JPH0125192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing synthetic hydrochloric acid while generating direct current electricity using a fuel cell, and more specifically, a method for producing synthetic hydrochloric acid using a fuel cell, and more specifically, a method for producing synthetic hydrochloric acid using a fuel cell that uses a solid membrane having an anion selective permeation ability as an electrolyte. By using this technology, chlorine and hydrogen are electrochemically reacted, and a part of the chemical energy, which is the heat of reaction, is directly converted into electrical energy, which can be effectively used for other purposes, while synthesizing a product with higher purity than the generated hydrogen chloride. This invention relates to a method for producing hydrochloric acid. The conventional industrial method for producing synthetic hydrochloric acid, except for by-product hydrochloric acid, is to make a product by chemically reacting chlorine and hydrogen in a graphite combustion tower and absorbing the generated hydrogen chloride with water or diluted hydrochloric acid. Generally, the heat produced by the reaction is removed by cooling water and is wasted. On the other hand, the idea of synthesizing hydrochloric acid by using hydrogen as the fuel in a fuel cell and chlorine as the oxidizing agent, and recovering the generated chemical energy as electrical energy, is as follows.
It has already been known for a long time. In recent years, research and development of fuel cells using hydrogen fuel and chlorine oxidizer has been progressing in the United States as a means of energy storage.
The technical outline is as follows. In other words, the purpose of this fuel cell is power generation, and it can be used to handle moment-to-moment or day-to-night fluctuations in the power load in the electric power industry, which is mainly driven by private demand, and constant load operation for highly efficient and stable operation of power plants. To adjust the gap, for example, when there is a lot of private electricity during the day, hydrogen fuel and chlorine oxidizer are reacted to generate DC power in a fuel cell, which is converted to AC using an inverter to make up for the shortfall in the supply from general power plants, and to generate electricity for private electricity demand at night. The electricity that is left in surplus due to the decrease in electricity is converted from alternating current to direct current, and then supplied to the fuel cell.The hydrochloric acid produced during the day is then electrolyzed and stored as hydrogen and chlorine, in preparation for daytime power generation. This method uses regenerative fuel cells. In this case, hydrogen chloride is generated in the oxidizer chamber using a cation permselective membrane as an electrolyte, and this is extracted to the outside of the battery together with unreacted chlorine to separate the chlorine and obtain hydrochloric acid, which is then stored. In preparation for electrolysis at night, a system is adopted in which the separated chlorine is recycled back to the battery and used as an oxidizing agent. Although this type of hydrochloric acid synthesis method using a fuel cell was known, it has not been put into practical use because of technical problems and profitability of the fuel cell itself, as well as the use of a hydrochloric acid solution as an electrolyte. A fatal problem in this case is that the produced hydrogen chloride mixes with both chlorine, hydrogen, and the electrolyte hydrochloric acid solution, and in addition, chlorine dissolves in the electrolyte hydrochloric acid solution by diffusion and osmosis through the gas diffusion electrode, so the product hydrochloric acid with high purity is Substantially, only hydrochloric acid is produced from hydrogen chloride in hydrogen gas, and as a practical matter, high-purity hydrochloric acid can only be obtained in a low yield. In addition, in the above-mentioned example of technological development in the United States, hydrogen is oxidized at the negative electrode by using a cation selectively permeable membrane, and the hydrogen ions selectively pass through the membrane and reach the positive electrode, where chlorine is reduced to chlorine. Hydrogen chloride is produced by association with ions. That is, hydrogen chloride is generated in the oxidizing agent chamber, and hydrochloric acid obtained by absorbing hydrogen chloride gas with water contains a large amount of chlorine, so it is impossible to obtain hydrochloric acid of high purity. The inventors of the present invention have completed the present invention as a result of intensive studies aimed at obtaining high yield and high purity hydrochloric acid without wastefully disposing of the heat produced by the reaction. The positive electrode is brought into close contact with a solid membrane that has the ability to selectively permeate anions.
