GB1158566A - Extractive Distillation - Google Patents

Abstract

1,158,566. Extractive distillation. UNION CARBIDE CORP. 4 Aug., 1966 [6 Aug., 1965], No. 34909/66. Heading B1B. [Also in Division C5] In a process for the separation of two components of a liquid mixture by extractive distillation in the presence of a relatively non- volatile solvent having a greater affinity for the less volatile component of the mixture, the extractive distillation is carried out in two zones 75, 81 and the average pressure in zone 75 is maintained greater than the average pressure in the zone 81. A vapour stream comprising the more volatile component flows out of the head of zone 75. The liquid .flowing out of the base of zone 75 passes, through pressure-reducing valve 77 and is fed into the top of zone 81. Vapours from the top of zone 81 are drawn into compressor 43, and then introduced into the bottom of zone 75. The pressure difference between zones 75 and 81 is preferably maintained such that the maximum and minimum temperatures in the two zones are the same. More than two. extractive distillation zones may be employed, the number being such that the temperature-differential across each zone is about '10‹C. A liquid stream comprising the solvent containing the less volatile component, and possibly a residual amount of the more volatile component, flows out of the base of zone 81 into adiabatic vaporizer 83 where a portion (e.g. 80%) of the solute is vaporized at a pressure slightly above atmospheric. The vapours are introduced into zone 81 via line 123 and compressor 99. The liquid flows from vaporizer 83 through line 126 and heat-exchanger 85 into the side of rectification column 87, where the solute is separated as a overhead vapour stream. The stripped solvent, withdrawn from the base of column 87, is pumped via line 143, heat-exchanger 85 and line 109 to the top of zone 75. A portion of the overhead vapour from column 87 is drawn through line 131 into compressor 101, and then introduced' into the lower part of zone 81. The remainder of the overhead vapour from column 87 flows through line 135 into refining column 93, which serves to separate volatile contaminants as an overhead vapour stream. Liquid, withdrawn from the base of column 93, is further refined in column 95, from which the desired less volatile component of the original feed-stream is withdrawn overhead. The vapours from the head of column 93 and the liquid from the base of column 95 are introduced after suitable treatment (e.g. hydrogenation), into the lower part of. zone 81 through lines 147 and 155, respectively. If the overhead vapour from zone 75 contains a small proportion of the less volatile component, the latter is separated and may then be introduced into the lower part of zone 81. Column 87 may be heated by a reboiler 89 (as shown), or it may be supplied with an inert gas (e.g. nitrogen), or operated under vacuum. The process may be used for the separation of butane from vinyl chloride using acetone, methanol or ethanol, as solvent, or it may be used for the separation of butenes from crude butadiene using aqueous dimethylacetamide as solvent.