Preparation method of tetramethyl m-xylylene diisocyanate

Abstract

The invention provides a preparation method of tetramethyl m-xylylene diisocyanate, which comprises the following steps: mixing tetramethyl xylylene dicarbamate with a catalyst, and carrying out thermal cracking reaction in a microchannel reactor. According to the preparation method provided by the invention, by designing the structure of the micro-channel reactor and optimizing the selection of a reaction catalyst and reaction parameters, the preparation of tetramethyl m-xylylene diisocyanate with the total yield of 90% or above and the high purity of 99% is realized.

Description

Technical Field

[0001] This invention relates to the field of separation technology, and in particular to a method for preparing tetramethylm-phenylenedimethyl diisocyanate. Background Technology

[0002] Tetramethyl-m-phenylenedimethyl diisocyanate (TMXDI) is a structurally unique isocyanate compound. The presence of four methyl substituents in its molecular structure increases steric hindrance, effectively protecting the isocyanate group at the meta position, thus exhibiting unique chemical and physical properties. TMXDI possesses low reactivity, high stability, and low toxicity, making it a high-performance alternative to traditional isocyanates. It excels particularly in environments with stringent environmental requirements and complex operating conditions (such as humidity and strong ultraviolet radiation), making it a key raw material in high-end coatings, adhesives, and elastomers. However, only a few countries, such as American Cyano Corporation and Mitsui Chemicals Corporation of Japan, possess the industrial-scale production capacity for TMXDI.

[0003] Currently, the main methods for producing tetramethyl-m-phenylenedimethyl diisocyanate (TMXDI) include the phosgene method, isocyanate method, cyanate method, and carbamate cracking method. Among these, the phosgene method uses highly toxic phosgene, which is highly corrosive to equipment, and the raw material tetramethylphenylenedimethyldiamine is difficult to obtain, making industrial-scale production challenging. While the isocyanate and cyanate methods offer higher yields, the toxicity and hazards of the isocyanates or cyanates used in the reaction process make industrial production difficult. Compared to other methods, the carbamate thermal cracking method uses less toxic raw materials, and the reaction process is easier to control, making it more suitable for industrial production. The highest yield of TMXDI prepared by the existing carbamate cracking method is 56.9%, which is relatively low. This is because carbamate cracking often uses batch or fixed-bed cracking. In batch cracking, the material stays in the reactor for a long time, and the resulting isocyanates are prone to self-polymerization, generating a large number of byproducts. Fixed-bed cracking requires a solid catalyst for fixation; the material undergoes cracking after flowing through the solid catalyst, and the material flow is difficult to mix thoroughly, affecting the cracking efficiency.

[0004] Therefore, how to provide a method for the efficient preparation of tetramethyl-m-phenylenedimethyl diisocyanate via pyrolysis has become an urgent problem to be solved. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, which can achieve a total yield of over 90% and a high purity of 99% in preparing tetramethyl-m-phenylenedimethyl diisocyanate.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing tetramethylmethylenedimethyl diisocyanate, the method comprising: mixing tetramethylmethylenedicarbamate with a catalyst and then carrying out a thermal pyrolysis reaction in a microchannel reactor.

[0008] This invention uses a microchannel reactor to prepare tetramethyl-m-phenylenedimethyl diisocyanate. The microchannel reactor has a large specific surface area at the reaction interface, sufficient heat exchange, and uniform temperature, providing a highly efficient and rapid reaction environment.

[0009] Preferably, the tetramethylphenyldimethyl dicarboxylate is mixed with the catalyst in a molten state.

[0010] Preferably, the mixing temperature is 140-190°C, for example, it can be 140°C, 150°C, 160°C, 170°C, 180°C or 190°C.

[0011] The melting temperature of tetramethylphenyldimethyl dicarboxylate is 130-132℃. This invention limits the mixing temperature of tetramethylphenyldimethyl dicarboxylate and catalyst to 140-190℃, so that tetramethyl-m-phenylenedimethyl diisocyanate and catalyst are premixed to ensure that the two can be in uniform contact and improve mass transfer efficiency.

