Gas recovery device and recovery method

Abstract

The present application relates to a kind of gas recovery device and recovery method.The gas recovery device includes absorption tower, solvent recovery tower and desorption tower;Wherein, the top gas phase outlet of the absorption tower is connected with the bottom material inlet of solvent recovery tower by pipeline, the kettle liquid outlet of the absorption tower is connected with the material inlet of desorption tower by pipeline, the kettle liquid outlet of the desorption tower is connected with the top material inlet of absorption tower by pipeline;The kettle liquid outlet of the desorption tower 3 is connected with the top material inlet of absorption tower on the connecting pipeline, and cooling unit is arranged;Tower top condenser is arranged in the tower top of the desorption tower, and tower kettle reboiler is arranged in the tower kettle of the desorption tower.By the tail gas recovery device and recovery method of the present application, chloromethane can be effectively recovered, VOC value in exhaust gas is reduced, and VOC emission standard is reached.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation technology, and relates to a gas recovery device and recovery method, particularly to a device and recovery method for recovering chloromethane tail gas in the production process of glyphosate. Background Technology

[0002] Glyphosate is a systemic, highly effective, low-toxicity, broad-spectrum, non-selective herbicide, holding a 30% market share and being the most commonly used herbicide on the market. Currently, glyphosate is mainly produced in China via the glycine route and the iminodiacetic acid route. Both of these routes inevitably produce chloromethane during the production of glycine.

[0003] Traditional chloromethane recovery typically involves cryogenic liquefaction. However, with increasingly stringent environmental regulations, even with cryogenic temperatures as low as -50°C, the VOC concentration in the exhaust gas still falls short of environmental standards, necessitating biochemical or combustion treatment. Furthermore, chloromethane is difficult to biochemically process, making its treatment extremely costly; while combustion of the waste gas generates HCl that severely corrodes equipment, impacting safe operation. Summary of the Invention

[0004] To address the aforementioned problems, the present invention provides a gas recovery device, comprising an absorption tower 1, a solvent recovery tower 2, and a desorption tower 3;

[0005] The top gas phase outlet of the absorption tower 1 is connected to the bottom material inlet of the solvent recovery tower 2 via a pipeline, the bottom liquid outlet of the absorption tower 1 is connected to the material inlet of the desorption tower 3 via a pipeline, and the bottom liquid outlet of the desorption tower 3 is connected to the top material inlet of the absorption tower 1 via a pipeline.

[0006] A cooling unit is installed on the connecting pipe between the bottom liquid outlet of the desorption tower 3 and the top material inlet of the absorption tower 1.

[0007] Between the outlet of the desorption tower 3 and the top material inlet of the absorption tower 1, a desorption tower feed heat exchanger 9 is also provided. The feed heat exchanger 9 is located between the outlet of the desorption tower 3 and the cooling unit.

[0008] The desorption tower 3 is equipped with a top condenser and a bottom reboiler.

[0009] According to an embodiment of the present invention, the gas recovery device is selected from a tail gas recovery device, preferably a device for recovering tail gas generated during glyphosate synthesis.

[0010] According to an embodiment of the present invention, the material inlet of the desorption tower 3 is located at the top or middle of the desorption tower 3.

[0011] According to an embodiment of the present invention, the absorption tower 1, the solvent recovery tower 2, and the desorption tower 3 are independently selected from atmospheric pressure towers or pressurized towers. Exemplarily, at least one of the absorption tower 1, the solvent recovery tower 2, or the desorption tower 3 is a pressurized tower.

[0012] According to an embodiment of the present invention, the absorption tower 1, the solvent recovery tower 2, and the desorption tower 3 are independently selected from plate towers or packed towers.

[0013] According to an embodiment of the present invention, the reboiler is selected from any one of a thermosiphon reboiler, a forced circulation reboiler, a kettle reboiler, or a falling film reboiler.

[0014] According to an embodiment of the present invention, the tower top condenser is selected from any one of a shell-and-tube heat exchanger, a plate heat exchanger, or an air cooler.

[0015] According to an embodiment of the present invention, the cooling unit may be selected from the absorbent cooling unit, which includes at least one of the absorbent cooler 6, the absorbent cryogenic cooler 7, or the absorbent cryogenic cooler 8.

[0016] According to a preferred embodiment of the present invention, the absorbent cooling unit includes an absorbent cooler 6, an absorbent cryogenic cooler 7, and an absorbent deep cooler 8.

