Method for preparing diphenylmethane-based diisocyanate and polyisocyanate

Abstract

The present invention relates to a method for preparing a diphenylmethane-based diisocyanate and polyisocyanate. The method comprises the following steps: S1. performing a phosgenation reaction on a diphenylmethane-based diamine and polyamine and phosgene in a solvent to obtain a first mixed solution; S2. performing phosgene removal treatment on the first mixed solution to obtain a second mixed solution; S3. performing stripping treatment on the second mixed solution by using HCl gas to obtain a third mixed solution; and S4. performing solvent removal treatment on the third mixed solution to obtain a crude diphenylmethane-based diisocyanate and polyisocyanate product. In the method for preparing a diphenylmethane-based diisocyanate and polyisocyanate as provided by an embodiment of the present invention, by optimizing process parameters of the stripping treatment step, a diphenylmethane-based diisocyanate and polyisocyanate product having a light color can be prepared.

Description

A method for preparing diisocyanates and polyisocyanates of diphenylmethane series Technical Field

[0001] The present invention relates to isocyanate, in particular to the preparation of diisocyanate and polyisocyanate of a light-colored diphenylmethane series. Background Art

[0002] The diisocyanates and polyisocyanates (MDI) of the diphenylmethane series are one of the important raw materials for producing rigid polyurethane foams and are mainly used in the fields such as household appliances, cold storages, containers, building insulation materials, etc. At present, the production of diisocyanates and polyisocyanates of the diphenylmethane series is well-known in the art. The main industrial preparation method is: first, aniline and formaldehyde are condensed under the action of an acid catalyst to generate DAM (diamines and polyamines of the diphenylmethane series, referred to as polyamines), DAM is reacted with phosgene in a solvent under an inert solvent environment through liquid phase phosgenation to obtain a reaction mixture, and the reaction mixture can obtain corresponding pure MDI product after phosgene removal, hydrogen chloride stripping, solvent removal and refined separation.

[0003] During the phosgenation reaction and solvent removal steps, dark products are often formed due to various factors. These products cannot be removed during the separation process, resulting in a pale yellow discoloration of the subsequently produced polyurethane foam. This discoloration adversely affects its practical application. Therefore, it is desirable to prepare isocyanates that are lighter in color or contain fewer dark components as raw materials for polyurethane production.

[0004] Currently, there is considerable research on the preparation of light-colored isocyanates, particularly those from the diphenylmethane series. Published methods for improving the color of polymeric MDI often require the introduction of new materials into the system, increasing operating costs and introducing new impurities, which can lead to other adverse effects. Furthermore, raw material control is difficult, often increasing procurement costs.

[0005] Summary of the Invention

[0006] To overcome at least one of the above-mentioned defects of the prior art, in a first aspect, one embodiment of the present invention provides a method for preparing diisocyanates and polyisocyanates of a diphenylmethane series, comprising the following steps:

[0007] S1: performing a phosgenation reaction of diphenylmethane series diamines and polyamines with phosgene in a solvent to obtain a first mixed solution;

[0008] S2: removing phosgene from the first mixed solution to obtain a second mixed solution;

[0009] S3: stripping the second mixed liquid with HCl gas to obtain a third mixed liquid; and

[0010] S4: removing the solvent from the third mixed liquid to obtain crude diisocyanates and polyisocyanates of the diphenylmethane series;

[0011] The stripping treatment in step S3 is performed in a stripping tower, the reflux ratio R of the stripping tower is 0.05-0.3, the contact time t between the second mixed liquid and the gaseous material containing HCl gas in the stripping tower is 1-10 min, the flow velocity v of the gaseous material in the stripping tower is 2-15 m / s, the mass ratio of the HCl gas to the solute of the second mixed liquid is m1:m2=(0.03-0.2):1; the mass percentage c1 of the solute of the second mixed liquid is 15-35%; and the mass percentage c2 of the solute of the third mixed liquid is 40-65%.

