RU2757206C1 - Electrolyzer with reinforced membrane - Google Patents

Abstract

FIELD: electrochemistry.

SUBSTANCE: invention relates to an electrolyzer with a reinforced membrane containing a housing, a cathode and an anode chamber with an electrode in each, separated by an ion exchange membrane, having holes for supplying an electrolyte solution and holes for the exit of electrolysis products. The electrolyzer is characterized by the fact that mesh inserts with through holes are embedded between the membrane and both electrodes, located at a distance of no more than 1 mm from each side of the membrane, through holes are directed from the membrane to the electrode.

EFFECT: proposed design of the electrolyzer increases the lifetime of the ion exchange membrane in a continuous technological process, stabilizes the parameters of the electrolysis process and, due to its simplicity and high efficiency, will find wide application in the manufacture of electrolyzers of this type.

6 cl, 2 dwg

Description

2. The technical field to which the invention relates.

The invention is used in the chemical industry for the production of chlorine and alkali, chlorates and perchlorates, persulfuric acid and persulfates, potassium permanganate, organic compounds, chemically pure hydrogen, oxygen, fluorine and a number of other valuable products.

3. State of the art.

Today, the industry mainly uses several types of electrolysis plants, namely: dry, flow, membrane and diaphragm.

The claimed invention relates to membrane electrolysers.

Membrane electrolyzers in most cases consist of a body with an anode and cathode chambers, which respectively have anode and cathode electrodes, and the chambers are separated by an ion-exchange membrane and have holes for supplying electrolyte solution and removing electrolysis products. Electrolyzers use cation-exchange, anion-exchange and bipolar membranes.

The ion-exchange membrane is hermetically and firmly fixed in the electrolyzer body and will not allow arbitrarily, without electrical influence, to mix the electrolyte solutions located in the anode and cathode chambers. In addition to tightness, the membrane must be fixed so as not to allow it to move towards the anode or cathode. To do this, when installing the membrane, it is pulled between the walls of the electrolyzer. It is very important not to damage the diaphragm when pulling on the diaphragm. any damage will result in the inability to use the membrane. The tightness of the membrane fastening can be ensured by using sealants.

The principle of operation of an ion-exchange membrane is based on its main properties: the possibility of sorption of ions and their selective transport through the membrane. Upon contact with the electrolyte solution, the membrane swells, i.e. absorbs the surrounding liquid and becomes an electrical conductor, otherwise the membrane is called a solid electrolyte, and when exposed to an electric field, the membrane selectively passes anions or cations. Due to the ability to pass cations or anions through itself, active chemical-physical processes take place in the thickness of the membrane, which heats the membrane from the inside. In addition to internal heating, the membrane is heated by the surrounding electrolyte.

In addition to the indicated physicochemical reactions during electrolysis, the membrane operates under difficult conditions. For example, when chlorine, hydrogen and caustic soda are produced, a highly aggressive gas, chlorine, is released in the anode chamber, and a concentrated alkali solution is formed in the cathode chamber. The electrolysis process in this case is accompanied by constant heating of the electrolyte and the entire electrolyzer to 80 - 90C °, as well as a sufficiently high current load per unit area of the membrane and ranging from 2000 to 6000 A / m2. Due to the intensive transfer of ions in the thickness of the membrane, its additional heating occurs and, as a result, gradual degradation, followed by a complete loss of ion-exchange properties. To restore the operation of the electrolyzer, a membrane replacement is required. Regular replacement of membranes in industrial electrolyzers significantly increases the cost of products (chlorine, hydrogen, hydrochloric acid, sodium hydroxide, sodium hypochlorite, etc.).

When the membrane is heated to an operating temperature of 80 - 90C ° and its additional swelling in the electrolyte solution during operation, a significant increase in its linear dimensions occurs, leading to the formation of folds and bulges. Folds and bulges move freely and chaotically over the entire surface of the membrane under the pressure of intense flows of evolved gases, changing the resistance of the electrolyte, creating gradients of gas flows at the membrane surface, which leads to surges in gas pressure in the chambers. These processes destabilize the operation of the electrolyzer and in some cases, in particular during the subsequent synthesis of hydrogen chloride, lead to the appearance of gaseous chlorine in hydrogen chloride, which is unacceptable. Under the influence of these factors, membrane degradation is accelerated. In addition, with prolonged alternating loads (repeated movements of the membrane from one electrode to another), mechanical damage to the membrane occurs with a violation of its integrity, which leads to its failure. In this case, it is possible to restore the operation of the electrolyzer only by replacing the membrane with a new one.

