The difference between RO reverse osmosis membrane and ultrafiltration membrane

The difference between RO reverse osmosis membrane and ultrafiltration membrane


First, the reverse osmosis membrane (RO membrane):
RO is the abbreviation of Reverse Osmosis membrane in English. Chinese means (reverse osmosis). Generally, the flow of water is from low concentration to high concentration. Once water is pressurized, it will flow from high concentration to low concentration, which is the so-called reverse osmosis principle: Since the pore size of the RO membrane is one-fifths (0.0001 microns) of the hair, it is generally invisible to the naked eye and bacteria and viruses are 5,000 times more. Therefore, only water molecules and some beneficial mineral ions can pass. Other impurities and heavy metals are discharged from the waste pipe. All seawater desalination processes and astronauts’ wastewater recycling and treatment are all adopted this method. Therefore, the RO membrane is also called an in vitro high-tech artificial kidney.

  1. What is reverse osmosis?
    Reverse osmosis is a new membrane separation technology developed in the 1960s. It is the process of separating the solvent and solute in solution by means of a reverse osmosis membrane. The full English name of reverse osmosis is REVERSE OSMOSIS, abbreviated as “RO”.
  2. The principle of reverse osmosis:
    The first thing to understand is the concept of “penetration.” Penetration is a physical phenomenon. When two waters containing different salts are separated by a semi-permeable membrane, the water with less salt will penetrate. The membrane penetrates into the water with high salt content, and the contained salt does not infiltrate. As a result, the concentration of salt on both sides gradually merges into equalization. However, it takes a long time to complete this process. This is called osmotic pressure. But if you try to add pressure on the high salt side of the water, the result can also stop the permeation. The pressure at this time is called the osmotic pressure. If the pressure increases, you can make the opposite direction. Infiltration, while the salt is left. Therefore, the principle of reverse osmosis desalination is to apply a pressure greater than the natural osmotic pressure in salty water (such as raw water) so that the percolation is carried out in the opposite direction and the water molecules in the raw water Pressure to the other side of the membrane, into clean water, so as to achieve the purpose of removing impurities and salt in the water.
  3. Origin of RO reverse osmosis:
    In 1950, the American scientist DR.S. Sourirajan had no intention of discovering that seagulls picked up a large sea of ​​water from the sea when they were flying at sea. After a few seconds, they spit out a small mouthful of seawater and have doubts because of the lung-breathing animals on land. It is absolutely impossible to drink high-salt seawater. After dissection, it was found that there is a film in the seagull body. The film is very precise. Seawater is inhaled through seagulls and then pressurized, and then water molecules penetrate through the membrane and turn into freshwater. Seawater contains impurities and highly concentrated salts is spouted out of the mouth, which is the basic theoretical framework for reverse osmosis; and was used by the University of Florida in desalination in 1953 to remove salt, and in 1960 by the U.S. federal government. Project support Dr. S. Sidney Lode, professor of UCLA University School of Medicine in the United States, and Dr. S. Soirirajan, who set about investigating reverse osmosis membranes, invested about 400 million U.S. dollars a year for research purposes to be used by astronauts to make space ships useless A large amount of drinking water evacuated, and more and more scholars and experts were engaged in research work in 1960, which made the quality and quantity of them more sophisticated, thus solving the problem of human water use. Problems.

Second, Ultrafiltration Membrane (UF):
A microporous filter membrane with uniform pore size and a nominal pore size range of 0.001-0.02 microns. Membrane filtration using ultrafiltration membranes with pressure differential as the driving force is ultrafiltration membrane filtration. Ultrafiltration membranes are mostly made from acetate fibers or polymer materials with similar properties. It is most suitable for the separation and thickening of solute in solution, and it is also commonly used for the separation of colloidal suspensions that are difficult to complete with other separation techniques. Its application is expanding.

Membrane filtration driven by pressure difference can be divided into three categories: ultrafiltration membrane filtration, microporous membrane filtration and reverse osmosis membrane filtration. Their distinction is based on the smallest particle size or molecular weight that the membrane layer can retain. When the nominal pore size range of the membrane is used as a criterion, the nominal pore size range of the microporous membrane (MF) is 0.02 to 10 μm, the ultrafiltration membrane (UF) is 0.001 to 0.02 μm, and the reverse osmosis membrane (RO) is 0.0001 to 0.001 μm. It can be seen that the ultrafiltration membrane is most suitable for the separation and concentration of solute in solution, or the separation of colloidal suspensions that are difficult to accomplish using other separation techniques. The technique of membrane formation of ultrafiltration membranes, ie, the technology to obtain the desired size and narrow distribution of micropores is extremely important. There are many control factors for the pores, such as ultrafiltration membranes with different pore sizes and pore size distributions, depending on the type and concentration of the solution during the membrane formation, evaporation, and condensation conditions. Ultrafiltration membranes are generally macromolecular separation membranes, and the polymer materials used as ultrafiltration membranes mainly include cellulose derivatives, polysulfone, polyacrylonitrile, polyamide, and polycarbonate. The ultrafiltration membrane can be made into a flat membrane, a rolling membrane, a tubular membrane, or a hollow fiber membrane, and is widely used in, for example, the pharmaceutical industry, food industry, and environmental engineering.

We all know that the sieve is used to screen things. It can release small objects and retain larger ones. However, have you heard of sieves that can sieve molecules? Super Membrane – This super sieve can separate molecular sieves of different sizes! So what exactly is an ultrafiltration membrane? The

Ultrafiltration membranes are porous membranes with a super “sieve” separation function. Its aperture is only a few nanometers to several tens of nanometers, that is to say, there is only one strand of hair! By applying a suitable pressure to one side of the membrane, solute molecules larger than the pore size can be sieved to separate particles with a molecular weight greater than 500 Daltons and a particle size greater than 2-20 nm. Ultrafiltration membrane structure is symmetrical and asymmetrical. The former is isotropic and has no cortex. The pores in all directions are the same and belong to deep filtration. The latter has a relatively dense surface layer and a base layer mainly composed of finger structures. The surface layer thickness is 0.1 micrometer or less. And has arranged micropores, the bottom layer thickness of 200 ~ 250 microns, is the surface layer filter. Industrially used ultrafiltration membranes are generally asymmetric membranes. The membrane materials of ultrafiltration membranes include cellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfone amide, sulfonated polysulfone, and the Polyvinyl alcohol, modified acrylic polymers, and the like. The

Ultrafiltration membrane is one of the earliest developed polymer separation membranes. In the 1960s, ultrafiltration devices were industrialized. Ultrafiltration membranes have a wide range of industrial applications and have become one of the new chemical unit operations. It is used in the separation, concentration, and purification of biological products, pharmaceutical products, and the food industry; it is also used in terminal treatment devices for blood processing, wastewater treatment, and preparation of ultrapure water. In China, we have successfully used ultrafiltration membranes to concentrate and purify Chinese herbal medicines. With the advancement of technology, ultrafiltration membranes will surely be improved and strengthened, and their contribution to human society will also increase. The
Reverse Osmosis is a separation method that separates the solute in the solution from the solvent by pressure-driven selective trapping with a semipermeable membrane. It can effectively treat salt (such as calcium, magnesium, and other hardness impurities), heavy metals, and chemical residues in water from 95% to 99%.


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