[0017] According to an embodiment of the present invention, the cooling medium of the absorbent cooler 6 is selected from water (such as circulating water or room temperature water) or air (such as room temperature air), and exemplaryly, the temperature of the cooling medium is 32 to 38°C.

[0018] According to an embodiment of the present invention, the cooling medium of the absorbent cryogenic cooler 7 is selected from cryogenic media, such as cryogenic water. Exemplarily, the temperature of the cryogenic medium is 7 to 12°C.

[0019] According to an embodiment of the present invention, the cooling medium of the absorbent cryostat 8 is a cryogenic medium, such as a cryogenic medium aqueous solution of ethylene glycol. Exemplarily, the temperature of the cryogenic medium is -15 to -10°C.

[0020] According to an embodiment of the present invention, the absorbent cooling unit may also be connected to a first absorbent replenishment device for replenishing the first absorbent.

[0021] According to an embodiment of the present invention, the absorption tower 1 contains a first absorbent.

[0022] According to an embodiment of the present invention, the solvent recovery tower 2 contains a second absorbent.

[0023] According to an embodiment of the present invention, the gas recovery device further includes a second absorbent recovery system. Preferably, the second absorbent recovery system is connected to the solvent recovery tower 2 via a pipeline.

[0024] According to an embodiment of the present invention, the first absorbent and the second absorbent are different. Preferably, the first absorbent is an organic compound; the second absorbent is an inorganic compound.

[0025] According to an embodiment of the present invention, the first absorbent is selected from one or a mixture of two or more of chloroform, diethyl ether, methanol, methyl acetal, and acetone.

[0026] According to an embodiment of the present invention, the second absorbent is selected from one or a mixture of two or more of water, alkali metal hydroxides, and ammonia. For example, the second absorbent is selected from one or a mixture of two or more of aqueous solutions of alkali metal hydroxides and aqueous solutions of ammonia.

[0027] Preferably, when the second absorbent is selected from alkali metal hydroxides or aqueous solutions of ammonia, its mass concentration is 1% to 30%, preferably 1%, 2%, 3%, 4%, 5%, 1%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, or a range between any two of the above values.

[0028] The present invention also provides the application of the above-mentioned gas recovery device in gas recovery, such as exhaust gas recovery.

[0029] According to an embodiment of the present invention, the gas or exhaust gas contains substances that are difficult to biochemically treat, such as chloromethane.

[0030] The present invention also provides a gas recovery method, comprising using the above-described gas recovery device to process a gas containing chloromethane.

[0031] According to an exemplary embodiment of the present invention, the recycling method includes the following steps:

[0032] (1) The gas to be treated containing chloromethane and the first absorbent are brought into countercurrent contact in the absorption tower 1. The gas containing chloromethane and the first absorbent is drawn out from the top of the absorption tower 1; the first absorbent rich in chloromethane is drawn out from the bottom of the absorption tower 1.

[0033] (2) The first absorbent rich in chloromethane obtained in step (1) enters the desorption tower 3, and chloromethane is obtained at the top of the desorption tower 3. The chloromethane is condensed by the top condenser of the desorption tower 3 to obtain chloromethane liquid or gas. The first absorbent is obtained at the bottom of the desorption tower 3 and is recycled as the first absorbent of the absorption tower 1 after cooling.

[0034] (3) The gas containing chloromethane and the first absorbent obtained in step (1) enters from the bottom of the solvent recovery tower 2 and comes into countercurrent contact with the second absorbent inside the solvent recovery tower 2. The second absorbent is discharged from the bottom of the solvent recovery tower 2, and the exhaust gas that meets the emission standards is discharged from the top of the solvent recovery tower 2.

[0035] According to an exemplary embodiment of the present invention, the recycling method includes the following steps:

[0036] (1) The gas to be treated containing chloromethane enters from the bottom of the absorption tower 1, and the first absorbent enters from the top of the absorption tower 1, so that they come into countercurrent contact with each other in the absorption tower 1 to realize the absorption of chloromethane by the first absorbent; the tail gas containing chloromethane and the first absorbent is taken out from the top of the absorption tower 1, and the chloromethane-rich first absorbent is taken out from the bottom of the absorption tower 1.

