Preparation method of polyisocyanate

Abstract

The invention provides a preparation method of polyisocyanate. The preparation method comprises the following steps: S1, feeding a polyamine solution and a phosgene solution into a first reactor, and carrying out phosgenation reaction to obtain a first reactant flow; s2, the first reactor outlet material flow is sent to a second reactor to be continuously subjected to phosgenation reaction, and a second reactant flow is obtained; s3, conveying an outlet material flow of the second reactor to a third reactor for further phosgenation reaction to obtain a third reactant flow; S4, carrying out phosgene removal and HCl steam stripping treatment on the outlet material flow of the third reactor to obtain a fourth reactant flow; and S5, carrying out desolventizing treatment on the fourth reactant flow to obtain a crude polyisocyanate product. According to the preparation method, the reaction yield of amine and phosgene can be increased, the NCO content of the product is further increased, and the application performance of the product is improved.

Description

Technical Field

[0001] The invention belongs to the field of isocyanate production, and particularly relates to a method for preparing polyisocyanate by reacting amine and phosgene in a liquid phase. Background Art

[0002] Polyisocyanate is one of the important raw materials for the production of polyurethane, and is mainly used in home appliances, cold storage, containers, building insulation materials and other fields. At present, the production of polyisocyanate mainly adopts the liquid phase phosgenation method, which is to mix the logistics containing polyamine and inert solvent with the logistics containing phosgene and inert solvent, and react them in the liquid phase, and then go through the steps of dephosgene, desolvation and separation and refining to obtain the corresponding isocyanate product.

[0003] In the process of generating polyisocyanates, after the mixture of polyamines and phosgene-containing logistics, carbamoyl chloride will be generated first and HCl will be released. HCl will react with amines to generate amine hydrochloride, of which amine hydrochloride is an undesirable product. On the one hand, carbamoyl chloride can be decomposed to generate isocyanate product by heating, while amine hydrochloride needs to react with phosgene to generate carbamoyl chloride first. In addition, hydrochloride is almost insoluble in solvents, so it will form fixed particles that precipitate in the solution, which is not conducive to its further reaction conversion. Unreacted amine hydrochloride will react with isocyanate to generate urea and further reaction products, resulting in loss of yield. At the same time, urea substances have strong viscosity and are easily deposited and attached to equipment and pipelines, causing system blockage, which is not conducive to the long-term stable operation of the device.

[0004] It is well known in the industry that good mixing helps improve the reaction and increase the yield, because when the phosgene concentration is too low, the isocyanate formed will react with excess amine to obtain urea or other unwanted high-viscosity solid byproducts. For this reason, rapid mixing and a short residence time in the reaction chamber are required. For example, patent EP322647 strengthens mixing by increasing the material flow rate of the mixer, but increasing the flow rate will limit the equipment throughput and increase the risk of blockage; patent CN102471071B discloses a structure of an amine and phosgene mixer, adding amine through a port coaxially arranged with the mixing chamber, and adding phosgene through at least two feed ports arranged at right angles to the axis of the mixing chamber, and ensuring that the average residence time of the mixture in the mixing chamber does not exceed 18.5ms, which can reduce urea generation and increase yield. However, the improvement of the reaction by mixing is not unlimited. When the mixing effect reaches a certain level, the effect of continued optimization on the reaction effect is very small, and it will bring other adverse effects, such as easy blockage of the equipment.

[0005] In addition, the reaction yield can be improved and the content of byproduct urea can be reduced by optimizing some reaction conditions. CN116034102A discloses that the amount of amine hydrochloride generated by the reaction can be controlled by adjusting the ratio of amine to phosgene, adjusting the amount of solvent mixed with amine, adjusting the content of HCl in the phosgene solution, etc., thereby improving the reaction quality. Patent CN111170890B discloses that the reaction effect can be improved by controlling the temperature of the reaction amine solution and the phosgene solution within a certain range, and then controlling the reaction mixer outlet temperature within a certain range. However, by increasing the ratio of phosgene to amine, increasing the amount of solvent mixed with amine, controlling the HCl content in the mixed phosgene solution, controlling the temperature of the amine solution and the phosgene solution, etc., it is inevitable to increase the operating cost, increase the equipment investment, or increase the circulation amount of the highly toxic substance phosgene in the system, etc., which are all disadvantageous. Summary of the invention

[0006] In order to overcome at least one defect of the above-mentioned prior art, the present invention provides a method for preparing polyisocyanate, which can further improve the reaction yield by improving the reaction of polyamine and phosgene in the liquid phase.

