Method for removing nitrogen oxides in tail gas generated in preparation of oxalate through CO coupling

Abstract

The invention provides a method for removing nitric oxide in tail gas generated in preparation of oxalate through CO coupling, and relates to the technical field of nitric oxide treatment. The invention relates to a method for removing nitrogen oxides in tail gas generated in preparation of oxalate through CO coupling, which comprises the following steps: in the shutdown process of a coupling reaction system, S1, introducing the tail gas material flow generated in preparation of oxalate through CO coupling into an absorption tower A to contact with an alcohol compound, discharging the obtained effluent I from the tower top, discharging the effluent II from the tower kettle, and circulating the effluent II back to the coupling reaction system; and S2, discharging the effluent I from the tower top, introducing the effluent I and oxygen-containing gas into an absorption tower B, and carrying out absorption treatment by adopting first absorption liquid. The method has the advantages of economy, high efficiency, environmental protection and the like.

Description

Technical Field

[0001] The invention relates to the technical field of nitrogen oxide treatment, and in particular to a method for removing nitrogen oxides from tail gas produced by CO coupling to produce oxalate. Background Art

[0002] Oxalate ester is an important organic chemical raw material. The conversion of synthesis gas into ethylene glycol through oxalate ester and then hydrogenation is a new large-scale industrial ethylene glycol synthesis process route. The technology is becoming more mature, and the CO coupling reaction to produce oxalate ester is one of the key steps.

[0003] In the process of CO coupling to oxalate, since the production process involves the recycling of two nitrogen oxides, nitrite and nitric oxide, a large amount of nitrogen oxides are contained in the system. Due to the accumulation of inert components such as carbon dioxide and nitrogen in the system, a certain amount of tail gas needs to be continuously discharged in order to ensure continuous and stable operation of the device. The discharged tail gas contains a certain concentration of nitrogen oxide gas, and the nitrogen oxide components in the above-mentioned exhaust gas must be removed.

[0004] In the prior art, Chinese patent CN106139898B discloses a method for regenerating, absorbing and removing NO, alkyl nitrite, CO and N2O in the tail gas of the CO carbonyl coupling synthesis oxalate process, which is mainly aimed at the normal start-up process and the normal tail gas discharge treatment method, and adopts regeneration absorption, high temperature combustion, catalytic reduction and other methods to treat the tail gas containing NOx. However, the prior art usually only provides a tail gas treatment method for normal start-up conditions, and there is no report on the treatment of a large amount of nitrogen oxides in the system during the parking process. The conventional absorption and regeneration method is used to treat the tail gas of the parking, which will cause the NO in the tail gas to regenerate nitrite and circulate back to the system, resulting in the inability to completely replace the nitrogen oxides in the coupling circulating gas system; if the NO is not recycled and regenerated into nitrite, the tail gas will not meet the emission standards and further treatment is required, and the NOx treatment system is heavily loaded and wastes materials. Summary of the invention

[0005] In order to solve the problems of difficulty in handling nitrogen oxides and slow parking speed during the parking process in the prior art, the present invention provides a method for removing nitrogen oxides in the tail gas of CO coupling to oxalate ester, which can efficiently convert nitrogen oxides into nitric acid and store them in the form of liquid phase, thereby significantly improving the parking speed.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] A method for removing nitrogen oxides from tail gas produced by CO coupling to produce oxalate, comprising:

[0008] During the shutdown of the coupling reaction system:

[0009] S1. The tail gas stream of the CO coupling oxalate is passed into the absorption tower A, and is contacted with the alcohol compound to react, and an effluent I is obtained at the top of the tower and an effluent II is obtained in the bottom of the tower, and the effluent II is circulated back to the coupling reaction system;

[0010] S2. The effluent I from the top of absorption tower A is introduced into absorption tower B together with the oxygen-containing gas and is absorbed by the first absorption liquid.

