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 (<8 mbar) during loading showing that the applied coated method on the filters was successfully. On the other hand, the catalytic filter coupled with the rotated cube cell was tested at the pilot plant to examine their interaction, the effect of the coating method and the penalty in pressure drop of all system. A pressure drop of 0 – 68 mbar obtained during the test proves that the coating method did not alter the operation of the plant. As for testing at the demonstration plant, firstly, a monolith (Rh/Pt) was tested close coupled with an uncoated filter using an O/C ratio from 0.9 to 1.3, S/C ratio equal to 2.0, an inlet temperature (Tin) of 450°C with a GHSV from 5000 to 14000 h-1. The overall result fully agrees with the prediction from the simulation. The thermodynamic equilibrium was reached during the testing time with a methane conversion of 98% and hydrogen yield of 2.0. Moreover, tests with the integration of the catalyzed conventional foam and the catalytic trap downstream of the reforming reactor were performed. The boundary conditions were a space velocity of 4000, S/C= 2 and O/C=1.1. A thermodynamic equilibrium and a methane conversion higher than 98% were achieved. The plant was able to reach the predicted conversions and concentrations at nominal capacities corresponding to 50 Nm3/h (100 Kg/day) of pure hydrogen, creating a negligible pressure drop during the operation time of the processor. Finally, this thesis also deals with a comparative LCA of three different hydrogen production process from biogas. The investigated processes are: the biogas ATR, the biogas steam reforming (SR) and the water hydrolysis (a biogas-fueled internal combustion engine (ICE) followed by an electrolyzer). They were compared using environmental (GWP) and energetic (GER) impacts in order to highlight their weaknesses and strengths. H2 from biogas ATR has been demonstrated to be the most promising process in terms of the emissions reduction and energetic efficiency considering its life cycle from the extraction and processing of raw materials to the production of high purity hydrogen. The ICE + Electrolyzer process require a large amount of energy and biogas to sustain the electrochemical reactions. This feature makes such system the least energetically efficient with the most negative environmental impact. With a process efficiency of 65%, 63% and 25% for ATR, steam reforming and electrolysis process, respectively. Lastly, the economic analysis was performed to evaluate the H2 final cost. On the one hand, it was found that the process is economically favorable for H2 production higher than 100 Nm3/h. On the other hand, in 10 years of amortization using this technology, the final cost for H2 production of 100 Nm3/h from biogas is 3€/Kg H2, lower than the European target (5€/kg H2). The longer the plant life is, the more affordable the initial investment is.