[0012] Preferably, the mixing time is 5-15 min, for example, it can be 5 min, 6 min, 8 min, 10 min, 12 min, 14 min or 15 min, etc.

[0013] Preferably, the catalyst comprises a liquid catalyst.

[0014] Preferably, the liquid catalyst comprises an organotin catalyst and / or an organotitanium catalyst.

[0015] Preferably, the organotin catalyst comprises dibutyltin dilaurate and / or stannous octoate, and more preferably dibutyltin dilaurate.

[0016] Preferably, the organotitanium catalyst comprises any one or a combination of at least two of tetrabutyl titanate, tetraisopropyl titanate, tetraoctyl titanate, or titanium citrate, and more preferably tetrabutyl titanate.

[0017] This invention employs a liquid catalyst, which can be fully mixed with tetramethylphenyldimethyl dicarboxylate in a microchannel reactor. Compared with conventional metal powder catalysts, the liquid catalyst can solve the problem of wall adhesion, thus resolving reactor clogging or difficulty in cleaning. Compared with a solid catalyst-solvent system, the solid catalyst-solvent system introduces solvent, which increases the complexity of subsequent purification processes and the generation of waste. In contrast, the liquid catalyst increases the contact surface area with the material, improves mass transfer efficiency, and enhances reaction conversion rate.

[0018] Preferably, the mass ratio of the tetramethylphenyldimethyl dicarboxylate to the catalyst is 100:(1-3), for example, it can be 100:1, 100:1.5, 100:2, 100:2.5 or 100:3, etc.

[0019] Preferably, the microchannel reactor has a Tesla flow channel structure.

[0020] Preferably, the Tesla flow channel structure has 40-200 Tesla valves, for example, 40, 50, 100, 150 or 200.

[0021] Figure 1 This is a cross-sectional schematic diagram of the microchannel reactor used in this invention; the Tesla valve is not fully shown.

[0022] Preferably, the length of the individual Tesla valve is 20-40 mm, for example, it can be 20 mm, 25 mm, 30 mm, 35 mm or 40 mm.

[0023] Preferably, the width of the individual Tesla valve is 20-40 mm, for example, it can be 20 mm, 25 mm, 30 mm, 35 mm or 40 mm.

[0024] Preferably, the length of the Tesla channel is 140-400 mm, for example, it can be 140 mm, 150 mm, 200 mm, 300 mm, 350 mm or 400 mm.

[0025] Preferably, the tetramethylphenyldimethyl dicarboxylate is mixed with the catalyst to obtain a pre-reactant.

[0026] Preferably, the flow rate of the premix in the microchannel reactor is 0.1-2 kg / min, for example, it can be 0.1 kg / min, 0.2 kg / min, 0.4 kg / min, 0.5 kg / min, 0.6 kg / min, 0.8 kg / min, 1 kg / min, 1.2 kg / min, 1.4 kg / min, 1.5 kg / min, 1.6 kg / min, 1.8 kg / min or 2 kg / min, etc.

[0027] Preferably, the residence time of the premix in the microchannel reactor is 5-10 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min.

[0028] This invention, through a special design of the microreactor channel structure, ensures that tetramethylphenyldimethyl dicarboxylate undergoes a complete reaction after flowing through the microchannel reactor at a certain flow rate, solving the problem of insufficient reaction due to the small specific surface area of ​​conventional pyrolysis reactors. The Tesla flow channel reactor is a microchannel reactor based on the Tesla valve structure design. Its unique flow channel design significantly enhances the mixing effect and mass transfer performance of the fluid. The Tesla valve utilizes fluid dynamics principles to generate a vortex effect in the flow channel, thereby enhancing the mixing effect and improving mass transfer performance. Its working principle is based on the pressure difference generated when the fluid flows in a channel with a specific geometry, causing the fluid to form a complex flow pattern within the channel, thus achieving efficient mixing.

[0029] Preferably, the temperature of the thermal decomposition reaction is 200-320℃, for example, it can be 200℃, 220℃, 240℃, 250℃, 260℃, 280℃, 300℃ or 320℃, etc., preferably 220-280℃.

