RU2494974C1 - Device for electrochemical deoxygenation of highly pure water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrochemical devices of water purification, namely to devices of deoxygenation of highly pure water. Device for electrochemical deoxygenation of highly pure water contains membrane electrolyser 1, consisting of, at least, one cell for membrane electrolysis, which contains cathode chamber 3 with cathode 1, anode chamber 4 with anode 8, separating cathode and anode cation-exchanging membrane 2 and catalytic reactor 16, connected with membrane electrolysis. Cathode chamber is formed with net from nickel or stainless steel, pressed to cathode surface, anode chamber is formed with porous plate from titanium or nickel, pressed to anode surface. Cathode is made in form of electron-conducting palladium layer, applied on surface of cation-exchange membrane, facing cathode chamber. Anode is made in form of electro-conducting platinum layer, applied on opposite surface of cation-exchange membrane, facing anode chamber. Net from nickel or stainless steel is covered with palladium layer. Porous plate from titanium or nickel is covered with layer of platinum or ruthenium or iridium oxides.

EFFECT: invention makes it possible to simplify construction of electrodes and technology of water deoxygenation, increase degree of highly pure water deoxygenation, and reduce energy consumption for carrying out the process.

3 cl, 1 dwg, 2 ex

Description

The invention relates to electrochemical devices for water purification, namely to devices for deoxygenation of water.

The content of dissolved oxygen in water in equilibrium with air depends on temperature, atmospheric pressure and is at the level of 8 mg / l. Oxygen dissolved in water causes intense corrosion of iron and its alloys. A tangible decrease in the corrosion rate of technological equipment can be achieved with a dissolved oxygen content of 50 μg / L or less in water. Therefore, deoxygenation of water is one of the most important stages of water treatment in almost all technological processes using water.

Deoxygenation of water can be carried out by physical, chemical or electrochemical methods [A.V. Tanners. Removing oxygen from feedwater of steam power plants. Leningrad, SZPI, 1981, 56 pp.].

Known devices for electrochemical deoxygenation of water, representing an electrochemical cell, the cathode and anode of which are separated by an ion-exchange membrane. The water to be deoxygenated continuously flows through the cathode chamber. The cell cathode is made of metal with a high overvoltage of hydrogen evolution - copper (application WO 9324412 (A1), publication date 12/09/1993) or silver (application WO 0064816 (A1), publication date 02/11/2000). The anode in both devices is made of inert metal (platinum, platinum titanium). When an electric field is applied to the cathode, the reaction of ionization of dissolved oxygen proceeds with the formation of water molecules. The ion-exchange membrane separating the anodic and cathodic spaces of the cell prevents the penetration of oxygen released at the anode into deoxygenated water. To increase productivity, deoxygenation is carried out on three-dimensional cathodes with a developed surface. The disadvantage of the above electrochemical devices is the relatively low rate of deoxygenation of water, associated with the delayed stage of ionization of dissolved oxygen.

Closest to the claimed invention is a device for electrochemical deoxygenation of deionized water (US patent No. 4830721 publication date: 05.16.1989, patent analogue EP 0276789 publication date 03.08.1988).

In accordance with the description of the prototype device, the deoxygenation process is carried out by sequentially supplying the source water to the membrane electrolyzer and then to the catalytic reactor. The membrane electrolyzer includes at least one cell containing a cathode and an anode separated by a cation exchange membrane. The cathode and anode have a multilayer structure. Each electrode is a set of metal grids in contact with each other. The mesh electrodes are pressed against the cation exchange membrane. As noted in the description of the prototype patent, the use of such mesh electrodes leads to a more uniform distribution of current on the membrane, which minimizes ohmic losses in high-purity water. High-purity water containing dissolved oxygen enters the cell’s flow-through cathode chamber. The auxiliary electrolytic solution or deionized water circulates with periodic renewal through the anode chamber of the cell. When an electric field is applied in the specified device, both the dissolved oxygen ionization reaction and the hydrogen evolution as a result of water electrolysis are realized at the cathode. The current in the system is set in such a way as to ensure at the outlet of the cell a stoichiometric ratio of dissolved oxygen and hydrogen in water. As a result of the oxygen ionization reaction at the cathode, the oxygen concentration in the water decreases to a level determined by the rate of dissolved oxygen ionization. Water leaving the electrolyzer containing the residual amount of dissolved oxygen and hydrogen (in a stoichiometric ratio) is sent to a catalytic reactor, in which they quantitatively interact with the formation of water molecules. A catalytic reactor is a flow tank filled with a catalyst to initiate the recombination of oxygen and hydrogen.

