Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Platinum group metal
Reexamination Certificate
2002-09-05
2004-02-03
Nazario-Gonzalez, Porfirio (Department: 1621)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Platinum group metal
C502S022000, C502S029000, C502S030000, C502S031000, C502S034000, C556S024000, C556S136000
Reexamination Certificate
active
06685896
ABSTRACT:
The present invention relates to an improved process for removing and recovering rhodium from oxo process reaction products.
The preparation of aldehydes and alcohols by addition of carbon monoxide and hydrogen to olefinic double bonds (hydroformylation) is well known. The reaction is catalyzed by metals or compounds thereof of the 8
th
transition group of the Periodic Table which form carbonyl or hydridocarbonyls under the reaction conditions. While cobalt and cobalt compounds used to be used as catalysts, rhodium catalysts are today finding use to an increasing extent, even though rhodium is several times more expensive than cobalt. Rhodium is used alone or in combination with complexing agents, for example organic phosphines. While the oxo process requires reaction pressures of from 25 to 30 MPa using rhodium as catalyst, pressures of from 1 to 5 MPa suffice when rhodium complexes are used.
In many cases, rhodium catalysts have distinct advantages. They have higher activity and selectivity and additionally facilitate uncomplicated operation of the production plants, in particular relating to conduct of the synthesis and the excavation of the products from the reactor. Finally, the classic oxo process based on cobalt catalysts may be converted in many cases to rhodium catalysts using the available apparatus parts with only minimal capital expenditure.
Despite the advantages mentioned of the rhodium-catalyzed oxo process, the classic cobalt process continues to be operated in existing old plants, in particular when conversion of the process to the rhodium method under the given economic conditions does not appear necessary.
Particular significance attaches to the recovery of rhodium which, after the reaction has ended, is present as the carbonyl compound dissolved in the hydroformylation product. The work up comprises depressurizing the crude oxo product in more than one stage by reducing the synthesis gas pressure from about 25 to 30 MPa initially to from 1.5 to 2.5 MPa. This releases synthesis gas dissolved in the crude product. The mixture can then be depressurized to atmospheric pressure. Before purification or further processing of the reaction product, by distillation, the dissolved rhodium compounds have to be removed. It has to be taken into account here that only a few ppm of the noble metal are present homogeneously dissolved in the crude product. Also, in the course of the depressurization procedure, rhodium can be converted to a metallic form or form multinuclear carbonyl compounds which separate from the liquid organic phase as solids.
In the process known from EP-A-147824, rhodium is removed and recovered by extracting it from the crude oxo product by means of complexing reagents.
The crude oxo product is the oxo process reaction mixture obtained after depressurizing and possible cooling.
In the known process, the complexing agents used are sulfonated or carboxylated organic phosphines, preferably sulfonated arylphosphines. The sulfonated or carboxylated organic phosphines form water-soluble complexes with rhodium. Accordingly, the rhodium may be extracted from the crude organic product using an aqueous solution of the substituted phosphine.
This transfers the rhodium to the aqueous phase which can be removed by simple decanting from the organic product mixture. Circulation of the complexing agent solution provides high rhodium concentrations in the aqueous phase.
According to EP-A-156253, the process disclosed by EP-A-0147824 is improved by adding a solubilizer to the aqueous solution of the complexing agent. Its effect is in particular to alter the physical properties of the surface area between the two liquid phases and thereby to accelerate the transfer of the aqueous extractants into the product phase and that of the rhodium from the product phase into the aqueous phase. However, the effectiveness of the process described depends on the quantity of solubilizer added. Its quantity cannot be increased without limitation because the materials added unnecessarily burden the aqueous solution of the extractant and compromise its stability.
In the process disclosed by EP-B1-0 183 200, the depressurized crude oxo product is likewise extracted using an aqueous solution of a complexing agent. However, this process does not operate with the addition of a solubilizer, but instead employs sulfonated arylphosphines having quaternary ammonium counter ions, for example the benzyltrimethylammonium cation, as water-soluble complexing agents.
The prior art processes employ a catalyst solution which results from hydroformylation reactions with rhodium catalysis.
However, problems occur where a hydroformylation plant initially operated under cobalt catalysis is to be converted to rhodium catalysis.
For instance, EP-B1-0 111 257 concerns a hydroformylation process which comprises reacting the off gas from a first hydroformylation step (which reacts olefin with carbon monoxide and hydrogen in the presence of a catalyst solution comprising an aqueous rhodium complex at low pressure) in a second step by the classical oxo process at high pressure and in the presence of cobalt catalysts.
The conversion of this process to the complete rhodium method, i.e. also carrying out the/second step under rhodium catalysis, is the subject matter of EP-A1-0 805 138.
The organic phase resulting from conversion to the rhodium method accordingly comprises both rhodium and cobalt as catalytically active metal.
Since rhodium is a precious metal, there is accordingly great interest in its removal, recovery and reuse as active catalyst metal from the cobalt-containing catalyst solution for economic reasons. It is of decisive importance that the rhodium occurs virtually completely in a form which allows reuse as a catalyst component. In order to obtain highly optimal activity and selectivity for the recovered catalyst, virtually complete removal of the cobalt from the rhodium is sought. It should likewise be possible to recover rhodium virtually completely while at the same time retaining the activity and selectivity of the catalyst solution after complete removal of the cobalt from the hydroformylation process or from the oxo process reaction products which were hitherto obtained by exclusive rhodium catalysis.
It is accordingly an object of the present invention to provide a process by which rhodium may be virtually completely recovered from an organic catalyst solution in a simple manner. The catalyst solution may additionally comprise cobalt-containing compounds as impurities. At the same time, it shall be ensured that rhodium is obtained in a form suitable for reuse as catalyst. The rhodium compounds obtained shall be suitable for reuse both in a homogeneous hydroformylation process carried out in the organic phase and also in the biphasic hydroformylation process in the presence of water disclosed by DE-C-26 27 354.
This object is achieved by a process for recovering rhodium from organic solutions comprising rhodium complexes with or without cobalt complexes and with or without complexing ligands, which comprises
extracting the organic phase with an aqueous solution of a phosphate of the formula (O)P(OR
1
)(OR
2
)(OR
3
), where R
1
, R
2
and R
3
are identical or different and are hydrogen, a straight-chain or branched alkyl radical having 1-10 carbon atoms or a substituted or unsubstituted aryl radical having 6-10 carbon atoms, and the aryl radical is substituted by straight-chain or branched alkyl radicals having 1-4 carbon atoms, or with a phosphonate of the formula R
4
P(O)(OR
5
)(OR
6
), where R
4
, R
5
and R
6
are identical or different and are hydrogen, a straight-chain or branched alkyl radical having 1-10 carbon atoms or a substituted or unsubstituted aryl radical having 6-10 carbon atoms, and the aryl radical is substituted by straight-chain or branched alkyl radicals having 1-4 carbon atoms;
washing the organic phase with water at a pH of from 0 to 8;
treating the organic phase after phase separation with an oxidizing agent at a temperature of from 0 to 100° C.;
treating the organic
Bohnen Hans-Willi
Fischer Richard
Hewlett Mark
Schopper Norbert
Zgorzelski Wolfgang
Celanese Chemicals Europe GmbH
Muserlian Lucas and Mercanti
Nazario-Gonzalez Porfirio
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