The production of pure hydrogen usually requires its extraction from a gas mixture. In fact, one of the critical stages related to the use of hydrogen as an energy carrier is the development of efficient and competitive techniques that separate hydrogen from other by-products such as steam, hydrocarbons, carbon dioxide and other gases. Membranes for hydrogen purification represent an appealing alternative to the current commercially available pressure swing adsorption (PSA) technology. In this context, mixed proton and electron conductors (MPEC) oxides are attractive candidates to be used as dense ceramic membranes for H2 separation due to their particular properties. These materials incorporate hydrogen into their lattice as charge protonic defects which means that, theoretically, they are 100% selective towards hydrogen separation. Furthermore, the properties of these oxides (i.e. working temperatures, durability) endow membranes that could be directly integrated into industrial processes or used in the so-called catalytic membrane reactors. Recently, BaCe0.65Zr0.20Y0.15O3-? (BCZ20Y15) and Ce0.85M0.15O2-? (M = Y and Gd) dual-phase membranes were explored by our group [1] reaching hydrogen permeability values among the highest ever reported for bulk MPEC membranes. The highest permeation flux was attained for the 50:50 volume ratio BaCe0.65Zr0.20Y0.15O3-? and Ce0.85Gd0.15O2-? membrane, reaching values of 1.27 mL·min-1·cm-2 at 755°C and 2.40 mL·min-1·cm-2 at 1040°C. The long term stability and degradation mechanisms are critical issues for these systems. Working conditions are really challenging: hydrogen purification is carried out at high temperatures in harsh environments containing H2O vapour, CO, CO2, and sulphides. Structural changes, chemical reactions, cation diffusion and other undesired phenomena could occur damaging the performance of membranes, even if TGA analysis and permeation tests indicate that the composites were stable in CO2. In this work, BCZ20Y15-GDC15 composites were exposed to different environments at high temperatures and then characterized by means of XRD and SEM techniques. The objective of this study is to systematically examine the chemical stability of the membranes in order to obtain a better understanding of their capability for practical applications.
Chemical stability study on BaCe0.65Zr0.20Y0.15O3-?-Ce0.85Gd0.15O2-? ceramic composites for hydrogen separation
Deambrosis SM;Fabrizio M
2016
Abstract
The production of pure hydrogen usually requires its extraction from a gas mixture. In fact, one of the critical stages related to the use of hydrogen as an energy carrier is the development of efficient and competitive techniques that separate hydrogen from other by-products such as steam, hydrocarbons, carbon dioxide and other gases. Membranes for hydrogen purification represent an appealing alternative to the current commercially available pressure swing adsorption (PSA) technology. In this context, mixed proton and electron conductors (MPEC) oxides are attractive candidates to be used as dense ceramic membranes for H2 separation due to their particular properties. These materials incorporate hydrogen into their lattice as charge protonic defects which means that, theoretically, they are 100% selective towards hydrogen separation. Furthermore, the properties of these oxides (i.e. working temperatures, durability) endow membranes that could be directly integrated into industrial processes or used in the so-called catalytic membrane reactors. Recently, BaCe0.65Zr0.20Y0.15O3-? (BCZ20Y15) and Ce0.85M0.15O2-? (M = Y and Gd) dual-phase membranes were explored by our group [1] reaching hydrogen permeability values among the highest ever reported for bulk MPEC membranes. The highest permeation flux was attained for the 50:50 volume ratio BaCe0.65Zr0.20Y0.15O3-? and Ce0.85Gd0.15O2-? membrane, reaching values of 1.27 mL·min-1·cm-2 at 755°C and 2.40 mL·min-1·cm-2 at 1040°C. The long term stability and degradation mechanisms are critical issues for these systems. Working conditions are really challenging: hydrogen purification is carried out at high temperatures in harsh environments containing H2O vapour, CO, CO2, and sulphides. Structural changes, chemical reactions, cation diffusion and other undesired phenomena could occur damaging the performance of membranes, even if TGA analysis and permeation tests indicate that the composites were stable in CO2. In this work, BCZ20Y15-GDC15 composites were exposed to different environments at high temperatures and then characterized by means of XRD and SEM techniques. The objective of this study is to systematically examine the chemical stability of the membranes in order to obtain a better understanding of their capability for practical applications.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