A fuel cell is constructed by attaching the negative electrode directly to the solid membrane or by bringing it into contact with a solid membrane having an anion selective permeability through a liquid electrolyte, and hydrogen gas is supplied to the fuel chamber and hydrogen gas is supplied to the oxidizer chamber. A method for producing hydrochloric acid, which is characterized by supplying chlorine gas or a chlorine-containing liquid to generate electricity between positive and negative electrodes, and contacting hydrogen chloride produced in the fuel chamber with water or dilute hydrochloric acid to obtain hydrochloric acid. It is. The present invention described above generates hydrogen chloride in the fuel chamber at the same time as power generation using a fuel cell using a solid membrane having an anion selective permeation ability such as an anion exchange membrane, and this hydrogen chloride is absorbed into water (or dilute hydrochloric acid). In this method, hydrogen chloride is produced in the fuel chamber using a solid membrane with anion selective permeability. It is possible to easily separate hydrogen gas by absorption into water or diluted hydrochloric acid, and to obtain high-purity synthetic hydrochloric acid, which is the main target product, at a high yield. However, if we also consider the advantage that the DC power generated by the fuel cell can be supplied as power for alkali chloride electrolysis, which is the source of chlorine and hydrogen, which are the raw materials for synthetic hydrochloric acid, without converting it to AC, it is extremely advantageous. It can be called a process. One embodiment of the method of the present invention will be explained below with reference to the drawings. In the process diagram of FIG. 1, 1 is a fuel cell main body, and this fuel cell has a gas diffusion positive electrode 4 in close contact with one surface of an anion exchange membrane 2, and a negative electrode 3.
The side of the positive electrode 4 is a fuel chamber 5, and the side of the positive electrode 4 is an oxidizer chamber 6. Hydrogen gas is fed into the fuel chamber 5 through a pipe 7, and chlorine gas is fed into the oxidizer chamber 6 through a pipe 8 and a chlorine gas circulation It is fed by a blower 9. As a result, the chlorine gas sent to the oxidizer chamber 6 is reduced at the positive electrode having catalytic ability, and passes through the anion exchange membrane 2 where it is hydrated as chlorine ions, and then passes through the fuel chamber 5.
There, the hydrogen gas combines with the hydrogen ions oxidized by the catalyst at the negative electrode to generate hydrogen chloride gas, and the DC electricity generated between the negative electrode and the positive electrode is led out through the generated electricity lead-out terminals 21 and 21'. . On the other hand, the generated hydrogen chloride gas is led out of the fuel cell 1 together with the unreacted hydrogen gas in the fuel chamber, and is sent to the hydrogen chloride gas absorption tower 15 via an exhaust gas circulation blower 13 and a cooler 14, where it is absorbed by the dilute hydrochloric acid flowing down. The hydrogen chloride is then absorbed and converted into hydrochloric acid, which is taken out from the pipe 16 as a product of high purity concentrated hydrochloric acid. On the other hand, a part of the liquid in the tower is sent to the receiving tank 17 and flows down from the top of the tower as an absorption liquid through the circulation pump 18 and the cooler 20, and is again circulated through the above cycle, but is replenished through the pipe 19 along the way. Water is pumped in. Unreacted hydrogen gas is discharged from the top of the absorption tower 15, joins the hydrogen gas in the pipe 7, and enters the fuel chamber 5 of the fuel cell.
is supplied to In this case, in order to reduce the polarization at the hydrogen electrode of the fuel cell 1, it is necessary to reduce the hydrogen chloride concentration in the fuel chamber as much as possible, but on the other hand, the low concentration hydrogen chloride is absorbed with dilute hydrochloric acid, and the hydrogen chloride concentration in the pipe 16 is increased. In order to obtain the product hydrochloric acid, it is desirable to maintain the internal pressure of the absorption tower 15 higher than the internal pressure of the battery 1 using the circulation blower 13 and the pressure regulating valve 22. The unreacted chlorine gas in the oxidizer chamber 6 is discharged from the fuel cell, and the impurity gas removal device 11 separates the trace amount of impurity gas accumulated in the circulating chlorine gas, which is then merged into the pipe 8 as reaction chlorine gas and reused. do. The separated impure gas is discharged from the discharge pipe 12. In this case, the absorption liquid flowing down to the hydrogen chloride gas absorption tower 15 may be directly absorbed by water instead of diluted hydrochloric acid. As is clear from the above, the most significant feature of the present invention is that a solid membrane having an anion selective permeability is used as at least a part of the electrolyte of the fuel cell, and this is continuously carried out at the positive electrode. It has the effect of selectively passing only the generated anions, that is, chlorine ions, and combining with the hydrogen ions generated at the negative electrode to generate hydrogen chloride gas. The hydrogen chloride thus generated is led out of the fuel cell together with unreacted hydrogen and absorbed with water or dilute hydrochloric acid in a hydrogen chloride gas absorption tower. However, as the hydrogen chloride gas concentration increases in the fuel chamber 5, hydrogen gas The partial pressure decreases and the electrochemical reaction decreases. In order for the reaction to proceed continuously, it is necessary to remove the product from the system so that the hydrogen chloride concentration does not increase.Hydrogen chloride can be effectively