JP2012184312A - Method of producing antifreezing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an antifreezing agent, wherein the antifreezing agent that meets the hazardous substance emission standards and that has excellent anticaking properties can be produced economically and efficiently from emission gas.SOLUTION: The method includes: a dust-removal bagfilter step of removing heavy metal particles; a desalination bagfilter step of spraying NaHCOto the emission gas separated through the dust-removal bagfilter step to capture desalted residues including NaCl and NaCOby a solid phase; a first NaCl-producing step of dissolving the desalted residues in water to produce an aqueous solution, then adding hydrochloric acid to the aqueous solution for acidification, thereby producing NaCl; a second NaCl-producing step of adding NaOH to the aqueous solution produced through the first NaCl-producing step to have pH of 6 to 7, thereby producing the NaCl; and a solid NaCl-producing step of producing the solid NaCl from the aqueous solution produced through the second NaCl-producing step.

Description

  The present invention relates to a method for producing an antifreezing agent, and more particularly to a method for producing an antifreezing agent for producing an anti-caking agent having a high anti-caking property from exhaust gas generated from a waste incineration facility.

  The “Act on the Prevention of Spike Tire Dust Generation” was enacted in fiscal 1990, and in recent years there are almost no vehicles equipped with spike tires. Began to occur.

  As countermeasures, road managers generally respond by spreading sodium chloride, which has an excellent anti-freezing effect, on the road surface as an anti-freezing agent, but further enhancement of road surface management is required. The amount of sodium chloride used is increasing year by year.

  According to the quality regulations established by the Ministry of Land, Infrastructure, Transport and Tourism Road Bureau National Road and Disaster Prevention Section Road Disaster Prevention Measures Committee in March 2004, anti-freezing agents are determined by the Water Pollution Control Law. It is considered appropriate to comply with the wastewater standards (Table 1).

  On the other hand, the treatment technology of the exhaust gas generated by incineration of waste or the like has attracted attention from the viewpoint of environmental protection.

  In particular, when the waste contains chlorinated substances such as vinyl chloride and heavy metals, the exhaust gas contains hydrogen chloride and heavy metals, and the environmental destruction is serious.

  Patent Document 1 discloses a technique for separating these hydrogen chloride and heavy metals from exhaust gas and producing an industrial aqueous sodium chloride solution.

Japanese Patent No. 3390433

  This inventor earnestly examined about manufacturing an antifreezing agent from waste gas, and paid its attention to the technique which manufactures the industrial sodium chloride aqueous solution disclosed by patent document 1. FIG.

  First, the technique of Patent Document 1 includes three techniques.

  The first is a dry solid residue recovery process. In this step, sodium hydrogen carbonate is reacted with hydrogen chloride in the exhaust gas to produce sodium chloride, and a solid residue containing solid sodium chloride and heavy metal is recovered.

  The second is a wet heavy metal treatment process. In this step, heavy metals are coagulated and separated from an aqueous solution containing sodium chloride and heavy metals. In Patent Document 1, an aqueous solution is made alkaline (pH 8 to 14) in order to precipitate heavy metals. Patent Document 1 lists Cd, Hg, Sb, Pb, Co, Cr, Cu, Mn, V, Sn, Fe, Ni, Al, Zn, and the like as heavy metals contained in the exhaust gas. Some of these heavy metals precipitate on the alkali side, but Pb, Cr, Sn, Al, and Zn are so-called amphoteric metals and have the property of dissolving in an alkaline solution. For this reason, there is a serious problem that heavy metals that do not precipitate at pH 8 to 14 are not separated. Therefore, the third processing step described below is essential.

  That is, as a third treatment step of Patent Document 1, a sodium chloride solution contaminated with heavy metals, which are harmful substances, is treated with a chelate resin.

  However, the chelate resin is considerably expensive, has a high initial cost, is rapidly deteriorated, and causes an increase in running cost. In particular, in the production of an antifreezing agent that requires a large amount of sodium chloride, the use of such a high-cost processing step does not satisfy practicality.

  Thus, the technique of Patent Document 1 is not suitable for the production of an antifreezing agent.

  Furthermore, in general, flexible containers (hereinafter abbreviated as “flexible containers”) are often used for storage of sodium chloride because of its ease of transport and loading, etc., and in the winter, each office and office is ready for spraying. The flexible containers are stored in two or three layers in a chemical warehouse or warehouse such as the snow removal station.

