Nitrobenzene wastewater reduction device and method

Abstract

The invention relates to a nitrobenzene wastewater reduction method and device, and belongs to the technical field of organic synthesis product separation and purification. Acid nitrobenzene is subjected to acid pickling-alkali washing-water washing instead of a traditional alkali washing-water washing process, acid pickling water and alkali washing water are treated separately, and phenol-containing biotoxic nitrobenzene alkaline wastewater is reduced. The phenol-containing wastewater generated in the acidic nitrobenzene washing process is reduced, the yield of phenol-containing alkaline wastewater is reduced by 50%-55%, the consumption of liquid caustic soda is reduced by 50%-55%, the investment cost and the operation cost of a nitrobenzene wastewater pretreatment device are greatly reduced, and the method is particularly suitable for the washing process of nitrobenzene products subjected to mixed acid nitration.

Description

Technical Field

[0001] A nitrobenzene wastewater reduction device and method belong to the technical field of organic synthesis, and specifically relate to a device and method for reducing the amount of difficult-to-degrade wastewater generated during the alkaline washing process of acidic nitrobenzene water. Background Art

[0002] In the production process of nitrobenzene, benzene undergoes nitration reaction under the action of mixed acid composed of sulfuric acid and nitric acid, and produces nitrobenzene as the main product, while producing dangerous nitrophenols as byproducts, which must be removed. Acidic nitrobenzene refers to the product after the initial separation of the acid remaining in nitrobenzene after the nitration reaction. In addition to the main component nitrobenzene, it also contains sulfuric acid, nitric acid, nitrophenol, etc. In industry, nitrobenzene washing is generally used to neutralize and wash acidic nitrobenzene by adding dilute alkali solution, and the sulfuric acid, nitric acid, and nitrophenol in the acidic nitrobenzene are all converted into sodium salts and transferred to the water phase. After the alkaline water is separated from nitrobenzene, the remaining sodium salt in nitrobenzene is further washed by water washing. The alkaline washing water and the water washing water are mixed and enter the nitrobenzene wastewater stripping tower. After the nitrobenzene in the wastewater is recovered, the wastewater discharged from the kettle of the nitrobenzene wastewater stripping tower is the alkaline nitrobenzene wastewater. Regardless of the washing method used, such as multi-kettle series washing, multi-injector series jet washing, and pipeline washing, the amount of wastewater generated is generally 0.7t wastewater / t acidic nitrobenzene.

[0003] The nitrobenzene wastewater produced by the traditional washing method of acidic nitrobenzene has a nitrophenol content of between 50mg / L and 150mg / L. It is dark in color, highly biotoxic, and poorly biodegradable. It is a difficult-to-degrade phenol-containing wastewater with biotoxicity. This type of nitrobenzene wastewater cannot be fed into a large biochemical treatment device for wastewater treatment. Complex pretreatment methods such as enhanced oxidation are required to convert nitrophenol into biodegradable small molecules for biochemical treatment, which results in high pretreatment costs. For nitrobenzene production enterprises supporting coal chemical enterprises, nitrobenzene wastewater is used as raw material water for pulverized coal pulping and mixed with coal for incineration. However, for enterprises without supporting coal chemical equipment, the amount of nitrobenzene wastewater generated directly determines the level of their pretreatment costs.

[0004] On the other hand, since the separation of the mixed acid and nitrobenzene of acidic nitrobenzene is often not thorough, sulfuric acid and nitric acid will consume a large amount of liquid alkali during direct alkaline washing, and the main purpose of acidic nitrobenzene washing is to remove the dangerous byproduct nitrophenol. Since the phenol content is low, only a small amount of liquid alkali is consumed, so the consumption of alkali liquid is large and deviates from the original intention of alkaline washing. Since sulfuric acid is used as a catalyst in the mixed acid nitration process, water is produced during the nitration reaction, resulting in the acid concentration of the nitration product separated to become dilute at about 68wt.%, and it is necessary to adopt a vacuum concentration method to evaporate the water, and the concentrated acid 86wt.% is returned for use. In the dilute acid concentration process, the concentrated water with an acid content of 0.3wt.% is also neutralized with the alkaline wastewater produced in the acidic nitrobenzene alkaline water washing process to become non-biodegradable nitrobenzene wastewater, increasing the amount of nitrobenzene wastewater generated. Summary of the invention

