Novel Structure Polyamide Composite Nanofiltration Membranes Prepared By Interfacial Polymerization

Nanofiltration membrane is a pressure-driven membrane between ultrafiltration and reverse osmosis. Its operating pressure is usually from 0.5MPa to 2.0MPa. The nanofiltration membrane is widely used to separate small molecules with the molecular weight between 200 and 2000, especially the divalent ions. The most common method of preparing nanofiltration membranes is composition. The composite membrane is comprised of a thin functional layer and a support. The functional layer is prepared by coating or interfacial polymerization (IP), and has a high selectivity. The support is usually ultrafiltration membrane which has a non-symmetrical structure. In this work, the composite membranes were prepared by interfacial polymerization on different supports, and the main works are as follow:Nanofiltration composite membrane was prepared by interfacial polymerization (IP) of m-phenylenediamine (MPDA) and trimesoyl chloride (TMC) on the surface of polyethersulfone (PES) support with big pores on the surface. The effects of monomer concentrations, reaction time of IP and prepressing time on separation performance of composite membranes were investigated. Based on the previous work, four different composite nanofiltration membranes were prepared by MPDA, piperazine (PIP), triethylenetetramine (TETA) and 1,2-ethylenediamine (EDA) reacting separately with TMC on PES supports. The success of the conducted IP procedure and morphology of composite membranes was confirmed by ATR-FTIR and SEM. Their nanofiltration performances were evaluated with solutions of Na2SO4, NaCl, MgSO4 and MgCl2. The experimental results showed that under the same conditions, MPDA/TMC membrane and PIP/TMC membrane had a excellent separation performance for bivalent anions, TETA/TMC membrane had a better separation performance for bivalent cations; however, EDA/TMC membrane had a poor separation performance because of defective functional layer.On the other hand, we chose polypropylene fiber membranes as supports of IP. Firstly, peroxide was introduced onto the surface of polypropylene fiber membrane through ozone treatment. The acrylamide monomer was then grafted onto the surface of the membrane via thermo-induced grafting polymerization. The effects of ozone treatment time on the mechanical properties of membrane, grafting ratio and contact angle were investigated. The results showed that ozone treatment time should not exceed 10 minutes. And then the novel structure composite membranes were prepared by IP method of MPDA with TMC on the modified PP fiber support. ATR-FTIR was employed to characterize the chemical changes of membranes. The surface and cross section morphology were studied by SEM. The nanofiltration performance was evaluated with solutions of Na2SO4 and Fast green (FCF). The results showed that under the same conditions, the composite membrane had a better nanofiltration performance when the modified PP support was more hydrophilic; the composite membrane had a better separation performance for Fast green than Na2SO4.