Process for increasing the yield of isocyanates and process for the preparation of isocyanates

Abstract

The present invention provides a method for increasing the yield of isocyanate and a method for preparing isocyanate, which employs the method of the present invention to prepare isocyanate of general formula (II) to help increase the yield of the product. The method controls the acid content of an isocyanate intermediate having general formula (I) to be > 0 and < 3000 ppm, and thermally cracks the isocyanate intermediate to obtain the isocyanate; the acid content refers to the ability to release H + of the compound.

Description

Technical Field

[0001] This invention belongs to the field of isocyanate technology, and specifically relates to a method for improving the yield of isocyanates and a method for preparing isocyanates. Background Technology

[0002] Compounds containing the -NCO group are collectively called isocyanates, and are classified into monoisocyanates, diisocyanates, and polyisocyanates based on the number of -NCO groups they contain. Isocyanates can react with compounds containing active hydrogen to prepare high-performance materials, and have wide applications in synthetic leather, foam plastics, adhesives, and many other fields.

[0003] Tetramethyl-methylene diisocyanate (TMXDI) is a diisocyanate with a benzene ring in its molecular structure, but the isocyanate group is not conjugated with the benzene ring. Its unique molecular structure gives it both aliphatic and aromatic characteristics, resulting in polyurethane products with excellent strength, abrasion resistance, elongation, and resistance to yellowing. Furthermore, due to its special structure, TMXDI can be used to prepare waterborne polyurethanes under solvent-free conditions, exhibiting significant advantages such as low viscosity and good leveling properties.

[0004] Currently, the chemical methods used to synthesize TMXDI are known. For example, the direct reaction of DIPEB with isocyanate can yield isocyanates (US 4377530A, US 3290350A). This method has simple synthetic steps, but it requires the use of large quantities of toxic isocyanate, which is volatile, explosive, and difficult to recover, making it unsuitable for industrial production.

[0005] For example, using DIPEB and HCl as raw materials, the intermediate product m-diisopropylchlorobenzene (TMXDC) is prepared in advance, purified by vacuum distillation, and then reacted with metal cyanate in the presence of a catalyst to obtain TMXDI (US 4130577A, US4399073A). However, this method easily generates waste salt containing cyanate and requires a large amount of solvent.

[0006] For example, using DIPEB and a carbonylating agent as raw materials, a mixture containing carbamate (TMXDU) is reacted under the action of an acidic catalyst. After neutralization and purification, the mixed reaction solution is subjected to vacuum distillation and cracking to obtain isocyanates (US 4439616A, US 4568761A). However, since TMXDU is a high-melting-point substance, the strong acid catalyst is difficult to remove, resulting in a large number of byproducts in subsequent reaction steps and cumbersome purification steps.

[0007] Improving the synthesis method of TMXDI to increase product yield remains one of the technical challenges in this field. Summary of the Invention

[0008] In view of this, the present invention provides a method for improving the yield of isocyanates and a method for preparing isocyanates. Using the method of the present invention to prepare isocyanates of general formula (II) helps to improve the product yield.

[0009] To achieve its objective, the present invention provides the following technical solution:

[0010] The present invention provides a method for improving the yield of isocyanates having general formula (II), wherein the acid content of an isocyanate intermediate having general formula (I) is controlled to be >0 and <3000ppm, and the isocyanate intermediate is subjected to thermal decomposition to obtain the isocyanate.

[0011]

[0012] Wherein, R is an alkylene, cycloalkylene, arylene, or arylalkylene, wherein the alkylene or cycloalkylene contains 1-12 carbon atoms, the arylene contains 6-10 carbon atoms, and the arylalkylene contains 7-10 carbon atoms; preferably, R is a substituted or unsubstituted —(CH2)n—, where n is a positive integer from 1 to 6. Wherein, the alkylene or cycloalkylene can be branched or linear.

[0013] The acid refers to the component that can release H+. + Compounds.

[0014] The inventors have discovered that by reducing the acid content of isocyanate intermediates having general formula (I) to below 3000 ppm, it is beneficial to improve the cracking efficiency of isocyanate intermediates and increase the yield of isocyanates of general formula (II).

[0015] In a preferred embodiment, the preparation steps of the isocyanate intermediate include:

[0016] 1) 1,3-Diisopropenylbenzene is reacted with a carbonylating agent in the presence of an acidic catalyst to obtain a reaction solution containing the isocyanate intermediate;

[0017] 2) Wash the reaction solution with an alcohol to obtain a washing solution; preferably, in step 2), an alkaline substance is also added, preferably the corresponding metal salt of the alcohol; more preferably, the amount of the metal salt added is 0.01 to 2.0 times the amount of the acidic catalyst, preferably 0.1 to 1.0 times.

[0018] 3) The washing liquid is subjected to separation treatment to separate the light component and the heavy component containing the isocyanate intermediate;

[0019] 4) The heavy component containing the isocyanate intermediate obtained in step 3) is crystallized and filtered to obtain the alcohol phase and isocyanate intermediate product;

[0020] Preferably, reusing the light component described in step 3) in steps 1) and 2), and reusing the alcohol phase described in step 4) in step 2) can improve the utilization rate of raw materials.

