Method for recovering nitric acid from nitrated yellow water

Abstract

The invention belongs to the technical field of waste recycling, and particularly relates to a method for recycling nitric acid in acid yellow water based on nitration. The method for recovering nitric acid based on nitration acid yellow water comprises the following steps: stirring nitration acid yellow water and toluene or nitrotoluene and other organic extraction agents in a mixer, adding a certain amount of sulfamic acid, fully extracting, standing for layering, and removing the organic extraction agents through a stripping tower to obtain the nitric acid. The acid yellow water after extraction-steam stripping is sent to a nitric acid absorption-concentration tower to obtain concentrated nitric acid, and the concentrated nitric acid is recycled to a nitration reaction unit as a raw material.

Description

Technical Field

[0001] The invention belongs to the technical field of waste recycling, and in particular relates to a method for recovering nitric acid from nitrified acidic yellow water. Background Art

[0002] Nitration reaction is an important reaction for producing isocyanates, explosives, fuels and medicines, and is widely used in the chemical industry. At present, the traditional toluene nitration process usually uses nitric-sulfuric acid mixed acid (concentrated sulfuric acid mixed with concentrated nitric acid) to react with organic matter for nitration, wherein sulfuric acid is used as a catalyst for the nitration reaction, and nitric acid is used as a raw material for the nitration reaction. After the toluene nitration reaction is completed, waste acid and crude dinitrotoluene (DNT) will be produced. At present, the separation of waste acid and dinitrotoluene is usually achieved in a layered manner in industry, that is, the density difference between sulfuric acid and dinitrotoluene is utilized, and crude DNT is extracted in the upper layer to the washing and refining unit, and refined DNT is finally obtained. In the washing process of the whole crude DNT, pickling is an indispensable process, because the crude DNT will dissolve or carry a certain amount of nitric acid and sulfuric acid into the subsequent washing unit (mainly nitric acid).

[0003] In the traditional recovery process, if the nitric acid and sulfuric acid in the crude DNT are directly removed by alkali washing, the nitric acid and sulfuric acid will be neutralized into nitric acid and sulfate and enter the aqueous phase, resulting in a large amount of nitric acid and sulfuric acid loss. In addition, the wastewater generated after washing contains a large amount of nitrate and sulfate, which makes wastewater treatment difficult and costly. Therefore, it is economically beneficial to recover the nitric acid and sulfuric acid dissolved or entrained in the crude DNT. In the existing industry, washing water and crude DNT are stirred and mixed for extraction, and nitric acid and sulfuric acid are extracted into the aqueous phase because they are easily soluble in water. The acid washing water (yellow water) and DNT are separated after phase separation, and the crude DNT enters the alkali washing unit to further remove the remaining trace nitric acid and sulfuric acid. The yellow water is dissolved with most of the acid and a small amount of DNT, and is finally recovered to the nitration reaction unit, thereby realizing the recycling and reuse of nitric acid and sulfuric acid.

[0004] However, although the acid washing process can recover the acid in the crude DNT, the concentration of nitric acid and sulfuric acid in the generated yellow water is low, and the main component is still water. After it is recycled to the nitration reaction system, a large amount of water will be further introduced. This part of water will eventually leave the nitration unit in the form of nitration waste acid, resulting in an increase in the amount of nitration waste acid generated, increasing the load of the waste acid concentration unit and steam consumption. Therefore, the art still needs to seek an efficient acid recovery process to avoid the loss of nitric acid and sulfuric acid in the system, while reducing the water intake of the nitration reaction unit. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to provide a method for recovering nitric acid from acidic yellow water based on nitration. The method mainly aims at the problem that the yellow water produced after the nitration of aromatic hydrocarbons is treated and recovered by conventional methods, but there is a problem that after the yellow water is reused in the nitration reaction system, a large amount of waste acid is generated, and the waste acid concentration load and energy consumption are high, thereby providing an economical and efficient method for recovering nitric acid from yellow water.

