Preparation method of hexamethylene diisocyanate

Abstract

This invention provides a method for preparing hexamethylene diisocyanate. The method includes: desolventizing an HDI synthesis solution to obtain a first recovered solvent and HDI desolventizing residue; subjecting the HDI desolventizing residue to light component removal treatment to obtain a light component and light component removal residue; subjecting the light component to alkaline washing and layering to obtain a second recovered solvent; distilling the light component removal residue to obtain HDI product and chlorinated HDI material; mixing HDI, a phenolic dechlorination agent, and an antioxidant to obtain a composite dechlorination agent solution, which is then mixed with the chlorinated HDI material for dechlorination treatment, yielding dechlorinated HDI material that is returned to the light component removal treatment. Using the preparation method of this invention, high-purity, high-yield HDI can be obtained. The process is simple, with high product and solvent recovery rates, low cost, and easy industrial implementation.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and more specifically, to a method for preparing hexamethylene diisocyanate. Background Technology

[0002] The gas-phase phosgene process is currently the most commonly used method for producing isocyanates. The principle of this synthesis method is well-known and widely understood within the industry. It involves mixing vaporized diamine, phosgene, and an inert gas, reacting them in a reactor, and then obtaining the isocyanate product through post-processing steps such as quenching and spraying. High-content isocyanates are typically obtained by improving the synthesis and post-processing techniques. Improving the uniformity of raw material mixing during the reaction and selecting appropriate reaction control points are common methods for improving the gas-phase synthesis process. Improved post-processing methods involve analyzing impurities and combining different impurity conversion and separation techniques to ultimately obtain a high-content isocyanate product.

[0003] During the synthesis of HDI using the gas-phase phosgene method, small amounts of impurities such as 1,6-dichlorohexane and chloroisocyanate are unavoidably generated. The national standard for HDI stipulates that the hydrolyzed chlorine content in the finished HDI product should be ≤100 mg / kg. Gas chromatography normalization analysis of the HDI synthesis liquid after spraying and degassing (excluding solvent peaks) revealed that the normalized contents of 1,6-dichlorohexane and chloroisocyanate were 0.2–0.6% and 0.5–1.5%, respectively. After conversion, the chlorine content of these impurities far exceeds the level required by the standard. These chlorine impurities can cause uncontrollable color changes in downstream HDI products, affecting the application of isocyanate products in high-end fields. Therefore, the content of chlorinated impurities must be minimized as much as possible during isocyanate production. Measurements showed that the boiling points of 1,6-dichlorohexane, chloroisocyanate, and HDI at atmospheric pressure increase sequentially to 204℃, 228℃, and 255℃, respectively. The three have similar structures and their boiling points are relatively close. Separating them through distillation would increase equipment and operating costs, hindering the reduction of production costs.

[0004] In existing technologies, the purification of crude isocyanates typically involves reacting a dechlorinating agent with the isocyanate impurities, causing changes in their chemical structure and properties, which are then removed by simple separation methods.

[0005] Patent CN111718282B discloses a method for preparing isocyanates with low chlorinated impurity content based on salt-forming phosgenation. This patent uses the salt-forming phosgenation method to synthesize isocyanates. By adjusting the average particle size of amine hydrochloride or amine carbonate to a suitable range, it reacts with phosgene in a solvent to prepare an HDI synthesis solution with low biuret content, thereby obtaining an isocyanate product with fewer chlorinated impurities. This patent effectively reduces chlorinated impurities to 1% by changing the isocyanate synthesis method. However, the space-time yield of this synthesis process is low and cannot meet the requirements of industrial production. Furthermore, the chlorinated impurity level is still relatively high, and the patent does not further explain how to reduce chlorinated impurities to a suitable range.

[0006] Patent CN107011214A discloses a method for preparing low-chlorinated isocyanates. This patent employs a gas-phase phosgene method to synthesize isocyanates. During gas-phase synthesis, CO with a phosgene mass fraction >0.5% is introduced into the phosgene stream, thereby reducing the total chlorine content of the synthesis solution after spray absorption. After purification through distillation, the synthesis solution yields an HDI product with a hydrolyzed chlorine content of 20 ppm and a total chlorine content of 190 ppm. This process can very effectively reduce the content of chlorinated impurities; however, the synthesis process is difficult, the results are unstable, and sometimes unexpected results occur with excessive chlorinated impurities.

