Method for improving L* color of polymerized MDI

Abstract

The invention provides a method for improving the L * color of polymerized MDI by using organic alkali and an oxidizing agent. By using the method, the L * color of a polymerized MDI product can be improved. Comprising the following steps: 1) adding organic alkali and an oxidizing agent into polymerized MDI; and 2) reacting the mixed solution obtained in the step 1) under a stirring or standing condition to obtain the treated polymerized MDI.

Description

Technical Field

[0001] This invention relates to MDI product quality improvement technology, and in particular to a method for improving the L* color of polymeric MDI. Background Technology

[0002] Polymeric MDI is an abbreviation for polyphenylmethane polyisocyanate. It is a crucial and irreplaceable raw material for manufacturing polyurethane polymer materials. Polymeric MDI is mainly used in rigid and semi-rigid polyurethane foams, applied in insulation materials, automotive parts, and the construction industry. In the CIE-LAB color system, the L* color of isocyanates is a key indicator for monitoring product quality and significantly influences the color of subsequent foams. Currently, both intermediate and finished isocyanate products require L* color analysis; generally, the L* color of polymeric MDI products must be greater than 65 to be considered a qualified product for sale.

[0003] Due to the numerous components in polymeric MDI and the complexity of its color-growth mechanism, the exact mechanism remains unclear. According to the Wiff chromophore theory, one end of the unsaturated conjugated chain (e.g., -C=C-, -N=N-, -NO) in the chromophore of the dye molecule is connected to an electron-donating group (e.g., -OH, -NH2) or an electron-withdrawing group (-NCO, -NO2, >C=O), while the other end is connected to a group with opposite charge. When a compound molecule absorbs light quantum energy of a certain wavelength, it becomes polarized and generates a dipole moment, causing valence electrons to transition between different energy levels, resulting in different colors. Molecular absorption typically manifests as n→π* and π→π* transitions, thus the absorption range is mostly between 200-800 nm. If the molecule contains two or more conjugated chromophores, the absorption of light shifts towards longer wavelengths. The longer the conjugated system, the longer the wavelength of absorbed light. When the wavelength of light absorbed by a substance shifts to the visible light region, the substance acquires color. The color tends to be darker when there are several chromophores within the same molecule, or when another group called an auxochrome is present. Auxochromes are groups containing lone pairs of electrons, such as amino, hydroxyl, and halogenated groups. These groups interact with the unsaturated bonds on the chromophore, thus deepening the color. In summary, the longer the conjugated chain in the molecular structure, the darker the color; an increase in the number of benzene rings leads to a darker color; and an increase in molecular weight, especially an increase in the number of conjugated double bonds, leads to a darker color. Therefore, removing the chromophore components from PM can enhance the L* color of PM.

[0004] Chinese patent CN113861129A provides a method for improving the L* color of polymeric MDI from the process end. The method involves treating the polymeric MDI obtained by distillation at 190℃-210℃ in an inert atmosphere for 10-120 minutes; then adding phenothiazine, propylene glycol or methylhydroquinone as a complexing agent to carry out a complexation reaction; dissolving the resulting product in chlorobenzene to obtain a suspension, which is then centrifuged and filtered; the filtrate is then distilled to obtain the treated polymeric MDI.

[0005] Chinese patent CN111910207A discloses a novel method for preparing diphenylmethane series diamines and polyamines (DAMs) with low color numbers. The method involves using hydrochloric acid as a raw material with a redox potential of -100 to 400 mV, and formaldehyde aqueous solution with a redox potential of -100 to 200 mV. The DAM product prepared by reacting formaldehyde with aniline in the presence of a hydrochloric acid catalyst has a color number less than 200#. The patent also relates to a method for preparing methylene diphenyl diisocyanate (MDI) from DAM via phosgenation.

[0006] Chinese Patent CN105289464 discloses a method for preparing a purified extruded attapulgite mineral oil decolorizing agent, which can be widely used in the field of edible oil decolorization. The purified extruded attapulgite mineral oil decolorizing agent of this invention is obtained by crushing, wet-purifying, and extruding attapulgite clay. After wet purification and extrusion modification, the attapulgite clay exhibits high purity, large specific surface area, and high porosity, significantly improving its activity and adsorption performance. The adsorption and decolorization effect is remarkable; the edible oil comes into full contact with the purified extruded attapulgite mineral oil decolorizing agent, effectively decolorizing the oil. After multiple tests, the average comprehensive decolorization rate of the purified extruded attapulgite mineral oil decolorizing agent reaches over 95%.

[0007] While the aforementioned patent can improve the color of polymerized MDI to some extent, it suffers from problems such as complex operation, equipment requirements, and high cost, and cannot well meet the requirements of low cost and simple operation for large-scale industrial applications. Therefore, this invention is proposed to fill the gap in this field. Summary of the Invention

[0008] This invention provides a novel method for improving the L* color of polymeric MDI, thereby enhancing the L* color of polymeric MDI and improving the product quality of polymeric MDI.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] This invention provides a method for improving the L* color of polymeric MDI, comprising the following steps:

[0011] 1) Add an organic base and an oxidizing agent to the polymerized MDI;

[0012] 2) React the mixture obtained in step 1) under stirring or standing conditions to obtain the treated polymerized MDI.

