A process for the preparation of diisocyanates and polyisocyanates of the diphenylmethane series

Abstract

The application relates to a preparation method of a diisocyanate and a polyisocyanate in a diphenylmethane series, which comprises the following steps: S1: performing a phosgenation reaction on a diphenylmethane series diamine and a polyamine with phosgene in a solvent to obtain a first mixed solution; S2: performing a phosgene removal treatment on the first mixed solution to obtain a second mixed solution; S3: performing a stripping treatment on the second mixed solution with HCl gas to obtain a third mixed solution; and S4: performing a solvent removal treatment on the third mixed solution to obtain a diphenylmethane series diisocyanate and polyisocyanate crude product. The preparation method of the diisocyanate and the polyisocyanate in the diphenylmethane series in one embodiment of the application can prepare a diphenylmethane series diisocyanate and polyisocyanate product with light color by optimizing process parameters of the stripping treatment step.

Description

Technical Field

[0001] This invention relates to isocyanates, and more particularly to the preparation of light-colored diphenylmethane series diisocyanates and polyisocyanates. Background Technology

[0002] Diphenylmethane diisocyanates and polyisocyanates (MDI) are important raw materials for the production of rigid polyurethane foam, mainly used in home appliances, cold storage, containers, and building insulation materials. The production of diphenylmethane diisocyanates and polyisocyanates is well-known in this field. The main industrial preparation method is as follows: First, aniline and formaldehyde undergo a condensation reaction under an acid catalyst to generate DAM (diphenylmethane diamines and polyamines, abbreviated as polyamines). Then, DAM is reacted with phosgene in an inert solvent via liquid-phase phosgenation to obtain a reaction mixture. After phosgene removal, hydrogen chloride stripping, solvent removal, and purification, the corresponding pure MDI product can be obtained.

[0003] In the phosgenation reaction and solvent removal processes, dark-colored products are often formed due to various factors. These products cannot be removed during separation, resulting in a pale yellow discoloration in the subsequently produced polyurethane foam. This discoloration negatively impacts its practical application. Therefore, it is desirable to prepare isocyanates that are light-colored or contain fewer dark-colored components as raw materials for polyurethane production.

[0004] Currently, there is considerable research on the preparation methods of light-colored isocyanates, especially diphenylmethane series isocyanates. In the published methods for improving the color of polymeric MDI, it is often necessary to introduce new materials into the system, which increases operating costs and introduces new impurities, potentially leading to other adverse effects. Furthermore, controlling the raw materials is difficult, often increasing procurement costs. Summary of the Invention

[0005] To overcome at least one of the defects of the prior art, in a first aspect, one embodiment of the present invention provides a method for preparing diphenylmethane series diisocyanates and polyisocyanates, comprising the following steps:

[0006] S1: Diphenylmethane series diamines and polyamines are reacted with phosgene in a solvent to produce a first mixture;

[0007] S2: The first mixture is subjected to a process to remove phosgene, resulting in a second mixture;

[0008] S3: The second mixture is stripped using HCl gas to obtain a third mixture; and

[0009] S4: The third mixture is subjected to solvent removal treatment to obtain crude diphenylmethane series diisocyanates and polyisocyanates;

[0010] In step S3, the stripping process is carried out in a stripping tower with a reflux ratio R of 0.05–0.3. The contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower is 1–10 min. The flow rate v of the gaseous substance in the stripping tower is 2–15 m / s. The mass ratio of HCl gas to the solute in the second mixture is m1:m2 = (0.03–0.2):1. The mass percentage of the solute in the second mixture, c1, is 15–35%. The mass percentage of the solute in the third mixture, c2, is 40–65%.

[0011] Secondly, one embodiment of the present invention provides a diphenylmethane series of diisocyanate and polyisocyanate products, which are prepared by the above-described preparation method.