[0006] In order to solve the above technical problems, the present invention discloses a method for recovering nitric acid from nitrated acidic yellow water, comprising the following steps:

[0007] (1) taking the nitrated acidic yellow water to be treated, adding an organic solvent and aminosulfonic acid to carry out mixed extraction, and collecting the organic solvent layer and the extracted acidic yellow water after stratification;

[0008] (2) subjecting the extracted acidic yellow water to a stripping treatment to obtain stripped acidic yellow water;

[0009] (3) collecting the stripping acidic yellow water and concentrating it to obtain concentrated nitric acid.

[0010] Specifically, in the method for recovering nitric acid from nitrified acidic yellow water, in step (1):

[0011] The amount of aminosulfonic acid added is 0.1-1wt% of the mass of the nitrated acidic yellow water; and / or,

[0012] The amount of the organic solvent added is 50-200 wt % of the mass of the nitrated acidic yellow water.

[0013] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, in step (1), in the mixed extraction step:

[0014] The extraction temperature is 30-70°C; and / or,

[0015] The extraction time is 1-20 min; and / or,

[0016] The stratification time is 1-20min.

[0017] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, in step (1), the mixed extraction step includes a step of performing paddle stirring;

[0018] Preferably, the rotation speed of the paddle stirring step is 50-300 rpm.

[0019] Specifically, in the method for recovering nitric acid from nitrification-based acidic yellow water, the organic solvent includes toluene and / or nitrotoluene;

[0020] Preferably, the step (1) further comprises the step of recycling the collected organic solvent to the nitration reaction unit.

[0021] Specifically, in the method for recovering nitric acid from nitrification-based acidic yellow water, in step (2), the stripping step includes the step of inputting the extractive digested yellow water into a stripping tower.

[0022] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, in step (2), the stripping step uses low-pressure steam feed, and the stripping ratio is controlled to be 1%-20%.

[0023] Specifically, the method for recovering nitric acid from acidic yellow water based on nitration, in the step (2), further comprises the step of recovering the top discharge product of the stripping step to the nitration reaction unit after condensation.

[0024] Specifically, in the method for recovering nitric acid from acidic yellow water based on nitration, in the step (3), the concentration step includes the step of returning the stripped acidic yellow water to the nitric acid absorption tower instead of fresh water, and finally forming dilute nitric acid with a concentration of 60%-70% and then entering the nitric acid concentration tower for concentration.

[0025] Specifically, the method for recovering nitric acid from nitrification acidic yellow water, in step (3), further comprises the step of collecting the concentrated nitric acid concentrated to 90%-98% and recycling it to the nitration reaction unit.

[0026] The method for recovering nitric acid from nitrated acidic yellow water of the present invention comprises the following steps: stirring the nitrated acidic yellow water and an organic extractant such as toluene or nitrotoluene in a mixer, adding a certain amount of aminosulfonic acid, and allowing the water to stand for stratification after sufficient extraction. The organic extractant is removed by a stripping tower, and the acidic yellow water after extraction and stripping is sent to a nitric acid absorption-concentration tower to obtain concentrated nitric acid, which is recovered as a raw material to a nitration reaction unit. The method for recovering nitric acid from nitrated acidic yellow water of the present invention has significant economic benefits in recovering nitric acid from nitrated yellow water without increasing the operating cost.

[0027] The method for recovering nitric acid from nitrated acidic yellow water of the present invention utilizes nitrated yellow water and a selected organic solvent for extraction, adds a certain amount of aminosulfonic acid during the extraction process, removes nitrobenzene compounds in the yellow water, and the pretreated yellow water can replace fresh water to enter a nitric acid absorption-concentration tower, and is finally recovered to a nitration reaction unit in the form of concentrated nitric acid, thereby avoiding the loss of nitric acid and sulfuric acid while reducing the water intake of the nitration unit, reducing the amount of waste acid generated, and reducing the waste acid concentration load and energy consumption.

[0028] The method for recovering nitric acid from nitrated acidic yellow water of the present invention comprises the following steps: the nitrated yellow water after extraction is stripped to remove aromatic hydrocarbons and then enters a nitric acid absorption tower to serve as a smoke absorption liquid to replace part of fresh water, thereby saving fresh water consumption.

