Dual temperature gradient elution liquid chromatography

Abstract

In a liquid chromatography commercial process for the separation of two or more components contained in admixture in a feedstream including the steps of (a) contacting the feedstream mixture containing the components to be separated with a bed of crystalline aluminosilicate adsorbent at conditions to effect the selective retention of two or more of the components by said adsorbent, (b) passing through said bed an eluent selected from the group consisting of aromatics and substituted aromatics, (c) increasing the strength of the eluting agent in the liquid carrier during the operation of the steps (a) and (b) above, (d) recovering from said bed a stream or streams containing at least a portion of the less selectively adsorbed components, and (e) recovering a stream substantially enhanced in concentration of said selectively adsorbed components relative to other components of feedstream wherein the improvement comprises preheating the eluting agent of step (c) above prior to passing it through said bed at temperatures of at least 160.degree. C., to thereby effect the desired separation under conditions that cause substantially lower elution volume to feed ratios. The improved liquid chromatography process is particularly applicable to the separation of paraxylene and ethylbenzene from a C8 aromatic isomer mixture containing ethylbenzene. The above process when operated with the eluting agent preheating step at temperatures of about 160.degree. C or higher causes temperature waves to flow through the bed with the final peak of each feed slug being eluted with the hotter eluting agent-carrier mixture, thus providing lower elution volume to feed ratios and thereby producing paraxylene more economically.