Membrane separation overview
Membrane separation is based on a membrane with selective transmission function as the separation medium. One or more driving forces are applied on both sides of the membrane to make a component in the raw material selectively pass through the membrane preferentially, so as to achieve mixture separation and Product extraction, concentration, purification and other purposes.
Characteristics of membrane separation
The membrane separation process does not change. Compared with other methods, the energy consumption is lower and the energy conversion efficiency is higher. The membrane separation process can be carried out at normal temperature, which is especially suitable for the separation of heat sensitive substances. It is usually not necessary to add other substances, which can save chemical agents and help not change the original properties of the separated substances. In the membrane separation process, separation and concentration are performed at the same time, which is conducive to the recovery of all valuable substances. The membrane separation device is simple, can realize continuous separation, has strong adaptability, easy operation and easy to realize automatic control.
Classification of membrane separation
According to the separation mechanism: mainly reaction membrane, ion exchange membrane, osmosis membrane, etc .;
According to the nature of the membrane: mainly natural membrane (biofilm) and synthetic membrane;
According to the shape of the membrane: there are flat membrane, tubular membrane and central control fiber membrane;
According to the structure of the film: there are pairs of film formation, asymmetric film and conforming film.
Membrane separation types
1. Reverse osmosis : The process is mainly a membrane process based on the principle of adsorption and diffusion of a solution, with pressure difference as the main driving force. Apply an external pressure (0.1-10 MPa) on the side of the concentrated solution. When this pressure is greater than the osmotic pressure of the solution, it will force the volume of the concentrated solution to flow through the asymmetric membrane with a pore diameter (0.0001-0.001 μm) to the dilute solution. On one side of the solution, this process is called reverse osmosis.
Application of reverse osmosis: desalination of seawater and brackish water, treatment of wastewater and harmful wastewater (industrial wastewater, municipal wastewater), application of chemical processing industry (paper industry, textile industry, petroleum industry, power industry), application of food processing industry .
2. Microfiltration : Also known as microfiltration , it belongs to precision filtration. The microfiltration device can filter micro- or nano-scale particles and bacteria, and retain particles such as gravel, silt, clay and giardia, cryptosporidium, algae and some bacteria in the solution, while a large number of solvents, small molecules and a small number of large molecules Solutes can pass through the membrane separation process.
Principle of microfiltration equipment: The basic principle of microfiltration equipment is the sieving process. The operating pressure is generally 0.7-7kPa. The raw material liquid passes through the filtration material of the microfiltration equipment under the effect of static pressure difference. The filter materials of the microfiltration device can be divided into a variety of types, such as folding filter elements, meltblown filter elements, bag filters, microfiltration membranes, and the like. The microfiltration equipment uses a microporous filter membrane made of cellulose or a polymer material, and uses its uniform pore size to trap particles, bacteria, and the like in the water, so that it cannot be removed through the microfiltration membrane of the microfiltration device.
Application of microfiltration: There are currently more than ten specifications of microporous membranes used in microfiltration devices, with pore sizes ranging from 0.1-75 μm. Microfiltration devices have a wide range of applications in the pharmaceutical, beverage, drinking water, video, electronics, petrochemical, analytical testing, and wastewater treatment fields.
3. Ultrafiltration : Ultrafiltration is one of the membrane separation technologies with pressure as the driving force. For the purpose of separating large and small molecules, the pore size of the membrane is between 20-1000A. The central control fiber membrane ultrafilter has the advantages of high filling density in a unit container and a small footprint.
Principle of ultrafiltration equipment: During the operation of the ultrafiltration equipment, the aqueous solution is driven by the pressure and flows through the surface of the membrane. The deep agent smaller than the membrane pores and the small molecule solute permeable membrane become the purification liquid (filtration liquid), which is larger than the membrane pores. The solutes and solute groups are trapped and patted with the water flow, becoming deep shrinkage. The working process of the ultrafiltration equipment is dynamic filtration, and the separation is completed in a flowing state. The solute is only deposited on the membrane surface to a limited extent, the ultrafiltration rate decays to a certain extent and tends to balance, and the performance of the ultrafiltration equipment can be restored by cleaning.
Application of ultrafiltration: Ultrafiltration device is like reverse osmosis device, including plate type, tube type, roll type, central control fiber type and so on. The advantages of the ultrafiltration device are simple operation, low cost, no need to add any chemical reagents, especially the experimental conditions of ultrafiltration technology are mild, there is no phase change compared with evaporation and freeze drying, and it does not cause changes in temperature and pH. Therefore, ultrafiltration equipment can prevent the denaturation, inactivation and autolysis of biological macromolecules. In the preparation technology of biological macromolecules, ultrafiltration devices are mainly used for desalination, dehydration and concentration of biological macromolecules.
4. Electrodialysis : The semi-osmosis used is actually an ion exchange. This ion exchange membrane can be divided into cation exchange membrane and anion exchange membrane according to the charge properties of ions. In the electrolyte aqueous solution, the positive membrane allows cations to pass through and rejects blocking anions, and the negative membrane allows ions to pass through and rejects blocking cations. This is the selective permeability of the ion exchange membrane.
Application of electrodialysis: in the field of desalination, in the food, pharmaceutical and chemical industries, there are many other industrial applications of the electrodialysis process, such as the treatment of industrial wastewater, mainly including the waste liquid formed from the cleaning of metal surfaces by acid solutions Recovery of acids and metals. Recovery of heavy metal ions from electroplating wastewater. Recovery of sulfate from synthetic fiber wastewater. Sulfite and the like are recovered from the pulp waste liquid.
Application of membrane separation
Water treatment : seawater and brackish water talk, ultrapure water preparation, power plant boiler water purification, wastewater treatment;
Food and biochemical industry : purification, concentration, disinfection, replacement of distillation, recycling of by-products;
Metal industry: metal recycling, pollution control, oxygen-rich combustion;
Textile and tanning industry: waste heat recovery, chemical recovery, pollution control;
Paper industry: replace distillation, pollution control, fiber and chemical recovery;
Pharmaceutical industry: artificial organs, controlled release, blood separation, disinfection;
National defense industry: supply of fresh water for ships, purification of polluted water in battlefields.
The research and application of membrane separation technology in the field of environmental protection has just begun, but a good start has been made. The interest and utilization of membrane technology will definitely increase with the increase of environmental protection requirements. With the increase of people's awareness of environmental protection, with the further development of membrane technology, membrane separation technology will rapidly develop in improving drinking water quality, water pollution control, and air pollution control. Membrane separation technology has great application potential in the field of environmental protection, and has a bright future.
There is still a large gap in the application of China's membrane technology to the world's cash level in the field of environmental protection. We develop and manufacture high-strength, long-life surface, anti-pollution, and high-throughput membrane materials. We use different membrane technologies for different pollution sources and corresponding The supporting process has reduced investment and operating costs, and better promoted the application of membrane separation technology in the field of environmental protection. Re-membrane use focuses on solving key issues such as membrane fouling, concentration polarization, and cleaning.