Apparatus and method for the thermal decomposition of a carbamate to produce isocyanate
By using a dynamic microchannel tubular continuous flow reactor and optimized reaction conditions, the problems of high reaction temperature and long residence time in the pyrolysis of carbamates were solved, achieving the preparation of isocyanates with high yield and high purity, which is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HAINAN HUASHENG CEMENT INVESTMENT CO LTD
- Filing Date
- 2022-09-19
- Publication Date
- 2026-07-31
AI Technical Summary
Existing pyrolysis methods for preparing isocyanates suffer from problems such as high reaction temperatures, long residence times, difficulty in separating byproducts, and frequent self-polymerization reactions, resulting in low isocyanate yields and making them unsuitable for industrial production.
A dynamic microchannel tubular continuous flow reactor was adopted, combined with a heating system and a product separation system. Through precise temperature control and mass transfer design, the self-polymerization reaction was suppressed, and the rapid separation of low-boiling-point by-products was achieved. Inert solvents and catalysts were used to optimize reaction conditions and improve the isocyanate yield.
The reaction achieved an isocyanate yield of over 99.5%, with high reaction efficiency, making it suitable for continuous industrial production. It also reduced side reactions and improved product purity and yield.
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Figure CN117181162B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of isocyanates, specifically to an apparatus and method for preparing isocyanates by thermal decomposition of carbamates. This invention combines reaction apparatus design with process optimization to obtain a method for preparing isocyanates by thermal decomposition of carbamates, thereby improving reaction efficiency and reducing side reactions. Background Technology
[0002] Isocyanates are important organic chemical intermediates. Their molecular structure contains isocyanate groups (-N=C=O), and they are crucial raw materials for the synthesis of polyurethanes, widely used in aerospace, construction, automotive, shipbuilding, refrigeration, and furniture industries. Based on the presence or absence of a benzene ring in their structure, isocyanates can be classified into aliphatic isocyanates and aromatic isocyanates. Based on the number of isocyanates in the molecule, isocyanates can be classified into monoisocyanates, diisocyanates, and polyisocyanates. Currently, commonly used industrial isocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 1,6-dimethylene diisocyanate (HDI).
[0003] Currently, the industrial production methods for isocyanates worldwide are largely similar, with at least 90% of organic isocyanate products produced using the phosgene process. While the phosgene synthesis technology is mature, produces high-quality products, and is economically viable, this method also has several problems, specifically the following four:
[0004] (1) The raw materials are toxic, and a large amount of highly toxic phosgene gas is required in the production process, which leads to strict restrictions on the storage, transportation and use of raw materials.
[0005] (2) The process is complex, the reaction conditions are harsh, and the production operation is difficult. Therefore, overall, the requirements for each process step are relatively high.
[0006] (3) Environmental protection issues have been given attention. In addition to using highly toxic raw material phosgene in the production process, a large number of by-products (hydrochloric acid) will be generated in the reaction, which can easily cause corrosion to the equipment. Therefore, the requirements for the materials, maintenance and management of the equipment have been increased.
[0007] (4) There are potential risks to product quality. Because there may be hydrolyzed chlorine residue in the isocyanate of the product, it will affect the use of the product and make subsequent processing procedures more complicated.
[0008] Non-phosgene methods for isocyanate synthesis mainly include one-step carbonylation of nitro compounds, transesterification, and pyrolysis of carbamates. One-step carbonylation of nitro compounds is the simplest route for isocyanate synthesis, directly generating isocyanates from the reaction of nitro compounds and carbon monoxide. However, this method requires reaction pressures above 30 MPa, has expensive catalysts, and is difficult to recover after reaction, thus limiting its widespread application. Transesterification involves exchanging the ester groups on carbamates with other isocyanates to prepare the desired isocyanate. The advantages of transesterification are high purity and good yield of the resulting isocyanate. The disadvantages are that the required isocyanates must be prepared in-house, and the process is lengthy, so it is rarely used. The pyrolysis of carbamates to prepare isocyanates is the most promising non-phosgene method.
[0009] Carbamate pyrolysis methods can be divided into gas-phase pyrolysis and liquid-phase pyrolysis based on the phase state. Gas-phase pyrolysis involves the material passing through a reactor in gaseous form, where the carbamate rapidly decomposes into isocyanate. This results in less backmixing and reduced self-polymerization, thus increasing the isocyanate yield. However, gas-phase pyrolysis requires rapid gasification of the material within a short time, leading to increased energy consumption, high economic costs, and hindering industrial scale-up. Therefore, gas-phase pyrolysis remains in the small-scale testing stage.
[0010] Liquid-phase pyrolysis involves adding urethane and solvent to a reactor in a specific ratio, and then pyrolyzing under reduced or increased pressure to obtain the isocyanate product. Liquid-phase pyrolysis offers several advantages: the urethane is dispersed in an inert solvent, reducing its concentration and improving dispersion, thus effectively minimizing side reactions. Compared to gas-phase pyrolysis, liquid-phase pyrolysis operates at lower temperatures, reducing isocyanate polymerization and resulting in higher isocyanate yields. However, the liquid-phase pyrolysis process also has the following characteristics:
[0011] (1) The pyrolysis reaction rate is very sensitive to temperature changes;
[0012] (2) The product isocyanate is a heat-sensitive substance containing isocyanate, which can undergo nucleophilic reactions, polymerization reactions, cycloaddition reactions and insertion reactions. Among them, the nucleophilic reaction and polymerization reaction of isocyanate are highly active and can occur even at low temperature without catalyst. Therefore, isocyanate should avoid contact with nucleophilic reagents (water, acid, alcohol, amine, base, etc.) as much as possible, especially since it is very easy to polymerize at high temperature, generating various self-polymerized products, including dimers, trimers and various polymers. Among them, the most important are dimer and trimer reactions.
