A method for preparing a crude isocyanate product with low copper content

Abstract

This invention discloses a method for preparing a crude isocyanate product with low copper content. The method uses copper-consuming substances and an inert solvent suitable for phosgenation processes as copper removal additives. The steps include: removing unreacted phosgene from a photochemical reaction solution containing isocyanate, phosgene, and other impurities; mixing the photochemical reaction solution with the unreacted phosgene removed and the copper removal additive, and performing a complexation reaction under ultrasonic conditions; cooling the resulting reaction solution to precipitate Cu complexes, followed by solid-liquid separation; stripping the liquid phase after solid-liquid separation with hydrogen chloride, and then removing the inert solvent under reduced pressure to obtain a crude isocyanate product with low copper content. After treatment by the above method, the copper impurity content in the crude isocyanate product is less than 3 ppm, thereby effectively improving product quality, reducing system blockage problems in subsequent separation processes, and the process is simple and has low operating costs.

Description

Technical Field

[0001] The invention belongs to the field of isocyanate and relates to a method for preparing a crude isocyanate product with low copper content in phosgenation reaction production. Background Art

[0002] Isocyanates all have -NCO functional groups in their molecular structures. Currently, phosgenation is mainly used to produce such substances at home and abroad. Under appropriate temperature and pressure conditions, polyamines, phosgene and inert solvents are mixed to obtain a photochemical reaction liquid containing isocyanates and hydrogen chloride. After separating the inert solvent and phosgene in the photochemical reaction liquid, a crude isocyanate product can be obtained. After separation of the crude product, an isocyanate product can be obtained.

[0003] During the production process of the above-mentioned crude isocyanate product, due to the trace amount of water contained in polyamines, phosgene and inert solvents, after combining with phosgene and hydrogen chloride during long-term operation, it corrodes the copper components contained in the main equipment materials, resulting in copper impurities in the photochemical reaction liquid and the crude isocyanate product.

[0004] In the process of producing isocyanates from polyamines and phosgene and separating them to obtain products, the presence of copper impurities is mainly affected by two aspects. First, in the process of separating phosgene, inert solvents and isocyanates, copper will promote the addition reaction of the -NCO group in the isocyanate molecule, especially the addition reaction with urea substances, and the molecular weight of the product will be further increased, making it difficult to dissolve in the crude isocyanate product. During the separation of the crude product, the vacuum unit and other equipment will be blocked, and the isocyanate will be consumed and the content of urea substances will be further increased, affecting the quality of the crude isocyanate product. Second, when the copper ion concentration of the crude isocyanate product is higher than 5ppm, the copper ions will gradually attach to the product poly-MDI during the separation process, thereby affecting the foaming strength of poly-MDI. Research on solving quality and clogging problems by controlling the content of copper impurities in the phosgenation reaction is currently rarely reported in patents and literature.

[0005] Patent CN113735377A discloses a method for removing copper from copper ammonia wastewater, which adds negative divalent sulfur ions to the wastewater in a precipitation unit to cause copper ions to react with the ions to form copper sulfide, which is then removed after a coagulation and precipitation step. This method can reduce the copper concentration to below 0.3 mg / , while the copper contaminant content in the crude isocyanate product needs to be reduced to below 1 ppm.

[0006] Patent CN201410685066.9 discloses a method for removing iron from a chloride salt solution containing iron ions and hydrogen ions. The method uses N, N-di(2-ethylhexyl)acetamide as an organic extractant and purifies the chloride salt by solvent extraction. The two phases in the extraction process of the patent are an organic phase and an aqueous phase. After adding the organic extractant, 2000-5000 ppm of amide compounds are easily mixed into the crude isocyanate product, which is difficult to remove in the existing separation system, resulting in a decrease in product quality.

[0007] Patent CN113981242 proposes a method for copper removal by adding an active agent to a nickel chloride solution, wherein nickel concentrate and water are uniformly mixed in a certain proportion, the mixed slurry is heated to 80-85°C and chlorine is introduced, and then the temperature is further raised to 100-110°C and an oxidation-reduction potential is applied at the same time, copper ions and nickel undergo a replacement reaction, are reduced to elemental copper and precipitate from the solution, thereby achieving the purpose of precipitation. Isocyanate will foam after reacting with water, and it is difficult to remove copper in an isocyanate system by replacement reaction.

