Process for synthesizing toluene diisocynate by low-energy-consumption non-phosgene method

Abstract

The invention relates to a process for synthesizing toluene diisocynate by a low-energy-consumption non-phosgene method, which comprises the following steps: reacting toluenediamine with dimethyl carbonate to synthesize toluene dicarbamate, and then decomposing the toluene dicarbamate to prepare the toluene diisocynate. According to the process, heat of a reaction product for synthesizing methyl toluenediamine and dimethyl carbonate is utilized, and part of light components are evaporated out through flash evaporation operation; and then adding a solvent for the decomposition reaction of toluene dicarbamate into the flashed material, continuously evaporating components such as dimethyl carbonate and the like, and enabling toluene dicarbamate and the solvent to enter a decomposition refining reaction tower together for reaction and separation to obtain a product. Compared with the prior art, the method has the advantages that the process is simple, the energy consumption, the equipment and the operation cost are saved, the purity of the obtained product and byproduct is high, and the total production cost of the toluene diisocyanate is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of energy-saving synthesis of high-purity toluene diisocyanate, and specifically to an energy-saving process for synthesizing toluene dicarbamate methyl using toluene diamine and dimethyl carbonate as raw materials, and then preparing high-purity toluene diisocyanate through catalytic decomposition. Background Art

[0002] Toluene diisocyanate (TDI) is an important organic chemical intermediate and one of the important raw materials for the polyurethane industry. At present, the industrial production of toluene diisocyanate adopts the phosgene method, but its raw material phosgene is highly toxic, the residual chlorine in the product affects the quality of toluene diisocyanate, and the byproduct HCl in the process is easy to cause equipment corrosion, resulting in high requirements for equipment materials and large equipment investment. With the enhancement of people's safety and environmental awareness, the development of non-toxic and pollution-free green synthesis methods has received more and more attention. Among them, the green synthesis process of synthesizing toluene dicarbamate (TDC) by reacting toluenediamine (TDA) with dimethyl carbonate (DMC), and then decomposing toluene dicarbamate to obtain toluene diisocyanate has considerable industrialization potential.

[0003] There are many patent documents on the synthesis of carbamates from amines and organic carbonates, and the decomposition of carbamates to prepare isocyanates. Patents US4268683, US4268684, CN03156418.6 and CN200710056664.X, etc., catalyze the reaction of organic carbonates and amines to synthesize carbamates, and zinc acetate is an efficient catalyst for the synthesis of toluene dicarbamate. Patents EP0672653A1 and CN0180578.5 are about the decomposition of carbamates to prepare isocyanates.

[0004] In addition, patent EP0323514A1 describes a process for preparing diisocyanate using diamine and dimethyl carbonate as raw materials: in the presence of a catalyst, diamine reacts with dimethyl carbonate to prepare carbamate, which is then washed, evaporated, and then the pure product is obtained; then the carbamate is catalytically decomposed to obtain the product isocyanate.

[0005] Patent US20030162995A1 provides a method for preparing aromatic isocyanates using aromatic amines and organic carbonates as raw materials. First, in the presence of a catalyst, the aromatic amines react with the organic carbonates to synthesize carbamates. Then, the catalyst is removed, and then the carbamates are gasified and thermally decomposed into isocyanates.

[0006] Patent CN201410148796.5 uses the deactivated catalyst ZnO, which is used in the reaction of toluenediamine and dimethyl carbonate catalyzed by zinc acetate to synthesize toluene dicarbamate, as a catalyst for the decomposition of toluene dicarbamate to prepare toluene diisocyanate. After the reactants are evaporated to remove the remaining dimethyl carbonate and by-products, toluene dicarbamate is used together with ZnO for catalytic decomposition to prepare toluene diisocyanate.

[0007] Although there are many related literatures, there are still many shortcomings in the process of synthesizing diisocyanates using amines and organic carbonates as raw materials:

[0008] (1) The process of synthesizing carbamates by reacting amines with organic carbonates: Generally, the catalyst is separated and then treated to obtain carbamates, but the heat of the reaction system is not reasonably utilized, resulting in energy loss.

[0009] (2) After synthesizing carbamate, the solid is obtained by separation and other post-treatment operations, and then the solid is gasified or dissolved in a solvent and then decomposed to prepare isocyanate. After obtaining the carbamate solid, the solid is dissolved, which also causes energy loss.