[0013]
[0014] (3) The pyrolysis of carbamates involves the removal of byproducts such as alcohols or phenols under heating conditions to generate isocyanates. The oxygen atom on the isocyanate group is highly electronegative and readily reacts with the hydrogen atoms on the molecules of active hydrogen compounds to form unstable intermediates. These intermediates are prone to rearrangement to form carbamates (with alcohols as reactants) or ureas (with amines as reactants).
[0015] RNCO+ROH→RNHCOOR (2);
[0016]
[0017] Since the reaction between RNH2 and RNCO is faster than that between water, the above reaction equation can be written as:
[0018] 2RNCO+H2O→RNHCONHR+CO2 (4);
[0019] (4) When urethane is kept at high temperature for a long time, side reactions may occur, such as the decarbonation reaction of two urethane molecules to generate a compound containing a urea group, or the reaction with the isocyanate group generated by the thermal decomposition of urethane to generate a urea-formate group.
[0020] Research on the thermal decomposition of urethane to prepare isocyanates is gradually increasing. For example, WO0156977 discloses a method for producing TDI using dimethyl carbonate as a raw material. This method involves reacting dimethyl carbonate with toluene diamine to generate urethane, which is then pyrolyzed to produce TDI. However, this method has drawbacks, including long reaction time, complex equipment, and a high pyrolysis temperature for urethane. Patent CN1281580C reports a method for preparing urethane and isocyanates. In a glass reaction flask, using dibutyltin dilaurate as a catalyst, under reaction pressure of 3.3 kPa and reaction temperature of 250 °C, the yield of 1,6-hexamethylene dicarboxylate (HDI), a product of the thermal decomposition of methyl 1,6-hexamethylene dicarboxylate, is 74.9%, with a corresponding monoisocyanate yield of 22.0%. Patent CN105102422A discloses a method for manufacturing isocyanates. The thermal decomposition reaction apparatus uses a multi-stage distillation column. Under the conditions of 10 kPa pressure and benzyl butyl phthalate as solvent, the HDI yield is 71%. In contrast, the thermal decomposition uses a falling film evaporator. Under the conditions of 1 kPa pressure and 250°C temperature and benzyl toluene as solvent, the HDI yield is only 18%. Patent CN101868445A discloses a method for manufacturing isocyanates and aromatic hydroxyl compounds. The thermal decomposition reaction apparatus uses a thin-film distillation apparatus, and the reaction conditions are 220°C and 13 kPa. The isocyanate separation apparatus uses a continuous multi-stage distillation column, with an HDI content of 99.8% and a yield of 85%. With the same thermal decomposition reaction apparatus and product separation apparatus, the yield of isophorone diisocyanate from urethane thermal decomposition is 74%, the yield of 4,4'-methylene di(cyclohexyl isocyanate) is 72%, the yield of 2,4-toluene diisocyanate is 79%, and the yield of 4,4'-diphenylmethane diisocyanate is 66%. Patent CN101386585A reports a method for preparing diisocyanate by thermal decomposition. In this method, methyl p-methylbenzoate is added as a solvent in a conventional reaction tube, ethyl 1,6-hexanedicarbamate is used as the raw material, and a catalyst is a combination of zinc powder, nickel powder, and copper powder. The reaction is carried out with electromagnetic stirring at 190°C under normal pressure for 1 hour in an open atmosphere, yielding 57% of 1,6-hexanediisocyanate. While these patents have achieved good research progress using different thermal decomposition reaction apparatus and process conditions, the overall isocyanate yield remains low.
[0021] Patent CN113024417A reports a method and apparatus for enhanced separation in the preparation of isocyanates. The thermal decomposition uses a batch reactor, with the forward reaction driven by countercurrent purging of a protective gas to rapidly remove byproducts. Using chlorobenzene as a solvent and zinc oxide as a catalyst, the reaction is carried out intermittently for 60 min at a reaction temperature of 280℃ and a pressure of 1.5 MPa, achieving a 100.0% conversion rate of diphenylmethane dicarboxylate and a 98.9% yield of MDI. Similarly, using benzene as a solvent and zinc oxide and alumina as a composite catalyst, the reaction is carried out intermittently for 50 min at a reaction temperature of 290℃ and a pressure of 1.5 MPa, achieving a 100.0% conversion rate of diphenylmethane dicarboxylate and a 98.9% yield of MDI. The conversion rate of phenyl dimethylene carbamate was 100%, and the yield of phenyl dimethylene isocyanate was 98.5%. Using chlorobenzene as solvent and cobalt oxide as catalyst, under a batch reaction at 290℃ and 1.0 MPa for 60 min, the conversion rate of propyl hexamethylene dicarbamate was 100%, and the yield of hexamethylene diisocyanate was 98.8%. Using chlorobenzene as solvent and zinc oxide and alumina as composite catalyst, under a batch reaction at 290℃ and 1.0 MPa for 60 min, the conversion rate of ethyl isophorone dicarbamate was 100%, and the yield of isophorone diisocyanate was 96.9%. Although this report shows high raw material conversion rates and isocyanate yields, the high reaction temperature, long residence time, and batch reaction method are not suitable for fully continuous industrial production.
[0022] Therefore, to solve the problems encountered in the pyrolysis of urethanes, such as the high reaction temperature and long reaction residence time leading to easy polymerization of isocyanates, the rapid separation of low-boiling-point byproducts after the thermal decomposition of urethanes, and the enhancement of mass and heat transfer in the reaction process, it is necessary not only to start from the optimization of catalysts and process conditions, but also to combine it with reactor structure design. Summary of the Invention
[0023] The purpose of this invention is to provide an apparatus and method for preparing isocyanate by thermal decomposition of urethane. The core component of the thermal decomposition reactor is a dynamic microchannel tubular continuous flow reactor, which fully considers the enhancement of mass and heat transfer during the reaction process, precise control of reaction temperature and residence time, and rapid separation of low-boiling-point byproducts from product isocyanate. This promotes the forward thermal decomposition reaction, inhibits the occurrence of self-polymerization reaction and side reactions caused by back-mixing of low-boiling-point byproducts, and achieves an isocyanate yield of greater than 99.5%.
