Preparation method of polyisocyanate

Abstract

The invention discloses a preparation method of polyisocyanate, which comprises the following steps: reacting polyisocyanate in the presence of a catalyst under the protection of an inert atmosphere to obtain polyisocyanate, then adding carbon dioxide to terminate the reaction, and separating and purifying to obtain a polyisocyanate product, the catalyst is one or more of quaternary ammonium salt and quaternary ammonium base. When the polyisocyanate polymerization reaction needs to be terminated, the carbon dioxide reacts with the quaternary ammonium salt and / or the quaternary ammonium base to consume the catalyst of the polyisocyanate polymerization reaction, so that the effect of terminating the polyisocyanate polymerization reaction is realized, that is, the carbon dioxide is adopted as the terminator of the polyisocyanate polymerization reaction, the feeding is convenient, and the cost is low. In addition, redundant carbon dioxide can be removed in a vacuumizing mode, and the terminating agent does not enter a diisocyanate light component to affect reuse of diisocyanate and also does not enter a polyisocyanate finished product to affect the stability of the polyisocyanate finished product.

Description

Technical Field

[0001] The present invention relates to the technical field of isocyanates, and particularly to a preparation method of polyisocyanate. Background Art

[0002] The method for preparing polyisocyanate from polyisocyanate is already well-known. Usually, polyisocyanate (such as HDI, etc.) obtains a crude product with a certain conversion rate under the action of a catalyst, and an acyl chloride or phosphonate terminator is added to terminate the reaction, and then the remaining monomers are separated by one-step or multi-step distillation to finally obtain a polyisocyanate product with a low free monomer content. For example, the patent specification with the publication number CN110372846A discloses a preparation method of a urea diketone group-containing polyisocyanate with stable color value storage, including: (1) polymerizing an organic isocyanate raw material under the catalytic action of a tertiary phosphine catalyst; (2) terminating the reaction with a terminator after the reaction reaches a set conversion rate; (3) separating and removing the unreacted organic isocyanate monomer by an appropriate separation method to obtain a polyisocyanate product containing a urea diketone group. Among them, the terminator includes one or more of acyl chloride, sulfonate, alkyl phosphate, and sulfate. The acyl chloride is selected from formyl chloride, acetyl chloride, benzoyl chloride, and phthaloyl chloride. The sulfonate is selected from methyl toluenesulfonate and ethyl toluenesulfonate. The alkyl phosphate is selected from monobutyl phosphate, dibutyl phosphate, monoethyl phosphate, diethyl phosphate, dioctyl phosphate, and diisooctyl phosphate. The sulfate is selected from dimethyl sulfate and diethyl sulfate. And the dosage of the terminator is 80%-120% of the molar amount of the catalyst used.

[0003] The current technical route has the following problems:

[0004] Since the catalyst may be deactivated during the reaction process, it is impossible to accurately confirm the addition amount of the terminator for completely terminating the catalyst. If too little terminator is added, the catalyst cannot be completely removed by the terminator, which will affect the properties such as the stability of the polyisocyanate product. If too much terminator is added, the following two problems will occur:

[0005] 1) When using low-boiling terminators such as benzoyl chloride, during the later process of removing polyisocyanate monomers, the remaining unreacted terminator will be removed together. The separated polyisocyanate light component and the terminator cannot be effectively separated. Since the terminator will seriously reduce the reaction activity of polyisocyanate, the polyisocyanate light component cannot be reused without removing the terminator, that is, recycled. Removing the terminator in the polyisocyanate light component will increase the process complexity.

[0006] 2) When using high-boiling terminators such as diisooctyl phosphate, during the later process of removing polyisocyanate monomers, the unreacted terminator remains in the polyisocyanate product, which will affect the properties such as the stability of the polyisocyanate product.