[0021] The inventors have discovered that washing with alcohols before the intermediate undergoes thermal decomposition can effectively reduce the acid content in the isocyanate intermediate, decrease the occurrence of side reactions during subsequent thermal decomposition, reduce byproducts, and improve the yield of the target isocyanate. In a preferred embodiment, in step 2), the alcohol is selected from one or more compounds with the structural formula R1-OH, wherein R1 is a straight-chain, branched, or cyclic hydrocarbon group having 1-6 carbon atoms; preferably, one or both of methanol and ethanol are preferred, which facilitates the rapid separation and recycling of the alcohol in the subsequent process.

[0022] As is well known in the art, the synthesis of TMXDU requires the use of a strong acid catalyst for catalysis, and the strong acid catalyst in the reaction system needs to be treated after the reaction. However, the inventors have discovered that the synthesis of TMXDU is an organic phase reaction. If post-treatment is performed through acid-base neutralization, the reaction is difficult to complete, easily resulting in the residue of acidic or basic substances. At the same time, the salts generated by acid-base neutralization are difficult to handle in an organic system. Introducing an aqueous phase into the system can promote acid-base neutralization, but TMXDU is poorly soluble in water and is a high-melting-point substance. During the introduction of an aqueous phase, it will precipitate rapidly, easily encapsulating acidic and / or basic substances and / or the generated salts within the TMXDU crystals, which is detrimental to the next step of the reaction. The present invention, through washing with alcohols, can effectively avoid the above-mentioned drawbacks caused by traditional post-treatment methods.

[0023] In a preferred embodiment, in step 2), an alkaline substance is further added, specifically a corresponding metal salt of an alcohol. The metal element in the corresponding metal salt of the alcohol is preferably selected from one or more alkali metals and alkaline earth metals, such as, but not limited to, one or more of Na, K, Ca, and Mg. For example, when methanol is used as the aforementioned alcohol, sodium methoxide is preferably added; when ethanol is used as the aforementioned alcohol, sodium ethoxide is preferably added. The inventors have found that, under the same process conditions, adding a corresponding metal salt of an alcohol in step 2) facilitates a more thorough treatment of acidic substances in the reaction solution, thereby further reducing the acid content in the isocyanate intermediate and ultimately improving the yield of the entire isocyanate production process. Preferably, the added alkaline substance is one that does not have the activity of promoting isocyanate polymerization.

[0024] In some embodiments, in step 2), the washing operation temperature is below 100°C, preferably below 85°C, for example below 80°C, or even below 70°C; and the operation temperature is above 0°C, preferably above 20°C, and more preferably above 40°C. Preferably, the washing operation temperature is 40-80°C. Using the preferred washing operation temperature balances cost and yield; excessively high temperatures may cause evaporation (volatilization) of alcohols during washing, weakening the treatment effect of alcohols and increasing energy consumption and costs related to alcohol recovery; while excessively low temperatures prevent the effective removal of acidic substances, requiring even lower temperatures in the subsequent crystallization operation, increasing costs and hindering the overall process.

[0025] In step 2) of this invention, the washing operation can be carried out in a reaction device such as a batch reactor, a tower reactor, a fixed bed reactor, a tubular reactor, etc., preferably in a tower reactor. The length-to-diameter ratio of the reaction device is not particularly limited, for example, it is 10 or more, preferably 15 or more, for example, it is 50 or less, preferably 35 or less. The packing material inside the reaction device is not particularly limited, and there may be no packing material. Non-metallic packing material is preferred, such as ceramic packing material, plastic packing material, polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC), etc.

[0026] In the method of this invention, in step 3), the washing liquid is separated to separate the light components and the heavy components containing the isocyanate intermediate. The separation method can be flash evaporation, vacuum distillation, and / or rectification to separate the alcohols, unreacted raw materials (e.g., DIPEB and carbonylating agents), residual acidic catalysts, and other light components. The remaining liquid is the heavy component, which is used for subsequent crystallization. The light components can be reused in steps 1) and 2).

[0027] In step 4) of the present invention, there are no particular limitations on the crystallization reactor used for crystallization. In a preferred embodiment, in step 4), the cooling rate of crystallization is controlled to be below 2°C / min, preferably below 0.5°C / min; during the crystallization process, the temperature is lowered to -10°C to 20°C at the aforementioned cooling rate; by adopting the preferred crystallization cooling rate, the amount of alcohols and acidic substances encapsulated in the target isocyanate for crystallization can be effectively reduced.

