RESUMO
Limiting the increase of CO2 in the atmosphere is one of the largest challenges of our generation1. Because carbon capture and storage is one of the few viable technologies that can mitigate current CO2 emissions2, much effort is focused on developing solid adsorbents that can efficiently capture CO2 from flue gases emitted from anthropogenic sources3. One class of materials that has attracted considerable interest in this context is metal-organic frameworks (MOFs), in which the careful combination of organic ligands with metal-ion nodes can, in principle, give rise to innumerable structurally and chemically distinct nanoporous MOFs. However, many MOFs that are optimized for the separation of CO2 from nitrogen4-7 do not perform well when using realistic flue gas that contains water, because water competes with CO2 for the same adsorption sites and thereby causes the materials to lose their selectivity. Although flue gases can be dried, this renders the capture process prohibitively expensive8,9. Here we show that data mining of a computational screening library of over 300,000 MOFs can identify different classes of strong CO2-binding sites-which we term 'adsorbaphores'-that endow MOFs with CO2/N2 selectivity that persists in wet flue gases. We subsequently synthesized two water-stable MOFs containing the most hydrophobic adsorbaphore, and found that their carbon-capture performance is not affected by water and outperforms that of some commercial materials. Testing the performance of these MOFs in an industrial setting and consideration of the full capture process-including the targeted CO2 sink, such as geological storage or serving as a carbon source for the chemical industry-will be necessary to identify the optimal separation material.
RESUMO
Activated carbons (ACs) are among the most commonly used sorbents for CO2 capture because of their high surface areas and micropore volumes, which depend on precursor and activation methods. In this study, we evaluated different ACs obtained from a low-value fraction of liquid-derived coal pyrolysis, namely phenolic oil, which was used as gel precursor before carbonization and KOH activation. CO2 capture performances were determined at temperatures between 25 and 120 °C, with CO2 concentrations ranging from 5 to 90 vol %. The most efficient sample captured 2.86 mmol of CO2/g AC at 25 °C and 1 bar, which is a highly competitive capture capacity, comparable to previously reported values for ACs without any modification/functionalization. Finally, their thermal stability and cyclability (i.e., for a minimum of six adsorption-desorption cycles) were evaluated. CO2 uptake was not affected by desorption temperature after six adsorption-desorption cycles. On the basis of the results obtained in this work, the role of the textural properties into the CO2 capture at realistic postcombustion temperatures and partial pressures was elucidated. In particular, we concluded that CO2 adsorption performance was more related to the volume of the narrowest pores and to the average pore size than to the surface area.
RESUMO
In this work, a regenerable sorbent for Hg retention based on carbon supported Au nanoparticles has been developed and tested. Honeycomb structures were chosen in order to avoid pressure drop and particle entrainment in a fixed bed. Carbon-based supports were selected in order to easily modify the surface chemistry to favour the Au dispersion. Results of Hg retention and regeneration were obtained in a bench scale experimental installation working at high space velocities (for sorbent, 53,000 h(-1); for active phase, 2.6 × 10(8) h(-1)), 120 °C for retention temperature and Hg inlet concentration of 23 ppbv. Gold nanoparticles were shown to be the active phase for mercury capture through an amalgamating mechanism. The mercury captured by the spent sorbent can be easily released to be disposed or reused. Mercury evolution from spent sorbents was followed by TPD experiments showing that the sorbent can be regenerated at temperatures as low as 220 °C.