Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Platinum group metal
Reexamination Certificate
2001-02-21
2004-06-08
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Platinum group metal
C423S138000, C423S139000, C423S148000, C423S417000, C423S594190, C502S038000
Reexamination Certificate
active
06746653
ABSTRACT:
The priority document of the present application, German patent application 10008904.6, filed Feb. 25, 2000, is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is a process for recovering transition metals from catalysts, in particular cobalt, from salt-containing reaction mixtures, and the conversion of the recovered metals into new catalysts.
2. Discussion of the Background
Many chemical reactions produce reaction mixtures composed of the desired product, as well as by products such as salts or salt-like materials in addition to the catalyst or catalysts used, and the decomposition products of these catalysts. For example, halogen-substituted compounds may be carbonylated in the presence of catalyst compounds based on transition metals of Group VIII of the Periodic Table of the Elements. Such metals include, for example, ruthenium, platinum and palladium salts or complexes, as well as cobalt compounds. Carbonylation reactions often employ cobalt carbonyl complexes and species which can be generated therefrom, e.g., alkali metal salts, particularly sodium salts of hydridocobalt carbonyls. These carbonylation reactions are usually carried out in the presence of a base, so that a mixture of the carbonylation product, any solvent used, dissolved carbon monoxide, catalyst and/or decomposition products of the catalyst, salts formed during the reaction, and other components, are obtained upon completion of the reaction.
Generally, reactions are “worked up” (i.e., products isolated and purified) with the intention of isolating the product in as high yield as is possible. However, implementing such processes on an industrial scale requires additional considerations. In addition to simply recovering the solvents used, it is also desirable to employ processes which allow virtually quantitative recovery of the catalyst, or its decomposition products, in a form which permits simple conversion of the recovered catalyst or catalyst decomposition products into new catalyst. Furthermore, for both economic and environmental reasons, any salts (“salts” includes a salt, or a mixture of salts) present in the reaction mixture should be recovered in a form which allows them to be used in other processes. For example, the recovered salts should not contain contaminants which would interfere with any other processes in which they may be used (e.g., a chloralkali electrolysis process).
Thus, for example, a simple work-up method for salt-containing reaction mixtures containing a cobalt catalyst is to mix the reaction mixture with aqueous acid, either by adding the reaction mixture to the aqueous acid, or the converse. The salt and the cobalt compounds would thereby tend to dissolve in the aqueous acid phase, and the product, together with any solvents present in the reaction mixture, would tend to form a separate organic phase. The aqueous acid phase containing the dissolved catalysts and the salts may then be separated more readily from the organic phase containing the desired product. After the addition of a suitable precipitating agent, the cobalt may then be precipitated and separated from the aqueous phase as water-insoluble cobalt compounds, for example as cobalt hydroxide.
The above-mentioned procedure has been described for the carbonylation of haloacetic esters with carbon monoxide, and their subsequent reaction with an alcohol and a base in the presence of a cobalt carbonyl complex catalyst (JP 60 033 376). Although the cobalt separated off in this manner can be converted, after washing and drying, into fresh cobalt carbonyl complex catalyst, the cobalt recovery process first requires acidification, and then gasification of the reaction mixture. Accordingly, this process consumes large amounts of reagents.
The above procedure may also be used to prepare diesters of malonic acid, which are versatile synthetic building blocks in organic chemistry used, for example, as intermediates in the synthesis of pharmaceuticals, crop protection agents, fragrances, flavors, dyes and plastics. However, the carbonylation procedure described above also requires an excess of alcohol in order to obtain high product yields. In the preparation of short chain malonic diesters, the excess alcohol is usually dissolved mostly in the aqueous phase. Even though the alcohol may be recovered by distillation, it is difficult to recover the salt or salt mixtures in a form which allows them to be used in other processes. The salt solution remaining after separation of the alcohol contains not only the desired product, but also small amounts of dissolved transition metals such as cobalt, as well as other water-soluble impurities such as saponification and condensation products.
It has been found that the desired product may be isolated by extraction from the reaction mixture with sparingly water-soluble or water-insoluble solvents and, for example, the residual dissolved cobalt may be separated from the mixture using suitable ion-exchange materials, preferably a selective chelating ion-exchange material such as TP 207 from Bayer AG. However, evaporation of the solvent and/or water from the remaining salt solution provides salts whose organic impurity content, for example 3% by weight, does not in practice allow the salts to be used in other processes. Improved salt purity was not obtained, regardless of the pH chosen for the activated carbon treatment, even after treating the remaining salt solution with activated carbon before evaporation of the solvents and/or water. In particular, the purity of sodium chloride obtained by the above process is unsuitable for many applications, for example, for use in chloralkali electrolysis.
In some cases, fractional crystallization of the salts dissolved in the aqueous phase provided salts of sufficient purity to be used in other processes. However, at industrially acceptable degrees of evaporation of greater than 75%, salt fractions having a relatively high proportion of organic impurities of approximately 3% by weight are typically produced.
Instead of separating the transition metal and the salt or salt mixture present in the reaction mixture from the other components of the reaction by dissolving them in water, it is also possible to separate the transition metal and salts from the reaction mixture by filtration. In some cases, this requires pretreatment of the reaction mixture. Thus, for example, cobalt carbonyl complexes can be oxidized by air oxidation, and thereby converted into cobalt compounds which are insoluble in the reaction mixture (JP 57 014 557). These insoluble cobalt compounds may then be filtered out of the reaction mixture.
However, it has been found that a mixture of salts and transition metal compounds which has been separated from the reaction mixture by filtration is also not sufficiently free of organic impurities to be used in other processes. Even after being washed multiple times with organic solvents, dissolved in water or aqueous acid, thereby completely removing the transition metal, and subsequent evaporating the residue to dryness, salts were obtained with organic impurity levels of typically 3% by weight. Again, the purity of the salt was not improved, even after treating the salt solution with activated carbon and subsequently evaporating the water and solvents, regardless of the pH chosen for the activated carbon treatment. Only at low levels of evaporation did an evaporative crystallization process provide salts with an organic impurity level below 0.5% by weight.
It is therefore an object of the present invention to develop a generally applicable process for recovering a catalyst metal from a reaction mixture, so that the catalyst metal may be isolated in a form which allows it to be readily recirculated to the synthesis process, for example by converting the recovered catalyst to fresh catalyst. Furthermore, the recovery process of the present invention makes it possible to isolate, in pure form, any salt present in the reaction mixture, so that it can be used in other processes.
SUMMA
Bauer Frank
Prange Uwe
Theis Christoph
Bos Steven
Degussa - AG
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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