[0030] Preferably, the thermal decomposition reaction is carried out under vacuum conditions.

[0031] Preferably, the vacuum degree is 0.5-50 kPa, for example, it can be 0.5 kPa, 1 kPa, 5 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 40 kPa or 50 kPa, etc., and preferably 1-20 kPa.

[0032] Preferably, the thermal pyrolysis reaction is followed by condensation and purification processes.

[0033] Preferably, the condensation temperature is -15~20℃, for example, it can be -15℃, -5℃, 0℃, 5℃, 10℃, 15℃ or 20℃, etc.

[0034] Preferably, the purification process includes distillation.

[0035] Preferably, the distillation temperature of tetramethyl-m-phenylenedimethyl diisocyanate in the distillation is 130-140°C, for example, it can be 130°C, 132°C, 134°C, 135°C, 136°C, 138°C or 140°C.

[0036] The distillation temperature of low-boiling-point impurity components in distillation is 115-125℃, for example, it can be 115℃, 116℃, 118℃, 120℃, 122℃, 124℃ or 120℃, etc.

[0037] Preferably, the distillation is carried out under vacuum conditions.

[0038] Preferably, the vacuum degree is 0.5-1.5 kPa, for example, it can be 0.5 kPa, 0.6 kPa, 0.8 kPa, 1 kPa, 1.2 kPa, 1.4 kPa or 1.5 kPa, etc.

[0039] Preferably, the preparation method includes:

[0040] (1) Heat tetramethylphenyldimethyl dicarboxylate until it melts, and mix it with the catalyst at 140-190℃ for 5-15 min to obtain the pre-reactant;

[0041] (2) The pre-reactant is injected into a microchannel reactor at a flow rate of 0.1-2 kg / min and reacted at 200-320℃ and 0.5-20 kPa vacuum for a residence time of 5-10 min to obtain the crude tetramethylm-isophthalic acid diisocyanate.

[0042] (3) The crude tetramethyl-m-phenylenedimethyl diisocyanate was subjected to condensation and purification treatment to obtain the tetramethyl-m-phenylenedimethyl diisocyanate.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects:

[0044] (1) This invention provides an innovative method for preparing tetramethylm-isophthalic acid diisocyanate with a total yield of over 90% and a purity of 99%.

[0045] (2) By specially designing the microreactor channel structure, the present invention ensures that tetramethyl phthalimide dicarboxylate can fully react after passing through the microchannel reactor at a certain flow rate, thus solving the problem of small specific surface area and insufficient reaction in conventional pyrolysis reactors.

[0046] (3) The present invention uses a liquid catalyst that can be fully mixed with tetramethylphenyldimethyl dicarboxylate. Compared with conventional metal powder catalysts, liquid catalysts can solve the problem of wall adhesion and solve the problem of reactor blockage or difficulty in cleaning. Attached Figure Description

[0047] Figure 1 This is a schematic cross-sectional view of the microchannel reactor used in this invention;

[0048] Among them, 1-microchannel reactor, 2-Tesla flow channel, 3-Tesla valve, 4-feed inlet, 5-discharge outlet. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0050] The specific information of the materials used in the following specific embodiments of the present invention is as follows:

[0051] Tetramethylphenyldimethylcarbamate (TMXDU) was prepared by adding 19.03 g of methyl carbamate and 0.13 g of p-toluenesulfonic acid to a three-necked flask and heating in a constant-temperature oil bath. When the temperature reached 90°C, 4.01 g of DIPEB was added dropwise over 0.5 h. After the addition was complete, the temperature was raised to 130°C, and the reaction was continued with stirring for 7 h until the reaction was stopped. The temperature was then lowered to 60°C, and sufficient sodium carbonate was added and stirred for 30 min to neutralize the solution. Unreacted methyl carbamate was recovered by vacuum distillation (85°C / 0.09 MPa). The solution was cooled to room temperature, and the vacuum was stopped. Ethyl acetate was added dropwise to the oily mixture while stirring. The product was collected, filtered, and dried to obtain a white solid, which was tetramethylphenyldimethylcarbamate.

