JP2008189587A - Method for producing aqueous cyanamide solution and dicyandiamide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for separating a carbon component, a nitrogen component in a cyanamide form, and a calcium component each contained in nitrolime and co-producing carbon, an aqueous cyanamide solution or dicyandiamide, and calcium carbonate individually as three separate products, which method solves problems associated with a prior art technique that the calcium component and carbon component of nitrolime cannot be separated and the raw material is not effectively utilized upon producing an aqueous cyanamide solution or dicyandiamide from nitrolime. <P>SOLUTION: An aqueous solution of cyanamide is prepared by treating nitrolime obtained by nitriding calcium carbide with an aqueous solution containing cyanamide, removing carbon which is an insoluble component, subsequently treating the clear liquid with carbon dioxide gas, and separating the calcium component by precipitating it as calcium carbonate. The cyanamide solution thus obtained is subjected to a polymerization reaction under an alkaline condition to obtain dicyandiamide. The method described above is capable of concurrently separating and co-producing the three components using nitrolime as a starting material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

Cyanamide aqueous solutions and dicyandiamide produced from lime nitrogen are widely used as agricultural raw materials, pharmaceutical raw materials, or industrial raw materials such as epoxy curing agents, dye fixing agents, and flocculants. High-purity calcium carbonate is used as a filler and modifier for plastics, rubber, pulp, etc., and carbon is used as graphite, as an electrode material for batteries, or in fields such as rubber and pigments. ing.

An object of the present invention is to provide a production method with less environmental load by simultaneously producing calcium carbonate and carbon in producing cyanamide aqueous solution or dicyandiamide from lime nitrogen as a raw material, thereby reducing industrial waste.

Industrially utilized lime nitrogen is produced according to the following reaction formula by a nitriding reaction of carbide, and therefore it is inevitable that carbon components in the lime nitrogen are mixed.

In the prior art, in order to obtain a cyanamide solution, lime nitrogen is dispersed in water (USP-3,300,281) or alcohol (USP-5,017,355), carbon dioxide is blown in, and the generated insoluble calcium component and carbon are filtered out as a mixture. The cyanamide solution was obtained.

For example, US Pat. No. 3,300,281 is an excellent patent for continuously producing an aqueous cyanamide solution, but describes a method in which lime nitrogen is suspended in water and contacted with carbon dioxide.

Therefore, the produced calcium carbonate becomes a mixture with carbon.

The obtained cyanamide solution is easily polymerized by selecting reaction conditions to produce dicyandiamide.

Regarding the method for producing dicyandiamide from lime nitrogen, there is a prior art such as Japanese Patent Publication No. Sho-5-017,355 Canadian Chemical and Process Industries 805 (Dec. 1944). In this method, carbon dioxide gas is reacted with lime nitrogen dispersed in the lime nitrogen, and the produced calcium carbonate becomes a mixture with carbon.

For this reason, in the conventional method, in order to obtain an aqueous cyanamide solution, the filter residue can be used as a mixture of the generated calcium carbonate and carbon, so the fields that can be used are limited. It was only used as. In addition, the amount used is very small as a whole, and most of it is treated as industrial waste.

As described above, prior to the present invention, when producing an aqueous cyanamide solution or dicyandiamide, a method for separating and producing calcium carbonate in the filtration residue simultaneously with the carbon component has not been known.

When one ton of dicyandiamide is produced, about 4 tons of filtration residue are produced simultaneously. A part of the filtration residue is used as a raw material, but there is no great economic advantage, and many of them are treated as industrial waste, and a great burden is imposed on the treatment. The present invention relates to a method for separating and producing a mixture of calcium carbonate and carbon in a filtration residue, which is impossible in the prior art, into calcium carbonate and a carbon component which are industrially useful.

In the prior art, since the filtrate after separating water or dicyandiamide is used as a solvent for dispersing lime nitrogen, the concentration of cyanamide present therein is 1% or less. Therefore, when lime nitrogen is dispersed in water, the following reaction occurs.

However, the calcium hydroxide produced at the same time inhibits the reaction, the reaction does not proceed completely, and most of the cyanamide nitrogen remains in the solid content as an insoluble matter. , Was not considered.

Therefore, industrially, carbon dioxide gas was directly introduced into this suspension to devise a method for reducing the residual cyanamide nitrogen in the solid content, thereby obtaining an aqueous cyanamide solution.

