JPS6041006B2 - Recovery method of sodium thiocyanate - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for recovering sodium thiocyanate, and more specifically, the present invention relates to a method for recovering sodium thiocyanate, and more specifically, a method for recovering sodium thiocyanate from waste liquid of coke oven gas wet desulfurization treatment using an aqueous solution of a sodium compound containing a redox catalyst as an absorption liquid. Regarding how to.

In general, coke oven gas wet desulfurization waste liquid that uses sodium compounds as an alkali source contains coloring substances such as sodium thiosulfate, sodium sulfate, catalysts, etc. in addition to sodium thiocyanate, and it takes a great deal of effort to remove these. cost was required.

Moreover, a method for recovering sodium thiocyanate has not yet been established. The present inventors have conducted intensive research on a method for recovering sodium thiocyanate from the desulfurization waste solution, and have found that sodium thiosulfate can be easily converted to sodium sulfate by liquid-phase oxygen oxidation, and that sodium sulfate and sodium thiocyanate are We obtained the knowledge that sodium sulfate can be easily separated and removed due to the difference in solubility.
The invention has been completed. That is, the method for recovering sodium thiocyanate according to the present invention involves adding at least twice the molar amount of sodium salt to the thiosulfuric acid in the coke oven gas wet desulfurization waste liquid using a sodium compound as an alkali source. , the sodium thiosulfate is converted to sodium sulfate by liquid phase oxygenation with an oxygen-containing gas at 150 to 20 psi under pressure, and then the sodium sulfate is crystallized and separated by concentration and/or cooling near the saturation of sodium thiocyanate. Then, sodium thiocyanate is recovered from the furnace liquid.

The desulfurization waste liquid usually contains 60% sodium thiocyanate.
Contains up to 200 evenings/1, sodium thiosulfate at 50 to 200 evenings/1, and 0.5% or less of catalyst, and exhibits a brown or deep red color. This is desirably decolorized with activated carbon and then subjected to liquid phase oxygen oxidation treatment. The treatment conditions are preferably conditions that oxidize sodium thiosulfate to sodium sulfate but do not cause decomposition of sodium thiocyanate. This reaction generally follows the following equation.

Na2S203 1202 12NaOH → 2Na2S04 10 days 20 ... [11
Therefore, the appropriate amount of sodium to be added is at least twice the molar amount of thiosulfuric acid contained in the waste liquid.

This reaction does not proceed under normal pressure or reduced pressure. In this case, the appropriate pH is in the weakly acidic to alkaline range, preferably neutral to alkaline, and the reaction temperature is about 2000 oo or less, which is the temperature at which it is difficult to separate sodium thiocyanate, especially when copper is added as a catalyst. , its temperature is about 15
00C can be lowered by The solution subjected to the liquid phase oxygen oxidation treatment in this manner is transparent and yellow in the case where a copper catalyst is added, and is colorless and transparent in the case where no copper catalyst is added.

When a copper catalyst is added, it is desirable to remove it using a chelate resin or the like. The solubility of sodium sulfate in this liquid-phase oxygen-oxidized mixed solution of sodium sulfate and sodium thiocyanate is much lower than the solubility of either of them alone in water; It has been found that there is not much difference in solubility (hereinafter referred to as mutual solubility) and solubility in water alone.

Figure 1 shows the mutual solubility curves of sodium sulfate a and sodium thiocyanate c, which were experimentally determined by the present inventors in a coexisting solution of sodium sulfate, sodium thiocyanate, and water, and are also based on literature values. The solubility curves of sodium sulfate (b) and sodium thiocyanate (d) in water are also examined.

As can be seen from this figure, the mutual solubility a of sodium sulfate in the sodium sulfate-sodium thiocyanate system is approximately 1/40 of the solubility b of sodium sulfate in the single system.
~1/10 Yuexing degree, and for sodium thiocyanate, there is no big difference between the mutual solubility c and the solubility d alone.

Moreover, there is a large difference between these mutual solubility a and c, and it is extremely easy to separate sodium sulfate and sodium thiocyanate due to the difference in solubility.The present invention was completed based on this new knowledge. It is something that Regarding the specific mutual solubility of sodium sulfate and sodium thiocyanate in this mutual dissolution, thiocyanate is more soluble than sodium sulfate, so the mutual solubility of sodium sulfate is lower than that of sodium sulfate due to the so-called salting-out effect. This is considered to be a significant decline.

Therefore, this property can be used to remove sodium sulfate. That is, when the solution is concentrated and/or cooled so that the concentration of sodium thiocyanate in the solution is close to the saturation point, almost all of the sodium sulfate is crystallized. Therefore, this is separated, and the remaining solution phase is subjected to cooling, concentration, and other means to recover highly pure sodium thiocyanate.

