Device for obtaining electrolysis products from an alkali metal chloride solution

Abstract

Device for obtaining electrolysis products from an alkali metal chloride solution where a cathode circuit contains a circulation pump with an overflow device for the return flow of pump liquid, which continuously secures the forced circulation of the catholyte via a heat exchanger, a cathode compartment and a capacitive separator for separating the hydrogen from the catholyte. In the discharge of the hydrogen from the capacitive separator for separation of the hydrogen from the catholyte, a cooled humidity separator is installed, the condensate collection container of which is connected via a dosage pump with the freshwater feed to the mixing device of the freshwater flow with the gaseous oxidant mixture.

Claims

1. A device for producing an oxidant solution from electrolysis products of an alkali metal chloride solution, the device comprising: an electrochemical reactor, being represented by one or more modular electrochemical cells, which are hydraulically connected in parallel, and an anode compartment and a cathode compartment of the reactor are separated by a porous, ceramic diaphragm, which is disposed coaxially between the electrodes of the electrochemical cells; a device for feeding the saline solution under pressure connected with an entrance to the anode compartment; a device for stabilizing a specified overpressure in the anode compartment, which is connected to an exit of the anode compartment; a mixing device for mixing gaseous products of the anodic electrochemical reaction with freshwater, the mixing device being connected with the exit of the anode compartment downstream of the device for stabilizing a specified overpressure in the anode compartment; a catholyte circuit comprising the cathode compartment of the electrochemical reactor, a separator for separating hydrogen from the catholyte, a facility for draining the excess catholyte from a receiving container of the separator, and a heat exchanger for cooling the circulating catholyte; and a dosage pump for adding the catholyte to the mixing device for mixing gaseous products of the anodic electrochemical reaction with freshwater, wherein the catholyte circuit contains a circulation pump with an overflow device for the return flow of the pump liquid, wherein the circulation pump continuously secures the forced circulation of the catholyte via the heat exchanger, the cathode compartment and the separator for separating the hydrogen from the catholyte, the receiving container of the separator, which is connected to a pump inlet of the circulation pump, is disposed at a lower position than the electrochemical reactor, such that the level of the catholyte in the receiving container of the separator, which is determined by the position of an overflow nozzle of the facility for draining the excess catholyte from the catholyte circuit, lies below an inlet nozzle from the cathode compartment of the electrochemical reactor, and, in a discharge line of the hydrogen from the separator for separation of the hydrogen from the catholyte, a cooled humidity separator comprising a condensate collection container is installed, wherein the condensate collection container is connected via the dosage pump with the freshwater feed to the mixing device for mixing gaseous products of the anodic electrochemical reaction with the freshwater.

2. The device according to claim 1, wherein the anode in the electrochemical reactor is provided with a cooling, and is disposed in an open cooling circuit of the elements of the device following the heat exchanger of the humidity separator and upstream of the heat exchanger of the catholyte in the circuit, wherein the water exiting from the cooling circuit is supplied to the mixing device for mixing the gaseous products of the anodic electrochemical reaction with the freshwater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the structure diagram of the device with reactor, the electrodes of which have no interior cooling.

(2) FIG. 2 shows the structure diagram of the device with reactor, which has a cooled anode that is integrated into the open heat regulation circuit of the assemblies of the device.

DETAILED DESCRIPTION OF THE INVENTION

(3) The device contains the reactor 1 with coaxially disposed electrodes, the anode 2, the cathode 3 and the diaphragm 4. The process chain of the anodic synthesis of the oxidant is represented by the anode compartment 5 of the reactor 1, the entrance of which is connected via the return valve 6 with the exit of the overpressure dosage pump 7, the entrance to which is connected to the filter 8, which is immersed in a container with the initial saline solution 9.

(4) The exit of the anode compartment 5 is connected to a stabilization pressure regulator 10 for gaseous products of the electrochemical anodic decomposition of the saline solution 9. On the feed line for the products of the anodic synthesis to the stabilization pressure regulator 10, a pressure gage 11 is installed, which is protected against chemically aggressive media by a separation element 12.

(5) The exit of the stabilization pressure regulator 10 for the gas is connected to the entrance of a mixing device 13 for gaseous products of the anodic synthesis with the freshwater flow.

(6) The cathode circuit of the device is formed by the cathode compartment 14, the entrance of which is connected to the exit of the catholyte from the heat exchanger 15. The entrance of the catholyte into the heat exchanger 15 is connected to the exit of a return conveyor pump 16, which is equipped with an overflow device 17 for the liquid return flow when the device 17 is shut down or brought briefly to a standstill. The entrance to the pump 16 is connected to the lower exit nozzle of the receiving container of a separator 18 for the separation of the hydrogen from the catholyte. This receiving container has a lower outlet nozzle for emptying the container, a central overflow nozzle for draining the excess catholyte, an upper nozzle for draining the hydrogen, and a nozzle for feeding the catholyte with hydrogen from the cathode compartment 14 of the electrochemical reactor 1, which is accordingly connected to the exit of the cathode compartment 14.

