Three-layer composite membrane of sodium alginate, polydopamine-polyethyleneimine and polyacrylonitrile, and preparation and application of three-layer composite membrane

The invention discloses a three-layer composite membrane of sodium alginate, polydopamine-polyethyleneimine and polyacrylonitrile. A polyacrylonitrile ultrafiltration membrane is used as a supporting layer, the polydopamine-polyethyleneimine is used as a middle layer, and the sodium alginate is used as a separation layer. The three-layer composite membrane is prepared from the following steps: prewetting the polyacrylonitrile ultrafiltration membrane by ethyl alcohol, fixing the prewetted polyacrylonitrile ultrafiltration membrane to a container, and then preparing a tris(hydroxymethyl)methyl aminomethane solution containing dopamine and polyethyleneimine; pouring the solution into the container, enabling the dopamine and the polyethyleneimine to react on the surface of a basement membrane so as to obtain a double-layer membrane of polydopamine-polyethyleneimine and polyacrylonitrile; coating a sodium alginate solution on the double-layer membrane of polydopamine-polyethyleneimine and polyacrylonitrile so as to obtain the three-layer composite membrane. The preparation process is simple, raw materials are easy to access, and conditions are moderate, the prepared three-layer composite membrane of sodium alginate, polydopamine-polyethyleneimine and polyacrylonitrile is used for separating ethyl alcohol from water, and has higher permeation flux and more separation factors.