JPH03257013A - Method for producing rhodan salt and thiourea from rhodan ammonium - Google Patents

Abstract

PURPOSE:To produce both of thiourea which has high additional value and high purity rhodan salt by adding amine to an aq. soln. of thiourea and unreacted NH4SCN prepared by dissolving transition reaction product of NH4 SCN in water and bringing the nonreacted NH4SCN into contact with an aq. soln. of alkali material. CONSTITUTION:Process (A); NH4SCN obtained from an aq. soln. containing NH4SCN such as waste water of desulfurized gas from coke oven is heated and dissolved to have a part of NH4SCN to transit to thiourea. Process (B); the above product is dissolved in water and brought into contact with amine, particularly comprising dicyclohexylamine to precipitate the addition product of NH4SCN and amine from which NH3 is removed. Process (C); The addition product is separated. Process (D); the addition product is brought into contact with an aq. soln. of alkali material such as NH3 to dissociate the addition product into rhodan salt and the original amine. Process (E); Thiourea is isolated from the filtrate containing thiourea in the process (C). Thus, rhodan salt and thiourea are both obtained from NH4SCN.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to obtaining thiourea, which is a rearrangement product, from a rearrangement reaction product obtained by heating and melting rhodan ammonium.
The present invention relates to a method for obtaining unreacted rhodan ammonium as a high purity rhodan salt.

Conventional technology] - Rhodan ammonium,
Ammonium thiosulfate, ammonium sulfate, coloring ingredients (
(picric acid, etc.), tar, solids, etc. This waste liquid is always a by-product of the coke manufacturing process, and cannot be disposed of as is.
In addition to treating this waste liquid, it is essential to separate and recover the active ingredient, Rodan salt, from the waste liquid.

The following method has been proposed as a method for separating and recovering rhodan salts such as rhodan ammonium and rhodan soda from coke oven gas desulfurization waste liquid.

■ Method using the difference in solubility JP-A-57-7825, JP-A-48-25699
Publication No. 17241/1983, Japanese Patent Application Laid-open No. 17241/1983
Publication No. 156325 ■ Method of solvent extraction using an organic polar solvent to selectively extract rhodanic ammonium JP-A-48-26699 ■ Method of distilling under reduced pressure or steam distillation after conversion to rhodanic acid JP-A-49-1989 -75490 Publication, JP-A-50-5800
Publication No. 0 (Special Publication No. 53-35800), Japanese Patent Publication No. 53-35800
3-91600 Publication ■ Method for gel separation of Rodan salt using polymer gel JP-A-49-106494, JP-A-50-386
Publication No. 95 (#Publication No. 53-4000), Japanese Unexamined Patent Publication No. 1973
No. 1-139600 Further, as a method for producing thiourea from rhodan ammonium, a method using an clathrate compound is known.

That is, in Japanese Patent Application Laid-Open No. 48-26730, rhodan ammonium as a by-product during coke oven gas production is recovered, a transfer reaction product obtained by heating and melting this rhodan ammonium is dissolved in water, and a guest compound ( cyclohexane, methylcyclopentane, 1,1.1-)lichloroethane, etc.) to form a thiourea clathrate, and the thiourea clathrate is separated and then dissolved in water to remove thiourea from the aqueous phase. A method for crystallization is shown.

Problems to be Solved by the Invention However, these methods still have room for improvement from an industrial standpoint.

For example, the above method (■) has limitations on the composition and concentration of the desulfurization waste liquid, requires adjustment before the vehicle, is difficult to satisfy both yield and product purity, and has problems with high-purity products. However, there are still problems such as the fact that it contains ammonium sulfate and ammonium thiosulfate.

The above method (1) requires a step of evaporation to dryness in advance, which is disadvantageous in terms of thermal energy, and the extract still contains ammonium sulfate and ammonium thiosulfate.

The above method (1) has problems such as requiring a step of first converting it into rhodanic acid and that vacuum distillation is disadvantageous in terms of operation and energy.

Method (■) above is considered to be more advantageous than methods (■) to (■) above when considering yield, product purity, ease of handling, equipment cost, economic efficiency, etc.; Sulfur is precipitated in a column filled with molecular gel,
This may cause problems such as column clogging and increased pressure drop.

