Treatment methods for HDI distillation vessel residues and hexamethylenediamine products

Abstract

This invention provides a method for treating HDI distillation vessel residue and a hexamethylenediamine product. The method includes: Step S1, performing a first decoking process on the HDI distillation vessel residue to obtain a decoked product and a decoked vessel residue; Step S2, subjecting the decoked product to molecular distillation to obtain recovered HDI and molecularly distilled heavy components; Step S3, mixing the molecularly distilled heavy components and the decoked vessel residue with an alkaline solution for alkaline hydrolysis, and purifying the reaction solution to obtain hexamethylenediamine. This application achieves efficient recovery of HDI from HDI distillation vessel residue through decoking and molecular distillation, reducing the amount of residue to be processed while recovering the effective components, thus saving costs. Furthermore, through alkaline hydrolysis, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymers in the HDI distillation vessel residue are converted into hexamethylenediamine, resulting in a simpler composition, reducing the difficulty of post-processing. The product, hexamethylenediamine, can be used as a raw material for HDI synthesis, resulting in high economic added value.

Description

Technical Field

[0001] This invention relates to the field of reactor residue treatment technology in chemical production processes, and more specifically, to a method for treating HDI distillation reactor residue and a hexamethylenediamine product. Background Technology

[0002] Hexamethylene diisocyanate (HDI) is the world's most widely used aliphatic isocyanate. Its products exhibit resistance to yellowing, aging, and sun exposure, and are widely used in defense, high-end coatings, high-end solvent-based polyurethanes, and adhesives. Industrial production of HDI is divided into gas-phase phosgene and liquid-phase phosgene processes. Phosgene reacts with hexamethylenediamine to produce an HDI reaction solution, which is then removed through phosgene removal, solvent removal, and distillation to obtain HDI. The post-processing generates distillation kettle residue, whose main components are hexamethylenediamine hydrochloride, urea diisocyanate, HDI monomers, and HDI polymers (dimers to nonameliters). The composition of the kettle residue is complex, making its reuse difficult. Most companies treat the kettle residue as solid waste and send it to qualified treatment plants, resulting in high treatment costs, resource waste, and increased business costs.

[0003] Patent CN115925580A describes a catalytic reaction between reactor residue and water and carbon monoxide to first generate a carbonylated product, which is then condensed with formic acid to prepare HDI biuret. Due to the complexity of the reactor residue and numerous side reactions during the reaction, the products include HDI biuret, ureoisocyanate, HDI monomer, and HDI polymer, making subsequent separation difficult.

[0004] There are currently few reports on the resource utilization of HDI distillation vessel residues, and how to improve the resource utilization of vessel residues remains an urgent problem to be solved. Summary of the Invention

[0005] The main objective of this invention is to provide a method for treating HDI distillation vessel residue and a hexamethylenediamine product, in order to solve the problems of high treatment costs and difficulty in resource utilization of HDI distillation vessel residue in the prior art.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for treating HDI distillation vessel residue is provided, characterized by comprising: step S1, performing a first decoking on the HDI distillation vessel residue to obtain decoked product and decoked vessel residue; step S2, performing molecular distillation on the decoked product to obtain recovered HDI and molecularly distilled heavy components; step S3, mixing the molecularly distilled heavy components and decoked vessel residue with an alkaline solution for alkaline hydrolysis, and purifying the reaction solution to obtain hexamethylenediamine.

[0007] Furthermore, the HDI distillation vessel residue includes any one or more of HDI, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymer;

[0008] Preferably, the HDI content in the HDI distillation vessel residue is 10% to 50%.

[0009] Furthermore, the vacuum degree of the first decoking process is 1~5 kPa; preferably, the kettle temperature of the first decoking process is less than or equal to 200℃, and the discharge temperature is 130℃~160℃.

[0010] Furthermore, the vacuum degree of molecular distillation is 1~50 Pa; preferably, the feed temperature of molecular distillation is 50~80℃, the heating temperature is 70~110℃, and the condenser temperature is -15~-5℃.

