Study Of The Preparation And Performance Of Polyamide/Polyetherimide Composite Nanofiltration Membranes

Nanofiltration(NF),as a relatively new membrane separation technique,is a pressure-driven membrane filtration process between ultrafiltration and reverse osmosis,with a molecular weight cut-off(MWCO)ranging from 200 to 1000.NF with advantages of low operation pressure,low energy consumption,high permeance and high rejection has been applied for water treatment,biological pharmaceutical industry,food industry and petrochemical industry.Interfacial polymerization is the commonly-used method for preparing composite NF membranes,and polyamide thin film composite(TFC)NF membranes are the most popular form of commercial nanofiltration membranes.However,during the development of NF membranes applied from aqueous solution system to organic solvent system,some problems have been occured for the polyamide TFC NF membranes,such as low rejection towards low-molecular-weight organics,low permeance,inferior chlorine resistance and inferior solvent resistance.To solve the above problems,in this article,the methods for improving the seperation permeance,chlorine resistance and solvent resistance of polyamide TFC NF membranes were investigated by using appropriate reaction monomers,preparation and modification methods.Firstly,poly(amic acid)TFC NF membranes were prepared on polyetherimide supports by the interfacial polymerization of 1,2,4,5-benzene tetracarbonyl chloride and m-phenylenediamine followed by modification with ethylenediamine.Polyamide TFC NF membranes with stable structure and low MWCO were prepared.The optimal polyamide TFC NF membrane exhibits a glucose rejection of 90.0% and a water permeance of 25.0 L m-2 h-1 MPa-1.After being immersed in a 200 ppm NaClO solution for 100 h,the polyamide TFC NF membrane demonstrates superior chlorine resistance due to the introduction of the methylene group into the structure of the polyamide membrane.Secondly,a polyamide TFC NF membrane with high permeance was prepared by the interfacial polymerization of 1,2,4,5-benzene tetracarbonyl chloride on the cross-linked polyetherimide support via the mixed amines of the linear ethylenediamine and the branched poly(ethyleneimine).The optimal polyamide TFC NF membrane thus prepared exhibits a glucose rejection of 98.0% and a water permeance of 58.5 L m-2 h-1 MPa-1.After the polar solvent activation,the polyamide TFC NF membrane exhibits a glucose rejection of 96.0% and a water permeance of 112.2 L m-2 h-1 MPa-1.Lastly,solvent resistance of the two aforementioned polyamide TFC NF membranes was investigated.The polyamide TFC NF membrane with mixed amines cross-linked support exhibits a rose bengal(RB)rejection of 99.9% and a methanol permeance of 14.2 L m-2 h-1 MPa-1.After the polar solvent activation,the polyamide TFC NF membrane exhibits a RB rejection of 90.4% and a methanol permeance of 30.4 L m-2 h-1 MPa-1.Combined with the experimental characterization,the effects of the solvent activation on the structure and performance of polyamide TFC NF membranes were investigated,as well as the structure changes of the polyamide TFC NF membranes in the solvents.Instead of the branched poly(ethyleneimine)monomer,p-xylylenediamine was selected to prepare the polyamide TFC NF membrane with solvent resistance.The polyamide TFC NF membrane exhibits a RB rejection of 96.0% and a DMF permeance of 0.7 L m-2 h-1 MPa-1.The separation performance of the polar solvent for the polyamide TFC NF membranes was improved effectively by the introduction of the hydrophobic rigid groups.