Method for absorbing phosgene by using solvent

Abstract

The invention relates to a method for absorbing phosgene by using a solvent, which can effectively improve the absorption effect of phosgene by controlling the gas-liquid two phases entering a vertical absorption tube to be operated at the corrected gas phase apparent rate and liquid phase apparent rate in a specific range, thereby reducing the use amount of the absorption solvent and reducing the production cost. And the concentration of the phosgene solution is improved.

Description

Technical Field

[0001] The 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] In industry, phosgene and polyamine compounds are usually used to react in a solvent to prepare isocyanates. In large-scale industrial production, the amount of phosgene and solvent used is often greatly excessive to ensure that the reaction is fully carried out and to avoid the generation of by-products. However, phosgene and solvent usually need to be removed in the subsequent process to obtain a high-purity isocyanate product, and this process consumes a lot of energy. Therefore, reducing the excess rate of phosgene and solvent as much as possible is of great significance to reducing the production cost and process difficulty of isocyanates.

[0003] In the common isocyanate preparation process, the solvent is added in two steps: the first step is to dissolve the raw material polyamine compound. The addition of additional solvent can make the raw material polyamine compound better dispersed 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. The addition of 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] CN1729169A discloses a method for partially or completely separating a mixture containing hydrogen chloride and phosgene, possible solvents, low boilers and inerts generally obtained in the process of preparing isocyanates by reacting amines with phosgene, which comprises firstly carrying out a partial or complete condensation of the phosgene, then carrying out 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 the process solvent with a process solvent. To remove solvent residues, a post-purification can then be carried out, for example by absorption on activated carbon or by other suitable methods.

[0005] CN101062905A discloses a method for producing isocyanate, 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 stages of absorption steps carried out in sequence, 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 isocyanate, which comprises reacting a suitable amine with phosgene, condensing the obtained gas mixture, stripping the obtained liquid phase, returning the residual solvent in liquid form to the reaction stage, and then further purifying the gaseous components in an absorption process. The method further adds a tower stripping component on the basis of CN101062905A, and by introducing energy, hydrogen chloride and phosgene are discharged from the lower part of the tower in gaseous form, and the purified solvent is removed from the bottom of the stripper and can be added to the amine phosgenation reaction as a solvent for 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] In order to reduce the amount of solvent added, isothermal absorption can be used, but the isothermal absorption process requires the formation of a uniform annular liquid film in the absorption tube to improve the absorption efficiency, thereby minimizing the amount of solvent added. Under the condition of keeping the exhaust gas treatment volume unchanged, when the amount of solvent added is too small, the liquid film may be unstable and ruptured, forming a trickle or even a mist flow, which will have an adverse effect on the absorption process and limit the further reduction of the amount of solvent added.

[0009] Therefore, in view of the shortcomings of the existing technology, it is urgently necessary to provide a method that can reduce the usage of the absorption solvent and increase the concentration of the 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 usage of the absorption solvent and achieving an increase in the concentration of the 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 introduced uniformly into the top of the vertical absorption tube, and a liquid film is formed along the inner wall of the vertical absorption tube and moves toward the bottom. The exhaust gas containing phosgene and non-condensable gas is introduced uniformly 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 are in contact at the gas-liquid interface and a substance exchange occurs. 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 where the outer wall of the vertical absorption tube is located, and the refrigerant is used to remove the heat inside the vertical absorption tube.

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

[0015]

[0016] Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, in 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, in m 3 / h;

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

[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 by 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 the corrected gas phase apparent velocity and liquid phase apparent velocity within a specific range, thereby reducing the usage of the absorption solvent 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 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 causing less exhaust gas to enter the vertical absorption tube, causing the exhaust load in other vertical absorption tubes to increase, and the drag effect 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 affected and the effect is poor, in order to ensure that the phosgene content in the non-condensable gas discharged from the top of the device is low enough, it is necessary to add additional solvents or add other tower internals such as trays and fillers for absorption, which leads to an increase in operating costs or fixed investment, and will cause the concentration of the phosgene solution obtained at the bottom of the device to decrease. Therefore, the gas-liquid two-phase apparent velocity needs to be controlled within a reasonable range to improve the absorption effect and reduce the amount of solvent.

[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 flows through the space where the outer wall of the vertical absorption tube is located, and the refrigerant can remove the heat generated in the vertical absorption tube during the absorption process and conducted 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 frozen 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 values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the solvent comprises any one of chlorobenzene, o-dichlorobenzene or diethyl carbonate or a combination of at least two thereof, 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 unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, 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. 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 exhaust gas to solvent is (400-1400):1, for example, 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 for 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, and other unlisted values ​​within the numerical range are also applicable, preferably 3-4 bar.

[0033] The operating temperature of the solvent absorbing 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 unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the diameter of the vertical absorption tube is 20-80 mm, for example, 20 mm, 30 mm, 50 mm, 60 mm or 80 mm, but is not limited to the listed values, and 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, and other unlisted values ​​within the numerical range are also applicable, preferably 50-200 ppm (V / V%).

