Enhanced hydrogen production from thermochemical processes

To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil fuels is the development of a H2 economy. Not only can H2 be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H2 is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H2 yields owing to their reversible nature. Removing H2 with membranes and/or extracting CO2 with solid sorbents in situ can overcome these issues by shifting the component equilibrium towards enhanced H2 production via Le Chatelier's principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research

Nafion®/H-ZSM-5 composite membranes with superior performance for direct methanol fuel cells

Solution cast composite direct methanol fuel cell membranes (DEZ) based on DE2020 Nafion® dispersion and in-house prepared H-ZSM-5 zeolites with different Si/Al ratios were prepared and thoroughly characterized for direct methanol fuel cell (DMFC) applications. All composite membranes have indeed lower methanol permeability and higher proton conductivity than pure DE2020 membrane. The composite membranes with Si/Al ratio 25 and 5 wt.% of zeolites (DEZ25-5) having the lowest methanol permeability and the membrane with Si/Al ratio 50 and 1 wt.% of zeolites (DEZ50-1) having the highest proton conductivity were tested in the DMFC for several days. The DEZ25-5 has the best performance; namely high power density and stable performance in time

How can microwave heating contribute to the development of zeolite membranes

In this work the growth of both a zeolite (MFI) and a zeolite-like material (SOD) were investigated in/on αAlO tubular support, using hydrothermal conditions and microwave (MW) heating. The method reveals efficient for the rapid synthesis of MFI/αAlO membranes although gentle conditions were required in order to limit the thermal degradation of the template. Promising results were also obtained for directly growing SOD in/on the support. In both MFI and SOD MW synthesis the chemical dissolution of the αAlO support influences the final membrane characteristics. In the case of SOD synthesis, this phenomena which increases with both temperature and support size, alters the membrane homogeneity (composition and structure). In order to get round it, MWs were used to prepare SOD small crystals which were deposited on/in the αAlO support and submitted to a secondary growth. Homogeneous membranes were then obtained whose ideal selectivities αH/N and αHe/N reaches respectively 4.5 at 20°C and 6.2 at 115°C (these selectivities are lower than 2 for a ZSM-5 membrane in similar conditions)

Ryškinamos Lietuvos dirvožemių skyrimo ribos

Vytauto Didžiojo universitetasŽemės ūkio akademij

Méthode de synthèse robuste de membranes zéolithes MFI et prediction de leurs performance pour la séparation éthanol/eau par pervaporation

International audienceDans ce travail, un protocole robuste a été mis au point pour la synthèse à grande échelle demembranes zéolithes MFI (silicalite-1) sur des supports céramiques industriels. La méthode estbasée sur la synthèse hydrothermale de nano-germes de zéolithe par chauffage micro-ondes,leur dépôt sur le support, suivi par la croissance secondaire assistée par chauffage classique.Les performances des membranes MFI ont été validées pour l'extraction d'éthanol dans l’eaupar pervaporation.Une variété de supports commerciaux tubulaires en céramique fournis par Pall-Exekia,Inocermic, CTI, Atech, ainsi que des modules multi-capillaires produits par Hyflux CEPArationTechnologies, ont été testés afin de valider la robustesse du protocole de synthèse. Uneattention particulière a également été portée à la diminution des coûts de synthèse (quantité deproduits chimiques, nombre d'étapes de synthèse, recyclage) ainsi que des coûts du contrôlede qualité (méthodes simples de contrôle de l'homogénéité des membranes et de lareproductibilité de leurs performances).La formation de membranes homogènes (observée par FESEM) a été confirmée sur tous lestypes de supports, y compris sur les tubulaires mono ou multi-canaux et sur les assemblagesmulti-capillaires (20 cm de long). Afin d’optimiser les synthèses et de les valider sur cessupports industriels, une méthode simple et rapide a dû être développée pour prédire lesperformances des membranes pour l’extraction de l’éthanol dans l’eau. L’objectif était d’éviter,pendant cette étape de screening, la mise en oeuvre de protocoles complexes et coûteuxnécessitant une analyse de mélanges à l’échelle semi-industrielle. Dans ce cadre, unecorrélation originale a été mise en évidence entre la sélectivité des membranes en perméancedes gaz purs N2 et SF6 et le facteur de séparation éthanol/eau en pervaporation. Ainsi, les performances des membranes de silicalite-1 (S-1) pour la séparation de mélanges éthanol/eaus’avèrent être directement prévisibles à partir de valeurs de permsélectivités idéales a*(N2/SF6): par exemple un facteur de séparation éthanol/eau d’environ 60 (avec un flux d’éthanol de ~1,1kg.m-2s-1) est typiquement attendu pour une permsélectivité a*(N2/SF6) supérieure à 100. Lacourbe de corrélation empirique a ainsi permis d’optimiser à moindre coût les conditions desynthèse pour l’obtention de modules industriels intégrant des membranes organophilesperformantes pour l'extraction d’éthanol

