GB818845A - Process and device for testing solids, liquids or gases for the presence of substances forming azo dyes - Google Patents

Abstract

In a process for testing solids, liquids or gases for the presence of substances forming azo dyes the production of diazo components from the corresponding aromatic amines or their derivatives and their coupling with phenols or amines or their derivatives to form the azo dyes is effected continuously at 0-40 DEG C. The process is of particular importance in the phenol industry and is effected by a close regulation of the flow of reagents and liquids to be tested. The dyestuff formation may be detected visually or by an automatic means such as a photoelectric cell connected to an acoustic or optical signalling device. Phenols and their chlorinated, nitrated or sulphonated derivatives, aromatic amines and aromatic hydroxy-carboxylic acids may be detected.ALSO:In a process for testing solids, liquids or gases for the presence of substances forming azo dyes the production of diazo components from the corresponding aromatic amines or their derivatives and their coupling with phenols or amines or their derivatives to form the azo dyes is effected continuously at 0-40 DEG C. The process is of particular importance in the phenol industry and is effected by a close regulation of the flow of reagents and liquids to be tested. The dyestuff formation may be detected visually or by an automatic means such as a photo-electric cell connected to an acoustic or optical signalling device. Phenols and their chlorinated, nitrated or sulphonated derivatives, aromatic amines and aromatic hydroxycarboxylic acids may be detected. Solids or gases are washed with a liquid which is then treated as above. In examples: (1) a measured quantity of a phenol waste liquor is mixed with solutions of sodium nitrite in water and p-nitraniline in hydrochloric and phosphoric acid and an aqueous solution of sodium hydroxide conveyed thereto and any brown colour produced estimated against standards to give the phenol concentration which may be 0-100 m.g. of phenols per litre; (2) water from pre-heaters in a phenol-oil distillation plant is treated as in (1) using o-snisidine instead of p-nitraniline; (3) air from a room in which a -naphthylamine is dried and ground is washed with hydrochloric acid and the solution thus obtained diazotized by the addition of an aqueous sodium nitrite solution, is added to a solution of sodium a -oxynaphthoate and the colour is developed by the addition of caustic soda solution; (4) is the reverse of (3) a -oxynaphthoic acid being estimated in waste liquors; and in (5) waste liquors containing 1,8-dihydroxynaphthalene -3,6 - disulphonic acid tested as in (1) the amine solution being obtained from sulphanilic acid. A diagram of suitable apparatus for effecting the tests is provided.