An apparatus and method for continuously producing 1,5-pentamethylene diisocyanate by thermal cracking

Abstract

The application belongs to the technical field of fine chemical synthesis, and particularly relates to a device and method for continuously preparing 1,5-pentamethylene diisocyanate through thermal cracking. 1,5-pentamethylene diurethane and bismuth neodecanoate are mixed, preheated, and then pumped into a reaction kettle containing tetraethylene glycol dimethyl ether to perform a thermal cracking reaction. The obtained reaction liquid is subjected to primary purification, and then secondary purification is continuously performed to obtain 1,5-pentamethylene diisocyanate. The application provides a device and method for continuously preparing 1,5-pentamethylene diisocyanate through thermal cracking. The preparation process adopts a non-phosgene method, is green and environmentally friendly, has small safety hazards, has mild reaction conditions, and is simple in process. The yield of 1,5-pentamethylene diisocyanate reaches more than 80%, and the purity reaches 99%.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical synthesis technology, specifically relating to an apparatus and method for the continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis. Background Technology

[0002] Polyurethane is a polymer with excellent thermal, mechanical, viscoelastic, abrasion-resistant, and bio-compatible properties, making it widely used in coatings, fibers, adhesives, thermosetting materials, thermoplastic materials, biomimetic materials, and nanocomposite materials. The main raw material for polyurethane is isocyanate, including aromatic isocyanates such as toluene diisocyanate and aliphatic isocyanates such as 1,6-hexamethylene diisocyanate. Among these, 1,6-hexamethylene diisocyanate, due to its superior straight-chain aliphatic structure, is the preferred choice for high-end polyurethane coatings. However, with increasing demands for green and environmentally friendly materials, bio-based materials are gradually becoming a focus of research. Therefore, compared to 1,6-hexamethylene diisocyanate produced using petrochemical resources, 1,5-pentamethylene diisocyanate synthesized from bio-based raw materials has broader development potential.

[0003] In industrial production, isocyanates are primarily synthesized via the phosgene process. However, this method still faces several unresolved issues. Firstly, the phosgene process requires excessive amounts of phosgene, a highly toxic substance, posing significant safety risks and posing operational risks to companies. Secondly, the phosgene process generates highly corrosive hydrochloric acid as a byproduct, which can damage production equipment and increase management and maintenance costs. Finally, isocyanates produced using the phosgene process often contain persistent chloride impurities, such as hydrolyzed chlorine, which reduce the isocyanate's reactivity and affect the efficiency of subsequent reactions. Therefore, from an environmental protection and health safety perspective, non-phosgene methods have become crucial for achieving greener isocyanate synthesis and related processes.

[0004] Reported one-step non-phosgene synthesis methods mainly include the reductive carbonylation of nitro groups, the oxidative carbonylation of amino groups, and rearrangement methods. Two-step methods primarily involve the pyrolysis of carbamates, where carbamates are first synthesized, followed by thermal decomposition to obtain the corresponding isocyanates. These two-step methods have attracted considerable research attention due to their feasibility in synthesis. Chinese patent CN108689884A reports a method for producing 1,5-pentanediisocyanate, utilizing the direct reaction of an extraction mixture of 1,5-pentanediamine with urea to generate carbamates, followed by thermal decomposition of the carbamates to obtain 1,5-pentanediisocyanate. However, its PDI yield is low, approximately 50%, making industrial-scale production difficult.

[0005] Therefore, it is of great significance to use new thermal pyrolysis solvents and new catalysts in the thermal pyrolysis process of carbamates, and to develop a continuous thermal pyrolysis method for preparing 1,5-pentamethylene diisocyanate. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an apparatus and method for the continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis, which addresses the shortcomings of the prior art. The method provided by the present invention uses a new thermal pyrolysis solvent and a new catalyst for the reaction, and adopts a continuous reaction separation coupling device, which is pollution-free, has few safety hazards, few by-products, and has a high yield and high purity of 1,5-pentamethylene diisocyanate.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] This invention discloses a method for the continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis. The method involves mixing 1,5-pentamethylene dicarboxylate compounds with tetraethylene glycol dimethyl ether and bismuth neodecanoate, and then subjecting the mixture to thermal pyrolysis. The resulting reaction solution is then separated and purified to obtain 1,5-pentamethylene diisocyanate.