(7) In the drainage line of the hydrogen, a humidity separator 19 is disposed, which is determined for the removal of the condensation water from the hydrogen, which predominantly contains free hydroxyl groups. The exit of the condensation chamber of the humidity separator 19 of the hydrogen is connected via a dosage pump 20 to the feed of the cooling water to the mixing device 13 for gaseous oxidants with the freshwater flow.

(8) The freshwater from which the polyvalent metal ions have been removed is guided to the device at the entrance to the hydrogen-humidity separator 19 via a mechanical filter 21, an electromagnetic, normally closed, valve 22, a stabilization pressure regulator “according to the default setting” 23, and the flow controller 24. After exiting the hydrogen-humidity separator 19 the cooling water is guided to the entrance to the catholyte heat exchanger 15, and then travels from the exit of the heat exchanger 15 to the entrance to the mixing device 13 for the gaseous products of the anodic synthesis with the freshwater flow.

(9) FIG. 2 shows an additional element of the cooling system, the cooled anode 2 of the reactor 1, which is disposed for the cooling water between the hydrogen-humidity separator 19 and the catholyte heat exchanger 15.

(10) The device functions as follows.

(11) The sodium chloride initial solution 9, which is produced with purified (softened) or distilled water and chemically pure salt, is filled into the container. Distilled water is filled into the receiving container of the separator 18 via the nozzle for the hydrogen draining, for the purpose of separating the hydrogen from the catholyte. This is a one-off procedure and is only required when the device is first put into operation. The following are connected: the water feed nozzle at the entrance to the mechanical filter 21 to the fresh (drinking) water pressure line. The device is switched on by applying voltage to the normally closed electromagnetic valve 22. The water flow volume through the device is regulated with a stabilization pressure regulator 23 “according to the default setting”, wherein the set value is set. The water flow, which flows through the flow controller 24, triggers it and switches on the pumps 16, 20 or 7 and the current supply unit of the electrochemical reactor 1 (not shown in FIGS. 1 and 2). After filling the anode compartment 5 with saline solution, the pressure in the anode compartment 5 is regulated with the stabilization gas pressure regulator 10 “up to the default setting”, wherein the set value is set and controlled by means of the pressure gage 11. During circulation in the cathode circuit, the distilled water is enriched with sodium ions, which are selected via the porous ceramic diaphragm 4 in the reactor 1 from the saline solution that fills the anode compartment 5. The volume flow of saline solution, which reaches the anode compartment 5 of the reactor 1, is selected such that at the exit of the anode compartment, only gas is obtained, which is above all represented by chlorine with a small quantity of chlorine dioxide, oxygen and ozone. This gas is saturated with water, the microdroplets of which contain hydrogen peroxide and additional metastable hydroperoxide compounds.

(12) In the electrochemical reactor 1, the release of molecular chlorine in the anode compartment 5 and the formation of sodium hydroxide in the cathode compartment 14 is the decisive reaction:
NaCl+H.sub.2O−e.fwdarw.NaOH+0.5H.sub.2+0.5Cl.sub.2.

(13) At the same time, in the anode compartment 5 with a low current yield, the synthesis reaction occurs of chlorine dioxide directly from the saline solution and from hydrochloric acid, which is formed during the dissolution of molecular chlorine close to the anode:
(Cl.sub.2+H.sub.2O.Math.HOCl+HCl):
2NaCl+6H.sub.2O−10e.fwdarw.2ClO.sub.2+2NaOH+5H.sub.2;
HCl+2H.sub.2O−5e.fwdarw.ClO.sub.2+5H.

(14) In the anode compartment 5 of the reactor, ozone is form through direct decomposition of water and through oxidation of released oxygen:
3H.sub.2O−6e.fwdarw.O.sub.3+6H.;2H.sub.2O−4e.fwdarw.4H.+O.sub.2;.Math.O.sub.2+H.sub.2O−2e.fwdarw.O.sub.3+2H.

(15) The formation of active oxygen compounds occurs with a lower current yield:
H.sub.2O−2e.fwdarw.2H.+O.;H.sub.2O−e.fwdarw.HO.+H.;2H.sub.2O−3e.fwdarw.HO.sub.2+3H.

(16) When the gaseous product of the anodic oxidation of the sodium chloride solution is dissolved in water, a reaction usually occurs that can be expressed by the following equation:
Cl.sub.2+H.sub.2O.Math.HOCl+HCl.

