Method of separating and regenerating rhodiummcontaining catalysts from distillation residues obtained at hydroformylation

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76-04-06 DE 2614799

85-08-12 (30) (11)

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BASF AG, Ludwigshafen DE

1) R. Kummer, 2) HW. Schneider rankenthal, 2.3) Ludwigshafen Forsheden J

Process for separation and rhodium-phosphine catalysts (56) Published publications: DE 2 311 388

Applicant Inventor, 3) K. Schwirten, 1) F (74) (54)

Agent

The term regeneration of

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7703986-5 SEQUENCE

The present invention relates to a novel process for separating and regenerating rhodium containing catalysts from distillation residues, obtained from hydroformylation of olefins with carbon monoxide and hydrogen.

It is generally known to convert olefins at elevated temperature and elevated pressure with carbon monoxide and hydrogen to aldehydes in the presence of certain catalytically active metal carbonyl complexes.

F-CH = CH,₂

R-CH, .- CI1 ,, - CHO + R-CH-CH, vU j ti2 £. £. | U n-aldehyde CHO isoaldehyde lb

R represents an organic group

If, as is very common, cobalt-containing catalysts are used, the necessary reaction temperatures become relatively high, thereby promoting the formation of the usually undesired isoalide fluids. Rhodium-containing catalysts allow significantly milder reaction conditions, saying that n-aldehydes are formed to a greater extent (compare Catalysis Reviews, band 6, l'J / 2, p. 68), but so far these catalysts have only slowly gained entry on hydroformylation on a technical scale, as the recovery and regeneration of the precious precious metal present considerable difficulties.

Both in discontinuous and in continuous operation, the more volatile constituents of the reaction mixture, including the process products, are separated by distillation, the catalysts being enriched in the more high boiling distillation residue. Admittedly, this catalyst-containing residue can be returned to the hydroformylation. In the long run, however, the entire amount cannot be recycled, as the residue continuously becomes noisy and the activity of the catalyst decreases with time.

Therefore, the recovery and regeneration of the expensive rhodium cold-light lamps is of economical importance, but hitherto known methods have proved to be of little benefit. Had in the process according to German publication specification 2,262,885 (decomposition of the catalysts with higher vapor water) and in the process according to German Laid-Open No. 1,954,815 (adsorption of rhodium on basic ion exchangers) the precious metal is obtained in elemental form, from which only very laborious can be recovered the active complex.

In the process of the US patent

547 964, treating the catalyst-containing destination residue with aqueous acids and peroxides, separating the precious metal saline aqueous phase, destroying excess hydrogen peroxide by heating, and reacting the aqueous solution under pressure with carbon monoxide in the presence of an inert, water-complexing solvent. such as triphenylphosphine. An organic solution is obtained of a noble metal carbonyl complex which can be returned to the hydroformylation. However, this process also has drawbacks, since the regeneration of the catalyst takes place under pressure in a system of two liquids and therefore does not proceed sufficiently quickly and especially not sufficiently quantitatively. In addition, the known method only allows the preparation of solutions in which the catalyst consists only of the central noble metal atom and the zero-worthy ligands CO and L, where L represents, for example, a tertiary phosphine. However, for reasons of stability, such complexes in which an L is replaced by halogen are often preferred.

The basis of the invention lay the problem of separating the rhodium from the distillation residues obtained by hydroformylation and simply returning it to active form.

In addition, the invention aims to recover from type I or II catalysts from the destination residues.

Rh (CO) (PR), C1I ^island HRh (CO) (PR₃) II wherein R represents the same or different hydrocarbon groups.

A process for separating and regenerating type I or II catalysts was found ₃₅ Rh (C0) (PR₃ )₂C1I

HRh (CO) (PR₃)₃II

7703986-5 wherein R represents the same or different hydrocarbon groups, in pure form, by regenerating aqueous solutions of rhodium salts, such as are obtained in the treatment of distillation residues from hydroformylation mixtures with oxygen-containing mineral acids and peroxides, which is characterized by treating these aqueous solutions with a cationic solution. separates the cation exchanger from the solution, desorbs the absorbed rhodium ions with hydrochloric acid, reacting the hydrochloric hexachlorododate solutions in the presence of a water-soluble organic solvent with a tertiary phosphine PR 2 at 0 - 150 ° C and 1 - 250 bar with carbon monoxide or carbon monoxide scavenging compounds and separating the resulting complexes I or, if operating under hydration conditions , the complexes also obtained II.