[0009] In some embodiments, the 1,5-pentamethylenedicarbamate compound is any one or a combination of several of methyl 1,5-pentamethylenedicarbamate, ethyl 1,5-pentamethylenedicarbamate, and butyl 1,5-pentamethylenedicarbamate, preferably butyl 1,5-pentamethylenedicarbamate.

[0010] In some embodiments, the amount of tetraethylene glycol dimethyl ether used is not particularly required; it is sufficient to disperse or dissolve the raw material evenly and achieve a suitable viscosity. Preferably, the mass of the 1,5-pentamethylene dicarboxylate compound accounts for 5% to 20% of the mass of the tetraethylene glycol dimethyl ether.

[0011] In some embodiments, the bismuth neodecanoate accounts for 3% to 10% of the mass of the 1,5-pentamethylenedicarbamate compound.

[0012] In some embodiments, preferably, the bismuth neodecanoate accounts for 3% to 9% of the mass of the 1,5-pentamethylenedicarbamate compound, more preferably 5% to 9%, and even more preferably 5% to 7%.

[0013] In some embodiments, the thermal decomposition reaction is carried out at a temperature of 180–260°C, a reaction time of 0.5–3 h, and a reaction pressure of 0.02–0.08 MPa.

[0014] In some embodiments, preferably, the thermal decomposition reaction is carried out at a temperature of 220–250°C, more preferably 230–250°C, and even more preferably 230–240°C.

[0015] In some embodiments, preferably, the thermal decomposition reaction takes 0.5 to 1.5 hours.

[0016] In some embodiments, preferably, the thermal decomposition reaction is carried out at a reaction pressure of 0.04 to 0.08 MPa, more preferably 0.04 to 0.06 MPa.

[0017] In some embodiments, the thermal decomposition reaction is carried out under inert gas protection.

[0018] The inert gas is any one or a combination of helium, nitrogen and argon, preferably nitrogen.

[0019] In some embodiments, 1,5-pentamethylene dicarboxylate compounds and bismuth neodecanoate are mixed, preheated, and then pumped into a reactor containing tetraethylene glycol dimethyl ether for thermal pyrolysis. The resulting reaction solution is subjected to primary purification and then secondary purification to obtain 1,5-pentamethylene diisocyanate.

[0020] The reactor is purged with inert gas.

[0021] The 1,5-pentamethylene dicarboxylate compound and bismuth neodecanoate are mixed and preheated at a temperature of 40°C to 100°C, preferably 70°C to 90°C, and more preferably 80°C to 90°C.

[0022] The inert gas is any one or a combination of helium, nitrogen and argon, preferably nitrogen.

[0023] The flow rate of the mixture of 1,5-pentamethylene dicarboxylate and bismuth neodecanoate, after preheating, being pumped into a reactor containing tetraethylene glycol dimethyl ether is 180 g / h to 450 g / h, preferably 200 g / h to 400 g / h, and more preferably 300 g / h to 400 g / h.

[0024] In some embodiments, during the primary purification process, the separation temperature is 140–300°C, the rotation speed is 150–500 rpm, and the reaction pressure is 0.002–0.100 MPa; during the secondary purification process, the separation temperature is 160–350°C, the rotation speed is 150–500 rpm, and the reaction pressure is 0.002–0.100 MPa; and the purge flow rate of the inert gas is 20–300 mL / min.

[0025] In some embodiments, preferably, the separation temperature during the primary purification process is 150–170°C, and more preferably 160–170°C.

[0026] In some embodiments, preferably, during the primary purification process, the rotation speed is 200-400 rpm, more preferably 300-400 rpm, and even more preferably 350-400 rpm.

[0027] In some embodiments, preferably, the reaction pressure during the primary purification process is 0.002–0.010 MPa, more preferably 0.002–0.005 MPa.