The method described in JP-A No. 48-26730, that is, the method of obtaining thiourea from the rearrangement reaction product of rhodan ammonium using an clathrate, requires that the guest compound has a low boiling point, is flammable, and is toxic. Therefore, it is disadvantageous in terms of handling, the recovery rate of thiourea in the inclusion process is low, the inclusion equilibrium is greatly affected by the thiourea concentration and temperature, and the product thiourea is bulky. There are disadvantages such as In addition, when trying to apply the above-mentioned methods ■ to ■ to obtain high-purity rhodan salt from unreacted rhodan ammonium during the rearrangement reaction, the recovery rate will be low in the case of ■, and the recovery rate will be low in the case of ■ to ■. There are similar disadvantages.

The present invention employs a principle completely different from the method described in JP-A No. 48-26730 or the methods ① to ① above, and obtains thiourea, a transfer product, from a transfer reaction product of rhodan ammonium. In addition, it is an object of the present invention to provide a method for obtaining unreacted rhodan ammonium as highly pure rhodan salt.

Means for Solving the Problems The method of producing rhodan salt and thiourea from rhodan ammonium of the present invention includes a transfer reaction step A in which a part of rhodan ammonium is transferred to thiourea by heating and melting rhodan ammonium; The reactant containing the thiourea and unreacted rhodan ammonium obtained in the rearrangement reaction step A is dissolved in water, and the aqueous solution is mixed with the rhodan ammonium, which is sparingly water-soluble and containing a sparingly water-soluble deammoniated adduct between the rhodan ammonium and the rhodan ammonium. an adduct generation step B of precipitating a deammoniated adduct of rhodan ammonium and an amine by contacting it with an amine that can be formed;
A solid-liquid separation step in which the adduct precipitated in the adduct generation step B is separated from the filtrate and washed with water if necessary, and the adduct obtained in the solid-liquid separation step C is brought into contact with an aqueous solution of an alkaline substance. , an adduct decomposition step D in which the rhodan salt is decomposed into the original amine, and a thiourea in which thiourea is isolated by subjecting the filtrate containing thiourea or the filtrate and washing liquid to a separation and purification means in the solid-liquid separation step C. The method is characterized by carrying out the isolation step E.

The present invention will be explained in detail below.

<Rhodan ammonium> Rodan ammonium as a raw material in the present invention can be produced by various methods from an aqueous solution containing rhodan ammonium such as coke oven gas desulfurization waste liquid.

A typical example of an aqueous solution containing rhodan ammonium is a coke oven gas desulfurization waste liquid or an aqueous solution derived therefrom. The coke oven gas desulfurization waste liquid obtained in a typical process has a deep red color and contains ammonium rhodan, ammonium thiosulfate, ammonium sulfate, coloring components (picric acid, etc.), tar, solids, etc.

Aqueous solution derived from coke oven gas desulfurization waste liquid refers to coke oven gas desulfurization waste liquid that has been subjected to concentration treatment, dilution treatment, aeration treatment, impurity removal treatment (activated carbon treatment, static treatment, filtration treatment, centrifugation treatment, etc.). refers to the aqueous solution applied.

<Transfer reaction step A) The transfer reaction step A is a step in which a portion of rhodan ammonium is transferred to thiourea by heating and melting rhodan ammonium.

rhodan ammonium crystals at high temperatures (e.g. 120-18
When the rhodan ammonium is thermally melted at 0° C. for about 1 to 10 hours, approximately 20 to 30% by weight of rhodan ammonium is converted to thiourea.

<Adduct production step B) In the adduct production step B, the reactant containing the thiourea and unreacted rhodan ammonium obtained in the transfer reaction step A is dissolved in water, and the aqueous solution is mixed with the reactant containing the thiourea and unreacted rhodan ammonium. This is a step in which a deammoniated adduct of rhodan ammonium and an amine is precipitated by contacting with an amine that can form a poorly water-soluble deammoniated adduct with rhodan ammonium.

There is no particular limitation on the concentration of the aqueous solution, but in order to perform the process operation smoothly, it is desirable to maintain the concentration of the reactant at 5 to 20% by weight. It is better to separate and remove this undissolved content before contacting with the amine.

