A method for absorbing phosgene by utilizing solvent

Abstract

The present invention relates to a method for absorbing phosgene using a solvent. By controlling the gas and liquid phases entering a vertical absorption tube to operate at a modified gas phase superficial velocity and liquid phase superficial velocity within a specific range, the absorption effect of phosgene can be effectively improved, thereby reducing the amount of absorption solvent used and achieving an increase in the concentration of the phosgene solution.

Description

Technical Field

[0001] The present invention relates to the technical field of isocyanate preparation, and in particular to a method for absorbing phosgene by utilizing a solvent. Background Art

[0002] Isocyanates are commonly prepared industrially by reacting phosgene with polyamine compounds in a solvent. In large-scale industrial production, phosgene and solvent are often used in significant excess to ensure a full reaction and avoid the formation of by-products. However, these substances must be removed in subsequent steps to obtain a high-purity isocyanate product, a process that consumes significant amounts of energy. Therefore, minimizing the excess of phosgene and solvent is crucial for reducing the production cost and process complexity of isocyanates.

[0003] In the common isocyanate preparation process, solvents are added in two steps: the first step is to dissolve the raw material polyamine compound. Adding additional solvent can better disperse the raw material polyamine compound in the solvent to obtain better reaction performance. With the advancement of the reaction process, the amount of solvent added for mixing and dispersing the polyamine compound has been greatly reduced; the second step is to absorb excess phosgene in the production process. Adding additional solvent can recover as much excess gaseous phosgene as possible to prepare a phosgene solution, which can be recycled and used in the isocyanate preparation reaction.

[0004] CN 1729169 A discloses a process for the partial or complete separation of a mixture comprising hydrogen chloride and phosgene, possibly solvents, low boilers, and inerts typically obtained in the preparation of isocyanates by reacting amines with phosgene. This process comprises firstly partial or complete condensation of the phosgene, then a distillation or stripping step in a column to remove hydrogen chloride from the bottom product phosgene, and then washing the top product hydrogen chloride by absorbing the phosgene in a process solvent. To remove solvent residues, subsequent post-purification can be carried out, for example, by absorption on activated carbon or by other suitable methods.

[0005] CN101062905A discloses a method for producing isocyanates, which is produced by the following steps: reacting at least one amine with phosgene, optionally in the presence of a solvent, to obtain the corresponding isocyanate and a stream containing hydrogen chloride, phosgene, and optionally a solvent, low-boiling compounds, and inert substances; separating the stream containing hydrogen chloride, phosgene, and optionally a solvent, low-boiling compounds, and inert substances in at least two absorption steps carried out sequentially, the absorption steps comprising at least one isothermal absorption step and at least one adiabatic absorption step, to obtain a hydrogen chloride stream containing at most 0.5% by weight of phosgene, based on the total weight of the hydrogen chloride stream, and a liquid phosgene stream; and recycling the liquid phosgene stream to the reaction of the amine with the phosgene.

[0006] CN101514172A discloses a method for preparing isocyanates, which comprises reacting a suitable amine with phosgene, condensing the resulting gas mixture, stripping the resulting liquid phase, returning the residual liquid solvent to the reaction stage, and then further purifying the gaseous components in an absorption process. This method, based on CN101062905A, further incorporates a tower stripping component. By introducing energy, hydrogen chloride and phosgene are discharged as gases from the lower portion of the tower. The purified solvent is removed from the bottom of the stripper and can be added to the amine phosgenation reaction as a solvent for the phosgene and amine.

[0007] In order to recover the phosgene exhausted in the isocyanate preparation reaction process, the above technical solution still needs to add a large amount of solvent. The recovered phosgene solution has a high solvent content, which will cause a large waste of energy consumed in removing the solvent during the isocyanate production process.

[0008] To reduce the amount of solvent added, isothermal absorption can be used. However, this process requires the formation of a uniform annular liquid film within the absorption tube to improve absorption efficiency, thereby minimizing the amount of solvent added. While maintaining the same exhaust gas throughput, if the amount of solvent added is too low, the liquid film may become unstable and rupture, forming a trickle or even a mist flow. This can adversely affect the absorption process and limit further reductions in solvent addition.

