Tail gas pretreatment system suitable for chloroacetic acid production process by acetic acid method

Abstract

The utility model discloses a hydrogen chloride removal system suitable for a process of producing chloroacetic acid by an acetic acid method, and belongs to the technical field of glycine production. The hydrogen chloride removal system comprises a separation kettle, a condenser, a packing absorption tower and an acetyl chloride recovery tank, the separation kettle is connected with the chlorination reaction kettle, and the separation kettle is connected with the condenser; the condenser is connected with the separation kettle through a return pipe, a non-condensable gas outlet on the condenser is connected with the packing absorption tower through a non-condensable gas outlet pipe, and a vacuum pump is arranged on the non-condensable gas outlet pipe; the packing absorption tower is connected with an acetic acid inlet pipe, an upper gas phase outlet of the packing absorption tower is connected with a tail gas treatment system, and the packing absorption tower is connected with an acetyl chloride recovery tank through an acetyl chloride outlet pipe; the acetyl chloride recovery tank is connected with the chlorination reaction kettle through a recycling pipe and is also connected with the packing absorption tower through a circulating pipe. Acetyl chloride in a chloroacetic acid finished product is recovered and used for a chlorination process, so that the consumption of raw material acetic anhydride is reduced; and meanwhile, the loss amount of raw material liquid ammonia in the subsequent ammoniation process is reduced.

Description

Technical Field

[0001] This utility model relates to a tail gas treatment system, specifically a tail gas pretreatment system suitable for the acetic acid process in the production of chloroacetic acid, belonging to the field of clean production technology of glycine. Background Technology

[0002] Industrial glycine is mostly produced by the ammonolysis of chloroacetic acid. In this process, chloroacetic acid and liquid ammonia (or ammonia water) are used as raw materials, and hexamethylenetetramine is used as a catalyst. The mixture is produced by ammonolysis (75-85 °C, atmospheric pressure) to obtain a mixture of glycine and ammonium chloride (byproduct). The mixture is then separated to obtain the glycine product.

[0003] In the preparation of chloroacetic acid, acetic acid, chlorine, and acetic anhydride are used as raw materials. Acetic acid and acetic anhydride are added to the main reactor and top reactor respectively in a certain proportion. Chlorine gas is continuously introduced for chlorination while controlling the reaction temperature at 95-105℃ to obtain the finished chloroacetic acid product (chlorination reaction solution). Acetic anhydride is mainly used to provide acetyl chloride, which plays a catalytic role in the entire chlorination reaction. The finished chloroacetic acid product contains approximately 94-95% chloroacetic acid, approximately 3-4% dichloroacetic acid, approximately 1.3% hydrogen chloride, and small amounts of acetic acid and acetyl chloride.

[0004] Currently, chloroacetic acid is generally produced without further processing. Water is directly added to the mixed acid reactor to prepare an aqueous solution with a chloroacetic acid content of approximately 74.5%, which is then used in the next process—ammoniation (i.e., glycine synthesis). This presents the following technical problems:

[0005] In the finished chloroacetic acid product, acetyl chloride reacts with water to produce hydrogen chloride and acetic acid. The hydrogen chloride produced will consume ammonia gas, the raw material for ammoniation, in the subsequent ammoniation process. This not only wastes acetyl chloride in the chlorination process, but also seriously affects the subsequent ammoniation process.

[0006] Although the prior art CN108854490A discloses "a new process for purifying chloroacetic acid tail gas and desulfurizing by-product hydrochloric acid", it is mainly applicable to the production process of intermittent chlorination of acetic acid using sulfur as a catalyst, and its main purpose is desulfurization and dechlorination; CN114777421A discloses "a system and method for purifying hydrogen chloride from chloroacetic acid or chloroacetyl chloride synthesis tail gas", but it mainly purifies hydrogen chloride from chloroacetic acid (or chloroacetyl chloride) synthesis tail gas and co-produces sulfur dioxide; CN118558268A discloses "equipment and method for the joint preparation of acetyl chloride and chloroacetic acid", but it mainly co-produces acetyl chloride and chloroacetic acid, etc.

