CN115925581B - Method for preparing isocyanate - Google Patents
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- CN115925581B CN115925581B CN202110905383.7A CN202110905383A CN115925581B CN 115925581 B CN115925581 B CN 115925581B CN 202110905383 A CN202110905383 A CN 202110905383A CN 115925581 B CN115925581 B CN 115925581B
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Abstract
本发明公开了一种制备异氰酸酯的方法，主要方案包括：在胺类与光气溶液的冷光气化反应中添加异氰酸酯封闭剂，并进一步进行热光气化反应，使异氰酸酯封闭剂与最先形成的异氰酸酯反应，从而与胺类与异氰酸酯生成脲的反应形成竞争，从本质上降低脲的生成；封闭剂与异氰酸酯的反应产物可以在后续产品精制过程中进一步分解为产品异氰酸酯和封闭剂，该封闭剂可以回用。通过本方法制备得到的异氰酸酯具有脲类物质含量低的特点，有利于提高产品品质并降低系统运行成本。The invention discloses a method for preparing isocyanate, and the main scheme includes: adding an isocyanate blocking agent to the cold phosgenation reaction of amines and phosgene solution, and further performing a hot phosgenation reaction, so that the isocyanate blocking agent reacts with the first formed isocyanate, thereby competing with the reaction of amines and isocyanates to form urea, and essentially reducing the formation of urea; the reaction product of the blocking agent and isocyanate can be further decomposed into product isocyanate and blocking agent in the subsequent product refining process, and the blocking agent can be reused. The isocyanate prepared by this method has the characteristics of low content of urea substances, which is conducive to improving product quality and reducing system operation costs.
Description
Technical Field
The invention relates to a preparation method, in particular to a method for preparing isocyanate.
Background
Isocyanate is used as an organic reaction intermediate, and can be further synthesized into materials such as polyisocyanate, polyurethane, polyurea, spandex and the like, so that the isocyanate is widely applied to various industries such as industry, agriculture, construction, automobiles, heat preservation and the like. At present, the mainstream isocyanate synthesis method in industry is a phosgenation method, namely, amine corresponding to a target product is firstly mixed with an inert solvent and then reacts with a phosgene solution to obtain a phosgenation reaction solution, wherein the phosgenation reaction solution contains isocyanate products, the inert solvent, residual phosgene and reaction products of hydrogen chloride, and the phosgene, the hydrogen chloride and the solvent are sequentially removed through a separation procedure in the later stage, so that an isocyanate product is finally obtained.
The core of the method is that the reaction process is divided into a cold stage and a hot stage, and the principle is as follows:
Cold reaction stage:
RNH 2+COCl2 - & gt RNHCOCl (carbamoyl chloride) +HCl
RNH 2+HCl→RNH2 HCl (amino hydrochloride)
Thermal reaction stage:
RNHCOCl→RNCO+HCl
RNH2·HCl+COCl2→RNCO+3HCl
Wherein, the reaction speed is faster in the cold reaction stage and the reaction is complete rapidly, while in the hot reaction stage, the following side reactions are highlighted:
RNH2·HCl→RNH2+HCl
RNH 2 + RNCO → RNHCONHR (Urea)
The presence of urea, a by-product, catalyzes the polymerization of the product, thereby plugging the equipment lines, affecting the isocyanate yield, and requiring strict control of the amount of produced isocyanate. The prior art generally obtains higher product selectivity by greatly excessive phosgene to reduce urea generation, but the greatly excessive phosgene needs to be recycled, hydrogen chloride in the phosgene recycled by a condensation and absorption method cannot be effectively removed, the excessive hydrogen chloride content in the recycled phosgene can lead to the formation of amine hydrochloride in the phosgenation of amine, the phosgenation of the amine hydrochloride needs longer reaction residence time and higher excessive phosgene, the reaction of amine and isocyanate to generate urea is easy to occur, the quality and the product yield of the phosgenation reaction liquid are seriously affected, and the high phosgene excess rate means higher energy consumption for recycling. Therefore, how to better avoid the generation of urea substances as byproducts in the phosgenation reaction process is a key factor for improving the reaction effect and the product quality.