[0007] In addition, the patent specification with the publication number CN109651278A discloses a method for preparing polyisocyanate. The isocyanate is subjected to a self-polymerization reaction under the catalysis of a fluorine-containing catalyst. After the reaction is completed, a fluorine-containing terminator is added to terminate the reaction to obtain a reaction solution; the unreacted isocyanate monomer is removed to obtain polyisocyanate. The above problems also exist. Summary of the Invention

[0008] In view of the above technical problems and the deficiencies in the art, the present invention provides a method for preparing polyisocyanate. When it is necessary to terminate the polymerization reaction of polyisocyanate, carbon dioxide is used to react with quaternary ammonium salt and / or quaternary ammonium base to consume the catalyst for the polymerization reaction of polyisocyanate, thereby achieving the effect of terminating the polymerization reaction of polyisocyanate. That is, carbon dioxide is used as the terminator for the polymerization reaction of polyisocyanate. The feeding is convenient, and the excess carbon dioxide can be removed by vacuum pumping. The terminator will neither enter the light components of polyisocyanate and affect the reuse of polyisocyanate, nor enter the polyisocyanate finished product and affect its stability.

[0009] The specific technical solution is as follows:

[0010] A method for preparing polyisocyanate, comprising:

[0011] The polyisocyanate reacts under the protection of an inert atmosphere and in the presence of a catalyst to obtain polyisocyanate, and then carbon dioxide is added to terminate the reaction, and the polyisocyanate product is separated and purified.

[0012] The catalyst is one or more of quaternary ammonium salts and quaternary ammonium bases. Further, the catalyst may include at least one of ammonium tetramethylacetate, ammonium tetraethylacetate, ammonium tetrabutylacetate, dodecyltrimethylammonium octanoate, 2-hydroxy-N,N,N-trimethyl-1-propanamine formate, 2-hydroxypropyltrimethylammonium isooctanoate, trimethyl-2-methyl-2-hydroxyethyl ammonium hydroxide, and N,N,N-trimethylbenzyl ammonium hydroxide.

[0013] In some embodiments, based on the mass of the polyisocyanate, the dosage of the catalyst may be 10-10000 ppm, further preferably 20-1000 ppm, such as 25 ppm, 100 ppm, etc.

[0014] In some embodiments, the catalyst can be added in the form of a solution, and the solvent in the solution may include n-butanol, isopropanol, ethyl acetate, butyl acetate, N,N-dimethylformamide, N,N-dimethylacetamide, etc.

[0015] In the present invention, the inert atmosphere refers to a gas atmosphere that does not participate in the reaction, and may be, for example, one or more gas combinations including a noble gas atmosphere, a nitrogen atmosphere, etc.

[0016] The preparation method of the present invention does not have special requirements for the polyisocyanate, that is, the preparation method of the present invention has good universality and is applicable to various polymerizable polyisocyanates. In some embodiments, the polyisocyanate may include diisocyanate. Further, the diisocyanate may include one or several of toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, benzodimethylenebis(isocyanate), and hexamethylene diisocyanate.

[0017] In the preparation method of the polyisocyanate, the temperature for obtaining the polyisocyanate by the reaction may be 50-100 °C, further may be 60-80 °C, such as 70 °C, etc.

[0018] In the preparation method of the polyisocyanate, the carbon dioxide may be added in any one or more combinations of gaseous, liquid, solid, and supercritical states.

[0019] In the preparation method of the polyisocyanate, when the reaction is terminated, the free polyisocyanate monomer in the obtained crude polyisocyanate product is reduced to less than 90% compared with the initial dosage.

[0020] In the preparation method of the polyisocyanate, the separation and purification may include using a two-stage separation device, wherein the first-stage separation device may be a rotary evaporator, a thin-film evaporator or a molecular distillation device, and the second-stage separation device may be a molecular distillation device.

[0021] In some embodiments, the heating temperature of the first-stage separation device may be controlled at 100-190 °C, such as 120 °C, 130 °C, 140 °C, etc., the condensation separation temperature may be controlled at -40 to 40 °C, such as -20 °C, -10 °C, etc., and the vacuum degree may be controlled at 10-3000 Pa, such as 200 Pa, 500 Pa, etc., to separate some free polyisocyanate monomers.

