CN117101166A - System and method for refining isocyanate - Google Patents

Abstract

The application relates to a refining system and a refining method of isocyanate, wherein the refining system of isocyanate comprises: the device comprises a gas-liquid separation device, an intermediate separation device, a heater, an intermediate storage tank, a desolventizing rectifying tower and a finished rectifying tower, wherein 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 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 rectifying tower. The application can improve the yield of isocyanate by separating and decomposing the carbamoyl chloride.

Description

System and method for refining isocyanate

Technical Field

The application relates to the technical field of isocyanate preparation, in particular to a refining system and method of isocyanate.

Background

Isocyanate is widely applied to various fields of industrial production, military industry, aerospace and the like, hexamethylene Diisocyanate (HDI) belongs to a high-end product category in an isocyanate family, has unique and excellent yellowing resistance, weather resistance and chemical resistance, and is mainly applied to the fields of coating, adhesives, food packaging and the like. However, the isocyanate series products are heat-sensitive substances, and liquid isocyanate can automatically polymerize to form a polymer in a short time under the heated condition, so that the product yield is reduced, and the problems of blockage, coking and the like of production equipment are caused, and therefore, a simple and efficient method for purifying the isocyanate is urgently needed.

In CN103922969B, it is mentioned that hexamethylenediamine and phosgene are subjected to phosgenation reaction in a reaction zone, the content of low-boiling-point components in the fed hexamethylenediamine is reduced to be less than or equal to 50mg/kg, the content of impurities in raw materials is reduced, the generation of phosgenation reaction impurities is reduced, and finally the obtained isocyanate has good color stability.

CN110511164a patent states that in both gas phase phosgenation and liquid phase phosgenation, both the mixing of the raw materials and the reaction residence time are critical parameters, and proposes a scheme to limit residence time in the reaction section to reduce side reactions and retention of amine residues etc. in the reaction quench liquid.

The CN110891932a patent uses a reaction solution after quenching with less than 5% solvent, even without solvent, as a quenching agent, and operates with low solvent content, so that the post-treatment can be simplified, the downstream apparatus becomes smaller, and the energy consumption is reduced. However, lowering the quench solvent content increases the formation of byproducts, which may result in increased byproducts, poor product quality, or increased deposit formation.

US9593075 mentions the removal of HCl (hydrogen chloride) and phosgene from crude isocyanate because the co-existence of product isocyanate with hydrogen chloride and phosgene can lead to side reactions, so separation of HCl and phosgene is considered to reduce the formation of acid chlorides and urea compounds in the product.

In summary, most of the prior patents focus on improving the synthesis yield of isocyanate by reducing the content of impurities in raw materials and reducing or separating substances capable of generating side reactions, while the loss of the yield of isocyanate is mainly focused on recycling of the scraps, 20% -30% of components in the scraps are not recyclable, 5% -10% of isocyanate is not recyclable due to a high-temperature rectification mode during recycling of the scraps, and the content of isocyanate polymer in 25% -40% of non-recyclable components is as high as 50%, the polymer is mainly generated by isocyanate polymerization under heating, and the influence of temperature on isocyanate polymerization is hardly changed.

Disclosure of Invention

Accordingly, it is necessary to provide a system and a method for purifying isocyanate, which can simply and efficiently purify isocyanate and increase the yield of isocyanate.

A refining system for isocyanate comprising: the device comprises a gas-liquid separation device, an intermediate separation device, a heater, an intermediate storage tank, a desolventizing rectifying tower and a finished rectifying tower, wherein 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 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 rectifying tower.

In one embodiment, the intermediate separating device comprises a tower body, a flow guiding frame, a filter plate, a flow guiding plate and a heating element, wherein a feed inlet is formed in the top of the tower body, the feed inlet is an inlet of the intermediate separating device, a preheating zone is formed in the bottom of the tower body, the heating element is arranged in the preheating zone and used for heating the preheating zone, a first discharge outlet is formed in the preheating zone, the first discharge outlet is a solid outlet of the intermediate separating device, the flow guiding frame is arranged below the feed inlet, the filter plate is arranged below the flow guiding frame, a filter hole is formed in the filter plate, the filter plate is obliquely arranged, the lower end of the filter plate is communicated with the preheating zone through a pipeline, the flow guiding plate is arranged below the filter plate, the flow guiding plate is obliquely arranged, a second discharge outlet is further formed in the tower body and is a liquid outlet of the intermediate separating device, and the second discharge outlet is arranged on one side of the lower end of the filter plate.