removed by absorption with water or diluted hydrochloric acid, and at the same time dissolved chlorine can be removed. Less hydrochloric acid is produced as a product. In this case, as shown in FIG. 1, it is preferable to cool the high-temperature exhaust gas from the battery in the cooler 14 immediately before introducing it into the absorption tower 15, or/and to cool it in the cooler 20 immediately before introducing it into the absorption tower in the absorption liquid circulation path. Therefore, by cooling, the absorbed heat of dissolution and the heat generated within the fuel cell are removed, and can be absorbed efficiently. Although not shown in Figure 1, if impurity gas other than hydrogen chloride that is not absorbed by water or dilute hydrochloric acid accumulates in the circulating hydrogen gas, a portion of the gas that has left the absorption tower is released and accumulated. prevent. If there is an existing hydrochloric acid synthesis combustion tower, the impure gas-containing hydrogen released here and the impure gas-containing released chlorine can be effectively used by mixing it with the hydrogen and chlorine supplied to the existing hydrochloric acid synthesis combustion tower, respectively. I can do it. In the method of the present invention, when the product hydrochloric acid is extracted from the absorption tower 15, for example, a control valve is provided in the extraction pipe 16, and this is linked with a hydrochloric acid concentration meter of the outlet liquid of the absorption tower 15 to control the concentration of hydrochloric acid to meet product standards. It is also possible to continuously obtain hydrochloric acid of a quality that meets the requirements.
In this case, the operating point of the control valve 22 is such that the absorption tower 15 is maintained at a predetermined internal pressure depending on the concentration of hydrogen chloride in the absorbed gas supplied to the absorption tower 15, the temperature of the absorption liquid, and the concentration of hydrochloric acid taken out as a product. It is better to set In the present invention, the electrolyte used in the fuel cell must include a solid membrane having an anion selective permeability, and such a solid membrane having an anion selective permeability is formed of an organic polymer. It refers to solid membrane-like materials that have excellent permselectivity for anions, especially chlorine ions, such as anion exchange membranes and sheet-like sheets made by bonding inorganic anion exchangers with binders such as Teflon. In addition, an electrolyte may be formed by combining two or more types of solid membranes having anion selective permeability, or a composite electrolyte may be formed by combining the solid membrane having anion selective permeation ability with another liquid electrolyte. However, from the viewpoint of the structure of the fuel cell, it is most appropriate to use only the above-mentioned solid membrane. In such a combination of a solid membrane and a liquid electrolyte, a positive electrode is placed in close contact with one side of a solid membrane that has anion permselectivity, and a negative electrode is placed on the other side of the solid membrane at a predetermined interval. The gap between the negative electrode and the negative electrode is sealed with hydrochloric acid. In this case, by circulating the liquid electrolyte (hydrochloric acid) between the battery and a heat exchanger provided outside the battery without draining it out of the system, the battery temperature can be efficiently controlled and the temperature raised during startup. In an electrolyte with such a structure, chlorine gas in the oxidizer chamber reaches the liquid electrolyte as chlorine ions through the solid membrane, hydrogen chloride is generated in the liquid electrolyte, and the hydrogen chloride concentration in the electrolyte increases to the cell operating temperature. When saturation under pressure is reached, it is diffused as a gas into the fuel chamber through the negative electrode, which is a gas diffusion electrode, and thereafter can be converted into high-purity hydrochloric acid through a similar hydrogen chloride gas absorption process. In the method of the present invention, a chlorine-containing liquid, such as hydrochloric acid in which chlorine is dissolved, may be used instead of the chlorine supplied to the oxidizer chamber. In this case, the oxidizer chamber is filled with this chlorine-containing liquid and reacts, but the unreacted chlorine-containing liquid leaving the oxidizer chamber is chlorinated according to predetermined supply conditions (concentration, flow rate, temperature, etc.). It is desirable to replenish hydrochloric acid and circulate it to the oxidizer chamber. The electrodes used in the fuel cell of the method of the present invention may be porous breathable carbon plates, corrosion-resistant metal porous plates, mesh, etc., but the carbon fibers may be adhered to the anion exchange membrane with a suitable binder, or the carbon fibers may be further attached to the outside of the membrane. As a means for extracting electricity, it is preferable to have a structure in which a corrosion-resistant metal mesh is laminated to improve electrical contact with the membrane. In this case, the positive electrode is made of porous carbonaceous material or activated carbon fibers, etc., and if it has electrochemical activity without supporting a special catalyst, the reduction reaction will proceed, but the negative electrode is made of an anion exchange membrane and When used in close contact with the membrane, it is preferable to support a catalyst made of a platinum group metal or an alloy thereof on the contact surface of the electrode base material with the membrane. A more preferable bonding mode between the anion exchange membrane and the catalyst electrode is a substance having anion conductivity on the surface of the membrane (any inorganic or organic compound may be used).