[0007] Patent CN112824376B discloses a gas-phase method for preparing isocyanates with low hydrolyzable chlorine content. This patent employs a gas-phase phosgene method to synthesize isocyanates. By introducing reactive acidic carbon dioxide gas into the quenching zone after gas-phase synthesis, the gas interacts with trace amounts of moisture in the quenching solvent, altering the equilibrium reaction relationship for aminoacyl chloride formation. This makes it easier to obtain a reaction solution with low hydrolyzable chlorine content. This process can effectively reduce the chlorine content of HDI products, with an average hydrolyzable chlorine content between 16 and 22 ppm, meeting national standards. However, controlling the hydrolyzable chlorine content in the synthesis solution through trace amounts of moisture and carbon dioxide is technically challenging. Deviations in moisture control can easily lead to excessively high levels of other impurities.

[0008] Patent CN110396057B discloses a method for preparing isocyanates with low chlorine content. This process involves mixing crude HDI with high chlorinated impurities with a compound solvent, reacting it with a compound organic salt under acidic conditions, removing the precipitate through simple filtration, further reducing the acidity, and then removing the residual solvent through vacuum distillation. This method can reduce the chlorinated isocyanate impurity content to below 0.1%, significantly improving the quality of downstream products. However, this process requires the addition of multiple types of dechlorinating agents to remove chlorinated impurities and also uses a compound solvent. These factors increase the complexity of subsequent separation processes and reduce the yield of HDI.

[0009] Patent CN107382777B discloses a method for reducing the content of chlorinated derivatives in isocyanates. This patent involves reacting crude isocyanate with amine or thiocyanate salts, followed by simple post-treatment to reduce the content of chlorinated derivatives. This method can remove more than 90% of chlorinated derivatives from isocyanates. However, the isocyanate prepared by this method introduces substances such as isothiocyanates generated in the reaction, resulting in side reactions that affect the product yield and lead to a higher acid content. Summary of the Invention

[0010] The main objective of this invention is to provide a method for preparing hexamethylene diisocyanate, in order to solve the problems of excessive chlorinated impurities, complex dechlorination methods, and incomplete dechlorination in existing hexamethylene diisocyanate products.

[0011] To achieve the above objectives, according to one aspect of the present invention, a method for preparing hexamethylene diisocyanate is provided, comprising the following steps: Step S1, desolventizing an HDI synthesis solution to obtain a first recovered solvent and HDI desolventizing residue; the HDI synthesis solution is a reaction solution from which phosgene has been removed after HDI synthesis using the gas-phase phosgene method; Step S2, removing light components from the HDI desolventizing residue to obtain a light component and a light-removed residue; Step S3, alkali washing and layering of the light component to obtain an oil layer, followed by drying to obtain a second recovered solvent; Step S4, distilling the light-removed residue to obtain an HDI product and a chlorinated HDI material; Step S5, mixing HDI, a phenolic dechlorinating agent, and an antioxidant to obtain a composite dechlorinating agent solution, then mixing it with the chlorinated HDI material for dechlorination treatment to obtain a dechlorinated HDI material, which is then returned to the light-removing treatment.

[0012] Further, in step S1, the solvent in the HDI synthesis solution includes one or more of chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene; and / or the pressure of the desolventizing treatment is 50-150 mmHg; and / or the first recovered solvent accounts for 80-90% of the total mass of the solvent in the HDI synthesis solution.

[0013] Furthermore, in step S2, the pressure for removing light components is 10–50 mmHg; and / or the mass percentage of HDI in the light components is 0.5–1%.

[0014] Further, in step S3, an alkaline aqueous solution is used for alkaline washing and layering, wherein the mass fraction of the alkaline aqueous solution is 5-15%; and / or the alkaline aqueous solution includes an aqueous solution of sodium hydroxide and / or an aqueous solution of potassium hydroxide.

[0015] Furthermore, in step S3, the mass ratio of the light component to the alkaline aqueous solution is 1:(0.5-0.6).

[0016] Furthermore, in step S3, the temperature for alkaline washing and stratification is 80–100°C; and / or the water content of the second recovered solvent is ≤50 ppm.

[0017] Furthermore, in step S4, the distillation temperature is 95–120°C, the pressure is 3–10 mmHg, and / or the chlorine-containing HDI material accounts for 5–10% of the total mass of the light residue.

[0018] Furthermore, in step S5, the phenolic dechlorination agent includes o-cresol and / or p-cresol; and / or the antioxidant includes 2,6-di-tert-butyl-p-cresol.

