Adsorption of isomeric aryl- and diadamantane molecules on the surface of graphitized thermal carbon black

The thermodynamic characteristics of adsorption of isomeric molecules of 1,1??-, 1,2??-, and 2,2??-diadamantanes, 1- and 2-phenyladamantanes, and 1-cyclohexyladamantane on the surface of graphitized thermal carbon black (GTC) were experimentally determined. The influence of the molecular structure of adsorbates on their adsorption on the basis face of graphite was considered. A high selectivity of the GTC surface for the gas chromatographic separation of mixtures of the considered structural isomers was shown.     

Adsorption of tetramethylsilane molecules on the basal face of graphite

The thermodynamic adsorption characteristics of tetramethylsilane (TMS) molecules on graphitized carbon black (GCB) were for the first time determined experimentally and by molecular statistics methods. The potential function parameters of pair molecular interactions (φ(r)) between Si and C atoms on the basal face of graphite were calculated in the atom-atom approximation of the semiempirical molecular-statistical theory of adsorption. The contributions of Si and C atoms to thermodynamic adsorption characteristics are compared for the example of nonspecific adsorption of TMS and isostructural neopentane molecules on the flat surface of GCB.     

The influence of an intramolecular H-bond on the adsorption of sulfur-containing amino acids on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of sulfur-containing amino acids and their derivatives on the surface of graphitized thermal carbon black were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the S atom in amino acids and the graphite C atom were determined. It was shown that an intramolecular H-bond influenced the adsorption of amino acids on the surface of graphitized thermal carbon black.     

Molecular statistical calculation of thermodynamic characteristics of adsorption of O-, S-, and Se-containing heteroadamantanes on graphitized thermal carbon black

The thermodynamic characteristics of adsorption (TCA) on the basal face of graphite have been calculated in terms of the semiempirical molecular statistical theory of adsorption for molecules of O-, S-, and Se-containing heteroadamantanes of different structure and isostructural cyclohexane derivatives. The influence of the nature, number, and position of heteroatoms in the adamantane framework on the TCA values was studied in detail, which made it possible to predict the retention of the compounds considered on the surface of graphitized thermal carbon black under the conditions of equilibrium gas adsorption chromatography. The introduction of each subsequent heteroatom into a polyheteroadamantane molecule makes a non-additive contribution to the TCA values. The contributions of various fragments to the total adsorption energy were calculated by the TCA of isostructural heterocyclohexane molecules, and the most preferential orientations of the framework molecules of the adsorbates relative to the planar graphite surface were determined.     

The influence of intramolecular H-bond on chromatographic behavior of phenylalkylamines

The thermodynamic characteristics of adsorption on the surface of graphitized thermal carbon black at 300 K were determined by the molecular statistical method for three phenylalklylamines. The influence of the intramolecular H-bond on the conformation of the molecules compared with structurally related n-alkyl-benzenes was considered. It was shown that the conformations of the molecules could influence chromatographic retention. Conformational isomers stabilized by intramolecular H-bonds were found to retain their structure in adsorption on graphitized thermal carbon black.     

Thermodynamic characteristics of the adsorption of isomeric molecules of fluoroadamantanes on the surface of the basal face of graphite

The thermodynamic characteristics of adsorption (TCA) for isomeric molecules of mono-, di-, tri-, and tetrafluoroadamantanes were determined for the first time experimentally and by molecular statistics on the surface of graphitized thermal black (GTB). The parameters of atom-atom potential function of pair intermolecular interaction (φ(r)) for F atoms included in fluoroadamantanes with C atoms on the basal face of graphite were calculated for the first time within an atom-atom approximation of the semi-empirical molecular statistical theory of adsorption. The adsorption non-equivalence of F atoms in various positions of an adamantane framework, a consequence of the mutual effect of atoms in a framework molecule, was determined. On the basis of the definite TCA values, the conclusion was drawn as to the possibility of isolation of isomeric fluoroadamantanes under the conditions of gas-adsorption chromatography on GTB.     

Experimental and molecular statistical study of alkyladamantane adsorption on graphitized thermal carbon black

Experimental measurements and molecular statistics methods were used to calculate thermodynamic 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 additive group Lydersen method. A set of various topological indices used further for constructing structure-retention correlations on GTCB was obtained.     

A gas-solid chromatographic study of the adsorption of hydrocarbons and alcohols on graphite

Summary The Henry's law region of the adsorption isotherms for several hydrocarbons and alcohols on a graphite was studied by gas-solid chromatography. The thermodynamic functions at zero surface coverage were determined. The low heats of adsorption indicate a highly homogeneous surface. A constant increment of the standard free energy with the number of carbon atoms in the lineal adsorbates was found. Attemps were made to estimate the London contribution to the surface free energy of the adsorbents. A non-specific interaction between the graphite and the adsorbates was shown.     

