An isocyanate polymerization catalyst and a method for preparing the same, and a method for purifying isocyanate tar

Abstract

The application discloses an isocyanate polymerization catalyst and a preparation method thereof, and an isocyanate tar purification method. The polymerization catalyst comprises a main catalyst quaternary ammonium base, a first additive methylaluminoxane and / or trimethyl gallium, and a second additive sodium fatty acid. A mixed solution containing isocyanate polymers, urea, and isocyanate monomers in the system is removed of the monomers by catalytic polymerization in a reactor and by adding the catalyst to obtain isocyanate polymers, which are applied to downstream fields such as boards and adhesives. The application can convert waste tar liquid into by-products for sale, has significant economic benefits, and reduces the waste liquid treatment capacity of the running device and the operation cost of the device.

Description

Technical Field

[0001] This invention relates to the field of isocyanate preparation, specifically to a catalyst for isocyanate polymerization and its preparation method, and to its use in removing monomers from isocyanate tar. Background Technology

[0002] Isocyanates are a general term for various esters of isocyanate, and are important raw materials for the production of polyurethane. They are widely used in home appliances, building materials, furniture, coatings, adhesives, foams, leather, and other fields. Classified by structure, isocyanates are divided into aliphatic, alicyclic, and aromatic isocyanates; classified by the number of NCO groups, they can be divided into monoisocyanates, diisocyanates, and polyisocyanates. The production methods of isocyanates, depending on the raw materials, can be summarized as phosgenation and non-phosgenation methods. The phosgenation method is a mature and economical production process, and is currently the main method for industrial isocyanate production; 85%-90% of aliphatic isocyanates are produced using the phosgenation method.

[0003] At the end of the isocyanate synthesis process, crude isocyanate is obtained. Pure isocyanate is typically separated from the crude mixture using distillation. During this process, high-boiling-point solid residue or distillation residue, commonly known as isocyanate tar, is produced at the bottom of the distillation column. Tar is mainly a mixture of polymerized biuret, isocyanate polymers, byproducts, and various impurities. For example, tar is generated during the production of toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI). Taking TDI tar recovery as an example, many technologies exist for tar recycling, including forced distillation, extractive distillation, thin-film evaporation, continuous twin-shaft vacuum drying (LIST), and combined fluidized bed drying (CFT). Distillation and evaporation processes are more difficult to operate, and NCO easily polymerizes into solids at high temperatures, causing blockages, resulting in short continuous operation cycles. LIST and CFT processes are relatively new and simpler to operate, recovering isocyanate from tar to a residual level of less than 10%, but they suffer from high power consumption and high equipment investment costs.

[0004] Further processing of tar to extract economically viable chemicals can turn waste into treasure and generate more profits, possessing significant socio-economic value. Numerous publications and patents have reported on the resource utilization of TDI tar residue, but few address the treatment of ADI tar such as HDI. Due to the presence of isocyanate monomers in tar, which are highly allergenic, its application is limited, and the monomers generally need to be removed. Current tar residue and liquid treatment processes, including direct treatment, use as NCO-based solutions, and decomposition and recovery, are mostly still in the laboratory research stage and difficult to meet the requirements for industrial application.

[0005] CN102633651A discloses a method for recovering toluene diamine from TDI tar. The method involves crushing TDI waste residue particles, treating them with a catalyst and an alkaline aqueous solution to obtain a slurry, and then hydrolyzing it to produce toluene diamine with a recovery rate as high as 60%. The catalyst is recycled. This method is suitable for TDI tar residue, primarily recovering the effective components from polyurea hydrolysis. However, it is difficult to process HDI tar. HDI tar contains a large amount of NCO polymers and a small amount of monomers; hydrolysis yields esters of NCO polymers, and the reaction is prone to runaway, posing a certain degree of danger.