[0019] Further, in step S5, the molar ratio of HDI, phenolic dechlorinating agent and antioxidant in the composite dechlorinating agent solution is 1:(0.1~0.2):(0.008~0.012).

[0020] Furthermore, in step S5, the dechlorination treatment temperature is 100–130°C, the time is 30–60 s, and / or the mass ratio of the composite dechlorination agent solution to the chlorine-containing HDI material is 1:(0.9–1.5).

[0021] By applying the technical solution of this invention, the solvent in the HDI synthesis solution is removed in two separate processes: solvent removal and light component removal, which helps reduce the amount of solvent to be processed. Alkali washing and drying of the light component helps remove impurities such as 1,6-dichlorohexane and chloroisocyanurates from the light component solvent, resulting in high-content recovered solvent. A phenolic dechlorinating agent is used to further remove chloroisocyanurate impurities from the chlorinated HDI material, and the addition of antioxidants helps reduce HDI polymerization reactions that occur during light component removal and distillation. Using the preparation method of this invention, high-purity, high-yield HDI can be obtained. The process is simple, with high product and solvent recovery rates, low cost, and easy industrial implementation. Attached Figure Description

[0022] 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:

[0023] Figure 1 A process flow diagram according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0024] 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.

[0025] It should be noted that, unless otherwise specified, "pressure" in this invention refers to absolute pressure.

[0026] It should be noted that, unless otherwise specified, "purity" in this invention refers to mass purity.

[0027] It should be noted that the "vapor phase phosgene method" in this invention can be achieved using conventional synthesis processes in the art, and the "phosgene removal" can be achieved using conventional methods in the art. These are things that those skilled in the art can understand, and will not be elaborated here.

[0028] As described in the background section of this invention, existing technologies suffer from problems such as a high number of chlorinated impurities in hexamethylene diisocyanate products, complex dechlorination methods, and incomplete dechlorination. To address these issues, in a typical embodiment of this invention, a method for preparing hexamethylene diisocyanate is provided, comprising the following steps: Step S1, desolventizing an HDI synthesis solution to obtain a first recovered solvent and HDI desolventizing residue; the HDI synthesis solution is the reaction solution from which phosgene has been removed after HDI synthesis using the gas-phase phosgene method; Step S2, removing light components from the HDI desolventizing residue to obtain a light component and light-removed residue; Step S3, alkaline washing and layering of the light component to obtain an oil layer, followed by drying to obtain a second recovered solvent; Step S4, distilling the light-removed residue to obtain an HDI product and a chlorinated HDI material; Step S5, mixing HDI, a phenolic dechlorinating agent, and an antioxidant to obtain a composite dechlorinating agent solution, which is then mixed with the chlorinated HDI material for dechlorination treatment to obtain a dechlorinated HDI material, which is then returned to the light-removing treatment.

[0029] This invention removes the solvent from the HDI synthesis solution in two separate processes: solvent removal and light component removal. First, the HDI synthesis solution undergoes solvent removal treatment to obtain a first-stage recovered solvent with high recovery purity (i.e., the mass purity of the solvent compounds in the recovered material). This first-stage recovered solvent can be directly recycled, and most of the solvent is recovered in this process. The remaining HDI solvent removal material undergoes light component removal treatment to obtain a light component containing impurities and solvent, along with the remaining light component. The light component then undergoes further processing, which helps reduce the amount of solvent to be processed.

[0030] During their research, the inventors unexpectedly discovered that chlorinated impurities such as 1,6-dichlorohexane and chloroisocyanates can undergo hydrolysis with alkaline solutions to produce soluble alcohols and salts, as shown below:

[0031] The reaction formula between chloroisocyanates and liquid alkali is as follows:

[0032]

[0033] The reaction formula for 1,6-dichlorohexane with liquid alkali is as follows:

[0034]

[0035] Therefore, this invention performs alkaline washing and stratification of the light components, converting chlorinated impurities into water-soluble impurities that dissolve in the alkaline layer. After stratification, chlorinated impurities such as 1,6-dichlorohexane and chlorinated isocyanate can be removed, and the resulting oil layer is dried to obtain a high-purity second recovered solvent. Then, the residue from the light component removal is distilled to obtain a high-purity HDI product and chlorinated HDI material.

