GB580926A - Process of separating tar acids from tar - Google Patents

Abstract

Tar acids are separated from coal tar by mixing it with an aqueous caustic alkali solution at a temperature above 100 DEG C., but preferably below 300 DEG C., e.g. 125-175 DEG C., and at a pressure above the vapour pressure of the mixture to separate into two layers while maintaining the said temperature and pressure, and withdrawing at least one layer separately, the separated layers being cooled and the pressure simultaneously or subsequently reduced to atmospheric pressure. In a continuous method of operating, the coal tar and an aqueous caustic soda solution, e.g. of about 3-6 per cent strength, and preferably in amount in excess of that required to react with all the tar acids present in the tar, are pumped through heaters into the top and bottom respectively of an extraction column in which the required temperature is maintained by, for example, a heating jacket, and the required pressure by suitable means, e.g. by the pumps. The carbolate solution and the extracted tar are removed from the top and bottom respectively of the column and passed through coolers and then through pressure reducing valves into receivers. The process is also applicable to batch operation, the tar and caustic soda being introduced into the extraction vessel, which is then closed and the contents heated to the required temperature, thoroughly mixed, allowed to separate, cooled and the pressure released. The carbolate solution is obtained substantially free from tar, and the tar acids are recovered therefrom in known manner. The tar layer is for most purposes sufficiently free from alkali, but may, if desired, be further purified by agitating with 0.15-0.3 parts by volume of water at 80-90 DEG C. and allowing the mixture to separate into two layers at the same temperature.