JP2838897B2 - Recovery of rodan salt - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for recovering a rhodanate salt from a rhodanate-containing aqueous solution by a gel separation method using a polymer gel.

2. Description of the Related Art Waste coke oven gas desulfurization effluent contains rhodan ammonium (ammonium thiocyanate, NH ₄ SCN), ammonium thiosulfate ((NH ₄ ) ₂ S ₂ O ₃ ), and ammonium sulfate ((N
H ₄ ) ₂ SO ₄ ), coloring components (picric acid, etc.), tar content, solid content, etc. The waste liquid is always produced as a by-product from the coke production process, and cannot be disposed of as it is. Therefore, it is indispensable to separate and recover rhodan ammonium, which is an active ingredient, from the waste liquid, while also treating the waste liquid.

As a method for separating and recovering rhodan ammonium from coke oven gas desulfurization waste liquid, a method for separating and recovering rhodan ammonium using a difference in solubility (JP-A-57-7825, JP-A-48-25699, JP-A-57-17421), solvent extraction using an organic polar solvent that selectively extracts rhodan ammonium (JP-A-48-26699), and distillation under reduced pressure (JP-A-49-219). Japanese Patent No. 75490, Japanese Patent Application Laid-Open No. 50-58000, and the like are known.

Further, as a method for separating and recovering a rhodan salt from an aqueous solution containing a rhodan salt, a method of gel-separating a rhodan salt using a polymer gel (JP-A-49-106494, JP-A-50-38)
No. 695, Japanese Patent Application Laid-Open No. 51-139600).

Among the above-mentioned documents, JP-A-48-26699 discloses that coal-distilled gas-treated effluent is directly decolorized with activated carbon,
Alternatively, after passing through a pretreatment step of removing the precipitate by stirring with heated air and decoloring with activated carbon, evaporate to dryness, and then use an organic polar solvent that selectively dissolves rhodan ammonium to dissolve rhodan ammonium in the solvent. Extraction is described. The main precipitate upon addition of the heated air agitation step is sulfur according to the description in Example 1.

Further, among the above documents, JP-A-57-7825 and JP-A-57-17421 disclose the desulfurization waste liquid after decolorizing treatment with activated carbon, and then at a temperature of 200 ° C. or lower in a weakly acidic or alkaline region. If you perform wet oxidation by blowing oxygen,
Substantially all of the ammonium thiosulfate is converted to ammonium sulfate, and a solution in which rhodan ammonium remains as it is is obtained. On the other hand, the solubility of rhodanammonium is much lower than the solubility in water, but the solubility in mixed solution and the solubility in water alone are not so different, so that ammonium sulfate is crystallized and separated, and rhodanammonium is separated from the filtrate. It states that it can be recovered.

Japanese Patent Application Laid-Open No. 49-106494 discloses a method of gel separation of a rhodan salt using a polymer gel. An aqueous solution of a rhodan salt containing impurities is supplied to a dextran crosslinked layer, and impurities and rhodan are added to the crosslinked layer. A method is disclosed in which salts are trapped, impurities are allowed to flow out through the eluent to the crosslinked layer, and then rhodan salts are flowed out and separated through the eluent.

Similarly, Japanese Patent Application Laid-Open No. 50-38695 discloses that in separating an active ingredient from an aqueous solution containing a rhodan salt as a main component by using a dextran crosslinked product, a liquid to be treated and an eluent (or developing solution) are successively used. After the alternation, the eluent eluted before the colored eluent from the previous elution cycle has been drained off is separated as an inorganic sulfur oxyacid salt-containing eluent and then the colored eluent in the next elution cycle A method is disclosed in which an eluent flowing out before starting to flow out is separated as a rhodanate-containing eluent. The publication also discloses that activated carbon treatment is performed prior to gel separation.

JP-A-51-139600 discloses a method for performing the same gel separation using a crosslinked polymer containing acrylamide or a derivative thereof as a main component.

Problems to be Solved by the Invention These conventionally proposed methods of recovering rhodan salts, i.e., a method utilizing a difference in solubility, a method of extracting with a solvent, a method of distilling under reduced pressure, and gel separation using a polymer gel Comparing the methods, the method of gel separation of the rhodanate using a polymer gel is considered to be the most advantageous when the recovery rate, purity, handleability, equipment problems and the like are comprehensively judged.

However, when this gel separation method is applied to, for example, a coke oven gas desulfurization waste liquid, sulfur may precipitate in a column filled with a polymer gel during gel separation, causing problems such as blockage of the column and an increase in pressure loss. Also,
Precipitation of sulfur may also be observed in the piping before the gel separation step.

