Catalyst for preparing diisocyanate from carbamate and diisocyanate preparation method

Abstract

The invention provides a catalyst for preparing diisocyanate from carbamate and a diisocyanate preparation method, and belongs to the technical field of diisocyanate production. The catalyst is prepared by immersing a molecular sieve in ferric hydroxide colloid and performing high-temperature calcination. In the catalyst, ferric oxide forms a net structure in the pore channels of the molecular sieve, so that the contact area with carbamate is increased, the reaction process is accelerated, and the time is saved. When diisocyanate is prepared, the ferric oxide / molecular sieve catalyst catalyzes decomposition of carbamate under normal pressure, the reaction process is mild, the safety performance of production is improved, and the ferric oxide / molecular sieve catalyst has a good catalytic effect and can improve the yield of diisocyanate.

Description

Technical Field

[0001] The invention belongs to the technical field of diisocyanate production, and relates to a catalyst for preparing diisocyanate from carbamate and a method for preparing diisocyanate. Background Art

[0002] Diisocyanate is a chemical with an -NCO functional group, mainly used as a raw material for manufacturing polyurethane materials. It is commonly used in industries such as home appliances, automobiles, construction, footwear, furniture and adhesives.

[0003] Common diisocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), etc. Existing methods for preparing diisocyanates include phosgenation and non-phosgenation. However, the phosgene used in the phosgenation process is extremely toxic and dangerous, and the by-product hydrogen chloride is easy to corrode the equipment, which places high demands on the equipment. Based on this, the more environmentally friendly non-phosgenation process synthesis route has become a research hotspot.

[0004] At present, there are many non-phosgenation methods for synthesizing diisocyanates, which can be divided into multiple categories according to the reaction type, such as replacement method, reduction carbonylation method, carbamate thermal decomposition method, chloroformamide hydrolysis method, etc. Among them, the carbamate thermal decomposition method refers to: under the action of a catalyst, carbamate undergoes thermal decomposition reaction to generate diisocyanate. This process method has low requirements for raw material purity and mild reaction conditions. It is known as the most industrially applicable non-phosgenation production method for diisocyanates. When using the carbamate thermal decomposition method to synthesize diisocyanates, the commonly used catalyst is Fe 2 O 3 , Zn, ZnO and zinc acetate, etc. However, the catalytic efficiency is low, the reaction safety is low, the product yield is low, and at the same time, these catalysts are all in powder form and are difficult to recycle. Summary of the invention

[0005] The purpose of the present invention is to provide a catalyst for preparing diisocyanate from carbamate and a method for preparing diisocyanate, so as to solve the problem of low production safety when synthesizing diisocyanate by existing non-phosgenation process.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present application provides a catalyst for preparing diisocyanate from carbamate, the catalyst being an iron oxide / molecular sieve catalyst, and the catalyst being prepared by using a molecular sieve as a carrier loaded with iron oxide. In the present application, the pore size of the molecular sieve is 2-50nm, and the particle size of the iron hydroxide colloid is 1-45nm. The molecular sieve is a mesoporous molecular sieve, such as SBA-15 molecular sieve, MCM-41 molecular sieve, KIT-6 molecular sieve or MCM-48 molecular sieve.

[0007] In the present application, the preparation method of the iron oxide / molecular sieve catalyst comprises: S01: Immerse the molecular sieve in iron hydroxide colloid, immerse for 24-48 hours at room temperature, and then filter to obtain the molecular sieve containing iron hydroxide colloid.

[0008] Specifically, a molecular sieve with a pore size of 2-50 nm is immersed in a ferric hydroxide colloid with a colloidal particle size of 1-1.5 nm, and is immersed for 24-48 hours at room temperature. Since the colloidal particle size of the ferric hydroxide colloid is 1-45 nm and the pore size of the molecular sieve is 2-50 nm, during the impregnation process, the ferric hydroxide colloid easily enters the internal pores of the molecular sieve, forming a structure in which the molecular sieve has built-in ferric hydroxide colloid. After the impregnation is completed, the molecular sieve containing the ferric hydroxide colloid is filtered to obtain.