[0007] Therefore, a system is needed to effectively pretreat chlorination tail gas and to better integrate with the preceding chlorination process and the subsequent ammoniation process. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, a tail gas pretreatment system suitable for the acetic acid process in the production of chloroacetic acid is proposed. In this technical solution, by specifically arranging the separation vessel, condenser, packed absorption tower, and acetyl chloride recovery tank, the content of hydrogen chloride and acetyl chloride in the finished chloroacetic acid product is effectively reduced, thereby increasing the glycine crystallization rate.

[0009] Specifically, acetyl chloride in the finished chloroacetic acid product is recovered and reused in the chlorination process, thereby reducing the consumption of raw material acetic anhydride; at the same time, hydrogen chloride in the finished chloroacetic acid product is recovered, thereby reducing the loss of raw material liquid ammonia in the subsequent ammoniation process, etc.

[0010] To achieve the above technical objectives, the following technical solution is proposed:

[0011] The purpose of this technical solution is to provide: a tail gas pretreatment system suitable for the acetic acid process in the production of chloroacetic acid, including a separation vessel, a condenser, a packed absorption tower and an acetyl chloride recovery tank;

[0012] Separation vessel: Connected to the chlorination reaction vessel via a chlorination reaction liquid delivery pipe, the separation vessel is equipped with a perforated cylindrical distribution mechanism (e.g., a swivel disc), and the chlorination reaction liquid delivery pipe extends into the cylindrical distribution mechanism; the connecting shaft of the cylindrical distribution mechanism extends to the outside of the separation vessel and is connected to a drive mechanism (e.g., a motor); the gas outlet on the separation vessel is connected to the feed inlet on the condenser via a tail gas outlet pipe;

[0013] Condenser: The liquid outlet of the condenser is connected to the separator via a reflux pipe. A U-shaped tube is installed on the reflux pipe (to achieve liquid sealing and prevent gas leakage). More preferably, a heat tracing jacket is fitted on the outside of the reflux pipe and the U-shaped tube I to improve the chloroacetic acid reflux rate, reduce waste, and increase yield. The non-condensable gas outlet of the condenser is connected to the feed inlet of the packed absorption tower via a non-condensable gas outlet pipe. A vacuum pump is installed on the non-condensable gas outlet pipe. The vacuum pump ensures that a negative pressure is formed in the separator through the tail gas outlet pipe, the condenser, and the non-condensable gas outlet pipe, so as to achieve effective exhaust of tail gas.

[0014] Packed absorption tower: The gas phase outlet of the packed absorption tower is connected to the tail gas treatment system, and the liquid phase outlet of the packed absorption tower is connected to the acetyl chloride recovery tank through an acetyl chloride outlet pipe, which is equipped with a U-shaped pipe II; the packed absorption tower is connected to an acetic acid inlet pipe. The underlying mechanism in the packed absorption tower includes: acetyl chloride has a low boiling point (50.5℃), and acetyl chloride reacts with acetic acid. That is, within the packed absorption tower, acetyl chloride and hydrogen chloride are separated. Acetyl chloride is discharged into the acetyl chloride recovery tank along with acetic acid, while hydrogen chloride is discharged to the tail gas treatment system for centralized treatment.

[0015] Acetyl chloride recovery tank: It is connected to the chlorination reactor through a reuse pipe to enable the recovery of acetyl chloride to be reused in the chlorination process. The acetyl chloride recovery tank is also connected to the packed absorption tower through a circulation pipe to realize the recycling of acetic acid.

[0016] Furthermore, the liquid outlet of the separation vessel is connected to the chloroacetic acid transfer vessel via a chloroacetic acid outlet pipe, and a water supply pipe is connected to the chloroacetic acid outlet pipe; a transfer pump is also installed on the chloroacetic acid outlet pipe.

[0017] Furthermore, the chlorination reactor is connected to an acetic acid inlet pipe, a chlorine inlet pipe, and an acetic anhydride inlet pipe; the tail gas outlet of the chlorination reactor is connected to a packed absorption tower.