Chinese patent document CN101302174a discloses a method for producing isocyanate, which mentions that reducing the phosgene and isocyanate content in the recycled solvent is advantageous for improving the quality of isocyanate products, and therefore, the recycled solvent is treated before being used for producing the amine-containing solution, and the phosgene and diisocyanate content in the recycled solvent is controlled within a certain range. The patent effectively avoids the influence of impurities in the circulating solvent on the urea content in the reaction process, but does not fundamentally solve the problem that amine substances react with generated isocyanate to generate urea substances in the reaction process.
The Chinese patent document CN104892458A discloses a method for preparing isocyanate by a reactive distillation method, wherein the phosgenation reaction is described in the patent and is carried out in a rectifying tower, excessive phosgene and hydrogen chloride are separated by an external rectifying tower, the method effectively reduces the content of the hydrogen chloride in a circulating phosgene solution, further reduces the generation of amino hydrochloride, reduces the probability of urea substances, but consumes larger steam and cold energy, and hydrogen chloride is difficult to separate from phosgene under high pressure.
It can be seen that in the prior art, for example, the content of impurities in the circulating solvent is reduced, the content of hydrogen chloride in the circulating phosgene solution is reduced, and the urea content in the phosgenation reaction solution can be reduced to a certain extent, but the generation of urea cannot be fundamentally avoided, and the operation is complex and the energy consumption is high. Therefore, aiming at the reaction characteristics of the liquid-phase phosgenation method in the process of preparing isocyanate, development is needed to fundamentally avoid side reactions of amine substances and generated isocyanate to generate urea substances, so that the phosgenation reaction efficiency is improved, the product quality is further improved, and the system operation cost is reduced.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for preparing isocyanate, and the isocyanate prepared by the method has the characteristic of low urea substance content, thereby being beneficial to improving the product quality and reducing the system operation cost. The isocyanates referred to in the present invention may be diisocyanates and/or corresponding polyisocyanates prepared starting from the corresponding amines, in particular diphenylmethane diisocyanate (MDI) and/or polyphenyl polymethylene polyisocyanates (PAPI).
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a process for preparing an isocyanate comprising the steps of:
1) The method comprises the steps of mixing amine, inert solvent and isocyanate sealing agent, adding phosgene solution for cold gasification reaction to obtain gas-liquid-solid three-phase mixture, adding the isocyanate sealing agent in cold gasification stage, reacting with isocyanate formed first in thermal reaction stage, protecting isocyanate, avoiding contact with amine which is not completely reacted and amine formed by side reaction, and thus fundamentally solving the problem of urea substance generation.
2) And in the reaction process, the isocyanate sealing agent reacts with the isocyanate which is generated first rapidly to form competition with the reaction of amine and isocyanate, so that the generation of urea byproducts is reduced.
3) The liquid phase material is sent into a liquid phase refining system for two-stage rectification, the first stage rectification is used for removing low boiling point hydrogen chloride and phosgene to obtain a gas phase material B, and the second stage rectification is used for removing high boiling point solvent and sealing agent in the residual liquid phase to obtain a gas phase material C and isocyanate products.
Further, the gas phase material A, B generally comprises a part of solvent removed together with hydrogen chloride and phosgene, in order to remove the solvent, the gas phase material A, B is condensed and then non-condensable gas is sent to a gas phase absorption system, condensate flows back to the corresponding reactor respectively, the non-condensable gas absorbs phosgene through inert solvent in the gas phase absorption system, the obtained phosgene solution is recycled to the cold light gasification reaction, meanwhile, the produced gas phase hydrogen chloride enters a hydrochloric acid absorption system for post-treatment, and the gas phase material C is cooled and then recycled to the cold light gasification reaction.
The invention relates to a method for preparing isocyanate by a liquid-phase phosgene method, which aims to reduce the generation amount of urea byproducts in the reaction process, and protects NCO groups from reacting with unreacted complete amines by a blocking-deblocking mode, wherein the blocking-deblocking principle is as follows:
the mixing in step 1) according to the invention may be carried out using suitable mixing equipment known in the art, preferably static mixers.
The cold gasification reaction in step 1) according to the present invention may be carried out in a suitable reactor known in the art, preferably a jet reactor.
The thermal phosgenation reaction in step 2) of the present invention can be carried out using suitable reactors known in the art, preferably tank reactors.
The vapor phase absorption system of the present invention may employ any absorption column known in the art, preferably a packed column, a tray column, and more preferably a packed column.
