Membrane separation technology is a high and new technology that has risen rapidly in the past 40 years. It has developed into an industrialized high-efficiency energy-saving separation process and an advanced unit operation process.

At present, technologies such as microfiltration, ultrafiltration, reverse osmosis, nanofiltration, dialysis, electroosmosis, gas separation, pervaporation, and inorganic membrane, which have been mature and continuously developed, are widely used in petroleum, chemical, environmental protection, energy, electronics and other industries, and have produced obvious economic and social benefits. Especially, they will play an important strategic role in industrial technology transformation in the 21st century.

Several membrane water treatment technologies are described below.

Microfiltration technology

Microfiltration is one of the most widely used membrane water treatment technologies with the largest total sales, mainly used for filtration and sterilization in the pharmaceutical industry; At present, the preparation of high-purity water is the second largest market for the application of microfiltration technology.

In recent years, it has been industrialized in many fields of food industry and can be used for clarification of gelatin and glucose; It can replace the traditional diatomite to filter juice, and the effect is the same as ultrafiltration; It can also recycle beer dregs and white beer for sterilization.

It has potential market in drinking water production and urban sewage treatment. It can be used to remove the virus from urban sewage at a lower cost than ultrafiltration. It is used for industrial wastewater treatment, such as separating solvent from pigment, removing refractory particles from oily wastewater, and removing toxic heavy metals such as cadmium and mercury from electroplating wastewater.

The fuel industry can be used to remove wax and asphaltene from oil products. In addition, with the development of biotechnology industry, the market of microfiltration used to concentrate and separate biological products in fermentation broth will also grow

Pervaporation technology

The pervaporation technology will bring new changes to the traditional distillation technology. It uses the mechanism of dissolution and diffusion to transfer components, is not affected by the azeotropic system, and is particularly effective for the separation of azeotropes. It is mainly used for the dehydration of organic solvents, the removal of a small amount of solvents in water and the removal of organic/organic mixtures.

In the 1980s, foreign countries were the first to realize industrialization. The cross-linked polyvinyl alcohol (PVA) membrane of German GFT Company was first used for ethanol dehydration, production of anhydrous ethanol and isopropanol dehydration, etc. Now more than 100 factories have been built, with a maximum scale of 15 × 10 (superscript 4) L/d ／.

In addition, the separation of methanol and MTBF is also close to industrial application. With the development of pervaporation technology. Other applications will also grow rapidly, especially the separation of organic mixtures, which will be used as an alternative and supplementary technology for some distillation processes, and will have broad application prospects in the petrochemical industry.

Inorganic membrane

Inorganic membrane mainly includes ceramic membrane and metal oxide membrane (such as Υ- Al (subscript 2) O (subscript 3), ZnO, TiO (subscript 2) and metal film are suitable for use under high pressure, high temperature, high viscosity, high solid content, high chloride content and harsh pH conditions.

Therefore, it has broad application prospects in petrochemical, food, metallurgy, environmental engineering, bioengineering and other fields. After five years of efforts, ceramic microfiltration membrane and ultrafiltration membrane in China have been developed from scratch, and the industrial production has been preliminarily realized. The technical indicators of membrane materials and the scale and automatic control level of membrane devices have reached the international advanced technical level.

In the future, China's inorganic membrane will play an important role in gas separation and purification, as well as in reforming traditional processes by combining inorganic membrane with other processes, and gradually form a new integrated application technology with inorganic membrane as the core.

Ultrafiltration technology

1. Industrial wastewater treatment

Ultrafiltration technology can be used to recover coatings from electrophoresis painting wastewater, and it has been widely used in electrophoresis painting automation assembly lines around the world.

The membrane area of ultrafiltration equipment in large plants is 150 square meters, and the permeation flow rate is 3 square meters/h. It is now widely used in the treatment of oily wastewater in the metal processing and tinning industries, and the treatment process of oily wastewater in other fields is being developed. It is also widely used for the recovery and reuse of PVA, a sizing material in the textile industry. The membrane area of ultrafiltration equipment in large factories reaches 10000 square meters, and the treatment capacity is 60 cubic meters/h.

