Expandable anode for diaphragm cells

Abstract

The invention describes an anodic structure for electrolysis cell provided with a separator, in particular for a diaphragm chlor-alkali electrolysis cell, consisting of at least one movable surface suited to be put in contact with the separator. The movable surface comprises a component of higher thickness in contact with a porous layer of lower thickness, for instance a thin sheet provided with openings, and is characterised by the fact that a catalytic coating is applied only to the porous layer of lower thickness. The component of higher thickness has a substantially planar development and includes elements capable of promoting the local recirculation of electrolyte.

1 . An electrode structure for an electrolysis cell divided by a separator into an anodic compartment and a cathodic compartment, comprising at least one movable surface suited to be put in contact with the separator and provided with a component of higher thickness having a substantially planar development overlapped to a thin sheet provided with openings or to a thin mesh of wires, and a catalytic coating applied only to said component of higher thickness.  
   
   
       2 . The structure of  claim 1  characterized by being an anodic structure wherein the separator is a diaphragm or membrane for a chlor-alkali cell and said catalytic coating comprises a catalyst for chlorine evolution.  
   
   
       3 . The structure of  claim 1  wherein said component of higher thickness consists of a multiplicity of vertical and parallel plates.  
   
   
       4 . The structure of  claim 3  wherein said vertical plates have a width between 2 and 10 millimeters, a thickness between 0.3 and 2 millimetres and a spacing between 2 and 10 millimeters.  
   
   
       5 . The structure of  claim 1  wherein said component of higher thickness consists of a multiplicity of horizontal and parallel plates.  
   
   
       6 . The structure of  claim 5  wherein said plates have a thickness of at least 0.3 millimeters and are mutually spaced apart by at least 1 millimeter.  
   
   
       7 . The structure of  claim 5  wherein said horizontal plates are arranged in parallel and in off-set rows spaced apart by 1 to 5 millimeters, each of said plates being 5 to 30 millimeter long, said plates being obtained by deformation of a 0.3 to 2 millimeter thick sheet.  
   
   
       8 . The structure of  claim 1  wherein said component of higher thickness consists of a sheet provided with openings.  
   
   
       9 . The structure of  claim 8  wherein said sheet provided with openings is an unflattened expanded sheet.  
   
   
       10 . The structure of  claim 1  wherein said thin sheet provided with openings is a flattened expanded sheet or a perforated sheet or a sintered porous layer.  
   
   
       11 . The structure of  claim 10  wherein said flattened expanded sheet is 0.2 to 0.8 millimeter thick and is provided with rhomboidal openings with major diagonal between 3 and 7 millimeters and minor diagonal between 1 and 5 millimeters.  
   
   
       12 . The structure of  claim 1  wherein said thin sheet provided with openings has a ratio between opening clearance and overall geometric area at least equal to 0.5.  
   
   
       13 . The structure of  claim 12  wherein said ratio between opening clearance and overall geometric area is at least equal to 0.9.  
   
   
       14 . The structure of  claim 1  wherein said thin sheet provided with openings is made of a corrosion-resistant metal or of a polymeric material stable at the operating conditions of said cell.  
   
   
       15 . The structure of  claim 14  wherein said corrosion-resistant metal consists of titanium or titanium alloy.  
   
   
       16 . The structure of  claim 14  wherein said polymeric material consists of an optionally hydrophilized fluorinated polymer.  
   
   
       17 . The structure of  claim 1  wherein said thin sheet provided with openings or thin mesh of wires is secured to said component of higher thickness.  
   
   
       18 . The structure of  claim 1  wherein said thin sheet provided with openings or thin mesh of wires is placed in contact with the separator.  
   
   
       19 . A chlor-alkali membrane or diaphragm cell comprising at least a structure of  claim 1 .  
   
   
       20 - 21 . (canceled)  
   
   
       22 . A method of producing chlorine comprising electrolyzing an aqueous sodium chloride solution in a cell of  claim 19  at a voltage not higher than 3 volts at a current density of 2500 A/m 2  and an oxygen content in chlorine not higher than 2%.