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The interfacial design is critical in preparing high-performance mixed matrix membranes (MMMs), especially for the separation of larger sized components from mixtures. Herein, a facile and novel st...

Air pollution gradually aggravated, which accelerates the demand of clean energy (in particular clean natural gas) because of its abundant storage worldwide. However, raw natural gas commonly contains impurity gases, such as CO2 and N2, which reduce the heat of its combustion. Here, we reported new polyamide-poly(propylefne glycol) (PA-PPG) random and block copolymer materials with excellent CO2/CH4 separation performance. These copolymers were characterised by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), UV–vis absorption spectrum and X-ray diffraction (XRD). The gas permeation properties of these copolymers were investigated by using five single gases (CO2, H2, O2, CH4 and N2) at different temperatures (298–328 K) and a feed pressure of 76 cmHg. The effects of chemical structure, PPG content and operating temperature on the gas permeation properties of these copolymers were also further discussed. Results showed that PA-PPG random copolymer membranes exhibited better gas permeation properties than those of PA-PPG block copolymer membranes. PA-PPG random copolymer membrane with 20 wt% PPG exhibited the highest selectivity (CO2/CH4 = 37.31 and H2/CH4 = 33.44) at 298 K and 76 cmHg. The CO2 and H2 permeability values were 5.97 Barrer and 5.19 Barrer, respectively.

Poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS) crosslinked membranes containing poly(dimethylsiloxane-co-methylhydrosiloxane) (PDMS-co-PMHS) were prepared by hydrosilylation reaction toward CH4/N2 separation. The effect of an additive amount of PDMS-co-PMHS on the structure, morphology, and thermodynamic stability of crosslinked membranes were investigated by using FT-IR, SEM and TGA. Soxhlet extraction experiments were also performed to explore the crosslinking degree of membranes. In this work, the single-gas permeability of CH4 and N2 was measured using the constant volume–variable pressure method. Our experimental results showed that crosslinked membranes can significantly enhance CH4 permeability with increasing PDMS-co-PMHS content, whereas the CH4/N2 selectivity remains unchanged. Among these crosslinked membranes, the SBS-c-PDMS-co-PMHS-70 membrane exhibited optimal CH4 permeability at room temperature and the pressure of 1 bar. Specifically, the CH4 permeability was > 10-folds higher than that of the SBS membranes (37.6 barrer versus 443.6 barrer). Moreover, investigation of the effect of test temperature on the gas permeation of crosslinked membranes revealed a preferable CH4 permeability at 55 °C and 1 bar, at which the CH4 permeability reaches 679.2 barrer without a substantial compromise in selectivity.

Poly(styrene- b -butadiene- b -styrene) (SBS) block copolymer has been recently demonstrated to be a polymer membrane material with high selectivity for CH 4 /N 2 gas separation. In this study, two effective approaches of grafting and crosslinking have been explored to improve the gas permeability of SBS polymer by introducing polysiloxane (silicone) polymers to SBS backbone via hydrosilylation reaction. First, a series of novel poly(styrene- b -butadiene- b -styrene)- g -poly(dimethylsiloxane) (SBS- g -PDMS) graft copolymers were synthesized via the hydrosilylation reaction of SBS carbon double bonds and silanes (Si-H) from monohydride terminated PDMS. We found that CH 4 permeability was increased 40% by grafting only 1.24% PDMS in SBS. Second, to supplement additional silicone to SBS, the hydrosilylation reaction of SBS carbon double bonds and silanes from poly(methylhydrosiloxane) was used to prepare novel SBS-silicone cross-linked polymer membranes. It was demonstrated that CH 4 permeability could be improved by 214%, achieving 118 Barrer when 45 wt% silicone was incorporated in SBS. This successful example of improving gas permeation by molecular design could open up new avenues for researchers to develop future polymer membranes with both high selectivity and permeability for industrial applications including methane enrichment from coalbed gases.