[0011] Preferably, the rotation speed of the scraper for molecular distillation is 400~500 r / min.

[0012] Furthermore, the NCO value of the recovered HDI is ≥49.7%, and the purity is ≥99.5%; preferably, the HDI content in the molecularly distilled heavy component is 0.1~1.0%.

[0013] Furthermore, the alkaline solution is an aqueous solution of an alkali metal hydroxide, preferably selected from any one or more of NaOH aqueous solution and KOH aqueous solution;

[0014] Preferably, the concentration of the alkaline solution is 5-50 wt%;

[0015] Preferably, step S3 includes: mixing the molecular distillation heavy components and / or char removal residue with alkaline solution, so that the pH value of the mixture formed by the alkaline solution and the molecular distillation heavy components and / or char removal residue is 8~10, and continuing to add alkaline solution with a molar amount of alkali that is 2~10 times the molar amount of NCO in the molecular distillation heavy components and / or char removal residue.

[0016] Further, step S3 includes: mixing the molecular distillation heavy components and the residue from the decoction vessel to obtain the mixture to be alkali-hydrolyzed;

[0017] Preferably, the NCO value of the mixture to be alkali-hydrolyzed is tested, and preferably, the NCO value of the mixture to be alkali-hydrolyzed is 5~30%;

[0018] Preferably, the HDI content in the mixture to be alkali-hydrolyzed is <1%.

[0019] Furthermore, the alkaline hydrolysis temperature is 150~350℃, preferably, the alkaline hydrolysis pressure is 1~20MPa, preferably, the alkaline hydrolysis is carried out in an inert gas atmosphere; preferably, the alkaline hydrolysis time is 3~10h.

[0020] Further, the purification process includes dehydrating the reaction solution, performing a second decoking, and distilling; preferably, the dehydration is performed under normal pressure; preferably, the vacuum degree of the second decoking is 1~10 kPa; preferably, the vacuum degree of the distillation is 0.5~50 kPa.

[0021] According to another aspect of this application, a hexamethylenediamine product is provided, wherein the hexamethylenediamine purity of the hexamethylenediamine product is ≥99.7%, and the hexamethylenediamine product is obtained by treating the residue of an HDI distillation vessel.

[0022] By applying the technical solution of this invention, HDI in HDI distillation kettle residue is efficiently recovered through decoking and molecular distillation. This reduces the amount of kettle residue to be processed while simultaneously recovering the effective components, thus saving costs. Furthermore, through alkaline hydrolysis, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymers in the HDI distillation kettle residue are converted into hexamethylenediamine, resulting in a simpler composition and reduced post-processing difficulty. The product, hexamethylenediamine, can be used as a raw material for HDI synthesis, offering high economic added value. The above-described HDI distillation kettle residue treatment method has a simple process flow, is suitable for large-scale industrial processing, effectively reduces solid waste volume and treatment costs, and enables the resource utilization of HDI distillation kettle residue. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 A schematic diagram of the process for treating HDI distillation kettle residue according to an embodiment of the present invention is shown. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] As analyzed in the background section of this application, the prior art suffers from high costs in treating HDI distillation vessel residues and difficulties in resource utilization. To address these issues, this application provides a method for treating HDI distillation vessel residues and a hexamethylenediamine product.

[0027] According to a typical embodiment of this application, this application provides a method for treating HDI distillation vessel residue, the method comprising: step S1, performing a first decoking on the HDI distillation vessel residue to obtain decoked product and decoked vessel residue; step S2, performing molecular distillation on the decoked product to obtain recovered HDI and molecularly distilled heavy components; step S3, mixing the molecularly distilled heavy components and decoked vessel residue with an alkaline solution for alkaline hydrolysis, and purifying the reaction solution to obtain hexamethylenediamine.