[0022] In some embodiments, the heating temperature of the second-stage separation device may be controlled at 110-220 °C, such as 140 °C, 160 °C, 190 °C, etc., the condensation separation temperature may be controlled at -40 to 40 °C, such as -15 °C, -20 °C, etc., and the vacuum degree may be controlled at 1-500 Pa, such as 10 Pa, 20 Pa, etc., to separate the remaining free polyisocyanate monomers.

[0023] In some embodiments, in the method for preparing polyisocyanate, the polyisocyanate monomer obtained by separation and purification can be reused, that is, reused for preparing polyisocyanate, and the reaction activity is no different from that of fresh isocyanate.

[0024] In some embodiments, in the method for preparing polyisocyanate described in the present invention, the NCO mass fraction of the polyisocyanate product can be 15.5%-23.5%, wherein the mass fraction of free polyisocyanate monomer does not exceed 0.5%, for example 0.2%, 0.3%, etc., and can further be 0.1% to 0.5%.

[0025] In some embodiments, in the method for preparing polyisocyanate of the present invention, the process of obtaining polyisocyanate by reaction can be carried out under stirring.

[0026] In some embodiments, in the method for preparing polyisocyanate of the present invention, the timing of adding carbon dioxide to terminate the reaction can be determined according to the polyisocyanate reaction reaching a set target conversion rate.

[0027] In some embodiments, in the method for preparing polyisocyanate described in the present invention, the carbon dioxide can be introduced continuously, added all at once or in multiple times, or added in a combination of the above methods until the reaction is terminated (i.e., the conversion rate of the polyisocyanate monomer is stable and no longer changes).

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The invention provides a method for preparing polyisocyanate, using carbon dioxide as a reaction terminator, the terminator is easy to feed, and excess carbon dioxide can be removed by vacuuming, the terminator can just consume the catalyst completely, the terminator will neither enter the light component of polyisocyanate to affect the reuse of polyisocyanate monomers, nor enter the finished polyisocyanate to affect its stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the infrared spectrum of the hexamethylene diisocyanate-based polyisocyanate product of Example 1.

[0031] Figure 2 This is the HPLC spectrum of the hexamethylene diisocyanate-based polyisocyanate product of Example 1. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0033] For the operation methods without specified conditions in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0034] Example 1:

[0035] Under nitrogen protection, 1000 g of hexamethylene diisocyanate (HDI) was heated to 70 °C. Under stirring conditions, 2 g of a 5 wt% n-butanol solution of N,N,N-trimethylbenzylammonium hydroxide was added. The reaction temperature was controlled at 70 °C, and the reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content in the reaction system. When the conversion rate of HDI monomer reached 45%, carbon dioxide gas was introduced until the conversion rate of HDI monomer no longer changed, and stirring was continued for 1 h to obtain a crude product of hexamethylene diisocyanate-based polyisocyanate. The obtained crude product of hexamethylene diisocyanate-based polyisocyanate was transported through a pipeline to a thin-film evaporator in the primary separation device. The heating temperature of the thin-film evaporator was controlled at 120 °C, the temperature of the condensation device was controlled at -20 °C, and the vacuum degree was controlled at 500 Pa to separate some free hexamethylene diisocyanate monomers. The product of the thin-film evaporator in the primary separation device was transported through a pipeline to a molecular distillation device in the secondary separation device. The heating temperature of the molecular distillation device was controlled at 190 °C, the temperature of the secondary condensation device was controlled at -20 °C, and the vacuum degree was controlled at 10 Pa to separate the remaining free hexamethylene diisocyanate monomers, and a hexamethylene diisocyanate-based polyisocyanate product with a low free monomer content was prepared. Its infrared spectrum is as Figure 1 shown, and its high-performance liquid chromatography spectrum is as Figure 2 shown. After testing, the NCO mass fraction of the prepared hexamethylene diisocyanate-based polyisocyanate with a low free monomer content was 22.4%, and the mass fraction of free hexamethylene diisocyanate monomer was 0.2%. The hexamethylene diisocyanate-based polyisocyanate product of this example was diluted to 25% with butyl acetate and stored at room temperature for 10 days without change, showing excellent dilution stability.