[0024] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution:
[0025] An apparatus for the thermal decomposition of carbamate to prepare isocyanate includes a heating system, a feeding system, a dynamic microchannel tubular continuous flow reactor, and a product separation system. The heating system is connected to the feeding system, the dynamic microchannel tubular continuous flow reactor, and the product separation system, respectively. The feeding system, the dynamic microchannel tubular continuous flow reactor, and the product separation system are connected in sequence.
[0026] The heating system includes heating equipment such as heat exchangers, preferably integrated heating and cooling units, which are connected to the feeding system, dynamic microchannel tubular continuous flow reactor and product separation system respectively, and provide precise temperature control and heating.
[0027] Preferably, the feeding system includes a batching tank, a metering pump, and a preheater connected in sequence. The batched material is quantitatively fed by the metering pump, first passing through the preheater to be heated to a certain temperature, and then entering the dynamic microchannel tubular continuous flow reactor through the material inlet.
[0028] The preheater preheats the reactants according to the process conditions before the reaction to improve reaction efficiency. The preheater is connected to the heating system.
[0029] Preferably, the product separation system includes a thin-film evaporator, and more preferably a falling film evaporator.
[0030] Preferably, the interior of the dynamic microchannel tubular continuous flow reactor includes a first hot and cold chamber, a second hot and cold chamber, a reaction chamber, and a reaction chamber.
[0031] Both the first and second hot and cold chambers are configured as cylindrical structures, with the first hot and cold chamber located in the inner layer of the second hot and cold chamber; a reaction chamber is formed between the outer surface of the first hot and cold chamber and the inner surface of the second hot and cold chamber; preferably, the cylindrical structures of the first and second hot and cold chambers are coaxial.
[0032] The first hot and cold cavity is closed at the top and connected to a rotating motor, allowing it to rotate under the motor's drive. The bottom of the first hot and cold cavity is also closed, with an internal heat transfer medium outlet located at the center of the bottom. An inner cylinder, open at both ends, surrounds the internal heat transfer medium outlet at its lower end and is sealed to the bottom of the first hot and cold cavity. A gap exists between the upper end of the inner cylinder and the inner wall of the top of the first hot and cold cavity, creating a flow channel for the internal heat transfer medium within the cavity. An internal heat transfer medium inlet is located at the bottom of the first hot and cold cavity, outside the outer wall of the inner cylinder. An internal heat transfer medium inlet pipeline and an internal heat transfer medium outlet pipeline are connected to the internal heat transfer medium inlet and outlet at the bottom of the first hot and cold cavity, respectively.
[0033] The top and bottom of the second hot and cold cavity are both sealed; its cylinder wall is provided with an external heat transfer medium inlet that communicates with the external heat transfer medium input pipeline and an external heat transfer medium outlet that communicates with the external heat transfer medium output pipeline.
[0034] The first hot and cold chamber rotates together with the rotating motor, which promotes mass and heat transfer in the reaction system and facilitates the reaction. The internal heat transfer medium moves from bottom to top in the first hot and cold chamber, and then flows out from the flow channel in the central part, circulating back to the heating system.
[0035] The external heat transfer medium moves from bottom to top in the second hot and cold cavity, then flows out and circulates back to the heating system.
[0036] Preferably, the internal heat transfer medium input pipeline and the external heat transfer medium input pipeline are respectively connected to the liquid outlet of the heating system, and the internal heat transfer medium output pipeline and the external heat transfer medium output pipeline are respectively connected to the liquid inlet of the heating system.
[0037] More preferably, the top and bottom ends of the first and second hot and cold cavities are respectively sealed by the same sealing assembly.
[0038] Furthermore, a mixing zone is provided at the bottom of the reaction chamber, and a paddle is provided on the outer wall of the first hot and cold chamber in the mixing zone; a reaction enhancement zone and a reaction delay zone are arranged sequentially above the mixing zone, and baffles of different shapes and sizes are provided on the inner walls of the reaction enhancement zone and the reaction delay zone, and the baffles are arranged from bottom to top from dense to sparse, with dense baffles in the reaction enhancement zone and sparse baffles in the reaction delay zone.
[0039] Furthermore, the shape of the blades is not limited, and the number and size of the blades can be adjusted according to the mixing zone. The blades can help to quickly and evenly mix materials or rapidly dissolve raw materials in solvents, as well as rapidly heat to the reaction temperature.
[0040] Furthermore, it is preferable that the diameter of the first hot and cold cavity portion corresponding to the mixing zone is smaller than the diameter of the portion above it, and more preferably it is 1 / 2 to 3 / 4 of the diameter of the portion above it.
[0041] Furthermore, the baffle arrangement density decreases from dense to sparse from bottom to top. The baffle arrangement density is higher in the reaction enhancement zone, which is more conducive to enhancing mass and heat transfer. Preferably, 1 to 5 baffles are set per square centimeter in the reaction enhancement zone, more preferably 2 to 3 baffles. The baffle arrangement density is sparser in the reaction delay zone, which is more conducive to the rapid separation of low-boiling-point by-products and promotes the forward reaction. Preferably, the number of baffles in the reaction enhancement zone is 2 to 10 times the number of baffles in the reaction delay zone, more preferably 5 to 10.
[0042] Furthermore, the thickness of the reaction chamber is 10 μm to 10 mm, preferably 1 mm to 4 mm.
[0043] Further, the height of the mixing zone accounts for 1 / 10 to 1 / 3 of the height of the reaction chamber, the height of the reaction enhancement zone accounts for 1 / 5 to 2 / 3 of the height of the reaction chamber, and the height of the reaction delay zone accounts for 1 / 5 to 2 / 3 of the height of the reaction chamber. Preferably, the height of the mixing zone accounts for 1 / 6 to 1 / 4 of the height of the reaction chamber, the height of the reaction enhancement zone accounts for 1 / 3 to 1 / 2 of the height of the reaction chamber, and the height of the reaction delay zone accounts for 1 / 3 to 1 / 2 of the height of the reaction chamber.
