Improvements in the production of hard pitch and oils from medium soft coal tar pitch

摘要

PICT:0616730/III/1 Medium soft pitch is converted into hard pitch with simultaneous recovery of oils by passing the soft pitch in the molten state, at a temperature not exceeding 350 DEG C., through a cascade tower maintained under reduced pressure, from the bottom of which partially stripped pitch is withdrawn and re-circulated to the tower, preferably through a pipe-still; hard pitch is withdrawn from another section of the tower and the oil vapours evolved from the top are passed to a condenser. Soft pitch of melting point 80 DEG to 85 DEG C. is introduced at a temperature between 300 DEG and 350 DEG C., through pipe 1 into cascade tower 2 which is maintained at a pressure of 50 mm. by steam jet pump 3. The pitch cascades down the tower, with partial vaporization of the oils therein, to reservoir 4 from which it is withdrawn and pumped, through pipe-still 6 and line 7, to the upper section of tower 2. The pitch then cascades down to reservoir 8, evolving the remainder of the oil, from which it is removed by a barometric leg to seal pot 9. Superheated steam or air, to assist distillation, may be introduced, through pipes 10, into reservoirs 4 and 8; and also into the pipe-still. The vapours from the tower are passed to contact condenser 13 where the oil is condensed by a counter-current cascade of the distillate pumped up from balance tank 141 through cooler 16. Alternatively, another type of tar oil, such as creosote, may be used for condensing the vapours from tower 2. Any gases leaving condenser 13 are cooled in cooler 17 and pass on to reservoir 24 which is maintained at atmospheric pressure. A portion of these gases may be recycled to the cascade tower, the amount being controlled by controller 21. The production of hard pitch from the soft pitch derived from crude coal tar acids is referred to.