Study On Preparation And Formation Process Of Interfacially Polymerized Composite Membrane For CO₂ Separation

CO₂ capture is one of the most important subjects on energy and environment. Fixed carrier membrane for CO₂ capture is in the early development stage, and its performance is not very high due to few membrane materials and not enough variety in transport mechanism. Interfacial polymerization (IP) is a promising technique in the preparation of gas separation membrane. However, the formation process of IP membrane has not been realized sufficiently. This study makes attempts to develop novel fixed carrier membrane, solubility selective membrane and membrane with various permselective mechanisms by IP. The formation process of membrane prepared by IP is also explored.A tertiary amine group containing fixed carrier membrane was developed by IP with water-soluble 3,3'-Diamino-N-methyldipropylamine (DNMDAm) and organic phase-soluble trimesoyl chloride (TMC) on the polysulfone (PS) support membrane. Several techniques were employed to characterize the structure of the membrane. The permselectivity of the membrane was measured with CO₂/N₂ mixed gas. ATR-FTIR was employed to characterize the possible reactions between gases and the membrane. The transport mechanisms of CO₂ and N₂ in the membrane were hence studied. The effects of various parameters on membrane structure and performance were investigated. The results showed that the membranes possessed good CO₂ separation performance. In the tests with CO₂/N₂ mixed gas (containing 20 vol% CO₂ and 80 vol% N₂), the membrane prepared with 0.0062 mol/l DNMDAm and 0.0226 mol/l TMC had a CO₂ permeance of 173 GPU and CO₂/N₂ selectivity of 70 at 0.11 MPa feed pressure; In the tests with CO₂/CH₄ mixed gas (containing 10 vol% CO₂ and 90 vol% CH₄), the same membrane had a CO₂ permeance of 118 GPU and CO₂/N₂ selectivity of 37 at 0.11 MPa feed pressureAn ether group containing solubility selective membrane was prepared by IP with Diaminopolyethylene glycol (PEGda) as monomer of aqueous phase, trimesoyl chloride (TMC) as monomer of organic phase, polysulfone (PS) as support membrane. Several techniques were employed to characterize the structure of the membrane. The effect of PEGda concentration on the membrane was studied. Based on this, poly(PEGda-DNMDAm-TMC)/PS composite membrane was prepared, which contained tertiary amine and ether groups and thus had transport mechanisms of solubility selectivity and reaction selectivity (facilitated transport). Several techniques were employed to characterize the structure of the membrane. The permselectivity of poly(PEGda-DNMDAm-TMC) /PS membrane was measured with CO₂/N₂ mixed gas. The effect of DNMDAm/ PEGda concentration ratio on the membrane was studied. The results showed that in the tests with CO₂/N₂ mixed gas (containing 20 vol% CO₂ and 80 vol% N₂), the membrane prepared with DNMDAm/ PEGda concentration ratio of 12.4 had a CO₂ permeance of 190 GPU and CO₂/N₂ selectivity of 78 at 0.11 MPa feed pressure.The optical contact angle measuring device (OCA) and particle image velocimetry (PIV) were employed to visualize the film formation by interfacial polymerization with N-methyldiethanolamine (MEDA) and trimesoyl chloride (TMC). By observing the variations of the morphology of pendant drop of aqueous solution immersed in organic solution, the growth of interfacial film towards the organic phase was validated. The effects of various parameters on film morphology during IP process were investigated. The results showed that the concentration gradient of aqueous phase monomer near the aqueous-organic interface during IP process would cause the interfacial instability, which would result in the formation of the convexities on the films. These convexities on the films were responsible for the ultimately rough film surface.