[0009] S02: calcining the molecular sieve containing iron hydroxide colloid at a high temperature of 500-550° C. to obtain an iron oxide / molecular sieve catalyst.

[0010] The molecular sieve containing iron hydroxide colloid is placed in a calcining furnace and calcined at 500-550℃ for 2-5h. The iron hydroxide colloid inside the molecular sieve pores undergoes a high-temperature decomposition reaction to form iron oxide. In addition, under the calcination conditions of 500-550℃, the pore structure inside the molecular sieve will change. The iron oxide produced at this time will be embedded in the changed pore structure to form a structure in which the iron oxide is embedded in the molecular sieve pores; at the same time, more iron oxide produced by decomposition will form a mesh structure in the pore structure, that is, a mesh structure; thus, an iron oxide / molecular sieve catalyst with a mesh structure inside is obtained.

[0011] In a second aspect, the present application provides a method for preparing a diisocyanate, the method comprising: S01: Filling the iron oxide / molecular sieve catalyst in the first aspect into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80-90% of the volume of the decomposition tower.

[0012] S02: After the carbamate is dissolved in the solvent, it is added into the decomposition tower from the top, and circulated reflux reaction is carried out for 10-15h at a thermal decomposition temperature of 150-200°C under normal pressure to obtain diisocyanate.

[0013] The carbamate is added to a solvent and dissolved to form a mixed solution, wherein the solvent includes chlorobenzene, dimethyl succinate, dimethyl glutarate, dioctyl phthalate or dimethyl nonanoate. The mixed solution is added to the decomposition tower from the top of the decomposition tower. During the downward flow of the mixed solution, it passes through the pores of the iron oxide / molecular sieve catalyst, and then the carbamate in the mixed solution is fully in contact with the iron oxide in the pores. Under normal pressure and a thermal decomposition temperature of 150-200° C., the carbamate undergoes a decomposition reaction under the catalytic action of the iron oxide to obtain a gas phase product and a liquid phase material. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose, until the top of the tower no longer produces a gas phase product.

[0014] Since the filling amount of the iron oxide / molecular sieve catalyst in the decomposition tower accounts for 80-90% of the volume of the decomposition tower, the content of the iron oxide / molecular sieve catalyst in the decomposition tower is much greater than the added amount of carbamate, which is conducive to the iron oxide inside the molecular sieve catalyzing the thermal cracking of carbamate.

[0015] In the present application, when the carbamate is toluene dicarbamate (TDC), the prepared diisocyanate is toluene diisocyanate (TDI). The specific preparation process of TDI includes: S01: Add 2,4-diaminotoluene, dimethyl carbonate and iron oxide into a reaction kettle, seal and stir at a temperature of 120-160°C for 3-6 hours to obtain a reaction product.

[0016] Specifically, crystalline powdered 2,4-diaminotoluene, liquid dimethyl carbonate and powdered iron oxide are added to a reaction kettle, wherein the molar ratio of 2,4-diaminotoluene, dimethyl carbonate and iron oxide is 1:(15-25):(0.5-1.5). After the reaction kettle is sealed, the reaction is stirred at a temperature of 120-160°C for 3-6 hours; after the reaction is completed, the reaction product is obtained at the bottom of the kettle.

[0017] S02: The reaction product is distilled under reduced pressure to obtain methyl toluene dicarbamate.

[0018] The reaction product is subjected to reduced pressure distillation at 30-60° C. and 10-15 kPa to remove unreacted 2,4-diaminotoluene and dimethyl carbonate to obtain methyl toluene dicarbamate.

[0019] S03: Filling the iron oxide / molecular sieve catalyst into the decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80-90% of the volume of the decomposition tower.

