A method for recovering and treating ammonia-containing tail gas in the rear section of the synthesis of aromatic nitrile

Abstract

A method for recovering and treating ammonia-containing tail gas in the back stage for synthesizing aromatic nitrile comprises passing the ammonia-containing tail gas into a first spray absorption tower and a second spray absorption tower in sequence, absorbing ammonia in the ammonia-containing tail gas in a liquid phase, realizing ammonia recovery, and directly discharging waste gas; wherein the absorbent A of the first spray absorption tower is water; and the absorbent B of the first spray absorption tower comprises glycolic acid, vinylphosphonic acid and aluminum sulfate. The method greatly increases the recovery of ammonia in the ammonia-containing tail gas through two-stage spraying, and the ammonia content in the tail gas after treatment is low and meets the emission standards.

Description

Technical Field

[0001] The invention relates to the field of tail gas separation and treatment, and in particular to a method for recovering and treating ammonia-containing tail gas in the rear stage used for synthesizing aromatic nitrile. Background Art

[0002] Aromatic nitrile compounds are an important class of organic compounds containing cyano (CN) on the benzene ring, such as benzonitrile, isophthalonitrile, o-phthalonitrile, o-chlorobenzonitrile, p-chlorobenzonitrile, 2,6-dichlorobenzonitrile, 3,4-dichlorobenzonitrile, etc. They are widely used in the preparation of polymer materials, drugs and dyes. The traditional synthesis routes of aromatic nitrile compounds mainly include haloalkyl cyanation, ammoxidation, carboxyl cyanation, aldehyde cyanation, electrolytic synthesis, acetonitrile addition, acrylonitrile and diazotization. Among them, ammonia oxidation is a more commonly used method. For example, the synthesis of o-chlorobenzonitrile from o-chlorotoluene by ammonia oxidation is the mainstream method of industrial production at present. This method uses o-chlorotoluene, ammonia and air as reaction raw materials and adopts a transition metal heterogeneous catalyst. The tail gas produced by this method contains a large amount of ammonia. Ammonia is a highly water-soluble, colorless, alkaline, irritating and harmful gas that cannot be directly discharged. Ammonia can be used to produce ammonia water, nitrogen fertilizer, ammonium salt, compound fertilizer, soda ash, etc. Directly discharging the ammonia-containing tail gas causes a waste of resources. Therefore, it is necessary to recycle the tail gas.

[0003] In the prior art, ammonia-containing tail gas is generally condensed into dilute ammonia water, or ammonia is absorbed by a spray tower. However, due to the low concentration and large volume of the dilute ammonia water condensed in the former, only a small part can be recycled, and most of the dilute ammonia water is difficult to handle or the processing cost is extremely high. The latter generally uses water or hydrochloric acid to spray and absorb the ammonia tail gas into a corresponding ammonia nitrogen solution, and then evaporation and concentration are used for recycling. Spraying and absorbing with water requires repeated spraying, which has low processing efficiency, and the cost of hydrochloric acid spraying is high, and ammonia emissions cannot be avoided. Therefore, it is necessary to improve the existing tail gas treatment process for aromatic nitrile production. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, an embodiment of the present invention provides a method for recovering and treating ammonia-containing tail gas in the latter stage of synthesizing aromatic nitrile, which at least solves some of the problems in the prior art.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for recovering and treating ammonia-containing tail gas in the rear stage for synthesizing aromatic nitrile comprises passing the ammonia-containing tail gas into a first spray absorption tower and a second spray absorption tower in sequence, absorbing ammonia in the ammonia-containing tail gas in a liquid phase, recovering ammonia and discharging waste gas; wherein the absorbent of the first spray absorption tower comprises absorbent A and absorbent B, the absorbent A is water, and the absorbent B comprises hydroxyacetic acid, vinylphosphonic acid and aluminum sulfate.

