JP2012021221A - ELECTROLYSIS OF NaCl AQUEOUS SOLUTION BY CYLINDRICAL ELECTRODE OF CARBON FIBER OR CARBON - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide both electrodes of an anode and a cathode having large surface areas and exhibiting high electrolytic efficiency.SOLUTION: A flexible carbon fiber (CF) is spirally wound into a cylindrical shape, or a sheet-like carbon fiber is made cylindrical (they are called as a CF pipe) to make thick and thin CF pipes 9 and 10. The thin CF pipe 10 is inserted into the thick CF pipe 9 so that the inner face of the pipe 9 is parallel to the outer face of the pipe 10 to use the pipe 9 as the anode and the pipe 10 as the cathode, or the pipe 9 as the cathode and the pipe 10 as the anode. Thereby, an electrolyzer having large surface areas of the electrodes facing each other is obtained in an electrolytic bath having the same capacity by thickening both carbon-rod electrodes or dipping the plate electrodes parallel to each other.

Description

  In the present invention, a cylinder is made of carbon fiber (CF) having excellent flexibility, or a cylinder is made by molding carbon (graphite: C), and these are used as electrodes for electrolysis (electrolysis) of a NaCl aqueous solution. It is related with the technique to perform.

When two carbon electrodes are immersed in an aqueous NaCl solution (electrolyte) and a DC voltage is applied to both electrodes, electrons e ⁻ are transferred at the interface between the electrode and the electrolyte, and H ₂ O is reduced at the cathode to reduce H _{2. 2} occurs, Cl at the anode ^- is generating is oxidized Cl _2. Then, NaOH is generated near the cathode.
That is, at the cathode: 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ (1)
At the anode: 2Cl ⁻ → Cl ₂ + 2e ⁻ (2)
_{Total: 2NaCl + 2H 2 O → 2NaOH} + H 2 + Cl 2 (3)

Since the chemical reaction of electrolysis proceeds by the transfer of electrons e ⁻ at the interface between the electrode and the electrolyte, the transfer of electrons e ⁻ is more effectively performed as the surface area of the electrode increases if the applied DC voltage is constant. .
In order to produce an electrode with a large surface area in an electrolytic cell with a limited volume, it is sufficient to make the two electrodes thick as shown in FIG. 2, but there is a limit.
CF is spirally wound into a cylindrical shape, or sheet-shaped CF is formed into a cylindrical shape. Also, a cylinder is made by molding a subdivided CF chip. Hereinafter, these are referred to as CF pipes, and a thick CF pipe and a thin CF pipe are formed as electrodes.
The outer diameter of the thin CF pipe is smaller than the inner diameter of the thick CF pipe, and when conducting the electrolysis by placing the thin CF pipe in parallel into the thick CF pipe, the thick CF pipe and the thin CF pipe maintain the interval necessary for electrolysis And
Also, C is molded to form a cylinder, which is called a C pipe.
Since the main component of CF is C, C pipe is included in the category of CF pipe.
The CF pipe can be used as an electrode having a large surface area in an electrolytic cell having a limited volume (FIG. 3).
Therefore, it is a problem to be solved by the invention to show the features of electrolysis of NaCl aqueous solution by CF pipe electrode.
However, the CF pipe electrode is hardened with a water-resistant and chemical-resistant adhesive material (including a mixture of carbon allotropes) that does not contain metal and has conductivity.
Also, when the CF pipe electrode is immersed in the electrolyte, the electrolyte rises to the electrode terminal due to capillary action and affects the metal of the power connection terminal. To prevent this, a part of CF is used as shown in FIG. What is hardened with an adhesive is connected to an electrode to form an electrode terminal.
The samples used for the trial are shown below.
Carbon fiber (CF) pipe: Made with Mitsubishi Rayon TR50SI5L (PAN system) Carbon (C) bar: For electrolytic electrode made by Narica

As shown in FIG. 3, an electrolysis apparatus in which a thin CF pipe electrode is inserted into a thick CF pipe electrode is produced. However, the inner surface of the thick CF pipe and the outer surface of the thin CF pipe are parallel.
When an aqueous NaCl solution is placed in the apparatus of FIG. 3 and electrolysis is performed, H ₂ is generated on the cathode surface, Cl ₂ is generated on the anode surface, and NaOH is generated near the cathode.

  Even when an aqueous NaCl solution is electrolyzed using an iron (Fe) pipe (Fe pipe) as the cathode of FIG. 3, the same phenomenon as [0004] is observed.

  [0004] As confirmed in [0005], the development of a method for electrolyzing an NaCl aqueous solution in which a thin CF pipe electrode or an Fe pipe electrode is inserted as a cathode into a thick CF pipe electrode as an anode solves the problem. Means.

In the method of electrolyzing a NaCl aqueous solution using a CF pipe electrode, the transfer of electrons e ⁻ at the interface between the electrode and the electrolyte is uniformly performed over the entire interface, and the following invention effects are obtained.
1. When the electrode is CF-Fe: The CF pipe electrode is thick, the Fe pipe electrode is thinned, the Fe pipe electrode is inserted into the thick CF pipe electrode, the faces of each other are kept parallel, and the thick CF pipe electrode is used as the anode. Electrolysis is performed using the Fe pipe electrode as a cathode. This saves on the use of Fe rather than using Fe round bar electrodes.
2. When the electrode is CF-CF: A thin CF pipe electrode is placed in a thick CF pipe electrode, and electrolysis is performed while keeping the surfaces parallel to each other. In this case, the selection of anode and cathode depends on the purpose of use.
The C pipe can be replaced with a CF pipe.