[0006] CN114605288A discloses an efficient separation and recovery process and apparatus for isocyanate polymers. The method involves heating the isocyanate polymer in a decomposer, causing the contained urea diketone to decompose and produce methyl isocyanate monomers. The isocyanate polymer is then recovered after impurity adsorption. However, this method uses heating to decompose the isocyanate polymer, which carries the risk of uncontrolled isocyanate polymerization. Furthermore, while suitable for recovering monomers after urea diketone decomposition, its applicability is limited.

[0007] CN109749036A discloses a catalyst for preparing polyisocyanate compositions, which is an imine-type quaternary ammonium salt catalyst. It is primarily used to prepare low-color trimers and polymers for downstream applications. This catalyst is applicable to isocyanate monomers with low acidity, but the tar residue components are quite mixed, making the polymerization process difficult to control and stable, and easily resulting in high-viscosity materials. This limits the application of most isocyanate trimer and polymer catalysts in isocyanate tar. Therefore, there is a need to invent a polymerization catalyst suitable for isocyanate tar systems. Summary of the Invention

[0008] The purpose of this invention is to provide an isocyanate polymerization catalyst that is applicable to the purification of isocyanate tar and the removal of monomers in the polymerization reaction, thus broadening its application range. Furthermore, the catalyst is simple to prepare, easy to use, and has significant practical value.

[0009] Another object of the present invention is to provide the use of the catalyst in the purification of isocyanate tar, which can purify tar byproducts, remove isocyanate monomers from tar, thereby broadening the application space of tar byproducts in downstream markets, reducing the amount of waste liquid generated by the equipment, and creating additional economic benefits.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] An isocyanate monomer polymerization catalyst comprising the following components:

[0012] [R1R2R3NR4]OH 15wt%-35wt%,

[0013] R5COONa 10wt%-20wt%,

[0014] 50wt%-70wt% of methylaluminoxane (MAO) and / or trimethylgallium;

[0015] R1 to R4 are selected from alkyl groups with 4 or fewer carbon atoms, preferably ethyl or propyl groups; R5 is selected from alkyl groups with 15 or fewer carbon atoms, preferably alkyl groups with 8 to 10 carbon atoms.

[0016] A method for preparing an isocyanate polymerization catalyst includes the following steps:

[0017] a. Under a nitrogen atmosphere, weigh out [R1R2R3NR4]X quaternary ammonium salt and solvent, mix them in a certain proportion, stir and maintain the system temperature within a certain range;

[0018] b. Add an alkali, preferably KOH or NaOH solid powder, to the solution obtained in step a; c. After mixing is complete in step b, continue stirring and control the temperature within a certain range to ensure complete reaction;

[0019] d. The solution from process c is filtered and separated under a nitrogen atmosphere. The mother liquor is heated and concentrated to obtain the quaternary ammonium base product, which is then dried under vacuum.

[0020] e. Mix the quaternary ammonium base obtained in d with sodium fatty acid R5COONa in a certain proportion, add it to methylaluminoxane and / or trimethylgallium, stir evenly, and age at 40-60°C.

[0021] In step a of the present invention, the mass ratio of quaternary ammonium base to solvent is 1:1 to 1:4, and the temperature is maintained at 20 to 30°C, preferably 22 to 25°C; the solvent is selected from polar solvents such as methanol, ethanol, propanol, butanol, and ethyl acetate, preferably methanol or ethanol.

[0022] In step b of this invention, the molar ratio of quaternary ammonium salt to alkali is 1:1 to 1:2, and uniform dispersion is ensured during addition.

[0023] In step c of this invention, the preferred temperature range is 30–40°C, and the reaction time is 3–4 hours.

[0024] In step d of this invention, the heating and concentration temperature is controlled at 60-100°C, preferably under reduced pressure, with the pressure preferably being an absolute pressure of 30-50 kPa, and more preferably an absolute pressure of 1-10 kPa for vacuum drying.