The present inventors considered that in order to eliminate troubles due to sulfur precipitation when the gel separation method was adopted, an aeration step using air was provided prior to the gel separation step to remove sulfur in advance. Japanese Patent Application Laid-Open No. 48-26699 also discloses that "sulfur precipitates by stirring with heated air". However, sulfur can be removed by air aeration, but sulfur is newly generated in the subsequent steps. Therefore, it was not possible to sufficiently prevent the precipitated sulfur from adversely affecting the gel separation step. Further, it takes a number of days to precipitate sulfur after air aeration, and the separation and removal operation is not easy, so that it is hardly advantageous from an industrial point of view.

Therefore, the present inventors searched for a route for performing the gel separation step in a state where the precipitation of sulfur was prevented, contrary to the method of precipitating and separating sulfur.

The present invention has been accomplished as a result of intensive studies based on such an idea, and has as its object to provide an industrial method for recovering a rhodanate salt from a rhodanate-salt-containing aqueous solution by a gel separation method. is there.

Means for solving the problem The method for recovering a rhodanate salt of the present invention is a method for recovering a rhodanate salt from a rhodanate-salt-containing aqueous solution by a gel separation method using a polymer gel. An aeration step of aerating the aqueous solution containing a rodan salt with an inert gas is provided.

 Hereinafter, the present invention will be described in detail.

<Rhodan salt-containing aqueous solution> A typical example of a rodan salt-containing aqueous solution is a coke oven gas desulfurization waste liquid or a concentrated liquid thereof. The coke oven gas desulfurization waste liquid has a deep red color and contains rhodan ammonium, ammonium thiosulfate, ammonium sulfate, coloring components (picric acid, etc.), tar components, solid components, and the like. The amounts (% by weight) of the components vary widely, as follows in typical cases.

Rhodan ammonium 20-30% Ammonium thiosulfate 5-25% Ammonium sulfate 3-10% Coloring component 0.01-1% Tar content 0.01-1% Solid content 2-10% Water 40-60% The above example is for ammonium salt However, depending on the production process, it may be in the form of a sodium salt.

In addition, the method of the present invention can be applied to not only the coke oven gas desulfurization waste liquid but also an aqueous solution containing a rodane salt.

<Gel Separation Step> The gel separation step is a step of supplying an aqueous solution containing a rhodanate salt to a column filled with a polymer gel, and flowing it out with a developing solution to separate a fraction rich in a rhodanate salt.

As the polymer gel, a substantially nonionic hydrophilic gel is desirable. For example, a dextran-based crosslinked product, a starch-based crosslinked product, a cellulose derivative-based crosslinked product, an acrylamide polymer-based crosslinked product, a hydroxyalkyl (meth) acrylate polymer-based polymer Crosslinked product, hydroxyalkyl (meth)
Gels having a molecular sieve action, such as an allyl ether polymer crosslinked product, a polyalkylene glycol di (meth) acrylate polymer crosslinked product, a vinyl alcohol polymer crosslinked product, and a polyoxyethylene crosslinked product are used.

Among polymer gels, hydroxyalkyl (meth) acrylate polymer-based crosslinked products are particularly important. For example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate And crosslinked polymer gels. Such gels are suitable for use on an industrial scale where harsh operating conditions are required.

In the gel separation operation, the polymer gel is filled in the column in a state of being swollen in water, and the treatment solution that has undergone the aeration step, which is a pretreatment step, is diluted with water as needed and supplied into the column. deep. Then, when a developing solution is passed through one of the columns, a fraction rich in a specific component sequentially flows out of the other column.

Normally, water is used as the developing solution, but it is desirable to adjust the pH with ammonia or another alkali to make it slightly alkaline.

Typically, an aqueous solution rich in thiosulfate and sulfate flows out first, followed by an aqueous solution rich in rhodanate.

The supply amount of the processing solution and the supply amount of the developing solution to the polymer gel in the column are set to be the optimum ratios by a preliminary test so as to obtain a rhodan salt with few impurities.

<Aeration Step Using Inert Gas> This step is a step of aerating an aqueous solution containing a rhodanate with an inert gas, and is placed before the above-mentioned gel separation step. Usually, nitrogen gas is used as the inert gas.

When aerated with air, components that are easily decomposed into sulfur are decomposed into sulfur and precipitate sulfur, but when aerated with an inert gas, decomposition is prevented, and the deposition of sulfur in subsequent steps is effectively prevented.