[0028] In a preferred embodiment, the isocyanate intermediate product is pre-melted under continuous nitrogen purging before thermal pyrolysis. The inventors have found that pre-melting under nitrogen purging before thermal pyrolysis can further remove any remaining trace amounts of alcohols and acidic substances in the system, thus improving the thermal pyrolysis reaction yield. Preferably, the isocyanate intermediate product is pre-melted at 100-175°C, preferably 130-150°C, for a duration of 15 min to 4 h, such as 15 min to 60 min, or 0.5 h to 4 h. The present invention has found that using the preferred pre-melting temperature is beneficial for balancing the reduction of acidity in the intermediate with an increase in the yield of the final product. If the temperature is too low, the isocyanate intermediate (e.g., TMXDU) product is difficult to completely melt, failing to achieve the desired purging effect. If the temperature is too high, it does not significantly improve the acid cracking results of the isocyanate intermediate (e.g., TMXDU), but instead increases energy consumption and the amount of uncertain heavy components. Preferably, the nitrogen purging flux for continuous nitrogen purging is 50–150 L / h. Pre-melting under these preferred temperature and nitrogen purging flux conditions is beneficial for improving the removal of any remaining trace amounts of alcohols and acidic substances, thereby further increasing the yield of the target isocyanate. Preferably, the heating rate during pre-melting is 1–20 °C / min, more preferably 1–10 °C / min. The inventors have found that controlling the heating rate within this preferred range during pre-melting helps reduce the polymerization of TMU byproducts under the catalysis of any remaining trace amounts of acidic substances during TMXDU generation, thereby reducing the amount of tar-heavy components generated during pyrolysis, improving the separation efficiency of the pyrolysis step, and further increasing the yield of the target isocyanate. The TMU byproduct has the structural formula shown in formula (Ⅳ), and it decomposes during thermal pyrolysis to generate TMI (as shown in formula (Ⅴ)), which is a TMXDI byproduct.

[0029]

[0030] The meaning of R is the same as that of R in the general formula (I) above, and will not be repeated here.

[0031] In this invention, pre-melting must be carried out after the alcohol solvent washing in step 2) is completed, and the aforementioned alcohol washing operation cannot be omitted. The inventors have found that if the alcohol washing step is not performed, it is difficult to completely remove the large amount of acidic substances remaining in the TMXDU intermediate by purging with nitrogen gas alone. On the other hand, the large amount of these acidic substances remaining will easily catalyze the polymerization of TMU olefin double bonds, affecting the reaction yield.

[0032] Because 1,3-diisopropenylbenzene (DIPEB) has an olefinic double bond structure, it is easily catalyzed by strong acids to undergo cationic polymerization during the synthesis of TMXDU. Commonly used cationic polymerization inhibitors can affect the strong acid catalytic system in the TMXDU synthesis process. The inventors have discovered that appropriately increasing the supply ratio of the carbonylating agent can reduce the formation of polymerizable heavy components during the TMXDU synthesis process. Preferably, in step 1), the carbonylating agent is at least 4 times the amount of 1,3-diisopropenylbenzene, more preferably at least 6 times, more preferably at least 8 times, and at least 25 times the amount of 1,3-diisopropenylbenzene, more preferably at least 20 times, more preferably at least 15 times.

[0033] In the method of this invention, step 1) can be carried out under relatively mild reaction conditions. Preferably, the reaction temperature is 40-150°C, more preferably 45-120°C, for example 65-120°C. In some embodiments, the reaction temperature of step 1) is below 135°C, preferably below 120°C, more preferably below 105°C, for example above 45°C, preferably above 55°C, more preferably above 65°C. More preferably, the reaction in step 1) is carried out at a temperature of 65-105°C for 1-20 hours, preferably 2-10 hours. Preferably, the reaction in step 1) is carried out at atmospheric pressure. The inventors have found that using the preferred reaction temperature is beneficial for improving the reaction effect and for balancing reaction efficiency and high reaction yield. When the temperature is too high, the reaction rate of TMXDU is accelerated, but the increase in temperature will also promote the polymerization of DIPEB, resulting in yield loss. At the same time, it will increase the viscosity of the system, which is not conducive to material transportation and subsequent processing. Furthermore, the TMXDU synthesis process is a reversible reaction. Excessively high temperatures favor the reverse reaction, reducing the DIPEB conversion rate. Conversely, lower reaction temperatures lead to a slower reaction rate, prolonged production cycles, and increased polymerization of heavy components.

[0034] In some embodiments, in step 1), the acidic catalyst can be a Brønsted acid conventionally used in the art, preferably selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid; more preferably, it is one or more of methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid. The inventors have found that using these preferred organic acidic catalysts can achieve better catalytic effects, which is beneficial for further improving the yield of the target isocyanate. In this invention, the acid content in the "acid fraction" of the isocyanate intermediate having general formula (I) mainly originates from the raw material and / or acidic catalyst residues, for example, from Brønsted acid and / or compounds that can release Brønsted acid (e.g., compounds that can release Brønsted acid at room temperature). The amount of acidic catalyst used can be the conventional amount used in the art, for example, the amount of acidic catalyst is 0.005-0.2 times the mass of the raw material DIPEB.

[0035] In the method of the present invention, the carbonylating agent used in step 1) is not particularly limited, and can be any carbonylating agent conventionally used in the art, such as any one or a combination of at least two of urea, methyl carbamate, ethyl carbamate, n-propyl carbamate, isopropyl carbamate, n-butyl carbamate, isobutyl carbamate, sec-butyl carbamate, or tert-butyl carbamate. Typical but non-limiting examples of combined carbonylating agents include: combinations of urea and methyl carbamate, combinations of methyl carbamate and ethyl carbamate, combinations of ethyl carbamate and n-propyl carbamate, combinations of n-propyl carbamate and isopropyl carbamate, combinations of isopropyl carbamate and n-butyl carbamate, combinations of n-butyl carbamate and isobutyl carbamate, combinations of isobutyl carbamate and sec-butyl carbamate, combinations of sec-butyl carbamate and tert-butyl carbamate, or combinations of urea, methyl carbamate, and ethyl carbamate, etc.