[0044] A gas or low-boiling-point by-product outlet is provided directly above the reaction chamber. A first material outlet is provided on the side of the second hot and cold chamber wall corresponding to the reaction enhancement zone. A second material outlet is provided on the side of the second hot and cold chamber wall corresponding to the reaction delay zone. A third material outlet is provided on the side of the second hot and cold chamber wall corresponding to the top of the reaction chamber.
[0045] Furthermore, a gas phase feed inlet is provided at the bottom of the mixing zone, with gas phase feeding as the main method; a first material feed inlet and a second material feed inlet are respectively provided on the side wall of the second hot and cold chamber corresponding to the mixing zone, with liquid or liquid-solid mixture feeding as the main method.
[0046] Furthermore, the gas is selected to be fed through a gas phase inlet, and inert gas is continuously injected into the reactor to facilitate the rapid separation of low-boiling-point reaction byproducts.
[0047] Furthermore, a gas or low-boiling-point by-product outlet is provided directly above the reaction chamber. Inert gas can be continuously injected through the gas phase feed port and continuously discharged at the gas or low-boiling-point by-product outlet, or the low-boiling-point by-product generated by thermal decomposition can be rapidly separated at the gas or low-boiling-point by-product outlet under a certain negative pressure condition by vacuuming. The by-products can be recovered through a connected condensation device. A first material outlet is provided on the side wall of the second hot and cold chamber corresponding to the reaction enhancement zone, a second material outlet is provided on the side wall of the second hot and cold chamber corresponding to the reaction delay zone, and a third material outlet is provided on the side wall of the second hot and cold chamber corresponding to the top of the reaction chamber. The specific outlet position of the material can be determined according to the actual conversion effect of the reaction. The reaction delay zone can remain in a cavity state, which is more conducive to the rapid separation of low-boiling-point by-products from the reaction liquid.
[0048] A second aspect of the present invention provides a method for preparing isocyanate by thermal decomposition of urethane, comprising: preparing a reaction solution by mixing urethane, a catalyst and an inert solvent; preheating the reaction solution and then introducing it into a dynamic microchannel tubular continuous flow reactor for reaction; and separating the resulting product to obtain an isocyanate product.
[0049] Based on the above-mentioned thermal decomposition device for preparing isocyanates, after the reaction liquid enters the dynamic microchannel tubular continuous flow reactor, the thermal decomposition reaction is carried out under the purging of protective gas or under reduced pressure and vacuum negative pressure conditions, and the resulting products are separated to obtain isocyanate products.
[0050] Furthermore, the method includes the following steps:
[0051] The reaction solution, composed of raw material urethane and catalyst with an inert solvent, is first injected into a preheater via a metering pump. Then, it enters the mixing zone of the reactor through the first and / or second material inlet, subsequently proceeding to the reaction enhancement zone and reaction delay zone for thermal decomposition. Depending on the actual reaction effect, the pyrolysis solution can be collected through the first and / or second and / or third material outlets and rapidly fed into a product separation system, such as a thin-film evaporator, for product separation, ultimately yielding a high-content isocyanate product. The specific outlet location can be determined based on the actual conversion effect of the reaction; for example, for reactions with fast reaction times and short residence times, the material can exit through the bottom first material outlet, while for reactions with long reaction times and slow residence times, it can exit through the top third material outlet.
[0052] In the case of a reaction under positive or normal pressure conditions, the protective purging gas is preheated and continuously injected into the mixing zone of the reactor through the gas phase feed port, and the low-boiling-point byproduct low-carbon alcohol is rapidly separated and discharged from the gas or low-boiling-point byproduct outlet; in the case of a reaction under negative pressure conditions, the reaction byproduct low-carbon alcohol or phenol is discharged from the gas or low-boiling-point byproduct outlet by vacuuming.
[0053] The carbamate is one, two, or a combination of three or more of the following: aromatic monocarbamate, aromatic dicarbamate, aromatic polycarbamate, aliphatic monocarbamate, aliphatic dicarbamate, aliphatic polycarbamate, alicyclic monocarbamate, alicyclic dicarbamate, or alicyclic polycarbamate. Preferably, it is at least one of diphenylmethane dicarbamate, 1,6-hexamethylene dicarbamate, 1,5-pentanedicarbamate, toluene dicarbamate, and isophorone dicarbamate. The ester moiety of the carbamate has 1 to 10 carbon atoms, preferably methyl ester, ethyl ester, propyl ester, butyl ester, or phenyl ester.
[0054] The catalyst comprises one, two, or three of the following: a metallic element or a metal oxide; or a combination of a metallic element and / or a metal oxide with an acidic substance. The metallic element is selected from metals of groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIII of the periodic table. The metal in the metal oxide is selected from metals of groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIII of the periodic table. The acidic substance is an inorganic heteropolyacid or an organic sulfonic acid.
[0055] The inert solvent is selected from any one or a combination of at least two of alkanes, halogenated hydrocarbons, aromatic hydrocarbons, halogenated aromatic hydrocarbons, ethers, esters, thioethers, thioketones, or sulfones.
[0056] The concentration of urethane in the reaction solution is 1–50 wt%, preferably 3–25 wt%.
[0057] The concentration of the catalyst in the reaction solution is 1 ppm to 3%, preferably 30 ppm to 3‰.
[0058] The preheating temperature of the reaction solution is 70℃~220℃, preferably 120℃~180℃.
[0059] The thermal decomposition reaction temperature is 100℃~300℃, preferably 150℃~260℃, more preferably 150℃~250℃, for example, it can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 246℃, 247℃, 248℃, 249℃, 250℃, 255℃, 260℃, etc.
[0060] The thermal decomposition reaction pressure is 10 Pa to 1.5 MPa, preferably 300 Pa to 0.12 MPa.
