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Separation Mechanism Of Reverse Osmosis Membrane
- Aug 20, 2018 -

Separation mechanism of reverse osmosis membrane


The reverse osmosis membrane is a pressure-driven membrane filtration method, and the membrane used has no ion exchange property and can be called a neutral membrane. The semi-permeable membrane for reverse osmosis is a filter membrane, which must be operated under the osmotic pressure on both sides of the membrane. The operating pressure of the cellulose acetate membrane used in the past is 5-6 MPa (50-60 atm), and the operation of the polyamide composite membrane used today. The pressure is about 1.5 MPa (15 atm).


A semipermeable membrane refers to a membrane that can only pass through a certain component of a solution. The semipermeable membrane used for water treatment requires only water molecules. Of course, this selectivity to water does not exclude small amounts of other ions or small molecules that can pass through the membrane.


There are various explanations for the semi-permeable mechanism of the membrane, but neither explains the total penetration phenomenon.


One explanation is that this is a screening effect. That is, the pores of the membrane are between the water molecules and the solute molecules, so that water can pass through and the solute is impermeable. But this does not explain why the size of the water molecules is basically the same as the salt segregation.


The second explanation is that the reverse osmosis membrane is a hydrophilic polymer, the water molecules are adsorbed on the membrane wall, the channels of the solute molecules are blocked, and the inorganic salt ions in the water (Na+, K+, Ca2+, Mg2+, Cl-... ) is more difficult to pass.


Finally, there is a mechanism that is believed to be due to the fact that water can dissolve in the membrane and the solute cannot dissolve in the membrane.