[0009] Therefore, in view of the shortcomings of the existing technology, there is an urgent need to provide a method that can reduce the amount of absorption solvent used and increase the concentration of phosgene solution. Summary of the Invention

[0010] The object of the present invention is to provide a method for absorbing phosgene by using a solvent, which can effectively improve the absorption effect of phosgene, thereby reducing the amount of absorption solvent used and achieving an increase in the concentration of phosgene solution.

[0011] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0012] The present invention provides a method for absorbing phosgene by using a solvent, the method comprising the following steps:

[0013] The solvent is uniformly introduced into the top of the vertical absorption tube and forms a liquid film along the inner wall of the vertical absorption tube, which moves toward the bottom. The exhaust gas containing phosgene and non-condensable gas is uniformly introduced into the bottom of the vertical absorption tube and moves toward the top along the central axis of the vertical absorption tube. The solvent and the exhaust gas contact and exchange substances at the gas-liquid interface. The non-condensable gas is discharged from the top of the vertical absorption tube, and the phosgene solution is discharged from the bottom. A refrigerant flows through the space located on the outer wall of the vertical absorption tube, and the refrigerant is used to remove heat from the interior of the vertical absorption tube.

[0014] The apparent rate j of the solvent is calculated using formula (1) and formula (2) respectively L and the apparent velocity j of the exhaust G :

[0015]

[0016] Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, unit is m 3 / h; A is the cross-sectional area of ​​the vertical absorption tube, in m 2 ; Q2 is the volume flow rate of exhaust gas in the vertical absorption pipe, unit is m 3 / h;

[0017] Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: and the apparent velocity of exhaust

[0018]

[0019] Where: L is the density of the solvent in kg / m 3 ρ G is the density of the exhaust gas, in kg / m 3 ; g is the acceleration due to gravity, unit is m 2 / s; D is the diameter of the vertical absorption tube, in m;

[0020] control The value is 0.3-0.7.

[0021] The method for absorbing phosgene using a solvent provided by the present invention can effectively improve the absorption effect of phosgene by controlling the gas-liquid two phases entering the vertical absorption tube to operate at a corrected gas phase apparent velocity and liquid phase apparent velocity within a specific range, thereby reducing the amount of absorption solvent used and achieving an increase in the concentration of the phosgene solution; if the exhaust flow rate in the vertical absorption tube is significantly larger than the solvent flow rate, a phenomenon similar to "liquid flooding" may occur, that is, the solvent forms a blocked flow in the vertical absorption tube and cannot form a stable gas-liquid phase cross-sectional contact with the exhaust gas of similar motion; if the solvent flow rate in the vertical absorption tube is significantly larger than the exhaust flow rate, the pressure drop in the vertical absorption tube increases, thereby resulting in less exhaust gas entering the vertical absorption tube, causing the exhaust load in other vertical absorption tubes to increase, and the drag force of the exhaust gas on the liquid film on the tube wall is too large, thereby causing the liquid film to rupture, which also leads to poor absorption effect. When the absorption process is compromised, resulting in poor results, additional solvent or additional tower internals, such as trays and packing, are needed to ensure a sufficiently low phosgene content in the non-condensable gas discharged from the top of the unit. This increases operating costs and fixed investment, and reduces the concentration of the phosgene solution obtained at the bottom of the unit. Therefore, the gas-liquid superficial velocity must be controlled within a reasonable range to improve absorption efficiency and reduce solvent usage.

[0022] The term "uniform" means that when a plurality of vertical absorption tubes are arranged in parallel, the volume flow rate of the solvent or exhaust gas entering any vertical absorption tube is the same.

[0023] A refrigerant circulates within the space surrounding the outer wall of the vertical absorption tube. The refrigerant removes heat generated by the absorption process within the vertical absorption tube and transferred to the outer wall of the absorption tube. The refrigerant can be a halogenated hydrocarbon refrigerant that absorbs heat by evaporation, or low-temperature ethylene glycol water or chilled brine can be used as a coolant.

[0024] The control The value of is 0.3-0.7, for example, it can be 0.3, 0.5, 0.6 or 0.7, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the solvent comprises any one or a combination of at least two of chlorobenzene, o-dichlorobenzene or diethyl carbonate. Typical but non-limiting combinations include a combination of chlorobenzene and o-dichlorobenzene, a combination of o-dichlorobenzene and diethyl carbonate, or a combination of chlorobenzene, o-dichlorobenzene and diethyl carbonate.