[0010] (3) The decomposition reaction of carbamate is carried out in a single or multiple reactors, resulting in the incomplete decomposition of the intermediate monoisocyanate being mixed into the product, increasing the refining cost of the product diisocyanate. Summary of the invention

[0011] In view of the above defects, in order to overcome the deficiencies of the prior art, the present invention provides a low-energy non-phosgene process for synthesizing toluene diisocyanate, which is simple to operate, saves energy and reduces consumption, saves equipment investment and operating costs, and the obtained toluene diisocyanate product and by-product methanol have extremely high purity and are suitable for large-scale industrial production.

[0012] To achieve the above-mentioned object and other related objects, the present invention provides a process for synthesizing toluene diisocyanate by a low-energy non-phosgene method, the process steps comprising:

[0013] (1) Toluenediamine and dimethyl carbonate are reacted as raw materials to prepare toluene dicarbamate, and the resulting feed liquid is filtered and then flashed to evaporate part of the light components;

[0014] (2) the liquid after flash evaporation enters a toluene dicarbamate refining and batching tower, is mixed with the decomposition reaction solvent introduced into the tower to obtain a mixed liquid, and the remaining light components are extracted;

[0015] (3) adding a catalyst to a decomposition and refining reaction tower, adding the mixed solution obtained in step (2) to the decomposition and refining reaction tower for decomposition reaction, taking out toluene diisocyanate product from the side line of the tower, returning the incompletely reacted intermediate product toluene monoisocyanate to the decomposition and refining reaction tower for further decomposition, and collecting the by-product methanol at the top of the tower.

[0016] In one example of the present invention, the flash evaporation refers to flash evaporation of a liquid containing toluene dicarbamate at 80-110°C, for example, at 81°C, 83°C, 85°C, 87°C, 89°C, 90°C, 91°C, 93°C, 95°C, 97°C, 99°C, 101°C, 103°C, 105°C, 107°C, or 109°C. Preferably, the liquid is flash evaporated using its own heat.

[0017] In one example of the present invention, the light component includes one or more of dimethyl carbonate, methanol, methyl acetate, and H2O.

[0018] In one example of the present invention, the catalyst used in the step (1) for preparing methyl toluene dicarbamate is one or more of sodium methoxide, zinc acetate, and lead acetate.

[0019] In one example of the present invention, the top temperature of the toluene dicarbamate refining and batching tower in the step (2) is 70-150°C, for example, it can be 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C; the bottom temperature is 170-280°C, for example, it can be 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C.

[0020] In one example of the present invention, the temperature of the decomposition and refining reaction tower in step (3) is 170-280°C, for example, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C; the tower top temperature is 50-160°C, for example, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 10 The tower top pressure is 1-25kPa, for example, it can be 2kPa, 3kPa, 4kPa, 5kPa, 6kPa, 7kPa, 8kPa, 9kPa, 10kPa, 11kPa, 12kPa, 13kPa, 14kPa, 14kPa, 16kPa, 17kPa, 18kPa, 19kPa, 20kPa, 21kPa, 22kPa, 23kPa, 24kPa.

[0021] In one example of the present invention, the catalyst added to the decomposition and refining reaction tower may be one or more of zinc oxide, ferric oxide, and a deactivated catalyst for the synthesis of toluene dicarbamate.

[0022] In one example of the present invention, the decomposition reaction solvent in step (2) can be one or more high-boiling point solvents such as dimethyl phthalate, dibutyl phthalate, di(iso)octyl phthalate, n-butyl titanate, and cyclopentane sulfone.

[0023] In one example of the present invention, methyl toluene dicarbamate can be prepared according to CN03156418.6, CN200710056664.X, CN200710060033.5, CN201410148796.5, "Synthesis of toluene diisocyanate using dimethyl carbonate instead of phosgene I. Catalytic synthesis of methyl toluene dicarbamate" (Zhao Xinqiang et al.), "Research on the reaction of DMC and 2,4-diaminotoluene catalyzed by methyl formate to synthesize 2,4-methyl toluene dicarbamate" (Cong Jinsheng et al.) or other methods disclosed in the prior art.