[0061] Positive or atmospheric pressure conditions for the reaction are achieved by continuously injecting protective purge gas into the mixing zone of the reactor, preferably through a gas-phase feed inlet, so that low-boiling-point byproducts are rapidly separated and discharged from the gas or low-boiling-point byproduct outlet; negative pressure conditions for the reaction are achieved by removing the reaction byproducts through vacuuming at the gas or low-boiling-point byproduct outlet.
[0062] The thermal decomposition reaction time is 2 to 180 min, preferably 3 to 45 min, and specifically can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 60 min, 70 min, 80 min, 100 min, 150 min, etc.
[0063] The low-boiling-point byproducts include any one or a combination of at least two of phenol or alcohols having 1-10 carbon atoms.
[0064] The protective purging gas includes any one or a combination of at least two of the following gases: nitrogen, argon, helium, and neon.
[0065] The feed rate of the reaction liquid and the feed rate of the gas purging are determined by a combination of factors, such as the actual situation, reactor size, reaction residence time, and separation effect of low-boiling-point byproducts.
[0066] Compared with existing technologies, the present invention has the following advantages:
[0067] 1) The technology of this invention is simple, has strong operability for continuous production, high reaction efficiency, few isocyanate side reactions, and has good prospects for industrial application.
[0068] 2) The dynamic microchannel tubular continuous flow reactor used in this invention is equipped with a first hot and cold chamber and a second hot and cold chamber, resulting in a larger heating area. The reaction chamber thickness between the first and second hot and cold chambers reaches the microchannel level, leading to better heat transfer and more accurate temperature control, which can effectively reduce backmixing. In the reaction enhancement zone and the reaction delay zone, baffles of different shapes and sizes are arranged on the inner wall of the reaction chamber, with the baffle density decreasing from bottom to top. This special design is more conducive to enhancing mass and heat transfer and improving raw material conversion efficiency. In the reaction enhancement zone, the high-density baffles (especially the baffles on the outer wall of the first hot and cold chamber under high-speed rotation) are conducive to the rapid separation of light component by-products, while the low-density baffle arrangement in the reaction delay zone is more conducive to the rapid escape of low-boiling-point by-products.
[0069] 3) The dynamic microchannel tubular continuous flow reactor used in this invention is provided with a material mixing zone, and the mixing zone is equipped with stirring blades using a stirring rotating shaft. The material (including catalyst and inert gas used for purging, etc.) has been fully dissolved or mixed evenly before formally entering the reaction enhancement zone.
[0070] 4) The device of this invention integrates and couples the existing dynamic tubular reactor with the microchannel reactor and optimizes and improves it. It is first applied to the process of preparing isocyanate by thermal decomposition of carbamate. The reaction conditions are relatively mild, the carbamate conversion rate is 100%, the isocyanate yield is >95%, and the isocyanate content is >97%. Attached Figure Description
[0071] Figure 1 This is a schematic diagram of a dynamic microchannel tubular continuous flow reactor provided by the present invention.
[0072] Figure 1 In the middle: 1-First hot and cold chamber, 2-Second hot and cold chamber, 3-Internal heat transfer medium flow channel, 4-Blade, 5-Baffle, 6-Gas phase feed inlet, 7-First material feed inlet, 8-Second material feed inlet, 9-Mixing zone, 10-Reaction chamber, 11-Gas or low-boiling-point by-product outlet, 12-First material outlet, 13-Second material outlet, 14-Third material outlet, 15-External heat transfer medium input pipeline, 16-External heat transfer medium output pipeline, 17-Internal heat transfer medium input pipeline, 18-Internal heat transfer medium output pipeline, 19-Reaction enhancement zone, 20-Reaction delay zone, 21-Rotating motor, 22-Heating system, 23-Sealing assembly.
[0073] According to one embodiment of the present invention, a reaction solution composed of raw material carbamate, catalyst, and inert solvent is first injected into a preheater via a metering pump, and then enters the mixing zone 9 of the reactor through a first material inlet 7 and / or a second material inlet 8. A paddle 4 is provided on the outer wall of the first hot and cold chamber 1 within the mixing zone 9. Subsequently, the solution sequentially enters a reaction enhancement zone 19 and a reaction delay zone 20 for thermal decomposition. Baffles 5 of different shapes and sizes are provided on the inner walls of the reaction enhancement zone 19 and the reaction delay zone 20, arranged from dense to sparse from bottom to top. Depending on the actual reaction effect, the pyrolysis solution can be collected through a first material outlet 12 and / or a second material outlet 13 and / or a third material outlet 14 and quickly enters a product separation system for product separation, ultimately obtaining a high-content isocyanate product. Low-boiling-point byproducts are discharged from a gas or low-boiling-point byproduct outlet 11. Detailed Implementation
[0074] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.
[0075] All features disclosed in this specification, except for mutually exclusive features and / or steps, may be combined in any way.
[0076] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.
[0077] The quantitative detection method for the isocyanate product is to add a certain amount of ethanol and sonicate for a certain time to ensure complete derivatization of the product, and then use high performance liquid chromatography to quantitatively analyze the ethanol derivative of the product.
[0078] Example 1
[0079] Adopting such Figure 1 The dynamic microchannel tubular continuous flow reactor shown has a reaction chamber thickness of 3 mm. The height of the mixing zone is 1 / 5 of the reaction chamber height, the height of the reaction enhancement zone is 2 / 5 of the reaction chamber height, and the height of the reaction delay zone is 2 / 5 of the reaction chamber height. An average of 3 baffles are set per square centimeter in the reaction enhancement zone, and the number of baffles in the enhancement zone is 10 times the number of baffles in the delay zone. The diameter of the first hot and cold chamber part corresponding to the mixing zone is 1 / 2 of the diameter of the part above it.