[0036] Using 1000 g of the light component HDI separated by the separation device in this example as the raw material, polyisocyanate was synthesized again. Under stirring conditions, 2 g of a 5 wt% n-butanol solution of N,N,N-trimethylbenzylammonium hydroxide was added. The reaction temperature was controlled at 70 °C, and the reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content in the reaction system. The reaction rate was not significantly different from the reaction rate of synthesizing polyisocyanate using fresh HDI.

[0037] Example 2:

[0038] Under nitrogen protection, 1000 g of hexamethylene diisocyanate (HDI) was heated to 65 °C. Under stirring conditions, 1 g of a N,N-dimethylformamide solution of 20 wt% trimethyl-2-methyl-2-hydroxyethyl ammonium hydroxide was added, and the reaction temperature was controlled at 65 °C. The reaction was carried out under stirring conditions, and the reaction process was monitored by measuring the NCO content of the reaction system. When the conversion rate of HDI monomer reached 30%, liquid carbon dioxide was added until the conversion rate of HDI monomer no longer changed, and stirring was continued for 1 h to obtain a crude product of hexamethylene diisocyanate-based polyisocyanate. The obtained crude product of hexamethylene diisocyanate-based polyisocyanate was transported through a pipeline to a molecular distillation device of a primary separation device. The heating temperature of the molecular distillation device was controlled at 130 °C, the temperature of the condensation device was controlled at -10 °C, and the vacuum degree was controlled at 200 Pa to separate some free hexamethylene diisocyanate monomers. The product of the molecular distillation device of the primary separation device was transported through a pipeline to a molecular distillation device of a secondary separation device. The heating temperature of the molecular distillation device was controlled at 160 °C, the temperature of the secondary condensation device was controlled at -15 °C, and the vacuum degree was controlled at 20 Pa to separate the remaining free hexamethylene diisocyanate monomers, and a hexamethylene diisocyanate-based polyisocyanate product with a low free monomer content was prepared. After testing, the NCO mass fraction of the prepared hexamethylene diisocyanate-based polyisocyanate with a low free monomer content was 22.8%, and the mass fraction of free hexamethylene diisocyanate monomer was 0.15%. The hexamethylene diisocyanate-based polyisocyanate product of this example was diluted to 25% with butyl acetate and stored at room temperature for 10 days without change, and the dilution stability was excellent.

[0039] Using 1000 g of the light component HDI separated by the separation device of this example as a raw material, polyisocyanate was synthesized again. Under stirring conditions, 1 g of a N,N-dimethylformamide solution of 20 wt% trimethyl-2-methyl-2-hydroxyethyl ammonium hydroxide was added, and the reaction temperature was controlled at 65 °C. The reaction was carried out under stirring conditions, and the reaction process was monitored by measuring the NCO content of the reaction system. The reaction rate was not significantly different from the reaction rate of synthesizing polyisocyanate using fresh HDI.

