GB2207671A - Process for the removal of color-forming trace impurities from methylene bis (phenylisocyanates) - Google Patents

Process for the removal of color-forming trace impurities from methylene bis (phenylisocyanates) Download PDF

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Publication number
GB2207671A
GB2207671A GB8817132A GB8817132A GB2207671A GB 2207671 A GB2207671 A GB 2207671A GB 8817132 A GB8817132 A GB 8817132A GB 8817132 A GB8817132 A GB 8817132A GB 2207671 A GB2207671 A GB 2207671A
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United Kingdom
Prior art keywords
methylene bis
phenylisocyanate
mdi
purified
color
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GB8817132A
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GB8817132D0 (en
Inventor
Thirumurti Narayan
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BASF Corp
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BASF Corp
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C263/00—Preparation of derivatives of isocyanic acid
    • C07C263/18—Separation; Purification; Stabilisation; Use of additives
    • C07C263/20—Separation; Purification
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/65—Low-molecular-weight compounds having active hydrogen with high-molecular-weight compounds having active hydrogen
    • C08G18/66—Compounds of groups C08G18/42, C08G18/48, or C08G18/52
    • C08G18/6633—Compounds of group C08G18/42
    • C08G18/6637—Compounds of group C08G18/42 with compounds of group C08G18/32 or polyamines of C08G18/38
    • C08G18/664—Compounds of group C08G18/42 with compounds of group C08G18/32 or polyamines of C08G18/38 with compounds of group C08G18/3203
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
    • C08G18/72—Polyisocyanates or polyisothiocyanates
    • C08G18/74—Polyisocyanates or polyisothiocyanates cyclic
    • C08G18/76—Polyisocyanates or polyisothiocyanates cyclic aromatic
    • C08G18/7657—Polyisocyanates or polyisothiocyanates cyclic aromatic containing two or more aromatic rings
    • C08G18/7664—Polyisocyanates or polyisothiocyanates cyclic aromatic containing two or more aromatic rings containing alkylene polyphenyl groups
    • C08G18/7671—Polyisocyanates or polyisothiocyanates cyclic aromatic containing two or more aromatic rings containing alkylene polyphenyl groups containing only one alkylene bisphenyl group

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

A method for the removal of color-forming trace impurities from a two-ring methylene bis (phenylisocyanate) comprises heating the diisocyanate to about 190 DEG C in contact with an anhydrous metal silicate, silica or a mixture thereof. A white or light-colored thermoplastic polyurethane material can be made with the purified MDI.