[0029] According to the method for recovering nitric acid from nitrification acidic yellow water, the dilute nitric acid in the bottom of the nitric acid absorption tower enters the nitric acid concentration tower, and the concentrated nitric acid at the top of the tower enters the reaction unit as a nitration reaction raw material, thereby avoiding the introduction of water into the nitration system, reducing the amount of waste acid generated, and reducing the waste acid concentration load and energy consumption, with significant economic benefits. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and change made to the present invention will fall within the protection scope of the present invention.

[0031] In the present invention, unless otherwise specified, all parts and percentages are by weight, and all equipment and raw materials can be purchased from the market or are commonly used in the industry.

[0032] In the nitration process, if the nitrated yellow water is directly reused in the nitration reaction unit, or the yellow water is pre-concentrated and then reused, a large amount of water will be introduced into the nitration system, and finally enter the waste acid concentration unit in the form of waste acid, resulting in a large amount of waste acid production. Since the nitrated yellow water contains a certain amount of nitric acid and a small amount of sulfuric acid, and nitric acid and sulfuric acid have a high solubility in nitrobenzene compounds. Therefore, the mixture of yellow water and nitrobenzene will dissolve a certain amount of nitrobenzene compounds, with a content of about 1%-5%. If it is considered to directly replace the fresh water with the yellow water to enter the nitric acid absorption-concentration tower, the nitrobenzene compound enters the nitric acid concentration tower, and nitrobenzene is easy to decompose and explode under high temperature conditions, there is a safety risk. Therefore, the nitrobenzene in the yellow water needs to be removed before it is sent to the nitric acid absorption-concentration tower.

[0033] In order to solve the problem of recovering nitric acid in the above-mentioned acidic nitrated yellow water, the present invention provides a method for recovering nitric acid in nitrated acidic yellow water, comprising the following steps:

[0034] (1) taking the nitrated acidic yellow water to be treated, adding an organic solvent and aminosulfonic acid to carry out mixed extraction, and collecting the organic solvent layer and the extracted acidic yellow water after stratification;

[0035] (2) subjecting the extracted acidic yellow water to a stripping treatment to obtain stripped acidic yellow water;

[0036] (3) collecting the stripping acidic yellow water and concentrating it to obtain concentrated nitric acid.

[0037] Preferably, toluene compatible with the nitration reaction system is used as an extractant. In order to suppress the oxidation reaction of toluene and nitrous acid during the extraction process to generate oxidation byproducts such as benzaldehyde, a small amount of aminosulfonic acid is added to the acidic yellow water before extraction. Aminosulfonic acid can react with nitrous acid to generate sulfuric acid and N2, thereby quenching the nitrous acid. Then, toluene is mixed with nitrated yellow water for extraction, and the nitrobenzene compound in the yellow water will be extracted into toluene, thereby removing the nitrobenzene in the yellow water. At this time, the nitrobenzene content in the yellow water drops to less than 50ppm, but a certain amount of toluene is dissolved or entrained. Therefore, it is necessary to further remove the toluene in the nitrated yellow water by steam stripping. The nitrated yellow water after extraction-stripping can replace fresh water to enter the nitric acid absorption-concentration tower, and is finally recovered to the nitration reaction unit in the form of concentrated nitric acid.

[0038] Specifically, in the method for recovering nitric acid from nitrified acidic yellow water, in step (1):

[0039] The amount of aminosulfonic acid added is 0.1-1wt% of the mass of the nitrated acidic yellow water; and / or,

[0040] The amount of the organic solvent added is 50-200 wt % of the mass of the nitrated acidic yellow water.

[0041] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, in step (1), in the mixed extraction step:

[0042] The extraction temperature is 30-70°C; and / or,

[0043] The extraction time is 1-20 min; and / or,

[0044] The stratification time is 1-20min.

[0045] Preferably, the extraction process is carried out in an extraction-stratification tank, the stirring of the extraction kettle adopts a paddle type, the rotation speed is preferably 50-200rpm, and the standing time for stratification after extraction is preferably 10 minutes.

[0046] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, the mixed extraction step includes a step of performing paddle stirring;

[0047] Preferably, the rotation speed of the paddle stirring step is 50-300 rpm.

[0048] Specifically, the method for recovering nitric acid from nitrification acidic yellow water, in step (1), further comprises the step of recovering the collected organic solvent to the nitration reaction unit.

