| 摘要 |
<PICT:0690607/IV (b)/1> Phenols are extracted from industrial waste waters with low boiling-point solvents, e.g. butyl acetate, in two cycles, the bulk of phenol being removed, e.g. down to 50-100 milligrams/litre, from the water in the first cycle in which the solvent is used in small quantity, e.g. 10-20 per cent of volume of water under treatment and recovered by distillation and the residual quantities of phenol being removed e.g. down to 1 milligram/litre or less from the water in the second cycle in which the solvent used in large quantities, e.g. 100-300 per cent by volume is recovered by extraction with a stoichiometrical excess of lye. The cycles are so combined that the solvent in the first cycle is derived from the charged solvent from the second cycle and the solvent recovered from the first cycle by distillation is fed to the second cycle. The diagram illustrates a plant in which the first cycle A consists of four stages 2, 3, 4, 5 and the second cycle B consists of two stages 6, 7 each of the stages being constructed in known manner so that the water from the input 1 of the plant flows in counter-current to the solvent and is freed from the solvent at the end of each stage, leaving the plant at 8. The charged solvent from the first cycle which passes through the stages in succession is separated from the phenols in a distillation plant 9, the phenols leaving the plant at 18 while the solvent is fed at 13 into the solvent circuit of the second cycle B. After each of the stages 6, 7 the solvent is treated with a stoichiometrical excess of lye in co-current in stages 11, 12 for example, in washing towers packed with Raschig rings so as to ensure that the solvent is mechanically free from phenolate lye. The lye required for stages 11 and 12 is introduced at 16 and recycled several times through the stages 11, 12 and a small quantity which contains relatively small amounts of phenol is removed at 17. The solvent for the first cycle is taken from the stage 6 before treatment with lye in the stage 11. Alternatively, the solvent output from the distiller 9 may be fed back to the stage 5.
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