[0011] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0012] The present invention provides a method for removing nitrogen oxides in tail gas from oxalate produced by coupling of CO. In a normal parking process, the recovery rate of nitrogen oxides is high, the replacement speed of nitrogen oxides in the coupling reaction circulating gas system is fast, and the nitrogen oxides can be recovered in the form of liquid nitric acid, which is convenient for storage and reduces material loss; the nitrogen oxides can also be circulated back to the system during the next start-up process, and nitrites can be generated again by reduction with nitric acid; in summary, the method has the advantages of being economical, efficient, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 It is a schematic diagram of the process of normal driving in the present invention;

[0015] Figure 2 It is a schematic diagram of the flow of the normal parking process in the present invention.

[0016] Icons: 1- tail gas logistics inlet, 2- first air inlet, 3- second air inlet, 4- first liquid discharge port, 5- first exhaust port, 6- first liquid inlet, 7- second liquid discharge port, 8- second exhaust port, 9- second liquid inlet, 10- third liquid inlet, 100- absorption tower A, 200- absorption tower B. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0018] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0019] A method for removing nitrogen oxides from tail gas produced by CO coupling to produce oxalate, comprising:

[0020] During the shutdown of the coupling reaction system:

[0021] S1. The tail gas stream of the CO coupling oxalate is passed into the absorption tower A, and is contacted with the alcohol compound to react, and an effluent I is obtained at the top of the tower and an effluent II is obtained in the bottom of the tower, and the effluent II is circulated back to the coupling reaction system;

[0022] S2. The effluent I from the top of absorption tower A is introduced into absorption tower B together with the oxygen-containing gas and is absorbed by the first absorption liquid.

[0023] In some preferred embodiments of the present invention, the above method further comprises:

[0024] During the normal start-up of the coupling reaction system:

[0025] S3. The CO coupling oxalate tail gas stream and the oxygen-containing gas are introduced into the absorption tower A, contacted with the alcohol compound to react, and an effluent I is obtained at the top of the tower and an effluent II is obtained in the bottom of the tower, and the effluent II is circulated back to the coupling reaction system;

[0026] S4. The effluent I from the top of absorption tower A is introduced into absorption tower B and is absorbed by the first absorption liquid.

[0027] In some preferred embodiments of the present invention, the alcohol compound is a C1-C4 alkyl alcohol.

[0028] In some preferred embodiments of the present invention, the alcohol compound is methanol or ethanol.

[0029] In some preferred embodiments of the present invention, the alcohol compound is methanol.

[0030] In some preferred embodiments of the present invention, the temperature of the alcohol compound is 20-60°C.

[0031] In some preferred embodiments of the present invention, the temperature of the alcohol compound is 10-40°C.

[0032] In some preferred embodiments of the present invention, the oxygen-containing gas comprises air and oxygen.

[0033] It should be noted here that both air and oxygen can oxidize NO. The amount of oxygen required for exhaust gas is usually small, and the safety risk of using air is lower, so air is preferred.

[0034] It should be noted here that the coupling reaction system refers to the process of CO coupling to produce oxalate, which includes an oxidative esterification reactor, a CO coupling to produce oxalate reactor, and a reactor for reducing by-product nitric acid to nitrite. The effluent II can be returned to the oxidative esterification reactor, and the alcohol compounds in the effluent II are used as raw materials for the oxidative esterification reaction, while the nitrite components therein are recovered as raw materials for the CO coupling to produce oxalate reaction. When the coupling reactor system is used to generate dimethyl oxalate, the corresponding nitrite in the tail gas is methyl nitrite, the alcohol compound is methanol, and the alcohol compound in step S1 is also methanol. During normal start-up, the nitrite generated in step S1 is methyl nitrite.

[0035] In some preferred embodiments of the present invention, the oxalate is dimethyl oxalate or diethyl oxalate.

[0036] In some preferred embodiments of the present invention, the oxalate is dimethyl oxalate.

[0037] In some preferred embodiments of the present invention, the first absorption liquid is water.

[0038] In some preferred embodiments of the present invention, the temperature of the first absorption liquid is 10-60°C.

[0039] In some preferred embodiments of the present invention, the temperature of the first absorption liquid is 20-40°C.