[0026] Preferably, the feed temperature of the solvent is -30°C to -5°C, for example, -30°C, -25°C, -20°C, -10°C or -5°C, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably -25°C to -10°C.

[0027] Preferably, the temperature of the exhaust gas containing phosgene and non-condensable gas is 5°C to 40°C, for example, 5°C, 10°C, 25°C, 30°C or 40°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the volume proportion of phosgene in the exhaust gas containing phosgene and non-condensable gas is 10-50%, for example, it can be 10%, 20%, 30%, 40% or 50%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the non-condensable gas in the exhaust gas includes any one or a combination of at least two of hydrogen chloride, carbon monoxide or nitrogen. Typical but non-limiting combinations include a combination of hydrogen chloride and carbon monoxide, a combination of carbon monoxide and nitrogen, or a combination of hydrogen chloride, carbon monoxide and nitrogen.

[0030] Preferably, the feed volume ratio of the exhaust gas to the solvent is (400-1400):1, for example, it can be 400:1, 600:1, 800:1, 1000:1, 1200:1 or 1400:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the operating pressure of the solvent absorbing phosgene is 2-6 bar, and the operating temperature is -30°C to 0°C.

[0032] The operating pressure of the solvent absorbing phosgene is 2-6 bar, for example, 2 bar, 3 bar, 4 bar, 5 bar or 6 bar, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 3-4 bar.

[0033] The operating temperature for the solvent to absorb phosgene is -30°C to 0°C, for example, -30°C, -20°C, -10°C or 0°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the diameter of the vertical absorption tube is 20-80 mm, for example, it can be 20 mm, 30 mm, 50 mm, 60 mm or 80 mm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 20-50 mm.

[0035] Preferably, the non-condensable gas discharged from the top of the vertical absorption tube contains 10-500 ppm (V / V%) of phosgene, for example, it can be 10 ppm (V / V%), 50 ppm (V / V%), 100 ppm (V / V%), 200 ppm (V / V%), 300 ppm (V / V%) or 500 ppm (V / V%), but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 50-200 ppm (V / V%).

[0036] Preferably, the mass proportion of phosgene in the phosgene solution discharged from the bottom of the vertical absorption tube is 60-90%, for example, it can be 60%, 65%, 75%, 85% or 90%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 65-85%.

[0037] Preferably, the vertical absorption tube is arranged in a phosgene absorption device, and the phosgene absorption device also includes a film distributor, a gas distributor, a shell and a head. The film distributor is connected to the top of the vertical absorption tube, the gas distributor is connected to the bottom of the vertical absorption tube, and the shell is arranged outside the vertical absorption tube, and the top and bottom of the shell are respectively fastened with heads.

[0038] Preferably, the vertical absorption tubes are arranged in parallel.

[0039] Preferably, the phosgene absorption devices are arranged in series.

[0040] As a preferred technical solution of the method of the present invention, the method comprises the following steps:

[0041] A solvent with a feed temperature of -30°C to -5°C is uniformly introduced into the top of a vertical absorption tube with a diameter of 20-80mm, and a liquid film is formed along the inner wall of the vertical absorption tube and moves toward the bottom. Exhaust gas containing phosgene and non-condensable gas at a temperature of 5°C to 40°C is uniformly introduced into the bottom of the vertical absorption tube and moves toward the top along the central axis of the vertical absorption tube. The volume proportion of phosgene in the exhaust gas is 10-50%, and the non-condensable gas in the exhaust gas includes any one of hydrogen chloride, carbon monoxide or nitrogen or a combination of at least two of them. The solvent and the exhaust gas are mixed in the gas stream. The liquid two-phase interface contacts and material exchange occurs, the exhaust gas and solvent feed volume ratio is (400-1400):1, the operating pressure of the solvent absorption of phosgene is 2-6 bar, and the operating temperature is -30°C to 0°C; the top of the vertical absorption tube discharges non-condensable gas containing 10-500 ppm (V / V%) of phosgene, and the bottom discharges phosgene solution with a phosgene mass ratio of 60-90%; a refrigerant circulates in the space where the outer wall of the vertical absorption tube is located, and the refrigerant is used to remove heat from the vertical absorption tube;

[0042] The apparent rate j of the solvent is calculated using formula (1) and formula (2) respectively L and the apparent velocity j of the exhaust G :