[0025] In step e of this invention, the mass ratio of quaternary ammonium base to sodium fatty acid is 1:1 to 3:1, and the mass ratio of quaternary ammonium base to MAO and / or trimethylgallium is 1:1 to 1:5, preferably 1:2 to 1:3.

[0026] In a second aspect, the present invention provides the application of the catalyst in the removal of monomers from isocyanate tar, wherein the isocyanate is selected from TDI, HDI, IPDI, HMDI, PDI, and XDI.

[0027] A method for purifying isocyanate tar includes the following steps:

[0028] The isocyanate production system contains a heavy component solution of isocyanate monomers, polymers, and urea. The solution is heated and stirred at a certain temperature in a reactor equipped with a stirrer, thermometer, and reflux condenser heat exchanger. The catalyst is added in a certain proportion. The catalyst can be used directly or diluted with solvent. A certain reaction time is ensured. Then, a reaction terminator is added to obtain a tar-rich heavy component with low monomer content.

[0029] The isocyanate heavy component solution is obtained from the heavy components in the purification process of crude isocyanate products after deep separation treatment. The separation methods include, but are not limited to, distillation, evaporation, extrusion, etc. The composition of the resulting isocyanate heavy component solution is as follows:

[0030] NCO monomer Polymers, dimers, urea 6-12wt% 88-94wt%

[0031] The catalyst can efficiently catalyze the polymerization of isocyanate monomers, in which the quaternary ammonium base plays the main catalytic role. It combines with the isocyanate monomer to produce an active intermediate, which continues to combine with other monomers, and then removes the quaternary ammonium base to form a cyclization to form a trimer and a higher degree of polymerization.

[0032] Methylaluminoxane and / or trimethylgallium, as the primary co-catalyst, act as a phase transfer agent to effectively disperse the quaternary ammonium base and enhance its mixing effect with isocyanate. Furthermore, they form complexes with the quaternary ammonium base, producing a synergistic effect and preventing the insertion and growth of macromolecular polymers at the active sites. Therefore, they can inhibit the high polymerization of isocyanate and reduce the formation of gel-like polymers. Sodium fatty acid, as a co-catalyst, can itself form complexes with isocyanate, catalyzing the polymerization of isocyanate monomers. The trimer structure synthesized at high temperatures is relatively ideal, inhibiting the formation of dimers. The resulting catalytic product has less monomer residue and ensures that catalysis occurs at a lower degree of polymerization, preventing the product viscosity from becoming too high and causing gelation.

[0033] In the catalyst system prepared in this invention, a reaction terminator should be added after the catalytic reaction is completed. The terminator is a polymerization inhibitor such as phosphoric acid or benzoyl chloride.

[0034] The isocyanates include, but are not limited to, isocyanates such as HDI, TDI, XDI, PDI, and IPDI that are prone to producing tar-laden byproducts.

[0035] In the purification method of the present invention, a mixed solution containing isocyanate polymer, urea and isocyanate monomer is sent to a stirred tank reactor and a catalyst is added to catalyze polymerization to eliminate monomers. After the reaction is completed, a terminator is added to obtain isocyanate polymer with a monomer content of less than 1%, which does not require further separation and purification.

[0036] The isocyanate monomer content in the mixed solution containing isocyanate polymer, monomer, and urea described in this invention is about 6-12%.

[0037] In the purification method of the present invention, the catalyst accounts for 0.01%-0.1% of the mass fraction of isocyanate tar, the reaction time is maintained for 2-4 hours, and the reaction temperature is 70-100℃, preferably 80℃ (atmospheric pressure).

[0038] The isocyanate monomer content in the liquid phase after catalytic self-polymerization is less than 1%, preferably less than 0.5%.

[0039] The beneficial effects of this invention are as follows:

[0040] (1) After using this process, isocyanate monomer impurities in the tar heavy component system can be effectively removed, the toxicity of by-products can be reduced, the downstream application market can be broadened, and it can be used as a by-product to replace isocyanate in adhesives, boards and other fields, creating economic benefits.