[0040] In some preferred embodiments of the present invention, the tail gas stream includes nitrite and NO, the content of the nitrite is 1-25% mol, and the content of NO is 1-25% mol. It should be noted that nitrite includes methyl nitrite and ethyl nitrite; methyl nitrite is paired with methanol, and ethyl nitrite is paired with ethanol; when the component in the tail gas is methyl nitrite, methanol is used as the absorption liquid, and methyl nitrite is also generated by the reaction in the tower; when the component in the tail gas is ethyl nitrite, the absorption liquid is ethanol, and ethyl nitrite is also generated by the reaction in the tower.

[0041] It should be noted here that other major gas components in the exhaust gas include CO2, CO, nitrogen, alcohol compounds, etc.

[0042] In some preferred embodiments of the present invention, the content of the nitrite is 5-15 mol%, and the content of NO is 5-15 mol%.

[0043] In some preferred embodiments of the present invention, the molar ratio of the alcohol compound to the nitrite is (20-200):1.

[0044] In some preferred embodiments of the present invention, the molar ratio of the alcohol compound to the nitrite is (40-100):1.

[0045] In some preferred embodiments of the present invention, during the shutdown process of the coupling reaction system: in step S2, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.5-2.0):1.

[0046] In some preferred embodiments of the present invention, during the shutdown process of the coupling reaction system: in step S2, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.8-1.5):1.

[0047] In some preferred embodiments of the present invention, during the shutdown of the coupling reaction system: in step S2, before the effluent I obtained in step S1 is introduced into the absorption tower B, it is also washed with water.

[0048] In some preferred embodiments of the present invention, during the water washing process, the mass ratio of the water to the tail gas flow is (0.01-0.2):1.

[0049] In some preferred embodiments of the present invention, during the water washing process, the mass ratio of the water to the tail gas flow is (0.02-0.1):1.

[0050] In some preferred embodiments of the present invention, after the water washing, the content of alcohol compounds in the effluent I is less than 0.5 mol%.

[0051] In some preferred embodiments of the present invention, after the water washing, the content of alcohol compounds in the effluent I is less than 0.1 mol%.

[0052] In some preferred embodiments of the present invention, during the shutdown of the coupling reaction system: the weight ratio of the first absorption liquid to the tail gas flow is (0.1-2):1.

[0053] In some preferred embodiments of the present invention, during the shutdown of the coupling reaction system: the weight ratio of the first absorption liquid to the tail gas flow is (0.2-1):1.

[0054] In some preferred embodiments of the present invention, during the shutdown of the coupling reaction system: the operating pressures of the absorption tower A and the absorption tower B are both 0-2.0 MPaG.

[0055] In some preferred embodiments of the present invention, during the shutdown of the coupling reaction system: the operating pressures of the absorption tower A and the absorption tower B are both 0.2-0.5 MPaG.

[0056] In some preferred embodiments of the present invention, during the start-up of the coupling reaction system: in step S3, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.25-1.0):1.

[0057] In some preferred embodiments of the present invention, during the start-up of the coupling reaction system: in step S3, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.4-0.8):1.

[0058] In some preferred embodiments of the present invention, during the start-up of the coupling reaction system: the weight ratio of the first absorption liquid to the tail gas flow is (0.01-0.2):1, preferably (0.02-0.1):1.

[0059] In some preferred embodiments of the present invention, during the start-up of the coupling reaction system: the operating pressures of the absorption tower A and the absorption tower B are both 0-2.0 MPaG.

[0060] In some preferred embodiments of the present invention, during the start-up of the coupling reaction system: the operating pressures of the absorption tower A and the absorption tower B are both 0.2-0.5 MPaG.

[0061] (I) During normal operation, the working principle of the method for removing nitrogen oxides from the tail gas of CO coupling to oxalate ester is:

[0062] Air or oxygen is introduced at the first air inlet 2, and nitrogen oxide tail gas flow is introduced at the tail gas flow inlet 1, so that the air and nitrogen oxide tail gas flow are mixed to form a mixed gas and introduced into the absorption tower A100; the alcohol compound is added to the absorption tower A100 from the first liquid inlet 6 (the alcohol compound here is used as both a reaction medium and an absorption liquid to absorb nitrite; the nitrite is discharged from the absorption tower A100 from the first liquid discharge port 4 after absorption), and reacts with the aforementioned mixed gas to obtain an effluent I, and the effluent I flows into the absorption tower B200 from the pipeline where the first exhaust port 5 is located. Among them, the nitrite in the effluent I is circulated back to the coupling reaction system (not shown in the figure) after being absorbed by the alcohol compound; the first absorption liquid is added to the absorption tower B200 from the second liquid inlet 9 to absorb the alcohol compound in the effluent I; the final tail gas is discharged from the system from the second exhaust port 8, and the first absorption liquid that has absorbed the alcohol compound is discharged from the absorption tower B200 from the second liquid discharge port 7.