[0007] To achieve the above object, the present invention provides a method for preparing polyisocyanate, which comprises the following steps:

[0008] S1: sending the polyamine solution and the phosgene solution to the first reactor for phosgenation reaction to obtain a first reactant stream;

[0009] S2: sending the outlet stream of the first reactor to the second reactor to continue phosgenation reaction to obtain a second reaction stream;

[0010] S3: Send the outlet stream of the second reactor to the third reactor for further phosgenation reaction to obtain the third reaction stream

[0011] S4: removing phosgene and HCl from the outlet stream of the third reactor to obtain a fourth reaction stream;

[0012] S5: performing a desolventizing treatment on the fourth reaction stream to obtain a crude polyisocyanate product;

[0013] The parameters in step S2 satisfy the following relationship:

[0014]

[0015] Where: T represents the reaction temperature of the phosgenation reaction in the second reactor, in °C,

[0016] t represents the residence time of the phosgenation reaction in the second reactor, in seconds,

[0017] P represents the pressure of the phosgenation reaction in the second reactor, in bar.

[0018] C A Represents the concentration of amine hydrochloride in the second reactant stream, in mol / L.

[0019] It should be noted that the above formula (1) only represents the numerical relationship between the above parameters T, t, CA, and P, and there is no corresponding relationship between the units on both sides of the formula. The parameters in step S2 satisfying the above relationship can improve the reaction yield, make the NCO content of the final product crude isocyanate higher, and reduce scaling and clogging in the system.

[0020] In the present invention, the polyisocyanate is selected from diphenylmethylene diisocyanate (MDI), polyphenylmethylene polyisocyanate (PMDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI) or a combination of two or more thereof, preferably diphenylmethylene diisocyanate (MDI), polyphenylmethylene polyisocyanate (PMDI), toluene diisocyanate (TDI) or a combination of two or more thereof.

[0021] The inventor has found that in the process of synthesizing polyisocyanates by liquid phase phosgenation, the amount of amine hydrochloride generated is mainly affected by the concentration of polyamines. The higher the concentration of polyamines, the greater the proportion of amine hydrochloride generation, the lower the yield of the final reaction, and the more serious the blockage of the system. However, reducing the concentration of polyamines will lead to increased operating energy consumption and increased equipment size under the same operating load, and the corresponding equipment investment will also increase. These are all unfavorable, so how to quickly realize hydrochloride conversion and improve reaction quality under a higher amine hydrochloride generation ratio is crucial. The inventor has found through experiments that the conversion rate of amine hydrochloride is mainly related to the temperature, pressure, residence time in the reactor and the concentration of hydrochloride and phosgene in the liquid phase. It is also found that if some parameters in the reactor in a specific process such as temperature (not too high) and pressure (not too low) are controlled, the improvement of the reaction yield will also have a certain impact, because the decomposition rate of acyl chloride under high temperature and low pressure will also increase rapidly, and the isocyanate formed by decomposition will react with amine hydrochloride to form urea.

[0022] On this basis, the inventors further studied and found that by screening specific related reaction parameters through the reaction kinetics of generating amine hydrochloride, and establishing a fitting formula based on the relationship between the parameters, when these specific parameters meet the fitting formula in the patent, the reaction yield and product quality can be further improved.

[0023] Therefore, to achieve the above purpose, in the preparation method of the present invention, the relevant conditions of the reaction are defined in step S2. For the corresponding process operations and process conditions in other steps of the preparation method of the present invention, and the devices used therein, all can be selected and carried out using the corresponding conventional methods in the art, and there is no particular limitation thereto. The technicians can optimize the processes known in the prior art according to actual needs, and specifically, for example, the conditions listed in the following embodiments of the present invention can be used.

