Method and apparatus for the on-site generation of a gas

Abstract

This invention relates to an apparatus and a method for the on-site generation of gas of relatively small quantities of a halogen gas, preferably chlorine gas. The apparatus has at least one electrolytic cell having an anolyte section and a catholyte section. At least one of these sections is connected, by fluid conduits, to a fluid heater which heats an electrolyte solution prior to its ingress into the section. Heating also facilitates circulation of the electrolyte solution through the apparatus by means of a thermosyphon effect. The heating element is, in turn, connected to an electrolyte replenishment means. The apparatus includes at least one gas separator which separates gas produced in the electrolytic cell from electrolyte solution. The apparatus lacks a reservoir for the storage of electrolyte solution.

1 . A method for the on-site generation of a gas comprising the steps of: 
 a) forming a dissociatable electrolyte solution which, in use, dissociates into positively charged and negatively charged ions at least one of which is an ion of a gaseous element;    b) heating the electrolyte solution upstream of at least one electrolytic cell and thereby causing it to circulate and re-circulate through conduits and through the or each electrolytic cell by means of a thermosyphon effect;    c) liberating, from the solution, at one electrode of the or each electrolytic cell, a gas;    d) passing the liberated gas and electrolyte solution through at least one gas separator to separate the gas from the electrolyte solution prior to re-circulating the electrolyte solution through the electrolysis cell; and,    e) at no time storing the electrolyte in a reservoir.    
     
     
         2 . A method for the on-site generation of a gas as claimed in  claim 1  in which circulation of the electrolyte solution is facilitated by entraining gas bubbles produced in the or each electrolysis cell and orientating conduits leading from the or each electrolysis cell to the or each gas separator substantially vertically thereby providing a gas lift effect.  
     
     
         3 . A method for the on-site generation of a gas as claimed in  claim 1  or in  claim 2  in which the electrolyte in the solution is strengthened, if necessary, and any make up water is saturated by passing the electrolyte and make up water through an electrolyte salt dissolving tube.  
     
     
         4 . A method for the on-site generation of a gas as claimed in  claim 3  in which the electrolyte salt dissolving tube is mounted substantially horizontally.  
     
     
         5 . A method for the on-site generation of a gas as claimed in  claim 4  in which salt in electrolyte salt dissolving tube is replaced with fresh salt from a hopper.  
     
     
         6 . A method for the on-site generation of a gas as claimed in any one of the preceding claims in which the electrolyte solution is a metal halide and gas generated at the anolyte side of the electrolysis cell is a halogen.  
     
     
         7 . A method for the on-site generation of a gas as claimed in  claim 6  in which the metal halide salt is sodium chloride and the and gas generated at the anolyte side of the electrolysis cell is chlorine.  
     
     
         8 . A method for the on-site generation of a gas as claimed in  claim 6  in which the metal halide salt is potassium chloride and and gas generated at the anolyte side of the electrolysis cell is chlorine.  
     
     
         9 . A method for the on-site generation of a gas as claimed in any one of  claims 6  to  8  in which hydrogen gas and sodium hydroxide or potassium hydroxide to be generated at the catholyte side of the electrolysis cell.  
     
     
         10 . A method for the on-site generation of a gas as claimed in any one of the preceding claims in which the anolyte and catholyte sections of the or each electrolytic cell is or are separated from one another by an ion selective membrane which allows the passage of sodium or potassium, ions therethrough but which is impermeable to a halogen, to hydrogen gas and to hydroxyl ions.  
     
     
         11 . A method for the on-site generation of a gas as claimed in  claim 10  in which the ion selective membrane is a perfluoropolymer membrane.  
     
     
         12 . A method for the on-site generation of a gas as claimed in any one of the preceding claims in which water is added to the sodium hydroxide or potassium hydroxide solution at the catholyte side of the electrolyte cell to maintain a predetermined concentration of sodium hydroxide or potassium hydroxide in the catholyte solution.  
     
     
         13 . A method for the on-site generation of a gas as claimed in  claim 12  in which the water is distilled or demineralized, water.  
     
     
         14 . A method for the on-site generation of a gas as claimed in any one of  claims 6  to  13  in which sodium hypochlorite or potassium hypochlorite is also produced by mixing chlorine and sodium hydroxide, or chlorine and potassium hydroxide.  
     
