High-pressure tail gas recycling device and method for low-pressure carbonylation synthesis of acetic acid by methanol

Abstract

The application discloses a high-pressure tail gas recycling device for low-pressure carbonyl synthesis of acetic acid from methanol, and a buffer reactor is additionally arranged between a main reactor and a high-pressure separator and a flash evaporator, which is used as a reaction container for high-pressure tail gas and liquid-phase materials in the main reactor. The application also discloses a high-pressure tail gas recycling method, in which methanol and carbon monoxide are pressurized and then enter the main reactor for reaction, and part of high-pressure gas is discharged to a top condenser and a high-pressure separator for treatment to obtain high-pressure tail gas. The treatment steps are as follows: the high-pressure tail gas discharged from the high-pressure separator enters the buffer reactor; the high-temperature and high-pressure liquid-phase materials in the main reactor are partially extracted to the buffer reactor for reaction with the high-pressure tail gas; the liquid-phase materials in the buffer reactor are extracted to the flash evaporator for gas-liquid separation, the gas-phase components are sent to a product rectification system, and the liquid-phase components are returned to the main reactor. The application directly recycles iodomethane and carbon monoxide in the high-pressure tail gas, and reduces the consumption of raw materials and auxiliary catalysts for acetic acid synthesis products.

Description

Technical Field

[0001] This invention belongs to the field of acetic acid preparation technology, specifically relating to a high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol, and also relating to the corresponding recovery and utilization method. Background Technology

[0002] Currently, the methanol-to-acetic acid low-pressure carbonylation process is the most advanced acetic acid synthesis technology. The basic principle is that methanol and carbon monoxide are pressurized and introduced into a reactor. Under the action of a catalyst and co-catalyst, the reaction is carried out at a pressure controlled at 2.8–3.0 MPa and a temperature controlled at 180–200°C to synthesize acetic acid. To maintain catalyst stability and prevent precipitation, exhaust gas needs to be released from the top of the reactor to keep the carbon monoxide within a certain partial pressure range. The gas phase from the top of the reactor undergoes gas-liquid separation via a top condenser and a high-pressure separator. The liquid phase, mainly composed of catalyst, is returned to the reactor to participate in the reaction. The gas phase mainly consists of carbon monoxide (60%–80%), carbon dioxide (3%–6%), nitrogen (5%–10%), hydrogen (2%–5%), methane (1%–3%), iodomethane (1%–2%), and methanol or acetic acid (2%–5%), with emissions ranging from 1000 to 2000 Nm³. 3 The pressure is generally 0-0.05 MPa lower than that of the reactor, and the temperature is between 25℃ and 45℃. Currently, the common method for treating gaseous materials is to install a high-pressure absorption tower. Acetic acid or methanol is pressurized and enters the upper part of the high-pressure absorption tower to absorb iodomethane, methanol, and acetic acid from the gaseous material. (See attached...) Figure 1 As shown, the remaining exhaust gas is generally treated in the following ways: first, it is directly vented to a flare for combustion; second, it is vented under high pressure to the exhaust gas combustion furnace through an exhaust gas combustion furnace device; and third, carbon monoxide in the exhaust gas is separated and recovered using technologies such as pressure swing adsorption and membrane treatment.

[0003] The above three methods for treating exhaust gas all have significant drawbacks. The exhaust gas contains a large amount of carbon monoxide, and direct combustion in a flare would result in a huge waste of energy. Using the byproduct steam from the exhaust gas combustion furnace for acetic acid distillation systems has disadvantages such as high investment, long process, and low efficiency. Using pressure swing adsorption or membrane separation technology to recover carbon monoxide for acetic acid synthesis has disadvantages such as long process flow, large footprint, high investment, long payback period, and low purity of recovered carbon monoxide. Therefore, it is necessary to propose a new method for high-pressure exhaust gas recovery and utilization. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a high-pressure tail gas recovery and utilization device and method for the low-pressure carbonyl synthesis of acetic acid from methanol. The high-pressure tail gas is used as the raw material gas for acetic acid synthesis. A portion of liquid material is extracted from the main reactor as the raw material liquid to react with the high-pressure tail gas, directly recovering and utilizing iodomethane and carbon monoxide in the high-pressure tail gas to produce acetic acid products. This reduces the unit consumption of carbon monoxide and iodomethane, the raw materials for acetic acid synthesis products.

