Method for producing methylene-diphenylene-diisocyanates and polymethylene-polyphenylene-polyisocyanates

Patent metadata

Field	Value
Publication number	US-10947187-B2
Application number	US-201916957188-A
Country	US
Kind code	B2
Filing date	Jan 2, 2019
Priority date	Jan 5, 2018
Publication date	Mar 16, 2021
Grant date	Mar 16, 2021

Abstract

The invention relates to a method for producing methylene-diphenylene-diisocyanate and optionally a mixture of methylene-diphenylene-diisocyanate and polymethylene-polyphenylene-polyisocyanate, wherein, in a step α), a fraction (142) containing a methylene-diphenylene-diisocyanate and secondary components is provided, optionally via a step α.1), the separating of methylene-diphenylene-diisocyanate and secondary components from a fraction (100) containing methylene-diphenylene-diisocyanate and polymethylene-polyphenylene-polyisocyanate, and wherein, in a step β), the fraction (142) containing methylene-diphenylene-diisocyanate and secondary components is subjected to a purification comprising an isomer separation by distillation and/or crystallization in two or more sub-steps (a, b, . . . ), obtaining two or more methylene-diphenylene-diisocyanate-reinfractions (140-1, 140-2, . . . ) and a secondary component fraction (150), wherein the secondary component fraction (150) obtained in step β) is returned to one of the sub-steps of step β), wherein none of the methylene-diphenylene-diisocyanate-reinfractions (140-1, 140-2, . . . ) from step β) are obtained as distillation or crystallization, and/or to step α.1), insofar as carried out.

First claim

The invention claimed is:

1. A process for preparing methylene diphenylene diisocyanate and optionally a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate, comprising:
α) providing a fraction comprising methylene diphenylene diisocyanate and secondary components with a proportion by mass of methylene diphenylene diisocyanate, based on total mass of the fraction, of more than 98.0% when determined by gas chromatography, and
β) purifying, comprising an isomer separation, the fraction comprising methylene diphenylene diisocyanate and secondary components by distillation and/or crystallization in two or more partial steps to obtain at least (i) two or more pure methylene diphenylene diisocyanate fractions, each having a proportion by mass of methylene diphenylene diisocyanate, based on their total mass, of 99.9% or more when determined by gas chromatography and (ii) a secondary component fraction having a proportion by mass, based on their total mass, of methylene diphenylene diisocyanate of 20.0% to 98.0% when determined by gas chromatography,
wherein step α) optionally comprises:
α.1) separating methylene diphenylene diisocyanate and secondary components from a fraction comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate to obtain
(i) a polymethylene polyphenylene polyisocyanate-enriched mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate and
(ii) the fraction comprising methylene diphenylene diisocyanate and secondary components with a proportion by mass of methylene diphenylene diisocyanate, based on total mass of the fraction, of more than 98.0% when determined by gas chromatography;

and
wherein the secondary component fraction obtained in step β) is returned to:
(1) one of the partial steps of step β) in which none of the pure methylene diphenylene diisocyanate fractions from step β) is obtained in the form of distillate or crystallizate,
(2) step α.1), provided step α.1) is conducted, or
(3) both:
(a) one of the partial steps of step β) in which none of the pure methylene diphenylene diisocyanate fractions from step β) is obtained in the form of distillate or crystallizate, and

(b) step α.1), provided step α.1) is conducted.

2. The process as claimed in claim 1 , comprising step α.1).

3. The process as claimed in claim 2 , in which the fraction comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate is obtained by a process comprising:
A) reacting a mixture of methylene diphenylene diamine and polymethylene polyphenylene polyamine with phosgene in the presence of an organic solvent, using phosgene in a stoichiometric excess based on all the primary amino groups present, to obtain a liquid stream comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate and secondary components, and a gaseous stream comprising hydrogen chloride and phosgene;
B) working up at least the liquid stream comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate and secondary
components, by a process comprising a prepurification to remove a first portion of the secondary components to obtain the fraction comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate, which is depleted of secondary components.