In one embodiment, the flow guiding frame comprises a first flow guiding part and a second flow guiding part, wherein the first flow guiding part is conical, the sharp angle is upward, and the second flow guiding part is connected to the lower end of the first flow guiding part and extends downward.

In one embodiment, the filter plate is funnel-shaped;

and/or the mesh number of the filtering holes is 10 to 30 mesh.

In one embodiment, the pipeline is provided with a self-control valve for controlling the on-off of the pipeline.

In one embodiment, the device further comprises a phosgene cooler, a phosgene recovery device and a drying tower, wherein a gas outlet of the gas-liquid separation device is connected with an inlet of the phosgene cooler, the phosgene cooler is provided with a phosgene outlet and a hydrogen chloride gas outlet, the phosgene outlet is connected with an inlet of the phosgene recovery device, the hydrogen chloride gas outlet is connected with an inlet of the drying tower, and a gas outlet of the intermediate storage tank is connected with an inlet of the phosgene cooler.

In one embodiment, a first pump is arranged between the liquid outlet of the intermediate separating device and the inlet of the desolventizing rectifying tower;

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.

In one embodiment, the isocyanate comprises hexamethylene diisocyanate or isophorone diisocyanate.

A method for refining isocyanate using the above-described system for refining isocyanate, the method comprising:

conveying the isocyanate photochemical liquid after the phosgenation reaction into a gas-liquid separation device for gas-liquid separation, wherein heavy components are output from a heavy component outlet of the gas-liquid separation device and enter an intermediate separation device for solid-liquid separation, liquid phase components enter a desolventizing rectifying tower for desolventizing rectification, and the isocyanate liquid after the solvent removal enters a finished product rectifying tower for rectifying and purifying;

the solid phase component is heated and decomposed into isocyanate liquid and hydrogen chloride gas by a heater, the decomposed product enters an intermediate storage tank, and the isocyanate liquid in the intermediate storage tank enters a finished product rectifying tower for rectifying and purifying.

In one embodiment, the heavy component comprises isocyanate, solvent and carbamoyl chloride, and the separation efficiency of the carbamoyl chloride is 60% -80% after the heavy component is separated by the intermediate separation device.

Compared with the prior art, the system and the method for refining the isocyanate provided by the application have the advantages that the intermediate separating device is arranged to separate the solid-phase carbamoyl chloride from the liquid-phase isocyanate and the solvent, and then the liquid-phase and the solid-phase are subjected to subsequent treatment, wherein the liquid-phase is subjected to desolventizing rectification and finished product rectification, the solid-phase is subjected to thermal decomposition to form the isocyanate, and then the finished product rectification is carried out, so that the step that the carbamoyl chloride enters the falling film heater along with the isocyanate to be subjected to high-temperature treatment is omitted, the residence time of the isocyanate in the whole liquid-phase treatment process is shortened, the heating time of the isocyanate is shortened, the polymerization condition of the isocyanate is reduced, and the yield of the isocyanate is improved. And, by separating the carbamoyl chloride in the solid phase, the blockage of downstream pipeline equipment by the isocyanate entrained with a large amount of carbamoyl chloride can be avoided. In addition, because the hydrogen chloride has a catalytic effect on the polymerization of isocyanate, the application separates the carbamoyl chloride and then decomposes, and the gas-liquid separation device and the intermediate storage tank separate the gaseous hydrogen chloride from the liquid-phase isocyanate, the catalytic effect of the hydrogen chloride on the isocyanate in the rectification process can be avoided, thereby reducing the polymerization of isocyanate and improving the yield of isocyanate.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments or the conventional techniques of the present application, the drawings required for the descriptions of the embodiments or the conventional techniques will be briefly described below, and it is apparent that the drawings in the following descriptions are only some embodiments of the present application, and other drawings may be obtained according to the drawings without inventive effort for those skilled in the art.

FIG. 1 is a schematic diagram of an isocyanate refining system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of an intermediate separating device according to an embodiment of the application.

Reference numerals: 1. a gas-liquid separation device; 2. an intermediate separating device; 3. a heater; 4. an intermediate storage tank; 5. a desolventizing rectifying tower; 6. a finished product rectifying tower; 7. a phosgene cooler; 8. a phosgene recovery device; 9. a drying tower; 10. a first pump; 11. a second pump; 21. a tower body; 211. a feed inlet; 212. a first discharge port; 213. a second discharge port; 214. a preheating zone; 22. a flow guiding frame; 221. a first flow guiding part; 222. a second flow guiding part; 23. a filter plate; 24. a drainage plate; 25. a heating member; 26. a pipe; 27. and a self-control valve.