[0008] Patent CN108559844A discloses a method for deep copper removal in a nickel solution, in which a chelating ion exchange resin is pretreated with a sodium hydroxide solution, a nickel chloride solution with a pH of 3-3.5 is passed through the resin to adsorb copper ions, and the resin is eluted with hydrochloric acid to enrich the copper. The ion exchange resin treated by this method is prone to residual sodium hydroxide solution, and isocyanate is prone to react with it. This method is obviously not suitable for isocyanate systems.

[0009] Although the above patents have certain effects on the removal of copper impurities, the precipitation, extraction, oxidation-reduction and ion exchange methods used have disadvantages, such as incomplete removal, easy reaction with -NCO groups or introduction of new impurities, etc., which are obviously not suitable for isocyanate systems. Therefore, it is necessary to design a method with high separation efficiency, simple operation and low operating cost, so as to control the content of copper impurities in the crude isocyanate product, improve product quality and solve the problem of system blockage. Summary of the invention

[0010] In view of the above problems existing in the prior art, the present invention provides a method for preparing a crude isocyanate product with a low copper content. In the process of producing isocyanate by the phosgene method, a copper-consuming substance is added to strictly reduce the copper content in the crude isocyanate product. The contents of copper impurities and urea substances in the obtained crude isocyanate product can be effectively controlled, the process flow is simple, and the copper removal effect is significant.

[0011] The copper impurities involved in the present invention can be introduced into the phosgenation system by any factors, and are described in detail in each embodiment by way of example, wherein typical sources may be pipelines, valves, vacuum units, reactors, and gas-liquid separation equipment, etc. The copper impurities exist in the form of copper ions with a valence of +1 or +2 or zero-valent metallic copper nanoparticles.

[0012] To achieve the above-mentioned object of the invention, the scheme of the present invention is as follows:

[0013] In a first aspect, the present invention provides a copper removal additive for a phosgenation reaction process, comprising: a copper-consuming substance and an inert solvent suitable for a phosgenation production process;

[0014] The copper-consuming substance is selected from carbodiimide compounds with a -N=C=N- group, preferably one or more of dicyclohexylcarbodiimide, 1,3-diisopropylcarbodiimide, and a compound having a structure shown in Formula 1.

[0015]

[0016] In the formula, R 1 Each independently selected from H, n is an integer of 1-12, preferably n=1;

[0017] More preferably, the copper-consuming substance is a compound having a structure shown in Formula 2,

[0018]

[0019] The dicyclohexylcarbodiimide, 1,3-diisopropylcarbodiimide, and the compound having the structure shown in Formula 1 are all existing substances and can be obtained by purchase or self-production. The present invention does not specifically limit their sources. For example, dicyclohexylcarbodiimide and 1,3-diisopropylcarbodiimide can be purchased commercially, and the compound having the structure shown in Formula 1 can be separated from the by-products of the reaction of MDI and triethyl phosphate. The specific process will not be repeated in the present invention.

[0020] In the present invention, the copper-consuming substance in the copper-removing additive is 8-15wt% of the mass of the inert solvent, preferably 10-12wt%.

[0021] In the present invention, the inert solvent is selected from one or more of m-toluene, xylene, chlorobenzene and o-dichlorobenzene, preferably chlorobenzene and / or o-dichlorobenzene, more preferably chlorobenzene.

[0022] In a second aspect, the present invention provides a method for preparing a crude isocyanate product with a low copper content, comprising the following steps:

[0023] (1) removing unreacted phosgene from a photochemical reaction liquid containing isocyanate, phosgene and other impurities;

[0024] (2) mixing the photochemical reaction liquid from which unreacted phosgene is removed in step (1) with the copper removal additive, and performing a complexation reaction under ultrasonic conditions;

[0025] (3) cooling the reaction solution obtained in step (2) to precipitate the Cu complex, and then performing solid-liquid separation;

[0026] (4) The liquid phase after the solid-liquid separation in step (3) is subjected to a stripping treatment using hydrogen chloride, and then the inert solvent is removed under reduced pressure to obtain a crude isocyanate product with a low copper content.

