Preparation Of Mixed Matrix Membrane Based On Ag Functionalized Materials And Its Performances For Propylene/Propane Separation

Light olefins are essential feedstocks for the production of some industrially important chemicals,which propylene is second only to ethylene as an important petrochemical basic raw material.Due to the similar molecular size and close physical properties of light olefin/paraffin,the efficient separation of propylene/propane（C₃H₆/C₃H₈）is difficulty to be realized.Membrane-based technology for C₃H₆/C₃H₈separation is the current research focus and full of challenges.Mixed matrix membranes（MMMs）are a new type of separation membrane,which can combine the processability of organic polymer and the excellent performance of inorganic functional material.Besides,MMMs have received extensive attention since it can effectively overcome the trade-off effect of polymer membrane and shortcoming of inorganic membrane and the field has received extensive attention.In this study,MMMs for C₃H₆/C₃H₈separation were prepared by designing and synthesizing different Ag-functionalized materials using polymers of intrinsic microporosity（PIM-1）as the matrix.The contents of this thesis are listed as follows:（1）Ag pyrazole complexes（Ag₃pz₃）is a class of“molecular-based”functional complex that can be easily designed and regulated.Compared with traditional Ag salts,the Ag sites in Ag₃pz₃ complex exhibit better stability.The electron-withdrawing effect of substituents in the pyrazole ligand can be adjusted,through the control of pyrazole ligand in the Ag complex,to realize the regulation ofπ-acidity/basicity of Ag₃pz₃ and the activity of Ag site.Meanwhile,the selection of different substituents also has a great influence on the crystal structure and solubility of Ag₃pz₃.Ag₃pz₃ complexes can be dissolved in the certain organic solvent and exist in solvent at molecular level.Quantization calculation results shows that the stronger the electron-withdrawing effect,the stronger theπ-acidity of the Ag₃pz₃ complex,which is in consistent with the design expectation.The simulation results will provide some theoretical instruction for C₃H₆/C₃H₈ separation using Ag₃pz₃ complex.（2）Based on the“molecular type”structure of Ag₃pz₃ complexes,three kinds of Ag₃pz₃ based mixed matrix membranes were prepared using polymer of intrinsic microporosity（PIM-1）as the polymer matrix.Among them,the size of Ag₃pz₃-2 in the Ag₃pz₃-2/PIM-1 mixed matrix membrane is about 7 nm.The uniformly dispersion of the“molecular-based”filler in the“porous”polymer can effectively avoid the filler agglomeration problems and interface defects in the mixed matrix membrane.This novel mixed matrix membrane with molecular-based Ag₃pz₃ complex as functional filler is very stable and exhibits excellent C₃H₆/C₃H₈ separation performance,overcoming the trade-off effect of polymer membranes.For the optimum membrane,the single-component gas permeation test results show that the C₃H₆ permeability coefficient is 1299 Barrer and the C₃H₆/C₃H₈ selectivity is 25.9.The mixed gas permeability test results show that the C₃H₆ permeability coefficient is 1308 Barrer,and the C₃H₆/C₃H₈ selectivity was 20.5.This new type MMMs based on Ag functionalized materials may provide new ideas for the design of alkanes/alkanes separation membranes.（3）ZIF-8 is an ideal MOFs material for C₃H₆/C₃H₈ separation and Ag₃pz₃ complex shows favorable affinity towards C₃H₆.Thus,in this chapter,a ZIF-8@Ag₃pz₃composite material was designed and incorporated into PIM-1 matrix to prepare ZIF-8@Ag₃pz₃/PIM-1 MMMs.The ZIF-8@Ag₃pz₃ composite material combines theπ-acidity/basicity interaction of Ag₃pz₃ complex with C₃H₆,and the molecular sieving effect of ZIF-8 for C₃H₆/C₃H₈,which can effectively improve the gas permeability of the pure polymer.The best performance MMMs shows a C₃H₆ permeability of 3767Barrer and C₃H₆/C₃H₈ selectivity is 11.7 in single-gas test.While a C₃H₆ permeability of 3708 Barrer and C₃H₆/C₃H₈ selectivity is 9.5 is obtained in mixed-gas test.（4）To fully utilize the Ag facilitated C₃H₆ transport effect and the ideal kinetic selectivity of ZIF-8 for C₃H₆/C₃H₈,the Ag functionalization of ZIF-8 is carried out.According to the different coordination ability of Ag⁺/Zn²⁺with N in imidazole,the ZIF-8@Agmim hybrid material with core-shell structure was synthesized using a post-synthesis ion exchange method.The hybrid material with the core-shell structure shows excellent photostability and excellent C₃H₆/C₃H₈ adsorption kinetics.The as-prepared ZIF-8@Agmim/PIM-1 mixed matrix membrane exhibits outstanding C₃H₆/C₃H₈separation performance together with long-term stability,which can be attributed to the synergistic effect of kinetic C₃H₆/C₃H₈ separation of ZIF-8 in inner core and the facilitated C₃H₆ transport of Agmim in outer thin shell.In a word,the core-shell structure of ZIF-8@Agmim could provide an efficient C₃H₆ molecular transport channel in MMMs,which makes the C₃H₆ permeability coefficient reach to 4143 Barrer while maintaining the high selectivity.