Method for synthesizing hexamethylene diisocyanate

Abstract

The invention discloses a method for synthesizing hexamethylene diisocyanate, which is characterized in that hydrogen, carbon monoxide and 6-aminocapronitrile are used as raw materials, hexamethylene diisocyanate is synthesized in the presence of a catalyst, and the catalyst takes transition metal as an active component. According to the method for preparing hexamethylene diisocyanate through non-phosgenation, by optimizing the catalyst type and reaction conditions, the reaction selectivity is improved, the use of toxic raw materials is avoided, the method is environment-friendly, the production cost is reduced, the product is easy to separate and recover, and the method has obvious advantages in industrial application.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for synthesizing hexamethylene diisocyanate. Background Technology

[0002] Hexamethylene diisocyanate (HDI) is the most important monomer among aliphatic diisocyanates (ADI), accounting for approximately 60% of the total ADI demand. Most HDI is prepared as HDI biuret or HDI trimer. HDI, HDI biuret, and trimer are important raw materials for the production of polyurethane coatings and polyurethane elastomers. Polyurethane coatings produced using HDI, HDI biuret, or trimer as raw materials have characteristics such as non-yellowing and strong weather resistance, and are widely used in aerospace, automotive, construction, woodworking, plastics, and leather industries.

[0003] Currently, HDI production processes are mainly divided into phosgene and non-phosgene methods. Among them, the phosgene method for producing isocyanates is mature, economical, and the most widely industrialized production method. Patent document CN102627582B uses 1,6-hexanediamine (HDA) and phosgene as raw materials, aromatic monoisocyanates as catalysts, and aromatic hydrocarbons as inert solvents to prepare a mixture of HDI through a two-stage reaction at low and high temperatures. The aromatic monoisocyanates and aromatic hydrocarbons are then removed by distillation to obtain HDI. Patent document CN101805272A provides a method for synthesizing isocyanates through interfacial phosgenation, which can reduce the impact of byproduct hydrogen chloride on the reaction. However, ensuring phosgene reflux under a slightly negative pressure increases the load on the condenser and does not solve the problem of low photochemical efficiency, resulting in no substantial improvement in space-time conversion rate. Patent document CN103360282A discloses a continuous synthesis method for HDI, employing a series of batch reactors for synthesis. Materials are transported between reactors via overflow, improving the utilization rate of phosgene. However, to reduce the impact of hydrogen chloride on the conversion rate and selectivity of the reaction, this method uses methylchlorosilane as a protecting agent to protect the amino groups, leading to relatively complex post-processing and still exhibiting low reaction efficiency. Furthermore, because this type of method involves phosgene synthesis and processing, phosgenation reaction, phosgene removal, product separation and purification, and tail gas treatment, it mainly suffers from the following problems: 1. Using highly toxic phosgene as a raw material presents a series of engineering and technical issues related to safety and environmental protection during the production process; 2. Residual chlorine in the product is difficult to remove, affecting product quality.

[0004] To address the problems associated with the phosgene process, non-phosgene routes for isocyanate synthesis have become a new technological development direction. In non-phosgene processes, Monsanto in the US uses CO and hexamethylenediamine to prepare carbamates, which are then dehydrated with dehydrating agents such as phosphorus oxychloride to produce HDI. The addition of dehydrating agents complicates subsequent separation operations. Cyanotech in the US utilizes the direct reaction of nitro compounds and CO to generate HDI; this reaction requires pressures of 19.6–29.4 MPa, placing stringent pressure requirements on the equipment. BASF in Germany developed a process for preparing HDI using dibutyl carbonate and hexamethylenediamine as raw materials, but the high price of dibutyl carbonate makes HDI production costly.

[0005] Therefore, developing a highly efficient and environmentally friendly HDI synthesis method has significant theoretical and practical value, broad market prospects, and good social and environmental benefits. Summary of the Invention

[0006] The purpose of this invention is to provide a novel non-phosgene synthesis method for HDI, which uses hydrogen, carbon monoxide and 6-aminohexanonitrile as raw materials to efficiently synthesize HDI under the action of a catalyst, thereby improving the selectivity of the reaction, reducing environmental pollution and lowering production costs.