[0063] (II) During normal parking, the working principle of the method for removing nitrogen oxides from the tail gas of CO coupling to oxalate ester is as follows:

[0064] A nitrogen oxide tail gas flow is introduced at the tail gas flow inlet 1; an alcohol compound is added to the absorption tower A100 from the first liquid inlet 6 (the alcohol compound here is used as an absorption liquid to absorb nitrite) to obtain an effluent I; water is added to the absorption tower A100 through the third liquid inlet 10, and the effluent I is washed with water. After washing, the effluent I flows into the absorption tower B200 through the pipeline where the first exhaust port 5 is located, wherein the nitrite is absorbed by the alcohol compound and then circulated back to the coupling reaction system; at the same time, air or oxygen is introduced at the second air inlet 3; the first absorption liquid is added to the absorption tower B200 from the second liquid inlet 9 to absorb the nitric acid therein; the absorbed nitric acid is discharged from the absorption tower B200 from the second liquid discharge port 7; and the final tail gas is discharged from the system from the second exhaust port 8.

[0065] Example 1

[0066] Please refer to Figure 1 and Figure 2 The content of methyl nitrite in the nitrogen oxide tail gas is 20% mol, the content of NO is 8% mol, the content of CO is 25% mol, the content of CO2 is 8% mol, the content of N2 is 36% mol, and the remaining components are a small amount of methanol, methyl formate, etc.; the operating pressures of absorption tower A and absorption tower B are 0.25MPaG and 0.23MPaG respectively.

[0067] (I) During normal operation, the method for removing nitrogen oxides from the tail gas of CO coupling to oxalate comprises the following steps:

[0068] Air is introduced at the first air inlet 2, and nitrogen oxide tail gas flow is introduced at the tail gas flow inlet 1, so that the air and the nitrogen oxide tail gas flow are mixed to form a mixed gas and introduced into the absorption tower A100; the molar ratio of O2 in the air to NO in the tail gas is 0.75:1; 10°C methanol is added to the absorption tower A100 from the first liquid inlet 6 (the methanol here serves as both a reaction medium and an absorption liquid to absorb methyl nitrite; after absorption, methyl nitrite is discharged from the absorption tower from the first liquid discharge port 4 A100), and react with the aforementioned mixed gas to obtain an effluent I, which flows into the absorption tower B200 from the second air inlet 3 through the first exhaust port 5 (wherein methyl nitrite is absorbed by methanol and then recycled to the coupling reaction system; the molar ratio of methanol to methyl nitrite in the tail gas is 80:1); 40°C water (first absorption liquid) is added to the absorption tower B200 from the second liquid inlet 9 to absorb the methanol in the effluent I; the weight ratio of water to tail gas flow is 0.14:1.

[0069] (ii) During normal parking, the method for removing nitrogen oxides from the tail gas of CO coupling to oxalate comprises the following steps:

[0070] A nitrogen oxide tail gas stream is introduced at the tail gas stream inlet 1; methanol at 10°C is added to the absorption tower A100 from the first liquid inlet 6 (the methanol here is used as an absorption liquid to absorb methyl nitrite) to obtain an effluent I; water at 40°C is added to the absorption tower A100 through the third liquid inlet 10, and the effluent I is washed with water (the methanol content in the effluent I after washing is 20 ppm (mol)); the effluent I is washed with water and flows into the absorption tower B200 through the first exhaust port 5 (wherein, methyl nitrite is washed with water) After methanol absorption, it is circulated back to the coupling reaction system; the molar ratio of methanol to methyl nitrite in the tail gas is 80:1); air is introduced at the second air inlet 3, and the molar ratio of O2 in the air to NO in the tail gas flow is 1:1; 40°C water (first absorption liquid) is added to the absorption tower B200 from the second liquid inlet 9 to react and absorb the nitric acid therein (the absorbed nitric acid is discharged from the absorption tower B200 from the second liquid discharge port 7); the weight ratio of water to tail gas flow is 0.35:1. The final exhaust gas contains NO + The content of methyl nitrite was 20 ppm (mol), and the content of methanol was 5 ppm.