Unless otherwise specified, the operating pressures in the various embodiments of the present invention are all representative pressures.
In a preferred embodiment, the cold gasification reaction conditions are a reaction temperature of 60 to 140 ℃, preferably 70 to 130 ℃, more preferably 75 to 125 ℃, a reaction pressure of 1 to 30barG, preferably 2 to 20barG, more preferably 3 to 15barG.
In a preferred embodiment, the mass ratio of amine to isocyanate blocking agent in the cold gasification reaction is 1 (0.1-2), preferably 1 (0.5-1.5), more preferably 1 (0.8-1);
Preferably, the mass ratio of amine to phosgene solution is 1 (2-8), preferably 1 (3-5), and the phosgene content in the phosgene solution is 50-90%;
Preferably, the mass ratio of amine to inert solvent is 1 (2-6), preferably 1 (2.5-5), more preferably 1 (3-4).
In a preferred embodiment, in step 1), the amine is selected from one or more of the group consisting of diphenylmethane diamine, diaminodiphenylmethane, polymethylene polyphenyl polyamine, diaminotoluene, isophorone diamine, hexamethylene diamine, cyclohexane diamine, p-phenylene diamine, naphthalene diamine, xylylene diamine, cyclohexane dimethylene diamine, tetramethyl-m-xylylene diamine, and dimethyl-phenylene diamine.
The inert solvent is one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, dimethylbenzene, benzene and diethyl isophthalate, preferably one or two of chlorobenzene and dichlorobenzene;
the isocyanate blocking agent in the present invention is preferably selected from the group consisting of active hydrogen compounds, preferably one or more of diethyl malonate, ethyl acetoacetate, acetylacetone, t-butyl methyl malonate, 2, 4-pentanedione, preferably one or both of ethyl acetoacetate and acetylacetone, which can undergo deblocking reaction by temperature increase.
In a preferred embodiment, the thermal phosgenation reaction conditions are a reaction temperature of 110 to 160 ℃, preferably 115 to 150 ℃, more preferably 120 to 140 ℃, a reaction pressure of 2 to 20barG, preferably 2.5 to 15barG, more preferably 3 to 12barG.
In a preferred embodiment, the conditions for removing low boilers in step 3) are a temperature of from 100 to 180 ℃, preferably from 120 to 170 ℃, more preferably from 140 to 160 ℃, and a pressure of from-0.2 barG to 3barG, preferably from-0.1 barG to 2barG, more preferably from 0barG to 0.5barG. The low boilers are in particular hydrogen chloride and phosgene.
In a preferred embodiment, the conditions for removing the high boiling solvent and the blocking agent in step 3) are a temperature of 100-220 ℃, preferably 130-200 ℃, more preferably 150-180 ℃, a pressure of-1 barG to 0barG, preferably-0.9 barG to-0.2 barG, more preferably-0.7 barG to-0.4 barG.
In a preferred embodiment, the gas phase absorption system is operated at a temperature of from-15 ℃ to 15 ℃, preferably from-5 ℃ to 5 ℃, and a pressure of from 0 to 10barG, preferably from 1 to 8barG, more preferably from 3 to 5barG.
In a preferred embodiment, the inert solvent employed in the vapor phase absorption system is one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene and diethyl isophthalate, preferably one or both of chlorobenzene and dichlorobenzene.
In a preferred embodiment, the gas phase absorption system treats the resulting phosgene solution with a mass ratio of phosgene of 50-90%, preferably 60-85%, more preferably 70-80%.
In the isocyanate product prepared by the method, the mass ratio of urea is as low as less than 1%, even less than 0.05%, even less than 0.01%, compared with the prior art, the content of urea substances is effectively reduced, the method has outstanding product advantages, the phosgenation reaction effect can be improved, the equipment scaling and blocking risks are reduced, the quality of photochemical reaction liquid, the product quality and the phosgenation yield are improved, and the stable operation period of a production device is prolonged.
The isocyanate blocking agent and the amine compete for the-NCO group, so that the protection of the-NCO group is realized, the urea is prevented from being generated by the reaction of the isocyanate blocking agent and the amine, and the content of urea byproducts in the thermal reaction stage is greatly reduced, thereby improving the phosgenation reaction quality and the product yield and quality. In addition, the isocyanate sealing agent can be unsealed and recycled through unsealing and removing of the sealing agent, the process is simple, the operation is convenient, the energy consumption is saved, the cost is low, the efficiency is high, and the environment is friendly.