[0043]

[0044] Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, unit is m 3 / h; A is the cross-sectional area of ​​the vertical absorption tube, in m 2 ; Q2 is the volume flow rate of exhaust gas in the vertical absorption pipe, unit is m 3 / h;

[0045] Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: and the apparent velocity of exhaust

[0046]

[0047] Where: L is the density of the solvent in kg / m 3 ρ G is the density of the exhaust gas, in kg / m 3 ; g is the acceleration due to gravity, unit is m 2 / s; D is the diameter of the vertical absorption tube, in m;

[0048] control The value is 0.3-0.7.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The method for absorbing phosgene using a solvent provided by the present invention can effectively improve the absorption effect of phosgene by controlling the gas and liquid phases entering the vertical absorption tube to operate at a modified gas phase apparent velocity and liquid phase apparent velocity within a specific range, thereby reducing the amount of absorption solvent used and achieving an increase in the concentration of the phosgene solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 is a schematic diagram of the internal structure of a longitudinal section of the phosgene absorption device provided in Example 1 of the present invention;

[0052] Figure 2 This is a schematic diagram of three phosgene absorption devices provided in Example 1 of the present invention operating in series.

[0053] Among them: 1, membrane distributor; 2, vertical absorption tube; 3, gas distributor; 4, shell; 5, head. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0055] Phosgene in the present invention is produced by the company, and other raw materials can be purchased from commercial sources unless otherwise specified.

[0056] Example 1

[0057] This embodiment provides a method for absorbing phosgene using a solvent, the method comprising the following steps:

[0058] A solvent with a feed temperature of -30°C is uniformly introduced into the top of a vertical absorption tube 2 with a diameter of 30 mm, and a liquid film is formed along the inner wall of the vertical absorption tube 2 and moves toward the bottom. The solvent is chlorobenzene. Exhaust gas containing phosgene and non-condensable gas at 25°C is uniformly introduced into the bottom of the vertical absorption tube 2 and moves toward the top along the central axis of the vertical absorption tube 2. The non-condensable gas is hydrogen chloride, and the volume proportion of phosgene in the exhaust gas is 40%. The chlorobenzene contacts the exhaust gas at the gas-liquid interface and substance exchange occurs. The feed volume ratio of the exhaust gas to chlorobenzene is 1400:1. The operating pressure of chlorobenzene absorbing phosgene is 4 bar and the operating temperature is -20°C. A refrigerant is circulated in the space where the outer wall of the vertical absorption tube 2 is located. The refrigerant is 30% ethylene glycol water, which is used to remove heat from the inside of the vertical absorption tube 2.

[0059] The vertical absorption tubes 2 are arranged in parallel in the phosgene absorption device. The internal structure diagram of the longitudinal section of the phosgene absorption device is as follows: Figure 1 As shown, the phosgene absorption device further includes a film distributor 1, a gas distributor 3, a shell 4 and a head 5. The film distributor 1 is connected to the top of the vertical absorption tube 2, the gas distributor 3 is connected to the bottom of the vertical absorption tube 2, the shell 4 is arranged outside the vertical absorption tube 2, and the top and bottom of the shell 4 are respectively buckled with the head 5; the three phosgene absorption devices are arranged in series, as shown in FIG. Figure 2 As shown;

[0060] After calculation, we get The value of is 0.67.

[0061] After testing, the hydrogen chloride discharged from the top of the vertical absorption tube 2 contained 184 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom was 86%. This shows that the absorption of phosgene by the method provided in this embodiment can improve the absorption effect and thereby reduce the amount of solvent used, while achieving an increase in the concentration of the phosgene solution.