[0024] In one embodiment, the polyamine in step S1 is selected from diaminodiphenylmethane (MDA), polyphenyl polymethylene polyamines (such as diphenylmethane series diamines and polyamines, DAM), diaminotoluene (TDA), hexamethylenediamine (HDA), isophoronediamine (IPDA), xylene diamine (XDA) or a combination of two or more thereof, preferably a mixture of diaminodiphenylmethane, polyphenyl polymethylene polyamines (DAM), diaminotoluene (TDA) or a combination of two or more thereof.

[0025] In one embodiment, the solvent in the polyamine solution and the phosgene solution in step S1 is selected from an inert solvent such as benzene and its substituents, carbonate compounds, alkanes, cycloalkanes or a combination of two or more thereof, preferably chlorobenzene, dichlorobenzene, diethyl carbonate, toluene or a combination of two or more thereof, more preferably chlorobenzene;

[0026] Preferably, the feeding of the polyamine solution and the phosgene solution controls the mass ratio of polyamine to phosgene to be 1:(1.1-5), such as 1:1.1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or a range between any two thereof;

[0027] Preferably, in the polyamine solution, the mass ratio of the polyamine to the solvent is 1:(1.1-5), for example, 1:1.1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or a range between any two thereof;

[0028] Preferably, in the phosgene solution, the phosgene concentration is 50-90wt%, for example, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or any range therebetween.

[0029] In one embodiment, in step S1, the first reactor is selected from a static reactor or a dynamic reactor, preferably a dynamic reactor.

[0030] In one embodiment, the conditions for carrying out the phosgenation reaction in the first reactor in step S1 include: a reaction pressure of 5-40 bar, such as 5 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar or a range between any two thereof, preferably 10-30 bar; a reaction temperature of 60-120°C, such as 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or a range between any two thereof;

[0031] Preferably, the reaction residence time is 0.001-0.5 s, for example 0.001 s, 0.01 s, 0.05 s, 0.1 s, 0.15 s, 0.2 s, 0.25 s, 0.3 s, 0.35 s, 0.4 s, 0.45 s, 0.5 s or any range therebetween.

[0032] In one embodiment, the concentration of amine hydrochloride in the first reactant stream in step S1 is 0.1-0.6 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L or a range between any two thereof;

[0033] In one embodiment, the second reactor in step S2 is selected from a tubular reactor or a tank reactor, preferably a tubular reactor.

[0034] In one embodiment, the conditions for continuing the phosgenation reaction in the second reactor in step S2 include the following parameters: T, t, C A , P is further limited to the preferred range of:

[0035] The reaction temperature T of the phosgenation reaction in the second reactor is 85-130°C, for example, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C or any range therebetween, preferably 100-120°C; the temperature in the second reactor can be controlled by adjusting the temperature of the solvent mixed with the amine, preferably the solvent temperature is 45-120°C;

[0036] The pressure P of the phosgenation reaction in the second reactor is 5-25 bar, for example, 5 bar, 8 bar, 10 bar, 12 bar, 15 bar, 18 bar, 20 bar, 23 bar, 25 bar or any range therebetween, preferably 10-15 bar;

[0037] The residence time t of the phosgenation reaction in the second reactor is 2-100 s, for example, 2 s, 5 s, 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s or any range therebetween, preferably 5-30 s;

[0038] The concentration of amine hydrochloride in the second reactant stream is C A 0.001-0.05 mol / L, for example 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L or any range therebetween, preferably 0.003-0.01 mol / L;

[0039] Preferably, the concentration of phosgene in the second reactant stream is 0.5-4 mol / L, for example 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L or any range therebetween, preferably 1.5-3 mol / L.

[0040] In one embodiment, the third reactor in step S3 is selected from a kettle reactor or a tower reactor.

[0041] In one embodiment, a phosgenation reaction is further carried out in the third reactor of step S3, wherein a decomposition reaction of the acyl chloride is carried out simultaneously, and the reaction conditions include: a reaction temperature of 90-150° C., such as 90° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150° C. or a range between any two thereof, and a reaction pressure of 2-10 bar, such as 2 bar, 4 bar, 6 bar, 8 bar, 10 bar or a range between any two thereof;

[0042] Preferably, the reaction residence time is 10-200 min, for example, 10 min, 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 200 min or any range therebetween.