In addition to mechanical damage leading to the complete failure of the membrane, there may be damage that can be repaired without replacing the membrane with a new one. Such damage can be attributed to the stretching of the membrane. Elimination of this defect occurs by additional stretching of the membrane over the entire area. From a technical point of view, additional stretching of the ion-exchange membrane, and if the electrolyzer is multicellular, then many ion-exchange membranes, is a complex engineering task that requires at least stopping the operation of the electrolyzer and its partial disassembly, which subsequently leads to additional resource costs and temporary downtime. In addition to such disadvantages, with each additional tension, the membrane thickness decreases - it becomes thinner, which leads to a decrease in its service life.

As is known, to increase the resistance of the ion-exchange membrane to physical and chemical stress, the chemical composition of the membranes and their design are changed.

For example, to improve the mechanical characteristics of membranes, they are reinforced with fabrics made of fluorinated polymers, non-woven fibers, including carbon fibers, metal mesh or metal wire. Reinforcing fabric can be located both inside the membrane and on one of its surfaces (Industrial membrane electrolysis / AF Mazanko, GM Kamaryan, OP Romashin - M .: Chemistry, 1989 [43, 240s] ).

In addition to increasing the mechanical characteristics of the membranes, the uniform distribution of gas bubbles over the entire membrane area is important. Such a distribution improves the quality of the substances obtained, increases the speed of obtaining such substances and, in general, increases the efficiency of the electrolyzer.

To solve this problem, in the American patent US 2020283919 A1 - 2020-09-10 (information about the patent is taken from the information resource Espacenet) it is proposed to divide the inner space of the electrolyzer between the ion-exchange membrane and the electrodes by jumpers extending in the direction of the height of the device, having many holes in the upper region ... One of the objectives of the present invention is to sufficiently mix the electrolyte in the chambers in the longitudinal direction. The features of the invention under the patent US2020283919 A1 - 2020-09-10, coinciding with the features of the claimed invention, are an electrolyzer containing an anode and a cathode chambers, including at least one inlet and one outlet, providing an electrolyte flow in the chambers and having electrodes ... The disadvantages of this invention include insufficient horizontal mixing of gas bubbles, which will subsequently lead to an uneven horizontal distribution of pressure, in other words, in the upper part of the chambers, the gas pressure may be higher than in the lower one. Another disadvantage of this invention is the insufficient strengthening of the ion exchange membrane. Based on the description, jumpers or edges are located in the vertical direction, i.e. upwards. In the horizontal direction, such jumpers are not installed. This creates weak points between the bridges, which will allow the pressure of the outgoing gas bubbles to push the membrane between them, giving the membrane a wavy vertical shape.

The invention under the Korean patent KR20160074241 (A) - 2016-06-28 seems to be very interesting (information about the patent is taken from the information resource Espacenet). In this case, the authors aim to suppress the deformation of the ion-exchange membrane. Two options for such suppression are proposed: 1) installation of support protrusions between the membrane and the electrodes, which are attached to the electrodes; 2) installation of a membrane deformation suppression unit between the electrodes and the membrane, which is a porous mesh made of synthetic resin. The features of the patent KR20160074241 (A) - 2016-06-28 coinciding with the features of the claimed invention are: an electrolyzer containing an anode and a cathode chambers, including at least one inlet and one outlet, which provide the flow of electrolyte in the chambers having electrodes and the presence between the membrane and the electrodes on both sides of the anti-deformation device. The disadvantages of the first part of the invention under the Korean patent, in which it is proposed to install support protrusions in the electrodes as a deformation device, which are installed close to the membrane to prevent its deformation, include high requirements for the accuracy of manufacturing a pair "wall with pillars + perforated electrode". If you make a multi-cell electrolyzer, then the complexity of the manufacture of such electrodes with support protrusions increases significantly. The electrodes work only on one side (the one that faces the membrane. The other side is not tightly covered with a sheet with pillars. Any coatings (platinum, gold, silver, ruthenium, iridium, etc.) are expensive materials and the coating of the side of the electrode facing The solution proposed by the Korean patent is acceptable for water electrolysis, where a one-sided coating can be applied (no aggressive substances are released in this process), but this is definitely not suitable for table salt electrolysis. electrodes are a difficult task, since when the surfaces are fractured (the front surface of the electrode and the surface from drilling perpendicular to it), coating defects are always formed (thinning down to zero thickness). This leads to corrosion of the supporting layer of the electrode. Assuming that the electrode is free moves along the columns along the wall, then nothing prevents the electrode from being attracted to the membrane not close and start parasitic processes of heating and destruction of the membrane.