[0036] Preferably, the mass percentage 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, and other unlisted values ​​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, 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 to move toward the bottom, and 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, wherein 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 thereof; the solvent and the exhaust gas are mixed in the gas The liquid two-phase interface contacts and material exchange occurs, 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; the top of the vertical absorption tube discharges non-condensable gas containing 10-500ppm (V / V%) 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 the heat inside the vertical absorption tube;

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

[0043]

[0044] Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, in 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, in m 3 / h;

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

[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 by 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 modified gas phase apparent velocity and liquid phase apparent velocity within a specific range, thereby reducing the usage of the absorption solvent and achieving an increase in the concentration of the phosgene solution. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[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 specific implementation methods. It should be understood by those skilled in the art that the embodiments are only 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 through commercial channels unless otherwise specified.

[0056] Example 1

[0057] This embodiment provides a method for absorbing phosgene by 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 30mm, and a liquid film is formed along the inner wall of the vertical absorption tube 2 to move toward the bottom, and 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, and 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 a 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, and the refrigerant is 30% ethylene glycol water, which is used to remove the heat inside the vertical absorption tube 2;

[0059] The vertical absorption tubes 2 are arranged in parallel in the phosgene absorption device. The internal structure schematic 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] It has been detected that the hydrogen chloride discharged from the top of the vertical absorption tube 2 contains 184 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom is 86%. This shows that the method provided in this embodiment is used to absorb phosgene, which can improve the absorption effect and thus 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 by using a solvent, the method comprising the following steps:

[0064] The 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 of the vertical absorption tube 2 to move toward the bottom; the 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, and the volume proportion of phosgene in the exhaust gas is 15%; the o-dichlorobenzene contacts the exhaust gas at the gas-liquid two-phase interface and a substance exchange occurs, the feed volume ratio of the exhaust gas to o-dichlorobenzene is 400:1, the operating pressure of o-dichlorobenzene absorbing phosgene is 6 bar, and the operating temperature is 0°C; a refrigerant circulates in the space where the outer wall of the vertical absorption tube 2 is located, and the refrigerant is frozen brine, which is used to remove the heat inside 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] It has been detected that the carbon monoxide discharged from the top of the vertical absorption tube 2 contains 463 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom is 70.2%. This shows that the method provided in this embodiment is used to absorb phosgene, which 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 by 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 of the vertical absorption tube 2 to move 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 contacts the exhaust gas at the gas-liquid interface and a substance exchange occurs, 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 circulates 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 the heat inside 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] It has been detected that the nitrogen discharged from the top of the vertical absorption tube 2 contains 90 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom is 83.2%. This shows that the method provided in this embodiment is used to absorb phosgene, which can improve the absorption effect and thus 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 feed volume ratio of the exhaust gas to chlorobenzene is adjusted to 300:1, and the relevant parameters are adaptively adjusted so that The value of is 0.18, and the rest is the same as in Example 1.

[0076] After testing, the hydrogen chloride discharged from the top of the vertical absorption tube 2 contains 678 ppm (V / V%) of phosgene, and the mass proportion of phosgene in the phosgene solution discharged from the bottom is 35.2%. This shows that when absorbing phosgene using the method provided in this comparative example, 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 feed volume ratio of the exhaust gas to chlorobenzene is adjusted to 1500:1, and the relevant parameters are adaptively adjusted so that The value of is 0.89, and the rest is the same as in Example 1.

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

[0080] In summary, 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 phases entering the vertical absorption tube to operate at a modified gas phase superficial velocity and liquid phase superficial 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 implementation mode 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 are 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 introduced uniformly into the top of the vertical absorption tube, and a liquid film is formed along the inner wall of the vertical absorption tube and moves toward the bottom. The exhaust gas containing phosgene and non-condensable gas is introduced uniformly 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 are in contact at the gas-liquid interface and a substance exchange occurs. 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 where the outer wall of the vertical absorption tube is located, and the refrigerant is used to remove the heat inside the vertical absorption tube. The apparent rate j of the solvent is calculated using equations (1) and (2) respectively: L The apparent velocity of the exhaust gas j G : Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, in 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, in m 3 / h; Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: The apparent velocity of the exhaust gas 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, characterized in that: 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, characterized in that 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 to move toward the bottom, and 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, wherein 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; the solvent contacts the exhaust gas at the gas-liquid interface and a substance exchange occurs, the feed volume ratio of the exhaust gas to the solvent is (400-1400):1, the operating pressure of the solvent absorbing phosgene is 2-6bar, 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 flows through the space where the outer wall of the vertical absorption tube is located, and the refrigerant is used to remove the heat inside the vertical absorption tube; The apparent rate j of the solvent is calculated using equations (1) and (2) respectively: L The apparent velocity of the exhaust gas j G : Where: Q1 is the volume flow rate of the solvent in the vertical absorption tube, in 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, in m 3 / h; Then, the corrected apparent rate of the solvent is calculated using equations (3) and (4) respectively: The apparent velocity of the exhaust gas 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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