[0052] Dibutyltin dilaurate, purchased from Aladdin Reagent Co., Ltd.;

[0053] Tetrabutyl titanate was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0054] Example 1

[0055] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, the method comprising:

[0056] (1) 8 kg of tetramethyl phthalimide dicarboxylate (TMXDU) raw material was put into a 15 L reactor and melted at 155 °C. Then, 160 g of dibutyltin dilaurate catalyst was added and mixed. After mixing for 10 min, the pre-reactant was obtained.

[0057] (2) The pre-reactant is transported to the material pump through the feed valve of the reactor and the pipeline. The pre-reactant is injected into the feed port of the microchannel reactor (containing 100 Tesla valves of 40 mm × 40 mm and the length of the microchannel reactor is 400 mm) at a flow rate of 1 kg / min by the material pump (high temperature plunger pump). Tetramethylphenyl dimethyl dicarboxylate undergoes thermal decomposition reaction in the presence of dibutyltin dilaurate catalyst at a temperature of 260℃ and a vacuum of 1 kPa in the microchannel reactor. The residence time of the pre-reactant in the microchannel reactor is controlled at 8 min.

[0058] (3) The material flows out through the outlet and is transported through a pipeline to a column condenser for cooling (10°C). The cooling yields a crude product of tetramethyl-m-phenylenedimethyl diisocyanate with a conversion rate of 98.2%. The crude product is then distilled using a distillation apparatus (vacuum of 7 kPa, temperature of impurity fraction of 120°C, and temperature of target fraction of 165°C) to obtain tetramethyl-m-phenylenedimethyl diisocyanate. The purity of the purified tetramethyl-m-phenylenedimethyl diisocyanate is 99.6%, and the yield is 93.4%.

[0059] Example 2

[0060] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, the method comprising:

[0061] (1) 10 kg of tetramethyl phthalimide dicarboxylate (TMXDU) raw material was put into a 15 L reactor and melted at 150 °C. Then, 300 g of dibutyltin dilaurate catalyst was added and mixed. After mixing for 10 min, the pre-reactant was obtained.

[0062] (2) The pre-reactant is transported to the material pump via the reactor's discharge valve and pipeline. The material pump (high-temperature plunger pump) injects the pre-reactant into the microchannel reactor (with features such as...) at a flow rate of 0.5 kg / min. Figure 1 The structure shown contains 160 Tesla valves (20 mm × 20 mm each) and a microchannel reactor with a length of 320 mm. Tetramethylphenyldimethyl dicarboxylate undergoes thermal decomposition in the presence of a dibutyltin dilaurate catalyst at a temperature of 270 °C and a vacuum of 1 kPa in the microchannel reactor. The residence time of the pre-reactant in the microchannel reactor is controlled to be 5 min.

[0063] (3) The material flows out through the outlet and is transported through a pipeline to a column condenser for cooling (6°C). The cooling yields a crude product of tetramethyl-m-phenylenedimethyl diisocyanate with a conversion rate of 97%. The crude product is then distilled using a distillation apparatus (vacuum of 7 kPa, temperature of the impurity fraction of 120°C, and temperature of the target fraction of 165°C) to obtain tetramethyl-m-phenylenedimethyl diisocyanate. The purified tetramethyl-m-phenylenedimethyl diisocyanate has a purity of 99.5% and a yield of 92.6%.

[0064] Example 3

[0065] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, the method comprising:

[0066] (1) 10 kg of tetramethyl phthalimide dicarboxylate (TMXDU) raw material was put into a 15 L reactor and melted at 160 °C. Then, 100 g of dibutyltin dilaurate catalyst was added and mixed. After mixing for 10 min, the pre-reactant was obtained.

