GB760159A - Improvements in or relating to the purification of organic compounds by heat treatment and distillation - Google Patents

Abstract

<PICT:0760159/IV(b)/1> Organic compounds which contain volatile contaminants of a type which are convertible by heat-treatment (if necessary in the presence of a converting agent) into relatively non-volatile products, are purified by a continuous process comprising passing the organic compound in the liquid state through a multiplicity of chambers connected in series, wherein it is heated to a temperature sufficient for the conversion of the impurities, leading the vapours evolved in the chambers to a single reflux condensing system, feeding the condensate into the first and/or second chamber, and subjecting the discharge from the last chamber to distillation whereby the organic compound distils over in a purified state leaving the converted contaminants behind as distillation-residue. The process may be employed for the purification of phthalic anhydride, phenol, caprolactam and glycerol. Phthalic anhydride may be purified in the apparatus shown, which comprises a vessel 12 divided into six chambers by partitions 13 having lower openings 14 for the flow of liquid from chamber to chamber. The return pipe 6 of a reflux cooler (not shown) leads into the first chamber. Molten phthalic anhydride, containing small quantities of naphthoquinone and maleic anhydride as impurities, is introduced into the first chamber via the reflux cooler and pipe 6. The temperature in the chambers is kept at 284 DEG C., the temperature in the upper part of the reflux cooler being 155 DEG C. Openings 15 in the upper parts of the partitions enable the vapours evolved in the chambers toflow, via pipe 6, to the reflux cooler. The residence time of the anhydride in the apparatus is about 6 hours. The liquid discharged by conduit 3 is subjected to distillation, and pure white phthalic anhydride is obtained as distillate. In the case of phenol contaminated with thiophenol, the heat-treatment is carried out in the presence of air or other oxidation agent. The heat-treatment of caprolactam is effected in the presence of sodium hydroxide, sulphuric acid or potassium permanganate.ALSO:<PICT:0760159/III/1> Organic compounds which contain volatile contaminants of a type which are convertible by heat-treatment (if necessary in the presence of a converting agent) into relatively <PICT:0760159/III/2> non-volatile products, are purified by a continuous process comprising passing the organic compound in the liquid state through a multiplicity of chambers connected in series, wherein it is heated to a temperature sufficient for the conversion of the impurities, leading the vapours evolved in the chambers to a single reflux condensing system, feeding the condensate into the first and/or second chamber, and subjecting the discharge from the last chamber to distillation, whereby the organic compound distils over in a purified state leaving the converted contaminants as disstillation-residue. The process may be employed for the purification of glycerol, phthalic anhydride, phenol and caprolactam. Glycerol may be treated in the apparatus shown, which comprises seven chambers 1 connected in series by pipes 2. Vapour pipes 7 lead from the chambers to reflux cooler 4. The liquid return pipe 6 of cooler 4 leads to the central chamber 1. The impure glycerol is introduced into the central chamber through the reflux cooler. The temperature in the chambers is kept at about 300 DEG C., the temperature at the top of the reflux cooler being 250 DEG C. The residence time of the glycerol in the apparatus is about 12 hours. The glycerol discharged through pipe 3 has a dark brown colour. This dark brown glycerol is distilled to give a colourless product as distillate.