[0036] In the method of this invention, the isocyanate intermediate after pre-melting can be directly subjected to thermal pyrolysis. The thermal pyrolysis can be carried out with or without a catalyst, preferably in the presence of a catalyst. As the catalyst for the chemical pyrolysis of TMXDU, appropriate catalysts conventionally used in the art can be employed, such as any one or a combination of at least two of Group IB, IIB, IIIA, or VA metal monomers, metal salts, or metal oxides or metal chlorides. Zinc or tin chlorides and oxides of zinc, manganese, calcium, iron, tin, or cobalt are preferred. The amount of catalyst used is readily determined by those skilled in the art based on the reaction requirements; for example, the amount of catalyst added is 0.01-20 wt% of the TMXDU, preferably 0.05-10 wt%.

[0037] In thermal decomposition, when TMXDU is mixed with the catalyst, an inert solvent that is not reactive in the reaction can be added to enhance mixing. The solvent used can be conventionally used in the art, such as aromatic hydrocarbons like benzene, toluene, and xylene; aliphatic hydrocarbons like octane and decane; alicyclic hydrocarbons like cyclohexane, methylcyclohexane, and ethylcyclohexane; halogenated aromatic hydrocarbons like chlorotoluene, chlorobenzene, dichlorobenzene, dibromobenzene, and trichlorobenzene; and nitrobenzene, N,N-dimethylformamide, and N,N-dimethylformamide. Nitrogen-containing compounds such as acetamide and N,N'-dimethylimidazolinone; ethers such as dibutyl ether, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether; ketones such as heptanone, diisobutyl ketone, methyl isobutyl ketone, and methyl ethyl ketone; fatty acid esters such as ethyl acetate, butyl acetate, amyl acetate, and ethoxyethyl acetate; and aromatic carboxylic acid esters such as methyl salicylate, diethyl phthalate, dibutyl phthalate, and methyl benzoate. Inactive solvents can be used alone or in combination of two or more. Preferred inactive solvents include high-boiling-point solvents such as diethyl phthalate and dibutyl phthalate. The catalyst and solvent used in the thermal cracking can be added in advance during the pre-melting step.

[0038] In this invention, there are no particular limitations on the form of the pyrolysis reactor used for thermal pyrolysis. It can be a batch reactor, a tubular reactor, or a tower reactor, etc., and preferably a cylindrical pyrolysis reactor, such as a tubular furnace.

[0039] In some embodiments, the thermal pyrolysis reaction temperature is 150–320°C and the reaction pressure is 0–5.0 MPa.

[0040] In some embodiments, prior to step 2), a purification process is performed on the reaction solution obtained in step 1) by distillation and / or rectification to preliminarily remove low-boiling and medium-boiling substances. Specifically, the purification method is not particularly limited; when using distillation for purification, the distillation column can be a plate column or a packed column. Specifically, the theoretical plate number of the distillation column (packed column) is, for example, 2 or more, preferably 5 or more, for example, 60 or less, preferably 40 or less. Furthermore, the top pressure of the distillation column is, for example, 0.1 kPa or more, preferably 0.15 kPa or more, for example, 4 kPa or less, preferably 2.5 kPa or less. Regarding the top reflux ratio of the distillation column, it is, for example, 0.01 or more, preferably 0.1 or more, for example, 60 or less, preferably 40 or less.

[0041] In some embodiments, a step of separating and purifying the pyrolysis products is included after thermal cracking, as needed. This separation and purification may be, for example, distillation and / or rectification purification. For instance, impurities are preferably separated at a temperature of 105-265°C and a pressure of 0.05-10 kPa to obtain the target isocyanate product. When purification is performed using distillation and / or rectification, the distillation and / or rectification column can be a plate column or a packed column. Specifically, the theoretical number of plates in the distillation and / or rectification column (packed column) is, for example, 2 or more, preferably 5 or more, for example, 60 or less, preferably 40 or less. Furthermore, the top pressure of the distillation column is, for example, 0.1 kPa or more, preferably 0.15 kPa or more, for example, 4 kPa or less, preferably 2.5 kPa or less. Additionally, the top reflux ratio of the distillation and / or rectification column is, for example, 0.01 or more, preferably 0.1 or more, for example, 60 or less, preferably 40 or less.

[0042] In some embodiments, specifically, the isocyanate intermediate of formula (I) obtained from step 1) is tetramethyl isophthalimide dicarboxylate (TMXDU), which is thermally decomposed to obtain the target isocyanate of formula (II): tetramethyl isophthalimide diisocyanate (TMXDI).

[0043] For example, the reaction mechanism for preparing tetramethyl isophthalimide dicarboxylate from 1,3-diisopropenylbenzene (DIPEB) and one or more carbonylating agents in the presence of an acidic catalyst is shown below (using methyl carbamate as an example of a carbonylating agent):

[0044]

[0045] The present invention also provides a method for preparing an isocyanate having general formula (II), wherein the isocyanate having general formula (II) is prepared by the method described above;

[0046]

[0047] In some embodiments, the acid content in the isocyanate of general formula (II) prepared by the method of the present invention is less than 100 ppm, for example, greater than 0 ppm and less than 100 ppm.

