(329e) Development of High-Performance Polymeric Membranes for CO2 Separation

The development of cost-effective CO₂ separation process is the key for clean energy supply and environmental remediation. Much attention has been paid to polymeric membranes that preferentially permeate CO₂ with high permeances and selectivities for CO₂/N₂, CO₂/CH₄ and CO₂/H₂ gas pairs. However, most of polymeric membranes have not been commercialized and applied in practical processes due to the lack of materials possessing high separation performance and stability which could meet the purity, recovery and cost requirements of flue gas capture and fuel gas purification. In recent years, a series of high-performance polymeric membranes with good stability have been developed by our group, and the scale up and practical application of representative membranes are in progress.

  First, multiple permselectivities including diffusivity selectivity, solubility selectivity, and reactivity selectivity have been combined into membranes by modifying membrane structures at multiple levels, such as levels of atom and group, molecular chain, molecular aggregation, and macroscopic structure. Following this strategy, several high-performance membranes have been developed successfully. For example, a multi-permselective membrane has been fabricated by interfacial polymerization with hexane-soluble trimesoyl chloride and water-soluble diethylene glycol bis(3-aminopropyl) ether and 3,3-Diamino-N-methyldipropylamine, and this membrane exhibits favorable separation performance owing to the desirable membrane structure. Another example is the polyvinylamine (PVAm)-piperazine (PIP)/polysulfone (PS) membrane. PIP that contains carriers (secondary amino groups) was used to crosslink PVAm via hydrogen-bonding interactions, which modifies the membrane structure at the levels of groups and molecular aggregation. Moreover, two kinds of polymeric membranes with high CO₂-induced plasticization resistance were developed for high-pressure fuel gas purification: PVAm was modified with methylcarbamate (MC) containing amine and ester groups through adjusting atom, group and molecular aggregation, and the cyclic tertiary amino groups containing polymeric membrane was designed via adjusting group, molecular chain and molecular aggregation.

  Second, various high-speed transport channels for CO₂ have been constructed in mixed matrix membranes (MMMs) by introducing different microporous materials into membrane matrix. First example is the PVAm-(PMOF-5)/PS membrane: a novel polymer-induced metal organic framework (PMOF-5) was synthesized by using a polymer (PVAmcarbox)-terephthalic acid (H₂BDC) coordination ligand and Zn(NO₃)₂·6H₂O, and then incorporated into PVAm matrix. Here the polymer segment of PMOF-5 framework is similar to that of PVAm, which efficiently guarantees the uniform dispersion of PMOF-5 in the PVAm-(PMOF-5)/PS membrane. Meanwhile, the pores of PMOF-5 with the diameter of 0.7 nm can serve as CO₂ transport channels, which could remarkably enhance CO₂ transport based on surface diffusion mechanism. Another example is the PEIE-HT/PS membrane fabricated by establishing hydrotalcite (HT) channels in the polyetheramine (PEIE) membrane. The mobile carbonate ions as reactive carriers are cruised in the HT channels, which benefits them actively interact with CO₂ similar to that in liquid membranes or ion exchange membranes. In addition, charged layer of HT provides the stability for mobile carriers due to the electrostatic attractions.

  As one of the state-of-the-art membranes for CO₂ separation reported, the scale-up production of PVAm-PIP/PS membranes is in progress. The effects of technological parameters of large-scale synthesis of PVAm were investigated, such as reaction temperature, reaction time, the concentration of monomer and initiator. Then the flat-sheet composite membranes with the width of 1 m have been continuously produced by an auto-casting applicator. Industrial grade spiral wound modules, exhibiting favorable CO₂ separation performance, have been successfully manufactured, indicating promising application potentials in different gas separation processes involving CO₂.