Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Patent
1997-01-21
1998-07-21
Barts, Samuel
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C07C24900
Patent
active
057837279
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FR95/00366 filed Mar. 24, 1995.
The present invention relates to a process for the production of 2,6-toluylene diisocyanate from a mixture of the 2,4- and 2,6-isomers of toluylene diisocyanate.
The 2,4- and 2,6-isomers of toluylene diisocyanate (TDI hereinafter) are very important compounds which form the basis of the development of polyurethanes, which have many applications. Thus, these polymers may be used to manufacture flexible foams, among the main applications of which are household furniture and car seating. They may also be used for the manufacture of high-performance elastomers and enter into the composition of one- or two-component paints.
Most of the industrial applications of TDI use the 2,4- and 2,6-isomers as a mixture. The mixture most commonly used comprises 80% of the 2,4- isomer and 20% of the 2,6- isomer. The use of the 65/35 2,4-/2,6-isomer mixture is also known, although more restricted, in the field of high-lift flexible foams, for example.
However, polyurethanes synthesized from pure isomers have particularly advantageous properties when compared with those obtained from mixtures of these isomers. Thus, 2,6-TDI has noteworthy properties when it is used as a component in the synthesis of elastomers. The reason for this is that, in the particular case of polyester or polycaprolactam systems coupled with diamines, 2,6-TDI strongly improves the tear strength as well as the resistance to tear propagation. In addition, the hardness and resilience are improved and the modulus is increased from 100 to 200%. When diols are used as coupling agents, the tear strength and the resistance to tear propagation are also considerably improved.
There is consequently great value in obtaining the 2,6-TDI isomer pure. Various routes are known for gaining access to this product. Mention may be made in particular of chromatographic separation techniques, in which the mixture is treated on a column filled with zeolite, for example. These methods may be used directly on both TDI isomers, and they may likewise be used to separate the precursors of these compounds, such as, for example, the 2,4- and 2,6-isomers of dinitrotoluylene or of diaminotoluylene.
There are, however, drawbacks to proceeding in this way. Indeed, these techniques make it necessary to work with very dilute amounts of mixture and require the use of rigorously anhydrous solvent. However, the presence of traces of water is quite often inevitable and these traces react with the isocyanate groups to produce urea. This consequently results in the column being of reduced efficiency, or even becoming blocked. In addition, when the TDI precursors are treated, it is necessary subsequently to have available independent industrial means which allow each of the compounds purified to be converted into isocyanate.
The aim of the present invention is thus to propose a process for the production of the 2,6-TDI isomer which does not have the abovementioned drawbacks.
Moreover, the process according to the invention has the advantage of giving by-products which can be upgraded, in particular in the standard applications of isocyanates.
Thus, the subject of the present invention is a process for the production of a 2,6-TDI isomer from a mixture of 2,4- and 2,6-TDI isomers, in which the said mixture, comprising at least 50% 2,6-TDI isomer, is subjected to at least one cycle of crystallization-melting.
The subject of the invention is moreover a process for the production of a 2,6-TDI isomer from a mixture of 2,4- and 2,6-TDI isomers, in which the said mixture, comprising at least 50% 2,4-TDI isomer, is placed in contact with a compound or a catalyst capable of converting some of the 2,4-TDI isomer present, and in that the 2,4-isomer which has reacted is separated out, then the resulting mixture is subjected to at least one cycle of crystallization-melting.
Other advantages and characteristics of the invention will emerge more clearly on reading the description and the examples which follow.
The 2,4- and 2,6-TDI isomer mixture wh
REFERENCES:
patent: 2831012 (1958-04-01), Bernard
patent: 3591617 (1971-07-01), Buchsbaum
Parron Jean-Claude
Revelant Denis
Vachet Francois
Barts Samuel
Rhone-Poulenc Chimie
Seugnet Jean-Louis
Shedden John A.
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