[0028] This application utilizes decoking and molecular distillation to efficiently recover HDI from HDI distillation vessel residue. This reduces the amount of residue to be processed while simultaneously recovering the effective components, thus saving costs. Furthermore, through alkaline hydrolysis, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymers in the HDI distillation vessel residue are converted into hexamethylenediamine, resulting in a simpler composition and reduced post-processing difficulty. The hexamethylenediamine product can be used as a raw material for HDI synthesis, offering high economic added value. The above-described HDI distillation vessel residue treatment method has a simple process flow, is suitable for large-scale industrial processing, effectively reduces solid waste volume and treatment costs, and enables the resource utilization of HDI distillation vessel residue.

[0029] The HDI distillation kettle residue mentioned above is the kettle residue obtained from the distillation and purification of HDI during the HDI production process. In some embodiments of this application, the HDI distillation kettle residue includes any one or more of HDI, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymer. These components can all be recovered or converted and reused through the methods of this application.

[0030] The structural formula of the HDI polymer is as follows:

[0031] Dimer:

[0032] Trimer:

[0033] Pentamer:

[0034] heptameric:

[0035] Nonamer:

[0036] In some preferred embodiments of this application, the HDI content in the HDI distillation vessel residue is 10% to 50%, and the processing efficiency using the method of this application is relatively high.

[0037] The aforementioned first decoking refers to heating the HDI distillation vessel residue under normal or negative pressure to distill off components with lower boiling points. In some embodiments of this application, to improve the efficiency and safety of the first decoking, the vacuum degree of the first decoking is 1~5 kPa, which can reduce the heating temperature and accelerate the distillation rate of useful components; to prevent the HDI in the HDI distillation vessel residue from decomposing at excessively high temperatures, and considering system safety, the vessel temperature of the first decoking is preferably less than or equal to 200°C, and the discharge temperature is 130°C~160°C.

[0038] In step S2 above, HDI can be separated from the decoked material relatively efficiently by performing molecular distillation. In some embodiments of this application, to further improve the efficiency of molecular distillation, the vacuum degree of molecular distillation is 1~50 Pa; preferably, the feed temperature of molecular distillation is 50~80℃, the heating temperature is 70~110℃, and the condenser temperature is -15~-5℃, which not only results in high distillation efficiency but also provides high purity and recovery rate of the recovered HDI; preferably, the scraper speed of molecular distillation is 400~500 r / min.

[0039] In some embodiments of this application, the NCO value of the recovered HDI obtained after molecular distillation is ≥49.7%, and the purity is ≥99.5%. Preferably, the HDI content in the molecularly distilled heavy components is 0.1~1.0%. It can be seen that molecular distillation can not only obtain high-purity HDI, but also achieve a high HDI recovery rate.

[0040] In step S3, the molecularly distilled heavy components and char residue obtained from the above treatment are subjected to alkaline hydrolysis to convert them into hexamethylenediamine. In some embodiments of this application, the alkaline solution is an aqueous solution of an alkali metal hydroxide. Preferably, the alkaline solution is selected from any one or more of NaOH aqueous solution and KOH aqueous solution, which not only has a good alkaline hydrolysis effect but is also relatively inexpensive and readily available.

[0041] Taking NaOH aqueous solution as the alkali solution as an example, the above alkaline hydrolysis includes the following reactions:

[0042] Hexamethylenediamine hydrochloride reacts with base

[0043] ;

[0044] Urea isocyanates react with base

[0045]

[0046] Reaction of polymers with bases (taking HDI trimer as an example)

[0047]

[0048] In order to improve the efficiency of alkaline hydrolysis, in some embodiments of this application, the concentration of alkaline solution is 5~50wt%.