[0040] Example 3:

[0041] Under nitrogen protection, 1000 g of isophorone diisocyanate (IPDI) was heated to 60 °C. Under stirring conditions, 0.5 g of an isopropanol solution of 5 wt% 2-hydroxy-N,N,N-trimethyl-1-propanamine formate was added. The reaction temperature was controlled at 60 °C, and the reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content of the reaction system. When the conversion rate of IPDI monomer reached 45%, carbon dioxide gas was introduced until the conversion rate of IPDI monomer no longer changed, and stirring was continued for 1 h to obtain a crude product of isophorone diisocyanate-based polyisocyanate. The obtained crude product of isophorone diisocyanate-based polyisocyanate was transported through a pipeline to a thin-film evaporator in a primary separation device. The heating temperature of the thin-film evaporator was controlled at 120 °C, the temperature of the condensation device was controlled at -20 °C, and the vacuum degree was controlled at 500 Pa to separate some free isophorone diisocyanate monomers. The product of the thin-film evaporator in the primary separation device was transported through a pipeline to a molecular distillation device in a secondary separation device. The heating temperature of the molecular distillation device was controlled at 190 °C, the temperature of the secondary condensation device was controlled at -20 °C, and the vacuum degree was controlled at 10 Pa to separate the remaining free isophorone diisocyanate monomers, and a product of isophorone diisocyanate-based polyisocyanate with a low free monomer content was prepared. After testing, the NCO mass fraction of the prepared isophorone diisocyanate-based polyisocyanate with a low free monomer content was 17.2%, and the mass fraction of free isophorone diisocyanate monomer was 0.3%. The isophorone diisocyanate-based polyisocyanate product of this example was diluted to 25% with butyl acetate and stored at room temperature for 10 days without change, showing excellent dilution stability.

[0042] Using 1000 g of the light-component IPDI separated by the separation device of this example as the raw material, polyisocyanate was synthesized again. Under stirring conditions, 0.5 g of an isopropanol solution of 5 wt% 2-hydroxy-N,N,N-trimethyl-1-propanamine formate was added. The reaction temperature was controlled at 60 °C, and the reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content of the reaction system. The reaction rate was not significantly different from the reaction rate of synthesizing polyisocyanate using fresh IPDI.

[0043] Example 4:

[0044] Under nitrogen protection, 1000 g of isophorone diisocyanate (IPDI) was heated to 55 °C. Under stirring conditions, 1 g of a butyl acetate solution of 10 wt% trimethyl-2-methyl-2-hydroxyethyl ammonium hydroxide was added, and the reaction temperature was controlled at 55 °C. The reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content of the reaction system. When the conversion rate of IPDI monomer reached 65%, carbon dioxide gas was introduced until the conversion rate of IPDI monomer no longer changed, and stirring was continued for 1 h to obtain a crude product of isophorone diisocyanate-based polyisocyanate. The obtained crude product of isophorone diisocyanate-based polyisocyanate was transported through a pipeline to a thin film evaporator in a primary separation device. The heating temperature of the thin film evaporator was controlled at 140 °C, the temperature of the condensation device was controlled at -40 °C, and the vacuum degree was controlled at 200 Pa to separate some free isophorone diisocyanate monomers. The product of the thin film evaporator in the primary separation device was transported through a pipeline to a molecular distillation device in a secondary separation device. The heating temperature of the molecular distillation device was controlled at 140 °C, the temperature of the secondary condensation device was controlled at -20 °C, and the vacuum degree was controlled at 10 Pa to separate the remaining free isophorone diisocyanate monomers, and a product of isophorone diisocyanate-based polyisocyanate with a low free monomer content was prepared. After testing, the NCO mass fraction of the prepared isophorone diisocyanate-based polyisocyanate with a low free monomer content was 16.5%, and the mass fraction of free isophorone diisocyanate monomer was 0.2%. The isophorone diisocyanate-based polyisocyanate product of this example was diluted to 25% with butyl acetate and stored at room temperature for 10 days without change, and the dilution stability was excellent.

[0045] Using 1000 g of the light component IPDI separated by the separation device of this example as a raw material, polyisocyanate was synthesized again. Under stirring conditions, 1 g of a butyl acetate solution of 10 wt% trimethyl-2-methyl-2-hydroxyethyl ammonium hydroxide was added, and the reaction temperature was controlled at 55 °C. The reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content of the reaction system. The reaction rate was not significantly different from the reaction rate of synthesizing polyisocyanate using fresh IPDI.