A series of new aromatic polyamides (PAs) and copolyamides (CPAs) containing fluorene group have been synthesized through polycondensation reaction. The chemical structure was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR). PAs and CPAs exhibited the higher thermal stability ( Td15 > 378°C in nitrogen), the higher glass transition temperature ( Tg > 345°C), and excellent solubility in polar solvent. Gas transport properties of the PA and CPA membranes were investigated using different single gases (hydrogen (H2), carbon dioxide (CO2), oxygen (O2), methane (CH4), and nitrogen (N2)). We discussed the effect of chemical structure and operating temperature on gas transport properties. The results show that PA-1 containing a hexafluoroisopropylidene moiety exhibited the highest gas permeability ( PH2 = 12.71 Barrer, PCO2 = 12.26 Barrer, and PO2 = 2.62 Barrer) and reasonably good selectivity ( α(H2/N2) = 27.63, α(CO2/N2) = 26.65, and α(O2/N2) = 5.70) at 25°C and 1 atm. For all the membranes, gas permeability gradually increased with the increase in operating temperature, while the selectivity gradually decreased. These gas permeation results were well correlated with fractional free volume, interchain d-spacing ( dsp), and intermolecular interaction.

Emerging pervaporation technology is very promising to realize clean and renewable bioethanol recovery from biomass fermentation broth. The huge challenge of this technology is the need for a pervaporation membrane with high separation performance. Based on the solution-diffusion mechanism, pervaporation membrane for ethanol recovery should possess hydrophobic selective layer to improve sorption ability toward ethanol molecules, thereby enhancing the separation performance. In this study, a superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer with a nano-level bud-like surface morphology was grown on polydimethylsiloxane (PDMS) composite membrane via ZIF-8 particle dip-casting, secondary seeded growth, and hydrophobic modification by n-octadecylphosphonic acid for highly efficient ethanol/water separation. The mole ratio of 2-methylimidazole and zinc nitrate (Hmim/Zn2+) in the process of ZIF-8 secondary growth was systematically studied to construct appropriate micro-nano structure on PDMS composite membrane. The resultant optimal composite membrane exhibited a water contact angle of about 163° and an ethanol contact angle of 0°. In addition, it also displayed an outstanding separation factor of 17.4 corresponding to a total flux of 0.64 kg/m2 h with 5 wt% ethanol aqueous solution at 30 ℃, and thus the superior pervaporation performance to most other reported PDMS-based mixed matrix membranes. The strategy of constructing superhydrophobic layer on PDMS composite membrane may provide a meaningful guidance for preparing high-performance pervaporation membrane for organic recovery from aqueous solution.

In this study, ZIF-8@GO composites with continuous inner channels for ethanol molecules were prepared by the in-situ growth of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles onto the surface of graphene oxide (GO) nanosheets, and filled into polydimethylsiloxane (PDMS) matrix to fabricate PDMS/ZIF-8@GO mixed matrix membranes (MMMs) for ethanol recovery via pervaporation. The as-prepared ZIF-8@GO composites and PDMS/ZIF-8@GO MMMs were characterized by various techniques. The results showed that ZIF-8 nanoparticles were uniformly dispersed on the surface of GO nanosheets and the hydrophobicity of ZIF-8@GO composites was stronger than GO due to the surface modification of GO by hydrophobic ZIF-8. Moreover, ZIF-8@GO composites as the filler not only exhibited the excellent compatibility with PDMS but also showed the good dispersion in PDMS matrix as compared to ZIF-8 nanoparticles. Therefore, ZIF-8@GO-based MMMs showed better separation performance than ZIF-8-based MMMs. The pervaporation performance of PDMS/ZIF-8@GO MMMs was studied by adjusting the filler type, particle loading, membrane thickness, and feed temperature. The optimized PDMS/ZIF-8@GO MMMs displayed a prominent separation factor of 22.2 with a total flux of 443.8 g/m2 h with 5 wt% ethanol aqueous solution at 40 °C, and therefore the superior pervaporation performance to most other PDMS-based MMMs. The excellent pervaporation results were attributed to the synergistic effect of GO nanosheet as a strong barrier and hydrophobic ZIF-8 nanoparticles with the continuous inner channels. The synergistic effect of hybrid particles may provide valuable guidance to the development of high-performance PDMS-based MMMs for pervaporation recovery of various organic compounds.