  However, there is a problem that sodium chloride during storage congeals, causing obstacles to work and adverse effects on the spraying machine.

  Accordingly, an object of the present invention is to produce an antifreeze agent that economically and efficiently produces an antifreeze agent that satisfies the emission standards of harmful substances and has high anti-caking properties from exhaust gas generated from a waste incineration facility or the like. It is to provide a method.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

(Claim 1)
In the method for producing a cryoprotectant mainly composed of sodium chloride,
A dust-removing bug filter process that removes the heavy metal fine particles by treating exhaust gas containing at least hydrogen chloride and heavy metal fine particles generated from a garbage incineration facility with a dust-removing bug filter;
Sodium hydrogen carbonate is sprayed on the exhaust gas separated in the dust-removing bag filter process to react with hydrogen chloride gas in the exhaust gas, and the reaction product sodium chloride and unreacted sodium bicarbonate are thermally decomposed. A desalting bag filter step for collecting the desalting residue containing sodium carbonate generated in the solid phase,
A desalting residue collected in the desalting bag filter step is dissolved in water to form an aqueous solution and acidified by adding hydrochloric acid to produce sodium chloride as a reaction product of hydrochloric acid and sodium carbonate. A sodium chloride production step;
2nd sodium chloride which adds sodium hydroxide to the aqueous solution produced | generated at the said 1st sodium chloride production | generation process so that it may become pH 6-7, and produces | generates sodium chloride as a reaction product of hydrochloric acid and sodium hydroxide Generation process;
A solid sodium chloride production step for producing solid sodium chloride from the aqueous solution produced in the second sodium chloride production step;
A method for producing an antifreezing agent, comprising:

(Claim 2)
The exhaust gas contains fluorine gas, and calcium chloride is added to the aqueous solution between the second sodium chloride production step and the solid sodium chloride production step to produce sodium chloride by the following reaction. The method for producing an antifreezing agent according to claim 1, further comprising a third sodium chloride production step for capturing fluorine in a solid phase and removing fluorine.
2NaF (soluble) + CaCl ₂ → 2NaCl + CaF ₂ (precipitation)

(Claim 3)
The amount of calcium chloride added in the third sodium chloride production step is an excess amount equal to or more than an equivalent amount necessary for the reaction as long as the purity of sodium chloride in the cryoprotectant can be maintained at 95% or more The method for producing an antifreezing agent according to claim 2.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the antifreezing agent which manufactures the antifreezing agent with high anti-caking property economically and efficiently from the waste gas generated from a garbage incineration plant etc. can be provided.

It is a block flow figure showing the manufacturing method of the antifreezing agent concerning the present invention.

  Hereinafter, the present invention will be described based on preferred embodiments.

  In the present invention, the exhaust gas is exhaust gas generated from a waste incineration facility or the like, and these exhaust gases include at least hydrogen chloride and heavy metal fine particles.

  These exhaust gases are used as raw materials for the production of antifreezing agents. Examples of the heavy metal fine particles contained in the exhaust gas include one or more fine particles such as Cd, Hg, Sb, Pb, Co, Cr, Cu, Mn, V, Sn, Fe, Ni, Al, and Zn.

  As shown in FIG. 1, the method for producing an antifreezing agent of the present invention comprises a dust removal bag filter step 1, a desalting bag filter step 2, a first sodium chloride production step 3, and a second sodium chloride production step. 4 and solid sodium chloride production step 5. As a preferred embodiment, a third sodium chloride production step 6 is provided between the second sodium chloride production step 4 and the solid sodium chloride production step 5.

  The dust removal bag filter step 1 includes a dust removal bug filter, and separates ash and heavy metal fine particles contained in the introduced exhaust gas.

  In the present invention, it is important to separate and remove heavy metal fine particles contained in the exhaust gas, such as Cd, Sb, Pb, Co, Cr, Cu, Mn, V, Sn, Fe, Ni, Al, Zn, etc. The fine particles are separated and removed, and the fine particles that cause a quality problem as an antifreezing agent are removed from the exhaust gas.

  In addition, by using the dust removal bag filter, amphoteric metal fine particles such as Pb, Cr, Sn, Al, and Zn, which were difficult to remove by the alkali treatment of the solution in the prior art, are also removed. There is an effect that becomes unnecessary.

