Patent GB-687868-A (GB)
Title: Drying mixed solvents by distillation
IPC: B01D3/36
Filed: 1950-06-23
Abstract: A homogeneous mixture comprising methyl ethyl ketone, a hydrocarbon boil <PICT:0687868/III/1> ing between 100 DEG  and 400 DEG F, and water, such as is obtained in de-oiling paraffin wax, is introduced into the side of a fractionating column which is equivalent, above the feed-point, to a number of theoretical plates which is not sufficient to produce the ternary azeotrope (M.E.K.-hydrocarbon-water) as overhead vapour but which is sufficient to produce an overhead vapour which on condensation separates into two liquid layers; the condensed overhead from the column is decanted, the organic layer being returned to the column as reflux, and a partially or wholly dehydrated mixture of M.E.K. and hydrocarbon is withdrawn from the base of the column.  Oily wax is slurried with a solution consisting of 90 per cent M.E.K. and 10 per cent benzene; and the slurry is filtered.  The filtrate is passed, via surge-tank 1, through heat-exchangers 55 and 4, wherein it is heated to 200 DEG F; and is then introduced into flash-chamber 5 which is maintained at a pressure of 2 p.s.i.g.  Damp-solvent vapours, withdrawn overhead from chamber 5, are passed through lines 7 and 8 to p  condenser 9 and receiver 10.  The liquid withdrawn from the base of chamber 5 is heated to 450 DEG F in steam-heater 12 and is then introduced into flash-chamber 13 where a pressure of 35 to 40 p.s.i.g. is maintained.  Dry-solvent vapours, withdrawn overhead from chamber 13, are passed via heat-exchanger 4 to condenser 16 and receiver 17.  The liquid withdrawn from the base of chamber 13 is stripped with steam in stripper 19.  Oil is removed from the base of stripper 19; while wet solvent vapours are taken off overhead, condensed, and the condensate collected in receiver 24. Returning now to the wax collected in the filter: the wax is melted and passed successively from surge-tank 2 to flash-chambers 33, 38 and stripper 42, wherein it is subjected to the same treatment as that already described in connection with the filtrate.  The damp-solvent, dry-solvent and wet-solvent are collected in receivers 10, 17 and 24 respectively, while wax is withdrawn from the base of stripper 42. Two liquid phases separate in receiver 24: the upper phase, which contains 84 per cent M.E.K., 9 percent benzene and 7 per cent water, is introduced through line 25 on to the 25th tray of 30-tray fractionating-column 26.  Damp-solvent from receiver 10 is introduced through line 54 on to the 15th tray of column 26. Vapours at 170 DEG F are withdrawn from the head of column 26 and condensed; and the condensate is collected in decanter 29 where phase-separation occurs. The organic phase is returned through line 30 to the 30th tray of column 26.  Dry-solvent is withdrawn from the base of column 26, and is collected in receiver 17.  The aqueous phase withdrawn from decanter 29 through line 46, is introduced into fractionating-column 47 which is supplied with steam through line 48.  The overhead (M.E.K. + water) from column 47 is condensed; and the condensate is collected in receiver 24. The aqueous phase in receiver 24 is utilized as reflux for column 47.  The water withdrawn from the base of column 47, is rejected from the system.  Wet homogeneous mixtures of M.E.K. and toluene, or a naphtha, may be treated in a similar manner.