Method for reducing nitrides in waste acid based on mixed dinitrobenzene preparation process

Abstract

The invention discloses a method for reducing nitrides in waste acid based on a mixed dinitrobenzene preparation process, and relates to the technical field of mixed dinitrobenzene preparation. According to the method for reducing the nitrates in the waste acid based on the mixed dinitrobenzene preparation process, the mixed dinitrobenzene preparation process comprises first-stage nitration and second-stage nitration, and the waste acid is generated after the first-stage nitration; waste acid and benzene liquid are subjected to counter-current extraction in opposite flow directions through a filler layer, benzene is a continuous phase, and waste acid is a dispersed phase. According to the method, counter-current extraction is performed on the benzene liquid and the waste acid, the benzene liquid is a continuous phase, and the waste acid is a dispersed phase, so that nitrides in the waste acid are fully dissolved into the benzene liquid, the content of the nitrides in the waste acid after extraction is reduced, and the benzene liquid is continuously used as a raw material for preparing mixed dinitrobenzene.

Description

Technical Field

[0001] The present application relates to the technical field of mixed dinitrobenzene preparation, and in particular to a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process. Background Art

[0002] Mixed dinitrobenzene is mainly used for hydrogenation to produce phenylenediamine. It is also an inhibitor for molecular polymerization reactions and can be used to produce pesticides and medicines. Phenylenediamine includes three isomers, namely metaphenylenediamine, o-phenylenediamine, and p-phenylenediamine, which are widely used new materials industry and organic chemical intermediates. It is mainly used for aramid, azo dyes, sulfur dyes, acid dyes, etc. The current production process of mixed dinitrobenzene mainly includes the first stage nitration, second stage nitration and neutralization, and water washing. The process waste acid produced by the second stage nitration is used for the first stage. The waste acid (called 72 acid) with a mass concentration of 70-75% after the first stage nitration still contains nitrates with a mass concentration of 0.6%-0.8%. At present, the recovery and treatment of nitrates in waste acid often adopts traditional kettle extraction. Benzene and waste acid are continuously transported to the extraction kettle through the benzene shielded pump and the waste acid delivery pump in proportion, and the agitator on the extraction kettle is started for stirring and mixing. The extracted nitrate and benzene mixture flows into the acid benzene separator through the overflow pipe on the upper part of the kettle to the acid benzene tank for recycling. The extracted 72 acid is then concentrated. After the kettle stirring and mixing extraction, the nitrate content in the waste acid is reduced from 0.6-0.8% before extraction to 0.3%-0.5% after extraction. During the waste acid concentration treatment, only part of the nitrates are eliminated, while most of the nitrates and nitrogen oxides are brought into the alkaline water of the tail gas absorption tower, causing the nitrate concentration in the alkaline water to exceed the standard and become a pollution source. Therefore, it is very necessary to improve the recovery rate of the nitrates in the 72 acid. Summary of the invention

[0003] In order to solve at least one of the above technical problems, a method for improving the recovery rate of nitrates in 72 acid is developed. The present application provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process.

[0004] The present application provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first-stage nitration and a second-stage nitration, waste acid is generated after the first-stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and the waste acid as a dispersed phase.

[0005] Optionally, the two ends of the packing layer are quartz sand, and the middle is modified adsorption material.

[0006] Optionally, the adsorption material includes activated carbon and quartz sand.

[0007] Optionally, in the adsorption material, activated carbon accounts for 85-95wt%, and quartz sand accounts for 5-15wt%.

[0008] Optionally, the activated carbon is modified carbon.

[0009] Optionally, the modified carbon is modified by the following modification method, which comprises the following steps:

[0010] S1. Pickling

[0011] Use dilute nitric acid to clean the activated carbon;

[0012] S2. Drying

[0013] Drying the cleaned activated carbon;

[0014] S3, oxidation treatment

[0015] Soak the dried activated carbon in concentrated nitric acid;

[0016] S4. Cleaning and drying

[0017] The activated carbon after oxidation treatment was washed with deionized water and dried.

[0018] Optionally, in the step S2, drying, the drying temperature is 100-110°C.

[0019] Optionally, in the S3, oxidation treatment, the concentration of concentrated nitric acid is 65-70% and the temperature is 25-60°C.

