GB723875A - Distillation process for obtaining fractions rich in benzole from benzoleenriched wash oil - Google Patents

Abstract

In a process for the steam distillation of benzolized wash oil in a fractionating column, the vapours leaving the head of the column are submitted to partial condensation in order to condense naphthalene oil and water; the condensate is freed from water, then heated, and returned to the column at a position above the wash oil inlet. The vapours leaving the partial condenser are condensed to give a distillate rich in benzole hydrocarbons, part of which is returned to the head of the column, while the remainder is withdrawn <PICT:0723875/III/1> as product. A naphthalene oil fraction is withdrawn from the side of the fractionating column at a point above the return inlet of the naphthalene oil portion of the distillate. The initial condensate, before being heated and returned to the column, may be mixed with stripped wash oil; the mixture being vaporized, except for pitch and resinous residues, before being introduced into the column. This feature prevents the thickening of the wash oil. Benzolized wash oil, supplied through conduit 1, is passed through heat-exchangers 2, 4; and then through pipes 6, 8 of pipe-still 7. Pipe 6 is in a convection zone of the pipe-still, while pipe 8 is in the radiation zone. The wash oil, now at a temperature of about 185 DEG C., is introduced through line 9 into column 10, which is supplied with steam through line 11. The vapour mixture leaving the head of the column is passed through heat-exchanger 4, where it is brought to a temperature such as to cause the condensation of the naphthalene oil, any wash-oil components, steam, and a certain amount of the benzole hydrocarbons. This condensate flows through line 14 to separator 15, from which water is withdrawn through pipe 16. The water-free condensate is collected in vessel 18, and from there it is pumped through pipe 21 which is arranged in a convection zone of pipe-still 7. A partition wall 22 is provided between pipes 6 and 21, so that regulated quantities of heating gas can be brought into contact with each pipe. The heated condensate then passes at a temperature of about 250 DEG C., through pipe 23 to vaporizing-chamber 24, where it is vaporized, except for a pitch-like residue which is withdrawn through line 25. The vapour mixture is introduced into column 10 through line 26. Concentrated naphthalene oil is p withdrawn from the column through line 36. That portion of the vapour mixture from the head of the column which is not condensed in heat-exchanger 4, is passed through heat-exchanger 2 and condenser 30; and the condensate, which collects in vessel 31, contains 95 to 98 per cent of constituents boiling up to 180 DEG C. Part of the condensate from vessel 31 is pumped through line 34 to the head of the column; the remainder being withdrawn as product through line 32. Stripped wash oil can be introduced, continuously or batchwise, through line 37 into vessel 18; thus mixing with the primary condensate, and passing therewith through pipe 21 to vaporizing-chamber 24. To enable the temperature in the primary condenser 4 to be regulated to the required value, a by-pass conduit 39, controlled by valve 38, is arranged between lines 3 and 5, which supply the benzolized wash oil to the pipe-still. By appropriate adjustment of valve 38 the amount of wash oil flowing through heat-exchanger 4 can be so regulated that the temperature of the volatile mixture on the other side of the heat-exchanger can be reduced accurately to the level necessary for the fractional condensation.