KR100394085B1 - A feeding method of chlorine for the oxidation of aqueous ferrous chloride solution - Google Patents

Abstract

The present invention relates to a method for supplying chlorine gas for the oxidation of ferric chloride (FeCl ₂ ) aqueous solution, and more particularly, to oxidize ferrous chloride to ferric chloride (FeCl ₃ ) by adding chlorine gas to an aqueous solution containing ferrous chloride. In the method, the chlorine gas input rate is changed according to the concentration of ferrous chloride which is changed as the oxidation reaction proceeds, thereby introducing chlorine gas in the shortest time as well as chlorine which does not discharge unreacted chlorine gas. It relates to a gas supply method.

Description

A feeding method of chlorine for the oxidation of aqueous ferrous chloride solution}

The present invention relates to a method for supplying chlorine gas for the oxidation of ferric chloride (FeCl ₂ ) aqueous solution, and more particularly, to oxidize ferrous chloride to ferric chloride (FeCl ₃ ) by adding chlorine gas to an aqueous solution containing ferrous chloride. In the method, the chlorine gas input rate is changed according to the concentration of ferrous chloride which is changed as the oxidation reaction proceeds, thereby introducing chlorine gas in the shortest time as well as chlorine which does not discharge unreacted chlorine gas. It relates to a gas supply method.

Ferric chloride aqueous solution is used as an etchant for etching iron or an alloy of iron, the ferric chloride is reduced to ferric chloride in the etching process, the etching ability is lost. The solution used to etch pure iron can simply be oxidized and regenerated into ferric chloride solution. However, in the waste iron chloride solution used for etching the alloy, heavy metals such as nickel and copper are dissolved and present in the waste liquid. In order to reuse this waste solution, the dissolved heavy metals must be reduced and precipitated and removed. At this time, the ferric chloride is also reduced to ferrous chloride. Therefore, in order to reuse the etching solution, a regeneration process of oxidizing the reduced ferric chloride back to ferric chloride is required.

In general, a method of oxidizing an aqueous ferric chloride solution is a method of oxidizing ferric chloride (FeCl ₂ ) by contact with oxygen gas [US Patent No. 6,682,592] and a method of oxidizing by contact with chlorine gas [US Patent Registration No. 4,066,748, European Patent 340,070. Among the above methods, chlorine gas is used to oxidize ferrous chloride in aqueous solution, which is represented by the following Scheme 1.

Scheme 1

The reaction is exothermic and occurs spontaneously at room temperature and the reaction rate is very fast.

In a continuous process patent using a two-stage reactor [US Pat. No. 4,066,748], the ferric chloride aqueous solution is countercurrently contacted with excess chlorine gas in the primary reactor to oxidize ferric chloride and unreacted chlorine gas passes through the secondary reactor. To countercurrent contact with the ferric chloride aqueous solution. The aqueous iron chloride solution completed in the first reactor is discharged to the product, and the partially oxidized iron chloride solution in the secondary reactor is circulated back to the first reactor to complete the reaction. This process requires two or more reactors and is described to supply the reaction equivalent of chlorine gas, but there is no mention of feed rate. Therefore, in this method, sufficient reaction time (chlorine gas contact time) is required to complete the reaction in the primary reactor, and excess chlorine gas must be introduced. As a result, chlorine gas is dissolved in an aqueous solution completely oxidized with ferric chloride, with unreacted chlorine gas being excessively passed to the secondary reactor. When the ferric chloride aqueous solution in which chlorine gas remains is used or used as an etching solution, chlorine gas is discharged during transfer or during etching.

In European Patent No. 340,070, one filling tower is used to continuously feed chlorine gas containing some inert gas into the bottom of the tower, supply ferrous chloride solution to the top, and make countercurrent gas-liquid contact well. A method of oxidizing ferrous chloride has been proposed. When using chlorine gas containing an inert gas can increase the gas-liquid contact area, but there is a problem that unreacted chlorine gas remains in the bubble. The patent also discloses a method in which an excess amount of ferric chloride aqueous solution is supplied in the middle of the tower to ensure sufficient gas-liquid contact. In order to fully react the injected chlorine gas and to completely oxidize ferrous chloride, sufficient contact time is required along with a sufficient gas-liquid contact area, which causes an excessively large device. In addition, there is a problem that chlorine gas can not be completely reacted according to the use of inert gas.

