Application Of Ceramic Membrane And Sorbent In High Temperature Gases Separation And CO₂ Capture

This work focuses on high-temperature separation and enrichment of CO₂ and O₂, which are the most relevant separations with three CO₂ capture pathways: post-combustion capture, pre-combustion capture, and oxy-combustion, with dense ionic conducting membrane and ceramic sorbent.In chapter 2, a theoretical model is developed for CO₂/O₂ permeation through a dual-phase membrane consisting of mixed-conducting oxide ceramic (MCOC) and molten carbonate (MC) phases. Somewhat simpler theoretical CO₂ permeation equation is obtained for the pure CO₂ permeation case. The results show that CO₂ permeation flux (J CO₂) with involving oxygen permeation is more than one order of magnitude higher than the corresponding J CO₂ for a pure CO₂ permeation case. The fluxes of CO₂ and O₂ (J O₂) increase with increasing O₂ partial pressure in the feeding gases. Both J CO₂and J O₂ increase with increasing electronic conductivity (σ_h·) of the MCOC phase. J CO₂increases with increasing ionic conductivity (σ _V··) of the MCOC phase atσ_h·≤0.1 S/cm, while decreases with an increase ofσ _V··atσ_h·>1 S/cm. For the pure CO₂ permeation case, J CO₂ increases with the increase ofσ _V··and decreases with increasing MC volume fraction. An ordered ceramic pore structure benefits CO₂ and O₂ permeation.In chapter 3, a dense Bi_1.5Y_0.3Sm_0.2O₃ (BYS)-MC dual-phase membrane is synthesized by the direct infiltration method and used for selective permeation of CO₂ at high temperatures. Permeation takes a long time to reach a steady state at the initial stage due to the reversible phase change of the oxygen ions conduction phase between the rhombohedral structure and cubic fluorite structure. J CO₂increases with increasing temperature (500-650°C), with apparent activation energy of 113.4 kJ/mol. J CO₂ increases with increasing sweep gas flow rate(25-125 mL/min).In chapter 4, a one-dimensional dense oxygen permeation membrane reactor (DMR) model is developed to simulate the partial oxidation of methane (POM) to syngas. A combustion-reforming mechanism is adopted and the oxidation of reforming products, i.e. H₂ and CO, is considered. The results show that the model with incorporation of the product oxidation steps is more reasonable than those ignoring the product oxidation reactions. The model predicts that if methane is consumed completely in the reactor, a temperature runaway occurs. The reactor inlet temperature is chosen as a major factor to demonstrate the correspondence of the reactor performance and this phenomenon. A borderline inlet temperature (BIT) is defined. Simulation results show that when the reactor inlet temperature approaches to this value, an optimized reactor performance is achieved.In chapter 5, the oxygen permeation through oxygen ionic or mixed-conducting ceramic membranes under reaction conditions is examined with a model taking into account of different transport mechanisms, i.e. p-type and n-type transport, and finite reaction rate. It is demonstrated that with a reaction consuming oxygen in one side of the membrane, the oxygen partial pressure in the reaction side decreases, whileJ O₂ increases from the value of no reaction case to that of complete reaction case, with the increase of the reaction rate. The increase of reaction rate causes a transition of the transport mechanism from p-type to n-type, which leads to an increase of J O₂ by up to 30 times of magnitude.In chapter 6, perovskite-type SrCo0.8Fe0.2O3-δ(SCF) is prepared by a liquid citrate method and used to produce O₂-CO₂ gas mixture for oxyfuel combustion. O₂ is desorbed and an O₂-enriched CO₂ stream is obtained when SCF is exposed in a CO₂ stream at high temperature. O₂ is adsorbed when SCF is regenerated in an air stream. A carbonation-reaction mechanism for O₂-desorption is identified with the evidences of XRD and TGA analysis. Optimal temperatures for O₂ sorption and desorption processes are determined to be 900 and 850℃, respectively. Multiple sorption and desorption cycles indicate that SCF sorbent has high reactivity and cyclic stability.