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Reverse osmosis membrane
Name: reverse osmosis membrane
Applicable object: water use: water filtration thickness: 0.1 (mm)
Scope of application: pure water filtration, filtration method: reverse osmosis performance: acid resistance, alkali resistance, waterproof operating pressure: 11 (MPa)
Working temperature: 30 (℃)
Filtration accuracy: 0.01 nm Cut-off molecular weight: 3700 (million)
Aperture: 0.001 (μm)
Flux: 800-1000 (L / H)
Longitudinal strength: 6 (MPa)
Specifications: 8 inches
是实现反渗透的核心元件，是一种模拟生物半透膜制成的具有一定特性的人工半透膜。 I. Reverse osmosis membrane is the core element for realizing reverse osmosis. It is an artificial semi-permeable membrane with certain characteristics made of simulated biological semi-permeable membrane. Generally made of polymer materials. Such as cellulose acetate film, aromatic polyhydrazide film, aromatic polyamide film. The diameter of the surface micropores is generally between 0.5 and 10 nm, and the permeability is related to the chemical structure of the membrane itself. Some high-molecular materials have good repellency to salt, but water transmission rate is not good. Some polymer materials have more hydrophilic groups in their chemical structure, so the water transmission rate is relatively fast. Therefore, a satisfactory reverse osmosis membrane should have an appropriate amount of penetration or salt rejection.
The reverse osmosis membrane should have the following characteristics:
1. It should have a high salt removal rate at high flow rates;
2. Has higher mechanical strength and service life;
3. Can function under lower operating pressure;
4. Tolerant to chemical or biochemical effects;
5. It is less affected by factors such as pH value and temperature;
6. The source of the raw materials for the film is easy, the processing is simple, and the cost is low.
7. The structure of reverse osmosis membrane, there are two types of asymmetric membrane and homogeneous membrane. The membrane materials currently used are mainly cellulose acetate and aromatic polyamides. Its components are hollow fiber type, roll type, plate and frame type and tube type. Can be used for separation, concentration, purification and other chemical unit operations, mainly used in pure water preparation and water treatment industries.
Reverse osmosis membrane
反渗透又称逆渗透，一种以压力差为推动力，从溶液中分离出溶剂的膜分离操作。 Principle: Reverse osmosis, also known as reverse osmosis, is a membrane separation operation that uses pressure difference as the driving force to separate the solvent from the solution. Pressure is applied to the material liquid on one side of the membrane. When the pressure exceeds its osmotic pressure, the solvent will reversely permeate against the direction of natural permeation. Thus, a permeated solvent, ie, a permeate, is obtained on the low-pressure side of the membrane; a concentrated solution, ie, a concentrated liquid, is obtained on the high-pressure side. If seawater is treated with reverse osmosis, fresh water is obtained on the low-pressure side of the membrane, and brine is obtained on the high-pressure side.
During reverse osmosis, the permeation rate of the solvent, ie, the flow energy N, is: N = Kh (Δp-Δπ) where Kh is the hydraulic permeability coefficient, which increases slightly with 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 the 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 for reverse osmosis is mainly hollow fiber or roll membrane separation equipment.
The reverse osmosis membrane can trap various inorganic ions, colloidal substances and macromolecular solutes in water to obtain net water. It can also be used for preconcentration of macromolecular organic solution. Due to the simple reverse osmosis process and low energy consumption, it has developed rapidly in the past 20 years. It has been widely used in desalination of seawater and brackish water (see brine), softening of boiler water and wastewater treatment , and combined with ion exchange to produce high-purity water. Its application scope is expanding, and it has begun to be used for the concentration of dairy products, juices, and biochemical And concentration of biological agents.
Reverse osmosis membrane cutting principle
2. Reverse osmosis membrane filtration accuracy:
The reverse osmosis membrane can trap substances larger than 0.0001 microns, and it is a fine membrane separation product. It can effectively trap all dissolved salts and organic matter with a molecular weight greater than 100, while allowing water molecules to pass through.
3. Selection of reverse osmosis membrane:
Customers often ask what performance indicators we need to consider when selecting RO membranes. Usually divided into three: desalination rate, water production rate, recovery rate.
1.Desalting rate and salt permeability rate of RO reverse osmosis membrane The desalination rate of RO reverse osmosis membrane element has been determined at the time of its manufacture and formation. The degree of desalination depends on the density of the ultra-thin desalination layer on the surface of RO membrane element. The denser the desalination layer, the higher the desalination rate and the lower the water production. The desalination rate of reverse osmosis membranes for different substances is mainly determined by the structure and molecular weight of the substance. The desalination rates for high-valent ions and complex monovalent ions can exceed 99%. The desalination rates for monovalent ions such as sodium, potassium, and chloride are slightly higher. Low, but it can also exceed 98% (the longer the reverse osmosis membrane is used, the more the chemical cleaning is performed, and the lower the rate of desalination of the reverse osmosis membrane). The removal rate of organic matter with a molecular weight greater than 100 can also exceed 98%, but the The removal rate of organic matter with molecular weight less than 100 is low.
Calculation method of desalination rate and salt permeability of reverse osmosis membrane:
RO membrane salt transmission rate = RO membrane water production concentration / influent water concentration ¡Á 100%
RO membrane desalination rate = (1-RO membrane water content / influent water content) ¡Á 100%
Salt permeability of RO membrane = 100%-desalination rate 2. Water production and permeate flow rate of RO reverse osmosis membrane RO membrane water production-refers to the water production capacity of the reverse osmosis system, that is, The amount of water is usually expressed in tons / hour or gallons / day.
RO membrane osmotic flow rate-is also an important indicator of the water production of reverse osmosis membrane elements. Refers to the permeate flow rate per unit membrane area, usually expressed in gallons per square foot per day (GFD). An excessively high permeate flow rate will cause the water flow velocity perpendicular to the surface of the RO membrane to accelerate, and aggravate membrane fouling.
3. Recovery rate of RO reverse osmosis membrane The recovery rate of RO membrane-refers to the percentage of feed water in the reverse osmosis membrane system to produce water or permeate. It depends on the quality of the feed water and water requirements in the pre-treatment of the reverse osmosis system. The recovery rate of the RO membrane system was determined at the time of design.
(1). Recovery rate of RO membrane = (produced water flow / inflow water flow of RO membrane) ¡Á 100%
(2). The formulas for the recovery rate, salt transmission rate, and salt rejection rate of reverse osmosis (nanofiltration) membrane modules are as follows:
Recovery rate of reverse osmosis membrane module = RO membrane module water production / water intake ¡Á 100%
Salt permeability of reverse osmosis membrane module = RO membrane module water production concentration / water intake concentration ¡Á 100%