Thermodynamic analysis of molecular simulations of CO 2 and CH 4 adsorption in FAU zeolites Junfang Zhang a,n , N. Burke b , Shuichang Zhang c , Keyu Liu a,c , M. Pervukhina a a CSIRO CESRE, 26 Dick Perry Ave, WA 6151, Australia b CSIRO CESRE, Ian Wark Laboratory, Bayview Ave, Clayton, Vic 3168, Australia c Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China HIGHLIGHTS  NaX has a higher affinity for CO 2 and CH 4 than NaY has.  NaY exhibits higher maximum adsorption capacity compared with NaX.  Both NaX and NaY present a heterogeneous surface.  Adsorbed CO 2 and CH 4 are in ordered arrangement in both NaX and NaY.  Adsorbed CO 2 and CH 4 have more orderly arrangement in NaX than in NaY. article info Article history: Received 26 November 2013 Received in revised form 24 February 2014 Accepted 3 April 2014 Available online 13 April 2014 Keywords: CO 2 /CH 4 adsorption isotherm Monte Carlo simulation Faujasite zeolite Langmuir/Toth isotherm model Heat of adsorption abstract Adsorption of carbon dioxide (CO 2 ) and methane (CH 4 ) in faujasite (FAU)-type zeolites NaX and NaY was studied by performing the grand-canonical Monte Carlo (GCMC) simulations at 288, 298 and 308 K and a pressure range up to 10 MPa. Simulation results have been analyzed using Langmuir and Toth model. The latter provides a better description of CH 4 and CO 2 adsorption with respect to the former suggesting that NaX and NaY present a heterogeneous surface in the adsorption especially for CO 2 . Thermodynamic parameters of Gibb's free energy change, enthalpy change, and entropy change were calculated using adsorption equilibrium constant obtained from the GCMC simulations. The results suggested that NaX has higher affinity for both CH 4 and CO 2 than NaY and it is more favorable for CO 2 than CH 4 to adsorb in NaX and NaY. Although NaX has higher affinity than NaY, NaY exhibits higher maximum adsorption capacity due to the volume effect of sodium cations at high pressure. Adsorbed molecules are in ordered arrangement in both NaX and NaY and they have more orderly arrangement in NaX than in NaY. This study provides a quantitative evaluation of CO 2 and CH 4 adsorption in FAU-zeolites. Crown Copyright & 2014 Published by Elsevier Ltd. All rights reserved. 1. Introduction Adsorption plays an important role in the gas processing industry. There is a growing research interest in the synthesis, characterization and implications of porous nanomaterials, such as zeolites (Yang, 1997). Zeolites are crystalline, microporous materi- als with large surface areas and molecular size pore structure. Therefore, they are commercially important and widely used in applications such as separations, purification, ion exchange and catalysis. The research on gas adsorption and separation has benefited from the recent advancement in synthetic zeolites development (Beerdsen et al., 2002), pressure swing adsorption design (Anson et al., 2009; Neddenri, 1968; Tagliabue et al., 2009) and molecular simulation techniques (Denayer et al., 1998; Fuchs et al., 2006; Garcia-Perez et al., 2006; Keil et al., 2000; Kim et al., 2012; Palmas et al., 1991; Palomino et al., 2010). Separation of methane and carbon dioxide mixtures is a challenging research topic due to environmental and economic concerns and inherent difficulties in conducting experiments. It is beneficial to remove carbon dioxide from natural gas prior to converting it to liquefied natural gas (LNG) via low temperature processing. There are several technologies used in the removal of carbon dioxide from natural gas through the amine based solvents (Singh et al., 2007, 2009) and membrane systems (Scholes et al., 2012). Major challenges facing those methods are to keep the solvent clean and to attain the low carbon dioxide levels. In a cost effective Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science http://dx.doi.org/10.1016/j.ces.2014.04.001 0009-2509/Crown Copyright & 2014 Published by Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: Junfang.zhang@csiro.au (J. Zhang). Chemical Engineering Science 113 (2014) 54–61