[0049] Specifically, in the method for recovering nitric acid from nitrification-based acidic yellow water, in step (2), the stripping step includes the step of inputting the extractive digested yellow water into a stripping tower.

[0050] Specifically, in the method for recovering nitric acid from nitrated acidic yellow water, in step (2), the stripping step uses low-pressure steam feed, and the stripping ratio is controlled to be 1%-20%.

[0051] Preferably, the yellow water stripping is carried out in a stripping tower, the operating temperature of the stripping tower is 99-100°C, and the operating pressure is atmospheric pressure. The condensate at the top of the stripping tower consists of toluene, nitric acid, and water, which can be reused in the nitration reaction system; the yellow water extracted from the bottom of the tower is cooled and sent to the nitric acid absorption-concentration tower. Preferably, the stripping tower bottom is heated in the form of a reboiler, the heating medium is low-pressure steam, and the stripping ratio is 1%-10%.

[0052] Specifically, the method for recovering nitric acid from acidic yellow water based on nitration, in the step (2), further comprises the step of recovering the top discharge product of the stripping step to the nitration reaction unit after condensation.

[0053] Specifically, in the method for recovering nitric acid from acidic yellow water based on nitration, in the step (3), the concentration step includes the step of returning the stripped acidic yellow water to the nitric acid absorption tower instead of fresh water, and finally forming dilute nitric acid with a concentration of 60%-70% and then entering the nitric acid concentration tower for concentration.

[0054] Preferably, the pre-treated nitrated yellow water is firstly recycled to the nitric acid absorption tower, and is extracted as dilute nitric acid in the absorption tower kettle after replacing fresh water to absorb NOx gas, and the nitric acid concentration is preferably 60%-70%. Preferably, the dilute nitric acid enters the nitric acid concentration tower, is concentrated into concentrated nitric acid after extraction and rectification, and is finally recycled to the nitration reaction unit as a reaction raw material. Preferably, the concentration of concentrated nitric acid is preferably 90%-98%, so as to avoid introducing water into the nitration reaction system and reduce the amount of waste acid generated.

[0055] Specifically, the method for recovering nitric acid from nitrification acidic yellow water, in step (3), further comprises the step of collecting the concentrated nitric acid concentrated to 90%-98% and recycling it to the nitration reaction unit.

[0056] Example 1

[0057] In the process of producing dinitrotoluene by using a toluene-nitric acid and sulfuric acid mixed acid nitration system in this embodiment, the nitration pickling wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to form acidic nitrated yellow water. According to the test, the acidic nitrated yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0058] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and toluene and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.005, and the mass ratio of the acidic nitrated yellow water to toluene to be 1:1. Start the paddle stirring, adjust the speed to 200rpm, set the extraction temperature to 50℃, control the extraction time to 10min, and the extraction level to be one. After the extraction is completed, stand for 10min to separate the layers, and then collect the organic solvent layer and the acidic nitrated yellow water after extraction. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to 50ppm, and the content of toluene is 2000ppm. The toluene collected after extraction enters the nitration reaction unit, recovers the dinitrotoluene in the nitrated yellow water, and the organic matter recovery rate is determined to be 99.9%.

[0059] The acidic nitrated yellow water after the above extraction is collected and enters the stripping tower, and the stripping ratio is controlled to be 10%. After stripping, the toluene content in the nitrated yellow water in the tower bottom is reduced to undetectable, and the condensate at the top of the tower contains 80% toluene, 15% nitric acid and 5% water. The condensate at the top of the tower is collected as a nitration reaction raw material and enters the nitration reaction system, and the nitrated yellow water collected after the tower bottom stripping enters the nitric acid absorption-concentration tower.

[0060] The nitrated yellow water after stripping replaces fresh water and enters the nitric acid absorption tower, and 68% dilute nitric acid is extracted from the bottom of the tower. The dilute nitric acid enters the nitric acid concentration tower, and 98% concentrated nitric acid is extracted from the top condensate after sulfuric acid extraction and rectification. The dilute sulfuric acid in the bottom of the tower is concentrated and reused. The concentrated nitric acid finally enters the nitration reaction unit as a reaction raw material, and the recovery rate of nitric acid and sulfuric acid in the nitrated yellow water is 100%.