[0080] The raw material diphenylmethane dicarboxylate was prepared into a 15% reaction solution with the solvent diisooctyl sebacate. Then, ZnO catalyst with a concentration of 1.5 × 10⁻⁶ was added. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 175℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 240℃, and the reaction residence time is controlled at 25min. The reaction pressure is maintained at 3KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the first material outlet and quickly enters the thin film evaporator for product separation. Finally, a diphenylmethane diisocyanate product with a content of 99.5% is obtained, with a yield of 96.2% and a conversion rate of 100% for diphenylmethane dicarboxylate.
[0081] Example 2
[0082] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0083] The raw material diphenylmethane dicarboxylate was prepared into a 10% reaction solution with the solvent diisooctyl sebacate. Then, ZnO catalyst with a concentration of 1.5 × 10⁻⁶ was added. -4 g / ml, stir evenly, and while stirring, inject the reaction solution into the preheater through a peristaltic pump. The preheating temperature is 175℃, and then it enters the mixing zone of the reactor through the second feed port. Subsequently, it enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 245℃, and the reaction residence time is controlled at 30min. During the reaction, N2 is continuously injected into the mixing zone of the reactor through the first gas phase feed port (6) after passing through the preheater. The low-boiling point byproduct methanol is rapidly separated and continuously discharged from the gas or low-boiling point byproduct outlet (11). The reaction pressure is maintained at 1.2×105 Pa, the pyrolysis reaction liquid is collected through the second material outlet and quickly enters the thin film evaporator for product separation, finally obtaining a diphenylmethane diisocyanate product with a content of 99.5% and a yield of 97.5%, and a diphenylmethane dicarboxylate conversion rate of 100%.
[0084] Example 3
[0085] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0086] The raw material diphenylmethane dipropylcarbamate was prepared into a 15% reaction solution with the solvent diisooctyl sebacate. Then, the catalyst ZnO with a concentration of 1.5 × 10⁻⁶ was added. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 175℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 235℃, and the reaction residence time is controlled at 20min. The reaction pressure is maintained at 2.6KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the second material outlet and quickly enters the thin film evaporator for product separation. Finally, a diphenylmethane diisocyanate product with a content of 99.5% is obtained, with a yield of 98.3% and a conversion rate of 100% for diphenylmethane dicarboxylate.
[0087] Example 4
[0088] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0089] The raw material diphenylmethane dicarboxylic acid phenyl ester was prepared into a 10% reaction solution with the solvent diisooctyl sebacate. Then, the catalyst ZnO with a concentration of 1.5 × 10⁻⁶ was added. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 175℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 225℃, and the reaction residence time is controlled at 15min. The reaction pressure is maintained at 2.0KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the first material outlet and quickly enters the thin film evaporator for product separation. Finally, a diphenylmethane diisocyanate product with a content of 99.5% is obtained, with a yield of 99.2% and a conversion rate of 100% for diphenylmethane dicarboxylate.
[0090] Example 5
[0091] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0092] The raw material methyl toluene dicarboxylate and the solvent dioctyl phthalate were mixed to prepare a 10% reaction solution. Then, the catalyst Fe2O3 with a concentration of 3×10⁻⁶ was added. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 170℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 600r / min, the reaction temperature is 240℃, and the reaction residence time is controlled at 45min. The reaction pressure is maintained at 4KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the second material outlet and quickly enters the thin film evaporator for product separation. Finally, a toluene diisocyanate product with a content of 99.2% is obtained, with a yield of 97.4% and a conversion rate of methyl toluene dicarboxylate of 100%.
[0093] Example 6
[0094] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0095] The raw material methyl toluene dicarboxylate and the solvent dioctyl phthalate were mixed to prepare a 10% reaction solution. Then, the catalyst Fe2O3 with a concentration of 3×10⁻⁶ was added. -4 g / ml, stir evenly, and while stirring, inject the reaction solution into the preheater through a peristaltic pump. The preheating temperature is 170℃, and then it enters the mixing zone of the reactor through the second feed port. Subsequently, it enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 600r / min, the reaction temperature is 240℃, and the reaction residence time is controlled at 45min. During the reaction, N2 is continuously injected into the mixing zone of the reactor through the first gas phase feed port (6) after passing through the preheater. The low-boiling point byproduct methanol is rapidly separated and continuously discharged from the gas or low-boiling point byproduct outlet (11). The reaction pressure is maintained at 1.2×10 5 Pa, the pyrolysis reaction liquid is collected through the second material outlet and quickly enters the thin film evaporator for product separation, finally obtaining toluene diisocyanate product with a content of 99.2% and a yield of 95.3%, with a conversion rate of 100% for methyl toluene dicarboxylate.
[0096] Example 7
[0097] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0098] The raw material phenyl toluene dicarboxylate was prepared into a 10% reaction solution with the solvent dioctyl phthalate. Then, the catalyst Fe2O3 with a concentration of 3×10⁻⁶ was added. -4g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 170℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 600r / min, the reaction temperature is 220℃, and the reaction residence time is controlled at 30min. The reaction pressure is maintained at 2.5KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the first material outlet and quickly enters the thin film evaporator for product separation. Finally, a toluene diisocyanate product with a content of 99.2% is obtained, with a yield of 99.4% and a conversion rate of methyl toluene dicarboxylate of 100%.
[0099] Example 8
[0100] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0101] The raw material methyl 1,6-hexamethylene dicarboxylate was prepared into a 6% reaction solution with the solvent dibutyl terephthalate. Then, the catalyst dibutyltin dilaurate was added at a concentration of 5 × 10⁻⁶. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 175℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 245℃, and the reaction residence time is controlled at 40min. The reaction pressure is maintained at 3.5KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the second material outlet and quickly enters the thin film evaporator for product separation. Finally, 1,6-hexamethylene diisocyanate product with a content of 97.5% is obtained, with a yield of 95.8% and a conversion rate of methyl 1,6-hexamethylene dicarboxylate of 98.7%.