For this reason, the filtration residue was a mixture of a carbon component and calcium carbonate.

The present inventors have found that when cyanamide is present when lime nitrogen is dispersed in water, acidic cyanamide calcium soluble in an aqueous solution is formed very quickly by the following reaction, and the present invention is completed. It came. That is, when an equimolar amount of cyanamide is present with respect to lime nitrogen in the aqueous solution, the following reaction is quickly completed, and cyanamide calcium in lime nitrogen is dissolved as acidic cyanamide calcium.

Carbon present in lime nitrogen is insoluble in water, while acidic cyanamide calcium is soluble in water. Impurities such as iron and silicon in lime nitrogen are insoluble in water and can be separated from the reaction solution together with carbon, so that the acidic cyanamide calcium aqueous solution can prevent these impurities from being mixed.

By treating with the transparent acidic cyanamide calcium aqueous solution thus obtained and carbon dioxide, the calcium component is precipitated from the reaction solution as highly water-soluble high-purity calcium carbonate by the reaction of the following (formula 7). Generate.

By filtering the precipitated calcium carbonate, a transparent aqueous solution containing cyanamide is obtained.
The cyanamide aqueous solution thus obtained can be returned to the step shown in Formula 6 to obtain a higher concentration of cyanamide aqueous solution, or dicyandiamide can be produced in accordance with Formula 8. It is industrially produced by diluting with, returning to Formula 6 and reusing and producing the remainder as a cyanamide aqueous solution, or adjusting the pH to 8 to 11 by adding an alkali component and producing dicyandiamide according to the following reaction (Formula 8) ,preferable.

In producing an aqueous dicyandiamide or cyanamide solution, an environmentally friendly and economical production method that simultaneously produces industrially useful calcium carbonate and carbon materials is provided.

As shown in Formula 6, it is desirable that the amount of cyanamide present in the solution to be used be present in an equimolar amount or more with respect to calcium cyanamide in the lime nitrogen to be added. Since cyanamide nitrogen in industrially produced lime nitrogen is 18% to 24%, an aqueous solution of cyanamide concentration of 1% requires 27 liters per 1 kg of lime nitrogen, increasing the actual equipment, The amount of solution processed is large and impractical. Further, if the cyanamide concentration exceeds 50%, the amount of cyanamide aqueous solution can be reduced to about 0.6 liters per 1 kg of lime nitrogen, which is advantageous. However, precipitation of diacid diamide by acid cyanamide calcium and dimerization are advantageous. Production needs to be taken into consideration, and it is disadvantageous to implement the patent in this case from an industrial perspective. To implement this patent, preferably 3% to 30% cyanamide aqueous solution is used, and more preferably 5% to 20% cyanamide aqueous solution is recommended.

The lime nitrogen used is preferably finely pulverized powder, but need not be extremely fine, but an average particle size of 20 to 200 microns is recommended.

When adding lime nitrogen to a cyanamide aqueous solution, it is preferable to stir, and the temperature is 60 ° C. or lower, preferably 40 ° C. or lower, especially when the production of a high-quality cyanamide aqueous solution is performed for 20 ° C. or lower. Is preferred.

The completion of the reaction of Formula 6 is practically determined by measuring the concentration of cyanamide and dicyandiamide in the solution. Usually completed in one hour in a batch reaction. Even in a continuous reaction, the reaction is substantially completed within a residence time of 1 hour. Insoluble carbon is filtered off to obtain a clear acidic cyanamide calcium aqueous solution.

The carbon content thus obtained can be used as it is as a plastic filler or fuel, but also contains impurities such as iron and silicon, so it must be washed with alkali and acid and further purified. You can also. The purified carbon can also be used as a pigment and an electrode material.

The higher the concentration of the carbon dioxide gas used in Formula 7, the better, but if there is a concentration of 10% or more, it can be used industrially. When using carbon dioxide gas from a lime furnace, it is preferable to use a concentration of 20% to 41%. Further, purified carbon dioxide gas of 99% or more may be used. However, it is necessary to reduce harmful components such as hydrogen sulfide, sulfurous acid, and ammonia as much as possible.

The reaction between the carbon dioxide gas and the acidic cyanamide calcium aqueous solution may be carried out by using a gas absorption tower or by introducing the acidic cyanamide calcium aqueous solution into the reaction tank and introducing the carbon dioxide gas from the bottom.

