• Energy Research

There is an urgent need to develop materials and processes that reduce the energy penalty associated to the CO2 capture step. Biochars are appealing adsorbents for post-combustion CO2 capture applications due to their low cost, stability in moisture conditions and microporous nature. Series of carbon adsorbents were prepared from almond shells and olive stones by single-step activation with air at 400–500 °C, and with lower O2 concentration in the activating gas, 3–5%, at higher temperatures (500–650 °C). This process entails energy savings compared to conventional activation with carbon dioxide or steam. It has been found that the pore size distribution can be tailored by adequately selecting the activating conditions. Carbons obtained under lower oxygen partial pressures and higher temperatures present narrow microporosity, which is essential for the adsorption of CO2 at low partial pressures. These appealing low-cost adsorbents have competitive CO2 working capacities and high CO2/N2 equilibrium selectivity in conditions that can be considered representative for post-combustion CO2 capture, thus showing potential for this application. Work carried out with financial support from the Spanish MINECO (Project ENE2011-23467), co-financed by the European Regional Development Fund (ERDF). M.G.P. acknowledges funding from the CSIC (JAE-Doc program), and A.S.G. acknowledges a contract from the MINECO (FPI program); both programs are co-financed by the European Social Fund. Peer reviewed

GHGT-11 Post-combustion CO2 capture can contribute to mitigate anthropogenic CO2 emissions in the short-to-medium term at relatively low technology risk. However, there are not post-combustion units installed yet on a commercial scale, and the considered first generation capture processes, based on absorption with amines, are energy intensive. Adsorption processes present scope for reducing the energy penalty of the capture step. In this work, carbons prepared from spent coffee grounds are evaluated as potential adsorbents for this application. They present high CO2/N2 selectivity, and a working capacity competitive to that of zeolite 13X with the appealing advantages of a significant lower cost, higher stability and easier regeneration. Work carried out with financial support from the Spanish MINECO (Project ENE2011-23467), cofinanced by the European Regional Development Fund (ERDF). A.S.G. and M.G.P. acknowledge contracts from the MICINN FPI and CSIC JAE-Doc programs, respectively, co-financed by the European Social Fund. Peer reviewed

12th International Conference on Greenhouse Gas Control Technologies, GHGT-12 Water vapor is the third component of flue gases after N2 and CO2. The permanent dipole moment of the water molecule makes it strongly adsorbable on many adsorbents, which can negatively affect the adsorption capacity of carbon dioxide (even causing an irreversible loss in certain cases). Carbon materials have high stability in moist conditions and present a hydrophobic nature that makes these materials appealing adsorbents for post-combustion CO2 capture. Furthermore, these adsorbents present the added advantage that can be obtained from a globally available, cheap and renewable source of carbon: biomass. In the present work the effect of water vapor on the adsorption performance of CO2 using a microporous biochar developed from olive stones by single- step oxidation is evaluated. The equilibrium of adsorption of water vapor on the selected biochar was studied in a wide temperature range that is considered of interest for the post-combustion case (12.5-85 °C). This biochar presents a moderate water adsorption capacity and type V adsorption isotherms, which will facilitate the desorption of water vapor during cyclic operation. Breakthrough curves were obtained using a gas mixture which composition resembled flue gas in the presence and absence of water vapor. The breakthrough curves of CO2 obtained under dry and humid conditions overlap each other, which indicates that the presence of water vapor does not hinder CO2 adsorption in the short time scale. Moreover, the adsorbent recovered its full adsorption capacity after regeneration. These findings point out that this material could be used to separate CO2 from humid flue gas using cyclic adsorption processes. Work carried out with financial support from the Spanish MINECO (Project ENE2011-23467), co-financed by the European Regional Development Fund (ERDF). M.G.P. acknowledges funding from the CSIC (JAE-Doc program) and A.S.G. acknowledges a contract from the Spanish MINECO (FPI program), both programs are co-financed by the European Social Fund Peer reviewed

Sustainable carbon adsorbents have been produced from biomass residues by single-step activation with CO2. The activation conditions were optimised to develop narrow micropores in order to maximise the CO2 adsorption capacity of the carbons under post-combustion conditions. The equilibrium of adsorption of pure CO2 and N2 was measured between 0 °C and 50 °C up to 120 kPa for the outstanding carbons. The CO2 adsorption capacity measured at low pressures is among the highest ever reported for carbon materials (0.6–1.1 mmol g−1 at 15 kPa and 25–50 °C), and the average isosteric heat of adsorption is typical of a physisorption process: 27 kJ mol−1. Dynamic experiments carried out in a fixed-bed adsorption unit showed fast adsorption and desorption kinetics and a high CO2-over-N2 selectivity. These adsorbents are able to separate a mixture with 14% CO2 (balance N2) at 50 °C, conditions that can be considered as representative of post-combustion conditions, and they can be easily regenerated. This work was carried out with financial support from the Spanish MINECO (Project ENE2011‐ 23467), co‐financed by the European Regional Development Fund (ERDF). M.G.P. acknowledges funding from the CSIC (JAE‐Doc program), and A.S.G. acknowledges a contract from the MINECO (FPI program); both programs are co‐financed by the European Social Fund. Peer reviewed

In this work, the entire manufacturing process of electrostatic supercapacitors using the atomic layer deposition (ALD) technique combined with the employment of nanoporous anodic alumina templates as starting substrates is reported. The structure of a usual electrostatic capacitor, which comprises a top conductor electrode/the insulating dielectric layer/and bottom conductor electrode (C/D/C), has been reduced to nanoscale size by depositing layer by layer the required materials over patterned nanoporous anodic alumina membranes (NAAMs) by employing the ALD technique. A thin layer of aluminum-doped zinc oxide, with 3 nm in thickness, is used as both the top and bottom electrodes’ material. Two dielectric materials were tested; on the one hand, a triple-layer made by a successive combination of 3 nm each layers of silicon dioxide/titanium dioxide/silicon dioxide and on the other hand, a simple layer of alumina, both with 9 nm in total thickness. The electrical properties of these capacitors are studied, such as the impedance and capacitance dependences on the AC frequency regime (up to 10 MHz) or capacitance (180 nF/cm2) on the DC regime. High breakdown voltage values of 60 V along with low leakage currents (0.4 μA/cm2) are also measured from DC charge/discharge RC circuits to determine the main features of the capacitors behavior integrated in a real circuit.

In this work spent coffee grounds from single-use capsules were used as the starting material for producing low-cost activated carbons. The activation conditions were selected and optimised to produce microporous carbons with high CO2 adsorption capacity and selectivity, thus with potential to be used as adsorbents in postcombustion CO2 capture applications. Two activation methods are compared: physical activation with CO2 and chemical activation with KOH. The first method is considered less contaminant; however, leads to carbons with lower textural development and thus lower CO2 adsorption capacity than those obtained by activation with KOH. On the other hand, multicomponent adsorption cyclic experiments pointed out that the CO2/N2 selectivity of physically activated carbons is higher than that of chemically activated carbons. Work carried out with financial support from the Spanish MICINN (Project ENE2008-05087). A.S.G. acknowledges a contract from the MICINN (FPI program), co-financed by the European Social Fund. Peer reviewed