[0020] S04: After the toluene dicarbamate is dissolved in a solvent, it is added to the decomposition tower from the top of the decomposition tower, and circulated reflux reaction is carried out for 10-15 hours at a thermal decomposition temperature of 150-200°C under normal pressure. The gas phase product obtained at the top of the tower is condensed to obtain toluene diisocyanate.

[0021] Toluene dicarbamate is added to a solvent and dissolved to form a mixed solution, wherein the solvent includes dimethyl succinate, dimethyl glutarate, dioctyl phthalate or dimethyl nonanoate. The mixed solution is added to the decomposition tower from the top of the decomposition tower. During the downward flow of the mixed solution, it passes through the pores of the iron oxide / molecular sieve catalyst, and then the toluene dicarbamate in the mixed solution is fully in contact with the iron oxide in the pores. Under normal pressure and a thermal decomposition temperature of 150-200° C., toluene dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce a gas phase product and a liquid phase material. Among them, the gas phase product is gaseous toluene diisocyanate, and the liquid phase material includes reaction byproducts and unreacted toluene dicarbamate.

[0022] After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 20-30°C to obtain liquid toluene diisocyanate. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower and circulates and refluxes for decomposition until no more gas phase products are produced at the top of the tower.

[0023] When the carbamate is methyl 4,4'-diaminodiphenylmethane dicarbamate (MDC), the prepared diisocyanate is diphenylmethane diisocyanate (MDI). The specific preparation process of the MDI includes: S01: Filling the iron oxide / molecular sieve catalyst into the decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80-90% of the volume of the decomposition tower.

[0024] S02: 4,4'-diaminodiphenylmethane diaminomethyl ester is dissolved in a solvent and added into the decomposition tower from the top thereof, and circulated and refluxed for 10-15h at a thermal decomposition temperature of 150-200°C under normal pressure to obtain diphenylmethane diisocyanate.

[0025] 4,4'-diaminodiphenylmethane diaminomethyl formate is added to a solvent and dissolved to form a mixed solution, wherein the solvent includes chlorobenzene, dimethyl succinate, dimethyl glutarate, dioctyl phthalate or dimethyl nonanoate. The mixed solution is added to the decomposition tower from the top of the decomposition tower. During the downward flow of the mixed solution, it will pass through the pores of the iron oxide / molecular sieve catalyst, and then the 4,4'-diaminodiphenylmethane diaminomethyl formate in the mixed solution will be fully in contact with the iron oxide in the pores. Under normal pressure and a thermal decomposition temperature of 150-200°C, 4,4'-diaminodiphenylmethane diaminomethyl formate undergoes a decomposition reaction under the catalysis of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous methanol, and the liquid phase material includes diphenylmethane diisocyanate, reaction by-products and unreacted 4,4'-diaminodiphenylmethane diaminomethyl formate.

[0026] After the gaseous product escapes from the top of the tower, it is condensed and fractionated at 20-30°C to obtain liquid methanol. After the liquid material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower and circulates and refluxes to decompose until no gaseous product is produced at the top of the tower. Finally, a mixture of diphenylmethane diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by existing distillation and other separation operations to obtain diphenylmethane diisocyanate.

[0027] When the carbamate is hexamethylene diaminodicarboxylic acid methyl ester (HDU), the prepared diisocyanate is hexamethylene diisocyanate (HDI). The specific preparation process of the HDI includes: S01: Filling the iron oxide / molecular sieve catalyst into the decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80-90% of the volume of the decomposition tower.

[0028] S02: After hexamethylenediaminodicarboxylic acid methyl ester is dissolved in a solvent, it is added into the decomposition tower from the top of the decomposition tower, and circulated reflux reaction is carried out for 10-15 hours at a thermal decomposition temperature of 150-200° C. under normal pressure to obtain hexamethylene diisocyanate.