[0018] The reaction equations involved in this technical solution are as follows:

[0019] The main reaction equation for chlorination is:

[0020] Chlorination reaction mechanism: (CH3CO)2O + Cl2 = ClCH2COOCOCH3 + HCl

[0021] ClCH2COOCOCH3+CH3COOH=ClCH2COOH+(CH3CO)2O

[0022] (CH3CO)2O+HCl=CH3COCl+CH3COOH

[0023] CH3COCl + Cl2 = ClCH2COCl + HCl

[0024] ClCH2COCl+CH3COOH=ClCH2COOH+CH3COCl

[0025] ClCH2COCl+ClCH2COOH=Cl2CHCOOH+CH3COCl

[0026] amination reaction equation:

[0027] .

[0028] The terms "inner," "outer," and "upper" used in this technical solution are defined based on the actual usage conditions and are conventional terms used in this technical field, as well as in the actual use by those skilled in the art.

[0029] The beneficial technical effects of adopting this technical solution are as follows:

[0030] In this invention, by specifically arranging the separation vessel, condenser, packed absorption tower, and acetyl chloride recovery tank, the tail gas in the finished chloroacetic acid is pretreated to recover acetyl chloride from the finished chloroacetic acid and reuse it in the chlorination process, thereby reducing the amount of raw material acetic anhydride fed in and lowering production costs. At the same time, hydrogen chloride in the finished chloroacetic acid is recovered (which can be reduced to 0.5%), thereby reducing the loss of raw material liquid ammonia in the subsequent ammoniation process.

[0031] By effectively reducing the content of hydrogen chloride and acetyl chloride in the finished chloroacetic acid product, the crystallization rate of glycine is improved, and the sustainability and efficiency of the chlorination and ammoniation processes are ensured. Attached Figure Description

[0032] Figure 1 This is a structural block diagram of the present utility model;

[0033] In the diagram, 1. Separation vessel; 101. Cylindrical distribution mechanism; 102. Drive mechanism; 2. Condenser; 3. Packed absorption tower; 4. Tail gas outlet pipe; 5. Reflux pipe; 6. Non-condensable gas outlet pipe; 7. Vacuum pump; 8. Tail gas treatment system; 9. Acetyl chloride outlet pipe; 10. U-shaped pipe I; 11. Acetyl chloride recovery tank; 12. Reuse pipe; 13. Circulation pipe; 14. Chloroacetic acid outlet pipe; 15. Chloroacetic acid transfer vessel; 16. Water supply pipe; 17. Transfer pump I; 18. Acetic acid inlet pipe; 19. U-shaped pipe II; 20. Transfer pump II; 21. Chlorination reaction liquid transfer pipe; 22. Chlorination reaction vessel. Detailed Implementation

[0034] The technical solutions in the embodiments of this utility model will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0035] Example 1

[0036] A tail gas pretreatment system suitable for the acetic acid process in the production of chloroacetic acid, such as Figure 1 As shown, it includes a separation vessel 1, a condenser 2, a packed absorption tower 3, and an acetyl chloride recovery tank 11;

[0037] Separation vessel 1 is connected to chlorination reaction vessel 22 via chlorination reaction liquid delivery pipe 21. The gas outlet of separation vessel 1 is connected to the feed inlet of condenser 2 via tail gas outlet pipe 4. The liquid outlet of condenser 2 is connected to separation vessel 1 via reflux pipe 5. The non-condensable gas outlet of condenser 2 is connected to the feed inlet of packed absorption tower 3 via non-condensable gas outlet pipe 6, and a vacuum pump 7 (e.g., diaphragm vacuum pump) is installed on non-condensable gas outlet pipe 6. The packed absorption tower 3 is connected to acetic acid inlet pipe 18. The gas phase outlet of packed absorption tower 3 is connected to tail gas treatment system 8. The liquid phase outlet of packed absorption tower 3 is connected to acetyl chloride recovery tank 11 via acetyl chloride outlet pipe 9. The mechanism in packed absorption tower 3 includes: acetyl chloride has a low boiling point (50.5℃), and acetic acid absorbs acetyl chloride. That is, in packed absorption tower 3, acetyl chloride and hydrogen chloride are separated. Acetyl chloride is discharged into acetyl chloride recovery tank 11 along with acetic acid, while hydrogen chloride is discharged to tail gas treatment system 8 for centralized treatment.

