Preparation And The Study Of CO₂/N₂ Separation Performance Of Polyether Block Amide ?PEBA? Based Mixed Matrix Membranes

As one of greenhouse gas,CO₂ separation and purification is one of important methods to solve greenhouse effect,which has been an important part of green chemistry research.Compared with traditional methods,gas separation membrane has many advantages,such as simple equipment,easy operation,high efficiency,low energy consumption,etc.Mixed matrix membranes?MMMs?are composite membranes consisted of nano/micro-sized fillers,usually more selective,dispersed homogeneously in a continuous polymer phase.They merge desirable properties from both polymeric membranes and inorganic membranes:high permeability and selectivity of inorganic membranes?molecular sieve mate-rials?and cost and processing convenience of polymeric membranes.The incorporated fillers play an important role in design of MMMs,since their morphologies,structures,physical and chemical properties,and interaction with CO₂,mainly determine the performance of gas separation.Therefore,in this thesis,we design four different MMMs with ZIF-8@GO,functional MMT,metallo-supramolecular polymers and PDA@ZIF-8 as fillers,and polyether block amide?PEBA?as polymeric matrix for the CO₂/N₂ separation.Physical and chemical properties and performance of CO₂/N₂ separation of the prepared MMMs was systematically investigated.An in-depth study about the intrinsically linked between the physical and chemical properties and CO₂/N₂ separation of MMMs was also conducted.Main conclusions are as follows:?1?ZIF-8@GO composites was prepared via in-situ growth of ZIF-8 on the surface of GO.Then PEBA2533/ZIF-8@GO MMMs were fabricated by incorporating ZIF-8@GO into PEBA2533 matrix.The ZIF-8@GO played multiple roles in enhancing membrane performance.First,the high-aspect ratio GO nanosheets in polymer matrix increased the length of the tortuous path of gas diffusion,restricting the diffusion of larger molecules and favoring the diffusion of small molecules with less resistance,which enhanced the diffusivity selectivity.Second,the inherent high permeability of ZIF-8 with ultra-microporosity was anticipated to optimize fractional free volume and enhance the gas permeability and solubility selectivity of MMMs.The MMMs doped with ZIG-8@GO had better gas separation performance than those doped with only ZIF-8 or GO.The membrane containing 6 wt%of ZIF-8@GO exhibited the optimum performance with a CO₂ permeability of 249 Barrer and a CO₂/N₂ selectivity of 47.6.Compared with the pure PEBA2533 membrane,the CO₂ permeability and CO₂/N₂selectivity of the PEBA2533/ZIF-8@GO-6 MMMs were increased by 191%and 174%,respectively.?2?PEBA2533/functional MMT mixed matrix membrane was fabricated by establishing montmorillonite?MMT?functionalized with poly?ethylene glycol?methyl ether?PEG?and aminosilane coupling agents in a PEBA2533 membrane.The functional MMT played multiple roles in enhancing membrane performance.First,the MMT channels could be used as high-speed facilitated transport channels,in which the movable metal cations acted as carriers of CO₂ to increase the CO₂ permeability.Second,due to mobility of long-chain aminos and reversible reactions between CO₂and amine groups,the functional MMT could actively catch the CO₂,not passively wait for arrival of CO₂,which can facilitate the CO₂ transport.At last,PEG consisting of EO groups had excellent affinity for CO₂ to enhance the CO₂/N₂ selectivity.Thus,the as-prepared functional MMMs exhibited good CO₂ permeability and CO₂/N₂ selectivity.The functional MMM doped with 40 wt%of MMT-HD702-PEG5000 displayed optimal gas separation with a CO₂ permeability of 448.45 Barrer and a CO₂/N₂selectivity of 70.73,surpassing the upper bound lines of the Robeson study of 2008.?3?The metallo-supramolecular polymers based on F127 was prepared and incorporated into PEBA2533 to fabricate gas separation membranes.PEO segments of prepared metallo-supramolecular polymers,F127-Tpy-M,can improve the interficail compatibility with PEBA2533.Meanwhile,based on the synergistic effect of PEO segments and metal ions,incorporation of F127-Tpy-M can simultaneously enhance the CO₂ permeability and CO₂/N₂ selectivity of MMMs.The MMMs doped with 60 wt%of F127-Tpy-Co displayed optimal gas separation with a CO₂ permeability of 442.18Barrer and a CO₂/N₂ selectivity of 50.58,surpassing the upper bound lines of the Robeson study of 2008.?4?A novel PDA@ZIF-8 was prepared coating polydopamine?PDA?on the surface of ZIF-8.PDA@ZIF-8 played multiple roles in enhancing the membrane performance.First,the inherent high permeability of ZIF-8 with ultra-microporosity was anticipated to optimize the fractional free volume and enhance the gas permeability of MMMs.Second,the PDA coating can mitigate the interfacial defects and improve the adhesion between ZIF-8 and the polymer matrix.Finally,the abundant-OH and amino groups in PDA have strong interaction with CO₂ molecules,which can effectively facilitate CO₂ transport.The performance of CO₂/N₂ separation of the PEBA4033/PDA@ZIF-8 MMMs was investigated and compared with that of the ZIF-8-incorporated membrane without the PDA coating.An anti-trade off effect was obtained by addition of PDA@ZIF-8.In particular,the PEBA4033/PDA@ZIF-8-15MMM showed the best gas separation performance with a CO₂ permeability of 267.74Barrer and a CO₂/N₂ selectivity of 62.65,surpassing Robeson's upper bound from 2008...