[0007] To achieve the above objectives, the present invention provides a method for synthesizing hexamethylene diisocyanate, using hydrogen, carbon monoxide and 6-aminohexanonitrile as raw materials, and synthesizing hexamethylene diisocyanate in the presence of a catalyst, wherein the catalyst is a transition metal as the active component.

[0008] The present invention is further configured such that the molar ratio of hydrogen, carbon monoxide and 6-aminohexanonitrile is 20~2:20~2:1.

[0009] The present invention is further configured such that the transition metal is selected from one or more of nickel, cobalt, copper, ruthenium, rhodium, palladium, and platinum.

[0010] The present invention is further configured such that the transition metal includes palladium, and the mass content of palladium is 0.5-5% based on the total mass of the catalyst.

[0011] The present invention is further configured such that the catalyst comprises a transition metal and a support, the support being selected from one or more of alumina and molecular sieves, and the mass content of the transition metal is 0.1-10% based on the total mass of the catalyst.

[0012] The present invention is further configured such that the amount of catalyst added is 0.01~10% of the mass of 6-aminohexanonitrile, preferably 0.5~5%.

[0013] The present invention is further configured such that the catalyst preparation method includes the following steps: a) dissolving a transition metal nitrate in water to prepare a mixed solution, wherein the nitrate is selected from one or more of nickel nitrate, cobalt nitrate, copper nitrate, ruthenium nitrate, rhodium nitrate, palladium nitrate, and platinum nitrate; b) immersing a support in the mixed solution for 0.5-6 h, filtering, to obtain a modified catalyst precursor, wherein the support is selected from one or more of molecular sieves and alumina particles; c) calcining the modified catalyst precursor at 400-500℃ for 5-12 h to obtain the catalyst.

[0014] The present invention is further configured to include the following steps: 1) dissolving 6-aminohexanonitrile in a solvent to form a 6-aminohexanonitrile solution; 2) adding a catalyst to the 6-aminohexanonitrile solution under inert gas protection, introducing hydrogen and carbon monoxide, and reacting at a certain reaction temperature and reaction pressure to obtain a reaction mixture; 3) separating the hexamethylene diisocyanate product from the reaction mixture.

[0015] The present invention is further configured such that the solvent is selected from one or more of benzene, toluene, xylene, chlorobenzene and dichlorobenzene.

[0016] The present invention is further configured such that the reaction temperature is 100℃~200℃ and the reaction pressure is 0.1MPa~10MPa.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1) High selectivity: By optimizing the type of catalyst and reaction conditions, the selectivity of HDI has been significantly improved.

[0019] 2) Environmentally friendly: It avoids the use of toxic raw materials and reduces environmental pollution.

[0020] 3) Cost-effectiveness: It reduces production costs and is conducive to large-scale industrial production.

[0021] 4) The raw materials and catalysts used in the method of the present invention are widely available and easy to separate and recover. The method is simple to operate and has obvious advantages in industrial application. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] This invention provides a method for synthesizing hexamethylene diisocyanate, using hydrogen, carbon monoxide and 6-aminohexanonitrile as raw materials, and synthesizing hexamethylene diisocyanate in the presence of a catalyst, wherein the catalyst has a transition metal as the active component.

[0024] The reaction formula for the synthesis of HDI from hydrogen, carbon monoxide, and 6-aminohexanonitrile in the presence of a catalyst is as follows: .

[0025] Traditional industrial production of HDI mainly relies on the phosgene process. Although this process carries toxicity risks, it is technically mature and offers high yields. Non-phosgene processes (such as the dimethyl carbonate process) are still under optimization, and new raw material systems require breakthroughs in key technologies such as catalysis and separation. During their research, the inventors unexpectedly discovered that, in the presence of the preferred catalyst of this invention, the activation and directed conversion of 6-aminohexanenitrile to isocyanate were achieved, avoiding side reactions such as excessive hydrogenation to generate amine compounds. The reaction raw materials are inexpensive, readily available, non-toxic, and harmless. The catalyst exhibits high selectivity, and the reaction conditions are mild. This solves the environmental pollution and low efficiency problems associated with the phosgene process for HDI production, and thus has high economic value.