[0062] Example 2

[0063] This embodiment provides a method for absorbing phosgene using a solvent, the method comprising the following steps:

[0064] o-Dichlorobenzene with a feed temperature of -10°C is uniformly introduced into the top of a vertical absorption tube 2 with a diameter of 20 mm, and a liquid film is formed along the inner wall surface of the vertical absorption tube 2 and moves toward the bottom; exhaust gas containing phosgene and carbon monoxide at 5°C is uniformly introduced into the bottom of the vertical absorption tube 2 and moves toward the top along the central axis of the vertical absorption tube 2, with the volume proportion of phosgene in the exhaust gas being 15%; the o-Dichlorobenzene and the exhaust gas contact at the gas-liquid interface and undergo material exchange, the feed volume ratio of the exhaust gas to o-Dichlorobenzene is 400:1, the operating pressure of the o-Dichlorobenzene absorption of phosgene is 6 bar, and the operating temperature is 0°C; a refrigerant is circulated in the space located on the outer wall of the vertical absorption tube 2, and the refrigerant is chilled brine, which is used to remove heat from the vertical absorption tube 2;

[0065] The vertical absorption tubes 2 are arranged in parallel in the phosgene absorption device, and the phosgene absorption device is the same as that in Example 1;

[0066] After calculation, we get The value of is 0.7.

[0067] After testing, the carbon monoxide discharged from the top of the vertical absorption tube 2 contained 463 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom was 70.2%. This shows that the absorption of phosgene by the method provided in this embodiment can improve the absorption effect and thereby reduce the amount of solvent used, while achieving an increase in the concentration of the phosgene solution.

[0068] Example 3

[0069] This embodiment provides a method for absorbing phosgene using a solvent, the method comprising the following steps:

[0070] Diethyl carbonate with a feed temperature of -5°C is uniformly introduced into the top of a vertical absorption tube 2 with a diameter of 80 mm, and a liquid film is formed along the inner wall surface of the vertical absorption tube 2 and moves toward the bottom; exhaust gas containing phosgene and nitrogen at 40°C is uniformly introduced into the bottom of the vertical absorption tube 2 and moves toward the top along the central axis of the vertical absorption tube 2, and the volume proportion of phosgene in the exhaust gas is 50%; the diethyl carbonate and the exhaust gas contact at the gas-liquid two-phase interface and undergo substance exchange, the feed volume ratio of the exhaust gas to diethyl carbonate is 400:1, the operating pressure of diethyl carbonate absorbing phosgene is 2 bar, and the operating temperature is -30°C; a refrigerant is circulated in the space where the outer wall of the vertical absorption tube 2 is located, and the refrigerant is Freon-134a, which is used to remove heat from the vertical absorption tube 2;

[0071] The vertical absorption tubes 2 are arranged in parallel in the phosgene absorption device, and the phosgene absorption device is the same as that in Example 1;

[0072] After calculation, we get The value of is 0.3.

[0073] After testing, the nitrogen discharged from the top of the vertical absorption tube 2 contained 90 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom was 83.2%. This shows that the absorption of phosgene by the method provided in this embodiment can improve the absorption effect and thereby reduce the amount of solvent used, while achieving an increase in the concentration of the phosgene solution.

[0074] Comparative Example 1

[0075] This comparative example provides a method for absorbing phosgene by using a solvent. The difference from Example 1 is that the volume ratio of the exhaust gas to the chlorobenzene feed is adjusted to 300:1, and the relevant parameters are adaptively adjusted so that The value of is 0.18, and the rest are the same as in Example 1.

[0076] After testing, the hydrogen chloride discharged from the top of the vertical absorption tube 2 contained 678 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom was 35.2%. This shows that when the method provided in this comparative example is used to absorb phosgene, the absorption effect is reduced, thereby increasing the amount of solvent used, and the concentration of the phosgene solution is significantly reduced.

[0077] Comparative Example 2

[0078] This comparative example provides a method for absorbing phosgene by using a solvent. The difference from Example 1 is that the volume ratio of the exhaust gas to the feed volume of chlorobenzene is adjusted to 1500:1, and the relevant parameters are adaptively adjusted so that The value of is 0.89, and the rest are the same as in Example 1.

[0079] After testing, the hydrogen chloride discharged from the top of the vertical absorption tube 2 contained 142670 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom was 78.5%. This shows that the absorption effect of phosgene by the method provided in this comparative example is reduced, thereby increasing the amount of solvent used, and the concentration of the phosgene solution is significantly reduced.

[0080] In summary, the method of absorbing phosgene using a solvent provided by the present invention can effectively improve the absorption effect of phosgene by controlling the gas and liquid phases entering the vertical absorption tube to operate at a corrected gas phase apparent velocity and liquid phase apparent velocity within a specific range, thereby reducing the amount of absorption solvent used and achieving an increase in the concentration of the phosgene solution.

