Structure Regulation And Performance Optimization Of Solvent Resistant Nanofiltration Membrane Based On The Functionalizedized Silicon Materials

Organic solvent nanofiltration (OSNF) as an emerging technology uses selective membrane as a medium to separate and purify organic solvent mixture. Due to its easy to operate, green and efficient, OSNF receives extensive attention. The core component of the OSNF system is the OSNF membrane, which should simultaneously possess good solvent resistance ability and separation performances. The structure of membrane which depends on the membrane material and the preparation method, is the key to determine its solvent resistance ability and separation performances. In this study, we coupled hybridizing technology with cross-linking technology via interfacial polymerization for preparing two types of hybrid composite film, using functionalized silicon materials (polydimethylsiloxane, functionalized silica nanospheres) to regulate the structure of polyetherimide (PEI) membrane. The Composition and microstructure of composite membranes were investigated using SEM, TEM, FTIR, TGA, DSC, contact angle measurement and tensile testing. The solvent resistance ability and separation performances of the membrane were investigated in detail. The relationship between membrane material-membrane structure-membrane performance were proposed for providing some theoretical basis and technical support for the application of different organic solvent nanofiltration systems.The main works and conclusions in this paper are as follows:1. PAN/PEI-PDMS hybrid composite membranes were prepared via interfacial polymerization by using polyacrylonitrile(PAN) ultrafiltration membrane as support, polyethyleneimine(PEI) as aqueous monomer, polydimethylsiloxane (PDMS) as organic monomer, and trimesoyl chloride (TMC) as cross-linker. The FTIR results showed the amide bond which generated by the polymerisation reaction between PEI and TMC had produced in the active layer, which indicated polyamine layer has been coated upon the surface of PAN support successfully. SEM images showed the active layer can be observed clearly and formed precisely on upper surface the PAN support. It verified the formation of polymer-inorganic composite membrane through interfacial polymerization. The tests results showed that, the increasing amount of PDMS and the extension of polymerization time led to the reduced solvent uptake and area swelling as well as flux decline of all as-prepared membranes, while elevated rejecton. When the amount of PDMS up to1.0wt%, and120s of polymerization time, the prepared membrane flux of acetone could be attained10L/m2h under operating pressure of4bar, while the rejection of PEG200still remained at more than92%. In addition, the rejection of lotus seedpod procyanidins was higher than94.5%in the ethanol-water system. In conclusion, the PAN/PEI-PDMS hybrid composite membrane prepared by coupling cross-linking with hybridizing techniques, revealed excellent solvent resistance property in polar organic solvents (ketones and esters) and good separating effect for organic molecule whose molecular weight over200.2. Silica-polymer spheres with four various functional groups on the surface(SiO2-OH, SiO2-SO3H, SiO2-C6H6, SiO2-Py) were prepared by surface modified based on silica nanospheres which were prepared through St ber method; PAN/PEI-XSi hybrid membranes (PAN/PEI-Si, PAN/PEI-SSi, PAN/PEI-CSi, PAN/PEI-NSi) were prepared by incorporating functionalized silica nanospheres into PEI matrix through interfacial polymerization with TMC, and finally, the compound layer was formed on PAN membrane.The SEM results showed that, the average diameter of silicon nanospheres were about210nm, and the thickness of surface polymer layer after modified were about5nm, the modified nanospheres can be evenly dispersed in polymer matrix. The results of TGA and DSC showed that, the glass transition temperature and thermal degradation temperature of membranes were increased, in order, PAN/PEI-NSi, PAN/PEI-Si, PAN/PEI-CSi and PAN/PEI-SSi. The results of contact angle measurement revealed that, hydrophilicity of hybrid membranes were improved after blending with silicon-spheres. Five kinds of solvents: ethanol, acetone, ethyl acetate, n-heptane and toluene were selected to test the solvent resistance and separation performance of membranes. The results indicated that, the existence of the inorganic phase in the hybrid membrane reduced the membrane adsorption of solvent, and the area of swelling degree were below4.0%.The flux of both polar and nonpolar solvents were improved greatly compared to PAN/PEI membrane, among them, for PAN/PEI-Si membrane, the flux of ethanol and ethyl acetate raised from9.2and12.5L/m2h to21.6and23L/m2h respectively; and the flux of n-heptane, toluene raised from0to23and4L/m2h respectively. For PAN/PEI-SSi membrane, the flux of ethanol and ethyl acetate raised to23and50L/m2h respectively; and the flux of n-heptane, toluene were29and1L/m2h respectively. The retention of hybrid membrane had declined，however, retention for PEG1000of PAN/PEI-NSi and PAN/PEI-CSi membranes were remained90%, and retention for PEG1000of PAN/PEI-Si and PAN/PEI-SSi membranes were84%and81%respectively. These results demonstrated that the hybrid membranes had flux for both polar and nonpolar solvents after filling silicon nanospheres, which illustrated a wide practicability in solvents; The silica spheres with various functional groups had an different impact on the membrane structure and performance, and the laws discovered in this experiment established the foundation for continued research.