[0026] Furthermore, the molar ratio of hydrogen, carbon monoxide, and 6-aminohexanonitrile is 20~2:20~2:1.

[0027] Furthermore, the transition metal is selected from one or more of nickel, cobalt, copper, ruthenium, rhodium, palladium, and platinum. Preferably, the transition metal includes palladium, with a palladium content of 0.5-5% based on the total mass of the catalyst. More preferably, a combination of multiple transition metals is used, including but not limited to palladium-nickel-rhodium and palladium-cobalt-ruthenium. The inventors have discovered that palladium metal can enhance the activity of the catalyst, wherein zero-valent palladium promotes hydrogenation and divalent palladium promotes the formation of HDI, thereby promoting the reaction.

[0028] Furthermore, the catalyst comprises a transition metal and a support, the support being selected from one or more of alumina and molecular sieves, and the mass content of the transition metal is 0.1-10% based on the total mass of the catalyst. Preferably, the catalyst is prepared using an impregnation method, in which the transition metal is impregnated onto the support.

[0029] Furthermore, the BET specific surface area of ​​the catalyst is between 200 and 410 m². 2 Catalysts with a specific surface area between 2.5 and 3.0 nm and a pore size between 2.5 and 3.0 nm exhibit higher activity.

[0030] Furthermore, the amount of catalyst added is 0.01 to 10% of the mass of 6-aminohexanonitrile, preferably 0.5 to 5%, more preferably 1 to 2%.

[0031] Furthermore, the catalyst preparation method includes the following steps: a) dissolving a transition metal-containing nitrate in water to prepare a mixed solution, wherein the nitrate is preferably one or more selected from nickel nitrate, cobalt nitrate, copper nitrate, ruthenium nitrate, rhodium nitrate, palladium nitrate, and platinum nitrate; b) immersing the support in the mixed solution for 0.5-6 h, filtering, to obtain the modified catalyst precursor, wherein the support is preferably one or more selected from molecular sieves and alumina particles; c) calcining the modified catalyst precursor at 400-500℃ for 5-12 h to obtain the catalyst.

[0032] The catalyst obtained using the preparation method of the present invention has high HDI selectivity.

[0033] Furthermore, the method for synthesizing hexamethylene diisocyanate according to the present invention includes the following steps: 1) dissolving 6-aminohexanonitrile in a solvent to form a 6-aminohexanonitrile solution; 2) adding a catalyst to the 6-aminohexanonitrile solution under inert gas protection, introducing hydrogen and carbon monoxide, and reacting at a certain reaction temperature and reaction pressure to obtain a reaction mixture, wherein the inert gas is preferably one or more of nitrogen, argon, and helium; 3) separating the hexamethylene diisocyanate product from the reaction mixture, preferably using separation methods such as solvent removal and distillation to recover the hexamethylene diisocyanate.

[0034] 6-Aminohexanonitrile is easily oxidized to heavy components at high temperatures, reducing reaction selectivity; simultaneously, carbon buildup in the system affects catalyst lifetime, therefore, inert gas is needed to replace oxygen in the reaction system. The reaction mixture of this invention has a simple composition, a simple separation process, is easy to recover, and the product is free of residual chlorine pollution and of high quality.

[0035] Furthermore, the solvent is selected from one or more of benzene, toluene, xylene, chlorobenzene, and dichlorobenzene. Preferably, the mass concentration of the 6-aminohexanonitrile solution is 1-60%, more preferably 20-40%.

[0036] Furthermore, the reaction temperature is 100℃~200℃, preferably 150℃~200℃, and the reaction pressure is 0.1MPa~10MPa, preferably 5MPa~10MPa.

[0037] This invention reduces the severity of reaction conditions by using a highly selective catalyst, simplifies operation, and has significant advantages for industrial applications.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments. The scope of protection of the present invention is not limited to the following embodiments; these examples are provided for illustrative purposes only and do not limit the present invention in any way.

[0039] Examples 1-4 are examples of catalyst preparation.

[0040] Example 1:

[0041] Weigh 27.38g palladium nitrate, 29.53g nickel nitrate and 46.69g rhodium nitrate and dissolve them in 700 mL deionized water. Add 80g Al2O3 particles and impregnate for 2 hours. Filter to obtain a catalyst intermediate. Calcine the catalyst intermediate at 450℃ for 3 hours. Activate it with hydrogen gas in a fixed bed at 300℃ for 6 hours to obtain the catalyst.