[0043] In the present invention, after the phosgenation reaction is completed, the process further includes phosgene removal and HCl stripping treatment in step S4, and solvent removal treatment in step S5, which are conventional operations in the art.

[0044] In some embodiments, for reference, the conditions for phosgene removal treatment include: temperature of 100-180°C, operating pressure of 1-5 bar. The treatment conditions of the HCl stripping tower include: temperature of 130-210°C, operating pressure of 1-5 bar. Phosgene removal and hydrogen chloride stripping can also be combined for treatment, and phosgene removal and hydrogen chloride stripping can be achieved in the same device, which is a common design in the art and will not be described in detail. The conditions for desolventization treatment include: temperature of 100-230°C, pressure of 20-50kpa.

[0045] In the present invention, the pressure involved refers to absolute pressure unless otherwise specified.

[0046] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0047] The present invention establishes a fitting formula by screening relevant reaction parameters, optimizes the reaction process to obtain a phosgenation reaction liquid, and then adopts conventional methods to remove phosgene, strip hydrogen chloride and remove solvents from the reaction liquid to obtain a crude polyisocyanate product. The obtained polyisocyanate product has a higher NCO content and reduces blockage during the equipment operation cycle.

[0048] In the MDI production of one embodiment of the present invention, the NCO content of the crude polyisocyanate product produced by the above method is 32.00-32.60wt%, which improves the yield of the product, reduces the generation of urea by-products, and reduces system blockage caused by urea. DETAILED DESCRIPTION

[0049] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the rights claimed by the present invention.

[0050] Unless otherwise specified, the reagents, materials, instruments and analytical methods used in the following examples are conventional reagents, conventional materials, conventional instruments and conventional analytical methods in the art, which can be obtained commercially, and the reagents involved can also be synthesized by conventional methods in the art. The experimental methods in the following examples that do not indicate specific conditions are all conventional operating conditions.

[0051] Raw material information:

[0052] Diphenylmethane series diamines and polyamines (DAM): Wanhua Chemical (Ningbo) Co., Ltd., purity >99.99%.

[0053] Preparation method of DAM: Aniline is reacted with hydrochloric acid at 60°C and 1 bar to generate aniline hydrochloride, which is then reacted with formaldehyde to obtain a transfer liquid through a condensation transfer process, and polyamines are obtained after neutralization and water washing, and DAM is obtained after distillation and stripping.

[0054] Diaminodiphenylmethane (MDA): Wanhua Chemical Group Co., Ltd., purity >99.99%.

[0055] Chlorobenzene: Wanhua Chemical (Ningbo) Co., Ltd., purity >99.99%.

[0056] Phosgene: Wanhua Chemical (Ningbo) Co., Ltd., purity>95.0%.

[0057] Analytical methods:

[0058] NCO content: It is determined by the national standard titration analysis method, which is mainly based on the reaction between isocyanate group and di-n-butylamine. The NCO content is calculated by titrating the remaining di-n-butylamine.

[0059] Urea content: Determined by liquid chromatography after the reaction solution is derivatized with methanol.

[0060] Example 1

[0061] Diphenylmethane series diamines and polyamines (DAM) are mixed with chlorobenzene in a mass ratio of 1:2.0 to obtain a polyamine solution, and a phosgene chlorobenzene solution with a phosgene concentration of 70wt% and a polyamine solution (the mass ratio of DAM to phosgene is controlled to be 1:2.5) are fed into a dynamic reactor with a reaction pressure of 30bar, a reaction temperature of 110°C, a residence time of 0.1S, and a first reaction stream is obtained at an outlet, and the amine hydrochloride concentration in the first reaction stream is 0.4mol / L.

[0062] The first reaction stream is sent into a tubular reactor, the reaction pressure P in the tubular reactor is 25 bar, the reaction temperature T is 120° C., the residence time t is 20 s, and the second reaction stream is obtained at the outlet, and the amine hydrochloride concentration C A is 0.005 mol / L, the liquid phase phosgene concentration C B 2.5 mol / L;

[0063] The calculated value according to formula (1) is 16.51.

