CA2104509A1

CA2104509A1 - Process for the recovery of rhodium from distillation residues of products of the oxo synthesis

Info

Publication number: CA2104509A1
Application number: CA002104509A
Authority: CA
Inventors: Gerhard Diekhaus; Harald Kappesser
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1992-08-28
Filing date: 1993-08-20
Publication date: 1994-03-01
Also published as: AU4492093A; MX9305089A; KR940003962A; DE4228724A1; JPH06182232A; BR9303432A; TW287114B; KR100290221B1; JPH0767532B2; ATE153026T1; EP0584720A1; DE59306435D1; EP0584720B1; ES2103051T3

Abstract

Frankfurt, 27.08.1992 PAT/rcht-sei Hoe92/Y014 Abstract of the disclosure For the recovery of the rhodium contained in them as soluble compounds, the distillation residues of products of the oxo synthesis are treated with oxygen or an oxygen-containing gas in the presence of an alkali metal salt of a C2- to C5-monocarboxylic acid. The noble metal is then extracted from the organic phase with the aqueous solution of a complexing reagent, if appropriate after it has already been extracted beforehand with water by itself.

Description

5 0 ~
_roces~ for the recovery of rhodium from distillation residues of products of the oxo synthesis The pr~sent invention relates to an improved process for the recovery of rhodium from the distillation residues o~
products of the oxo synthesis.

The preparation of aldehydes and alcohols by catalytic addition of carbon monoxide and hydrogen onto olefinic double bonds (hydroformylation) is known. Modern pro-ce~ses operate with metallic rhodium or with rhodium compounds as catalysts, which are employed by themselves or in combination with complexing ligands, for example organic phosphines or esters of phosphorous acid. Accord-ing to the unanimous opinion of experts, hydridocarbonyl compounds of rhodium which can be represented by the lS general formula ~[Rh(CO)4~Lx], in which L is a ligand and x is 0 or an integer from 1 to 3, are active as the catalyst under the reaction condi~ions.

Compared with the conventional oxo synthesis using cobalt catalysts, the use of rhodium catalysts has a number of advantageq. The activity of rhodium catalysts i9 higher than that o~ cobalt catalysts, and terminal olefins are converted into unbranched aldehycles in the presence of rhodium (in the form of rhodium complex compounds) to a greater extent than in the presence of cobalt. Moreover, production plants can be operated largely without problems when rhodium catalysts are used, which applies in particular to the synthesis procedure and the dis-charge of the products.

A determining factor for the profitability of the rhodium process is~the removal and recovery of the noble metal as far as possible without losses, regardless of whether it has been employed as the catalyst with or without an additional complexing agent~ After the end of the reaction, the rhodium is present as a carbonyl compound, which may also contain other ligands, dissolved in the hydroformylation product.

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For working up, the crude product from the synthe~is is first let down to normal pressure in one or more stages, dissolved synthesis gases being relea ed. The rhodium i8 removed either directly from the crude product which has been let clown or from the residue of the crude product distillation. The first route is taken if the rhodium has been employed as the catalyst in the preceding hydro-formylation stage without an additional complexing agent.
The second variant is used if the rhodium catalyst a1BO
contains other ligands in addition to carbon monoxide, for example phosphines or phosphites, bonded as com-plexes. It can also be used if the hydroformylation had indeed been carried out with rhodium by itself, but a complexing agent had been added to the crude product after letting down in order to stabilize the rhodium, or it is ensured otherwise, for example by distillation under prescure, that the rhodium does not escape from the material for distillation or the distillation residue in the form of volatile compounds.

Regardless of the form of working up the reaction mixture chosen, it should be taken into laccount that the noble metal iR present in the crude procluct in a concentration of only a few ppm, and its removal therefore requires very circumspect operation. Additional difficulties may also arise from the fact that the rhodium is partly converted into the metal or forms polynuclear carbonyls duxing the letting-down operation, especially if it has be~n employed without a ligand. A hetero~eneous system then forms, which comprises the liguid organic phase and the solid phase containing rhodium or rhodium compounds.

