Method and system for recovering hydrochloric acid

Abstract

This invention provides a method for efficiently recovering hydrochloric acid from an aqueous solution containing iron chloride at low temperatures. [Solution] A method for recovering hydrochloric acid from an aqueous solution containing iron(II) chloride, comprising: a first step of heating an aqueous solution containing iron(II) chloride to below 110°C; a second step of introducing an oxygen-containing gas into the aqueous solution to produce iron(III) chloride and iron(III) hydroxide; a third step of adding heated water to the aqueous solution to produce iron(III) hydroxide and hydrogen chloride through a reaction between iron(III) chloride and water; and a fourth step of separating iron(III) hydroxide from the aqueous solution as a residue and recovering hydrochloric acid obtained by dissolving hydrogen chloride in the aqueous solution.

Description

Technical Field

[0001] The present invention relates to a method for recovering hydrochloric acid from an aqueous solution containing iron(II) chloride and a system for recovering hydrochloric acid.

Background Art

[0002] Aqueous solutions such as waste acid containing iron chloride discharged in various industrial fields have a low recycling rate of about 30 to 40%, which has become an important issue related to industrial waste treatment. In waste acid treatment facilities such as steelworks, waste acid is sprayed in a high-temperature atmosphere of 800°C or higher to perform waste acid regeneration treatment, but the process is complicated and the equipment scale tends to be large, and in addition, high-temperature treatment also incurs high operating costs. Therefore, if waste acid regeneration treatment can be performed in a relatively low temperature range at low cost with a simpler process, it will be easier to introduce the process into various industrial fields, which is thought to lead to an increase in the recycling rate of waste acid.

[0003] In addition, most of the energy supplied to various industrial fields is derived from fossil fuels, and reduction of carbon dioxide emissions is required from the perspective of global warming. Therefore, in recent years, hydrogen gas has attracted attention as an energy source, and the utilization of hydrogen gas is being promoted. Accordingly, hydrogen gas that can be supplied at low cost is in demand.

[0004] Patent Document 1 reports an iron oxide production facility that decomposes an aqueous solution containing iron chloride into hydrochloric acid and iron oxide by a spray roasting method, recovers the hydrochloric acid, and produces iron oxide used as a raw material for magnetic materials and the like. In Patent Document 1, an aqueous solution containing iron chloride is treated in a roasting furnace at a heating amount of 3500×10 3 kcal / hr at a high temperature, thereby separating the aqueous iron chloride solution into iron oxide and hydrogen chloride. Patent Document 2 reports a method for treating industrial furnace residue and waste acid, which comprises reacting the residue of a magnesium melting furnace and the residue of a magnesium die casting furnace with waste acid discharged from industry.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-147718 [Patent Document 2] Japanese Patent Publication No. 2020-139731 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when extracting hydrogen chloride from an aqueous solution and regenerating it into hydrochloric acid, as described in Patent Document 1, the process tends to be complex and require large-scale equipment, as well as high-temperature processing. On the other hand, Patent Document 2 describes reacting magnesium die-casting furnace residue with waste acid containing iron chloride at a relatively low temperature of 55°C to 110°C, but this is a technique to dissolve the residue in the waste acid to reduce its concentration and thus its harmfulness, and it does not disclose a process for regenerating hydrochloric acid or the like from waste acid.

[0007] In view of the above issues, the present invention aims to provide a method and system for recovering hydrochloric acid that can efficiently recover hydrochloric acid from an aqueous solution containing iron chloride by low-temperature treatment. [Means for solving the problem]

[0008] The inventors of the present invention have diligently studied to solve the above problems and have obtained the following findings. Hydrochloric acid can be recovered by low-temperature treatment using the following method. An aqueous solution containing iron(II) chloride is heated to below 110°C. Next, an oxygen-containing gas is introduced into the aqueous solution to produce iron(III) chloride and iron(III) hydroxide. Next, heated water is added to the aqueous solution to produce iron(III) hydroxide and hydrogen chloride through the reaction of iron(III) chloride with water. Next, iron(III) hydroxide is separated from the aqueous solution as a residue, and hydrochloric acid, which is obtained by dissolving hydrogen chloride in the aqueous solution, is recovered. Furthermore, if the aqueous solution contains hydrogen chloride in addition to iron(II) chloride, pure iron can be added to the aqueous solution before introducing an oxygen-containing gas to generate hydrogen gas through the reaction of pure iron with hydrogen chloride, and the hydrogen gas can be recovered.