[0049] In some preferred embodiments of this application, step S3 includes: to fully alkali-hydrolyze the hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymer in the molecular distillation heavy components and char removal residue to generate hexamethylenediamine, mixing the molecular distillation heavy components and / or char removal residue with an alkaline solution, adjusting the pH of the mixture to 8-10, and then adding an alkaline solution with a molar amount of alkali equal to 2-10 times the molar amount of NCO in the molecular distillation heavy components and / or char removal residue. This method allows for relatively accurate determination of the amount of alkaline solution used. The molar amount of NCO in the molecular distillation heavy components and / or char removal residue can be calculated by testing the NCO value of the molecular distillation heavy components, char removal residue, or a mixture thereof.

[0050] The aforementioned molecular distillation heavy components and char removal residue can be separately mixed with alkaline solution for alkaline hydrolysis, or they can be combined and then alkaline solution is added for alkaline hydrolysis. In some embodiments of this application, to improve efficiency, step S3 includes: mixing the molecular distillation heavy components and char removal residue to obtain a mixture to be alkaline hydrolyzed; preferably, testing the NCO value of the mixture to be alkaline hydrolyzed, and subsequently determining the amount of alkaline solution to be added based on the NCO value. Preferably, the NCO value of the mixture to be alkaline hydrolyzed is 5~30%, resulting in higher alkaline hydrolysis efficiency. Preferably, the HDI content in the mixture to be alkaline hydrolyzed is <1%.

[0051] To further improve the efficiency of the alkali solution, in some embodiments of this application, the alkali hydrolysis temperature is 150~350℃. Exemplarily, the alkali hydrolysis temperature can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, or any range between the two.

[0052] In some embodiments of this application, to further improve the efficiency of alkaline hydrolysis, the pressure of alkaline hydrolysis is 1~20 MPa. Preferably, alkaline hydrolysis is carried out in an inert gas environment. Specifically, for example, the system is purged with an inert gas before alkaline hydrolysis to remove air; nitrogen is preferred as the inert gas. In some embodiments of this application, the alkaline hydrolysis time is 3~10 hours.

[0053] In some embodiments of this application, the purification process in step S3 above includes dehydration of the reaction solution, second decoking, and distillation. Since the product after alkaline hydrolysis is relatively simple, high-purity hexamethylenediamine can be obtained by the above purification method.

[0054] The dehydration method can be selected from the existing technology. In some embodiments of this application, the dehydration is atmospheric pressure dehydration, that is, atmospheric pressure distillation dehydration.

[0055] The second decoking process described above is similar to the first decoking process, also involving the separation of heavy components from the reaction solution through heating and distillation. In some embodiments of this application, the vacuum level for the second decoking process is 1~10 kPa.

[0056] The coke-removed effluent from the second decoking process can be distilled to obtain high-purity hexamethylenediamine. In some embodiments of this application, the vacuum degree of distillation is 0.5~50 kPa. In some embodiments of this application, the purity of the hexamethylenediamine obtained by distillation is ≥99.7%.

[0057] In some embodiments of this application, the method for treating HDI distillation vessel residue is as follows: Figure 1 As shown, the HDI distillation vessel residue is first decoked to obtain decoked product and decoked vessel residue. The decoked product is then subjected to molecular distillation to obtain HDI product and molecularly distilled heavy components. The decoked vessel residue and molecularly distilled heavy components are combined and then alkali solution is added for pressurized alkaline hydrolysis. The alkaline hydrolysis reaction solution is then subjected to dehydration, second decoking, and distillation to obtain hexamethylenediamine product.

[0058] According to another typical embodiment of this application, a hexamethylenediamine product is provided, wherein the hexamethylenediamine purity of the product is ≥99.7%, and the product is obtained by any of the above-described methods for treating HDI distillation kettle residue. This hexamethylenediamine product is obtained through alkaline hydrolysis of HDI distillation kettle residue; the processing technology is relatively simple, and it can be used as a raw material for HDI synthesis, significantly improving the economic added value of HDI distillation kettle residue.

[0059] The beneficial technical effects that this application can achieve will be further explained below with reference to embodiments and comparative examples.

