Evidence of Chromatographic Effect During Flow of Gases Through Oilfield Cores

Abstract

Introduction The chromatographic effect refers to the separation of constituents in a moving fluid phase which occurs when the phase is passed over a stationary phase, either solid or liquid, or large areal extent. In performing chemical analyses, the large surface contact area is provided in the case of gas-solid chromatography bypassing the gas over a porous solid and for gas-liquid chromatography bypassing the gas over a porous solid which has been coated with a nonvolatile liquid. The porous medium is usually placed in a cylindrical tube, although it may be a relatively flat sheet as in paper chromatography. According to one theory, the separation results from the difference in time spent by various components in the stationary phase. A gaseous component which is completely insoluble in the stationary phase, or is not adsorbed on the solid, proceeds unimpeded through the column. The versatility and power of the various types of chromatography for the analysis of complex mixtures are evident from their widespread use in performing chemical analyses and from the large number of symposia, books, and papers devoted to the subject in recent years. Associated developments are the application of chromatography to the determination of heats of solution, heats of adsorption, solubilities or K-values, etc. Gas-liquid chromatography analyses may be characterized by the manner in which the samples are introduced and displaced from the column. The three techniques used are known as(1) frontal analysis, (2) displacement analysis, and (3) elution analysis. The frontal analysis is performed by displacing an inert gas from the column by a continuous stream of the sample. As indicated in Fig. 1(A), all but the first fraction leaving the column represent mixtures rather than pure components. The displacement analysis is conducted by filling the column with a sample, then displacing it with a more strongly adsorbed or absorbed vapor. The resulting chromatogram is illustrated by Fig. 1(B). Finally, in the elution analysis a small sample of the mixture to be analyzed is introduced as a "plug" into a flowing stream of carrier gas to give an elution-type chromatogram, Fig. 1(C). The three techniques may be used to provide models to which flow patterns in other physical situations may be compared.