[0036] During their research, the inventors unexpectedly discovered that chloroisocyanates, due to the higher electronegativity of chlorine, have slightly higher isocyanate reactivity than HDI, resulting in a faster reaction rate with phenolic substances. An exemplary reaction formula is as follows:

[0037]

[0038] Therefore, in the final step of this invention, HDI, phenolic dechlorination agents, and antioxidants are mixed to obtain a composite dechlorination agent solution. This solution is then mixed with chlorinated HDI material for dechlorination treatment. The phenolic dechlorination agent further removes the chlorinated isocyanates that have not been removed from the HDI, generating high-boiling-point impurities that dissolve in the HDI. At the same time, the addition of antioxidants can reduce the polymerization reactions that occur during the HDI light-light removal and distillation process. Finally, the dechlorinated HDI material is returned to the light-light removal process. The high-boiling-point impurities and a small amount of antioxidants remain at the bottom of the distillation unit as residues. The side stream of the distillation unit yields a high-purity, high-yield HDI product.

[0039] This invention, based on the use of alkaline washing to remove chlorinated impurities from light component solvents, further employs phenolic dechlorinating agents to remove chlorinated impurities from chlorinated HDI materials. By combining these two methods to remove all chlorinated impurities in the preparation process of hexamethylene diisocyanate, the yield and purity of the product and the recovered solvent can be significantly improved.

[0040] In summary, the preparation method of the present invention can obtain high-content, high-yield HDI and recovered solvent. The process is simple, the product and solvent recovery rate is high, the cost is low, and it is easy to implement industrially.

[0041] In a preferred embodiment, in step S1, the solvent in the HDI synthesis solution includes one or more of chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene; and / or the desolventizing pressure is 50–150 mmHg; and / or the first recovered solvent accounts for 80–90% of the total mass of the solvent in the HDI synthesis solution. Under these conditions, it is more conducive to the large-scale recovery of solvents, and the first recovered solvent with high purity can be directly recycled, thereby further reducing the amount of solvent to be processed.

[0042] To further improve the solvent recovery effect of the light component removal process, in a preferred embodiment, in step S2, the pressure of the light component removal process is 10-50 mmHg; and / or the mass percentage of HDI in the light component is 0.5-1%.

[0043] In a preferred embodiment, in step S3, an alkaline aqueous solution is used for alkaline washing and layering, wherein the mass fraction of the alkaline aqueous solution is 5-15%; and / or the alkaline aqueous solution includes an aqueous solution of sodium hydroxide and / or an aqueous solution of potassium hydroxide, thereby further enabling the chlorinated impurities to undergo a hydrolysis reaction and achieving more complete removal of the impurities.

[0044] For similar reasons, in a preferred embodiment, in step S3, the mass ratio of the light component to the alkaline aqueous solution is 1:(0.5-0.6).

[0045] In a preferred embodiment, in step S3, the temperature of the alkaline washing and layering is 80-100°C, which is beneficial to further improve the layering efficiency; and / or the water content of the second recovered solvent is ≤50ppm.

[0046] To ensure more complete separation of HDI through distillation while preventing isocyanate polymerization at prolonged high temperatures, in a preferred embodiment, in step S4, the distillation temperature is 95–120°C, and the pressure is 3–10 mmHg, with a direct correlation between pressure and temperature. When the material is in reflux, the pressure is also determined if the temperature is fixed; and / or the chlorine-containing HDI material accounts for 5–10% of the total mass of the light residue.

[0047] In a preferred embodiment, in step S5, the phenolic dechlorination agent includes o-cresol and / or p-cresol, which react with chlorinated impurities in chlorinated HDI materials at a faster rate and can more fully remove chlorinated impurities such as chlorinated isocyanates; and / or the antioxidant includes 2,6-di-tert-butyl-p-cresol, which is beneficial to further reduce the polymerization reaction that occurs during the HDI desulfurization and distillation process, and improve the purity and yield of HDI products.

[0048] To further improve the separation effect after dechlorination and subsequent return to the light removal step, in a preferred embodiment, in step S5, the molar ratio of HDI, phenolic dechlorinator and antioxidant in the composite dechlorinator solution is 1:(0.1-0.2):(0.008-0.012).

[0049] In a preferred embodiment, in step S5, the dechlorination treatment temperature is 100-130°C and the time is 30-60 seconds; and / or the mass ratio of the composite dechlorination agent solution to the chlorine-containing HDI material is 1:(0.9-1.5), which improves the dechlorination effect.