[0041] (2) The materials that would otherwise need to be sent to waste liquid treatment are treated, which solves the waste liquid treatment problem with a smaller operating cost, saves the cost of hazardous waste treatment, and is friendly to the social environment. Detailed Implementation

[0042] The following embodiments will further illustrate the method provided by the present invention, but the present invention is not limited to the listed embodiments and should also include any other known modifications within the scope of the claims of the present invention.

[0043] Example 1: Preparation of Catalyst A:

[0044] a. Under a nitrogen atmosphere, weigh 28g of tetramethylammonium bromide and 50g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0045] b. Add 10g of KOH solid powder in batches within half an hour;

[0046] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0047] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0048] e. Take 15g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Add the mixture to 40g of methylaluminoxane solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0049] Example 2: Preparation of Catalyst B:

[0050] a. Under a nitrogen atmosphere, weigh 28g of tetramethylammonium bromide and 50g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0051] b. Add 10g of KOH solid powder in batches within half an hour;

[0052] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0053] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0054] e. Take 10g of the quaternary ammonium base obtained in d and mix it with 6g of sodium cyclohexane, add it to 35g of methylaluminoxane solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0055] Example 3: Preparation of catalyst C:

[0056] a. Under a nitrogen atmosphere, weigh 45g of tetrabutylammonium bromide and 80g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0057] b. Add 10g of KOH solid powder in batches within half an hour;

[0058] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0059] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0060] e. Take 10g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Add the mixture to 40g of methylaluminoxane solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0061] Example 4: Preparation of catalyst D:

[0062] a. Under a nitrogen atmosphere, weigh 45g of tetrabutylammonium bromide and 80g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0063] b. Add 10g of KOH solid powder in batches within half an hour;

[0064] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0065] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0066] e. Take 10g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Add the mixture to a solution of 15g of methylaluminoxane and 15g of trimethylgallium, stir evenly, and age at 50°C for 3 hours to obtain the polymerization catalyst.

[0067] Example 5: Preparation of catalyst E:

[0068] a. Under a nitrogen atmosphere, weigh 45g of tetrapropylammonium bromide and 60g of ethanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0069] b. Add 10g of NaOH solid powder in batches within half an hour;

[0070] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0071] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0072] e. Take 10g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Add the mixture to 30g of trimethylgallium solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0073] Preparation of catalyst F in Comparative Example 1:

[0074] a. Under a nitrogen atmosphere, weigh 28g of tetramethylammonium bromide and 50g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0075] b. Add 10g of KOH solid powder in batches within half an hour;

[0076] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0077] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0078] e. Take 15g of the quaternary ammonium base obtained in d, add it to 40g of methylaluminoxane solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0079] Preparation of catalyst G in Comparative Example 2:

[0080] a. Under a nitrogen atmosphere, weigh 28g of tetramethylammonium bromide and 50g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0081] b. Add 10g of KOH solid powder in batches within half an hour;

[0082] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0083] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0084] e. Take 15g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Stir well to obtain the polymerization catalyst.

[0085] Preparation of catalyst H in Comparative Example 3:

[0086] a. Under a nitrogen atmosphere, weigh 28g of tetramethylammonium bromide and 50g of methanol, mix them, place them in a three-necked flask, stir and maintain the temperature at 30℃;

[0087] b. Add 10g of KOH solid powder in batches within half an hour;

[0088] c. After the mixture in step b is complete, continue stirring for 4 hours and control the temperature in an oil bath at 40°C to ensure complete reaction;

[0089] d. The solution from process c is filtered and separated under a nitrogen atmosphere, and the mother liquor is concentrated by heating at 80°C to obtain tetramethylammonium hydroxide product, which is then dried under vacuum at an absolute pressure of 5 kPa for 10 h.