[0046] Comparative Example 1:

[0047] Under nitrogen protection, 1000 g of hexamethylene diisocyanate was heated to 70 °C. Under stirring conditions, 2 g of a n-butanol solution of 5 wt% N,N,N-trimethylbenzylammonium hydroxide was added, and the reaction temperature was controlled at 70 °C. The reaction was carried out under stirring conditions. The reaction process was monitored by measuring the NCO content of the reaction system. When the reaction conversion reached 45%, 0.1 g of benzoyl chloride was added until the conversion no longer changed, and stirring was continued for 1 h to obtain a crude product of hexamethylene diisocyanate-based polyisocyanate. The obtained crude product of hexamethylene diisocyanate-based polyisocyanate was transported through a pipeline to a thin-film evaporator of a primary separation device. The heating temperature of the thin-film evaporator was controlled at 120 °C, the temperature of the condensation device was controlled at -20 °C, and the vacuum degree was controlled at 500 Pa to separate some free hexamethylene diisocyanate monomers. The product of the thin-film evaporator of the primary separation device was transported through a pipeline to a molecular distillation device of a secondary separation device. The heating temperature of the molecular distillation device was controlled at 190 °C, the temperature of the secondary condensation device was controlled at -20 °C, and the vacuum degree was controlled at 10 Pa to separate the remaining free hexamethylene diisocyanate monomers, and a hexamethylene diisocyanate-based polyisocyanate product with a low free monomer content was prepared. After testing, the NCO mass fraction of the prepared hexamethylene diisocyanate-based polyisocyanate with a low free monomer content was 22.7%, and the mass fraction of free hexamethylene diisocyanate monomers was 0.3%. The content of benzoyl chloride in the HDI light components removed by the separation device was 28 ppm. Benzoyl chloride polluted the HDI, making the separated HDI monomers unable to be directly reused again. The hexamethylene diisocyanate-based polyisocyanate product of this comparative example was diluted to 25% with butyl acetate and remained unchanged after being stored at room temperature for 10 days, showing excellent dilution stability.

[0048] Using 1000 g of the light component HDI separated by the separation device of this comparative example as raw material, polyisocyanate was synthesized again. Under stirring conditions, 2 g of a n-butanol solution of 5 wt% N,N,N-trimethylbenzylammonium hydroxide was added, and the reaction temperature was controlled at 70 °C. The reaction was carried out under stirring conditions, and the reaction rate was very slow. No polyisocyanate was formed under this condition.

[0049] Comparative Example 2:

[0050] Under nitrogen protection, 1000 g of hexamethylene diisocyanate was heated to 70 °C. Under stirring conditions, 2 g of a n-butanol solution of 5 wt% N,N,N-trimethylbenzylammonium hydroxide was added, and the reaction temperature was controlled at 70 °C. The reaction was carried out under stirring conditions. The reaction progress was monitored by measuring the NCO content of the reaction system. When the reaction conversion rate reached 45%, 0.2 g of diisooctyl phosphate was added until the conversion rate no longer changed, and stirring was continued for 1 h to obtain a crude product of hexamethylene diisocyanate-based polyisocyanate. The obtained crude product of hexamethylene diisocyanate-based polyisocyanate was transported through a pipeline to a thin-film evaporator of a primary separation device. The heating temperature of the thin-film evaporator was controlled at 120 °C, the temperature of the condensation device was controlled at -20 °C, and the vacuum degree was controlled at 500 Pa to separate some free hexamethylene diisocyanate monomers. The product of the thin-film evaporator of the primary separation device was transported through a pipeline to a molecular distillation device of a secondary separation device. The heating temperature of the molecular distillation device was controlled at 190 °C, the temperature of the secondary condensation device was controlled at -20 °C, and the vacuum degree was controlled at 10 Pa to separate the remaining free hexamethylene diisocyanate monomers, and a hexamethylene diisocyanate-based polyisocyanate product with a low free monomer content was prepared. After testing, the NCO mass fraction of the prepared hexamethylene diisocyanate-based polyisocyanate with a low free monomer content was 22.0%, and the mass fraction of free hexamethylene diisocyanate monomers was 0.2%. The content of diisooctyl phosphate in the hexamethylene diisocyanate-based polyisocyanate product of this comparative example was 45 ppm. The hexamethylene diisocyanate-based polyisocyanate product of this comparative example was diluted to 25% with butyl acetate and gelled after being stored at room temperature for 5 days, and the dilution stability was poor.