[0012] In a second aspect, an embodiment of the present invention provides a diphenylmethane series of diisocyanate and polyisocyanate products, which are prepared by the above-mentioned preparation method.

[0013] In a third aspect, an embodiment of the present invention provides a method for preparing diisocyanates and polyisocyanates of a diphenylmethane series, comprising the following steps:

[0014] S1: performing a phosgenation reaction of diphenylmethane series diamines and polyamines with phosgene in a solvent to obtain a first mixed solution;

[0015] S2: removing phosgene from the first mixed solution to obtain a second mixed solution;

[0016] S3: stripping the second mixed liquid with HCl gas to obtain a third mixed liquid; and

[0017] S4: removing the solvent from the third mixed liquid to obtain crude diisocyanates and polyisocyanates of the diphenylmethane series;

[0018] The stripping treatment in step S3 is performed in a stripping tower, R represents the reflux ratio of the stripping tower; t represents the contact time between the second mixed liquid and the gaseous material containing HCl gas in the stripping tower, in minutes; v represents the flow rate of the gaseous material in the stripping tower, in m / s; m1 represents the mass flow rate of HCl gas during the stripping treatment, in t / h; m2 represents the mass flow rate of the solute in the second mixed liquid during the stripping treatment, in t / h; c1 represents the mass percentage of the solute in the second mixed liquid, and c2 represents the mass percentage of the solute in the third mixed liquid; R, t, v, m1, m2, c1, and c2 satisfy the following relationship:

[0019] The method for preparing diphenylmethane series diisocyanates and polyisocyanates according to one embodiment of the present invention can produce diphenylmethane series diisocyanates and polyisocyanates products having a higher L* value and lighter color by optimizing the process parameters of the stripping treatment step, thereby reducing the impact on the subsequently produced polyurethane products. DETAILED DESCRIPTION

[0020] Typical embodiments that embody 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 is capable of various variations in different embodiments without departing from the scope of the present invention, and the descriptions herein are intended to be illustrative rather than limiting.

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

[0022] S1: phosgenating a diphenylmethane series diamine or polyamine (DAM) with phosgene in a solvent to obtain a first mixed solution;

[0023] S2: removing phosgene from the first mixed solution to obtain a second mixed solution;

[0024] S3: stripping the second mixed liquid with HCl gas to obtain a third mixed liquid; and

[0025] S4: removing the solvent from the third mixed liquid to obtain crude diisocyanates and polyisocyanates of the diphenylmethane series (crude MDI);

[0026] The stripping treatment in step S3 is performed in a stripping tower, the reflux ratio R of the stripping tower is 0.05-0.3, the contact time t between the second mixed liquid and the gaseous material containing HCl gas in the stripping tower is 1-10 minutes, the flow velocity v of the gaseous material in the stripping tower is 2-15 m / s, the mass ratio of HCl gas to the solute in the second mixed liquid is m1:m2=(0.03-0.2):1; the mass percentage c1 of the solute in the second mixed liquid is 15-35%; and the mass percentage c2 of the solute in the third mixed liquid is 40-65%.

[0027] In one embodiment, the solvent used for the liquid-phase phosgenation reaction in step S1 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, 150°C; the reaction pressure can be 2-30 bar, for example, 5 bar, 8 bar, 10 bar, 15 bar, 20 bar, 25 bar; the mass ratio of DAM to solvent can be 1:(1.1-5), for example, 1:1.5, 1:2, 1:3, 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, 1:4.

[0029] In one embodiment, in step S2, the first mixed liquid may be treated to remove phosgene in a distillation tower, and the phosgene is discharged from the top of the tower in a gaseous form.

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

[0031] In one embodiment, the gaseous material (gas) in the stripping tower includes evaporated solvent and HCl gas, and the flow rate v of the gaseous material can be 5 to 15 m / s, and further can be 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, and 14 m / s.

[0032] In one embodiment, HCl gas enters the stripping tower from the lower part, and the second mixed liquid enters the stripping tower from the upper part. The gaseous material containing HCl gas moves from bottom to top, and the second mixed liquid moves from top to bottom. The two contact and react in the tower.

