Pure MDI with low hydrolysis chlorine and preparation method thereof

Abstract

The invention discloses pure MDI with low hydrolysis chlorine and a preparation method thereof. The invention relates to pure MDI with low hydrolytic chlorine, which is prepared from the following components in percentage by weight: 0.05 to 0.10 percent of 2, 2-MDI, 0.50 to 2.00 percent of 2, 4-MDI, 97.9 to 99.45 percent of 4, 4-MDI and 5 to 10 ppm of chlorinated substance. The structural formula of the chloro compound is as shown in formula I: # imgabs0 #, and the content of hydrolyzed chlorine in the pure MDI product is less than 10ppm, so that the activity of the pure MDI product can be kept stable in the downstream application process, and the problem that the color of the pure MDI is darkened in the storage process is avoided.

Description

Technical Field

[0001] The invention relates to a method for preparing low-hydrolyzed chlorine pure MDI, belonging to the technical field of isocyanate. Background Art

[0002] At present, the production process of diphenylmethane diisocyanate (MDI) is mainly phosgenation: first, aniline and formaldehyde react in the presence of a catalyst to form a mixture of diphenylmethylenediamine and polyphenylmethylenepolyamine (DAM); then, DAM reacts with phosgene to form crude MDI, which is a mixture of dicyclic MDI (including three isomers of 2,2'-MDI, 2,4'-MDI and 4,4'-MDI) and polycyclic MDI (polyphenylmethylene polyisocyanate); crude MDI is prepared by distillation to obtain pure MDI (4,4'-MDI) and polymerized MDI. Among them, pure MDI has a wide range of applications in microporous elastomers, thermoplastic elastomers, synthetic leather, adhesives, coatings and other fields.

[0003] A large amount of chlorine-containing byproducts will be generated during the reaction of DAM and phosgene, resulting in an increase in the hydrolysis chlorine of pure MDI separated from crude MDI. The hydrolysis chlorine will affect the reactivity of pure MDI products in the downstream application process of isocyanate. The higher the hydrolysis chlorine in pure MDI, the lower the product application activity and the darker the color of downstream products. Therefore, reducing the hydrolysis chlorine of pure MDI products can effectively improve the application performance of pure MDI downstream products.

[0004] How to reduce the hydrolyzed chlorine in pure MDI products? Currently, the technologies disclosed at home and abroad are mainly the following:

[0005] Patent US2885420A adds 0.01-0.5wt% of aromatic, cyclic aliphatic or fatty ether or thioether according to the weight of polyisocyanate, thereby reducing the color of the isocyanate product.

[0006] Patent EP0561225B treats isocyanate with hydrogen at 100-180°C under a pressure of 1-150 bar to reduce the hydrolysis chlorine content and color of the isocyanate product.

[0007] Patent CN1148056A adds a certain amount of water or a mixture of monohydroxy or polyhydroxy polyoxyalkylene alcohols after the phosgenation reaction and then removes excess phosgene, thereby reducing the chlorine content and color of isocyanate.

[0008] Patent EP0866057A describes that the color of the final product isocyanate can be lightened by treating diamine or polyamine with Lewis acid or Bronsted acid solid substances.

[0009] Patent US6900348B provides a method for preparing light-colored isocyanate by reacting diamine or polyamine with phosgene containing less than 50 ppm of bromine compound or iodine compound.

[0010] Patent CN112430295B provides a dechlorinating agent and its application in reducing the chlorine content and color in isocyanate, which reduces the chlorine content of crude MDI and significantly improves the color through chemical and physical adsorption.

[0011] The above methods have certain effects on reducing the chlorine content and color of isocyanates, but they all have certain limitations. On the one hand, the treatment methods of raw materials such as amines or phosgene have limited effects. On the other hand, adding water or other organic substances to the photochemical reaction liquid or isocyanate will lead to the generation of other impurities, affecting the purity and NCO content of the product. Summary of the invention

[0012] The existing isocyanate dechlorination method mainly processes the raw materials before and after the phosgene reaction, and there is a problem of introducing new impurities during the dechlorination process. The purpose of the present invention is to provide a process for reducing the hydrolysis chlorine of the isocyanate product. Through this method, a low-hydrolysis chlorine pure MDI product can be obtained, avoiding the introduction of new impurities.

