3D Multiphysics model for tubular co-ionic ceramic reactor for CO2/H2O electro-conversion to light olefins

The development of storage systems that could manage the fluctuations of the energy production from intermittent renewable sources (solar and wind) is a fundamental element of the energy transition. In particular, with the electrification of the different industrial sectors, research on Power-to-x technologies is growing extensively. Thus, electrolysers, which can be employed to balance the overproduction of electricity from renewables by exploiting them for the production of green hydrogen and chemicals (like light olefins), are being largely studied and commercialised. The importance of light olefins in today’s world, can be highlighted by their extensive use in chemical industry, where they represent the most important platform molecules for the crafting of different products such as: polymers, solvents, detergents, fuels and additives. However, even today, the main technologies for production of light olefins (Steam Cracking and Fuel Catalytic Cracking) entirely depend on fossil feedstocks with consequent high Green House Gase emissions. Moreover, in the old production routes the selectivity to light olefins is generally low (especially for propylene and butylene). Thus, new technologies for the synthesis of light olefins are being investigated. Among these, the electrochemical synthesis of light olefins from CO2 and H2O, is the main focus of this thesis. In particular, in this work, it has been performed the development of a computational model, in COMSOL Multiphysics® Version 6.2, of a tubular proton-ceramic electrolysis cell (PCEC), for the production of light olefins via thermos-catalytic routes such as methanol-to-olefins and Fischer-Tropsch-to-olefins, with CO2 and H2O as feedstock. The model solves a multi-physics problem by implementing simultaneously different models related to chemistry, electrochemistry and thermal fluid dynamics, on a 2D axisymmetric domain meshed with triangular and rectangular cells. In particular, for the electrochemical modelling the tertiary current distribution interface has been implemented, which permits to model the distribution and motion of the multiple defect species conducted within the multi ionic-electronic membrane (MIEC). From a chemical point of view, the model implements different reaction processes. The production of hydrogen within the cell is modelled with the water electrolysis reaction and the defect incorporation reactions while the synthesis of light olefins is modelled with the introduction of the reactions from the methanol-to-olefins process and Fischer-Tropsch-to-olefins process. The final results of the model simulations, show the electrochemical performances of the cell, product concentrations and temperature distributions.