[0048] The present invention also provides a method for reducing the acid content of isocyanate intermediates having the general formula (I), wherein the acid content of the isocyanate intermediate is >0 and <3000 ppm, and the acid content refers to the acidity that can release H+. + The compound; the method includes the following steps:

[0049] 1) 1,3-Diisopropenylbenzene is reacted with a carbonylating agent in the presence of an acidic catalyst to obtain a reaction solution containing the isocyanate intermediate;

[0050] 2) Wash the reaction solution with an alcohol to obtain a washing solution; preferably, in step 2), an alkaline substance is also added, preferably the corresponding metal salt of the alcohol; more preferably, the amount of the metal alkoxide added is 0.01 to 2.0 times the amount of the acidic catalyst, preferably 0.1 to 1.0 times.

[0051] 3) The washing liquid is subjected to separation treatment to separate the light component and the heavy component containing the isocyanate intermediate;

[0052] 4) The heavy component containing the isocyanate intermediate obtained in step 3) is crystallized and filtered to obtain the alcohol phase and isocyanate intermediate product;

[0053] Preferably, the light component described in step 3) is reused in steps 1) and 2), and the alcohol phase described in step 4) is reused in step 2).

[0054] In a preferred embodiment, in step 2), the alcohol is selected from one or more compounds with the structural formula R1-OH, wherein R1 is a straight-chain, branched, or cyclic hydrocarbon group having 1-6 carbon atoms; preferably one or two of methanol and ethanol.

[0055] In a preferred embodiment, in step 2), the metal element in the metal alkoxide of the alcohol solvent is selected from one or more alkali metal elements and alkaline earth metal elements, such as one or more selected from K, Na, Ca, Mg, etc.

[0056] In some embodiments, in step 2), the washing operation temperature is below 100°C, preferably below 85°C, more preferably below 80°C; and the operation temperature is above 0°C, preferably above 20°C, more preferably above 40°C.

[0057] In some embodiments, in step 1), the reaction temperature is 40-150°C, preferably 45-120°C;

[0058] In some embodiments, in step 1), the acidic catalyst is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid, preferably one or more of methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid.

[0059] In the method provided by the present invention for reducing the acid content of isocyanate intermediates having general formula (I), unless otherwise specified, please refer to the relevant content in the text concerning the preparation of isocyanate intermediates of the present invention, which will not be repeated here.

[0060] The technical solution provided by this invention has the following beneficial effects:

[0061] (1) By controlling the acid content of the isocyanate intermediate of general formula (I), the present invention can effectively improve the yield of the target isocyanate.

[0062] (2) In the preparation of the isocyanate intermediate of general formula (I) in this invention, the acid content in the isocyanate intermediate can be significantly reduced by washing the reaction solution with alcohol, thereby increasing the yield of the target isocyanate. In a preferred embodiment, the isocyanate intermediate is pre-melted under nitrogen purging after washing with alcohol and before thermal decomposition, which can further improve the yield of the target isocyanate.

[0063] (3) The method of the present invention can significantly reduce side reactions and reduce the amount of by-products generated; and the light components and alcohol phases obtained during the separation process can be recycled without generating a large amount of wastewater, which is economical and environmentally friendly.

[0064] (4) The method provided by the present invention requires simple equipment and is easy to industrialize. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the process flow for preparing isocyanates of general formula (II) in one embodiment. Detailed Implementation

[0066] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0068] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the corresponding conventional experimental steps or conditions in this technical field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. Where the detection and analysis methods involved are not specifically described in the text, they can be performed using corresponding conventional detection and analysis methods and conventional detection operations in this field.

[0069] TMXDI products were analyzed qualitatively and quantitatively by liquid chromatography; Instrument: Agilent 1260; Column: Agilent Extend C18 RRHD 2.1×100mm 1.8μm; Column temperature: 40℃; Flow rate: 0.2ml / min; Mobile phase: A: pure water, B: pure acetonitrile; Injection volume: 20μL; Detection wavelength: 210nm.

[0070] The acid content in TMXDU and TMXDI products was qualitatively and quantitatively analyzed by titration. Specific parameters are as follows:

[0071] Accurately weigh mg of the sample, accurate to 0.1 mg (when the sample acidity is less than 0.0050%, the sample amount m is 10 g; when the sample acidity is greater than 0.0050%, the sample amount m is 5 g), and place it in two clean and dry 250 ml Erlenmeyer flasks.

[0072] Using graduated cylinders of 50ml and 100ml, add appropriate amounts of toluene (10ml for a 5g sample, 20ml for a 10g sample) and methanol (50ml for a 5g sample, 100ml for a 10g sample) to each Erlenmeyer flask. Then, add the magnetic rotor to the flask. (While adding methanol, rinse the mouth and inner wall of the Erlenmeyer flask to flush any sample splashed onto the walls to the bottom of the flask.)

[0073] Connect the Erlenmeyer flask to the reflux condenser tube, tighten the ground glass joint, put the ground glass plug on the top, and turn on the condenser.

[0074] Place the flask in an oil bath, set the oil bath temperature to 80℃, and turn on the magnetic stirrer while adjusting the speed. Start timing when liquid droplets begin to drip from the condenser and reflux for 1 hour.

[0075] After the sample reflux reaction is complete, cool to room temperature, remove the ground glass stopper from the condenser, rinse the inner wall of the reflux condenser with 20 ml of methanol, and then remove the Erlenmeyer flask.

