to the improvement of heat transfer and weakening of polarization phenomenon in boundary layer. The dominated crystallization behavior converted from surface crystallization to bulk crystallization with the help of turbulent intensification, which in turn increased the limiting concentration of the feed solution. The size and distribution of crystallized product could be regulated by selecting an optimal intensification mode. With the combined effect of stirring rate at 1350 rpm and aeration rate at 0.20 m3/h, 31.85% NaCl crystals with relative desirable size distribution could be recovered from bulk solution. This study provided an alternative perspective to understand the enhancement effect of turbulent intensification strategy in S-VMDC process for concentrating saturation solution in both qualitative and quantitative ways. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrophobic FAS-PDMS/PEEK composite membranes were prepared by dip-coating method. • Honeycomb-like structures were observed dispersing on composite membrane surface. • The wetting resistance of membrane was improved after coating with FAS-PDMS layer. • Effects of gas and liquid flow velocities on CO 2 absorption performance were studied. • FAS-PDMS/PEEK composite membrane contactor exhibited good application potential. In this study, as an efficient technology membrane absorption was applied with newly developed polyetheretherketone (PEEK) hollow fiber membrane (HFM) to remove CO 2 from flue gas. To alleviate membrane wetting issue, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS) was integrated into polydimethylsiloxane (PDMS) and then crosslinked FAS-PDMS was coated on porous PEEK membranes to prepare composite membranes. Surface characterization verified that PDMS layer containing fluoroalkylsilane had been successfully formed on membrane surface. As mass ratio of FAS to PDMS in coating solution raised, an interesting honeycomb-like structure was observed dispersing on composite membrane surface. Meanwhile, water contact angle was improved from 90.0° to 133.5° indicating enhanced membrane hydrophobicity. The effects of gas and liquid flow velocities on CO 2 absorption performance of FAS-PDMS/PEEK HFM were systematically studied. The highest CO 2 removal efficiency of 99.6% was achieved when gas and liquid velocity were 0.027 and 0.019 m s−1. When gas velocity raised to 0.110 m s−1, the maximum absorption flux of 1.22 × 10-4 mol m−2 s−1 and overall mass-transfer coefficient of 2.69 × 10−5 m s−1 could be obtained. Compared with the original membrane, the CO 2 absorption flux of FAS-PDMS-0.6 HFM was increased by 50.9%, and the performance had no degradation in 36 h test. This study provides a novel strategy to alleviate the membrane wetting problem during CO 2 membrane absorption process. [ABSTRACT FROM AUTHOR]

[Display omitted] • New polyamide layer with rigid-flexible microstructure was constructed. • Both internal pores and positive charge density were remolded at molecular level. • "Useless pores" were widened and "defect pores" were repaired simultaneously. • Modified membrane exhibited much higher Mg2+/Li+ selectivity factor of 15.38. Lithium extraction from salt-lake brine with a high Mg2+/Li+ ratio is crucial for mitigating lithium supply shortage. Positively charged polyamide nanofiltration membranes, which are often prepared by performing interfacial polymerization (IP) using polyethyleneimine and trimesoyl chloride, are considered to be promising candidates for Mg2+/Li+ separation owing to their high energy efficiency and low environmental impact. However, the performance of these membranes is severely hindered by "useless pores" and "defects" present in the flexible polyamide layer. Herein, we provide a facile strategy for modifying flexible semi-aromatic polyamide chains by intercalating a rigid electropositive monomer, histamine, to remold the internal pores and positive charge density at a molecular level. Two routes, namely, "swelling-embedding-reacting-shrinking (SERS)" and "in-situ interposition (SIP)" were used to construct a new polyamide layer with rigid–flexible microstructures. The fabricated SERS-0.50 membrane showed a 5-fold higher water flux and 2-fold increase in the Mg2+/Li+ separation factor compared with the IP membrane. Moreover, the SIP-0.15 membrane with an enhanced positive charge density exhibited a considerably higher Mg2+/Li+ separation factor (15.38, 500 % increase compared with that of the IP membrane) for brine with a Mg2+/Li+ ratio of 20. This study provides a reference for developing nanofiltration membranes used for high-efficiency Mg2+/Li+ separation. [ABSTRACT FROM AUTHOR]