[0027] The photochemical reaction liquid containing isocyanate, phosgene and other impurities in step (1) of the present invention has a phosgenation reaction process that is a method disclosed in the prior art. The present invention does not specifically limit its specific preparation process. The technicians can prepare it by any feasible method based on the prior art according to the needs; for example, polyamine, phosgene and an inert solvent can be mixed under corresponding temperature and pressure conditions and then subjected to phosgenation reaction to obtain a photochemical reaction liquid containing isocyanate, unreacted phosgene and other impurities such as hydrogen chloride;

[0028] The isocyanate raw material monomer suitable for the method of the present invention is selected from diisocyanates, preferably diphenylmethylene diisocyanate (MDI), polydiphenylmethylene diisocyanate (PMDI), toluene diisocyanate (TDI), metaxylylene diisocyanate (XDI) or isophorone diisocyanate (IPDI);

[0029] The photochemical reaction liquid containing isocyanate, phosgene and other impurities, wherein the copper impurity content is 6-15ppm;

[0030] In the photochemical reaction liquid, the content of urea substances is 10000-25000ppm.

[0031] In addition, it is well known in the art that in the process of producing isocyanate by phosgenation, polyamine and isocyanate are prone to side reactions to generate urea substances, the general structural formula of which is shown in Formula 3:

[0032]

[0033] In the formula, R 2 for n is an integer of 1-12, preferably n=1;

[0034] The content of the urea substance in the photochemical reaction liquid after removing the unreacted phosgene is 10000-25000 ppm.

[0035] The inventors found during the research process that if the copper impurity content in the photochemical reaction liquid after the removal of unreacted phosgene is higher than 8 ppm and is not treated, the subsequent hydrogen chloride vaporization to remove the inert solvent will gradually catalyze the urea substance and isocyanate to generate urea addition products, resulting in the gradual consumption of isocyanates with lower molecular weight (such as 2,4-diphenylmethane diisocyanate) and the gradual increase of impurity content, ultimately resulting in the total content of urea substances and urea addition products in the crude isocyanate product (measured in mass fraction in the crude product) of 50,000-60,000 ppm.

[0036] The reaction equation of the above side reaction is as follows:

[0037]

[0038] In step (1) of the present invention, unreacted phosgene is removed by heat treatment. The heat treatment process is performed at a temperature of 150-170° C., preferably 160-165° C., for 10-30 min, preferably 25-28 min. The phosgene content in the reaction solution after treatment is reduced to 80-200 ppm.

[0039] In step (2) of the present invention, the copper removal additive is added in an amount of 1-1.5% by mass of the photochemical reaction liquid, preferably 1.25-1.3%.

[0040] In step (2) of the present invention, the complexation reaction is carried out in an ultrasonic stirring kettle, in which an ultrasonic generator is provided, and the ultrasound has a frequency of 25-35 kHz, preferably 28-30 Hz;

[0041] The stirring speed in the kettle is 1000-1500 rpm, preferably 1300-1350 rpm.

[0042] In step (2) of the present invention, the complexing reaction is carried out at a temperature of 100-120° C., preferably 110-113° C., and for a time of 10-20 min, preferably 17-18 min.

[0043] The inventors have found that the reaction time between copper and the carbodiimide copper-consuming substances added in the present invention is relatively long. Ultrasonic waves can form local high-temperature and high-pressure points through their cavitation effect, mechanical effect and thermal effect, thereby greatly accelerating the reaction process between copper and the carbodiimide structure, and the formed larger molecular complex can be precipitated in the reaction solution containing an inert solvent after cooling.