[0005] The purpose of the present invention is to provide a nitrobenzene wastewater reduction device and method to solve the problems that nitrobenzene wastewater is non-biodegradable, highly toxic, produces a large amount of wastewater in traditional washing methods, and has high pretreatment investment and operating costs.

[0006] The invention proposes a combined washing scheme of acid washing-alkali washing-water washing for acidic nitrobenzene, which makes full use of low-content acid-containing wastewater generated by dilute acid concentration of a nitrobenzene device to wash the acidic nitrobenzene first, remove most of the sulfuric acid and nitric acid that are not completely separated and carried in the acidic nitrobenzene, then use a small amount of dilute alkali to neutralize a small amount of mixed acid and nitrophenol remaining in the nitrobenzene, and finally use water washing to further wash the inorganic sodium salt and nitrophenol sodium salt in the nitrobenzene.

[0007] The present invention is implemented as follows: a nitrobenzene wastewater reduction device, characterized in that it includes an acid wash, an alkali wash and a water wash system connected in sequence; the acid wash system includes an acid wash mixer, an acid wash separator, an acidic water stripping tower and an acidic water stripping tower top condenser; the alkali wash system includes an alkali wash mixer, an alkali wash separator, an alkaline water stripping tower, and an alkaline water stripping tower top condenser; the water wash system includes a water wash mixer and a water wash separator.

[0008] The present invention also provides a nitrobenzene wastewater reduction method using the above device, which is characterized in that acidic nitrobenzene is sent into a pickling mixer by an acidic nitrobenzene delivery pump to be mixed with condensed water from the top of an acidic water stripping tower and pickling water replenishment water, residual sulfuric acid and nitric acid in the acidic nitrobenzene are dissolved into water to form an aqueous phase, and nitrobenzene, nitrophenol and a small amount of water form an oil phase; the aqueous phase and the oil phase formed in the pickling mixer are separated into oil and water in a pickling separator, and water is drawn out at the top of the pickling separator. The acidic water stripping tower is connected to the acidic water stripping tower. The steam at the top of the acidic water stripping tower is condensed in the top condenser of the acidic water stripping tower and then returned to the pickling mixer for recycling. The acidic wastewater from the acidic water stripping tower kettle, which has been freed of nitrobenzene and other organic substances, is directly sent to the biochemical system by the acidic wastewater delivery pump; the oil phase drawn out from the bottom of the pickling separator is mixed with the dilute alkali solution in the alkali washing mixer, and the remaining dissolved acid, free acid and nitrophenol in the acidic nitrobenzene react with the alkali to neutralize the sodium sulfate, sodium nitrate, Sodium nitrophenol salt is transferred to water to form an aqueous phase, and nitrobenzene, a small amount of sodium salt and water form an oil phase; the aqueous phase and the oil phase formed in the alkali washing mixer are separated into oil and water in the alkali washing separator, and the aqueous phase is drawn out from the top of the alkali washing separator to the alkaline water stripping tower. The steam at the top of the alkaline water stripping tower is condensed by the alkaline water stripping tower top condenser and then enters the water washing mixer for the next process. The alkaline water stripping tower kettle is the alkaline wastewater from which organic matter such as nitrobenzene has been removed, and the alkaline wastewater delivery pump is used to send wastewater to the alkaline water stripping tower. Pretreatment: The oil phase drawn out from the bottom of the alkali wash separator is mixed with the condensed water from the top of the alkaline water stripping tower and the water make-up water of the wash water in the water wash mixer to further wash and remove the residual sodium salt in the oil phase nitrobenzene. The mixed oil and water phases are separated into oil and water in the water wash separator, and the water phase drawn out from the top of the water wash separator is mixed with the water phase drawn out from the top of the alkali wash separator and enters the alkaline water stripping tower. The oil phase drawn out from the bottom of the water wash separator is sent to the refining system by the crude nitrobenzene delivery pump.