[0028] In some embodiments, preferably, the separation temperature during the secondary purification process is 160–200°C, more preferably 170–190°C, and even more preferably 180–190°C.

[0029] In some embodiments, preferably, during the secondary purification process, the rotation speed is 200-400 rpm, more preferably 300-400 rpm, and even more preferably 350-400 rpm.

[0030] In some embodiments, preferably, the reaction pressure during the secondary purification process is 0.002–0.010 MPa, more preferably 0.002–0.005 MPa.

[0031] In some embodiments, preferably, the purging flow rate of the purging inert gas is 50–300 mL / min.

[0032] Furthermore, this invention discloses an apparatus for the continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis. The apparatus includes connecting pipes, a raw material preheater, an inert gas interface, a first stirring device, a reactor, a condenser, a second stirring device, a first-stage falling film reactor, a first light component outlet, a first heavy component outlet, a third stirring device, a second-stage falling film reactor, a second light component outlet, and a second heavy component outlet. The raw material preheater is connected in series with the reactor, the first-stage falling film reactor, and the second-stage falling film reactor via pipes. The outlet of the raw material preheater is connected to the inlet of the reactor via a pipe, and a feed pump is installed on the connecting pipe for conveying material into the reactor. The outlet of the reactor and the inlet of the first-stage falling film reactor are connected via pipes, and a feed pump is installed on the connecting pipe for conveying material into the first-stage falling film reactor. The first heavy component outlet of the first-stage falling film reactor is connected to the inlet of the second-stage falling film reactor via a pipe.

[0033] In some embodiments, the falling film reactor is a scraped falling film evaporator reactor with a built-in condenser or a roller falling film evaporator reactor with a built-in condenser. Preferably, the falling film reactor is a roller falling film evaporator reactor with a built-in condenser.

[0034] In some embodiments, the reactor is provided with an inert gas inlet for inputting inert gas; the reactor is provided with a first stirring device for stirring the materials.

[0035] In some embodiments, the outlet of the reactor and the inlet of the first-stage falling film reactor are connected by a pipe, and a condenser is provided on the connecting pipe for cooling the material; a second stirring device is provided in the first-stage falling film reactor for stirring the material; the first-stage falling film reactor is provided with a first light component outlet.

[0036] In some embodiments, the second-stage falling film reactor is provided with a third stirring device for stirring the materials; the second-stage falling film reactor is provided with a second light component outlet for outputting the product 1,5-pentamethylene diisocyanate; the second-stage falling film reactor is provided with a second heavy component outlet.

[0037] Specifically, the above-described apparatus is used to continuously prepare 1,5-pentamethylene diisocyanate via thermal pyrolysis, comprising the following steps:

[0038] 1,5-Pentamethylene dicarboxylate compounds and bismuth neodecanoate were mixed and preheated in a feed preheater. After preheating, the mixture was pumped into a reactor and stirred for thermal pyrolysis. Inert gas was purged from the reactor via an inert gas port. After the thermal pyrolysis, the resulting reaction solution was pumped into a first-stage falling film reactor for primary purification, while being cooled by a condenser during the pumping process. After primary purification, the reaction solution flowed out of the first heavy component outlet of the first-stage falling film reactor and continued to flow into a second-stage falling film reactor for secondary purification. After secondary purification, 1,5-pentamethylene diisocyanate flowed out from the second light component outlet of the second-stage falling film reactor. The substances flowing out of the first light component outlet of the first-stage falling film reactor were mainly byproduct alcohols, while the substances flowing out of the second heavy component outlet of the second-stage falling film reactor were mainly residual high-boiling-point solvents.