[0037] (2) The first absorbent rich in chloromethane obtained in step (1) and the first absorbent obtained in the bottom of the desorption tower 3 exchange heat in the feed heat exchanger 9 of the desorption tower and then enter the desorption tower 3. Chloromethane is obtained at the top of the desorption tower 3. The chloromethane is condensed by the top condenser of the desorption tower 3 to obtain chloromethane. The first absorbent obtained in the bottom of the desorption tower 3 is cooled and recycled as the first absorbent of the absorption tower 1.

[0038] (3) The tail gas containing chloromethane and the first absorbent obtained in step (1) enters from the bottom of the solvent recovery tower 2 and comes into countercurrent contact with the second absorbent inside the solvent recovery tower 2. The second absorbent is then used to absorb the chloromethane and the first absorbent in the tail gas. The second absorbent is discharged from the bottom of the solvent recovery tower 2 and the tail gas that meets the emission standards is discharged from the top of the solvent recovery tower 2.

[0039] According to an embodiment of the present invention, the second absorbent discharged from the bottom of the solvent recovery tower 2 enters the second absorbent recovery system and is recycled after treatment.

[0040] According to an embodiment of the present invention, the gas to be treated is selected from gases containing chloromethane, such as tail gas containing chloromethane, preferably tail gas containing chloromethane generated in glyphosate synthesis.

[0041] According to an embodiment of the present invention, the gas containing chloromethane may be selected from gases produced during compound synthesis, such as chloromethane-containing gases produced during glyphosate synthesis.

[0042] According to an embodiment of the present invention, in step (1), the feed mass ratio of the first absorbent to the gas to be treated is 0.2 to 50:1, for example, 0.2:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1:1, 30:1, 35:1, 40:1, 45:1, 50:1, or a range between any two of the above values. Preferably, the feed mass ratio of the first absorbent to the gas to be treated is 0.2 to 10:1; more preferably, the feed mass ratio of the first absorbent to the gas to be treated is 0.2 to 5:1.

[0043] According to an embodiment of the present invention, in step (1), the feed temperature of the gas to be treated is -25 to 50°C, preferably -10°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or a range between any two of the above values.

[0044] According to an embodiment of the present invention, in step (1), the feed temperature of the first absorbent is -25 to 50°C, preferably -10°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or a range between any two of the above values.

[0045] According to an embodiment of the present invention, in step (1), the operating pressure at the top of the absorption tower 1 is 0.01 to 2 MPa, preferably 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.11 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.5 MPa, or 2 MPa, or a range between any two of the above values. Preferably, the operating pressure at the top of the absorption tower 1 is 0.01 to 1.0 MPa.

[0046] According to an embodiment of the present invention, the operating temperature at the top of the absorption tower 1 is -25 to 50°C, preferably -10 to 30°C, for example -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or a range between any two of the above values.

[0047] Preferably, the operating temperature at the top of the absorption tower 1 is 0–50°C.

[0048] According to an exemplary embodiment of the present invention, the operating temperature at the top of the absorption tower 1 is 10°C, the feed temperature of the first absorbent is 10°C, and the feed temperature of the chloromethane-containing tail gas is 20°C.

[0049] According to an embodiment of the present invention, in step (2), the operating pressure at the top of the desorption tower 3 is 0.01 to 2 MPa, preferably 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.11 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.5 MPa, 2 MPa, or a range between any two of the above values.

[0050] According to an embodiment of the present invention, in step (2), the operating temperature of the top of the desorption tower 3 is -25 to 50°C, preferably -10°C, 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, or a range between any two of the above values.

[0051] According to an embodiment of the present invention, in step (2), at least a portion of the obtained chloromethane liquid can be refluxed back to the desorption tower 3. Preferably, the reflux ratio is 0.5 to 20. The reflux ratio mentioned in this invention refers to the ratio of the chloromethane liquid reflux rate to the produced rate.

[0052] According to an embodiment of the present invention, in step (2), additional first absorbent may be added and used as the first absorbent of absorption tower 1; for example, before or after the first absorbent is cooled, the additional first absorbent is mixed with it and used as the first absorbent of absorption tower 1.

[0053] According to the embodiments of the present invention, the cooling method of the absorbent cooling unit is not specifically limited, as long as it can meet the feeding temperature requirements of the first absorbent as described above.

[0054] According to an embodiment of the present invention, in step (3), the feed mass ratio of the second absorbent to the gas to be treated is 0.2 to 50:1, for example, 0.2:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, or a range between any two of the above values. Preferably, the feed mass ratio of the second absorbent to the gas to be treated is 0.2 to 10:1; more preferably, the feed mass ratio of the second absorbent to the gas to be treated is 0.2 to 5:1.