Detailed Description

In order that the above objects, features and advantages of the application will be readily understood, a more particular description of the application will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the application, whereby the application is not limited to the specific embodiments disclosed below.

It will be understood that when an element is referred to as being "mounted" or "disposed" on another element, it can be directly on the other element or intervening elements may also be present. When a component is considered to be "connected" to another component, it can be directly connected to the other component or intervening components may also be present. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and the like are used in the description of the present application for the purpose of illustration only and do not represent the only embodiment.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present application, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.

In the present application, unless expressly stated or limited otherwise, a first feature "up" or "down" on a second feature may be that the first feature is in direct contact with the second feature, or that the first feature and the second feature are in indirect contact through intermedial media. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely under the second feature, or simply indicating that the first feature is less level than the second feature.

Unless defined otherwise, 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 this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used in the description of the present application includes any and all combinations of one or more of the associated listed items.

The application provides a refining system of isocyanate, which takes isocyanate photochemical liquid as a raw material to refine and purify isocyanate. Wherein the isocyanate comprises any one of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate and diphenylmethane diisocyanate.

The isocyanate photochemical liquid is a product obtained after phosgenation reaction, and the reaction equation for generating isocyanate by the phosgenation reaction is as follows:

through a plurality of experiments, it is found that an intermediate carbamoyl chloride is inevitably present after the reaction is quenched by an photochemical liquid in the presence of a large amount of hydrogen chloride because the reaction is reversible. Thus, the main components of the isocyanate photochemical liquid include: phosgene, hydrogen chloride, isocyanates, solvents and carbamoyl chloride. Among them, the solvent may be chlorobenzene, xylene, dichlorobenzene, or meta-xylene, etc. Carbamoyl chloride has a low freezing point and is poorly soluble in isocyanate and solvents and breaks down into isocyanate and hydrogen chloride at high temperatures. Due to the low solidifying point and indissolvable property of the carbamoyl chloride, the carbamoyl chloride is solid in isocyanate photochemical liquid, and is easy to block downstream liquid phase rectifying equipment. In the prior art, before liquid phase rectification, carbamoyl chloride is firstly introduced into a falling film heater along with isocyanate for high-temperature treatment, and then decomposed into isocyanate and hydrogen chloride, and then liquid phase rectification is carried out. However, since hydrogen chloride has a catalytic effect on isocyanate polymerization, carbamoyl chloride firstly enters a falling film heater along with isocyanate for high-temperature treatment and then is subjected to liquid phase rectification, so that the isocyanate is heated for a long time, and the isocyanate is easy to polymerize, so that the yield of the isocyanate is low. The application provides a refining system of isocyanate, which can reduce the heating time of isocyanate by separating intermediate carbamoyl chloride, thereby reducing the occurrence of polymer and improving the yield of isocyanate.

Referring to fig. 1, the refining system of isocyanate provided by the present application includes: a gas-liquid separation device 1, an intermediate separation device 2, a heater 3, an intermediate storage tank 4, a desolventizing rectifying tower 5 and a finished product rectifying tower 6. In FIG. 1, a represents an isocyanate photochemical liquid, b represents a light component, c represents a hydrogen chloride gas, d represents a heavy component, e represents isocyanate and a solvent, f represents carbamoyl chloride, g represents a hydrogen chloride gas, h represents an isocyanate liquid, i represents a rectified tail gas, j represents a pure isocyanate liquid, and k represents a heel.

