Adsorption of binary and ternary hydrocarbon gas mixtures on activated carbon: Experimental determination and theoretical prediction of the ternary equilibrium data

Abstract

Experimental binary and ternary equilibrium data for the adsorption of hydrocarbon mixtures of methane, ethane, ethylene, and propylene on activated carbon at 20°C are presented and discussed. Reproduction of binary adsorption equilibria and prediction of ternary adsorption equilibria exclusively with data of binary systems have been carried out using a real adsorbed solution theory, which requires the calculation of the activity coefficients for the components in the adsorbed phase.Predicted equilibrium data are found to be in excellent agreement with experimental values using Wilson and UNIQUAC equations to calculate the activity coefficients. The real absorbed solution theory provides a much more accurate method for predicting multicomponent adsorption equilibria than the ideal adsorbed solution theory. SCOPEThe use of adsorption for the separation of gas mixtures has been continuously increasing. The main advantages of adsorption as compared with other separation techniques are the high selectivity that can be attained and the relatively high capacity of the adsorbents for volatile compounds, even at low partial pressures. Some applications of interest include the purification of methane, ethylene, and other light hydrocarbons; the covery of LPG from natural and refinery gas streams; the separation of olefins from cracked gases; and the recovery of acetylene and other pretrochemicals from dilute mixtures with other hydrocarbon gases.Although there are a great deal of publications on adsorption of mixtures of hydrocarbons on porous solids (Hill, 1949 On the other hand, most of the theoretical work based on the analogy between the thermodynamics of solutions and the thermodynamics of mixed adsorbates predicts adsorption equilibria using the assumption of an ideal behavior of the adsorbates on the solid surface, which can be expressed in terms of a Raoult's type law (Myers, 1965). However, predicted adsorption equilibria are not always found to be in good agreement with experimental data. Certainly, there is a competition of the adsorbed molecules for the active centers of the solid surface, due to the different adsorption capacity of the adsorbates, so that the ideal adsorbed solution theory can be improved modifying the Raoult's law by the introduction of the activity coefficients for the components in the adsorbed phase. This paper discusses new experimental data on adsorption for binary and ternary hydrocarbon mixtures on activated carbon at 20°C and a total pressure up to 760 mm Hg (101.33 K Pa). A thermodynamic method based on a real adsorbed solution theory is applied to reproduce experimental binary adsorption equilibria and to predict ternary adsorption equilibria, only with binary systems data, calculating the activity coefficients for the components in the adsorbed phase by means of Wilson and UNIQUAC equations for vapor-liquid equilibrium. CONCLUSIONS AND SIGNIFICANCEAn experimental technique based on a fluidized adsorbent bed can be used to determine adsorption equilibria of gaseous mixtures in por...

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