The chemical properties and structure of membrane materials
Requirements for membrane materials: It has good film formation, thermal stability, chemical stability, and acid, alkali, microbial erosion and oxidation resistance. Membrane for reverse osmosis, ultrafiltration, and microfiltration is preferably hydrophilic to obtain high water flux and anti-fouling ability. Electrodialysis membranes place special emphasis on acid resistance, alkalinity, and thermal stability of membranes. Gas separation, especially pervaporation, requires membrane materials to have preferential dissolution and diffusion capabilities for permeable components. If used for organic solvent separation, membrane materials are also required to be solvent-resistant. Most of the current membrane materials are obtained by screening existing commercial polymer materials, and few specific materials are designed and synthesized for a certain separation process. It is often difficult to obtain membrane materials that can meet the above conditions at the same time, and membrane material modification or membrane surface modification methods are often used to make the membrane have certain required properties.
1. Polymer membrane materials mainly include cellulose, polyamide, aromatic heterocyclic, polysulfone, polyolefin, silicone rubber, fluorine-containing polymers, other polycarbonates, polyelectrolyte complexes, etc.
2. Inorganic membranes are mostly made of metals, metal oxides, ceramics, and porous glass. Advantages of inorganic membranes: stable at high temperatures; stable chemical properties, especially resistance to organic solvents; easy to achieve electrocatalysis and electrochemical changes; large material permeability, less pollution; easy to control pore size and pore neck size distribution. Disadvantages of inorganic membranes: film is brittle and fragile, requiring special configurations and assembly systems; relatively high equipment costs; high maintenance costs when there are further defects; high temperature applications, sealing is more complicated.
