Isocyanate refining system and method

Abstract

The application relates to an isocyanate refining system and method, the isocyanate refining system comprising a gas-liquid separation device, an intermediate separation device, a heater, an intermediate storage tank, a desolventizing rectifying tower and a finished product rectifying tower, the gas-liquid separation device is provided with a heavy component outlet, the heavy component outlet is connected with an inlet of the intermediate separation device, a liquid outlet of the intermediate separation device is connected with an inlet of the desolventizing rectifying tower, a liquid outlet of the desolventizing rectifying tower is connected with an inlet of the finished product rectifying tower, a solid outlet of the intermediate separation device is connected with an inlet of the heater, an outlet of the heater is connected with an inlet of the intermediate storage tank, and a liquid outlet of the intermediate storage tank is connected with an inlet of the finished product rectifying tower. The application can improve the yield of isocyanate by separating and decomposing carbamoyl chloride.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of isocyanate preparation, in particular to an isocyanate refining system and method. BACKGROUND

[0002] Isocyanate is widely used in industrial production, military industry, aerospace and many other fields. Hexamethylene diisocyanate (HDI) is a high-end product in the isocyanate family, which has unique and excellent yellowing resistance, weather resistance and chemical resistance, and is mainly used in the fields of coatings, adhesives and food packaging. However, isocyanate series products are a class of heat-sensitive materials. Liquid isocyanate can self-polymerize into a polymer in a short time under heat conditions, which not only leads to a decrease in product yield, but also causes problems such as production equipment blockage and coking. Therefore, it is urgent to find a simple and efficient method for purifying isocyanate.

[0003] CN103922969B mentions that hexanediamine and phosgene are subjected to phosgenation reaction in a reaction zone, the content of low-boiling-point components in the feed hexanediamine is reduced to ≤50 mg / kg, the content of impurities in the raw material is reduced, the generation of phosgenation reaction impurities is reduced, and finally the obtained isocyanate has good color stability.

[0004] CN110511164A patent specification mentions that in gas-phase phosgenation and liquid-phase phosgenation, the mixing of raw materials and the reaction residence time are both key parameters. A scheme of limiting the residence time in the reaction section is proposed to reduce side reactions and the retention of amine residues in the reaction quenching liquid.

[0005] CN110891932A patent uses a reaction liquid with less than 5% solvent or even no solvent as a quenching agent after quenching. Low solvent content operation can simplify post-treatment, reduce the size of downstream devices and reduce energy consumption. However, due to the low solvent content, the generation of by-products increases, the product quality deteriorates, or the formation of increased deposits is caused. Therefore, reducing the quenching solvent content increases the generation of by-products.

[0006] US9593075 mentions that HCl (hydrogen chloride) and phosgene are removed from the crude isocyanate. The coexistence of product isocyanate and hydrogen chloride, phosgene can cause side reactions to occur. Therefore, HCl and phosgene are separated to reduce the generation of acyl chloride and urea substances in the product.

[0007] In summary, most of the existing patents focus on improving the synthesis yield of isocyanate by reducing the content of impurities in raw materials, reducing or separating substances that can cause side reactions, while the loss of isocyanate yield is mainly concentrated in the recovery of footnotes, 20%-30% of the components in the footnotes cannot be recovered, and 5%-10% of the isocyanate cannot be recovered when using high-temperature rectification for footnotes recovery. Among the 25%-40% of the unrecoverable components, the isocyanate polymer content is as high as 50%, and the polymer is mainly produced by the polymerization of isocyanate under heat. The effect of temperature on isocyanate polymerization is difficult to change. SUMMARY

[0008] Therefore, it is necessary to provide an isocyanate refining system and method, which can simply and efficiently purify isocyanate and improve the yield of isocyanate.

[0009] An isocyanate refining system, comprising: a gas-liquid separation device, an intermediate separation device, a heater, an intermediate storage tank, a desolventizing rectification tower, and a finished product rectification tower, the gas-liquid separation device has a heavy component outlet, the heavy component outlet is connected with the inlet of the intermediate separation device, the liquid outlet of the intermediate separation device is connected with the inlet of the desolventizing rectification tower, the liquid outlet of the desolventizing rectification tower is connected with the inlet of the finished product rectification tower, the solid outlet of the intermediate separation device is connected with the inlet of the heater, the outlet of the heater is connected with the inlet of the intermediate storage tank, and the liquid outlet of the intermediate storage tank is connected with the inlet of the finished product rectification tower.

[0010] In one embodiment, the intermediate separation device comprises a tower body, a flow guide frame, a filter plate, a flow guide plate, and a heating element, the top of the tower body is provided with a feed inlet, the feed inlet is the inlet of the intermediate separation device, the bottom of the tower body is provided with a preheating zone, the heating element is arranged in the preheating zone for heating the preheating zone, the preheating zone is provided with a first discharge outlet, the first discharge outlet is the solid outlet of the intermediate separation device, the flow guide frame is arranged below the feed inlet, the filter plate is arranged below the flow guide frame, the filter plate is provided with filter holes, the filter plate is arranged obliquely, the lower end of the filter plate is connected with the preheating zone through a pipeline, the flow guide plate is arranged below the filter plate, the flow guide plate is arranged obliquely, the tower body is further provided with a second discharge outlet, the second discharge outlet is the liquid outlet of the intermediate separation device, and the second discharge outlet is located on one side of the lower end of the flow guide plate.

