The adsorption of high nitrogen compounds (HNCs) on the selected adsorption sites of carbonaceous materials from the gas phase has been investigated by ab initio quantum chemical methods at the density functional level applying both periodic and cluster approaches with M06-2X and BLYP functionals including dispersion forces (BLYP-D2). Among the possible structures of the adsorption complexes, the most stable systems possess nitrogen-containing heterocycles in a parallel orientation toward the modeled carbon surface. The adsorption enthalpies, calculated using the rigid rotor-harmonic oscillator approach (RRHO), were in good agreement with available experimental data. This approach was shown to provide sufficiently accurate adsorption enthalpies from the gas phase for the HNC−carbon systems. The vibrational, rotational, and translation contributions to the adsorption entropy were also analyzed by the approach extended beyond the RRHO scheme. The effects of anharmonic vibrations and internal rotations of the adsorbate on the adsorption sites of the modeled carbon surface were estimated. The Gibbs free energies calculated using the RRHO approach were adjusted to take into account the heterogeneity of the carbon surfaces and underestimation of the adsorption enthalpies at the BLYP-D2(PBC) level. The corrected Gibbs free energy values of adsorption are negative for all of the investigated HNC−carbon systems, and they agree well with available experimental data. This suggests an effective adsorption of selected high nitrogen compounds on carbonaceous materials from the gas phase at 298.15 K. Partition coefficients for distribution of high nitrogen compounds on modeled carbon surfaces were also predicted in good agreement with the experimental results.

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Experimental measurements and molecular statistics methods were used to calculate ther modynamic characteristics of adsorption (TCA) of alkyladamantanes of different structure on the surface of hydrogen treated graphitized thermal carbon black (GTCB) Carbopack C HT. High selectivity of separation of isomeric alkyladamantanes on GTCB is due to specific features of their geometry and electronic structure. The influence of the spatial structure of adsorbates on the TCA was established. Special attention was given to analysis of the heat capacities of adsorption. The best agreement between the experimental TCA and those calculated by the molecular statistics methods is achieved when the "cage effect" in the adamantane ring is taken into account. The corresponding corrections are introduced into the parameters of the atom atomic potential function of pair intermolecular interaction of the Me groups with the carbon atoms of the basal face of graphite, which are localized in the nodal positions of the lattice. The critical parameters for a large group of alkyladamantanes were calculated in terms of the addi tive group Lydersen method. A set of various topological indices used further for constructing structure-retention correlations on GTCB was obtained.At present the single natural source of adamantane and its alkyl derivatives is petroleum. 1-8 Alkyladamantanes of certain molecular weight are usually presented by mixtures of many isomers differed by both the structure of the alkyl group and the number and position of substituents in the adamantane skeleton. Isomeric alkyladamantanes often differ insignificantly from each other by physicochemical properties, which impedes their analysis and separation. There are a number of methods of isolating and concen trating alkyladamantanes such as thermodiffusion separa tion, formation of adducts with thiocarbamide, azeotropic distillation with steam or with tri(perfluorobutyl)amine. 2-4 A leading role belongs to preparative GLC followed by identification of isomers by high performance capil lary GLC on stationary phases (SP). 2,9-14 However, in spite of achieved success in studying the chromatographic behavior of this group of compounds under the GLC con ditions, a series of questions related to efficient separation and identification of some isomers with similar structure even in relatively narrow fractions remains unanswered so far. 2-5,10,12-14 The influence of specific features of the molecular structure of the adamantane framework on the chromato graphic behavior of adamantane derivatives under the con ditions of gas chromatography was studied by many au thors. It was found 15-19 by gas adsorption chromatogra phy (GAC) of adamantyl containing compounds on graphitized thermal carbon black (GTCB) that a possible reason for the different adsorption behavior of 1 and 2 functional adamantane derivatives is the "cage effect" in the adamantane system resulting in adsorption nonequiv alence of the substituents in the nodal and bridging posi tions of the adamantane framework. Analo...

Adsorption properties of blacks and their graphitized analogues were examined by the inverse gas chromatography at extremely low surface coverage.