As shown in [0007], the use of a CF pipe electrode has enabled the use of an Fe pipe electrode that saves Fe, and the use of a thick CF pipe and a thin CF pipe.
Therefore, by combining these electrodes in accordance with the electrolysis method, an electrolysis apparatus having a large electrode area in which the transfer of electrons e ⁻ can be efficiently performed in an electrolytic cell having a limited volume.

As shown in FIG. 4, the industrial production of NaOH is a device in which a carbon rod is placed as an anode in a cathode made of iron (Fe) net and a cation exchange membrane is provided between the cathode chamber and the anode chamber. As a basic practice, the CF pipe was developed as shown in Fig. 5. As shown in Fig. 5, a carbon fiber rod in Fig. 4 was provided with a thick CF pipe (opening a water passage hole) at the position of the iron mesh in Fig. 4 as an anode. It is possible to produce an industrial production apparatus of NaOH in which an Fe pipe is provided at the position to serve as a cathode and a cation exchange membrane is provided between the cathode chamber and the anode chamber.
Since the hydrogen generation overvoltage of Fe is small after rare metal and expensive Pt, Fe is used in the industrial production equipment of NaOH (published by Maruzen, Masa et al. 3 “Electrochemistry”), but CF pipe electrode The amount of Fe used can be saved by using the apparatus shown in FIG.

In the apparatus of FIG. 4, a thick CF pipe can be provided instead of the iron net, and a thin CF pipe can be provided instead of the carbon rod.
Further, in the apparatus of FIG. 5, a thin CF pipe can be used instead of the Fe pipe.

  Diagram showing electrodes and electrode terminals   Cross section showing electrolysis with two carbon electrodes   Cross-sectional view of an electrolyzer with a thin CF pipe electrode inserted into a thick CF pipe electrode (the same phenomenon occurs regardless of which is the anode or cathode)   Side sectional view showing the principle of conventional industrial production equipment for NaOH   Side sectional view showing the principle of NaOH industrial production equipment using thick CF pipe electrode (anode) and thin CF pipe electrode (cathode) or thick CF pipe electrode (anode) and Fe pipe electrode (cathode)

1 Electrode (CF or graphite)
2 Electrode terminal (CF)
3 Adhesive (eg epoxy)
4 Combine electrode and electrode terminal 5 Electrolyte (NaCl aqueous solution)
6 Anode (carbon rod)
7 Cathode (carbon rod)
8 Electrolyte (NaCl aqueous solution)
9 Anode (thick CF pipe) or cathode 10 Cathode (fine CF pipe) or anode 11 Anode chamber (NaCl aqueous solution)
12 Anode (carbon rod)
13 Cathode chamber (water)
14 Cation exchange membrane 15 Mesh of plastic 16 Cathode (iron mesh)
17 Anode chamber (NaCl aqueous solution)
18 Cation exchange membrane (used by Asahi Kasei Chemicals)
19 Net of plastic 20 Anode (thick CF pipe)
21 Cathode chamber (water)
22 Cathode (Fe pipe or fine CF pipe)

Claims (2)

Extremely fine and long carbon fiber (abbreviated as CF, regardless of whether it is CF PAN or pitch) is flexible and can be processed into a shape that requires flexibility. ) Electrode.
Make a cylinder by spiraling CF. Also, a cylinder is made of CF processed into a sheet. In addition, a cylinder is made by molding a chip obtained by subdividing CF into a sheet. These cylinders are called CF pipes, and a thick CF pipe and a thin CF pipe are made.
A thin CF pipe having an outer diameter smaller than the inner diameter of the thick CF pipe is inserted into the thick CF pipe so that the inner surface of the thick CF pipe is parallel to the outer surface of the thin CF pipe. In this case, the large CF pipe and the thin CF pipe are spaced apart from each other for electrolysis.
However, the thick CF pipe and the thin CF pipe are hardened with a water-resistant and chemical-resistant adhesive material (including a mixture of carbon allotropes) that does not contain metal and has conductivity.
When a thick CF pipe and a thin CF pipe of this combination are immersed in an NaCl aqueous solution and a DC voltage is applied using the thick CF pipe as an anode and the thin CF pipe as a cathode, Cl ₂ is generated at the anode and H ₂ is generated at the cathode. Electrolysis method in which NaOH is generated on the cathode side (the same phenomenon occurs even when the thick CF pipe is used as a cathode and the thin CF pipe is used as an anode).
Carbon (including a mixture of carbon and carbon allotropes) can be formed into a cylindrical shape (referred to as a C pipe) and replaced with a CF pipe.   The method of electrolysis by replacing the outer diameter iron (Fe) pipe smaller than the inner diameter of the thick CF pipe in the method of claim 1 with a thin CF pipe.

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