[0064] The second reaction stream was continuously sent to a tank reactor with a temperature of 140° C., a pressure of 5 bar, and a residence time of 60 min. A third reaction stream was obtained at the outlet. The urea content was analyzed to be 0.5 wt % and the polyisocyanate yield was 99.97%.

[0065] The third reactant stream is subjected to phosgene removal and hydrogen chloride stripping heat treatment at 2 bar and 170°C, the treated reaction liquid is subjected to dechlorobenzene treatment at 40 kPa and 200°C, the dechlorobenzeneed mixed liquid is sent to a nitrogen stripping tower for treatment at 40 kPa and 195°C, the mass ratio of nitrogen to the reaction liquid after solvent removal is controlled to be 0.04, and crude polyisocyanate can be obtained in the bottom of the tower, and the NCO content is analyzed to be 32.5%.

[0066] Example 2

[0067] Diaminodiphenylmethane (MDA) and chlorobenzene are mixed in a mass ratio of 1:2.5 to obtain a polyamine solution, and a phosgene chlorobenzene solution with a phosgene concentration of 60wt% and a polyamine solution (the mass ratio of DAM and phosgene is controlled to be 1:3.0) are fed into a dynamic reactor with a reaction pressure of 9 bar, a reaction temperature of 85°C, a residence time of 0.2S, and a first reaction stream is obtained at the outlet. The amine hydrochloride concentration in the first reaction stream is 0.3mol / L.

[0068] The first reaction stream is sent into a tubular reactor, the reaction pressure P in the tubular reactor is 7 bar, the reaction temperature T is 110° C., the residence time t is 7 s, and the second reaction stream is obtained at the outlet, and the amine hydrochloride concentration C A is 0.03 mol / L, and the liquid phase phosgene concentration C B 3.5 mol / L;

[0069] The calculated value according to formula (1) is 1.46.

[0070] The second reaction stream was continuously sent to a tank reactor with a temperature of 130° C., a pressure of 4 bar, and a residence time of 90 min. A third reaction stream was obtained at the outlet. The urea content was analyzed to be 0.8 wt % and the polyisocyanate yield was 99.85%.

[0071] The third reactant stream is subjected to phosgene removal and hydrogen chloride stripping heat treatment at 2.5 bar and 180° C., the treated reaction liquid is subjected to dechlorobenzene treatment at 30 kPa and 195° C., the dechlorobenzeneed mixed liquid is sent to a nitrogen stripping tower for treatment at 40 kPa and 195° C., the mass ratio of nitrogen to the reaction liquid after solvent removal is controlled to be 0.04, and crude polyisocyanate can be obtained in the bottom of the tower, and the NCO content is analyzed to be 32.05%.

[0072] Example 3

[0073] Diphenylmethane series diamines and polyamines (DAM) are mixed with chlorobenzene in a mass ratio of 1:3.0 to obtain a polyamine solution, and a phosgene chlorobenzene solution with a phosgene concentration of 80wt% and a polyamine solution (the mass ratio of DAM to phosgene is controlled to be 1:3.0) are fed into a dynamic reactor with a reaction pressure of 20bar, a reaction temperature of 100°C, a residence time of 0.4S, and a first reaction stream is obtained at an outlet, and the amine hydrochloride concentration in the first reaction stream is 0.2mol / L.

[0074] The first reaction stream is sent into a tubular reactor, the reaction pressure P in the tubular reactor is 15 bar, the reaction temperature T is 115° C., the residence time t is 10 s, and the second reaction stream is obtained at the outlet, and the amine hydrochloride concentration C Ais 0.003 mol / L, and the liquid phase phosgene concentration C B 2.0mol / L;

[0075] The calculated value according to formula (1) is 4.48.

[0076] The second reaction stream was continuously sent to the autoclave reactor, the reactor temperature was 145° C., the pressure was 7 bar, and the residence time was 40 min. The third reaction stream was obtained at the outlet. The urea content was 0.7 wt % and the polyisocyanate yield was 99.91%.