Description

PROCESS FOR THE REMOVAL OF COLOR FORMING TRACE IMPURITIES FROM METHYLENE BIS(PHENYLISOCYANATES) Background of the Invention 1. Field of the Invention The present invention relates to a process to remove color forming trace impurities from a methylene bis(phenylisocyanate) and particularly from 4,4'-methylene bis(phenylisocyanate) (MDI). The invention also relates to a white thermoplastic polyurethane material formed from MDI which is purified of substantially most of the color forming trace impurities.
2. Description of the Material Art Cuscurida et al., U.S. Patent 3,759,971, disclose purification of isocyanates. The purification is achieved by reacting a polymeric isocyanate with a synthetic metal silicate to greatly reduce the amount of hydrolyzable chlorines and acidity present in the isocyanate. The isocyanates formed are useful in making polyurethane materials. The present invention differs from Cuscurida et al in that the present invention relates to the formation of a thermoplastic polyurethane material from a purified two-ring MDI material. The pure MDI material of the present invention has a reduced amount of hydrolyzable chlorines to begin with.The pure MDI is then heated in contact with an anhydrous metal silicate to remove the trace amounts of chlorine containing compound impurity to form a purified two-ring MDI material which will form a white or light colored thermoplastic material. In other words, the purified isocyanate of Cuscurida et al is not suitable as a direct raw material with which to make white thermoplastic polyurethane materials.
Ellendt et al., U.S. Patent 4,414,074, discloses a process for the production of a very pure 4,4'-diisocyantodiphenylmethane in which diisocyantodiphenyimethane isomers which are obtained by distillation from the phosgenation products of aniline/formaldehyde condensates, are initially freed from 2,2'- and 2,4' -isomers under certain distillation conditions. Distillation is continued so that the first stage, from 50 to 90 percent by weight of the diisocyanate is freed from the 2,2'- and 2,4'-isomers and the head product is in the form of pure 4,4'-methylene bis(phenylisocyanate). A second stage is then encountered where another quantity of pure 4,4'-methylene bis(phenylisocyanate) is separated as a head product from the distillation of the sump of the first stage.In other words, Ellendt et al disclose a complex distillation process in order to isolate a pure 4,4'-methylene bis(phenylisocyanate). Ellendt et al differ from the present invention in that there is no disclosure in Ellendt et al to use metal silicate to remove the trace chlorine content of the 4,4'-methylene bis(phenylisocyanate).
Further, the present invention does not depend upon a plurality of distillations in order to arrive at a pure MDI product.
Kataoka et al., U.S. Patent 4,065,362, disclose a purification of organic isocyanates by heating the isocyanate in admixture with a treating agent selected from a metal salt of a mercaptobenzothiazol, a dithiocarbamic acid derivative, an alkyl-substituted phenol, a thio-bisphenol, and a triaryl phosphite at a temperature of 1000C or above. The mixture is subsequently distilled to recover the purified organic isocyanate.
The present invention differs from Kataoka et al in that the isocyanate of the present invention is purified with an anhydrous metal silicate and silica . Further, the present invention is operable at temperatures of about 1900 to 2300C whereas the Kataoka et al disclosure states that a temperature of around 1000 will suffice. Finally, the present invention does not utilize a metal salt of the type indicated in Kataoka et al.
Cheng, U.S. Patent 3,458,558, discloses a purification of isocyanates by reducing the hydrolyzable chlorine content. The patent relates to a process for treating organic isocyanates with certain metals whereby the hydrolyzable chlorine content of the treated material is sub stantially reduced. The reaction temperature occurs at a temperature above about 1000C but below that at which substantial decomposition of the isocyanate occurs. The metal is selected from the group consisting of copper, silver, nickel, iron and zinc. The reaction mixture is afterwards separated by distilling the treated isocyanate to obtain a substantially pure isocyanate material.
The present invention differs from Cheng in that Cheng discloses that metals such as magnesium, antimony and chromium have no significant effect and lithium and tin were found to cause polymerization of the isocyanate. Further, the present invention has found that magnesium, in the form of an anhydrous magnesium silicate will purify MDI according to this invention.
Buchsbaum, U.S. Patent 3,591,617, discloses a process for the purification of toluene diisocyanate by a fractional crystallization technique. The present invention is not concerned with fractional crystallization of isocyanates out of a solvent and then placing those recovered crystals into a different solvent and recrystallizing and separating the new crystals from the new solvent continuously until the purified product is reached.