[0007] In a further embodiment, the ammonia-containing tail gas is the tail gas generated in the production of aromatic nitrile compounds by ammonia oxidation; the aromatic nitrile compounds include but are not limited to any one of isophthalonitrile, orthophthalonitrile, ortho-chlorobenzonitrile, p-chlorobenzonitrile, 2,6-dichlorobenzonitrile, and 3,4-dichlorobenzonitrile.

[0008] In a further embodiment, the absorbent B comprises glycolic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 3-5:0.8-1:0.1-0.15.

[0009] The ammonia in the ammonia-containing tail gas first passes through the first spray absorption tower, part of the ammonia is absorbed by water in the liquid phase to obtain the first ammonia water, and part of the ammonia remains in the tail gas. The remaining tail gas is passed into the second spray absorption tower, and the absorbent B in the second spray absorption tower has a higher solubility in ammonia, so that the ammonia in the tail gas is absorbed in the liquid phase to the greatest extent, thereby realizing the efficient removal and recovery of ammonia.

[0010] In a further preferred embodiment, the absorbent B further comprises pyrimethamine, and the molar ratio of pyrimethamine to glycolic acid in the absorbent B is 1:0.3-0.5.

[0011] In a further preferred embodiment, the pressure in the first spray absorption tower is 1.6 MPa to 2.0 MPa, and the temperature is 25° C. to 38° C.

[0012] In a further preferred embodiment, the ammonia-containing tail gas is passed into a dust removal tower for dust removal before being passed into the first spray absorption tower.

[0013] During the process of treating the tail gas in the first spray absorption tower, applying a certain pressure and appropriately increasing the temperature will help improve the absorption of ammonia by water, improve the recovery efficiency of ammonia, reduce the ammonia content in the remaining tail gas, and reduce the pressure for subsequent spray absorption.

[0014] In a further preferred embodiment, during the process of the ammonia-containing tail gas being introduced into the second spray absorption tower, pressure is also applied in the second spray absorption tower; the pressure is 14.3 MPa to 20 MPa.

[0015] In a further embodiment, the method for recovering and treating the ammonia-containing tail gas in the rear stage for synthesizing aromatic nitrile further comprises the following steps: using a nanofiltration membrane, filtering the ammonia-containing absorbent B obtained by absorbing ammonia in the second spray absorption tower to obtain secondary ammonia water. Using an ammonium ion selective permeable nanofiltration membrane to treat the ammonia-containing absorbent B can efficiently remove impurities and other ions therein, thereby improving the recovery of ammonia.

[0016] In a further embodiment, the method for recovering and treating the rear-stage ammonia-containing tail gas used for synthesizing aromatic nitriles also includes the following steps: passing the ammonia-containing tail gas into a first spray tower to obtain primary ammonia water, combining the primary ammonia water with the secondary ammonia water, and then heating under vacuum conditions to recover the ammonia gas.

[0017] In a further preferred embodiment, the heating temperature during the heating process is 80°C to 90°C.

[0018] The above-mentioned method for recovering and treating the ammonia-containing tail gas in the rear section for synthesizing aromatic nitrile comprises the following steps:

[0019] S1, the ammonia-containing tail gas is passed into a dust removal tower for dust removal to obtain tail gas I;

[0020] S2, the tail gas I is passed into the first spray tower, and is absorbed by the absorbent A to reduce the ammonia content in the tail gas, thereby obtaining primary ammonia water and tail gas II;

[0021] S3, the tail gas II is passed into the second spray tower, and is absorbed by absorbent B to obtain ammonia-containing absorbent B, and the remaining tail gas is discharged;

[0022] S4, filtering the ammonia-containing absorbent B with a nanofiltration membrane to obtain secondary ammonia water;

