Apparatus for Chlorine Dioxide Generation
Apparatus for producing chlorine dioxide comprises an electrolysis cell having an anode and a cathode which receives sodium chlorite solution as an anolyte flow and water as a catholyte flow, a chlorine dioxide gas separator which releases chlorine dioxide gas from the anolyte flow which leaves the cell and a separator which releases hydrogen gas from the catholyte flow which leaves the cell. The anolyte and catholyte flows are recirculated from the separators to the cell.
This invention relates to apparatus for the generation of chlorine dioxide by electrolysis which is used as a sterilizing agent in reservoirs of water such as in air conditioning and cooling systems. Of particular concern are legionnaires' disease carrying organisms which are best treated with chlorine dioxide and in flowing water such as potable water, recycled water and process water.
BACKGROUND OF THE INVENTIONThere are many patent documents relating to chlorine dioxide generators. For example GB692763 discloses an electrolytic diaphragm cell which produces chlorine dioxide from an aqueous solution of a chlorite eg sodium chlorite in the presence of a water soluble sulphate. The anode may be of platinum and the cathode of lead and the anode chamber is provided with cooling means. In GB1044769 the initial solution subjected to electrolysis may comprise a chromate, a mineral acid or a soluble calcium salt.
U.S. Pat. No. 4,542,008 teaches a continuous process for electrolyzing an aqueous sodium chlorite solution to produce chlorine dioxide which dissolves to produce an aqueous solution of NaClO2 containing chlorine dioxide. This solution is passed through a photometric cell which measures and controls concentration of sodium chlorite ions which when electrolysed avoid the formation of by-products such as dark colored chlorine dioxide complex and sodium chlorate. US2004149571 employs a porous anode through which the aqueous feed solution passes to maximize the conversion of chlorite to chlorine dioxide.
WO2008090367 discloses an electrolytic cell in which a porous barrier or membrane is provided between anodes and cathodes in order to restrict flow of sodium hydroxide formed around cathodes of the cell towards the anodes. As a result, the pH of the solution around the anodes is maintained low (around 2 or 3) and there is no need to add acid to the electro-chlorinator ton facilitate the production of the chlorine dioxide. US2008308428 discloses a method for generating high concentration chlorine dioxide having purity over 90% using an electrolytic material prepared from NaCl and NaClO2 subject to the control of optimal operation parameters of current 80-110 Amp, concentration of sodium chloride to be 20-25% and sodium chlorite to be 5% minimum, operation temperature 55-65 C and material feeding speed 30-50 ml/min.
OBJECT OF THE INVENTIONHowever the present inventor has found that the prior art apparatus can be improved upon and it is therefore an object of the present invention to provide chlorine dioxide generation with improved efficiency or at least to provide an alternative to the prior art.
STATEMENT OF THE INVENTIONAccording to the present invention apparatus for producing chlorine dioxide comprises an electrolysis cell having an anode and a cathode which receives sodium chlorite solution as an anolyte flow and water as a catholyte flow, a separator which releases chlorine dioxide gas from the anolyte flow which leaves the cell and a separator which releases hydrogen gas from the catholyte flow which leaves the cell.
Preferably the anode is formed from coated titanium mesh with an electrocatalytic coating and the cathode is formed from plain titanium mesh.
Preferably the anode and cathode chambers are separated by an ion exchange membrane.
Preferably the gap between the anode and cathode is between 0 and 5 mm.
Preferably the shadow area current of the anode is between 1000 and 3500 amps/m2.
Preferably the flow velocity of the anolyte solution over the anode is between 5 and 100 m/min.
Preferably the cell is provided with channels carrying coolant to cool the anolyte and catholyte flows.
Preferably the cell is encased within metallic plates.
Preferably the cyclonic separator is a generally conical tube which receives the anolyte flow tangentially facilitating the release of chlorine dioxide gas through the top of the separator and allowing residual chlorine dioxide and sodium chlorite solution to fall to a reservoir in the bottom of the separator to be recirculated in the anolyte flow.
Preferably air is introduced into the centre of the separator to increase the release of chlorine dioxide gas.
Preferably the separator is constructed in three axial sections joined by pairs of flanges and sealed by gaskets.
Preferably the hydrogen separator is an open pipe which receives the catholyte flow and allows the hydrogen gas to escape out of the top of the pipe and the residual catholyte to fall to the bottom of the separator whence it is recycled to the cell.
An embodiment of the invention is now described by way of example only with reference to the accompanying drawings in which:
In
NaClO2+H2O+energy→ClO2+NaOH+H2
Accordingly, anolyte outflow 5 is a chlorine dioxide solution and gas which enters separator 2 and the catholyte outflow 13 is a dilute sodium hydroxide solution with hydrogen gas which enters gas separator 3.
Separator 2 extracts chlorine dioxide gas 6 which flows to storage tank 4 and the residual solution of chlorine dioxide and sodium chlorite combines with anolyte input 10 or drains to waste 7. In gas separator 3, hydrogen 14 is vented to the atmosphere and the residual catholyte 11 is recirculated to cell 1 or drained to waste 12 and 15.