Drawings
FIG. 1 is an overall process flow diagram of the present invention.
Wherein, 1, a static mixer, 2, a jet reactor, 3, a thermal phosgenation reactor, 4, a dephosgene tower, 5, a phosgene absorption tower and 6, a solvent and sealing agent removal tower.
Detailed Description
The invention is further illustrated by the drawings and by the following examples, which are given solely as illustrations of the invention and do not limit the scope of the invention.
The detection method comprises the following steps:
the NCO content of isocyanate is measured by using a GB/T2009-3-2009 method;
The urea content analysis adopts a liquid chromatography method, a liquid chromatography instrument is Shimadzu LC-20A, an SIL-20A autosampler, a CT0-20A column incubator, an SPD-M20A detector, and a chromatographic column is ODSP (250 x 4.6 mm) (Inertsil) and 5 μm.
[ Example 1]
According to the process flow in FIG. 1, 10t/h of MDA (diphenylmethane diamine) with the pressure of 20barG, 20t/h of chlorobenzene with the pressure of 20barG and 3t/h of acetylacetone with the pressure of 20barG are mixed in a static mixer 1 and then are mixed with a phosgene solution (phosgene content 60 wt%) with the pressure of 20barG with the pressure of 25t/h, and the mixture is fed into a jet reactor 2 for cold light gasification reaction under the conditions of 80 ℃ and 3barG, and then fed into a hot light gasification reactor 3 for hot light gasification reaction under the conditions of 3barG and 120 ℃ for hot light gasification reaction. The gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 for absorption and recycling (condensate flows back to a thermal phosgenation reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 for removing phosgene and hydrogen chloride, the temperature of the tower bottom of the phosgene removal tower 4 is 130 ℃, the tower top pressure is 0.2barG, the gas phase at the tower top of the phosgene removal tower 4 is firstly condensed and then is pressurized and sent to the tower bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is led into the tower top of the phosgene absorption tower 5 to be in countercurrent contact with gas phase phosgene, the temperature of the tower bottom of the phosgene absorption tower 5 is-5 ℃, and the tower top pressure is 3barG. The liquid phase after the dephosgene enters a solvent and sealing agent removing tower 6 for sealing agent deblocking and solvent and sealing agent removing, the tower bottom temperature is 145 ℃, the tower top pressure is-0.9 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.45% and a crude MDI NCO content of 32.20% and a crude MDI product inlet pot filter cleaning cycle of 200d.
[ Example 2]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 25t/h of chlorobenzene with the pressure of 20barG and 8t/h of acetylacetone with the pressure of 20barG are mixed in a static mixer 1, then are mixed with 35t/h of phosgene solution with the pressure of 20barG (the phosgene content is 70 wt%) and enter a jet reactor 2 to carry out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, the cold light gasification reaction condition is that the temperature is 100 ℃, the pressure is 10barG, then enter a hot light gasification reactor 3 to carry out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG, the temperature is 130 ℃, the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 to be absorbed and recycled (condensate flows back to the hot light gasification reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 to remove phosgene and hydrogen chloride, the temperature of the tower kettle of the phosgene removal tower 4 is 140 ℃, and the tower top pressure is 0.2barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-2 ℃, and the pressure of the tower top is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 180 ℃, the tower top pressure is-0.6 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.09% and an NCO content of 32.54% in the crude MDI product and a filter cleaning cycle of 300d in the inlet tank.
[ Example 3]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 35t/h of chlorobenzene with the pressure of 20barG and 15t/h of ethyl acetoacetate with the pressure of 20barG are mixed in a static mixer 1, then mixed with 50t/h of phosgene solution with the pressure of 20barG (the phosgene content is 60 wt%) and enter a jet reactor 2 to carry out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, the cold light gasification reaction condition is that the temperature is 120 ℃ and the pressure is 25barG, then enter a hot light gasification reactor 3 to carry out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG and the temperature is 140 ℃ and the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 to be absorbed and recycled (condensate flows back to the hot light gasification reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 to remove phosgene and hydrogen chloride, the temperature of the tower 4 is 140 ℃ and the tower top pressure is 1.5barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-10 ℃, and the pressure of the tower top is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 140 ℃, the tower top pressure is-0.8 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.08% and an NCO content of 32.62% in the crude MDI product and a filter cleaning cycle of 320d in the inlet tank.