Powers, U.S. Patent 3,264,336, discloses a method for the purification of isocyanates by reduction of the hydrolyzable chlorine and acid content. The process contemplates a method for adjusting the hydrolyzable chlorine and acidity of an organic isocyanate to a predetermined level by reducing it through polymerization or decomposition in the presence of a metallic compound selected from the group consisting of cadmium laurate, cobaltic benzoate and ferric naphthenate. The resulting mixture is then distilled to remove the isocyanate. The present invention differs from Powers in that the present invention does not contemplate the use of cadmium laurate, cobaltic benzoate and ferric naphthenate to reduce the hydrolyzable chlorine and acid content.
Kantyka et al., U.S. Patent 3,144,474, disclose a purification process for producing pure isocyanates from crude isocyanates obtained by phosgenating primary amines.
Kantyka et al disclose a process which utilizes inert solvents selected from chlorinated aromatic hydrocarbons and orthochlorobenzene to make an MDI. The MDI is then placed into a petroleum fraction such as a petroleum ether or kerosene to cause MDI to precipitate out of the solvent.
The yield and purity can be affected by the ratio of the solvent to petroleum fraction. The present invention does not utilize a petroleum fractionation system to obtain a purified MDI.
Christian et al., U.S. Patent 3,585,229, relate to a process for the decoloration of aromatic isocyanates by bleaching and decolorizing colored methylene bis(phenylisocyanate) by the selective addition of diphenyl decyl phosphite and enable the use of those isocyanates for purposes where yellow or brownish isocyanates are unsuitable. The present invention differs from Christian et al in that the present invention does not utilize diphenyldecyl phosphite to decolorize diisocyanates.
Summary of the Invention The present invention relates to a process for the purification of two ring methylene bis(phenylisocyanate) and, more particularly, 4,4'-methylene bis(phenylisocyanate) by the removal of trace impurities. The trace impurities are chlorine containing compounds which render the MDI products a yellow or brown color. This makes them unsuit able for applications wherein a light colored or white material is desired. Removal of the trace impurities had been known in the prior art by utilizing conventional fractional distillation processes. This is expensive and arduous and so, economically less attractive to the industry.
The present process consists of heating two-ring MDI in contact with an anhydrous metal silicate at a temperature range of about 1900 to 2300C for a period of about one-half hour to about two hours. The purified MDI may be recovered directly from the reaction or may be subjected to distillation. A thermoplastic polyurethane product may be formed by use of the purified MDI which is white in color and suitable for applications where a colorless or white material is desired.
The purification process of the present invention utilizes an anhydrous metal silicate or silica to insure that substantially most of the chlorine-containing compound impurities are removed. Since excess water is reactive with MDI and detrimental to stability, it has been found that anhydrous metal silicate or silica and mixtures thereof are preferred. The preferred reaction temperature range is about 1900C to 2300C.
Detailed Description of the Preferred Embodiment The process of the present invention is carried out by contacting a two-ring MDI, with an anhydrous metal silicate silica or mixtures thereof, for a time period sufficient to remove substantially most of the chlorinecontaining compound trace impurities. A thermoplastic polyurethane material which is white or colorless may be obtained by using two-ring methylene-bis-(phenylisocyanates) which are purified of color forming impurities according to the present invention, economically and efficiently. The anhydrous metal silicates which are useful in the present invention may be selected from the group consisting of sodium, potassium, magnesium, calcium, zinc, lithium, barium, aluminum and mixtures thereof.It is essential that the metal silicate be substantially anhydrous as the presence of any amount of water is detrimental to the stability of the isocyanate. Insofar as is known by the inventor, the prior art is not able to remove trace chlorine compound impurities from MDI without resort to distillation processes. By use of anhydrous metal silicates, this can be achieved without resort to distillation. Thus, it is the unexpected result of using anhydrous metal silicates to purify MDI which is the subject of the present invention.
The two-ring methylene bis(phenylisocyanate) may be selected from the group consisting of 2,2'-methylene bis(phenylisocyanate) 2,4'-methylene bis(phenylisocyanate) 4,4'-methylene bis(phenylisocyanate) and mixtures thereof.
Of particular importance, it is recognized that 4,4'methylene bis(phenylisocyanate) is most economical to use and has the most commercial applications.