[0050] Typically, but not limitingly, in step S1, the pressure for solvent removal is 50 mmHg, 60 mmHg, 70 mmHg, 80 mmHg, 90 mmHg, 100 mmHg, 110 mmHg, 120 mmHg, 130 mmHg, 140 mmHg, 150 mmHg, or any two of these ranges as boundary values; the first recovered solvent accounts for 80%, 82%, 84%, 86%, 88%, 90% of the total mass of solvent in the HDI synthesis solution, or any two of these ranges as boundary values.

[0051] Typically, but not limitingly, in step S2, the pressure for the removal of light components is 10 mmHg, 20 mmHg, 30 mmHg, 40 mmHg, 50 mmHg, or any two of these values ​​forming a boundary value; the mass percentage of HDI in the light components is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these values ​​forming a boundary value.

[0052] Typically, but not limitingly, in step S3, the mass fraction of the alkaline aqueous solution is 5%, 7%, 9%, 11%, 13%, 15%, or any two of these ranges; the mass ratio of the light component to the alkaline aqueous solution is 1:0.5, 1:0.52, 1:0.54, 1:0.56, 1:0.58, 1:0.6, or any two of these ranges; and the temperature for alkaline washing and stratification is 80°C, 85°C, 90°C, 95°C, 100°C, or any two of these ranges.

[0053] Typically, but not limitingly, in step S4, the distillation temperature is 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, or any two of these values ​​forming a boundary value; the pressure is 3 mmHg, 4 mmHg, 5 mmHg, 6 mmHg, 7 mmHg, 8 mmHg, 9 mmHg, 10 mmHg, or any two of these values ​​forming a boundary value; and the chlorine-containing HDI material accounts for 5%, 6%, 7%, 8%, 9%, 10% of the total mass of the light residue, or any two of these values ​​forming a boundary value.

[0054] Typically, but not limitingly, in step S5, the molar ratio of HDI to the phenolic dechlorinating agent is 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, 1:0.2, or any two of these ranges forming a boundary value; the molar ratio of HDI to the antioxidant is 1:0.008, 1:0.009, 1:0.01, 1:0.011, 1:0.012, or any two of these ranges forming a boundary value; and the dechlorination treatment temperature is 100℃. Boundary values ​​consisting of 0.5℃, 110℃, 115℃, 120℃, 125℃, 130℃ or any two of these values; time values ​​consisting of 30s, 35s, 40s, 45s, 50s, 55s, 60s or any two of these values; and a mass ratio of the composite dechlorinating agent solution to the chlorine-containing HDI material of 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or any two of these values.

[0055] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0056] Example 1

[0057] See process flow diagram Figure 1 .

[0058] In step S1, 958g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 402.5g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0059] In step S2, 92.3g of light components (the proportions of each substance in the light components are: chlorobenzene: 95.63%, 1,6-dichlorohexane: 1.66%, chloroisocyanurate: 2.17%, HDI: 0.54%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 463.0g of light component residue.

[0060] In step S3, 92.3g of the light component was mixed and reacted with 50g of a 12.5% ​​sodium hydroxide solution at 90°C and separated under normal pressure. The oil layer obtained from the separation was dried to obtain 83.8g of chlorobenzene solvent with a water content of 32ppm.

[0061] In step S4, 463.0g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 32g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0062] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain 22g of a composite dechlorination agent solution. This solution is then mixed with 32g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then applied to the light-light removal process.

[0063] Example 2

[0064] In step S1, 1025.4g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 120mmHg to remove 413.6g of o-dichlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0065] In step S2, 102.5g of light components (the proportions of each substance in the light components are: o-dichlorobenzene: 94.66%, 1,6-dichlorohexane: 2.51%, chloroisocyanurate: 2.15%, HDI: 0.68%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 15mmHg, resulting in 509g of light component residue.

[0066] In step S3, 102.5g of the light component was mixed and reacted with 58.1g of a 14.2% sodium hydroxide solution at 95°C and separated under normal pressure. The oil layer obtained from the separation was dried to obtain 91g of o-dichlorobenzene solvent with a water content of 19ppm.

