Reverse osmosis is a membrane separation operation that uses the pressure difference as a driving force to separate the solvent from the solution. Because it is opposite to the direction of natural penetration, it is called reverse osmosis. According to the different osmotic pressure of various materials, reverse osmosis pressure greater than osmotic pressure can be used, that is, reverse osmosis method, to achieve the purpose of separation, extraction, purification and concentration.
Process principle of reverse osmosis
1. Semi-permeable membrane: A membrane that can only allow solvent molecules to pass through, but does not allow solute molecules to pass through, is called ideal semi-permeable.
2. Penetration: Under the same external pressure, when the solution is separated from the pure solvent by the semi-permeable membrane, the pure solvent will pass through the semi-permeable membrane and the phenomenon of the solution thinning is called penetration.
3. Osmotic balance: During the osmotic process, the number of solvent molecules passing through the semi-permeable membrane from two opposite directions per unit time is equal to each other, that is, osmotic balance is achieved.
4. Osmotic pressure: When the semi-permeable membrane separates the solution from the pure solvent, the additional pressure applied to the original solution to prevent the pure solvent from entering the solution is called osmotic pressure. Usually the thicker the solution, the greater the osmotic pressure of the solution.
5. Reverse osmosis: If the pressure added to the solution exceeds the osmotic pressure, the solvent in the solution instead flows in the direction of the pure solvent, this process is called reverse osmosis.
Reverse osmosis is a membrane process that use of reverse osmosis membrane can only selectively through the solvent (usually water) and intercept the ionic material, use the static pressure difference on both sides of the membrane as a driving force to overcome the osmotic pressure of the solvent, so that the solvent through the reverse osmosis membrane to achieve the separation of the liquid mixture.
Its operating pressure difference is generally 1.5 ~ 10.5MPa, and intercept the size of 1 ~ 10197 small molecule solute. In addition, all other suspended matter, dissolved matter and colloids can be removed from the liquid mixture.
Technical characteristics of reverse osmosis process
1. Under the condition of no phase change at room temperature, the solute and water can be separated, which is suitable for the separation and concentration of heat-sensitive substances, and has lower energy consumption compared with the separation method with phase change.
2. The impurity removal range is wide, which can not only remove dissolved inorganic salts, but also remove all kinds of organic impurities.
3. High desalting rate and water reuse rate, can intercept solute with particle size above a few nanometers.
4. Because only pressure is used as the driving force for membrane separation, the separation device is simple, easy to operate, control and maintain.
5. The reverse osmosis device requires the water to reach a certain index in order to operate normally, and certain pretreatment measures should be adopted before the raw water enters the reverse osmosis device. In order to extend the service life of the membrane, the membrane should also be cleaned regularly to remove dirt.
Routine use
Reverse osmosis technology is usually used in desalination of seawater, brackish water; Water softening treatment; Wastewater treatment and purification, concentration, separation of food, pharmaceutical industry and chemical industry.
In addition, reverse osmosis technology applied to pre-salt treatment has also achieved good results, which can reduce the load of ion exchange resin by more than 90%, and the amount of regenerant of resin can also be reduced by 90%.
Therefore, it not only saves costs, but also benefits environmental protection. Reverse osmosis technology can also be used to remove particles, organic substances and colloids in water, which has a good effect on reducing the pollution of ion exchange resin and extending the service life.
