Preparation Of PES Hollow Fiber Loose Nanofiltration Membrane And Study Of Its Dye/salt Separation Properties

Loose nanofiltration membranes have excellent performance in the selective separation of dyes and inorganic salts,and have good prospects for the resource treatment of printing and dyeing wastewater.Hollow fiber membranes have attracted a lot of attention from researchers in recent years due to their high packing density and self-supporting structure,their high resistance to contamination and low replacement cost.However,hollow fiber nanofiltration membranes have high curvature and high stress surface properties,so they are challenging to precisely regulate and scale up the preparation of separation layer.Therefore,this study proposes a strategy of coupled interfacial assembly by dry-wet spinning method to prepare hollow fiber loose nanofiltration membranes（LNM）,and the hollow fiber LNM with good hydrophilicity,stable filtration performance and contamination resistance was prepared by using PES as the membrane forming polymer,and the conditions affecting its structure and separation performance were investigated,and the main research contents and conclusions are as follows:（1）The hollow fiber LNM was prepared by simultaneous coordination assembly during the dry-wet spinning process,and the PES/Fe-TA hollow fiber LNM was produced by in situ coordination assembly of co-mingled metal ions in the spinning solution and tannic acid（TA）in the core solution on the inner side of the hollow fiber membrane.The effects of core solution concentration and air bath height on the morphological structure of the membrane surface and the separation performance of dyed salts were investigated.The results showed that a homogeneous functional layer of TA-Fe polymerization network was successfully formed on the inner surface of the hollow fiber membrane.The optimized preparation conditions were 21 cm air bath height and 1.5 g/L core liquid concentration,under which the membrane achieved a pure water flux of 136.1 L·m^-2·h^-1 at 0.1 MPa and a retention rate of 99.8%for chromium black T dye and less than 7%for inorganic salts,showing excellent dye and salt separation.（2）PES/Fe-TA-PEI hollow fiber LNM was prepared by chemical cross-linking reaction between polyethyleneimine（PEI）and TA on the PES/Fe-TA hollow fiber LNM.The charge property of the membrane surface was changed and thickness of the separation layer increased with introduction of PEI.The PES/Fe-TA-PEI hollow fiber LNM was prepared under optimal conditions with a pure water flux of 106 L·m^-2·h^-1 at 0.1 MPa,and the retention rates of Congo Red,Alcian Blue and Bromophenol Blue were 99.7%,98.4%and 86.4%,respectively,and the retention rates of Sodium Chloride,Sodium Sulfate,Magnesium Sulfate and Magnesium Chloride were 3.9%,4.2%,6.3%and 7.8%,respectively.A up to 24 h filtration test of the dye/salt mixture was also conducted,and the results showed that the membrane retained more than 98%of the dye Alcian Blue and less than 4.5%of Sodium Chloride.Meanwhile,the membrane also showed good dye and salt separation and stable permeate flux in strong acidic and alkaline environments.This study provides theoretical guidance and technical support for the development of new hollow fiber nanofiltration membranes for printing and dyeing wastewater treatment.