[0024] The process provided by the present invention uses the heat of the material after synthesizing toluene dicarbamate to flash off part of the light components, which can fully utilize the heat of the system, reduce subsequent investment, and save energy and reduce consumption; there is no need to obtain toluene dicarbamate solid, and the decomposition reaction solvent is directly added to the material liquid after flashing, and the mixed material directly enters the decomposition and refining reaction tower, which saves the energy required for phase change; the intermediate product toluene monoisocyanate produced in the decomposition reaction is returned to the tower kettle to continue the decomposition reaction, and the product is refined while the decomposition reaction is being carried out, which saves equipment and cost, and obtains a high-purity toluene diisocyanate product and a methanol byproduct that meet the accuracy requirements.

[0025] The beneficial effects of the present invention are as follows: the present invention is a technology for preparing toluene diisocyanate by a dimethyl carbonate method, which has the advantages of simple process, mild operating conditions, equipment saving, energy saving and consumption reduction, and low production cost. The heat of the reaction materials can be fully utilized for flash evaporation operation, thereby realizing the rational utilization of energy; toluene dicarbamate methyl ester dissolved in dimethyl carbonate is transferred to a decomposition reaction solvent, thereby saving the energy required for phase change; the decomposition reaction of toluene dicarbamate methyl ester, separation of intermediate products, and refining of byproducts and product toluene diisocyanate are carried out in the same equipment, thereby saving equipment costs, phase change energy consumption, and operating costs.

[0026] The above beneficial effects are specifically embodied in:

[0027] 1. Energy saving and consumption reduction

[0028] (1) Flash evaporation operation is used to achieve heat recovery and utilization.

[0029] After the reaction of toluenediamine and dimethyl carbonate to synthesize toluene dicarbamate is completed, the material is filtered and further flash-evaporated using the heat of the material to evaporate part of the dimethyl carbonate, by-product methanol and other light components, which not only fully utilizes the heat of the material, but also reduces the energy required for the subsequent evaporation of dimethyl carbonate, methanol and other light components. The rational use of energy can be achieved, and the energy consumption of the toluene diisocyanate production process can be reduced. Based on a toluene diisocyanate production capacity of 100,000 tons / year, the energy consumption can be saved by about 1.5×10 11 kJ, saving costs of approximately RMB 4.14 million and reducing carbon dioxide emissions by 14,000 tons.

[0030] (2) Toluene dicarbamate dissolved in dimethyl carbonate is transferred to the decomposition reaction solvent to save the energy required for phase change.

[0031] The post-treatment of the flashed material is carried out in the toluene dicarbamate refining and batching tower. While dimethyl carbonate, methanol and other light components are being evaporated, the solvent used for the decomposition reaction is added to the tower to transfer the toluene dicarbamate dissolved in dimethyl carbonate to the solvent. This avoids the multi-step operation of evaporating dimethyl carbonate and other components to obtain toluene dicarbamate solids, and then dissolving the toluene dicarbamate solids in the solvent in conventional operations, saving the phase change heat required for the precipitation and redissolution of toluene dicarbamate. Based on a toluene diisocyanate production capacity of 100,000 tons / year, the energy consumption can be saved by about 4.0×10 9 kJ, can save 110,000 yuan in costs and reduce 372 tons of carbon dioxide emissions.

[0032] (3) The decomposition reaction of toluene dicarbamate and the refining of the product are carried out in a decomposition and refining reaction tower, which saves energy consumption.

[0033] In the traditional method, the decomposition of toluene dicarbamate is carried out in a reactor, and after the product and the intermediate product are condensed, they are separated in a refining tower to obtain a toluene diisocyanate product that meets the precision requirements. The present invention integrates the decomposition reaction of toluene dicarbamate with the separation of toluene monoisocyanate, the byproduct methanol and the product toluene diisocyanate in the same equipment, avoiding the phase change latent heat required for the product and the byproduct to be condensed into liquid after leaving the reactor and then vaporized in the separation and refining tower, saving energy consumption. Based on a toluene diisocyanate production capacity of 100,000 tons / year, the energy consumption can be saved by about 1.2×10 11 kJ, saving about 3.31 million yuan in costs and reducing 12,000 tons of carbon dioxide emissions.

[0034] 2. Save equipment investment

[0035] (1) The post-treatment of the flash-evaporated material is carried out in a toluene dicarbamate refining and batching tower. While dimethyl carbonate, methanol and other light components are evaporated, the toluene dicarbamate dissolved in dimethyl carbonate is transferred to a solvent to prepare raw materials that meet the requirements of the toluene dicarbamate decomposition reaction. The operations that require multiple devices in the conventional method are combined into one device, which saves equipment investment and can save costs of about 300,000 yuan.

