A process for efficiently treating the wastewater from the production of thiosemicarbazide

Abstract

The present invention discloses a process for treating the production wastewater of thiosemicarbazide, which comprises the following steps: Quantitatively adding thiosemicarbazide wastewater and a quantitative aldehyde or ketone into a reaction flask. After the reaction ends, the organic phase is distilled to recover the corresponding aldehyde or ketone. The aqueous phase is heated, air is blown through it for stripping, and then it is cooled and filtered. The filter cake of sulfur is dried and used as a by-product. The filtrate is adjusted to strong alkalinity with an alkali, and then heated and blown through with air until the ammonia nitrogen reaches a predetermined value. After cooling to room temperature, the pH of the wastewater is adjusted to neutral with dilute hydrochloric acid, and then it is discharged to the company's three wastes treatment center for biochemical treatment and discharged after reaching the standard. This process uses aldehyde or ketone to remove hydrazine hydrate in the wastewater and uses the stripping method to remove ammonia nitrogen in the wastewater. After the wastewater treatment, the removal rate of the COD amount reaches 88%, and the removal rate of the ammonia nitrogen amount is as high as 99%. This process is simple, efficient, energy-saving and environment-friendly, enables the degradation of high-COD and high-ammonia-nitrogen thiosemicarbazide wastewater, and 95% of the by-product sulfur can be sold, which can generate certain economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of fine chemical engineering, and particularly relates to a simple and efficient method for treating thiosemicarbazide production wastewater with high COD and high ammonia nitrogen. Background Art

[0002] Thiosemicarbazide, also known as 1,3-diaminothiourea; thiocarbazide; thiocarbamide; sym-diaminothiourea, is widely used in organic synthesis and is an important raw material for the production of the highly efficient broad-spectrum herbicide - metribuzin. Currently, on the market, thiosemicarbazide is mainly produced by the reaction of 80% hydrazine hydrate and carbon disulfide. Producing 1 ton of thiosemicarbazide will generate approximately 2 tons of wastewater. This wastewater is purplish-red in color, contains approximately 10% hydrazine hydrate, a small amount of hydrogen sulfide and a large amount of ammonia gas, and has a strong smell of rotten eggs. After testing related indicators, the ammonia nitrogen value of this wastewater is as high as 60,000 mg / L, the COD value is 180,000 mg / L, and B / C = 0.14. This wastewater is high ammonia nitrogen and high COD wastewater and does not have biodegradability, failing to meet the wastewater discharge standard, so it must be treated to meet the standard before discharge. Patent CN108862217 directly treats thiosemicarbazide wastewater with dilute sulfuric acid, converting hydrazine hydrate and sulfur-containing compounds in the wastewater into hydrazine sulfate and sulfur, but then further separation and purification of hydrazine sulfate are required. Moreover, the ammonia nitrogen value of the wastewater treated by this process is 500 mg / L, and the ammonia nitrogen in the wastewater needs to be further deeply treated. Patent CN108840425 jointly treats thiosemicarbazide wastewater with chlorine and dilute sulfuric acid, also converting hydrazine hydrate and sulfur-containing compounds in the wastewater into hydrazine sulfate and sulfur. The disadvantage is that this process requires the use of chlorine with relatively high toxicity and the ammonia nitrogen value of the treated wastewater is also relatively high, and the ammonia nitrogen in the wastewater needs to be further deeply treated. Therefore, for thiosemicarbazide wastewater, a process that can treat ammonia nitrogen in the wastewater while treating hydrazine hydrate and COD is needed. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a low-cost, efficient, green and safe process for treating thiosemicarbazide wastewater in view of the deficiencies of the prior art.

[0004] Technical Solution: The process for efficiently treating thiosemicarbazide production wastewater described in the present invention specifically includes the following steps:

[0005] (1) Put a quantitative amount of thiosemicarbazide wastewater and a quantitative amount of aldehyde or ketone into a reaction flask, heat and stir, cool and layer to obtain an aqueous phase and an organic phase;

[0006] (2) Distill the organic phase in step (1) to recover the corresponding aldehyde or ketone;

[0007] (3) Heat the aqueous phase in step (1) to a certain temperature, blow air for a certain period of time, cool to room temperature and filter. The filter cake is dried with sulfur as a by-product, and the filtrate aqueous phase continues to be processed in the next step;

[0008] (4) Adjust the filtrate aqueous phase obtained in step (3) to alkaline pH with an alkali, raise the temperature to a certain level and continue stripping for a certain period of time, cool down to room temperature, adjust the pH of the stripped wastewater to neutral with dilute hydrochloric acid, and discharge it to the three-waste treatment center for the next step of biochemical treatment. After reaching the standard, it is discharged.