[0011] In one embodiment, the flow guide frame comprises a first flow guide part and a second flow guide part, the first flow guide part is conical and the sharp corner is arranged upward, and the second flow guide part is connected with the lower end of the first flow guide part and is arranged downward.

[0012] In one of the embodiments, the filter plate is funnel-shaped.

[0013] And / or, the filter hole has a mesh number of 10-30.

[0014] In one of the embodiments, a self-control valve is arranged on the pipeline to control the opening and closing of the pipeline.

[0015] In one of the embodiments, a phosgene cooler, a phosgene recovery device, and a drying tower are further included, the gas outlet of the gas-liquid separation device is connected with the inlet of the phosgene cooler, the phosgene cooler has a phosgene outlet and a hydrogen chloride gas outlet, the phosgene outlet is connected with the inlet of the phosgene recovery device, the hydrogen chloride gas outlet is connected with the inlet of the drying tower, and the gas outlet of the intermediate storage tank is connected with the inlet of the phosgene cooler.

[0016] In one of the embodiments, a first pump is arranged between the liquid outlet of the intermediate separation device and the inlet of the desolvation rectifying tower.

[0017] And / or, a second pump is arranged between the liquid outlet of the intermediate storage tank and the inlet of the finished product rectifying tower.

[0018] In one of the embodiments, the isocyanate includes hexamethylene diisocyanate or isophorone diisocyanate.

[0019] A refining method of isocyanate is performed by using the refining system of isocyanate as described above, and the refining method of isocyanate includes:

[0020] The isocyanate photochemical liquid after the phosgenation reaction is transported to the gas-liquid separation device for gas-liquid separation, wherein the heavy components are output from the heavy component outlet of the gas-liquid separation device and enter the intermediate separation device for solid-liquid separation, the liquid phase components enter the desolvation rectifying tower for desolvation rectification, and the isocyanate liquid after the removal of the solvent enters the finished product rectifying tower for rectification and purification.

[0021] The solid phase components are heated and decomposed into isocyanate liquid and hydrogen chloride gas by the heater, the decomposition products enter the intermediate storage tank, and the isocyanate liquid in the intermediate storage tank enters the finished product rectifying tower for rectification and purification.

[0022] In one of the embodiments, the heavy components include isocyanate, solvent, and carbamoyl chloride, and after the separation of the heavy components by the intermediate separation device, the separation efficiency of the carbamoyl chloride is 60%-80%.

[0023] Compared with the prior art, the isocyanate refining system and method provided by the application first separates the solid-phase carbamoyl chloride from the liquid-phase isocyanate and solvent, and then performs subsequent treatment on the liquid phase and the solid phase, wherein the liquid phase is subjected to subsequent desolventization rectification and product rectification, and the solid phase is subjected to subsequent heating decomposition to form isocyanate and then product rectification, thereby omitting the step of carbamoyl chloride entering the falling film heater together with isocyanate for high-temperature treatment, reducing the residence time of isocyanate in the entire liquid phase treatment process, thereby reducing the heating time of isocyanate and reducing the polymerization of isocyanate, and thus improving the yield of isocyanate. Moreover, by separating out the solid-phase carbamoyl chloride, the downstream pipeline equipment can be prevented from being blocked by isocyanate entraining a large amount of carbamoyl chloride. In addition, since hydrogen chloride has a catalytic effect on the polymerization of isocyanate, by separating out the carbamoyl chloride for decomposition and separating the gaseous hydrogen chloride from the liquid-phase isocyanate by the gas-liquid separation device and the intermediate storage tank, the catalytic effect of hydrogen chloride on isocyanate in the rectification process can be avoided, thereby reducing the polymerization of isocyanate and improving the yield of isocyanate. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0025] Figure 1 FIG. 1 is a structural schematic diagram of an isocyanate refining system according to an embodiment of the present application.

[0026] Figure 2 FIG. 2 is a structural schematic diagram of an intermediate separation device according to an embodiment of the present application.

[0027] FIG. 1 is a structural schematic diagram of an isocyanate refining system according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the above objectives, features and advantages of the present application more clear and comprehensible, the detailed description of the specific embodiments of the present application will be made below with reference to the accompanying drawings. In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many different ways other than the one described herein, and one of ordinary skill in the art can make similar improvements without departing from the scope of the present application, and therefore the present application is not limited to the specific embodiments disclosed below.

