Reverse osmosis membranes can be divided into three forms based on the different membrane raw materials: cellulose acetate, polyamide, and composite membranes. According to their physical structure, they can be divided into two forms: asymmetric membranes and homogeneous membranes.

Several forms of reverse osmosis membranes:
The structure of reverse osmosis membranes comes in two forms: asymmetric membranes and homogeneous membranes. The currently used membrane materials are mainly cellulose acetate and aromatic polyamide. Its components include hollow fiber type, roll type, plate and frame type, and tube type. It can be used for chemical unit operations such as separation, concentration, and purification, mainly in the pure water preparation and water treatment industries.

cellulose acetate
Cellulose acetate, also known as acetyl cellulose or cellulose acetate. Cellulose containing cotton, wood, and other materials are often used as raw materials to produce cellulose acetate through esterification and hydrolysis reactions, which is then processed into reverse osmosis membranes.

polyamide
Polyamides include two major categories: aliphatic polyamides and aromatic polyamides. In the 1970s, aliphatic polyamides such as nylon-4, nylon-6, and nylon-66 membranes were mainly used; The most commonly used currently is aromatic polyamide film. The membrane materials include aromatic polyamide, aromatic polyamide acyl liver, and some nitrogen-containing aromatic polymers.
The pH range suitable for aromatic polyamide membranes can be as wide as 2-11, but they are sensitive to free chlorine in water.

composite film
The characteristic of composite membrane is mainly made of the above two materials, which are composed of a very thin dense layer and a porous support layer. Porous support layer, also known as base film, plays a role in enhancing mechanical strength; The dense layer, also known as the epidermal layer, plays a role in desalination, hence it is also called the desalinated layer. The thickness of the desalination layer is generally 50nm, with the thinnest being 30nm.

Reverse osmosis membranes can be divided into two categories based on their chemical composition: cellulose membranes and non cellulose membranes. According to the physical structure of membrane materials, they can be roughly divided into asymmetric membranes and composite membranes.

The most widely used cellulose membrane is the cellulose acetate membrane (CA membrane for short). The total thickness of the membrane is about 100 μ m, and the thickness of the entire skin layer is about 0.25 μ m. The skin layer is filled with micropores with a pore size of about 5-10 angstroms, which can filter out extremely fine particles. The pore size in the porous support layer is very large, about several thousand angstroms, so this asymmetric structure of the membrane is also called an asymmetric membrane. In reverse osmosis operation, the cellulose acetate membrane can only achieve the expected desalination effect when the skin layer comes into contact with high-pressure raw water, and must not be inverted.

Non cellulose membranes are mainly composed of aromatic polyamide, as well as polyamide membranes, benzoquinone membranes, polysulfone membranes, polytetrafluoroethylene graft membranes, polyethyleneimine membranes, and so on.