[0055] According to an embodiment of the present invention, in step (3), the operating pressure at the top of the solvent recovery tower 2 is 0.1 to 2 MPa, preferably 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.5 MPa, 2 MPa, or a range between any two of the above values.

[0056] According to an embodiment of the present invention, in step (3), the operating temperature of the top of the solvent recovery tower 2 is -25 to 50°C, preferably -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or a range between any two of the above values.

[0057] According to an embodiment of the present invention, the content of chloromethane in the exhaust gas discharged from the top of the tower in step (3) is less than 20 mg / Nm³. 3 Preferably, the content of both chloromethane and the first absorbent is less than 20 mg / Nm³. 3 More preferably, the total content of the chloromethane and the first absorbent is less than 10 mg / Nm³. 3 .

[0058] According to an exemplary embodiment of the present invention, the operating pressure at the top of the absorption tower 1 is greater than the operating pressure of the solvent recovery tower 2. For example, the operating pressure at the top of the absorption tower 1 is greater than 0.5 MPa, preferably greater than 0.6 MPa; the operating pressure of the solvent recovery tower 2 is slightly less than the operating pressure of the absorption tower 1, so as to ensure that the gas phase at the top of the absorption tower 1 can enter the solvent recovery tower 2. Exemplarily, the operating pressure at the top of the absorption tower 1 is 0.7 MPa, the operating pressure at the top of the solvent recovery tower 2 is 0.6 MPa, and the operating pressure at the top of the desorption tower 3 is 1 MPa.

[0059] Beneficial effects

[0060] Because substances that are difficult to biodegrade (such as chloromethane) typically have very low solubility in inorganic absorbents, organic absorbents are required for absorption. Based on the principle of phase equilibrium, the exhaust gas discharged from the top of the absorption tower will inevitably contain a certain proportion of organic absorbent, which cannot meet VOC requirements and achieve emission standards. However, by using absorption tower 1, solvent recovery tower 2, and desorption tower 3 to recover the difficult-to-biodegrade substances (such as chloromethane) in the exhaust gas, the VOC index in the exhaust gas can be reduced to meet emission standards while ensuring the recovery rate of chloromethane. This can be achieved by simplifying the process operation conditions of absorption tower 1 (such as increasing the feed temperature) and using a second absorbent to perform secondary absorption of the first absorbent in the exhaust gas from absorption tower 1.

[0061] Furthermore, by employing organic and inorganic solvents sequentially as absorbents, this invention enables more efficient recovery of residual recalcitrant substances (such as chloromethane) and the first absorbent from the tail gas, significantly improving the VOC content in the tail gas. Simultaneously, absorption tower 1 does not require stringent process conditions; chloromethane recovery can be achieved by increasing the feed temperature of the first absorbent and the tail gas, and reducing the amount of the first absorbent (e.g., the mass ratio of the first absorbent to the feed containing tail gas). This effectively reduces the energy consumption generated during the recovery process of maintaining the low-temperature absorption in absorption tower 1 and the solvent recovery in desorption tower 3. Through the tail gas recovery device and method of this invention, the VOC value in the tail gas can be reduced without increasing the system's material consumption and operating costs, achieving VOC emission standards.

[0062] Furthermore, the apparatus and process of this invention not only achieve the recovery of chloromethane, a recalcitrant substance in exhaust gas, but also produce high-purity chloromethane with a high recovery rate. Moreover, after recovering chloromethane from the exhaust gas, the exhaust gas recovery apparatus and method of this invention can reduce the content of recalcitrant substances in the emitted exhaust gas to below 20 mg / Nm³. 3 The recovery rate of chloromethane is >99%. Furthermore, the apparatus and process of this invention avoid the generation of HCl during waste gas combustion, which causes severe equipment corrosion, resulting in higher production safety. Attached Figure Description

[0063] Figure 1 The present invention relates to a device for recovering chloromethane tail gas;

[0064] Figure 2 This is a recovery device for chloromethane tail gas as described in Comparative Example 1.

[0065] Figure 3 The device for recovering chloromethane tail gas in Comparative Example 2;

[0066] Figure 1 In the middle: 1-Absorption tower, 2-Solvent recovery tower, 3-Desorption tower, 4-Reboiler at the bottom of the tower, 5-Condenser at the top of the tower, 6-Absorbent cooler, 7-Absorbent cryogenic cooler, 8-Absorbent cryogenic cooler, 9-Desorption tower feed heat exchanger.