[0036] (2) The decomposition reaction of toluene dicarbamate is carried out in a decomposition and refining reaction tower, saving equipment costs.

[0037] The decomposition reaction of toluene dicarbamate, the separation of toluene monoisocyanate, and the refining of by-product methanol and product toluene diisocyanate are carried out in the same equipment, so that the reaction and separation operations that must be completed by multiple equipment in the traditional method can be completed in only one equipment, the decomposition and refining reaction tower, saving equipment investment and saving equipment costs of about 600,000 yuan.

[0038] 3. Save operating costs

[0039] (1) In the post-treatment process of the material after flash evaporation, the methyl toluene dicarbamate in dimethyl carbonate is transferred to the decomposition reaction solvent, thereby avoiding the multi-step operation of distilling out dimethyl carbonate and other components to obtain the methyl toluene dicarbamate solid, and then dissolving the methyl toluene dicarbamate solid in the solvent in the conventional operation, thereby reducing the operating cost. In addition, the liquid material is convenient to transport, which also reduces the operating cost.

[0040] (2) The decomposition reaction of toluene dicarbamate is carried out in a decomposition and refining reaction tower, so that the decomposition reaction of toluene dicarbamate and the separation of toluene monoisocyanate, by-product methanol and product toluene diisocyanate are carried out in the same equipment, which concentrates the conventional multi-equipment operation on a single equipment operation, simplifies the operation steps and saves the operation cost. DETAILED DESCRIPTION

[0041] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the features in the following embodiments and the embodiments can be combined with each other without conflict. It should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturers.

[0042] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" etc. used in this specification are only for the convenience of description and are not intended to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be regarded as the scope of implementation of the present invention.

[0043] The present invention is illustrated by the following examples, but the present invention is not limited to the following examples.

[0044] Example 1. After the reaction of toluenediamine and dimethyl carbonate catalyzed by sodium methoxide to synthesize toluene dicarbamate was completed, the material was discharged, the catalyst was filtered out, and flash distillation was performed at 80°C. The amount of material flashed out accounted for 27.7% of the liquid amount of the reaction completed material except the catalyst and toluene dicarbamate;

[0045] The material after flash evaporation goes to the toluene dicarbamate refining and batching tower, and dimethyl carbonate, methanol and other components in the feed are evaporated at a tower top temperature of 150°C and normal pressure; the tower bottom temperature is 280°C, and the materials of toluene dicarbamate and dioctyl phthalate are taken out and go to the toluene dicarbamate decomposition and refining reaction tower;

[0046] The toluene dicarbamate and dioctyl phthalate materials from the previous step were decomposed and refined in the reactor, and the decomposition reaction was carried out at a reactor temperature of 280° C. The byproduct methanol with a mass content of 99.4% was extracted; and the product toluene diisocyanate with a mass content of 99.98% was collected.

[0047] Example 2. After the reaction of toluenediamine and dimethyl carbonate catalyzed by sodium methoxide to synthesize toluene dicarbamate was completed, the material was discharged, the catalyst was filtered out, and flash distillation was performed at 90°C. The amount of material flashed out accounted for 29.2% of the liquid amount of the material after the reaction except the catalyst and toluene dicarbamate;

[0048] The material after flash evaporation goes to the toluene dicarbamate refining and batching tower, and dimethyl carbonate, methanol and other components in the feed are evaporated at a tower top temperature of 110°C and normal pressure; the tower bottom temperature is 240°C, and the materials of toluene dicarbamate and dioctyl phthalate are taken out and go to the toluene dicarbamate decomposition and refining reaction tower;

[0049] The toluene dicarbamate and dioctyl phthalate materials from the previous step were decomposed and refined in the reactor, and the decomposition reaction was carried out at a reactor temperature of 240° C. The byproduct methanol with a mass content of 99.5% was extracted; and the product toluene diisocyanate with a mass content of 99.98% was collected.