[0067] In step S4, 532.8g of the residue from the light residue removal process is distilled at an absolute pressure of 5mmHg and a temperature of 105℃. 29g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0068] Step S5: Mix HDI, p-cresol, and 2,6-di-tert-butyl-p-cresol in a molar ratio of 1:0.14:0.011 to obtain 24g of a composite dechlorination agent solution. Mix this solution with 29g of chlorine-containing HDI material in a static mixer at 125°C for 40s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0069] Example 3

[0070] In step S1, 982g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) was subjected to an absolute pressure of 50 mmHg to remove 417.54g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0071] In step S2, 83.7g of light components (the proportions of each substance in the light components are: chlorobenzene: 94.14%, 1,6-dichlorohexane: 2.93%, chloroisocyanurate: 2.09%, HDI: 0.84%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 10mmHg, resulting in 478.24g of light component residue.

[0072] In step S3, 83.7g of the light component was mixed and reacted with 46g of a 12.5% ​​sodium hydroxide solution at 90°C and separated under normal pressure. The oil layer obtained from the separation was dried to obtain 73.8g of chlorobenzene solvent with a water content of 25ppm.

[0073] In step S4, 478.24g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 38g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0074] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 32g. This solution is then mixed with 38g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then applied to the light-light removal process.

[0075] Example 4

[0076] In step S1, 1012g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 150mmHg to remove 439g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0077] In step S2, 83.2g of light components (the proportions of each substance in the light components are: chlorobenzene: 93.22%, 1,6-dichlorohexane: 3.89%, chloroisocyanurate: 2.16%, HDI: 0.72%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 50mmHg, resulting in 489g of light component residue.

[0078] In step S3, 83.2g of the light component was mixed and reacted with 44.9g of a 12.5% ​​sodium hydroxide solution at 90°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 71.9g of chlorobenzene solvent with a water content of 30ppm.

[0079] In step S4, 489g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 41.2g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0080] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 31.7g. This solution is then mixed with 41.2g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0081] Example 5

[0082] In step S1, 994g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 417.3g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0083] In step S2, 97.2g of light components (the proportions of each substance in the light components are: chlorobenzene: 93.64%, 1,6-dichlorohexane: 3.48%, chloroisocyanurate: 2.26%, HDI: 0.62%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 477.9g of light component removal residue.

[0084] In step S3, 97.2g of the light component was mixed and reacted with 58.3g of a 5% sodium hydroxide solution at 100°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 84.4g of chlorobenzene solvent with a water content of 35ppm.

[0085] In step S4, 477.9g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 39.2g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0086] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 31.7g. This solution is then mixed with 39.2g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0087] Example 6

[0088] In step S1, 1025g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 422.6g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0089] In step S2, 98.1g of light components (the proportions of each substance in the light components are: chlorobenzene: 93.8%, 1,6-dichlorohexane: 3.03%, chloroisocyanurate: 2.55%, HDI: 0.61%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 502.3g of light component residue.

[0090] In step S3, 98.1g of the light component was mixed and reacted with 49.1g of a 15% sodium hydroxide solution at 80°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 88.6g of chlorobenzene solvent with a water content of 21ppm.

[0091] In step S4, 502.3g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 40.2g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0092] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 33.5g. This solution is then mixed with 40.2g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then applied to the light-light removal process.

[0093] Example 7

[0094] In step S1, 1050g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 440.2g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0095] In step S2, 102.2g of light components (the proportions of each substance in the light components are: chlorobenzene: 94%, 1,6-dichlorohexane: 3.29%, chloroisocyanurate: 2.15%, HDI: 0.59%) are removed from the HDI desolventizing residue under an absolute pressure of 12mmHg, resulting in 505.2g of light component residue.

[0096] In step S3, 102.2g of the light component was mixed and reacted with 56.2g of a 12.5% ​​sodium hydroxide solution at 90°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 90.3g of chlorobenzene solvent with a water content of 24ppm.

[0097] In step S4, 505.2g of the residue from the light residue removal process is distilled at an absolute pressure of 10mmHg and a temperature of 120℃. 35g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0098] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 29.2g. This solution is then mixed with 35g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0099] Example 8

[0100] In step S1, 1022g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 425.5g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0101] In step S2, 99g of light components (the proportions of each substance in the light components are: chlorobenzene: 94.2%, 1,6-dichlorohexane: 2.88%, chloroisocyanurate: 2.41%, HDI: 0.6%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 495.9g of light component removal residue.

[0102] In step S3, 101.3g of the light component was mixed and reacted with 55.7g of a 12.5% ​​sodium hydroxide solution at 90°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 87.7g of chlorobenzene solvent with a water content of 22ppm.