[0023] S5. Pass the primary ammonia water and the secondary ammonia water into a heating kettle, heat under vacuum conditions, and recover ammonia gas.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a method for recovering and treating ammonia-containing tail gas in the rear section for synthesizing aromatic nitrile, wherein the tail gas is subjected to secondary spraying absorption by an absorbent, then filtered through a membrane, and finally ammonia is recovered by vacuum heating. The process method greatly increases the recovery of ammonia in the ammonia-containing tail gas through the cooperation of various working sections, and the ammonia content in the tail gas after treatment is low, thereby reducing pollution to the atmosphere. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0027] The disclosure below provides many different embodiments or examples for implementing the present invention. In order to simplify the disclosure of the present invention, the implementation of specific examples is described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0028] Ammonia oxidation is the mainstream method for the industrial production of aromatic nitrile compounds. The tail gas produced by this method contains a large amount of ammonia. Directly discharging the ammonia-containing tail gas will cause waste of resources and pollution. In the prior art, the ammonia tail gas is generally condensed into dilute ammonia water by condensation, or the ammonia is absorbed by a spray tower. However, due to the low concentration and large volume of the dilute ammonia water condensed into the former, only a small part can be recycled, and most of the dilute ammonia water is difficult to handle or the processing cost is extremely high. The latter generally uses water or hydrochloric acid to spray and absorb the ammonia tail gas into the corresponding ammonia nitrogen solution, and then evaporation and concentration are used for recycling. Spraying and absorbing with water requires repeated spraying, and the processing efficiency is low. The cost of hydrochloric acid spraying is high, and ammonia emissions cannot be avoided.

[0029] The embodiment of the present invention uses an absorbent to perform secondary spray absorption on the tail gas, which can recover ammonia in the ammonia-containing tail gas to the maximum extent, and the remaining tail gas can be directly discharged. The absorbent that absorbs ammonia is then filtered through a membrane, and finally the ammonia is recovered by vacuum heating to obtain ammonia with high purity. The process method greatly increases the recovery of ammonia in the ammonia-containing tail gas through the cooperation of various work sections, and the ammonia content in the tail gas after treatment is low, reducing pollution to the atmosphere.

[0030] To solve the above problems, an embodiment of the present invention provides a method for recovering and treating ammonia-containing tail gas in the rear stage for synthesizing aromatic nitriles, comprising sequentially passing the ammonia-containing tail gas into a first spray absorption tower and a second spray absorption tower, absorbing the ammonia in the ammonia-containing tail gas in the liquid phase, thereby realizing the recovery of ammonia and directly discharging the waste gas.

[0031] Wherein, the absorbent A of the first spray absorption tower is water;

[0032] The absorbent B of the first spray absorption tower contains hydroxyacetic acid, vinylphosphonic acid and aluminum sulfate.

[0033] In a further embodiment, the ammonia-containing tail gas is the tail gas generated in the production of aromatic nitrile compounds by ammonia oxidation; the aromatic nitrile compounds include but are not limited to any one of isophthalonitrile, orthophthalonitrile, ortho-chlorobenzonitrile, p-chlorobenzonitrile, 2,6-dichlorobenzonitrile, and 3,4-dichlorobenzonitrile.

[0034] In a further embodiment, the absorbent A of the first spray absorption tower is water; the absorbent B of the first spray absorption tower comprises hydroxyacetic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of (3-5): (0.8-1): (0.1-0.15).

[0035] In a further preferred embodiment, the absorbent B further comprises pyrimethamine, and the molar ratio of pyrimethamine to glycolic acid in the absorbent B is 1:(0.3-0.5).

[0036] It should be noted that the ammonia in the ammonia-containing tail gas first passes through the first spray absorption tower, part of the ammonia is absorbed by water in the liquid phase to obtain the first ammonia water, and part of the ammonia remains in the tail gas. The remaining tail gas is passed into the second spray absorption tower, and the absorbent B in the second spray absorption tower has a higher solubility in ammonia, so that the ammonia in the tail gas is absorbed in the liquid phase to the greatest extent, thereby achieving efficient removal and recovery of ammonia.