[0013] The present invention controls the chlorine content to be 5-10 ppm so that the hydrolyzed chlorine of pure MDI is less than 10 ppm.

[0014] In the present invention, the contents of chlorinated substances and chlorobenzene are calculated based on the sum of dicyclic MDI and polycyclic MDI.

[0015] The present invention provides a low-hydrolyzed chlorine pure MDI, comprising the following components:

[0016]

[0017] In the present invention, through mass spectrometry analysis technology, the structural formula of the chlorinated substance affecting the hydrolysis chlorine index of the pure MDI product of the present invention is as follows:

[0018]

[0019] In a specific embodiment, the content of the chlorinated compound of formula I described in the present invention in the crude MDI obtained by phosgenation reaction is 50-180 ppm, wherein the chlorinated compound content is related to the phosgenation reaction conditions and the raw material composition. It is difficult to reduce the chlorinated compound content in the crude MDI to below 10 ppm by the existing process.

[0020] A method for preparing low-hydrolyzed chlorine pure MDI comprises the following steps:

[0021] (1) stripping the crude MDI with reduced pressure gas at high temperature;

[0022] (2) The product of distillation step (1).

[0023] The crude MDI of the present invention comprises the following components:

[0024]

[0025]

[0026] The crude MDI described in the present invention is crude MDI prepared by phosgenation technology. The preparation of crude MDI by phosgenation technology is an existing process well known in the art and will not be described in detail.

[0027] The gas stripping temperature of the present invention is 150-200° C., preferably 170-190° C. At this temperature, the chlorinated compound of the present invention is helpful for decomposition, and the color of the crude MDI is not increased, and the product quality is not affected.

[0028] The pressure of the gas stripping described in the present invention is 10.0-25.0 kPaA.

[0029] The gas stripping gas described in the present invention is a gas that will not cause adverse effects on the materials in the method, including but not limited to nitrogen, helium, argon, carbon dioxide, etc.

[0030] The stripping time of the present invention is 20-60 minutes, preferably 30-45 minutes. Although extending the stripping time is beneficial to reducing the chlorinated compound content in the crude MDI, since the crude MDI will generate dimers at high temperatures, the stripping time needs to be strictly controlled.

[0031] As a preferred solution, the gas flow rate in the gas stripping process of the present invention is 300-800 Nm 3 / h, corresponding to the crude MDI processing capacity of 20t / h, considering the removal effect and economy of chlorinated substances in crude MDI, 400-600Nm 3 / h, corresponding to a crude MDI processing capacity of 20t / h. In the MDI production process, the crude MDI processing capacity is higher than 800Nm 3 / h, or less than 300Nm 3 / h, the flow rate of the gas in the gas stripping of the present invention can be adjusted according to the processing capacity.

[0032] The present invention uses gas stripping treatment to decompose the chloro compound of formula I in the crude MDI into MDI and hydrogen chloride, and the hydrogen chloride enters the vacuum unit in the form of gas, thereby avoiding the increase of hydrolyzed chlorine in the downstream of the product, which affects the activity and storage stability of the pure MDI product. The gas stripping treatment reduces the content of the chloro compound of formula I in the crude MDI to less than 10ppm.

[0033] Separating isocyanate isomers by distillation tower is a well-known industrial method in the industry. The distillation tower can be in the form of a side-line distillation tower or a dividing wall tower. The control means of the distillation separation process are well known to those skilled in the art. For example, by controlling parameters such as steam volume, distillation tower temperature, side-line extraction volume, etc., the distillation separation is carried out as expected and a pure MDI product is obtained.

[0034] As a preferred embodiment, the distillation of the present invention comprises the following steps:

[0035] (1) The crude MDI after high-temperature and reduced-pressure stripping is preheated and then enters the first distillation tower for separation. By adjusting the preheating temperature, the pressure at the top of the first distillation tower and the bottom temperature, the two-ring MDI is produced from the top of the tower and the polymerized MDI is produced from the bottom of the tower;

[0036] (2) The two-ring MDI is sent to the second distillation tower for purification, and the low-hydrolyzed chlorine pure MDI product is obtained by adjusting the distillation tower top pressure, tower bottom temperature and side line extraction ratio.

