Construction And Separation Performance Of A Solvent-resistant Polyimide Membrane With A Siliceous Sponge-like Structure

Solvent-resistant nanofiltration membranes have become one of the academic frontiers and research hotspots in the field of separation membranes.The development of solvent-resistant nanofiltration membranes is of great practical significance for solving the increasing separation needs in chemical,pharmaceutical and other fields.However,traditional nanofiltration membranes still exist common problems such as low permeation flux and easy swelling in an organic solvent environment,and problems such as membrane pore shrinkage,permeation flux attenuation and unstable separation performance are prone to occur during long-term use.Inspired by the special structure of siliceous sponge formed by the growth of multi-stage silicon dioxide in organisms,this paper uses polyimide(PI)as the matrix membrane material,starting from the intermediate link of PI synthesis,and introducing tetraethyl silicate(TEOS)to construct a three-dimensional interwoven siliceous sponge structure with"silica hard phase-polymer soft phase"in the membrane in situ to prepare a polyimide silica(PI/SiO₂)modified membrane.Realize the stability of the membrane in the organic solvent environment,and study its application characteristics in dye wastewater treatment and other occasions.Related research can enrich the preparation strategies of solvent-resistant nanofiltration membranes and the basic theories of membrane structure regulation.The main research contents and conclusions are as follows:(1)Construction of solvent-resistant polyimide membrane with siliceous sponge structure.FTIR,EDX,XPS and SEM were used to analyze the molecular structure and microstructure of the membrane material before and after the modification,which proved the successful introduction of SiO₂ in the membrane and the successful preparation of PI/SiO₂ modified membrane.The solvent resistance,mechanical properties and separation properties of the membrane were investigated.The results showed that under the condition of 21%TEOS content,the comprehensive performance of PI/SiO₂ modified membrane is higher.A comparative experiment was designed to investigate the pore shrinkage and flux attenuation of the pure polyimide membrane and the 21%PI/SiO₂ modified membrane in the typical organic solvent separation process and to analyze the influence of the internal structure of the membrane on the overall performance of the membrane.The crosslinking degree of the pure membrane and the modified membrane were 8.9%and 88.89%,respectively.The swelling degree of the modified membrane in different organic solvent environments was about 30%,which was greatly reduced compared with the pure membrane and the mechanical strength was 2.34 MPa,which is 0.77 MPa larger than the pure membrane.The improvement of membrane performance is mainly due to the construction of a siliceous sponge structure.(2)Application characteristics of siliceous sponge structure membrane in separation of dye/inorganic salt.Through post-treatment,the structure of the membrane was further optimized,and the permeation flux of the membrane was increased.In particular,its application characteristics in the dye/inorganic salt separation system were investigated.The results showed that the post-treatment had an important influence on the improvement of membrane structure and separation performance.When the heat treatment parameter of PI/SiO₂ modified membrane was at 50?for 8 min,its pure water permeation flux reached 152.87 L·m^-2·h^-1·bar^-1.The rejection of Congo Red(CR),Coomassie Brilliant Blue(CBB),Direct Black 38(DB38)and Triphenyl Blue(TB)were 91.21%,98.20%,97.55%and 99.51%,respectively,and the corresponding permeation fluxes were 133.76,95.54,110,and 84.21L·m^-2·h^-1·bar^-1.The rejection of Na₂SO₄ and Na Cl,the typical inorganic salts in dyes,was less than 10%,showing an excellent dye/inorganic salt separation effect.And when the inorganic salt concentration was 2?30 g·L^-1 and under 18 h continuous operation conditions,it had good separation performance for the dye/inorganic salt mixed solution system.The optimized PI/SiO₂ modified membrane has good application characteristics in the dye/inorganic salt separation system.