Specific examples of amines include poorly water-soluble amines such as synchlohexylamine or its N-alkylated products, dibenzylamine or its N-alkylated products, di-n-octylamine, cetylamine, etc., and desirably liquid at room temperature. It's better to be. Particularly preferred among the amines is synchlohexylamine or its N-alkylated product, especially synchlohexylamine.

The contact between the aqueous solution and the amine is usually carried out by adding the amine to the aqueous solution containing unreacted rhodan ammonium while stirring it.

The amine may be added dropwise, in portions, or all at once, but it is recommended to add it in small amounts. The pH of the aqueous solution is preferably about 4 to 9.

The temperature of the aqueous solution containing unreacted rhodan ammonium can be set at any temperature as long as it is below the boiling point of water, but there is no particular advantage in using a higher or lower temperature than necessary, so it is usually around room temperature. Do it with However, when the melting point of the amine is higher than room temperature, it is better to adopt the temperature at which the amine remains liquid.

Since the addition reaction proceeds almost quantitatively, it is desirable that the amount of amine added be approximately equivalent to the amount of rhodan ammonium in the aqueous solution; however, an excess of either may be used.

Ammonia is generated during the addition reaction and is removed from the system. The product becomes a deammoniated adduct.

<Solid-liquid separation step C> The solid-liquid separation step C is a step in which the adduct precipitated in the adduct generation step B is separated from the filtrate and washed with water if necessary.

The adduct produced in adduct production step B is poorly water soluble,
Since it precipitates in an aqueous solution, the precipitate is separated by solid-liquid separation means such as filtration or centrifugation, and washed with water if necessary.

<Adduct Decomposition Step D) The adduct decomposition step D is a step in which the adduct obtained in the solid-liquid separation step C is brought into contact with an aqueous solution of an alkaline substance to decompose it into rhodan salt and the original amine.

As the alkaline substance, ammonia, alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.) are used.

In the above decomposition reaction, a method is usually adopted in which an adduct is added to an aqueous solution of an alkaline substance while stirring it. The addition may be done dropwise, in portions, or all at once, but a method of adding in small amounts is recommended. A reaction temperature of room temperature or slightly higher than room temperature is sufficient.

Since this decomposition reaction also proceeds almost quantitatively, it is desirable to use the alkaline substance in an amount approximately equivalent to or slightly larger than that of the adduct. However, even if other ratios are adopted, the decomposition reaction proceeds accordingly.

When the system is left to stand after the decomposition reaction, the system separates into an aqueous layer and an amine layer. (When the melting point of the amine is high, the amine may precipitate in a dispersed state in the aqueous solution without forming an amine layer.) Since the rhodan salt is dissolved in the aqueous layer, the pH
Processes or operations such as conditioning, concentration, crystallization, separation of crude crystals, washing, and drying are performed to obtain a product in crystalline form. Depending on the product specifications, the product may be in the form of an aqueous solution.

On the other hand, from an industrial perspective, it is particularly desirable to recycle the amine layer as the amine in the adduct formation step B described above.

Thiourea isolation step E) The thiourea isolation step E is a step of isolating thiourea by subjecting the filtrate containing thiourea in the solid-liquid separation step C or the filtrate and washing liquid to a separation and purification means. .

Separation and purification means include, for example, vacuum concentration, precipitation removal of components other than thiourea by cooling, reconcentration, cooling crystallization,
Conventional means such as filtration, drying etc. are employed.

Effect The rearrangement reaction in the rearrangement reaction step A is represented by the following formula.

NH4SCN4H2N-C-NH2I Since this reaction is a healing reaction, the aqueous solution in which the rearrangement reaction product is dissolved in water contains a large amount of unreacted rhodan ammonium along with the rearrangement product thiourea.

In the adduct formation step B, a sparingly water-soluble deammoniated adduct is formed between rhodan ammonium and the amine. This addition reaction is shown by the following formula, taking as an example the case where the amine is synchlohexylamine.

According to the inventor's experiments, both the reactions in the above formula - are exothermic reactions, and the ΔH per mole of synchlohexylamine is 13.
It is 6kcal.