[0061] This embodiment recycles the nitration yellow water. Compared with the process of directly reusing the nitration yellow water in the reaction system, this embodiment recovers the nitric acid in the acidic yellow water in the form of 98% nitric acid while almost completely recovering the dinitrotoluene in the yellow water and saving the amount of fresh water used in the nitric acid absorption tower, which can reduce the generation of nitration waste acid by about 9t / h.

[0062] Example 2

[0063] In the process of producing dinitrotoluene using a toluene-nitric acid and sulfuric acid mixed acid nitration system in this embodiment, the nitration pickling wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to become acidic nitrated yellow water. After testing, the acidic nitrated yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0064] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and toluene and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.005, and the mass ratio of the acidic nitrated yellow water to toluene to be 1:1. Start the paddle stirring, adjust the speed to 200rpm, set the extraction temperature to 50℃, control the extraction time to 10min, and the extraction level to two levels. After the extraction is completed, stand for 10min to separate the layers, and then collect the organic solvent layer and the acidic nitrated yellow water after extraction. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to 10ppm, and the content of toluene is 2000ppm. The toluene collected after extraction enters the nitration reaction unit, recovers the dinitrotoluene in the nitrated yellow water, and the organic matter recovery rate is determined to be 99.9%.

[0065] The acidic nitrated yellow water after the above extraction is collected and enters the stripping tower, and the stripping ratio is controlled to be 10%. After stripping, the toluene content in the nitrated yellow water in the tower bottom is reduced to undetectable. The condensate at the top of the tower is collected as the raw material for the nitration reaction and enters the nitration reaction system. The nitrated yellow water collected after the stripping in the tower bottom enters the nitric acid absorption-concentration tower.

[0066] The nitrated yellow water after stripping replaces fresh water and enters the nitric acid absorption tower, and 68% dilute nitric acid is extracted from the bottom of the tower. The dilute nitric acid enters the nitric acid concentration tower, and 98% concentrated nitric acid is extracted from the top condensate after sulfuric acid extraction and rectification. The dilute sulfuric acid in the bottom of the tower is concentrated and reused. The concentrated nitric acid finally enters the nitration reaction unit as a reaction raw material, and the recovery rate of nitric acid and sulfuric acid in the nitrated yellow water is 100%.

[0067] This embodiment recycles the nitration yellow water. Compared with the process of directly reusing the nitration yellow water in the reaction system, this embodiment recovers the nitric acid in the yellow water in the form of 98% nitric acid while completely recovering the dinitrotoluene in the yellow water and saving the amount of fresh water used in the nitric acid absorption tower, which can reduce the generation of nitration waste acid by about 9t / h.

[0068] Example 3

[0069] In the process of producing dinitrotoluene by using a toluene-nitric acid and sulfuric acid mixed acid nitration system in this embodiment, the nitration pickling wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to form acidic nitrated yellow water. According to the test, the acidic nitrated yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0070] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and nitrotoluene and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.005, and the mass ratio of the acidic nitrated yellow water to nitrotoluene to be 1:1.5. Start the paddle stirring, adjust the speed to 200rpm, set the extraction temperature to 50℃, control the extraction time to 10min, and the extraction level to be one. After the extraction is completed, stand for 10min to separate the layers, and then collect the organic solvent layer and the acidic nitrated yellow water after extraction. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to 15ppm, and the content of nitrotoluene is 1000ppm. The nitrotoluene collected after extraction enters the nitration reaction unit, recovers the dinitrotoluene in the nitrated yellow water, and the organic matter recovery rate is determined to be 99.9%.

[0071] The acidic nitrated yellow water after the above extraction is collected and enters the stripping tower, and the stripping ratio is controlled to be 10%. After stripping, the nitrotoluene content in the nitrated yellow water in the tower bottom is reduced to undetectable. The condensate at the top of the tower is collected as the raw material for the nitration reaction and enters the nitration reaction system. The nitrated yellow water collected after stripping in the tower bottom enters the nitric acid absorption-concentration tower.