[0037] In addition, the present invention selects three substances to be mixed in a certain proportion to form an absorbent B. Compared with the traditional spray absorption using sulfuric acid and phosphoric acid, the spray liquid has improved affinity with ammonia and high solubility for ammonia, thereby improving the recovery rate of ammonia, and its structure and phase state remain unchanged before and after absorption, thereby achieving efficient removal and recovery of ammonia. In addition, the absorbent has high stability, still has excellent ammonia adsorption efficiency after being placed for a long time, can be continuously recycled, and has reduced costs. It is found in actual production that adding a certain amount of pyrimethamine to the absorbent helps to further improve the absorption of ammonia and improve its stability.

[0038] In a further embodiment, the pressure in the first spray absorption tower is 1.6 MPa to 2.0 MPa, and the temperature is 25° C. to 38° C.

[0039] It should be noted that in the process of treating the tail gas in the first spray absorption tower, applying a certain pressure and appropriately increasing the temperature can help improve the absorption of ammonia by water, improve the recovery efficiency of ammonia, reduce the ammonia content in the remaining tail gas, and reduce the pressure for subsequent spray absorption.

[0040] In a further embodiment, the ammonia-containing tail gas is passed into a dust removal tower for dust removal before being passed into the first spray absorption tower.

[0041] In a further embodiment, during the process of the ammonia-containing tail gas being passed into the second spray absorption tower, pressure is also applied in the second spray absorption tower; the pressure is 14.3MPa to 20MPa.

[0042] It should be noted that, during the process of treating the tail gas in the second spray absorption tower, applying appropriate pressure can further increase the absorption of ammonia in the ammonia-containing tail gas in the absorbent, thereby improving the recovery of ammonia.

[0043] In a further embodiment, the method for recovering and treating the ammonia-containing tail gas in the rear stage for synthesizing aromatic nitrile further comprises the following steps: using a nanofiltration membrane, filtering the ammonia-containing absorbent B obtained by absorbing ammonia in the second spray absorption tower to obtain secondary ammonia water. Using an ammonium ion selective permeable nanofiltration membrane to treat the ammonia-containing absorbent B can efficiently remove impurities and other ions therein, thereby improving the recovery of ammonia.

[0044] In a further embodiment, the method for recovering and treating the rear-end ammonia-containing tail gas for synthesizing aromatic nitriles also includes the following steps: passing the ammonia-containing tail gas into a first spray tower to obtain primary ammonia water, combining the primary ammonia water with the secondary ammonia water, and then heating under vacuum conditions to recover the ammonia gas.

[0045] In a further embodiment, the heating temperature during the heating process is 80°C to 90°C.

[0046] The present invention will be further described below by way of specific embodiments.

[0047] Embodiment 1: A method for recovering and treating ammonia-containing tail gas in the rear section for synthesizing aromatic nitrile, comprising the following steps:

[0048] S1, ammonia-containing tail gas (tail gas from isophthalonitrile production) is passed into a dust removal tower for dust removal to obtain tail gas I;

[0049] S2, the tail gas I is introduced into the first spray tower, where a pressure of 1.6 MPa and a temperature of 25° C. are applied, and water is used for absorption to reduce the ammonia content in the tail gas, thereby obtaining primary ammonia water and tail gas II;

[0050] S3, the tail gas II is passed into the second spray tower, and is absorbed by absorbent B to obtain ammonia-containing absorbent B, and the remaining tail gas meets the emission standards;

[0051] The absorbent B is prepared by mixing glycolic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 3:0.8:0.1;

[0052] S4, the absorbent B is filtered using a nanofiltration membrane to obtain secondary ammonia water;

[0053] S5. Pass the primary ammonia water and the secondary ammonia water into a heating kettle, heat to 80° C. under vacuum conditions, and recover ammonia gas.