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

[0006] In a first aspect, the present invention provides a high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol, comprising a main reactor, a top condenser and a high-pressure separator connected in sequence. The high-pressure gas discharged from the main reactor is separated by the top condenser and the high-pressure separator to form high-pressure tail gas, and the liquid phase material generated in the top condenser and the high-pressure separator is returned to the main reactor.

[0007] The high-pressure tail gas recovery and utilization device also includes a buffer reactor and a flash evaporator. The high-pressure separator is connected to the buffer reactor through a first pipeline to introduce the high-pressure tail gas into the buffer reactor. The main reactor is connected to the buffer reactor through a second pipeline to extract some liquid phase material from the main reactor into the buffer reactor. The buffer reactor is connected to the flash evaporator.

[0008] Preferably, a pressure reducing valve is installed on the second pipeline to reduce the pressure of the extracted liquid phase material, so that the pressure of the liquid phase material entering the buffer reactor is slightly lower than that of the high-pressure tail gas.

[0009] Preferably, the first pipe and the second pipe are connected by an auxiliary pipe, wherein the connection point between the auxiliary pipe and the second pipe is located between the pressure reducing valve and the buffer reactor.

[0010] In a second aspect, this invention provides a method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol. The method is applicable to a high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol. Methanol and carbon monoxide are pressurized and then enter the main reactor, where they react under the catalysis of a catalyst. A portion of the high-pressure gas is discharged to a top condenser and a high-pressure separator for further treatment to obtain high-pressure tail gas. The treatment steps for the high-pressure tail gas are as follows:

[0011] S1. The high-pressure tail gas discharged from the high-pressure separator enters the buffer reactor;

[0012] S2. Extract a portion of the high-temperature and high-pressure liquid phase material in the main reactor to the buffer reactor and react it with the high-pressure tail gas in step (1).

[0013] S3. Extract some of the liquid phase material in the buffer reactor to the flash evaporator for gas-liquid separation. The gas phase component in the flash evaporator goes to the product distillation system, and the liquid phase component returns to the main reactor.

[0014] This invention differs from existing high-pressure tail gas treatment methods. It utilizes the fact that the tail gas discharged from the top of the main reactor contains iodomethane (a co-catalyst) and a significant amount of carbon monoxide. The carbon monoxide is directly recycled by participating in the reaction again to synthesize acetic acid, thus increasing the acetic acid yield. This is achieved by separating and recovering carbon monoxide from the high-pressure tail gas discharged from the high-pressure separator. Regarding the recovery of iodomethane, this invention extracts a portion of the liquid phase material from the main reactor into a buffer reactor. The main component of this liquid phase material is acetic acid, which, in addition to reacting with carbon monoxide to synthesize acetic acid, also contributes to the recovery of iodomethane.

[0015] Preferably, in step S2, after some liquid phase material is extracted from the main reactor, it is depressurized and then enters the buffer reactor.

[0016] Preferably, in step S2, the pressure of the liquid material extracted from the main reactor is controlled to be lower than the pressure of the high-pressure tail gas after depressurization, and the difference is 0.01 to 0.3 MPa, so that the high-pressure tail gas can enter the buffer reactor.

[0017] Preferably, in step S1, the pressure of the high-pressure tail gas discharged through the high-pressure separator is lower than the pressure inside the main reactor, and the pressure difference between the high-pressure tail gas and the pressure inside the main reactor is 0-0.05 MPa.

[0018] Preferably, in step S2, the liquid phase material is extracted from the middle of the main reactor.

[0019] Beneficial effects:

[0020] This invention uses high-pressure tail gas as raw material gas and extracts a portion of liquid material from the main reactor as raw material liquid. The methanol / methyl acetate in the liquid material reacts with carbon monoxide in the high-pressure tail gas to synthesize acetic acid, thereby increasing the yield of acetic acid and reducing the consumption of raw materials carbon monoxide and methanol. Iodomethane in the high-pressure tail gas is absorbed and recovered by the liquid material, effectively reducing the consumption of co-catalyst. This invention changes the existing technology for treating high-pressure tail gas, shortens the treatment process, and effectively reduces the production cost of enterprises. Attached Figure Description

[0021] Figure 1 The diagram shows a schematic of the recovery and utilization of high-pressure tail gas in the existing methanol low-pressure carbonyl synthesis of acetic acid process.

[0022] Figure 2 The diagram shown is a schematic diagram of the process for recovering and utilizing high-pressure tail gas in the methanol low-pressure carbonyl synthesis of acetic acid according to the present invention.

