CN111424287A - A kind of electrolysis-electrodialysis cell for hydrogen iodide concentration - Google Patents

Abstract

An electrolysis-electrodialysis cell for hydrogen iodide concentration belongs to the technical field of electrochemistry. The electrolysis-electrodialysis cell includes at least one single cell, and each single cell includes a proton selective permeation membrane, a cathode side support, an anode side support, a sealing ring, and an upper electrode plate and a lower electrode plate. The cathode side support body and the anode side support body use graphite felt; the upper electrode plate and the lower electrode plate use a flat plate structure. The characteristic of the invention is that the graphite felt material with large porosity is used, which can not only provide good filling and supporting functions, but also the HIx material can pass through it uniformly and quickly, and can be used for a long time under the conditions of HIx material liquid immersion and high current electrochemical reaction. Stable use, thereby further improving the efficiency of the electrochemical reaction inside the electrolysis-electrodialysis cell. The upper and lower pole plates adopt a flat plate structure, which avoids the problems of high processing difficulty and high processing cost caused by engraving the flow channel, and has the advantages of high efficiency, stability, compactness and low cost.

Description

A kind of electrolysis-electrodialysis cell for hydrogen iodide concentration

technical field

The invention relates to an electrochemical treatment device, in particular to an electrolysis _- electrodialysis cell, which is suitable for _hydrogen iodide (HI ) concentration, and the application of the electrochemical preparation of HI or hydroiodic acid, belong to the field of electrochemical technology.

Background technique

Electrolysis-electrodialysis (EED, also known as ion exchange membrane electrolysis, or membrane electrolysis) is an efficient electrochemical concentration method that can also be used for the electrochemical synthesis of specific chemicals. The electrolytic-electrodialysis cell (EED cell) can be used under harsh conditions such as high temperature, acid, alkali, strong oxidant, etc., and is of great practical value.

Electrolysis-electrodialysis has been applied in the thermochemical iodine-sulfur cycle splitting water for hydrogen production. The iodine-sulfur cycle is an efficient and clean method for large-scale hydrogen production, which is particularly interesting for its potential to be coupled with nuclear heating (eg, from high temperature gas-cooled reactors). In this process, hydrogen is obtained from the decomposition of HI in the HI-I ₂ -H ₂ O mixture (ie, HIx), but due to the formation of an azeotrope with a molar ratio of 1:5 between HI and H ₂ O, HIx When using direct distillation or rectification, although HI can be obtained, a large amount of thermal energy will be used for water evaporation, and the economics of the process will be significantly reduced. In view of this situation, researchers at home and abroad proposed that: firstly, the EED concentration of HIx is carried out to increase the concentration of HI in HIx, which exceeds the constant boiling composition, that is, HI:H ₂ O>1:5, then in the distillation/rectification process, A large amount of HI will be distilled out, while the amount of water will be very small. After optimizing the process, even pure HI gas can be obtained, which is very beneficial to the improvement of the overall efficiency of the IS process.

The specific principle of EED of HIx is: when HIx material flows through both the cathode and anode, H ⁺ passes through the proton selective permeable membrane under the action of the electric field, and enters the cathode area from the anode area, and the following electrode reactions occur on the two electrode plates at the same time:

Anode: 2I ^- -2e→I ₂

Cathode: I ₂ +2e→2I ^-

The combined result is that H ⁺ and I ^- decrease and I ₂ increases in the anode area, while I ₂ decreases in the cathode area and H ⁺ and I ^- increase, that is, HI is concentrated in the cathode area.

In addition, if in the above process, the cathode material is still HIx, and the anode material is a solution such as sulfuric acid, hydrochloric acid or nitric acid, it will still happen: 1) H ⁺ passes through the proton selective permeation membrane under the action of the electric field, and is formed by The anode area enters the cathode area, 2) the cathode reaction I ₂ +2e→2I ⁻ . On the anode side, the electrode reactions corresponding to acid radicals such as sulfuric acid, hydrochloric acid, and nitric acid occur, for example, the anolyte is sulfuric acid, and the anode is oxygen evolution reaction. To sum up, the anode area consumes H ⁺ , the cathode area I ₂ decreases, and H ⁺ , I ^- The increase is equivalent to the synthesis of HI in the cathode region. Therefore, the production of HI can be carried out by the method of EED.