[0042] Measurements showed that the mass content of transition metals in the catalyst was: palladium 1.49%, nickel 0.31%, and rhodium 0.83%.

[0043] Example 2:

[0044] Weigh 27.38 g palladium nitrate, 29.57 g cobalt nitrate and 51.25 g ruthenium nitrate and dissolve them in 600 mL deionized water. Add 80 g β-molecular sieve particles (manufacturer: 3A Company) and impregnate for 1 h. Filter to obtain a catalyst intermediate. Calcinate the catalyst intermediate at 500 °C for 2 h. Activate with hydrogen gas in a fixed bed at 270 °C for 8 h to obtain the catalyst.

[0045] Example 3

[0046] Weigh 82.10g of palladium nitrate and dissolve it in 600mL of deionized water. Add 80g of Al2O3 particles and impregnate for 1h. Filter to obtain a catalyst intermediate. Calcinate the catalyst intermediate at 500℃ for 2h. Activate it with hydrogen gas through a fixed bed at 270℃ for 8h to obtain the catalyst.

[0047] Example 4

[0048] Weigh 41.07g palladium nitrate and 45.47g copper nitrate and dissolve them in 600mL deionized water. Add 80g β-molecular sieve particles (manufacturer: 3A Company), impregnate for 1h, and filter to obtain a catalyst intermediate. Calcinate the catalyst intermediate at 500℃ for 2h. Activate it with hydrogen gas in a fixed bed at 270℃ for 8h to obtain the catalyst.

[0049] Calculations using the BET method showed that the specific surface areas of the catalysts in Examples 1-4 ranged from 200 to 410 m². 2 The pore size is between 2.5 and 3.0 nm. Measurements showed that the catalysts in Examples 1-4 contained 0.5-5% palladium by mass and 0.1-10% transition metal by mass.

[0050] In Examples 5-8, hexamethylene diisocyanate was synthesized using the catalysts prepared in Examples 1-4, respectively.

[0051] Example 5:

[0052] Under nitrogen protection, 0.61 g of the catalyst from Example 1 was transferred to a 1 L reactor containing 56.65 g of 6-aminohexanonitrile and 100 g of toluene. After sealing the reactor, the air inside was replaced with hydrogen. The mixture was stirred at 500 rpm / min and heated to 150 °C. 5.02 g of hydrogen (excluding the replacement hydrogen) and 60.87 g of carbon monoxide were slowly introduced. The reaction pressure was maintained at 8.0 MPa. After reacting for 4 hours, the pressure was released to atmospheric pressure to obtain the reaction solution. Gas chromatography analysis showed that the conversion rate of 6-aminohexanonitrile was 68.12% and the selectivity of HDI was 84.67%. After solvent removal and vacuum distillation, HDI with a purity >99.5% was obtained.

[0053] Example 6:

[0054] Under nitrogen protection, 0.63 g of the catalyst from Example 2 was transferred to a 1 L reactor containing 56.65 g of 6-aminohexanonitrile and 100 g of chlorobenzene. After sealing the reactor, the air inside was replaced with hydrogen. The mixture was stirred at 600 rpm / min and heated to 180 °C. 5.02 g of hydrogen (excluding the replacement hydrogen) and 60.87 g of carbon monoxide were slowly introduced. The reaction pressure was maintained at 9.5 MPa. After reacting for 6 h, the pressure was released to atmospheric pressure to obtain the reaction solution. Gas chromatography analysis showed that the conversion rate of 6-aminohexanonitrile was 74.03% and the selectivity of HDI was 79.96%. After solvent removal and vacuum distillation, HDI with a purity >99.5% was obtained.