[0009] In other words, the gist of the present invention is as follows:

[0010] [1] A first step involves heating an aqueous solution containing iron(II) chloride to a temperature below 110°C, Next, a second step is performed in which an oxygen-containing gas is introduced into the aqueous solution to produce iron(III) chloride and iron(III) hydroxide. Next, a third step is performed in which heated water is added to the aqueous solution, and iron(III) hydroxide and hydrogen chloride are produced by the reaction of iron(III) chloride and water. Next, a fourth step is to separate the iron(III) hydroxide from the aqueous solution as a residue and recover the hydrochloric acid obtained by dissolving the hydrogen chloride in the aqueous solution. A method for recovering hydrochloric acid from an aqueous solution containing iron(II) chloride, wherein the method is as follows:

[0011] [2] The method for recovering hydrochloric acid according to [1] above, wherein the aqueous solution used in the first step contains hydrogen chloride in addition to iron(II) chloride.

[0012] [3] The method for recovering hydrochloric acid according to [2] above, further comprising the step of adding pure iron to the aqueous solution before the second step to generate hydrogen gas by a reaction between the pure iron and hydrogen chloride, and recovering the hydrogen gas.

[0013] [4] The method for recovering hydrochloric acid according to any one of the above [1] to [3], wherein the first step involves heating the aqueous solution to 40°C or higher.

[0014] [5] The method for recovering hydrochloric acid according to any one of the above [1] to [4], wherein the gas used in the second step has an oxygen concentration of 5% by volume or more.

[0015] [6] A method for recovering hydrochloric acid according to any one of the above [1] to [5], wherein in the third step, the water is heated to 40°C or higher and then added to the aqueous solution.

[0016] [7] A container for holding an aqueous solution containing iron(II) chloride, a heating device for heating the aqueous solution contained in the container to below 110°C, a gas supply device for introducing an oxygen-containing gas into the aqueous solution contained in the container to generate iron(III) chloride and iron(III) hydroxide, a water supply device for adding heated water to the aqueous solution contained in the container to cause a reaction between the iron(III) chloride and the water to generate iron(III) hydroxide and hydrogen chloride, a separation and recovery device for separating iron(III) hydroxide from the aqueous solution as a residue and recovering hydrochloric acid formed by dissolving the hydrogen chloride in the aqueous solution, A hydrochloric acid recovery system from an aqueous solution containing iron(II) chloride, comprising

[0017] [8] The aqueous solution contained in the container further contains hydrogen chloride in addition to the iron(II) chloride, a pure iron supply device for adding pure iron to the aqueous solution contained in the container to cause a reaction between the pure iron and the hydrogen chloride to generate hydrogen gas, a hydrogen gas recovery device for recovering the hydrogen gas, The hydrochloric acid recovery system according to the above [7], comprising [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a hydrochloric acid recovery method and a hydrochloric acid recovery system that can efficiently recover hydrochloric acid from an aqueous solution containing iron chloride through low-temperature treatment. In addition, by performing any optional step of the present invention, hydrogen gas can also be efficiently recovered. [Brief Description of the Drawings]

[0019] [Figure 1] It is a diagram showing the process flow of a hydrochloric acid recovery method according to one embodiment of the present invention. [Figure 2] It is a diagram showing the process flow of a hydrochloric acid recovery method including a step of recovering hydrogen gas according to one embodiment of the present invention. [Figure 3] It is a schematic diagram of a hydrochloric acid recovery system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] The following describes a method for recovering hydrochloric acid and a hydrochloric acid recovery system according to one embodiment of the present invention. Note that the embodiments described below are examples that embody the present invention, and these specific examples do not limit the configuration of the present invention.