[0023] Attached reference numerals: 1-Main reactor, 2-Pressure reducing valve, 3-Buffer reactor, 4-Flash evaporator, 5-Top condenser, 6-High pressure separator, 7-High pressure absorption tower, 8-High pressure absorption methanol / acetic acid feed pump, 9-First pipeline, 10-Second pipeline, 11-Auxiliary pipeline. Detailed Implementation

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0025] like Figure 1 As shown, existing devices for recovering and utilizing high-pressure tail gas generally include a main reactor 1, a top condenser 5, a high-pressure separator 6, and a high-pressure absorption tower 7. The high-pressure tail gas discharged from the high-pressure separator 6 enters the high-pressure absorption tower 7 from the bottom. Methanol / acetic acid used to absorb iodomethane enters the high-pressure absorption tower 7 from the top via a high-pressure absorption methanol / acetic acid feed pump 8. The purified high-pressure tail gas is then treated according to the corresponding treatment methods to recover carbon monoxide for reuse or directly used as fuel for combustion.

[0026] Existing technologies for recovering carbon monoxide from high-pressure exhaust gas generally involve purifying and recovering the high-pressure exhaust gas or using it directly as fuel. For example, in the case of recovering carbon monoxide, the recovered carbon monoxide can be reintroduced into the main reactor 1 as a raw material. However, existing recovery methods have various problems such as high investment costs and long process flow.

[0027] The technical solution of the present invention will be described in detail below with specific embodiments.

[0028] This invention provides a high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol, such as... Figure 2 As shown, it includes at least a main reactor 1, a top condenser 5, a high-pressure separator 6, a buffer reactor 3, and a flash evaporator 4. The main reactor 1, the top condenser 5, and the high-pressure separator 6 are connected in sequence to process the high-pressure gas discharged from the top of the main reactor 1. A first pipe 9 connects the high-pressure separator 6 to the buffer reactor 3 to introduce the high-pressure tail gas discharged from the high-pressure separator 6 into the buffer reactor. A second pipe 10 connects the main reactor 1 to the buffer reactor 3 to extract the liquid phase material in the main reactor 1 into the buffer reactor 3.

[0029] Furthermore, the second pipeline 10 is equipped with a pressure reducing valve 2 to reduce the pressure of the extracted liquid phase material, and then the liquid phase material enters the buffer reactor 3 to avoid affecting the high-pressure tail gas entering the buffer reactor 3.

[0030] Furthermore, the auxiliary pipe 11 connects the first pipe 9 and the second pipe 10. The connection between the auxiliary pipe 11 and the second pipe 10 is located between the pressure reducing valve 2 and the buffer reactor 3. Some of the high-pressure tail gas enters the liquid phase material in the second pipe 10 through the auxiliary pipe 11, and the high-pressure tail gas and the liquid phase material are in full contact.

[0031] Combination Figure 2 This invention provides a method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol. This method is applicable to the aforementioned high-pressure tail gas recovery and utilization device. For the high-pressure tail gas obtained after treatment by the high-pressure separator 6, this invention introduces the high-pressure tail gas into a buffer reactor 3, and extracts a portion of the liquid phase material from the main reactor 1 into the buffer reactor 3 to react with carbon monoxide in the high-pressure tail gas to achieve the recovery and utilization of carbon monoxide. Simultaneously, iodomethane in the high-pressure tail gas is also recovered. The steps are as follows:

[0032] S1. The high-pressure tail gas discharged from the high-pressure separator 6 enters the buffer reactor 3;

[0033] S2. The high-temperature and high-pressure liquid phase material in the main reactor 1 is partially extracted into the buffer reactor 3 and reacted with the high-pressure tail gas in step (1).

[0034] S3. The liquid phase material in the buffer reactor 3 is extracted to the flash evaporator 4 for gas-liquid separation. The gas phase component in the flash evaporator 4 goes to the product distillation system, and the liquid phase component returns to the main reactor 1.

[0035] It should be noted that the order of steps S1 and S2 can be interchanged, or steps 1 and 2 can be performed simultaneously.

