Studies On Preparation And Performance Of Antioxidative And Acid Resistant Membrane For CO₂Separation

Fixed carrier membranes for CO₂separation are promising membranes. However,most of the fixed carrier membranes contain amine groups as carriers, which may beoxidized by the oxidant gases （mainly O₂） and react with the acidic gas （mainly SO₂）contained in the flue gas. In this work, different methods are used to fixed thecarboxylate group as the carrier in the membrane to get excellent permselectivity,antioxidizability and acid resistance.The method of the radical polymerization was used to fixed the carboxylate groupas the carrier. Poly（sodium acrylate）（PAAS） and a seriers of poly（sodiumacrylate-co-acrylamide）（P（AAS-co-AAm）） were synthesized by sodium acrylate andmixture of sodium acrylate and acrylamide through radical polymerization. Thecomposite membranes were developed respectively with the above materials as activelayers and polysulfone （PS） as the supports. ATR-FTIR was employed to characterizethe possible reactions between the gases and the membrane, and the permselectivityof the membrane was measured with CO₂/N2mixed gas. The transport mechanisms ofCO₂and N2in the membrane were hence studied. The effects of AAS content of thepolymer and the wet coating thickness of the active layer on the membranepermselectivity were investigated. The antioxidizability and the acid resistance of thiskind of membrane were verified. The results showed that the membranes possessedgood CO₂separation performance, antioxidizability and acid resistance. In the testswith CO₂/N2mixed gas （containing15vol%CO₂and85vol%N2）, the membraneprepared by using P（AAS-co-AAm） containing47.68mol%AAS with wet coatingthickness of200μm had a CO₂permeance of163GPU and CO₂/N2selectivity of90at0.11MPa feed pressure.The method of polymer blending was used to fixed the carboxylate group as thecarrier. The composite membranes were developed with the blend materialPAAS-PEG as the active layers and PS as the supports. The effects of the molecularweight of PEG and the mass ratio of PAAS to PEG on the membrane permselectivitywere investigated. The results showed that the membranes possessed good CO₂separation performance. In the tests with CO₂/N2mixed gas （containing15vol%CO₂and85vol%N2）, when MWPEGwas20,000，mPAAS:mPEGwas1:2, the PAAS-PEG/PS blend composite membrane had a CO₂permeance of700GPU and CO₂/N2selectivityof80at0.11MPa feed pressure.Interfacial polymerization （IP） was used to fixed the carboxylate group as thecarrier. The （DAmBS-TMC）/PDMS/PS membrane and（DAmBS-DEGBAmPE-TMC）/PDMS/PS membranes were developed withcrosslinked polydimethylsiloxane （PDMS） coating PS as support membranes,trimesoyl chloride （TMC） as monomer of organic phase, sodium3,5-Diaminobenzoate （DAmBS） or mixture of DAmBS and diethylene glycolbis（3-aminopropyl） ether （DEGBAmPE） as monomers of aqueous phase. The effectsof various parameters on membrane performance were investigated. The resultsshowed that the membranes possessed good CO₂separation performance. Theantioxidizability and the acid resistance of this kind of membrane were verified. Theresults showed that the membranes possessed good CO₂separation performance,antioxidizability and acid resistance. In the tests with CO₂/N2mixed gas （containing15vol%CO₂and85vol%N2）, the membrane prepared with0.003mol/L of TMC,0.004mol/L of DAmBS and0.006mol/L of DGBAmPE had a CO₂permeance of5831GPU and CO₂/N2selectivity of86at0.11MPa feed pressure.Taking the （DAmBS-DEGBAmPE-TMC）/PDMS/PS membrane prepared in thiswork for example, the energy and the total cost required for the process werecalculated. The results showed that the membrane prepared in this work wascompetitive with the traditional chemical absorption method, and had a potential to beused for CO₂separation from the flue gas.