[0009] Generally, the acidic wastewater is acidic wastewater that does not contain nitrophenols and other substances with biological toxicity characteristics, and has a B / C value of 0.5-0.7. It can be used as a pH regulator instead of sulfuric acid in the biochemical treatment process of wastewater.

[0010] The sulfuric acid concentration in the acidic wastewater is 0.5 wt.%~7 wt.%, and the amount of wastewater generated is 30%-35% of the volume flow of acidic nitrobenzene.

[0011] The alkaline wastewater is alkaline wastewater containing 50mg / L-150mg / L nitrophenols and other biologically toxic characteristics, with a B / C value of less than 0.3. Chemical pretreatment is required to remove biological toxicity before biochemical treatment.

[0012] The pH value of the alkaline wastewater is 12-13, and the amount of wastewater produced is 30%-35% of the volume flow of acidic nitrobenzene.

[0013] The dilute alkali solution is a 14% to 18% NaOH aqueous solution, preferably 15.8%, and the added amount is 1.2% to 1.5% of the volume flow of acidic nitrobenzene.

[0014] The amount of material discharged from the top of the acidic water stripping tower is 15%-25% of its feed amount.

[0015] The amount of material discharged from the top of the alkaline water stripping tower is 15%-25% of its feed amount.

[0016] The content of sodium 2,4-dinitrophenolate in the crude nitrobenzene is ≤5 mg / L.

[0017] The pickling water replenishment comes from the condensate at the top of the waste acid concentration tower, and the sulfuric acid content is 0.1% to 0.5wt.%, preferably 0.3wt.%.

[0018] The advantages and effects achieved by the present invention are: a method and device for reducing the amount of nitrobenzene wastewater, acid washing-alkali washing-water washing are used for acidic nitrobenzene in sequence, and biodegradable acidic wastewater and non-biodegradable alkaline wastewater are respectively produced, the acidic wastewater is directly sent to the wastewater treatment large biochemical system as a pH value regulator after stripping to remove nitrobenzene, and the alkaline wastewater is sent to the nitrophenol wastewater pretreatment process after stripping to recover nitrobenzene. Compared with the traditional alkaline washing-water washing dephenolization and acid removal process, the present invention can reduce the amount of refractory phenol-containing wastewater by 50%-55%, reduce the amount of dilute alkali required for neutralization by 50%-55%, and make full use of soft water resources such as acidic wastewater and steam condensate generated by waste acid concentration, reduce the amount of alkaline phenol-containing wastewater produced, and reduce the investment cost and operation cost required for alkaline wastewater pretreatment, and is particularly suitable for the deacidification and phenol removal chemical process of preparing nitrobenzene by mixed acid nitration. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of the process flow of a nitrobenzene wastewater reduction method using the inventive device.

[0020] In the figure, 1 is an acidic nitrobenzene tank, 2 is an acidic nitrobenzene delivery pump, 3 is an acid washing mixer, 4 is an acid washing separator, 5 is an alkaline washing mixer, 6 is an alkaline washing separator, 7 is a water washing mixer, 8 is a water washing separator, 9 is a crude nitrobenzene delivery pump, 10 is an acidic water stripping tower, 11 is an acidic water stripping tower top condenser, 12 is an acidic wastewater delivery pump, 13 is an alkaline water stripping tower, 14 is an alkaline water stripping tower top condenser, and 15 is an alkaline wastewater delivery pump. Implementation

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Example

[0022] A nitrobenzene wastewater reduction device reference attachment Figure 1, mainly including acid washing, alkali washing and water washing systems connected in sequence; the acid washing system includes an acid washing mixer 3, an acid washing separator 4, an acidic water stripping tower 10 and an acidic water stripping tower top condenser 11; the alkali washing system includes an alkali washing mixer 5, an alkali washing separator 6, an alkaline water stripping tower 13, and an alkaline water stripping tower top condenser 14; the water washing system includes a water washing mixer 7 and a water washing separator 8.