  As the dust removal bag filter, a filter medium having a property that the DOP particle blocking rate is 99.9% or more is used from the viewpoint of removing fine particles which are problematic in quality as an antifreezing agent from the exhaust gas. The DOP particle blocking rate is indicated as a ratio (100 fraction) at which DOP particles (dioctyl phthalate aerosol having a particle size of 0.5 μm) can be prevented from passing through the filter medium under a wind speed of 3.2 m / min. .

  The particle diameter of the heavy metal particles contained in the exhaust gas is in the range of 1 μm to 500 μm, and the same applies to other fine particles. Accordingly, these heavy metal fine particles can be removed with a dust-removing bag filter having the above performance.

  The dust-removing bag filter material is preferably a heat-resistant material because the temperature of the exhaust gas is preferably in the range of 100 to 250 ° C., more preferably 150 to 200 ° C. Further, the corrosiveness of hydrogen chloride Is considered to be a corrosion-resistant material, for example, PTFE felt, a glass woven fabric processed with a PTFE membrane, and the like. Among them, a glass woven fabric processed with a PTFE membrane is preferable.

  The desalting bag filter step 2 includes a desalting bag filter, the exhaust gas from which heavy metal fine particles have been removed in the dust removing bag filter step 1 is introduced into the desalting bag filter, and sodium bicarbonate is sprayed into the desalting bag filter. To react with hydrogen chloride gas to produce sodium chloride (salt).

  In order to add sodium hydrogen carbonate to the exhaust gas, it is preferable to supply sodium hydrogen carbonate as a powder having a particle size of 5 μm to 40 μm.

  Sodium bicarbonate generates sodium chloride as a desalted residue in the solid phase by the following reaction with gaseous hydrogen chloride present in the exhaust gas.

HCl + NaHCO ₃ → NaCl + CO ₂ + H ₂ O

  The exhaust gas introduced into the desalting bag filter step 2 may contain hydrogen fluoride, and when it contains hydrogen fluoride, sodium fluoride by-produced by the following reaction is contained in the desalting residue.

HF + NaHCO ₃ → NaF + CO ₂ + H ₂ O

  As a result, the desalting residue containing the reaction products sodium chloride and sodium fluoride is captured by the desalting bag filter.

  Moreover, the unreacted part with the exhaust gas component in the sprayed sodium hydrogen carbonate is captured as sodium carbonate by being thermally decomposed and included in the desalting residue. As described above, when the temperature of the exhaust gas is preferably in the range of 100 to 250 ° C, more preferably in the range of 150 to 200 ° C, unreacted sodium hydrogen carbonate is suitably thermally decomposed into sodium carbonate.

  On the other hand, the exhaust gas that has passed through the desalting bag filter can be diffused into the atmosphere after heat recovery. In the subsequent crystallization, it may be used as a heat source.

  The filter included in the desalting bag filter used in the desalting bag filter step 2 of the present invention desirably has a high DOP particle blocking rate in consideration of being released to the atmosphere after passing through the filter. Specifically, it is preferable to use a filter medium having a characteristic that the DOP particle rejection is 99.9% or more.

  The particle size of the desalted residue produced is in the range of 5 μm to 40 μm, and if a filter material made of glass woven fabric having a DOP particle blocking rate of 99.9% or more is used, the desalted residue is preferably captured. Can be collected.

  The present invention collects heavy metal fine particles with the first-stage dust-removing bag filter and allows hydrogen chloride to pass through in the form of a gas. After the reaction with sodium hydrogen carbonate, the heavy metal fine particles are removed with the second-stage desalting bag filter. It is possible to recover a desalted residue mainly composed of the removed salt.

  The present inventor uses the dust removal bag filter step 1 and the desalination bag filter step 2 together, actually conducts a test for passing exhaust gas through this, conducts component analysis of the collected matter in the desalination bag filter, and removes fluorine and mercury. In addition, it has been confirmed that it is possible to recover desalted residues that satisfy the criteria for antifreezing agents for heavy metals (Table 2).

  On the other hand, in the case where only the dust removal bag filter step 1 or the case of only the desalting bag filter step 2 is tested, Zn, Pb, in addition to fluorine and mercury, are collected from the recovered residue. It has been confirmed that Cu may be detected in excess of the reference value of the antifreezing agent.

  In each of the above tests, the filter cloth of the dust removal bag filter was a glass woven cloth processed with a PTFE membrane, and the filter cloth of the desalting bag filter was a glass woven cloth.