[ Example 4]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 50t/h of o-dichlorobenzene with the pressure of 20barG and 4t/h of ethyl acetoacetate with the pressure of 20barG are mixed in a static mixer 1, then are mixed with a phosgene solution (the phosgene content is 60 wt%) with the pressure of 20barG with the pressure of 60t/h, enter a jet reactor 2 for carrying out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, the cold light gasification reaction condition is that the temperature is 85 ℃, the pressure is 4barG, then enter a hot light gasification reactor 3 for carrying out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG, the temperature is 160 ℃, the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 for absorption and recycling (condensate flows back to the hot light gasification reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 for removing phosgene and hydrogen chloride, the temperature of the tower kettle of the phosgene removal tower 4 is 140 ℃, and the tower top pressure is 0.5barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), o-dichlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, a phosgene solution is produced by absorption, the temperature of the bottom of the phosgene absorption tower 5 is-10 ℃, and the pressure of the top of the phosgene absorption tower is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 150 ℃, the tower top pressure is-0.8 barG, and the tower bottom solution is collected to obtain a crude TDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.18% and a crude TDI NCO content of 32.36% and a crude MDI product inlet pot filter cleaning cycle of 260d.
[ Example 5]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 35t/h of chlorobenzene with the pressure of 20barG and 15t/h of diethyl malonate with the pressure of 20barG are mixed in a static mixer 1, then mixed with 50t/h of phosgene solution with the pressure of 20barG (the phosgene content is 60 wt%) and enter a jet reactor 2 to carry out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, the cold light gasification reaction condition is that the temperature is 120 ℃ and the pressure is 25barG, then enter a hot light gasification reactor 3 to carry out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG and the temperature is 140 ℃ and the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 to be absorbed and recycled (condensate flows back to the hot light gasification reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 to remove phosgene and hydrogen chloride, the temperature of the tower 4 is 140 ℃ and the tower top pressure is 1.5barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-10 ℃, and the pressure of the tower top is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 180 ℃, the tower top pressure is-0.5 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.20% and a crude MDI NCO content of 32.30% and a crude MDI product inlet pot filter cleaning cycle of 250d.
[ Example 6]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 35t/h of chlorobenzene with the pressure of 20barG and 15t/h of tert-butyl methyl malonate with the pressure of 20barG are mixed in a static mixer 1, then 50t/h of phosgene solution with the pressure of 20barG (the phosgene content is 60 wt%) is added into a jet reactor 2 to carry out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, the cold light gasification reaction condition is that the temperature is 120 ℃ and the pressure is 25barG, then the gas enters a hot light gasification reactor 3 to carry out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG, the temperature is 140 ℃, the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 to be absorbed and recycled (condensate flows back to the hot light gasification reactor 3), the liquid phase obtained by the reaction enters a phosgene removal tower 4 to remove phosgene and hydrogen chloride, the temperature of the tower kettle of the phosgene removal tower 4 is 140 ℃, and the tower top pressure is 1.5barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-10 ℃, and the pressure of the tower top is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 160 ℃, the tower top pressure is-0.8 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.12% and a crude MDI NCO content of 32.42% and a crude MDI product inlet pot filter cleaning cycle of 285d.
[ Example 7]
10T/h of MDA (diphenyl methane diamine) with the pressure of 20barG, 35t/h of chlorobenzene with the pressure of 20barG and 15t/h of 2, 4-pentanedione with the pressure of 20barG are mixed in a static mixer 1 and then enter a jet reactor 2 to carry out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixture, wherein the cold light gasification reaction condition is that the temperature is 120 ℃ and the pressure is 25barG, then enter a hot light gasification reactor 3 to carry out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG, the temperature is 140 ℃, the gas phase generated by the reaction is condensed and then enters a phosgene absorption tower 5 to be absorbed and recycled (condensate flows back to the hot light gasification reactor 3), the phosgene and hydrogen chloride are removed from the liquid phase obtained by the reaction enters a phosgene removal tower 4, the temperature of the tower top of the tower 4 is 140 ℃, and the pressure of the tower top is 1.5barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-10 ℃, and the pressure of the tower top is 3barG. And (3) the liquid phase after the phosgene removal enters a solvent and sealant removal tower 6 for sealant deblocking and solvent and sealant removal, the tower bottom temperature is 150 ℃, the tower top pressure is-0.6 barG, and the tower bottom solution is collected to obtain a crude MDI product. The procedure is as in this example, the reaction mixture having a urea content of 0.34% and a crude MDI NCO content of 32.26% and a crude MDI product inlet pot filter cleaning cycle of 235d.