[0071] In this embodiment, during normal driving, the content of NO+methyl nitrite in the exhaust gas finally discharged is 25ppm (mol), and the content of methanol is 12ppm (mol); during normal parking, the content of NO in the exhaust gas finally discharged is 25ppm (mol). + The content of methyl nitrite was 20 ppm (mol), and the content of methanol was 2 ppm; the conversion rate of NO in the tail gas to HNO3 reached 99.98%, indicating that the parking process can well convert nitric acid into nitric acid for storage.

[0072] Example 2

[0073] Please refer to Figure 1 and Figure 2 This embodiment is basically the same as Embodiment 1, except that:

[0074] The content of methyl nitrite is 5% mol, the content of NO is 15% mol, the content of CO is 25% mol, the content of CO2 is 8% mol, the content of N2 is 44% mol, and the remaining components are a small amount of methanol, methyl formate, etc.; the operating pressures of absorption tower A and absorption tower B are 0.5 MPaG and 0.48 MPaG respectively.

[0075] (I) During normal driving

[0076] The molar ratio of O2 in the air to NO in the exhaust gas in absorption tower A is 0.3:1; the temperature of methanol is 40°C, and the molar ratio of methanol to methyl nitrite in the exhaust gas is 200:1; the temperature of water (first absorption liquid) in absorption tower B is 40°C; the weight ratio of water to exhaust gas flow is 0.03:1.

[0077] (II) During normal parking

[0078] The temperature of methanol in absorption tower A is 20°C, and the temperature of water (first absorption liquid) is 40°C; the molar ratio of methanol to methyl nitrite in tail gas is 200:1; the methanol content in effluent I after water washing is 100 ppm (mol); the molar ratio of O2 in the air to NO in tail gas in absorption tower B is 1.5:1; the weight ratio of water to tail gas flow is 1:1.

[0079] In this embodiment, during normal driving, the content of NO+methyl nitrite in the final exhaust gas is 30ppm (mol), and the content of methanol is 100ppm (mol); during normal parking, the content of NO+methyl nitrite in the final exhaust gas is 20ppm (mol), and the content of methanol is 1ppm (mol); the conversion rate of NO in the exhaust gas to HNO3 reaches 99.99%, and the parking process can well convert nitric acid into nitric acid for storage.

[0080] Example 3

[0081] Please refer to Figure 1 and Figure 2 This embodiment is basically the same as Embodiment 1, except that:

[0082] The content of methyl nitrite is 10% mol, the content of NO is 10% mol, the content of CO is 25% mol, the content of CO2 is 8% mol, the content of N2 is 44% mol, and the remaining components are a small amount of methanol, methyl formate, etc.; the operating pressures of absorption tower A and absorption tower B are 0.5 MPaG and 0.48 MPaG respectively.

[0083] (I) During normal driving

[0084] The molar ratio of O2 in the air to NO in the tail gas in absorption tower A is 0.5:1; the temperature of methanol is 10°C, and the molar ratio of methanol to methyl nitrite in the tail gas is 50:1; the temperature of water (first absorption liquid) in absorption tower B is 40°C; the weight ratio of water to tail gas flow is 0.05:1.

[0085] (II) During normal parking

[0086] The temperature of methanol in absorption tower A is 10°C, and the temperature of water (first absorption liquid) is 40°C; the molar ratio of methanol to methyl nitrite in tail gas is 200:1; the methanol content in effluent I after water washing is 50 ppm (mol); the molar ratio of O2 in the air to NO in tail gas in absorption tower B is 0.8:1; the weight ratio of water to tail gas flow is 1:1.