[0029] Methyl hexamethylenediaminodicarboxylate is added to a solvent and dissolved to form a mixed solution, wherein the solvent includes chlorobenzene, dimethyl succinate, dimethyl glutarate, dioctyl phthalate or dimethyl nonanoate. The mixed solution is added to the decomposition tower from the top of the decomposition tower. During the downward flow of the mixed solution, it will pass through the pores of the iron oxide / molecular sieve catalyst, and then the methyl hexamethylenediaminodicarboxylate in the mixed solution will fully contact the iron oxide in the pores. Under normal pressure and a thermal decomposition temperature of 150-200° C., methyl hexamethylenediaminodicarboxylate undergoes a decomposition reaction under the catalytic action of iron oxide to produce a gas phase product and a liquid phase material. Among them, the gas phase product is carbon dioxide, and the liquid phase material includes hexamethylene diisocyanate, reaction byproducts and unreacted methyl hexamethylenediaminodicarboxylate.

[0030] The gaseous product escapes from the top of the tower, and the liquid material flows out from the bottom of the tower, and then reenters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until the top of the tower no longer produces a gaseous product. Finally, a mixture of hexamethylene diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by existing distillation and other separation operations to obtain hexamethylene diisocyanate.

[0031] The present invention has the following beneficial effects: (1) In the present application, the iron oxide / molecular sieve catalyst is prepared by immersing the molecular sieve in iron hydroxide colloid and calcining at high temperature. In the catalyst, the iron oxide forms a network structure in the pores of the molecular sieve, which increases the contact area with the carbamate, accelerates the reaction process, and saves time.

[0032] (2) When preparing diisocyanate, carbamate is circulated through the iron oxide / molecular sieve catalyst, which prolongs the contact time between carbamate and iron oxide, making the carbamate decompose more thoroughly under the catalytic action of the iron oxide / molecular sieve catalyst, thereby improving the product yield.

[0033] (3) When preparing diisocyanate, the iron oxide / molecular sieve catalyst has a good catalytic effect and can improve the yield of diisocyanate.

[0034] (4) The decomposition of toluene dicarbamate catalyzed by iron oxide / molecular sieve catalyst is carried out under normal pressure. The reaction process is mild, which improves the safety performance of production.

[0035] (5) When preparing diisocyanate, the iron oxide / molecular sieve catalyst is fixed in the decomposition tower, and there is no need to filter and separate the catalyst, thus reducing the process procedures. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0037] Example 1 The present application provides a catalyst for preparing diisocyanate from carbamate, and the preparation method of the catalyst comprises: S101: Immerse a molecular sieve with a pore size of 30 nm in a colloid of iron hydroxide with a colloidal particle size of 1.2 nm at room temperature for 36 hours. After the immersion is completed, filter to obtain a molecular sieve containing iron hydroxide colloid.

[0038] S102: placing the molecular sieve containing iron hydroxide colloid into a calcining furnace and calcining at a temperature of 520° C. for 4 hours.

[0039] Example 2 The present application provides a catalyst for preparing diisocyanate from carbamate, and the preparation method of the catalyst comprises: S201: Immerse a molecular sieve with a pore size of 50 nm in iron hydroxide colloid with a colloidal particle size of 1.5 nm at room temperature for 48 hours. After the immersion is completed, filter to obtain a molecular sieve containing iron hydroxide colloid.

[0040] S202: placing the molecular sieve containing iron hydroxide colloid into a calcining furnace and calcining at a temperature of 500° C. for 5 hours.

[0041] Example 3 The present application provides a catalyst for preparing diisocyanate from carbamate, and the preparation method of the catalyst comprises: S301: Immerse the molecular sieve with a pore size of 2 nm in the iron hydroxide colloid with a colloidal particle size of 1 nm at room temperature for 24 hours. After the immersion is completed, filter to obtain the molecular sieve containing the iron hydroxide colloid.

[0042] S302: placing the molecular sieve containing iron hydroxide colloid into a calcining furnace and calcining at a temperature of 550° C. for 2 hours.

[0043] Example 4 The present invention provides a method for preparing toluene diisocyanate (TDI), which comprises: S401: Add crystalline powdered 2,4-diaminotoluene, liquid dimethyl carbonate and powdered iron oxide into a reactor at a molar ratio of 1:20:1. After sealing the reactor, stir and react at a temperature of 150°C for 5 hours; after the reaction is completed, a reaction product is obtained at the bottom of the reactor.