In addition, after applying a material having the same composition as the ion exchange membrane (preferably a material having the same composition as the ion exchange membrane in the sense that it also serves as a binder), a porous electrode (for example, carbon fiber cloth or fine mesh of tantalum, titanium, etc.) carrying an electrode catalyst material thereon is applied.
If an electrode and an exchange membrane are integrated by stacking them and heating and pressing them together, the contact gap between the anion exchange membrane, which is an electrolyte, and the electrode carrying a catalyst can be filled with an anion conductive substance. By increasing the contact area between the ion exchange membrane and the electrode, good electrical contact and smooth ion movement can be achieved. In addition, in order for the anion exchange membrane to maintain anion permselectivity as an electrolyte, it is necessary to keep the exchange membrane in a moist state, which can be done by spraying saturated steam or hydrochloric acid into the oxidizer chamber, or For each electrode sandwiching the membrane, carbon fibers that serve as catalyst electrodes and electrolyte holders are closely attached to the surface of the exchange membrane, and a metal mesh as a current collector is pressed onto the surface, making use of the capillary action of the carbon fibers. A method of moistening by supplying water or hydrochloric acid from the upper part, respectively, or a method of kneading a substance having anionic conductivity with a substance having a water-retentive property to form a paste and applying it to the matrix, etc., are employed. However, this method applies when the oxidizing agent supplied to the oxidizing agent chamber is chlorine gas, and when the oxidizing agent is a liquid obtained by dissolving chlorine in hydrochloric acid, for example, this provides a wet state to the membrane. There is no need to do so. Furthermore, in this case, by providing a heat exchanger in the solution circulation system, it is possible to efficiently remove the heat generated within the battery during battery operation, control the battery temperature, and increase the temperature when starting the battery. . Since both the oxidizer chamber and the fuel chamber in a fuel cell are in contact with corrosive gases or liquids, plastic or airtight resin-impregnated graphite is used as a corrosion-resistant material that can withstand chlorine and hydrochloric acid and can withstand operating temperatures of, for example, 90°C. , carbon fiber-filled plastic, etc. can be used. As described above, the present invention generates electricity using a hydrogen-chlorine fuel cell using a solid membrane with anion selective permeability, extracts the generated hydrogen chloride gas from the cell, and absorbs it with water or diluted hydrochloric acid. By doing so, it is possible to obtain higher purity hydrochloric acid in a higher yield.This is an excellent and useful invention in that it skillfully combines the structure of the above-mentioned fuel cell and the accompanying process for obtaining high-purity hydrochloric acid. be. The present invention will be explained below with reference to Examples and Comparative Examples. Example 1 Carbon cloth manufactured by Nippon Carbon Co., Ltd. (Carboron Cloth)
GF-8# 509) 4 cm x 6.5 cm is impregnated with platinum in the form of chloroplatinic acid solution, and one side is coated with an anion conductive adhesive (Aronfloc C-303 (manufactured by Toagosei Chemical Industry Co., Ltd.)) Two sheets coated with a high viscosity aqueous solution of 1 were adhered to both sides of an anion exchange membrane (Celemion AMV manufactured by Asahi Glass Co., Ltd.) with their adhesive surfaces in contact.The membrane also served as a current collector. An 8-mesh titanium lath mesh was pressed from both sides to form a fuel cell in which the positive and negative electrodes were in close contact with one side of each anion exchange membrane.The oxidizer chamber of such a fuel cell was placed in 35% hydrochloric acid. A liquid containing 4.8 g of chlorine dissolved in it, and a hydrogen gas of 0.3 g/H in the fuel chamber.