The design of the electrodes of the prototype device increases the efficiency of the device due to the fact that the electrode additionally performs the function of a flow distributor and, thereby, provides more efficient delivery of deoxygenated water to the electrode surface, moreover, this design allows to reduce ohmic losses during water electrolysis by minimizing the distance between the membrane and the surface of the electrodes. Moreover, the design complexity of such electrodes is one of the disadvantages of such a device, since it does not completely solve the problem of ohmic losses during electrolysis. This is due to the fact that a layer of high-purity water with high electrical resistance remains between the membrane and electrodes, which leads to a significant increase in the energy consumption of the process. At the same time, on the surface of the electrodes of the prototype device there is an intensive evolution of gaseous oxygen and hydrogen and, accordingly, gas filling of the cathode and anode chambers, resulting in an even more noticeable increase in the electrical resistance of water and, accordingly, an increase in the energy consumption of the process.

Also, the disadvantages of the device include the complexity of the process, which consists in the need to organize (periodic or constant) the flow of the washing solution through the anode chamber. In the absence or stoppage of the duct in this chamber, concentration of ionic impurities can be observed, a decrease in the liquid level until the chamber is completely drained and electrolysis ceases due to the electrolysis decomposition of water in this chamber.

The objective of the invention is to provide a simpler and less energy-consuming device that provides a higher degree of deoxygenation of high-purity water.

The technical result consists in simplifying the design of the electrodes and the technology of deoxygenation of water, the absence of ohmic losses, and, as a result, reducing energy consumption, increasing the degree of deoxygenation of high-purity water.

The specified technical result is achieved by the fact that in the device for electrochemical deoxygenation of high-purity water, comprising a membrane electrolyzer, consisting of at least one cell for membrane electrolysis, comprising a cathode chamber with a cathode, an anode chamber with an anode that separates the cathode and anode, a cation exchange membrane, and a catalytic a reactor filled with a catalytic sorbent and connected to a membrane electrolyzer according to the invention, the cathode chamber is formed by a grid of nickel or stainless steel, pressed to the surface of the cathode, the anode chamber is formed by a porous plate of titanium or nickel pressed to the surface of the anode, the cathode is made in the form of an electrically conductive layer of palladium deposited on the surface of the cation exchange membrane facing the cathode chamber, and the anode is made in the form of an electrically conductive layer of platinum deposited on the opposite facing the anode chamber the surface of the cation exchange membrane. A mesh of nickel or stainless steel may be coated with a layer of palladium, and a plate of porous metal may be coated with a layer of platinum or oxides of ruthenium or iridium.

The simplification of the design is achieved by the fact that instead of multilayer mesh electrodes in the membrane electrolyzer of the proposed device, electrodes are used in the form of metal layers deposited on the surface of the cation exchange membrane.

The reduction of ohmic losses and, as a consequence, the energy consumption of the process is achieved by the fact that the electrodes in the proposed device are deposited directly on the cation exchange membrane and electrode processes occur directly at the phase boundary of the membrane - porous metal layer. As a result, there is no water layer with high electrical resistance between the membrane and the electrode, and gas evolution at the electrodes does not change the electrical resistance of the membrane - electrode phase boundaries.

Simplification of water deoxygenation technology and ease of operation is achieved due to the fact that the anode chamber in the proposed device constructively ensures the absence of contamination and, as a result, does not need to be washed.

In addition, in the inventive device, a technical result is achieved, which consists in increasing the degree of deoxygenation of the source water due to the interaction of oxygen with atomic hydrogen dissolved in the palladium electrode of the cell of the membrane cell.

The figure 1 shows a schematic view of the inventive device - cell membrane electrolyzer with a series-connected catalytic reactor.

The cell of the membrane electrolyzer 1 includes a cation exchange membrane 2, a cathode chamber 3 formed by a stainless steel or nickel mesh, an anode chamber 4 formed by a porous nickel or titanium plate, and compression plates 5 and 6 of an inert non-conductive material. The surface of the cation exchange membrane 2 is coated on both sides with electronically conducting porous layers 7 and 8, which perform the functions of a cathode and anode, respectively. The layers are made of palladium (layer 7) and platinum (layer 8) by the deposition method on the surface of the cation exchange membrane 2. The mesh of the cathode chamber 3 is insulated around its perimeter by a sealant layer 9, for example, a silicone composition. In the pressing plate 5, two nozzles are installed - a nozzle 10 for introducing water and a nozzle 11 for withdrawing water. Using the clamping plates 5, 6 and pins 12, the cathode chamber 3 is pressed against the layer 7 of the surface of the cation exchange membrane 2, which also performs the functions of current collector and flow turbulator, and the anode chamber 4 is pressed against the layer 8 of the surface of the cation exchange membrane 2, which also performs the functions of current collector and oxygen removal from the surface of the cation exchange membrane 2 into the volume of the anode chamber 4. Current conductors 13 and 14 from the cathode chamber 3 and the anode chamber 4, respectively, are brought out through the compression plates 5 and 6.

