Developing High-performance Thin-fim Composite (TFC) Hollow Fiber Membranes For Alcohol Dehydration Via Pervaporation

Membrane-based pervaporation technology,has been widely concerned by researchers because of its strengths of low energy consumption,environmental benignity and outstanding separation efficiency.Compared with other traditional separation processes,pervaporation can break the limit of vapor-liquid equilibrium and achieve excellent separation efficiency,especially for azeotrope liquid mixtures or those with close boiling points.To obtain a desirable pervaporation performance,it is crucial to design and prepare appropriate membranes as the separation medium.Thin film composite（TFC）membrane,as one of typical polymer membrane,can be prepared by interfacial polymerization to form an ultrathin polyamide selective layer on the top of the porous substrate.Hollow fiber membrane can be used as substrate to obtain a high permeability flux,but the polyamide selective layer is relatively hydrophobic and not dense enough,leading to insufficient separation selectivity and limiting the application of TFC membranes for alcohol dehydration.In this thesis,the secondary interface polymerization（SIP）of TFC membrane is performed in order to optimize the chemical structure and surface morphology of the selective layer and thus solving above problems.In this thesis,hollow fiber membrane with optimized morphology is firstly prepared as substrate,followed by a relatively hydrophobic TFC-control membrane is prepared on substrate by IP reaction between amine and acyl chloride monomers.Finally,β-cyclodextrin（β-CD）with strong hydrophilicity and multiple hydroxyl groups is employed for SIP modification of TFC membrane,to form an additional hydrophilic selective layer and provide a transport channel for water molecules,thereby enhancing dehydration performance.Based on the above work,in view of the poor reactivity of the hydroxyl groups ofβ-CD with acyl chloride,3 kinds of amine-CDs are further synthesized by modifyingβ-CD with ammonia（NH4OH）,ethylenediamine（EDA）and tris（2-aminoethyl）amine（TAEA）,respectively,and employed for the SIP reaction of TFC membrane.The characterization of chemical properties of amine-CDs and SIP-modified TFC membranes shows that among three successfully synthesized amine-CDS,CD-EDA possess the largest grafting degree and the largest loading amount on the surface of SIP-modified TFC membranes,bringing the largest cross-linking degree,the highest hydrophilicity and the thinnest selective layer.Moreover,the effects of amine-CD type and SIP parameters（pH or concentration of CD-EDA solution）are systematically studied to acquire the optimized selective layer of TFC membranes for ethanol dehydration at 50℃ with 85 wt%ethanol as feed solution.The optimized TFC membrane exhibits the most outstanding separation performance with an ultra-high permeation flux of 3018.0 g·m^-2·h^-1 and separation factor of 415,contributed by the incorporation of CD with rich hydrophilic functional groups and intrinsic nanocavities,improving the hydrophilicity of the membrane and providing a transport channel for water molecules.