GB639137A - Improvements relating to the refining of naptha produced by the distillation of coaltar - Google Patents

Abstract

Coal tar naphtha which has been washed with strong sulphuric acid, is freed from acid-tar by sedimentation, agitated with aqueous alkali at a temperature between 90 DEG and 200 DEG C., and distilled. The hot alkali treatment, which may be carried out by boiling the naphtha and alkali together under a reflux condenser or by heating them together with agitation in a closed vessel under pressure, enables a distillate to be obtained having an acidity less than one-third of that given when cold alkali washing is employed. The treatment is preferably effected by agitating the naphtha with a solution of caustic soda, the amount of caustic soda being at least 0.3 per cent w : v of the naphtha, in a closed vessel at a temperature between 130 DEG and 200 DEG C. In an example, a naphtha fraction boiling between 100 DEG and 200 DEG C. was freed from tar acid and bases, and then agitated with 3 per cent by volume of 94.4 per cent sulphuric acid for 65 minutes at 40 DEG C. The mixture was allowed to settle for 15 minutes, as much acid-tar as possible was run off and the rest was, as far as possible, washed out with 20 per cent by volume of water. The oil was refluxed for 1 hour with 5 per cent by volume of a 50 per cent solution of caustic soda, and then distilled. The distillate had zero acidity. In another example, a naphtha fraction distilling up to 200 DEG C. was washed with 3 per cent of 94.6 per cent sulphuric acid for one hour at 40 DEG C. The acid-tar was separated and the oil washed twice with 20 per cent by volume of water. A portion of the oil was heated for one hour with 30 per cent by volume of a 2 per cent caustic soda solution under a pressure of 90 lbs. per square inch (about 146 DEG C.), and then distilled. The acidity of the distillate was about one-ninth of the distillate obtained from another portion of the acid-washed oil which was treated in the normal way, i.e. washed first with cold caustic soda solution and then with water until the water was neutral on leaving the oil.