[0054] Embodiment 2: A method for recovering and treating ammonia-containing tail gas in the rear section for synthesizing aromatic nitrile, comprising the following steps:

[0055] S1, ammonia-containing tail gas (tail gas from o-chlorobenzonitrile production) is passed into a dust removal tower for dust removal to obtain tail gas I;

[0056] S2, the tail gas I is introduced into the first spray tower, where a pressure of 2.0 MPa and a temperature of 38° C. are applied, and water is used for absorption to reduce the ammonia content in the tail gas, thereby obtaining primary ammonia water and tail gas II;

[0057] S3, the tail gas II is passed into the second spray tower, and is absorbed by absorbent B to obtain ammonia-containing absorbent B, and the remaining tail gas meets the emission standards;

[0058] Absorbent B is prepared by mixing glycolic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 5:1:0.15;

[0059] S4, filtering the ammonia-containing spray liquid with a nanofiltration membrane to obtain secondary ammonia water;

[0060] S5. Pass the primary ammonia water and the secondary ammonia water into a heating kettle, heat to 90° C. under vacuum conditions, and recover ammonia gas.

[0061] Embodiment 3: The difference from Embodiment 2 is that no pressure is applied in the first spray tower in this embodiment.

[0062] Example 4: The difference from Example 2 is that the absorbent B in the second spray tower in this example is prepared by mixing hydroxyacetic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 2:1:0.05.

[0063] Example 5: The difference from Example 2 is that the absorbent B in the second spray tower in this example is prepared by mixing hydroxyacetic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 6:1:0.2.

[0064] Embodiment 6: The difference from Embodiment 2 is that the absorbent B in the second spray tower in this embodiment is only glycolic acid.

[0065] Example 7: The difference from Example 2 is that the absorbent B in the second spray tower in this example is prepared by mixing hydroxyacetic acid and vinylphosphonic acid in a molar ratio of 5:1.

[0066] Example 8: The difference from Example 2 is that the absorbent B in the second spray tower in this example is prepared by mixing hydroxyacetic acid and aluminum sulfate in a molar ratio of 5:0.15.

[0067] Example 9: The difference from Example 2 is that the spray liquid B in the second spray tower in this example is prepared by mixing hydroxyacetic acid, vinylphosphonic acid, aluminum sulfate and pyrimethamine in a molar ratio of 5:1:0.15:1.5.

[0068] Example 10: The difference from Example 2 is that a pressure of 14.3 MPa is also applied in the second spray tower in this example.

[0069] Example 11: The difference from Example 2 is that a pressure of 20 MPa is also applied in the second spray tower in this example.

[0070] Example 12: The difference from Example 2 is that a pressure of 25 MPa is also applied in the second spray tower in this example.

[0071] Comparative Example 1: The difference from Example 2 is that the absorbent B in the second spray tower in this comparative example is sulfuric acid.

[0072] Comparative Example 2: The difference from Example 2 is that there is no step of spraying absorbent B in this comparative example, and the specific steps are as follows:

[0073] S1, the ammonia-containing tail gas is passed into a dust removal tower for dust removal to obtain tail gas I;

[0074] S2, the tail gas I is passed into the first spray tower, where a pressure of 2.0 MPa and a temperature of 38° C. are applied, and water is used for absorption to reduce the ammonia content in the tail gas, thereby obtaining primary ammonia water and tail gas;

[0075] S3. Pass the first-grade ammonia water into the heating kettle, heat it to 90° C. under vacuum conditions, and recover the ammonia gas.

[0076] Comparative Example 3: The difference from Example 2 is that there is no water spraying step in this comparative example, and the specific steps are as follows:

[0077] S1, the ammonia-containing tail gas is passed into a dust removal tower for dust removal to obtain tail gas I;

[0078] S2, the tail gas I is passed into the second spray tower, and is absorbed by absorbent B to obtain ammonia-containing absorbent B, and the remaining tail gas meets the emission standards;

[0079] Absorbent B is prepared by mixing glycolic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 5:1:0.15;

[0080] S3, the ammonia-containing absorbent B is filtered using a nanofiltration membrane to obtain secondary ammonia water;

[0081] S4. Pass the primary ammonia water and the secondary ammonia water into a heating kettle, heat under vacuum conditions, and recover ammonia gas.

