Preparation And Performance Studies Of Polydimethylsiloxane-Based Pervaporation Membranes For Alcohol Recovery

Membrane-based pervaporation is considered as an advanced technique for liquid-liquid separation in virtue of its high separation efficiency,mild operation conditions,low energy consumption,etc.Polydimethylsiloxane(PDMS)owns excellent hydrophobicity,organophilicity,chemical stability,and membrane-formation ability,but the alcohol/water separation performance has yet to be improved.In this thesis,the PDMS membrane structure was modulated in terms of both the introduction of the pore-containing particles and optimization of the crosslinked structure to enhance alcohol/water separation performance of PDMS membrane and to reveal the structure-properties relationships and separation mechanism of the prepared PDMS-based membranes.(1)Amine-modified zeolite imidazolate framework-8(AZIF-8)particles were prepared by displacing the organic ligand strategy,and then embedded into hydroxyl terminated PDMS(HPDMS)matrix to fabricate the covalently crosslinked AZIF-8@HPDMS mixed matrix membrane(MMM)by one-step method.The developed AZIF-8@HPDMS MMM achieved an ethanol/water separation factor of 17.7,a total flux of 585.6g/m~2·h,and good long-term stability when separating a 5 wt%ethanol aqueous solution at 40℃.The covalent crosslinking strategy eliminated interfacial defects between AZIF-8particles and the HPDMS matrix and improved the dispersion of AZIF-8 particles within the membrane,thereby enhancing the total flux and separation factor of PDMS membrane.(2)ZIF-8@GO composite particles with highly-selective transport paths were prepared by growing ZIF-8 particles in situ on the surface of graphene oxide(GO)and modulating their mass ratio,and then introduced into HPDMS matrix to prepare high-performance HPDMS/ZIF-8@GO MMM.When separating a 5 wt%ethanol aqueous solution at 40℃,the prepared MMM exhibited an ultra-high ethanol/water separation factor(22.2)and good total flux(443.8 g/m~2·h),superior to that of other PDMS-based MMMs in the literature.The introduction of ZIF-8@GO composite particles provided a highly-selective transfer path within the PDMS membrane,significantly improving the separation factor of PDMS membrane.(3)A novel PDMS-based viscoelastic membrane with controllable crosslinking structure was prepared by polycondensation reaction between bis(3-aminopropyl)terminated PDMS(APDMS)and highly reactive crosslinker 3/4 trimesoyl chloride(TMC).APDMS-TMC viscoelastic membrane exhibited ultra-high total flux(5.8 kg/m~2·h)and excellent ethanol/water separation factor(8.9)when separating 5 wt%ethanol aqueous solutions at 80℃,outperforming the separation performance of conventional PDMS-based elastic membranes.The membranes also showed good long-term stability.The regulation of the crosslinking density within the membrane optimized the flexibility of the polymer molecular chains and the free volume within the membrane,significantly enhancing the total flux of PDMS membrane.(4)The hydrogen-bonding crosslinked PDMS-based supramolecular membranes were prepared by the condensation reaction between PDMS macromers(APDMS and HPDMS)and diisocyanate coupling agent,which changed the crosslinked structure of conventional PDMS membranes.The resultant PDMS-based supramolecular membrane exhibited the optimal ethanol recovery performance(total flux of 4.1 kg/m~2·h and ethanol/water separation factor of 8.5)and n-butanol recovery performance(total flux of 7.8 kg/m~2·h and n-butanol/water separation factor of 14.2)in separating 5 wt%alcohol aqueous solution at 80℃.The membranes also showed good long-term stability.The strategy of hydrogen bonding crosslinking in replace of the traditional covalent crosslinking improved the flexibility of the polymer chains,thereby facilitating the rapid transport of permeate molecules.