[0039] Beneficial effects:

[0040] This invention provides an apparatus and method for the continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis. The preparation process employs a non-phosgene method, which is environmentally friendly and has minimal safety risks. This invention utilizes a novel thermal pyrolysis solvent and a novel catalyst in the thermal pyrolysis process of 1,5-pentamethylene dicarboxylate, and employs a continuous reaction separation coupling device. The reaction conditions are mild, the process is simple, and the yield of 1,5-pentamethylene diisocyanate reaches over 80%, with a purity of 99%. Attached Figure Description

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0042] Figure 1 The diagram shows the reaction apparatus for preparing 1,5-pentamethylene diisocyanate in an embodiment of the present invention. Detailed Implementation

[0043] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0044] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0045] Figure 1 This diagram illustrates the reaction apparatus for preparing 1,5-pentamethylene diisocyanate according to an embodiment of the present invention. In the diagram: 1-raw material preheater; 2-nitrogen inlet; 3-first stirring device; 4-reaction vessel; 5-condenser; 6-second stirring device; 7-first-stage falling film reactor; 8-first light component outlet; 9-first heavy component outlet; 10-third stirring device; 11-second-stage falling film reactor; 12-second light component outlet; 13-second heavy component outlet. Both the first-stage and second-stage falling film reactors are roller falling film evaporators.

[0046] The raw material preheater 1 is connected in series with the reactor 4, the first-stage falling film reactor 7, and the second-stage falling film reactor 11 via pipelines. The outlet of the raw material preheater 1 is connected to the inlet of the reactor 4 via a pipeline, with a feed pump on the connecting pipeline for supplying materials to the reactor 4. The reactor 4 is equipped with a nitrogen inlet 2 for supplying nitrogen gas. A first stirring device 3 is installed inside the reactor 4 for stirring the materials. The outlet of the reactor 4 is connected to the inlet of the first-stage falling film reactor 7 via a pipeline, with a feed pump on the connecting pipeline for supplying materials to the first-stage falling film reactor 7. A condenser 5 is also installed on the connecting pipeline for cooling the materials. A second stirring device 6 is installed inside the first-stage falling film reactor 7 for stirring the materials. The first light component outlet 8 of the first-stage falling film reactor 7 is used to separate byproduct alcohols. The first heavy component outlet 9 of the first-stage falling film reactor 7 is connected to the inlet of the second-stage falling film reactor 11 via a pipeline; the second-stage falling film reactor 11 is equipped with a third stirring device 10 for stirring the materials; the second heavy component outlet 13 of the second-stage falling film reactor 11 is used to separate residual high-boiling-point solvents; the second light component outlet 12 of the second-stage falling film reactor 11 is used to output the product 1,5-pentamethylene diisocyanate.

[0047] Example 1:

[0048] Bismuth neodecanoate was mixed with butyl 1,5-pentamethylenedicarbamate and placed in a raw material preheater and preheated to 70°C; wherein, bismuth neodecanoate was 3% of the mass fraction of butyl 1,5-pentamethylenedicarbamate. The mixture was then pumped into a reactor containing tetraethylene glycol dimethyl ether (1,5-pentamethylene dicarboxylate was 12% of the mass fraction of tetraethylene glycol dimethyl ether) at a flow rate of 200 g / h. The reaction was carried out for 0.5 hours at a reaction temperature of 220℃, a reaction pressure of 0.02 MPa, and a nitrogen purging flow rate of 50 mL / min. After the reaction was completed, the reaction solution was cooled by a condenser and then pumped into a first-stage roller falling film evaporator. The first step of separation to remove the byproduct alcohol was carried out at a separation temperature of 150℃, a roller speed of 300 rpm, and a reaction pressure of 0.01 MPa. Then it flowed into a second-stage roller falling film evaporator, where the second step of separation to remove the residual solvent was carried out at a separation temperature of 170℃, a roller speed of 300 rpm, and a reaction pressure of 0.01 MPa, finally yielding 1,5-pentamethylene diisocyanate.