Since amines are only slightly soluble in aqueous solutions, only the dissolved portion immediately reacts with rhodan ammonium in the aqueous solution to form adducts, and the adducts formed are poorly soluble in water, so they precipitate immediately in the order in which they are formed. , placed outside the system. In other words, the added amine is always surrounded by an aqueous solution containing unreacted rhodan ammonium, and the by-product ammonia is also removed from the system, so the reaction proceeds smoothly despite the fact that the amine is poorly soluble in water. As a result, the reaction progresses in one direction until it is completed without reaching equilibrium. and,
Since the reaction proceeds with the rate of dissolution of the amine being rate-determining, reaction heat is not accumulated and process control becomes easy.

In the adduct decomposition step after the solid-liquid separation step C, the adduct is decomposed into rhodan salt and the original amine by reaction with an alkaline substance. This decomposition reaction is expressed by the following equation, taking as an example the case where an aqueous NaOH solution is used as the alkaline substance.

The reaction of the above formula is considered to be an endothermic reaction commensurate with the calorific value in the above addition reaction.

The adduct is poorly soluble in water, but the amine produced by zero decomposition, in which only the dissolved portion immediately reacts with the alkaline substance in the aqueous solution and is decomposed, is poorly soluble in water, so it is separated from the aqueous solution and placed outside the system. It will be destroyed. In other words, since the added adduct is always surrounded by an aqueous solution of an alkaline substance, the reaction proceeds smoothly even though the adduct is poorly soluble in water, and the reaction progresses in one direction without reaching equilibrium. We proceed to Since the reaction proceeds with the rate of dissolution of the adduct being rate-determining, the system is not rapidly cooled due to an endothermic reaction, and process control becomes easy.

Since the filtrate after the solid-liquid separation step C or the filtrate and the washing liquid contain thiourea, which is a transfer product, thiourea is isolated by appropriate separation and purification means.

Example Next, the present invention will be further explained with reference to Examples.

Example 1 Odanammonium crystals were heated and melted at a temperature of 170°C for 1 hour to perform a transition reaction having a composition of 23.5% by weight of thiourea, 74.8% by weight of unreacted rhodanammonium, and 1.7% by weight of other components. I got something.

100 g of this rearrangement reaction product was added to water 9201 and dissolved, and a small amount of undissolved matter was removed by filtration.

While stirring the aqueous solution prepared above at room temperature, 178 g of synchlohexylamine (equivalent to rhodan ammonium) was gradually added dropwise thereto, and after the dropwise addition was completed, stirring was continued for an additional 10 minutes to complete the reaction. During this time, the generation of precipitates and ammonia was also observed.

The generated slurry was filtered under reduced pressure, and the precipitate was dissolved in 100ml of water.
After washing with water three times and drying, 204 g of the adduct was obtained. The capture rate of rhodan ammonium by synchlohexylamine was 88%.

The filtrate and washing liquid were combined to form an aqueous solution containing thiourea, which was concentrated under reduced pressure to obtain 446 g of a concentrated solution. This concentrated solution was cooled to 5° C., a small amount of dissolved amine adduct was precipitated and removed, and then reconcentrated to obtain 94 g of a concentrated solution.

This concentrated solution was cooled and crystallized at 5° C., and further filtered and dried to obtain 16 g of thiourea crystals. The purity of this crystal is 9
The content was 9% by weight, and the specific gravity was 0.5. Incidentally, the specific gravity of commercially available thiourea, which is thought to be produced by the clathrate compound utilization method described in the prior art section, is 0.7.

Note that the above precipitate becomes needle-like crystals when recrystallized from water, and foliate crystals when recrystallized from ethanol.

The melting point of this crystal is 243-246°C, and the results of elemental analysis correspond to 3H24S N2. When an ethanol solution of this crystal is reacted with an AgNO3 aqueous solution,
Ag5CN is produced quantitatively. Furthermore, as will be described later, the oil obtained by alkaline decomposition of these crystals is confirmed by FTIR (Fourier transfer infrared spectroscopy) to be almost pure synchhexylamine. Therefore, it is confirmed that the chemical formula of the above crystal (adduct) is as follows. The solubility of this adduct in water is 0.5% by weight at 25°C, 1.1% by weight at 50°C,
It is 1.7% by weight at 65°C.