[0012] Thirdly, one embodiment of the present invention provides a method for preparing diphenylmethane series diisocyanates and polyisocyanates, comprising the following steps:

[0013] S1: Diphenylmethane series diamines and polyamines are reacted with phosgene in a solvent to produce a first mixture;

[0014] S2: The first mixture is subjected to a process to remove phosgene, resulting in a second mixture;

[0015] S3: The second mixture is stripped using HCl gas to obtain a third mixture; and

[0016] S4: The third mixture is subjected to solvent removal treatment to obtain crude diphenylmethane series diisocyanates and polyisocyanates;

[0017] In step S3, the stripping process is carried out in a stripping tower. R represents the reflux ratio of the stripping tower; t represents the contact time (in minutes) between the second mixture and the gaseous substance containing HCl gas in the stripping tower; v represents the flow rate (in m / s) of the gaseous substance in the stripping tower; m1 represents the mass flow rate (in t / h) of HCl gas during the stripping process; m2 represents the mass flow rate (in t / h) of the solute in the second mixture during the stripping process; c1 represents the mass percentage of solute in the second mixture; and c2 represents the mass percentage of solute in the third mixture. R, t, v, m1, m2, c1, and c2 satisfy the following relationship:

[0018]

[0019] The present invention discloses a method for preparing diphenylmethane series diisocyanates and polyisocyanates. By optimizing the process parameters of the stripping step, diphenylmethane series diisocyanate and polyisocyanate products with higher L* values ​​and lighter colors can be obtained, thereby reducing the impact on subsequent polyurethane product production. Detailed Implementation

[0020] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the description herein is for illustrative purposes only and not intended to limit the present invention.

[0021] One embodiment of the present invention provides a method for preparing diphenylmethane series diisocyanates and polyisocyanates (MDI), comprising the following steps:

[0022] S1: Diphenylmethane series diamines and polyamines (DAM) are reacted with phosgene in a solvent to produce a first mixture;

[0023] S2: The first mixture is subjected to a process to remove phosgene, resulting in a second mixture;

[0024] S3: The second mixture is stripped using HCl gas to obtain the third mixture; and

[0025] S4: The third mixture is subjected to solvent removal treatment to obtain crude diphenylmethane series diisocyanates and polyisocyanates (crude MDI);

[0026] In step S3, the stripping process is carried out in a stripping tower with a reflux ratio R of 0.05–0.3. The contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower is 1–10 min. The flow rate v of the gaseous substance in the stripping tower is 2–15 m / s. The mass ratio of HCl gas to the solute in the second mixture is m1:m2 = (0.03–0.2):1. The mass percentage of the solute in the second mixture, c1, is 15–35%. The mass percentage of the solute in the third mixture, c2, is 40–65%.

[0027] In one embodiment, the solvent used in step S1 for the liquid-phase phosgenation reaction can be one or more of chlorobenzene, dichlorobenzene, diethyl carbonate, and toluene, preferably chlorobenzene.

[0028] In one embodiment, in step S1, the reaction temperature can be 60–160°C, for example 80°C, 90°C, 95°C, 100°C, 120°C, 140°C, or 150°C; the reaction pressure can be 2–30 bar, for example 5 bar, 8 bar, 10 bar, 15 bar, 20 bar, or 25 bar; the mass ratio of DAM to solvent can be 1:(1.1–5), for example 1:1.5, 1:2, 1:3, or 1:4; the mass ratio of DAM to phosgene can be 1:(1.1–5), for example 1:1.5, 1:2, 1:2.5, 1:3, or 1:4.

[0029] In one embodiment, in step S2, the first mixture may be dephosgene-removed in a distillation column, with the phosgene discharged from the top of the column in gaseous form.

[0030] In one embodiment, in step S2, the temperature for phosgene removal treatment (e.g., the temperature at the bottom of the column) can be 100–180°C, such as 120°C, 140°C, 150°C, or 160°C; and the pressure (e.g., the pressure at the top of the column) can be 1–5 bar, such as 2 bar, 3 bar, or 4 bar.