[0049] Example 2:

[0050] Bismuth neodecanoate was mixed with butyl 1,5-pentamethylenedicarbamate and placed in a raw material preheater and preheated to 80°C; wherein, bismuth neodecanoate was 5% of the mass fraction of butyl 1,5-pentamethylenedicarbamate. The mixture was then pumped into a reactor containing tetraethylene glycol dimethyl ether (1,5-pentamethylene dicarboxylate was 12% of the mass fraction of tetraethylene glycol dimethyl ether) at a flow rate of 300 g / h. The reaction was carried out for 1 hour at a reaction temperature of 230℃, a reaction pressure of 0.04 MPa, and a nitrogen purging flow rate of 100 mL / min. After the reaction, the reaction solution was cooled by a condenser and then pumped into a first-stage roller falling film evaporator. The first step of separation to remove the byproduct alcohol was carried out at a separation temperature of 160℃, a roller speed of 350 rpm, and a reaction pressure of 0.005 MPa. Then it flowed into a second-stage roller falling film evaporator, where the second step of separation to remove the residual solvent was carried out at a separation temperature of 180℃, a roller speed of 350 rpm, and a reaction pressure of 0.005 MPa, finally yielding 1,5-pentamethylene diisocyanate.

[0051] Example 3:

[0052] Bismuth neodecanoate was mixed with butyl 1,5-pentamethylenedicarbamate and placed in a raw material preheater and preheated to 90°C; wherein, bismuth neodecanoate was 7% of the mass fraction of butyl 1,5-pentamethylenedicarbamate. The mixture was then pumped into a reactor containing tetraethylene glycol dimethyl ether (1,5-pentamethylene dicarboxylate was 12% of the mass fraction of tetraethylene glycol dimethyl ether) at a flow rate of 400 g / h. The reaction was carried out for 1.5 hours at a reaction temperature of 240℃, a reaction pressure of 0.06 MPa, and a nitrogen purging flow rate of 150 mL / min. After the reaction was completed, the reaction solution was cooled by a condenser and then pumped into a first-stage roller falling film evaporator. The first step of separation to remove the byproduct alcohol was carried out at a separation temperature of 170℃, a roller speed of 400 rpm, and a reaction pressure of 0.002 MPa. Then it flowed into a second-stage roller falling film evaporator, where the second step of separation to remove the residual solvent was carried out at a separation temperature of 190℃, a roller speed of 400 rpm, and a reaction pressure of 0.002 MPa, finally yielding 1,5-pentamethylene diisocyanate.

[0053] Example 4:

[0054] Bismuth neodecanoate was mixed with butyl 1,5-pentamethylenedicarbamate and placed in a raw material preheater and preheated to 90°C; wherein, bismuth neodecanoate was 9% of the mass fraction of butyl 1,5-pentamethylenedicarbamate. The mixture was then pumped into a reactor containing tetraethylene glycol dimethyl ether (1,5-pentamethylene dicarboxylate was 12% of the mass fraction of tetraethylene glycol dimethyl ether) at a flow rate of 350 g / h. The reaction was carried out for 1 hour at a reaction temperature of 250 °C, a reaction pressure of 0.08 MPa, and a nitrogen purging flow rate of 200 mL / min. After the reaction was completed, the reaction solution was cooled by a condenser and then pumped into a first-stage roller falling film evaporator. The first step of separation to remove the byproduct alcohol was carried out at a separation temperature of 160 °C, a roller speed of 350 rpm, and a reaction pressure of 0.005 MPa. Then it flowed into a second-stage roller falling film evaporator, where the second step of separation to remove the residual solvent was carried out at a separation temperature of 180 °C, a roller speed of 350 rpm, and a reaction pressure of 0.005 MPa, finally yielding 1,5-pentamethylene diisocyanate.

[0055] Example 5:

[0056] Bismuth neodecanoate was mixed with butyl 1,5-pentamethylenedicarbamate and placed in a raw material preheater and preheated to 90°C; wherein, bismuth neodecanoate was 9% of the mass fraction of butyl 1,5-pentamethylenedicarbamate. The mixture was then pumped into a reactor containing tetraethylene glycol dimethyl ether (1,5-pentamethylene dicarboxylate was 12% of the mass fraction of tetraethylene glycol dimethyl ether) at a flow rate of 350 g / h. The reaction was carried out for 1 hour at a reaction temperature of 250 °C, a reaction pressure of 0.08 MPa, and a nitrogen purging flow rate of 300 mL / min. After the reaction, the reaction solution was cooled by a condenser and then pumped into a first-stage roller falling film evaporator. The first step of separation to remove the byproduct alcohol was carried out at a separation temperature of 170 °C, a roller speed of 400 rpm, and a reaction pressure of 0.002 MPa. Then it flowed into a second-stage roller falling film evaporator, where the second step of separation to remove the residual solvent was carried out at a separation temperature of 190 °C, a roller speed of 400 rpm, and a reaction pressure of 0.002 MPa, finally yielding 1,5-pentamethylene diisocyanate.