As described above, a method of oxidizing a ferric chloride solution to a ferric chloride solution using chlorine gas has already been proposed, and various methods for preparing a ferric chloride solution by a continuous reaction have also been proposed. However, there is no suggestion on how to efficiently introduce chlorine gas, that is, the proper rate of chlorine gas depending on the concentration of ferrous chloride in the aqueous solution. The method of oxidizing the ferric chloride aqueous solution to chlorine gas may be a batch method in which, in addition to the continuous method mentioned above, the aqueous iron chloride solution is placed in a reactor and continuously supplied with chlorine gas. In this batch method, the control of the feed rate of chlorine gas according to the concentration of ferric chloride is a very important operation factor to determine the production amount, because it is necessary to reduce the reaction time by supplying as much chlorine gas as possible while suppressing the discharge of unreacted chlorine gas.

An object of the present invention is to provide a chlorine gas input method for effectively shortening the reaction time in oxidizing the ferric chloride aqueous solution containing ferric chloride with chlorine gas to regenerate the ferric chloride aqueous solution. In other words, it is to provide a method for determining the input rate of the chlorine gas so as to supply the chlorine gas required for the reaction as soon as possible while not reacting the unreacted chlorine gas.

1 is a block diagram of a batch oxidation apparatus for oxidizing the aqueous iron chloride solution according to the present invention.

2 is a graph showing the relationship between the concentration of ferric chloride, the amount of circulation of the iron chloride aqueous solution and the chlorine gas injection rate.

[Description of Symbols for Main Parts of Drawing]

1: reactor

2: circulation pump

3: heat exchanger

4: storage tank

The present invention provides a method of oxidizing ferrous chloride to ferric chloride by supplying chlorine gas to an aqueous solution of iron chloride,

It is characterized by the method of controlling the input speed of the chlorine gas according to the following equation (1).

Equation 1

C _max / W _circ ∝ F _conc

In Equation 1: C _max is the chlorine gas input rate (kg / hr), W _circ is the circulation amount of the iron chloride solution (kg / hr), F _conc is the concentration of ferrous chloride (wt%).

Such a chlorine gas supply method according to the present invention is configured based on the following principle.

According to Scheme 1, the reaction rate at which ferric chloride (FeCl ₃ ) is produced is dependent on the amount of chlorine gas (Cl ₂ ) and the concentration of ferrous chloride (FeCl ₂ ) as reactants when the type of the reactor is the same. In the case of a batch reactor, the opportunity for the reaction of chlorine gas in the gas phase to react with ferric chloride is very high in the early stage of the reaction with high concentration of ferric chloride, and the reaction rate gradually decreases as the concentration of ferrous chloride decreases. Will also be lowered. That is, when chlorine gas is supplied at a constant flow rate, unreacted chlorine gas is not discharged at the initial reaction of high concentration of ferrous chloride as a reactant, but unreacted chlorine gas is discharged at the end of the reaction when the concentration of ferrous chloride is lowered.

This phenomenon occurs not only in a batch process but also in a continuous process. The reaction rate with chlorine gas is determined according to the concentration of ferric chloride in the iron chloride solution supplied or circulated to the reactants under constant reaction equipment and reaction conditions (temperature, pressure, etc.). Emissions of gas or unreacted ferric chloride remain in the aqueous solution.

The chlorine gas supply method of the present invention based on this principle will be described in more detail as follows. In the present invention, an arbitrary reactor is selected, and the exact equations based on 'concentration of ferrous chloride', 'chlorine gas input rate' and 'circulating amount of aqueous iron chloride solution' are found. Then, by substituting 'circulation amount of iron chloride solution' and 'concentration of ferrous chloride' into the above equation, the optimum chlorine gas input rate is estimated, and chlorine gas is not supplied by supplying chlorine gas according to this rate. It can be controlled so as not to overdose.

That is, the oxidation of ferrous chloride is first performed at an arbitrary reactor and reaction temperature to find the values of the constants k and b in Equation 2 below.

Equation 2

C _max / W _circ = k × F _conc + b

In equation (2): C _max is the maximum possible chlorine gas input rate (kg / hr), W _circ is the flow rate of the iron chloride solution circulated (in contact with chlorine gas) (kg / hr), F _conc is the aqueous solution Is the concentration of ferrous chloride in weight percent, and k and b are arbitrary constants.

