Reverse osmosis, also known as reverse osmosis, is a membrane separation operation that uses pressure difference as the driving force to separate solvent from solution. Pressure is applied to the material liquid on one side of the membrane. When the pressure exceeds its osmotic pressure, the solvent will reverse osmosis against the direction of natural permeation. In this way, the permeated solvent is obtained on the low pressure side of the membrane, that is, the permeate; the high pressure side is the concentrated solution, that is, the concentrated solution. If reverse osmosis is used to treat seawater, fresh water is obtained on the low pressure side of the membrane and brine is obtained on the high pressure side. In reverse osmosis, the permeation rate of the solvent, that is, the liquid flow energy N is: N=Kh(Δp－Δπ) where Kh is the hydraulic permeability coefficient, which increases slightly with the increase of temperature; Δp is the static pressure difference between the two sides of the membrane ; Δπ is the osmotic pressure difference of the solution on both sides of the membrane. The osmotic pressure π of the dilute solution is: "π=iCRT" where i is the number of ions generated by the ionization of solute molecules; C is the molar concentration of the solute; R is the molar gas constant; T is the absolute temperature. Reverse osmosis usually uses asymmetric membranes and composite membranes. The equipment used in reverse osmosis is mainly hollow fiber type or roll type membrane separation equipment. Reverse osmosis membrane can intercept various inorganic ions, colloidal substances and macromolecular solutes in water to obtain clean water. It can also be used for pre-concentration of macromolecular organic solutions. Due to the simple process of reverse osmosis and low energy consumption, it has developed rapidly in the past 20 years. It has been widely used in seawater and brackish water (see brine) desalination, boiler water softening and wastewater treatment, and combined with ion exchange to produce high-purity water. Its application range is expanding, and it has begun to be used in the concentration of dairy products and juices and biochemical products And the separation and concentration of biological agents.