The distillation residues obtained in hydroformylation by rhodium catalysts consist essentially of volatile aldehydes, alcohols, aldols, carboxylic acids and esters and generally contain 0.001 - 1% of the precious metal.

Preferably, per 100 parts by weight of such a residue, under intensive mixing, 10 - 1000 parts by weight of 1- to 2020 percent aqueous solution of mineral acid and 10 - 100 parts by weight of peroxide are reacted at 20 - 120 ° C.

A suitable acidic mineral acid is especially nitric acid, but sulfuric acid and phosphoric acid are also suitable. Halogenated acids, especially at higher concentrations, are not suitable because they form chloro-rhodates which are not retained in the cation exchangers used in the process. Suitable peroxides are those which decompose upon heating, thus primarily hydrogen peroxide, but also alkali metal peroxides or persulfates and persulfuric acids. Organic peroxides such as benzoyl peroxide can also be used.

In the oxidative treatment of the hydroformylation residue, the rhodium goes virtually quantitatively to the 3+ aqueous gas such as Rh. It is an advantage of the present process that any excess peroxide excess present should not be destroyed before carrying out the next process step, namely the cation exchange treatment.

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Suitable cation exchangers are primarily cross-linked polymers with sulfonic acid groups or carboxy groups, e.g. styrene-divinylbenzene resins. These and similar cation exchangers are known in the trade under the designations Amberlite and

Lewatit *⁰.

The amount of cation exchanger is usually chosen so that 3+ per mole of Rh is used 10 - 100 moles of acid equivalent. Since mah in the process receives 0.01- to 0.5-percent. (weight) +

in aqueous solutions of Rh, this means in practice that about 10 - 1000 g of cation exchanger is used per 10 liters of such a solution. Treatment with the cation exchanger is preferably done at room temperature by stirring the solution with the ion exchanger for 30 - 120 minutes or by passing the solution through an ion exchange column while observing the corresponding residence times. The residual, possibly still peroxide-containing rhodium-free or (which is usually sufficient) in the nearest rhodium-free solution can be used to treat further hydroformylation residue. A particularly advantageous embodiment of the present process is, therefore, that the hydroformylation residues are treated portionwise with a limited volume of aqueous phase and supplemented each time the solution is recovered only with so much peroxide and acid which corresponds to the consumption on the oxidation. For the desorption, the cation exchanger is preferably treated with a 20-100 times larger mole amount, based on rhodium, of 1 - 5 M hydrochloric acid.

In the following process step, it is transferred in the form of [RhClg]² anions of the present rhodium with phosphines PR 2 and carbon monoxide in the presence of water-soluble solvents in the hydrochloric aqueous phase of complex I, or, in addition, under hydration conditions, of complex II.

Based on the amount of rhodium, the amount of phosphine corresponds at least stoichiometric to formula I or II, but it is advantageous if phosphine is added in up to 100-fold molar excess.

The function of the aqueous organic solvent is to keep the free phosphine in solution in the aqueous organic phase. The amount of solvent thus depends on the amount

7703986-5 ί

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ϊ &amp; ί 'in' aqueous hydrochloric acid, on the nature of the solvent, on the nature and amount of phosphine, and to a certain extent on the nature and amount of the other constituent elements of the aqueous phase. This amount varies on a case by case basis, but it may vary. without difficulty is determined on precious metal-free model solutions. It is expedient that the required minimum amount is not underestimated, but the progress of the process does not cease, according to observations so far, even when the proportion of water in the whole system is only 10% by weight.

Suitable water-soluble organic solvents are

e.g. acetone, tetrahydrofuran and dioxane, and in particular alcohols having 1-4 carbon atoms, such as methanol, ethanol, propanol, isopropanol, n-butan-1-ol, n-butan-2-ol, isobutan-1-ol and isobutan-2 ol.

It is convenient to dissolve the phosphine in the solvent and add it in this form to the aqueous solution of hexachlororodate.

The choice of the phosphine PR₃ depends on the nature of the hydroformylation reaction in which the rhodium catalyst will find use. Preferably, catalysts uv Lyp 1 or 11 are used in which the phosphine organic groups are the same or different alkyl, aralkyl, aryl or alkylaryl groups, each having a maximum of 12 carbon atoms, the total number of carbon atoms in the phosphine being 12 - 36 . All of these phosphines, whose hydrocarbon groups may also contain halogen atoms as substituents or be interrupted by oxygen atoms, have the important property of the present catalyst regeneration process to be sufficiently soluble even in homogeneous aqueous organic solvents and to form therein highly soluble carbon monoxide or hydrogen halide or hydrogen halide. The chemical properties of the phosphines are of minor importance, so they should preferably use trialkylphosphines or triarylphosphines having 12-24 carbon atoms or especially Lriienylphosphine only expressing that these phosphines as rhodium 35 ligands have found widespread application in the technology of hydroxylation.

