Preparation And Performance Of Cellulose Acetate Solvent-resistant Nanofiltration Membranes

As a new membrane separation technology,nanofiltration membrane which can realize molecular-level separation,has been widely paid attention to because of its advantages of no phase change,no pollution and simple process.However,most nanofiltration membrane separation processes are used in aqueous solution system,but few solvent-resistant nanofiltration（SRNF）membranes are used in organic solvent systems（e.g.petrochemical engineering,food processing and other fields）.At present,commercial SRNF membrane has problems such as poor solvent resistance,serious membrane pollution and high price,as a result,the development of SRNF membrane with excellent performance,good solvent resistance and stability is of great significance for large-scale industrial application.As membrane material,acetate cellulose（CA）has the advantages of low price,easy accessing,high water flux,easy processing and so on.In this paper,we chose cellulose acetate as membrane material,and prepared the positive CA/LSCF solvent-resistant nanofiltration membrane with the phase conversion method,adding appropriate amount of nano-inorganic additive LSCF to the casting membrane solution,and explored the effect of polymer concentration,LSCF content on membrane structure and separation performance.The results showed that with the increase of LSCF content,the flux of membrane increased,while the rejection of the membrane first increased then reduced,and when the LSCF content was 2 wt.%,the rejection to MgCl₂ was relatively high,reaching 46.2%,with the flux of 14.3 L/（m²·h）at 0.3 MPa;when the LSCF content was 1 wt.%,the membrane had the highest rejection to Congo Red dye,reaching 88.2%,with the flux of 4.5 L/（m²·h）at 0.2 MPa.The charge density of the membrane increased after treatment with 3-chlorine-2-hydroxypropylene ammonium chloride（TTAC）,and the test showed that the membrane had a high rejection to high valence cations.5 wt.%glutaraldehyde（GA）was used to crosslink to improve the solvent resistance of the membrane.Result showed that after immersion in 50%DMAc solution,there was no significant change in the separation performance of the membrane treated with GA,while the separation performance of the membrane without cross-linking decreased significantly,which indicated that the solvent resistance of the membrane was improved by crosslinking.In this work,we prepared the MXene/CA mixed matrix membrane with the phase conversion method,adding appropriate amount of inorganic additive MXene material to the casting membrane solution,and explored the influence rule of MXene content on membrane structure and separation performance,then tested the solvent resistance and antifouling performance of the membrane.The experimental results showed that the antifouling performance of the membrane improved after the addition of MXene,and when MXene content was 3 wt.%,the membrane had the highest rejection to salt ions and dyes.The flux of Na₂SO₄ at 0.3 MPa was 4.8 L/（m²·h）with the rejection of 89.6%;the flux of Gentian Violet solution at 0.2 MPa was 4.2 L/（m²·h）with the rejection of100%,and the membrane had the best hydrophilicity.After crosslinking with GA,the separation performance of the membrane did not decrease significantly after 12 days of immersion in 50%DMAc.