     
         15 . A method for the on-site generation of a gas substantially as herein described with reference to and as illustrated in the accompanying drawings.  
     
     
         16 . An apparatus for the on-site generation of a gas comprising at least one electrolytic cell having an anolyte section and a catholyte section, at least one section being connected, by fluid conduits, to a fluid heater which, in use, heats an electrolyte solution prior to its ingress into said section and facilitates circulation of the electrolyte solution through the apparatus by means of a thermosyphon effect, the electrolytic solution being dissociatable into positively charged and negatively charged ions at least one of which is an ion of a gaseous element, the heating element in turn being connectable by fluid conduits to an electrolyte replenishment means, at least one gas separator which, in use, separates gas produced in the electrolytic cell from electrolyte solution, the apparatus lacking a reservoir for the storage of electrolyte solution.  
     
     
         17 . An apparatus for the on-site generation of a gas as claimed in  claim 16  in which the or each gas separator is positioned operatively above the or each electrolysis cell and in which conduits linking the or each electrolysis cell is orientated operatively substantially vertically thereby facilitating circulation of the electrolytic solution by means of a gas lift effect.  
     
     
         18 . An apparatus for the on-site generation of a gas as claimed in  claim 16  or in  claim 17  in which the replenishment means is a substantially horizontally orientated electrolyte salt dissolving tube through which electrolyte solution from the or each gas separator flows prior to flowing through the heating element.  
     
     
         19 . An apparatus for the on-site generation of a gas as claimed in  claim 18  in which the salt dissolving tube is connected to an electrolyte salt replenishment hopper which contains a desired salt, and is also connected to a salt separator, which is connected to the heating element, the salt separator removing particulate salt from the electrolyte prior to its introduction into the heating element.  
     
     
         20 . An apparatus for the on-site generation of a gas as claimed in  claim 19  in which the salt separator is a strainer.  
     
     
         21 . An apparatus for the on-site generation of a gas as claimed in any one of  claims 16  to  20  in which the electrolyte is a metal halide solution, the gas generated at the anolyte side of the electrolysis cell to be a halogen and hydrogen gas and a metal halide hydroxide are generated at the catholyte side of the electrolysis cell.  
     
     
         22 . An apparatus for the on-site generation of a gas as claimed in  claim 21  in which the metal halide is sodium chloride, the gas generated at the anolyte side of the electrolysis cell is chlorine and hydrogen gas and sodium hydroxide are generated at the catholyte side of the electrolysis cell.  
     
     
         23 . An apparatus for the on-site generation of a gas as claimed in  claim 21  in which the metal halide is potassium chloride, the gas generated at the anolyte side of the electrolysis cell is chlorine and hydrogen gas and potassium hydroxide are generated at the catholyte side of the electrolysis cell.  
     
     
         24 . An apparatus for the on-site generation of a gas as claimed in any one of  claims 16  to  24  in which the anolyte and catholyte sections of the or each electrolytic cell are separated from one another by an ion selective membrane which allows the passage of sodium or potassium, ions therethrough but which is impermeable to chlorine and hydrogen gas.  
     
     
         25 . An apparatus for the on-site generation of a gas as claimed in  claim 24  in which the ion selective membrane is a perfluoropolymer membrane.  
     
     
         26 . An apparatus for the on-site generation of a gas as claimed in any one of  claims 16  to  25  in which water is added to the sodium hydroxide or potassium hydroxide solution at the catholyte side of the electrolyte cell to maintain the concentration of sodium hydroxide or potassium hydroxide in the catholyte solution.  
     
     
         27 . An apparatus for the on-site generation of a gas as claimed in  claim 26  in which the water is distilled or demineralized water.  
     
     
         28 . An apparatus for the on-site generation of a gas as claimed in any one of  claims 22  to  27  in which the apparatus also produces sodium hypochlorite, or potassium hypochlorite, by mixing chlorine and sodium hydroxide, or by mixing chlorine and potassium hydroxide, produced by the apparatus.  
     
     
         29 . An apparatus for the on-site generation of a gas substantially as herein described with reference to and as illustrated in the accompanying drawings.