[0044] Taking the reaction of copper in the reaction solution with the compound having the structure shown in general formula 2 to form a Cu(II) complex as an example, the reaction equation in the ultrasonic stirring tank is as follows:

[0045]

[0046] In step (3) of the present invention, the cooling and precipitation is preferably carried out by heat exchange through a heat exchanger after the Cu complex reaction liquid to control the temperature of the reaction liquid. During the entire cooling and precipitation period, the temperature is 70-93°C, preferably 80-85°C.

[0047] In step (3) of the present invention, the solid-liquid separation is preferably carried out by filtering and separating the solid and liquid phases through a filtering device, and the filter diameter is 50-100 μm, preferably 65-75 μm;

[0048] Preferably, the equipment used for the filtering operation is a centrifugal filter with a rotation speed of 200-2000 rpm, preferably 1000-1100 rpm.

[0049] In the method of the present invention, the copper content in the reaction liquid after the treatment in step (3), i.e. the liquid phase entering the hydrogen chloride stripping step, can be reduced to 0.2-0.9 ppm (based on all substances in the liquid phase except the inert solvent), preferably less than 0.3 ppm.

[0050] In step (4) of the present invention, the stripping treatment and the reduced pressure removal of the inert solvent are both conventional operations in the art and are not specifically limited in the present invention. For example, in the stripping treatment, the mass ratio of the introduced HCl to the liquid phase is 0.05-0.15:1, preferably 0.09-0.1:1;

[0051] The stripping treatment has a pressure of 200-300 kPaA, preferably 240-250 kPaA; a temperature of 160-190°C, preferably 170-175°C; and a time of 20-40 min, preferably 23-27 min;

[0052] The inert solvent is removed under reduced pressure at a pressure of 1.2-40 kPaA, preferably 1.5-2 kPaA; a temperature of 180-200° C., preferably 195-198° C.; and a time of 15-20 min, preferably 16-18 min.

[0053] The copper impurity content in the crude isocyanate product prepared by the present invention is lower than 3 ppm, preferably 0.6-2.4 ppm.

[0054] The total content of urea substances and urea addition products in the crude isocyanate product prepared by the present invention (based on the mass fraction in the crude product) is less than 30000 ppm, preferably 15000-30000 ppm.

[0055] After the technical solution of the present invention is implemented, the cleaning period of the vacuum unit used in the separation process of the crude isocyanate product is extended from 30 days to 50-60 days, preferably 55-58 days.

[0056] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0057] (1) The present invention adds a purification process for copper impurities on the basis of the traditional photochemical reaction process, and the total content of urea substances and urea addition products in the obtained crude isocyanate product is significantly reduced, and the removal effect is better. The crude isocyanate product obtained after treatment can be directly used in the separation process to produce poly-MDI products, eliminating the subsequent treatment process and reducing the product refining cost;

[0058] (2) By optimizing the parameters in the purification process and selecting the reaction process parameters of copper-consuming compounds corresponding to the phosgenation reaction (for example, the type and amount of amine compounds, and the residence time), the total amount of copper impurities in the recovered solvent can be controlled within a reasonable range, thereby avoiding the occurrence of side reactions during the removal of hydrogen chloride vapor and inert solvent to a great extent, reducing the loss of isocyanate in the production process, thereby reducing the risk of corrosion and blockage of the reaction materials during transportation and storage, extending the stable operation time of the reaction device, and improving the quality of the isocyanate product. DETAILED DESCRIPTION

[0059] In order to better understand the technical solution of the present invention, the content of the present invention is further described below in conjunction with embodiments, but the content of the present invention is not limited thereto.

[0060] In the various embodiments and comparative examples of the present invention, the sources of the main raw materials are as follows. Unless otherwise specified, other raw materials and reagents are purchased through common commercial channels:

[0061] Phosgene: Produced by the Yantai MDI unit in Yantai Wanhua Industrial Park, industrial product;

[0062] Polyphenylmethane series diamines / polyamines: produced by Yantai MDI unit in Yantai Wanhua Industrial Park, industrial products;

[0063] Toluenediamine: Produced by Yantai TDI unit in Yantai Wanhua Industrial Park, industrial product;

[0064] Toluene: purchased from Shandong Jincheng Chemical Co., Ltd., industrial product, 99%;

[0065] Chlorobenzene: purchased from Jiangsu Longchang Chemical Co., Ltd., industrial product, 99%;

[0066] Diphenylmethane diisocyanate: MDI-100 produced by Wanhua Chemical Group Co., Ltd.