[0060] Example 1

[0061] Analysis of the HDI distillation vessel residue showed that the HDI content was 35.2%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0062] (1) The HDI distillation vessel residue was decoked under a vacuum of 3 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 140 and 152°C. The decoked product was then subjected to molecular distillation under a feed temperature of 60°C, a heating temperature of 80°C, a condenser temperature of -15°C, a vacuum of 10 Pa, and a scraper rotation speed of 400 r / min. The HDI content in the heavy component of the molecular distillation was 0.85%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.6%. The HDI recovery rate was calculated to be 95.8% by weight.

[0063] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 15.6%. Add 15wt% NaOH aqueous solution to the combined reactor residue at room temperature to adjust the pH of the solution to 8. The material is a slurry. Then add alkali with a molar amount of 4 times the NCO, replace it with nitrogen gas, and then carry out alkaline hydrolysis. The reaction temperature is 200℃, the pressure is 5MPa, and the alkaline hydrolysis time is 5h.

[0064] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 3 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.82%. The weight of hexamethylenediamine accounts for 40.5% of the initial HDI distillation vessel residue.

[0065] Example 2

[0066] Analysis of the HDI distillation vessel residue showed that the HDI content was 35.2%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0067] (1) The HDI distillation vessel residue was decoked under a vacuum of 1 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 130 and 145°C. The decoked product was then subjected to molecular distillation at a feed temperature of 70°C, a heating temperature of 95°C, a condenser temperature of -10°C, a vacuum of 5 Pa, and a scraper rotation speed of 450 r / min. The HDI content in the heavy component of the molecular distillation was 0.55%, and the molecular distillation product was the finished HDI product with an NCO value of 49.7% and a purity of 99.5%. The HDI recovery rate was calculated to be 96.6% by weight.

[0068] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 13.2%. Add 20% KOH to the combined reactor residue at room temperature to adjust the pH of the solution to 9. The material is a slurry. Then add alkali with a molar amount of 5 times the NCO, replace it with nitrogen, and then carry out alkaline hydrolysis. The reaction temperature is 250℃, the pressure is 7MPa, and the alkaline hydrolysis time is 6h.

[0069] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 5 kPa. The decoked product is then distilled at 1 kPa. The product is hexamethylenediamine with a purity of 99.85%. The weight of hexamethylenediamine accounts for 45.6% of the initial HDI distillation vessel residue.

[0070] Example 3

[0071] Analysis of the HDI distillation vessel residue showed that the HDI content was 35.2%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0072] (1) The HDI distillation vessel residue was decoked under a vacuum of 5 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 148 and 156°C. The decoked product was then subjected to molecular distillation under a feed temperature of 50°C, a heating temperature of 70°C, a condenser temperature of -5°C, a vacuum of 40 Pa, and a scraper rotation speed of 500 r / min. The HDI content in the heavy component of the molecular distillation was 0.95%, and the molecular distillation product was the finished HDI product with an NCO value of 49.7% and a purity of 99.61%. The HDI recovery rate was calculated to be 93.2% by weight.

[0073] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 17.1%. Add 30% NaOH to the combined reactor residue at room temperature to adjust the pH of the solution to 10. The material is a slurry. Then add alkali with a molar amount of 6 times the NCO, replace it with nitrogen, and then carry out alkaline hydrolysis. The reaction temperature is 350℃, the pressure is 17MPa, and the alkaline hydrolysis time is 8h.

[0074] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 5 kPa. The decoked product is then distilled at 1 kPa. The product is hexamethylenediamine with a purity of 99.7%. The weight of hexamethylenediamine accounts for 47.8% of the initial HDI distillation vessel residue.