The pH of the reaction is kept at 10 or less, preferably 9 or less, suitably 8 or less. In particular, when producing a high-quality cyanamide aqueous solution, it is preferable to maintain the pH at 7 or less. However, in any case, it is practical to take a part of the reaction solution, analyze it, and determine the pH for the purpose of production.

The temperature is 60 ° C. or lower, preferably 40 ° C. or lower. In particular, when the purpose is to produce a high-quality cyanamide aqueous solution, the temperature is preferably 20 ° C or lower. On the other hand, if it is too low, the cost of cooling increases, which is industrially disadvantageous. Taking this into account, it is preferable to carry out at 0 ° C. or higher.

In order to produce dicyandiamide by the diamideization reaction of cyanamide, conventionally, alkaline components such as calcium hydroxide, sodium hydroxide and ammonia were made alkaline by adding cyanamide aqueous solution, but acidic cyanamide calcium aqueous solution was added to adjust the pH of cyanamide solution. It is preferable to set it as 8-11. The calcium component in the filtrate after separation of dicyandiamide is removed as calcium carbonate by carbon dioxide gas when reused, so that it does not accumulate in the reaction solution. Of course, when a filtration step is provided to remove insolubles after the dicyandiamide reaction, calcium hydroxide and lime nitrogen may be added as alkali components. On the other hand, when sodium hydroxide, ammonia, or the like is used, sodium ions and ammonium ions accumulate in the filtrate after separation of dicyandiamide, making it difficult to reuse.

The reaction temperature of dicyandiamide by the dimerization reaction is recommended to be 60-80 ° C. The reaction is completed within 4 hours, and the unreacted cyanamide concentration is 1% or less. If the temperature is lower than that, it takes a long reaction time, and if it is higher, the production of impurities increases, resulting in poor quality and yield.

In order to always produce high-quality cyanamide aqueous solution and / or dicyandiamide at a constant quality, a continuous production process is recommended, but considering the investment of production equipment, management level, and production scale, A manufacturing process can also be taken.

The calcium carbonate produced in the present invention is once dissolved in an aqueous solution as acidic cyanamide calcium, and impurities in the raw material can be removed. Therefore, the purity of calcium carbonate is extremely high, and a high-purity product having a purity of 99% or more must be obtained. Can do.

Hereinafter, in order to deepen the understanding of the present invention, examples and comparative examples will be shown and described. However, in order to carry out industrially, facilities should be created with reference to prior art and the like, and the implementation of the present invention is limited to this example. It is not a thing.

The quality of the lime nitrogen used is as follows: Cyanamide nitrogen 20.0%
Calcium content As CaO 64.0%
Average particle size 100 microns

Example of Batch Extraction Using 5% Cyanamide Aqueous Solution 200 g (pH 7.5) of a 5.00% cyanamide aqueous solution is placed in a 500 ml beaker equipped with a stirrer, and the beaker is cooled from outside. While stirring, 10 g of lime nitrogen is charged at once. Keep the temperature in the beaker below 20 ° C. After 10 minutes, the stirring is stopped and the contents are vacuum filtered using a 10 cm diameter Buchner funnel with filter paper. The insoluble matter on the filter paper is washed with a small amount of water and combined with the filtrate.

The main component of the insoluble matter on the filter paper was carbon, which was 2.83 g, contained 30% water, and the concentration of cyanamide nitrogen contained 0.17%. The black matter on the filter paper is treated with 5% caustic soda, washed with water, further treated with 5% hydrochloric acid, purified through a washing process, and dried.
1.17 g of black carbon was obtained.
Moisture 0.5%
Ashes 2.1%
Met.

The filtrate was transferred to a beaker, a tube was put into the liquid, and carbon dioxide gas was blown into it. As a result, a white precipitate immediately formed. Carbon dioxide gas was blown until the pH in the liquid showed 7, and the resulting calcium carbonate was separated by vacuum filtration using a Buchner funnel with a diameter of 10 cm on which filter paper was laid.
The calcium carbonate on the filter paper was washed with a small amount of water. When the picked calcium carbonate was dried, the yield was 11.1 g.
The analysis results of calcium carbonate were as follows.
Purity 99.8%,
Loss on drying 0.1%
Average particle size 20.7 microns,
Specific surface area 2100cm ² / g
Bulk specific gravity 0.65g / ml
It was heavy calcium carbonate.

