Fabrication Of Zn（BDC）（TED）_0.5/PDMS Mixed Matrix Membranes And Their Pervaporation Performance

The development and application of pervaporation(PV) technology provided an efficient and energy-saving approach for recovery of the organics in chemical waste water, removing the water from organics, separation of organic mixture and utilizing the waste heat in chemical plant. The PV alcohol permselective membranes have gained great attention during the last two decades. But the instability of the separating performance of PV membrane and the lack of membrane materials restrict heavily the development of PV. Metal organic frameworks(MOFs) are applied in the separartion membranes quickly because of their high porosity, large specific surface area and good thermal stability. But the fabrication of pure inorganic membrane of MOFs will be very expensive. In view of this, we adopt MOFs particle filling to fabricate mixed matrix membranes(MMMs) to improve the PV separation performances.Firstly, the PVDF ultrafiltration membrane was used as a supporting membrane. Polydimethylsiloxane(PDMS) was taken as the solute, n-heptane as the solvent, tetraethoxysilane(TEOS) as the crosslinking agent and dibutyltin dilaurate(DBTDL) as the catalyst, to prepare the casting membrane solution. Then the membrane solution was cast on the surface of PVDF membrane and the PDMS would be crosslinked thermally under 120℃ to form a composite membrane with a smooth thin defect-free separation function layer. The effect of the mass fraction of PDMS in the prepared casting solution on membrane separation performances was explored.Then, solvothermal method was used to synthesize Zn(BDC)(TED)0.5. The effects of reactant ratio on the crystallinity of as-synthesized MOFs particles were investigated. Under the optimized PDMS content, Zn(BDC)(TED)0.5 particles were filled into PDMS to prepare Zn(BDC)(TED)0.5/PDMS mixed matrix membrane.In addition, the as-synthesized Zn(BDC)(TED)0.5 particles and MMMs were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), Fourier transform infrared spectroscopy(FT-IR), contact angle(CA) and the glass transition temperature(Tg) to test and analyze the crystal morphology and chemical composition of Zn(BDC)(TED)0.5 particles and changes of MMMs surface morphology, the functional group information, hydrophobicity and the rigid changes of polymer chains, respectively. As the results showed, the water contact angle of the prepared MMMs increased from 112.7° to 147°, but the ethanol contact angle decreased from 47.2° to 12.1°.Most importantly, the separation performances of membranes were tested via pervaporation experiment using 5 wt% ethanol aqueous solution. It was found that the separation performance of MMMs was improved significantly. Although the penetration flux decreased due to the increase in membrane hydrophobicity, the separation factor was greatly increased. When the content of Zn(BDC)(TED)0.5 was 10 wt%, separation factor improved significantly(from 5.69 to 10.57) under 40℃. When the temperature increased to 60℃, the flux increased from 285.9 to 498.7 g·m-2·h-1, and the separation factor increased slightly to 10.87. In addition, this membrane with the feed of 5 wt% n-butanol aqueous solution showed higher separation factor and flux which were 26.3 and 746 g·m-2·h-1,respectively, under 40℃.In summary, the PV separation performance of MMMs prepared herein is significantly higher than that of PDMS membrane. Its comprehensive separation performance was close to or better than that of the reported similar type MMMs, which is of significance on the application of alcohol permselective membranes in industrial production.