Preparation And Properties Of Modified Pervaporation Membranes For Ethanol-Water/Isopropanol-Water Separation

Pervaporation（PV）is an efficient membrane separation technology,which uses the chemical potential difference between the upstream and downstream of the membrane as the driving force to achieve mass transfer,and uses the different affinities between the components in the feed liquid and the different mass transfer resistances in the membrane to achieve effective separation of alcohol-water mixture.How to construct new membrane materials with high permeability and high selectivity is one of the hot issues in this field.In this paper,graphene oxide（GO）and polyimide（PI）are used as basic materials to prepare two kinds of modified pervaporation membranes for separation of ethanol-water and isopropanol-water system by adjusting the structure of GO or PI membranes.The main research results are as follows:（1）Taking advantage of difference in the reactivity of phenylenediamine isomers,o-phenylenediamine（OPD）,m-phenylenediamine（MPD）and p-phenylenediamine（PPD）are selected to react with oxygen-containing functional groups of GO nanosheets,and then the phenylenediamine modified GO membranes are prepared by vacuum filtration.The effect of the structure of phenylenediamine on the separation performance of modified GO pervaporation membranes for ethanol-water mixture is investigated.The results show that phenylenediamine can react with the oxygen-containing functional groups of GO and adjust the channel between GO nanosheets.OPD can effectively expand the interlayer spacing and increase the hydrophilicity of GO membrane,and has better pervaporation performance than MPD modified GO membrane and PPD modified GO membrane.The GO-OPD-10 membrane has the best separation performance for 90 wt%ethanol-water mixture at 50°C:the permeation flux is 549 g m^-2 h^-1,which is 1.25 times that of the pristine GO membrane;the separation factor is90.58,which is 1.14 times that of the pristine GO membrane.（2）Taking advantages of high selectivity properties of PI and high hydrophilicity characteristics of imidazolium-based ionic liquid,using PI as basic membrane material,1-vinyl-3-butylimidazolium bromide（VBIMBr）as modified monomer,divinylbenzene（DVB）as crosslinking agent and azobisisobutyronitrile（AIBN）as initiator,VBIMBr is polymerized in PI solution by in situ polymerization.Imidazolium-based ionic liquid modified PI membrane（PI/c-P（VBIMBr））is prepared by casting and used for pervaporation separation of isopropanol-water system.The results show that the introduction of crosslinked copolymer of VBIMBr and DVB（c-P（VBIMBr））increases the surface hydrophilicity,water swelling degree and flexibility of PI membrane,and thus improves the pervaporation performance of PI membrane for isopropanol-water system.Among all modified membranes,PI/c-P（VBIMBr）-15 membrane has the best separation performance for 90 wt%isopropanol-water mixture at 50°C:the permeation flux is 116 g m^-2 h^-1,which is 2.25 times that of the pristine PI membrane;the separation factor is 163.19,which is 1.18 times that of the pristine PI membrane.Using the advantages of two materials to achieve the improvement of membrane separation performance,which will provide a general strategy for constructing other high-efficiency pervaporation membrane materials.