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

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

[0035] In one embodiment, the operating temperature of the stripping tower (bottom temperature) can be 130-210°C, further 160-190°C, for example 150°C, 170°C, 180°C, 200°C; the operating pressure of the stripping tower (tower top pressure) can be 1-5 bar, further 2-4 bar, for example 3 bar.

[0036] In one embodiment, the reflux ratio R of the stripping tower may be 0.05 to 0.2, and further may be 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 measured according to gel permeation chromatography as described below. That is, c1 or c2 is obtained by measuring the mass percentage of the solvent in the mixed solution (the second mixed solution or the third mixed solution) by gel permeation chromatography, and then subtracting the mass percentage of the corresponding solvent from 100%. In other words, c3 is the mass percentage of the solvent in the second mixed solution, c1 = 100% - c3; c4 is the mass percentage of the solvent in the third mixed solution, c2 = 100% - c4.

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

[0039] In one embodiment, in the second mixed solution, the mass percentage c1 of the solute may be 23-35%, further may be 23-30%, for example, 18%, 20%, 25%, 26%, 28%, 33%.

[0040] In one embodiment, in the third mixed solution, the mass percentage c2 of the solute can be 45-65%, and further can be 50-60%, for example, 42%, 45%, 48%, 52%, 54%, 55%, 56%, 58%.

[0041] In one embodiment, the ratio of the mass flow rate m1 of the HCl gas in step S3 to the mass flow rate m2 of the solute in the second mixed solution can be m1:m2 = (0.05-0.25):1, further (0.05-0.2):1, further (0.05-0.15):1, and further (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, or 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 mixed solution by 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 column; t represents the contact time between the second mixed liquid and the gaseous material containing HCl gas in the stripping column in minutes; v represents the flow rate of the gaseous material in the stripping column 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 mixed liquid during the stripping process in t / h; c1 represents the mass percentage of the solute in the second mixed liquid, and c2 represents the mass percentage of the solute in the third mixed liquid; c1, c2, and R are all dimensionless numbers; R, t, v, m1, m2, c1, and c2 satisfy the following relationship:

[0043] The above formula represents only the numerical relationship between the parameters; the units on either side of the inequality do not correspond. Satisfying this relationship for parameters like t can improve the stripping efficiency of the HCl stripper and result in a higher L* and lighter color for the final crude MDI product.

[0044] In one embodiment, the desolventizing process includes a first desolventizing process and a second desolventizing process. The first desolventizing process can be performed in a distillation tower. Specifically, the third mixed liquid is fed into the distillation tower kettle, the produced liquid from the distillation tower kettle is fed into an evaporator, and the gaseous phase produced by the evaporator is returned to the distillation tower. The liquid phase is the desolventized reaction liquid. Furthermore, the desolventized reaction liquid can be subjected to a second desolventizing process to remove trace solvents therein. The second desolventizing process can be performed using a nitrogen stripping tower.

[0045] In one embodiment, the method for preparing MDI further includes the step of separating the crude MDI product. The separation step may be: refining and separating the crude MDI product in a distillation tower, wherein the bottom temperature of the distillation tower may be 180-250°C, for example, 180°C, 200°C, 230°C, 250°C, etc., and the top pressure may be 10-1000 Pa, for example, 10 Pa, 50 Pa, 100 Pa, 1000 Pa, etc., to obtain a polymerized MDI product in the bottom of the tower.

[0046] In one embodiment, the solvent content in the crude MDI is less than 1 wt %, further less than 2000 ppm, further less than 1500 ppm, for example, 1200-1400 ppm.

[0047] One embodiment of the present invention provides an MDI product, which is prepared by the above-mentioned preparation method.

[0048] In one embodiment, the L* of the MDI product is 85-93, such as 86, 87, 88, 90, 91, 92.