Under these circumstances, it is not surprising that the recovery o~ rhodium from the products of the oxo syn-thes~s, including the residues of crude oxo products, has been investigated on many occasions. The studies have led to the development of numerous processes, a few of which have also found use on an industrial scale.

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,.~: . '`:. . .' 2 ~ 9 According to a proceqs which is proven in practiae for the recovery of rhodium contained in the residues of the distillatio~ of products of the oxo synthesi3 bonded a~
a complex with an organic phosphorus(III) compound, the residues are treated with oxygen or an oxygen-containing gas at 60 to 120C under normal pressure or under pres-sure in the presence o~ a C2- to C5-monocarboxylic acid and the alkali metal salt of a C2- to Cs-monocarboxylic acid, and the rhodium compound is then extracted with water (cf. EP 424 736 A1).

US Patent 42 92 196 relates to the extraction of metals of group 8, which are present as catalysts in the form of metal carbo~yls or organometallic compounds dissolved homogeneously in hydroformylation products, using water~
soluble, nitrogen-containing compounds. The removal is carried out at temperatures which lie between room temperature and 100C and in a range from normal pressure up to an inareased pressure of 7 MPa. Ammonia, ammonium hydroxide and amines are employed as the nitrogen-containing compounds for the extraction.

Another process for the removal of rhodium from theproducts of the oxo synthesis which i6 based on extrac-tion with a complexing reagent is described in EP 147 824 B1. Water-~oluble sulfonates or carboxylates of organic phosphines in the form of an agueous solution which is immiscible with the crude oxo product ar~
employed a~ complexing reagents.

In the last two casPs described, the metal carbonyl compounds or organometallic compounds present in the hydroformylation products are treated with the extraction agent without prior cleavage of the coordinative or metal-carbon bonds.

The known processes allow up to 90% of the rhodium originally employed to be recovered in an industrial 3~ procedure, the remainder of the noble metal being lost.
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Problems during working up of the rhodium extracts some-times occur because the rhodium concentration in the aqueous solutions is low and either large volumes of liquid have to be treated or the ~olution~ must first be concentr~ted. There is therefore interest in perfecting the recovery of rhodium from the products of the oxo synthesis, reducing the rhodium loss~s further and simplifying the handling of the extracts.

The invention achieves the object described above by a process or the recovery of rhodium which is contained in the distillation residue of products of the oxo syn-thesis, if appropriate bonded as a complex, by treatment of the residue with oxygen or an oxygen-containing gas at 60 to 120C, under normal pressure or under pressure in the presence of a C2- to Cs-monocaxboxylic acid and of the alkali metal salt of a C2- to Cs-monocarboxylic acid and subsequent extraction of the rhodium present as a water-soluble compound. This proces~ comprises extracting the residue with the aqueous solution of a reagent which complexes with rhodium, if appropriate after it has already been extracted beforehand with water by itself.

The novel process ensures that a very high proportion of the `rhodium contained in the crude oxo product is removed. With the aid of this process it is possible for rhodium also to be recovered if, for example, water by itself is ineffective or has only little effect when very low metal concentrations are present. In this process, the rhodium is obtained either mainly as a binary com-pound which i easy to process further or exclusively as a catalytically active, water-soluble complex compound.
In this connection, it should be emphasized in particular that the extraction solution contains rhodium in a concentration which allows its working up or its reuse without problems.

The novel process starts from the residues of the hydro-formylation of olefinically unsaturated compounds, which 2 ~

resi~ues ar~ obtained as the distillation bottom product after the removal of the aldehydes and alcohols by di~tillation. They essentially comprise higher molecular weight compounds which have been formed from the aldehydes by aldol condensation and can also split off watex in a secondaxy reaction to form unsaturated com-pounds. The nature of the compounds which have been hydroformylated is of no significance for the procedure claimed. Accordingly, both residues which result from the reaction of olefins with carbon monoxide and hydrogen and residues which are formed from the reaction of olefinically unsaturated compounds which also contain functional groupæ in the molecule can be employed. The novel process is of primary importance for the recovery of rhodium from the residues of hydroformylation of olefins having 2 to 12 carbon atoms, corresponding to the economic importance of the aldehydes prepared from them.
In addition to aldehydes and alcohols and the saturated and unsaturated condensation products, the mixtures to be processed can also contain, as essential constituents, solvents and furthermore compounds which react with rhodium compounds or rhodium carbonyl compounds to form complexes and are usually present in excess compared with the rhodium. These compounds include organic phosphorus(III) compounds, in par.ticular phosphines and phosphites, preferably the aryl compounds, such as triphenylphosphine and triphenyl phosphiteO

