Preparation and use of biocidal solutions

Abstract

An apparatus for delivering dissolved chlorine dioxide into a water system comprises sources for acid, a chlorite, and a chlorine donor solutions and metering pumps. The solutions are mixed whereby chlorine dioxide is generated, which is then fed into a water system.

1 . A stable solution for the production of chlorine dioxide comprising: 
 a chlorite,    a chlorine donor,    an alkali, and    water,    the chlorite and chlorine donor being present in a molar ratio from 1.0:0.1 to 1.0:15.0 chlorite to chlorine donor, the alkali being present in an amount sufficient to ensure a pH of at or above 10 and the water being present in an amount to give a theoretical minimum concentration of 0.5 ppm chlorine dioxide.    
     
     
         2 . A solution as claimed in  claim 1 , in which the water is present in an amount to give a theoretical minimum concentration of 500 ppm chlorine dioxide.  
     
     
         3 . A solution as claimed in  claim 1  or  2 , wherein the chlorite is an alkali metal chlorite.  
     
     
         4 . A solution as claimed in  claim 3 , wherein the alkali metal chlorite is sodium or potassium chlorite.  
     
     
         5 . A solution as claimed in any of the previous claims wherein the chlorine donor is an alkali metal hypochlorite.  
     
     
         6 . A solution as claimed in  claim 5  wherein the alkali metal hypochlorite is magnesium or calcium hypochlorite.  
     
     
         7 . A solution as claimed in any of  claims 1  to  4  wherein the chlorine donor is a chloroisocyanurate.  
     
     
         8 . A solution as claimed in any of  claims 1  to  7  wherein the chlorite is sodium chlorite and the chlorine donor is sodium hypochlorite.  
     
     
         9 . A solution as claimed in any of the preceding claims in which the molar ratio of chlorite to chlorine donor is from 1.0:0.3 to 1.0:5.0.  
     
     
         10 . A solution as claimed in  claim 9  in which the molar ratio of chlorite to chlorine donor is from 1.0:0.3 to 1.0:2.0.  
     
     
         11 . A solution as claimed in any of the previous claims wherein the pH is above 11.  
     
     
         12 . A solution as claimed in any of the previous claims wherein the pH is above 12.  
     
     
         13 . A solution as claimed in any of the preceding claims wherein the theoretical concentration of chlorine dioxide is from 20,000 to 50,000 ppm.  
     
     
         14 . A solution as claimed in any of the preceding claims which further comprises a biocide.  
     
     
         15 . A solution as claimed in  claim 14  wherein the biocide is selected from the group consisting of quaternary ammonium and phosphonium compounds, amines, iso-thiazolone mixtures and thiocyanates.  
     
     
         16 . A solution as claimed in any of the preceding claims which further comprises a penetrating agent.  
     
     
         17 . A solution as claimed in  claim 16  wherein the penetrating agent is a surfactant.  
     
     
         18 . A method of manufacturing the solution of any of  claims 1  to  17 , the method comprising sequentially adding the alkali, chlorine donor and chlorite to water, in that order, whilst maintaining the pH at or above 10 and the temperature at or below 30° C.  
     
     
         19 . A method as claimed in  claim 18  wherein the pH is maintained at or above 12.  
     
     
         20 . A method as claimed in claims  18  or  19  wherein the temperature is maintained at or below 20° C.  
     
     
         21 . A method of introducing chlorine dioxide to a system for bleaching or disinfection, the method comprising reacting a solution as claimed in any of  claims 1  to  17  with an acid to generate chlorine dioxide.  
     
     
         22 . A method as claimed in  claim 21  wherein the acid is a weak acid.  
     
     
         23 . A method as claimed in  claim 22  wherein the weak acid is citric acid or acetic acid.  
     
     
         24 . A method as claimed in any of claims  21  to  23  therein the pH of the solution is reduced to below 6.  
     
     
         25 . A method as claimed in  claim 24  wherein the of the solution is reduced to between 2 and 4.  
     
     
         26 . A method as claimed in any of claims  21  to wherein the reaction is conducted in situ in the system.  
     
     
         27 . A method as claimed in any of  claims 21  to  25  wherein the reaction is carried out and then the resulting solution is dosed into the system.  
     
     
         28 . A method of introducing chlorine dioxide to a system for bleaching or disinfection, the method comprising reacting a chlorite, a hypochlorite and an acid to generate chlorine dioxide in situ.