Patent GB-742898-A (GB)
Title: Improvements in or relating to manufacture of chlorine dioxide hydrate
Inventor: WILLIAMSON HILDING VICTOR
IPC: C01B11/02
Filed: 1953-07-07
Abstract: Chlorine dioxide hydrate, usually the decahydrate, free from liquid chlorine dioxide is prepared by absorbing chlorine dioxide vapour from a gas mixture consisting of chlorine dioxide and inert diluent <PICT:0742898/III/1> gas in a saturated aqueous solution of chlorine dioxide maintained at below 15 DEG C. and above the freezing point of the solution, the partial pressure of the chlorine dioxide in the gaseous mixture being at least equal to the vapour pressure of the chlorine dioxide in the aqueous phase over chlorine dioxide hydrate and, preferably, being at least 100 mm. Hg. and recovering chlorine dioxide hydrate formed.  Chlorine dioxide generated in 1 by the action of sulphur dioxide fed at 10 on sodium chlorate acidified with sulphuric acid although other specified methods of generation may be used, is diluted with air entering at 2 and passes to scrubber 4 to remove acid mist, water, and chlorine.  The gases are cooled to 0-5 DEG C. and pass to absorber 6 containing the solution obtained by first passing the gas through water at 0-2 DEG C. Lean gas is recycled through 7 together with make-up air from 9 to generator 2. The slurry of hydrate crystals is withdrawn to separator 30, wherein it is centrifuged or filtered and recovered solution is recycled to absorber 6 with fresh make-up water from 12.  The isolated crystals may be treated as a filter cake with a gas mixture containing chlorine dioxide and inert gas to form hydrate with any included water.  The crystals may be compressed into blocks and the blocks cooled below freezing and dipped in, or sprayed with water to form a coating layer of ice to permit storage and transportation of the blocks in refrigerated containers without loss of chlorine dioxide. The slurry of crystals from 6 may without separation be frozen into cakes or granulated.  Chlorine dioxide concentrations in the gas mixture to be absorbed of 12 to 65 per cent are referred to, preferred contents being 13-30 per cent., and the chlorine dioxide pressure may be up to 500 mm.  The solution usually contains about 3 per cent chlorine dioxide.  The absorption may be effected under pressure not exceeding 15 p.s.i.g.  If the chlorine dioxide content of the gaseous mixture is too low the gas may be passed to a concentrator (Figs. 3 or 4, not shown) wherein the chlorine dioxide is condensed and revaporized into an air stream in the desired concentration, and in this case the lean gas from the absorber is recycled to the concentrator, while that from the concentrator is recycled to the generator.  Alternatively, the chlorine dioxide may be absorbed in solid or liquid absorbents, e.g. sulphuric acid, aqueous ethylene glycol, silica gel, or carbon, at low temperature and stripped therefrom at higher temperature.  Specified freezing point depressants including metal salt electrolytes, organic compounds, or mineral acids, e.g. sulphuric acid, may be added to the absorbing solution.  The chlorine dioxide may be regenerated from the blocks of hydrate by dissolving with agitation below 16 DEG C. in water and stripping with a countercurrent of air in a column or by passing air over the block at 0-15 DEG C.  Solid carbon dioxide may be added to the absorbing solution to begin crystallization. Specification 577,054 is referred to.