Electrodes 27 and 28 are positioned close to membrane 24 with an electrode gap 31 ranging between zero and 5 mm. The preferred material for electrode 27 is coated titanium mesh and for electrode 28, plain titanium mesh. The mesh is built up from multiple layers of 0.5 to 1.5 mm mesh material to give an extended surface area.
DC power is applied to electrodes 27 and 28 by conductors 32 and 33 which are fastened to electrodes 27 and 28 via current distributors 34 and 35. The power loading is optimized to maximize chlorine dioxide production and to minimize pH build up in the anolyte chamber. The preferred shadow area anodic current density is less than 2000 amps/m2 although current densities may range up to 3,500 amps/m2.
Recirculation of anolyte solution is adjusted to maintain a flow velocity over electrode 27 of 20 m per minute but flow rates may be in the range from 5 to 100 m per minute. Membrane 24 is maintained in position by Viton rubber strip and plastic or rubber O ring material. Cell 1 is also provided with internal waterways 36 and 37 to allow cooling of anolyte 25 and catholite 26. External metallic plates 38 and 39 increase the strength of cell casing 21 and also assist in cooling.
Air 49 is introduced through pipe 48 to facilitate the release of chlorine dioxide gas 45. The casing of separator 2 is formed from a plastic tube 41 with a conical insert 42 which creates a cyclonic flow which enhances the release of chlorine dioxide gas 45.
The apparatus of the present invention improves the efficiency of chlorine dioxide generation in two different aspects. First the efficiency of the electrolysis cell is improved so that more chlorine dioxide is produced from a given input. Second the chlorine dioxide gas and hydrogen gas separators with their attendant recirculation of anolyte and catholyte flows further increases the yield of chlorine dioxide and minimises waste.
Test ResultsA test was set up to compare a prior art cell to the cell described in the present invention. A 7.5% Sodium Chlorite Solution was pumped at a rate of 0.34 litres/hour into each cell in turn and a DC current of 10 Amps was applied. A recirculation flow of 4.57 litres/min was used and the conversion from Sodium Chlorite to Chlorine Dioxide was measured using a colorimeter. Over 3 tests, the conversion efficiency of the prior art cell was averaged at 67% and the conversion efficiency of the Cell described in the present invention was averaged at 86%.
VariationsIt will be realized that the foregoing has been given by way of illustrative example only and that all other modifications and variations as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth. Throughout the description and claims of this specification the words “comprise” and variations of that word such as “comprises” and “comprising” are not intended to exclude other additives components integers or steps.
The reference to any prior art in this specification is not and should not be taken as an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. It will be appreciated that the invention is not limited to the embodiments disclosed but is capable of numerous rearrangements, modifications and substitutions without departing form the scope of the invention as set forth and defined by the following claims.
Claims
1. Apparatus for producing chlorine dioxide comprising an electrolysis cell having an anode and a cathode which receives sodium chlorite solution as an anolyte flow and water as a catholyte flow, a separator which releases chlorine dioxide gas from the anolyte flow which leaves the cell and a separator which releases hydrogen gas from the catholyte flow which leaves the cell.
2. The apparatus of claim 1 in which the anode is formed from coated titanium mesh with an electrocatalytic coating and the cathode is formed from plain titanium mesh.
3. The apparatus of claim 1 in which the anode and cathode chambers are separated by an ion exchange membrane.
4. The apparatus of claim 1 in which the gap between the anode and cathode is between 0 and 5 mm.
5. The apparatus of claim 1 in which the shadow area current of the anode is between 1000 and 3500 amps/m2.
6. The apparatus of claim 1 in which the flow velocity of the anolyte solution over the anode is between 5 and 100 m/min.
7. The apparatus of claim 1 in which the cell is provided with channels carrying coolant to cool the anolyte and catholyte flows.
8. The apparatus of claim 1 which the cell is encased within metallic plates.
9. The apparatus of claim 1 in which the chlorine dioxide gas separator is a tube which receives the anolyte flow tangentially facilitating the release of chlorine dioxide gas through the top of the separator and allowing residual chlorine dioxide and sodium chlorite solution to fall to a reservoir in the bottom of the separator to be recirculated in the anolyte flow.
10. The apparatus of claim 9 in which air is introduced at the top of the separator to assist the release of chlorine dioxide gas.
11. The apparatus of claim 9 in which the tube has a conical.
12. The apparatus of claim 1 in which the hydrogen separator is an open pipe which receives the catholyte flow and allows the hydrogen gas to escape out of the top of the pipe and the residual catholyte to fall to the bottom of the separator whence it is recycled to the cell.
Type: Application
Filed: Mar 28, 2013
Publication Date: Jan 15, 2015
Inventor: Kenneth Roland Varcoe (Molendinar)
Application Number: 14/388,995
International Classification: C25B 9/08 (20060101); C25B 1/26 (20060101);