Ethane adsorption in slit-shaped micropores: influence of molecule orientation on adsorption capacity
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Ethane adsorption in slit-shaped micropores: influence of molecule orientation on adsorption capacity G. Calleja · B. Coto · A. Pinar · A. M. Morales-Cas
Received: 30 December 2005 / Revised: 6 June 2006 / Accepted: 23 June 2006 C Springer Science + Business Media, LLC 2006
Abstract Adsorption of ethane in a slit shaped micropore system has been studied by Monte Carlo molecular simulation by considering this hydrocarbon as a two interacting sites molecule. Ethane adsorption in pore sizes from 0.41 to 1.66 nm was simulated at 303 K. Microscopic characteristics of the adsorbed phase have been studied for pores of different size, comparing two density profiles: the molecule centre of mass profile and the molecular interaction site profile. Averaged angle distribution of molecule positions with respect to the slit plane across the pore width has been also obtained by simulation. These results were related to ethane molecule packing efficiency, which is also related to the adsorption capacity in terms of the adsorbed phase density. Packing efficiency presents an oscillation shape as the result of the adsorbate disorder inside the pore. Pressure influence on the adsorption has been studied by following pore filling by simulation. When pore condensation takes place and for pressures above condensation, fluid-fluid interactions are determinant in molecule disorder observed between the two adsorbed layers. Keywords Activated carbon . Slit pore model . Molecular simulation . Monte Carlo simulation . Ethane G. Calleja () . B. Coto . A. Pinar . A. M. Morales-Cas Department of Chemical and Environmental Technology, ESCET, Rey Juan Carlos University, c/ Tulip´an s/n 28933 M´ostoles, Madrid (Spain) e-mail: [email protected]
1 Introduction Microporous carbons are among the most used adsorbents for liquid and gas streams. Characteristics of adsorbed light hydrocarbons in microporous carbons have been widely studied (Mota, 1999; Liu and Monson, 2005). As the second component of natural gas, ethane is a compound of special interest for the energy industry (Gall and Sanders, 2002) due to the increasing development of natural gas driven automobile devices. These applications require a high efficiency in natural gas storage, being adsorption in porous materials one of the most attractive alternatives, as suggested in several studies (Lozano-Castell´o, 2002). Adsorption selectivity of methane and ethane is highly influenced by the presence of heavier hydrocarbons such as propane and butane. The adsorption behaviour of ethane and its mixtures with various light hydrocarbons such as methane and propane in microporous carbons has been considered widely in recent years (Cracknell and Nicholoson, 1994; Zhou et al., 2005). Besides these experimental studies, advanced computational methods such as Monte Carlo or Density Functional Theory have been applied to adsorption studies of several adsorbate-adsorbent systems, pointing up the applications in textural characterization of porous media based on adsorption data of several molecule
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