Experimental study of a chemical looping process using SFNM-04 perovskite to dissociate carbon dioxide

Earth’s global average temperature has been rising since the industrial period, and the anthropogenic emissions of greenhouse gases, carbon dioxide especially, have been widely recognized as the main cause. The energy sector is a main contributor of emissions. As the energy demand is expected to grow in the near future, new pathways to produce energy are needed. A path to meet part of the energy demand using renewable energy as the primary source, but without eliminating fuels and the devices that require them, is the use of solar fuels. A solar fuel is similar to fossil fuels in terms of properties, but is produced from solar energy and simple molecules like carbon dioxide and water, and not extracted from underground deposits. Thus, carbon dioxide is not just a waste to emit to the atmosphere. It becomes a resource for fuel production. If carbon capture processes are added to a plant that uses solar fuels, the recovered carbon dioxide can be the raw material to produce new fuel, closing a cycle with no emissions. The intermediate product between carbon dioxide and a fuel is syngas, a mixture of hydrogen and carbon monoxide. Among the several processes to produce syngas using renewable energy, two-step chemical looping is one of the most promising. Chemical looping consists in using thermal energy, in this case coming from a system of solar concentrators, to split carbon dioxide into carbon monoxide and oxygen, or water into hydrogen and oxygen. If the process is divided into two steps, the oxygen is absorbed by an oxygen carrier material during the first step, and later the oxygen carrier is regenerated with thermal energy, making it release the oxygen previously absorbed. In this work, a perovskite metal oxide with formula Sr2FeNi0.4Mo0.6O6 (SFNM-04 or SFNM for short) is investigated as a new possible high-performance oxygen carrier. The material was synthetized by the University of Udine, and it is studied in a collaboration project that also includes the Massachusetts Institute of Technology (M.I.T.) and Politecnico di Torino. Several experimental tests were carried out with SFNM-04 in the CO2 Circle Lab of the Environmental Park of Turin. In these experiments, the material was placed inside a reactor at temperatures as high as 850°C and exposed to a carbon dioxide flow in order to study the production of carbon monoxide. The tests highlighted a carbon monoxide specific yield for SFNM-04 that depends on temperature, gas flow rate and sample mass. In general, the specific yield was in the order of magnitude of thousands or tens of thousands of μmol/g. This thesis also presents a simplified model of the reactor implemented in the Aspen Plus® software, with several assumptions made in order to model the new material and a specific point of operation. The results of one of the reactor tests are used as input parameters for the simulations on the software, in order to estimate the thermal efficiency of a process using SFNM as oxygen carrier material to produce syngas. As the tests carried out with the reactor only studied the production of carbon monoxide, the hydrogen in this preliminary model is supposed to come from a different process driven by renewable sources. Therefore, more tests will be needed in the future, in order to analyze the possibility of producing hydrogen from SFNM together with CO. In this way, a proper solar fuel could be produced, with the aim of finding new ways to decarbonize the energy sector and help mitigating the causes of climate change.