[0023] Embodiment Nitrobenzene wastewater reduction method adopts the above device, and the process flow is referred to the attached Figure 1 The specific process is as follows: the acidic nitrobenzene in the acidic nitrobenzene storage tank 1 is delivered to the pickling mixer 3 by the acidic nitrobenzene delivery pump 2 and mixed with the condensed water from the top of the acidic water stripping tower 10 and the pickling water replenishment water; the residual sulfuric acid and nitric acid in the acidic nitrobenzene are dissolved into the water to form an aqueous phase; nitrobenzene, nitrophenol and a small amount of water form an oil phase; the aqueous phase and the oil phase formed in the pickling mixer 3 are separated into oil and water in the pickling separator 4; the aqueous phase is drawn out from the top of the pickling separator 4 to the acidic water stripping tower 10; the acidic water stripping tower 10 is used for the separation of oil and water; The steam from the top of tower 10 is condensed in the top condenser 11 of the acidic water stripping tower and then returned to the acid washing mixer 3 for recycling. The acidic wastewater from the bottom of the acidic water stripping tower, which has been freed of organic matter such as nitrobenzene, is directly sent to the large biochemical plant by the acidic wastewater delivery pump 12 for adjusting the pH value of the wastewater instead of using sulfuric acid. The oil phase drawn out from the bottom of the acid washing separator 4 is mixed with the dilute alkali solution in the alkali washing mixer 5. The dissolved acid, free acid and nitrophenol remaining in the acidic nitrobenzene react with the alkali to neutralize the sodium sulfate, sodium nitrate and nitrophenol. The sodium phenol salt is transferred to water to form an aqueous phase, and nitrobenzene, a small amount of sodium salt and water form an oil phase; the aqueous phase and the oil phase formed in the alkali washing mixer 5 are separated into oil and water in the alkali washing separator 6, and the aqueous phase is drawn out from the top of the alkali washing separator 6 to the alkaline water stripping tower 13. The top steam of the alkaline water stripping tower 13 is condensed by the alkaline water stripping tower top condenser 14 and then enters the water washing mixer 7 for the next process. The bottom of the alkaline water stripping tower 13 is the alkaline wastewater from which organic matter such as nitrobenzene has been removed, and is sent to the waste water by the alkaline wastewater delivery pump 15. Water treatment: The oil phase drawn out from the bottom of the alkaline washing separator 6 is mixed with the condensed water from the top of the alkaline water stripping tower 13 and the washing water makeup water in the water washing mixer 7, and the residual sodium salt in the oil phase nitrobenzene is further washed and removed. The mixed oil and water phases are separated into oil and water in the water washing separator 8, and the water phase drawn out from the top of the water washing separator 8 is mixed with the water phase drawn out from the top of the alkaline washing separator 6 and enters the alkaline water stripping tower 13. The oil phase drawn out from the bottom of the water washing separator 8 is sent to the refining system by the crude nitrobenzene delivery pump 9. Example 1

[0024] A nitrobenzene plant, nitrobenzene production capacity 90,000 tons / year, acid nitrobenzene flow rate 12.5m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 8m 3After the acid-alkali-water washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.53, and the sulfuric acid concentration in the acidic wastewater was 5 wt.%. The amount of acidic wastewater generated was 4.13m 3 / h, which is 33% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 80 mg / L, a pH value of 12, a B / C value of 0, and an alkaline wastewater volume of 3.87 m 3 / h, which is 31% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 175L / h, which is 1.4% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 20% of its feed amount, and the discharge amount of the alkaline water stripping tower is 18% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 3.7m 3 / h, which is 29.6% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 4.2 mg / L. Example 2