[0009] Further, as a preferred embodiment, the aldehyde in step (1) is benzaldehyde or phenylacetaldehyde or n-butanal or n-pentanal; the ketone in step (1) is benzophenone or acetophenone or diisobutyl ketone or methyl ethyl ketone or acetylacetone or aliphatic ketones such as 4-methyl-2-pentanone; in step (1), the temperature is raised to 20°C - 80°C and the stirring time is 1 - 5 h.

[0010] Further, as a preferred embodiment, for the distillation of the organic phase in step (2), atmospheric distillation or vacuum distillation is used.

[0011] Further, as a preferred embodiment, in step (3), the stripping temperature is 50°C - 70°C; the stripping gas-liquid ratio is 1000 - 10000; the stripping time is 1 h - 7 h.

[0012] Further, as a preferred embodiment, in step (4), the pH of the wastewater is adjusted to 11 - 13 and the pH is maintained not lower than 11 during the stripping process; the stripping temperature is 50°C - 70°C; the stripping gas-liquid ratio is 1000 - 10000; the stripping time is 1 h - 7 h.

[0013] Further, as a preferred embodiment, the alkali in step (4) is one or more of potassium hydroxide, sodium hydroxide, calcium hydroxide or calcium oxide.

[0014] Beneficial effects: (1) In the present invention, the reaction of aldehyde or ketone with hydrazine hydrate in the wastewater can completely remove the highly toxic hydrazine hydrate; (2) In the present invention, the stripping method is used to treat the high ammonia-nitrogen substances in the wastewater, which has a simple process, stable treatment effect, low capital construction cost and operation cost, and strong practicability. After treatment, the ammonia-nitrogen value is reduced from 60000 mg / L to 80 mg / L, and the effect is remarkable; (3) The by-product sulfur obtained by the present invention has a purity as high as 95% and can be directly sold without further purification; (4) After being treated by the present invention, the COD value of the thiocarbamide wastewater is reduced from the original 180000 mg / L to 20000 mg / L, and the COD removal rate is 88%. (5) After being treated by the present invention, the smell of the thiocarbamide wastewater changes from a strong smell of rotten eggs to odorless, and the color changes from purplish red to light yellow; (6) After being treated by the present invention, the thiocarbamide wastewater can reach the discharge standard after simple biochemical treatment, which reduces the difficulty for the next step of biochemical treatment. Specific embodiments

[0015] The technical solution of the present invention will be described in detail below through embodiments, but the protection scope of the present invention is not limited to the described embodiments.

[0016] Example 1: 600 g of the original thiocarb wastewater was put into a clean 1000 ml four-necked flask, and 164 g of diisobutyl ketone was added. The four-necked flask was equipped with a condenser, and the outlet of the condenser was connected by a white rubber tube to a secondary tail gas absorption system composed of 25% sodium hydroxide and 30% dilute sulfuric acid. It was kept warm at 50 °C for 4 h with stirring, cooled to room temperature, and allowed to stand for 20 min to obtain 597 g of an aqueous phase and 167 g of an organic phase. 15 g of diisobutyl ketone was recovered under the conditions of a vacuum degree of 0.8 Mpa and a maximum temperature of 159 °C. The wastewater phase was heated to 60 °C, and air was blown by an air pump for 3 h. The tail gas was absorbed by the secondary tail gas absorption system composed of 25% sodium hydroxide and 30% dilute sulfuric acid. After cooling to room temperature, it was filtered, and the filter cake was dried to obtain 10 g of 95% sulfur. 5 g of flake caustic soda was added to the filtrate wastewater to adjust the pH to 12. The tail gas absorption device was opened, and air was continuously blown while heating to 60 °C for 4 h. After cooling to room temperature, 2.2 g of 38% dilute hydrochloric acid was used to adjust the pH of the wastewater to 7, obtaining 560 g of a light yellow transparent solution, which was detected to meet the discharge standard.

