Abstract:
A method for production of disinfectant with active chlorine concentration in the range 0-6000 ppm from a flow through diaphragm-electrolyser with one of the aims to reduce the volume of disinfectant for its transportation to the point of usage.

Description:
PRIORITY 
       [0001]    This application claims priority of the Estonian national patent application number 201400004 filed on Feb. 4, 2014 the contents of which are incorporated herein by reference in entirety. 
       FIELD OF INVENTION 
       [0002]    The invention belongs in the field of catering to the vital needs of people, specifically in the field of hygiene by means of disinfectants produced from aqueous solutions, especially from the aqueous solution of sodium chloride through electrolysis in a flow through diaphragm electrolyser. The invention provides a method for the production of disinfectants with active chlorine concentration in the range of 0-6000 ppm from a flow through diaphragm electrolyser, and at reducing the volume of the disinfectant for its transportation to the point of usage. 
       BACKGROUND 
       [0003]    Electrolysis of the aqueous solution of sodium chloride in an anode compartment results in an anolyte that contains active chlorine compounds. An anolyte obtained with a prescribed concentration of active chlorine is a disinfectant that is widely used in various fields for disinfection and sterilisation. 
         [0004]    The disinfectants that are normally used have the active chlorine concentration of not more than 500-800 ppm, and in case of production with diaphragm electrolysis, approximately 1500 g active chlorine is obtained per hour per one device. With the increase in the output of electrolysis devices by up to 8000 grams per hour, the opportunities for the application of the anolyte become wider in industrial technologies that require disinfectants with the active chlorine concentration of 2000-6000 ppm. Furthermore, the existence of high output electrolysis devices gave the possibility of centralised disinfectant production and delivery to consumers. In order to reduce transportation costs, the disinfectants with a high concentration of active chlorine became highly in demand. 
         [0005]    A known method for the production of disinfectants with a high active chlorine concentration, whereby the chlorine is obtained from the electrolyser as gas which is then dissolved in water, such as chlorine dioxide, is provided in U.S. Pat. No. 7,833,392 [1]. The disadvantage of this method is that it requires higher safety precautions on account of leaking gas, and inadequate dissolution of the gas in water—less than 2.9 g/l. 
         [0006]    U.S. Pat. No. 7,897,023 [2] describes a method for obtaining a mixture of oxidants from an electrolyser, mainly gaseous chlorine with the following dissolution in water. Besides the certain efficiency of this method, the disadvantage of this method is that it requires higher safety precautions due to leaking gaseous chlorine and the complexity of hydraulic connections for the production of large quantities of disinfectant, since the electrolyser on which the method [2] is based has low productivity—only about 40 grams of active chlorine per hour. This method [2] is also complicated due to the need to use a circulation circuit and special external heat exchangers for the cooling of electrolytes. 
         [0007]    There are methods for the production of disinfectant in a liquid state by means of an electrolyser. Such disinfectants include the known sodium hypochlorite which is obtained through electrolysis. The methods for its production are not viewed, because sodium hypochlorite is obtained in another type of electrolyser—an electrolyser without a diaphragm, therefore the method for the production of sodium hypochlorite is not comparable with the method presented herein. 
         [0008]    A method for the production of disinfectant with an electrolyser by means of sodium chloride electrolysis with the output capacity of more than 600 grams of active chlorine per hour is possible on the basis of the description of electrolyser provided in U.S. Pat. No. 8,298,383 [3]. The disadvantage of patent [3] is that the reduction of flows passing through the electrode compartment for the purpose of producing disinfectants with active chlorine concentration of up to 2000 ppm causes the electrodes to heat up to 100° C. 
         [0009]    Patent GB 1396765 [4] describes a method for the production of disinfectant, wherein the heat of an anode as the inner electrode is lowered by passing coolant through a hollow inside the anode. The disadvantage of this method is its complexity due to the auxiliary external circulation circuit and a heat exchanger required for the cooling of the liquid. 
         [0010]    Patent RU2350692 [5] describes a method, wherein the flow of electrolyte from the outside is channelled into a hollow in the anode, cooling it, and then flowing into the cathode compartment for producing the catholyte. The disadvantage of this method is that the method is not intended for the production of disinfectants and that the electrolyte enters the hollow in the anode from internal space through perforation in the anode wall, reducing the durability of the anode coating and the functioning order of the anode. 
         [0011]    For the reduction of catholyte heating, the method of cooling by means of a Peltier element is also used in a known method (Thermoelectric Cooler—TEC), see e.g. patent JP2000051860 [6]. The disadvantage of this method is its low output caused by the low capacity of the Peltier element—up to 100 W/h, which allows taking out heat of no more than 4 litres per hour when producing disinfectants with active chlorine concentration of up to 6000 ppm. 
         [0012]    In terms of embodiment and the achieved result, patent EE05608 [7] is the closest method, where the whole flow of water that passes into the electrolyser is initially divided into two parts: one part is guided into the cathode compartment, the second part is divided into two flows, one of which is guided into the anode compartment and the second flow is guided into an inner hollow in the cathode and then to the upper cover of the electrolyser for the purpose of diluting the anolyte to the required active chlorine concentration in the disinfectant, i.e. only part of the total water intended for the dilution of anolyte in the upper cover is guided to the cooling of the cathode. The active chlorine concentration in the anolyte before the anolyte reaches the upper cover of the electrolyser is up to 3000 ppm. This method [7] is regarded as the closest analogue. However, the disadvantage of this method, which was initially planned for the production of disinfectant at 500 ppm, is its limited capacity to yield disinfectants with high concentration, because the flow that is intended for the anode compartment enters the anode compartment, bypassing the inner hollow of the cathode, not participating in the cooling of the cathode and also not participating in the cooling of the catholyte, whereby the catholyte is only cooled by the flow that is intended for the reduction of active chlorine concentration in the disinfectant of less than 3000 ppm. However, with the need for production of disinfectants with active chlorine concentration of 3000 ppm, diluting the anolyte will no longer be necessary, i.e. the dilution flow that passes through the inner hollow of the cathode is stopped and only 2 flows will pass through the electrolyser: one flow through the cathode compartment, the other flow through the anode compartment, and method [7] becomes method [3] with a disadvantage that is related to the heating of electrolytes in the electrode compartments. As a result, application of method [7] in practice yields disinfectants with active chlorine concentration of no more than 2000 ppm, or cooling circulation circuits were to be used in order to obtain higher concentrations. 
       SUMMARY OF THE INVENTION 
       [0013]    The objective of the invention is to extend the range of active chlorine concentration in the disinfectant and to produce disinfectants with adjustable active chlorine concentration from 0 to 6000 ppm with a simple method by means of a diaphragm electrolyser, without using external cooling circulation circuits and Peltier elements. 
         [0014]    The objective is solved on account of the method for the production of disinfectants with a diaphragm electrolyser, which includes the formation of flow through a cathode compartment, as it foresees branching only a very small portion of fresh water through an inner hollow of the cathode, whereas the following differences have been planned:
       the whole volume of water for the formation of flow in the anode compartment passes initially through the inner hollow of the cathode;   the flow rate through the anode compartment shall not be less than 3.3 litres per hour per anode compartment at electric power 100 W/h, which in the viewed examples accounts for 4 litres per hour per 1 dm 2  of anode surface facing the cathode.       
 