[0067] Figure 2 In the middle: 1-Absorption tower, 3-Desorption tower, 4-Reboiler at the bottom of the tower, 5-Condenser at the top of the tower, 6-Absorbent cooler, 7-Low-temperature cooler for absorbent, 9-Deep cooler at the top of the absorption tower, 10-Storage tank at the top of the absorption tower, 11-Deep cooler for the gas phase feed of the absorption tower, 12-Storage tank for absorbent.

[0068] Figure 3In the middle: 1-Absorption tower, 3-Desorption tower, 4-Reboiler at the bottom of the tower, 5-Condenser at the top of the tower, 6-Absorbent cooler, 7-Low-temperature cooler for absorbent, 8-Deep cooler for absorbent, 11-Deep cooler for gaseous feed to the absorption tower. Detailed Implementation

[0069] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0070] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0071] like Figure 1 As shown, this invention provides a device for recovering chloromethane tail gas, the device comprising an absorption tower 1, a solvent recovery tower 2, and a desorption tower 3;

[0072] The top gas phase outlet of the absorption tower 1 is connected to the bottom material inlet of the solvent recovery tower 2 via a pipeline, and the bottom liquid outlet of the absorption tower 1 is connected to the material inlet of the desorption tower 3 via a pipeline; the bottom liquid outlet of the desorption tower 3 is connected to the top material inlet of the absorption tower 1 via a pipeline, and a first absorbent cooling unit is installed on the connecting pipeline for cooling the first absorbent; a top condenser 5 and a bottom reboiler 4 are respectively installed at the top and bottom of the desorption tower 3; the material inlet of the desorption tower 3 is located at the top or middle of the desorption tower 3.

[0073] Between the outlet of the desorption tower 3 and the top material inlet of the absorption tower 1, a desorption tower feed heat exchanger 9 is also provided. The feed heat exchanger 9 is located between the outlet of the desorption tower 3 and the cooling unit.

[0074] The absorption tower 1 is a pressurized tower or an atmospheric tower, preferably a pressurized tower; the solvent recovery tower 2 is a pressurized tower or an atmospheric tower, preferably a pressurized tower; the desorption tower 3 is a pressurized tower or an atmospheric tower, preferably a pressurized tower.

[0075] The absorption tower 1, solvent recovery tower 2, and desorption tower 3 are selected from plate towers or packed towers.

[0076] The reboiler 4 is selected from any one of a thermosiphon reboiler, a forced circulation reboiler, a kettle reboiler, or a falling film reboiler. The top condenser 5 is selected from any one of a shell-and-tube heat exchanger, a plate heat exchanger, or an air cooler.

[0077] The first absorbent cooling unit includes an absorbent cooler 6, an absorbent cryogenic cooler 7, an absorbent cryogenic cooler 8, and an absorbent heat exchanger 9. The cooling medium of the absorbent cooler 6 is selected from circulating water or air, and its temperature is 32–38°C. The cooling medium of the absorbent cryogenic cooler 7 is a cryogenic medium, such as cryogenic water, and its temperature is 7–12°C. The cooling medium of the absorbent cryogenic cooler 8 is a cryogenic medium, such as a cryogenic ethylene glycol aqueous solution, and its temperature is -15 to -10°C. The heat exchange medium of the absorbent heat exchanger 9 is the bottom product of the absorption tower 1 and the bottom product of the desorption tower.

[0078] The first absorbent cooling unit is also connected to a first absorbent replenishment device for replenishing the first absorbent.

[0079] Example 1

[0080] In the above Figure 1 The recovery device shown is used to recover chloromethane tail gas.