The above electrolysis-electrodialysis (EED) process needs to be carried out in the range of normal temperature to 130 °C. In order to improve the compactness of the equipment and control the cost, it is required to operate at a higher current density. Structural design and material selection are very important.

At present, the existing EED cell or EED cell stack is composed of a series of single cells with the same structure. Otherwise, the proton selective permeation membrane will oscillate in the direction perpendicular to the membrane surface when the feed liquid flows. When the proton selective permeation membrane area is large, this oscillation is particularly obvious, which is very detrimental to the operation stability. The function of the cathode side and anode side supports is to fill the space between the polar plate and the proton selective permeation membrane, to support and fix the proton selective permeation membrane, and to avoid the above swing. At present, the cathode side and anode side supports in EED cells are mostly made of PTFE mesh, carbon fiber cloth, graphite cloth and other materials. Such as document 1 "Yoshida M, et al. Concentration of HIx solution by electro-electrodialysis using Nafion117 for thermochemical water-splitting IS process. Int J Hydrogen Energy, 2008, 33: 6913-6920" uses PTFE mesh, since PTFE is an insulator, The electric charge is conducted between the plates through the HIx feed liquid (HIx has strong conductivity), so the internal resistance of the battery is large, and the energy consumption is therefore high. Literature 2 "Hong SD, et al. Evaluation of the membrane properties with changing iodine molar ratio in HIx(HI-I ₂ -H ₂ O mixture) solution to concentrate HI by electro-electrodialysis. Journal of Membrane Science, 2007, 291(1- 2): 106-110" uses activated carbon fiber cloth. Compared with PTFE mesh, these materials themselves have electrical conductivity, which can play the role of current collector and reduce the internal resistance of the battery. At the same time, carbon fiber cloth and graphite cloth can provide The place where the electrode reaction occurs, so the overall performance is better than that of PTFE mesh.

In the actual use process, carbon fiber cloth (including activated carbon fiber cloth) and graphite cloth are used as thin-layer materials, which are not easy to be fixed inside the battery. Affect battery performance and even cause EED battery failure. In addition, if activated carbon fiber cloth is used as the cathode side and anode side support, due to the large number of non-carbonized and non-graphitized components, it is very unstable in HIx immersion and electrochemical environment, and is prone to pulverization and peeling. Therefore, the activated carbon fiber cloth in the middle will be lost, the EED efficiency will be reduced, and the flaking powder or fluff will gradually enter the material liquid, causing the material liquid to be polluted.

From the perspective of the overall structure of the EED cell, in a normal EED cell, when using the PTFE mesh cathode side and anode side supports, in most cases, the two sides of the upper and lower plates need to be grooved to produce flow channel to optimize the flow of the material and liquid, especially when using carbon fiber cloth and graphite cloth, the prefabrication of the flow channel is more necessary, this is because the carbon fiber cloth and graphite cloth are very thin; In the flow channel, the fluid resistance of the feed liquid will be very large, and it is difficult for the feed liquid to flow smoothly and uniformly in the space between the polar plate and the proton selective permeable membrane, especially the EED operation with large flow cannot be performed. In the case of making runners, the processing requirements are high and the production cost is high, especially when the thin plate is slotted, it is difficult to ensure the consistency of the groove depth and the yield and reliability of the plate due to the deformation caused by the machining process. The problems of cost and processing difficulty are more prominent, which significantly restricts the multi-cell stacking of EED cells and hinders the lightweight and compactness of EED equipment.