[0067] Toluene diisocyanate: produced by Yantai TDI unit in Yantai Wanhua Industrial Park, industrial product;

[0068] Dicyclohexylcarbodiimide: purchased from Jinan Xinda Chemical Co., Ltd., industrial product, 99%;

[0069] The compound having the structure shown in Formula 2 is prepared by adding 10% by mass of triethyl phosphate to MDI-100 produced by Wanhua Chemical Group Co., Ltd., reacting at 220°C for 2h, and removing triethyl phosphate by reduced pressure distillation at 15kPaA and 160°C to obtain a compound having the structure shown in Formula 2, with a yield of 93%;

[0070] 1H NMR (500MHz, DMSO-d6): δ7.23(d,8H),7.21(d,8H),3.96(s,4H);

[0071] The preparation method of the photochemical reaction liquid containing isocyanate, phosgene and other impurities is as follows: the solvent chlorobenzene and the diamine / polyamine of the methylene cross-linked polyphenylmethane series are mixed in a static mixer at a mass ratio of 3:1 to generate a mixed solution, the phosgene and the mixed solution are mixed in a dynamic mixer at a mass ratio of phosgene to diamine / polyamine of 4:1, and the mixture is subjected to cold and hot phosgenation reactions after mixing, the cold reaction temperature is controlled at 70°C and the pressure is 270KPaG, and the hot reactor temperature is controlled at 125°C and the pressure is 270KPaG. After the reaction, the photochemical reaction liquid used in the subsequent embodiments can be obtained.

[0072] The main instruments and test methods used in the embodiments of the present invention are:

[0073] Method for determining copper ions in photochemical reaction liquid and crude isocyanate products: The method for determining copper ions in photochemical reaction liquid and crude isocyanate products is carried out by fluorescence spectrophotometry, and the analytical instrument is Bruker S2 PUMA SeriesⅡ.

[0074] Determination method of urea substances and urea addition products in photochemical reaction liquid and crude isocyanate products: The determination method of each component in the photochemical reaction liquid and crude isocyanate products is carried out by liquid chromatography derivatization method, and the analytical instrument is Agilent 1260.

[0075] Example 1

[0076] The copper removal additive comprises a copper-consuming substance having a compound with a structure shown in Formula 2 and an inert solvent chlorobenzene. Based on the total mass of the inert solvent, the content of the compound with a structure shown in Formula 2 is 8wt%.

[0077] A photochemical reaction liquid containing diphenylmethane diisocyanate, phosgene and other impurities, wherein the content of copper impurities is 6 ppm; the content of urea substances is 10000 ppm.

[0078] The preparation of a crude isocyanate product having a low copper content comprises the following steps:

[0079] (1) The photochemical reaction liquid at a flow rate of 500 kg / h was passed into a phosgene removal tower and heat-treated at normal pressure and 150° C. for 10 min to remove unreacted phosgene. The phosgene content in the reaction liquid after the treatment was reduced to 200 ppm.

[0080] (2) The reaction solution after dephosgenesis is fed into an ultrasonic stirring kettle, and 5 kg / h of copper removal additive is added under ultrasonic stirring conditions. The frequency of the applied ultrasound is 25 kHz, the stirring speed in the kettle is 1000 rpm, and the average residence time of the complexation reaction at 100° C. is 10 min.

[0081] (3) The complex reaction liquid was heat exchanged by a heat exchanger and cooled to 93° C. to precipitate the Cu complex. After the heat exchange, the reaction liquid was filtered by a centrifugal filter with a filter diameter of 100 μm and a rotation speed of 200 rpm. The copper content in the liquid phase after centrifugal separation was 0.5 ppm.