Abstract: A novel cellulose membrane used for isopropanol (IPA) dehydration was prepared by using N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) as the solvent that can dissolve cellulose through a purely physical process. Scanning electron microscopy (SEM) images show that the prepared membrane had a homogeneously dense structure after natural drying. X-ray diffraction (XRD) and mechanical properties characterizations show that the prepared cellulose membrane owned much higher crystallization degree and better mechanical strength compared with traditional cellulose acetate (CA) or cellophane membranes coming from chemical process. The effects of operation conditions including feed concentration and operation temperature on pervaporation (PV) performance were investigated systemically. The results indicate that the permeation flux increased obviously with the increase of either water concentration in feed or operation temperature. Under the condition of 20wt.% water-containing IPA feed and at 65°C, a highest total flux of 349g/m2 h was achieved with a lowest water content in permeate of 99.50wt.% (with a separation factor of 972) among all the tested conditions. Water content in permeate reached 99.97wt.% (with a separation factor of 61,271) with a total flux of 13.4g/m2 h at the condition of 5wt.% water in feed at 25°C. Compared with other pure polymer membranes such as chitosan and poly(vinyl alcohol) (PVA), the prepared novel cellulose membranes exhibited acceptable fluxes and much higher separation factors. All these results demonstrate that cellulose membrane has great application potential in IPA dehydration process. [Copyright &y& Elsevier]

• A novel aqueous-organic membrane contactor process was applied. • The novel membrane contactor process was more favorable to treat low-ammonia-content feeds. • Accompanying water transport was avoided. Nafion-PTFE hollow fiber composite membranes were applied in the ammonia removal and recovery with a novel aqueous-organic membrane contactor (AOMC) process, in which an aqueous solution and an organic solution were separated by the composite membrane. A kerosene-diluted di-(2-ethylhexyl) phosphoric acid (D2EHPA) solution was used to receive the ammonia, which could be recycled and reused after regeneration by the stripping agent (a dilute solution of H 2 SO 4 , HNO 3 , or H 3 PO 4). The new-type membrane contactor can avoid the accompanying water transport in conventional membrane contactors. The effects of experimental factors including the pH, the velocity and the initial ammonia concentration of the feed on the overall mass transfer of the ammonia were investigated. Meanwhile, how the regeneration experiment parameters influenced the stripping ratio was also studied. The results showed that the AOMC process was more favorable to treat ammonia feed with low ammonia concentrations. The ammonia removal could be over 99% under certain conditions. Additionally, the ammonia was concentrated 26.4 times after four cycles. It was found that the accompanying water transport was non-negligible in the traditional aqueous-aqueous membrane contactor (AAMC) process when treating ammonia feed of low concentrations, with the maximum water flux two orders of magnitude higher than ammonia. [ABSTRACT FROM AUTHOR]

• TR-polymer hollow fiber membranes with high flexibility were prepared. • Thermal densification was employed to induce selective skin layer. • Solvent exchange drying caused severer shrinkage than direct drying. • Coating can effectively obtain ultrathin skin and high selectivity. Flexible poly(benzoxazole-co-amide) (PBOA) gas separation hollow fiber membranes were successfully prepared deriving from ether-containing polyamide precursors by thermal densification with or without a supplementary coating treatment. Compared with polyimide precursors, thermally rearrangement in this work required lower treatment temperature but generated better mechanical properties. Both spinning process and thermal treatment conditions were systemically manipulated to intensify the membrane densification aiming at achieving greatly improved selectivity of the obtained TR-PBOA hollow fiber membranes. It was found that draft ratio had little contribution to selectivity enhancement. Separation performance was substantially improved when precursor fibers were dried using ethanol-hexane exchange method and then thermally treated at 350–390 °C TR hollow fibers obtained by combined thermal treatment with coating method exhibited the highest selectivity values in this study. [ABSTRACT FROM AUTHOR]