SUMMARY OF THE INVENTION

The object of the present invention is for the deficiencies and defects of the prior art, a kind of electrolysis-electrodialysis cell for hydrogen iodide concentration is provided, aiming at solving the following problems existing in the existing electrolysis-electrodialysis cell: 1) up and down The electrode plate needs to be engraved with flow channels on both sides, which is difficult to process and has high processing cost; 2) The internal resistance of the battery is relatively large when PTFE mesh is used for the cathode side and anode side supports; 3) The cathode side and anode side supports use activated carbon fiber cloth 4) When carbon fiber cloth (including activated carbon fiber cloth) and graphite cloth are used for the cathode side and anode side supports, they are not easy to be fixed inside the battery, and problems such as movement and folding are prone to occur. , which seriously affects the battery performance.

The technical scheme of the present invention is as follows:

An electrolysis-electrodialysis cell for hydrogen iodide concentration, the electrolysis-electrodialysis cell comprises one or more single cells arranged in sequence, and each single cell comprises a proton selective permeable membrane, a cathode side support, a The anode side support body, the sealing ring, and the upper and lower electrode plates are characterized in that: the cathode side support body and the anode side support body are made of graphite felt; the upper electrode plate and the lower electrode plate are of flat plate structure.

Preferably, a single-layer or multi-layer carbon fiber grid or metal grid is attached on the surface or inside of the graphite felt.

Another technical feature of the present invention is that the porosity of the graphite felt is greater than or equal to 70%, the carbon content is greater than or equal to 98%, and the thickness of the graphite felt is 0.5 mm to 10 cm.

The technical solution of the present invention is also that: the cathode side support body and the anode side support body are supported with a catalyst. A cathode sealing ring is wrapped around the cathode side support body, and an anode sealing ring is wrapped around the anode side support body. The upper and lower plates are made of corrosion-resistant metal plates, rigid graphite plates or flexible graphite plates.

Compared with the prior art, the present invention has the following advantages and outstanding technical effects: the present invention adopts the high-porosity graphite felt as the cathode side support and the anode side support, and makes full use of the porosity of the high-porosity graphite felt. , high conductivity and resistance to electrochemical corrosion, to achieve high efficiency and low cost of electrolysis-electrodialysis cells. This is because: 1) The large-porosity graphite felt is compressible, and can be firmly placed inside the battery with the assistance of carbon fiber grids or metal grids, which can not only provide good filling and support, but also achieve The HIx material passes through it uniformly and quickly; 2) The graphite felt can make the electrolysis-electrodialysis cell have a small internal resistance and high chemical stability due to its high conductivity. It can be used stably for a long time under chemical reaction conditions. Because the graphite felt has porosity and a certain thickness, it is easier to support catalysts on it, thereby further improving the efficiency of the electrochemical reaction in the electrolysis-electrodialysis cell. 3) Since the large porosity graphite felt solves the problem of uniform flow of HIx in the electrode area of the electrolysis-electrodialysis cell, the electrolysis-electrodialysis cell can use a flat plate/bipolar plate to avoid engraving flow channels on it The problems of high processing difficulty and high processing cost are brought about.

To sum up, by using the technical solution of the present invention, an electrolytic-electrodialysis cell for hydrogen iodide concentration can be constructed with high efficiency, stability, compactness and low cost.

Description of drawings

FIG. 1 is a schematic diagram of a typical structure of an electrolysis-electrodialysis cell single cell used for hydrogen iodide concentration in the prior art.

2 is a schematic structural diagram of a single cell of an electrolysis-electrodialysis cell for hydrogen iodide concentration in the present invention.

In the figure: 1-upper plate; 2-cathode side support; 3-cathode sealing ring; 4-proton selective permeable membrane; 5-anode side support; 6-anode sealing ring; 7-lower plate.

Detailed ways

The structure, principle and implementation manner of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can understand and implement the present invention.

FIG. 1 is a schematic diagram of a typical structure of an electrolysis-electrodialysis cell single cell used for hydrogen iodide concentration in the prior art. With the proton selective permeation membrane 4 as the center, the cathode side support body 2 and the upper plate 1 with flow channels are distributed in sequence; the cathode side is sequentially distributed with the anode side support body 5 and the lower electrode with flow channels. Plate 7; the outer peripheries of the cathode side support body 2 and the anode side support body 5 are sealed by the cathode sealing ring 3 and the anode sealing ring 6 respectively, and the outer side of the sealing ring is flush with the outer edge of the electrode plate. The cathode sealing ring 3 is located between the upper plate 1 and the proton selective permeation membrane 4, and the cathode side support 2 is wrapped in the center; the anode sealing ring 6 is located between the lower plate 7 and the proton selective permeation membrane 4, and the center The anode side support body 5 is wrapped to realize the isolation between the yin and yang chambers in the battery, and can prevent the leakage of substances in the battery to the environment.