[0081] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for absorbing phosgene using a solvent, characterized in that: The method comprises the following steps: The solvent is uniformly introduced into the top of the vertical absorption tube and forms a liquid film along the inner wall of the vertical absorption tube, which moves toward the bottom. The exhaust gas containing phosgene and non-condensable gas is uniformly introduced into the bottom of the vertical absorption tube and moves toward the top along the central axis of the vertical absorption tube. The solvent and the exhaust gas contact and exchange substances at the gas-liquid interface. The non-condensable gas is discharged from the top of the vertical absorption tube, and the phosgene solution is discharged from the bottom. A refrigerant flows through the space located on the outer wall of the vertical absorption tube, and the refrigerant is used to remove heat from the interior of the vertical absorption tube. The apparent rate j of the solvent is calculated using formula (1) and formula (2) respectively L and the apparent velocity j of the exhaust G : Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, unit is m 3 / h; A is the cross-sectional area of ​​the vertical absorption tube, in m 2 ; Q2 is the volume flow rate of exhaust gas in the vertical absorption pipe, unit is m 3 / h; Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: and the apparent velocity of exhaust Where: L is the density of the solvent in kg / m 3 ρ G is the density of the exhaust gas, in kg / m 3 ; g is the acceleration due to gravity, unit is m 2 / s; D is the diameter of the vertical absorption tube, in m; control The value is 0.3-0.

7.

2. The method according to claim 1, characterized in that The solvent includes any one of chlorobenzene, o-dichlorobenzene or diethyl carbonate, or a combination of at least two of them.

3. The method according to claim 1, characterized in that The feed temperature of the solvent is -30°C to -5°C.

4. The method according to claim 1, wherein The temperature of the exhaust gas containing phosgene and non-condensable gas is 5°C to 40°C.

5. The method according to claim 1, wherein The volume proportion of phosgene in the exhaust gas containing phosgene and non-condensable gas is 10-50%.

6. The method according to claim 1, characterized in that The non-condensable gas in the exhaust gas includes any one of hydrogen chloride, carbon monoxide or nitrogen, or a combination of at least two of them.

7. The method according to claim 1, characterized in that The feed volume ratio of the exhaust gas to the solvent is (400-1400):

1.

8. The method according to claim 1, characterized in that The operating pressure of the solvent absorbing phosgene is 2-6 bar, and the operating temperature is -30°C to 0°C.

9. The method according to claim 1, characterized in that The diameter of the vertical absorption tube is 20-80 mm.

10. The method according to claim 1, characterized in that The method comprises the following steps: A solvent with a feed temperature of -30°C to -5°C is uniformly introduced into the top of a vertical absorption tube with a diameter of 20-80mm, and a liquid film is formed along the inner wall of the vertical absorption tube and moves toward the bottom. Exhaust gas containing phosgene and non-condensable gas at a temperature of 5°C to 40°C is uniformly introduced into the bottom of the vertical absorption tube and moves toward the top along the central axis of the vertical absorption tube. The volume proportion of phosgene in the exhaust gas is 10-50%, and the non-condensable gas in the exhaust gas includes any one of hydrogen chloride, carbon monoxide or nitrogen, or a combination of at least two of them. The solvent and the exhaust gas contact at the gas-liquid interface and undergo substance exchange. The feed volume ratio of the exhaust gas to the solvent is (400-1400):

1. The operating pressure of the solvent absorbing phosgene is 2-6 bar, and the operating temperature is -30°C to 0°C. Non-condensable gas is discharged from the top of the vertical absorption tube, and phosgene solution is discharged from the bottom. A refrigerant is circulated in the space where the outer wall of the vertical absorption tube is located, and the refrigerant is used to remove heat from the inside of the vertical absorption tube. The apparent rate j of the solvent is calculated using formula (1) and formula (2) respectively L and the apparent velocity j of the exhaust G : Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, unit is m 3 / h; A is the cross-sectional area of ​​the vertical absorption tube, in m 2 ; Q2 is the volume flow rate of exhaust gas in the vertical absorption pipe, unit is m 3 / h; Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: and the apparent velocity of exhaust Where: L is the density of the solvent in kg / m 3 ρ G is the density of the exhaust gas, in kg / m 3 ; g is the acceleration due to gravity, unit is m 2 / s; D is the diameter of the vertical absorption tube, in m; control The value is 0.3-0.7.

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