Comparative example 1 As compared with example 2, no acetylacetone was added only at the time of feeding
Mixing 10t/h of MDA (diphenyl methane diamine) with the pressure of 20barG with 25t/h of chlorobenzene with the pressure of 20barG in a static mixer 1, mixing with a phosgene solution (the phosgene content is 70 wt%) with the pressure of 20barG at 35t/h, entering a jet reactor 2 for carrying out cold light gasification reaction to obtain a gas-liquid-solid three-phase mixed material, wherein the cold light gasification reaction condition is 100 ℃ and the pressure is 10barG, then entering a hot light gasification reactor 3 for carrying out hot light gasification reaction, the pressure of the hot light gasification reactor 3 is 3barG and the temperature is 130 ℃, condensing a gas phase generated by the reaction, then entering a phosgene absorption tower 5 for absorption recycling (condensate flows back to the hot light gasification reactor 3), removing phosgene and hydrogen chloride in a liquid phase obtained by the reaction, entering a phosgene removal tower 4, wherein the tower kettle temperature of the phosgene removal tower is 140 ℃, and the tower top pressure is 0.2barG. The gas phase at the top of the phosgene removal tower 4 is condensed and then pressurized and sent to the bottom of the phosgene absorption tower 5 (condensate flows back to the phosgene removal tower 4), chlorobenzene is introduced into the top of the phosgene absorption tower 5 and is in countercurrent contact with gas phase phosgene, the gas phase is absorbed to generate phosgene solution, the temperature of the tower bottom of the phosgene absorption tower 5 is-2 ℃, and the pressure of the tower top is 3barG. The liquid phase after the dephosgene enters a solvent removal tower for removing the solvent, the temperature of the tower bottom is 180 ℃, the pressure at the tower top is-0.6 barG, and the solution at the tower bottom is collected to obtain a crude MDI product. Operating according to this comparative example, the reaction mixture had a urea content of 1.25% and a crude MDI NCO content of 31.83% and a crude MDI product inlet pot filter cleaning cycle of 10d.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and additions may be made to those skilled in the art without departing from the method of the present invention, which modifications and additions are also to be considered as within the scope of the present invention.
Claims (22)
1. A process for preparing isocyanates, comprising the steps of:
1) Mixing amine, inert solvent and isocyanate sealing agent, adding phosgene solution for cold light gasification reaction to obtain gas-liquid-solid three-phase mixture;
2) Carrying out a thermal phosgenation reaction on the mixed material under a thermal phosgenation reaction condition to obtain a liquid phase material containing isocyanate and a gas phase material A containing hydrogen chloride and phosgene;
3) The liquid phase material is sent into a liquid phase refining system for two-stage rectification, wherein the first-stage rectification is used for removing low-boiling hydrogen chloride and phosgene to obtain a gas phase material B, and the second-stage rectification is used for removing high-boiling solvent and sealing agent in a residual liquid phase to obtain a gas phase material C and isocyanate products;
the isocyanate blocking agent is one or more of diethyl malonate, ethyl acetoacetate, acetylacetone, tert-butyl methyl malonate and 2, 4-pentanedione.
2. The method for preparing isocyanate according to claim 1, wherein non-condensable gas generated by condensing gas phase material A, B is sent to a gas phase absorption system, phosgene is absorbed by inert solvent, the obtained phosgene solution is recycled to cold light gasification reaction, and meanwhile produced gas phase hydrogen chloride enters a hydrochloric acid absorption system for post treatment, and gas phase material C is recycled to cold light gasification reaction after being cooled.
3. The process for preparing isocyanates according to claim 1, wherein the cold gasification reaction conditions are a reaction temperature of from 60 to 140℃and a reaction pressure of from 1 to 30barG.