Fig. 2 is a kind of electrolysis-electrodialysis cell for concentration of hydrogen iodide provided by the present invention, the electrolysis-electrodialysis cell comprises one or more single cells arranged in sequence, and each single cell comprises proton selective permeation Membrane 4, cathode side support 2, anode side support 5, upper plate 1 and lower plate 7; cathode sealing ring 3 is wrapped around the cathode side support 2, and anode sealing ring is wrapped around the anode side support 5 6. A catalyst is supported on the cathode-side support 2 and the anode-side support 5 . The technical feature of the present invention is that both the cathode side support body 2 and the anode side support body 5 are made of graphite felt material; in order to enhance the ability of the graphite felt to maintain the shape, a single layer or multiple layers can also be attached to the surface or inside of the graphite felt. Layer carbon fiber mesh or metal mesh. The porosity of the graphite felt in the cathode side support body 2 and the anode side support body 5 should be greater than or equal to 70%, the carbon content should be greater than or equal to 98%, and the thickness of the graphite felt is preferably 0.5 mm to 10 cm.

The upper electrode plate 1 and the lower electrode plate 7 of the present invention do not need to process the flow channel, and can adopt a flat plate structure; the upper electrode plate and the lower electrode plate should preferably be made of corrosion-resistant metal plate, rigid graphite plate or flexible graphite plate.

When the electrolysis-electrodialysis cell is stacked with a plurality of single cells, end plates are installed on the outer sides of the single cells located on both sides, and the electrolysis-electrodialysis cell is pressed to a set pressure by a press and then fastened and formed. Tie rods run through between the end plates, and the tie rods are fastened by nuts.

The present invention adopts high porosity graphite felt (porosity not less than 70%) as cathode side support and anode side support, and fully utilizes and exerts the porosity, compressibility and high electrical conductivity of the high porosity graphite felt material. , anti-electrochemical corrosion and low cost, etc., effectively solve various problems existing in the current electrolysis-electrodialysis cell used for hydrogen iodide concentration.

Several specific embodiments are given below in order to further understand the present invention.

Example 1:

By adopting the scheme of the present invention, an electrolysis-electrodialysis cell composed of 10 single cells arranged in sequence is fabricated, the proton selective permeation membrane is selected from Nafion 117CS (DuPont) proton exchange membrane, and the effective membrane of each single cell is With an area of 36 cm ² , the cathode side support body, the upper electrode plate, the anode support side support body, and the lower electrode plate are symmetrically distributed on both sides of the proton selective permeation membrane in sequence. Both the cathode-side support and the anode-side support were 0.5 mm graphite felt (porosity 70%, carbon content 98%). The upper electrode plate and the lower electrode plate are both 1mm thick tantalum metal plates. On the cathode side and the anode side, carbon fiber meshes are added between the electrode plate and the graphite felt to enhance the ability of the graphite felt to maintain its shape.

The cathode side support body and the anode side support body are surrounded by a cathode sealing ring and an anode sealing ring, and the materials are VitonA fluorine rubber.

After the above 10 single battery cells are stacked and arranged, aluminum alloy end plates are installed on the outermost two sides, and there are tie rods passing through the above end plates. Fasten the entire electro-electrodialysis cell.

At 60°C, electrolysis-electrodialysis was performed on the iodine-containing hydriodic acid solution of HI:H ₂ O:I ₂ =1:6.3:0.5 with the above-mentioned device, and the hydriodic acid concentration (ie [HI]) was measured as 5.48 mol/l, the iodine concentration (ie [I ₂ ]) was 2.74 mol/l. 1500mL of this solution circulated on the cathode side, and another 4500mL of the above solution circulated on the anode side, and the external direct current kept the current constant at 7.2A. After 1 hour of treatment, the catholyte [HI] increased to 6.56mol/l, while [I ₂ ] Reduced to 2.22mol/l. That is, HI is concentrated on the cathode side, and _I2 is reduced accordingly.