[0049] Unless otherwise specified, the raw materials, steps, process conditions, etc. of the method for preparing diphenylmethane series diisocyanates and polyisocyanates of the present invention can be the existing technology. For example, the preparation of diphenylmethane series diisocyanates and polyisocyanates can be carried out with reference to the methods disclosed in CN116217439A, CN108147979B, CN116034102A, CN102471241A, and CN111630027B.

[0050] Unless otherwise specified, the pressures referred to in the present invention refer to absolute pressures.

[0051] The inventors have discovered that, in addition to parameters such as operating temperature and pressure, the stripping effect is influenced by factors such as the gas velocity within the stripping column, the stripping column reflux ratio, the concentration of the mixed liquid before and after stripping, and the contact time between the mixed liquid and the stripping HCl within the stripping column. By optimizing the combination of these factors, in addition to temperature and pressure, the stripping effect can be further improved, thereby increasing the L* of the crude MDI product.

[0052] A method for preparing diphenylmethane-based diisocyanates and polyisocyanates according to one embodiment of the present invention reduces the impurity content by optimizing relevant parameters of the HCl stripping process, thereby obtaining a crude MDI product with a higher L* and lighter color. Furthermore, this method does not require modification of existing MDI processes and does not adversely affect existing processes and products.

[0053] The method for preparing diphenylmethane series diisocyanates and polyisocyanates according to one embodiment of the present invention can produce a crude MDI product with an L* of 85 to 93, thereby improving the quality of the product and the downstream application effect.

[0054] The following is a further description of the preparation method of diphenylmethane series diisocyanates and polyisocyanates according to one embodiment of the present invention, with reference to examples. The raw materials and testing methods used are as follows:

[0055] 1. Raw materials

[0056] Diphenylmethane diamines and polyamines (DAM): Wanhua Chemical (Ningbo) Co., Ltd., purity >99.99%. DAM is prepared by reacting aniline with hydrochloric acid at 60°C and 1 bar to produce aniline hydrochloride. This is then reacted with formaldehyde through a condensation-transfer process to produce a transfer solution. This solution is neutralized and washed with water to produce polyamines, which are then distilled and stripped to yield DAM.

[0057] Chlorobenzene: Wanhua Chemical (Ningbo) Co., Ltd., purity >99.9%.

[0058] Phosgene: Wanhua Chemical (Ningbo) Co., Ltd., purity >95.0%.

[0059] 2. Determination of L* of crude MDI

[0060] The colorimeter was measured using a VTS spectrophotometer from Hunterlab. The specific process was as follows: a colorimetric cell was placed in the instrument's detection tank for blank calibration. After the calibration was complete, the sample to be tested was placed in the colorimetric cell and placed in the instrument's detection tank for reading.

[0061] 3. Determination of mass percentage of solute in a mixture (e.g., c1 or c2)

[0062] The mass percentage of solutes in the mixed solution was determined and calculated using gel permeation chromatography (GPC). The analysis method was as follows: 10 μL of the mixed solution was injected directly into the sample. The chromatographic columns were Waters HR01*1 and Waters HR01*3, and the column oven temperature was 35°C. The detector type was an FID detector at 35°C, and the mobile phase was tetrahydrofuran at a flow rate of 1 mL / min. The mass percentage of the solvent in the mixed solution was obtained by integrating the chromatogram: 100% - the mass percentage of the solvent.

[0063] 4. The solvent content in crude MDI was determined by gel permeation chromatography (GPC). The crude MDI was diluted 10 times with dichloromethane and then sampled for analysis. The rest of the method was the same as above.

[0064] Example 1

[0065] S1: DAM and chlorobenzene were mixed to obtain a mixed solution with a DAM concentration of 33 wt%, and a phosgene chlorobenzene solution with a phosgene concentration of 65 wt% (the mass ratio of DAM to phosgene was 1:2.5) was added to the mixed solution. The mixture was reacted at 5 bar and 95°C for 0.5 h to obtain a first mixed solution.

[0066] S2: removing phosgene from the first mixed liquid at 1 bar and 130° C. to obtain a second mixed liquid; in the second mixed liquid, the mass percentage c1 of the solute containing MDI is 27%.