[0025] A nitrobenzene plant, nitrobenzene production capacity 190,000 tons / year, acid nitrobenzene flow 26m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 17m 3 / h. After the acid-wash-alkali-wash-water-washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.68, and the sulfuric acid concentration in the acidic wastewater was 0.5 wt.%. The amount of acidic wastewater generated was 7.8 m 3 / h, which is 30% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 50 mg / L, a pH value of 12, a B / C value of 0, and an alkaline wastewater volume of 9.1 m 3 / h, which is 35% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 390L / h, which is 1.5% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 15% of its feed amount, and the discharge amount of the alkaline water stripping tower is 25% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 8.71 m 3 / h, which is 33.5% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 3.5 mg / L. Example 3

[0026] A nitrobenzene plant, nitrobenzene production capacity 290,000 tons / year, acid nitrobenzene flow 36m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 25m 3After the acid-alkali-water washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.61, and the sulfuric acid concentration in the acidic wastewater was 7 wt.%. The amount of acidic wastewater generated was 12.6 m 3 / h, which is 35% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 150 mg / L, a pH value of 12, a B / C value of 0, and an alkaline wastewater volume of 10.8 m 3 / h, which is 30% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 432 L / h, which is 1.2% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 25% of its feed amount, and the discharge amount of the alkaline water stripping tower is 15% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 10.37 m 3 / h, which is 28.8% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 4.8 mg / L. Example 4

[0027] A nitrobenzene plant, nitrobenzene production capacity 50,000 tons / year, acid nitrobenzene flow 6m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 4.2 m 3 After the acid-alkali-water washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.5, and the sulfuric acid concentration in the acidic wastewater was 2 wt.%. The amount of acidic wastewater generated was 1.9 m 3 / h, which is 32% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 100 mg / L, a pH value of 12.5, a B / C value of 0.1, and an alkaline wastewater volume of 1.86 m 3 / h, which is 31% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 78 L / h, which is 1.3% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 20% of its feed amount, and the discharge amount of the alkaline water stripping tower is 22% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 1.82 m 3 / h, which is 30.4% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 3 mg / L. Example 5

[0028] A nitrobenzene plant with a nitrobenzene capacity of 150,000 tons / year and an acidic nitrobenzene flow rate of 18.6 m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 13m 3 / h. After the acid-wash-alkali-wash-water-washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.65, and the sulfuric acid concentration in the acidic wastewater was 4 wt.%. The amount of acidic wastewater generated was 6.3 m 3 / h, which is 34% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 120 mg / L, a pH value of 12.4, a B / C value of 0.2, and an alkaline wastewater volume of 6.3 m 3 / h, which is 34% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 260 L / h of 15.8 wt.% dilute alkali solution is added, which is 1.4% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 18% of its feed amount, and the discharge amount of the alkaline water stripping tower is 21% of its feed amount. The water wash water is replenished with recycled steam condensate, and the replenishment amount is 10.37 m 3 / h, which is 28.8% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 4.8 mg / L. Example 6

[0029] A nitrobenzene plant, nitrobenzene production capacity 350,000 tons / year, acid nitrobenzene flow 43.5m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 30.5 m 3 / h. After the acid-wash-alkali-wash-water-washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.65, and the sulfuric acid concentration in the acidic wastewater was 5.6 wt.%. The amount of acidic wastewater generated was 13.9 m 3 / h, which is 32% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 80 mg / L, a pH value of 12.3, a B / C value of 0, and an alkaline wastewater volume of 14.8m 3 / h, which is 34% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 609 L / h, which is 1.4% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 23% of its feed amount, and the discharge amount of the alkaline water stripping tower is 19% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 14.2 m 3 / h, which is 32.6% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 3.2 mg / L. Example 7