[0050] Example 3. After the reaction of toluenediamine and dimethyl carbonate catalyzed by zinc acetate to synthesize toluene dicarbamate was completed, the material was discharged, the deactivated catalyst was filtered out, and flash distillation was performed at 95°C. The amount of the flashed material accounted for 31.1% of the liquid amount of the reaction completed material except the deactivated catalyst and toluene dicarbamate;

[0051] The material after flash evaporation goes to the toluene dicarbamate refining and batching tower, and dimethyl carbonate, methanol, methyl acetate and other components in the feed are evaporated at a tower top temperature of 90°C and normal pressure; the tower bottom temperature is 200°C, and the materials of toluene dicarbamate and dioctyl phthalate are taken out and go to the toluene dicarbamate decomposition and refining reaction tower;

[0052] The toluene dicarbamate and dioctyl phthalate materials from the previous step were decomposed and refined in the reactor, and the decomposition reaction was carried out at a reactor temperature of 220° C. The byproduct methanol with a mass content of 99.5% was extracted; and the product toluene diisocyanate with a mass content of 99.99% was collected.

[0053] Example 4. After the reaction of toluenediamine and dimethyl carbonate catalyzed by lead acetate to synthesize toluene dicarbamate was completed, the material was discharged, the deactivated catalyst was filtered out, and flash distillation was performed at 100° C. The amount of the flashed material accounted for 45.4% of the liquid material in the reaction completed material except the deactivated catalyst and toluene dicarbamate;

[0054] The material after flash evaporation goes to the toluene dicarbamate refining and batching tower, and dimethyl carbonate, methanol, methyl acetate and other components in the feed are evaporated at a tower top temperature of 70°C and normal pressure; the tower bottom temperature is 170°C, and the materials of toluene dicarbamate and dioctyl phthalate are taken out and go to the toluene dicarbamate decomposition and refining reaction tower;

[0055] The toluene dicarbamate and dioctyl phthalate materials from the previous step were decomposed and refined in the reactor, and the decomposition reaction was carried out at a reactor temperature of 170° C. The byproduct methanol with a mass content of 99.6% was extracted; and the product toluene diisocyanate with a mass content of 99.99% was collected.

[0056] From the results of the above examples, it can be seen that the process provided by the present invention has mild operating conditions, saves equipment, saves energy and reduces consumption, and has low production costs. It can fully utilize the heat of the reaction materials, realize the rational use of energy, save equipment costs and operating costs, and obtain products and by-products with extremely high purity, meeting various commercial and practical production needs.

[0057] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A process for synthesizing toluene diisocyanate by a low-energy non-phosgene method, characterized in that: The steps include: (1) Toluenediamine and dimethyl carbonate are reacted as raw materials to prepare toluene dicarbamate, and the resulting feed liquid is filtered and then flashed to evaporate part of the light components; (2) the liquid after flash evaporation enters a toluene dicarbamate refining and batching tower, is mixed with the decomposition reaction solvent introduced into the tower to obtain a mixed liquid, and the remaining light components are extracted; (3) adding a catalyst to a decomposition and refining reaction tower, adding the mixed solution obtained in step (2) to the decomposition and refining reaction tower for decomposition reaction, taking out toluene diisocyanate product from the side line of the tower, returning the incompletely reacted intermediate product toluene monoisocyanate to the decomposition and refining reaction tower for further decomposition, and collecting the by-product methanol at the top of the tower.

2. The process according to claim 1, characterized in that: The flash evaporation in step (1) refers to flash evaporation at 80-110°C.

3. The process according to claim 1, characterized in that: The light components in step (1) include one or more of dimethyl carbonate, methanol, methyl acetate, and H2O.

4. The process according to claim 1, characterized in that: The catalyst used in the preparation of toluene dicarbamate in step (1) is one or more of sodium methoxide, zinc acetate and lead acetate.

5. The process according to claim 1, characterized in that: In the step (2), the top temperature of the toluene dicarbamate refining and batching tower is 70-150°C, and the bottom temperature is 170-280°C.

6. The process according to claim 1, characterized in that: The decomposition reaction solvent in step (2) is one or more of dimethyl phthalate, dibutyl phthalate, di(iso)octyl phthalate, n-butyl titanate, and cyclopentane sulfone.

7. The process according to claim 1, characterized in that: In the step (3), the reactor temperature of the decomposition and purification reaction tower is 170-280°C.

8. The process according to claim 1, characterized in that: The catalyst added to the decomposition and refining reaction tower in step (3) is one or more of zinc oxide, ferric oxide, and a deactivated catalyst for the synthesis of toluene dicarbamate.

9. The process according to claim 1, characterized in that: The flash evaporation in step (1) refers to flash evaporation of the feed liquid using its own heat.

10. The process according to claim 1, characterized in that: In the step (3), the top temperature of the decomposition and purification reaction tower is 50-160° C. and the pressure is 1-25 kPa.