[0029] It is to be noted that when a component is referred to as being "on" or "disposed on" another component, it can be directly on the other component or there can be intervening components present. When a component is referred to as being "connected" to another component, it can be directly connected to the other component or there can be intervening components present. The terms "vertical", "horizontal", "upper", "lower", "left", "right", and similar terms as used in the description of the specification are for the purpose of illustration only and do not indicate an exclusive orientation.

[0030] In addition, the terms "first", "second", and the like, are used only to describe the features and do not imply or suggest relative importance or a number of the features indicated. Thus, the features defined with "first", "second" can include at least one of the features explicitly or implicitly. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified.

[0031] In the present application, unless otherwise explicitly specified and limited, the "on", "under", "above", and "over" of a first feature to a second feature can be that the first feature is in direct contact with the second feature, or the first feature is indirectly in contact with the second feature through an intermediate medium. Moreover, the "above", "over", and "on" of the first feature to the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature is horizontally higher than the second feature. The "below", "under", and "under" of the first feature to the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature is horizontally lower than the second feature.

[0032] Unless otherwise defined, all technical and scientific terms used in the specification of the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. The term "and / or" used in the specification of the present application includes any and all combinations of one or more of the related listed items.

[0033] The application provides a refining system of isocyanate, which takes isocyanate photochemical liquid as raw material to refine and purify isocyanate. The isocyanate includes any one of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate and diphenyl methane diisocyanate.

[0034] The isocyanate photochemical liquid refers to the product after the phosgenation reaction, and the reaction equation of the phosgenation reaction to generate isocyanate is shown as follows:

[0035]

[0036] Through a large number of experiments, it is found that after the reaction is completed, under the condition that a large amount of hydrogen chloride exists, the photochemical liquid is quenched, and due to the reversibility of the reaction, the intermediate carbamoyl chloride will inevitably exist. Therefore, the main components of the isocyanate photochemical liquid include phosgene, hydrogen chloride, isocyanate, solvent and carbamoyl chloride. The solvent can be chlorobenzene, xylene, dichlorobenzene or m-xylene, etc. Carbamoyl chloride has a low freezing point and is difficult to dissolve in isocyanate and solvent, and will decompose into isocyanate and hydrogen chloride at high temperature. Due to the low freezing point and poor solubility of carbamoyl chloride, in the isocyanate photochemical liquid, carbamoyl chloride is in solid state and is easy to block the downstream liquid phase rectification equipment. In the prior art, the method commonly used is to first put carbamoyl chloride into the falling film heater together with isocyanate for high-temperature treatment to decompose into isocyanate and hydrogen chloride, and then perform liquid phase rectification. However, since hydrogen chloride has a catalytic effect on the polymerization of isocyanate, the first putting of carbamoyl chloride into the falling film heater together with isocyanate for high-temperature treatment and then performing liquid phase rectification makes the isocyanate be heated for a long time, which is easy to cause the polymerization of isocyanate, thereby reducing the yield of isocyanate. The application provides a refining system of isocyanate, which can separate the intermediate carbamoyl chloride, thereby reducing the heating time of isocyanate and reducing the occurrence of polymerization, and improving the yield of isocyanate.

[0037] Please refer to Figure 1 The refining system of isocyanate provided by the application includes a gas-liquid separation device 1, an intermediate separation device 2, a heater 3, an intermediate storage tank 4, a desolventizing rectification column 5 and a finished product rectification column 6. Figure 1 Among them, a represents isocyanate photochemical liquid, b represents light components, c represents hydrogen chloride gas, d represents heavy components, e represents isocyanate and solvent, f represents carbamoyl chloride, g represents hydrogen chloride gas, h represents isocyanate liquid, i represents rectification tail gas, j represents pure isocyanate liquid, and k represents foot.

[0038] The gas-liquid separation device 1 is used for gas-liquid separation of the isocyanate photochemical liquid, and has a heavy component outlet and a light component outlet. The light component (including hydrogen chloride and phosgene in gas phase) in the isocyanate photochemical liquid is discharged from the light component outlet, and the heavy component (including isocyanate in liquid phase, solvent in liquid phase and carbamoyl chloride in solid phase) is discharged from the heavy component outlet and enters the intermediate separation device 2 through the inlet. The intermediate separation device 2 is used for solid-liquid separation of the substance entering the same, and has a liquid outlet and a solid outlet. The isocyanate and solvent in liquid phase are discharged from the liquid outlet of the intermediate separation device 2, and the carbamoyl chloride in solid phase is discharged from the solid outlet of the intermediate separation device 2. The liquid outlet of the intermediate separation device 2 is connected with the inlet of the desolventizing rectification tower 5, and the isocyanate and solvent in liquid phase enter the desolventizing rectification tower 5 for rectification. The desolventizing rectification tower 5 has a liquid outlet and a gas outlet, and the liquid outlet of the desolventizing rectification tower 5 is connected with the inlet of the product rectification tower 6. The isocyanate liquid after removal of the solvent by rectification enters the product rectification tower 6 for rectification and purification, so that the isocyanate product is obtained, and the rectification tail gas is discharged from the gas outlet of the desolventizing rectification tower 5. The solid outlet of the intermediate separation device 2 is connected with the inlet of the heater 3, and the outlet of the heater 3 is connected with the inlet of the intermediate storage tank 4, so that the carbamoyl chloride in solid phase is heated and decomposed into isocyanate in liquid phase and hydrogen chloride in gas phase by the heater 3 and enters the intermediate storage tank 4. The intermediate storage tank 4 has a liquid outlet and a gas outlet, and the decomposition products of the heated carbamoyl chloride are subjected to gas-liquid separation in the intermediate storage tank 4. The hydrogen chloride in gas phase is discharged from the gas outlet, and the isocyanate in liquid phase is discharged from the liquid outlet. The liquid outlet of the intermediate storage tank 4 is connected with the inlet of the product rectification tower 6, and the isocyanate liquid from the intermediate storage tank 4 enters the product rectification tower 6 for rectification and purification, so that the isocyanate product is obtained.