Molecular statistical calculations of the adsorption of proline and its hydroxy derivatives on graphitized thermal carbon black

The thermodynamic characteristics of adsorption of proline and its hydroxy derivatives on the surface of graphitized thermal carbon black (GTCB) were calculated. The arrangement of hydroxyl groups in the amino acid molecule was shown to influence their adsorption on GTCB. The influence of internal rotation angles in proline and its hydroxy derivative molecules on their adsorption on GTCB was studied.     

甲烷在石墨化热解碳黑和活性炭上的吸附

为研究影响碳基吸附剂吸附超临界温度气体的主要因素,选择石墨化热解碳黑BP280和Ajax活性炭,分析超临界温度高压甲烷在其上的吸附平衡。应用容积法,在压力0~20.5 MPa、温度253 K~313 K测定甲烷的吸附平衡数据,并由等量吸附线标绘和亨利定律常数确定等量吸附热。引入通用吸附等温方程,再由方程的Langmuir标绘确定最大吸附容量,进而通过方程的线性化计算吸附平衡态中甲烷分子的作用能。结果表明,甲烷在两种吸附剂上的最大吸附容量均随温度而变化,并都小于液态甲烷的密度;甲烷在碳黑和活性炭上的等量吸附热分别为11.9 kJ/mol~12.5 kJ/mol和17.5 kJ/mol~22.5 kJ/mol,体现了两种吸附剂不同的表面能量分布;甲烷分子间作用能随吸附量的变化特点反映了超临界温度甲烷以类似于压缩气体状态聚集的特点和吸附剂结构上的差异。碳基吸附剂的比表面积和微孔容积是影响其储存甲烷容量的重要因素。     

Adsorption and separation of isomeric methyl- and dimethylaminoadamantanes on graphitized thermal carbon black

The thermodynamic characteristics of adsorption (TCA) of isomeric molecules of methyl- and dimethylaminoadamantanes on the surface of the basis face of graphite were determined experimentally and calculated by the molecular statistical method. A relationship between the geometric structure of adsorbate molecules and the values of their TCA on graphitized thermal carbon black was established. The data obtained were used for the gas chromatographic identification of the amination products of a mixture of Z,E-isomers of 1,4-dimethyladamantane and 1,3-dimethyladamantane.     

Molecular statistical calculation of thermodynamic characteristics of adsorption of polymantane molecules on the basis face of graphite

The thermodynamic characteristics of adsorption (TCA) of polymantane molecules and their some derivatives on the basis face of graphite were calculated for the first time in terms of the atom-atomic approximation of the semiempirical molecular statistical theory of adsorption. The graphite surface exhibits high structural selectivity to isomeric polymantanes. A model for adsorption of cage molecules on the planar surface was proposed. The model is based on the idea that contributions of atoms of the adsorbate molecule to the total adsorption energy can be discriminated according to the distance of these atoms from the surface of a solid. Advantages and limitations of using the data on adsorption of molecules of isomeric alkanes, including rotamers, for the analysis of equilibrium TCA values of isomeric polymantanes on graphite are discussed. The possibility of separation of representatives of the polymantane hydrocarbon family by gas adsorption chromatography on columns with graphitized thermal carbon black was suggested on the basis of the calculated TCA values and logarithmic retention indices.     

Identification of peptides with protected functional groups by chromatography,mass spectrometry,and molecular statistics

The retention of peptides with protected functional groups on the Hypercarb carbon sorbent was studied by reversed phase HPLC. The peptides were identified by tandem mass spectrometry with electrospray ionization. The thermodynamic characteristics of adsorption (TCA) of the peptides on the graphitized thermal carbon black were determined by the molecular statistical method and compared with the retention values obtained by liquid chromatography on the Hypercarb carbon sorbent. Relationships between the calculated values of TCA and experimental retention values were shown.     

Adsorption of cyclic amines on graphitized thermal carbon black

Thermodynamic characteristics of adsorption (TCA) for aniline and its methyl derivatives on the surface of graphitized thermal carbon black (GTC, Carbopack C HT trade mark) were determined using equilibrium gas adsorption chromatography in the range of the lowest adsorbate concentrations in the gas phase. A series of relationships relating the TCA of the studied amines to their physicochemical parameters was obtained. The theoretical values of entropy of adsorption were calculated in the framework of the model of two-dimensional ideal gas and compared with the corresponding experimental values, which allowed one to reveal specific features of the molecular structure of the adsorbates. A similarity between the thermal component of entropy of the studied compounds in the adsorbed state and that of the entropy of the pure liquid adsorbates made it possible to refine the physical state and mobility of the adsorbate molecules in the force field of the adsorbent. The regression equation relating the heats of adsorption on the GTC to such molecular constants of adsorbates as polarizability, molecular surface area, and molecular weight were proposed for the first time. A high predictive power of the equations derived in the work for the preliminary estimation of the adsorption characteristics of alkylanilines and alkylbenzenes on the GTC was shown.     