[0031] In one embodiment, the gaseous substance (gas) in the stripping tower includes evaporated solvent and HCl gas, and the flow rate v of the gaseous substance can be 5 to 15 m / s, or more specifically 5 to 10 m / s, for example 3 m / s, 4 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s, 11 m / s, 12 m / s, 13 m / s, or 14 m / s.

[0032] In one embodiment, HCl gas enters the stripping tower from the bottom, and the second mixture enters the stripping tower from the top. The gaseous substance containing HCl gas moves upward from bottom to top, and the second mixture moves downward from top to bottom. The two come into contact and react within the tower.

[0033] In one embodiment, the contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower can be 3 to 6 minutes, more specifically 5 to 6 minutes, for example, 2 minutes, 4 minutes, 5 minutes, 7 minutes, 8 minutes, or 9 minutes. The contact time t is obtained based on the residence time of the second mixture in the stripping tower; in other words, the contact time t can also be described as the residence time of the second mixture in the stripping tower.

[0034] In one implementation, the stripping column can be an existing distillation column.

[0035] In one embodiment, the operating temperature (bottom temperature) of the stripping column can be 130–210°C, more preferably 160–190°C, such as 150°C, 170°C, 180°C, or 200°C; the operating pressure (top pressure) of the stripping column can be 1–5 bar, more preferably 2–4 bar, such as 3 bar.

[0036] In one embodiment, the reflux ratio R of the stripping tower can be 0.05 to 0.2, and more specifically 0.08 to 0.15, for example 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.2, or 0.25.

[0037] In one embodiment, c1 and c2 are determined by gel permeation chromatography as described below. Specifically, the mass percentage of the solvent in the mixture (second or third mixture) is determined by gel permeation chromatography, and then the corresponding mass percentage of the solvent is subtracted from 100% to obtain c1 or c2. In other words, c3 is the mass percentage of the solvent in the second mixture, c1 = 100% - c3; c4 is the mass percentage of the solvent in the third mixture, c2 = 100% - c4.

[0038] In one embodiment, c1 and c2 refer to the total content of solute in the mixed solution. For example, the second mixture may include solvent, MDI, and a small amount of impurities, and c1 may be the sum of the mass content of MDI and impurities. Similarly, the third mixture may include solvent, MDI, and a small amount of impurities, and c2 may be the sum of the mass content of MDI and impurities.

[0039] In one embodiment, the mass percentage of the solute c1 in the second mixture can be 23-35%, more specifically 23-30%, for example 18%, 20%, 25%, 26%, 28%, or 33%.

[0040] In one embodiment, the mass percentage of the solute c2 in the third mixture can be 45% to 65%, more preferably 50% to 60%, for example 42%, 45%, 48%, 52%, 54%, 55%, 56%, or 58%.

[0041] In one embodiment, the ratio of the mass flow rate m1 of HCl gas in step S3 to the mass flow rate m2 of the solute in the second mixture can be m1:m2 = (0.05~0.25):1, further can be (0.05~0.2):1, even further can be (0.05~0.15):1, and still further can be (0.08~0.1):1, for example 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.12:1, 0.15:1, 0.18:1. Here, m1 is measured by a flow meter; m2 is obtained by first measuring the total mass flow rate of the second mixture using a mass flow meter, and then multiplying the total mass flow rate by the concentration of the solute.

[0042] In one embodiment, R represents the reflux ratio of the stripping tower; t represents the contact time in minutes between the second mixture and the gaseous substance containing HCl gas in the stripping tower; v represents the flow rate of the gaseous substance in the stripping tower, in m / s; m1 represents the mass flow rate of HCl gas during the stripping process, in t / h; m2 represents the mass flow rate of the solute in the second mixture during the stripping process, in t / h; c1 represents the mass percentage of the solute in the second mixture; c2 represents the mass percentage of the solute in the third mixture; c1, c2, and R are all dimensionless numbers; R, t, v, m1, m2, c1, and c2 satisfy the following relationship:

[0043]

[0044] The above formulas only represent the numerical relationships between the parameters; the units on both sides of the inequality do not correspond. Parameters such as t satisfying the above relationships can improve the stripping effect of the HCl stripping tower and result in a higher L* and lighter color for the final product, crude MDI.