The gas-liquid separation device 1 is used for performing gas-liquid separation on isocyanate photochemical liquid, and the gas-liquid separation device 1 is provided with a heavy component outlet and a light component outlet, and the heavy component outlet is connected with the inlet of the intermediate separation device 2. The light components (including gaseous hydrogen chloride and phosgene) in the isocyanate photochemical liquid are discharged from the light component outlet, and the heavy components (including liquid-phase isocyanate, liquid-phase solvent and solid-phase carbamoyl chloride) are discharged from the heavy component outlet and enter the intermediate separating device 2 through the inlet. The intermediate body separating device 2 is used for carrying out solid-liquid separation on substances entering the intermediate body separating device 2, and the intermediate body separating device 2 is provided with a liquid outlet and a solid outlet. The isocyanate and solvent in the liquid phase are discharged from the liquid outlet of the intermediate separating device 2, and the carbamoyl chloride in the solid phase is discharged from the solid outlet of the intermediate separating device. The liquid outlet of the intermediate separating device 2 is connected with the inlet of the desolventizing rectifying tower 5, and the isocyanate and the solvent in liquid phase enter the desolventizing rectifying tower 5 for rectification. The desolventizing rectifying tower 5 is provided with a liquid outlet and a gas outlet, the liquid outlet of the desolventizing rectifying tower 5 is connected with the inlet of the finished rectifying tower 6, the isocyanate liquid after the solvent removal by rectification enters the finished rectifying tower 6 for rectification and purification, so that an isocyanate product is obtained, and the rectification tail gas is discharged from the gas outlet of the desolventizing rectifying tower 5. The solid outlet of the intermediate separating 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 solid-phase carbamoyl chloride is heated and decomposed into liquid-phase isocyanate and gas-phase hydrogen chloride by the heater 3 and enters the intermediate storage tank 4. The intermediate tank 4 has a liquid outlet and a gas outlet, the decomposition product after the carbamoyl chloride is heated is subjected to gas-liquid separation in the intermediate tank 4, the gaseous hydrogen chloride is discharged from the gas outlet, and the liquid isocyanate is discharged from the liquid outlet. The liquid outlet of the intermediate storage tank 4 is connected with the inlet of the finished product rectifying tower 6, and the isocyanate liquid from the intermediate storage tank 4 enters the finished product rectifying tower 6 for rectifying and purifying, so that an isocyanate product is obtained.

According to the isocyanate refining system, the intermediate separating device 2 is arranged to separate the solid-phase carbamoyl chloride from the liquid-phase isocyanate and the solvent, and then the liquid-phase and the solid-phase are subjected to subsequent treatment, wherein the liquid-phase is subjected to solvent removal rectification and finished product rectification, the solid-phase is subjected to thermal decomposition to form isocyanate, and then the finished product rectification is performed, so that the step that the carbamoyl chloride enters the falling film heater 3 along with the isocyanate to perform high-temperature treatment is omitted, the residence time of the isocyanate in the whole liquid-phase treatment process is shortened, the heating time of the isocyanate is shortened, the polymerization of the isocyanate is reduced, and the yield of the isocyanate is improved. And, by separating the carbamoyl chloride in the solid phase, the blockage of downstream pipeline equipment by the isocyanate entrained with a large amount of carbamoyl chloride can be avoided. In addition, because the hydrogen chloride has a catalytic effect on the polymerization of isocyanate, the application separates the carbamoyl chloride and then decomposes, and the gas-liquid separation device 1 and the intermediate storage tank 4 separate the gaseous hydrogen chloride from the liquid-phase isocyanate, so that the catalytic effect of the hydrogen chloride on the isocyanate in the rectification process can be avoided, the polymerization of isocyanate can be reduced, and the yield of isocyanate can be improved.

The isocyanate refining system further includes 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 a phosgene cooler 7, the phosgene cooler 7 is provided with a phosgene outlet and a hydrogen chloride gas outlet, the phosgene outlet is connected with the inlet of a phosgene recovery device 8, and the hydrogen chloride gas outlet is connected with the inlet of a drying tower 9. The gas outlet of the intermediate tank 4 is connected to the inlet of a phosgene cooler 7. Thus, the hydrogen chloride gas discharged from the gas outlet of the gas-liquid separator 1 and the phosgene enter the phosgene cooler 7, the hydrogen chloride gas discharged from the gas outlet of the intermediate storage tank 4 also enters the phosgene cooler 7, the phosgene and the hydrogen chloride are separated in the phosgene cooler 7, and the phosgene enters the phosgene recovery device 8 and the hydrogen chloride enters the drying tower 9 for drying.

Further, a first pump 10 is provided between the liquid outlet of the intermediate separating apparatus 2 and the inlet of the desolventizing rectifying column 5, and thus, the liquid discharged from the intermediate separating apparatus 2 is fed into the desolventizing rectifying column 5 by the first pump 10, and the first pump 10 may be a centrifugal pump.

Further, a second pump 11 is provided between the liquid outlet of the intermediate storage tank 4 and the inlet of the final rectifying tower 6, so that the liquid discharged from the intermediate storage tank 4 is transferred into the final rectifying tower 6 by the second pump 11, and the second pump 11 may be a slurry type canned motor pump.

