Tubular nanofiltration membrane with multi-layer structure and preparation method thereof

The invention relates to a tubular nanofiltration membrane with a multi-layer structure and a preparation method thereof. The tubular nanofiltration membrane with the multi-layer structure is four-layered, and the four layers comprises a first layer, a second layer, a third layer and a fourth layer from inside to outside in sequence, wherein the first layer is a microfiltration supporting tube made from a carboxyl-contained fiber knitting tube which is filled with inorganic minerals; the second layer is a ultrafiltration layer formed by coating carboxyl-contained polymer on the outer surface of the first layer; the third layer is a nanofiltration layer made of polyamide formed by interfacial polymerization; and the fourth layer is a water loving layer forming covalent binding with the third layer. The tubular nanofiltration membrane with the multi-layer structure is obtained through the steps of forming functional layers from indie to outside in sequence, and stable chemical binding is formed among layers, so that the tubular nanofiltration membrane has excellent resistance to pressure and mechanical strength, and good water loving property, water permeability and antifouling ability; and moreover, the flux reaches more than 30 L/m h, the removal rate of singlevalent salt is more than 30%, and the removal rate of bivalent salt is more than 95%.