The aeration step with an inert gas can be carried out without pH adjustment unless the aqueous solution containing the rodan salt as the stock solution is acidic, but under alkaline conditions sulfur precipitation can be more effectively prevented. It is desirable to carry out the reaction under alkaline conditions such as .5 or more, more preferably 8 or more, especially 8.5 or more. The pH is adjusted by adding an alkali such as ammonia or sodium hydroxide.

Aeration conditions (temperature, blowing amount, time) are determined by preliminary experiments. But not so severe,
It is sufficient that dissolved oxygen can be removed.

<Other Steps> In order to make the recovery of the rodane salt more industrially advantageous, it is preferable to appropriately add the following steps in addition to the above steps.

1. Before the aeration step, a solid impurity removal step is provided. This step is usually carried out by allowing a stock solution of a rodan salt, which is a stock solution, to stand. After standing, a floating substance or a precipitate is separated and removed. This facilitates subsequent process operations.

2. An activated carbon treatment step is provided before or / and after the gel separation step. This step is usually performed by passing a treatment solution through a column filled with activated carbon. By performing this activated carbon treatment step, coloring components and other impurities that cannot be completely removed by other steps are removed.

3. Concentration step, crystallization step, crystal separation step, etc. are provided in order to obtain the product rhodanate from the effluent rich in rhodanate after the gel separation step.

4. A step for separating thiosulfate and sulfate from the thiosulfate and sulfate-rich effluent after the gel separation step is provided.

Operation The operation of the present invention will be described with reference to specific examples.

Fig. 2 is a graph showing how pH or the presence or absence of aeration affects the prevention of sulfur deposition when a concentrated solution of coke oven gas desulfurization waste solution (pH 7.3) is used as a rodane salt-containing aqueous solution. is there.

Curve a shows the case where no pH adjustment was performed. If the pH is not adjusted, a considerable amount of sulfur is deposited on standing.

Curves b, c, d show the pH of the system at 8.5, 9.0, 9.
In this case, the amount of sulfur is smaller than that of the curve a, but the amount of sulfur that cannot be ignored is recognized. Therefore, it is understood that the precipitation of sulfur cannot be sufficiently prevented only by adjusting the pH.

Curve e shows the case where the pH of the system was adjusted to 9.0 and aeration with air was performed, and it can be seen that the amount of sulfur deposited becomes extremely large.

Curve f shows the case where aeration with nitrogen gas was performed without performing pH adjustment, and it can be seen that the precipitation of sulfur was significantly reduced as compared with curve a.

Curve g shows the case where the pH of the system was adjusted to 9.0 and aeration with nitrogen gas was performed, and it can be seen that sulfur is more difficult to precipitate than curve f.

Sulfur deposition has a significant effect on process operation. Precipitation of sulfur is mainly caused by easily decomposable sulfur compounds such as ammonium polysulfide, and some are caused by thiosulfate.

As a measure to prevent sulfur precipitation in the gel separation step, utilizing the phenomenon of curve e, an air aeration step is provided in advance to decompose sulfur compounds that are easily decomposed into sulfur in advance,
As described above, an attempt was made to remove the precipitated sulfur so as not to affect the subsequent operation of the process.
However, according to this method, although sulfur caused by easily decomposable sulfur compounds can be removed, since a large amount of thiosulfate still exists in the stock solution,
The formation of sulfur from the dissolved thiosulfate in subsequent steps cannot be prevented.

The present invention focuses on the phenomena of the curves f and g, and aims to prevent the precipitation of sulfur by aeration with an inert gas.

EXAMPLES Next, the present invention will be further described with reference to examples. Hereinafter, “parts” and “%” are expressed on a weight basis unless otherwise specified.

Example 1 FIG. 1 is a flow sheet showing an example of the method of the present invention.

A is a solid impurity removing device, B is an aeration device, C is an alkaline tank for pH adjustment, D is an activated carbon adsorption device, E is a gel separation device, F is a developing solution tank, G is an alkaline tank for pH adjustment, and H is a recovery solution. A tank, I is an activated carbon adsorption device, J is a concentrator, K is a crystallization device, L is a crystal separation device, M is a separation liquid tank, and N is a separation liquid treatment device.

1 is a stock solution, 2 is an aeration gas, 3 is an alkali, 4 is a developing solution, 5 is a pretreatment solution, 6 is a recovery solution, 7 is a separation solution, and 8 is a product.