To improve electrical contact between the palladium layer 7 and the grid of the cathode chamber 3, the surface of the grid is platinized.

To improve electrical contact between the platinum layer 8 and the porous plate of the anode chamber 4, the surface of the plate is plated or coated with a layer of ruthenium or iridium oxides.

To increase the productivity of the process in the inventive device, the membrane cell may contain several cells connected in parallel.

The water outlet from the cell of the membrane electrolyzer 1 is carried out through the nozzle 11, which is connected to the nozzle 15, which is the inlet of the catalytic reactor 16, filled with a catalytic sorbent 17. As the latter, industrially produced ion-exchange resins, the surface of which is coated with a palladium layer (type Lewatit МС 145, Amberlyst CH28) and widely used for the implementation of catalytic processes. Deoxygenated water leaves the catalytic reactor 16 through the fitting 18.

The claimed device operates as follows. High-purity water through the nozzle 10 enters the cell of the membrane electrolyzer 1 and fills the cathode chamber 3. When an electric field is applied between the cathode and the anode on the porous layer of palladium 7, cathodic electrochemical reactions occur:

- oxygen ionization:

- hydrogen evolution:

As a result of ionization of dissolved oxygen by reaction (1), its concentration in water decreases. The degree of decrease in the concentration of dissolved oxygen by reaction (1), as in the case of the prototype device, is largely determined by the intensity of mixing of the water flow, which in the proposed device is provided by the grid of the cathode chamber 3.

Hydrogen released by reaction (2) on the cathode surface of layer 7 is dissolved in palladium in atomic form. Atomic hydrogen in palladium interacts with dissolved oxygen to form water molecules, thereby further reducing the concentration of dissolved oxygen. This process of deoxygenation of water in the prototype device is not implemented.

Hydrogen released by reaction (2) on the cathode surface of layer 7 and did not have time to react with dissolved oxygen, passes into high-purity water in molecular form. Then, hydrogen, together with the residual amount of oxygen dissolved in water, is carried out with a stream from the cell of the membrane electrolyzer 1 and enters the catalytic reactor 16, in which oxygen and hydrogen dissolved in water react on the surface of the catalytic sorbent 17.

The current in the cell of the membrane electrolyzer 1 is selected based on the conditions for the formation of a stoichiometric amount of hydrogen with respect to the oxygen content in the source water.

On the porous layer of platinum 8, an anodic electrochemical reaction of oxygen gas evolution occurs:

In this case, water undergoes electrolysis, diffusing from the cathode chamber 3 through the cation exchange membrane 2 and the membrane 2 located at the phase boundary is a porous layer of platinum 8. Gaseous oxygen is released into the volume of the anode chamber 4, without affecting the ohmic resistance of the device, which ensures no gas filling characteristic of the prototype device.

The application of electron-conducting layers of palladium 7 and platinum 8 on the surface of the cation exchange membrane 2 was carried out by chemical deposition. The choice of these layer materials is due to the high chemical resistance of platinum and palladium when they work as anodes and cathodes in high-purity water, as well as the high solubility of hydrogen in palladium. To apply an electronically conductive layer of platinum or palladium, the following technique was used, which consists of two stages - applying a catalytic sublayer and applying an electronically conductive layer.

To apply a catalytic sublayer, the cation exchange membrane was soaked for 1-2 hours in water for swelling. After that, a catalytic sublayer was deposited on the membrane surface. For this, the membrane surface was brought into contact with a solution of the following composition for 20 minutes:

palladium chloride - 5 g / l;

ammonium hydroxide - 100 g / l.

After that, the membrane surface was washed with water and brought into contact for 1 minute with a solution of hydrazine (100 g / l) heated to 80 ° C. As a result, a catalytic sublayer was formed on the membrane surface.