[0044] S402: The reaction product is subjected to reduced pressure distillation at 50° C. and 12 kPa to remove unreacted 2,4-diaminotoluene and dimethyl carbonate to obtain methyl toluene dicarbamate.

[0045] S403: Filling the iron oxide / molecular sieve catalyst in Example 1 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 85% of the volume of the decomposition tower.

[0046] S404: Add toluene dicarbamate to dimethyl succinate to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 180°C, toluene dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous toluene diisocyanate, and the liquid phase material includes reaction by-products and unreacted toluene dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 25°C to obtain liquid toluene diisocyanate TDI. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose, until no gas phase product is produced at the top of the tower.

[0047] Example 5 The present invention provides a method for preparing toluene diisocyanate (TDI), which comprises: S501: Add crystalline powdered 2,4-diaminotoluene, liquid dimethyl carbonate and powdered iron oxide into a reactor at a molar ratio of 1: 15: 1.5. After sealing the reactor, stir and react at a temperature of 160° C. for 3 hours; after the reaction is completed, a reaction product is obtained at the bottom of the reactor.

[0048] S502: The reaction product is subjected to reduced pressure distillation at 30° C. and 15 kPa to remove unreacted 2,4-diaminotoluene and dimethyl carbonate to obtain methyl toluene dicarbamate.

[0049] S503: Filling the iron oxide / molecular sieve catalyst in Example 2 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80% of the volume of the decomposition tower.

[0050] S504: Add toluene dicarbamate to dimethyl glutarate to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 200°C, toluene dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous toluene diisocyanate, and the liquid phase material includes reaction by-products and unreacted toluene dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 30°C to obtain liquid toluene diisocyanate TDI. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose, until the top of the tower no longer produces a gas phase product.

[0051] Example 6 The present invention provides a method for preparing toluene diisocyanate (TDI), which comprises: S601: Add crystalline powdered 2,4-diaminotoluene, liquid dimethyl carbonate and powdered iron oxide into a reactor at a molar ratio of 1: 25:0.5. After sealing the reactor, stir and react at a temperature of 120° C. for 6 hours; after the reaction is completed, a reaction product is obtained at the bottom of the reactor.

[0052] S602: The reaction product is distilled under reduced pressure at 60° C. and 10 kPa to remove unreacted 2,4-diaminotoluene and dimethyl carbonate to obtain methyl toluene dicarbamate.

[0053] S603: Fill the iron oxide / molecular sieve catalyst in Example 3 into the decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 90% of the volume of the decomposition tower.

[0054] S604: Add methyl toluene dicarbamate to dioctyl phthalate to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 150°C, methyl toluene dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous toluene diisocyanate, and the liquid phase material includes reaction by-products and unreacted toluene dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 20°C to obtain liquid toluene diisocyanate TDI. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose, until no gas phase product is produced at the top of the tower.

[0055] Example 7 The present invention provides a method for preparing diphenylmethane diisocyanate (MDI), which comprises: S701: Fill the iron oxide / molecular sieve catalyst in Example 1 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 85% of the volume of the decomposition tower.

[0056] S702: 4,4'-diaminodiphenylmethane dicarbamate is added to chlorobenzene to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 180°C, 4,4'-diaminodiphenylmethane dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous methanol, and the liquid phase material includes diphenylmethane diisocyanate, reaction by-products and unreacted 4,4'-diaminodiphenylmethane dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 25°C to obtain liquid methanol. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase products are produced at the top of the tower. Finally, a mixture of diphenylmethane diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by conventional distillation or the like to obtain diphenylmethane diisocyanate.

[0057] Example 8 The present invention provides a method for preparing diphenylmethane diisocyanate (MDI), which comprises: S801: Fill the iron oxide / molecular sieve catalyst in Example 2 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80% of the volume of the decomposition tower.