[0067] S3: The second mixed liquid is fed into a hydrogen chloride stripping tower operating at a pressure of 2 bar, a bottom temperature of 180°C, and an overhead reflux ratio R of 0.1. HCl gas is introduced from the bottom of the tower for stripping, with a mass ratio m1:m2 of the stripped HCl gas to the solutes in the second mixed liquid being 0.08:1. The contact time t between the stripped HCl-containing gas and the second mixed liquid in the tower is controlled to be 5 minutes, and the gas velocity v in the tower is controlled to be 7 m / s. A third mixed liquid is obtained in the bottom of the tower after stripping. The mass percentage c2 of the solutes containing MDI in the third mixed liquid is 55%.

[0068] S4: The third mixed liquid is subjected to dechlorobenzene treatment in a distillation tower at a top pressure of 30 kPa and a bottom temperature of 195°C to obtain dechlorobenzeneed MDI (i.e., a desolvated reaction liquid). The dechlorobenzeneed MDI is then fed into a nitrogen stripping tower at 35 kPa and 190°C to further remove trace solvents. The mass ratio of nitrogen to desolvated reaction liquid is controlled to be 0.04, yielding crude MDI in the bottom of the tower. The crude MDI is tested using a colorimeter, and its L* is measured to be 92. The solvent content in the crude MDI is 1200 ppm.

[0069] Example 1-1

[0070] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.05.

[0071] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0072] Example 1-2

[0073] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.08.

[0074] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0075] Examples 1-3

[0076] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.15.

[0077] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0078] Examples 1-4

[0079] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.2.

[0080] The L* of the obtained crude MDI was 87; the solvent content in the crude MDI was 1200 ppm.

[0081] Examples 1-5

[0082] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.3.

[0083] The L* of the obtained crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0084] Examples 1-6

[0085] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the reflux ratio R of the stripping tower is 0.35.

[0086] The L* of the obtained crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0087] Example 2

[0088] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 1 min.

[0089] The L* of the obtained crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0090] Example 2-1

[0091] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 3 minutes.

[0092] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0093] Example 2-2

[0094] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 6 minutes.

[0095] The L* of the obtained crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0096] Example 2-3

[0097] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 8 minutes.

[0098] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0099] Examples 2-4

[0100] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 10 min.

[0101] The L* of the obtained crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0102] Examples 2-5

[0103] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the contact time t between the second mixed liquid and the gaseous material containing HCl gas is 11 minutes.

[0104] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0105] Example 3

[0106] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the flow rate v of the gas phase material in the stripping tower is 2 m / s.

[0107] The L* of the obtained crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0108] Example 3-1

[0109] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the flow rate v of the gas phase material in the stripping tower is 5 m / s.

[0110] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0111] Example 3-2

[0112] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the flow rate v of the gas phase material in the stripping tower is 10 m / s.

[0113] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0114] Example 3-3

[0115] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the flow rate v of the gas phase material in the stripping tower is 15 m / s.

[0116] The L* of the obtained crude MDI was 87; the solvent content in the crude MDI was 1200 ppm.

[0117] Examples 3-4

[0118] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3 , the flow rate v of the gas phase material in the stripping tower is 17 m / s.

[0119] The L* of the obtained crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0120] Example 4

[0121] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.02:1.

[0122] The L* of the obtained crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0123] Example 4-1

[0124] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.03:1.

[0125] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0126] Example 4-2

[0127] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid is m1:m2=0.05:1.

[0128] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0129] Example 4-3

[0130] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.1:1.

[0131] The L* of the obtained crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0132] Example 4-4

[0133] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.15:1.

[0134] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0135] Examples 4-5

[0136] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.2:1.

[0137] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0138] Examples 4-6

[0139] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that in step S3, the mass ratio of the stripped HCl gas to the mass of the solute in the fed second mixed liquid, m1:m2, is 0.25:1.