[0082] (4) The liquid phase after centrifugal separation enters the HCl stripping tower, the mass ratio of HCl entering the stripping tower to the mass ratio of the reaction liquid after phosgene removal is 0.05:1, the treatment pressure is 200 kPaA, the temperature is 160°C, and the treatment time is 20 min. Then it is continuously sent to the solvent removal tower to remove chlorobenzene at 1.2 kPaA and 180°C for 15 min, and the crude isocyanate product with low copper content is obtained in the bottom of the tower.

[0083] The copper impurity content in the crude isocyanate product with low copper content is 1.5 ppm, and the total content of urea substances and urea addition products (calculated by mass fraction in the crude product) is 14000 ppm.

[0084] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 60 days.

[0085] Example 2

[0086] The copper removal additive comprises dicyclohexylcarbodiimide (a copper-consuming substance) and toluene (an inert solvent). The content of dicyclohexylcarbodiimide is 15 wt % based on the total mass of the inert solvent.

[0087] A photochemical reaction liquid containing toluene diisocyanate, phosgene and other impurities, wherein the content of copper impurities is 15 ppm; the content of urea substances is 25000 ppm.

[0088] The preparation of a crude isocyanate product having a low copper content comprises the following steps:

[0089] (1) The photochemical reaction liquid at a flow rate of 500 kg / h was passed into a phosgene removal tower for heat treatment at normal pressure and 170° C. for 30 min to remove unreacted phosgene. The phosgene content in the reaction liquid after the treatment was reduced to 80 ppm.

[0090] (2) The reaction solution after dephosgenesis is fed into an ultrasonic stirring kettle, and 7.5 kg / h of a copper removal additive is added under ultrasonic stirring conditions. The frequency of the applied ultrasound is 34 kHz, the stirring speed in the kettle is 1500 rpm, and the average residence time of the complexation reaction at 120° C. is 20 min.

[0091] (3) The complex reaction liquid was heat exchanged by a heat exchanger and cooled to 70° C. to precipitate the Cu complex. After the heat exchange, the reaction liquid was filtered by a centrifugal filter with a filter diameter of 50 μm and a rotation speed of 2000 rpm. The copper content in the liquid phase after centrifugal separation was 0.9 ppm.

[0092] (4) The liquid phase after centrifugal separation enters the HCl stripping tower, the mass ratio of HCl entering the stripping tower to the mass ratio of the reaction liquid after phosgene removal is 0.15:1, the treatment pressure is 300 kPaA, the temperature is 190°C, and the treatment time is 40 min. Then it is continuously sent to the solvent removal tower, toluene is removed at 40 kPaA and 200°C for 20 min, and a crude isocyanate product with a low copper content is obtained in the bottom of the tower.

[0093] The copper impurity content in the crude isocyanate product with low copper content is 2.8 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) is 30000 ppm.

[0094] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 52 days.

[0095] Example 3

[0096] The copper removal additive comprises a copper-consuming substance having a compound with a structure shown in Formula 2 and an inert solvent chlorobenzene. Based on the total mass of the inert solvent, the content of the compound with a structure shown in Formula 2 is 12 wt%.

[0097] A photochemical reaction liquid containing diphenylmethane diisocyanate, phosgene and other impurities, wherein the copper impurity content is 18 ppm; the urea substance content is 14000 ppm.

[0098] The preparation of a crude isocyanate product having a low copper content comprises the following steps:

[0099] (1) The photochemical reaction liquid with a flow rate of 500 kg / h was passed into a phosgene removal tower and heat-treated at normal pressure and 160° C. for 25 min to remove unreacted phosgene. The phosgene content in the reaction liquid after the treatment was reduced to 160 ppm.

[0100] (2) The reaction solution after dephosgenesis was sent to an ultrasonic stirring kettle, and 6.25 kg / h of copper removal additive was added under ultrasonic stirring conditions. The frequency of the applied ultrasound was 30 kHz, the stirring speed in the kettle was 1350 rpm, and the average residence time of the complexation reaction at 110° C. was 18 min.

[0101] (3) The complex reaction liquid was heat exchanged by a heat exchanger and cooled to 80° C. to precipitate the Cu complex. After heat exchange, the reaction liquid was filtered by a centrifugal filter with a filter diameter of 75 μm and a rotation speed of 1100 rpm. The copper content in the liquid phase after centrifugal separation was 0.25 ppm.

