Retos actuales para la captura y almacenamiento de CO2

Las grandes emisiones de CO2 procedentes de la combustión de combustibles fósiles están provocando un calentamiento global en nuestro planeta. Estos problemas medioambientales están obligando a los diferentes gobiernos a buscar soluciones que permitan reducir esas emisiones y mitigar sus efectos adversos. Una de las soluciones más prometedoras consiste en la captura selectiva de CO2 en efluentes industriales mediante el uso de materiales adsorbentes porosos (zeolitas, carbón activado y materiales híbridos MOFs) que combinen una elevada capacidad de adsorción y una adecuada selectividad a CO2 frente al resto de gases del proceso industrial, además de una adecuada regeneración.Large CO2 emissions coming from the combustion of fossil fuels are responsible for the global warming in the Earth. These environmental concerns are forcing the different governments to find solutions to reduce CO2 emissions and mitigate these adverse effects. One of the most promising solutions consists in the selective CO2 capture on industrial streams using porous adsorbents (zeolites, activated carbons and MOFs) combining a high adsorption capacity and a proper selectivity to CO2 versus other molecules from flue gas, together with a proper regeneration

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO2 capture both at atmospheric (∼168 mg CO2/g at 298 K) and high pressure (∼1500 mg CO2/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO2/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.Financial support from MINECO: Strategic Japanese-Spanish Cooperative Program (PLE2009-0052) and Generalitat Valenciana (PROMETEO/2009/002)

Methane Hydrate in Confined Spaces: An Alternative Storage System

Methane hydrate inheres the great potential to be a nature‐inspired alternative for chemical energy storage, as it allows to store large amounts of methane in a dense solid phase. The embedment of methane hydrate in the confined environment of porous materials can be capitalized for potential applications as its physicochemical properties, such as the formation kinetics or pressure and temperature stability, are significantly changed compared to the bulk system. We review this topic from a materials scientific perspective by considering porous carbons, silica, clays, zeolites, and polymers as host structures for methane hydrate formation. We discuss the contribution of advanced characterization techniques and theoretical simulations towards the elucidation of the methane hydrate formation and dissociation process within the confined space. We outline the scientific challenges this system is currently facing and look on possible future applications for this technology.L.B. gratefully acknowledges the Daimler und Benz Stiftung (award number 32–01/16) and the Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) for support of the Mechanocarb project (award number 03SF0498). M.E.C. acknowledges the Alexander von Humboldt foundation for financial support. J.S.A. acknowledges financial support from MINECO (Project MAT2016-80285-P) and Generalitat Valenciana (PROMETEOII/2014/004)

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1 cm3/g) and high packing density (0.7 g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160 cm3 (STP)/cm3 at 25 °C and 3.5 MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700 °C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175 cm3 (STP)/cm3 at 25 °C and 5 MPa and 200 cm3 (STP)/cm3 at 25 °C and 10 MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5 nm at pressure up to 10 MPa was estimated to understand their contribution to the total adsorption capacity.Authors acknowledge financial support from MINECO: Project MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) and Generalitat Valenciana (PROMETEO/2009/002)

High-Pressure Methane Storage in Porous Materials: Are Carbon Materials in the Pole Position?

Natural gas storage on porous materials (ANG) is a promising alternative to conventional on-board compressed (CNG) or liquefied natural gas (LNG). To date, Metal–organic framework (MOF) materials have apparently been the only system published in the literature that is able to reach the new Department of Energy (DOE) value of 263 cm3 (STP: 273.15 K, 1 atm)/cm3; however, this value was obtained by using the ideal single-crystal density to calculate the volumetric capacity. Here, we prove experimentally, and for the first time, that properly designed activated carbon materials can really achieve the new DOE value while avoiding the additional drawback usually associated with MOF materials (i.e., the low mechanical stability under pressure (conforming), which is required for any practical application).Authors acknowledge financial support from MINECO: Strategic Japanese−Spanish Cooperation Program (No. PLE2009-0052), Concert Project-NASEMS (No. PCIN-2013-057) and Generalitat Valenciana (No. PROMETEO/2009/002)

Improved mechanical stability of HKUST-1 in confined nanospace

One of the main concerns in the technological application of several metal–organic frameworks (MOFs) relates to their structural instability under pressure (after a conforming step). Here we report for the first time that mechanical instability can be highly improved via nucleation and growth of MOF nanocrystals in the confined nanospace of activated carbons.Financial support from MINECO projects MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057) is gratefully acknowledged

