Author: Site Editor Publish Time: 2022-12-22 Origin: Site
Microfiltration membranes are capable of retaining particles between 0.1 and 1 micron. They allow the passage of large molecules and dissolved solids (inorganic salts), but retain suspended matter, bacteria and large molecular weight colloids. Microfiltration is the world's first membrane technology to be developed and used with natural or synthetic polymeric compounds as membrane materials. For microfiltration membranes, the separation mechanism is mainly sieving and retention.
Microfiltration also uses the sieving mechanism of microfiltration membranes to retain particles between 0.1-1 μm in diameter, such as suspended matter, bacteria, some viruses and large-sized colloids, under pressure-driven conditions, and is mostly used in water pre-treatment systems.
The membrane used in microfiltration is a microporous membrane with an average pore size of 0.02-10, capable of retaining particles with a diameter of 0.05-10 or macromolecules with a molecular weight of more than 1 million, with an operating differential pressure of 0.01-0.2 MPa. The particles larger than the membrane pores are retained, thus achieving the separation of the particles from the solvent in the raw material. The mechanism of particle retention in the microfiltration process is sieving, and it is the physical structure of the membrane, the shape and size of the pores, that determines the separation effect.
1. Aqueous microfiltration membranes: are generally used for the filtration of pure aqueous phases. Aqueous membranes should be avoided in the filtration of mixed solvents containing organic phases to prevent the membrane from being dissolved, as they are generally made from cellulose based materials. Cellulose membranes are characterised by good hydrophilicity, good porosity and wide availability, but have poor resistance to acids, alkalis and organic solvents and poor creep resistance. Aqueous membranes include: cellulose acetate membranes, cellulose nitrate membranes, mixed ester membranes, regenerated cellulose membranes, polyethersulfone, etc.
2. Organic microfiltration membranes: for the filtration of organic solvents. Commonly used organic microporous membranes: polytetrafluoroethylene membrane (PTFE), polyvinylidene fluoride membrane (PVDF), polyvinylidene fluoride.
3. Mixed membrane filtration: generally used for aqueous and organic systems in general. Mixed membrane filtration: nylon membranes, modified polyvinylidene fluoride (modified hydrophilic), polytetrafluoroethylene membranes (modified hydrophilic), polyvinylidene difluoride membranes (modified hydrophilic). Aliphatic nylon, with good hydrophilicity and resistance to appropriate concentrations of acids and bases, is not only suitable for aqueous solutions containing acids and bases, but also for organic solvents such as alcohols, hydrocarbons, ethers, esters, ketones, benzene and benzene homologues, dimethylformamide, dimethyl sulfoxide, etc. It is one of the most widely used microfiltration membranes.