[0077] The third reactant stream is subjected to phosgene removal and hydrogen chloride stripping heat treatment at 3 bar and 185°C, the treated reaction liquid is subjected to dechlorobenzene treatment at 35 kPa and 205°C, the dechlorobenzeneed mixed liquid is sent to a nitrogen stripping tower for treatment at 40 kPa and 195°C, the mass ratio of nitrogen to the reaction liquid after solvent removal is controlled to be 0.04, and crude polyisocyanate can be obtained in the bottom of the tower, and the NCO content is analyzed to be 32.2%.

[0078] Comparative Example 1

[0079] Diphenylmethane series diamines and polyamines (DAM) are mixed with chlorobenzene in a mass ratio of 1:1.5 to obtain a polyamine solution, and a phosgene chlorobenzene solution with a phosgene concentration of 90wt% and a polyamine solution (the mass ratio of DAM to phosgene is controlled to be 1:1.8) are fed into a dynamic reactor with a reaction pressure of 4.5bar, a reaction temperature of 70°C, a residence time of 0.6S, and a first reaction stream is obtained at an outlet, and the amine hydrochloride concentration in the first reaction stream is 0.7mol / L.

[0080] The first reaction stream is sent into a tubular reactor, the reaction pressure P in the tubular reactor is 4 bar, the reaction temperature T is 80°C, and the residence time t is 120S, and the second reaction stream is obtained at the outlet, and its amine hydrochloride concentration C A is 0.1 mol / L, the liquid phase phosgene concentration C B 0.3 mol / L;

[0081] The calculated value according to formula (1) is 0.33.

[0082] The second reaction stream was continuously sent to the autoclave reactor, the reactor temperature was 145° C., the pressure was 7 bar, and the residence time was 40 min. The third reaction stream was obtained at the outlet. The urea content was 1.5 wt % and the polyisocyanate yield was 98.88%.

[0083] The third reactant stream is subjected to phosgene removal and hydrogen chloride stripping heat treatment at 2.5 bar and 185° C., the treated reaction liquid is subjected to dechlorobenzene treatment at 35 kPa and 210° C., the dechlorobenzeneed mixed liquid is sent to a nitrogen stripping tower for treatment at 40 kPa and 210° C., the mass ratio of nitrogen to the reaction liquid after solvent removal is controlled to be 0.04, and crude polyisocyanate can be obtained in the bottom of the tower, and the NCO content is analyzed to be 31.3%.

[0084] Comparative Example 2

[0085] Diphenylmethane series diamines and polyamines (DAM) are mixed with chlorobenzene in a mass ratio of 1:3.0 to obtain a polyamine solution, and a phosgene chlorobenzene solution with a phosgene concentration of 40wt% and a polyamine solution (the mass ratio of DAM to phosgene is controlled to be 1:4.0) are fed into a dynamic reactor with a reaction pressure of 45bar, a reaction temperature of 125°C, a residence time of 0.05S, and a first reaction stream is obtained at an outlet, and the amine hydrochloride concentration in the first reaction stream is 0.08mol / L.

[0086] The first reaction stream is sent into a tubular reactor, the reaction pressure P in the tubular reactor is 30 bar, the reaction temperature T is 129 ° C, the residence time t is 15S, and the outlet is the second reaction stream, whose amine hydrochloride concentration C A is 0.0001mol / L, the liquid phase phosgene concentration C B 0.4 mol / L;

[0087] The calculated value according to formula (1) is 31.78.

[0088] The second reaction stream was continuously sent to a tank reactor with a temperature of 140° C., a pressure of 5 bar, and a residence time of 60 min. A third reaction stream was obtained at the outlet. The urea content was analyzed to be 1.3 wt % and the polyisocyanate yield was 99.12%.

[0089] The third reactant stream is subjected to phosgene removal and hydrogen chloride stripping heat treatment at 3 bar and 200°C, the treated reaction liquid is subjected to dechlorobenzene treatment at 40 kPa and 210°C, the dechlorobenzeneed mixed liquid is sent to a nitrogen stripping tower for treatment at 35 kPa and 205°C, the mass ratio of nitrogen to the reaction liquid after desolventization is controlled to be 0.03, and crude polyisocyanate can be obtained in the bottom of the tower, and the NCO content is analyzed to be 31.5%.