[0067] (2) The pre-reactant is transported to the material pump via the reactor's discharge valve and pipeline. The material pump (high-temperature plunger pump) injects the pre-reactant into the microchannel reactor (with features such as...) at a flow rate of 0.5 kg / min. Figure 1 The structure shown contains 60 Tesla valves (40 mm × 40 mm) and a microchannel reactor with a length of 240 mm. Tetramethylphenyldimethyl dicarboxylate undergoes thermal decomposition in the presence of dibutyltin dilaurate catalyst at a temperature of 280 °C and a vacuum of 1 kPa in the microchannel reactor. The residence time of the pre-reactant in the microchannel reactor is controlled to be 5 min.

[0068] (3) The material flows out through the outlet and is transported through a pipeline to a column condenser for cooling (6°C). The cooling yields tetramethyl-m-phenylenedimethyl diisocyanate with a crude product conversion rate of 95.2%. The crude product is then distilled using a distillation apparatus (vacuum of 7 kPa, temperature of impurity fraction of 120°C, and temperature of target fraction of 165°C) to obtain tetramethyl-m-phenylenedimethyl diisocyanate. The purity of the purified tetramethyl-m-phenylenedimethyl diisocyanate is 99.5%, and the yield is 90.3%.

[0069] Example 4

[0070] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the temperature of the microchannel reactor in step (2) is 220°C, which is the same as in Example 1.

[0071] Example 5

[0072] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the temperature of the microchannel reactor in step (2) is 280°C, which is the same as in Example 1.

[0073] Example 6

[0074] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the temperature of the microchannel reactor in step (2) is 200°C, which is the same as in Example 1.

[0075] Example 7

[0076] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the temperature of the microchannel reactor in step (2) is 240°C, which is the same as in Example 1.

[0077] Example 8

[0078] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that: the flow rate of the pre-reactant in step (2) is 0.1 kg / min, and the residence time in the microchannel reactor is 8 min, which are the same as in Example 1.

[0079] Example 9

[0080] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that the flow rate of the pre-reactant in step (2) is 2 kg / min and the residence time in the microchannel reactor is 6 min, which are the same as in Example 1.

[0081] Example 10

[0082] This embodiment provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, which differs from Example 1 in that: the flow rate of the pre-reactant in step (2) is 0.05 kg / min, and the residence time in the microchannel reactor is 10 min, which are the same as in Example 1.

[0083] Example 11

[0084] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that the flow rate of the pre-reactant in step (2) is 3 kg / min and the residence time in the microchannel reactor is 5 min, which are the same as in Example 1.

[0085] Example 12

[0086] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the vacuum degree in step (2) is 0.5 kPa, which is the same as in Example 1.

[0087] Example 13

[0088] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the vacuum degree in step (2) is 20 kPa, which is the same as in Example 1.

[0089] Example 14

[0090] This embodiment provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, which differs from Example 1 in that the vacuum degree in step (2) is 50 kPa, which is the same as in Example 1.

[0091] Example 15

[0092] This embodiment provides a method for preparing tetramethylmethylene diisocyanate, which differs from Example 1 in that the mass ratio of tetramethylmethylene dicarboxylate to dibutyltin dilaurate is 100:1, which is the same as in Example 1.

[0093] Example 16

[0094] This embodiment provides a method for preparing tetramethylmethylene diisocyanate, which differs from Example 1 in that the mass ratio of tetramethylmethylene dicarboxylate to dibutyltin dilaurate is 100:2.5, which is the same as in Example 1.

[0095] Example 17

[0096] This embodiment provides a method for preparing tetramethylmethylene diisocyanate, which differs from Example 1 in that the mass ratio of tetramethylmethylene dicarboxylate to dibutyltin dilaurate is 100:3, which is the same as in Example 1.

[0097] Example 18

[0098] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that: the equimolar amount of dibutyltin dilaurate is replaced with tetrabutyl titanate, while the rest is the same as in Example 1.

[0099] Example 19

[0100] This embodiment provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, which differs from Example 1 in that: the equimolar amount of dibutyltin dilaurate is replaced with stannous octoate (purchased from Sinopharm Chemical Reagent Co., Ltd.), while the rest is the same as in Example 1.

