Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-02-19
2004-04-20
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S451000, C568S453000
Reexamination Certificate
active
06723884
ABSTRACT:
Hydroformylation or the oxo process is an important industrial process and is employed for preparing aldehydes from olefins, carbon monoxide and hydrogen. These aldehydes can, if desired, be hydrogenated to the corresponding alcohols in the same operation or subsequently in a separate hydrogenation step using hydrogen. The hydroformylation is carried out in the presence of catalysts which are homogeneously dissolved in the reaction medium. Catalysts used are generally the carbonyl complexes of metals of transition group VIII, in particular Co, Rh, Ir, Pd, Pt or Ru, which can be unmodified or can be modified with, for example, amine- or phosphine-containing ligands. A review of processes carried out industrially may be found in J. Falbe, “New Syntheses with Carbon Monoxide”, Springer Verlag 1980, p. 162 ff.
While short-chain olefins having up to 5 carbon atoms are at present hydroformylated using predominantly ligand-modified rhodium carbonyls as catalysts, in the case of longer-chain olefins cobalt has a dominant position as catalytically active central atom. This is due firstly to the high catalytic activity of the cobalt carbonyl catalyst regardless of the position of the olefinic double bonds, the branching structure and the purity of the olefin to be reacted. Secondly, the cobalt catalyst can be separated comparatively easily from the hydroformylation products and be returned to the hydroformylation reaction. In addition, catalyst losses during the work-up can be tolerated more readily because of the lower price of cobalt.
The known methods for separating off and recirculating the cobalt catalyst are based essentially on two principles: (1) no valence change takes place in the circuit, i.e. the cobalt remains in the formally negative monovalent form during the entire cycle of hydroformylation, separation and recirculation to the reactor; and (2) a valence change on the central atom from negative monovalent to metallic or positive divalent cobalt takes place in the circuit.
The prototype of principle (1) is the Kuhlmann process (cf. U.S. Pat. No. 3,188,351). In this process, the hydroformylation catalyst which is homogeneously dissolved in the reaction product and is in the form of hydridocobalt carbonyl is converted into its water-soluble sodium salt by means of sodium carbonate solution and is extracted into water. After phase separation, the volatile hydridocobalt carbonyl is liberated again from the aqueous alkaline solution by reaction with dilute sulfuric acid, stripped out by means of synthesis gas, taken up by the olefin to be reacted and returned to the reactor. However, owing to the instability of the hydridocobalt carbonyl and the large number of steps to be carried out successively, this process principle requires a number of expensive engineering precautions.
Processes based on principle (2), in which the organic phase of the reactor output is freed of the cobalt carbonyl complexes by treatment with oxygen or air in the presence of slightly acidic water (cf. DE-B 2404855), are simpler. Here, the cobalt catalyst is destroyed by oxidation and the central atom is formally converted from the oxidation state −1 to +2 and can then be removed by extraction with the aqueous solution. This step is also referred to as “oxidative decobalting”. The cobalt complex required for the hydroformylation can be prepared again from the aqueous cobalt(II) salt solution by reaction with carbon monoxide and hydrogen. The cobalt catalyst produced is then extracted from the aqueous phase using an organic phase, preferably the olefin to be hydroformylated. Apart from the olefin, it is also possible to use the reaction products and by-products of the hydroformylation for the catalyst extraction. The olefins laden with the cobalt catalyst are then hydroformylated in a reactor under superatmospheric pressure and elevated temperature.
DE-A 2139630 describes a process for preparing predominantly straight-chain aldehydes by hydroformylation of olefinically unsaturated compounds, in which aqueous cobalt salt solutions are treated with carbon monoxide and hydrogen in a first stage, the aqueous solution is then extracted with an organic phase in a second stage and the organic phase and a mixture of carbon monoxide and hydrogen are transferred to a third stage where, if desired after introduction of the olefinically unsaturated compounds if they have not been used, or only part of them has been used, for the extraction in the second stage, the hydroformylation is carried out.
EP 0 850 905 describes a hydroformylation process in which the formation of the cobalt catalyst, the extraction of the cobalt catalyst formed into the organic phase and the hydroformylation of the olefins are carried out in a single-stage process in the hydroformylation reactor. The cobalt salt solution obtained after decobalting is circulated. In the examples of EP 0 850 905, the aqueous cobalt(II) salt solution used is an aqueous cobalt acetate solution containing 1% by weight of cobalt, calculated as metal. It has been found that when using such dilute aqueous cobalt(II) salt solutions, particularly when relatively long-chain olefins are employed, only a low loading of the olefins to be hydroformylated with active cobalt catalyst is achieved, since the volume of aqueous phase required for introducing higher amounts of cobalt can be dispersed only insufficiently in the organic reaction medium. This is reflected in unsatisfactory yields of the desired product.
However, when an attempt is made to use more highly concentrated aqueous cobalt salt solutions, e.g. cobalt acetate solution, it is found that stable, continuous operation over relatively long periods of time with complete recycling of the aqueous cobalt(II) salt solution is not possible without problems. Thus, precipitates of cobalt-containing salts in plant components carrying the aqueous cobalt salt solution are observed. The catalyst deficit has to be made up by continual introduction of fresh cobalt acetate solution. Consequently, part of the aqueous cobalt salt solution continually has to be taken from the circuit and worked up in a separate work-up step, e.g. by precipitation of cobalt hydroxide and dissolution of this in acetic acid, and returned to the process in concentrated form. This circuitous route is costly and associated with wastewater problems since cobalt ions damage the microorganisms in biological wastewater treatment plants.
It is an object of the present invention to hydroformylate olefins having from 6 to 20 carbon atoms continuously and in stable long-term operation in high yield on an industrial scale using aqueous cobalt(II) salt solutions in a process in which the catalyst circuit should be as simple as possible, largely loss-free and environmentally friendly.
The inventors have found that, regardless of the cobalt(II) salt originally used, the cobalt in the aqueous cobalt(II) salt solution is predominantly present as cobalt(II) formate after relatively long continuous operation. This is because formic esters of the alkanols having one more carbon atom than the olefins used are, in particular, formed as by-product of the cobalt-catalyzed hydroformylation. These are partly hydrolyzed in the reaction zone, with the formate anion going over into the aqueous cobalt(II) salt solution. However, at ambient temperature cobalt(II) formate has a water solubility of only about 1% by weight, calculated as cobalt metal, i.e. the water solubility of cobalt(II) formate is less than a fifth of that of cobalt(II) acetate. A sufficient catalyst availability requires, however, more highly concentrated starting solutions.
The inventors have found that stable long-term operation using aqueous cobalt(II) formate solution having a concentration of from 1.1 to 1.7% by weight, based on cobalt, can be achieved if this is continually maintained under conditions under which the solubility limit of cobalt(II) formate in water is not exceeded.
The present invention accordingly provides a continuous process for the hydroformylation of olefins having from 6 to
Grenacher Armin Volker
Stepp Hans
BASF - Aktiengesellschaft
Keil & Weinkauf
Richter Johann
Witherspoon Sikarl A.
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