亲/疏水Janus PVDF复合膜制备及其膜蒸馏性能

为改善聚偏氟乙烯(PVDF)膜的膜蒸馏渗透通量,以PVDF为成膜聚合物,在亲水无纺布表面涂覆PVDF铸膜液,通过溶液相转化(NIPS)法制得亲/疏水Janus PVDF复合膜;考察PVDF铸膜液中添加剂邻苯二甲酸二辛酯(DOP)含量对复合膜结构与性能的影响;将所得亲/疏水复合膜用于直接接触式膜蒸馏(DCMD)过程,分析复合膜中亲水层对DCMD过程的影响。结果表明:随着铸膜液中DOP含量的增加,促进了PVDF铸膜液的相分离过程,使得膜孔隙率和膜孔径尺寸逐渐增加,而膜的液体渗透压(LEP)和断裂强度逐渐降低;复合膜中的亲水层可有效促进DCMD过程中水蒸汽的传质和冷凝过程,进而提高膜蒸馏通量,Janus PVDF复合膜的通量相较于PVDF膜提高了28.39%,提高冷侧渗透液流速和降低渗透液温度均可有效提高DCMD的渗透通量,而保持脱盐率在99%以上。

Preparation of hydrophilic/hydrophobic Janus PVDF composite membrane and its membrane distillation performance

In order to improve the membrane distillation flux of polyvinylidene fluoride(PVDF)membrane,a kind of Janus PVDF composite membrane with hydrophilic/hydrophobic structure was prepared by coating PVDF casting solution on the surface of hydrophilic non-woven fabric through phase inversion process(NIPS)method.The effects of dioctyl phthalate(DOP)addition on the structure and performance of the composite membrane were studied.The obtained hydrophilic/hydrophobic composite membrane was used in the direct contact membrane distillation(DCMD)process,and the effect of the hydrophilic non-woven of the composite membrane on the performance of DCMD process was investigated.The results show that the increase of the DOP content induces the phase separation process of PVDF casting solution,which further brings about the promotion of membrane porosity and pore size.The membrane′s liquid entrance pressure(LEP)and breaking strength gradually decreased.The hydrophilic layer effectively promotes the mass transfer and steam condensation in the DCMD process,thereby improves the membrane distillation flux.Compared with PVDF membrane,the flux of Janus PVDF composite membrane is increased by 28.39%.The permeation flux of DCMD can be effectively increased by increasing the permeation flow rate on the cold side and decreasing the permeation temperature,while the salt rejection keeps above 99%.