  In the case of only the dust removal bag filter step 1 or only in the case of the desalination bag filter step 2, Zn, Pb and Cu, in addition to fluorine and mercury, exceed the standard value of the antifreezing agent in the desalination residue. In addition, conventionally, a process of adding a hydroxide or the like to perform a precipitation treatment under an alkaline condition or a treatment with a chelate resin is required, and this is a problem of high cost and low efficiency when producing an antifreezing agent. was there.

  On the other hand, in the present invention, except for fluorine and mercury, it is possible to recover a desalted residue that satisfies the criteria of antifreezing agents for heavy metals, so that under alkaline conditions by adding a hydroxide or the like A step of performing a precipitation treatment or a treatment with a chelate resin becomes unnecessary.

  In the present invention, it is only necessary to remove only fluorine and mercury as necessary in the subsequent processing. Therefore, as will be described in detail later, in the present invention, a removal method that is low in cost and simple and leads to an increase in the yield of the cryoprotectant can be suitably used for removing fluorine and mercury.

  The 1st sodium chloride production | generation process 3 is equipped with a salt dissolution tank, introduce | transduces the desalination residue collected by the solid phase in the desalination bag filter process 2, and melt | dissolves in water, and produces | generates aqueous solution.

  The residence time (tank volume) of the salt dissolution tank may be any time or volume in which sodium chloride (salt), which is a soluble substance in the desalting residue, dissolves, and the dissolved water is not particularly limited, but will be described later. The condensed water produced by the analysis can be preferably used.

  Furthermore, in the 1st sodium chloride production | generation process 3, while producing | generating an aqueous solution as mentioned above, this aqueous solution is acidified by addition of hydrochloric acid. Specifically, the pH of the aqueous solution is preferably in the range of 3 to 6, more preferably 3 to 5.

In the present invention, by using sodium hydrogen carbonate in the desalting bag filter step 2, the desalting residue contains sodium carbonate (Na ₂ CO ₃ ) as a thermal decomposition product or as an impurity of sodium hydrogen carbonate. ing.

  Accordingly, by adding hydrochloric acid, the aqueous solution is preferably acidified within the range of pH 3 to 6, more preferably 3 to 5, so that sodium chloride is produced as a reaction product of hydrochloric acid and sodium carbonate.

  The 1st sodium chloride production | generation process 3 may each be equipped with the 1st sodium chloride production | generation tank for producing | generating sodium chloride separately from the salt dissolution tank mentioned above, and even if one tank serves as these. Good.

  Further, in the first sodium chloride production step 3, hydrochloric acid may be added at any timing before or after the desalted residue is dissolved in water. For example, it is also preferable to dissolve the desalted residue in water in which hydrochloric acid has been previously dissolved to produce an aqueous solution because of the effect of improving the dissolution rate of the desalted residue.

  As described above, the present invention has one feature in that sodium constituting sodium carbonate is effectively used for improving the yield of the purified salt.

  Furthermore, by adjusting the pH to preferably 3 to 6, more preferably 3 to 5 by adding hydrochloric acid, it becomes possible to suitably remove carbonic acid from the solution by the following reaction.

Na ₂ CO ₃ + 2HCl → 2NaCl + CO ₂ + H ₂ O

  The second sodium chloride production step 4 includes a second sodium chloride production tank, and sodium hydroxide is added to the aqueous solution produced in the first sodium chloride production step 3 so that the pH is 6-7. Further sodium chloride is produced as a reaction product of hydrochloric acid added in the first sodium chloride production step 3 and sodium hydroxide. Thereby, there exists an effect which the yield of refined salt improves further.

  In this invention, the 3rd sodium chloride production | generation process 6 provided as a preferable aspect is equipped with the 3rd sodium chloride production | generation tank, and adds calcium chloride to the aqueous solution sent from the 2nd sodium chloride production | generation process 4. FIG.

  Thereby, three important effects described below can be obtained.

  First, as shown in the following formula, when sodium fluoride derived from exhaust gas is present in an aqueous solution, calcium chloride reacts with sodium fluoride to generate sodium chloride. This makes it possible to further improve the yield of the purified salt.

2NaF (soluble) + CaCl ₂ → 2NaCl + CaF ₂ (precipitation)

  Secondly, in the above reaction, fluorine dissolved in the aqueous solution can be supplemented to the solid phase and removed. Thereby, it becomes easy for the refined salt obtained in the latter stage to satisfy the criteria as an antifreezing agent, and the harmlessness is further improved.