[0013] In step 1 of this invention, there is no particular limitation on the specific grade of polymeric MDI, and the polymeric MDI is selected from PM-200, PM-400, PM-2025, PM-700, etc.

[0014] In step 1) of this invention, there is no particular restriction on the order of adding the oxidant, polymeric MDI and organic base. Two of them can be mixed in advance and then the third can be added to improve the L color effect. For example, the organic base can be treated with an oxidant in advance and then the treated organic base can be added to the polymeric MDI for reaction.

[0015] In step 1) of this invention, the organic base is selected from hindered amines, alkaloids, and alkali metal salts of alcohols, preferably hindered amines, more preferably poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol) ester, benzoic acid (2,2,6,6-tetramethyl-4-hydroxypiperidine) ester, and tris(1,2,2,6,6-pentamethyl-4-hydroxypiperidine) ester of phosphite. The oxidant is selected from inorganic oxidants and organic oxidants, more preferably hydrogen peroxide, peracetic acid, sodium dichromate, bromine, iodine, air, ozone, and nitric acid.

[0016] In a preferred embodiment, in step 1), the amount of organic base used accounts for 0.001%-1% of the mass of polymeric MDI. Using the preferred amount of organic base allows the organic base to play an effective role. Too much organic base may remain in the polymeric MDI and increase costs, while too little will not have a good effect on improving the L* color.

[0017] In a preferred embodiment, in step 1), when the selected oxidant is a solid or liquid, the amount of the oxidant is 0.01-1% of the mass of the polymeric MDI, preferably 0.05%-0.1%, more preferably 0.02%-0.05%; if the selected oxidant is a gas, the aeration rate is 0.1-1000 times the volume of the polymeric MDI, preferably 1-100 times. Using the preferred amount of oxidant allows the oxidant to exert its optimal effect. Excessive addition of oxidant may affect product quality, while insufficient addition may result in insufficient improvement in the product's color (L).

[0018] In a preferred embodiment, in step 2), the reaction temperature is 25-120℃, preferably 50-80℃, and the reaction time is 8-144h, preferably 24-48h. Preferably, the reaction is carried out under stirring, which increases intermolecular mobility and enhances reactivity.

[0019] The technical solution provided by this invention has the following beneficial effects:

[0020] This invention involves adding an organic base and an oxidizing agent to polymerized MDI and reacting the mixture. This method can effectively improve the L* color of polymerized MDI without affecting product quality and shelf life. Detailed Implementation

[0021] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0022] All reagents used in the examples are conventional reagents in the art. Unless otherwise specified, the detection methods or experimental methods described below are conventional techniques known to those skilled in the art based on their existing knowledge.

[0023] In the following text, the percentage content "%" refers to "wt%".

[0024] The test methods involved in the following experiments are described below:

[0025] ①Medimer content analysis method

[0026] 1. Instruments

[0027] The Fourier transform infrared spectrometer (Nicolet iS20) is equipped with a light source, beam splitter, detector, and data processing system.

[0028] 2. Utensils

[0029] Infrared liquid pool

[0030] 3. Methods

[0031] The peak position of the dimer in the infrared spectrum was determined to be 1780 cm⁻¹ using the internal standard method. -1 .

[0032] ②L* color analysis method

[0033] The L* color of polymeric MDI was determined using an integrating sphere spectrophotometer with pure solvent (dichloromethane) as the standard.

[0034] ③ Bicyclic content

[0035] Determination was performed using gel permeation chromatography (GPC).

[0036] Detector: FID 300℃; H2: 30mL / min; Air: 300mL / min; Make-up gas: 25mL / min;

[0037] Chromatographic column: Agilent 19091J-413HP-5 30m×320μm×0.25μm.

[0038] Example 1

[0039] In this embodiment, the quality evaluation data of polymeric MDI is as follows:

[0040] Analysis Project Analysis results Dimer content / % 1.33 Bicyclic content / % 44.5 L* color 59

[0041] The steps of the method for improving L* color by polymerizing and processing MDI as described above are as follows:

[0042] 1) Divide the above-mentioned polymeric MDI into four portions. Add 0.02% polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) ester and 10 times the volume of air to the first portion; add only 10 times the volume of air to the second portion; add 0.02wt% polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) to the third portion and react at 60°C for 24 hours with stirring at 250 rpm.

[0043] 2) The results of relevant index analysis on the polymerized MDI after the above treatment are as follows:

[0044]

[0045] By comparing the pre-treatment MDI testing data with the data from step 2), it can be seen that the method of this invention can improve the quality of L* color in PM without significantly affecting other product indicators (dimer content and dicyclic content).