         [0017]    In the presented method, the causal relations between the achieved results and flow directions and volumes have been reached. In the viewed examples the entire flow that is intended for the formation of flow is passed through the anode compartment, the inner hollow of the cathode, whereas the volume of flow through the inner hollow of the cathode is not less than 4 litres per hour calculated per 1 dm 2  of the anode surface facing the cathode, while the volume of flow guided to the anode compartment also accounts for not less than 4 litres per hour per 1 dm 2  of the anode surface facing the cathode. These characteristics of the method are related to the operating conditions of the electrolyser: low volume of flow through the cathode compartment, difficulties in the heat exchange due to the diaphragm between the anode and cathode compartments (the presented method was tested, using a ceramic diaphragm), the method employs operating voltage not exceeding 24 A per 1 dm 2  and is not destructive for the protective coating of the anode surface facing the cathode. The voltage between the electrodes does not exceed 10 V. As an example of the calculation, an electrolyser is viewed where the area of anode surface is 1 dm 2 . Anolyte from the sodium chloride solution flows through the anode compartment into fresh water at 4 litres per hour, almost 15 g/l. Catholyte flows from the fresh water through the cathode compartment at 0.16 litres per hour. This catholyte is the alkali sodium hydroxide in which fresh water was generated during the electrolysis, flowing through the inner hollow of the cathode at 4 litres per hour. 
         [0018]    Since the electric conductivity of the flows through the anode compartment and through the cathode compartment is approximately the same, the distance from the anode to the diaphragm and the distance from the cathode to the diaphragm is approximately the same, and the voltage drop in both compartments can be 5 V at maximum, the current used in the calculation is 24 A. If there was no flow passing through the inner hollow of the cathode, the temperature of the catholyte at the flow rate of 0.16 litres per hour could increase within 1 hour to: 
         [0000]    
       