[0103] In step S4, 495.9g of the residue from the light residue removal process is distilled at an absolute pressure of 3mmHg and a temperature of 95°C. 39.6g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0104] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.15:0.01 to obtain a composite dechlorination agent solution of 33g. This solution is then mixed with 39.6g of chlorinated HDI material in a static mixer at 120°C for 45s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0105] Example 9

[0106] In step S1, 1032g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) was subjected to an absolute pressure of 100mmHg to remove 426.4g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0107] In step S2, 99.25g of light components (the proportions of each substance in the light components are: chlorobenzene: 93.5%, 1,6-dichlorohexane: 3.1%, chloroisocyanurate: 2.8%, HDI: 0.55%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 504.4g of light component residue.

[0108] In step S3, 99.25g of the light component was mixed and reacted with 54.6g of a 12.5% ​​sodium hydroxide solution at 90°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 87.1g of chlorobenzene solvent with a water content of 21ppm.

[0109] In step S4, 505.4g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 39.3g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0110] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.1:0.008 to obtain 42g of a composite dechlorination agent solution. This solution is then mixed with 39.3g of chlorinated HDI material in a static mixer at 130°C for 30s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0111] Example 10

[0112] In step S1, 1012g of HDI synthesis solution (containing the following components in the HDI synthesis solution after phosgene removal, using the gas-phase phosgene method) is subjected to an absolute pressure of 100mmHg to remove 415.5g of chlorobenzene solvent, yielding the remaining material from the HDI desolventizing reactor.

[0113] In step S2, 97.9g of light components (the proportions of each substance in the light components are: chlorobenzene: 93.62%, 1,6-dichlorohexane: 3.62%, chloroisocyanurate: 2.14%, HDI: 0.61%) are removed from the residual material in the HDI desolventizing reactor under an absolute pressure of 12mmHg, resulting in 496.7g of light component residue.

[0114] In step S3, 97.9g of the light component was mixed and reacted with 53.8g of a 12.5% ​​sodium hydroxide solution at 90°C, and the mixture was separated under normal pressure. The oil layer obtained from the separation was dried to obtain 85.4g of chlorobenzene solvent with a water content of 25ppm.

[0115] In step S4, 496.7g of the residue from the light residue removal process is distilled at an absolute pressure of 8mmHg and a temperature of 110℃. 38.2g of chlorine-containing HDI material is collected from the top of the column, and a high-content HDI product is collected from the side stream.

[0116] In step S5, HDI, o-cresol, and 2,6-di-tert-butyl-p-cresol are mixed in a molar ratio of 1:0.2:0.012 to obtain a composite dechlorination agent solution of 26.3g. This solution is then mixed with 38.2g of chlorinated HDI material in a static mixer at 100°C for 60s to obtain dechlorinated HDI material, which is then used in the light-light removal process.

[0117] Comparative Example 1

[0118] In step S1, 1032g of HDI synthesis solution (containing the following components: chlorobenzene: 52.2%, 1,6-dichlorohexane: 0.23%, chloroisocyanurate: 0.65%, HDI: 46.1%, biuret: 0.38%, polymer: 0.44%) after phosgene removal was obtained by removing all 539.96g of chlorobenzene solvent (containing the following components: chlorobenzene: 98.97%, 1,6-dichlorohexane: 0.44%, chloroisocyanurate: 0.46%, HDI: 0.13%) from the solvent under an absolute pressure of 115mmHg, thus obtaining the residue from the HDI desolventizing reactor.

[0119] Step S2: 487.63g of the remaining material in the HDI desolventizing vessel is desorbed under an absolute pressure of 9mmHg to obtain 459.1g of HDI product.

[0120] Comparative Example 2

[0121] Step S1: 1032g of HDI synthesis solution (containing the following components: o-dichlorobenzene: 50.2%, 1,6-dichlorohexane: 0.26%, chloroisocyanurate: 0.64%, HDI: 48.08%, biuret: 0.35%, polymer: 0.46%) after phosgene removal using the gas-phase phosgene method is subjected to an absolute pressure of 100mmHg to remove all 580.24g of o-dichlorobenzene solvent (containing the following components: o-dichlorobenzene: 98.86%, 1,6-dichlorohexane: 0.52%, chloroisocyanurate: 0.48%, HDI: 0.14%), obtaining the HDI desolventizing residue.

[0122] Step S2: 567.49g of the remaining material in the HDI desolventizing vessel is desorbed under an absolute pressure of 8mmHg to obtain 540.13g of HDI product.