[0017] Example 2: 600 g of the original thiocarb wastewater was put into a clean 1000 ml four-necked flask, and 118 g of 4-methyl-2-pentanone was added. The four-necked flask was equipped with a condenser, and the outlet of the condenser was connected by a white rubber tube to a secondary tail gas absorption system composed of 25% sodium hydroxide and 30% dilute sulfuric acid. It was kept warm at 50 °C for 3 h with stirring, cooled to room temperature, and allowed to stand for 20 min to obtain 598 g of an aqueous phase and 118 g of an organic phase. 11 g of 4-methyl-2-pentanone was recovered under the conditions of a vacuum degree of 0.8 Mpa and a maximum temperature of 110 °C. The wastewater phase was heated to 70 °C, and air was blown by an air pump for 2 h. The tail gas was absorbed by the secondary tail gas absorption system composed of 25% sodium hydroxide and 30% dilute sulfuric acid. After cooling to room temperature, it was filtered, and the filter cake was dried to obtain 10 g of 95% sulfur. 5 g of flake caustic soda was added to the filtrate wastewater to adjust the pH to 12. The tail gas absorption device was opened, and air was continuously blown while heating to 70 °C for 3 h. After cooling to room temperature, 2.2 g of 38% dilute hydrochloric acid was used to adjust the pH of the wastewater to 7, obtaining 562 g of a light yellow transparent solution, which was detected to meet the discharge standard.

[0018] As can be seen from the above embodiments, in the present invention, hydrazine hydrate with high toxicity can be completely treated by reacting aldehyde or ketone with hydrazine hydrate in wastewater; the stripping method is adopted to treat high ammonia-nitrogen substances in wastewater, which has the advantages of simple process, stable treatment effect, low capital construction cost and operation cost, and strong practicability. After treatment, the ammonia-nitrogen value is reduced from 60000 mg / L to 80 mg / L, and the effect is remarkable; the by-product sulfur obtained by the present invention has a purity as high as 95%, and can be directly sold without further purification; after being treated by the present invention, the COD value of the thiocarbamide wastewater is reduced from the original 180000 mg / L to 20000 mg / L, and the COD removal rate is 88%. After being treated by the present invention, the smell of the thiocarbamide wastewater changes from a strong rotten-egg smell to odorless, and the color changes from purplish red to light yellow; after being treated by the present invention, the thiocarbamide wastewater can reach the discharge standard after simple biochemical treatment, which reduces the difficulty for the next-step biochemical treatment.

[0019] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation to the present invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A process for efficiently treating the wastewater produced in the production of thiosemicarbazide, characterized in that it comprises the following steps: (1) Put a quantitative amount of thiosemicarbazide wastewater and a quantitative amount of aldehyde or ketone into a reaction flask, heat up and stir, heat up to 20°C - 80°C, the stirring time is 1 - 5 h, cool down and separate layers to obtain an aqueous phase and an organic phase. The aldehyde is benzaldehyde or phenylacetaldehyde or n-butanal or n-pentanal, and the ketone is benzophenone or acetophenone or diisobutyl ketone or methyl ethyl ketone or acetylacetone or 4-methyl-2-pentanone fatty ketone; (2) Distill the organic phase in step (1) to recover the corresponding aldehyde or ketone; (3) Heat up the aqueous phase in step (1) to a certain temperature, then blow air for a certain time, cool down to room temperature and filter. The filter cake is dried with sulfur as a by-product, and the filtrate aqueous phase continues for the next treatment; (4) Adjust the pH of the filtrate aqueous phase obtained in step (3) to be alkaline with an alkali, heat up to a certain temperature and continue to blow air for a certain time, cool down to room temperature, adjust the pH of the blown wastewater to neutral with dilute hydrochloric acid, discharge it to the three-waste treatment center for the next biochemical treatment, and discharge it after reaching the standard. The alkali is one or several of potassium hydroxide, sodium hydroxide, calcium hydroxide or calcium oxide.

2. The process for efficiently treating the wastewater produced in the production of thiosemicarbazide according to claim 1, characterized in that: For the distillation of the organic phase in step (2), atmospheric distillation or vacuum distillation is adopted.

3. The process for efficiently treating the wastewater produced in the production of thiosemicarbazide according to claim 1, characterized in that: In step (3), the stripping temperature is 50°C - 70°C; the stripping gas-liquid ratio is 1000 - 10000; the stripping time is 1 h - 7 h.

4. The process for efficiently treating the wastewater produced in the production of thiosemicarbazide according to claim 1, characterized in that: In step (4), the pH of the wastewater is adjusted to 11 - 13 and the pH is maintained not lower than 11 during the stripping process; the stripping temperature is 50°C - 70°C; the stripping gas-liquid ratio is 1000 - 10000; the stripping time is 1 h - 7 h.