Green hydrogen production from biogas autothermal reforming processor coupled with soot trap

The present Ph.D. thesis deals with the hydrogen production via a novel process involving a biogas autothermal reforming (ATR) unit with the adoption of a catalytic wall-flow filter located downstream from the ATR processor to effectively filter and in-situ gasify the carbon emissions eventually generated. This work was aimed to produce 50 Nm3/h of green hydrogen from the ATR of a model biogas (60:40 Vol ratio) by using catalytic structured supports. Moreover, a solution for the eventual carbon formation during the biogas ATR was addressed. A nanostructured delafossite catalyst to ensure the gasification of soot in absence of O2 was synthesized. In addition, a Life Cycle Assessment (LCA) and a techno-economic analysis for the hydrogen production from biogas were also carried out. Concerning the identification of the suitable support structure to improve the coupling of exothermic and endothermic reactions during the hydrogen production from biogas ATR, homogenous SiSiC lattices composed of Cubic, Octet and Kelvin cells and the Conventional Foam structure coated with Ni based catalysts doped with noble metals were investigated. The different catalytic geometries were tested using a model biogas composed of clean methane and carbon dioxide (60:40 Vol ratio) with a steam to carbon ratio (S/C) fixed at 2.0. The effect of the space velocity, inlet temperature and oxygen to carbon ratio (O/C) on methane conversion and hydrogen yield were studied for each catalytic support. The O/C ratios evaluated was equal to 1.0, 1.1 and 1.2. Space velocity (GHSV) values from 2000 to 20000 h-1 in standard conditions (equivalent to 5000- 85000 h-1 in operating conditions), and, inlet temperatures of 500, 600 and 700°C were employed. The combined effect of chemical reaction and some properties and parameters such as: pressure drop and specific surface area on the steady-state performances of an adiabatic reactor at high flow rates has been analyzed. ASPEN simulations were performed to calculate the thermodynamic equilibrium at the different boundary conditions to validate the data and to determine the hydrodynamic properties. This study has demonstrated that the rotated cubic cell support shows the best performance in transforming the biogas into hydrogen with high CH4 conversion (<95%) and an H2 yield higher of 2.1 using an O/C ratio of 1.0, 1.1 and 1.2, S/C ratio of 2 and GHSV of 20000 h-1. Besides, this support can ensure a high reliability of the ATR process due to its lower pressure drop (6-40 Pa/m) with the lower specific surface area comparing to the other structures tested. The conventional foam has presented also good performances for all the GHSV values in terms of CH4 conversion but it is less selective for hydrogen production. With respect to the catalyst for gasification of carbon in a reducing atmosphere (H2, CO, H2O, CO2), nano-materials based on transition metal were synthesized via a solution combustion synthesis (SCS) method. LiFeO2 catalyst was selected as the most promising candidate for the soot gasification catalyst on the soot trap application close coupled to the ATR reactor for syngas post-treatment process. Afterwards, some issues in mixed atmosphere, i.e., when simultaneous carbon gasification with CO2 and steam in the presence of H2 and CO take place, were studied. It was demonstrated that the carbon gasification is inhibited during an isothermal reaction at 650°C for 40 minutes when CO and H2 are used as co-reagents. But even in these extreme reduced conditions, the LiFeO2-catalyst gasified 32.9% of the initial carbon, compared to 8% for the non-catalytic case. when H2 is used as co-reagent in the steam carbon gasification, the reaction is inhibited, the carbon conversion decreases from 73.1% to 46.6%. Analogously, when CO is a co-reactant in the carbon gasification with CO2, the reaction is inhibited, the soot conversion declines from 70.2% to 31.6 %. However, it was observed that in mixed atmosphere gasification reactions, when CO2 and H2O simultaneously reacts with carbon, there is a passive combination of steam and carbon dioxide in the gasification reaction. This means that the two gases operate on separated active sites without influencing each other. LiFeO2 was also coated on the monoliths (15/20 μm mean pore size and 45% porosity) and the coated filters’ performance was evaluated during the soot particles loading. The pressure drop across the filters was very low (