[0081] The treatment capacity for chloromethane-containing tail gas is 1000 kg / h, where chloromethane accounts for 80% by mass, with the remainder being air. The chloromethane feed temperature is 20℃. The first absorbent is methanol, with a feed temperature of 10℃, and the second absorbent is water, with a feed temperature of 35℃. The mass ratio of the first absorbent to the tail gas feed is 5, and the mass ratio of the second absorbent to the tail gas feed is 4. The pressure of absorption tower 1 is 0.7 MPa, the operating pressure of solvent recovery tower 2 is 0.6 MPa, and the operating pressure of desorption tower 3 is 1 MPa. The top temperature of absorption tower 1 is 10℃, the top temperature of solvent recovery tower 2 is 35℃, and the top temperature of desorption tower 3 is 45℃. The specific recovery method is as follows:

[0082] (1) Chloromethane-containing tail gas and methanol, the first absorbent, enter the absorption tower 1 through the lower part and the top of the absorption tower 1 respectively, and come into countercurrent contact in the tower to realize the absorption of chloromethane by the first absorbent; the tail gas containing trace amounts of chloromethane and the first absorbent is taken out from the top of the absorption tower 1; the chloromethane-rich first absorbent is taken out from the bottom of the absorption tower 1.

[0083] (2) The first absorbent rich in chloromethane at the bottom of the absorption tower 1 and the first absorbent obtained from the bottom of the desorption tower exchange heat in the feed heat exchanger 9 of the desorption tower and then enter the desorption tower 3. Chloromethane is obtained at the top of the desorption tower 3. The first absorbent obtained from the bottom of the desorption tower 3 is cooled by the cooling unit and then returned to the absorption tower 1 for recycling.

[0084] (3) The tail gas containing chloromethane and the first absorbent at the top of the absorber tower 1 enters from the bottom of the solvent recovery tower 2. After countercurrent contact with the second absorbent in the solvent recovery tower 2, it further absorbs the first absorbent and chloromethane in the tail gas. The second absorbent is discharged from the bottom of the solvent recovery tower 2 and enters the second absorbent treatment system. After treatment, it is recycled. The tail gas obtained at the top of the solvent recovery tower 2 is directly discharged.

[0085] The process parameters and material extraction status of each tower are shown in Table 1.

[0086] Table 1. Material extraction status of each tower in Example 1

[0087]

[0088] The exhaust gas obtained from the top of solvent recovery tower 2 contains, after conversion, 2.58 mg / Nm³ of chloromethane. 3 The methanol content of the first absorbent is 0.02 mg / Nm³. 3 Total 2.6 mg / Nm 3 All are less than the emission standard limit of 20 mg / Nm³. 3 The chloromethane recovery rate is greater than 99%, and the exhaust gas meets higher VOC emission standards.

[0089] In this embodiment, the circulating absorbent collected from the bottom of the absorption tower first exchanges heat with the material in the bottom of the absorption tower 1. On the one hand, this can save energy consumption of the desorption tower reboiler, and on the other hand, it can save the amount of circulating water required for cooling the absorbent.

[0090] Comparative Example 1

[0091] The raw material composition and absorbent for the chloromethane-containing tail gas are the same as in Example 1. The absorbent is dichloroethane, and the mass ratio of its dosage to the amount of chloromethane tail gas to be treated is 8. A single absorption tower recovery process is used. See details below. Figure 2 The recovery operation is carried out using a recovery device. The operating pressure of absorption tower 1 is 0.3 MPa, the operating pressure of desorption tower 3 is 0.6 MPa, the cooling temperature of the absorbent is 20℃, the feed temperature of the chloromethane-containing tail gas is 0℃, and the top temperature of desorption tower 3 is 28℃. The tail gas exiting the top of absorption tower 1, after being cooled to 0℃, enters the top storage tank 10. After flash evaporation, the gas phase is the exhaust tail gas, and the liquid phase is mixed with the absorbent collected from the bottom of desorption tower 3, cooled to 20℃, and then re-enters absorption tower 1. The liquid phase collected from the top condenser of the desorption tower is qualified chloromethane, and the gas phase is chloromethane-containing waste gas. The process parameters and material collection status of each tower are shown in Table 2.

[0092] Table 2 Material recovery status of each tower in Comparative Example 1

[0093]

[0094] In this comparative example, the chloromethane recovery rate was greater than 97%, but the chloromethane content in the exhaust gas obtained from the top of absorber 1 was 0.39 mg / Nm³. 3 However, the content of the absorbent dichloroethane is as high as 41925 mg / Nm³. 3 The amount of the first absorbent in the exhaust gas far exceeds the emission standard limit of 20 mg / Nm³. 3 Meanwhile, at the top of the desorption tower, there is also 25 kg / h of substandard gas containing 90% chloromethane, which is far above the emission standards.