Example 2:

By adopting the scheme of the present invention, an electrolysis-electrodialysis cell composed of 10 single cells arranged in sequence is fabricated, the proton selective permeation membrane is selected from Nafion 117CS (DuPont) proton exchange membrane, and the effective membrane of each single cell is The area of the proton selective permeable membrane is 1200 cm ² . The cathode side support, the upper electrode plate, the anode side support body, and the lower electrode plate are symmetrically distributed on both sides of the proton selective permeation membrane. Both the cathode-side support and the anode-side support were 1.5 cm graphite felt (porosity 92%, carbon content 99.8%). Before the graphite felt was assembled, the Pt/C catalyst dispersed in the Nafion solution was sprayed on the side facing the proton selective permeation membrane, and then dried at 120 °C for 5 h to obtain the graphite felt support loaded with the Pt catalyst.

The upper electrode plate and the lower electrode plate are both hard graphite flat plates with a thickness of 3 mm (purchased from POCO Company in the United States).

On the cathode side and the anode side, metal tantalum meshes are added between the electrode plate and the graphite felt to enhance the ability of the graphite felt to maintain its shape.

The cathode side support body and the anode side support body are surrounded by a cathode sealing ring and an anode sealing ring, and the materials are Viton A fluorine rubber.

After the above 10 battery cells are stacked and arranged, aluminum alloy end plates are installed on the outermost two sides, and there are tie rods passing through the above end plates. Fasten the entire electro-electrodialysis cell.

Using the above-mentioned electrolysis-electrodialysis device, the iodine-containing hydriodic acid solution of HI:H ₂ O:I ₂ =1:5.36:1.5 was subjected to electrolysis-electrodialysis treatment at 80°C, and the hydriodic acid concentration (ie [[ HI]) was 4.32 mol/l and the iodine concentration (ie [I ₂ ]) was 6.50 mol/l. 100.0L of this solution circulated on the cathode side, and the other 100.0L of the above solution circulated on the anode side. The external direct current was kept constant at 600A. After 1 hour of treatment, the catholyte [HI] increased to 5.70mol/l, while [I ₂ ] It decreased to 4.77 mol/l, at which time HI:H ₂ O:I ₂ =1:4.42:0.84. That is, HI is concentrated on the cathode side, and _I2 is reduced accordingly.

Example 3:

By adopting the scheme of the present invention, an electrolysis-electrodialysis cell composed of 50 single cells arranged in sequence is fabricated. The area of the proton selective permeable membrane is 2000cm ² . The cathode side support, the upper electrode plate, the anode side support body, and the lower electrode plate are symmetrically distributed on both sides of the proton selective permeation membrane. Both the cathode-side support and the anode-side support were graphite felts of 5.6 mm (porosity 92%, carbon content 99.8%). A layer of carbon fiber mesh was wrapped in the above graphite felt. Before its assembly, the Pt/C catalyst dispersed in Nafion solution was sprayed to the side of the proton selective permeation membrane, and then dried at 120 ° C for 5 hours. A graphite felt support loaded with Pt catalyst was obtained.

The upper electrode plate and the lower electrode plate are both 2mm flexible graphite flat plates (purchased from SGL, Germany).

The cathode side support body and the anode side support body are surrounded by a cathode sealing ring and an anode sealing ring, and the materials are Viton A fluorine rubber.

After the above-mentioned 50 battery cells are stacked and arranged, aluminum alloy end plates are installed on the outermost two sides, and there are tie rods passing through the above end plates. Fasten the entire electro-electrodialysis cell.

