Effect of Water and Carbon Dioxide on the Performance of Basolite Metal-Organic Frameworks for Methane Adsorption.

MOFs are potential adsorbents for methane separation from nitrogen, including recovery in diluted streams. However, water and carbon dioxide can seriously affect the adsorption performance. Three commercial MOFs, basolite C300, F300, and A100, were studied under similar conditions to fugitive methane streams, such as water (75 and 100% relative humidity) and carbon dioxide (0.33%) presence in a fixed bed. The presence of available open metal sites of copper (Cu2+) and aluminum (Al3+) in the case of basolite C300 and A100, respectively, constitutes a clear drawback under humid conditions, since water adsorbs on them, leading to significant methane capacity losses. Surprisingly, basolite F300 is the most resistant material due to its amorphous structure, which hinders water access. The combination of carbon dioxide and water creates a synergy that seriously affects basolite A100, closely related to its breathing effect, but does not constitute an important issue for basolite C300 and F300.

Dolomite industrial by-products as active material for CO2 adsorption and catalyst for the acetone condensation.

The feasibility of using dolomite powders, by-product from the refractory industry, as a CO2 adsorbent and as a catalyst for the acetone liquid-phase self-condensation is demonstrated in this article. The performance of this material can be largely improved by combining physical pretreatments (hydrothermal ageing, sonication) and thermal activation at different temperatures (500-800 °C). The highest CO2 adsorption capacity was observed for the sample after sonication and activated at 500 °C (46 mg·g-1). As to the acetone condensation, the best results were obtained also with the sonicated dolomites, mainly after activation at 800 °C (17.4% of conversion after 5 h at 120 °C). The kinetic model reveals that this material optimizes the equilibrium between catalytic activity (proportional to the total basicity) and deactivation by water (specific adsorption process). These results demonstrate that the valorisation of dolomite fines is feasible, proposing attractive pretreatments for obtaining activated materials with promising results as adsorbents and basic catalysts.

Metal-Organic Frameworks (MOFs) as methane adsorbents: From storage to diluted coal mining streams concentration.

Ventilation Air Methane emissions (VAM) from coal mines lead to environmental concern because their high global warming potential and the loss of methane resources. VAM upgrading requires pre-concentration processes dealing with high flow rates of very diluted streams (<1% methane). Therefore, methane separation and concentration is technically challenging and has important environmental and safety concerns. Among the alternatives, adsorption on Metal-Organic Frameworks (MOFs) could be an interesting option to methane selective separation, due to its tuneable character and outstanding physical properties. Most of the works devoted to the methane adsorption on MOFs deal with methane storage. Therefore, these works were reviewed to determine the properties governing methane-MOF interactions. In addition, the metallic ions and organic linkers roles have been identified. With these premises, decisive effects in the methane adsorption selectivity in nitrogen/methane lean mixtures have been discussed, since nitrogen is the most concentrated gas in the VAM stream, and it is very similar to methane molecule. In order to fulfill this overview, the effect of other aspects, such as the presence of polar compounds (moisture and carbon dioxide), was also considered. In addition, engineering considerations in the operation of fixed bed adsorption units and the main challenges associated to MOFs as adsorbents were also discussed.

Densification-Induced Structure Changes in Basolite MOFs: Effect on Low-Pressure CH4 Adsorption.

Metal-organic frameworks' (MOFs) adsorption potential is significantly reduced by turning the original powder into pellets or granules, a mandatory step for their use at industrial scale. Pelletization is commonly performed by mechanical compression, which often induces the amorphization or pressure-induced phase transformations. The objective of this work is the rigorous study of the impact of mechanical pressure (55.9, 111.8 and 186.3 MPa) onto three commercial materials (Basolite C300, F300 and A100). Phase transformations were determined by powder X-ray diffraction analysis, whereas morphological changes were followed by nitrogen physisorption. Methane adsorption was studied in an atmospheric fixed bed. Significant crystallinity losses were observed, even at low applied pressures (up to 69.9% for Basolite C300), whereas a structural change occurred to Basolite A100 from orthorhombic to monoclinic phases, with a high cell volume reduction (13.7%). Consequently, adsorption capacities for both methane and nitrogen were largely reduced (up to 53.6% for Basolite C300), being related to morphological changes (surface area losses). Likewise, the high concentration of metallic active centers (Basolite C300), the structural breathing (Basolite A100) and the mesopore-induced formation (Basolite F300) smooth the dramatic loss of capacity of these materials.