[0072] The nitrated yellow water after stripping replaces fresh water and enters the nitric acid absorption tower, and 68% dilute nitric acid is extracted from the bottom of the tower. The dilute nitric acid enters the nitric acid concentration tower, and 98% concentrated nitric acid is extracted from the top condensate after sulfuric acid extraction and rectification. The dilute sulfuric acid in the bottom of the tower is concentrated and reused. The concentrated nitric acid finally enters the nitration reaction unit as a reaction raw material, and the recovery rate of nitric acid and sulfuric acid in the nitrated yellow water is 100%.

[0073] This embodiment recycles the nitration yellow water. Compared with the process of directly reusing the nitration yellow water in the reaction system, this embodiment recovers the nitric acid in the yellow water in the form of 98% nitric acid while almost completely recovering the dinitrotoluene in the yellow water and saving the amount of fresh water used in the nitric acid absorption tower, which can reduce the generation of nitration waste acid by about 9t / h.

[0074] Example 4

[0075] In the process of producing dinitrotoluene by using a toluene-nitric acid and sulfuric acid mixed acid nitration system in this embodiment, the nitration pickling wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to form acidic nitrated yellow water. According to the test, the acidic nitrated yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0076] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and nitrotoluene and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.005, and the mass ratio of the acidic nitrated yellow water to nitrotoluene to be 1:2. Start the paddle stirring, adjust the speed to 200rpm, set the extraction temperature to 50℃, control the extraction time to 10min, and the extraction level to two levels. After the extraction is completed, stand for 10min to separate the layers, and then collect the organic solvent layer and the acidic nitrated yellow water after extraction. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to undetectable, and the content of nitrotoluene is 1000ppm. The nitrotoluene collected after extraction enters the nitration reaction unit, recovers the dinitrotoluene in the nitrated yellow water, and the organic matter is completely recovered.

[0077] The acidic nitrated yellow water after the above extraction is collected and enters the stripping tower, and the stripping ratio is controlled to be 10%. After stripping, the nitrotoluene content in the nitrated yellow water in the tower bottom is reduced to undetectable. The condensate at the top of the tower is collected as the raw material for the nitration reaction and enters the nitration reaction system. The nitrated yellow water collected after stripping in the tower bottom enters the nitric acid absorption-concentration tower.

[0078] The nitrated yellow water after stripping replaces fresh water and enters the nitric acid absorption tower, and 68% dilute nitric acid is extracted from the bottom of the tower. The dilute nitric acid enters the nitric acid concentration tower, and 98% concentrated nitric acid is extracted from the top condensate after sulfuric acid extraction and rectification. The dilute sulfuric acid in the bottom of the tower is concentrated and reused. The concentrated nitric acid finally enters the nitration reaction unit as a reaction raw material, and the recovery rate of nitric acid and sulfuric acid in the nitrated yellow water is 100%.

[0079] This embodiment recycles the nitration yellow water. Compared with the process of directly reusing the nitration yellow water in the reaction system, this embodiment recovers the nitric acid in the yellow water in the form of 98% nitric acid while almost completely recovering the dinitrotoluene in the yellow water and saving the amount of fresh water used in the nitric acid absorption tower, which can reduce the generation of nitration waste acid by about 9t / h.

[0080] Example 5

[0081] In the process of producing dinitrotoluene by using a toluene-nitric acid and sulfuric acid mixed acid nitration system in this embodiment, the nitration pickling wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to form acidic nitrated yellow water. According to the test, the acidic nitrated yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0082] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and nitrotoluene and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.005, and the mass ratio of the acidic nitrated yellow water to nitrotoluene to be 1:1. Start the paddle stirring, adjust the speed to 200rpm, set the extraction temperature to 70℃, control the extraction time to 10min, and the extraction level to two levels. After the extraction is completed, stand for 10min to separate the layers, and collect the organic solvent layer and the acidic nitrated yellow water after extraction respectively. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to undetectable, and the content of nitrotoluene is 1000ppm. The nitrotoluene collected after extraction enters the nitration reaction unit, recovers the dinitrotoluene in the nitrated yellow water, and the organic matter is completely recovered.