The thermodynamic characteristics of adsorption and retention of adamantane derivatives on graphitized carbon black under the conditions of gas-adsorption chromatography

The experimentally determined thermodynamic characteristics of adsorption of adamantane derivatives with different numbers and chemical natures of functional groups on graphitized carbon black under the conditions of gas-adsorption chromatography were analyzed. The theoretical values of the entropy of adsorption calculated in terms of the two-dimensional ideal gas model were correlated with the corresponding experimental values, and some special features of the molecular structure of the compounds studied were determined. Using the method of structural fragments and sorption-structure correlations for the adamantane derivatives and cyclohexane, it was established that the adsorption potential of cage adamantane molecules was largely determined by the cyclohexane fragment with the largest number of substituents, which was situated in the immediate vicinity of the flat graphite-like adsorbent surface.     

Adsorption of nitrobenzene, aniline and nitroanilines on the surface of a basal face of graphite

Thermodynamic characteristics of the adsorption of nitrobenzene, aniline, and isomeric nitro-anilines are determined experimentally and from molecular statistics in the range of the closest packing of a graphite surface according to equilibrium gas adsorption chromatography. It is found that graphitized thermal carbon black is characterized by high selectivity upon the chromatographic separation of isomeric nitro-anilines (retention increases in the series of ortho, meta, and para isomers). Using the atom-atomic approximation of the semi-empirical molecular statistical theory of adsorption, parameters are calculated for the potential function of the pair intermolecular interaction of the NO₂ group in nitrobenzene and the N atom in aniline with the C atoms in a basal face of graphite. The effect of the NH₂ and NO₂ groups on the parameters of adsorption for isomeric nitroanilines as a result of direct polar conjugation is demonstrated and must be assumed when performing molecular statistical calculations.     

The influence of intramolecular hydrogen bonds on the adsorption properties of aromatic alcohols and thiols

The thermodynamic characteristics of adsorption equilibria of primary aromatic alcohols and thiols on graphitized carbon black at 300 K were determined by the molecular-statistical method. The influence of intramolecular effects under the action of the force field of the sorbent on the conformation of the molecules studied was considered in comparison with n-alkylbenzenes having similar structures. An increase in the chain length by one-CH₂ group was shown to influence the formation of intramolecular H-bonds in alcohol and thiol molecules. In adsorption, a considerable fraction of molecules assumed configurations close to planar. An exception was the nonplanar conformation of the 2-phenylethanol molecule stabilized by the intramolecular H-bond.     

Cooperative and Competitive Adsorption of Ethylene,Ethane, Nitrogen and Argon on Graphitized Carbon Black and in Slit Pores

In this paper we investigate the mixture adsorption of ethylene, ethane, nitrogen and argon on graphitized thermal carbon black and in slit pores by means of the Grand Canonical Monte Carlo simulations. Pure component adsorption isotherms on graphitized thermal carbon black are first characterized with the GCMC method, and then mixture simulations are carried out over a wide range of pore width, temperature, pressure and composition to investigate the cooperative and competitive adsorption of all species in the mixture. Results of mixture simulations are compared with the experimental data of ethylene and ethane (Friederich and Mullins, 1972) on Sterling FTG-D5 (homogeneous carbon black having a BET surface area of 13 m²/g) at 298 K and a pressure range of 1.3–93 kPa. Because of the co-operative effect, the Henry constant determined by the traditional chromatography method is always greater than that obtained from the volumetric method.     

The adsorption of organic compounds on a modified carbon adsorbent Carbopack B

The thermodynamic characteristics of adsorption of several organic compounds on the carbon adsorbent Carbopack B before and after its modification by a monomolecular layer of cholesteryl-n-pentyl oxybenzoate were determined by gas chromatography. The initial adsorbent was close in its properties to graphitized carbon black. Modification weakened adsorbate-adsorbent attraction and increased the mobility of adsorbed molecules, to a greater extent for nonpolar adsorbents and to a lesser extent for compounds capable of specifically interacting with modifier molecules.     

Interaction of Water and Methanol Molecules with the Surface of Carbonaceous Materials According to Gas Chromatographic Data

We have used gas chromatography to study the interaction of water and methanol molecules with active hydrophilic centers on the surface of thermally expanded graphite and graphitized thermal carbon black. We have determined the concentration of carboxyl and phenol hydroxyl groups on the surface of the sorbents and the heats of adsorption for adsorption of the studied substances on these groups. We have shown that water molecules are adsorbed as clusters on the hydrophilic centers of the studied sorbents at very low relative pressures, with n = 2 molecules in the cluster.