[0046] Example 2

[0047] In this embodiment, the quality evaluation data of polymeric MDI is as follows:

[0048] Analysis Project Analysis results Dimer content / % 1.33 Bicyclic content / % 44.6 L* color 60

[0049] 1) Add the above polymerized MDI to 0.001% benzoic acid (2,2,6,6-tetramethyl-4-hydroxypiperidine) ester and 0.1% bromine water to obtain a mixture. React at 25°C for 144 h with stirring at 250 rpm.

[0050] 2) The polymeric MDI with improved quality was obtained. Relevant index analyses were performed on the treated polymeric MDI, and the results are as follows:

[0051] Dimer content / % Bicyclic content / % L* color 1.33 44.6 75

[0052] By comparing the data from step 2) with the data before processing in this example, it can be seen that this processing method can improve the aggregated MDI L color.

[0053] Example 3

[0054] In this embodiment, the quality evaluation data of polymeric MDI is as follows:

[0055]

[0056]

[0057] 1) The above-mentioned polymerized MDI was added to 0.02% by mass of polysuccinic acid (4-hydroxy-2,2,6,6-tetramethyl)

[0058] 1-Piperidineethanol ester was purged with air at 1000 times the volume of polymerized MDI and reacted at 80°C for 48 hours with stirring at 250 rpm.

[0059] 2) The polymeric MDI with improved quality was obtained. Relevant index analyses were performed on the treated polymeric MDI, and the results are as follows:

[0060]

[0061] By comparing the data from step 2) with the data before processing in this example, it can be seen that this processing method can improve the aggregated MDI L color.

[0062] Example 4

[0063] In this embodiment, the quality evaluation data of polymeric MDI is as follows:

[0064] Analysis Project Analysis results Dimer content / % 1.33 Bicyclic content / % 44.6 L* color 60

[0065] 1) Add the above polymeric MDI to 0.05% benzoic acid (2,2,6,6-tetramethyl-4-hydroxypiperidine) ester, and 0.1 times the volume of the polymeric MDI with oxygen to obtain a mixture. React at 50°C for 24 hours with stirring at 250 rpm.

[0066] 2) The polymeric MDI with improved quality was obtained. Relevant index analyses were performed on the treated polymeric MDI, and the results are as follows:

[0067]

[0068] By comparing the data from step 2) with the data before processing in this example, it can be seen that this processing method can improve the aggregated MDI L color.

[0069] Example 5

[0070] In this embodiment, the quality evaluation data of polymeric MDI is as follows:

[0071]

[0072]

[0073] 1) Divide the above-mentioned polymeric MDI into two portions. For the first portion, directly add 0.02% (w / w) of poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) ester, and purge with air at 10 times the volume of the polymeric MDI to obtain a mixture. React at 60°C for 24 hours with stirring at 250 rpm. For the second portion, first purge with air at 10 times the volume of the polymeric MDI into the poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) ester, and then add the treated poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol) ester...

[0074] 2,2,6,6-Tetramethyl-1-piperidineethanol ester was added to polymerized MDI to obtain a mixture, which was then reacted at 60°C for 24 h with stirring at 250 rpm.

[0075] 2) The polymeric MDI with improved quality was obtained. Relevant index analyses were performed on the treated polymeric MDI, and the results are as follows:

[0076]

[0077] By comparing the data from step 2) with the data before processing in this example, it can be seen that different ways of adding oxidant can achieve a good effect in improving L color.

Claims

1. A method for improving the L* color of polymeric MDI, comprising the following steps: 1) Add an organic base and an oxidizing agent to the polymerized MDI; 2) React the mixture obtained in step 1) under stirring or standing conditions to obtain the treated polymerized MDI.

2. The method as described in claim 1, characterized in that, The organic base is selected from hindered amines, alkaloids, and alkali metal salts of alcohols, preferably hindered amines, and more preferably poly(4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol) ester, benzoic acid (2,2,6,6-tetramethyl-4-hydroxypiperidine) ester, and tris(1,2,2,6,6-pentamethyl-4-hydroxypiperidine) ester of phosphite.

3. The method as described in claim 1 or 2, characterized in that, The oxidant is selected from inorganic oxidants, organic oxidants, and more preferably hydrogen peroxide, peracetic acid, sodium dichromate, bromine, iodine, air, ozone, and nitric acid.

4. The method according to any one of claims 1-3, characterized in that, In step 1), the amount of organic base used is 0.001%-1% of the mass of polymerized MDI.

5. The method according to any one of claims 1-4, characterized in that, In step 1), when the oxidant is solid or liquid, the amount of the oxidant is 0.01-1% of the mass of the polymerized MDI. If the selected oxidant is gas, the aeration amount of the oxidant is 0.1-1000 times the volume of the selected polymerized MDI.

6. The method according to any one of claims 1-5, characterized in that, In step 2), the reaction temperature is 25-120℃, preferably 50-80℃, and the reaction time is 8-144h, preferably 24-48h.

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