It is widely used for the treatment of waste liquid in the adhesive industry, concentration and recovery of styrene, butadiene, PVC and other latex.

Ultrafiltration technology has been used to treat industrial waste water from some paper mills in Japan and other countries. In the mining and metallurgical industry, acid mineral effluent is treated. Its permeate can be recycled, and useful substances can be recovered from the concentrate. The application of ultrafiltration in this field is increasingly being paid attention.

2. Urban sewage treatment

Ultrafiltration technology has been used in urban and domestic sewage treatment. It is possible to realize small-scale water circulation in the newly-built residential buildings with more than 500 households, that is, flush toilets with ultrafiltration treated domestic sewage, which can reduce domestic water consumption by 40%. Ultrafiltration technology has been widely used in the production of integrated circuits in the electronic industry and in the process of water use in the pharmaceutical industry. It mainly uses hollow fiber modules, with high membrane permeability and low energy consumption.

3. Food and medicine industry

The recovery of protein from whey ultrafiltration is one of the most widely used fields in the dairy industry, with an annual growth rate of 20%. The membrane area of large ultrafiltration modules reaches 1800 square meters. Ultrafiltration of milk can increase the yield of cheese. This process is gradually replacing the traditional process, which will have great economic benefits. Ultrafiltration technology is widely used to clarify fruit juice abroad, but it has not been popularized in China.

Ultrafiltration for the recovery of blood components from slaughtered animals will have a large market and is technically feasible. In addition, ultrafiltration has been used for the recovery of plant protein and will be extended to the recovery of plankton protein such as algae. In pharmaceutical and glucose manufacturers, it is used to separate and concentrate components with biological activity from fermentation broth. Ultrafiltration has the advantages of maintaining its biological activity and high recovery rate. Its application in this field will grow with the growth of genetic engineering technology industry. Ultrafiltration technology has been widely used to concentrate glucose oxidase, trypsin, chymosin, and pectinase hormones, and also to concentrate new substances produced by genetically engineered bacteria, such as interferon, growth hormone, and insulin in human blood to extract serum albumin.

Reverse osmosis technology

Reverse osmosis technology has become the most economic means for desalination of seawater and brackish water, preparation of pure and ultra-pure water and material preconcentration. With the industrialization of reverse osmosis membranes and membrane modules with excellent performance, the application scope of reverse osmosis technology has expanded from the initial desalination to the fields of electronics, chemical industry, medicine, food, beverage, metallurgy and environmental protection. With the comprehensive promotion of this technology, reverse osmosis technology will become the main means to solve the problem of drinking water shortage in the 21st century.

Reverse osmosis technology can also be used for municipal wastewater treatment, semiconductor and medical water, power plants and utilities, and condensate tower discharge recycling. Currently, reverse osmosis technology is being developed for the production and reuse of chemical and petrochemical process water, waste liquid treatment, separation of water and organic liquids, reuse of electroplating rinse water and metal recovery. The food industry is using reverse osmosis technology to develop dairy processing, sugar concentration, juice and dairy processing, wastewater treatment, and production of low-alcohol alcohol alcohol and beer.

Nanofiltration technology

Nanofiltration is a new separation technology developed on the basis of reverse osmosis. Although its market development history is only more than 10 years, it has been well applied in the fields of water softening, purification, separation and concentration of antibiotics, polysaccharides, dyes, etc. It can replace or partially replace precipitation, evaporation, pH adjustment and other processes, and become an important energy-saving unit operation of biopharmaceuticals and fine chemicals.

The precursor of trihalomethane (THM) in water can be removed by nanofiltration membrane to prevent the formation of THM in water. In the food industry, Japan has been used for whey concentration, which can be conducted simultaneously with desalting, lactose removal and protein concentration, and has reached the industrial level.

It can also be used for food decolorization, separation of certain amino acid, purification and concentration of polypeptides. In the aspect of wastewater treatment, nanofiltration membrane was used to decolorize the waste liquor formed in the alkali extraction stage of wood pulping, and the decolorization rate was more than 98%. The metal sulfate and nitrate can also be separated from acidic solution by nanofiltration membrane, and the rejection rate of nickel sulfate can reach 95%.