[0021] (Method for recovering hydrochloric acid) Referring to Figure 1, a method for recovering hydrochloric acid according to one embodiment of the present invention comprises: a first step of heating an aqueous solution containing iron(II) chloride (FeCl2) to less than 110°C; a second step of introducing an oxygen-containing gas into the aqueous solution to produce iron(III) chloride (FeCl3) and iron(III) hydroxide (Fe(OH)3); a third step of adding heated water to the aqueous solution to produce iron(III) hydroxide and hydrogen chloride through a reaction between iron(III) chloride and water; and a fourth step of separating iron(III) hydroxide from the aqueous solution as a residue and recovering hydrochloric acid obtained by dissolving hydrogen chloride in the aqueous solution.

[0022] [Aqueous solution containing iron(II) chloride] In this invention, an aqueous solution containing iron(II) chloride is used. If the aqueous solution contains metal elements other than iron, when the residue is separated from the aqueous solution and hydrochloric acid is recovered as described later, the metal elements other than iron will remain in the solution. Therefore, it is preferable that metal elements other than iron are not present in the aqueous solution. Furthermore, it is preferable that the aqueous solution contains hydrogen chloride in addition to iron(II) chloride. This makes it possible to recover hydrogen gas in addition to hydrochloric acid. Therefore, it is preferable that the aqueous solution containing iron(II) chloride consists of iron(II) chloride, any hydrogen chloride, and water.

[0023] [1st step] First, the aqueous solution containing iron(II) chloride is heated to below 110°C. If the aqueous solution is heated above 110°C, the acidic components will evaporate due to fumes, causing the hydrogen chloride generated in the third step (described later) to detach from the aqueous solution, and reducing the amount of hydrochloric acid recovered in the fourth step. On the other hand, if the aqueous solution is heated below 40°C, the reactivity between the aqueous solution and oxygen decreases, and when pure iron is added to generate hydrogen gas, the reactivity is low and almost no hydrogen gas is generated. Therefore, in the first step, it is preferable to heat the aqueous solution containing iron(II) chloride to above 40°C. After heating the aqueous solution in the first step, the temperature of the aqueous solution is maintained below 110°C during the subsequent second and third steps. At this time, temperature control is performed including the reaction heat in the second and third steps.

[0024] [Second process] Next, an oxygen-containing gas is introduced into an aqueous solution containing iron(II) chloride to produce iron(III) chloride and iron(III) hydroxide. As shown in equations (1) and (2) below, the iron(II) chloride in the aqueous solution reacts with oxygen to produce iron(III) chloride. Also, as shown in equation (3) below, some of the iron(II) chloride becomes iron(III) hydroxide. Fe 2+ +H + +1 / 4O2→Fe 3+ +1 / 2H2O ···(1) Fe 3+ +3Cl - →FeCl3···(2) Fe 2+ +2OH - +1 / 4O2+1 / 2H2O→Fe(OH)3···(3)

[0025] The oxygen-containing gas may be pure oxygen gas or air. However, when the oxygen concentration of the gas is 5% by volume or higher, the oxidation efficiency of iron chloride ions can be preferably obtained. Therefore, it is preferable that the oxygen-containing gas has an oxygen concentration of 5% by volume or higher. Furthermore, if the gas does not contain acidic gases other than carbon dioxide and basic gases, it is possible to suitably prevent a decrease in the recovery efficiency of hydrochloric acid. Therefore, it is preferable that the oxygen-containing gas consists of oxygen, any carbon dioxide, and any inert gas.

[0026] In the second step, if the gas flow rate of the oxygen-containing gas is 1 L / min or more, a good stirring effect can be obtained when the gas is introduced into the aqueous solution. Therefore, a gas flow rate of 1 L / min or more is preferable. On the other hand, the gas flow rate of the oxygen-containing gas is preferably (50 × V1) L / min or less, where V1 L / min is the transport rate from the pump 76 described later.

[0027] From the viewpoint of allowing the reaction to proceed sufficiently, the time for introducing an oxygen-containing gas into the aqueous solution containing iron(II) chloride is preferably (10 × V1 / V2) minutes or more and (100 × V1 / V2) minutes or less, with a gas flow rate of V2 L / min. After starting the introduction of the oxygen-containing gas in the second step, the introduction of the oxygen-containing gas may be continued until the third step, which will be described below, is completed.

