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What Types Of Membranes Are Used In Industrial Water Treatment?
- Aug 17, 2018 -

The membrane separation technologies used in industrial water treatment mainly include reverse osmosis (RO), ultrafiltration (UF) and electrodialysis (ED). Reverse osmosis is the most widely used. However, in recent years, nanofiltration (NF) and different general microfiltration (MF) technologies have also begun to be applied to various fields of water treatment.


Reverse osmosis membranes are mainly composed of cellulose and non-cellulose. The cellulose film is cellulose acetate, cellulose triacetate or the like; the non-cellulose film is mainly an aromatic polyamide film. Reverse osmosis is a semi-permeable membrane that is highly selective for water and has low permeability to most solutes in water. The reverse osmosis membrane is made into a modular device when it is used, and its type includes a scroll type, a tube type, a plate and frame type, a hollow fiber type, and a strip type. The film thickness is about several μm to about 0.1 mm.


Both ultrafiltration membranes and reverse osmosis membranes are neutral membranes that do not have ion exchange properties and are pressure-driven membranes. The two membranes are basically similar, mainly composed of cellulose acetate and non-cellulose polymer membranes, and the assembly device can be made into a scroll type, a tube type and a plate type.


The cellulose membranes in the ultrafiltration membrane and the reverse osmosis membrane are: 1 ultrathin membrane: a cellulose acetate membrane having an asymmetric structure, such as a 0.06-0.3 μm diacetyl cellulose membrane; 2 composite membrane: such as nitrocellulose and Cellulose acetate composite is 0.1 μm triacetyl cellulose film; 3 mixed film: mixed film of diacetyl and triacetyl cellulose; 4 hollow fiber membrane: hollow fiber tube with inner diameter of 24-30 μm and outer diameter of 45-65 μm formula.


The non-cellulose membranes in the ultrafiltration membrane and reverse osmosis membrane are: 1 aromatic polyamide hollow cellulose membrane (originally nylon 66 as cellulose, later changed to aromatic amide); 2 charged membrane, such as sulfonation 2 , 6-dimethylphenylene ether ion membrane; 3 polyimidazopyranone membrane; 4 polydiazolium membrane; 5 glass membrane, such as Na2O‧B2O3‧SiO2 hollow fiber membrane; 6 dynamic membrane.


The electrodialysis membrane is an ion exchange membrane and is an electric push membrane. There are mainly three types of heterogeneous membranes, homogeneous membranes and semi-homogeneous membranes. The electrodialytic component devices are of the pressure filter type and the water tank type. Among them, the pressure filter type has two types of vertical type and horizontal type.


The nanofiltration membrane (NF) is interposed between the reverse osmosis membrane and the ultrafiltration membrane. It is a membrane variety that has developed rapidly in the past ten years. It has special advantages in water softening and separation of different anions and is widely used.


Microfiltration (MF), also known as fine filtration, is based on sieve filtration. Under the action of static pressure difference, particles smaller than the pores of the membrane pass through the membrane, and particles larger than the pores of the membrane are trapped on the membrane surface. Components of different sizes are separated.