[0037] As a preferred solution, the temperature of the first distillation tower kettle is 185-215°C, and the pressure at the top of the distillation tower is 0.1-1 kPaA.

[0038] As a preferred solution, the bottom temperature of the second distillation tower is 190-210° C., and the top pressure is 0.1-2 kPaA, wherein the pure MDI product is withdrawn from the side line of the second distillation tower.

[0039] The present invention has been found through research that, during the preparation process of MDI, the diamine in the raw material DAM that is not completely transferred will react with phosgene to generate a chlorinated product of formula I and enter the crude MDI. The chlorinated product is difficult to separate through a distillation tower. During the MDI separation process, the chlorinated product will be extracted from the distillation tower gas phase and enter the pure MDI product, thereby causing an increase in the hydrolysis chlorine of the pure MDI.

[0040] The inventors of the present invention unexpectedly found that the chlorinated substance of formula I in crude MDI can be effectively reduced to below 10 ppm by high-temperature gas stripping treatment at a specific temperature, and the hydrolyzed chlorine of the pure MDI product can be further reduced to below 10 ppm, thereby solving the color development problem of the pure MDI product during storage and improving the quality of the pure MDI product.

[0041] The technical solution of the present invention does not introduce new impurities into the crude MDI raw material, so the prepared pure MDI product has high purity and the hydrolyzed chlorine content is stable and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 , 2 They are the gas phase and fragment peak mass spectra of pure MDI chloride respectively. DETAILED DESCRIPTION

[0043] 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 the embodiments, but the content of the present invention is not limited to the following embodiments.

[0044] The reagents used in the examples are all conventional reagents in the art. The following detection methods or experimental methods, unless otherwise specified, are all conventional technical means known to those skilled in the art based on the prior art they possess.

[0045] The percentages "%" hereinafter all refer to "wt %".

[0046] The test methods involved in the following experimental process are described as follows:

[0047] Qualitative and quantitative methods for chlorinated compounds

[0048] The chlorinated compounds of formula I in the pure MDI product were qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS), and the MDI composition was quantitatively analyzed by gas chromatography. The specific gas chromatography conditions are as follows:

[0049] Heating program: 150°C, hold for 0.5 min, then increase to 300°C at 10°C / min, hold for 15 min; injection volume: 1 μL;

[0050] Front inlet temperature: 280°C, split ratio: 20:1;

[0051] Chromatographic column: Agilent 19091J-413HP-5 30m x 320μm x 0.25μm;

[0052] Column flow rate: 1 mL / min;

[0053] The solvent was dichloromethane, HPLC grade.

[0054] Figure 1 This is the gas phase spectrum, in which the peak time of the chlorinated product is 17.5min. Figure 2 The mass spectrum of chlorinated substances shows that the molecular weight of the chlorinated substance is 286. The impurity is the phosgenation product of the untransposed MDA substance. The formation of the acyl chloride chemical bond weakens the chemical bond between the methylene group and the benzene ring. After bombardment by the mass spectrometry ion source, obvious PI fragments appear. The 167 / 168 fragment intensity ratio is close to 3:1, which is consistent with the existence law of chlorine in nature. The chlorinated substance content is analyzed by the area normalization method.

[0055] Hydrolyzed Chlorine Analysis Method

[0056] (1) Weigh two parallel samples, about 0.5 g, and record the weighing data m;

[0057] (2) Add 20 ml of acetone to both the sample and the blank;

[0058] (3) Continue to add 50 ml of anhydrous ethanol and react for 30 min. Move the sample after alcoholysis to a high-temperature heating stirrer;

[0059] (4) Add 150 ml of pure water, raise the temperature to 70°C, and stir at this constant temperature for 30 min;

[0060] (5) After cooling the sample to 30°C, add 5 ml of 20% nitric acid;

[0061] (6) Automatic potentiometric titration was used, with the standard solutions being 1 mg / ml sodium chloride standard solution and 0.05 mol / L silver nitrate standard solution. The concentration of the silver nitrate standard solution was recorded as C.