Next, 204 g of the adduct obtained above was gradually added to a 50% by weight aqueous solution of NaOH (the amount of NaOH was 1.04 equivalents relative to the adduct) while stirring.

When the reactant was allowed to stand after the reaction was completed, it separated into an aqueous layer and an amine layer, so the aqueous layer (pH was 13.0) was separated, diluted sulfuric acid was added to adjust the pH to 5.5, and the pressure was reduced. The mixture was concentrated and crystallized in a conventional manner to obtain crude crystals. The crude crystals were washed with approximately the same amount of a 60% by weight aqueous rhodan soda solution and dried to obtain 28 g of rhodan soda crystals.

The purity of this crystal was 99% by weight, and the pH when a 5% by weight aqueous solution was prepared was Ei, 1.

On the other hand, it was confirmed by FTIR that the amine layer was almost pure synchlorohexylamine. The recovery rate of synchhexylamine was 95%.

Example 2 Using the synchlohexylamine recovered in Practical IM Example 1,
When Example 1 was repeated, almost the same results as Example 1 were obtained.

Example 3 Example 1 was repeated except that an N-lower alkylated product of synchlohexylamine was used in place of synchlohexylamine, and results similar to those of Example 1 were obtained.

Effects of the Invention By dissolving the transfer reaction product of rhodan ammonium in water, an aqueous solution containing thiourea and unreacted rhodan ammonium can be obtained.

When a specific amine such as synchlohexylamine is added to this aqueous solution, a deammoniated adduct of rhodan ammonium and the amine is precipitated.

The adduct generation process is a heterogeneous reaction, and the reaction proceeds in a short time even at room temperature. Moreover, the adducts formed are immediately precipitated and placed outside the reaction system, so it is difficult to control the reaction rate, reaction temperature, and reactants. separation is extremely easy. Since this reaction proceeds almost quantitatively, almost all of the unreacted rhodan ammonium in the transfer reaction product can be precipitated as an adduct.

By contacting the separated adduct with an aqueous solution of an alkaline substance, the adduct decomposes almost quantitatively into the rhodan salt and the original amine. This adduct decomposition process is also a heterogeneous reaction, and the reaction proceeds in a short time at room temperature or slightly higher than that, and the amine produced is immediately separated and placed outside the reaction system, so the reaction rate can be controlled and the reaction temperature controlled. control and separation of reactants is extremely easy. Since a highly concentrated and highly purified aqueous solution of Rodan salt is obtained by this reaction, the concentration cost for isolating Rodan salt is low.

In the adduct production step B and the adduct decomposition step, no special equipment is required, and there is no risk of temperature or pressure during operation.

Since the filtrate or washing liquid after separating the adduct is a substantially pure aqueous thiourea solution, highly pure thiourea can be obtained from the aqueous solution.

As described above, the present invention allows co-production of high value-added thiourea and highly purified rhodan salt from rhodan ammonium, and therefore the present invention has extremely great industrial significance.

Claims (1)

[Claims] 1. A transfer reaction step A in which a part of rhodan ammonium is transferred to thiourea by heating and melting rhodan ammonium; thiourea obtained in the transfer reaction step A and unreacted rhodan ammonium; The reaction product containing rhodan ammonium and amine is dissolved in water, and the aqueous solution is brought into contact with an amine that is itself sparingly soluble in water and can form a sparingly water-soluble deammoniated adduct with rhodan ammonium. an adduct generation step B in which the deammoniated adduct is precipitated; a solid-liquid separation step in which the adduct precipitated in the adduct generation step B is separated from the filtrate and washed with water as necessary; Adduct decomposition step D in which the adduct is decomposed into rhodan salt and the original amine by contacting with an aqueous solution of an alkaline substance, separation and purification into the thiourea-containing filtrate or the filtrate and washing liquid in the solid-liquid separation step C A method for producing rhodan salt and thiourea from rhodan ammonium, which comprises performing a thiourea isolation step E of isolating thiourea by applying means. 2. The method according to claim 1, wherein the amine is synchlohexylamine or an N-alkylated product thereof. 3. The method according to claim 1, wherein the amine obtained in the adduct decomposition step D is recycled as an amine in the adduct production step B.