A monolithic bipolar film roll with mesh support and its manufacturing method

Abstract

The invention discloses a single-piece bipolar film roll supported by a mesh cloth and a manufacturing method thereof. The single-piece type bipolar film roll is supported by a high-strength ultra-high molecular weight polyethylene mesh cloth, and one side is made of The cation exchange layer of sulfonic acid group, the anion exchange layer containing benzyldimethylbutylammonium quaternary amine group on the other side, and the water dissociation catalytic layer containing benzylmethylbutylamine tertiary amine group in the middle. The layers form a monolithic bipolar membrane. By setting a wider protective film and a narrower spacer film, the soaking film roll is polymerized to obtain a composite base film roll; after continuous sulfonation, a single-sided sulfonated composite cation film roll is obtained, and then the unreacted composite film roll is prepared. The blank surface is subjected to three-step chemical reactions of complete chloromethylation, complete tertiary amination and incomplete methylation in sequence, and a monolithic bipolar membrane with dense structure, clear intermediate interface, high mechanical strength and stable quaternary amine group is obtained. It has a high product qualification rate and is especially suitable for bipolar membrane electrodialysis engineering applications containing organic material systems.

Description

technical field [0001] The invention belongs to the field of functional polymer film processing, in particular to a monolithic bipolar film roll supported by a mesh cloth and a manufacturing method thereof. Background technique [0002] Bipolar membranes generally have a three-layer structure in the thickness direction (see: Bipolar Membrane Technical Manual, Chemical Press, July 2004, pp. 75-89), that is, an anion exchange layer (generally containing strongly basic quaternary amines) group), intermediate interface layer (generally containing weak acid groups such as carboxylic acid groups, weak base groups such as tertiary amine groups or metal ion complexes to play a catalytic role in water dissociation) and cation exchange layer (generally containing strong acid groups) sulfonic acid group). Among them, the interfacial layer can be positioned very clearly between the anion-exchange layer and the cation-exchange layer, with only nanoscale thickness. For example, as descr...

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Problems solved by technology

However, because the catalytic groups (such as tertiary amino groups) are covered in one layer, that is, the catalytic interface is not clear, so the transmembrane voltage required for catalyzing the dissociation of water molecules will be higher; at the same time, the anion exchange layer The hydrogen ions obtained by the dissociation of middle water cannot be transmitted through the cation exchange layer in time (the same positively charged quaternary ammonium group will delay the transmission of hydrogen ions), and will be neutralized with hydroxide ions, reducing the rate of water dissociation. current efficiency

In addition, the existing monolithic bipolar membranes based on imbibed base membranes are not embedded with high-strength support mesh, resulting in too soft membranes, that is, insufficient density and strength

In this way, there will be obvious "salt pollution" in the application of bipolar membrane electrodialysis engineering, resulting in a decrease in the purity of the acid and alkali produced (it will contain 1 to 2% salt), because any layer of it is not dense enough. , so it cannot completely block the migration of the same ion

At the same time, this kind of bipolar membrane "loosens more and more with use" under high current density, constantly wrinkling and deforming, and it is difficult to recover, which is caused by the insufficient overall strength of the bipolar membrane

Moreover, the quaternary ammonium group obtained by the reaction of trimethylamine in the anion exchange layer (i.e. benzyltrimethylammonium group, commonly known as strong base type I quaternary ammonium group), does not survive the long-term transmission of hydroxide in a strong alkaline solution environment. Unstable and will slowly degrade into tertiary amino groups or benzyl alcohol groups (see: 1) Journal of Power Sources, 2018, 375: 170-184; 2) Bipolar Membrane Technical Handbook, Chemical Press, published in July 2004 , page 136), which will lead to the gradual increase of the resistance of the anion exchange layer, which is not conducive to the timely transfer of the hydroxide ions produced by water dissociation out of the bipolar membrane

Taken together, the main structural defects of the existing monolithic bipolar membranes are the unclear catalytic interface, insufficient compact base membrane structure, insufficient overall mechanical strength, and understabilization of the type I quaternary amine group, which seriously affect its performance and performance. life span

[0005] At the same time, the existing monolithic bipolar membranes are manufactured one by one, which is difficult to mass-produce in rolls, and the production efficiency is low, so there will be obvious performance differences between batches

Because the base film is obtained after soaking the styrene polymerization solution from the polyolefin base film, then the base film is sulfonated on one side to obtain a positive film, and finally the positive film is completely chloromethylated and aminated to obtain a bipolar film, all The implementation steps will cause the membrane body to swell continuously, so it is difficult to realize large-scale manufacturing in rolls without wrinkles, but only by "cutting the base membrane into multiple pieces for impregnation", "putting one side of the base membrane close to the ceramic plate , to achieve single-sided sulfonation" and other methods to prepare one by one, not only the production efficiency is low, but also the repeatability and stability of each membrane between batches are difficult to be fully guaranteed; therefore, the monolithic bipolar membrane is in the There are also obvious flaws in the manufacturing method

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