According to the invention, the distillation residue is treated with oxygen in order to convert the rhodium present as a carbonyl compound or bonded as -another complex into a form which is easily extractable. The oxidizing agent is employ~d in the pure form or as an oxygen-containing gas mixture, in particular air. The amount of oxygen can be varied within wide limits. It depends on the rhodium concentration and on the concen-tration of the ligands, that is to say preferably the phosphorus(III) compounds in the residue. It is advisable to use 100 to 2000, in particular 300 to 1200 mol of ... . . . .

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2 ~ 9 oxygen per mol of rhodium and per mol of ligand.

According to the invention, the treatment of the distil-lation residua with oxygen is carried out in the pre ence of a saturated straight-chain or branched monocarboxylic acid having 2 to 5 carbon atoms. Examples of suitable acids are acetic acid, propionic acid, n butyric acid, i-butyric acid and n-valeric acid. Acetic acid and propionic acid have proven to be particularly suitable.
They are employed in the commercially available form and in an amount such that about 2 to 150, preferably 3 to 50 mol of acid are pre~ent per mol of rhodium. The acid is added to the mixture before the reaction with oxygen, regardless of whether acid can likewise be formed in the course of the reaction because of the aldehyde present.

Another important feature of the process according to the invention is the presence of an alkali metal carboxylate in the starting material during the oxygen treatment.
Alkali metal carboxylates which are used in the context of the novel process are salts of saturated straight-chain or branched monocarboxylic acids having 2 to 5 carbon atoms. The sodium and potassium salts of acetic acid, of propionic acid, of n- and iso-butyric acid and of n-valeric acid have proved to be particularly ~uit-able. They are used in an amount of 10 to 250, preferably 20 to 180 mol per mol of rhodium. The commercially available salts are suitable, but these gradually dis-solve only in the course of the oxidation. It is there-fore more advantageous to add to the residue free acid and the equivalent amount of alkali metal hydroxide, which are immediately dissolved homogeneously and there-fore become fully effective.

The reaction with oxygen is carried out at 60 to 120, preferably 80 to 100C. It can be carried out under normal pressure or under pressure, pressures of between 0.2 and 1.0 MPa having proved to be particularly suitable~
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2 1 ~ 9 The reaction time depe~ds on the rhodium concentration and the ligand concentration in the starting material. It is furthermore determined by the amount of oxygen employed and by the reaction temperature and pressure.
High concentrations of the dissolved substances require longer treatment times than low concentrations. A large supply of oxygen and increased pressure reduce the reaction time, as does intensive mixing of the residue with the oxygen. Temperatures in the lower and upper region of the range claimed are somewhat less effective than those in the middle temperature region.

The reaction of the distillation residues can be carried out continuously or discontinuously in conventional apparatuses. The oxygen or the oxygen-containing gas is passed into the reactor via distribution devices, and uniform mixing of the liquid and gaseous phase is assisted by stirring, if appropriate.

After conclusion of the treatment with oxygen, the organic phase is extracted with the aqueous solution of a reagent which bonds rhodium as a complex. According to the invention, compounds which enter into stable water-soluble complex compounds with 1:he rhodium under the prevailing temperature and pxessure conditions are called complexing reagents. The greater the tendency of the complexing reagents to re~ct with the rhodium, the more complete the removal of the noble metal from the crude product or distillation residue pretreated with oxygen.
The complexing aqents can be mono- or polydentate, that is to say can occupy one or more coordination sites on the central atom.

Preferred complexing agents for the rhodium are compounds of nitrogen and of phosphorus which contain nitrogen or phosphorus atoms capable of forming coordination bonds with the rhodium, i~e. atoms which have free electron pairs. Examples of nitrogen compounds are ammonia, water-soluble primary, secondary or tertiary amines and -: ~ . . . . . .. .

