Aromatic hydrocarbon isomer separation process by adsorption

Abstract

A process for separating the para-isomer from a feed mixture containing at least two bi-alkyl substituted monocyclis aromatic isomers, including the para isomer, said isomers having from 8 to about 18 carbon atoms per molecule which process comprises contacting said mixture with an adsorbent prepared by the steps of: contacting a base material comprising type X or type Y zeolite with a fluoride-containing aqueous sodium hydroxide solution at first ion exchange conditions to effect the addition of sodium to and the extraction of alumina from said base material; treating the sodium-exchanged base material at second ion exchange conditions to effect the essentially complete exchange of sodium cations; and, drying the material at conditions to reduce the LOI at 900.degree. C. to less than about 10 wt. % thereby selectively adsorbing at adsorption conditions said para isomer. The first ion exchange with a fluoride-containing aqueous sodium hydroxide solution prior to the second ion exchange with a selected cation or cations produces a superior adsorbent for separating the para isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para isomer, the isomers having from 8 to about 18 carbon atoms per molecule. The adsorbent so produced has faster para isomer transfer rates and higher aromatic capacity than one produced either from untreated base material or from base material treated with fluoride or caustic alone. Additionally, a fluoride treatment of base material alone or in combination with or subsequent to a caustic treatment, prior to potassium and barium or barium ion exchange, essentially eliminates a troublesome dustiness characteristic of adsorbents prepared from untreated base material.