The disadvantages of the second part of the invention according to the Korean patent, in which it is proposed to insert checkered grids between the membrane on one side and the electrodes and the housing with the reaction space on the other side, can be attributed to the dense arrangement of the checkered grid to the membrane, which prevents the free movement of gas bubbles to the outlet of the electrolyzer , and also reduces the useful area of the membrane, since in the places where the checkered mesh adjoins the membrane, the migration of ions through the membrane is reduced. Also, the design of the electrolyzer itself can be attributed to the disadvantages of the invention under the Korean patent, which, due to the presence of reaction chambers, has 7 sealing points, since the electrode from the membrane, in addition to the checkered mesh, is separated by reaction chambers. Thus, the junction of the membrane with the checkered grids on both sides, the junction of the checkered grids with housings that are reaction chambers and the junction of the reaction chambers with the electrodes are the weak points of the electrolyzer, most susceptible to damage during the operation of the electrolyzer.

The closest analogue of the claimed invention is patent KR20160074241 (A) - 2016-06-28, which acts as a prototype.

The technical problem to be solved by the present invention is to improve the performance of the membrane by eliminating its deformation during electrolysis with simultaneous stabilization of the electrolyzer by reducing or completely eliminating pressure surges in the exhaust gases, uniform distribution of exhaust gas bubbles over the entire area of the ion-exchange membrane.

4. Disclosure of the essence of the invention.

To solve the existing technical problem, the authors of the claimed invention propose to manufacture and install in the electrolyzer between the electrodes and the ion-exchange membrane jumpers, fastened together in such a way that they form a mesh insert with through holes directed from the membrane to the electrodes. Mesh liners are located at equal distances from the membrane to the cathode on one side and from the membrane to the anode on the other side. The mesh liner is not attached to any electrode, membrane or cell body. The mesh liner is made to fit the space formed between one electrode, the membrane and the cell body. The mesh insert is installed in the space between the electrode, membrane and electrolyzer. With this arrangement of the mesh insert, there is a significant decrease in the gradients of ohmic resistance of electrolyte solutions arising during the operation of the electrolyzer over the area and height of the membrane. The reason for this is the averaging of the gas content of electrolytes (catholyte and anolyte) from top to bottom in the electrolyzer and a significant limitation of the possibility of membrane shift from the middle position under the pressure of the evolved gases and under the influence of heating. Hence, we obtain a significant decrease in membrane shifts towards any electrode, no deformation of the membrane.

Experiments have found that the mesh insert is best positioned at a distance from the membrane on each side. The experiments were carried out at different distances in the range from 0 to 2 mm, inclusive. Based on the results of the experiments, it was found that the distance between the mesh liners on each side of the membrane should be no more than 1 mm from each side of the membrane. It is precisely when the mesh inserts are located from the membrane at a distance in the specified range that gas bubbles better move away and move up to the outlet.

However, depending on the specific operating conditions, namely: on the type and type of electrolyzer, on the materials and substances used in the electrolyzer, on the desired results when using the electrolyzer, the presence of a distance of 1 mm between the mesh liners and the membrane may be too small for optimal waste. gas bubbles. But in this case, it is necessary to take into account that by increasing the distance of the mesh liner in relation to the membrane from either side of this membrane or from both sides, the effect of eliminating membrane deformation is immediately lost and it becomes wavy again.