[0083] The acidic nitrated yellow water after the above extraction is collected and enters the stripping tower, and the stripping ratio is controlled to be 10%. After stripping, the nitrotoluene content in the nitrated yellow water in the tower bottom is reduced to undetectable. The condensate at the top of the tower is collected as the raw material for the nitration reaction and enters the nitration reaction system. The nitrated yellow water collected after stripping in the tower bottom enters the nitric acid absorption-concentration tower.

[0084] The nitrated yellow water after stripping replaces fresh water and enters the nitric acid absorption tower, and 68% dilute nitric acid is extracted from the bottom of the tower. The dilute nitric acid enters the nitric acid concentration tower, and 98% concentrated nitric acid is extracted from the top condensate after sulfuric acid extraction and rectification. The dilute sulfuric acid in the bottom of the tower is concentrated and reused. The concentrated nitric acid finally enters the nitration reaction unit as a reaction raw material, and the recovery rate of nitric acid and sulfuric acid in the nitrated yellow water is 100%.

[0085] This embodiment recycles the nitration yellow water. Compared with the process of directly reusing the nitration yellow water in the reaction system, this embodiment recovers the nitric acid in the yellow water in the form of 98% nitric acid while almost completely recovering the dinitrotoluene in the yellow water and saving the amount of fresh water used in the nitric acid absorption tower, which can reduce the generation of nitration waste acid by about 9t / h.

[0086] Comparative Example 1

[0087] In the process of producing dinitrotoluene by toluene-nitric acid and sulfuric acid mixed acid nitration system in this comparative example, the nitration acid washing wastewater generated in the process of washing crude dinitrotoluene is separated from the organic phase to form acidic nitration yellow water. After testing, the acidic nitration yellow water contains 18% nitric acid, 2% sulfuric acid and 2% dinitrotoluene.

[0088] Add the acidic nitrated yellow water to be treated into a reactor with a stirrer, add aminosulfonic acid and dichloromethane and mix thoroughly, control the mass ratio of the acidic nitrated yellow water to the aminosulfonic acid to be 1:0.001, and the mass ratio of the acidic nitrated yellow water to dichloromethane to be 1:0.5. Start the paddle stirring, adjust the speed to 50rpm, set the extraction temperature to 30℃, control the extraction time to 10min, and the extraction level to be one. After the extraction is completed, stand for 10min to separate the layers, and then collect the organic solvent layer and the acidic nitrated yellow water after extraction. After testing, the content of dinitrotoluene in the acidic nitrated yellow water after extraction is reduced to 55ppm, and the content of dichloromethane is 3000ppm. However, the dichloromethane collected after extraction cannot enter the nitration reaction unit, and the dinitrotoluene in the nitrated yellow water is recovered, and the organic matter recovery rate is determined to be 0%.

[0089] Comparative Example 2

[0090] The method for recovering nitric acid from nitrated yellow water in this comparative example is the same as that in Example 1, the only difference being that aminosulfonic acid is not added during the extraction process.

[0091] It has been determined that toluene contains 0.5%-1% benzaldehyde after extraction. Toluene is recycled as a nitration raw material. After entering the nitration system, benzaldehyde further reacts to form benzoic acid, which will seriously affect the stratification of the nitration reaction liquid and cause emulsification problems.

[0092] Comparative Example 3

[0093] The method for recovering nitric acid from nitrated yellow water in this comparative example is the same as that in Example 1, the only difference is that the nitrated yellow water after extraction is not subjected to corresponding stripping treatment.

[0094] It has been determined that the yellow water after extraction contains 2000ppm toluene. If the yellow water directly enters the nitric acid absorption tower and then further enters the nitric acid concentration tower, in the highly concentrated sulfuric acid, nitric acid and high temperature environment in the nitric acid concentration tower, toluene reacts with nitric acid to generate TNT, which has a high process safety risk. TNT enters the nitration system as an impurity, which also leads to a decrease in the yield of dinitrotoluene.

[0095] Comparative Example 4

[0096] The method for recovering nitric acid from nitrated yellow water in this comparative example is the same as that in Example 1, the only difference being that aminosulfonic acid is not added during the extraction process and corresponding stripping treatment is not performed.