4. The process as claimed in claim 3 , in which the organic solvent used in step A) comprises monochlorobenzene, dichlorobenzene, dioxane, toluene, xylene, methylene chloride, perchloroethylene, trichlorofluoromethane or butyl acetate.

5. The process as claimed in claim 3 , in which the prepurification comprises:
(1) separating a gas stream comprising hydrogen chloride and phosgene from the stream comprising methylene diphenylene diisocyanate, polymethylene polyphenylene polyisocyanate and secondary components;
(2) separating a gas stream comprising organic solvent from the liquid phase remaining in step 1) after separation of the gas stream comprising hydrogen chloride and phosgene to obtain the liquid fraction depleted of secondary components and comprising methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate; and optionally
(3) separating the gas stream comprising organic solvent into a liquid stream comprising organic solvent and a gas stream comprising phosgene.

6. The process as claimed in claim 3 , in which, in step B), the gaseous stream comprising hydrogen chloride and phosgene is also worked up, where this workup comprises:
separating phosgene from the gaseous stream comprising hydrogen chloride and phosgene to obtain a gas stream comprising hydrogen chloride, where, if present, the gas stream comprising phosgene is also subjected to this phosgene separation step;
and optionally
separating hydrogen chloride from the gas stream comprising hydrogen chloride.

7. The process as claimed in claim 3 , in which step β) is performed by distillation.

8. The process as claimed in claim 7 , in which step β) comprises four to eight partial steps, wherein each partial step corresponds to a distillation in a distillation column without a dividing wall, wherein a first pure methylene diphenylene diisocyanate fraction and a second pure methylene diphenylene diisocyanate fraction are each obtained as distillate in different distillation columns, wherein the secondary component fraction is obtained as distillate in a distillation column other than that for obtaining the first and second pure methylene diphenylene diisocyanate fraction, wherein a third pure methylene diphenylene diisocyanate fraction is obtained as bottom product in the distillation column other than that for obtaining the first and second pure methylene diphenylene diisocyanate fraction.

9. The process as claimed in claim 8 , in which the secondary component fraction is fed into the feed of the distillation column in which the secondary component fraction is obtained.

10. The process as claimed in claim 7 , in which step β) comprises two or more partial steps, of which at least one partial step is performed in a dividing wall column.

11. The process as claimed in claim 10 , in which the stream which comprises methylene diphenylene diisocyanate and secondary components and is obtained in step α.1) is transferred, in step β), into a dividing wall column from which two prepurified methylene diphenylene diisocyanate fractions are withdrawn as side streams in liquid form, and from which a top stream comprising secondary components and methylene diphenylene diisocyanate is withdrawn, wherein the prepurified methylene diphenylene diisocyanate fractions are subjected to fine purification in further distillation stages to give a first and a second pure methylene diphenylene diisocyanate fraction, wherein the top stream from the dividing wall column in a distillation column that comprises secondary components and methylene diphenylene diisocyanate, which may optionally be configured as a side draw column with or without dividing wall, is distilled to obtain the secondary component fraction as top stream, a third pure methylene diphenylene diisocyanate fraction as bottom stream, and optionally a fourth pure methylene diphenylene diisocyanate fraction as side stream, wherein the secondary component fraction is recycled into step α.1) or into the dividing wall column from step β).

12. The process as claimed in claim 1 , in which step β) comprises at least one partial step in which a crystallization is performed, wherein the crystallizate obtained in the crystallization is a pure methylene diphenylene diisocyanate fraction or can be converted to

Assignees

• Covestro Intellectual Property Gmbh & Co Kg

Inventors

• Knauf Thomas
• Plathen Peter
• Manzel Dirk
• Wershofen Stefan

Classifications

• C07C263/10

  by reaction of amines with carbonyl halides, e.g. with phosgene · CPC title

• C07C265/14

  containing at least two isocyanate groups bound to the same carbon skeleton · CPC title

• C07C263/20 Primary

  Separation; Purification · CPC title

• C08G18/022

  the polymeric products containing isocyanurate groups · CPC title

• C08G18/7664

  containing alkylene polyphenyl groups · CPC title