Example 4:

By adopting the scheme of the present invention, an electrolysis-electrodialysis cell composed of 5 single cells arranged in sequence is fabricated, the proton selective permeation membrane is selected from Nafion 117CS (DuPont) proton exchange membrane, and the effective membrane of each single cell is The area of the proton selective permeable membrane is 80 cm ² . The cathode side support, the upper electrode plate, the anode side support body, and the lower electrode plate are symmetrically distributed on both sides of the proton selective permeation membrane. Both the cathode-side support and the anode-side support were 7 cm of graphite felt (porosity 92%, carbon content 99.8%). Before its assembly, the Pt/C catalyst dispersed in the Nafion solution was sprayed on the side facing the proton selective permeable membrane, and then dried at 120 °C for 5 h to obtain a graphite felt support loaded with the Pt catalyst.

The upper electrode plate and the lower electrode plate are both 3mm flexible graphite flat plates (purchased from SGL, Germany).

The cathode side support body and the anode side support body are surrounded by a cathode sealing ring and an anode sealing ring, and the materials are Viton A fluorine rubber.

After the above-mentioned 5 battery cells are stacked and arranged, aluminum alloy end plates are installed on the outermost two sides, and there are tie rods passing through the above end plates. Fasten the entire electro-electrodialysis cell.

At 90°C, electrolysis-electrodialysis was carried out on the iodine-containing hydriodic acid solution with HI:H ₂ O:I ₂ =1:6.3:0.5 with the above-mentioned device, and the measured hydriodic acid concentration (ie [HI]) was 5.48 mol/l, the iodine concentration (ie [I ₂ ]) was 2.74 mol/l. 1500mL of this solution circulated on the cathode side, and another 4500mL of the above solution circulated on the anode side, and the external direct current kept the current constant at 7.1A. After 1 hour of treatment, the catholyte [HI] increased to 6.67mol/l, while [I ₂ ] Reduced to 2.10 mol/l. That is, HI is concentrated on the cathode side, and _I2 is reduced accordingly.

Example 5:

Using the electrolysis-electrodialysis device described in Example 1, the cathode feed solution was an iodine-containing hydroiodic acid solution, [HI]=5.08 mol/l, [I ₂ ]=1.20 mol/l, a total of 150 ml, and circulated. The anolyte is 1.75mol/l phosphoric acid, with a total of 350ml, which is circulated. At 70 °C, the external direct current was kept constant at 15 A, and after 1.5 hours of treatment, the catholyte was converted into colorless hydriodic acid without iodine, and the [HI] was increased to 6.87 mol/l. That is, I ₂ is consumed on the cathode side, and HI is produced.

Claims (6)

1. An electrolysis-electrodialysis cell for hydrogen iodide concentration, comprising one or more unit cells arranged in sequence, each unit cell comprising a proton permselective membrane (4), a cathode-side support (2), an anode-side support (5), and an upper plate (1) and a lower plate (7), characterized in that: the cathode side support body (2) and the anode side support body (5) adopt graphite felts; the upper polar plate (1) and the lower polar plate (7) adopt a flat plate-shaped structure.

2. An electrolysis-electrodialysis cell for hydrogen iodide concentration according to claim 1, wherein: and a single-layer or multi-layer carbon fiber grid or metal grid is attached to the surface or the interior of the graphite felt.

3. An electrolysis-electrodialysis cell for hydrogen iodide concentration according to claim 1 or 2, characterized in that: the porosity of the graphite felt is more than or equal to 70%, the carbon content is more than or equal to 98%, and the thickness of the graphite felt is 0.5 mm-10 cm.

4. An electrolysis-electrodialysis cell for hydrogen iodide concentration according to claim 3, wherein: the cathode-side support (2) and the anode-side support (5) carry a catalyst.

5. An electrolysis-electrodialysis cell for hydrogen iodide concentration according to claim 1, wherein: the periphery of the cathode side supporting body (2) is wrapped with a cathode sealing ring (3), and the periphery of the anode side supporting body (5) is wrapped with an anode sealing ring (6).

6. An electrolysis-electrodialysis cell for hydrogen iodide concentration according to claim 1, wherein: the upper polar plate (1) and the lower polar plate (7) adopt corrosion-resistant metal plates, rigid graphite plates or flexible graphite plates.

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