[0095] Comparative Example 2

[0096] The raw material composition and the first absorbent for the chloromethane-containing tail gas are the same as in Example 1, and the following method is used. Figure 3 The recovery device performs the recovery operation. Absorption tower 1 operates at atmospheric pressure, the feed temperature of the first absorbent is 10℃, the mass ratio of the first absorbent dosage to the amount of chloromethane processed is 8, the operating pressure of desorption tower 3 is 1MPa, the reflux ratio is 2, and the material output of each tower is shown in Table 3.

[0097] Table 3 Material recovery status of each tower in Comparative Example 2

[0098]

[0099] The chloromethane recovery rate in this comparative example is greater than 99%. However, calculations show that the chloromethane content in the mixed exhaust gas obtained from the top of absorption tower 1 and the top of the desorption tower is as high as 11197 mg / Nm³. 3 The content of the first absorbent is as high as 88210 mg / Nm³. 3 It is far greater than the emission standard limit of 20 mg / Nm³. 3 .

[0100] The comparison of the above experimental results shows that the content of chloromethane in the gas emitted by the recovery device and method of the present invention is 2.58 mg / Nm³. 3 The content of the first absorbent is 0.02 mg / Nm³. 3 The exhaust emissions meet higher VOC emission standards; however, the chloromethane content in the exhaust emissions of Comparative Examples 1 and 2 is 0.06 mg / Nm³, respectively. 3 and 11197mg / Nm 3 The content of the first absorbent was 41925 mg / Nm³. 3 and 88210mg / Nm 3 Therefore, the content of chloromethane and the first absorbent in the exhaust gas emitted by Comparative Examples 1 and 2 is difficult to meet the higher VOC emission standards.

[0101] Furthermore, compared with Comparative Examples 1 and 2, the apparatus and operating conditions of the present invention are simple, the feeding conditions of the absorption tower 1 are mild, and the energy consumption is low. Table 4 shows a comparison of the energy consumption results of Example 1 and Comparative Examples 1 and 2.

[0102] Table 4 Energy consumption comparison between Example 1 and Comparative Examples 1-2

[0103]

[0104] Comparing the data in Table 4, it can be seen that the total energy consumption of the device of the present invention is lower than that of Comparative Example 1 and Comparative Example 2. For example, under the same chloromethane tail gas treatment capacity, the load of the reboiler in Example 1 is 77% and 40.7% of that in Comparative Example 1 and Comparative Example 2, respectively. The top temperature of the desorption tower 3 in Example 1 is 45°C, so both the desorption tower condenser and the absorbent cooler can be cooled with circulating water; while the top temperature of the desorption tower 3 in Comparative Example 1 is 20°C, so the top condenser cannot be cooled with circulating water; the top condenser in Comparative Example 2 can be cooled with circulating water. As can be seen from Table 4, the total load of the low-temperature water and cryogenic water coolers used in the present invention is 33% and 62% of that in Comparative Example 1 and Comparative Example 2, respectively, and the total load of the circulating water is 99% and 34.2% of that in Comparative Example 1 and Comparative Example 2, respectively. By comparing the data in Table 4, it can be seen that because the device and operating conditions of the present invention are simple and the feed conditions of the absorption tower 1 are mild, the energy consumption of the present invention is lower.

[0105] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of this application.

Claims

1. A gas recovery method, characterized in that, The recovery method includes using a gas recovery device to treat the gas containing chloromethane; The recycling method specifically includes the following steps: 1) The gas to be treated containing chloromethane and the first absorbent are brought into countercurrent contact in the absorption tower (1). The gas containing chloromethane and the first absorbent is drawn out from the top of the absorption tower (1); the first absorbent rich in chloromethane is drawn out from the bottom of the absorption tower (1); the feed mass ratio of the first absorbent to the gas to be treated is 0.2~50:

1. 2) The first absorbent rich in chloromethane obtained in step 1) exchanges heat with the first absorbent in the bottom of the desorption tower (3) and then enters the desorption tower (3). Chloromethane is obtained at the top of the desorption tower (3). The chloromethane is condensed by the top condenser of the desorption tower (3) to obtain chloromethane liquid or gas. The first absorbent obtained in the bottom of the desorption tower (3) is cooled and recycled as the first absorbent of the absorption tower (1). 3) The gas containing chloromethane and the first absorbent obtained in step 1) enters from the bottom of the solvent recovery tower (2) and comes into countercurrent contact with the second absorbent inside the solvent recovery tower (2). The second absorbent is discharged from the bottom of the solvent recovery tower (2), and tail gas that meets the emission standards is discharged from the top of the solvent recovery tower (2). The operating pressure at the top of the absorption tower (1) is greater than 0.6 MPa, and the operating pressure of the solvent recovery tower (2) is less than that of the absorption tower (1) to ensure that the gas phase at the top of the solvent recovery tower (2) can enter the solvent recovery tower (2). The first absorbent is selected from one or a mixture of two or more of chloroform, diethyl ether, methanol, methyl acetal, and acetone; the second absorbent is selected from one or a mixture of two or more of water, alkali metal hydroxide, and ammonia. The gas recovery device includes an absorption tower (1), a solvent recovery tower (2), and a desorption tower (3); the absorption tower (1), solvent recovery tower (2), and desorption tower (3) are selected from plate towers or packed towers; The top gas phase outlet of the absorption tower (1) is connected to the bottom material inlet of the solvent recovery tower (2) through a pipeline, the bottom liquid outlet of the absorption tower (1) is connected to the material inlet of the desorption tower (3) through a pipeline, and the bottom liquid outlet of the desorption tower (3) is connected to the top material inlet of the absorption tower (1) through a pipeline. A cooling unit is installed on the connecting pipe between the outlet of the desorption tower (3) and the top material inlet of the absorption tower (1); The desorption tower (3) is provided with a top condenser at the top and a bottom reboiler at the bottom. Between the outlet of the desorption tower (3) and the top material inlet of the absorption tower (1), a desorption tower feed heat exchanger (9) is also provided, which is located between the outlet of the desorption tower (3) and the cooling unit. The gas recovery device is selected from the recovery device for chloromethane-containing tail gas generated during glyphosate synthesis.

2. The gas recovery method according to claim 1, characterized in that, The material inlet of the desorption tower (3) is located at the top or middle of the desorption tower (3); The absorption tower (1), solvent recovery tower (2) and desorption tower (3) are independently selected from atmospheric pressure towers or pressurized towers; At least one of the absorption tower (1), the solvent recovery tower (2), and the desorption tower (3) is a pressurized tower.

3. The gas recovery method according to claim 1, characterized in that, The reboiler in the column is selected from any one of the following: thermosiphon reboiler, forced circulation reboiler, reboiler in a kettle, or falling film reboiler. The condenser at the top of the tower is selected from any one of shell-and-tube heat exchangers, plate heat exchangers, or air coolers.

4. The gas recovery method according to claim 1, characterized in that, The cooling unit is selected from the absorbent cooling unit, which includes at least one of the absorbent cooler (6), absorbent cryogenic cooler (7), or absorbent deep cooler (8).

5. The gas recovery method according to claim 4, characterized in that, The absorbent cooling unit includes an absorbent cooler (6), an absorbent cryogenic cooler (7), and an absorbent deep cooler (8).

6. The gas recovery method according to claim 1, characterized in that, The absorption tower (1) contains a first absorbent; The solvent recovery tower (2) contains a second absorbent.

7. The gas recovery method according to claim 4, characterized in that, The absorbent cooling unit is also connected to the first absorbent replenishment device.

8. The gas recovery method according to claim 1, characterized in that, The gas recovery device also includes a second absorbent recovery system, which is connected to the solvent recovery tower (2) via a pipeline.

9. The gas recovery method according to claim 1, characterized in that, The second absorbent is selected from one or a mixture of two or more of the following: aqueous solutions of alkali metal hydroxides and aqueous solutions of ammonia.

10. The gas recovery method according to claim 1, characterized in that, The gas recovery method includes the following steps: The second absorbent discharged from the bottom of the solvent recovery tower (2) enters the second absorbent recovery system and is recycled after treatment; The gas to be treated is the tail gas containing chloromethane produced during the synthesis of glyphosate.

11. The gas recovery method according to claim 1, characterized in that, In step 1), the operating pressure at the top of the absorption tower (1) is greater than 0.6 MPa and not greater than 2 MPa, and the operating temperature at the top of the absorption tower (1) is -25~50℃; In step 2), the operating pressure at the top of the desorption tower (3) is 0.01~2MPa, and the operating temperature at the top of the desorption tower (3) is -5~50℃; In step 3), the feed mass ratio of the second absorbent to the gas to be treated is 0.2~50:1, the operating pressure at the top of the solvent recovery tower (2) is 0.1~2MPa, and the operating temperature at the top of the solvent recovery tower (2) is -25~50℃.

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