[0082] Test Example 1: The treatment results of the ammonia-containing tail gas in the latter stage of the synthesis of o-chlorobenzonitrile / isophthalonitrile in the above-mentioned embodiments and comparative examples are shown in Table 1 below.

[0083] Table 1

[0084]

[0085] As shown in Table 1, the ammonia concentration of the tail gas treated by the ammonia tail gas treatment and recovery method provided by the present invention is less than 0.3 mg / m 3 , the lowest reached 0.06mg / m 3 , in line with the provisions of the "Comprehensive Emission Standards for Air Pollutants" and below 1.5 mg / m 3 The recovery rate of ammonia is over 98%, and the highest is over 99.5%. The recovery rate of ammonia is high.

[0086] Test Example 2: Take absorbent B in Examples 1, 2, and 4 to 9, place it in an absorption tank, introduce ammonia gas under stirring at room temperature, and wait for the ammonia absorbent to reach absorption equilibrium, and calculate the amount of ammonia absorbed by the change in ammonia pressure in the absorption tank.

[0087] After the spray liquid B was exposed to the air for 100 days, its ammonia absorption capacity was tested to examine its stability.

[0088] The test results are shown in Table 2 below.

[0089] Table 2

[0090]

[0091] As shown in Table 2, the absorbent B provided by the present invention has excellent ammonia absorption capacity, and its ammonia absorption capacity is more than 8 mol / kg, and the ammonia absorption capacity is still higher than 7 mol / kg after being placed for 100 days, and the stability is high. That is to say, the present invention selects three or four substances to mix in a certain proportion to form the absorbent B, which improves the ammonia absorption capacity and stability of the absorbent.

[0092] The present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for recovering and treating ammonia-containing tail gas in the rear section for synthesizing aromatic nitrile, characterized in that: The following steps are involved: S1, the ammonia-containing tail gas is passed into a dust removal tower for dust removal to obtain tail gas I; S2, the tail gas I is passed into the first spray tower, and is absorbed by the absorbent A to reduce the ammonia content in the tail gas to obtain primary ammonia water and tail gas II; S3, the tail gas II is passed into the second spray tower, and is absorbed by absorbent B to obtain ammonia-containing absorbent B, and the remaining tail gas is discharged; S4, filtering the ammonia-containing absorbent B with a nanofiltration membrane to obtain secondary ammonia water; S5, passing the primary ammonia water and the secondary ammonia water into a heating kettle, heating under vacuum conditions, and recovering ammonia gas; Wherein, the absorbent A is water; The absorbent B comprises glycolic acid, vinylphosphonic acid and aluminum sulfate in a molar ratio of 3-5:0.8-1:0.1-0.15; The pressure in the first spray absorption tower is 1.6MPa-2.0MPa, and the temperature is 25°C-38°C.

2. The method for recovering and treating the rear-stage ammonia-containing tail gas for synthesizing aromatic nitrile according to claim 1, characterized in that: The absorbent B also contains pyrimethamine, and the molar ratio of pyrimethamine to glycolic acid in the absorbent B is 1:0.3-0.

5.

3. The method for recovering and treating the rear-stage ammonia-containing tail gas for synthesizing aromatic nitrile according to claim 1, characterized in that: During the process of the ammonia-containing tail gas being introduced into the second spray absorption tower, pressure is also applied in the second spray absorption tower.

4. The method for recovering and treating the rear-stage ammonia-containing tail gas for synthesizing aromatic nitrile according to claim 3, characterized in that: The applied pressure is 14.3 MPa to 20 MPa.

5. The method for recovering and treating the rear-stage ammonia-containing tail gas for synthesizing aromatic nitrile according to claim 1, characterized in that: In step S5, the heating temperature during the heating process is 80°C to 90°C.

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