         
           
             
               
                 5 
                  
                 V 
                 × 
                 24 
                  
                 A 
                 × 
                 3600 
                  
                 
                     
                 
                  
                 sec 
               
               
                 4187 
                  
                 
                     
                 
                  
                 g 
                  
                 
                   / 
                 
                  
                 l 
                 × 
                 0.161 
               
             
             = 
             
               644.8 
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                
               
                 
                   ° 
                    
                   C 
                 
                 . 
               
             
           
         
       
     
         [0019]    In other words, the catholyte would start boiling, 7 minutes in this example. However, in 7 minutes the catholyte actually heats up to 45° C., therefore, in connection with the high electric conductivity of the metal wall of the cathode, the heat from 120 W/h transfers not only to the catholyte at the rate of 0.16 litres per hour, but also to the flow 4 litres per hour through the inner hollow of the cathode. In a case of ideal thermal conductivity of the cathode wall, the temperature of the cathode should increase to 24.8° C. In the actual process of disinfectant production the catholyte initially heats up by 45° C. in comparison with the initial temperature of fresh water; the fresh water in the inner hollow of the cathode heats up by 16° C. The water from the inner hollow of the cathode is guided to mixing with sodium chloride, and the sodium chloride solution is guided to the anode compartment, where the solution is heated up by further 25.8° C., i.e. the calculated temperature of the solution in the anode compartment exceeds the initial temperature of water by 40.8° C. Actually, the temperature of the solution discharged from the anode compartment exceeds the initial temperature of water by less than 35° C., because in the actual process of method embodiment the heat is transmitted into the ambient environment through the metal wall of the anode. The flow of fresh water through the inner hollow of the cathode is necessary primarily during the first operating hour of the electrolyser until the diaphragm has gained supplementary heat conductivity. 
         [0020]    The diaphragm, which has become completely wet, allows the anolyte to be involved in the cooling of the catholyte. At the current of 24 A per 1 dm 2  of the anode surface facing the cathode, every 4 litres per hour of sodium chloride solution yields anolyte at 4 litres per hour, which contains no less than 24 grams of active chlorine, i.e. producing a disinfectant with the active chlorine concentration of not less than 6000 ppm. In order to prevent further heating of electrolytes, the current passing through the anode compartment is 100 W/h, not less than 3.3 litres per hour per anode compartment, and the current passing through the cathode compartment is 100 W/h, not less than 0.13 litres per hour per cathode compartment. 
         [0021]    Thereby, the presented method has the following important features: 
         [0000]    1) the whole flow of water intended for the formation of flow through the anode compartment and the whole flow that is necessary for the dilution of anolyte to a concentration below 6000 ppm is guided to the inner hollow of the cathode;
 
2) the rate of anolyte flow through the anode compartment by not less than 3.3 litres per hour at converted electric energy of 100 W/h applied in the anode compartment, and the rate of catholyte flow through the cathode compartment by not less than 0.13 litres per hour at converted electric energy of 100 W/h applied in the cathode compartment, are required and sufficient for the achievement of technical results for extending the range of active chlorine concentration in disinfectants to up to 6000 ppm and for producing disinfectants with active chlorine concentration of 6000 ppm in an acceptable heat schedule without using any cooling circulation circuits and Peltier elements.
 
