GB702823A - Improvements in or relating to continuous fractional distillation - Google Patents

Abstract

<PICT:0702823/III/1> In a continuous fractional distillation process carried out under reduced pressure, particularly for the dehydration of crude tar acids, the feed is preheated and partially vaporized by indirect heating with low grade steam at 3 to 15 pounds per square inch (gauge), and the vapours from this preheating stage are passed to a rectification stage, while the liquors from the preheating stage are passed to a stripping stage. The liquid withdrawn from the stripping stage is submitted to rectification, and the vapours so obtained may be condensed in water-cooled "evaporative condensers", the steam from which is used for the preheating stage. Liquor consisting of tar acids containing water, is pumped through pipe 2 into preheater 3 which contains a heating-coil 4 supplied, through pipe 5, with steam at a pressure of 3 to 10 p.s.i.g., from evaporative condensers 28 and 35. Preheater 3 is disposed between the rectification-section 7 and the stripping-section 11 of a distillation column, which is maintained under reduced pressure by pump 43. Some of the water in the feed is vaporized in preheater 3. The vapours liberated in preheater 3 enter rectifier 7, while the residual liquor overflows through pipe 10 into stripper 11. The remainder of the water is vaporized in stripper 11, the vapours from which are passed, through pipe 12 into the rectifier. Dehydrated tar acids collect in reboiler 13 which is heated by live-steam heater 14. The vapours (steam and some tar acids) which leave the head of the column, are condensed in condenser 8; and the condensate is withdrawn through pipe 9. The dehydrated tar acids are transferred from reboiler 13 into column 25, which is also maintained under reduced pressure by pump 43. The base of column 25 is connected to a heat-exchanger 26 supplied with steam at 150 to 250 lbs. pressure. Phenol and cresols vapours leave the head of column 25, and are condensed in water-cooled evaporative condenser 28; and that part of the condensate which is not returned to the column as reflux, is withdrawn from the system as product via barometric seal 30. The liquor collecting in heat-exchanger 26 is transfered via pipe 31 to evaporator 32, where the xylenols fraction is vaporized. The xylenols are condensed in water-cooled evaporative condenser 35, which is maintained under reduced pressure by pump 46. Pitch is withdrawn from the base of the evaporator. Specification 608,038 is referred to.