[0045] In one embodiment, the solvent removal process includes a first solvent removal process and a second solvent removal process. The first solvent removal process can be carried out in a distillation column, and the specific process can be as follows: the third mixture is fed into the bottom of the distillation column, and then the liquid collected from the bottom of the distillation column is fed into an evaporator. The gaseous substance produced by the evaporator is returned to the distillation column, and the liquid substance is the solvent-removed reaction liquid. Further, the solvent-removed reaction liquid can be subjected to a second solvent removal process to remove trace amounts of solvent. The second solvent removal process can be carried out using a nitrogen stripping column.

[0046] In one embodiment, the method for preparing MDI further includes a step of separating crude MDI. The separation step may involve purifying and separating the crude MDI in a distillation column. The reboiler temperature of the distillation column may be 180–250°C, for example, 180°C, 200°C, 230°C, 250°C, etc., and the top pressure of the column may be 10–1000 Pa, for example, 10 Pa, 50 Pa, 100 Pa, 1000 Pa, etc., to obtain polymerized MDI product in the reboiler.

[0047] In one embodiment, the solvent content in the crude MDI is less than 1 wt%, further less than 2000 ppm, and even further less than 1500 ppm, for example, 1200 to 1400 ppm.

[0048] One embodiment of the present invention provides an MDI product prepared by the above-described preparation method.

[0049] In one implementation, the L* of the MDI product is 85 to 93, for example, 86, 87, 88, 90, 91, or 92.

[0050] Unless otherwise specified, the raw materials, steps, and process conditions of the preparation methods of the diphenylmethane series diisocyanates and polyisocyanates of the present invention can all be existing technologies. For example, the methods disclosed in CN116217439A, CN108147979B, CN116034102A, CN102471241A, and CN111630027B can be used to prepare the diphenylmethane series diisocyanates and polyisocyanates.

[0051] Unless otherwise specified, all pressures mentioned in this invention refer to absolute pressure.

[0052] The inventors discovered that in the HCl stripping process of MDI preparation, in addition to parameters such as operating temperature and pressure, factors such as gas velocity in the stripping tower, reflux ratio in the stripping tower, concentration of the pre- and post-stripping mixture, and contact time between the mixture and stripped HCl in the stripping tower all have a certain impact on the stripping effect. By optimizing the combination of other influencing factors besides temperature and pressure, the stripping effect can be further improved, thereby increasing the L* of crude MDI products.

[0053] The present invention discloses a method for preparing diphenylmethane series diisocyanates and polyisocyanates. By optimizing the relevant parameters of the HCl stripping process, the content of impurities is reduced, resulting in crude MDI products with higher L* and lighter color. Furthermore, this method does not require modification of the existing MDI process and will not have any adverse effects on the existing process and products.

[0054] The present invention provides a method for preparing diphenylmethane series diisocyanates and polyisocyanates, which can produce crude MDI products with an L* of 85-93, thereby improving product quality and downstream application effects.

[0055] The following describes, with reference to embodiments, a method for preparing diphenylmethane-based diisocyanates and polyisocyanates according to one embodiment of the present invention. The raw materials and testing methods used are as follows:

[0056] 1. Raw materials

[0057] Diphenylmethane series diamines and polyamines (DAM): Wanhua Chemical (Ningbo) Co., Ltd., purity >99.99%. The preparation method of DAM is as follows: aniline is reacted with hydrochloric acid at 60℃ and 1 bar to generate aniline hydrochloride, which is then reacted with formaldehyde through a condensation and transposition process to obtain a transposition liquid. After neutralization and washing with water, a polyamine is obtained, which is then obtained by distillation and stripping to obtain DAM.