Also during the experiments, the authors found that in some cases, for reliable fixation of the membrane, a complete absence of the distance between the mesh liners, the membrane and the electrodes is required. These elements of the cell must be installed close to each other. For such cases, the inventors found that if the mesh insert is installed close to the electrodes and the membrane, and in the part of the mesh insert facing the membrane, vertical recesses directed from bottom to top are made, then such recesses, regardless of their geometric shape, serve as additional channels for the exit of bubbles gas to the outlet openings of the electrolyzer, which in turn improves the escape of gas bubbles from the membrane and their movement to the outlet openings and uniform distribution over all areas of the membrane. In this case, the mesh insert can be made of a one-piece plate with through holes. The plate must be chemically inert to the electrolysis solution and not conductive.

To increase the working area of the electrode at the mesh insert on the side of contact with the electrodes, you can make recesses in both the vertical and horizontal directions. By reducing the area of contact between the mesh insert and the electrode, the free area of the electrode will increase.

The authors carried out practical experiments with a membrane electrolyser for the production of chlorine, hydrogen and caustic soda. Therefore, hereinafter, examples from this experiment will be given. However, this does not mean that the technical solution proposed by the authors is not applicable to other membrane electrolyzers. Therefore, the authors declare that the claimed invention is suitable for all types of membrane electrolyzers, in which there is a free space filled with electrolysis solution between the electrode and the membrane.

To obtain chlorine, hydrogen and caustic soda, a membrane electrolyzer was used in which the anode and cathode chambers are separated by a cation-exchange membrane (of the "NAFION" type or similar). The anode was a titanium sheet coated with ruthenium oxide or a mixture of ruthenium and iridium oxide, and the cathode was a nickel plate. Such electrolyzers are widely used in the chlorine industry. The membrane operated under difficult conditions of the release of a highly aggressive gas - chlorine in the anode chamber, the presence of a concentrated alkali solution in the cathode chamber, constant heating of the electrolyte (and the entire electrolyzer) to 80 - 90 ° C, as well as the current load per unit area of the membrane and the component 2000 - 6000 A / sq.m. As a result of the intensive transfer of ions in the thickness of the membrane, its additional heating took place and, as a consequence, gradual degradation followed by a complete loss of ion-exchange properties, which led to the regular replacement of membranes in industrial electrolysers.

With this design, without grids fixing the membrane, and the current load on the membrane is 3000 ± 200A / sq.m. the life of the membrane in a continuous electrolysis process is 300 ± 10 days. The life of the membrane is taken as the period from the start of operation to the fall in chlorine output by 30% of the initial value.

After additional fixation of the position of the membrane relative to the electrodes by placing special dielectric mesh liners that restrict the movement of the membrane from one electrode to another, a significant decrease or complete elimination of membrane movement from one electrode to another was noted, a uniform distribution of gas bubbles over the entire surface area of the membrane, the absence of pressure surges on either side of the diaphragm.

Therefore, fixing the membrane with mesh inserts that do not impede the movement of gases and ions, improved the operation of the electrolyzer. This, in particular, led to the stabilization of gas flows.

After fixing the membrane with mesh inserts located on either side of it, the membrane lifespan increased to 360 days or more. In addition, there was a stabilization of the flows of evolved gases, which had a positive effect on the stability of the burner, in which the synthesis of gaseous hydrogen chloride took place and on the absence of chlorine in the produced hydrogen chloride.

In the course of the experiments, the material for the manufacture of mesh liners was selected from a number of polymers that are most corrosion-resistant to chlorine and alkali: polytetrafluoroethylene, polyvinylidene fluoride, or polypropylene. Hence, the authors concluded that in order to use the claimed invention, the mesh liners must be made of a material that is chemically inert to the solution of the electrolyte used, as well as not being a current conductor in the used electrolyte solution.

The size of the mesh in the manufacture of mesh liners is important. But it is undesirable to indicate all possible sizes of such cells for the present invention, since this will lead to an unreasonable narrowing of the scope of protection of the invention. But it is possible to establish certain principles of such dimensions.