[0058] S802: Add 4,4'-diaminodiphenylmethane dicarbamate to dimethyl succinate to dissolve and form a mixed liquid. Add the mixed liquid to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 150°C, 4,4'-diaminodiphenylmethane dicarbamate undergoes a decomposition reaction under the catalysis of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous methanol, and the liquid phase material includes diphenylmethane diisocyanate, reaction by-products and unreacted 4,4'-diaminodiphenylmethane dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 20°C to obtain liquid methanol. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase products are produced at the top of the tower. Finally, a mixture of diphenylmethane diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by conventional distillation or the like to obtain diphenylmethane diisocyanate.

[0059] Example 9 The present invention provides a method for preparing diphenylmethane diisocyanate (MDI), which comprises: S901: Fill the iron oxide / molecular sieve catalyst in Example 3 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 90% of the volume of the decomposition tower.

[0060] S902: Add 4,4'-diaminodiphenylmethane dicarbamate to dimethyl glutarate to dissolve and form a mixed liquid. Add the mixed liquid to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 200°C, 4,4'-diaminodiphenylmethane dicarbamate undergoes a decomposition reaction under the catalysis of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is gaseous methanol, and the liquid phase material includes diphenylmethane diisocyanate, reaction by-products and unreacted 4,4'-diaminodiphenylmethane dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 30°C to obtain liquid methanol. After the liquid phase material flows out from the bottom of the tower, it re-enters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase products are produced at the top of the tower. Finally, a mixture of diphenylmethane diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by conventional distillation or the like to obtain diphenylmethane diisocyanate.

[0061] Example 10 The present application provides a method for preparing hexamethylene diisocyanate (HDI), the method comprising: S1001: Fill the iron oxide / molecular sieve catalyst in Example 1 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 85% of the volume of the decomposition tower.

[0062] S1002: Add hexamethylenediaminodicarboxylic acid methyl ester to chlorobenzene to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 190°C, hexamethylenediaminodicarboxylic acid methyl ester undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is carbon dioxide, and the liquid phase material includes hexamethylene diisocyanate, reaction by-products and unreacted hexamethylenediaminodicarboxylic acid methyl ester. The gas phase product escapes from the top of the tower, and the liquid phase material flows out from the bottom of the tower and then reenters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase products are produced at the top of the tower. Finally, a mixture of hexamethylene diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by existing distillation to obtain hexamethylene diisocyanate.

[0063] Embodiment 11 The present application provides a method for preparing hexamethylene diisocyanate (HDI), the method comprising: S1101: Fill the iron oxide / molecular sieve catalyst in Example 2 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 80% of the volume of the decomposition tower.

[0064] S1102: Add hexamethylenediaminodicarboxylic acid methyl ester to dimethyl succinate to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 150°C, hexamethylenediaminodicarboxylic acid methyl ester undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is carbon dioxide, and the liquid phase material includes hexamethylene diisocyanate, reaction by-products and unreacted hexamethylenediaminodicarboxylic acid methyl ester. The gas phase product escapes from the top of the tower, and the liquid phase material flows out from the bottom of the tower, and then reenters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase products are produced at the top of the tower. Finally, a mixture of hexamethylene diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by existing distillation to obtain hexamethylene diisocyanate.

[0065] Example 12 The present application provides a method for preparing hexamethylene diisocyanate (HDI), the method comprising: S1201: Fill the iron oxide / molecular sieve catalyst in Example 3 into a decomposition tower, wherein the filling amount of the iron oxide / molecular sieve catalyst accounts for 90% of the volume of the decomposition tower.