[0058] Chlorobenzene: Wanhua Chemical (Ningbo) Co., Ltd., purity >99.9%.

[0059] Phosgene: Wanhua Chemical (Ningbo) Co., Ltd., purity >95.0%.

[0060] 2. Determination of L* in crude MDI

[0061] The measurement was performed using a Hunterlab VTS spectrophotometer. The specific procedure was as follows: the cuvette was placed in the instrument's detection cell for blank calibration. After calibration, the sample to be tested was placed in the cuvette and then placed in the instrument's detection cell for reading.

[0062] 3. Method for determining the mass percentage of solute in the mixture (e.g., c1 or c2)

[0063] The mass percentage of solute in the mixture was determined and calculated using gel permeation chromatography (GPC). The analytical method was as follows: 10 μL of the mixture was directly injected for analysis. Chromatographic columns: Waters HR01*1 and Waters HR01*3, column oven temperature 35℃; detector type: FID detector, detector temperature 35℃; mobile phase: tetrahydrofuran, flow rate 1 mL / min. The mass percentage of solvent in the mixture was obtained by integrating the chromatogram. The mass percentage of solute was calculated as: 100% - mass percentage of solvent.

[0064] 4. The solvent content in crude MDI was determined by gel permeation chromatography (GPC). The crude MDI was diluted 10 times with dichloromethane before injection for analysis. The remaining methods were the same as above.

[0065] Example 1

[0066] S1: DAM and chlorobenzene are mixed to obtain a mixture with a DAM concentration of 33wt%. A phosgene-chlorobenzene solution with a phosgene concentration of 65wt% (the mass ratio of DAM to phosgene is 1:2.5) is added to the mixture. The mixture is reacted at 5 bar and 95°C for 0.5 h to obtain the first mixture.

[0067] S2: Remove phosgene from the first mixture at 1 bar and 130°C to obtain the second mixture; in the second mixture, the mass percentage of solute containing MDI, c1, is 27%.

[0068] S3: The second mixture is fed into a hydrogen chloride stripping tower. The operating pressure of the stripping tower is 2 bar, the bottom temperature is 180℃, and the reflux ratio R is 0.1. HCl gas is introduced into the bottom of the tower for stripping. The mass ratio of the stripped HCl gas to the solute in the feed second mixture, m1:m2 = 0.08:1, is controlled. The contact time t between the stripped HCl gas and the second mixture in the tower is controlled at 5 min, and the gas flow velocity v in the tower is 7 m / s. A third mixture after stripping is obtained in the bottom of the tower. The mass percentage c2 of MDI solute in the third mixture is 55%.

[0069] S4: The third mixture was subjected to dechlorobenzene treatment in a distillation column at a top pressure of 30 kPa and a bottom temperature of 195 °C to obtain dechlorobenzene-treated MDI (i.e., the reaction solution after solvent removal). This dechlorobenzene-treated MDI was then sent to a nitrogen stripping column at 35 kPa and 190 °C for further removal of trace amounts of solvent. The mass ratio of nitrogen to the reaction solution after solvent removal was controlled at 0.04. Crude MDI was obtained at the bottom of the column. The crude MDI was tested using a colorimeter, and its L* value was measured to be 92; the solvent content in the crude MDI was 1200 ppm.

[0070] Example 1-1

[0071] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.05.

[0072] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0073] Examples 1-2

[0074] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.08.

[0075] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0076] Examples 1-3

[0077] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.15.

[0078] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0079] Examples 1-4

[0080] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.2.

[0081] The L* of the crude MDI was 87; the solvent content in the crude MDI was 1200 ppm.

[0082] Examples 1-5

[0083] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.3.

[0084] The L* of the crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0085] Examples 1-6

[0086] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.35.