Since the calcium carbonate purity in the natural limestone used for the manufacture of carbide was 95.6%, according to the present invention, extremely high-quality calcium carbonate could be obtained from low-grade limestone.

The filtrate thus obtained was 210 g and contained 5.85% cyanamide and 0.30% dicyandiamide.

The mass balance of cyanamide was calculated and evaluated as shown below.
{enter}
Number of moles of cyanamide in the lime nitrogen used 10 × 20% ÷ 28 × 1000 = 71.43 mmol
Added lime nitrogen 10.00g
20% cyanamide nitrogen in lime nitrogen
Molecular weight of nitrogen 2 atoms (N2) 28
Number of moles of cyanamide present in the aqueous cyanamide solution used 200 × 5% ÷ 42 × 1000 = 238.10 mmol
200g aqueous solution
Aqueous solution concentration 5%
Cyanamide molecular weight 42
{Out}
After the reaction, the number of moles of cyanamide present in the reaction solution 210 × 6.15% ÷ 42 × 1000 = 307.5 mmol
210 g of aqueous solution
Cyanamide equivalent concentration 5.85% + 0.30% = 6.15%

{Material balance}
The increase in cyanamide in the solution is
307.5-238.1 = 69.4mmol
And
The extraction efficiency from lime nitrogen was 69.4 ÷ 71.43 = 97.16%.

Example of Extraction by Batch Using Cyanamide Aqueous Solution Made in Example 1 Using the cyanamide aqueous solution made in Example 1 and performing the same operation as shown in Example 1, the cyanamide concentration 6.57% dicyan concentration 220 g of 0.65% liquid was obtained. When the mass balance was the same as in Example 1, the extraction efficiency was 98.0%.
By repeating this batch operation, a cyanamide solution with a higher concentration can be obtained.

{Comparative example}
For the purpose of further clarifying the present invention, an extraction experiment example using a dilute cyanamide aqueous solution as a comparative example is shown below.

The same operation as in Example 1 was performed except that the cyanamide concentration of the aqueous solution to be used was changed. However, the extraction processing time was not only 10 minutes, but an experiment with an extended extraction time was also added.
200 g of the aqueous solution was used, and 10.0 g of lime nitrogen was added all at once while stirring. After a predetermined time, the insoluble matter was filtered off, the insoluble matter was washed with a small amount of water, and the washing was combined with the filtrate. Carbon dioxide gas was blown into the filtrate thus obtained to precipitate calcium carbonate. The produced calcium carbonate was filtered, and the calcium carbonate was washed with a small amount of water. The washing was combined with the filtrate and adjusted to 205 g, and cyanamide and dicyandiamide in the filtrate were analyzed and evaluated. The calculation method followed the method described in Example 1.

以下に、その結果を示す。

シアナミド濃度が、高くなるに従って、抽出効率の向上が見られるが、２％以下では、効果が薄く、本発明を実施するのは困難である。

The results are shown below.

As the cyanamide concentration increases, the extraction efficiency is improved. However, when the cyanamide concentration is 2% or less, the effect is small and it is difficult to carry out the present invention.

Examples 1 and 2 showed examples with cyanamide concentrations of 5.0% and 6.15%, but the extraction efficiency was almost complete despite a short time of 10 minutes, 97.16%, 98.8. % Value is obtained. In order to carry out the present invention smoothly, it is preferable to use an aqueous cyanamide solution of 3% or more.

Example of continuous production of cyanamide aqueous solution A cyanamide aqueous solution was produced according to the production flow shown in FIG.
An aqueous solution having a cyanamide concentration of 5.00% is fed to a conical funnel indicated by 2 at a rate of 200 kg / hr. At the same time, ground lime nitrogen is added to the conical funnel at a rate of 20.00 Kg / Hr and mixed. A conical funnel is directly attached to the reaction tank A, and the introduction pipe indicated by 1 extends below the surface of the slurry water in the reaction tank A. The slurry (suspension) in the reaction tank A is supplied to the conical funnel through the pipe 3 and circulated. The reaction tank A was stirred, cooled from the outside, and kept at 15 ° C. or lower.