Zinc-doped BSCF perovskite membranes for oxygen separation

This work investigates the partial substitution of Zn in the B-site of perovskite as Ba 0.5 Sr 0.5 (Co 0.8 Fe 0.2 ) 1- x Zn x O 3- d . The membranes were tested for oxygen separation from air and Zn incorporation into the BSCFZ cubic crystal structure proved to be effective as oxygen fluxes increased as compared with a pure BSCF (x = 0, no Zn). This was attribute to the increase in oxygen vacancy concentration as a function of Zn concentration. As a result, oxygen fluxes for the BSCFZ membranes were 200% (700 °C) and 32% (900 °C) higher than the BSCF analogue membrane. However, the correlation between oxygen vacancy concentration and oxygen flux diverged for Zn concentrations x = 0.08, which was associated with the shift and broadening of the main XRD peak 2? = 31.81° of the BSCFZ cubic structure caused by an additional oxide phase (ZnO). Zn doping also affected the microstructure of the sintered BSCFZ membranes. Grain boundary dimensions reduced as Zn substitution in the B-site increased to x = 0.06 up to 800 °C, resulting in improved oxygen fluxes. Contrary to this, high Zn concentration x = 0.08 increased grain boundary and reduced oxygen fluxes. Therefore, the Zn solubility into BSCF impact upon the oxygen vacancy and microstructural formation, which in turn affected the transport of oxygen ions through the membrane

Catalytic investigation of in situ generated Ni metal nanoparticles for tar conversion during biomass pyrolysis

In order to promote process intensification in syngas production from biomass gasification, our research team has already considered the integration of transition metal-based nanocatalysts in the biomass feedstock through its impregnation with metal salt aqueous solutions. The purpose of this work is to provide new insights into the complex physicochemical and catalytic mechanisms involved in this catalytic pathway from nickel salt. Applying a primary vacuum during impregnation allowed the rate of nickel insertion to be optimized and the generation of strong interactions between the metal cations and the lignocellulosic matrix. During biomass pyrolysis, Ni nanoparticles (NPs) form in situ below 500 C through carbothermal reduction and provide the active sites for adsorption of aromatic hydrocarbons and subsequent catalytic conversion. In order to test whether it was possible to improve the catalytic efficiency of Ni NPs by making them available right from the pyrolysis onset, some preformed Ni NPs were inserted into the biomass prior to pyrolysis. The in situ generated Ni NPs exhibit higher catalytic efficiency, particularly for aromatic tar conversion, than preformed Ni NPs. The high decrease in hard-to-destroy aromatic hydrocarbons formation during pyrolysis is of particular interest in the overall gasification process. The proposed catalytic strategy reveals promising for simplifying the cleaning up of the producer gas

Synthesis and properties of MFI zeolite membranes prepared by microwave assisted secondary growth, from microwave derived seeds

The objective of this work is to evaluate the use of microwave (MW) heating to accelerate the synthesis of silicalite-1 membranes by secondary growth. Silicalite-1 seeds (50-60 nm) were first prepared by MW-assisted hydrothermal synthesis from fresh sols. The MW seed suspension was deposited by slip-casting on commercial α-AlO supports and zeolite membranes were obtained after a synthesis time as short as 30-60 min, by MW-assisted secondary growth at 393-453 K. The membrane thickness varied typically from 200 nm to a few μm, with glassy like or columnar morphologies respectively, depending on the synthesis conditions. The very first single gas permeation results revealed a relatively high single gas permeance for the membranes prepared during 2 hours at 403-453 K, and a n/i-butane selectivity which tends to reach a maximum (40-50) for the membrane prepared at 433 K