[0062] (7) Record the volume V0 of the silver nitrate solution before titration and the volume V1 after titration.

[0063] The hydrolyzable chlorine content is calculated using the following formula:

[0064] Cl(%)=(V1-V0)×C×0.03546×100 / m

[0065] The data were considered valid if the relative error between two parallel results was no greater than 10%.

[0066] Example 1

[0067] In this embodiment, the gas phase composition data of the crude MDI before gasification are as follows:

[0068]

[0069]

[0070] The method steps for treating the crude MDI to reduce the hydrolyzed chlorine in the pure MDI are as follows:

[0071] 1) 20t / h crude MDI is stripped with nitrogen at 10kPaA, 190℃ and a nitrogen flow rate of 600Nm 3 / h, gas stripping time 40min.

[0072] Wherein, after the high-temperature gas stripping treatment in step 1), the crude MDI is rapidly cooled to 50°C and then sampled and analyzed. The gas phase composition data of the crude MDI after gas stripping are as follows:

[0073]

[0074] 2) The crude MDI after gas stripping is separated into polymerized MDI and two-ring MDI by the first distillation tower. The operating temperature of the distillation tower is controlled to be 195°C, and the operating pressure at the top of the tower is 0.2 kPaA. Low-chlorinated two-ring MDI is obtained at the top of the first distillation tower. The gas phase composition is as follows:

[0075]

[0076]

[0077] 3) The two-ring MDI obtained at the top of the first distillation tower in step 2) is used as a raw material to separate isomers through a second distillation tower, wherein pure MDI is obtained from the side line of the tower. The operating temperature of the distillation tower is controlled to be 200°C, the operating pressure at the top of the tower is 0.3 kPaA, and the gas phase composition data of the pure MDI from the side line of the second distillation tower are as follows:

[0078]

[0079] Example 2

[0080] In this embodiment, the gas phase composition data of the crude MDI before gasification are as follows:

[0081]

[0082]

[0083] The method steps for treating the crude MDI to reduce the hydrolyzed chlorine in the pure MDI are as follows:

[0084] 1) 20t / h crude MDI is stripped with nitrogen at 15kPaA, 180℃ and a nitrogen flow rate of 500Nm 3 / h, gas stripping time 30min.

[0085] Wherein, after the high-temperature gas stripping treatment in step 1), the crude MDI is rapidly cooled to 50°C and then sampled and analyzed. The gas phase composition data of the crude MDI after gas stripping are as follows:

[0086]

[0087] 2) The crude MDI after gas stripping is separated into polymerized MDI and two-ring MDI by the first distillation tower. The operating temperature of the distillation tower is controlled to be 195°C, and the operating pressure at the top of the tower is 0.2 kPaA. Low-chlorinated two-ring MDI is obtained at the top of the first distillation tower. The gas phase composition is as follows:

[0088]

[0089]

[0090] 3) The two-ring MDI obtained at the top of the first distillation tower in step 2) is used as a raw material to separate isomers through a second distillation tower, wherein pure MDI is obtained from the side line of the tower. The operating temperature of the distillation tower is controlled to be 200°C, the operating pressure at the top of the tower is 0.3 kPaA, and the gas phase composition data of the pure MDI from the side line of the second distillation tower are as follows:

[0091]

[0092] Example 3

[0093] In this embodiment, the gas phase composition data of the crude MDI before gasification are as follows:

[0094]

[0095] The method steps for treating the crude MDI to reduce the hydrolyzed chlorine in the pure MDI are as follows:

[0096] 1) 20t / h crude MDI is stripped with nitrogen at 20kPaA, 170℃ and a nitrogen flow rate of 400Nm 3 / h, gas stripping time 20min.

