Patent GB-701591-A (GB)
Title: Distillation of coal tar
IPC: C10C1/04
Filed: 1951-01-16
Abstract: <PICT:0701591/III/1> Coal tar is subjected to fractional distillation in a series of fractionating columns, and the components which boil between 140 DEG  and 360 DEG C. at normal atmospheric pressure are withdrawn in a plurality of fractions, e.g. 12 fractions, having boiling ranges not exceeding 25 DEG C.  The columns are preferably connected together so that the liquid withdrawn from the sump of each column (except the last) may be introduced into the side of the next column; and the columns are maintained at progressively increasing temperatures and decreasing pressures, a vacuum prevailing in the last column.  The number of main columns required is reduced by the provision of side columns attached to them.  Pure components, e.g. indene, acenapthene, may be isolated from the narrow fractions by re-distillation, crystallization, solvent extraction, or extractive distillation.  Raw tar is introduced through pipe 1 into main column 2 which is heated by external tube furnace 14 connected to its base, and is maintained at an absolute pressure of 1000 mm. Hg.  Benzole and water vapours are withdrawn from the head of column 2, and are condensed.  The condensate is decanted in separator 5; and part of the benzole is returned as reflux to column 2 through pipe 7, while the remainder is withdrawn as product.  Two side columns 8 and 10 each having an external heater attached to the base, are connected at different levels to main column 2, the head of each side column being connected to the main column by two pipes.  A tar fraction is withdrawn from the base of each side column.  Thus the fraction c obtained from the base of column 8 may have a boiling range of 178-186 DEG C.  (This may be re-distilled to give indene.)  Part of the liquid from the base of column 2 is transferred through pipe 15 into the side of main column 16, which is heated at the base by external tubular furnace 23, and is maintained at an absolute pressure of 600 mm. Hg.  Column 16 is provided with three side columns, 18, 19 and 20; and thus four more fractions are obtained-one fraction, e, as overhead from column 16, and one fraction from the base of each of the three side columns.  The fraction obtained from column 20 may contain 85-90 per cent. acenaphthene.  Part of the liquid from the base of column 16 is transferred through pipe 24 into column 25, which is maintained at an absolute pressure of 300 mm. Hg. Column 25 is also provided with three side columns; and thus four more fractions are obtained.  Part of the liquid withdrawn from the base of column 25 is re-circulated to the column through tubular furnace 32; and the remainder is passed through pipe 33 to tubular furnace 34, where it is heated to 370 DEG  and thereby partly vaporized.  The partly vaporized mixture is introduced into column 35, which is maintained at an absolute pressure of 40 mm. Hg., and is also provided with three side columns.  Thus four more fractions are obtained.  The fraction obtained from side column 37 may contain 85-90 per cent. carbazol.  Pitch is withdrawn from the base of column 35.  Specification 692,364 is referred to.