Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-08-07
2003-11-18
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S331000
Reexamination Certificate
active
06649798
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a process for the production of methylenedianiline (MDA) with a high monomer content and low ortho content by rearrangement of a condensation product (known as aminal or N,N-diphenylmethylenediamine) from aniline and formaline or another suitable methylene group-supplying agent such as trioxan or p-formaldehyde, catalysed on solid acids.
MDA (particularly the 4,4′-isomer) is an extremely suitable starting material from which—optionally after further purification—diisocyanates that represent an important raw product for polyurethane systems, for example, can be obtained by phosgenation. At the same time, the aliphatic systems that are obtained from MDA by hydrogenation of the aromatic ring also play an important role as paint resins.
Of the many conceivable methods described in the literature for the production of MDA, manufacture from the aniline-formaldehyde condensation product (known as aminal) is the most important because it is the most economically advantageous. Depending on the variant, the condensation product is produced first and then rearranged in the presence of (mostly) mineral acids such as HCl or alternatively the condensation itself is performed in the presence of acids under rearrangement conditions.
The disadvantages of such methods in regard to the synthesis of monomeric MDA can be summarised as follows: depending on the reaction conditions, the methods lead to mixtures consisting of excess aniline, MDA monomer (2,2′-, 2,4′- and 4,4′-isomeric) and polynuclear compounds (known as polymer bases), from which the monomeric MDA—optionally after conversion to the corresponding isocyanates—can be obtained. A preparation consisting of almost polymer-free MDA bases can be obtained only with extreme excesses of aniline in comparison to the methylene group-supplying agent, leading to low space-time yields and large circulating flows of aniline.
A further disadvantage of the preparation by catalysis of mineral acids is the accumulation of salt-containing waste waters that occur during neutralisation of the acid. Moreover, aqueous mineral acids lead to corrosion problems in plants.
A whole series of suggestions for the industrial implementation of the rearrangement, including the use of solid acids, has therefore already been made in order to overcome these disadvantages.
However, a feasible method for the production of MDA monomer bases avoiding mineral acids must meet the following conditions, for example:
a) Quantitative yields: an intermediate-free (aminobenzylaniline-free) product must be obtained in order to ensure that it is capable of being phosgenated (these can be extremely troublesome in the subsequent processing of the MDA to MDI (phosgenation).
b) Isomer distribution: similarly to the mineral acid-catalysed method, the product composition must be able to be controlled to some extent by varying the process parameters.
c) Service life: a catalyst used in industry must achieve an economic service life with high space-time yields before its activity can be restored by means of regeneration.
d) Foreign substances: the catalyst used must release no trace components in the product that have a negative influence on product quality. In addition, the method must cause no foreign matter, e.g. in the form of a solvent that is foreign to the system, to be brought into the reaction mixture.
Various attempts to obtain the pure binuclear molecule selectively have already been described, whereby a distinction has to be made between (a) methods for the material separation of mixtures of isomers and homologues and (b) the selective synthesis of the binuclear compounds:
(a) Methods for selective 4,4′-MDA crystallisation from halogenated solvents were described for example in U.S. Pat. No. 4,172,847. The disadvantage of this process, however, is that a foreign solvent has to be used in a complex additional process step, as a result of which additional material cycles and separating operations are required.
(b) U.S. Pat. No. 4,011,278 reports on numerous conversions of polar organic compounds using ZSM-5 zeolites and other zeolite types. It also mentions the conversion of N-alkylaniline with formaldehyde in the presence of zeolitic catalysts, without making any reference to reaction conditions, yields and selectivities, however.
It is known from DE-A-2 202 500 that if aminal is rearranged using amorphous silicon-aluminium-mixed oxide cracking catalysts, high yields of 4,4′-isomers are obtained if the reaction is itself performed in the presence of ortho isomers (obtained from another batch, for example). No additional proportions of 2,2′- and 2,4′-MDA are obtained in the presence of these isomers, since after their primary formation they preferentially react to higher-functional oligomeric MDA grades. A high proportion of polymer bases is therefore conventionally obtained, which have to be separated off from the desired 4,4′-isomer. Furthermore, this process requires the o-isomers formed to be recycled as an additional step.
It would be more advantageous to establish conditions during the actual synthesis of MDA that ensure high proportions of 4,4′-MDA, whereby the above-mentioned problems of salts and corrosion can be circumvented at the same time by synthesis using solid acids.
Thus it has already become known from the above-mentioned U.S. Pat. No. 4,011,278 that high selectivities in terms of the binuclear compound and particularly of 4,4′-MDA can sometimes be obtained using solid oxidic acids, for example, but particularly using zeolites.
EP-A-0 264 744 describes the condensation of aniline with trioxan or free formaldehyde and the rearrangement to MDA bases using solid boron-containing zeolites. Simultaneous condensation and rearrangement as well as isolation of aminobenzylanilines with subsequent rearrangement to MDA were both performed. Although high monomer selectivities were obtained by rearrangement of the aminobenzylanilines to MDA (approx. 90 mol % binuclear isomers in the aniline-free mixture), a complete conversion was not achieved and furthermore the reaction is preferably performed in benzene as solvent.
Attempts have also already been made to perform the rearrangement of aminal via aminobenzylaniline to MDA according to the prior art in several steps, for example in two steps, using solid acids in more than one step. U.S. Pat. No. 4,039,581 describes the rearrangement of an aminal from formaldehyde and aniline using solid acids, whereby it is first dried and then rearranged using zeolites, for example, in several reaction stages—characterised by temperature stages. A temperature of 100° C. is not exceeded, however, since it is assumed that high temperatures in the presence of water would be damaging to selectivity. A full rearrangement of the amino-benzylaniline intermediates to the MDA bases cannot be achieved under these conditions. An MDA with a binuclear content of approx. 90 mol % in the aniline-free mixture is obtained as product.
EP-A-0 329 367 describes the rearrangement of a dried aminal using zeolitic catalysts for the purpose of selective production of binuclear MDA. An aminal is rearranged isothermally at 120° C. using dealuminised HY zeolites and fluorinated derivatives thereof to a blend of MDA, which although consisting of approx. 94 mol % (relative to aniline-free solution) of binuclear MDA is characterised by incomplete conversion of the intermediates to the MDA bases. Approx. 5 mol % polymer bases are additionally formed.
SUMMARY OF THE INVENTION
The object of the present invention was therefore to find a process by which, contrary to the opinion represented in the literature, the conversion of aminal to low-polymer binuclear MDA can be performed using solid acid catalysts and thereby to utilise the advantages of catalysis with solids with sufficiently long catalyst residence times such as are required for industrial processes, without obtaining significant residual quantities of polymeric MDA bases or incompletely rearra
Grotjohann Dirk
Klein Stephan
Koch Daniel
Mendoza-Frohn Christine
Müller Heinz-Herbert
Barts Samuel
Bayer Aktiengesellschaft
Brown N. Denise
Gil Joseph C.
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