[0097] It has been determined that the yellow water contains 2000ppm toluene and 1000ppm benzaldehyde after extraction, and 0.5-1% benzaldehyde in toluene after extraction. If the yellow water directly enters the nitric acid absorption tower and then further enters the nitric acid concentration tower, toluene reacts with nitric acid to produce TNT in the highly concentrated sulfuric acid, nitric acid and high temperature environment in the nitric acid concentration tower. The process has high safety risks. TNT enters the nitration system as an impurity, resulting in a decrease in the yield of dinitrotoluene. After extraction, the benzaldehyde in the toluene is further oxidized to benzoic acid, resulting in stratified emulsification of the nitration reaction.

[0098] In summary, the method for recovering nitric acid from nitrated acidic yellow water of the present invention comprises the following steps: stirring the nitrated acidic yellow water and an organic extractant such as toluene or nitrotoluene in a mixer, and adding a certain amount of aminosulfonic acid. After sufficient extraction, the water is allowed to stand for stratification, and the organic extractant is removed by a stripping tower. After extraction and stripping, the acidic yellow water is sent to a nitric acid absorption-concentration tower to obtain concentrated nitric acid, which is recovered as a raw material to the nitration reaction unit. The method for recovering nitric acid from nitrated acidic yellow water of the present invention has significant economic benefits in recovering nitric acid from nitrated yellow water without increasing the operating cost.

[0099] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for recovering nitric acid from nitrated acidic yellow water, characterized in that: The steps include: (1) taking the nitrated acidic yellow water to be treated, adding an organic solvent and aminosulfonic acid to carry out mixed extraction, and collecting the organic solvent layer and the extracted acidic yellow water after stratification; (2) subjecting the extracted acidic yellow water to a stripping treatment to obtain stripped acidic yellow water; (3) collecting the stripping acidic yellow water and concentrating it to obtain concentrated nitric acid.

2. The method for recovering nitric acid from nitrated acidic yellow water according to claim 1, characterized in that: In the step (1): The amount of aminosulfonic acid added is 0.1-1wt% of the mass of the nitrated acidic yellow water; and / or, The amount of the organic solvent added is 50-200 wt % of the mass of the nitrated acidic yellow water.

3. The method for recovering nitric acid from nitrated acidic yellow water according to claim 1 or 2, characterized in that: In the step (1), in the mixed extraction step: The extraction temperature is 30-70°C; and / or, The extraction time is 1-20 min; and / or, The stratification time is 1-20min.

4. The method for recovering nitric acid from nitrated acidic yellow water according to any one of claims 1 to 3, characterized in that: In the step (1), the mixed extraction step includes a step of performing paddle stirring; Preferably, the rotation speed of the paddle stirring step is 50-300 rpm.

5. The method for recovering nitric acid from nitrated acidic yellow water according to any one of claims 1 to 4, characterized in that: In the step (1), the organic solvent comprises toluene and / or nitrotoluene; Preferably, the step (1) further comprises the step of recycling the collected organic solvent to the nitration reaction unit.

6. The method for recovering nitric acid from nitrated acidic yellow water according to any one of claims 1 to 5, characterized in that: In the step (2), the stripping step includes the step of inputting the extractive digestion yellow water into a stripping tower.

7. The method for recovering nitric acid from nitrated acidic yellow water according to claim 6, characterized in that: In the step (2), the stripping step uses low-pressure steam as feed, and the stripping ratio is controlled to be 1%-20%.

8. The method for recovering nitric acid from nitrated acidic yellow water according to any one of claims 1 to 7, characterized in that: The step (2) also includes the step of condensing the top discharge product of the stripping step and recycling it to the nitration reaction unit.

9. The method for recovering nitric acid from nitrated acidic yellow water according to any one of claims 1 to 8, characterized in that: In the step (3), the concentration step includes the step of recycling the stripped acidic yellow water to the nitric acid absorption tower instead of fresh water, and finally forming dilute nitric acid with a concentration of 60%-70% and then entering the nitric acid concentration tower for concentration.

10. The method for recovering nitric acid from nitrated acidic yellow water according to claim 9, characterized in that: The step (3) also includes the step of collecting the concentrated nitric acid concentrated to 90%-98% and recycling it to the nitration reaction unit.