  Further, in the third sodium chloride production step, preferably, the calcium chloride is added in excess of the amount necessary for removing fluorine (equivalent amount required for the reaction), whereby the purified salt (antifreezing agent raw material) is solidified. There is an effect that the anti-settling property can be improved.

  That is, the excessively added calcium chloride is contained in the purified salt together with sodium chloride. Purified salt containing calcium chloride prevents the formation of dihydrate crystals by transferring water molecules in sodium chloride to calcium chloride due to the high hygroscopicity of calcium chloride, preventing caking during salt transport and storage In addition, when this is granulated to produce an antifreeze product, an effect of eliminating the trouble of releasing the caking is obtained.

  According to the quality regulations established in March 2004 by the National Road and Disaster Prevention Division Road Disaster Prevention Section Examination Committee of the Ministry of Land, Infrastructure, Transport and Tourism, the purity of sodium chloride used as an antifreezing agent is basically 95% or more. It is described to do. Therefore, the amount of calcium chloride to be excessively added in the calcium chloride addition step of the present invention is preferably excessively added within a range in which the purity of sodium chloride in the purified salt can be maintained at 95% or more.

  However, the amount of calcium chloride excessively added in the calcium chloride addition step of the present invention is not limited to the above range, and an appropriate amount can be excessively added. For example, the above-mentioned quality regulations by the Ministry of Land, Infrastructure, Transport and Tourism are only applicable to sodium chloride among chlorides used as antifreezing agents. Mixtures of sodium chloride and other chlorides are not considered. Yes. On the other hand, regarding the anti-caking property of the antifreeze agent, a mixture of sodium chloride and calcium chloride was verified, and a study that a mixture containing 20 to 40% calcium chloride with respect to sodium chloride is excellent in anti-caking property. The results have also been reported (Shuji Miyamoto and four others, “Survey on Storage of Antifreeze Agents” Hokkaido Development Civil Engineering Research Institute Monthly Report No. 593, p. 36-41, October 2002).

  Calcium chloride also has the advantage that it is inexpensive and has no toxicity, so there is no problem in spraying it mixed with an antifreezing agent. Calcium chloride itself is also used as an antifreezing agent, and it is known that it is more effective than sodium chloride. It has been confirmed that an effect can be obtained with respect to improvement of immediate effect.

  As described above, in the present invention, the third sodium chloride production step makes it possible to improve the yield of sodium chloride, remove fluorine, and improve the properties as an antifreeze agent in one step. It is valid.

  The solid sodium chloride production step 5 is preferably a crystallization step, in which sodium chloride is precipitated and separated in the aqueous solution introduced into the storage tank by an evaporation method or a cooling method.

  In the present invention, as described above, since the concentration of sodium chloride in the solution is improved by the first to second sodium chloride production steps, preferably the first to third sodium chloride production steps, crystallization is performed. The crystallization speed and the amount of crystals produced in the process are improved, the efficiency of the crystallization process is improved, and the yield of the purified salt is improved.

  When the evaporation method is used as the crystallization step, as described above, the heat energy generated in the first to second sodium chloride generation steps, preferably the first to third sodium chloride generation steps, is effective as latent heat. Available. At that time, it is preferable to reuse the evaporated water as the solvent (water) in the first sodium chloride production step, as described above, in order to recover the condensed water as condensed water and effectively use the water resources.

  When the cooling method is used as the crystallization step, sodium chloride remains in the condensed water, and therefore, it is preferable to return it to the storage tank together with the salt water generated in the subsequent dehydration step in order to improve the yield.

  The salt precipitated in the crystallization step is recovered and subjected to a dehydration step to obtain an antifreezing agent. The dehydration step may be any as long as salt can be dehydrated, and preferred examples include a drying method and a centrifugal separation method.

  The salt water generated from the dehydration process is preferably returned to the storage tank and subjected to the crystallization process again in order to improve the yield.

  The water content of the purified salt obtained in the dehydration step is preferably 3% or less, and more preferably 1% or less. As described above, by sufficiently reducing the water content of the purified salt, it is possible to further improve the anti-caking property of the antifreezing agent.

In the present invention, the precipitate (CaF ₂ ) generated in the third sodium chloride production step 6 can be removed from the aqueous solution by including a sand filtration step.

  The sand filtration method used in the sand filtration step may be either a fixed bed type or a fluidized bed type, and the liquid flow direction may be either a downward flow method or an upward flow method.

