Patent GB-824582-A (GB)
Title: Improvements in and relating to the solvent extraction of aromatic concentrates
Filed: 1957-09-10
Abstract: A solvent extraction process for obtaining pure aromatic hydrocarbons from an aromatic concentrate containing at least 70 wt. per cent of aromatics comprises the following steps: (i) diluting the feed with a saturated hydrocarbon boiling lower than the most volatile aromatic hydrocarbon; (ii) introducing the diluted feed to an intermediate point in an extraction zone, preferably near the middle; (iii) countercurrently contacting the feed in the liquid phase and at superatmospheric pressure with a solvent which is selective for aromatics and higher boiling than the feed; (iv) removing a raffinate comprising the non-aromatics and at least a portion of the diluent from one end of the zone; (v) introducing a light reflux stream of saturated hydrocarbons boiling below the aromatic extract at a point near the other end of the zone; (vi) withdrawing a rich solvent stream comprising solvent, aromatic and a portion of the light reflux from said other end of the zone; (vii) reducing the pressure thus vaporizing a lowboiling hydrocarbon fraction from the rich solvent stream and returning it to the zone as the light reflux stream; and (viii) recovering the aromatic hydrocarbon extract from the remainder of the rich solvent stream.  Solvents mentioned are alcohols, glycols, ethers, phenols, nitriles and esters, with or without an antisolvent such as water to increase their selectivity.  They may be used in amounts of 2 to 20 volumes per volume of feed.  Saturated hydrocarbon diluents mentioned are naphthalene and paraffinic (particularly branched-chain paraffinic) hydrocarbons preferably having boiling points at least 5 DEG  C. lower than the most volatile hydrocarbon but sufficiently high to remain in the liquid phase under the temperature and pressure prevailing in the extraction zone.  The diluent should constitute 2% to 75%, preferably 5% to 50% of the feed mixture.  The light reflux stream introduced in step (v) displaces higher boiling saturated hydrocarbons from the rich solvent and replaces them with lighter hydrocarbons which can be flash vaporized in step (vii).  Steam distillation may be employed in steps (vii) and (viii).  The extracted aromatic hydrocarbon may be subjected to a final purification with an adsorbent, e.g. silica/alumina or clay. In an example substantially pure benzene, toluene, xylene and ethyl benzene are obtained from a coal tar distillate containing 93% aromatics.ALSO:A solvent extraction process for obtaining pure aromatic hydrocarbons from an aromatic concentrate containing at least 70 wt. per cent of aromatics comprises the following steps :-(i) diluting the feed with a saturated hydrocarbon boiling lower than the most volatile aromatic hydrocarbon; (ii) introducing the diluted feed to an intermediate point in an extraction zone, preferably near the middle; (iii) countercurrently contacting the p feed in the liquid phase and at superatmospheric pressure with a solvent which is selective for aromatics and higher boiling than the feed; (iv) removing a raffinate comprising the non-aromatics and at least a portion of the diluent from one end of the zone; (v) introducing a light reflux stream of saturated hydrocarbons boiling below the aromatic extract at a point near the other end of the zone; (vi) withdrawing a rich solvent stream comprising solvent, aromatic and a portion of the light reflux from said other end of the zone; (vii) reducing the pressure thus vaporizing a low boiling hydrocarbon fraction from the rich solvent stream and returning it to the zone as the light reflux stream; and (viii) recovering the aromatic hydrocarbon extract from the remainder of the rich solvent stream. Solvents mentioned are alcohols, glycols, ethers, phenols, nitriles and esters, with or without an anti-solvent such as water to increase their selectivity.  They may be used in amounts of 2 to 20 volumes per volume of feed.  Saturated hydrocarbon diluents mentioned are naphthenic and paraffinic (particularly branched-chain paraffinic) hydrocarbons preferably having boiling-points at least 5 DEG  C. lower than the most volatile hydrocarbon but sufficiently high to remain in the liquid phase under the temperature and pressure prevailing in the extraction zone.  The diluent should constitute 2 to 75%, preferably 5 to 50% of the feed mixture.  The light reflux stream introduced in step (v) displaces higher boiling saturated hydrocarbons from the rich solvent and replaces them with lighter hydrocarbons which can be flash vaporized in step (vii).  Steam distillation may be employed in steps (vii) and (viii).  The extracted aromatic hydrocarbon may be subjected to a final purification with an adsorbent, e.g. silica/alumina or clay.  In an example substantially pure benzen, toluene, xylene and ethyl benzene are obtained from a coal tar distillate containing 93% aromatics.