[0102] (4) The liquid phase after centrifugal separation enters the HCl stripping tower, the mass ratio of HCl entering the stripping tower to the mass ratio of the reaction liquid after phosgene removal is 0.1:1, the treatment pressure is 250 kPaA, the temperature is 170°C, and the treatment time is 25 min. Then it is continuously sent to the solvent removal tower to remove chlorobenzene at 1.5 kPaA and 195°C for 17 min, and the crude isocyanate product with low copper content is obtained in the bottom of the tower.

[0103] The copper impurity content in the crude isocyanate product with low copper content is 0.8 ppm, and the total content of urea substances and urea addition products (calculated as mass fraction in the crude product) is 15000 ppm.

[0104] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 58 days.

[0105] Example 4

[0106] Referring to the method in Example 1, the only difference is that the isocyanate monomer in the photochemical reaction liquid is replaced by m-xylylene diisocyanate, and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0107] The copper impurity content in the crude isocyanate product was 2.0 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 21000 ppm.

[0108] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 55 days.

[0109] Comparative Example 1

[0110] The method of Example 1 is referred to, except that the compound of formula 2 is not added in step (2), and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0111] The copper impurity content in the crude isocyanate product was 18 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 55000 ppm.

[0112] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 30 days.

[0113] Comparative Example 2

[0114] The method of Example 1 is referred to, except that chlorobenzene is not added in step (2), and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0115] The copper impurity content in the crude isocyanate product was 4.5 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 32000 ppm.

[0116] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 50 days.

[0117] Comparative Example 3

[0118] Referring to the method in Example 1, the only difference is that in step (2), only the compound of the structure shown in Formula 2 is replaced by 4,4-diphenylmethane diisocyanate, and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0119] The copper impurity content in the crude isocyanate product was 18 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 55000 ppm.

[0120] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 30 days.

[0121] Comparative Example 4

[0122] The method of Example 1 is referred to, except that in step (2), chlorobenzene is replaced by aniline (reactive solvent), and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0123] The copper impurity content in the crude isocyanate product was 7 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 48000 ppm.

[0124] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 38 days.

[0125] Comparative Example 5

[0126] The method of Example 1 is referred to, except that: in step (2), after the copper removal additive is added, ultrasonic treatment is not performed, and other parameters and operations remain unchanged to obtain a crude isocyanate product.

[0127] The copper impurity content in the crude isocyanate product was 10 ppm, and the total content of urea substances and urea addition products (based on the mass fraction in the crude product) was 50000 ppm.

[0128] The cleaning cycle of the vacuum unit used in the separation process of crude isocyanate products is 36 days.

Claims

1. A copper removal additive in a phosgenation reaction process, characterized in that: include: Copper-consuming substances and inert solvents suitable for phosgenation production processes; The copper-consuming substance is selected from one or more of dicyclohexylcarbodiimide, 1,3-diisopropylcarbodiimide, and a compound having a structure shown in Formula 1. In the formula, R1 is independently selected from n = 1; The inert solvent is selected from one or more of m-toluene, xylene, chlorobenzene and o-dichlorobenzene.

2. The copper removal additive according to claim 1, characterized in that The copper-consuming substance is a compound having a structure shown in Formula 2, 3. The copper removal additive according to claim 1, characterized in that The copper-consuming substances are 8-15wt% of the mass of the inert solvent.

4. The copper removal additive according to claim 3, characterized in that The copper-consuming substances account for 10-12 wt % of the mass of the inert solvent.

5. The copper removal additive according to claim 1, characterized in that The inert solvent is chlorobenzene and / or o-dichlorobenzene.