[0028] [3rd step] Next, heated water is added to the aqueous solution to produce iron(III) hydroxide and hydrogen chloride through the reaction of iron(III) chloride with water. As shown in equation (4) below, iron(III) chloride reacts with water to produce iron(III) hydroxide and hydrogen chloride. FeCl3+3H2O→Fe(OH)3+3HCl ···(4)

[0029] In the third step, it is preferable to heat the water to 40°C or higher before adding it to the aqueous solution. This allows for favorable reactivity between the iron ions in the aqueous solution and the water. On the other hand, there is no particular upper limit to the temperature of the water in the third step, but the temperature of the water is generally 110°C or lower.

[0030] In the third step, if the flow rate of the heated water is 1 L / min or more, a good stirring effect can be obtained when the heated water is added to the aqueous solution. Therefore, a flow rate of 1 L / min or more is preferable. On the other hand, it is preferable that the flow rate of the heated water be (50 × V1) L / min or less. Furthermore, the amount of water added is preferably 36 × 3y [mL], where y [mol] is the amount of iron dissolved in the aqueous solution.

[0031] [4th step] Next, iron(III) hydroxide is separated from the aqueous solution as a residue, and hydrochloric acid, which is obtained by dissolving hydrogen chloride in the aqueous solution, is recovered. The method for separating the residue from the aqueous solution is not particularly limited, but methods such as a semipermeable membrane or centrifugation can be used.

[0032] [Hydrogen gas recovery process (optional)] If the aqueous solution contains hydrogen chloride in addition to iron(II) chloride, pure iron may be added to the aqueous solution after the first step and before the second step to generate hydrogen gas through the reaction between the pure iron and hydrogen chloride, and then the hydrogen gas may be recovered. As pure iron, slag ingots can be used. The weight of the pure iron to be added is preferably 55.8 / 2 × z [g], where z [mol] is the hydrochloric acid content of the aqueous solution. By adding pure iron, hydrogen gas is generated as shown in equation (5) below, and the hydrogen gas can be recovered. Figure 2 shows the process flow of a method for recovering hydrochloric acid including the hydrogen gas recovery step. After recovering the hydrogen gas, the second step and subsequent steps can be carried out as described above. Fe+2HCl→FeCl2+H2↑ ···(5)

[0033] (Hydrochloric acid recovery system) Next, a hydrochloric acid recovery system according to one embodiment of the present invention will be described. Figure 3 shows a schematic diagram of a hydrochloric acid recovery system 100 according to one embodiment of the present invention. The hydrochloric acid recovery system 100 includes a container 30 for containing an aqueous solution 32 containing iron(II) chloride, a heating device 34 for heating the aqueous solution 32 contained in the container 30 to less than 110°C, a gas supply device 20 for introducing an oxygen-containing gas into the aqueous solution 32 contained in the container 30 to produce iron(III) chloride and iron(III) hydroxide, a water supply device 10 for adding heated water to the aqueous solution 32 contained in the container 30 to produce iron(III) hydroxide and hydrogen chloride through a reaction between iron(III) chloride and water, and a separation and recovery device 70 for separating iron(III) hydroxide as a residue from the aqueous solution and recovering the hydrochloric acid obtained by dissolving hydrogen chloride in the aqueous solution. The aqueous solution 32 containing iron(II) chloride is supplied to the container 30 by the aqueous solution supply device 50.

[0034] By using the hydrochloric acid recovery system 100 equipped with the above-described apparatus, the first to fourth steps described above can be carried out. Each step is as described above.

[0035] The water supply device 10 supplies water to the container 30 via piping 12. The gas supply device 20 supplies oxygen-containing gas to the container 30 via piping 22. The positions of the water supply piping 12 and the oxygen-containing gas supply piping 22 are not particularly limited, but it is preferable that the ends of each pipe are immersed in the aqueous solution 32 as shown in Figure 3. This facilitates agitation by convection during supply. However, if the ends of each pipe are immersed in the aqueous solution 32, the pressure p of the supplied water or gas must satisfy p > ρgh. Here, ρ is the density of the aqueous solution, g is the acceleration due to gravity, and h is the vertical distance from the liquid surface to the pipe outlet.