  Since the components of the exhaust gas largely depend on the waste to be incinerated, there is a fact that the uncertain part is large. Therefore, hydrochloric acid, sodium hydroxide and calcium chloride used in the first to second sodium chloride production steps, preferably the first to third sodium chloride production steps, are suitable for decarboxylation, neutralization and fluorine removal, respectively. Therefore, it is desirable to add an excessive amount with a certain margin. In general, adding an excessive amount of reagent is considered to cause an increase in cost and other adverse effects. However, in the present invention, as described above, the first to second sodium chloride production is performed. In the process, preferably, the excess addition in the first to third sodium chloride production steps cooperates to increase production of sodium chloride, so that the yield of purified salt is improved, and further, the yield is improved. The purity is increased, and preferably the anti-caking property of the antifreezing agent is improved by the coexistence of calcium chloride.

  Furthermore, in the present invention, hydrochloric acid, sodium hydroxide and calcium chloride added in the first to second sodium chloride production steps, preferably the first to third sodium chloride production steps, all have a high heat of hydration. Since the heat of neutralization is generated, this heat energy can be retained and used as latent heat in the subsequent crystallization process, and the effect of reducing the energy cost can be obtained.

  By the way, in the present invention, heavy metals are removed in the dust-removing bag filter process described above. However, when Hg is contained, since the boiling point is significantly lower than other heavy metals, some of them evaporate in the exhaust gas. In some cases, it is relatively difficult to collect with a dust bag filter. In the present invention, in order to further remove Hg, the aqueous solution in which the desalted residue is dissolved is preferably subjected to the activated carbon adsorption step before being subjected to the crystallization step. Thereby, the harmlessness of the antifreezing agent is further improved.

  Activated carbon is inferior in adsorption to general heavy metals, but is known to exhibit high adsorption to Hg. In this invention, since heavy metals other than Hg are removed by the dust removal bag filter process, the activated carbon adsorption method can be preferably used. The activated carbon adsorption method has a merit that the cost is low, and is particularly suitable for a method for producing an antifreezing agent in which a large amount of purified salt needs to be produced. On the other hand, when the chelate resin adsorption method is used as the mercury removal step, it is not preferable because the step becomes expensive and impairs the practicality in the production method of the antifreezing agent that needs to produce a large amount of purified salt. .

  The purified salt obtained in the present invention may be used as it is as an antifreezing agent or may be used by appropriately adding additives.

1: Dedusting bag filter process 2: Desalination bag filter process 3: First sodium chloride production process 4: Second sodium chloride production process 5: Solid sodium chloride production process 6: Third sodium chloride production process

Claims (3)

In the method for producing a cryoprotectant mainly composed of sodium chloride,
A dust-removing bug filter process that removes the heavy metal fine particles by treating exhaust gas containing at least hydrogen chloride and heavy metal fine particles generated from a garbage incineration facility with a dust-removing bug filter;
Sodium hydrogen carbonate is sprayed on the exhaust gas separated in the dust-removing bag filter process to react with hydrogen chloride gas in the exhaust gas, and the reaction product sodium chloride and unreacted sodium bicarbonate are thermally decomposed. A desalting bag filter step for collecting the desalting residue containing sodium carbonate generated in the solid phase,
A desalting residue collected in the desalting bag filter step is dissolved in water to form an aqueous solution and acidified by adding hydrochloric acid to produce sodium chloride as a reaction product of hydrochloric acid and sodium carbonate. Sodium chloride production step;
2nd sodium chloride which adds sodium hydroxide to the aqueous solution produced | generated at the said 1st sodium chloride production | generation process so that it may become pH 6-7, and produces | generates sodium chloride as a reaction product of hydrochloric acid and sodium hydroxide Generation process;
A solid sodium chloride production step for producing solid sodium chloride from the aqueous solution produced in the second sodium chloride production step;
A method for producing an antifreezing agent, comprising: The exhaust gas contains fluorine gas, and calcium chloride is added to the aqueous solution between the second sodium chloride production step and the solid sodium chloride production step to produce sodium chloride by the following reaction. The method for producing an antifreezing agent according to claim 1, further comprising a third sodium chloride production step for capturing fluorine in a solid phase and removing fluorine.
2NaF (soluble) + CaCl ₂ → 2NaCl + CaF ₂ (precipitation)   The amount of calcium chloride added in the third sodium chloride production step is an excess amount equal to or more than an equivalent amount necessary for the reaction as long as the purity of sodium chloride in the cryoprotectant can be maintained at 95% or more. The method for producing an antifreezing agent according to claim 2.

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