At this time, the reaction temperature is maintained while changing the factors of 'concentration of ferrous chloride' and 'circulation amount of the iron chloride solution' which may affect the reaction rate, and the chlorine gas is discharged unreacted chlorine gas Check the 'maximum chlorine gas feed rate' by inputting to the point. And, through these relationships it is possible to calculate the value of k and b, the value of k and b may vary depending on the type of reactor or the reaction temperature. As a reaction apparatus that can be used here, for example, there is a device combining the reaction portion and the circulation portion as shown in Figure 1, in the case of Figure 1 reactor (1), circulation pump (2), heat exchanger (3), It consists of a storage tank (4) and corresponds to a batch device. Referring to the path of the reactants according to this device, first the aqueous solution of iron chloride is introduced into the storage tank (4) made of fiber-reinforced plastic (FRP), and then the reactor installed on the storage tank (4) using the circulation pump ( Circulate 1) through the storage tank. Here, the circulating iron chloride aqueous solution is adjusted to pass through the heat exchanger (3) to be a constant temperature before entering the reactor, the oxidation reaction is preferably carried out in a temperature range of 40 ~ 80 ℃, the reactor (1) The furnace may be a column-type packed column or ejector. In addition, the total concentration of ferric chloride and ferric chloride contained in the iron chloride solution is preferably 0.1 to 50% by weight, and the concentration of ferrous chloride is preferably 0.1% by weight or more. The present invention may proceed in a batch manner using the reaction apparatus, or may proceed continuously in a continuous reaction apparatus.

In this way, it was confirmed that the 'maximum chlorine gas input rate' in which unreacted chlorine gas is not discharged is proportional to the concentration of ferrous chloride and the circulation amount of the aqueous iron chloride solution, and this relationship is shown in FIG. Follow Equation 2. In addition, the values of k and b may vary depending on the type of reactor and the reaction temperature, but Equation 2 has been experimentally confirmed that it can be generally applied in the oxidation reaction of ferric chloride aqueous solution by chlorine gas. In this case, in the case of reacting in a batch manner, the optimum chlorine gas input rate is predicted at a time by substituting the circulation amount of the aqueous iron chloride solution and the changing concentration of ferrous chloride into the above equation as the reaction proceeds. At the same time, the chlorine gas input rate should be controlled, so that the analysis of the ferric chloride concentration and the adjustment of the chlorine gas input rate accordingly will be able to utilize the present invention more simply and efficiently.

Hereinafter, the present invention will be described in more detail based on the following examples, which are not intended to limit the present invention. Examples of changes in the constants according to the reactor and the effects of the present invention may be obtained through the following examples. It will certainly prove.

Example 1 In the case of using a column-type packed column as a reactor at a reaction temperature of 70 ℃

Ferric chloride solution containing 33.7% by weight of FeCl _{2 and} 1.8% by weight of FeCl ₃ in a 1.8 m3 FRP tank equipped with an internal diameter of 250 mm, a height of 2.4 m, and a 3/8 inch polypropylene Pall ring reactor made of FRP. 500 liters was charged. Using a pump, the solution of the tank was adjusted to 70 ° C. through a heat exchanger, and then introduced into the reactor at a constant flow rate (100 l / min) to circulate into the tank. At this time, the reaction was carried out in a batch until the ferric chloride concentration is from 33.7% by weight to about 0.5% by weight, and chlorine gas was supplied to the bottom of the reactor at a flow rate in which unreacted chlorine gas was not discharged. The discharge of unreacted chlorine gas is chlorine gas detector by continuously sampling the gas discharged from the upper part of the reactor where nitrogen gas injected with a small amount for analysis is discharged along with chlorine gas (product of Mars Instruments Co., Ltd., model TS-2000CL2). ). Through repeated experiments, it was confirmed that the 'maximum chlorine gas input rate' according to 'ferrous chloride concentration' changed as shown in Table 1 below.

As a result, the tendency of Equation 1 shown in the graph of FIG. 2 was confirmed, and for Equation 2, constants k and b were calculated to be 0.196 × 10 ⁻³ and 1.65 × 10 ⁻³ , respectively. As a result of performing the oxidation reaction while changing the supply flow rate of chlorine gas according to the completed equation, 66.9 kg of chlorine gas required for oxidation can be supplied in 2.4 hours without chlorine gas discharge. At this time, the aqueous solution was taken every 30 minutes to check the concentration of ferric chloride by wet analysis, and after completing the supply of the required chlorine gas, the concentration of the iron chloride solution was circulated for another 1 hour to analyze the concentration, FeCl ₂ 0.3% by weight, FeCl _{3 The} oxidation rate was 99.3% at 44.6% by weight.

Example 2 In the case of using a column-type packed column as a reactor at a reaction temperature of 50 ℃

The same amount and concentration of iron chloride solution was oxidized in the same manner as in Example 1, but the temperature of the circulated solution was 50 ° C. As shown in Example 1, the 'maximum chlorine gas input rate' according to the 'iron iron chloride concentration' could be expressed by the above equation, and the constants k and b were calculated as 0.131 × 10 ^-3 and 1.84 × 10 ^-3 , respectively. . In addition, when the supply flow rate of chlorine gas was changed according to the equation, 66.9 kg of chlorine gas required for oxidation could be supplied in 3.6 hours without chlorine gas discharge. After completion of the required chlorine gas was supplied to 1 more hour cycle the iron chloride aqueous solution analyzed concentration, FeCl ₂ 0.4% by weight, 44.4% by weight of FeCl ₃ in oxidation rate was 98.8%.

