GB448712A - Improvements in the purification of aqueous liquids from phenols and contingently other accompanying substances - Google Patents

Abstract

Aqueous liquids containing phenols, with or without other substances, are treated with a solid adsorbent such as active carbon, from which the adsorbed substances, including the phenols, are afterwards extracted by means of liquid ammonia. In detail, the procedure may be as follows. The aqueous liquid is passed upwardly through two or more adsorption chambers in series, and when the adsorbent in the first chamber is sufficiently charged the feed of liquid thereto is stopped and the liquid in the chamber is displaced. This displacement may be effected with a gas such as nitrogen or hydrogen, but is preferably effected with gaseous ammonia, in which event the last portion of the liquid displaced from the chamber (solution a) contains dissolved ammonia, and may be collected separately and worked up as described below. The moist adsorbent is then treated with liquid ammonia until the liquid leaving the chamber is free from extracted substances; this treatment may be effected at atmospheric or raised pressure and a corresponding temperature, but is preferably effected at atmospheric temperature or at the adsorption temperature. Ammonia is then expelled from the adsorption chamber, preferably by warming and passing steam into the chamber; the aqueous ammonia recovered (solution b) may be worked up as described below. The adsorbent is then ready for use again. The liquid ammonia containing extracted substances and water from the moist adsorbent may be evaporated at atmospheric pressure, but is preferably distilled under pressure in two stages; in the first stage, the bulk of the liquid ammonia is recovered as such by distillation at a slightly raised temperature and 10--15 atm. pressure without rectification; the residue (residue c) may then be freed from ammonia by evaporation, or it may be distilled at 150--180 DEG C. and 10--15 atm. pressure, with rectification, to yield a distillate of liquid ammonia and a residue of water and extracted substances; solutions (a) and (b) may be added to residue (c) before the latter is distilled. The process is particularly applicable to aqueous liquids containing phenols obtained in the destructive hydrogenation or low-temperature carbonization of carbonaceous materials. Examples are given in which the treatment of such liquids by the process of the invention is compared with the known process in which benzene is used as the extracting agent instead of liquid ammonia.