A new adsorption isotherm for C5 hydrocarbons on metal-organic framework Cu3(BTC)2

A new equation describing isotherms of C5 hydrocarbons on metal-organic framework Cu-3(BTC)(2) in the temperature range from 273 to 333 K was developed. The isotherms of n-pentane, isopentane and cyclopentane on Cu-3(BTC)(2) belonging to the Type 5 according to the IUPAC classification are characterized by a long vertical part in the low pressure region. An analysis of isosteric adsorption heats has revealed that lateral interactions among pentane molecules adsorbed on Cu-3(BTC)(2) dominate over gas-solid interactions. Because there is no equation in the literature, which can be used for the description of isotherms under investigation, equation based on the Dubinin theory of S-shaped adsorption isotherms was developed. According to this theory each adsorbed molecule is a secondary center, which is capable to adsorb other molecules. The equation was suggested with respect to the leveling-off of the isotherms as at the end of the adsorption process the whole adsorption volume becomes filled with adsorbed molecules. Despite only three constants included in the equation, its accuracy in experimental data description is satisfactory.