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POOR, quality

If the phosphines are very soluble in the aqueous organic medium, the use of dispersants may be advantageous. In this case, no homogeneous solution is obtained, but fine dispersions, which, however, behave as solutions.

In some cases, it may be appropriate to heat the aqueous organic solution prior to carbonylation so that the phosphine is able to deposit with the precious metal.

In the aqueous organic solution containing the rhodium-chlorophosphine complex and phosphine, there is initiated after carbon monoxide at 0 - 120 ° C and 1-5 bar, preferably slightly below the boiling temperature of the solution and at normal pressure. In this case, the complexes I fall practically quantitatively, possibly together with some of the excess phosphine. Instead of carbon monoxide, carbon monoxide splitting compounds can also be used, e.g. formaldehyde.

If the carbonylation takes place under hydrating conditions, the equally insoluble hydride complexes II are obtained. For this purpose, either hydride ion emitting reducing agents such as sodium borohydride at 0 - 100 ° C under normal pressure or hydrogen at 0 - 150 ° C and 1 - 300 bar are used.

Chloro complexes II can also be subsequently transferred to the hydride complexes II by dissolving them in water-soluble organic solvents, hydrating and precipitating the hydride complexes by adding water.

The 95% to 100% of the rhodium content recovered and regenerated catalysts I or II are returned to the hydroformylation by passing to the distillation residue cycle.

The process allows economical use of the chemically technically important rhodium-catalyzed hydroformylation.

It can be harmoniously incorporated into syntheses on a technical scale and, above all, allows the recovery of the catalysts in the form of the particularly important chloro and hydride complexes I, II. A particular advantage of the method is that it can be used successfully even in cases of particularly troublesome rhodium recovery. Such troublesome cases have so far always been observed when the hydroformylation residues from continuous operation are recycled.

7703986-5 for longer than one week. In this case, the rhodium losses in the work-up for unknown reasons rise to about 50%. The present method, on the other hand, permits practically free recovery of the balance over several months from rhodium losses.

The process finds, for example, use in the preparation of, in particular, n-aldehydes and monoolefins, such as propionaldehyde from ethylene, n-butyraldehyde from propylene and n-nonanal from octene, and also especially in bishydroformylation of conjugated unsaturated compounds with olefinic double bonds.

e.g. butadiene, a reaction which has not been economically feasible with conventional cobalt catalysts.

Example

1000 g of a distillation residue which had been formed over the course of 8 months in continuous hydroformylation of propylene to mainly n-butyraldehyde and contained 340 mg of rhodium, predominantly in the form of the HRh (CO) (PRg) 5 (R - phenyl) complex, was stirred with 1000 g of 1M nitric acid and 300 g of 50% hydrogen peroxide first for 20 hours at room temperature and then another 4 hours at 40 - 60 ° C. Thereby, this was transmitted

98 % of the rhodium to the acidic aqueous phase, which over the course of 60 minutes was then added to a column of 250 g of a sulfo group-containing cation exchanger (Amberlite JR 120; 1.9 mole acid per 1) The remaining rhodium-free solution was slightly concentrated, adjusted with nitric acid. and hydrogen peroxide back to the starting amount and initial concentration and used to treat an additional 10,000 g of distillation residue. After a total of 10 cycles of this kind, thus after reprocessing of 10 kg remained, 3.4 g of rhodium had thus accumulated in the cation exchanger. The rhodium was then eluted with 1000 ml of 3M hydrochloric acid, then the volume of the solution was reduced to 300 ml and to the solution was added 600 ml of isopropanol and 26.5 g of triphenylphosphine and the solution was treated at 100 ° C and normal pressure within 15 minutes with carbon monoxide. After cooling, the yellow crystals of Rh (CO) (PR) were separated₃)₂C1 (R = phenyl). The yield of recycled rhodium was 97%, calculated over all process steps.

Reduction of the chloro complex in isopropanol and water with sodium carbonate and additionally triphenylphosphine gave quantitatively the corresponding hydride complex.

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