of hydrocarbon molecules and graphite basal planes (1). The purpose of this work is to find a suitable method to correlate Isosteric heats of adsorption have been found for various Henry's law adsorption energies such as the isosteric heat or the aliphatic alcohols on a gold surface at different temperatures gas-solid interaction energy. Available adsorption energies for a (2). The short-range repulsive interaction of alkanes with total of 63 gases distributed among five adsorbents-a zeolite, a graphite has been determined from the difference between silica gel, a carbon black, and two microporous carbons adsorbents the total energy of the adsorbate graphite system and the were correlated with the boiling point, a critical constant ratio energy of the separated species (3). The energies of interacinvolving critical temperature and critical pressure, the log of the tion of the molecules CH 4 , C 2 H 6 , C 3 H 8 , n-C 4 H 10 , n-C 5 H 12 , octanol-water partition coefficient, and molecular structural enand n-C 6 H 14 with a graphite lattice surface have been calcuergy. In the structural approach each gas molecule is considered to be composed of a series of structural units that each make a fixed lated employing a Monte Carlo method based on the assumpcontribution to the total molecular adsorption energy. Multiple tion that the interaction energy is expressible as a sum of regression analyses were done for each of the five adsorbent systhe pair interactions between carbon atoms of the graphite tems using the four main correlation methods. The method based lattice and those constituting the adsorbate molecule (4). on the structural units of a molecule and its dipole moment was Adsorption of nine different gases and vapors on a silica gel found to give a 0.99 correlation coefficient for all five gas-solid was studied based on ab initio molecular orbital calculations systems. This structural method was superior to correlations based by setting up a model of a single-type adsorption site with on boiling points, critical constants, partition coefficients, and varione silanol group and a model of a paired-type adsorption ous combinations of other physical properties that were also examsite with two silanol groups. Interaction energies were deterined. Since there has been a variety of interest in either predicting mined for the models and compared to measured heats of the energy of adsorption or extent of adsorption for specific adadsorption (5).
sorbate-adsorbent pairs, our correlation results could be useful in future quantitative structure-activity relationship (QSAR) corre-QSAR methods have been used to predict activated carbon lations of adsorption. แญง 1997 Academic Press adsorption capacities for organic vapors (6). A linear solva-Key Words: adsorption energy; isosteric heat; gas-solid interaction energy relationship of QSAR has been used to calculate tion energy; Henry's law adsorption; gas-solid virial coefficient.
limiting adsorption coefficients (7). A molecular connectivity approach of QSAR was used for estimating the adsorption of organic chemicals on activated carbon (8). Adsorption