Study On Preparation And CO₂ Separation Performance Of Metal Organic Framework-Polymer Mixed Matrix Membranes

Carbon dioxide?CO₂?is one of gases that contribute to global warming,corrosion of natural gas pipeline and reducing of natural gas combustion efficiency.To alleviate these problems,realizing effective separation of CO₂/N₂ and CO₂/CH₄ has become a hot spot in recent years.Compared with other separation technologies,membrane separation has evolved as an important CO₂ separation methods,owing to its low energy consumption,simple operation,low cost,and no phase transition in the process of separation.However,the existing gas separation membrane has been known to have a near-universal trade-off between permeability and selectivity.Therefore,mixed matrix membranes?MMMs?have been studied as an alternative approach to solve the trade-off phenomena of membranes in gas separation.For the gas separation,the interface morphology between inorganic particle and polymer matrix and the properties of separated gases are very important factors to the separation performance.In order to improve the affinity between inorganic particle and polymer matrix,Cu-BTC,a kind of metal organic framework?MOFs?wasfunctionalized by chemical modification and decreasing the size of crystal method in this paper.The Cu-BTC/Ethyl Cellulose?EC?and Cu-BTC/Pebax composite membranes were prepared by mixing method,and the gas separation performance of the membranes was studied.In the part of modifying MOFs by chemical modification method and preparation of Polymer/MOFs mixed matrix membrane,Cu-BTC was functionalized via amine-functional groups at first.SEM indicated the increase of roughness on the surface of Cu-BTC,resulting better affinity between Cu-BTC and polymer matrix.FTIR and XPS confirmed that the functionalization had introduced amino group on the surface of Cu-BTC.Then the Cu-BTC/EC and Cu-BTC/Pebax composite membranes were synthesized by mixing method.The morphology and structure of the membranes were characterized by SEM and XRD.The result suggested that the addition of Cu-BTC had not change the basic structure of polymer matrix,but reducing the crystallinity of EC to a certain extent.The Cu-BTC/Polymer and NH₂-Cu-BTC/Polymer composite membranes showed better CO₂ separate performance compared to pure polymer membrane.For EC composite membranes,the permeability of CO₂increased from 71.02 Barrer to 101.6 Barrer and 75.76 Barrer with 5 wt.%Cu-BTC and 4wt.%NH₂-Cu-BTC,respectively.The selectivity of CO₂/N₂ increased from 12.87 to 16.72and 18.35 with 4 wt.%Cu-BTC and 3 wt.%NH₂-Cu-BTC,and the selectivity of CO₂/CH₄increased from 7.51 to 9.18 and 9.57 with same MOFs loadings.For Pebax composite membranes,the permeability of CO₂ increased from 26.89 Barrer to 136.2 Barrer and 119.6Barrer with 4 wt.%Cu-BTC and NH₂-Cu-BTC,respectively.The selectivity of CO₂/N₂increased from 38 to 55.13 and 60.88 with 3 wt.%Cu-BTC and NH₂-Cu-BTC,and the selectivity of CO₂/CH₄ increased from 14.24 to 20.4 and 25.94 with 2 wt.%Cu-BTC and 3wt.%NH₂-Cu-BTC.In the part of modifying MOFs by submicron modification method,the Cu-BTC was functionalized via sodium formate.SEM showed that crystal size decreased obviously.The sub-MOFs/EC and sub-MOFs/Pebax composite membranes were also synthesized by mixing method.The morphology and structure of the membranes were characterized by SEM and XRD.The result showed that the sub-MOFs had excellent affinity with polymer matrix.Gas separation tests showed that the addition of sub-MOFs can improve the CO₂ separation performance of the membranes.For EC composite membranes,the selectivity of CO₂/N₂increased from 12.87 to 22.42 and 29.05 with 2.5 wt.%sub-Cu-BTC and 3 wt.%sub-NH₂-Cu-BTC,and the selectivity of CO₂/CH₄ increased from 7.51 to 10.87 and 11.38with 3 wt.%sub-Cu-BTC and 2.5 wt.%sub-NH₂-Cu-BTC.For Pebax composite membranes,the selectivity of CO₂/N₂ increased from 38 to 64.38 and 66.27 with 4 wt.%Cu-BTC and 3wt.%NH₂-Cu-BTC,and the selectivity of CO₂/CH₄ increased from 14.24 to 26.66 and 29.05with 3 wt.%Cu-BTC and 3 wt.%NH₂-Cu-BTC.Finally,the comparison of the two kinds of modification methods on gas separation performance was carried out.The result indicated that the two kinds of modification methods can both improve the gas separation performance of membrane by improving the solubility of gas in the composite membrane.