Referring to fig. 2, the intermediate separating apparatus 2 includes a tower 21, a flow guiding frame 22, a filter plate 23, a flow guiding plate 24, and a heating member 25. The top of the tower body 21 is provided with a feed inlet 211, and the feed inlet 211 is an inlet of the intermediate separating device 2. The bottom of the tower body 21 is provided with a preheating zone 214, a 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 hole 212, and the first discharge hole 212 is a solid outlet of the intermediate separating device 2. The water conservancy diversion frame 22 is located the feed inlet 211 below, and water conservancy diversion frame 22 below is located to the filter 23, and the slope of filter 23 sets up, and the lower extreme of filter 23 passes through pipeline 26 intercommunication preheating zone 214, and the filter 23 below is located to the drainage board 24, and the drainage board 24 slope sets up, and tower body 21 still is equipped with second discharge gate 213, and second discharge gate 213 is the liquid outlet of midbody separator 2, and second discharge gate 213 is located drainage board 24 lower extreme one side. Thus, the isocyanate in liquid phase, the solvent in liquid phase and the carbamoyl chloride in solid phase enter the tower body 21 from the feed inlet 211 and flow-guide by the flow-guide frame 22 and fall onto the filter plate 23, and since the filter plate 23 is provided with the filter holes, the liquid can flow below the filter plate 23 through the filter holes, and the solids remain above the filter plate 23, thereby separating the liquid phase components (isocyanate and solvent) and the solid phase components (carbamoyl chloride). Since the drainage plate 24 is arranged below the filter plate 23, the drainage plate 24 can drain the isocyanate and the solvent in the liquid phase to the second discharge port 213 and discharge the isocyanate and the solvent from the second discharge port 213. The kinetic energy of the liquid is reduced after passing through the filter plate 23, the flow speed is slowed, the drainage plate 24 is obliquely arranged, the liquid flow is guided, a certain liquid level can be kept at a position close to the second discharge hole 213 in the tower body 21, and the risk that gas enters the first pump 10 and causes cavitation of the first pump 10 due to small instantaneous flow can be avoided. Since the lower end of the filter plate 23 is communicated with the preheating zone 214 through the pipe 26, the carbamoyl chloride above the filter plate 23 enters the preheating zone 214 through the pipe 26 and is discharged from the first discharge port 212 after being heated by the heating member 25. The inclined arrangement of the filter plates 23 facilitates the dropping of the carbamoyl chloride into the conduit 26. The preheating zone 214 is arranged at the bottom of the tower body 21 to preheat the carbamoyl chloride, so that the carbamoyl chloride can be changed into a molten state, the conveying of the carbamoyl chloride in a downstream pipeline is facilitated, and the heating of the carbamoyl chloride to the decomposition temperature by the heater 3 is facilitated.

In one embodiment, preheating zone 214 may be preheated to a temperature of from 100 ℃ to 130 ℃ to bring the carbamoyl chloride to a molten state. The heating element 25 is a heat tracing pipe, the preheating zone 214 may be provided with a plurality of channels, the heating element 25 is disposed between the plurality of channels, and the carbamoyl chloride may be simultaneously conveyed from the plurality of channels to the first discharge port 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 flowable molten state.

Further, the guiding frame 22 includes a first guiding portion 221 and a second guiding portion 222, the first guiding portion 221 is tapered, and the tip angle is upward, and the second guiding portion 222 is connected to the lower end of the first guiding portion 221 and extends downward. In this way, the first guide 221 guides the fluid to the upper end of the filter plate 23, and by setting the proper inclination angle and length of the filter plate 23, a sufficient residence time can be provided so that the liquid phase component and the solid phase component can be sufficiently separated. The second guiding part 222 is arranged to make the distance between the guiding frame 22 and the filter plate 23 smaller, so that the speed of the fluid falling to the filter plate 23 can be reduced, and the solid-phase carbamoyl chloride is prevented from impacting below the filter plate 23 along with the liquid-phase component due to the overlarge fluid flow speed, thereby ensuring the filtering effect.

In this embodiment, the filter plate 23 is funnel-shaped, and the upper end of the filter plate 23 is connected to the tower 21 and the lower end is connected to the pipe 26. The funnel-shaped filter plate 23 facilitates the automatic sliding of the carbamoyl chloride in solid phase into the conduit 26 and through the conduit 26 down to the preheating zone 214.

Further, the mesh number of the filtration pores is 10 to 30 mesh, and the carbamoyl chloride can be effectively separated.

Further, a self-control valve 27 is arranged on the pipeline 26 for controlling the on-off of the pipeline 26. In this way, the transport speed of the carbamoyl chloride and thus the residence time of the fluid on the filter plate 23 can be controlled as desired, and thus the separation efficiency of the carbamoyl chloride can be controlled.