[0038] Acetyl chloride recovery tank 11 is connected to chlorination reactor 22 via reuse pipe 12, so that the recovered acetyl chloride can be reused in the chlorination process; acetyl chloride recovery tank 11 is also connected to packed absorption tower 3 via circulation pipe 13, and a transfer pump I 17 is installed on circulation pipe 13 to realize the recycling of acetic acid.

[0039] A continuous passage is formed between the separator 1, the tail gas outlet pipe 4, the return pipe 5, and the separator 1 to condense and return vaporized chloroacetic acid in the tail gas pretreatment.

[0040] A continuous pathway for the recovery and reuse of acetyl chloride in the pretreatment of tail gas is formed between the separation vessel 1, tail gas outlet pipe 4, condenser 2, vacuum pump 7, packed absorption tower 3, acetyl chloride outlet pipe 9, acetyl chloride recovery tank 11, reuse pipe 12 and chlorination reaction vessel 22.

[0041] A continuous pathway for hydrogen chloride recovery and treatment in tail gas pretreatment is formed between the separation vessel 1, tail gas outlet pipe 4, condenser 2, vacuum pump 7, packed absorption tower 3, and tail gas treatment system 8.

[0042] Example 2

[0043] Based on Example 1, this example further defines the separation vessel 1 to further illustrate the technical solution.

[0044] The separation vessel 1 is equipped with a cylindrical distribution mechanism 101 with holes, and the chlorination reaction liquid delivery pipe 21 extends into the cylindrical distribution mechanism 101; the connecting shaft of the cylindrical distribution mechanism 101 extends to the outside of the separation vessel 1 and is connected to a drive mechanism 102.

[0045] In addition, the liquid outlet of the separation vessel 1 is connected to the chloroacetic acid transfer vessel 15 through the chloroacetic acid outlet pipe 14, and the chloroacetic acid outlet pipe 14 is connected to the water supply pipe 16; the chloroacetic acid outlet pipe 14 is also equipped with a transfer pump II 20.

[0046] The work process involved is as follows:

[0047] 1) The chlorination reaction liquid discharged from the chlorination reactor 22 is fed into the separation reactor 1. The separation reactor 1 is kept under negative pressure by the vacuum pump 7, so that the chloroacetic acid in the chloroacetic acid product is discharged from the bottom of the separation reactor 1, and then enters the chloroacetic acid transfer reactor 15 after water replenishment; the gas in the chlorination reaction liquid is condensed and refluxed by the condenser 2, while the non-condensable gas enters the packed absorption tower 3.

[0048] The chlorination reaction solution mainly consists of chloroacetic acid, as well as approximately 1.3% hydrogen chloride and acetyl chloride dissolved in chloroacetic acid, with an acetyl chloride boiling point of 50.5℃.

[0049] 2) Non-condensable gas is introduced into the packed absorption tower 3. After being absorbed by the spray in the packed absorption tower 3, the gas phase - hydrogen chloride - enters the tail gas treatment system 8, and the liquid phase - enters the acetyl chloride recovery tank 11.

[0050] 3) Acetic acid and chloroacetic acid in acetyl chloride recovery tank 11 are pumped out, part of which is recycled to chlorination reactor 22, and part of which is sprayed into packed absorption tower 3 to absorb the gas.

[0051] Example 3

[0052] Based on Examples 1-2, this example uses a U-shaped tube for liquid sealing to prevent gas leakage during liquid transportation, as follows:

[0053] A U-shaped tube I10 is installed on the reflux pipe 5, and both the reflux pipe 5 and the outer sleeve of the U-shaped tube I10 are equipped with heat tracing sleeves. This improves the chloroacetic acid reflux rate, reduces waste, and increases yield.

[0054] In addition, a U-shaped tube II19 is provided on the acetyl chloride outlet tube 9.

[0055] Example 4

[0056] Based on Examples 1-3, this example further defines the chlorination reactor 22 to further illustrate the technical solution.

[0057] The chlorination reactor 22 is connected to an acetic acid inlet pipe 18, a chlorine inlet pipe, and an acetic anhydride inlet pipe; the tail gas outlet of the chlorination reactor 22 is connected to the packed absorption tower 3.

