GB733796A - Method of working up aqueous liquors containing phenols, hydrogen sulphide, carbon dioxide, ammonia, and possible other organic or inorganic substances - Google Patents

Abstract

<PICT:0733796/III/1> Aqueous liquors containing phenols, ammonia, carbon dioxide, hydrogen sulphide and possibly other organic or inorganic substances are worked up in a process in which the phenols are first recovered from the liquors by extraction with oxygen-containing organic solvents which are insoluble or only slightly soluble in water and which have a lower boiling point than the phenols and from the thus treated liquor the residual solvent together with the free ammonia, carbon dioxide and hydrogen sulphide are stripped out, the ammonia being recovered from the gases and vapours driven off, preferably as ammonium sulphate, and the bulk of residual organic solvent by condensation. Suitable solvents are butyl acetate, isopropyl acetate, methylethyl ketone, isopropyl ether and other suitable ethers, esters and alcohols. Fixed ammonia may also be recovered from the liquors by adding milk of lime. As shown in Fig. 1 dephenolized liquor after treatment with a solvent for the phenols is fed by a pipe 2 into a direct condensing column 4 where it is used to condense solvent vapours and absorb NH3 from the gases and vapours fed into the column from a deacidifier 10. At the bottom of the column 4 condensed solvent is led off at 141 and the liquor at a temperature of 40-70 DEG C., for example 50 DEG C., passes to the deacidifier 10 via a heat exchanger 6, and a direct steam heater 8 where the temperature of the liquor is raised to 90 DEG C. Steam is admitted to deacidifier 10 by line 11 and the H2S,CO2, solvent residues and some NH3 pass out of the deacidifier into the column 4 by line 12. The gases leaving the column 4 chiefly CO2 and H2S and a little solvent vapour are washed, e.g. by phenol-containing liquor, to recover the last traces of the solvent and the H2S may be burnt to SO2 and converted to H2SO4. Deacidified dephenolized liquor passes to a still 19 and is stripped of its free ammonia by steam admitted by line 20. Hot effluent from the still 19 passes through the heat exchanger 6 and the vapours from the still are led into a saturator 22 containing H2SO4. Ammonium sulphate is recovered from the saturator and steam and a little CO2 and H2S is led off from the saturator via line 25 and used either in the still 19 or deacidifier 10. Some of the steam may be discarded through line 28 to prevent an excess of CO2 in the system. If the fixed ammonia is also to be recovered milk of lime is added to the lower part of the still 19 or milk of lime is added to the liquor from the still 19 in a separate still. In a modification the deacidifier 10 is omitted and the H2S, CO2, solvent residues and at least the free ammonia are stripped from the dephenolized liquor in a still, the vapours being passed to a saturator containing H2SO4 for direct absorption of the NH3, the unabsorbed gases then passing to a direct condenser for recovery of the solvent residues.