Influence of the oxygen-containing surface functional groups in the methane hydrate nucleation and growth in nanoporous carbon

Petroleum pitch-derived activated carbon (PP-AC) has proved to be an excellent platform to promote the methane hydrate formation in milder condition than nature, even though the water-to-hydrate yield at the threshold formation pressure of 3.3 MPa is rather low (ca. 13%). Herein, we report that the presence of oxygen-containing surface functional groups in the oxidized carbon analogue (PP-AC_Ox) plays a significant role in the nucleation and growth in the low-pressure region. High-pressure methane adsorption/desorption isotherms revealed an enhancement in the water-to-hydrate yield up to ca. 51% around 3.3 MPa and 2 °C, in an extremely narrow working pressure window, with no hysteresis associated.Authors acknowledge financial support from MINECO Projects: MAT2016-80285-P and CONCERT Project-NASEMS (PCIN-2013-057), and Generalitat Valenciana (PROMETEOII/2014/004). MEC thanks Alexander von Humboldt foundation for financial support

HKUST-1@ACM hybrids for adsorption applications: A systematic study of the synthesis conditions

This work constitutes a guide towards the preparation of metal-organic framework materials (MOF) supported and/or confined in activated carbon monoliths (ACM). The resulting hybrid porous materials exhibit improved physico-chemical properties as compared with their parent constituents. The different hybrids were obtained exploring several experimental approaches, which were thoroughly discussed. All hybrids were characterized by N2 adsorption isotherms, SEM, TGA and XRD techniques. The characterization studies pointed out that the preparation conditions are of paramount importance in defining the nucleation and growth of HKUST-1, either outside of the carbon grains (surface coating), and/or in the internal pores (bulk confinement). While the surface coating was achieved by directly synthesizing the MOF in presence of the ACM (i.e. in-situ synthesis), bulk confinement is favored after applying an additional step that involves a pre-nucleation at low temperatures (5 °C). The hybrid material with the best performance, sample A5(1), shows enhanced mechanical properties compared to its parent counterparts, combined with high apparent surface area (up to 1300 m2/g), an improved crushing strength (about 8 times superior to ACM) and a geometrical density of around 0.45 cm3/g, which almost duplicates that of ACM. Last but not least, the adsorption behavior of the hybrid was tested for CO2 and CH4 adsorption. Application of IAST equation to the single component adsorption isotherms at room temperature gives rise to a CO2/CH4 selectivity factor of 5.5 in the hybrid material, larger than that on ACM (S = 3.5).This work was supported by MINECO projects: MAT2013-45008-p. MEC wants to thank the Spanish Government for the fellowship FPU AP2010-4920

Gate-opening effect in ZIF-8: the first experimental proof using inelastic neutron scattering

The gate-opening phenomenon in ZIFs is of paramount importance to understand their behavior in industrial molecular separations. Here we show for the first time using in situ inelastic neutron scattering (INS) the swinging of the –CH3 groups and the imidazolate linkers in the prototypical ZIF-8 and ZIF-8@AC hybrid materials upon exposure to mild N2 pressure.The authors acknowledge financial support from MINECO projects: MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057). EVRF gratefully acknowledge support from MINECO (Spain) for his Ramón y Cajal grant (RyC-2012-11427). DFJ thanks the Royal Society (UK) for funding through a University Research Fellowship and Dr Axel Zeitler for interesting discussions. This research benefited from the use of the VISION beamline (IPTS-13608) at ONRL’s Spallation Neutron Source and the VirtuES (Virtual Experiments in Spectroscopy) project, (LDRD 7739), which are supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC

Oxidative Dehydrogenation of Ethylbenzene Over Poly(furfuryl alcohol)-Derived CMK-1 Carbon Replica

Poly(furfuryl alcohol) was introduced into a pore system of MCM-48 silica by the precipitation polycondensation of furfuryl alcohol (FA). The complete filling of the pores without the deposition of significant amounts of polymer on the external surface of MCM-48 was obtained at the FA/MCM-48 mass ratio close to 1.0. The final structure of carbon replica was formed by subsequent carbonization and extraction of SiO2 with HF. The carbonization temperature strongly influenced the surface composition of the formed carbon replicas. The highest catalytic activity in the oxidative dehydrogenation of ethylbenzene was observed for CMK-1 with the highest concentration of phenol and carbonyl groups, recognized as active sites of the studied reaction.This work was supported by the National Science Centre under the Grant No. 2013/09/B/ST5/03419. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08)