[0101] Example 20

[0102] This embodiment provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, which differs from Example 1 in that: the equimolar amount of dibutyltin dilaurate is replaced with zinc oxide (purchased from Sinopharm Chemical Reagent Co., Ltd.), and the zinc oxide is dispersed in 1,2-dichloroethane (5 L), which is the same as in Example 1.

[0103] Example 21

[0104] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that the Tesla channel structure has 80 Tesla valves and the length of the Tesla channel is 320 mm.

[0105] Example 22

[0106] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that the Tesla channel structure has 70 Tesla valves and the length of the Tesla channel is 280 mm.

[0107] Example 23

[0108] This embodiment provides a method for preparing tetramethylm-phenylenedimethyl diisocyanate, which differs from Example 1 in that the Tesla channel structure has 50 Tesla valves and the length of the Tesla channel is 200 mm.

[0109] Example 24

[0110] This embodiment provides a method for preparing tetramethylm-isophthalic acid diisocyanate, which differs from Example 1 in that the Tesla channel structure has 90 Tesla valves and the length of the Tesla channel is 360 mm.

[0111] Comparative Example 1

[0112] This comparative example provides a method for preparing tetramethyl-m-phenylenedimethyl diisocyanate, using a commonly used laboratory batch reaction glass bottle apparatus.

[0113] In a 500 mL three-necked round-bottom glass flask, 200 g of tetramethylphenyldimethyl dicarboxylate was melted at 155 °C and then mixed with dibutyltin dilaurate (2 g) catalyst. After mixing for 10 min, a spherical condenser was attached to the three-necked flask, and a vacuum tube was connected above the condenser. The vacuum mode was turned on, and the vacuum degree was 1 kPa. The reaction flask was heated to 260 °C and the reaction was maintained under these conditions for another 20 min. After the reaction was completed, a sample was quickly taken to test the conversion rate of the crude product. The condenser was replaced with a distillation apparatus, and the product was purified at 160 °C and 5 kPa to obtain tetramethyl-m-phenylenedimethyl diisocyanate.

[0114] Test methods

[0115] High performance liquid chromatography (HPLC) was used to test the tetramethylm-m-phenylenedimethyl diisocyanate prepared in the examples and comparative examples using the normalization method.

[0116] The high-performance liquid chromatography (HPLC) used a Poroshell 120-EC-C18 column (4.6×50 mm, 2.7 μm); a column temperature of 40℃; a wavelength of 210 nm; a flow rate of 1.5 mL / min; an injection volume of 5 μL; a sample concentration of 0.5±0.1 mg / mL; and mobile phases: phase A (water, Watson's distilled water) and phase B (ACN, HPLC grade). The elution gradient is shown in Table 1 below.

[0117] Table 1

[0118]

[0119] The test results are shown in Table 2 below:

[0120] Table 2

[0121]

[0122] The test results show that:

[0123] (1) As can be seen from Examples 1 to 24, the present invention provides an innovative method for preparing tetramethylm-isomethyl diisocyanate with a total yield of 78.5-93.4% or more and a purity of 99%.

[0124] (2) As can be seen from Examples 1 to 4-7, the present invention can achieve better preparation results by further limiting the reaction temperature, vacuum degree, material residence time and molar ratio of substrate to catalyst.

[0125] (3) As can be seen from Examples 1 and 19-20, the present invention uses a liquid catalyst, which can solve the problem of wall adhesion and reactor blockage or difficulty in cleaning compared with conventional metal powder catalysts. Compared with solid catalyst-solvent system, solid catalyst-solvent system introduces solvent, which increases the complexity of subsequent purification process and increases the generation of waste. In addition, the presence of solvent increases the contact surface area with the material, improves mass transfer efficiency, and can improve reaction conversion rate.

[0126] (4) As can be seen from Examples 1 and 21-24, the present invention further optimizes the structure of the microchannel reactor to ensure that tetramethyl phthalimide dicarboxylate can fully react after passing through the microchannel reactor at a certain flow rate, thus solving the problem of small specific surface area and insufficient reaction in conventional pyrolysis reactors.