Since the use of membrane electrolysis is very widespread in the chemical industry, it makes no sense to describe all possible uses of the present invention. During the experiments, the authors used a mesh insert with cells measuring 40 mm by 40 mm, with a wall thickness or diameter of 4 mm. However, these mesh sizes were optimal only in the experiment conducted by the authors. Therefore, specific values of the cell sizes for other cases of using the invention must be established based on the model of the membrane electrolyzer used. But at the same time, it is necessary to establish a balance between a sufficiently dense strengthening of the membrane and the presence of the largest free area of the membrane for contact with the electrolyte solution and the release of gas bubbles. Because the more the membrane area is covered due to smaller cell sizes, larger cell walls or more frequent arrangement of cells, the lower the cell performance will be. And vice versa - if the cells are too large, then the capacity of the electrolyzer will be higher, but the mesh liner will not be able to secure the membrane tightly enough and prevent deformation. In addition, the stiffness of the membrane must be taken into account. the higher it is, the stronger and more resistant to deformation the membrane and the larger the possible cell dimensions and the smaller the cell walls.

It should also be noted that for the manufacture of the mesh liner, rods of dielectric material can be used, in cross-section of which represent any geometric figure - a square, a circle, an oval, a rectangle, a rhombus, etc.

5. Shapes

Figure 1 depicts an example of the structure of an electrolytic cell with two mesh grids located on either side of the ion exchange membrane. Figure 2 shows a variant of the finished mesh with an indication of the possible sizes.

6. Implementation of the invention.

The cell consists of a polypropylene body (1), a cation-exchange membrane (2) dividing the cell into a cathode and anode chambers, and two electrodes: a titanium anode (3) coated with ruthenium oxide (or a mixture of ruthenium and iridium oxide) and a nickel cathode (4) and two mesh inserts located on both sides of the membrane (11) at a distance of 0.9 mm from the membrane on each side. An electrolyte is continuously fed into the electrolyzer through the choke (5) - a saturated solution of sodium chloride (concentration of at least 25%), acidified with hydrochloric acid to pH5. The electrolyte is prepared from deionized water and technical salt (sodium chloride), after which it undergoes one- or multi-stage purification according to standard [salt] methods. The content of calcium and magnesium ions after cleaning does not exceed 0.15 mg / l. The outlet of the electrolyte depleted in sodium chloride comes from the upper part of the anode chamber through the fitting (6). Also on top of the anode chamber is the outlet of gaseous chlorine (7), which is released at the anode. In the cathode chamber, a dilute sodium hydroxide solution (8) is fed from below, a more concentrated solution (9) is taken from above. Hydrogen liberated at the cathode leaves the electrolyzer through a branch pipe (10) located in the upper part of the cathode chamber. Mesh liners (11) fixing the membrane are conventionally shown not for the entire thickness of the chamber (anodic or cathodic). After fixing the membrane with mesh inserts located on either side of it, the membrane lifespan increased to 360 days or more. In addition, there was a stabilization of the flows of evolved gases, which had a positive effect on the stability of the burner, in which the synthesis of gaseous hydrogen chloride took place.

Figure 2 separately shows one of the possible mesh designs. The shapes and sizes of the cells, as well as the size of the walls of the cells, are set individually.

The given embodiment of the invention shows how it can be used in a single cell electrolyzer. However, the invention can be used in multi-cell electrolysers that are common in the industry.

Claims (6)

1. An electrolyzer with a reinforced membrane, containing a housing, a cathode and anode chambers with an electrode in each, separated by an ion-exchange membrane, having holes for supplying an electrolyte solution and holes for leaving electrolysis products, characterized in that between the membrane and both electrodes, mesh inserts with through holes located at a distance of no more than 1 mm from each side of the membrane, through holes directed from the membrane to the electrode. 2. An electrolyzer according to claim 1, in which the mesh liners are installed close to the electrodes and the membrane and have vertical recesses. 3. An electrolyzer according to claim 1, wherein there are vertical recesses at the ends of the mesh liners on the side of the membrane. 4. An electrolyzer according to claim 1, wherein the material from which the mesh liners are made is not a current conductor. 5. An electrolyzer according to claim 1, wherein the material from which the mesh liners are made is chemically inert to the electrolyte solution. 6. An electrolyzer according to claim 1, wherein the mesh inserts are equidistantly spaced between the membrane and the anode on one side and between the membrane and the cathode on the other side.

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