[0039] The isocyanate refining system, by setting the intermediate separation device 2, first separates the solid phase carbamoyl chloride and the liquid phase isocyanate and solvent, and then carries out subsequent treatment on the liquid phase and the solid phase, wherein the liquid phase is subsequently subjected to desolventization rectification and product rectification, and the solid phase is subsequently subjected to heating decomposition to form isocyanate and then product rectification, thereby omitting the step of carbamoyl chloride entering the falling film heater 3 with isocyanate for high-temperature treatment, reducing the residence time of isocyanate in the entire liquid phase treatment process, thereby reducing the heating time of isocyanate and reducing the polymerization of isocyanate, thereby improving the yield of isocyanate. Moreover, by separating out the solid phase carbamoyl chloride, the isocyanate can be prevented from plugging downstream piping equipment due to the entrainment of a large amount of carbamoyl chloride. In addition, since hydrogen chloride has a catalytic effect on the polymerization of isocyanate, the carbamoyl chloride is separated out and then decomposed in the present application, and the gas-liquid separation device 1 and the intermediate storage tank 4 separate the gaseous hydrogen chloride and the liquid isocyanate, which can avoid the catalytic effect of hydrogen chloride on isocyanate during the rectification process, thereby reducing the polymerization of isocyanate and improving the yield of isocyanate.

[0040] The isocyanate refining system further comprises a phosgene cooler 7, a phosgene recovery device 8 and a drying tower 9. The gas outlet of the gas-liquid separation device 1 is connected with the inlet of the phosgene cooler 7, the phosgene cooler 7 has a phosgene outlet and a hydrogen chloride gas outlet, the phosgene outlet is connected with the inlet of the phosgene recovery device 8, and the hydrogen chloride gas outlet is connected with the inlet of the drying tower 9. The gas outlet of the intermediate storage tank 4 is connected with the inlet of the phosgene cooler 7. In this way, the hydrogen chloride gas and the phosgene discharged from the gas outlet of the gas-liquid separation device 1 enter the phosgene cooler 7, and the hydrogen chloride gas discharged from the gas outlet of the intermediate storage tank 4 also enters the phosgene cooler 7, and the phosgene and the hydrogen chloride are separated in the phosgene cooler 7, the phosgene enters the phosgene recovery device 8, and the hydrogen chloride enters the drying tower 9 for drying.

[0041] Further, a first pump 10 is arranged between the liquid outlet of the intermediate separation device 2 and the inlet of the desolventization rectification tower 5, so that the liquid discharged from the intermediate separation device 2 is transported into the desolventization rectification tower 5 through the first pump 10. The first pump 10 can be a centrifugal pump.

[0042] Further, a second pump 11 is arranged between the liquid outlet of the intermediate storage tank 4 and the inlet of the product rectification tower 6, so that the liquid discharged from the intermediate storage tank 4 is transported into the product rectification tower 6 through the second pump 11. The second pump 11 can be a slurry type canned pump.