[0020] In summary, the present application includes at least one of the following beneficial technical effects:

[0021] 1. Through countercurrent extraction of benzene liquid and waste acid, with benzene liquid as a continuous phase and waste acid as a dispersed phase, the nitrate in the waste acid is fully dissolved in the benzene liquid, thereby reducing the content of nitrate in the waste acid after extraction, and the benzene liquid is continuously used as a raw material for preparing mixed dinitrobenzene;

[0022] 2. By setting a packing layer, the benzene liquid and the waste acid are extracted in the packing layer, which not only allows the benzene liquid and the waste acid to fully contact and improve the extraction effect; but also the activated carbon in the packing layer can further adsorb the nitrate in the waste acid, thereby further reducing the content of the nitrate in the waste acid. DETAILED DESCRIPTION

[0023] The present application is further described in detail below with reference to the embodiments.

[0024] In the following examples of the present application, the main components involved, unless otherwise specified, were purchased from commercially available products.

[0025] The following examples of the present application exemplarily adopt a vertically arranged cylindrical reactor as an extraction device, with a diameter of 0.5m and a height of 1.8m; benzene liquid enters from the bottom with a flow rate of 15L / min; waste acid enters from the top with a comprehensive flow rate of 10L / min; the nitrate content in the waste acid is 0.8%. The upper and lower ends of the packing layer are quartz sand, the thickness of the end close to the benzene liquid inlet is 5cm, and the distance from the bottom to the benzene liquid inlet is about 50cm; the thickness of the upper end is 15cm, and the distance from the top to the waste acid inlet is about 80cm, and the adsorption material in the middle is 30cm thick.

[0026] The modified carbon used in the following embodiments of the present application is modified by the following modification method: the activated carbon is cleaned with dilute nitric acid; the cleaned activated carbon is dried at a temperature of 100 to 110°C; the dried activated carbon is immersed in concentrated nitric acid at a concentration of 65 to 70% at a temperature of 25 to 60°C; the activated carbon after oxidation is washed with deionized water and dried. Specific embodiments

[0028] Example 1

[0029] The present embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of the present embodiment, activated carbon accounts for 80wt% and quartz sand accounts for 20wt%.

[0030] Example 2

[0031] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of this embodiment, activated carbon accounts for 85wt% and quartz sand accounts for 15wt%.

[0032] Example 3

[0033] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, activated carbon accounts for 88wt% and quartz sand accounts for 12wt%.

[0034] Example 4

[0035] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, activated carbon accounts for 90wt% and quartz sand accounts for 10wt%.

[0036] Example 5

[0037] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of this embodiment, activated carbon accounts for 92wt% and quartz sand accounts for 8wt%.

[0038] Example 6

[0039] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, activated carbon accounts for 95wt% and quartz sand accounts for 5wt%.

[0040] Example 7

[0041] The present embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of the present embodiment, activated carbon accounts for 100wt% and quartz sand accounts for 0wt%.

[0042] After being treated by the methods in Examples 1 to 7 above, the content of nitrate in the waste acid is shown in Table 1.

[0043] Table 1

[0044]

[0045]

[0046] It can be seen from Examples 1 to 7 and Table 1 that, for removing nitrates from waste acid produced in the preparation of mixed dinitrobenzene, compared with a 50% removal rate in the prior art, the technical solution of the present application can reduce the nitrate content of 0.800% to below 0.100%.

[0047] Further analysis of Table 1 shows that the nitrate content of the waste acid in Examples 2 to 6 is reduced to below 0.050%, which is significantly lower than that in Examples 1 and 7. This indicates that in the technical solution of the present application, when the adsorption material used includes 85 to 95 wt% of activated carbon and 5 to 15 wt% of quartz sand, the removal rate of nitrate in the waste acid can be further improved.

[0048] The nitrate content of the waste acid in Example 4 and Example 5 is reduced to 0.016-0.018%, which is more significantly improved compared with other embodiments. Therefore, it can be seen that when the activated carbon accounts for 90-92wt% and the quartz sand accounts for 8-10wt% of the adsorption material used in the technical solution of the present application, the removal rate of the nitrate in the waste acid can be further improved.

[0049] Based on the above technical solution, the inventor modified the activated carbon. The following Examples 8 to 14 are used to verify the effect of the modified carbon technical solution of this application on the removal rate of nitrate in waste acid; the details are as follows.