[0102] Example 9
[0103] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0104] The raw material methyl 1,5-pentanedicarbamate was prepared into a 6% reaction solution with the solvent dibutyl terephthalate. Then, the catalyst dibutyltin dilaurate was added at a concentration of 5 × 10⁻⁶. -4g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 175℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 250℃, and the reaction residence time is controlled at 40min. The reaction pressure is maintained at 3.5KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the second material outlet and quickly enters the thin film evaporator for product separation. Finally, a 1,5-pentanediisocyanate product with a content of 98.0% is obtained, with a yield of 97.9% and a methyl 1,5-pentanedicarbamate conversion rate of 99.5%.
[0105] Example 10
[0106] The same dynamic microchannel tubular continuous flow reactor as in Example 1 was used.
[0107] The raw material isophorone dicarboxylate methyl ester and the solvent chlorobenzene were mixed to prepare a reaction solution with a concentration of 10%. Then, copper powder catalyst with a concentration of 8 × 10⁻⁶ was added. -4 g / ml, stir evenly, and inject the reaction solution into the preheater through a peristaltic pump while stirring. The preheating temperature is 185℃. Then, it enters the mixing zone of the reactor through the second feed port, and then enters the reaction enhancement zone and the reaction delay zone in sequence. The motor stirring speed is 700r / min, the reaction temperature is 245℃, and the reaction residence time is controlled at 45min. The reaction pressure is maintained at 3KPa by vacuuming at the gas or low boiling point by-product outlet (11). The pyrolysis reaction solution is collected through the second material outlet and quickly enters the thin film evaporator for product separation. Finally, isophorone diisocyanate product with a content of 99.8% is obtained, with a yield of 99.0% and a conversion rate of 100% for isophorone dicarboxylate.
[0108] Comparative Example 1
[0109] The experiment was conducted using a batch reaction glass bottle, a common laboratory reaction method.
[0110] In a 250ml three-necked round-bottom glass flask, 100ml of a 10% reaction solution was prepared by mixing diphenylmethane dicarboxylate with diisooctyl sebacate as solvent. ZnO catalyst with a concentration of 1.5 × 10⁻⁶ was then added. -4After mixing the solution at g / ml, quickly transfer the round-bottom flask to an oil bath preheated to 270°C. Connect an air condenser to the three-necked flask, and connect a vacuum tube above the condenser. Turn on the vacuum mode and gradually increase the vacuum. After about 5 minutes, the temperature of the reaction solution reaches 245°C and the vacuum degree is 3 kPa. Maintain this reaction condition and continue the reaction for 30 minutes. After the reaction is complete, quickly take a sample and perform derivatization analysis. The conversion rate of the raw material diphenylmethane dicarboxylate is 100%, the yield of diphenylmethane diisocyanate is 78%, the yields of diphenylmethane diisocyanate dimers and trimers are 10%, the yield of diphenylmethane diisocyanate polymers is 8%, and the yield of the raw material unilateral pyrolysis product is 4%.
[0111] This invention's thermal decomposition reactor uses a dynamic microchannel tubular continuous flow reactor as its core component. In the process of preparing isocyanates from urethane thermal decomposition, it enhances mass and heat transfer, accurately controls temperature, reduces backmixing, accelerates the separation of low-boiling-point byproducts, and promotes the forward reaction. It is particularly suitable for reactions with short reaction times, difficult temperature control, numerous side reactions including substances prone to condensation, and heat-sensitive materials. The technology of this invention is simple, highly operable for continuous production, has high reaction efficiency, few isocyanate side reactions, and shows promising prospects for industrial application.
[0112] The above content should not be construed as limiting the specific implementation of this invention to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this invention, and all such deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.
Claims
1. An apparatus for the thermal decomposition of carbamates to prepare isocyanates, comprising a heating system, a feeding system, a dynamic microchannel tubular continuous flow reactor, and a product separation system, wherein, The heating system is connected to the feeding system, the dynamic microchannel tubular continuous flow reactor, and the product separation system, respectively. The feeding system, the dynamic microchannel tubular continuous flow reactor, and the product separation system are connected in sequence. The interior of the dynamic microchannel tubular continuous flow reactor includes a first hot and cold chamber, a second hot and cold chamber, and a reaction chamber. Both the first hot and cold chamber and the second hot and cold chamber are cylindrical structures, with the first hot and cold chamber located in the inner layer of the second hot and cold chamber. A reaction chamber is formed between the outer surface of the first hot and cold chamber and the inner surface of the second hot and cold chamber. A mixing zone is provided at the bottom of the reaction chamber, and blades are provided on the outer wall of the first hot and cold chamber within the mixing zone. A reaction enhancement zone and a reaction delay zone are sequentially provided above the mixing zone. The inner walls of the reaction enhancement zone and the reaction delay zone are provided with baffles of different structural shapes, and the baffles are arranged from dense to sparse from bottom to top, with denser baffles in the reaction enhancement zone and sparser baffles in the reaction delay zone.
2. The apparatus according to claim 1, characterized in that: The heating system includes a heat exchange unit; and / or, The feeding system includes a batching tank, a feed metering pump, and a preheater connected in sequence; and / or, The product separation system includes a thin-film evaporator.
3. The apparatus according to claim 2, characterized in that: The product separation system includes a falling film evaporator.
4. The apparatus according to claim 1, characterized in that: The cylindrical structures of the first and second hot and cold chambers are coaxial.
5. The apparatus according to claim 4, characterized in that: The first hot and cold cavity is closed at the top and connected to a rotating motor, allowing it to rotate under the motor's drive. The bottom of the first hot and cold cavity is also closed, with an outlet for the internal heat transfer medium at its center. An inner cylinder, open at both ends, surrounds the outlet for the internal heat transfer medium at its lower end and is sealed to the bottom of the first hot and cold cavity. A distance is left between the upper end of the inner cylinder and the inner wall of the top of the first hot and cold cavity, creating a flow channel for the internal heat transfer medium within the cavity. An inlet for the internal heat transfer medium is located at the bottom of the first hot and cold cavity, outside the outer wall of the inner cylinder. The internal heat transfer medium inlet pipeline and the internal heat transfer medium outlet pipeline are respectively connected to the internal heat transfer medium inlet and the internal heat transfer medium outlet at the bottom of the first hot and cold cavity; and / or, The top and bottom of the second hot and cold cavity are both sealed; its cylinder wall is provided with an external heat transfer medium inlet that communicates with the external heat transfer medium input pipeline and an external heat transfer medium outlet that communicates with the external heat transfer medium output pipeline.