6. A method for preparing a crude isocyanate product with a low copper content, comprising the following steps: (1) removing unreacted phosgene from a photochemical reaction liquid containing isocyanate, phosgene and other impurities; (2) mixing the photochemical reaction liquid from which unreacted phosgene is removed in step (1) with the copper removal additive according to any one of claims 1 to 5, and performing a complexation reaction under ultrasonic conditions; (3) cooling the reaction solution obtained in step (2) to precipitate the Cu complex, and then performing solid-liquid separation; (4) The liquid phase after the solid-liquid separation in step (3) is subjected to a stripping treatment using hydrogen chloride, and then the inert solvent is removed under reduced pressure to obtain a crude isocyanate product with a low copper content.

7. The preparation method according to claim 6, characterized in that: In the photochemical reaction liquid containing isocyanate, phosgene and other impurities in step (1), the suitable isocyanate raw material monomer is selected from diisocyanate; The photochemical reaction liquid containing isocyanate, phosgene and other impurities has a copper impurity content of 6-15 ppm and a urea substance content of 10000-25000 ppm.

8. The preparation method according to claim 7, characterized in that: The isocyanate raw material monomer is selected from diphenylmethylene diisocyanate, polydiphenylmethylene diisocyanate, toluene diisocyanate, meta-xylylene diisocyanate or isophorone diisocyanate.

9. The preparation method according to claim 6, characterized in that: In step (1), unreacted phosgene is removed by heat treatment, wherein the temperature of the heat treatment is 150-170° C. and the time is 10-30 min; The phosgene content in the reaction solution after treatment is reduced to 80-200 ppm.

10. The preparation method according to claim 9, characterized in that: The heat treatment process has a temperature of 160-165° C. and a time of 25-28 min.

11. The preparation method according to claim 6, characterized in that: In step (2), the copper removal additive is added in an amount of 1-1.5% of the mass of the photochemical reaction liquid.

12. The preparation method according to claim 11, characterized in that: The copper removal additive is added in an amount of 1.25-1.3% of the mass of the photochemical reaction liquid.

13. The preparation method according to claim 6, characterized in that: In step (2), the complexation reaction is carried out in an ultrasonic stirring kettle, the ultrasonic frequency is 25-35kHz; the stirring speed is 1000-1500rpm; In step (2), the complexation reaction is carried out at a temperature of 100-120° C. and for a time of 10-20 min.

14. The preparation method according to claim 13, characterized in that: The ultrasonic frequency is 28-30 Hz; the stirring speed is 1300-1350 rpm.

15. The preparation method according to claim 13, characterized in that: The complexation reaction is carried out at a temperature of 110-113° C. and a time of 17-18 minutes.

16. The preparation method according to claim 6, characterized in that: In step (3), the precipitation is carried out by cooling at a temperature of 70-93°C; In step (3), the solid-liquid separation is performed to obtain solid-liquid two phases by filtration separation, and the filtration diameter is 50-100 μm.

17. The preparation method according to claim 16, characterized in that: The precipitation is carried out by cooling down, and the temperature is 80-85°C.

18. The preparation method according to claim 16, characterized in that: The filter diameter is 65-75 μm.

19. The preparation method according to claim 16, characterized in that: The equipment used for the filtration operation is a centrifugal filter with a rotation speed of 200-2000 rpm.

20. The preparation method according to claim 19, characterized in that: The rotation speed is 1000-1100 rpm.

21. The preparation method according to claim 6, characterized in that: In step (4), the stripping treatment has a mass ratio of HCl to liquid phase of 0.05-0.15:1; The stripping treatment has a pressure of 200-300 kPaA, a temperature of 160-190°C, and a time of 20-40 min. The inert solvent is removed under reduced pressure at a pressure of 1.2-40 kPaA, a temperature of 180-200° C., and a time of 15-20 min.

22. The preparation method according to claim 21, characterized in that: In the stripping treatment, the mass ratio of the introduced HCl to the liquid phase is 0.09-0.1:

1.

23. The preparation method according to claim 21, characterized in that: The stripping treatment has a pressure of 240-250 kPaA, a temperature of 170-175° C., and a time of 23-27 min.

24. The preparation method according to claim 21, characterized in that: The inert solvent is removed under reduced pressure at a pressure of 1.5-2 kPaA, a temperature of 195-198° C., and a time of 16-18 min.

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