GB849987A - Process for treating coke oven tar - Google Patents

Abstract

849,987. Coke oven tar. ALLIED CHEMICAL CORPORATION. Nov. 6, 1958 [Dec. 2, 1957], No. 35707/58. Drawings to Specification. Class 55 (2). An automatic continuous process for treating coke oven tar containing water-soluble salts comprises continuously charging streams of coke oven tar and " wash " (as hereinafter defined), at approximately constant rates, into a mixing zone, continuously flowing said mixture of tar and wash at a temperature above 90‹ C. and under superatmospheric pressure through a pressurised settling and decanting zone wherein said mixture separates into an aqueous upper layer and a tarry lower layer, alternately and cyclically withdrawing, at substantially equal rates, material only from the tap and only from the bottom, respectively, of the pressurised settling and decanting zone so that for each cycle (1) the total withdrawal is equal to the total charge during the cycle, and (2) the withdrawal from the bottom is less than the anhydrous tar content of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing water-soluble salts and difficultly decantable tar and the material withdrawn from the bottom comprises product tar relatively free of watersoluble salts and aqueous liquor. " Wash " is defined as an aqueous material consisting of fresh water or a mixture of fresh water with up to 80% by volume of aqueous liquor containing water-soluble salts derived from the process. Preferably the withdrawal from the bottom for each cycle is about 5-20% by volume less than the anhydrous tar content of the total charge during the cycle. Withdrawn aqueous liquor and difficultly decantable tar may be continuously passed through a cooling zone, the cooled aqueous liquor may be continuously passed through an atmospheric pressure and decanting zone in which aqueous liquor containing water-soluble salts separates as an upper layer and difficultly decantable tar as a lower layer. the aqueous liquor may be continuously withdrawn from the top and the difficultly decantable tar from the bottom of the atmospheric settling and decanting zone, and all of the difficultly decantable tar may be continuously recycled to the mixing zone. Preferably the mixture of tar and wash is caused to flow continuously through the pressurised settling and decanting zone at a temperature of about 145-180 C. and under a pressure of about 150-175 p.s.i.g. U.S.A. Specification 2,440,311 is referred to.