4. A process for preparing isocyanates according to claim 3, wherein the mass ratio of amine to isocyanate blocking agent in the phosgenation is 1 (0.1-2).
5. The process for preparing isocyanates according to claim 4, wherein the mass ratio of amine to isocyanate blocking agent in the phosgenation is 1 (0.5-1.5).
6. The process for preparing isocyanates according to claim 5, wherein the mass ratio of amine to isocyanate blocking agent in the phosgenation is 1 (0.8-1).
7. The method for producing isocyanates according to claim 3, wherein the mass ratio of amine to phosgene solution is 1 (2-8), wherein the phosgene content of the phosgene solution is 50-90%.
8. The method for preparing isocyanate according to claim 7, wherein the mass ratio of amine to phosgene solution is 1 (3-5).
9. A process for preparing isocyanates according to claim 3, wherein the mass ratio of amine to inert solvent is from 1 (2) to 6.
10. The process for preparing isocyanates according to claim 9, wherein the mass ratio of amine to inert solvent is 1 (2.5-5).
11. The method for preparing isocyanate according to claim 10, wherein the mass ratio of amine to inert solvent is 1 (3-4).
12. The process for preparing isocyanates according to claim 3, wherein in step 1), said amine is selected from one or more of the group consisting of diphenylmethane diamine, diaminodiphenylmethane, polymethylene polyphenyl polyamines, diaminotoluene, isophorone diamine, hexamethylene diamine, cyclohexane diamine, p-phenylene diamine, naphthalene diamine, xylylene diamine, cyclohexane dimethylene diamine, tetramethyl m-xylylene diamine and dimethylbiphenyl diamine;
The inert solvent is one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, dimethylbenzene, benzene and diethyl isophthalate.
13. The method for producing an isocyanate according to claim 12, wherein the inert solvent is one or both of chlorobenzene and dichlorobenzene.
14. The process for preparing isocyanates according to any of claims 1 to 13, wherein the thermal phosgenation reaction conditions are a reaction temperature of from 110 to 160 ℃ and a reaction pressure of from 2 to 20barG.
15. The process for preparing isocyanates according to claim 14, wherein the conditions for removing low boilers in step 3) are a temperature of 100 to 180 ℃ and a pressure of-0.2 barG to 3barG.
16. The process for preparing isocyanates according to claim 14, wherein the conditions for removing the high boiling solvents and blocking agents in step 3) are a temperature of 100-220 ℃ and a pressure of-1 barG to 0barG.
17. The process for preparing isocyanates according to claim 16, wherein the conditions for removing the high boiling solvents and blocking agents in step 3) are a temperature of 130 to 200 ℃ and a pressure of-0.9 barG to-0.2 barG.
18. The process for preparing isocyanates according to claim 16, wherein the conditions for removing the high boiling solvents and blocking agents in step 3) are a temperature of 150 to 180 ℃ and a pressure of-0.7 barG to-0.4 barG.
19. The process for preparing isocyanates according to claim 2, wherein the operating conditions of said vapor phase absorption system are a temperature of from-15 ℃ to 15 ℃ and a pressure of from 0 to 10barG.
20. The method for producing isocyanate according to claim 2, wherein the inert solvent used in the gas phase absorption system is one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene and diethyl isophthalate.
21. The method for producing isocyanates according to claim 20, wherein said inert solvent used in said vapor phase absorption system is one or both of chlorobenzene and dichlorobenzene.
22. The method for producing isocyanates according to claim 2, wherein the mass ratio of phosgene in the phosgene solution obtained by the gas phase absorption system treatment is 50-90%.
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| CN101072806A (en) * | 2004-09-03 | 2007-11-14 | 陶氏环球技术公司 | Blocked isocyanates and their use in coating compositions |
| CN108147979A (en) * | 2017-12-25 | 2018-06-12 | 万华化学集团股份有限公司 | A kind of method for preparing methyl diphenylene diisocyanate and/or polyphenyl polymethylene polyisocyanates |
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| CN101072806A (en) * | 2004-09-03 | 2007-11-14 | 陶氏环球技术公司 | Blocked isocyanates and their use in coating compositions |
| CN108147979A (en) * | 2017-12-25 | 2018-06-12 | 万华化学集团股份有限公司 | A kind of method for preparing methyl diphenylene diisocyanate and/or polyphenyl polymethylene polyisocyanates |
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