[0050] Example 8

[0051] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 80wt% and quartz sand accounts for 20wt%.

[0052] Example 9

[0053] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 85wt% and quartz sand accounts for 15wt%.

[0054] Example 10

[0055] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 88wt% and quartz sand accounts for 12wt%.

[0056] Embodiment 11

[0057] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 90wt% and quartz sand accounts for 10wt%.

[0058] Example 12

[0059] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, benzene is a continuous phase, and the waste acid is a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 92wt% and quartz sand accounts for 8wt%.

[0060] Example 3

[0061] This embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of this embodiment, modified carbon accounts for 95wt% and quartz sand accounts for 5wt%.

[0062] Embodiment 14

[0063] The present embodiment provides a method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first stage nitration and a second stage nitration, and waste acid is produced after the first stage nitration; the waste acid and benzene liquid are passed through a packing layer in opposite directions for countercurrent extraction, with benzene as a continuous phase and waste acid as a dispersed phase. In the adsorption material of the present embodiment, modified carbon accounts for 100wt% and quartz sand accounts for 0wt%.

[0064] After being treated by the methods in Examples 8 to 14 above, the content of nitrate in the waste acid is shown in Table 2.

[0065] Table 2

[0066] Treatment Modified carbon / wt% Quartz sand / wt% Nitrate content / wt% Example 8 80 20 0.046 Example 9 85 15 0.039 Example 10 88 12 0.008 Embodiment 11 90 10 0.006 Example 12 92 8 0.015 Embodiment 13 95 5 0.032 Embodiment 14 100 0 0.098

[0067] It can be seen from Examples 8 to 14 and Table 2 and Examples 1 to 7 and Table 1 that replacing the activated carbon in the technical solution of the present application with modified carbon has a significant effect on the removal rate of nitrates in the waste acid, among which Examples 8 to 13 are improved relative to Examples 1 to 6, while Example 7 is significantly decreased relative to Example 14; this may be because the activated carbon is too dense, resulting in part of the nitrates in the benzene solution being absorbed by the modified carbon, resulting in a decrease in the overall nitrate removal rate of the waste acid.

[0068] It can be seen from Examples 10 to 11 and Table 2 that after replacing with modified carbon, a higher nitrate removal rate can be achieved using less adsorption carbon; the content of nitrate in the treated waste acid can be reduced to below 0.01%.

[0069] This indicates that after the activated carbon in the modified carbon is treated with concentrated nitric acid, many carboxyl groups and other groups are formed in the internal pores. When adsorbing nitrates in the waste acid, it is protonated under acidic conditions and can provide positive charges to attract nitrates. And because the conductivity of nitrates in the benzene liquid is weaker than that in the waste acid, it can selectively adsorb nitrates in the waste acid, thereby further improving the overall nitrate removal rate of the waste acid.

[0070] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for reducing nitrates in waste acid based on a mixed dinitrobenzene preparation process, wherein the mixed dinitrobenzene preparation process includes a first-stage nitration and a second-stage nitration, and waste acid is generated after the first-stage nitration; characterized in that: The waste acid and benzene liquid are passed through the packing layer in opposite directions for countercurrent extraction, with benzene as the continuous phase and the waste acid as the dispersed phase.

2. The method according to claim 1, characterized in that: The two ends of the packing layer are quartz sand, and the middle is adsorption material.

3. The method according to claim 2, characterized in that The adsorption material includes activated carbon and quartz sand.

4. The method according to claim 3, characterized in that In the adsorption material, the activated carbon accounts for 85-95wt%, and the quartz sand accounts for 5-15wt%.

5. The method according to claim 3 or 4, characterized in that: The activated carbon is modified carbon.

6. The method according to claim 5, characterized in that The modified carbon is modified by the following modification method, which comprises the following steps: S1. Pickling Use dilute nitric acid to clean the activated carbon; S2. Drying Drying the cleaned activated carbon; S3, oxidation treatment Soak the dried activated carbon in concentrated nitric acid; S4. Cleaning and drying The activated carbon after oxidation treatment was washed with deionized water and dried.

7. The method according to claim 6, characterized in that In the step S2, drying, the drying temperature is 100-110°C.

8. The method according to claim 6, characterized in that In the oxidation treatment of S3, the concentration of concentrated nitric acid is 65-70% and the temperature is 25-60°C.

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