[0057] Comparative Example 1:

[0058] This comparative example provides a method and process for the thermal pyrolysis preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2 except that the solvent is replaced with dibutyl sebacate.

[0059] Comparative Example 2:

[0060] This comparative example provides a method and process for the thermal pyrolysis preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2 except that the solvent is replaced with dioctyl azelate.

[0061] Comparative Example 3:

[0062] This comparative example provides a method and process for the thermal pyrolysis preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2 except that the solvent is replaced with dioctyl phthalate.

[0063] Comparative Example 4:

[0064] This comparative example provides a method and process for the thermal pyrolysis preparation of 1,5-pentamethylene diisocyanate. The method is the same as that in Example 2, except that the solvent is replaced with p-xylene.

[0065] Comparative Example 5:

[0066] This comparative example provides a method and process for the thermal cracking preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2 except that the catalyst is replaced with zinc acetate.

[0067] Comparative Example 6:

[0068] This comparative example provides a method and process for the thermal cracking preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2 except that the catalyst is replaced with zinc oxide.

[0069] Comparative Example 7:

[0070] This comparative example provides a method and process for the thermal cracking preparation of 1,5-pentamethylene diisocyanate. The method is the same as that in Example 2, except that the catalyst is replaced with ferric oxide.

[0071] Comparative Example 8:

[0072] This comparative example provides a method and process for the thermal cracking preparation of 1,5-pentamethylene diisocyanate. The method is the same as in Example 2, except that the catalyst is replaced with bismuth trioxide.

[0073] Comparative Example 9:

[0074] This comparative example provides a thermal cracking preparation method and process for 1,5-pentamethylene diisocyanate. The method is the same as that in Example 2, except that the reaction solution obtained in the reaction vessel is not separated and purified by a two-stage roller falling film evaporation reactor, and 1,5-pentamethylene diisocyanate is obtained directly.

[0075] The mass of 1,5-pentamethylene diisocyanate after reaction in Examples 1-5 and Comparative Examples 1-9 was determined and its mass yield and purity were calculated. The results are shown in Table 1.

[0076] Purity determination of 1,5-pentamethylene diisocyanate: The product was analyzed using an Agilent 7890B gas chromatograph equipped with an Agilent DB-17 (30 m × 0.32 mm × 0.25 μm) capillary column and a flame ionization detector (FID). The injection temperature and detector temperature were 280 °C and 300 °C, respectively. The temperature program for GC analysis was 120 °C for 5 min, increased from 120 °C to 300 °C at a rate of 20 °C / min, and then maintained at 300 °C for 5 min. Nitrogen and tetradecane were used as the carrier gas and internal standard for quantitative analysis, respectively.

[0077] Table 1. Mass yield and purity of 1,5-pentamethylene diisocyanate in different examples and comparative examples.

[0078]

[0079]

[0080] The following conclusions can be drawn from Table 1:

[0081] (1) As can be seen from the comprehensive examples 1-5, after optimizing the reaction process, the mass yield of 1,5-pentamethylene diisocyanate in the method for continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis provided by the present invention can reach 83.7% and the purity can reach 99.6%.

[0082] (2) As can be seen from the comparison of Example 2 and Comparative Examples 1-4, the solvent used in Example 2 is tetraethylene glycol dimethyl ether, which is much higher than the solvents used in Comparative Examples 1-4, namely dibutyl sebacate, dioctyl azelate, dioctyl phthalate, and p-xylene. The mass yield of 1,5-pentamethylene diisocyanate in Example 2 is 83.7%, while the mass yields of 1,5-pentamethylene diisocyanate in Comparative Examples 1-4 are 67.1%, 63.5%, 54.8%, and 61.5%, respectively. The mass yield is much lower than that of Example 2. This shows that when tetraethylene glycol dimethyl ether is preferred as the solvent in this invention, the mass yield of 1,5-pentamethylene diisocyanate prepared is higher.