[0043] Please refer to Figure 2The intermediate separation device 2 comprises a tower body 21, a flow guide frame 22, a filter plate 23, a flow guide plate 24, and a heating element 25. The tower body 21 is provided with a feed inlet 211 at the top, which is the inlet of the intermediate separation device 2. The tower body 21 is provided with a preheating zone 214 at the bottom, and the heating element 25 is arranged in the preheating zone 214 for heating the preheating zone 214. The preheating zone 214 is provided with a first discharge outlet 212, which is the solid outlet of the intermediate separation device 2. The flow guide frame 22 is arranged below the feed inlet 211, the filter plate 23 is arranged below the flow guide frame 22, and the filter plate 23 is arranged obliquely. The lower end of the filter plate 23 is connected to the preheating zone 214 through a pipeline 26. The flow guide plate 24 is arranged below the filter plate 23 and is arranged obliquely. The tower body 21 is also provided with a second discharge outlet 213, which is the liquid outlet of the intermediate separation device 2, and the second discharge outlet 213 is located on one side of the lower end of the flow guide plate 24. In this way, the isocyanate in the liquid phase, the solvent in the liquid phase, and the carbamoyl chloride in the solid phase enter the tower body 21 from the feed inlet 211, and after being guided by the flow guide frame 22, they fall onto the filter plate 23. Since the filter plate 23 is provided with filter holes, the liquid can flow through the filter holes to the lower side of the filter plate 23, while the solid remains on the upper side of the filter plate 23, thereby separating the liquid phase components (isocyanate and solvent) and the solid phase components (carbamoyl chloride). Since the flow guide plate 24 is arranged below the filter plate 23, the flow guide plate 24 can guide the isocyanate and solvent in the liquid phase to the second discharge outlet 213 and discharge them from the second discharge outlet 213. After passing through the filter plate 23, the kinetic energy of the liquid decreases, and the flow rate slows down. The inclined arrangement of the flow guide plate 24 is conducive to guiding the flow of the liquid, and can maintain a certain liquid level in the tower body 21 near the second discharge outlet 213, thereby avoiding the risk of gas entering the first pump 10 and causing cavitation of the first pump 10 due to the small instantaneous flow. Since the lower end of the filter plate 23 is connected to the preheating zone 214 through the pipeline 26, the carbamoyl chloride above the filter plate 23 enters the preheating zone 214 through the pipeline 26, and after being heated by the heating element 25, it is discharged from the first discharge outlet 212. The oblique arrangement of the filter plate 23 is conducive to the falling of the carbamoyl chloride into the pipeline 26. The preheating zone 214 arranged at the bottom of the tower body 21 preheats the carbamoyl chloride, which can make the carbamoyl chloride become a molten state, thereby facilitating the transportation of the carbamoyl chloride in the downstream pipeline and facilitating the subsequent heating of the carbamoyl chloride by the heater 3 to the decomposition temperature.

[0044] In an embodiment, the preheating temperature of the preheating zone 214 is 100-130°C, which can make the carbamoyl chloride become a molten state. The heating element 25 is a heating pipe, and the preheating zone 214 can be provided with multiple channels. The heating element 25 is arranged between the multiple channels, and the carbamoyl chloride can be simultaneously transported from the multiple channels to the first discharge outlet 212, so that when the carbamoyl chloride passes through the preheating zone 214, the heating element 25 can sufficiently heat the carbamoyl chloride, so that the carbamoyl chloride becomes a molten state that is easy to flow.

[0045] Further, the flow guide frame 22 comprises a first flow guide part 221 and a second flow guide part 222, the first flow guide part 221 is tapered and the acute angle is upward, and the second flow guide part 222 is connected to the lower end of the first flow guide part 221 and extends downward. In this way, the first flow guide part 221 can guide the fluid to the upper end of the filter plate 23, and by setting a suitable inclination angle and length of the filter plate 23, sufficient residence time can be provided, so that the liquid phase component and the solid phase component can be fully separated. The second flow guide part 222 is arranged to make the distance between the flow guide frame 22 and the filter plate 23 smaller, so as to reduce the speed of the fluid falling on the filter plate 23, avoid the solid phase carbamoyl chloride from being impacted with the liquid phase component to the lower side of the filter plate 23 due to too large flow rate of the fluid, and thus ensure the filtering effect.

[0046] In the embodiment, the filter plate 23 is funnel-shaped, the upper end of the filter plate 23 is connected to the tower body 21, and the lower end is connected to the pipeline 26. The funnel-shaped filter plate 23 is beneficial to the automatic sliding of the solid phase carbamoyl chloride into the pipeline 26, and the falling of the solid phase carbamoyl chloride to the preheating zone 214 through the pipeline 26.

[0047] Further, the filter hole has a mesh number of 10 to 30, which can effectively separate the carbamoyl chloride.

[0048] Further, the pipeline 26 is provided with an automatic valve 27 for controlling the opening and closing of the pipeline 26. In this way, the delivery speed of the carbamoyl chloride can be controlled according to the needs, so as to control the residence time of the fluid on the filter plate 23, and thus the separation efficiency of the carbamoyl chloride can be controlled.

[0049] Please refer to Figure 1 and Figure 2 , the application further provides a method for refining isocyanate, which is carried out by using the isocyanate refining system as described above, and the method comprises:

[0050] The isocyanate photochemical liquid after the phosgenation reaction is transported to a gas-liquid separation device 1 for gas-liquid separation. The heavy components (including isocyanate, solvent and carbamoyl chloride) are output from the heavy component outlet at the bottom of the gas-liquid separation device 1 and enter an intermediate separation device 2 for solid-liquid separation. The liquid phase components enter a desolventizing rectification tower 5 for desolventizing rectification. The isocyanate liquid after removal of the solvent enters a product rectification tower 6 for rectification and purification. The solid phase components are heated by a heater 3 to decompose into isocyanate liquid and hydrogen chloride gas. The decomposition products enter an intermediate storage tank 4. The isocyanate liquid in the intermediate storage tank 4 enters the product rectification tower 6 for rectification and purification. The isocyanate purification method separates the carbamoyl chloride and then decomposes it by heating, thereby omitting the step of feeding the carbamoyl chloride into the falling film heater 3 together with the isocyanate for high-temperature treatment. The residence time of the isocyanate in the entire liquid phase treatment process is reduced, thereby reducing the heating time of the isocyanate and the polymerization of the isocyanate, and improving the yield of the isocyanate. The method can simply and efficiently purify the isocyanate and improve the yield of the isocyanate. Moreover, the separation of the solid-phase carbamoyl chloride can avoid the blockage of the downstream pipeline equipment by the isocyanate entraining a large amount of carbamoyl chloride. In addition, since the hydrogen chloride has a catalytic effect on the polymerization of the isocyanate, the separation of the carbamoyl chloride and the separation of the gas-phase hydrogen chloride and the liquid-phase isocyanate in the gas-liquid separation device 1 and the intermediate storage tank 4 can avoid the catalytic effect of the hydrogen chloride on the isocyanate in the rectification process, thereby reducing the polymerization of the isocyanate and improving the yield of the isocyanate.

[0051] The isocyanate purification method further includes that the light components (including hydrogen chloride and phosgene) after the gas-liquid separation in the gas-liquid separation device 1 are output from the light component outlet at the top of the gas-liquid separation device 1 and enter a phosgene cooler 7. The hydrogen chloride gas in the intermediate storage tank 4 also enters the phosgene cooler 7. In the phosgene cooler 7, the hydrogen chloride and the phosgene are separated. The phosgene enters a phosgene recovery device 8. The hydrogen chloride enters a drying tower 9. The dried hydrogen chloride gas can be obtained after drying in the drying tower 9.

[0052] Further, the isocyanate photochemical liquid is cooled to 80-90°C before entering the gas-liquid separation device 1. Since the intermediate carbamoyl chloride exists in the isocyanate photochemical liquid, the carbamoyl chloride is in a solid phase at 80-90°C, which facilitates the separation of the carbamoyl chloride from the liquid-phase isocyanate and solvent.

[0053] Since the phosgenation reaction is a reversible reaction, increasing the residence time of the coexistence of isocyanate and hydrogen chloride will increase the content of carbamoyl chloride in the isocyanate photochemical liquid. The residence time of the coexistence of isocyanate and hydrogen chloride can be controlled by controlling the feeding speed and discharging speed of the gas-liquid separation device 1, thereby controlling the content of carbamoyl chloride in the photochemical liquid.

[0054] The heavy component outputted from the gas-liquid separation device 1 is subjected to solid-liquid separation in the intermediate separation device 2. By selecting filter plates 23 with different mesh sizes and controlling the opening and closing time of the automatic valve 27, different separation efficiencies can be obtained. In this application, the separation efficiency of carbamoyl chloride is 60%-80% after the heavy component is separated by the intermediate separation device 2. It can be understood that the separation efficiency of carbamoyl chloride = the separated carbamoyl chloride divided by the total carbamoyl chloride in the heavy component. Since it is cumbersome to replace the filter plate 23, the filter plate 23 is usually not replaced, but the opening and closing time of the automatic valve 27 is controlled to obtain different separation efficiencies. In an embodiment, the automatic valve 27 is opened for 30s and closed for 30s, and the separation efficiency of carbamoyl chloride can reach 80%; the automatic valve 27 is opened for 30s and closed for 15s, and the separation efficiency of carbamoyl chloride is 70%; the automatic valve 27 is kept in an open state, and the separation efficiency of carbamoyl chloride is 60%.

[0055] Further, the heater 3 is heated to 140-170°C. At 140-170°C, the solid-phase carbamoyl chloride is decomposed into isocyanate and hydrogen chloride. Heating the heater 3 to 140-170°C is conducive to the complete decomposition of carbamoyl chloride.

[0056] The purification method of isocyanate is described in detail below in combination with specific embodiments.

[0057] Example 1

[0058] The hexamethylene diisocyanate photochemical liquid (85°C) is fed into the gas-liquid separation device 1 for separation. The light component is outputted from the top of the gas-liquid separation device 1 and enters the phosgene cooler 7 for separation of phosgene and hydrogen chloride. The heavy component is outputted from the bottom of the gas-liquid separation device 1 and enters the intermediate separation device 2, and the heavy component contains 10wt% of carbamoyl chloride solid, 50wt% of chlorobenzene solvent, and 40wt% of hexamethylene diisocyanate. The “wt%” represents the weight percentage. After the heavy component is separated by the intermediate separation device 2, the separation efficiency of carbamoyl chloride is 80%. The separated liquid enters the desolventization rectification column 5 for rectification, and then enters the product rectification column 6 for rectification and purification. The separated carbamoyl chloride is heated to 160°C by the heater 3, and is decomposed into hexamethylene diisocyanate liquid and hydrogen chloride gas, which are subjected to gas-liquid phase separation by the intermediate storage tank 4. The liquid enters the product rectification column 6 for rectification and purification, and finally the yield of isocyanate is 97.8%.