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~ r~ ~9 diamines, alcoholamines and aminocarboxyic acids. Poss-ible phosphorus compounds are, in particular, sulfonated or carboxylated arylphosphines or aryldiphosphines.
Iminodiacetic acid, nitrilotriacetic acid, ethylene-diaminetetraaceti~ acid and triphenylphosphinetri-sulfonates and triphenylphosphinedisulfonates of the alkali metals and of ammonium are preferred.

The complexing reagents are used in excess with respect to the rhodium. Since they can be circulated, the level of the excess can be as desired, but at least 5 mol of a monodentate complexing agent or at least ~ mol of an n-dentate complexing agent must be present per mol of rhodium. It has proven suitable to use 10 to 50 mol of a monodentate complexing agent or ' to 50 mol of an n-dentate complexing agent per mol of rhodium.

The concentration of the complexing reagent in the solvent can be varied within wide limits. It depends in particular on the extent to which the rhodium is to be concentrated. Accordingly, not on:Ly very dilute but, if appropriate, even saturated solut:ions can be used. As a rule, solutions which contain 0.5 to 25% by weight of the complexing agent, based on the solution, are employed.

The extraction of the rhodium with the dissolved complex-ing agent is carried out at temperatures of 20 to 120C.
The removal can be carried out under normal pressure, but also under increased pressures of up to 1.0 MPa, the range from 0.2 to l.0 MPa being preferred. ~;

In many cases, a single treatment of the distillation residue with the solution of the complexing reagent is sufficient. The solution can of course be recirculated in order to bring the removal of rhodium to completion and to increase the rhodium concentration in the extraction agent by several treatments of the organic phase. A
multi-stage extraction is also possible. An extraction with water can precede the extraction with the aqueous .
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solution of a complexing reagent. It is u~ually carried out with deionized water at 20 to 120C under normal pressure or under pressures of up to 1.0 MPa, preferably O.2 to ~.O MPa, in particular in several stages. The amount of water employed depends on the distribution equilibrium of the substance to be extracted between the organic and aqueous phase and the xhodium concentration required in the ~queous phase. The aqueous extraction solution can be circulated until the distribution equili-brium is established and thus used repeatedly for removalof rhodium in order to achieve concentration of the metal in the solution. In general, two to three extraction stages are envisaged. The transition from one extraction agent to the other is to be matched to the individual circumstances. Deciding factors are, in particular, the decrease in the effectiveness of the pure water for the removal of rhodium, which is detectable from the amount of rhodium absorbed per unit volume of water, and the rhodium concentration required in the aqueous extraction solution.

The novel process can be carried out batchwise or continuously in the reactors c:ustomary for solvent extraction. The extraction can be carried out either in cocurrent or in countercurrent.

Further treatment or further use of the phases containing the rhodium removed depends on the particular circum-stances. The rhodium extracted as a binary compound can thus be precipitated from an aqueous solution as a salt of a higher carboxylic acid. It is likewise possible for the aqueous solution of the binary rhodium compound to be reused as the catalyst pha~e in the oxo synthesis, for example after addition of a water-soluble phosphine. The aqueous phase containing rhodium bonded as a complex is preferably used as a catalyst, if appropriate after addition of further rhodium and/or further complexing agent.

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The invention is illu~trated in the following examples.
However, thP intention is not to limit it to the~e specific embodiments.

Example 1 90.3 kg of a distillation residue of ethylene hydro-formylation are diluted in a stirred reactor with toluene in an amount such that the rhodium concentration in the solution is 70 ppm. 534 g of Na propionate and 55 g of propionic acid are added, and 120 m3 of air are passed through the stirred contents of the reactor at 80C under a pressure of 0.25 MPa over a period of 6 hours. The mixture is then cooled to below 60C and stirred with 25 l of water under normal pressure for 15 minutes, and ^~
the aqueous and organic phase are separatecl from one another. This treatment is repeated twice with 10 l of water each time. It leads to the removal of a total of 83.5% of the rhodium originally contained in the organic phase. Thereafter, the organic phase, which still con-tains rhodium in a concentration of 13.5 ppm, is stirred under normal pressure at room temperature for 15 minutes with an amount of a trisodium triphenylphosphine-tri~ulfonate solution (1% strengt:h by weight in water) such that 32.2 mol of the phosphine are present per mol of rhodium. The amount of rhodium removed is increased by this extraction step to 88.8% in total, and the organic phase still contains the metal in a concentration of 10.2 ppm. ;