Referring to fig. 1 and 2, the present application further provides a method for refining isocyanate, which is performed by using the system for refining isocyanate as described above, and the method for refining isocyanate includes:

conveying isocyanate photochemical solution after phosgenation reaction into a gas-liquid separation device 1 for gas-liquid separation, wherein heavy components (comprising isocyanate, solvent and carbamoyl chloride) are output from a heavy component outlet at the bottom of the gas-liquid separation device 1 and enter an intermediate separation device 2 for solid-liquid separation, liquid phase components enter a desolventizing rectifying tower 5 for desolventizing rectification, and isocyanate liquid after solvent removal enters a finished rectifying tower 6 for rectifying and purifying; the solid phase component is heated and decomposed into isocyanate liquid and hydrogen chloride gas by a heater 3, the decomposed product enters an intermediate storage tank 4, and the isocyanate liquid in the intermediate storage tank 4 enters a finished product rectifying tower 6 for rectification and purification. According to the method for refining the isocyanate, the intermediate separation device 2 is used for separating the carbamoyl chloride and then carrying out heating decomposition, so that the step that the carbamoyl chloride enters the falling film heater 3 along with the isocyanate for high-temperature treatment is omitted, the residence time of the isocyanate in the whole liquid phase treatment process is shortened, the heating time of the isocyanate is shortened, the polymerization of the isocyanate is reduced, and the yield of the isocyanate is improved. The method can simply and efficiently purify the isocyanate and improve the yield of the isocyanate. And, by separating the carbamoyl chloride in the solid phase, the blockage of downstream pipeline equipment by the isocyanate entrained with a large amount of carbamoyl chloride can be avoided. In addition, because the hydrogen chloride has a catalytic effect on the polymerization of isocyanate, the application separates the carbamoyl chloride and then decomposes, and the gas-liquid separation device 1 and the intermediate storage tank 4 separate the gaseous hydrogen chloride from the liquid-phase isocyanate, so that the catalytic effect of the hydrogen chloride on the isocyanate in the rectification process can be avoided, the polymerization of isocyanate can be reduced, and the yield of isocyanate can be improved.

The refining method of isocyanate further comprises the following steps: the light components (including hydrogen chloride and phosgene) after gas-liquid separation in the gas-liquid separation device 1 are output from a 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 a phosgene cooler 7, hydrogen chloride and phosgene are separated in the phosgene cooler 7, the phosgene enters a phosgene recovery device 8, the hydrogen chloride enters a drying tower 9, and the dried hydrogen chloride gas can be obtained after the hydrogen chloride enters the drying tower 9 for drying.

Further, the isocyanate photochemical liquid is cooled to 80-90 ℃ before entering the gas-liquid separation device 1. As the intermediate carbamoyl chloride exists in the isocyanate photochemical liquid, the carbamoyl chloride is in a solid phase at 80-90 ℃ so as to be convenient for separation from the liquid phase isocyanate and the solvent.

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

The heavy components output from the gas-liquid separation device 1 are subjected to solid-liquid separation in the intermediate separation device 2, and different separation efficiencies can be obtained by selecting filter plates 23 with different mesh numbers of filter holes and controlling the opening and closing time of the self-control valve 27. In the application, after heavy components are separated by the intermediate separating device 2, the separating efficiency of the carbamoyl chloride is 60-80%. It is understood that the separation efficiency of carbamoyl chloride = isolated carbamoyl chloride divided by the total carbamoyl chloride in the heavy fraction. Because the operation of replacing the filter plate 23 is complicated, the filter plate 23 is not replaced normally, and different separation efficiencies are obtained by controlling the opening and closing time of the self-control valve 27. In one embodiment, the automatic control valve 27 is opened for 30 seconds and closed for 30 seconds, and the separation efficiency of the carbamoyl chloride can reach 80%; the self-control valve 27 is opened for 30s and closed for 15s, and the separation efficiency of the carbamoyl chloride is 70%; the self-control valve 27 is kept in a fully opened state, and the separation efficiency of carbamoyl chloride is 60%.

Further, the heater 3 is heated to 140-170 ℃. At 140-170 c, the carbamoyl chloride in the solid phase is decomposed into isocyanate and hydrogen chloride. The heater 3 is heated to 140-170 ℃ to facilitate the full decomposition of the carbamoyl chloride.

The method for purifying isocyanate will be described in detail with reference to specific examples.