The liquid overflowing from the reaction tank A (overflow) is filtered through the filter A to remove insoluble solid content (black cake mainly composed of carbon). Further, the filter residue is washed with a small amount of water and combined with the filtrate. The filtration residue was a black powder and was dried with a drier kept at 105 ° C.

The clear filtrate is introduced into reaction vessel B. In the reaction tank B, 35% carbon dioxide gas was introduced from the bottom. The reaction tank B was kept at a pH of 7 or less and a reaction temperature of 20 ° C. or less.

When the white slurry liquid overflows from the reactor B, the supply of the 5.00% cyanamide aqueous solution is stopped, and instead the filtrate (clarified liquid) of the filter B is passed through the pipe 4 at a rate of 200 kg / hr. Supplied to the conical funnel indicated by 2 and circulated cyanamide aqueous solution.

The white calcium carbonate filtered off with the filter B was further washed with a small amount of water and combined with the filtrate.
The calcium carbonate was further dried with a drier kept at 105 ° C.

9 hours later, the concentration of cyanamide flowing through the pipe 4 reached 12%, so make-up water was added to the reaction tank A at a rate of 42 kg / hr, and at the same time the filtrate from the filter B was stored at a speed of 46.72 kg / hr. Extracted. In this way, a 12% cyanamide aqueous solution was continuously produced.

Addition of raw materials (input) under regular production conditions
Lime nitrogen 20.00Kg / Hr
Make-up water 42.0Kg / Hr
Production (out)
Cyanamide aqueous solution 46.72Kg / Hr
Cyanamide concentration 12.0%
Dicyandiamide concentration 0.2%
The yield of cyanamide based on the added lime nitrogen was 92.2%.
Calcium carbonate 22.5Kg / Hr
Purity 99.7%
Moisture 0.1%
Carbon component 3.6Kg / Hr
Moisture 0.5%
The result was obtained.

The 12.0% cyanamide aqueous solution was adjusted to pH 4-5 and concentrated under reduced pressure at 40 ° C. or lower using a rotary evaporator to obtain a transparent clear solution having a cyanamide concentration of 50%.
Dicyandiamide formation was negligible.
The analysis results were as follows.
Cyanamide concentration 50.0%
Dicyandiamide 1.1%
Urea 0.1% or less Thiourea 0.1% or less

In industrial production facilities, the filter is a filter press, drum filter, centrifugal filter, belt filter, Nutsche, etc., and the dryer is a vibratory fluid dryer, fluid dryer, stationary dryer, vacuum dryer, etc. In consideration of ease of use, efficiency, economy, etc., it can be selected according to the purpose.

Example of continuous production of dicyandiamide Dicyandiamide was produced according to the production flow shown in FIG.

An aqueous solution having a cyanamide concentration of 5.00% is fed to a conical funnel indicated by 2 at a rate of 200 kg / hr. At the same time, ground lime nitrogen is added to the conical funnel at a rate of 20.00 Kg / Hr and mixed. A conical funnel is directly attached to the reaction tank A, and an introduction pipe indicated by 1 extends below the slurry water surface of the reaction tank A. The slurry (suspension) in the reaction tank A is supplied to the conical funnel through the pipe 3 and circulated. The reaction vessel A was stirred and cooled from the outside and kept at 30 ° C. or lower.

The liquid overflowing from the reaction tank A (overflow) is filtered and removed through the filter A to remove insoluble solids (black cake mainly composed of charcoal). Further, insoluble solids are washed with a small amount of fresh water and combined with the filtrate. The filtration residue was a black powder and was dried with a drier kept at 105 ° C.

The clear filtrate is introduced into reaction vessel B. In the reaction tank B, 35% carbon dioxide gas was introduced from the bottom. The reaction vessel B was kept at pH 7.5 or lower and reaction temperature 40 ° C. or lower.

When the white slurry liquid overflows from the reaction tank B, the supply of the 5.00% cyanamide aqueous solution is stopped. Instead, the filtrate (clarified liquid) of the filter B is passed through the pipe 4 at a rate of 200 kg / hr. Supply to a conical funnel and circulate cyanamide aqueous solution.

The white calcium carbonate filtered off with the filter B was further washed with a small amount of water and combined with the filtrate.
The resulting calcium carbonate was dried with a drier kept at 105 ° C.

