Preparation of Pd membranes for steam reforming of biomass derivatives in a membrane reactor

Hydrogen is vital for the chemical and petrochemical industries and as an energy source, but its current production from fossil fuels leads to significant carbon emissions. Biomass-derived resources, such as bio-oil and bioethanol, offer an eco-friendly alternative to fossil-based production. Bioethanol, generated from sugar fermentation, possesses favorable attributes including a high octane number, low greenhouse gas emissions and compatibility with existing infrastructure. It not only reduces dependence on fossil fuels but also lowers net CO2 emissions significantly. Ethanol steam reforming (ESR) technologies, particularly in membrane reactors (MR), provide high-purity H2 production by integrating catalysis and selective separation . Pd-based membranes excel at extracting H2 from gas mixtures. The experimental part has been carried out at the Faculty of Science and Technology, in Leioa, belonging to the University of the Basque Country (UPV-EHU). This master thesis aims to assess pure H2 production through ESR in a MR for a sustainable transition from fossil to renewable feedstocks. The membranes, used in this work, were commercial membranes (REB) and composite membranes prepared in the laboratory. Then, two catalysts were prepared and characterized: a Ni/Al2O3 catalyst from the reduction of a NiAl2O4 spinel and a Ni/MgAl2O4 catalyst from the reduction of a NiO/MgAl2O4 material (NiO impregnated onto MgAl2O4 spinel). The results can be divided in three different sections: membrane selection, catalyst selection and performance comparison between the CR and MR. The first section discusses permeation tests conducted on various membranes, including laboratory-made ones (MP-550, MCP-550, MCP-575) and a commercial membrane (REB). The REB membrane required activation, increasing H2 permeance over time. In contrast, the laboratory-made membranes needed stabilization, resulting in a decrease in H2 permeance over time until reaching stability. Some membranes (MCP-550 and MCP-575) used a CeO2 intermediate layer to prevent these interactions, with MCP-575 showing the highest H2 permeability. The second section discusses a comparison between Ni/Al2O3 and Ni/MgAl2O4 catalysts for the ESR reaction. The characterization results reveal that Ni/Al2O3 consists solely of Ni crystals on Al2O3, while Ni/MgAl2O4 contains Ni crystals on MgAl2O4 and some Al2O3. Both catalysts have inherent acidity due to Al2O3, but Ni/MgAl2O4 has lower acidity due to its mixed support. The differences in catalyst performance in ESR reaction-regeneration cycles are attributed to the support structure and inherent acidity, influenced by Al2O3 presence. Despite lower initial activity, Ni/MgAl2O4 exhibits improved activity in subsequent reactions and better reproducible regeneration, making it the most interesting catalyst for the following ESR tests. The last section discusses the performance of the ESR reaction using a Ni/MgAl2O4 catalyst in a CR and in a MR. It notes that increasing pressure in the CR decreases yields of H2, CO, and CO2 wherease in the MR, higher pressure slightly improves H2 recovery and pure H2 yield. The study highlights the complex interplay between pressure and temperature for the ESR reaction performance in a MR using the selected Ni/MgAl2O4 catalyst and the Pd membrane (MCP-575 prepared in the laboratory). The results are favourable considering that the yield of pure H2 may come up to 60% at 550 ºC and 3 bar, with a total H2 yield of about 70%, keeping a low steam/ethanol ratio.