Constructing Transport Passageways And Intensifying Transport Process Of CO₂ In Membranes

The development of energy-efficient and environment-friendly CO₂ capture technologies has recently become a key issue in energy gas purification and greenhouse gas reduction. Membrane technology has shown a great potential in CO₂ capture. It has important theory value and practical significance in developing high permeability and high selectivity membrane materials for CO₂ separation. In this study, multiple functionalized fillers were designed and prepared to control the membrane structures, water environments, transport sites, chemical microenvironments and multi-permselective mechanisms for constructing CO₂ transport passageways, obtaining the strategies for improving CO₂ separation performance. It is expected that these strategies provide a theory basis for the rational design and fabrication of high performance CO₂ separation membranes. The main research contents are as follows:（1） Based on the synergistic effect between the two fillers, one-dimensional carbon nanotubes（CNTs） and two-dimensional graphene oxide（GO） were selected as the two fillers to control membrane structure for constructing CO₂ transport passageways in Matrimid® 5128 membrane. CNTs acted as highways to render high permeability, whereas GO acted as a selective barrier to render high selectivity, intensifying CO₂ diffusivity selectivity mechanism. Compared with the pristine membrane, hybrid membrane shows 4.3-fold increase in the CO₂ permeability, 2.5-fold increase in the CO₂/CH4（or CO₂/N2） selectivity, respectively.（2） Based on the high solubility of CO₂ in water, carboxylic acid nanogels were selected as super water-absorbing fillers to control water environments and CO₂ transport sites for constructing CO₂ transport passageways in membranes. Carboxylic acid nanogels act as "reservoirs" to improve the water uptake and water retention in the membrane, and carboxyl groups provide CO₂ transport sites, intensifying CO₂ solubility selectivity mechanism. CO₂ permeability and CO₂/gas selectivity were significantly enhanced, well surpassing the Robeson’s upper bound limit reported in 2008.（3） Based on the reversible reaction between CO₂ and amino groups, amine functionalized mesoporous silica was designed as a functional filler to control chemical microenvironments for constructing CO₂ transport passageways in membranes. The amine groups reacted reversibly with CO₂, intensifying the reactivity selectivity mechanism. The hybrid membrane showed CO₂/CH4 and CO₂/N2 selectivity of 41 and 102 with a CO₂ permeability of 1521 Barrer.（4） Based on the simultaneous enhancement of diffusivity selectivity, solubility selectivity and reactivity selectivity, GO functionalized with ethylene oxide groups and amino groups was designed as a versatile filler to control multi-permselective mechanisms for constructing CO₂ transport passageways in membranes. The two-dimensional GO intensified diffusivity selectivity mechanism, ethylene oxide groups intensified solubility selectivity mechanism and amino group intensified reactivity selectivity mechanism. The as-prepared membrane exhibits the excellent CO₂ permeability of 1330 Barrer, CO₂/CH4 and CO₂/N2 selectivity of 45 and 120, respectively.