Separation of hydrocarbon isomers by thermal diffusion

Abstract

The separation of gaseous hydrocarbon isomers by thermal diffusion has been demonstrated, Experiments were made in a Clusius column and mixtures analyzed by a mass spectrometer. Binary mixtures ofn-pentane withneo-pentane,iso-pentane withneo-pentane,n-pentane withiso-pentane, andn-butane withiso-butane showed a marked degree of separation. In each case the former component concentrated in the cold zone. The phenomenon may be correlated with anomalies in the ratio between viscosity and thermal conductivity, which have previously been shown to occur for flexible chain molecules, and were attributed to the occurrence of ‘wrestling’ collisions between such molecules. Discussion in terms of an elementary theory of thermal diffusion leads to the conclusion that the more flexible molecules should concentrate in the cold zone. This is in complete accord with the expense: mental results.