[0140] The L* of the obtained crude MDI was 89; the solvent content in the crude MDI was 1200 ppm.

[0141] Example 5

[0142] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 13%.

[0143] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0144] Example 5-1

[0145] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 15%.

[0146] The L* of the obtained crude MDI was 86; the solvent content in the crude MDI was 1200 ppm.

[0147] Example 5-2

[0148] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 23%.

[0149] The L* of the obtained crude MDI was 90; the solvent content in the crude MDI was 1200 ppm.

[0150] Example 5-3

[0151] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 30%.

[0152] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0153] Example 5-4

[0154] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 35%.

[0155] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0156] Example 5-5

[0157] This embodiment uses substantially the same raw materials and process as in Example 1 to prepare MDI, with the only difference being that the mass percentage c1 of the solute in the second mixed solution is 38%.

[0158] The L* of the obtained crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0159] Example 6

[0160] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 38%.

[0161] The L* of the obtained crude MDI was 83; the solvent content in the crude MDI was 1200 ppm.

[0162] Example 6-1

[0163] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 40%.

[0164] The L* of the obtained crude MDI was 85; the solvent content in the crude MDI was 1200 ppm.

[0165] Example 6-2

[0166] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 45%.

[0167] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0168] Example 6-3

[0169] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 50%.

[0170] The L* of the obtained crude MDI was 91; the solvent content in the crude MDI was 1200 ppm.

[0171] Example 6-4

[0172] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 60%.

[0173] The L* of the obtained crude MDI was 92; the solvent content in the crude MDI was 1200 ppm.

[0174] Example 6-5

[0175] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 65%.

[0176] The L* of the obtained crude MDI was 88; the solvent content in the crude MDI was 1200 ppm.

[0177] Example 6-6

[0178] This embodiment uses substantially the same raw materials and process as in embodiment 1 to prepare MDI, with the only difference being that the mass percentage content c2 of the solute in the third mixed solution is 68%.

[0179] The L* of the obtained crude MDI was 84; the solvent content in the crude MDI was 1200 ppm.

[0180] Example 7

[0181] S1: DAM and chlorobenzene were mixed to obtain a mixed solution with a DAM concentration of 20 wt%, and a phosgene chlorobenzene solution with a phosgene concentration of 65 wt% (the mass ratio of DAM to phosgene was 1:3) was added to the mixed solution. The mixture was reacted at 5 bar and 95°C for 0.5 h to obtain a first mixed solution.

[0182] S2: removing phosgene from the first mixed liquid at 1 bar and 130° C. to obtain a second mixed liquid; in the second mixed liquid, the mass percentage c1 of the solute containing MDI is 18%.

[0183] S3: The second mixed liquid is fed into a hydrogen chloride stripping tower operating at 6 bar, a bottom temperature of 215°C, and an overhead reflux ratio (R) of 0.04. HCl gas is introduced from the bottom of the tower for stripping, with a mass ratio (m1:m2) of the stripped HCl gas to the solute in the second mixed liquid being 0.02:1. The contact time (t) of the stripped HCl-containing gas and the second mixed liquid in the tower is controlled to be 0.5 min, and the gas velocity (v) in the tower is controlled to be 16 m / s. A third mixed liquid is obtained in the bottom of the tower after stripping. The mass percentage (c2) of the solute containing MDI in the third mixed liquid is 45%.

[0184] S4: The third mixed liquid was subjected to dechlorobenzene treatment at 30 kPa and 195°C. The dechlorobenzeneed MDI (i.e., the desolventized reaction liquid) was then fed into a nitrogen stripping tower and treated at 35 kPa and 190°C. The mass ratio of nitrogen to desolventized reaction liquid was controlled to be 0.04, yielding crude MDI in the bottom of the tower. The crude MDI was tested using a colorimeter, and its L* was measured to be 80. The solvent content in the crude MDI was 1400 ppm.

[0185] Table 1 below lists the parameters related to the stripping process and the L* values ​​of the obtained products of various examples.

