Research On Porous Materials And High-performance Mixed Matrix Membranes For Separation Applications

At present,the global energy structure is still dominated by traditional fossil fuels.Energy conservation and emission reduction in energy consumption as well as the efficient utilization of traditional fossil fuels are the long-term major problems in the process of sustainable development.Membrane separation,as a new separation technology,has the advantages of high efficiency,energy saving,environmental friendliness and less occupation area.In recent years,it has become one of the research hotspots in the field of chemical separation.Mixed matrix membranes(MMMs)combining the mechanical properties,processability and low-cost of the polymer with the permeability and selectivity of the filler,has attracted the attention of many researchers,especially in the fields of mixture gas separation and dye wastewater treatment.However,the interface compatibility between filler and polymer matrix,the singleness of separation system and the difficulty in fully using the properties of membrane materials limit the further application of MMMs.In this paper,in order to broaden the separation system application range of porous material and enhance the gas separation performance of MMMs,we made a systematically study on the pore size regulation of nanoporous materials,the influence of functional groups on separation performance and theoretical simulation,the precise control of interfacial gap between polymer and filler interface,and the construction of pore structure.The main research contents are as follows:(1)we proposed an air-steam etched strategy by controlling protonation reaction between the imidazole in metal-organic frameworks(MOFs)and water vaporand for preparing ZIFs(H-ZIFs)with mesoporous structure,such as H-ZIF-8,H-ZIF-14,H-ZIF-69,and H-ZIF-71.During the etching process,water vapor is used to control the H-ZIFs pore structure by adjusting the etching time and etching temperature;(2)we combined theoretical simulation with experimental verification method to explore the influence of fillers containing different functional groups on membrane separation performance.Three kinds of IL@ZIF-8 composites with different microenvironments are designed,three of which contain different functional groups(-CH₃,-SO₃H,and-NH₂).Molecular simulation results showed that the addition of IL increased CO₂ adsorption capacity and CO₂/CH₄ selectivity.Then,the experiment of the synthesis of IL@ZIF-8 was conducted by free-solvent mechanochemical synthesis method and IL@ZIF-8/Pebax^?1657 MMMs were prepared.The prepared IL@ZIF-8MMMs showed the gas permeability was almost constant and the selectivity of CO₂/CH₄ increased from 16.4 to 35.2;(3)we proposed an interface self-assembly strategy of MMMs to realize the enhancement for membrane separation performance by utilizing interface defects between the polymer and the filler.First,a series of hydrophobic halogen induced metal polymer(HMP)fillers were prepared in situ on the hydrophilic organic interface layer.And hydrophilic polymer PVAm was further coated on the filler particles to form regular gaps between the PAVm matrix and the HMP particles and high-speed gas transport channels were in-situ constructed.The gap sizes were tuned from 0.76 nm to1.20 nm by regulating the electronegativity differences between the fillers and PVAm.Mixed matrix membranes has excellent gas separation performance.The CO₂permeance of PVAM-HMP(F)/MPSF membrane is 1800-1900 GPU,and the CO₂/N₂selectivity is 65-69;(4)we preparaed a series of new halogen-induced porous coordination polymers(H-PCPs)MMMs which has the characteristics of adsorption capacity selection.The H-PCPs synthesized by using Zr⁴⁺and X-isophthalic acid(where X=Cl or Br)exhibit increased gas adsorption capacity with the increase in carbon number and without adsorption of H₂,which realized that the preferred separation of C₁-C₄ alkane gas prior to H₂.Then,H-PCPs were used to fabricate MMMs.The permeances of the MMMs show that the of high adsorption separation behavior,and the selectivity for C₄/H₂,C₃/H₂,C₂/H₂,and C₁/H₂ can reach?40,?15,?5,and?2 respectively.Compared with H₂-preferential permeation membranes,the prepared MMMs realized the preferential penetration of large-size gas,which is expected to promote the application of membrane separation technology in the purification of low carbon hydrocarbon;(5)Futhermore,the synthesized H-PCPs were extended to the separation other systems,and showed good ideal selectivity for CO₂/N₂ and CO₂/CH₄.The H-PCPs has good dispersion in the polymer matrix,and it is incorporated into the polysulfone(PSf)matrix to prepare MMMs for CO₂ separation.The prepared MMMs can effectively separate CO₂.In particular,the MMMs incorporated with 15 wt%5-Cl-PCP display the CO₂/CH₄,CO₂/N₂ selectivity of 49.60,59.42,respectively.