[0097] Wherein, after the high-temperature gas stripping treatment in step 1), the crude MDI is rapidly cooled to 50°C and then sampled and analyzed. The gas phase composition data of the crude MDI after gas stripping are as follows:

[0098]

[0099] 2) The crude MDI after gas stripping is separated into polymerized MDI and two-ring MDI by the first distillation tower. The operating temperature of the distillation tower is controlled to be 195°C, and the operating pressure at the top of the tower is 0.2 kPaA. Low-chlorinated two-ring MDI is obtained at the top of the first distillation tower. The gas phase composition is as follows:

[0100]

[0101] 3) The two-ring MDI obtained at the top of the first distillation tower in step 2) is used as a raw material to separate isomers through a second distillation tower, wherein pure MDI is obtained from the side line of the tower. The operating temperature of the distillation tower is controlled to be 200°C, the operating pressure at the top of the tower is 0.3 kPaA, and the gas phase composition data of the pure MDI from the side line of the second distillation tower are as follows:

[0102]

[0103] After being treated by the method of the present invention, the content of the chlorinated compound of formula I in the crude MDI is greatly reduced, and the chlorinated compound is separated from the crude MDI and enters the vacuum unit through high-temperature gas stripping treatment, thereby solving the problem that the chlorinated compound enters the pure MDI through gas phase extraction in the second distillation tower, resulting in an increase in product hydrolysis chlorine.

[0104] Comparative Example 1

[0105] In this comparative example, the gas phase composition data of crude MDI are as follows:

[0106]

[0107] The crude MDI obtained by phosgenation reaction is separated into polymerized MDI and two-ring MDI by the first distillation tower. The operating temperature of the distillation tower is controlled to be 195°C, and the operating pressure at the top of the tower is 0.2 kPaA. High-chlorinated two-ring MDI is obtained at the top of the first distillation tower. The gas phase composition data are as follows:

[0108]

[0109] 2) High-chlorinated bicyclic MDI is separated into isomers through the second distillation tower, and pure MDI is obtained from the side line of the distillation tower. The operating temperature of the distillation tower is controlled to be 200°C, and the operating pressure at the top of the tower is 0.3kPaA. The gas phase composition data of pure MDI are as follows:

[0110]

[0111] Compared with the embodiment, in the distillation process of crude MDI without gas stripping treatment, the chlorinated product of formula I is withdrawn from the side line of the second distillation tower into pure MDI, resulting in an increase in its hydrolysis chlorine.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A low hydrolyzable chlorine pure MDI, comprising the following components: The structural formula of the chlorinated compound is as shown in Formula I:

2. A method for preparing the low-hydrolyzable chlorine pure MDI according to claim 1, comprising the following steps: (1) stripping the crude MDI with reduced pressure gas at high temperature; (2) The product of distillation step (1).

3. The method according to claim 2, characterized in that The crude MDI comprises the following components:

4. The method according to claim 2, characterized in that The stripping temperature is 150-200°C, preferably 170-190°C.

5. The method according to claim 2, characterized in that: The pressure of the gas stripping is 10.0-25.0 kpaA.

6. The method according to claim 2, characterized in that The stripping gas is a gas that will not adversely affect the materials in the method, preferably one or more of nitrogen, helium, argon, and carbon dioxide.

7. The method according to claim 2, characterized in that: The stripping time is 20-60 min, preferably 30-45 min.

8. The method according to claim 2, characterized in that: The gas flow rate in the gas stripping is 300-800Nm 3 / h, corresponding to a crude MDI processing capacity of 20t / h, preferably 400-600Nm 3 / h, and the corresponding crude MDI processing capacity is 20t / h.

9. The method according to claim 2, characterized in that: The content of the chlorinated compound of formula I in the crude MDI is reduced to below 10 ppm by gas stripping.

10. The method according to claim 2, characterized in that The distillation comprises the following steps: (1) The crude MDI after high-temperature and reduced-pressure stripping is preheated and then enters the first distillation tower for separation. By adjusting the preheating temperature, the pressure at the top of the first distillation tower and the bottom temperature, the two-ring MDI is produced from the top of the tower and the polymerized MDI is produced from the bottom of the tower; (2) The two-ring MDI is sent to the second distillation tower for purification, and the low-hydrolyzed chlorine pure MDI product is obtained by adjusting the distillation tower top pressure, tower bottom temperature and side line extraction ratio.

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