[0186] Table 1

[0187] Examples 1 to 1-6 differ in the reflux ratio R of the stripping column in step S3. The results in Table 1 show that the L* of the products produced 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 produced 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 column in step S3 is preferably 0.05 to 0.2, and more preferably 0.08 to 0.15.

[0188] Examples 1, 2, and 2-5 differ in that, in step S3, the contact time t between the second mixed liquid and the gaseous phase containing HCl gas varies. Table 1 shows that the L* values ​​of the products produced in Examples 1, 2-1, and 2-4 are higher than those of the products produced in Examples 2 and 2-5. Furthermore, the L* values ​​of the products produced in Examples 1, 2-1, and 2-2 are higher than those of the products produced in Examples 2-3 and 2-4. Therefore, in step S3, the contact time t between the second mixed liquid and the gaseous phase containing HCl gas is preferably 3 to 10 minutes, more preferably 3 to 6 minutes, and even more preferably 5 to 6 minutes.

[0189] The difference between Examples 1, 3, and 3-4 is that the flow rate v of the gaseous phase in the stripping tower in step S3 is different. According to the results in Table 1, the L* of the products produced in Examples 1, 3, and 3-3 is higher than the L* of the product in Example 3-4. Furthermore, the L* of the products produced in Examples 1, 3-1, and 3-3 is higher than the L* of the product in Example 3. Furthermore, the L* of the products produced in Examples 1, 3-1, and 3-2 is higher than the L* of the product in Example 3-3. Therefore, in step S3, the flow rate v of the gaseous phase is preferably 2 to 15 m / s, more preferably 5 to 15 m / s, and even more preferably 5 to 10 m / s.

[0190] The difference between Examples 1, 4, and 4-6 is that in step S3, the mass ratio m1:m2 of the stripped HCl gas to the solute in the second mixed liquid is different. According to the results in Table 1, the L* of the products obtained in Examples 1, 4-2, and 4-6 is higher than the L* of the product in Example 4 and 4-1. Furthermore, the L* of the products obtained in Examples 1, 4-2, and 4-5 is higher than the L* of the product in Example 4-6. Furthermore, the L* of the products obtained in Examples 1, 4-3, and 4-4 is higher than the L* of the product in Example 4-2 and 4-5. Therefore, the value of m1:m2 is preferably (0.05-0.25):1, more preferably (0.05-0.2):1, further preferably (0.05-0.15):1, and even more preferably (0.08-0.1):1.

[0191] The difference between Examples 1, 5, and 5-5 lies in the different mass percentages of the solute c1 in the second mixed solution. The results in Table 1 show that the L* values ​​of the products obtained in Examples 1, 5-1, 5-4, and 5-5-6 are higher than the L* values ​​of the product obtained in Example 5 and 5-1. Furthermore, the L* values ​​of the products obtained in Examples 1, 5-2, 5-4, and 5-6 are higher than the L* values ​​of the product obtained in Example 5-1. Furthermore, the L* values ​​of the products obtained in Examples 1, 5-2, and 5-3 are higher than the L* values ​​of the product obtained in Example 5-4. Therefore, c1 is preferably 15-35%, more preferably 23-35%, and even more preferably 23-30%.

[0192] Examples 1, 6, and 6-6 differ in the mass percentage of the solute, c2, in the third mixed solution. The results in Table 1 show that the L* values ​​of the products produced in Examples 1, 6-1, 6-5, and 6-6 are higher than those of the products produced in Examples 6 and 6-6. Furthermore, the L* values ​​of the products produced in Examples 1, 6-2, 6-5, and 6-1 are higher than those of the product produced in Example 6-1. Furthermore, the L* values ​​of the products produced in Examples 1, 6-3, and 6-4 are higher than those of the products produced in Examples 6-2 and 6-5. Therefore, c2 is preferably 40-65%, more preferably 45-65%, and even more preferably 50-60%.

[0193] Unless otherwise defined, the terms used in the present invention have the same meanings as those commonly understood by those skilled in the art.