[0030] A nitrobenzene plant, nitrobenzene production capacity 100,000 tons / year, acid nitrobenzene flow 12.4m 3 / h, using the original alkali washing-water washing process, the amount of wastewater generated is 8.7 m 3 / h. After the acid-wash-alkali-wash-water-washing transformation using the device in the embodiment, the B / C value of the acidic wastewater was 0.58, and the sulfuric acid concentration in the acidic wastewater was 6 wt.%. The amount of acidic wastewater generated was 4.0 m 3 / h, which is 32% of the volume flow of acidic nitrobenzene. The alkaline wastewater produced has a nitrophenol content of 90 mg / L, a pH value of 12.8, a B / C value of 0.5, and an alkaline wastewater volume of 3.8m 3 / h, which is 31% of the volume flow of acidic nitrobenzene. During the alkaline washing process, 15.8 wt.% dilute alkali solution is added at 161 L / h, which is 1.3% of the volume flow of acidic nitrobenzene. The discharge amount of the acidic water stripping tower is 24% of its feed amount, and the discharge amount of the alkaline water stripping tower is 22% of its feed amount. The water replenishment of the washing water is recycled steam condensate, and the replenishment amount is 3.64 m 3 / h, which is 29.3% of the volume flow of acidic nitrobenzene. The content of sodium nitrophenolate (calculated as sodium 2,4-dinitrophenolate) in crude nitrobenzene after acid washing, alkali washing and water washing is 3.1 mg / L.

[0031] Comparative example: The current nitrobenzene plant adopts isothermal nitration process, with a nitrobenzene production capacity of 290,000 tons / year and an acidic nitrobenzene flow rate of 36m 3 / h, using alkali washing-water washing process, the amount of wastewater generated is 25m 3 / h, using alkaline neutralization + secondary water washing process, the alkaline washing water and water washing water are mixed and sent to the alkaline wastewater stripping tower. The amount of alkaline wastewater produced after stripping is 22m 3 / h, the condensate at the top of the tower is supplemented to the water washing section. Because the acidic nitrobenzene contains some sulfuric acid and nitric acid, the alkali consumption is large. The amount of 15.8% dilute alkali added is 950L / h, totaling 1.16t / h. The content of sodium nitrophenol in the generated alkaline wastewater is 130mg / L, and the pH value is 12.5.

[0032] As can be seen from the above embodiments, the present invention uses dilute acid to concentrate the acidic nitrobenzene after the initial separation of the product of the nitration reaction, first washes it with water, then adds a small amount of dilute alkali to neutralize and remove the residual sulfuric acid, nitric acid and nitrophenol, and finally uses steam condensation or other soft water to wash it. The acidic wastewater after acid washing is sent to biochemical treatment for adjusting the pH value to replace 86 wt.% sulfuric acid after stripping in the acidic water stripping tower, and the tower top condensate is reused for acid washing; the alkaline nitrobenzene wastewater after alkaline water washing is sent to the pretreatment process after stripping in the alkaline water stripping tower, and the tower top condensate is returned for washing. Compared with the traditional acid nitrobenzene alkali washing-water washing process, the amount of alkaline nitrobenzene wastewater generated is reduced by 50%-55%, and the alkali consumption is reduced by 50%-55%, which reduces the investment cost and operating cost required for the pretreatment of alkaline nitrobenzene wastewater, and is particularly suitable for the washing, neutralization and phenol removal process of acid nitrobenzene.

Claims

1. A nitrobenzene wastewater reduction device, characterized in that it includes an acid wash, an alkali wash and a water wash system connected in sequence; the acid wash system includes an acid wash mixer, an acid wash separator, an acidic water stripping tower and an acidic water stripping tower top condenser; the alkali wash system includes an alkali wash mixer, an alkali wash separator, an alkaline water stripping tower, and an alkaline water stripping tower top condenser; the water wash system includes a water wash mixer and a water wash separator.