[0036] The high-pressure exhaust gas in step S1 originates from the gaseous material within the main reactor 1. Specifically, carbon monoxide and methanol, as raw materials, are introduced into the main reactor 1, which contains the main catalyst and a co-catalyst (iodomethane). The reaction produces acetic acid under conditions controlled at a pressure of 2.8 MPa–3.0 MPa and a temperature of 180°C–200°C. Because it is necessary to maintain the carbon monoxide within a certain partial pressure range within the main reactor 1, high-pressure gas needs to be discharged from its top. This gas is then separated by the top condenser 5 and the high-pressure separator 6. Subsequently, the gas phase in the high-pressure separator 6 is discharged as high-pressure tail gas, while the liquid phase returns to the main reactor 1. At this time, the main components of the high-pressure tail gas are 60% to 80% carbon monoxide, 3% to 6% carbon dioxide, 5% to 10% nitrogen, 2% to 5% hydrogen, 1% to 3% methane, 1% to 2% iodomethane, and 2% to 5% methanol or acetic acid. It can be seen that the high-pressure tail gas is mainly composed of carbon monoxide. For the methanol low-pressure carbonyl synthesis of acetic acid process, carbon monoxide is a raw material. Therefore, it is feasible to use the high-pressure tail gas as a raw material gas for the synthesis of acetic acid in this invention.

[0037] This invention uses the liquid phase material in the main reactor 1 as the raw material liquid. Specifically, the composition and content of the liquid phase material in the main reactor 1 in step S2 are as follows: 50%–80% acetic acid, 4%–25% iodomethane, 0.2%–15% hydroiodic acid, 2%–15% water, 0.2%–15% methyl acetate, 0.05%–0.3% main catalyst, and 0.01%–1% methanol. Methanol or methyl acetate can react with carbon monoxide to produce acetic acid, and the total content of methanol and methyl acetate in the liquid phase material is not low. Therefore, it is feasible to use the liquid phase material in the main reactor 1 to react with high-pressure tail gas to produce acetic acid and recover carbon monoxide.

[0038] It should be noted that the advantage of this invention in introducing high-pressure tail gas and part of the liquid phase material from the main reactor 1 into the buffer reactor 3 is that this invention does not introduce new materials, but uses substances already present in the original reaction system to react and recover carbon monoxide to produce the target product acetic acid. For the main reactor 1, part of the product (acetic acid) is extracted, and the reaction equilibrium of the main reaction in the main reactor 1 shifts to the positive direction, which is beneficial to improving the conversion rate in the main reactor 1. In addition, the extracted liquid phase material is mainly acetic acid, and acetic acid can be used to absorb iodomethane in the high-pressure tail gas. It can be seen that this invention solves the problem of recovering both iodomethane and carbon monoxide.

[0039] Furthermore, iodomethane is a co-catalyst in the low-pressure carbonyl synthesis of acetic acid from methanol. Iodomethane absorbed by the liquid phase material has a positive impact on the reaction between the liquid phase material and the high-pressure tail gas, which is beneficial to improving the reaction efficiency of methanol / methyl acetate and carbon monoxide.

[0040] It should be noted that this invention does not directly return the high-pressure tail gas to the main reactor 1, or use it as a substitute for carbon monoxide feed gas in the main reactor 1. This is because the high-pressure tail gas is originally discharged from the main reactor 1 to control and ensure the partial pressure of carbon monoxide within the main reactor 1. If the high-pressure tail gas were directly returned to the main reactor 1, although the carbon monoxide in the high-pressure tail gas would react with the methanol / methyl acetate in the main reactor 1 to synthesize acetic acid, the partial pressure of carbon monoxide in the main reactor 1 would be relatively high, while the carbon monoxide in the high-pressure tail gas contains... The amount of carbon monoxide in the high-pressure tail gas is not high (compared to the raw material carbon monoxide), so the carbon monoxide in the high-pressure tail gas has little effect on the main reactor 1. The partial pressure of carbon monoxide in the buffer reactor 3 is relatively low, and the material from the main reactor 1 to the flash evaporator 4 contains a certain amount of methanol / methyl acetate. Therefore, the carbon monoxide in the high-pressure tail gas will dissolve in the buffer reactor 3 and react with the methanol / methyl acetate in the liquid phase material of the buffer reactor 3 to synthesize acetic acid. This increases the acetic acid content and decreases the methanol / methyl acetate content in the material entering the flash evaporator 4, thereby increasing the acetic acid yield.

