NO751906L

1505722 Extractive distillation PHILLIPS PETROLEUM CO 16 May 1975 [30 May 1974] 20909/75 Heading C5E [Also in Division B1] In extractive distillation, a portion of the condensed overhead is returned to an upper portion of the column as reflux, the extract is removed as a vaporous side stream, the recovered selective solvent is recycled to the top of the column and two immiscible liquid phases, one rich in the solvent and the other rich in the compounds to be separated, are maintained in the upper portion of the column. The process can be applied to (a) the separation of butadiene from butanes and/or butenes; (b) the separation of isoprene from pentanes and/or pentenes; (c) the separation of cyclohexane from hexane; (d) the separation of aromatics and/or sulphur compounds from cracked gasolines, and (e) the separation of a C 7-10 thermal or catalytically cracked gasoline into an overhead comprising paraffins, naphthenes and olefins and a bottoms comprising aromatics and n- C 9+ paraffins which can be fractionated to separate a benzene, toluene and xylene fraction and a fraction containing C 9+ aromatics and n-C 9+ paraffins which can be further separated by extractive distillation. The selective solvent can be a sulpholane or a sulpholene which can also contain diethylene glycol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, acetone, methanol and/or 0À1-20 wt. per cent water. A C 7-10 gasoline fraction 21 is separated in a column 30 which comprises an upper extractive distillation portion and a lower portion in which the extract 39 is stripped from the solvent 25 which is recycled in part as the stream 32 and in part through a reboiler 48. The overhead 33 is separated at 35 into a water stream 38 and a raffinate which is in part refluxed as the stream 36. The extract 39 is removed as a vapour and, after returning entrained liquid 42 to the column, is separated at 45 into the extract 47 and a water stream 46 which is returned to the column.