The two-ring methylene bis(phenylisocyanate) most useful in the present invention preferably has an initial chlorine-containing compound analyzed as chlorine of less than about 200 ppm and preferably less than about 145 ppm.
In other words, it is preferred that the readily removable chlorine compound be removed prior to subjecting the two -ring MDI to the process of the present invention. Removing the readily removable chlorine compound prior to the process of the invention renders more efficient the removal of the trace chlorine-containing compound from the two-ring methylene bis(phenylisocyanate) and arrive at a colorless or white thermoplastic polyurethane material.
The process of the present invention comprises heating the two ring MDI to a temperature sufficient to induce the interaction of an anhydrous metal silicate and the trace chlorine-containing compound. The contact time is sufficient to insure interaction of substantial amount of the said inpurities present in the two ring MDI material.
Preferably, the period of reaction is from 0.5 to 2 hours in duration and the temperature is in the range of about 1900C to 2300C and most preferably at around 2000C. The method further includes filtering the mixture either in column or through filtering processes which are conventional in the art to recover a pure MDI. Although it is not necessary, flash distillation may also be used to expedite retrival of the purified MDI.
The following examples illustrate the invention and the processes of forming a method for the removal of color forming trace impurities from two ring methylene bis(phenylisocyanates). Those skilled in the art will understand that the examples are-only illustrative and are not to be construed as limiting the scope or spirit of the invention.
Examples General Procedure for the Heat Treatment of Methylene bis(phenylisocyanate) with a Silicate A reaction vessel equipped with a thermometer and a stirrer was charged with the shown amount of 4,4'-MDI and MAGNESOL or molecular sieves and heated to the indicated temperature with stirring. After the required reaction time elapsed, the contents were filtered to recover the purified MDI. Several examples of heat treatment of 4,4'-MDI using this procedure are summarized in Table I. Note the dramatic reduction in the amount of chlorine impurity when the 4,4' MDI was treated 5 percent MAGNESOL at 2000C. The efficiency of purification is poor at a lower MAGNESOL* concentration or lower heat treatment temperature.
General Procedure for the Distillation of 4,4' Methylene bis(phenylisocyanate) in the Presence of a Silicate A distillation vessel equipped with a thermometer, 18" Vigreaux column, a take-off, and a receiver was charged with molten 4,4'-MDI and the indicated amount of MAGNESOL.
*Dried at 1200C (essentially anhydrous).
Vacuum was applied and after stabilization between 1 to 2 mm of Hg, the contents were heated and flashed at the indicated pot temperature. The product is essentially flashed over employing the shortest residence time. The results summarized in Table II clearly show the effect of distillation of 4,4'-MDI in the presence of MAGNESOL. Reduction in the amount of chlorine impurity is clearly evident.
Preparation and Evaluation of TPU Discs Using the Stabilizer Package Polyester diol based on adipic acid and 1,4-butanediol (OH No. 56) 50 parts 1, 4-butanediol 10.25 parts Methylenetbis(phenylisocyanate) 35 parts The molten polyester diol (900C) was placed in an appropriate vessel and blended with 1,4-butanediol. The temperature of the mixture dropped to 700C. After 30 seconds, the pure MDI was added, a decrease in temperature to 630 was observed. Shortly, an exothermic reaction ensued. When the reaction temperature was 950C, the material was poured onto a heated mold (having a film of mold release agent), the surface of which was at 1250C. The thickness of the layer was 6 to 8 mm.The discs were removed six minutes after the beginning of the mixing process and post cured at 100 to 1100C for 15 hours. The color of the TPU discs was compared in both Table I and II.
Table I Purification of 4,4'-Methylene bis(phenylisocyanate) by Treating with a Silicate React.
Silicate Time, hr/ MDI Amount Temp. Clc Color of Sample Used* Used % C Before After TPU Disc 1 A MAGNESOLa 4.76 0.5/200 109 15, 17 white 2 B MAGNESOL 4.76 0.5/200 -- -- white 3 A MAGNESOL 1.00 24/48 109 86 4 A MAGNESOL 4.76 0.5/100 109 95 5 A Mol.Sievesb 4.76 0.5/200 109 -- white 6 C MAGNESOL 4.76 0.5/200 145 35 white * Different lots of 4,4'-MDI.
a) MAGNESOL is magnesium silicate, dried at 120 C (essentially anhydrous) b) Molecular sieves is aluminum silicate.
c) Amt in ppm of chlorine-containing compounds measured as hydrolyzable chlorine.
TABLE II Purification of 4,4'-Methylene bis(phenylisocyanate) by Distillation in the Presence of a Silicate Silicate Dist.
MDI Amount Temp. Clc Color of Sample Used* Used % C Before After TPU Disc 7 D MAGNESOL 4.99 192 87 7 white 8 C MAGNESOL 4.99 198-204 145 35 9 A MAGNESOL 1.96 196-204 109 29 10 A MAGNESOL 0.99 197-198 109 20 11 A none -- 187-194 109 75 light brown *Different lots of 4,4'-MDI.