6. The apparatus according to claim 5, characterized in that: The internal heat transfer medium input pipeline and the external heat transfer medium input pipeline are respectively connected to the liquid outlet of the heating system, and the internal heat transfer medium output pipeline and the external heat transfer medium output pipeline are respectively connected to the liquid inlet of the heating system.
7. The apparatus according to claim 6, characterized in that: The top and bottom ends of the first and second hot and cold cavities are respectively sealed by the same sealing component.
8. The apparatus according to claim 1, characterized in that: A gas or low-boiling-point by-product outlet is provided directly above the reaction chamber. A first material outlet is provided on the side of the second hot and cold chamber wall corresponding to the reaction enhancement zone. A second material outlet is provided on the side of the second hot and cold chamber wall corresponding to the reaction delay zone. A third material outlet is provided on the side of the second hot and cold chamber wall corresponding to the top of the reaction chamber.
9. The apparatus according to claim 1, characterized in that: The thickness of the reaction chamber is 10 μm ~ 10 mm; and / or, The height of the mixing zone is 1 / 10 to 1 / 3 of the height of the reaction chamber, the height of the reaction enhancement zone is 1 / 5 to 2 / 3 of the height of the reaction chamber, and the height of the reaction delay zone is 1 / 5 to 2 / 3 of the height of the reaction chamber; and / or, A gas phase feed inlet is provided at the bottom of the mixing zone, and a first material feed inlet and a second material feed inlet are respectively provided on the side wall of the second hot and cold chamber corresponding to the mixing zone.
10. The apparatus according to claim 9, characterized in that: The thickness of the reaction chamber is 1 mm to 4 mm; and / or, The height of the mixing zone is 1 / 6 to 1 / 4 of the height of the reaction chamber, the height of the reaction enhancement zone is 1 / 3 to 1 / 2 of the height of the reaction chamber, and the height of the reaction delay zone is 1 / 3 to 1 / 2 of the height of the reaction chamber.
11. A method for preparing isocyanate by thermal decomposition of carbamate, using the apparatus described in any one of claims 1 to 10, comprising: A reaction solution is prepared by mixing urethane, catalyst, and inert solvent. After preheating, the reaction solution is introduced into a dynamic microchannel tubular continuous flow reactor for reaction. The resulting product is separated to obtain the isocyanate product.
12. The method according to claim 11, characterized in that... include: The reaction solution is quantitatively fed by a metering pump, first passing through a preheater, then entering the mixing zone of the reactor through the first and / or second material inlet, and subsequently entering the reaction enhancement zone and the reaction delay zone in sequence. The reaction byproducts are discharged through the gas or low-boiling-point byproduct outlet, and the reaction pyrolysis liquid is collected through the first and / or second and / or third material outlets and enters the product separation system for product separation, finally obtaining the isocyanate product.
13. The method according to claim 11, characterized in that: The carbamate is at least one of aromatic monocarbamate, aromatic dicarbamate, aromatic polycarbamate, aliphatic monocarbamate, aliphatic dicarbamate, aliphatic polycarbamate, alicyclic monocarbamate, alicyclic dicarbamate, and alicyclic polycarbamate; and / or, The catalyst is at least one of a metallic element or a metal oxide, or a composition of a metallic element and / or a metal oxide with an acidic substance, wherein the metallic element is selected from metals of groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIII; the metal in the metal oxide is selected from metals of groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, or VIII; and the acidic substance is an inorganic heteropolyacid or an organic sulfonic acid; and / or, The inert solvent is selected from at least one of alkanes, halogenated hydrocarbons, aromatic hydrocarbons, halogenated aromatic hydrocarbons, ethers, esters, thioethers, thioketones, and sulfones.
14. The method according to claim 13, characterized in that: The carbamate is at least one of diphenylmethane dicarbamate, 1,6-hexamethylene dicarbamate, 1,5-pentanedicarbamate, toluene dicarbamate, and isophorone dicarbamate, wherein the ester moiety of the carbamate has 1 to 10 carbon atoms.
15. The method according to claim 11, characterized in that: The concentration of carbamate in the reaction solution is 1-50 wt%; and / or, The concentration of the catalyst in the reaction solution is 1 ppm to 3%; and / or, The preheating temperature is 70~220℃; and / or, The reaction temperature is 100~300℃, the reaction residence time is 3~180min, and the reaction pressure is 10Pa~1.5MPa.
16. The method according to claim 15, characterized in that: The concentration of carbamate in the reaction solution is 3-25 wt%; and / or, The concentration of the catalyst in the reaction solution is 30 ppm to 3‰; and / or, The preheating temperature is 120~180℃; and / or, The reaction temperature is 150~260℃, the reaction residence time is 3~45min, and the reaction pressure is 300Pa~0.12MPa.
17. The method according to claim 11, characterized in that: Positive or atmospheric pressure conditions for the reaction are achieved by continuously injecting protective purge gas into the mixing zone of the reactor, which rapidly separates the low-boiling-point byproducts and discharges them from the gas or low-boiling-point byproduct outlet; negative pressure conditions for the reaction are achieved by removing the reaction byproducts through vacuuming at the gas or low-boiling-point byproduct outlet.
18. The method according to claim 17, characterized in that: The positive or atmospheric pressure conditions of the reaction are achieved by introducing protective purging gas into the mixing zone of the reactor through the gas phase feed port.