[0059] Example 2

[0060] The difference from Example 1 is that the separation efficiency of carbamoyl chloride is 70% after the heavy component is separated by the intermediate separation device 2, and the final yield of isocyanate is 97.5%.

[0061] Example 3

[0062] The difference from Example 1 is that the separation efficiency of carbamoyl chloride after the recombined components are separated by the intermediate separation device 2 is 60%, and the final yield of isocyanate is 97.4%.

[0063] Example 4

[0064] The difference from Example 1 is that the temperature of the raw material hexamethylene diisocyanate photochemical solution is 80°C, and the carbamoyl chloride separated by the intermediate separation device 2 is heated to 140°C by the heater 3, and the final yield of isocyanate is 97.6%.

[0065] Example 5

[0066] The difference from Example 1 is that the recombined components entering the intermediate separation device 2 contain 15wt% of carbamoyl chloride solid, 50wt% of chlorobenzene solvent, and 35wt% of hexamethylene diisocyanate, and the final yield of isocyanate is 97.6%.

[0067] Example 6

[0068] The difference from Example 5 is that the separation efficiency of carbamoyl chloride after the recombined components are separated by the intermediate separation device 2 is 70%, and the final yield of isocyanate is 97.3%.

[0069] Example 7

[0070] The difference from Example 5 is that the separation efficiency of carbamoyl chloride after the recombined components are separated by the intermediate separation device 2 is 60%, and the final yield of isocyanate is 97.2%.

[0071] Example 8

[0072] The difference from Example 5 is that the carbamoyl chloride separated by the intermediate separation device 2 is heated to 140°C by the heater 3, and the final yield of isocyanate is 97.4%.

[0073] Example 9

[0074] The difference from Example 1 is that the recombined components entering the intermediate separation device 2 contain 20wt% of carbamoyl chloride solid, 50wt% of chlorobenzene solvent, and 20wt% of hexamethylene diisocyanate, and the final yield of isocyanate is 97%.

[0075] Example 10

[0076] The difference from Example 9 is that the separation efficiency of carbamoyl chloride after the recombined components are separated by the intermediate separation device 2 is 70%, and the final yield of isocyanate is 96.9%.

[0077] Example 11

[0078] The difference from Example 9 is that the carbamoyl chloride separated by the intermediate separation device 2 has a separation efficiency of 60%, and the final isocyanate yield is 96.7%.

[0079] Example 12

[0080] The difference from Example 9 is that the carbamoyl chloride separated by the intermediate separation device 2 is heated to 140°C by the heater 3, and the final isocyanate yield is 96.6%.

[0081] Example 13

[0082] The difference from Example 1 is that the isocyanate photochemical liquid fed into the gas-liquid separation device 1 is isophorone diisocyanate photochemical liquid (90°C). The recombined components contain 10wt% carbamoyl chloride solid, 50wt% chlorobenzene solvent, and 40wt% isophorone diisocyanate. After the recombined components are separated by the intermediate separation device 2, the separation efficiency of the carbamoyl chloride is 80%. The separated carbamoyl chloride is heated to 170°C by the heater 3, and decomposed into isophorone diisocyanate liquid and hydrogen chloride gas. The final isocyanate yield is 98.2%.

[0083] Comparative Example 1

[0084] The hexamethylene diisocyanate photochemical liquid (85°C) is fed into the gas-liquid separation device 1 for separation. The light components are output from the top of the gas-liquid separation device 1 and enter the phosgene cooler 7 for separation of phosgene and hydrogen chloride. The recombined components (containing 10wt% carbamoyl chloride solid, 50wt% chlorobenzene solvent, and 40wt% hexamethylene diisocyanate) all enter the rectification tower for rectification purification, and the temperature in the rectification tower is 160°C. Due to the slow decomposition of the carbamoyl chloride caused by the solvent, the decomposed hydrogen chloride is not separated in time, and more catalyst is generated, resulting in a decrease in the final isocyanate yield to 95.8%.

[0085] Comparative Example 2

[0086] The difference from Comparative Example 1 is that the recombined components contain 15wt% carbamoyl chloride solid, 50wt% chlorobenzene solvent, and 35wt% hexamethylene diisocyanate, and the final isocyanate yield is 95.5%.

[0087] Comparative Example 3

[0088] The difference from Comparative Example 1 is that the recombined components contain 20wt% carbamoyl chloride solid, 50wt% chlorobenzene solvent, and 20wt% hexamethylene diisocyanate, and the final isocyanate yield is 94.7%.

[0089] Comparative Example 4

[0090] The difference between the example 1 and the comparative example 1 is that the isocyanate photochemical solution fed into the gas-liquid separation device 1 is isophorone diisocyanate photochemical solution (90℃). The heavy component contains 10wt% carbamoyl chloride solid, 50wt% chlorobenzene solvent and 40wt% isophorone diisocyanate, the temperature in the rectifying tower is 170℃, and the final isocyanate yield is 96.3%.