[0090] e. Take 5g of the quaternary ammonium base obtained in d and mix it with 10g of sodium decanoate. Add the mixture to 40g of methylaluminoxane solution, stir evenly, and age at 50℃ for 3h to obtain the polymerization catalyst.

[0091] Application Example 1

[0092] The tar was derived from the heavy component byproduct of the isocyanate production process at Wanhua Chemical's plant. It was used as a raw material in a small-scale test, and the HDI monomer content in the tar was determined by gel permeation chromatography (GPC). The GPC used was an Agilent 1260 model, and the method was as follows: three Waters Styragel HR0.5 columns were used in series; the mobile phase was THF; the column temperature was 45 degrees Celsius; and a RID detector was used. This method was used for GPC testing in the following application examples.

[0093] Viscosity testing was performed using a DV-79+PRO viscometer from Shanghai Nirun Technology. The method was as follows: a water bath was used to control the temperature at 25°C. The liquid to be tested was added, and after the material reached the target temperature, it was stabilized for 10 minutes. Then, the rotor was connected and the viscosity was set for testing. This method was used for viscosity testing in the following application examples.

[0094] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70°C for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80°C, and 0.1g of catalyst A was added dropwise. The temperature was maintained between 80 and 100°C, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0095] Application Example 2

[0096] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70°C for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80°C, and 0.1g of catalyst B was added dropwise. The temperature was maintained between 80 and 100°C, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0097] Application Example 3

[0098] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70℃ for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80℃, and 0.1g of catalyst C was added dropwise. The temperature was maintained between 80 and 100℃, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0099] Application Example 4

[0100] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70℃ for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80℃, and 0.1g of catalyst D was added dropwise. The temperature was maintained between 80 and 100℃, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0101] Application Example 5

[0102] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70°C for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80°C, and 0.1g of catalyst E was added dropwise. The temperature was maintained between 80 and 100°C, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0103] Application Example 6

[0104] Under nitrogen protection, 200 g of HMDI tar (monomer content 12%) was added to a four-necked flask. The mixture was stirred at 70°C for 20 min using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80°C, and 0.1 g of catalyst A was added dropwise. The temperature was maintained between 80 and 100°C, and the reaction was stirred for 3 h. 1 g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 min. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0105] Comparative Example 1

[0106] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70℃ for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80℃, and 0.1g of catalyst F was added dropwise. The temperature was maintained between 80 and 100℃, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0107] Comparative Example 2

[0108] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70℃ for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80℃, and 0.1g of catalyst G was added dropwise. The temperature was maintained between 80 and 100℃, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and stirring was continued for another 30 minutes to terminate the reaction. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0109] Comparative Example 3

[0110] Under nitrogen protection, 200g of HDI tar (monomer content approximately 10%) was added to a four-necked flask. The mixture was stirred at 70°C for 20 minutes using a magnetic stirrer with temperature monitoring. The temperature was then raised to 80°C, and 0.1g of catalyst H was added dropwise. The temperature was maintained between 80 and 100°C, and the reaction was stirred for 3 hours. 1g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 minutes. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0111] Comparative Example 4

[0112] Under nitrogen protection, 200 g of HMDI tar (monomer content 12%) was added to a four-necked flask. The mixture was stirred at 50°C for 20 min using a magnetic stirrer with temperature monitoring. Then, 0.1 g of catalyst A was added dropwise, and the temperature was maintained between 40-60°C. The reaction was stirred for 3 h. Finally, 1 g of phosphoric acid was added, and the reaction was terminated by stirring for another 30 min. The mixture was then cooled and discharged to obtain a black, viscous tar. The HDI monomer content in the reacted tar was determined using gel permeation chromatography (GPC).