Recovery of rhodan ammonium was carried out according to the flow sheet of FIG. The stock solution 1 was a concentrated solution of a coke oven gas desulfurization waste solution having a pH of 7.3, the aeration gas 2 was nitrogen gas, the alkali 3 was ammonia, and the developing solution 4 was water containing a small amount of ammonia. . Further, a stationary separation tank is used as the solid impurity removing device A,
As the gel separation device E, a column filled with a polymer gel prepared as described below was used. PH of pretreatment liquid 5
Was 9.0 in the steady state.

<Production of polymer gel> Methacrylic acid / sodium p-styrenesulfonate = 70/30
Was dissolved in 656 parts of water and charged in a polymerization tank equipped with a paddle-type stirrer.

Next, glycidyl methacrylate 178 parts, ethylene glycol dimethacrylate 22 parts, epichlorohydrin 120
2 parts of 2,2-azobis- (2,4-dimethylvaleronitrile) was dissolved in 2 parts of the mixture, and the mixture was charged into a polymerization tank and polymerized at 60 ° C. for 3 hours.

Then, formic acid (5 parts) was added to the polymerization solution, and the mixture was heated at 90 ° C. for 3 hours. As a result, a water-swollen bead polymer having a gel moisture content of 63% was obtained.
The intermediate of 200 mesh and 350 mesh was taken out.

 Table 1 shows the material balance.

The recovery of rhodan ammonium was 90.2%, and the purity of the product rhodan ammonium excluding water was 99.9%.

During the operation of the process, no sulfur deposition was observed in the columns of the aeration device B, the activated carbon adsorption device D, the gel separation device E, the recovery liquid tank H, and the columns between the activated carbon adsorption devices I and between the columns. The operation was able to be performed in the following.

Example 2 Example 1 was repeated except that the concentrated solution used in Example 1 was converted into a sodium salt as the undiluted solution 1, sodium hydroxide was used as the alkali 3, and water to which a trace amount of sodium hydroxide was added was used as the developing solution 4, respectively. Example 1
Preferred results according to the above were obtained.

Effect of the Invention In the present invention, since an aeration step using an inert gas is provided before the gel separation step, no sulfur precipitation is observed in the subsequent steps including the gel separation step, and the process operation is smoothly performed throughout. Can be done.

In the gel separation step, since the fraction rich in rhodanate is separated from the aqueous solution containing rhodanate, thiosulfate, sulfate, etc., the rhodanate contained in the stock solution is recovered in high yield and high purity. . Note that thiosulfate and sulfate can be separated and recovered from other fractions obtained in the gel separation step.

 Therefore, the present invention has great industrial significance.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of the method of the present invention. Fig. 2 is a graph showing how pH or the presence or absence of aeration affects the prevention of sulfur deposition when a concentrated solution of coke oven gas desulfurization waste solution (pH 7.3) is used as a rodane salt-containing aqueous solution. is there. A: Solid impurity removal device, B: Aeration device, C: pH
Adjustment alkaline tank, D: activated carbon adsorption device, E:
Gel separation device, F: developing liquid tank, G: alkaline tank for pH adjustment, H: recovered liquid tank, I: activated carbon adsorption device, J: concentrating device, K: crystallizing device, L: Crystal separation device, M: Separation liquid tank, N: Separation liquid treatment device, 1 ... Undiluted solution, 2 ... Aeration gas, 3 ... Alkali, 4 ...
... Developing liquid, 5 ... Pretreatment liquid, 6 ... Recovery liquid, 7 ... Separation liquid, 8 ... Product

Continuation of the front page (72) Inventor Ryosuke Nishida 122-2 Haji, Nagafuna-cho, Oku-gun, Okayama Prefecture (58) Field surveyed (Int. Cl. ⁶ , DB name) C01C 3/20

Claims (5)

(57) [Claims] When recovering a rhodanate from an aqueous solution containing a rhodanate by a gel separation method using a polymer gel, the aqueous solution containing a rhodanate is aerated with an inert gas before the gel separation step. A method for recovering rodan salt, which comprises an aeration step. 2. The method according to claim 1, wherein the aeration step is performed under alkaline conditions. 3. The recovery method according to claim 1, wherein the aqueous solution containing a rodane salt is a coke oven gas desulfurization waste liquid or a concentrated liquid thereof. 4. The recovery method according to claim 1, wherein a solid impurity removing step is provided before the aeration step. 5. An activated carbon treatment step is provided before or / and after the gel separation step.
The recovery method according to any one of the above.