Example 1

The hexamethylene diisocyanate photochemical liquid (85 ℃) is fed into the gas-liquid separation device 1 for separation, and the light component is output 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 output from the bottom of the gas-liquid separation device 1 and enters the intermediate separation device 2, wherein the heavy component contains 10 weight percent of carbamoyl chloride solid, 50 weight percent of chlorobenzene solvent and 40 weight percent of hexamethylene diisocyanate, and the weight percent is expressed as the weight percent. After the heavy component is separated by the intermediate separating device 2, the separating efficiency of the carbamoyl chloride is 80 percent. The separated liquid enters a desolventizing rectifying tower 5 for rectification and then enters a finished product rectifying tower 6 for rectification and purification. The separated carbamoyl chloride is heated to 160 ℃ by a heater 3 and is decomposed into hexamethylene diisocyanate liquid and hydrogen chloride gas, gas-liquid phase separation is carried out by an intermediate storage tank 4, the liquid enters a finished product rectifying tower 6 for rectification and purification, and the yield of the final isocyanate is 97.8%.

Example 2

The difference from example 1 is that the separation efficiency of carbamoyl chloride after the heavy component was separated by the intermediate separating apparatus 2 was 70% and the yield of the final isocyanate was 97.5%.

Example 3

The difference from example 1 is that the separation efficiency of carbamoyl chloride after the heavy component was separated by the intermediate separating apparatus 2 was 60% and the yield of the final isocyanate was 97.4%.

Example 4

The difference from example 1 is that the temperature of the raw material hexamethylene diisocyanate photochemical liquid was 80℃and the carbamoyl chloride separated by the intermediate separating device 2 was heated to 140℃by the heater 3, and the yield of the final isocyanate was 97.6%.

Example 5

The difference from example 1 is that the heavy fraction entering the intermediate separating device 2 contains 15% by weight of carbamoyl chloride solid, 50% by weight of chlorobenzene solvent, 35% by weight of hexamethylene diisocyanate and the final isocyanate yield is 97.6%.

Example 6

The difference from example 5 is that the separation efficiency of carbamoyl chloride after the heavy component was separated by the intermediate separating apparatus 2 was 70% and the yield of the final isocyanate was 97.3%.

Example 7

The difference from example 5 is that the separation efficiency of carbamoyl chloride after the heavy component was separated by the intermediate separating apparatus 2 was 60% and the yield of the final isocyanate was 97.2%.

Example 8

The difference from example 5 is that the carbamoyl chloride separated by the intermediate separating apparatus 2 was heated to 140 c by the heater 3 and the final isocyanate yield was 97.4%.

Example 9

The difference from example 1 is that the heavy fraction entering the intermediate separating device 2 contains 20% by weight of carbamoyl chloride solid, 50% by weight of chlorobenzene solvent, 20% by weight of hexamethylene diisocyanate and the final isocyanate yield is 97%.

Example 10

The difference from example 9 is that the separation efficiency of carbamoyl chloride after the heavy component was separated by the intermediate separating apparatus 2 was 70% and the yield of the final isocyanate was 96.9%.

Example 11

The difference from example 9 is that the separation efficiency of carbamoyl chloride after the heavy components were separated by the intermediate separating apparatus 2 was 60% and the yield of the final isocyanate was 96.7%.

Example 12

The difference from example 9 is that the carbamoyl chloride separated by the intermediate separating apparatus 2 was heated to 140 c by the heater 3 and the final isocyanate yield was 96.6%.

Example 13

The difference from example 1 is that the isocyanate actinic liquid fed to the gas-liquid separation device 1 is isophorone diisocyanate actinic liquid (90 ℃). The heavy component contains 10wt% of carbamoyl chloride solid, 50wt% of chlorobenzene solvent and 40wt% of isophorone diisocyanate. After the heavy component is separated by the intermediate separating device 2, the separating efficiency of the carbamoyl chloride is 80 percent. The separated carbamoyl chloride was heated to 170 c by a heater 3 to decompose isophorone diisocyanate liquid and hydrogen chloride gas, and the final isocyanate yield was 98.2%.

Comparative example 1

The hexamethylene diisocyanate photochemical liquid (85 ℃) is fed into the gas-liquid separation device 1 for separation, and the light component is output 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 components (the heavy components contain 10 weight percent of carbamoyl chloride solid, 50 weight percent of chlorobenzene solvent and 40 weight percent of hexamethylene diisocyanate) are all fed into a rectifying tower for rectification and purification, and the temperature in the rectifying tower is 160 ℃. The solvent causes slow decomposition time of the carbamoyl chloride, and the decomposed hydrogen chloride is not separated in time, so that more leftovers are generated by catalysis, and the yield of the final isocyanate is reduced to 95.8%.