         [0022]    The invention in the presented method allows extending the range of active chlorine concentration in disinfectants of 0-2000 ppm from the concentration of the closest analogue to the concentration of 0-6000 ppm, and reduces the volume of the disinfectant for its transportation to the point of usage. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  provides a chart of the method for the production of disinfectants with a diaphragm electrolyser. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIG. 1 : The initial fresh water flow  1  is divided into two flows by means of a T-piece  2  through which fresh water flow  3  is guided into cathode compartment  4 , while fresh water flow  5  is guided into an inner hollow  6  inside cathode  7 . From the inner hollow  6  the flow  5  is guided into T-piece  8  that divides the flow  5  into two flows of which fresh water flow  9  is guided to the upper cover  10  of the electrolyser for the purpose of mixing with anolyte  11  that arises through the anolyte compartment  12  to the upper cover  10 , while fresh water flow  13  is guided into mixer  14 , where flow  13  is mixed with the flow of concentrated sodium chloride solution  15 . After the mixer  14  the electrolyte flow  16  in the form of sodium chloride solution is guided into anode compartment  12 . 
         [0025]    The rate of flow  9  is adjusted by means of regulator  17 , the rate of flow  13  is adjusted by means of regulator  18 , and the rate of the flow of concentrated sodium chloride solution  15  is adjusted by means of regulator  19 . Regulators  17 ,  18 ,  19  can be typical attachments: valves, dampers, dispenser pumps, etc. When the volume of electrolyte  16  that passes through anode compartment  12  is not less than 3.3 litres per hour at electric power 100 W/h per anode compartment, then at sufficient electric power the electrolyte  16  becomes anolyte  11  with the active chlorine concentration of 6000 ppm, which at such concentration is a ready disinfectant  20  and at this point the flow  9  is not used, or in case of producing a disinfectant with the active chlorine concentration of less than 6000 ppm, the anolyte is mixed in the upper cover  10  with the fresh water coming from flow  9 . The pH of the disinfectant is adjusted similarly to flow  3  in the method of the method of [7], where it is guided to cathode compartment  12  due to changes in mineralisation. The figure presents a version where the solution of concentrated sodium chloride is added to fresh water flow  3  by means of T-piece  21  and regulator  22  of the volume of sodium chloride solution. 
         [0026]    The products of the electrolysis in the form of catholyte  23  and hydrogen  24  in cathode compartment  12  are discharged for disposal. 
         [0027]    Thereby  FIG. 1  illustrates how in the embodiment of the presented method the catholyte flow  4  is protected against overheating by means of fresh water flow  5 , which always flows through the inner hollow of cathode  7 , cooling down catholyte  4 , and the amount of which is at least equal with the amount of anolyte  11 . 
         [0028]    The results of tests conducted with the presented method confirm the functioning of the method and are presented in the table below. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 
               
             
             
               
                   
               
               
                 Temperature of disinfectant and catholyte in the presented method 
               
               
                 at initial water temperature 12° C. 
               
             
          
           
               
                   
                 Temperature ° C. after 
                   
               
               
                 Concentration of active 
                 120 minutes of electrolysis 
               
             
          
           
               
                 chlorine in the disinfectant 
                 disinfectant 
                 catholyte 
               
               
                   
               
               
                  500 ppm 
                 16 
                 14 
               
               
                 2000 ppm 
                 22 
                 20 
               
               
                 3000 ppm 
                 25 
                 23 
               
               
                 6000 ppm 
                 42 
                 40