Example 3 In the case of using an ejector as an reactor

Titanium ejectors were used instead of column-type packed towers as reactors to promote gas (chlorine gas) -liquid (iron chloride solution) contact reactions. Aqueous solution of iron chloride was circulated to the ejector having a diameter of 1 inch and a length of 35 cm, and chlorine gas was simultaneously supplied. At this time, the temperature of the aqueous solution was adjusted to 70 ℃, the circulation amount of the aqueous iron chloride solution was to be 100 l / min as in Example 1, the solution in contact with the chlorine gas in the ejector was configured to circulate into the solution in the tank. . As shown in Example 1, the 'maximum chlorine gas input rate' according to the 'iron iron chloride concentration' could be expressed by the above Equation 2, and the constants k and b were calculated as 0.234 × 10 ⁻³ and 1.41 × 10 ⁻³ , respectively. It became. In addition, when the supply flow rate of chlorine gas was changed according to the equation, 66.9 kg of chlorine gas required for oxidation could be supplied in 2.1 hours without chlorine gas discharge. As a result of after completion of the supply of the chlorine gas required by the ferric chloride aqueous solution one more time circulation analyzing the concentration, 0.2% by weight of FeCl _2, FeCl ₃ 44.7% by weight of oxidation rate was 99.5%.

Comparative Example 1

The aqueous solution of iron chloride in the same amount and concentration as in Example 1 was oxidized, but was added while maintaining a constant rate of 27.875 kg / hr so that 66.9 kg of chlorine gas required to oxidize all of the iron chloride aqueous solution could be added in 2.4 hours. Unreacted chlorine gas was released when the concentration of ferrous chloride reached 8.2 wt% after 1.9 hours of chlorine gas injection. The reaction was continued under the condition that the unreacted chlorine gas was discharged, and the chlorine gas injection was stopped in 66.9 kg and 2.4 hours, which was the planned chlorine gas input time, and the concentration of the unreacted ferrous chloride was 6.1% by weight. The ferrous chloride concentration was lowered to 0.8% by weight when 1.4 wt% was further fed at the same chlorine gas input rate to completely react the unreacted ferric chloride. The concentration was analyzed by further circulating for 1 hour. As a result, 0.01 wt% FeCl ₂ and 44.9 wt% FeCl ₃ were present, and chlorine gas remained in the aqueous iron chloride solution.

As described above, the chlorine gas supply method for the oxidation of the ferric chloride aqueous solution according to the present invention by optimizing the chlorine gas supply method using the relationship between the concentration change of the reactant and the reaction rate, the iron chloride in a shorter time than the conventional Terminating the oxidation reaction of the has the effect of preventing the remaining or discharge of chlorine gas. In addition, in order to oxidize the iron chloride aqueous solution to chlorine gas by a continuous process, the input rate of chlorine gas suitable for the concentration of the aqueous solution is specified, so that the most efficient use of the reactor and of course, no excess chlorine gas is used.

Claims (7)

In the method of supplying chlorine gas to an aqueous solution of iron chloride to oxidize ferrous chloride to ferric chloride, Chlorine gas supply method for the oxidation of the ferric chloride aqueous solution, characterized in that for adjusting the input rate of chlorine gas according to the following equation (1). Equation 1 C _max / W _circ ∝ F _conc In Equation 1: C _max is the chlorine gas input rate (kg / hr), W _circ is the circulation amount of the iron chloride solution (kg / hr), F _conc is the concentration of ferrous chloride (wt%). According to claim 1, wherein the total concentration of ferric chloride and ferric chloride contained in the aqueous solution of iron chloride is in the range of 0.1 to 50% by weight, the concentration of ferric chloride is at least 0.1% by weight of chlorine for the oxidation of the ferric chloride solution Gas supply method. The method of claim 1, wherein the oxidation reaction is carried out at a temperature range of 40 ~ 80 ℃ chlorine gas supply method for the oxidation of the ferric chloride aqueous solution. The method of claim 1, wherein the oxidation reaction is performed according to a batch operation method, and the chlorine gas supply method for the oxidation of the ferric chloride aqueous solution, characterized in that continuously changing the input rate of the chlorine gas according to the equation (1). The method of claim 1, wherein the oxidation reaction is performed according to a continuous operation method, and the chlorine gas supply method for the oxidation of the ferric chloride aqueous solution, characterized in that for changing the input rate of the chlorine gas according to the equation (1). The method of claim 1, wherein the reactor is a column-type packed column chlorine gas supply method for the oxidation of the ferric chloride aqueous solution. The method of claim 1, wherein the reactor is an ejector (ejector).