2. A method for reducing nitrobenzene wastewater using the device of claim 1, characterized in that Acidic nitrobenzene is sent to the pickling mixer by the acidic nitrobenzene delivery pump to be mixed with the condensed water from the top of the acidic water stripping tower and the pickling water replenishment water. The residual sulfuric acid and nitric acid in the acidic nitrobenzene are dissolved into the water to form an aqueous phase, and nitrobenzene, nitrophenol and a small amount of water form an oil phase; the aqueous phase and the oil phase formed in the pickling mixer are separated into oil and water in the pickling separator, and the aqueous phase is drawn out from the top of the pickling separator to the acidic water stripping tower. The steam at the top of the acidic water stripping tower is condensed in the top condenser of the acidic water stripping tower and returned to the pickling mixer for recycling. The acidic wastewater from the acidic water stripping tower kettle is directly sent to the biochemical system by the acidic wastewater delivery pump to remove organic matter; the oil phase drawn out from the bottom of the pickling separator is mixed with the dilute alkali solution in the alkali washing mixer, and the remaining dissolved acid, free acid and nitrophenol in the acidic nitrobenzene react with the alkali to form an aqueous phase. Sodium sulfate, sodium nitrate and sodium nitrophenol are transferred to the water to form an aqueous phase. , nitrobenzene, a small amount of sodium salt and water form an oil phase; the water phase and the oil phase formed in the alkali washing mixer are separated into oil and water in the alkali washing separator, and the water phase is drawn out from the top of the alkali washing separator to the alkaline water stripping tower. The steam at the top of the alkaline water stripping tower is condensed by the alkaline water stripping tower top condenser and then enters the water washing mixer for the next process. The alkaline water stripping tower kettle is the alkaline wastewater with organic matter removed, which is sent to wastewater pretreatment by the alkaline wastewater delivery pump; the oil phase drawn out from the bottom of the alkali washing separator is mixed with the condensed water from the top of the alkaline water stripping tower and the water washing water makeup water in the water washing mixer, and the residual sodium salt in the oil phase nitrobenzene is further washed and removed. The mixed oil and water phases are separated into oil and water in the water washing separator, and the water phase drawn out from the top of the water washing separator is mixed with the water phase drawn out from the top of the alkali washing separator and enters the alkaline water stripping tower. The oil phase drawn out from the bottom of the water washing separator is sent to the refining system by the crude nitrobenzene delivery pump.

3. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The acidic wastewater is acidic wastewater that does not contain nitrophenols and biologically toxic substances, and has a B / C value of 0.5-0.

7. It is used as a pH regulator instead of sulfuric acid in the biochemical treatment of wastewater.

4. The method for reducing nitrobenzene wastewater according to claim 2 or 3, characterized in that The sulfuric acid concentration in the acidic wastewater is 0.5 wt.%~7 wt.%, and the amount of wastewater generated is 30%-35% of the volume flow of acidic nitrobenzene.

5. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The alkaline wastewater is alkaline wastewater containing 50 mg / L-150 mg / L nitrophenols with biological toxicity characteristics, with a B / C value of less than 0.

3. Chemical pretreatment is used to remove biological toxicity and then biochemical treatment is performed.

6. The method for reducing nitrobenzene wastewater according to claim 2 or 5, characterized in that The pH value of the alkaline wastewater is 12-13, and the amount of wastewater produced is 30%-35% of the volume flow of acidic nitrobenzene.

7. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The dilute alkali solution is a 14% to 18% NaOH aqueous solution, preferably 15.8%; the added amount is 1.2% to 1.5% of the volume flow of acidic nitrobenzene.

8. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The amount of material discharged from the top of the acidic water stripping tower is 15%-25% of its feed amount.

9. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The amount of material discharged from the top of the alkaline water stripping tower is 15%-25% of its feed amount.

10. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The wash water makeup water is recycled steam condensate or other soft water, and the makeup amount is 28%-34% of the volume flow of acidic nitrobenzene.

11. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The content of sodium 2,4-dinitrophenolate in the crude nitrobenzene is ≤5 mg / L.

12. The method for reducing nitrobenzene wastewater according to claim 2, characterized in that The pickling water replenishment comes from the condensate at the top of the waste acid concentration tower, and the sulfuric acid content is 0.1% to 0.5%, preferably 0.3%.

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