[0076] Transfer the liquid from the Erlenmeyer flask to a 300ml beaker in three portions using 50ml of methanol. Perform potentiometric titration with a potassium hydroxide-ethanol standard titration solution, and take the largest jump as the titration endpoint.

[0077] Acidity (as HCl) is expressed as a mass fraction W1, with the value expressed as a percentage (%).

[0078]

[0079] In the formula:

[0080] V1—The volume of potassium hydroxide-ethanol standard titration solution consumed in titrating the sample, in ml;

[0081] V0—The volume of potassium hydroxide-ethanol standard titration solution consumed in the blank titration, in ml;

[0082] C—Concentration of potassium hydroxide-ethanol standard titration solution, mol / L;

[0083] m—sample mass (g);

[0084] 3.646 — constant.

[0085] TMXDI product yield is expressed as a percentage (%), calculated as the molar amount of product divided by the molar amount of raw material (η).

[0086]

[0087] In the formula:

[0088] m1—Product TMXDI mass, g;

[0089] m2—Mass of raw material DIPEB, in g;

[0090] n1—Molar mass fraction of TMXDI in the product, g / mol;

[0091] n2—Molar mass fraction of DIPEB in raw material, g / mol;

[0092] Example 1

[0093] The process flow diagram for this embodiment can be found in [reference]. Figure 1 .

[0094] The preparation method of TMXDI in this embodiment specifically includes the following steps:

[0095] 1): TMXDU Synthesis Process

[0096] A 500ml glass reactor was used as the TMXDU synthesis reactor. First, 120g of methyl carbamate was placed in the TMXDU synthesis apparatus 3 and melted at 60℃. After the methyl carbamate was completely melted, the acidic catalyst p-toluenesulfonic acid was added through feed line 2, and the acidic catalyst was mixed with the methyl carbamate. After mixing, DIPEB was slowly fed through a peristaltic pump at a rate of 1ml / min from the DIPEB raw material inlet line 1. The reaction was carried out at 60℃ and atmospheric pressure for 6 hours. After the reaction was completed, the resulting TMXDU reaction solution was discharged through the TMXDU reaction solution outlet 4. In this process, the molar ratio of methyl carbamate to DIPEB was 8:1. The amount of acidic catalyst used was 0.05 times the mass of the raw material DIPEB.

[0097] 2) Alcohol washing process

[0098] The TMXDU reaction solution is fed into the alcohol washing unit 7 via the TMXDU reaction solution inlet 5 using a peristaltic pump at a rate of 1 ml / min. Methanol is fed into the alcohol washing unit via the alcohol solvent inlet line 6 using a peristaltic pump at a rate of 1 ml / min. Sodium methoxide, an alkaline reagent, is added to the alcohol washing unit. The methanol, sodium methoxide, and TMXDU reaction solution are thoroughly mixed and washed in the alcohol washing unit 7. The washing temperature is controlled at 60°C. In the alcohol washing process, the amount of alkaline reagent used is 0.1 times the amount of the acidic catalyst, and the washing time is 60 min.

[0099] 3) Separation process

[0100] The washed reaction solution is discharged from the reaction solution outlet 8 of the alcohol washing device and flows into the feed inlet 9 of the thin film evaporator 10 for separation treatment;

[0101] In the thin-film evaporation device, the evaporation temperature is controlled at 60°C. The rapidly removed light component methanol is removed through the light component outlet 11, while the heavy component reaction liquid is discharged through the discharge outlet 12 and enters the subsequent crystallization and filtration process.

[0102] 4) Crystallization and filtration process

[0103] Step 3) The separated heavy component reaction solution enters the crystallization filter 14 through the reaction solution inlet 13. In the crystallization filter 14, the temperature is slowly reduced to 0°C at a rate of 0.5°C / min, during which crystals gradually precipitate. The resulting TMXDU suspension is filtered. The methanol phase enters the post-processing process through the alcohol light component outlet 15 of the crystallization filter 14; the TMXDU product enters the subsequent pre-melting process through the TMXDU product outlet 16 of the crystallization filter 14.

[0104] 5) Pre-melting process

[0105] In the pyrolysis pre-melting unit 18, TMXDU product, calcium oxide catalyst, and dibutyl phthalate are mixed and heated to 140°C (i.e., the pre-melting temperature) at a rate of 5°C / min, and held at this temperature for 1 hour. During the pre-melting period, N2 is purged at a rate of 100 L / h. After pre-melting, the pre-melted material is pumped into the pyrolysis unit 22 for pyrolysis reaction. Based on the mass of TMXDU product, the amount of calcium oxide catalyst added is 5% of the mass of TMXDU, and the amount of dibutyl phthalate added is 9 times the mass of TMXDU.

[0106] 6) Thermal pyrolysis process

[0107] The pyrolysis unit 22 is a tubular reactor with an inner diameter of 20 mm and a length of 500 mm, filled with regular packing material (glass θ-ring packing). The pyrolysis reaction temperature is 220℃ and the reaction pressure is 6 kPa. The pyrolysis light component (methanol) is output and recovered through the light component outlet 23 of the pyrolysis unit 22, while the pyrolysis heavy component is output through the heavy component outlet 24 of the pyrolysis unit 22 and enters the downstream distillation process.