[0091] The relevant data of the examples 1-13 and the comparative examples 1-4 are shown in the following table.

[0092]

[0093]

[0094] As can be seen, by separating the carbamoyl chloride and then heating and decomposing and then rectifying and purifying, the yield of isocyanate can be improved.

[0095] The technical features of the above examples can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above examples are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the description.

[0096] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are all within the scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A purification system for isocyanates, characterized in that, include: Gas-liquid separation unit, intermediate separation unit, heater, intermediate storage tank, solvent removal distillation column, and product distillation column. The gas-liquid separator has a heavy component outlet, which is connected to the inlet of the intermediate separation device. The liquid outlet of the intermediate separation device is connected to the inlet of the solvent removal distillation column, and the liquid outlet of the solvent removal distillation column is connected to the inlet of the product distillation column. The solid outlet of the intermediate separation device is connected to the inlet of the heater, the outlet of the heater is connected to the inlet of the intermediate storage tank, and the liquid outlet of the intermediate storage tank is connected to the inlet of the finished product distillation column. The heavy components include liquid isocyanate, liquid solvent and solid carbamoyl chloride, and the separation efficiency of carbamoyl chloride after separation by the intermediate separation device is 60%-80%. The solid carbamoyl chloride is heated and decomposed into liquid isocyanate and hydrogen chloride gas by the heater, and the decomposition products enter the intermediate storage tank.

2. The isocyanate purification system according to claim 1, characterized in that, The intermediate separation device includes a tower body, a flow guide frame, a filter plate, a flow diversion plate, and a heating element. The tower body has a feed inlet at the top, which serves as the inlet for the intermediate separation device. A preheating zone is located at the bottom of the tower body, and a heating element is disposed in the preheating zone to heat it. The preheating zone has a first discharge outlet, which serves as the solid outlet for the intermediate separation device. The flow guide frame is located below the feed inlet, and the filter plate is located below the flow guide frame. The filter plate has filter holes and is inclined. The lower end of the filter plate is connected to the preheating zone via a pipe. The flow guide plate is located below the filter plate and is inclined. The tower body is also provided with a second discharge port, which is the liquid outlet of the intermediate separation device. The second discharge port is located on one side of the lower end of the flow guide plate.

3. The isocyanate purification system according to claim 2, characterized in that, The flow guide includes a first flow guide and a second flow guide. The first flow guide is conical with its pointed corner facing upwards. The second flow guide is connected to the lower end of the first flow guide and extends downwards.

4. The isocyanate purification system according to claim 2, characterized in that, The filter plate is funnel-shaped; And / or, the mesh size of the filter holes is 10 to 30 mesh.

5. The isocyanate purification system according to claim 2, characterized in that, The pipeline is equipped with a self-regulating valve to control the opening and closing of the pipeline.

6. The isocyanate purification system according to claim 1, characterized in that, It also includes phosgene coolers, phosgene recovery units, and drying towers. The gas outlet of the gas-liquid separator is connected to the inlet of the phosgene cooler. The phosgene cooler has a phosgene outlet and a hydrogen chloride gas outlet. The phosgene outlet is connected to the inlet of the phosgene recovery device, and the hydrogen chloride gas outlet is connected to the inlet of the drying tower. The gas outlet of the intermediate storage tank is connected to the inlet of the phosgene cooler.

7. The isocyanate purification system according to claim 1, characterized in that, A first pump is provided between the liquid outlet of the intermediate separation device and the inlet of the solvent removal distillation column; And / or, a second pump is provided between the liquid outlet of the intermediate storage tank and the inlet of the finished product distillation column.

8. The isocyanate purification system according to claim 1, characterized in that, The isocyanate includes hexamethylene diisocyanate or isophorone diisocyanate.

9. A method for purifying isocyanates, characterized in that, The purification of isocyanates is carried out using the isocyanate purification system as described in any one of claims 1-8, wherein the isocyanate purification method comprises: The isocyanate photochemical liquid after phosgenation reaction is transported to a gas-liquid separation device for gas-liquid separation. The heavy component is output from the heavy component outlet of the gas-liquid separation device and enters the intermediate separation device for solid-liquid separation. The liquid component enters the solvent removal distillation column for solvent removal distillation. The isocyanate liquid after solvent removal enters the product distillation column for distillation purification. The solid component is heated and decomposed into isocyanate liquid and hydrogen chloride gas by a heater. The decomposition products enter the intermediate storage tank, and the isocyanate liquid in the intermediate storage tank enters the product distillation column for distillation and purification.

10. The method for purifying isocyanate according to claim 9, characterized in that, The heavy components include isocyanate, solvent and carbamoyl chloride. After the heavy components are separated by the intermediate separation device, the separation efficiency of carbamoyl chloride is 60%-80%.

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