Preparation of polyvinylidene fluoride dewatering microporous film

Abstract

The invention relates to a preparation method for a PVDF hydrophobic microporous membrane and belongs to the field of separation membrane and membrane separation. The invention aims at solving the problem of relatively low flux in the prior art and providing the preparation method for a PVDF microporous membrane with hydrophobic nature, which prepares the PVDF hydrophobic microporous membrane through the following steps: 1) preparing a casting solution adding with an alkoxy silane reagent; 2) placing the membrane in water with a moisture ranging from 60 percent to 85 percent or a steam atmosphere with a pH value of 0.5 to 3 or 10 to 13 for 1 to 4 min after scraping the casting membrane into a liquid membrane with a thickness ranging from 0.12 to 0.15mm; 3) immersing the membrane into water at room temperature or a coagulation bath with the pH value of 0.5 to 3 or 9 to 11. The method of the invention is simple in operation, low in cost, with the surface of the membrane prepared being a network cellular structure and accompanied by spherical particles and the cross section being a symmetrical spongy structure, while the hydrophobic nature and the pure water flux of the membrane are greatly improved.

Description

technical field [0001] The invention belongs to the field of separation membrane and membrane separation, and in particular relates to a preparation method of a highly hydrophobic polyvinylidene fluoride microporous membrane. Background technique [0002] Membrane Distillation (MD for short) is a new membrane separation process combining membrane technology and volatilization process. Findly first introduced this separation technology in the 1960s. This technology is based on the effect of the water vapor pressure difference on both sides of the membrane. The water vapor on the hot side enters the cold side through the membrane pores, and then condenses on the cold side. This process is the same as the evaporation-transfer-condensation process in conventional distillation. Compared with other membrane separation processes, membrane distillation has the unique advantage of being able to separate at normal pressure and slightly higher than normal temperature. It can make full...

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Problems solved by technology

Kong Ying and others prepared polyvinylidene fluoride membranes with inorganic salt lithium chloride (LiCl) as additives (Kong Ying, Wu Yonglie, Yang Jinrong, et al. Preparation and morphology of hydrophobic polyvinylidene fluoride microporous membranes for membrane distillation Research on the structure. Membrane Science and Technology, 1990, 10 (3)), improved the shortcoming that polymer additives are easy to remain in the membrane, the results show that the prepared membrane has high porosity, low pore size and high rejection rate, The hydrophobicity of the membrane has also been significantly improved, and the morphological structure of the membrane has undergone obvious changes, including finger-like structure and sponge-like structure, but the problem is that the membrane flux is not high due to the small average pore size of the membrane; Du Qiyun et al. Ammonium chloride (NH 4 The saturated aqueous solution of Cl) is an additive to prepare polyvinylidene fluoride film (Du Qiyun, Wu Liqun. Pore-causing effect of aqueous solution in film-forming process. Water Treatment Technology, 1996,22 (6)), the maximum average pore diameter of making film is 0.28 um, but the problem is: due to the inorganic salt NH 4 Cl is added in the form of an aqueous solution. The introduction of water accelerates the film-forming speed, and a dense layer is easily formed on the surface, resulting in smaller pore size and thicker skin layer, and the inorganic salt does not play the proper pore-forming effect; Mao Peng et al. Preparation of PVDF porous hydrophobic membranes under gel conditions (Mao Peng, LiHongbing, Wu Lijuan, et al. Porous Poly(Vinylidene Fluoride) Membrane with Highly Hydrophobic Surface. Applied Polymer Science, 2005, 98.), that is, using a mixed solution of water / DMAC to replace Pure water gel bath and gel in air instead of immersion precipitation method gel, the results show that when the mixed solution with DMAC content greater than 50% is used as the gel bath, the gel process of the membrane is slowed down, resulting in a dense skin on the surface disappears, the membrane cross-section is a symmetrical sponge-like structure, and the contact angle of the upper and lower surfaces of the membrane reaches 140°, which improves the hydrophobicity of the membrane, but the disadvantage is that the mixed solution is used as a gel bath, which makes the amount of organic solvent DMAC too large; The film prepared by the glue has a micro-nano composite structure on the film surface, so that the contact angle reaches 144°~149°

Hyun prepared a polysulfone membrane (Hyun Chae Park, YoonPo Kim, Hwa Yong Kim, Yong Soo Kang. Membrane formation by water vapor induced phase inversion. Membr Sci, 1999, 156) by steam-induced film-forming method, at a rate higher than 65% The membrane formed under high humidity has a symmetrical sponge-like structure, but the problem is that the pores of the formed membrane are basically impermeable, and the flux of pure water is extremely low.

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