Theoretical and Experimental Investigation of the Influence of Molecular Structure on the Retention on Graphitized Carbon Black

Abstract

The thermodynamic characteristics of retention of different molecules on graphitized thermal carbon black (GTCB) are investigated. For hydrocarbons, a molecular-statistical method is developed for the calculation of retention volumes for small (zero) sample size per unit surface area of GTCB, VA,1 (the Henry constants). This method is based on consideration of the structure of the molecules and of the adsorbent, on an atom-atom approximation for the intermolecular interaction potential function of a molecule with the adsorbent, and on introducing corrections into the quantum mechanical values of the constants of the potential functions by comparison with the experimental VA,1 values for one representative of each class of compounds considered. The VA,1 values are calculated for the series of alkanes, cyclanes, alkenes, alkyldienes, alkynes and aromatic hydrocarbons. The influence of the valence state of carbon atoms in different hydrocarbons on the constants in atom-atom potential functions are taken into account. The hydrocarbons which form rotamers are considered as the equilibrium mixtures of these rotamers. The calculated VA,1 values are close to the measured ones. The VA,1 values for halogenated derivatives of C1–C3 alkanes on GTCB and for oxygen-containing derivatives, i.e., ethers, esters, aldehydes, ketones and alcohols, on hydrogen treated GTCB are measured at different temperatures. The influence of replacing hydrogen in alkanes by F, Cl, Br and I on the retention characteristics are studied. The influence of the halogen atom radius, polarizability and geometry of molecules, as well as mutual influence of polarizability and geometry in the case of polyhalogen derivatives are also studied. The influence of different valence states of oxygen in ethers, esters, aldehydes, ketones and alcohols, as well as of oxygen position in the hydrocarbon chain on the thermodynamic characteristics of retention is demonstrated. The possibility of predicting the retention characteristics on graphitized thermal carbon black of different halogen and oxygen derivatives of hydrocarbons using the corresponding increments is demonstrated.