Patent GB-1392735-A (GB)
Title: Extractive distillation process
IPC: C10G21/30
Filed: 1972-05-26
Abstract: 1392735 Distilling hydrocarbons UNIVERSAL OIL PRODUCTS CO 26 May 1972 24887/72 Heading C5E In the separation of aromatic from non- aromatic hydrocarbons by extractive distillation, the loss of aromatics in the non-aromatic product is controlled by controlling the temperature of the solvent returned to the extractive-distillation zone. Solvent is washed out of the raffinate by water, the resulting aqueous phase is stripped, and solvent recovered in the solvent stripping zone is cooled by indirect heatexchange in the reboiler of the water-stripping zone. This cooled solvent is supplied to the distillation zone, and its temperature is adjusted by adjusting the pressure, and therefore the temperature, in the water-stripping zone, or by by-passing part of the recovered solvent round the heat-exchanger, or both. As shown, a feed stream derived from a catalytic reformate and containing about 90% of aromatics, of which more than 90% are C 8 , enters by line 1 and makeup or wet solvent by line 2. The two are mixed and go by line 3 to extractive-distillation column 4. Recycled solvent enters by line 5, predominantly non-aromatic vapours are taken off by line 6, solvent and aromatics by line 13. The overhead in line 6 is condensed at 7 and separated at 8 into a stream 9 of hydrocarbons and a stream 11 of water, each containing a little solvent; part of each may be, but normally is not, refluxed by line 10. The hydrocarbon stream passes by line 9 to column 24, where solvent is washed out by water from line 23; solvent-free, non-aromatic hydrocarbons are taken off by line 25. The extract in line 13 is distilled in a column 14 to separate hydrocarbons from solvent. This column has a hot-oil reboiler 15 in a tray 16, to which steam is supplied by line 37. The aromatic overhead is mixed with make-up water from line 18, condensed at 19 and separated at 20. Solventfree water from this separator provides (by line 23) the water needed in the wash column 24; of the aromatic hydrocarbons, part is refluxed by line 22 and part taken off by line 21. Lean solvent is removed from the column 14 by line 29; part is taken by line 30 through valve 31 to be mixed with cooled solvent in line 5, but most goes by line 29 to reboiler 32. Aqueous streams from the separator 11 and wash column 24 are mixed and taken by line 27 to a stripping zone 28, where part of the water evaporates and is taken off by line 38 to mix with the overhead from column 4. Portions of the remaining liquid go by lines 34 and 35 or 35<SP>1</SP> to heatexchangers 32 and 33 where they are heated by hot solvent in line 29; the heated aqueous solvent from 32 returns to the stripping zone by line 34<SP>1</SP>; that from 33 is mixed with another portion of aqueous solvent in line 36 to provide the stripping steam in line 37. Cooled solvent in line 29<SP>11</SP> is mixed with a portion of hot solvent from line 30 and passes by line 5 to the extractive distillation column 4. The amount of aromatics taken overhead is measured in line 6, 9 or 25, and when this exceeds a predetermined level, part of the aqueous stream 11 is diverted as reflux to the column 4, or the temperature of the solvent stream 5 is lowered by passing a greater proportion of it through the heat-exchangers 32 and 33, or by lowering the pressure at 28 or 33 or both, so that a greater proportion of the water is vaporized.