[0036] Furthermore, the hydrochloric acid recovery system 100 in Figure 3 shows a separation and recovery device 70 that includes a semipermeable membrane 72. The separation and recovery device 70 includes a semipermeable membrane 72, liquid input equipment before and after the semipermeable membrane 72, a container 74 for recovering the filtered hydrochloric acid 80, and a pump 76 for transporting the aqueous solution 32 from the container 30. Thus, the generation reaction and separation and recovery may be carried out in separate containers, or they may be carried out in a single container.

[0037] Furthermore, the hydrochloric acid recovery system 100 may optionally include a pure iron supply device 40 and a hydrogen gas recovery device 60. This allows the hydrogen gas recovery process described above to be performed when the aqueous solution contains hydrogen chloride in addition to iron(II) chloride.

[0038] For processes and conditions not described in this specification, conventional methods may be used. [Examples]

[0039] The function and effects of the present invention will be described below using examples. However, the present invention is not limited to the following examples. Hydrochloric acid was recovered using a hydrochloric acid recovery system 100 as shown in Figure 3. Waste acid generated in the steel manufacturing process was used as the aqueous solution containing iron(II) chloride. This waste acid is free of acidic components other than hydrogen chloride. Air or O2 gas (100%) was used as the oxygen-containing gas; in Comparative Example 3, N2 gas was used instead. Tap water was used as the water.

[0040] First, 100 mL of aqueous solution (waste acid) was placed in a container and heated (Step 1). Next, oxygen-containing gas was introduced into the aqueous solution (Step 2). The gas pressure was set to 0.1 MPa using an air compressor, and the gas flow rate was set to 5 L / min. Then, heated water was added to the aqueous solution (Step 3). The amount of iron dissolved in the aqueous solution was calculated, and 35 mL of water was added. After stirring, the heating of the aqueous solution and the introduction of gas were stopped, and the aqueous solution was transferred from the container to the separation device. The oxygen-containing gas was supplied for 2 minutes. Next, the residue was separated from the aqueous solution using a semipermeable membrane, and hydrochloric acid was recovered (Step 4). Tables 1 and 2 show the temperature of the aqueous solution, the type of gas added and the oxygen concentration, as well as the temperature of the added water in each example. Note that in Comparative Example 2, the aqueous solution was not heated, and in Comparative Example 4, the added water was not heated.

[0041] The concentration of hydrogen chloride in the obtained hydrochloric acid was measured. The total chloride ion concentration in the waste acid before treatment (T-HCl), the chloride ion concentration present as hydrogen chloride in the waste acid before treatment (Be-HCl), and the chloride ion concentration present as hydrogen chloride in the hydrochloric acid after treatment (Af-HCl) were determined, and the hydrochloric acid recovery capacity ({(Af-HCl)-(Be-HCl)} / T-HCl) was calculated from these values. Furthermore, the total chloride ion concentration in the waste acid before treatment and the total chloride ion concentration in the hydrochloric acid after treatment were compared, and the rate of change in concentration (degree of hydrochloric acid desorption) was determined. Tables 1 and 2 show the hydrochloric acid recovery capacity and degree of hydrochloric acid desorption. Note that a higher hydrochloric acid recovery capacity is preferable, and a lower degree of hydrochloric acid desorption is preferable.

[0042] [Table 1]

[0043] [Table 2]

[0044] As shown in Tables 1 and 2, in Invention Examples 1 to 4, which satisfy the requirements of the present invention, hydrochloric acid was efficiently recovered by low-temperature treatment. In contrast, in Comparative Examples 1 to 4, which do not satisfy the requirements of the present invention, the hydrochloric acid recovery capacity was low or the degree of hydrochloric acid desorption was high, and hydrochloric acid could not be efficiently recovered.

