Study On Poisoning Mechanism Of Sulfur-containing Gas On Ceramic-carbonate Dual Phase Membrane For CO₂ Separation

This paper mainly focuses on the effect of two surfur-containing gases on ceramic-carbonate dual phase membrane during CO₂ capture technology.There are two S-containing gases that include SO₂ in the post-combustion process and H₂S in the pre-combustion process.Ce_0.8Sm_0.2O_1.9（SDC）-carbonate dual phase membrane,as a CO₂ separation membrane,has many advantages such as high CO₂ permeation flux,good stability and potential application in the future.Thus,SDC-carbonate membrane is utilized as research object to investigate.In the last part,film-forming property and sulfur resistance of Sm_0.9Sr_0.1Cr_0.5Fe_0.5O_3-δthat has a perovskite structure are investigated.In chapter 2,we synthetize Ce_0.8Sm_0.2O_1.9 powder with co-precipitation method,and then directly compress the SDC powder to prepare the SDC support.Ce_0.8Sm_0.2O_1.9/Li₂CO₃-Na₂CO₃ dual phase membrane is prepared with direct infiltration method.The SDC-carbonate membranes are exposed to different SO₂concentrations of gas mixture to investigate SO₂-poisoning effect and mechanism.The results show that CO₂ permeation flux of the SDC-carbonate membranes decline after SO₂ exposure.SO₂ has little influence on the SDC phase,but it has great effect on the carbonate phase due to stronger SO₂ interaction with the carbonate.SO₂ can change carbonate into sulfate finally.The results show that the CO₂ flux goes down gradually as the incorporating sulfate in the carbonate phase goes up.The mixted sulfate lowers the carbonate ionic conductivity in the molten salt phase,which causes a switch of the CO₂ rate-limiting transport from the oxygen ionic conduction in SDC to the carbonate ionic conduction in the sulfated carbonate phase.In addition,activation energy for permeation increases for the membranes with increasing sulfate content in the molten salt phase.These reasons lead to decline of the CO₂ flux.In chapter 3,the SDC-carbonate dual phase membrane is selected as research object to investigate H₂S-poisoning effect.Different consentrations of H₂S are introduced into the feed gas during the stability test of the CO₂ permeation of the membrane.The results show that the CO₂ flux of the SDC-carboante membrane is stable in H₂/N₂/CO₂ mixture feed gas,but introduced H₂S could make the CO₂ flux decline gradually.The main reason of the flux decline is that the SDC reacts with H₂S in the reducing stream forming the Ce-O-S.The formation of Ce-O-S phase decreases the quantity and mobility of the lattice oxygen of the SDC phase,lowering the oxygen ionic conductivity of the SDC phase,and hence the CO₂ flux in the dual-phase membrane.In chapter 4,the perovskite structure of Sm_0.9Sr_0.1Cr_0.5Fe_0.5O_3-δ（SSCF）powder is prepared with a citrate–nitrate combustion method.SSCF-carbonate dual phase membrane is prepared by direct pressing and infiltration method to investigate its film-forming property and sulfur resistance.The results show that the SSCF has a good sulfur-resistance that is compared with SDC material.The CO₂ flux of the SSCF-carbonate membrane reaches 0.49 ml min^-1 cm^-2 in the 10%H₂/45%N₂/45%CO₂gas mixture at 750 ℃.In addition,the CO₂ flux of the SSCF-carbonate membrane merely declined 8%after H₂S exposure,suggesting that the SSCF membrane also has sulfur-resistance ability.However,the SSCF membrane is unstable during the stability test due to Sr instability in CO₂-containing gas.