[0087] In this embodiment, during normal driving, the content of NO+methyl nitrite in the exhaust gas is 100ppm (mol), and the content of methanol is 50ppm (mol); during normal parking, the content of NO+methyl nitrite in the exhaust gas is 75ppm (mol), and the content of methanol is 1ppm; the conversion rate of NO in the exhaust gas to HNO3 reaches 99.9%, and the nitric acid can be well converted into nitric acid for storage during the parking process.

[0088] Example 4

[0089] Please refer to Figure 1 and Figure 2 This embodiment is basically the same as Embodiment 1, except that:

[0090] The content of methyl nitrite is 5% mol, the content of NO is 15% mol, the content of CO is 25% mol, the content of CO2 is 8% mol, the content of N2 is 44% mol, and the remaining components are a small amount of methanol, methyl formate, etc.; the operating pressures of absorption tower A and absorption tower B are 0.5 MPaG and 0.48 MPaG respectively.

[0091] (I) During normal driving

[0092] The molar ratio of O2 in the air to NO in the exhaust gas in absorption tower A is 0.8:1; the temperature of methanol is 20°C, and the molar ratio of methanol to methyl nitrite in the exhaust gas is 100:1; the temperature of water (first absorption liquid) in absorption tower B is 40°C; the weight ratio of water to exhaust gas flow is 0.1:1.

[0093] (II) During normal parking

[0094] The temperature of methanol in absorption tower A is 20°C, and the temperature of water (first absorption liquid) is 40°C; the molar ratio of methanol to methyl nitrite in tail gas is 100:1; the methanol content in effluent I after water washing is 30 ppm (mol); the molar ratio of O2 in the air to NO in tail gas in absorption tower B is 1:1; the weight ratio of water to tail gas flow is 2:1.

[0095] In this embodiment, during normal driving, the content of NO + methyl nitrite in the exhaust gas is 35ppm (mol), and the content of methanol is 30ppm (mol); during normal parking, the content of NO + methyl nitrite in the exhaust gas is 35ppm (mol), and the content of methanol is 1ppm; the conversion rate of NO in the exhaust gas to HNO3 reaches 99.99%, and the nitric acid can be well converted into nitric acid for storage during the parking process.

[0096] Comparative Example 1

[0097] This comparative example is basically the same as Example 1, except that: absorption tower B is not used to further absorb nitrogen oxide tail gas, and absorption tower A only has methanol absorption liquid; air is introduced into absorption tower A during normal start-up and normal shutdown.

[0098] During normal parking, the exhaust gas passes through absorption tower A, and most of the NO in the exhaust gas is converted into methyl nitrite and recycled back to the system.

[0099] In this comparative example, during normal operation, the methanol content in the exhaust gas discharged after treatment by the absorption tower A is as high as 2.1% mol, and methanol is seriously wasted; during normal parking, the conversion rate of NO into nitric acid is only 5%, and the rest is converted into methyl nitrite.

[0100] Comparative Example 2

[0101] This comparative example is basically the same as Example 1, except that during the shutdown process, only methanol absorption liquid is contained in absorption tower A, and the absorption liquid without being washed directly enters absorption tower B.

[0102] In this comparative example, the methanol content in the effluent I is 2.1% (mol). Due to the presence of methanol, part of the NO in the absorption B is converted into methyl nitrite. The conversion rate of NO to nitric acid in the shutdown process system is reduced to 85%, and the rest is converted into methyl nitrite.

[0103] Comparative Example 3

[0104] This comparative example is basically the same as Example 1, except that:

[0105] 1. During normal operation, the weight ratio of water (first absorption liquid) to tail gas flow in absorption tower B is 0.01:1.

[0106] 2. During normal parking, the weight ratio of water (first absorption liquid) to tail gas flow in absorption tower B is 0.1:1.

[0107] In this comparative example, during normal driving, the methanol content in the exhaust gas is as high as 0.5%; during normal parking, the content of NO+methyl nitrite in the exhaust gas is 300 ppm (mol), the conversion rate of NO into nitric acid is reduced to 90%, and the rest is converted into methyl nitrite.