[0055] Example 7

[0056] Under nitrogen protection, 0.62 g of the catalyst from Example 3 was transferred to a 1 L reactor containing 56.63 g of 6-aminohexanonitrile and 100 g of benzene. After sealing the reactor, the air inside was replaced with hydrogen. The mixture was stirred at 500 rpm / min and heated to 150 °C. 5.03 g of hydrogen (excluding the replacement hydrogen) and 60.29 g of carbon monoxide were slowly introduced. The reaction pressure was maintained at 8.5 MPa. After reacting for 6 h, the pressure was released to atmospheric pressure to obtain the reaction solution. Gas chromatography analysis showed that the conversion rate of 6-aminohexanonitrile was 68.93% and the selectivity of HDI was 57.43%. After solvent removal and vacuum distillation, HDI with a purity >99.5% was obtained.

[0057] Example 8

[0058] Under nitrogen protection, 0.61 g of the catalyst from Example 4 was transferred to a 1 L reactor containing 56.71 g of 6-aminohexanonitrile and 100 g of xylene. After sealing the reactor, the air inside was replaced with hydrogen. The mixture was stirred at 600 rpm / min and heated to 180 °C. 4.99 g of hydrogen (excluding the replacement hydrogen) and 61.18 g of carbon monoxide were slowly introduced. The reaction pressure was maintained at 9.0 MPa. After reacting for 4 h, the pressure was released to atmospheric pressure to obtain the reaction solution. Gas chromatography analysis showed that the conversion rate of 6-aminohexanonitrile was 73.61% and the selectivity of HDI was 60.21%. After solvent removal and vacuum distillation, HDI with a purity >99.5% was obtained.

[0059] The experimental results of Examples 5-8 are summarized in the table below:

[0060] The technical solution described in this invention improves the conversion rate of 6-aminohexanonitrile and the selectivity of HDI by using a highly selective catalyst, reduces the harshness of the reaction for synthesizing HDI from hydrogen, carbon monoxide and 6-aminohexanonitrile, and provides a low-pollution, non-phosgene method for preparing HDI with good economic benefits.

[0061] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for synthesizing hexamethylene diisocyanate, characterized in that, Hexamethylene diisocyanate was synthesized using hydrogen, carbon monoxide, and 6-aminohexanonitrile as raw materials in the presence of a catalyst, wherein the catalyst is a transition metal as the active component.

2. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The molar ratio of hydrogen, carbon monoxide and 6-aminohexanonitrile is 20~2:20~2:

1.

3. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The transition metal is selected from one or more of nickel, cobalt, copper, ruthenium, rhodium, palladium, and platinum.

4. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The transition metal includes palladium, and the palladium content is 0.5-5% based on the total mass of the catalyst.

5. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The catalyst comprises a transition metal and a support, wherein the support is selected from one or more of alumina and molecular sieves, and the mass content of the transition metal is 0.1-10% based on the total mass of the catalyst.

6. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The amount of catalyst added is 0.01~10% of the mass of 6-aminohexanonitrile, preferably 0.5~5%.

7. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, The method for preparing the catalyst includes the following steps: a) Dissolve a transition metal-containing nitrate in water to prepare a mixed solution, wherein the nitrate is selected from one or more of nickel nitrate, cobalt nitrate, copper nitrate, ruthenium nitrate, rhodium nitrate, palladium nitrate, and platinum nitrate; b) Immerse the support in the mixed solution for 0.5-6 hours, filter, and obtain the modified catalyst precursor. The support is selected from one or more of molecular sieves and alumina particles. c) The modified catalyst precursor is calcined at 400-500℃ for 5-12 hours to obtain the catalyst.

8. The method for synthesizing hexamethylene diisocyanate according to claim 1, characterized in that, Specifically, the following steps are included: 1) Dissolve 6-aminohexanonitrile in a solvent to form a 6-aminohexanonitrile solution; 2) Under inert gas protection, a catalyst is added to the 6-aminohexanonitrile solution, and hydrogen and carbon monoxide are introduced. The reaction is carried out at a certain reaction temperature and reaction pressure to obtain a reaction mixture. 3) Hexamethylene diisocyanate product is separated from the reaction mixture.

9. The method for synthesizing hexamethylene diisocyanate according to claim 8, characterized in that, The solvent is selected from one or more of benzene, toluene, xylene, chlorobenzene, and dichlorobenzene.

10. The method for synthesizing hexamethylene diisocyanate according to claim 8, characterized in that, The reaction temperature is 100~200℃ and the reaction pressure is 0.1~10MPa.

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