was supplied, and power generation and hydrochloric acid production were performed according to the process shown in FIG. The following results were obtained after 27.5 hours of discharge. Output voltage: 0.15 to 0.2 V (D, C) Output current: 0.18 to 0.24 A (D, C) Hydrogen chloride absorption liquid composition: Hcl = 8.2 wt% Dissolved chlorine <1 mg/ Example 2 Carbon cloth manufactured by Nippon Carbon Co., Ltd. Carbon Cross
The adhesive used in Example 1 was applied to one side of GF-8#509) 4 cm x 6.5 cm, and this coated surface was brought into close contact with one side of an anion exchange membrane (Flemion AMV manufactured by Asahi Glass Co., Ltd.), and further concentrated. An 8-mesh titanium lath net, which also served as an electric body, was placed on the opposite side of the carbon cloth to which the anion exchange membrane was in close contact, to obtain an integrated cathode and membrane. On the other hand, on the other side of the anion exchange membrane, an 8-mesh polypropylene mesh was placed on the other side of the anion exchange membrane, and the average pore diameter was
20μ, porosity 50%, thickness 6mm, electrode area 4cm x 6.5
cm porous carbon plate (P-170 manufactured by Nippon Carbon Co., Ltd.)
After impregnating with chloroplatinic acid solution and baking at 450℃,
Furthermore, a Teflon dispersion impregnated and sintered was placed as a negative electrode. Then, a 35% hydrochloric acid solution was interposed in the gap between the negative electrode and the anion exchange membrane to seal it. Chlorine gas was flowed at 0.3/H into the oxidizer chamber of the fuel cell thus formed, and hydrogen gas was flowed into one fuel chamber.
Power generation and hydrochloric acid production were carried out in accordance with the process shown in FIG. 1 above by flowing at a ratio of 0.3/H. The results were as follows. Discharge time 27.5hv Output voltage 0.08~0.05V (DC) Output current 0.1~0.06A (DC) Hydrogen chloride absorption liquid composition (based on pure water) Hcl: 3.2wt% Dissolved chlorine <1mg/ Comparative example 1 35% hydrochloric acid as electrolyte Using only the solution, a porous carbon plate (Nippon Carbon Co., Ltd. P-
170) was used as a hydrogen electrode, and the porous carbon plate was impregnated with a chloroplatinic acid solution, sintered, and then impregnated with Teflon dispersion and sintered to construct a fuel cell. Power is generated by flowing chlorine gas into the chlorine electrode chamber of this fuel cell and hydrogen gas flowing into the hydrogen electrode.At the same time, the hydrogen and chlorine released from the cell are reacted in a quartz combustion tube to form hydrogen chloride, which is then converted into pure water. Hydrochloric acid was obtained. The results were as follows. Discharge time 27.5hv Output voltage 0.07~0.06V (DC) Output current 0.09~0.07A (DC) Battery exhaust hydrogen composition _H2 : 84~88vol% Hcl: 16~12vol% _Cl2 : 0vol% Battery exhaust chlorine composition _Cl2 : 82 to 86 vol% HCl: 18 to 14 vol% H ₂ : 0 Composition of hydrogen chloride absorption liquid (based on pure water) HCl: 3.5 wt% H ₂ O: 96.5 wt% Dissolved chlorine: 85 mg/ [Table]

[Brief explanation of drawings]

FIG. 1 is a process diagram showing one embodiment of the present invention. 1... fuel cell, 2... anion exchange membrane, 3...
... Gas diffusion negative electrode, 4 ... Gas diffusion positive electrode, 5 ... Fuel chamber, 6 ... Oxidizer chamber, 11 ... Impurity gas removal device, 14, 20 ... Cooler, 15 ... Hydrogen chloride gas absorption tower.

Claims (1)

[Claims] 1. A fuel cell is produced by bringing a positive electrode and a solid membrane having an anion selective permeability into close contact with each other, and by directly contacting the negative electrode with the solid membrane or by contacting the solid membrane with an anion selective permeability through a liquid electrolyte. Hydrogen gas is supplied to the fuel chamber, and chlorine gas or chlorine-containing liquid is supplied to the oxidizer chamber to generate electricity between the positive and negative electrodes, and the hydrogen chloride generated in the fuel chamber is converted into water. Or a method for producing hydrochloric acid, which is characterized by contacting with dilute hydrochloric acid to obtain hydrochloric acid.