[0075] Example 4

[0076] Analysis of the HDI distillation vessel residue showed that the HDI content was 35.2%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0077] (1) The HDI distillation vessel residue was decoked under a vacuum of 1 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 130 and 145°C. The decoked product was then subjected to molecular distillation under a feed temperature of 80°C, a heating temperature of 100°C, a condenser temperature of -15°C, a vacuum of 10 Pa, and a scraper rotation speed of 450 r / min. The HDI content in the heavy component of the molecular distillation was 0.55%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.7%. The HDI recovery rate was calculated to be 97.1% by weight.

[0078] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 12.8%. Add 5% KOH to the combined reactor residue at room temperature to adjust the pH of the solution to 9. The material is a slurry. Then add alkali with a molar amount of NCO twice the amount of alkali, replace it with nitrogen, and then carry out alkaline hydrolysis. The reaction temperature is 150℃, the pressure is 2MPa, and the alkaline hydrolysis time is 7h.

[0079] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 5 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.71%. The weight of hexamethylenediamine accounts for 36.1% of the initial HDI distillation vessel residue.

[0080] Example 5

[0081] Analysis of the residue from the HDI distillation vessel showed that the HDI content was 15.8%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0082] (1) The HDI distillation vessel residue was decoked under a vacuum of 1 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 130 and 145°C. The decoked product was then subjected to molecular distillation at a feed temperature of 75°C, a heating temperature of 105°C, a condenser temperature of -10°C, a vacuum of 10 Pa, and a scraper rotation speed of 400 r / min. The HDI content in the heavy component of the molecular distillation was 0.35%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.72%. The HDI recovery rate was calculated to be 94.2% by weight.

[0083] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 22.3%. Add 15% NaOH to the combined reactor residue at room temperature to adjust the pH of the solution to 8. The material is a slurry. Then add 8 times the molar amount of alkali of NCO, replace it with nitrogen, and then carry out alkaline hydrolysis. The reaction temperature is 250℃, the pressure is 8MPa, and the alkaline hydrolysis time is 5h.

[0084] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 3 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.76%. The weight of hexamethylenediamine accounts for 60.3% of the initial HDI distillation vessel residue.

[0085] Example 6

[0086] Analysis of the HDI distillation vessel residue showed that the HDI content was 26.3%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0087] (1) The HDI distillation vessel residue was decoked under a vacuum of 2 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 135 and 148°C. The decoked product was then subjected to molecular distillation under a feed temperature of 80°C, a heating temperature of 100°C, a condenser temperature of -15°C, a vacuum of 10 Pa, and a scraper rotation speed of 400 r / min. The HDI content in the heavy component of the molecular distillation was 0.56%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.68%. The HDI recovery rate was calculated to be 93.8% by weight.

[0088] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 18.9%. Add 15% NaOH to the combined reactor residue at room temperature to adjust the pH of the solution to 10. The material is a slurry. Then add alkali at 5 times the molar amount of NCO, replace it with nitrogen, and then perform alkaline hydrolysis. The reaction temperature is 300℃, the pressure is 10MPa, and the alkaline hydrolysis time is 5h.

[0089] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 3 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.71%. The weight of hexamethylenediamine accounts for 48.5% of the initial HDI distillation vessel residue.

[0090] Example 7

[0091] Analysis of the HDI distillation vessel residue showed that the HDI content was 45.5%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0092] (1) The HDI distillation vessel residue was decoked under a vacuum of 3 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 140 and 152°C. The decoked product was then subjected to molecular distillation at a feed temperature of 80°C, a heating temperature of 105°C, a condenser temperature of -15°C, a vacuum of 10 Pa, and a scraper rotation speed of 400 r / min. The HDI content in the heavy component of the molecular distillation was 0.62%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.7%. The HDI recovery rate was calculated to be 93.2% by weight.

[0093] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 10.3%. Add 15% KOH to the combined reactor residue at room temperature to adjust the pH of the solution to 9. The material is a slurry. Then add alkali with a molar amount of 6 times the NCO, replace it with nitrogen, and then carry out alkaline hydrolysis. The reaction temperature is 300℃, the pressure is 10MPa, and the alkaline hydrolysis time is 5h.