[0127] (5) As can be seen from Example 1 and Comparative Example 1, the prior art uses a batch reactor to prepare tetramethyl-m-phenylenedimethyl diisocyanate. Due to the long residence time in the reactor, the isocyanate generated by the reaction is prone to self-polymerization, generating a large number of by-products, which has a significant impact on the reaction. Only a yield of 52.3% and a purity of <99% can be obtained. In contrast, the present invention uses a microchannel reactor to prepare tetramethyl-m-phenylenedimethyl diisocyanate. The microchannel reactor has a large specific surface area of ​​reaction interface, sufficient heat exchange, and uniform temperature, providing an efficient and rapid reaction environment for the reaction.

[0128] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing tetramethylm-isophthalic acid diisocyanate, characterized in that, The preparation method includes: mixing tetramethyl phthalimide dicarboxylate with a catalyst and then carrying out a thermal pyrolysis reaction in a microchannel reactor.

2. The method for preparing tetramethylm-isophthalic acid diisocyanate according to claim 1, characterized in that, The tetramethyl phthalimide dicarboxylate was mixed with the catalyst in a molten state; Preferably, the mixing temperature is 140-190°C; Preferably, the mixing time is 5-15 minutes.

3. The method for preparing tetramethylm-isophthalic acid diisocyanate according to claim 1 or 2, characterized in that, The catalyst includes a liquid catalyst; Preferably, the liquid catalyst comprises an organotin catalyst and / or an organotitanium catalyst; Preferably, the organotin catalyst comprises dibutyltin dilaurate and / or stannous octoate, more preferably dibutyltin dilaurate; Preferably, the organotitanium catalyst comprises any one or a combination of at least two of tetrabutyl titanate, tetraisopropyl titanate, tetraoctyl titanate, or titanium citrate, and more preferably tetrabutyl titanate.

4. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-3, characterized in that, The mass ratio of the tetramethylphthalimide dicarboxylate to the catalyst is 100:(1-3).

5. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-4, characterized in that, The microchannel reactor has a Tesla flow channel structure; Preferably, the Tesla flow channel structure has 40-200 Tesla valves; Preferably, the length of a single Tesla valve is 20-40 mm; Preferably, the width of the individual Tesla valve is 20-40 mm; Preferably, the length of the Tesla channel is 140-400 mm.

6. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-5, characterized in that, The tetramethylphenyldimethyl dicarboxylate was mixed with the catalyst to obtain a pre-reactant. Preferably, the flow rate in the microchannel reactor is 0.1-2 kg / min; Preferably, the residence time of the premix in the microchannel reactor is 5-10 min.

7. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-6, characterized in that, The temperature of the thermal decomposition reaction is 200-320℃, preferably 220-280℃.

8. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-7, characterized in that, The thermal decomposition reaction is carried out under vacuum conditions; Preferably, the vacuum degree is 0.5-50 kPa, more preferably 0.5-20 kPa.

9. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-8, characterized in that, The thermal decomposition reaction is followed by condensation and purification processes. Preferably, the condensation temperature is -15~20℃; Preferably, the purification process includes distillation; Preferably, the distillation temperature of tetramethyl-m-phenylenedimethyl diisocyanate in the distillation is 130-140°C; Preferably, the distillation is carried out under vacuum conditions; Preferably, the vacuum degree is 0.5-1.5 kPa.

10. The method for preparing tetramethylm-isophthalic acid diisocyanate according to any one of claims 1-9, characterized in that, The preparation method includes: (1) Heat tetramethylphenyldimethyl dicarboxylate until it melts, and mix it with the catalyst at 140-190℃ for 5-15 min to obtain the pre-reactant; (2) The pre-reactant is injected into a microchannel reactor at a flow rate of 0.1-2 kg / min and reacted at 200-320℃ and 0.5-20 kPa vacuum for a residence time of 5-10 min to obtain the crude tetramethylm-isophthalic acid diisocyanate. (3) The crude tetramethyl-m-phenylenedimethyl diisocyanate was subjected to condensation and purification treatment to obtain the tetramethyl-m-phenylenedimethyl diisocyanate.

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