[0123] Comprehensive calculation

[0124] The total yield, total purity, total impurity detection amount, total solvent recovery rate, and solvent recovery purity of the HDI products in the above embodiments and comparative examples are shown in Table 1.

[0125] Table 1

[0126]

[0127] As can be seen, the purity of the HDI product in the comparative sample was lower than the standard requirement of 99.5%, and the chlorinated impurities were high, which could easily lead to unqualified hydrolyzed chlorine. The purity of the recovered solvent was also lower than 99.5%.

[0128] As can be seen from the above, compared with the comparative example, the embodiments of the present invention remove the solvent from the HDI synthesis solution separately in two steps: solvent removal and light component removal, which helps to reduce the amount of solvent to be processed. Alkali washing and drying of the light component helps to remove impurities such as 1,6-dichlorohexane and chloroisocyanurate from the light component solvent, resulting in a high content of recovered solvent. The use of a phenolic dechlorinating agent further removes chloroisocyanurate impurities from the chlorinated HDI material, while the addition of an antioxidant helps to reduce the HDI polymerization reaction that occurs during light component removal and distillation. Using the preparation method of the present invention, high-purity, high-yield HDI can be obtained. The process is simple, the product and solvent recovery rates are high, the cost is low, and it is easy to implement industrially. Furthermore, it can be seen that when all process parameters are within the preferred range of the present invention, the yield and purity are even better.

[0129] 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 process for the preparation of hexamethylene diisocyanate, characterized in that, The method comprises the following steps: S1, desolventizing the HDI synthesis solution to obtain a first recovered solvent and HDI desolventizing residue; the HDI synthesis solution is a reaction solution after removing phosgene after synthesizing HDI by using a gas-phase phosgene method; S2, desolventizing the HDI desolventizing residue to obtain light components and desolventizing residue; S3, performing alkali washing and layering on the light components to obtain an oil layer, and then drying the oil layer to obtain a second recovered solvent; S4, rectifying the desolventizing residue to obtain HDI products and chlorine-containing HDI materials; S5, mixing HDI, a phenolic dechlorination agent and an antioxidant to obtain a composite dechlorination agent solution, and then mixing the composite dechlorination agent solution with the chlorine-containing HDI materials to perform dechlorination treatment to obtain dechlorinated HDI materials, which are returned to the desolventizing step; In the step S3, an aqueous alkali solution is used for the alkali washing and layering, and the mass ratio of the light components to the aqueous alkali solution is 1: (0.5-0.6); In the step S5, the phenolic dechlorination agent comprises o-cresol and / or p-cresol, and the antioxidant comprises 2,6-di-tert-butyl-p-cresol; in the composite dechlorination agent solution, the molar ratio of the HDI, the phenolic dechlorination agent and the antioxidant is 1: (0.1-0.2): (0.008-0.012).

2. The production method according to claim 1, characterized by, In the step S1, The solvents in the HDI synthesis solution comprise one or more of chlorobenzene, o-dichlorobenzene and p-dichlorobenzene; and / or The pressure of the desolventizing treatment is 50-150 mmHg; and / or The first recovered solvent accounts for 80-90% of the total mass of the solvents in the HDI synthesis solution.

3. The production method according to claim 1 or 2, characterized by, In the step S2, The pressure of the desolventizing treatment is 10-50 mmHg; and / or The mass percentage of HDI in the light components is 0.5-1%.

4. The production method according to claim 1 or 2, characterized by, In the step S3, The mass fraction of the aqueous alkali solution is 5-15%; and / or The aqueous alkali solution comprises an aqueous sodium hydroxide solution and / or an aqueous potassium hydroxide solution.

5. The production method according to claim 1 or 2, characterized by, In the step S3, The temperature of the alkali washing and layering is 80-100℃; and / or The water content of the second recovered solvent is ≤50 ppm.

6. The production method according to claim 1 or 2, characterized by, In the step S4, The temperature of the rectification is 95-120℃, and the pressure is 3-10 mmHg; and / or The chlorine-containing HDI materials account for 5-10% of the total mass of the desolventizing residue.

7. The production method according to claim 1 or 2, characterized by, In the step S5, The temperature of the dechlorination treatment is 100-130℃, and the time is 30-60 s; and / or The mass ratio of the composite dechlorination agent solution to the chlorine-containing HDI materials is 1: (0.9-1.5).

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