[0194] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, but is only limited by the claims.

Claims

1. A method for preparing diisocyanates and polyisocyanates of a diphenylmethane series, comprising the following steps: S1: performing a phosgenation reaction on a diphenylmethane series diamine and polyamine with phosgene in a solvent to obtain a first mixed solution; S2: removing phosgene from the first mixed solution to obtain a second mixed solution; S3: stripping the second mixed liquid with HCl gas to obtain a third mixed liquid; and S4: removing the solvent from the third mixed liquid to obtain crude diisocyanates and polyisocyanates of the diphenylmethane series; in, The stripping treatment in step S3 is carried out in a stripping tower, the reflux ratio R of the stripping tower is 0.05-0.3, the contact time t between the second mixed liquid and the gaseous material containing HCl gas in the stripping tower is 1-10 min, the flow rate v of the gaseous material in the stripping tower is 2-15 m / s, the mass ratio of the HCl gas to the solute of the second mixed liquid is m1:m2=(0.03-0.2):1; the mass percentage content c1 of the solute of the second mixed liquid is 15-35%; the mass percentage content c2 of the solute of the third mixed liquid is 40-65%.

2. The preparation method according to claim 1, wherein The contact time t between the second mixed liquid and the gas phase material containing HCl gas in the stripping tower is 3 to 6 minutes, and can further be 5 to 6 minutes.

3. The preparation method according to claim 1, wherein The reflux ratio R of the stripping tower is 0.05 to 0.2, and can further be 0.08 to 0.

15.

4. The preparation method according to claim 1, wherein The flow velocity v of the gas phase material in the stripping tower may be 5 to 15 m / s, and further may be 5 to 10 m / s.

5. The preparation method according to claim 1, wherein c1 is 23-35%, and can further be 23-30%; c3 is the mass percentage of the solvent in the second mixed solution, and the sum of c1 and c3 is 100%; and / or, c2 is 45-65%, and can further be 50-60%; c4 is the mass percentage of the solvent in the third mixed liquid, and the sum of c2 and c4 is 100%.

6. The preparation method according to claim 1, wherein The mass ratio of the HCl gas to the solute of the second mixed liquid is m1:m2=(0.05-0.25):1, further can be (0.05-0.2):1, further can be (0.05-0.15):1, and further can be (0.08-0.1):

1.

7. The preparation method according to claim 6, wherein: R, t, v, m1, m2, c1, c2 satisfy the following relationship:

8. The preparation method according to claim 1, wherein The operating temperature of the stripping tower is 130-210° C., further 160-190° C.; and / or, The operating pressure of the stripping tower is 1 to 5 bar, further 2 to 4 bar; and / or, The L* of the crude diisocyanate and polyisocyanate of the diphenylmethane series is 85-93.

9. A method for preparing diisocyanates and polyisocyanates of a diphenylmethane series, comprising the following steps: S1: performing a phosgenation reaction on a diphenylmethane series diamine and polyamine with phosgene in a solvent to obtain a first mixed solution; S2: removing phosgene from the first mixed solution to obtain a second mixed solution; S3: stripping the second mixed liquid with HCl gas to obtain a third mixed liquid; and S4: removing the solvent from the third mixed liquid to obtain crude diisocyanates and polyisocyanates of the diphenylmethane series; in, The stripping treatment in step S3 is carried out in a stripping tower, R represents the reflux ratio of the stripping tower; t represents the contact time between the second mixed liquid and the gaseous substance containing HCl gas in the stripping tower, in minutes; 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 treatment, in t / h; m2 represents the mass flow rate of the solute in the second mixed liquid during the stripping treatment, in t / h; c1 represents the mass percentage of the solute in the second mixed liquid, and c2 represents the mass percentage of the solute in the third mixed liquid; R, t, v, m1, m2, c1, and c2 satisfy the following relationship:

10. A diphenylmethane series of diisocyanate and polyisocyanate products, prepared by the preparation method according to any one of claims 1 to 9.

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