[0108] 7) Distillation process

[0109] The obtained pyrolysis heavy components were desolventized using a Widmanstätten distillation column at a pressure of 3 kPa and a reboiler temperature of 110 °C. After solvent removal, the pressure was reduced to 0.1 kPa and the reboiler temperature was increased to 140 °C for tar removal. The distillate was then distilled off to obtain the TMXDI product. The obtained TMXDI product had a TMXDI content of 97.1% and a yield of 69.7%. The finished product was a colorless liquid.

[0110] Some process conditions and experimental results are shown in Table 1.

[0111] Example 2-15

[0112] The operation steps were performed according to Example 1, with the difference being the modification of some process parameters, as shown in Table 1. Specifically, in the alcohol washing step (step 2), Examples 9 and 10 used ethanol as the washing reagent, while the other examples used methanol. Experimental results are shown in Table 1.

[0113] Comparative Examples 1-3

[0114] Step 1) is carried out in accordance with Example 1, except that after the reaction is completed in Step 1), an alkaline quencher is added to quench the strong acid catalyst. The reaction temperature and alkaline quencher used in Step 1) are shown in Table 2.

[0115] After quenching, the solvent is removed directly by vacuum distillation and the TMXDU is purified. Then, a thermal cracking process is carried out as described in step 6) of Example 1, and a distillation process is carried out as described in step 7) of Example 1.

[0116] The experimental results are shown in Table 2.

[0117] Comparative Example 4

[0118] The experiment was conducted in accordance with Comparative Example 1, except that no alkaline quencher was added. The experimental results are shown in Table 2.

[0119] Table 1. Summary of some process conditions and experimental results of Examples 1-15

[0120]

[0121]

[0122] Table 2 Comparative Examples 1-4: Process Conditions and Experimental Results

[0123]

[0124] As can be seen from the experimental results of Examples 1-15 and Comparative Examples 1-4 above, the method of the present invention can obtain low-acid TMXDU products with an acid content of <3000ppm. The pyrolysis of low-acid TMXDU can significantly reduce the generation of by-products during the pyrolysis process and obtain a relatively higher reaction yield. The acid content of the final isocyanate products obtained in Examples 1-15 was tested and found to be <20ppm.

[0125] As can be seen from the experimental results of Examples 1-2, the main difference between Example 2 and Example 1 is that no corresponding metal salt of alcohol is added during the alcohol washing process. As a result, the acid content in the isocyanate intermediate increased significantly, and the yield of isocyanate product decreased.

[0126] As can be seen from the experimental results of Examples 3-5, under basically the same experimental conditions, Example 5 used a higher heating rate during pre-melting instead of the preferred heating rate (1-10℃ / min), resulting in a relatively high acid content in the obtained isocyanate intermediate and a decrease in the yield of the isocyanate product.

[0127] As can be seen from the experimental results of Examples 11-13, under basically the same experimental conditions, Example 11 uses a preferred pre-melting temperature (130-150°C) in step 5), which is beneficial to further improve the yield of isocyanate products. However, the pre-melting temperature in Example 13 is higher, which may lead to more side reactions and a decrease in product yield.

[0128] As can be seen from the experimental results of Examples 1 and 14-15, under essentially the same experimental conditions, the intermediate of Example 1, which uses an organic acid catalyst (e.g., p-toluenesulfonic acid, trifluoromethanesulfonic acid, methanesulfonic acid), has a lower acid content and a higher final product yield; while the intermediates of Examples 14 and 15, which use inorganic catalysts, have an increased acid content and a decreased isocyanate product yield.

[0129] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for improving the yield of isocyanates having the general formula (II), characterized in that, The acid content of the isocyanate intermediate having general formula (I) is controlled to be >0 and <3000ppm, and the isocyanate intermediate is subjected to thermal decomposition to obtain the isocyanate. (Ⅰ)， (Ⅱ)； Wherein, R is an alkyl group, and the alkyl group contains 1-12 carbon atoms; The acid refers to the component that can release H+. + Compounds; The preparation steps of the isocyanate intermediate include: 1) 1,3-Diisopropenylbenzene is reacted with a carbonylating agent in the presence of an acidic catalyst to obtain a reaction solution containing the isocyanate intermediate; the acidic catalyst is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid; 2) The reaction solution is washed with an alcohol to obtain a washing solution; in step 2), an alkaline substance is also added, wherein the alkaline substance is the corresponding metal salt of the alcohol; the amount of the metal salt added is 0.01 to 2.0 times the amount of the acidic catalyst; the metal element in the corresponding metal salt of the alcohol is selected from one or more alkali metals and alkaline earth metals; 3) The washing liquid is subjected to separation treatment to separate the light component and the heavy component containing the isocyanate intermediate; 4) The heavy component containing the isocyanate intermediate obtained in step 3) is crystallized and filtered to obtain the alcohol phase and isocyanate intermediate product.

2. The method according to claim 1, characterized in that, R is substituted or unsubstituted —(CH2)n—, and n is a positive integer from 1 to 6.

3. The method according to claim 1, characterized in that, In step 2), the amount of metal salt added is 0.1 to 1.0 times the amount of the acidic catalyst.

4. The method according to claim 1, characterized in that, The light component described in step 3) is reused in steps 1) and 2), and the alcohol phase described in step 4) is reused in step 2).

