Preparation And CO₂ Separation Performance Of ZIF-8-IPTMS Induced Zeolitic Imidazolate Framework Membranes

The importance of carbon capturing,utilization and storage（CCUS）is increasingly prominent due to the worsening global warming.The separation of CO₂ from exhaust gas streams is high-profile because it is indispensable in CCUS process.Among the methods that can achieve the effective separation of CO₂,membrane separation technology stands out with its advantages of low-energy and continuous and stable operation.As a subclass of metal-organic frameworks（MOFs）,the pore size of zeolitic imidazolate frameworks（ZIFs）is comparable with the gas kinetic diameter.This provides ZIF membranes the promising application prospect in the field of the gas separation.In view of the extremely high requirements for performances of the gas permeability and separation,scale and operation stability of ZIF membranes in actual industrial applications,the effective and innovative methods to synthesize ZIF membranes becomes the current research focus.Thus,the synthesis strategy was proposed in this paper through using amine solid adsorbent to repair the surface defects of the macroporous support and induce the preparation of ZIF membranes in this paper.The amine-based solid adsorbent not only provided sufficient heterogeneous nucleation sites for the growth of ZIF membranes on the support surface but also improved the CO₂ permeability of as-prepared ZIF membranes due to its abundant amino groups and relatively high CO₂ adsorption capacity.Thus,ZIF membranes with excellent CO₂ separation performance were successfully prepared.The main research contents and results in this paper are outlined as follows:1.Surfaces of macroporous supports were modified by different methods,including depositing functional inorganic particles and depositing Ti O₂ liquid sol.And then ZIF-8 membranes were successfully prepared on the modified surface of these supports by the in-situ method with the thickness about 13.5μm,8μm,4μm and 3.5μm,respectively.The influence of test temperature and feed gas pressure on the H₂/CO₂ separation performance of ZIF-8 membranes was explored through the gas permeation experiment.It can be found that the gas separation performance of the ZIF-8 membrane was the best,which was prepared on the surface of macroporous support repaired by depositing functionalα-Al₂O₃-APTMS-Hm IM inorganic particles.The ideal H₂/CO₂selectivity of the as-prepared ZIF-8 membrane was 8.24,while the permeance of CO₂ was maintained at approximately 4.68×10^-8 mol·m^-2·s^-1·Pa^-1 at 90℃and0.1 MPa.In addition,the separation factor of the equimolar binary H₂/CO₂ was6.92,while the permeance of CO₂ was maintained at approximately 4.53×10^-8mol·m^-2·s^-1·Pa^-1 at 90℃and 0.1 MPa.2.ZIF-8 seeds were deposited onto the surface of the macroporous support with the help of the silane coupling agent,and then ZIF-8 membranes were successfully prepared by the seeded growth method with the thickness about 2μm,1.8μm,1.6μm and 1.2μm,respectively.The effect of different silane coupling agents and various weight concentrations of ZIF-8 crystals on the growth of the ZIF-8 membranes were explored in this work.The experimental results showed that the growth effect and H₂/CO₂ separation performance of the ZIF-8 membrane was the best,which was prepared on the surface of the macroporous support modified by coating 0.1 wt%ZIF-8 crystals with the help of the 3-isocyanatopropyltrimethoxysilane（IPTMS）coupling agent.The ideal H₂/CO₂ selectivity of the as-prepared ZIF-8 membrane was 7.96,while the permeance of CO₂ was maintained at approximately 8.71×10^-7 mol·m^-2·s^-1·Pa^-1at 90℃and 0.1 MPa.Additionally,the separation factor of the equimolar binary H₂/CO₂ was 6.01,while the permeance of CO₂ was maintained at approximately6.51×10^-7 mol·m^-2·s^-1·Pa^-1 at 90℃and 0.1 MPa.3.The novel spherical porous hybrid material（ZIF-8-IPTMS）,which was synthesized with the reaction between the ZIF-8 crystals and IPTMS,was used to repair surface defects of the macroporous support and induce the preparation of ZIF membranes.The ZIF-8 membrane and ZIF-67 membrane were successfully synthesized with the thickness of approximately 0.9μm and 1.2μm,respectively.It can be found that the gas separation performance of the as-prepared ZIF-8 membrane is better than that of the as-prepared ZIF-67membrane.The ideal H₂/CO₂ selectivity of the as-prepared ZIF-8 membrane reached 13.8,while the permeance of CO₂ was maintained at approximately1.05×10^-6 mol·m^-2·s^-1·Pa^-1 at 90℃and 0.1 MPa.In addition,the separation factor of the equimolar binary H₂/CO₂ was 9.2,while the permeance of CO₂ was maintained at approximately 9.02×10^-7 mol·m^-2·s^-1·Pa^-1 at 90℃and 0.1 MPa.4.The class 1 and class 2 amine-based solid adsorbents were synthesized by modifying ZIF-8-IPTMS hybrid materials with the polyethyleneimine（PEI）and N-[（3-trimethoxysilyl）propyl]diethylenetriamine（3N-APS）,respectively.And then,the ZIF-8-IPTMS-3N-APS-15 was selected to repair surface defects of the macroporous support and induce the preparation of the ZIF-8 membrane,which possessed the highest amount of amino grafting among the as-prepared amine-based solid adsorbents.The ZIF-8 membrane with the thickness of approximately 0.6μm was successfully synthesized,which realized the effective combination of the amine-based solid adsorbent and the ZIF-8membrane.The separation factors of the binary CO₂/N₂（v/v,15/85）and CO₂/CH₄（v/v,15/85）were respectively 3.74 and 4.91,while the permeances of CO₂ were maintained at approximately 3.49×10^-6 mol·m^-2·s^-1·Pa^-1 and 3.36×10^-6 mol·m^-2·s^-1·Pa^-1 respectively at 35℃and 0.1 MPa.In summary,ZIF-8 membranes were successfully prepared,which were suitable for the separation of H₂/CO₂ and CO₂/N₂,CO₂/CH₄ respectively in this experiment.Most importantly,the research idea of preparing ZIF-8 membranes induced by the amine-based solid adsorbent was put forward.This idea can not only significantly improve the CO₂ separation performance of the as-prepared ZIF-8 membrane,but also avoid the regeneration process in the application of adsorptive CO₂ separation of the amine solid adsorbent.The whole membrane system can realize continuous and stable operation in the process of CO₂separation.This result can provide a new idea for the synthesis of ZIF membranes,and it is significant for industrial applications of ZIF membranes in the future.