[0066] S1202: Add hexamethylenediaminodicarboxylic acid methyl ester to dioctyl phthalate to dissolve and form a mixed liquid. The mixed liquid is added to the decomposition tower from the top of the decomposition tower. Under normal pressure and a thermal decomposition temperature of 200°C, hexamethylenediaminodicarboxylic acid methyl ester undergoes a decomposition reaction under the catalytic action of iron oxide to produce gas phase products and liquid phase materials. Among them, the gas phase product is carbon dioxide, and the liquid phase material includes hexamethylene diisocyanate, reaction by-products and unreacted hexamethylenediaminodicarboxylic acid methyl ester. The gas phase product escapes from the top of the tower, and the liquid phase material flows out from the bottom of the tower and then reenters the decomposition tower from the top of the decomposition tower, circulates and refluxes to decompose until no gas phase product is produced at the top of the tower. Finally, a mixture of hexamethylene diisocyanate and reaction by-products is obtained at the bottom of the tower. The mixture is separated by existing distillation to obtain hexamethylene diisocyanate.

[0067] Comparative Example 1 The comparative example of the present application provides a method for preparing toluene diisocyanate, which comprises: D101: Add crystalline powdered 2,4-diaminotoluene, liquid dimethyl carbonate and powdered iron oxide into a reactor at a molar ratio of 1:20:1. After sealing the reactor, stir and react at a temperature of 150°C for 5 hours; after the reaction is completed, the reaction product is obtained at the bottom of the reactor.

[0068] D102: The reaction product was distilled under reduced pressure at 50°C and 12 kPa to remove unreacted 2,4-diaminotoluene and dimethyl carbonate to obtain methyl toluene dicarbamate.

[0069] D103: Add methyl toluene dicarbamate to dimethyl succinate to dissolve and form a mixed liquid. Add the mixed liquid and iron oxide to the decomposition tower. Under normal pressure and a thermal decomposition temperature of 180°C, methyl toluene dicarbamate undergoes a decomposition reaction under the catalytic action of iron oxide to produce a gas phase product and a solid-liquid mixture. Among them, the gas phase product is gaseous toluene diisocyanate, and the solid-liquid mixture includes iron oxide, reaction by-products and unreacted toluene dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 25°C to obtain liquid toluene diisocyanate.

[0070] Comparative Example 2 The comparative example of the present application provides a method for preparing diphenylmethane diisocyanate MDI, which comprises: Add 4,4'-diaminodiphenylmethane dicarbamate to chlorobenzene to dissolve and form a mixed solution. Add the mixed solution and iron oxide to the decomposition tower. Under normal pressure and a thermal decomposition temperature of 180°C, 4,4'-diaminodiphenylmethane dicarbamate undergoes a decomposition reaction under the catalysis of iron oxide to produce gas phase products and a solid-liquid mixture. Among them, the gas phase product is gaseous methanol, and the solid-liquid mixture includes iron oxide, diphenylmethane diisocyanate, reaction by-products and unreacted 4,4'-diaminodiphenylmethane dicarbamate. After the gas phase product escapes from the top of the tower, it is condensed and fractionated at 25°C to obtain liquid methanol. After filtering, distilling and other operations, the solid-liquid mixture obtains diphenylmethane diisocyanate.

[0071] Comparative Example 3 The comparative example of the present application provides a method for preparing hexamethylene diisocyanate HDI, which comprises: Methyl hexamethylenediaminodicarboxylate is added to chlorobenzene to dissolve and form a mixed solution. The mixed solution and iron oxide are added to a decomposition tower. Under normal pressure and a thermal decomposition temperature of 190°C, methyl hexamethylenediaminodicarboxylate undergoes a decomposition reaction under the catalytic action of iron oxide to produce a gas phase product and a solid-liquid mixture. Among them, the gas phase product is carbon dioxide, and the solid-liquid mixture includes iron oxide, hexamethylene diisocyanate, reaction by-products and unreacted methyl hexamethylenediaminodicarboxylate. The gas phase product escapes from the top of the tower, and the solid-liquid mixture is filtered, distilled, and other operations to obtain hexamethylene diisocyanate.

[0072] The diisocyanates prepared in Examples 4-12 and Comparative Examples 1-3 were analyzed by high performance liquid chromatography, and the yields of the diisocyanates were calculated based on the amount of carbamate added, as shown in Table 1.

