Evaluation of the thermodynamic parameters for the adsorption of some hydrocarbons on chemically treated-bentonites by inverse gas chromatography
Inverse gas chromatography has been used to evaluate the adsorption parameters (?H a, ?H st, ?S a and ?G a) of some probe molecules, each representing a class of organic (n-hexane, cyclohexane, benzene, n-octane, 1-octene and isooctane) on bentonite and chemically treated-bentonites. The adsorption parameters of the probes on the bentonite samples were determined in infinite dilution region. Adsorption of the organic species was investigated in the temperature range of 200-275°C, using a flame ionization detector, and nitrogen as a carrier gas. The net retention volumes (V n ) of the probes were determined by the help of the retention times (t R ) observed on gas chromatograms for each probe. Injection was made at least three times for each probe, obtaining reproducible results of ± 0.5%. It was found that benzene exhibits more negative ?H than for n-hexane and cyclohexane on all of the adsorbents. In addition, it was found that 1-octene exhibits more negative ?H than for n-octane and isooctane on the chemically treated-bentonites, whereas n-octane exhibits more negative ?H than for 1-octene and isooctane on the natural bentonite. Also, interactions of benzene with the natural- and chemically treated-bentonites were found to be stronger than those of n-hexane and cyclohexane with the same carbon number. Again, interactions of the 1-octene with the chemically treated-bentonites were found to be stronger those of n-octane and isooctane with the same carbon number. On the contrary, interactions of n-octane with the untreated-bentonite were found to be stronger than those of 1-octene and isooctane. © 2005 Springer Science + Business Media, Inc.