Example 2 61 kg of a distillation residue of ethylene hydroformyl-ation is diluted in a stirred tank with toluene in an amount such that the rhodium concentration in the solution is 70 ppm. 655 g of Na propionate and 67 g of propionic acid are added, and 120 m3 of air are passed through the stirred contents of the xeactor at 80C under a pressure of 0.25 MPa over a period of 6 hours. The . ::: ~ ' . :.
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2 ~ 9 mixture is then cooled to below 60C and stirred with 25 l of water under normal pressure for 15 minutes, and the aqueous and organic phase are separated from one another. ~his treatment is repeated three times with 10 l of water each time. It leads to the removal of a total of 8~.9% of the rhodium ori~inally contained in the organic phase~ Thereafter, the organic phase, which still con-tains rhodium in a concentration of 12.8 ppm, is stirred under normal pressure ~t room temperature for 15 minutes with an amount of a trisodium triphenylphosphinetri-sulfonate solution (1% strength by weight in water) such that 28.3 mol of the phosphine are present per mol of rhodium. The amount of rhodium removed is increased by this extraction step to 91.4% in total, the organic phase still containing the metal in a concentration of 7 4 ppm.
Example 3 150 kg of a distillation residue of ethylene hydroformylation are diluted in a stirred reaction with toluene in an amount such that the rhodium concentration in the solution is 70 ppm. 557 g of Na propionate and 58 g of propionic acid are added and 120 m3 of air are passed through the stirred reactor at 80C under a pressure of 0.25 MPa over a p~riod of 6 hours. The mixture is then cooled to below 60C and stirred wikh 25 l of water under normal pressure for 15 minutes, and the aqueous and organic phase are separated from one ~nother. This treatment is repeated three times with 10 1 of water each time. It leads to the r~moval of a total of 72.7% of the rhodium originally contained in the organic 3C phase. Thereafter, the organic phase, which still con-tains rhodium in a concentration of 19.7 ppm, is stirred under normal pressure at room temperature for 15 minutes with an amount of an ethylenediamine-tetraacetic acid solution (1% strength by weight in water) such that 10.7 mol of the diamine (corresponding to 21~4 mol of the amine nitrogen capable of complexing) are present per mol of rhodium. The amount of rhodium removed is increased by this extraction step to 31.7% in total, the organic phase still containing the metal in a concentration of 14.9 ppm.

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Exam~e 4 150 kg of a distillation residue of ethylene hydroformylation are diluted in a stirred reactor with toluene in an amount such that the rhodium concentration in the solution is 70 ppm. 557 g of Na propionate and 58 g of propionic acid are added and 120 m3 of air are passed through the stirred contents of the reactor at 80C under a pressure of 0.25 MPa over a period of 6 hours. The mixture is then coolad to below 60C and stirred under normal pressure at room temperature for 15 minutes with 25 1 of water under normal pressure for 15 minutes, and the aqueous and organic phase are separ-ated from one another. This treatment is repeated three times with 10 1 of water each time. It leads to th~
removal of a ~otal of 76.7% of the rhodium originally contained in the organic phase. Thereafter, the organic phase, which still contains rhodium in a concentration of 19.7 ppm, is stirred under normal pressure at room temperature for 15 minutes with an amount of nitrilo-triacetic acid solution (1% strength by weight in water) such that 10.9 mol of the phosphine are present per mol of rhodium. The amount of rhodium removed is increased by this extraction step to 83.3% in total, the organic phase still containing the metal in a concentration of 12.8 ppm.