[0087] The L* of the crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0088] Example 2

[0089] This embodiment uses the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 1 min.

[0090] The L* of the crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0091] Example 2-1

[0092] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 3 min.

[0093] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0094] Example 2-2

[0095] This embodiment uses the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 6 min.

[0096] The L* of the crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0097] Example 2-3

[0098] This embodiment uses the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 8 min.

[0099] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0100] Examples 2-4

[0101] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 10 min.

[0102] The L* of the crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0103] Examples 2-5

[0104] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is 11 min.

[0105] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0106] Example 3

[0107] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the flow rate v of the gaseous substance in the stripping tower is 2 m / s.

[0108] The L* of the crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0109] Example 3-1

[0110] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the flow rate v of the gaseous substance in the stripping tower is 5 m / s.

[0111] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0112] Example 3-2

[0113] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the flow rate v of the gaseous substance in the stripping tower is 10 m / s.

[0114] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0115] Example 3-3

[0116] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the flow rate v of the gaseous substance in the stripping tower is 15 m / s.

[0117] The L* of the crude MDI was 87; the solvent content in the crude MDI was 1200 ppm.

[0118] Examples 3-4

[0119] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the flow rate v of the gaseous substance in the stripping tower is 17 m / s.

[0120] The L* of the crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0121] Example 4

[0122] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.02:1.

[0123] The L* of the crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0124] Example 4-1

[0125] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of stripped HCl gas to the mass of solute in the second mixed liquid is m1:m2 = 0.03:1.

[0126] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0127] Example 4-2

[0128] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.05:1.

[0129] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0130] Example 4-3

[0131] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.1:1.

[0132] The L* of the crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0133] Example 4-4

[0134] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.15:1.

[0135] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0136] Examples 4-5

[0137] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.2:1.

[0138] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0139] Examples 4-6

[0140] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the second mixed liquid is m1:m2 = 0.25:1.

[0141] The L* of the crude MDI was 89; the solvent content in the crude MDI was 1200 ppm.

[0142] Example 5

[0143] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the second mixture, c1, is 13%.

[0144] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0145] Example 5-1

[0146] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the second mixture, c1, is 15%.

[0147] The L* of the crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0148] Example 5-2

[0149] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the second mixture, c1, is 23%.

[0150] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0151] Example 5-3

[0152] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the second mixture, c1, is 30%.

[0153] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0154] Example 5-4

[0155] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the second mixture, c1, is 35%.

[0156] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0157] Example 5-5

[0158] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of solute c1 in the second mixture is 38%.

[0159] The L* of the crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0160] Example 6

[0161] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 38%.

[0162] The L* of the crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0163] Example 6-1

[0164] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 40%.

[0165] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0166] Example 6-2

[0167] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 45%.

[0168] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0169] Example 6-3

[0170] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 50%.

[0171] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0172] Example 6-4

[0173] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 60%.

[0174] The L* of the crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0175] Example 6-5

[0176] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of the solute in the third mixture, c2, is 65%.

[0177] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0178] Example 6-6

[0179] This embodiment uses essentially the same raw materials and processes as Example 1 to prepare MDI, the only difference being that the mass percentage of solute in the third mixture, c2, is 68%.

[0180] The L* of the crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0181] Example 7

[0182] S1: DAM and chlorobenzene are mixed to obtain a mixture with a DAM concentration of 20wt%. A phosgene-chlorobenzene solution with a phosgene concentration of 65wt% (the mass ratio of DAM to phosgene is 1:3) is added to the mixture. The mixture is reacted at 5 bar and 95°C for 0.5 h to obtain the first mixture.

[0183] S2: Remove phosgene from the first mixture at 1 bar and 130°C to obtain the second mixture; in the second mixture, the mass percentage of solute containing MDI, c1, is 18%.