To apply a porous electrically conductive palladium layer, the surface of the membrane with a supported catalytic sublayer was brought into contact with a solution of the following composition:

palladium chloride - 4 g / l;

ammonium hydroxide (25%) - 300 ml / l;

Trilon B - 12 g / l;

hydrazine - 2 g / l (introduced into the solution immediately before use).

The temperature of the solution is 20 ° C. The contact time of the membrane surface with the solution is 2-4 hours. A shorter contact time leads to the formation of an electrically conductive layer with high electrical resistance. A longer contact time leads to the formation of a non-porous layer of palladium, which prevents the transfer of ions through the membrane.

To apply a porous electrically conductive layer of platinum, the surface of the membrane with the applied catalytic sublayer of palladium was brought into contact with a solution of the following composition:

ammonium hexachloroplatinate - 40 g / l;

ammonium chloride - 320 g / l.

The temperature of the solution is 50 ° C. The contact time of the membrane surface with the solution is 2-4 hours. A shorter contact time leads to the formation of an electrically conductive layer with high electrical resistance. A longer contact time leads to the formation of a non-porous layer of platinum, which prevents the transfer of ions through the membrane.

The effectiveness of the proposed device is confirmed by the following examples. It should be noted that the possibility of using the proposed device is not limited to the conditions implemented in the examples.

Example 1. The cell of the membrane electrolyzer, shown in figure 1, included a perfluorinated cation exchange membrane MF-4SK (thickness 0.15 mm, working dimensions 40 × 200 mm). Electrically conductive porous layers are deposited on the membrane: palladium (from the side of the cathode chamber) and platinum (from the side of the anode chamber). The cathode chamber (working dimensions 1.7 × 40 × 200 mm) was formed by a stainless steel mesh (size 40 × 200 mm, thickness 1.7 mm, mesh mesh size 1 × 1 mm), the perimeter of which was sealed with a silicone composition. The anode chamber was formed by a plate of porous titanium (size 40 × 200 mm, thickness 1 mm). The cell of the membrane electrolyzer was assembled by tightening with an inert plate a stainless steel grid (cathode chamber), a cation exchange membrane and a porous titanium plate (anode chamber).

High purity water with a specific conductivity of 0.075 μS / cm and a dissolved oxygen concentration of 8.3 mg / L was supplied to the cathode chamber with a flow rate of 110 l / h. A current of 4.1 A was applied to the cell. The voltage at the cell was 2.2 V. 30 minutes after turning on the current, the oxygen concentration measured at the outlet of the cell stabilized and amounted to 5.0 mg / L. As a result of the experiment, the concentration of dissolved oxygen decreased by 40%. The conductivity of the finishing water is 0.075 μS / cm.

Example 2. In experiment 1: high-purity water (with the following parameters: specific conductivity 0.075 μS / cm, dissolved oxygen concentration 8.3 mg / l, flow rate 110 l / h) was sequentially fed to a membrane electrolyzer similar to that described in example 1, and a catalytic reactor, which is a cylindrical column (diameter 50 mm, height 400 mm), filled with ion exchange resin type Lewatit MC. The volume of resin in the reactor is 0.8 liters. 120 minutes after turning on the current (current strength 4.1 A, voltage 2.2 V), the concentration of dissolved oxygen measured at the outlet of the catalytic reactor stabilized and did not exceed 0.010 mg / L. Thus, when implementing Example 2, the concentration of dissolved oxygen in the finishing water decreased by more than 99.9%, while the conductivity remained at the level of 0.075 μS / cm.

Claims (3)

1. Device for electrochemical deoxygenation of high-purity water, comprising a membrane electrolyzer, consisting of at least one cell for membrane electrolysis, comprising a cathode chamber with a cathode, an anode chamber with an anode separating the cathode and anode, a cation-exchange membrane, and a catalytic reactor connected to the membrane electrolyzer, characterized in that the cathode chamber is formed by a mesh of nickel or stainless steel pressed against the surface of the cathode, the anode chamber is formed by a porous plate of titanium or nickel When pressed against the surface of the anode, the cathode is made in the form of an electrically conductive palladium layer deposited on the surface of the cation exchange membrane facing the cathode chamber, and the anode is made in the form of an electrically conductive layer of platinum deposited on the opposite surface of the cation exchange membrane facing the anode chamber. 2. The device according to claim 1, characterized in that the mesh of nickel or stainless steel is coated with a layer of palladium. 3. The device according to claim 1, characterized in that the porous plate of titanium or nickel is coated with a layer of platinum or oxides of ruthenium or iridium.