Comparative example 2

The difference from comparative example 1 is that the heavy component contains 15% by weight of carbamoyl chloride solid, 50% by weight of chlorobenzene solvent, 35% by weight of hexamethylene diisocyanate, and the final isocyanate yield is 95.5%.

Comparative example 3

The difference from comparative example 1 is that the heavy component contains 20% by weight of carbamoyl chloride solid, 50% by weight of chlorobenzene solvent, 20% by weight of hexamethylene diisocyanate, and the final isocyanate yield is 94.7%.

Comparative example 4

The difference from comparative example 1 is that the isocyanate actinic liquid fed to the gas-liquid separation apparatus 1 is isophorone diisocyanate actinic liquid (90 ℃). The heavy component contains 10wt% of carbamoyl chloride solid, 50wt% of chlorobenzene solvent and 40wt% of isophorone diisocyanate, the temperature in the rectifying tower is 170 ℃, and the final isocyanate yield is 96.3%.

The data relating to examples 1-13 and comparative examples 1-4 are shown in the following table.

Therefore, the application can improve the yield of isocyanate by separating the carbamoyl chloride, then carrying out thermal decomposition and then rectification purification.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the claims. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of the application should be determined from the following claims.

Claims (10)

1. An 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 which is connected with the inlet of the intermediate separation device,

the liquid outlet of the intermediate separating device is connected with the inlet of the desolventizing rectifying tower, the liquid outlet of the desolventizing rectifying tower is connected with the inlet of the finished product rectifying tower,

the solid outlet of the intermediate separating 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 rectifying tower.

2. The isocyanate refining system according to claim 1, wherein the intermediate separating device comprises a tower body, a guide frame, a filter plate, a guide plate and a heating element,

the top of the tower body is provided with a feed inlet which is an inlet of the intermediate separating 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 which is a solid outlet of the intermediate separating 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 obliquely arranged, the lower end of the filter plate is communicated with the preheating zone through a pipeline,

the drainage plate is arranged below the filter plate, the drainage plate is obliquely arranged, the tower body is further provided with a second discharge hole, the second discharge hole is a liquid outlet of the intermediate separating device, and the second discharge hole is positioned at one side of the lower end of the drainage plate.

3. The isocyanate refining system according to claim 2, wherein the guide frame comprises a first guide portion and a second guide portion, the first guide portion is tapered and has an upward pointed end, and the second guide portion is connected to the lower end of the first guide portion and extends downward.

4. The isocyanate refining system of claim 2, wherein the filter plate is funnel-shaped;

and/or the mesh number of the filtering holes is 10 to 30 mesh.

5. The isocyanate refining system according to claim 2, wherein the pipeline is provided with a self-control valve for controlling the on-off of the pipeline.

6. The isocyanate refining system according to claim 1, further comprising a phosgene cooler, a phosgene recovery device and a drying tower,

the gas outlet of the gas-liquid separation device is connected with the inlet of the phosgene cooler, the phosgene cooler is provided with 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,

the gas outlet of the intermediate storage tank is connected with the inlet of the phosgene cooler.

7. The isocyanate refining system according to claim 1, wherein a first pump is provided between the liquid outlet of the intermediate separating device and the inlet of the desolventizing rectifying column;

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.

8. The isocyanate refining system according to claim 1, wherein the isocyanate comprises hexamethylene diisocyanate or isophorone diisocyanate.

9. A method for refining isocyanate using the system for refining isocyanate according to any one of claims 1 to 8, comprising:

conveying the isocyanate photochemical liquid after the phosgenation reaction into a gas-liquid separation device for gas-liquid separation, wherein heavy components are output from a heavy component outlet of the gas-liquid separation device and enter an intermediate separation device for solid-liquid separation, liquid phase components enter a desolventizing rectifying tower for desolventizing rectification, and the isocyanate liquid after the solvent removal enters a finished product rectifying tower for rectifying and purifying;

the solid phase component is heated and decomposed into isocyanate liquid and hydrogen chloride gas by a heater, the decomposed product enters an intermediate storage tank, and the isocyanate liquid in the intermediate storage tank enters a finished product rectifying tower for rectifying and purifying.

10. The method for refining isocyanate according to claim 1, wherein the heavy component comprises isocyanate, solvent and carbamoyl chloride, and the separation efficiency of the carbamoyl chloride is 60% -80% after the heavy component is separated by the intermediate separating device.