Experimental characterization and process simulation of thermochemical redox cycles with LSMA perovskite

Rapid economic growth has contributed to the increasing energy demand observed nowdays with a consequent increase in the use of fossil fuels. Their combustion and following carbon dioxide (CO2) emissions recently arose as a cause of concern due to the adverse effect on the environment, since CO2 has been widely recognized as a major greenhouse gas and as the main cause of global warming. Energy demand is still expected to grow in the decades to come, thus, new pathways for its production should be pursued. Renewable enery sources (RES) have been identified as the long term solution to reduce CO2 emissions, but their intermittency can hinder the effectiveness of such technologies. Energy storage is therefore a crucial remedy to this issue, and, specifically chemical energy storage, when coupled with solar energy plants, has an undoubted potential. Solar energy can be converted and stored into chemicals such as hydrogen and/or carbon monoxide (H2 and/or CO) through dissociation of zero-energy molecules such as H2O and or CO2, respectively. The synthetic molecules produced in this way are referred to as solar fuels. A mixture of the two - i.e syngas - can serve as a precursor for more complex fuel synthesis. If a carbon capture (CC) technology is coupled with solar fuels production plants, the captured CO2 can be used as raw material to the process, thereby closing the carbon cycle ideally with zero emissions. Among the different pathways to produce solar fuels, solar thermochemical redox cycles are a promising option. Such cycles are composed of two reaction steps. The first step is described by the higher temperature endothermic reduction, in which the oxygen carrier (OC) is reduced upon heating with concentrated solar thermal (CST) energy. The second step is the lower temperature oxidation, in which the reduced OC is re-oxidized with H2O to produce H2, or with CO2 to produce CO. In this work, La0.6Sr0.4Mn0.6Al0.4O3 (LSMA) perovskite was investigated as OC in CO2 based oxidation cycles. This material has been studied extensively in literature due to its excellent redox performances when compared with perovskites tested for the same application. Experimental tests were carried out in the CO2 Circle Lab at Environment Park (Turin). Two different experimental techniques were used to study the CO production starting from CO2, one involving a tubular microreactor coupled with online evolved gas analysis (EGA) connected in series, and the other involving a thermogravimetric analyzer (TGA). The tests allowed to assess the material behavior in the examined conditions and the CO production yield. The information on the yield was the used within a simplified reactor model developed with Aspen Plus\textregistered \, software. The aim of the numerical model was to give a first estimate of the process efficiency, although several simplifying assumptions were made, and to show the potential of combining experimental tests with process simulation. Some hypotheses were needed in the material modelling, since the investigated perovskite was not available in the software database. More work will be carried out in the future in order to define the actual material properties and enhance the coupling between experiments and simulation.