The liquid phase after sodium thiocyanate recovery is returned to the concentration and other previous steps to minimize the loss of sodium thiocyanate. Since the present invention is configured as described above, high purity sodium thiocyanate and also sodium sulfate can be recovered by relatively simple operations.

Examples of the present invention will be shown below.

In addition, all parts expressing proportions mean parts by weight. Example 1 0.0% NaOH was added to desulfurization waste liquid that had been decolorized with activated carbon.
After adding 77 mol/1 and CaS04 at a ratio of 0.001 mol/1, the temperature was 150 to 15,500, the oxygen partial pressure was 1 to 5 kg/1, and the residence time was 2. Liquid-phase oxygen oxidation treatment was carried out in an autoclave under insect-hour conditions.

The composition of the obtained treatment liquid is as follows. After treating the treatment liquid with a chelate resin to remove copper ions, this liquid 101 (11.2k9) was heated to a temperature of 70 to 800C.
It was concentrated under reduced pressure to 3.73k9, and the crystals that had crystallized were separated in a furnace at this temperature to recover 2.15k9 of sodium sulfate. On the other hand, the furnace liquid was cooled to 30 oo to crystallize sodium thiocyanate, which was taken out from the furnace.

It was 0.275k9 and 99.8% pure. Since the furnace solution still contains a large amount of sodium thiocyanate, it can be returned to the concentration step. Example
2 In the flow sheet shown in FIG.
(Sodium sulfate 22 cities and sodium thiocyanate 1
1,120 parts/hour of the separated liquid 9 from the centrifuge 4 (containing 0.3 parts of sodium sulfate and 175 parts of sodium thiocyanate) were added to the concentrator. 1, and the rhomboids were added to sodium thiocyanate/
The mixture was concentrated under reduced pressure at a temperature of 7,000 so that the water ratio was 1.8.

Sodium sulfate crystallized by concentration was separated and removed by centrifuge 2, and 224 parts of sodium sulfate crystals 6 were obtained.
It was collected at the time. It had a purity of 97.8% (after drying) and a sodium thiocyanate content of 2.1%. On the other hand, the separated liquid 7 from the centrifugal separator 2 is introduced into the crystallization tank 3, and the temperature is 200.
It was cooled to 0 and sodium thiocyanate was crystallized.
This was separated by a centrifuge 4 to obtain 95.2 parts/hour of purified sodium thiocyanate crystals 8. It has a purity of 99.8% (after drying) and contains 0.0% sodium sulfate.
It was 2%. Example 3 In the flow sheet shown in FIG. 3, 14 parts of treated liquid 14 (containing 22 parts of sodium sulfate and 10 parts of sodium thiocyanate) obtained by subjecting green desulfurization waste to liquid phase oxygen oxidation treatment , 12 eaves concentrator 1
1, and the sodium thiocyanate/water ratio was 1.
It was concentrated under reduced pressure at a temperature of 7,000 to a concentration of 8.

Sodium sulfate crystallized by concentration was separated and removed by Liaoxin separator 12, and sodium sulfate crystals 16 were separated into 216
Parts were collected. It had a purity of 97.5% (after drying) and a sodium thiocyanate content of 2.5%. On the other hand, the separated liquid 17 from the centrifugal separator 12 was placed in a bag in the concentrator 13 and concentrated to dryness under reduced pressure at a temperature of 70°C. In this way, 94 parts of sodium thiocyanate crystal 19 were obtained. This is purity 99
．． The sodium sulfate content was 0.9%. In addition,
15 indicates concentrated water, and 18 indicates evaporated water.

[Brief explanation of drawings]

FIG. 1 is a graph showing the solubility of sodium sulfate and sodium thiocyanate, and FIGS. 2 and 3 are flow sheets of Examples 2 and 3 of the present invention, respectively. Figure 2 Figure 3 Figure 1

Claims (1)

[Claims] 1 Add sodium salt in an amount of at least twice the mole of thiosulfuric acid in the solution to a coke oven gas wet desulfurization waste solution using a sodium compound as an alkali source, and add 150 to 20 moles of sodium salt under pressure.
Sodium thiosulfate is converted to sodium sulfate by liquid phase oxygenation with oxygen-containing gas at 0°C, followed by concentration and/or
Alternatively, a method for recovering sodium thiocyanate, which comprises crystallizing and separating sodium sulfate near the saturation point of sodium thiocyanate by cooling, and recovering sodium thiocyanate from the filtrate.