(17) It is known that the most important anti-microbial agent is hypochlorous acid, the quantity of which in the solution is limited by the reduced pH value that results when hydrochloric acids are formed. The pH value can be changed by adding lye, i.e. sodium hydroxide, for example. However, this leads to the formation of damaging (sodium chloride) products and products with low reactivity (sodium hypochlorite). Sodium hypochlorite is a salt of a weak acid (hypochlorous acid) and a strong alkali (sodium hydroxide), but has anti-microbial activity, which in relation to the hypochlorous acid only constitutes 1/250 to 1/350 of its activity.
HOCl+HCl+2NaOH.fwdarw.NaOCl+NaCl+2H.sub.2O.

(18) The formation of sodium hypochlorite with simultaneous increase in the pH value with simultaneous increase in the concentration of the hypochlorous acid can be avoided by the addition of water to the reaction zone (the water contain free hydroxyl groups, which are formed during the condensation of water from the hydrogen, which is generated in the cathode compartment 14 of the electrochemical reactor 1).

(19) The condensate from the hydrogen-humidity separator 19 is added to the water flowing through with the aid of the pump 20, which contributes to the flow of an overconcentrated, hypochlorous acid and to a significant reduction in the concentration of the sodium ions in the product obtained, the oxidant solution, which is formed in the mixer 13 when the gaseous products of the anodic synthesis are dissolved in the flowing freshwater. Here, the pH value of the product created is in the region of 5.0-6.5.

(20) When the electrochemical system is brought to a standstill through the closure of the valve 22, the pumps 7, 16 and 20 and the current supply of the electrochemical reactor 1 switch off. Here, the catholyte flows out of the cathode compartment 14 as a result of gravity into the receiving container of the separator 18, thanks to the overflow device 17. The excess catholyte from the receiving container of the separator 18 is here discharged into the draining line through the overflow nozzle in the upper part of the receiving container (D). The anolyte remaining in the anode compartment 5 with a pH value of below 3 is filtered through the diaphragm 4 as a result of the overpressure, and in so doing, dissolves the hydroxide deposits of the polyvalent metals, which may occur in small quantities in the initial saline solution. When the device is next put into operation, all current consuming parts start working simultaneously in the previously set mode, wherein they secure a rapid stabilization of the process that lasts just a few seconds. During transportation of the device, the catholyte is drained from the receiving container of the separator 18 into the drainage line by means of outlet nozzles (D) with a valve disposed in the floor of the container.

(21) The device was tested in comparison with the prototype, which was produced according to U.S. Pat. No. 7,897,023 B2. Both comparable devices contained an electrochemical reactor, which is represented by an electrochemical, modular element (cell) according to GB 2479286 B (electrochemical cell no. 5, Table 2). The initial saline solution contains 250 g/l of sodium chloride; the content of chlorides and calcium and magnesium sulphates in the initial solution was 0.2 mg/l. The initial solution was used during operation of the two comparable devices. The tests were conducted at a temperature of the ambient air of 20° C., a temperature of the initial saline solution of 20° C., a temperature of the drinking tap water of 15° C. and at the same temperature of the electrochemical cells of 30° C. Here, the current strength over the electrochemical reactor 1 in the prototype of the device was 6 A, with a voltage of 6 V, in the device according to the new technical solution, these were 16 A and 5 V. Accordingly, the yield of oxidants in the prototype was 6.0 g/h, and in the device according to the new technical solution, 20.5 g/h. The oxidant solution produced in the prototype at a speed of 12 l/h had an oxidant concentration of 500 mg/l with a pH value of 2.8 and a total mineral content of 0.96 g/l. Following the dosed addition of the catholyte, which is formed during the synthesis of the oxidant solution, the pH value at the exit increased to 6.0 with a simultaneous increase in the mineral content of the solution to 1.5 g/l. The oxidant solution, which is produced at a speed of 41 l/h in the device according to the new technical solution, had a pH value of 3.1 with an oxidant concentration of 500 mg/l and a total mineral content of 0.67 g/l. When the condensate was fed from the hydrogen-humidity separator 19 at the entrance to the mixing device 13, the pH value of the oxidant solution increased to 6.0, with a simultaneous increase in the mineral content to 0.72 g/l.

(22) The time for achieving operating status following a standstill of the prototype device was 5 minutes, compared to 25 seconds for achieving operating status with the device according to the new technical solution. When cooling water was fed into the anode compartment 5 (according to the diagram in FIG. 2), the current strength over the reactor, with an unchanged temperature (30° C.) reached 20 A with a voltage of 6 V, which entailed a corresponding increase in the capacity of the device in relation to the end product, the oxidant solution, to 52 liters per hour with the above parameters.