[0045] As another example, a hydrogen gas recovery process was carried out. First, 500 mL of aqueous solution was placed in a container and heated (step 1). Next, pure iron was added to the container. After adding the pure iron, the generated hydrogen gas was recovered, and the amount of hydrogen produced was confirmed. Table 3 shows the temperature of the aqueous solution and the amount of hydrogen gas produced in each example. Note that in Comparative Example 5, the aqueous solution was not heated. Also, steps 2 and beyond have been verified above in each example and are therefore omitted.

[0046] [Table 3]

[0047] Table 3 shows that in Invention Examples 5 and 6, which satisfy the requirements of the present invention, hydrogen gas can be recovered efficiently, and in addition to hydrochloric acid, hydrogen gas can also be recovered efficiently. In contrast, in Comparative Example 5, which does not satisfy the requirements of the present invention, hydrogen gas could not be recovered sufficiently. [Industrial applicability]

[0048] According to the present invention, a method and system for recovering hydrochloric acid can be provided that enables efficient recovery of hydrochloric acid from an aqueous solution containing iron chloride by low-temperature treatment. Furthermore, hydrogen gas can also be efficiently recovered by performing any of the steps of the present invention. [Explanation of symbols]

[0049] 100 Hydrochloric Acid Recovery System 10 Water supply device 12 Piping 20 Gas supply equipment 22 Piping 30 containers 32. Aqueous solution containing iron(II) chloride 34 Heating device 40. Pure Iron Supply System 50 Aqueous solution supply device 60 Hydrogen gas recovery device 70 Separation and recovery device 72 Semi-permeable membrane 74 Container 76 pumps 80 Hydrochloric acid

Claims

1. The first step involves heating an aqueous solution containing iron(II) chloride to a temperature below 110°C, Next, a second step is performed in which an oxygen-containing gas is introduced into the aqueous solution to produce iron(III) chloride and iron(III) hydroxide. Next, a third step is performed in which heated water is added to the aqueous solution, and iron(III) hydroxide and hydrogen chloride are produced by the reaction of iron(III) chloride and water. Next, a fourth step is to separate the iron(III) hydroxide from the aqueous solution as a residue and recover the hydrochloric acid obtained by dissolving the hydrogen chloride in the aqueous solution. A method for recovering hydrochloric acid from an aqueous solution containing iron(II) chloride, wherein the method is as follows:

2. The method for recovering hydrochloric acid according to claim 1, wherein the aqueous solution used in the first step contains hydrogen chloride in addition to iron(II) chloride.

3. The method for recovering hydrochloric acid according to claim 2, further comprising the step of adding pure iron to the aqueous solution before the second step, generating hydrogen gas by the reaction of the pure iron with hydrogen chloride, and recovering the hydrogen gas.

4. The method for recovering hydrochloric acid according to any one of claims 1 to 3, wherein the first step involves heating the aqueous solution to 40°C or higher.

5. The method for recovering hydrochloric acid according to any one of claims 1 to 3, wherein the gas used in the second step has an oxygen concentration of 5% by volume or more.

6. A method for recovering hydrochloric acid according to any one of claims 1 to 3, wherein in the third step, the water is heated to 40°C or higher and then added to the aqueous solution.

7. A container for holding an aqueous solution containing iron(II) chloride, A heating device for heating the aqueous solution contained in the container to less than 110°C, A gas supply device that introduces an oxygen-containing gas into the aqueous solution contained in the container to generate iron(III) chloride and iron(III) hydroxide, A water supply device that adds heated water to the aqueous solution contained in the container to produce iron(III) hydroxide and hydrogen chloride through the reaction of iron(III) chloride and water, A separation and recovery apparatus for separating iron(III) hydroxide as a residue from the aqueous solution and recovering hydrochloric acid obtained by dissolving the hydrogen chloride in the aqueous solution, A system for recovering hydrochloric acid from an aqueous solution containing iron(II) chloride, comprising [the specified element].

8. The aqueous solution contained in the container contains hydrogen chloride in addition to iron(II) chloride, A pure iron supply device that adds pure iron to the aqueous solution contained in the container and generates hydrogen gas through a reaction between the pure iron and hydrogen chloride, A hydrogen gas recovery device for recovering the aforementioned hydrogen gas, A hydrochloric acid recovery system according to claim 7, comprising:

Images