Porous materials are interesting candidates for gas storage in different applications. The present study analyses at room temperature the high pressure storage of H 2 , CH 4 and CO 2 in a number of porous carbons (eight monoliths and two powdered activated carbons). The samples cover a wide range of porosities and densities (monoliths having high porosity with moderate density or moderate porosity with high density) with the aim to discuss the relative importance that the sample surface area has on the volumetric storage capacity, in relation to the importance of the density of the material. Our results show that the gravimetric storage capacities of the three studied gases are controlled by the textural properties of the adsorbent, whereas the volumetric storage capacities are mainly controlled by the adsorbent density. High volumetric excess adsorption capacity values (for example, H 2 : 10 g l À1 ; CH 4 : 110 g l À1 and CO 2 : 440 g l À1 ) correspond to monoliths having high densities, despite their moderately developed porosities. This paper also compares these results with those obtained similarly (same gases and same experimental conditions) using the highest known surface area material (MOF-210). In summary, our volumetric results, obtained with commercially available ATMI monoliths and their CO 2 activation, are, to the best of our knowledge, amongst the highest that have been reported; higher than the high surface area samples of the M3M monolith prepared from Maxsorb (S BET : 2610 m 2 g À1 ) or MOF-210 (S BET : 6240 m 2 g À1 ). Although a variety of MOFs have been reported to exceed our results, oftentimes these values are overestimated due to the fact that the volumetric capacity of MOFs was calculated using crystal density rather than experimentally measured density.

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Please cite this article as: Marco-Lozar, J.P., Kunowsky, M., Suárez-García, F., Linares-Solano, A., Sorbent design for CO 2 capture under different flue gas conditions, Carbon (2014), doi: http://dx.doi.org/10.1016/j.carbon. 2014.01.064This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Sorbent design for CO AbstractCO 2 capture by solid sorbents is a physisorption process in which the gas molecules are adsorbed in a different porosity range, depending on the temperature and pressure of the capture conditions. Accordingly, CO 2 capture capacities can be enhanced if the sorbent has a proper porosity development and a suitable pore size distribution. Thus, the main objective of this work is to maximize the CO 2 capture capacity at ambient temperature, elucidating which is the most suitable porosity that the adsorbent has to have as a function of the emission source conditions. In order to do so, different activated carbons have been selected and their CO 2 capture capacities have been measured. The obtained results show that for low CO 2 pressures (e.g., conditions similar to post-combustion processes) the sorbent should have the maximum possible volume of micropores smaller than 0.7 nm. However, the sorbent requires the maximum possible total micropore volume when the capture is performed at high pressures (e.g., conditions similar to oxy-combustion or pre-combustion processes). Finally, this study also analyzes the important influence that the sorbent density has on the CO 2 capture capacity, since the adsorbent will be confined in a bed with a restricted volume.

In a previous study, we investigated, at a laboratory scale, the chemical activation of two different carbon fibres (CF), their porosity characterization, and their optimization for hydrogen storage [1]. In the present work, this study is extended to: (i) a larger range of KOH activated carbon fibres, (ii) a larger range of hydrogen adsorption measurements at different temperatures and pressures (i.e. at room temperature, up to 20 MPa, and at 77 K, up to 4 MPa), and (iii) a scaling-up activation approach in which the obtained activated carbon fibres (ACF) are compared with those from laboratory-scale activation. The prepared samples cover a large range of porosities, which is found to govern their ability for hydrogen adsorption. The hydrogen uptake capacities of all the prepared samples have been analysed both in volumetric and in gravimetric bases. Thus, maximum adsorption capacities of around 5 wt.% are obtained at 77 K, and 1.1 wt.% at room temperature, respectively. The packing densities of the materials have been measured, turning out to play an important role in order to estimate the total storage capacity of a tank volume. Maximum values of 17.4 g l −1 at 298 K, and 38.6 g l −1 at 77 K were obtained.

In the literature, different approaches, terminologies, concepts and equations are used for calculating gas storage capacities. Very often, these approaches are not well defined, used and/or determined, giving rise to significant misconceptions. Even more, some of these approaches, very much associated with the type of adsorbent material used (e.g., porous carbons or new materials such as COFs and MOFs), impede a suitable comparison of their performances for gas storage applications. We review and present the set of equations used to assess the total storage capacity for which, contrarily to the absolute adsorption assessment, all its experimental variables can be determined experimentally without assumptions, ensuring the comparison of different porous storage materials for practical application. These materialbased total storage capacities are calculated by taking into account the excess adsorption, the bulk density (ρ bulk ) and the true density (ρ true ) of the adsorbent. The impact of the material densities on the results are investigated for an exemplary hydrogen isotherm obtained at room temperature and up * Tel.: +34 965 90 93 50; Fax: +34 965 90 34 54.Email address: kunowsky@ua.es (Mirko Kunowsky) February 5, 2013 to 20 MPa. It turns out that the total storage capacity on a volumetric basis, which increases with both, ρ bulk and ρ true , is the most appropriate tool for comparing the performance of storage materials. However, the use of the total storage capacities on a gravimetric basis cannot be recommended, because low material bulk densities could lead to unrealistically high gravimetric values. Preprint submitted to Microporous and Mesoporous Materials