Improvements in or relating to the separation of volatile components from mixtures containing pitch, by distillation

摘要

Volatile components are separated from liquid mixtures containing relatively non-volatile material, such as pitch, by causing the liquid mixture to flow by gravity in the form of a thin film over a heated surface at a pressure of 10 to 100 mm. Hg., and subjecting the film to contact with steam. The temperature conditions are selected with regard to the nature of the mixture so as to effect volatilization of the volatile components without causing polymerization of the volatiles or decomposition of the relatively non-volatile material. The process is applicable in the distillation of unrefined tall oil, crude tar acids, coal tar, acid-washed benzole, gasoline, and naphthalene. Falling-film type evaporator 1 comprises vertical tubes 3, 31 housed in a jacket 4 through which a heating medium, such as steam, hot oil or Dowtherm, is circulated via pipes 5, 6. The open upper ends of the tubes project into chamber 8. Steam injection pipes 2, 21 enter the upper ends of the tubes. The liquid to be treated is supplied to chamber 8 through pipe 7; and flows from chamber 8 down the tubes, wherein it is partially evaporated. The vapours together with the non-volatile components are discharged from the lower ends of the tubes into sump 9, which is connected to centrifugal separator 10. The liquid separated in the separator is returned to the sump via bypass 11. The vapours are passed via line 12 to condenser 13, which is connected to a vacuum pump. The liquid in sump 9 may be recycled. In an example, crude tar acids containing phenols, cresols, xylenols, water (10 per cent.) and pitch (55 per cent.), are distilled under an absolute pressure of 50 mm. Hg., the mean temperature in the tubes being 115 DEG C. In this case the water content of the mixture provides the steam to contact the film. A high yield of volatile constituents, and a pitch having a softening point of 110 DEG C., are obtained. In another example, crude tall oil is supplied to the evaporator, together with 1 lb. of steam per gram of oil. The tubes are maintained at about 170 DEG C., and the absolute pressure at 30-40 mm. Specification 703,476 is referred to.