Patent GB-1039542-A (GB)
Title: Improvements in bleaching processes utilizing chlorine dioxide solutions
IPC: D06L3/08
Filed: 1963-02-19
Abstract: Fats and soaps are bleached with an aqueous chlorine dioxide-containing bleaching solution by a process in which a proportion of the bleaching solution is continuously withdrawn, its chlorine dioxide content replenished and the replenished solution is returned at a dosage which will maintain the chlorine dioxide concentration of the solution in the bleaching bath substantially constant.  The bleaching solution may contain up to 8 g.p.l. of chlorine dioxide and may have a pH of between 2 and 8 and bleaching may be effected at 10-60 DEG  C.  The bleaching solution may also contain wetting agents, optical brightening agents and buffer substances.  The chlorine dioxide may be generated by the reaction of sulphuric acid or oxalic acid with sodium or potassium chlorate, of sulphur dioxide with sodium or potassium chlorite or chlorate or from an alkali metal chlorite and chlorine, and may be diluted with an inert gas, suitably air. During bleaching a proportion of the bleaching solution may be continuous withdrawn from the bleaching bath and passed through an absorption vessel, e.g. a packed tower counter currently to a gaseous stream of chlorine dioxide and inert diluent, the absorption vessel having in its upper part an inlet coupled to means for conveying to it solution from the bleaching bath, at or near its bottom an outlet for the chlorine dioxide-replenished solution coupled to means for recovering the solution to the bleaching bath and also in its lower part an inlet for the admission of chlorine dioxide diluted with inert gas.  The chlorine dioxide in the bleaching bath may be measured by an analyzer which is operatively connected to means for controlling the supply of chlorine dioxide gas so as in operation to adjust automatically the supply of gas to the requirements of the bleaching bath. The chlorine dioxide may be produced by passing a stream of chlorine up through a reaction vessel in countercurrent to a sodium chlorite solution, a source of inert gas, e.g. air, being introduced through a supply line in the bottom of the reaction vessel and the chlorine dioxide diluted with air being drawn off at the top of the reaction vessel while the salt solution produced is removed from the bottom of the reaction vessel.  A stream of air or inert gas practically free of chlorine dioxide is drawn off from the top of the absorption vessel and recirculated to the reaction vessel.  The analyzer may be installed in the pipe circulating the chlorine dioxide solution to the bleaching bath and is used to control the valve and feed-pump supplying the chlorine and sodium chlorite solution to the reaction vessel.ALSO:Chlorine dioxide for use in bleaching is generated by the reaction of sulphuric acid or oxalic acid with sodium or potassium chlorate, of sulphur dioxide with sodium or potassium chlorite or chlorate or from an alkali metal chlorite and chlorine, and may be diluted with an inert gas, suitably air.  During bleaching a proportion of the bleaching solution may be continuously withdrawn from the bleaching bath and passed through an absorption vessel, e.g. a packed tower counter currently to a gaseous stream of chlorine dioxide and inert diluent, the absorption vessel having in its upper part in inlet coupled to means for conveying to it solution from the bleaching bath, at or near its bottom an outlet for the chlorine dioxide-replenished solution coupled to means for reconveying the solution to the bleaching bath and also in its lower part an inlet for the admission of chlorine dioxide diluted with inert gas.  The chlorine dioxide may be produced by passing a stream of chlorine up through a reaction vessel in countercurrent to a sodium chlorite solution, a source of inert gas, e.g. air, being introduced through a supply line in the bottom of the reaction vessel and the chlorine dioxide diluted with air being drawn off at the top of the reaction vessel while the salt solution produced is removed from the bottom of the reaction vessel.  A stream of air or inert gas practically free of chlorine dioxide is drawn off from the top of the absorption vessel and recirculated to the reaction vessel.ALSO:Textile materials, e.g. cotton, viscose rayon and polyacrylonitrile yarns and fabrics, paper and pulp are bleached with an aqueous chlorine dioxide-containing bleaching solution by a process in which a proportion of the bleaching solution is continuously withdrawn, its chlorine dioxide content replenished and the replenished solution is returned at a dosage which will maintain the chlorine dioxide concentration of the solution in the bleaching bath substantially constant.  The bleaching solution may contain up to 8 g.p.l. of chlorine dioxide and may have a pH of between 2 and 8 and bleaching may be effected at 10 DEG -60 DEG C.  The bleaching solution may also contain wetting agents, optical brightening agents and buffer substances.  The chlorine dioxide may be generated by the reaction of sulphuric acid or oxalic acid with sodium or potassium chlorate, of sulphur dioxide with sodium or potoassium chlorite or chlorate or from an alkali metal chlorite and chlorine, and may be diluted with an inert gas, suitably air.  During bleaching a proportion of the bleaching solution may be continuous withdrawn from the bleaching bath and passed through an absorption vessel, e.g. a packed tower, counter currently to a gaseous stream of chlorine dioxide and inert diluent, the absorption vessel having in its upper part an inlet coupled to means for conveying to it solution from the bleaching bath, at or near its bottom an outlet for the chlorine dioxide-replenished solution coupled to means for reconveying the solution to the bleaching bath and also in its lower part an inlet for the admission of chlorine dioxide diluted with inert gas.  The chlorine dioxide in the bleaching bath may be measured by an analyser which is operatively connected to means for controlling the supply of chlorine dioxide gas so as in operation to adjust automatically the supply of gas to the requirements of the bleaching bath.  The chlorine dioxide may be produced by passing a stream of chlorine up through a reaction vessel in countercurrent to a sodium chlorite solution, a source of inert gas, e.g. air, being introduced through a supply line in the bottom of the reaction vessel and the chlorine dioxide diluted with air being drawn off at the top of the reaction vessel while the salt solution produced is removed from the bottom of the reaction vessel.  A stream of air or inert gas practically free of chlorine dioxide is drawn off from the top of the adsorption vessel and recirculated to the reaction vessel.  The analyser may be installed in the pipe circulating the chlorine dioxide solution to the bleaching bath and is used to control the valve and feedpump supplying the chlorine and sodium chlorite solution to the reaction vessel.