14 hours later Since the total of cyanamide concentration and dicyandiamide concentration flowing through 4 pipes exceeded 16%, water was replenished to reaction tank A at a rate of 35-40 kg / hr, and the total of cyanamide concentration and dicyandiamide concentration was 16%. Adjust to ~ 18%. At the same time, the filtrate of the filter B was extracted into the storage tank at a rate of 40 kg / hr. The clarified liquid overflowing from the cyanamide storage tank is put into the reaction tank C. The filtrate of the filter A is added to the reaction vessel C through the pipe 6 and adjusted so that the pH is always in the range of 9 to 11, and the reaction vessel C is kept at 65 to 75 ° C. Accelerated the quantification reaction. The reaction liquid overflowed from the reaction tank C in about 4 hours. The overflowing reaction solution is put into a continuous crystallization tank to precipitate crystals. The crystallization tank is kept at 30 ° C., and the produced white dicyandiamide crystals are continuously filtered by the filter C. The filtrate contained 4.5% dicyandiamide and 0.8% cyanamide. The filtrate is circulated to the reaction tank B through 7 pipes. When this circulation starts, the amount of water replenished to the reaction tank A is reduced, and the liquid level is adjusted to be constant.

The obtained crystals of dicyandiamide were washed with a small amount of water, and the washing was combined with the filtrate.
The obtained dicyandiamide was dried in a drier kept at 105 ° C.

In the continuous dicyandiamide production conditions that became steady state,
Raw material addition (in)
Lime nitrogen 20.00Kg / Hr
Cyanamide nitrogen 20.0%
Total of makeup water and washing water 6.3Kg / Hr
Production (out)
Dicyandiamide 5.68Kg / Hr
Purity 99.8%
Moisture 0.03%
The lime nitrogen required to obtain dicyandiamide 1 was 3.52.
Calcium carbonate 22.6Kg / Hr
Purity 99.8%
Moisture 0.1%
Carbon component 3.6Kg / Hr
Moisture 0.5%
The result was obtained.

Filters are filter presses, drum filters, centrifugal filters, belt filters, Nutsche, etc., and dryers are vibration fluid dryers, fluid dryers, stationary dryers, vacuum dryers, air dryers, etc. Can be selected according to the purpose, taking into account the efficiency and economic efficiency.

The crystallizer is preferably an Oslo crystallizer that continuously obtains crystals or a crystallizer equipped with a continuous scraping type cooling device, but is not limited to this, and a plurality of crystallizers are installed. Thus, crystals may be obtained.

Cyanamide aqueous solution and dicyandiamide production flow

Claims (7)

In producing cyanamide aqueous solution or dicyandiamide using lime nitrogen as a raw material, (a) lime nitrogen is introduced into an aqueous solution having a cyanamide concentration of 3% to 30%, and the cyanamide component in lime nitrogen is extracted into the aqueous solution. Then, an aqueous solution containing clear acidic cyanamide calcium is obtained by separating carbon and inorganic components insoluble in water in the raw material. (B) A method for producing a cyanamide aqueous solution by introducing a gas containing carbon dioxide into the obtained clear acidic cyanamide calcium solution, precipitating calcium carbonate, and filtering the precipitated calcium carbonate. (C) A method of producing dicyandiamide by adding an alkali component to the obtained cyanamide aqueous solution and adjusting the pH to 8-11. The method according to claim 1, wherein carbon dioxide gas is reacted with the clear acidic cyanamide calcium aqueous solution obtained in (a) to obtain high-purity calcium carbonate. The manufacturing method of Claim 1 performed by the batch operation which reuses a part or all of the cyanamide aqueous solution obtained at the process of (b) as the cyanamide aqueous solution of (a). The production method according to claim 1, wherein a part of the cyanamide aqueous solution obtained in the step (b) is reused as the aqueous solution of cyanamide in (a) to continuously produce the cyanamide aqueous solution. The acidic cyanamide aqueous solution obtained in the step (a) is used as the alkaline component to adjust the pH to 8 to 11, dicyandiamide is generated and separated, and the filtrate is returned to the step (b) to continuously produce dicyandiamide. The manufacturing method of Claim 3 and Claim 4. The manufacturing method of Claim 3 and Claim 4 which manufactures a dicyandiamide by batch operation whose alkaline component is the acidic cyanamide aqueous solution obtained at the process of (a). The manufacturing method according to claim 1, wherein the insoluble graphite obtained in the step (a) is treated with an alkali and an acid to obtain high-purity graphite.

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