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21~4~09 Example 5 70 kg of a distillation residue of methyl acry-late hydroformylation are diluted in a stirred reactor with toluene in an amount such that the rhodium concen-tration in the solution is 70 ppm. 737 g of Na propionateand 76 g of propionic acid are added and 100 m3 of air are passed through the stirred contents of the reactor at 100C under a pressure of 0.25 MPa over a period of 6 hours. The mixture is then cooled to below 60C and stirred with 32 l of water under normal pressure for 15 minutes, and the aqueous and organic phase are separated from one another. This treatment is repeated once with 10 l o~ water. It leads to the removal of a total of 81.4% of the rhodium originally contained in the organic phase. Thereafter, the organic phase, which still contains rhodium in a concentration of 15.5 ppm, is stirred under normal pressure at room temperature for 15 minutes with an amount of a trisodium triphenyl-phosphinetrisulfonate solution (1~ strength by weight in water) such that 14.5 mol of the phosphine are present per mol of rhodium. The amount of rhodium removed is increased by this extraction step to 84.5% in total, the organic phase still containing the metal in a concentration of 14.8 ppm.
Example 6 140 kg of a distillation residue of methyl acrylate hydroformylation are diluted in a stirred tank with toluene in an amount such that the rhodium concen-tration in the solution is 5.5 ppmO 701 g of Na propionate and 77 g o~ propionic acid are added and 100 m3 of air are passed through the stirred contents of the reactor at 100C under a pressure of 0.25 MPa over a period of 6 hours. The mixture is then cooled to below 60C and stirred with 10 l of water under normal pressure for 15 minutes, and the aqueous and organic phase are separated from one another. This treatment leads to the removal of 67.4~ of the rhodium originally contained in the organic phase. Thereafter, the organic phase, which still contains rhodium in a concentration of 4.3 ppm, is .. . .

- 14 - ~ ~ ~ 09 stirred under normal pressure at room temperature for lS minutes with an amount of a trisodium triphenyl-phosphinetri~ulfonate solution such that 45.2 mol of the phosphine are present per mol of rhodium~ The amount of rhodium removed is increased by this extraction step to 79~ in total, the organic phase still containing the metal in a concentration of 3.6 ppm.

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Claims

1.) A process for the recovery of rhodium which is contained in the distillation residue of products of the oxo synthesis, if appropriate bonded as a com-plex, by treatment of the residue with oxygen or an oxygen containing gas at 60 to 120°C, under normal pressure or under pressure in the presence of a C2-to C5-monocarboxylic acid and of the alkali metal salt of a C2- to C5-monocarboxylic acid and sub-sequent extraction of the rhodium present as a water-soluble compound, which comprises extracting the residue with the aqueous solution of a reagent which complexes with rhodium, if appropriate after it has already been extracted beforehand with water by itself.

2.) The process as claimed in claim 1, wherein the extraction with the solution of the complexing reagent is carried out at temperatures of 20 to 120°C and under pressures of up to 1.0 MPa, prefer-ably from 0.2 to 1.0 MPa.

3.) The process as claimed in claim 1, wherein the extraction is carried out with water at temperatures from 20 to 120°C and under pressures of up to 1.0 MPa, preferably from 0.2 to 1.0 MPa.

4.) The process as claimed in one or more of claims 1 to 3, wherein the extraction is carried out with water and/or with the solution of the complexing reagent in several stages.

5.) The process as claimed in one or more of claims 1, 3 and 4, wherein the complexing reagent is a com-pound which contains nitrogen or phosphorus atoms capable of forming coordination bonds with the rhodium.

6.) The process as claimed in claim 5, wherein the complexing reagent is iminodiacetic acid, nitrilo-triacetic acid, ethylenediaminetetraacetic acid, a triphenylphosphinetrisulfonate or a triphenyl-phosphinedisulfonate.

7.) The process as claimed in one or more of claims 1 and 3 to 6, wherein at least 5 mol of a monodentate or ? mol of an n-dentate, preferably 20 to 40 mol of a monodentate or ? to ? mol of an n-dentate, com-plexing agent are used per mol of rhodium.

8.) The process as claimed in one or more of claims 1 and 3 to 7, wherein the solution of the complexing agent contains 0.5 to 25% by weight of the complexing agent, based on the solution.