5. The method according to any one of claims 1-4, characterized in that, In step 2), the alcohol is selected from one or more compounds with the structural formula R1-OH, wherein R1 is a straight-chain or branched hydrocarbon group having 1-6 carbon atoms. And / or, the metallic element is selected from one or more of K, Na, Ca, and Mg.

6. The method according to claim 5, characterized in that, In step 2), the alcohol is methanol and / or ethanol.

7. The method according to any one of claims 1-4, characterized in that, In step 2), the washing operation temperature is below 100°C; and the operation temperature is above 0°C.

8. The method according to claim 7, characterized in that, In step 2), the washing operation temperature is below 85°C and above 20°C.

9. The method according to claim 7, characterized in that, In step 2), the washing operation temperature is below 80°C and above 40°C.

10. The method according to any one of claims 1-4, characterized in that, In step 4), the cooling rate of the crystallization is controlled to be below 2℃ / min; during the crystallization process, the temperature is reduced to -10℃ to 20℃ at the cooling rate mentioned above.

11. The method according to claim 10, characterized in that, In step 4), the cooling rate of the crystallization is controlled to be below 0.5℃ / min.

12. The method according to any one of claims 1-4, characterized in that, Before undergoing the thermal cracking, the isocyanate intermediate product is pre-melted under continuous nitrogen purging.

13. The method according to claim 12, characterized in that, The isocyanate intermediate product is heated to 100-175°C for pre-melting, and the heating is carried out at a heating rate of 1-20°C / min; the nitrogen purging flux is 50-150 L / h.

14. The method according to claim 12, characterized in that, The isocyanate intermediate product is heated to 130-150°C for pre-melting, and the heating is carried out at a heating rate of 1-10°C / min.

15. The method according to claim 12, characterized in that, The pre-melting time is 0.5-4 hours.

16. The method according to any one of claims 1-4, characterized in that, In step 1), the carbonylating agent is more than 4 times the amount of 1,3-diisopropenylbenzene and less than 25 times the amount of 1,3-diisopropenylbenzene. And / or, in step 1), the reaction temperature is 40-150°C; And / or, in step 1), the acidic catalyst is one or more of methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid; And / or, the thermal pyrolysis reaction temperature is 150–320°C, and the reaction pressure is 0–5.0 MPa.

17. The method according to claim 16, characterized in that, In step 1), the carbonylating agent is more than 6 times the amount of 1,3-diisopropenylbenzene and less than 20 times the amount of 1,3-diisopropenylbenzene. And / or, in step 1), the reaction temperature is 45-120°C.

18. The method according to claim 16, characterized in that, In step 1), the carbonylating agent is more than 8 times the amount of 1,3-diisopropenylbenzene and less than 15 times the amount of 1,3-diisopropenylbenzene.

19. A method for preparing an isocyanate having general formula (II), characterized in that, The isocyanate having general formula (II) is prepared by the method according to any one of claims 1-18; ( Ⅱ )。 20. A method for reducing the acid content of isocyanate intermediates having general formula (I), characterized in that, The isocyanate intermediate has an acid content >0 and <3000 ppm, where acidity refers to the ability to release H+. + Compounds; (Ⅰ) The method includes the following steps: 1) 1,3-Diisopropenylbenzene is reacted with a carbonylating agent in the presence of an acidic catalyst to obtain a reaction solution containing the isocyanate intermediate; the acidic catalyst is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid; 2) Wash the reaction solution with an alcohol to obtain a washing solution; in step 2), an alkaline substance is also added, wherein the alkaline substance is the corresponding metal salt of the alcohol; the amount of the metal salt added is 0.01 to 2.0 times the amount of the acidic catalyst; the metal element in the corresponding metal salt of the alcohol is selected from one or more of alkali metals and alkaline earth metals. 3) The washing liquid is subjected to separation treatment to separate the light component and the heavy component containing the isocyanate intermediate; 4) The heavy component containing the isocyanate intermediate obtained in step 3) is crystallized and filtered to obtain the alcohol phase and isocyanate intermediate product.

21. The method according to claim 20, characterized in that, In step 2), the amount of metal salt added is 0.1 to 1.0 times the amount of the acidic catalyst.

22. The method according to claim 20, characterized in that, The light component described in step 3) is reused in steps 1) and 2), and the alcohol phase described in step 4) is reused in step 2).

23. The method according to claim 20, characterized in that, In step 2), the alcohol is selected from one or more compounds with the structural formula R1-OH, wherein R1 is a straight-chain or branched hydrocarbon group having 1-6 carbon atoms. And / or, in step 2), the metallic element is selected from one or more of K, Na, Ca, and Mg; And / or, in step 2), the washing operation temperature is below 100°C; and the operation temperature is above 0°C; And / or, in step 1), the reaction temperature is 40-150°C; And / or, in step 1), the acidic catalyst is one or more of methanesulfonic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid.

24. The method according to claim 23, characterized in that, In step 2), the alcohol is methanol and / or ethanol; And / or, in step 2), the washing operation temperature is below 85°C and above 20°C; And / or, in step 1), the reaction temperature is 45-120°C.

25. The method according to claim 23, characterized in that, In step 2), the washing operation temperature is below 80°C and above 40°C.

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