[0083] (3) As can be seen from the comparison of Comparative Examples 6-8, Comparative Example 8 uses bismuth trioxide as a catalyst for the reaction. Compared with Comparative Examples 6 and 7, which use zinc oxide and ferric oxide as catalysts respectively, the mass yield of 1,5-pentamethylene diisocyanate obtained by Comparative Example 8 is greater than that of Comparative Examples 6 and 7. This shows that the catalyst containing metallic bismuth in the present invention has higher catalytic efficiency.

[0084] (4) It can be seen from the combination of Example 2 and Comparative Examples 5-8 that the catalyst used in Example 2 is bismuth neodecanoate. Compared with the catalysts used in Comparative Examples 5-8, which are zinc acetate, zinc oxide, ferric oxide and bismuth trioxide respectively, the mass yield of 1,5-pentamethylene diisocyanate in Example 2 is higher. This shows that when bismuth neodecanoate is preferred as the catalyst in this invention, its catalytic activity is high and it can greatly improve the mass yield of 1,5-pentamethylene diisocyanate.

[0085] In summary, the method for continuous preparation of 1,5-pentamethylene diisocyanate by thermal pyrolysis provided by this invention uses tetraethylene glycol dimethyl ether as a solvent and bismuth neodecanoate as a catalyst, which has high catalytic efficiency for the thermal pyrolysis system and achieves a high yield of 1,5-pentamethylene diisocyanate. At the same time, a continuous reaction separation coupling device is used to obtain high-purity 1,5-pentamethylene diisocyanate. The reaction conditions are mild, the process is simple, and it has good prospects for industrial application.

[0086] This invention provides an apparatus and method for the continuous preparation of 1,5-pentamethylene diisocyanate via thermal pyrolysis. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for the continuous production of 1,5-pentamethylene diisocyanate by thermal cracking, characterized in that, The 1,5-pentamethylene diisocyanate is obtained by mixing 1,5-pentamethylene dicarbamate compound and tetraethylene glycol dimethyl ether, bismuth neodecanoate, and then performing thermal cracking reaction, and then separating and purifying the reaction liquid.

2. The method of claim 1, wherein, The 1,5-pentamethylene dicarbamate compound is any one or combination of 1,5-pentamethylene dicarbamate methyl ester, 1,5-pentamethylene dicarbamate ethyl ester and 1,5-pentamethylene dicarbamate butyl ester.

3. The method of claim 1, wherein, The mass of the bismuth neodecanoate accounts for 3-10% of the mass of the 1,5-pentamethylene dicarbamate compound.

4. The method of claim 1, wherein, The thermal cracking reaction is performed at a reaction temperature of 180-260 DEG C, a reaction time of 0.5-3 h, and a reaction pressure of 0.02-0.08 MPa.

5. The method of claim 1, wherein, The thermal cracking reaction is performed under inert gas protection.

6. The method of claim 1, wherein, The 1,5-pentamethylene diisocyanate is obtained by mixing 1,5-pentamethylene dicarbamate compound and bismuth neodecanoate, preheating, pumping into a reaction kettle containing tetraethylene glycol dimethyl ether, and then performing thermal cracking reaction, and then performing primary purification on the reaction liquid, and then performing secondary purification. The inert gas is purged in the reaction kettle.

7. The method of claim 6, wherein, In the primary purification, the separation temperature is 140-300 DEG C, the rotation speed is 150-500 rpm, and the reaction pressure is 0.002-0.100 MPa; in the secondary purification, the separation temperature is 160-350 DEG C, the rotation speed is 150-500 rpm, and the reaction pressure is 0.002-0.100 MPa; the purging flow rate of the purged inert gas is 20-300 mL / min.

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