[0184] S3: The second mixture is fed into a hydrogen chloride stripping tower. The operating pressure of the stripping tower is 6 bar, the bottom temperature is 215℃, and the reflux ratio R is 0.04. HCl gas is introduced into the bottom of the tower for stripping. The mass ratio of the stripped HCl gas to the solute in the feed second mixture, m1:m2 = 0.02:1, is controlled. The contact time t between the stripped HCl gas and the second mixture in the tower is controlled at 0.5 min, and the gas flow velocity v in the tower is controlled at 16 m / s. A third mixture after stripping is obtained in the bottom of the tower. The mass percentage c2 of the solute containing MDI in the third mixture is 45%.

[0185] S4: The third mixture was subjected to dechlorobenzene treatment at 30 kPa and 195 °C. The dechlorobenzene-treated MDI (i.e., the reaction solution after solvent removal) was then fed into a nitrogen stripping tower and treated at 35 kPa and 190 °C. The mass ratio of nitrogen to the reaction solution after solvent removal was controlled at 0.04. Crude MDI was obtained in the bottom of the tower. The crude MDI was tested using a colorimeter, and its L* value was measured to be 80. The solvent content in the crude MDI was 1400 ppm.

[0186] Table 1 below lists the parameters related to the stripping process and the L* values ​​of the resulting products for each embodiment.

[0187] Table 1

[0188]

[0189]

[0190] The difference between Examples 1 to 1-6 lies in the reflux ratio R of the stripping tower in step S3. According to the results in Table 1, the L* of the products obtained in Examples 1 to 1-4 is higher than that of the products in Examples 1-5 and 1-6. Furthermore, the L* of the products obtained in Examples 1, 1-2, and 1-3 is higher than that of the products in Examples 1-1 and 1-4. Therefore, the reflux ratio R of the stripping tower in step S3 is preferably 0.05 to 0.2, and more preferably 0.08 to 0.15.

[0191] The difference between Examples 1, 2 to 2-5 lies in the contact time t between the second mixture and the gaseous substance containing HCl gas in step S3. According to the results in Table 1, the L* of the products obtained in Examples 1, 2-1 to 2-4 is higher than that of the products in Examples 2 and 2-5. Furthermore, the L* of the products obtained in Examples 1, 2-1, and 2-2 is higher than that of the products in Examples 2-3 and 2-4. Therefore, in step S3, the contact time t between the second mixture and the gaseous substance containing HCl gas is preferably 3–10 min, more preferably 3–6 min, and even more preferably 5–6 min.

[0192] The difference between Examples 1, 3 to 3-4 lies in the flow rate v of the gaseous substance in the stripping tower during step S3. According to the results in Table 1, the L* of the products obtained in Examples 1, 3 to 3-3 is higher than that of the product in Example 3-4. Further, the L* of the products obtained in Examples 1, 3-1 to 3-3 is higher than that of the product in Example 3. Even further, the L* of the products obtained in Examples 1, 3-1, and 3-2 is higher than that of the product in Example 3-3. Therefore, in step S3, the flow rate v of the gaseous substance is preferably 2–15 m / s, more preferably 5–15 m / s, and even more preferably 5–10 m / s.

[0193] The difference between Examples 1 and 4 to 4-6 lies in the mass ratio m1:m2 of the stripped HCl gas and the solute in the second mixed liquor of the feed. According to the results in Table 1, the L* of the products obtained in Examples 1 and 4-2 to 4-6 is higher than that of the products obtained in Examples 4 and 4-1. Further, the L* of the products obtained in Examples 1 and 4-2 to 4-5 is higher than that of the product obtained in Example 4-6. Even further, the L* of the products obtained in Examples 1, 4-3, and 4-4 is higher than that of the products obtained in Examples 4-2 and 4-5. Therefore, the preferred value of m1:m2 is (0.05–0.25):1, further preferably (0.05–0.2):1, even more preferably (0.05–0.15):1, and even more preferably (0.08–0.1):1.