[0108] In summary, by adopting the method for removing nitrogen oxides in tail gas produced by CO coupling to oxalate provided by the present invention, NO in the tail gas can be converted into methyl nitrite for recovery during normal operation; during parking, NO in the tail gas can be converted into nitric acid for storage. The NOx treatment speed in the system during the parking process is fast, and the recovered nitric acid can be used for the next operation.

[0109] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for removing nitrogen oxides from tail gas from CO coupling to oxalate esters, characterized in that: include: During the shutdown of the coupling reaction system: S1. The tail gas stream of the CO coupling oxalate is passed into the absorption tower A, and is contacted with the alcohol compound to react, and an effluent I is obtained at the top of the tower and an effluent II is obtained in the bottom of the tower, and the effluent II is circulated back to the coupling reaction system; S2. The effluent I from the top of absorption tower A is introduced into absorption tower B together with the oxygen-containing gas and is absorbed by the first absorption liquid.

2. The method according to claim 1, characterized in that Also includes: During the normal start-up of the coupling reaction system: S3. The CO coupling oxalate tail gas stream and the oxygen-containing gas are introduced into the absorption tower A, contacted with the alcohol compound to react, and an effluent I is obtained at the top of the tower and an effluent II is obtained in the bottom of the tower, and the effluent II is circulated back to the coupling reaction system; S4. The effluent I from the top of absorption tower A is introduced into absorption tower B and is absorbed by the first absorption liquid.

3. The method according to claim 1 or 2, characterized in that: The alcohol compound is a C1-C4 alkyl alcohol; preferably, the alcohol compound is methanol or ethanol, and most preferably methanol; and / or, the temperature of the alcohol compound is -20 to 60°C, preferably 10 to 40°C; And / or, the oxygen-containing gas includes air and oxygen.

4. The method according to any one of claims 1 to 3, characterized in that The oxalate is dimethyl oxalate or diethyl oxalate, preferably dimethyl oxalate; and / or, the first absorption liquid is water; And / or, the temperature of the first absorption liquid is 10-60°C, preferably 20-40°C.

5. The method according to any one of claims 1 to 4, characterized in that The tail gas stream includes nitrite and NO, wherein the content of nitrite is 1-25 mol%, preferably 5-15 mol%; the content of NO is 1-25 mol%, preferably 5-15 mol%.

6. The method according to claim 5, characterized in that The molar ratio of the alcohol compound to the nitrite is (20-200):1, preferably (40-100):

1.

7. The method according to any one of claims 1 to 6, characterized in that During the shutdown of the coupling reaction system: In step S2, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.5-2.0):1, preferably (0.8-1.5):

1.

8. The method according to any one of claims 1 to 7, characterized in that During the shutdown of the coupling reaction system: In step S2, the effluent I obtained in step S1 is further washed with water before being introduced into the absorption tower B; Preferably, during the water washing process, the mass ratio of the water to the tail gas stream is (0.01-0.2):1, and most preferably (0.02-0.1):1; And / or, after the water washing, the content of alcohol compounds in the effluent I is less than 0.5% mol; preferably, after the water washing, the content of alcohol compounds in the effluent I is less than 0.1% mol.

9. The method according to any one of claims 1 to 8, characterized in that: During the shutdown of the coupling reaction system: The weight ratio of the first absorption liquid to the tail gas stream is (0.1-2):1, preferably (0.2-1):1; And / or, the operating pressures of the absorption tower A and the absorption tower B are the same or different, and are independently selected from 0 to 2.0 MPaG; preferably selected from 0.2 to 0.5 MPaG.

10. The method according to any one of claims 2 to 9, characterized in that: During the normal start-up of the coupling reaction system: In step S3, the molar ratio of O2 in the oxygen-containing gas to the NO is (0.25-1.0):1, preferably (0.4-0.8):1; and / or, the weight ratio of the first absorption liquid to the tail gas stream is (0.01-0.2):1, preferably (0.02-0.1):1; And / or, the operating pressures of the absorption tower A and the absorption tower B are the same or different, and are independently selected from 0 to 2.0 MPaG; preferably selected from 0.2 to 0.5 MPaG.

Images