[0094] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 3 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.75%. The weight of hexamethylenediamine accounts for 31.3% of the initial HDI distillation vessel residue.

[0095] Example 8

[0096] Analysis of the HDI distillation vessel residue showed that the HDI content was 45.5%, with the remainder consisting of hexamethylenediamine hydrochloride, urea isocyanate, HDI polymer, etc.

[0097] (1) The HDI distillation vessel residue was decoked under a vacuum of 3 kPa, with the vessel temperature not exceeding 200°C and the discharge temperature between 140 and 152°C. The decoked product was then subjected to molecular distillation at a feed temperature of 80°C, a heating temperature of 105°C, a condenser temperature of -15°C, a vacuum of 10 Pa, and a scraper rotation speed of 400 r / min. The HDI content in the heavy component of the molecular distillation was 0.62%, and the molecular distillation product was the finished HDI product with an NCO value of 49.8% and a purity of 99.7%. The HDI recovery rate was calculated to be 93.2% by weight.

[0098] (2) The NCO values ​​of the residue from the decoking vessel and the heavy components from molecular distillation in step (1) were tested respectively, and the results were 8.3% and 13.2% respectively. 15% KOH was added to the residue from the decoking vessel and the heavy components from molecular distillation respectively, and the pH was adjusted to 9. Alkali was added with a molar amount of 6 times the NCO, and nitrogen was used for replacement. After replacement, alkaline hydrolysis was carried out. Alkaline hydrolysis was carried out at a temperature of 300℃ and a pressure of 10MPa respectively, and the alkaline hydrolysis time was 5h for both.

[0099] (3) The alkaline hydrolysate of the residue from the decoking vessel and the heavy molecular distillation components in step (2) were dehydrated under normal pressure. The residue from the dehydration vessel was decoked at 3 kPa. The decoked product was distilled at 0.5 kPa. The purity of the product hexamethylenediamine was 99.72% and 99.89%, respectively. The total weight of the prepared hexamethylenediamine accounted for 33.2% of the initial weight of the residue from the HDI distillation vessel.

[0100] Example 9

[0101] The only difference from Example 1 is that in step (2), the alkaline hydrolysis temperature is 120°C and the alkaline hydrolysis time is 10h.

[0102] The purity of the product hexamethylenediamine was 99.75%, and the total weight of the prepared hexamethylenediamine accounted for 23.1% of the initial HDI distillation vessel residue weight.

[0103] Comparative Example 1

[0104] The residue from the HDI distillation vessel was the same as in Example 1.

[0105] (1) The HDI distillation vessel residue was decoked under a vacuum of 3 kPa, with the vessel temperature not exceeding 200°C and the outlet temperature between 140 and 152°C. The decoked product was then subjected to vacuum distillation under a vacuum of 1 kPa. The HDI content in the heavy components was 3.5%, the NCO value in the distillate was 48.1%, and the HDI purity was 97.5%. The HDI recovery rate was calculated to be 88.5% by weight.

[0106] (2) Combine the residue from the char-free reactor and the heavy components from molecular distillation in step (1), and measure the NCO value to be 18.8%. Add 15wt% NaOH aqueous solution to the combined reactor residue at room temperature to adjust the pH of the solution to 8. The material is a slurry. Then add alkali with a molar amount of 4 times the NCO, replace it with nitrogen gas, and then carry out alkaline hydrolysis. The reaction temperature is 200℃, the pressure is 5MPa, and the alkaline hydrolysis time is 5h.

[0107] (3) The alkaline hydrolysate from step (2) is dehydrated under normal pressure. The residue in the dehydration vessel is decoked at 3 kPa. The decoked product is then distilled at 0.5 kPa. The product is hexamethylenediamine with a purity of 99.71%. The weight of hexamethylenediamine accounts for 38.5% of the initial HDI distillation vessel residue.