[0194] The difference between Examples 1, 5 to 5-5 lies in the different mass percentage (c1) of the solute in the second mixture. According to the results in Table 1, the L* of the products obtained in Examples 1, 5-1 to 5-4 is higher than that of the products in Examples 5 and 5-1. Further, the L* of the products obtained in Examples 1, 5-2 to 5-4 is higher than that of the product in Example 5-1. Even further, the L* of the products obtained in Examples 1, 5-2, and 5-3 is higher than that of the product in Example 5-4. Therefore, c1 is preferably 15-35%, more preferably 23-35%, and even more preferably 23-30%.

[0195] The difference between Examples 1 and 6 to 6-6 lies in the different mass percentage (c2) of the solute in the third mixture. According to the results in Table 1, the L* of the products obtained in Examples 1 and 6-1 to 6-5 is higher than that of the products in Examples 6 and 6-6. Further, the L* of the products obtained in Examples 1 and 6-2 to 6-5 is higher than that of the product in Example 6-1. Even further, the L* of the products obtained in Examples 1, 6-3, and 6-4 is higher than that of the products in Examples 6-2 and 6-5. Therefore, c2 is preferably 40-65%, more preferably 45-65%, and even more preferably 50-60%.

[0196] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0197] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A method for preparing diphenylmethane series diisocyanates and polyisocyanates, comprising the following steps: S1: Diphenylmethane series diamines and polyamines are reacted with phosgene in a solvent to produce a first mixture; S2: The first mixture is subjected to a process to remove phosgene, resulting in a second mixture; S3: The second mixture is stripped using HCl gas to obtain a third mixture; and S4: The third mixture is subjected to solvent removal treatment to obtain crude diphenylmethane series diisocyanates and polyisocyanates; in, The stripping process in step S3 is carried out in a stripping tower with a reflux ratio R of 0.05–0.

2. The contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower is 3–10 min. The flow rate v of the gaseous substance in the stripping tower is 2–15 m / s. The mass ratio of HCl gas to the solute in the second mixture is m1:m2 = (0.05–0.2):

1. The mass percentage of the solute in the second mixture, c1, is 15–35%. The mass percentage of the solute in the third mixture, c2, is 45–65%.

2. The preparation method according to claim 1, wherein, The contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower is 3 to 6 minutes.

3. The preparation method according to claim 1, wherein, The reflux ratio R of the stripping tower is 0.08 to 0.15; and / or, The contact time t between the second mixture and the gaseous substance containing HCl gas in the stripping tower is 5-6 min; and / or, The flow velocity v of the gaseous substance in the stripping tower is 5 to 15 m / s.

4. The preparation method according to claim 1, wherein, The flow velocity v of the gaseous substance in the stripping tower is 5 to 10 m / s.

5. The preparation method according to claim 1, wherein, c1 is 23-35%; c3 is the mass percentage of the solvent in the second mixture, and the sum of c1 and c3 is 100%; and / or, c2 is 50-60%; c4 is the mass percentage of the solvent in the third mixture, and the sum of c2 and c4 is 100%.

6. The preparation method according to claim 5, wherein, c1 is 23-30%.

7. The preparation method according to claim 1, wherein, The mass ratio of the HCl gas to the solute in the second mixture is m1:m2 = (0.05~0.15):

1.

8. The preparation method according to claim 7, wherein, m1:m2=(0.08~0.1):

1.

9. The preparation method according to claim 7, wherein, R, t, v, m1, m2, c1, c2 satisfy the following relationship:

10. The preparation method according to claim 1, wherein, The operating temperature of the stripping tower is 130–210°C; and / or, The operating pressure of the stripping tower is 1–5 bar; and / or, The L* of the crude diisocyanates and polyisocyanates of the diphenylmethane series is 85-93.

11. The preparation method according to claim 1, wherein, The operating temperature of the stripping tower is 160–190°C; and / or, The operating pressure of the stripping tower is 2 to 4 bar.

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