Claims

1. A tail gas pre-treatment system suitable for use in the process of producing chloroacetic acid by acetic acid method, characterized in that: The device comprises a separation kettle (1), a condenser (2), a packed absorption tower (3) and an acetyl chloride recovery tank (11); The separation kettle (1) is connected with the chlorination reaction kettle (22) through a chlorination reaction liquid conveying pipe (21), the gas outlet of the separation kettle (1) is connected with the feeding inlet of the condenser (2) through a tail gas outlet pipe (4), the liquid outlet of the condenser (2) is connected with the separation kettle (1) through a reflux pipe (5), the non-condensable gas outlet of the condenser (2) is connected with the feeding inlet of the packed absorption tower (3) through a non-condensable gas outlet pipe (6), and the non-condensable gas outlet pipe (6) is provided with a vacuum pump (7); the packed absorption tower (3) is connected with an acetic acid feeding pipe (18), the gas phase outlet of the packed absorption tower (3) is connected with a tail gas treatment system (8), and the liquid phase outlet of the packed absorption tower (3) is connected with the acetyl chloride recovery tank (11) through an acetyl chloride outlet pipe (9). The acetyl chloride recovery tank (11) is connected with the chlorination reaction kettle (22) through a recycling pipe (12), and is also connected with the packed absorption tower (3) through a circulating pipe (13), and the circulating pipe (13) is provided with a conveying pump I (17). The separation kettle (1), the tail gas outlet pipe (4), the reflux pipe (5) and the separation kettle (1) form a continuous path for condensation reflux of chloroacetic acid vapor in the tail gas pretreatment. The separation kettle (1), the tail gas outlet pipe (4), the condenser (2), the vacuum pump (7), the packed absorption tower (3), the acetyl chloride outlet pipe (9), the acetyl chloride recovery tank (11), the recycling pipe (12) and the chlorination reaction kettle (22) form a continuous path for acetyl chloride recovery and reuse in the tail gas pretreatment. The separation kettle (1), the tail gas outlet pipe (4), the condenser (2), the vacuum pump (7), the packed absorption tower (3) and the tail gas treatment system (8) form a continuous path for hydrogen chloride recovery and treatment in the tail gas pretreatment.

2. The tail gas pre-treatment system suitable for use in the process for the production of chloroacetic acid by acetic acid method as claimed in claim 1, wherein: The separation kettle (1) is provided with a cylindrical distribution mechanism (101) with holes, and the chlorination reaction liquid conveying pipe (21) extends into the cylindrical distribution mechanism (101); the connecting shaft of the cylindrical distribution mechanism (101) extends out of the separation kettle (1) and is connected with a driving mechanism (102).

3. The system for pretreatment of off-gas suitable for use in the process for production of chloroacetic acid by acetic acid method as claimed in claim 1 wherein: The reflux pipe (5) is provided with a U-shaped pipe I (10).

4. The tail gas pre-treatment system suitable for use in the process for the production of chloroacetic acid by acetic acid method as claimed in claim 3, wherein: The outer side of the reflux pipe (5) and the outer side of the U-shaped pipe I (10) are both provided with a heat tracing jacket.

5. The system for pretreatment of off-gas suitable for use in the process for production of chloroacetic acid by acetic acid method as claimed in claim 1 wherein: The acetyl chloride outlet pipe (9) is provided with a U-shaped pipe II (19).

6. The system for pretreatment of off-gas suitable for use in the process for production of chloroacetic acid by acetic acid method as claimed in claim 1 wherein: The liquid outlet of the separation kettle (1) is connected with a chloroacetic acid intermediate kettle (15) through a chloroacetic acid outlet pipe (14), the chloroacetic acid outlet pipe (14) is communicated with a water supplement pipe (16), and the chloroacetic acid outlet pipe (14) is also provided with a conveying pump II (20).

7. The system for pretreatment of off-gas suitable for use in the process for production of chloroacetic acid by acetic acid method according to any one of claims 1-6, characterized in that: The chlorination reaction kettle (22) is connected with an acetic acid feeding pipe (18), a chlorine feeding pipe and an acetic anhydride feeding pipe, and the tail gas outlet of the chlorination reaction kettle (22) is connected with the packed absorption tower (3).

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