[0108] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: This application efficiently recovers HDI from HDI distillation kettle residue through decoking and molecular distillation, reducing the amount of kettle residue to be processed while recovering the effective components, thus saving costs. Furthermore, through alkaline hydrolysis, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymers in the HDI distillation kettle residue are converted into hexamethylenediamine, resulting in a relatively simple composition, reducing the difficulty of post-processing. The product, hexamethylenediamine, can be used as a raw material for HDI synthesis, resulting in high economic added value. The above-mentioned HDI distillation kettle residue treatment method has a simple process flow, is suitable for large-scale industrial processing, effectively reduces the amount of solid waste and solid waste treatment costs, and enables the resource utilization of HDI distillation kettle residue.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for treating HDI distillation vessel residue, characterized in that, include: Step S1: Perform a first decoking process on the HDI distillation vessel residue to obtain a decoked product and a decoked vessel residue; the HDI distillation vessel residue includes any one or more of HDI, hexamethylenediamine hydrochloride, urea isocyanate, and HDI polymer; the HDI content in the HDI distillation vessel residue is 10%~50%; the vacuum degree of the first decoking process is 1~5 kPa; the vessel temperature of the first decoking process is less than or equal to 200℃, and the discharge temperature is 130℃~160℃; Step S2: The decoking effluent is subjected to molecular distillation to obtain recovered HDI and molecularly distilled heavy components; the vacuum degree of the molecular distillation is 1~50 Pa; the feed temperature of the molecular distillation is 50~80℃, the heating temperature is 70~110℃, and the condenser temperature is -15~-5℃. Step S3: Mix the molecularly distilled heavy components and the char removal residue with an alkaline solution to make the pH of the mixture 8-10. Continue to add an alkaline solution with a molar amount of alkali equal to 2-10 times the molar amount of NCO in the molecularly distilled heavy components and the char removal residue, and carry out alkaline hydrolysis. The reaction solution is purified to obtain hexamethylenediamine. The alkaline hydrolysis temperature is 150-350℃, the alkaline hydrolysis pressure is 1-20 MPa, and the alkaline hydrolysis time is 3-10 h.

2. The processing method according to claim 1, characterized in that, The rotation speed of the scraper in the molecular distillation is 400~500 r / min.

3. The processing method according to claim 1, characterized in that, The recovered HDI has an NCO value ≥ 49.7% and a purity ≥ 99.5%.

4. The processing method according to claim 1, characterized in that, The HDI content in the molecularly distilled heavy component is 0.1~1.0%.

5. The processing method according to claim 1, characterized in that, The alkaline solution is an aqueous solution of an alkali metal hydroxide.

6. The processing method according to claim 5, characterized in that, The alkaline solution is selected from any one or more of NaOH aqueous solution and KOH aqueous solution.

7. The processing method according to claim 5, characterized in that, The concentration of the alkaline solution is 5~50wt%.

8. The processing method according to claim 1, characterized in that, Step S3 includes: mixing the molecular distillation heavy components and the char removal vessel residue to obtain a mixture to be alkali-hydrolyzed.

9. The processing method according to claim 8, characterized in that, The NCO value of the mixture to be alkali-hydrolyzed was tested.

10. The processing method according to claim 9, characterized in that, The NCO value of the mixture to be alkali-hydrolyzed is 5-30%.

11. The processing method according to claim 8, characterized in that, The HDI content in the mixture to be alkali-digested is <1%.

12. The processing method according to claim 1, characterized in that, The alkaline hydrolysis is carried out in an inert gas atmosphere.

13. The processing method according to claim 1, characterized in that, The purification process includes dehydration of the reaction solution, secondary decoking, and distillation.

14. The processing method according to claim 13, characterized in that, The dehydration is performed under normal pressure.

15. The processing method according to claim 13, characterized in that, The vacuum degree of the second decoking process is 1~10 kPa.

16. The processing method according to claim 13, characterized in that, The vacuum degree of the distillation is 0.5~50kPa.

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