[0073] Table 1: Yields of diisocyanates prepared in Examples 4-12 and Comparative Examples 1-3 As can be seen from Table 1, relative to comparative example 1, the yield of toluene diisocyanate TDI prepared in Examples 4-6 of the present application is significantly improved; relative to comparative example 2, the yield of diphenylmethane diisocyanate MDI prepared in Examples 7-9 of the present application is significantly improved; relative to comparative example 3, the yield of hexamethylene diisocyanate HDI prepared in Examples 10-12 of the present application is also significantly improved. This shows that the iron oxide / molecular sieve catalyst provided in the examples of the present application has a good catalytic effect and can significantly improve the yield of diisocyanate.

[0074] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A catalyst for preparing diisocyanate from carbamate, characterized in that: The catalyst is an iron oxide / molecular sieve catalyst, which is prepared using molecular sieve as a carrier and iron hydroxide colloid as a raw material; Specifically made by the following method: Immerse the molecular sieve in the iron hydroxide colloid, soak for 24-48 hours at room temperature, and filter to obtain the molecular sieve containing the iron hydroxide colloid; The molecular sieve containing iron hydroxide colloid is calcined at a high temperature of 500-550° C. to obtain an iron oxide / molecular sieve catalyst.

2. The catalyst for preparing diisocyanate from carbamate according to claim 1, characterized in that: The molecular sieve is a mesoporous molecular sieve, and the pore size of the molecular sieve is 2-50 nm.

3. The catalyst for preparing diisocyanate from carbamate according to claim 2, characterized in that: The molecular sieve includes SBA-15 molecular sieve, MCM-41 molecular sieve, KIT-6 molecular sieve or MCM-48 molecular sieve.

4. The catalyst for preparing diisocyanate from carbamate according to claim 1, characterized in that: The particle size of the iron hydroxide colloid is 1-45 nm.

5. The catalyst for preparing diisocyanate from carbamate according to claim 1, characterized in that: The mass volume ratio of the molecular sieve to the iron hydroxide colloid is 1:(2-4).

6. A method for preparing diisocyanate, characterized in that: include: Filling the iron oxide / molecular sieve catalyst described in any one of claims 1 to 5 into a decomposition tower, wherein the filling amount accounts for 80-90% of the volume of the decomposition tower; After the carbamate is dissolved in a solvent, it is added into the decomposition tower from the top of the decomposition tower, and the reaction is carried out under normal pressure and a thermal decomposition temperature of 150-200° C. for 10-15 hours to obtain diisocyanate.

7. The method for preparing diisocyanate according to claim 6, characterized in that: The carbamate includes toluene dicarbamate, 4,4'-diaminodiphenylmethane dicarbamate or hexamethylene dicarbamate.

8. The method for preparing diisocyanate according to claim 6, characterized in that: The solvent includes chlorobenzene, dimethyl succinate, dimethyl glutarate, dioctyl phthalate or dimethyl nonanoate.

9. The method for preparing diisocyanate according to claim 7, characterized in that: When the carbamate is toluene dicarbamate, the method comprises: Add 2,4-diaminotoluene, dimethyl carbonate and iron oxide into a reaction kettle, seal and stir at a temperature of 120-160° C. for 3-6 hours to obtain a reaction product; The reaction product is distilled under reduced pressure to obtain toluene dicarbamate; Filling the iron oxide / molecular sieve catalyst described in any one of claims 1 to 5 into a decomposition tower, wherein the filling amount accounts for 80-90% of the volume of the decomposition tower; After the carbamate is dissolved in a solvent, it is added into the decomposition tower from the top thereof, and circulated and refluxed for 10-15 hours at a thermal decomposition temperature of 150-200° C. under normal pressure, and the gas phase product obtained at the top of the tower is condensed to obtain toluene diisocyanate.

10. The method for preparing diisocyanate according to claim 9, characterized in that: The condensation temperature of the gas phase product is 20-30°C.

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