Claims (8)

1. A method for removal of color-forming trace impurities from methylene bis(phenylisocyanate) (MDI), comprising heating the methylene bis(phenylisocyanate) to about 190"C to 230"C in contact with an anhydrous metal silicate, silica or a mixture thereof, and recovering the purified MDI.
2. The method of claim 1 wherein the metal silicate is selected from the group consisting of sodium, potassium, magnesium, calcium, zinc, lithium, barium and aluminum silicates and mixtures thereof.
3. The method of claim 1 wherein the methylene bis(phenylisocyanate) has an initial chlorine-containing impurity content of at most about 200 parts per million.
4. The method of claim 1 wherein the methylene bis(phenylisocyanate) is subjected to heating in contact with the metal silicate or silica for a period of about 0.5 to 2 hours.
5. The method of claim 1 further including filtering the mixture to recover purified methylene bis(phenylisocyanate).
6. The method of claim 1 wherein the two-ring methylene bis(phenylisocyanate) is selected from the group consisting of 2,4'-methylene bis(phenylisocyanate) 4,4'methylene bis(phenylisocyanate), 2,2'-methylene bis(phenylisocyanate) and mixtures thereof.
7. The method of claim 1, further including flash distillation to retrieve the purified two-ring methylene bis(phenylisocyanate).
8. A thermoplastic polyurethane made employing the two-ring MDI produced according to claim 1.
GB8817132A 1987-08-07 1988-07-19 Process for the removal of color-forming trace impurities from methylene bis (phenylisocyanates) Withdrawn GB2207671A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0524507A1 (en) * 1991-07-23 1993-01-27 Bayer Ag Process for the purification of polyisocyanates
EP0561225A2 (en) * 1992-03-16 1993-09-22 Bayer Ag Process for the preparation of isocyanates or isocyanate mixtures and their use in the preparation of polyurethane foams
EP0676391A1 (en) * 1994-04-07 1995-10-11 Bayer Ag Process for the preparation of isocyanates or isocyanate mixtures and their use for the manufacture of light coloured foams
EP0702000A1 (en) * 1994-09-19 1996-03-20 Bayer Ag Process for adjusting a certain amount of iron in diphenylmethane diisocyanate or in polyisocyanate mixtures of the diphenylmethane diisocyanate series

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3759971A (en) * 1971-01-20 1973-09-18 Jefferson Chem Co Inc Purification of isocyanates

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3759971A (en) * 1971-01-20 1973-09-18 Jefferson Chem Co Inc Purification of isocyanates

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0524507A1 (en) * 1991-07-23 1993-01-27 Bayer Ag Process for the purification of polyisocyanates
US5386054A (en) * 1991-07-23 1995-01-31 Bayer Aktiengesellschaft Process for the purification of polyisocyanates, the polyisocyanates thus purified and use thereof
EP0561225A2 (en) * 1992-03-16 1993-09-22 Bayer Ag Process for the preparation of isocyanates or isocyanate mixtures and their use in the preparation of polyurethane foams
EP0561225A3 (en) * 1992-03-16 1993-11-24 Bayer Ag Process for the preparation of isocyanates or isocyanate mixtures and their use in the preparation of polyurethane foams
US6140382A (en) * 1992-03-16 2000-10-31 Bayer Aktiengesellschaft Process for the preparation of isocyanates or isocyanate mixtures useful for the preparation of polyurethane foams
EP0676391A1 (en) * 1994-04-07 1995-10-11 Bayer Ag Process for the preparation of isocyanates or isocyanate mixtures and their use for the manufacture of light coloured foams
US5583251A (en) * 1994-04-07 1996-12-10 Bayer Aktiengesellschaft Process for the production of isocyanates and for the production of light-colored foams therefrom
EP0702000A1 (en) * 1994-09-19 1996-03-20 Bayer Ag Process for adjusting a certain amount of iron in diphenylmethane diisocyanate or in polyisocyanate mixtures of the diphenylmethane diisocyanate series

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