Porous LaxSr(1-x)CoyFe(1-y)O(3-d) - molten alkali metal carbonate membranes for CO2 permeation

Abstract

Dual-phase ceramic molten carbonate membranes have the ability to permeate carbon dioxide at high temperatures, with or without oxygen. This project studied the novel process of oxygen-driven carbon dioxide permeation, based on the mechanism of carbon dioxide transportation within the molten carbonate phase. In this process, carbonate ions transported across the membrane in the molten phase are driven by the oxygen partial pressure gradient. In our study, the carbon dioxide can permeate through the membrane without its own partial pressure gradient; to achieve this, oxygen potential gradient against the carbon dioxide is required to overcome the carbon dioxide potential (𝑝𝐶𝑂2 ′≤ 𝑝𝐶𝑂2′′ and 𝑝𝑂2 ′> 𝑝𝑂2′′). The carbon dioxide in 𝑝𝐶𝑂2 ′ permeation to 𝑝𝐶𝑂2 ′′is defined as the ‘up-hill’ permeation process. This study shows extremely high carbon dioxide permeation with the permeance of the order of 10-6 mol m-2 s-1 Pa-1 during up-hill experimentation, and, at this value of permeability, the order of magnitude for carbon dioxide separation is greater than for other membrane technologies in this field. The project also examined the stability of this dual-phase ceramic-carbonate membrane system consisting of La0.6Sr0.4Co0.2Fe0.8 (LSCF) and a eutectic carbonate mixture (Li/Na/K) at about 600ºC. The results showed that this up-hill permeation operating over 200 hours occurred without a dramatic decrease in carbon dioxide permeation. The most important advantage of this up-hill carbon dioxide separation is that there is no energy penalty during the carbon dioxide separation process. For the carbon dioxide removal process, the energy that the system required from the energy input to remove the carbon dioxide against its own chemical potential was the energy penalty for carbon dioxide separation. However, during carbon dioxide up-hill permeation, the oxygen provides a greater potential difference in the opposite direction to overcome that of the carbon dioxide during permeation. However, thermal energy for heating up the membrane is required; no energy is consumed continuously from the environment to maintain the up-hill permeation process at about 600℃.