[0041] In this invention, the pressure of the extracted liquid phase material needs to be lower than the pressure of the high-pressure tail gas. If the pressure of the liquid phase material is too high, the high-pressure tail gas will not be able to enter the buffer reactor 3. The reaction of carbon monoxide with methanol / methyl acetate to synthesize acetic acid has pressure requirements. Therefore, in this invention, the pressure of the high-pressure tail gas needs to be close to the pressure inside the main reactor 1. For example, the pressure of the high-pressure tail gas discharged through the high-pressure separator 6 is 0-0.05 MPa lower than the pressure inside the main reactor 1, and the pressure of the liquid phase material extracted from the main reactor 1 is controlled to be 0.01-0.3 MPa lower than the pressure of the high-pressure tail gas after depressurization.

[0042] In this invention, over 80% of the carbon monoxide in the high-pressure tail gas undergoes a carbonyl reaction with methanol and / or methyl acetate in the liquid phase to synthesize acetic acid. In step S3, acetic acid is synthesized in the buffer reactor 3, which increases the acetic acid content in the liquid entering the flash evaporator 4. The acetic acid content in the gas phase component at the top of the flash evaporator 4 increases, while simultaneously reducing the content of methanol and / or methyl acetate in the liquid entering the flash evaporator 4. Ultimately, this reduces the consumption of carbon monoxide, methanol, and iodomethane (a co-catalyst) for the low-pressure carbonyl synthesis of acetic acid from methanol, effectively lowering production costs.

[0043] In step S3, the gaseous components in flash evaporator 4 enter the product distillation system, thereby increasing the unit yield of acetic acid, while the liquid components are returned to the main reactor 1 for reuse.

[0044] The embodiments provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention, and the descriptions of the embodiments above are only for the purpose of helping to understand the core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol, comprising a main reactor (1), a top condenser (5), and a high-pressure separator (6) connected in sequence, characterized in that, It also includes a buffer reactor (3) and a flash evaporator (4). The high-pressure separator (6) is connected to the buffer reactor (3) through a first pipe (9) to introduce high-pressure tail gas into the buffer reactor (3). The main reactor (1) is connected to the buffer reactor (3) through a second pipe (10) to extract some liquid phase material in the main reactor (1) into the buffer reactor (3). The buffer reactor (3) is connected to the flash evaporator (4).

2. The high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol as described in claim 1, characterized in that, The second pipe (10) is equipped with a pressure reducing valve (2).

3. The high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol as described in claim 2, characterized in that, The first pipe (9) and the second pipe (10) are connected by an auxiliary pipe (11), wherein the connection between the auxiliary pipe (11) and the second pipe (10) is located between the pressure reducing valve (2) and the buffer reactor (3).

4. A method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol, characterized in that, The high-pressure tail gas recovery and utilization device for the low-pressure carbonyl synthesis of acetic acid from methanol as described in claim 3 is used in the following process: Methanol and carbon monoxide are pressurized and then enter the main reactor (1) to react under the catalysis of the catalyst. Part of the high-pressure gas is discharged to the top condenser (5) and high-pressure separator (6) for treatment to obtain high-pressure tail gas. The treatment steps of the high-pressure tail gas are as follows: S1. The high-pressure tail gas discharged from the high-pressure separator (6) enters the buffer reactor (3); S2. The high-temperature and high-pressure liquid phase material in the main reactor (1) is partially extracted into the buffer reactor (3) and reacted with the high-pressure tail gas in step S1. S3. The liquid phase material in the buffer reactor (3) is extracted into the flash evaporator (4) for gas-liquid separation. The gas phase component in the flash evaporator (4) goes to the product distillation system, and the liquid phase component returns to the main reactor (1).

5. The method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol according to claim 4, characterized in that, In step S2, after the liquid phase material in the main reactor (1) is extracted, it enters the buffer reactor (3) after being depressurized.

6. The method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol according to claim 5, characterized in that, In step S2, the pressure of the liquid material extracted from the main reactor (1) is controlled to be lower than the pressure of the high-pressure tail gas after depressurization, and the pressure difference between the liquid material and the high-pressure tail gas after depressurization is 0.01 to 0.3 MPa.

7. The method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol according to claim 4, characterized in that, In step S1, the pressure of the high-pressure tail gas discharged through the high-pressure separator (6) is lower than the pressure inside the main reactor (1), and the pressure difference between the high-pressure tail gas and the pressure inside the main reactor (1) is 0-0.05 MPa.

8. The method for recovering and utilizing high-pressure tail gas from the low-pressure carbonyl synthesis of acetic acid from methanol according to claim 4, characterized in that, In step S2, the liquid phase material is extracted from the middle of the main reactor (1).

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