Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
2003-12-10
2004-12-21
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C560S338000
Reexamination Certificate
active
06833469
ABSTRACT:
DESCRIPTION
The present invention relates to a process for the production of isocyanates by reaction of amines with phosgene using isocyanate as solvent, the isocyanate used as solvent being added to the reaction mixture only after the amine and phosgene have been physically combined.
Various processes for the production of isocyanates by reaction of amines with phosgene in the presence of isocyanate are known.
DE-A 1,192,641 describes a process for the production of isocyanates by reaction of amines with phosgene, the isocyanate produced during the reaction being used as solvent for phosgene.
DE-A 2,252,068 describes a process for the production of organic isocyanates, wherein amine is caused to react with preheated phosgene in the presence of an excess of isocyanate at temperatures and pressures selected so as to give a homogeneous liquid phase.
U.S. Pat. No. 2,822,373 describes a continuous process for the production of isocyanates, in which a phosgene solution is mixed with a solution of an organic amine in a turbulent reactor circulation system. In this case, the fresh phosgene solution is combined with the circulated reaction solution prior to blending with the amine solution.
WO 96/16028 describes a continuous process for the production of isocyanates by reaction of corresponding primary amines with phosgene in the presence of an isocyanate acting as solvent, wherein the amine is caused to react with phosgene, which is dissolved in the isocyanate in a concentration of from 10 to 60 wt %.
It is also known that the use of a high phosgene excess over the amino groups used leads to high selectivities toward the isocyanate produced and can thus have a decisive influence on the economical value of the process. However, with an increasing ratio of phosgene to amino groups there is a rise in the phosgene holdup of the plant, which should, however, be minimized on account of the toxicity of phosgene.
It is thus an object of the present invention to provide a process for the production of isocyanates which makes it possible to carry out the reaction with high selectivity without raising the phosgene hold-up or lowering the space-time yield.
The object of the invention is achieved, unexpectedly, in the production of isocyanates by the reaction of amine with phosgene, by adding an isocyanate as solvent, which solvent is added not, as described in the prior art, to the phosgene prior to the reaction, but to the reaction mixture formed by physically combining the phosgene and amine.
Thus the present invention relates to a process for the production of isocyanates by reaction of primary amines with phosgene, in which isocyanate is used as solvent, wherein some or all of the isocyanate used as solvent is added to the reactants only when the amine and phosgene have been physically combined.
The process of the invention includes continuous, semicontinuous, and batch processes. Preference is given to continuous processes. During the production of isocyanate by reaction of a primary amine with phosgene there is formed, in an initial fast step, &agr;-cording to following reaction scheme, the intermediate carbamoyl chloride, which decomposes in the rate-determining, slow step in a balanced reaction to form isocyanate and HCl.
R—NH
2
+COCl
2
→R—NH—COCl+HCl⇄R—NCO+2 HCl,
in which R is an organic radical.
Furthermore the resulting hydrogen chloride can react with amines to form amine hydrochlorides.
The essential feature of the process of the invention is that the addition of the isocyanate acting as solvent does not occur until the amine and phosgene have been physically combined, preferably by mixing. In one embodiment of the invention, the solvent is added at a time or point at which at least 50%, preferably at least 80%, more preferably at least 90%, and most preferably at least 95% of the amino groups used have already undergone reaction.
The rate of the reaction between phosgene and amine or between hydrogen chloride and amine is primarily governed by the type of isocyanate to be synthesized and the reaction temperature used. Correspondingly, the addition of isocyanate acting as solvent can take place some time between 0.1 milliseconds and 10 minutes following physical combination of phosgene and amine.
In the process of the invention, some or all of the isocyanate used as solvent is added to the reaction mixture, ie the reactants amine and phosgene, only after the amine and phosgene have been physically combined. In a preferred embodiment, the portion added to the reaction mixture after the amine and phosgene have been physically combined is at least 25 wt %, preferably at least 50 wt %, more preferably at least 75 wt %, and most preferably at least 90 wt %, based on the total amount of isocyanate to be used as solvent. The portion thereof which is not to be added after the amine and phosgene have been physically combined, can be added prior to the reaction either to the amine or, preferably, to the phosgene.
In the process of the invention, use can be made of any one primary amine or a mixture of two or more such amines. Preference is given to aromatic amines, particularly those in the diaminodiphenylmethane series or their higher homologs. Examples thereof are methylenediphenylamine (MDA; individual isomers, mixture of isomers and/or oligomers thereof), toluylenediamine (TDA), n-pentylamine, 6-methyl-2-aminoheptane, cyclopentylamine, R,S 1-phenylethylamine, 1-methyl-3-phenylpropylamine, 2,6-xylidine, 2-(N,N-di-methylamino)ethylamine. 2-(N,N-diisopropylamino)ethylamine, C11-neodiamine, isophoronediamine, 3,3′-diaminodiphenylsulfone, and 4-aminomethyl-1,8-octanediamine. MDA and TDA are preferably used.
The process of the invention is thus suitable for use in the synthesis of any desired isocyanates. The process can be used with particular advantage for the production of methylene (diphenyldiisocyanate) (MDI) and toluylene-diisocyanate (TDI).
The isocyanate used as solvent is preferably the isocyanate to be synthesized. It may come from an external source or, preferably, be taken from the process of the invention and recycled. Alternatively however, other suitable isocyanates, or mixtures thereof, may be used as solvent.
An additional inert solvent can be co-used in the process of the invention. This additional inert solvent is usually an organic solvent or a mixture thereof. Chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, hexane, diethyl isophthalate (DEIP), tetrahydrofuran (THF), dimethylformamide (DMF), benzene, and mixtures thereof are preferred. Particular preference is given to chlorobenzene. The additional inert solvent can be added to the amine preferably at the commencement of the reaction. The inert solvent is usually employed in a concentration of from 5 to 1000 wt %, and preferably from 50 to 500 wt %, based on the amount of amine used.
The process of the invention will now be described in detail with reference to a general flow sheet illustrating a continuous process, as shown in FIG.
1
. The elements depicted in
FIG. 1
are as follows:
I phosgene receiver
II amine receiver
III first mixing device
IV second mixing device
V reaction device
VI first separating device
VII second separating device
VIII isocyanate feedstock
IX phosgene purifier
X solvent purifier
1
phosgene feedline
2
amine feedline
3
inert solvent feedline
4
separated hydrogen chloride and inert solvent
5
recycled isocyanate stream
6
discharged hydrogen chloride
7
separated isocyanate
8
,
11
separated inert solvent
9
purified inert solvent
10
purified phosgene
The amine from amine receiver II and phosgene from phosgene receiver I are mixed in a suitable first mixing device III. The mixture of amine and phosgene is mixed, in a second mixing device IV, with isocyanate acting as solvent and passed to the reaction device V. Suitable mixing devices are, for example, nozzles or blender reactors. It is also possible to carry out the two mixing operations of mixing devices III and IV in a common mixing device but in discrete regions, as explained below with referen
Müller Christian
Stroefer Eckhard
Wölfert Andreas
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