GB673540A - Adsorption process for the separation of liquid mixtures - Google Patents

Abstract

<FORM:0673540/IV (b)/1> <FORM:0673540/IV (b)/2> <FORM:0673540/IV (b)/3> <FORM:0673540/IV (b)/4> A process of separating liquid mixtures into fractions by selective adsorption, in which alternately (a) the liquid mixture is passed through a solid adsorbent mass, and (b) the adsorbent mass is regenerated by passing a stripping liquid therethrough, is rendered more efficient, through reduction of the volume of liquid required to be distilled in secondary separations, by carrying out the process so that (i) the first effluent resulting from the passage of the liquid mixture through the adsorbent mass is recycled to the adsorbent mass during regeneration, and/or (ii) the first effluent resulting from the passage of stripping liquid through the adsorbent mass is recycled to the adsorbent mass after a subsequent step (a) but before regeneration. Liquid mixtures which may be fractionated are kerosene distillates, cracked and straight run naphthas, catalytically reformed naphthas, lubricating oils diluted to reduce viscosity, Diesel fuel distillates and Fisher - Tropsch and OXO synthesis products, while the solid adsorbent may be silica gel or a mixture of silica and alumina. In the examples, hydrocarbon mixtures are de-aromatized, using silica gel as the solid adsorbent, and the aromatic fraction is stripped from the solid adsorbent. Thus (1) a kerosene distillate is treated and isooctane is used as the stripping liquid; (2) a catalytically reformed gasoline is treated and refined kerosene is used as the stripping liquid, and (3) dehexanized thermally cracked naphtha is treated and pentane is used as the stripping liquid. The process may be applied to the cyclic adsorption process of Specification 642,911, [Group XXXV], employing a plurality of fixed adsorbent beds with moving feed and withdrawal points. In Fig. 2, the letters A to H represent masses of solid adsorbent, the liquid mixture being fed to mass E and stripping liquid being fed to mass A. The first effluent from mass H is recycled to mass A while, if desired, the first effluent from mass D may be fed directly into mass E or fed into the adsorption zone in a later cycle. In Fig. 3, the first effluent from mass C is recycled to mass D, while in Fig. 4, the first effluent from mass C is recycled to mass D, the first effluent from mass H is recycled to mass A, hot stripping liquid is fed into mass C and cold stripping liquid into mass A. Alternatively, in Fig. 4, the first effluent from mass H may be reheated and recycled to mass B. In Fig. 5, the first effluent from mass C is recycled to mass E, the first effluent from mass H is recycled to mass A, hot stripping liquid is fed to mass B, cold stripping liquid is fed to mass A and a desorbent liquid is fed to mass D. The desorbent liquid is a liquid for which the adsorbent shows an adsorptive preference equal to or greater than that which it shows for the preferentially adsorbed fraction of the feed. The effluent from mass H may be employed as stripping liquid.ALSO:<PICT:0673540/III/1> <PICT:0673540/III/2> <PICT:0673540/III/3> A process of separating liquid mixtures into fractions by selective adsorption, in which alternately (a) the liquid mixture is passed through a solid adsorbent mass and (b) the adsorbent mass is regenerated by passing a stripping liquid therethrough, is rendered more efficient, through reduction of the volume of liquid required to be distilled in secondary separations, by carrying out the process so that (i) the first effluent resulting from the passage of the liquid mixture through the adsorbent mass is recycled to the adsorbent mass during regeneration and/or (ii) the first effluent resulting from the pass <PICT:0673540/III/4> age of stripping liquid through the adsorbent mass is recycled to the adsorbent mass after a subsequent step (a) but before regeneration. Liquid mixtures which may be fractionated are kerosene distillates, cracked and straight run naphthas, catalytically reformed naphthas, lubricating oils diluted to reduce viscosity, Diesel fuel distillates and Fischer-Tropsch and Oxo synthesis products, while the solid adsorbent may be silica gel or a mixture of silica and alumina. In the examples, hydrocarbon mixtures are dearomatized, using silica gel as the solid adsorbent, and the aromatic fraction is stripped from the solid adsorbent. Thus (1) a kerosene distillate is treated and iso-octane is used as the stripping liquid, (2) catalytically reformed gasoline is treated and refined kerosene is used as the stripping liquid and (3) dehexanized thermally cracked naphtha is treated and pentane is used as the stripping liquid. The process may be applied to the cyclic adsorption process of Specification 670,091, employing a plurality of fixed adsorbent beds with moving feed and withdrawal points. In Fig. 2, the letters A to H represent masses of solid adsorbent, the liquid mixture being fed to mass E and stripping liquid being fed to mass A. The first effluent from mass H is recycled to mass A while, if desired, the first effluent from mass D may be fed directly into mass E or fed into the adsorption zone in a later cycle. In Fig. 3, the first effluent from mass C is recycled to mass D, while in Fig. 4, the first effluent from mass C is recycled to mass D, the first effluent from mass H is recycled to mass A, hot stripping liquid is fed into mass B and cold stripping liquid into mass A. Alternatively, in Fig. 4, the first effluent from mass H may be reheated and recycled to mass B. In Fig. 5, the first effluent from mass C is recycled to mass D, the first effluent from mass D is regulated to mass E, the first effluent from mass H is recycled to mass A, hot stripping liquid is fed to mass B, cold stripping liquid is fed to mass A and a desorbent liquid is fed to mass D. The desorbent liquid is a liquid for which the adsorbent shows an adsorptive preference equal to or greater than that which it shows for the preferentially adsorbed fraction of the feed. The effluent from mass H may be employed as stripping liquid.