[0113] Table 1 Results of tar monomer residues for each catalyst

[0114]

[0115] Summary of experimental results from the examples and comparative examples:

[0116] Through the experiments in the above examples and comparative examples, it was found that catalytic polymerization of a tar-containing heavy component in the isocyanate production process can effectively reduce the monomer content in the tar, significantly reduce the toxicity of the tar waste liquid, broaden the downstream applications of the by-product tar, and is environmentally friendly. The addition of two co-catalysts greatly improves the catalytic activity, and the resulting polymerized isocyanate has a low degree of polymerization, strong trimerization selectivity, does not form high-viscosity substances that would clog the equipment, and exhibits strong long-term operational stability.

[0117] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing an isocyanate polymerization catalyst, characterized in that, Includes the following steps: a. Under a nitrogen atmosphere, mix the [R1R2R3NR4]X quaternary ammonium salt and solvent, stir and maintain the system temperature within a certain range; b. Add alkali to the solution obtained in step a; c. After process b is complete, continue stirring until the reaction is complete; d. The solution obtained in process c is filtered and separated under a nitrogen atmosphere. The mother liquor is heated and concentrated to obtain the quaternary ammonium base product, which is then dried under vacuum. e. Mix the quaternary ammonium base obtained in d with sodium fatty acid R5COONa, add it to methylaluminoxane and / or trimethylgallium, stir evenly, and age at 40-60°C. The catalyst obtained by the method comprises the following components: [R1R2R3NR4]OH15wt%-35wt%, R5COONa 10wt%-20wt%, 50wt%-70wt% of methylaluminoxane (MAO) and / or trimethylgallium; R1 to R4 are selected from alkyl groups with 4 or fewer carbon atoms, and R5 is selected from alkyl groups with 15 or fewer carbon atoms.

2. The method according to claim 1, characterized in that, In step a, the mass ratio of quaternary ammonium salt to solvent is 1:1 to 1:4, and the temperature is maintained at 20-30°C; the solvent is selected from methanol, ethanol, propanol, butanol, and ethyl acetate.

3. The method according to claim 2, characterized in that, In step a, the temperature is maintained at 22–25°C.

4. The method according to claim 1, characterized in that, In step b, the alkali is KOH or NaOH solid powder.

5. The method according to claim 4, characterized in that, In step b, the molar ratio of quaternary ammonium salt to alkali is 1:1 to 1:

2.

6. The method according to claim 1, characterized in that, In step c, the reaction temperature is 30–40℃ and the reaction time is 3–4 hours.

7. The method according to claim 1, characterized in that, In step d, the heating and concentration temperature is controlled at 60–100°C.

8. The method according to claim 7, characterized in that, In step d, the heating and concentration are carried out under reduced pressure, with a pressure of 30–50 kPa.

9. The method according to claim 1, characterized in that, In step e, the mass ratio of quaternary ammonium base to sodium fatty acid is 1:1 to 3:1, and the mass ratio of quaternary ammonium base to MAO and / or trimethylgallium is 1:1 to 1:

5.

10. The method according to claim 9, characterized in that, In step e, the mass ratio of quaternary ammonium base to MAO and / or trimethylgallium is 1:2 to 1:

3.

11. The method according to claim 1, characterized in that, R1 to R4 are selected from ethyl or propyl groups, and R5 is selected from alkyl groups with 8-10 carbon atoms.

12. Use of the catalyst prepared by any one of claims 1-11 as an isocyanate polymerization catalyst, wherein the isocyanate is selected from one of MDI, TDI, HDI, IPDI, HMDI, PDI, and XDI.

13. A method for purifying isocyanate tar, characterized in that, The catalyst prepared by any one of the preparation methods described in claims 1-11 is added to a tar solution containing isocyanate monomers, polymers, and urea in an isocyanate production system and reacted. Then, a reaction terminator is added to obtain a tar component with low monomer content.

14. The method according to claim 13, characterized in that, The reaction temperature is 70-100℃, the catalyst dosage is 0.01%-0.1% of the mass fraction of isocyanate tar, and the reaction time is maintained for 2-4 hours.

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