[0051] Using 1000 g of the light component HDI separated by the separation device of this comparative example as a raw material, polyisocyanate was synthesized again. Under stirring conditions, 2 g of a n-butanol solution of 5 wt% N,N,N-trimethylbenzylammonium hydroxide was added, and the reaction temperature was controlled at 70 °C. The reaction was carried out under stirring conditions. The reaction progress was monitored by measuring the NCO content of the reaction system. The reaction rate was not significantly different from the reaction rate of synthesizing polyisocyanate using fresh HDI.

[0052] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for preparing polyisocyanate, characterized in that: include: The polyisocyanate is reacted under the protection of an inert atmosphere and in the presence of a catalyst to obtain a polyisocyanate, and then carbon dioxide is added to terminate the reaction, and the polyisocyanate product is separated and purified to obtain a polyisocyanate product; The catalyst is one or more of a quaternary ammonium salt and a quaternary ammonium base.

2. The preparation method according to claim 1, characterized in that: The catalyst comprises at least one of tetramethylammonium acetate, tetraethylammonium acetate, tetrabutylammonium acetate, dodecyltrimethylammonium octanoate, 2-hydroxy-N,N,N-trimethyl-1-propylamine formate, 2-hydroxypropyltrimethylisooctanoate ammonium salt, trimethyl-2-methyl-2-hydroxyethylammonium hydroxide, and N,N,N-trimethylbenzylammonium hydroxide; Based on the mass of the polyisocyanate, the amount of the catalyst is 10-10000 ppm, further 20-1000 ppm.

3. The preparation method according to claim 1, characterized in that: The polyisocyanate includes diisocyanate, and the diisocyanate includes one or more of toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, xylylene diisocyanate, and hexamethylene diisocyanate.

4. The preparation method according to claim 1, characterized in that: The temperature of the reaction to obtain polyisocyanate is 50-100°C, further 60-80°C.

5. The preparation method according to claim 1, characterized in that: The carbon dioxide is added in the form of any one or more combinations including gaseous, liquid, solid and supercritical states.

6. The preparation method according to claim 1, characterized in that: When the reaction is terminated, the free polyisocyanate monomer in the obtained crude polyisocyanate product is reduced to less than 90% compared with the initial dosage.

7. The preparation method according to claim 1, characterized in that: The separation and purification comprises using a two-stage separation device, wherein the first-stage separation device is a rotary evaporator, a thin film evaporator or a molecular distillation device, and the second-stage separation device is a molecular distillation device.

8. The preparation method according to claim 7, characterized in that: The heating temperature of the primary separation device is controlled at 100-190°C, the condensation separation temperature is controlled at -40-40°C, and the vacuum degree is controlled at 10-3000Pa to separate part of the free polyisocyanate monomers; The heating temperature of the secondary separation device is controlled at 110-220° C., the condensation separation temperature is controlled at -40 to 40° C., and the vacuum degree is controlled at 1-500 Pa to separate the remaining free polyisocyanate monomers.

9. The preparation method according to claim 1, characterized in that: The polyisocyanate monomer obtained by separation and purification is reused.

10. The preparation method according to claim 1, characterized in that: The NCO mass fraction of the polyisocyanate product is 15.5%-23.5%, wherein the mass fraction of free polyisocyanate monomer does not exceed 0.5%, and further is 0.1%-0.5%.

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