(61f) Development of Fixed Carrier Membranes for CO2 Separation: From Membrane Materials to Membrane Processes

The development of cost-effective CO₂ separation process is the key for clean energy supply and environmental remediation. Polymeric membranes containing fixed carriers show promising applications in CO₂ removal from energy gas (e.g. syngas, natural gas, and biogas) and flue gas, because the reversible reaction between carriers and CO₂ leads to the both high CO₂ permeance and high CO₂/gas selectivity of membranes. However, the fixed carrier membrane has 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 clean energy purification and CO₂ capture. In the recent years, several high-performance fixed carrier membrane materials with good stability have been developed by our group, and the scale up and practical applications of fixed carrier membranes are in progress.

In order to improve the gas separation performance and stability of fixed carrier membranes to meet the technological and economical requirements of practical applications, multiple permselectivities including diffusivity selectivity, solubility selectivity, and reactivity selectivity have been combined into membranes by modifying membrane structures in multiple levels, such as levels of atoms and groups, molecular chains, molecular aggregation, and macroscopic structures. By following this strategy, several high-performance membranes have been developed recently. For example, a multi-permselective membrane has been developed by interfacial polymerization with hexane-soluble trimesoyl chloride and water-soluble diethylene glycol bis(3-aminopropyl) ether and 3,3’-Diamino-N-methyldipropylamine. Crosslinked polyamide with both ether oxide groups and tertiary amino groups forms after polymerization, indicating the successful combination of multiple permselectivities. The multi-permselective membrane exhibits high CO₂ permeance and high selectivity of CO₂ over H₂, CH₄ and N₂. Another example is the polyvinylamine (PVAm)- piperazine (PIP)/ polysulfone(PS) membrane. PIP that contains carriers (secondary amino groups) was used to crosslink PVAm, a key membrane material with fixed carriers, by hydrogen bonds, which modifies the membrane structures in the level of groups and the level of molecular aggregation. Compared with pure PVAm, the amine group concentration of the PIP cross-linked PVAm has been increased, which enhances the reactivity selectivity of the membrane. Moreover, the hydrogen bond formed between the secondary amine groups of PIP and the primary amine groups of PVAm, which makes the molecular aggregation more densification and enhances the diffusivity selectivity of the membrane. The PVAm-PIP/PS composite membrane shows a state-of-the-art CO₂ separation performance.

Based on the novel materials mentioned above, the scale up and practical applications of fixed carrier membranes are in progress. The effects of technological parameters of large-scale synthesis of materials were investigated, such as reaction temperature, reaction time, the concentration of the monomer and the initiator. After that, the thin-film composite membranes were prepared on both hollow fiber support membranes and flat-sheet support membranes. The flat-sheet composite membranes with the width of 0.3m have been continuously produced by an auto-casting applicator. Industrial grade hollow fiber modules and spiral wound modules have been developed with effective areas of 4.5m² and 5m², respectively. The spiral wound module exhibits excellent CO₂ separation performance, for example, CO₂ permeance of 250~300GPU with CO₂/N₂ selectivity of 80, CO₂/CH₄ selectivity of 50, and CO₂/H₂ selectivity of 40. Recently, a demonstration unit based on fixed carrier membranes for removing CO₂ from biogas with largest treatment capacity of 1500 Nm³/day has been developed in Hebei, China. The results indicate that the scale up and practical applications of fixed carrier membranes are feasible.