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CN-121990948-A - Method for improving L-color of polymeric MDI

CN121990948ACN 121990948 ACN121990948 ACN 121990948ACN-121990948-A

Abstract

The invention provides a method for improving the L-color of a polymeric MDI (MDI) product by using an organic base and an oxidant. Comprises the steps of 1) adding organic alkali and oxidant into polymeric MDI, 2) reacting the mixed solution obtained in the step 1) under stirring or standing condition to obtain the treated polymeric MDI.

Inventors

  • WANG ZHUQI
  • GAO ZHENHUA
  • WANG PUZHAO
  • XU DAN
  • ZHAO DONGKE

Assignees

  • 万华化学(福建)异氰酸酯有限公司

Dates

Publication Date
20260508
Application Date
20241105

Claims (6)

  1. 1. A method of improving the L-color of a polymeric MDI comprising the steps of: 1) Adding an organic base and an oxidant into the polymeric MDI; 2) And (3) reacting the mixed solution obtained in the step (1) under stirring or standing conditions to obtain the treated polymeric MDI.
  2. 2. The process according to claim 1, wherein the organic base is selected from the group consisting of hindered amines, alkaloids, alkali metal salts of alcohols, preferably hindered amines, more preferably poly (4-hydroxy-2, 6-tetramethyl-1-piperidineethanol) succinate benzoic acid (2, 6-tetramethyl-4-hydroxypiperidine) ester, tris (1, 2, 6-pentamethyl-4-hydroxypiperidine) phosphite.
  3. 3. The method according to claim 1 or 2, wherein the oxidizing agent is selected from the group consisting of inorganic oxidizing agents, organic oxidizing agents, more preferably hydrogen peroxide, peracetic acid, sodium dichromate, bromine, iodine, air, ozone, nitric acid.
  4. 4. A process according to any one of claims 1 to 3, wherein in step 1) the organic base is used in an amount of from 0.001% to 1% by mass of the polymeric MDI.
  5. 5. The method according to any one of claims 1 to 4, wherein in step 1), when the oxidizing agent is solid or liquid, the amount of the oxidizing agent is 0.01 to 1% by mass of the polymeric MDI, and if the oxidizing agent is selected as a gas, the aeration amount of the oxidizing agent is 0.1 to 1000 times the volume of the polymeric MDI.
  6. 6. The process according to any one of claims 1 to 5, wherein in step 2) the reaction temperature is 25 to 120 ℃, preferably 50 to 80 ℃ and the reaction time is 8 to 144 hours, preferably 24 to 48 hours.

Description

Method for improving L-color of polymeric MDI Technical Field The invention relates to an MDI product quality improving technology, in particular to a method for improving the L-color of polymeric MDI. Background Polymeric MDI is an abbreviation for polyphenylmethane polyisocyanate, which is an important and irreplaceable raw material for the manufacture of polyurethane polymeric materials. The polymeric MDI is mainly used for polyurethane hard foam and semi-hard foam, and is applied to heat insulation materials, automobile ornaments and building industries. Under CIE-LAB color system, the L color project in isocyanate is an important index for monitoring the quality of products, and has great influence on the color of subsequent foams. Currently, isocyanate intermediates and products require analysis of the L color term, and polymeric MDI products generally require greater than 65L colors to be sold as acceptable products. The color development mechanism is complex due to the fact that polymeric MDI has more components, and is not clear at present. According to Wiff chromophores, one segment of the unsaturated conjugated chain (e.g., -c=c-, -n=n-, -N-O) in the chromophore of the dye molecule is linked to a group containing an electron donating group (e.g., -OH, -NH 2) or an electron withdrawing group (-NCO, -NO 2, > c=o), and the other end is linked to a group of opposite electrical polarity. After the compound molecule absorbs the light quantum energy with a certain wavelength, polarization occurs and a dipole moment is generated, so that valence electrons are transited between different energy levels to form different colors. Molecular absorption is generally represented by n→pi and pi→pi transitions, and thus absorption ranges between 200 and 800 nm. If two or more conjugated chromophores are contained in the molecule, the longer the absorption of light by the molecule is in the long-wave direction, the longer the conjugated system is, and the longer the wavelength of the absorbed light is, the color of the substance becomes when the wavelength of the absorbed light of the substance is shifted to the visible light region. If several chromophores are present within the same molecule, or if another group called a co-chromophore is present, the color tends to be darker. The color assisting group is a group containing a lone pair of electrons, such as amino, hydroxyl, halogenated groups and the like. These groups act on unsaturated bonds on the chromophore to darken the color. In summary, the longer the conjugated chain of the molecular structure, the darker the color, the more the benzene ring, the darker the color, and the more the molecular weight, particularly the number of conjugated double bonds, and the darker the color. Therefore, the effect of improving the color of PM L can be achieved from the beginning of removing the color-developing component in PM. Chinese patent CN113861129a provides a method for improving L-color of polymeric MDI from the process end, which comprises treating polymeric MDI obtained by rectification separation at 190-210 ℃ in inert atmosphere for 10-120min, then adding phenothiazine, propylene glycol or methylhydroquinone as complexing agent to carry out complexation reaction, adding chlorobenzene into the obtained product to dissolve, obtaining suspension, centrifuging, filtering, rectifying and separating the obtained filtrate, and obtaining the polymeric MDI after treatment. Chinese patent CN111910207A provides a new method for preparing low-color-number diphenyl methane series diamine and polyamine (DAM), wherein the oxidation-reduction potential value of hydrochloric acid in raw materials is-100-400 mV, the oxidation-reduction potential value of formaldehyde aqueous solution in raw materials is-100-200 mV, and formaldehyde reacts with aniline in the presence of a hydrochloric acid catalyst to prepare the DAM with the color number smaller than 200#. The patent also relates to a process for preparing methylene diphenyl diisocyanate (MDI) by phosgenation of DAM. Chinese patent CN105289464 provides a preparation method of purifying and extruding attapulgite mineral oil decolorizer, which can be widely applied to the field of edible oil decolorization. The purified extrusion type attapulgite mineral oil decolorizer is prepared by crushing attapulgite clay, purifying by a wet method and extruding and modifying. The attapulgite clay is subjected to wet purification, extrusion modification, has the characteristics of high purity, large specific surface area and high porosity, the activity and the adsorption performance of the attapulgite clay are greatly improved, the adsorption decolorization effect is obvious, and the edible oil is fully contacted with the purified extrusion type attapulgite mineral oil decolorizer, so that the edible oil can be fully decolorized. The comprehensive index of the decolorization rate of the purified extruded attapulgite mineral oil decolorizer i