Dual-Ion Conducting Lithium Zirconate-Based Membranes for High Temperature CO₂ Separation

Abstract

The processing and characterization of a novel membrane system for CO₂ separation is described. The membrane was made of lithium zirconate (Li₂ZrO₃), which has a potential to react reversibly with CO₂ molecules at high temperatures. The reaction of Li₂ZrO₃ with CO₂ essentially produced two electrolyte materials in situ. One of them, Li₂CO₃, is capable of carrying CO₂, and the other, ZrO₂, is a well-known O₂ ion conductor. This combination of selective reaction and electrolyte conduction permitted the design of a membrane system capable of selective CO₂ steady-state permeation across the membrane. Using the membrane, a separation factor of 4.9 was measured between CO₂ and CH₄ gas molecules at a temperature of 600°C. The measured separation value of 4.9 is very high compared with the Knudsen diffusion limit of 0.6 and therefore clearly supports the use of the membrane system for selective separation of CO₂.