GB829021A - Improvements in separation of butadiene from hydrocarbons by extractive distillation - Google Patents

Abstract

<PICT:0829021/III/1> In a process for separating butadiene from a mixture of hydrocarbons by extractive distillation the flow of the extractive solvent to the distillation zone, where butene-1 is being separated from the butadiene, is controlled in response to the butene-1 concentration determined at a selected position at the butadienerich end of the zone to maintain the butene-1 concentration below a predetermined maximum at that position. A feed stream comprising the effluent from a butane dehydrogenation zone, with substantially all the C3 and lighter hydrocarbons removed, is fed through line 1, which is controlled by ultra-violet controller 9, into fractionator 2 from which butene-2 and heavier material is removed via line 5. Butadiene and lighter material which leaves fractionator 2 by line 4 is led via line 13 into the 50th tray of a 100-tray distillation column 14, which is supplied with furfural through line 26. Butene-1, isobutane, isobutylene and some butene-2 leave column 14 via line 15, while the furfural stream, containing the butadiene, passes to stripper 21 via line 20. The stripped furfural is returned from stripper 21 to column 14 via line 26 through valve 34, which is controlled by recorder controller 32 which measures the flow at 33. Recorder controller 32 is regulated by an analytical recorder controller 31, e.g. of the infra-red type (see Group XL (b)) which continuously detects the butene-1 concentration on a selected tray below the feed inlet of column 14, e.g. the 24th. Butadiene, with minor amounts of butenes and acetylenes, leaves stripper 21 via line 22 and passes through line 38 to a 120-tray fractionator 37, from which butene-2 and heavier materials are removed via line 47. Butadiene and the lighter acetylenes pass from fractionator 37 via line 40 to accumulator 42, from which methylacetylene rich vapours are bled through valve 46. A controller 52, similar to 31, detects the butene-2 or total olefine content on a selected tray in fractionator 37 and controls valve 49 which determines whether the butadiene runs to storage via line 48 or to recycle via line 43. A modification for acetylene-rich vapours entering fractionator 37 is described in which an extra analytical recorder controller detecting the acetylenes content is used below, and in conjunction with, recorder 52. The Specification mentions several other solvents which may be used to replace the furfural.