| Organic solvents have been widely used in the industry. However, if being exhausted directly, organic solvents will cause severe harm to both environment and human bodies. Presently, solvents’recovery and purification in industries generally adopt conventional separation techniques such as energy-consuming distillations or waste-generating extractions. In comparison, solvent resistant nanofiltration (SRNF) is demonstrated to be a promising approach with green, high efficiency and low energy consumption features. For SRNF, the key and performance-dependent part is the solvent resistant nanofiltration membrane, which determines the separation efficiency and working life of SRNF. Developing high-performance, long-life and versatile solvent resistant nanofiltration membrane has become one of the most important challenges and issues that must to be addressed for the commercial application of about SRNF.Based on the chemical properties of organic solvent, solvent resistant nanofiltration membrane should meet the following requirements:(1) high performances:displaying satisfying separation performances in organic solvents (i.e., high flux and selectivity);(2) long life:displaying long-term operation in organic solvent (i.e. high chemical stability and mechanical stability);(3) versatility:can be used in the complex separation system (e.g., mixture of a variety of organic solvents). The vast majority of the solvent resistant nanofiltration membrane that have been explored usually cannot meet all the above-mentioned requirements; the commercial nanofiltration membrane can only be used for certain kinds of solvents. Currently, the commonly-utilized membrane materials include polyamides (PIs) and polysiloxanes (PDMS), which are hydrophilic and hydrophobic, respectively. In this study, these two materials are chemically crosslinked to create hydrophilic-hydrophobic networks that can possess moderate swelling for high flux and selectivity. The results and conclusions of this study are as follows:(1) In the study, a new solvent resistant nanofiltration membrane is prepared using polyacrylonitrile (PAN) ultrafiltration membrane as support layer and PA/PDMS hybrid materials as separating layer. Polyethyleneimine (PEI) solution is casted onto the PAN surface, followed by PDMS solution that contains cross-linking agent (trimesoyl chloride, TMC). PDMS and PEI chains are crosslinked by TMC through interfacial polymerization, and meanwhile the active imine groups in PEI will be reacted. In such a way, PEI becomes to polyamide (PA). Infrared spectra analysis (FTIR) shows that PDMS is successfully introduced into PEI thin layer by TMC. Scanning Electron Microscopy (SEM) shows a three-layer structure of the membrane composing of PAN support layer, PEI inter layer and PDMS out layer, is formed and thus generates crosslinked three-dimensional interpenetrating networks. Differential Scanning Calorimetry analysis (DSC) shows that the introduction of PDMS enhances the glass transition temperature of the membrane. Thermogravimetric Analysis (TGA) shows that the membrane dispalys excellent thermal stability. Tensile test shows that the mechanical stability of the membrane is improved by cross-linking polymerization, and the tensile strength is about45.8MPa.(2) Swelling behavior of the membrane in different organic solvents is investigated, which suggests that the membrane displays excellent solvent resistance properties. For example, the membrane swelling degrees in acetone, ethyl acetate, ethanol, octane are1.99%,0.07%,2.0%and1.99%, respectively. The solvent adsorption rates in these four solvents are9.96%,14.4%,14.4%and14.35%, respectively.(3) Separation performances reveal that the membrane has large enough flux and wonderful interception effect with a molecular cut off (MWCO) of600in alcohols, esters, and ketones. For instance, the flux in isopropanol under1MPa is up to9.6L m-2h-1with a MWCO of500. Filtration testing is performed for a long-term continuous8h, the membrane maintains a good operation stability were found, flux ranges from3.44L m-2h-1reduced to2.49L m-2h-1.In summary, the prepared solvent resistant nanofiltration membrane exhibits excellent solvent resistance and flux in esters, ketones, alcohols and alkanes, together with adequate thermal stability and mechanical stability. The Membrane achieves wonderful rejection for the mass with molecular weight above600. This study has made a preliminary exploration about the way to tune membrane swelling behaviors, which may provide some guidance for optimizing membrane performances. |
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