GB739200A - Process for the extraction and recovery of aromatic hydro-carbons from hydrocarbon mixtures - Google Patents

Abstract

A plurality of aromatic hydrocarbons of the benzene series are separated from a mixture thereof with non-aromatic hydrocarbons by introducing the mixture into a counterflow multi-stage extraction system at an intermediate point, introducing a glycollic selective solvent, which is substantially immiscible with non-aromatic hydrocarbons, into one end of the system into extractive contact with the hydrocarbon phase therein, maintaining the extractive system under pressure sufficient to keep the contents liquid at a temperature above 40 DEG C., preferably 80 DEG to 125 DEG C., withdrawing substantially aromatic-free and glycol-free raffinate from the same end of the system as that at which solvent is introduced, withdrawing the aromatic-rich glycollic extract from the other end of the system, pre-stripping said extract under evaporative conditions to liberate only the most volatile aromatic therefrom together with non-aromatics of equivalent volatility, condensing the so-liberated vapours and returning the condensate to the extraction system near its said other end, conducting the remainder of the extract to a heated zone, stripping the aromatic hydrocarbons from the solvent in said zone, subjecting the aromatic hydrocarbons to rectification and returning the substantially hydrocarbon-free solvent to the extraction zone. Suitable feedstocks are obtained by cracking aromatic or naphthenic petroleum or by catalytic reforming. The selective solvent is preferably diethylene glycol, alone or containing 0.5 to 10 per cent by weight of water, although ethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol and mixtures thereof may also be used. The extraction system is preferably operated at a temperature above the boiling point of the most volatile hydrocarbon and the reflux stream is obtained by flashing the vapours of the said aromatic from the extract at a lower pressure in the pre-stripping zone. In a modification, the pre-stripped vapours are fractionated to give an overhead portion rich in non aromatics which is condensed and returned to the extractor at a point nearer the middle than the point at which the aromatic bottoms are returned. The main stripper may be operated at atmospheric pressure or under vacuum, preferably with injection of small amounts of steam. The hot solvent drawn from the bottom of the still is returned to the extractor and maintains the desired extraction temperature therein. Examples are given of the treatment of a gasoline having a boiling range of 150 DEG to 300 DEG F., and obtained by "Platforming," with diethylene glycol containing 2 per cent of water as the selective solvent, using a 10 : 1 solvent to feed ratio at an extractor temperature of 50 DEG to 60 DEG C. Specification 718,909 is referred to.