Claims

1. A method for preparing a polyisocyanate, characterized in that: The steps include: S1: sending the polyamine solution and the phosgene solution to the first reactor for phosgenation reaction to obtain a first reactant stream; S2: sending the outlet stream of the first reactor to the second reactor to continue phosgenation reaction to obtain a second reaction stream; S3: Send the outlet stream of the second reactor to the third reactor for further phosgenation reaction to obtain the third reaction stream S4: removing phosgene and HCl from the outlet stream of the third reactor to obtain a fourth reaction stream; S5: performing a desolventizing treatment on the fourth reaction stream to obtain a crude polyisocyanate product; The parameters in step S2 satisfy the following relationship: Where: T represents the reaction temperature of the phosgenation reaction in the second reactor, in °C, t represents the residence time of the phosgenation reaction in the second reactor, in seconds, P represents the pressure of the phosgenation reaction in the second reactor, in bar, C A Represents the concentration of amine hydrochloride in the second reactant stream, in mol / L.

2. The preparation method according to claim 1, characterized in that: The polyisocyanate is selected from diphenylmethylene diisocyanate (MDI), polyphenylmethylene polyisocyanate (PMDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI) or a combination of two or more thereof, preferably diphenylmethylene diisocyanate (MDI), polyphenylmethylene polyisocyanate (PMDI), toluene diisocyanate (TDI) or a combination of two or more thereof.

3. The preparation method according to claim 1, characterized in that: Step S1: the polyamine is selected from diaminodiphenylmethane (MDA), polyphenyl polymethylene polyamine (DAM), diaminotoluene (TDA), hexamethylenediamine (HDA), isophorone diamine (IPDA), xylylene diamine (XDA) or a combination of two or more thereof, preferably a mixture of diaminodiphenylmethane, polyphenyl polymethylene polyamine (DAM), diaminotoluene (TDA) or a combination of two or more thereof; and / or The solvent in the polyamine solution and the phosgene solution in step S1 is selected from benzene and its substituents, carbonate compounds, alkanes, cycloalkanes or a combination of two or more thereof, preferably chlorobenzene, dichlorobenzene, diethyl carbonate, toluene or a combination of two or more thereof, more preferably chlorobenzene; and / or In step S1, the mass ratio of the polyamine solution and the phosgene solution is controlled to be 1:(1.1-5); and / or In the polyamine solution of step S1, the mass ratio of polyamine to solvent is 1:(1.1-5); and / or In the phosgene solution of step S1, the phosgene concentration is 50-90wt%.

4. The preparation method according to claim 1, characterized in that: In step S1, the first reactor is selected from a static reactor or a dynamic reactor, preferably a dynamic reactor.

5. The preparation method according to claim 1, characterized in that: Step S1: The conditions for carrying out the phosgenation reaction in the first reactor include: a reaction pressure of 5-40 bar, preferably 10-30 bar; a reaction temperature of 60-120° C.; Preferably, the reaction residence time is 0.001-0.5 s.

6. The preparation method according to claim 1, characterized in that: In step S1, the concentration of amine hydrochloride in the first reactant stream is 0.1-0.6 mol / L.

7. The preparation method according to claim 1, characterized in that: Step S2: The second reactor is selected from a tubular reactor or a kettle reactor, preferably a tubular reactor.

8. The preparation method according to claim 1, characterized in that: The reaction temperature T of the phosgenation reaction in step S2 is 85-130° C., preferably 100-120° C.; and / or The pressure P of the phosgenation reaction in step S2 is 5-25 bar, preferably 10-15 bar; and / or The residence time t of the phosgenation reaction in step S2 is 2-100 s, preferably 5-30 s; and / or Step S2: The concentration C of amine hydrochloride in the second reactant stream A 0.001-0.05 mol / L, preferably 0.003-0.01 mol / L; Preferably, the concentration of phosgene in the second reactant stream is 0.5-4 mol / L, preferably 1.5-3 mol / L.

9. The preparation method according to claim 1, characterized in that: The third reactor in step S3 is selected from a kettle reactor or a tower reactor.

10. The preparation method according to claim 1, characterized in that: The phosgenation reaction in step S3 has a reaction temperature of 90-150° C. and a reaction pressure of 2-10 bar; and / or Preferably, the reaction residence time is 10-200 min.

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