An investigation into the Development of Ceramic Sorbents for High Temperature Air Separation for OxyFiring

Abstract

Oxyfuel combustion as one of the alternatives to post-combustion carbon capture technologies requires an economically viable oxygen supply system. Cryogenic air separation, the main currently available technology, consumes above 30% of the energy produced as it involves separation of nitrogen from the oxygen in the inlet air stream. High temperature air separation is a promising technology for the purpose of oxygen production in oxyfuel combustion Non-stoichiometric perovskite sorbents developed for use in high temperature air separation suffer from shortcomings that can affect their large scale development . Development of alternatives to perovskite oxides as sorbents for high temperature air separation has been studied in this dissertation. Perovskite/spinel oxide has been considered as the first option for comparison of the properties as an oxygen sorbent to those of the traditional perovskites. Copper oxide has been chosen as the second and main alternative to nonstoichiometric oxides. Despite numerous advantages, copper oxide has its own shortcomings for use as a high temperature oxygen sorbent. Effect of synthesis method has been studied as the first approach for improving shortcomings of current sorbents - the most important of which is to increase the oxygen desorption rate. The citrate gel method has been shown to be the most effective ceramic synthesis method in this case by the positive effects that it has on surface chemistry of copper oxide as an oxygen sorbent. Doping with alumina has been chosen to improve the properties through the chemistry of reactions occurring between CuO, CuAl2O4, CuAlO2 and Cu2O during oxygen absorption and desorption. Addition of alumina up to 30% has been shown to improve desorption kinetics without significantly affecting the absorption kinetics. High temperature stability is the other property that has been improved by addition of alumina. Zirconia and its derivatives doped with yttria and ceria were explored as support materials for copper oxide. Yttria stabilized zirconia was shown to have positive effects on oxygen desorption kinetics, high temperature stability and attrition resistance of the sorbents.