CA2084022A1

CA2084022A1 - Process for working up waste waters comprising rhodium compounds, derivatives of organic phosphines and other impurities in dissolved form

Info

Publication number: CA2084022A1
Application number: CA002084022A
Authority: CA
Inventors: Gerhard Diekhaus; Harald Kappesser
Original assignee: Individual
Current assignee: Hoechst AG
Priority date: 1991-12-05
Filing date: 1992-11-27
Publication date: 1993-06-06
Also published as: JPH05237482A; KR930012595A; AU2992192A; KR960004302B1; DE4140062A1; TW219352B; ZA929234B; CN1073413A; BR9204629A; EP0545283A1; MX9206926A; AU654597B2

Abstract

Frankfurt, 02.12.1991 PAT/rcht-sei HOE 91/Y0ll Hoechst Aktiengesellschaft, Frankfurt am Main 80 Abstract of the disclosure:

For working up waste waters which comprise rhodium compounds, water-soluble derivatives of organic phos-phines and, if appropriate, other impurities, an inorganic acid is first added and the mixture is then extracted with a water-insoluble amine. According to a particular embodiment, the inorganic acid is used in the form of a salt of the amine used as the extraction agent.

Description

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Process for workiny up waste waters comprising rhodium compounds, derivatives of orqanic phos~hines and other impurities in dis~olved form The invention relates to a proces~ for working up wa~te waters which comprise rhodium compounds, water-soluble derivatives of organic phosphines, furthermore aryl-sulfonates and/or carboxylates and, if appropriate, other organic impurities in dissolved form. Its aim is to separate off the rhodium almost completely and to remove - lQ the dissolved phosphorus compounds and the other organic impurities to the extent that, where possible, the waste water can be introduced into conventional purification plants, in to river cGurses or other receiving waters or can b~ recycled into chemical reactions as proce~s water.

Wa~te waters which comprise, inter alia, rhodium com-pounds and organic pho6phorus compounds in dissolved form occur in various processes carried out industrially.
Thus, rhodium complex compounds which contain organic phosphines as ligands, together with excess complexing ligands, form a water-soluble catalyst system, the solubility of which is based on the presence of sulfon-ated or also carboxylated aryl radicals in the organic phosphines. According to the process described in DE 26 27 354 B1, the system is employed successfully for hydroformylation of olefins. The active catalyst system is formed under the reaction conditions from rhodium or a rhodium compound, the triarylphosphines used in the form of the alkali metal, ammonium or alkaline earth metal sulfonates, and synthesis gas. It is known from 3Q EP 0 176 398 A to add cyclic amines onto con~ugated dienes in the presence of the catalyst system mentioned, and furthermore the system is employed successfully for hydrogenation of organic compounds.

During longer use, the activity and selectivity of such catalyst systems decrease. In the case of the hydro-formylation reaction, for example, this reduction in quality is due to catalyst poisons, such as iron 2~3 ~2~

carbonyl, which can be formed by the action of synthesis gas on the transportation lines and the reactor material, and to higher-boiling condensation product of the aldehydes. The reduction in the concentration of the sulfonatPd phosphine employed in excess by oxidation to phosphine oxide , by degradation to aromatic sulfonic acids or by reduction of sulfo groups, or reaction with sulfur-containing impurities of the synthesis gas to give phosphine sulfides leads to a decrease in the activity of the catalysts. It is therefore necessary for the spent catalyst solution to be replaced by fresh catalyst solution from time to time, and for the rhodium to be separated off and recovered from the spent solution. The noble metal should be separated off here as completely as possible and in a form which allows its reuse as a catalyst component, since the profitability of the proces4 greatly depends on keeping the rhodium losses as low as possible.

A process for the recovery of rhodium from aqueous solutions comprising rhodium complex compounds and, if appropriate, excess complexing ligands i8 known from DE 36 26 536 Al. It comprises adding as water-soluble salt of a carboxylic acid having 7 to 22 carbon atoms in excess, based on the rhodium, to the solution, subse~
quently treating the solution with an oxidizing agent at 50 to 200C, and separating off the rhodium precipitated as a compound which i8 sparingly soluble in water. About 90 to 95~ of the rhodium present in the solution can be recovered in this manner. Oxygen, air or hydrogen per-oxide i3 used as the oxidizing agent.

A further development of the procedure outlined above isdescribed in DE 37 44 214 A1. The oxidative treatment of the solutions is carried out in two stages, in each case in the presence of a water-soluble salt of a carboxylic acid having 7 to 22 carbon atom~. In the first stage, the solutions are reacted with oxygen or an oxygen-containing O f~

ga8 at 80 to 140C, and in the second stage they are reacted with hypochlorite at 50 to 140C. The proce~s allows about 95~ of the rhodium present in the sol-ltions to be recovered.

DE 38 33 427 A1 also relate~ to a process for the recovery of rhodium from aqueous solutions comprising rhodium complex compounds and, if appropriate, complexing ligands by a one-stage or two-stage treatment of the solutions with oxidizing agents in the presence of a water-soluble salt of a carboxylic acid having 7 to 22 carbon atoms in exce~s, based on the rhodium. The aqueou~
solutions are treatedl simultaneously or in succession, with hydrogen peroxide or a substance which forms hydro-gen peroxide and with oxygen or an oxygen-containing gas.
g4 to 98~ of the rhodium originally present is separated off from the aqueous solutions by this route.

In the processe~ de~cribed above, the rhodium is obtained a~ a compound which i~ sparingly soluble in water and which can be extracted with an organic solvent. Residual amount~ of rhodium, a~ well as water-soluble organic phosphorus compounds, the main proportion of which are sulfonated arylphosphine oxides, sulfonated arylphosphine sulfide~ and sulfonated arylphosphinic acids, and furthermora aryl~ulfonic acids and carboxylic acids essentially still remain in the water. The above list of impurities contained in the waste water is given merely by way of example and i8 in no way complete. Other water-soluble substances may he formed, depending on the reactants and the reaction conditions.

The ob~ect of the invention is to recover further rhodium from the aqueous phase which remains after the rhodium has been separated off, and at the same time to reduce the content of phosphorus compounds and other organic impurities to the extent that, where possible, the water 3S can be introduced into conventional purification plants 20~J~f~r or receiving waters or, for partial or complete avoidance of wa~te waters, can be recycled into chemical reactions.

According to the invention, the ob~ect i8 achieved by a procef~s for working up waste waters which comprise rhodium compounds, water-soluble derivatives of organic phosphine~, furthermore arylsulfonates and/or carboxy-lates and, if appropriate, other organic impurities. It comprises adding to the waste waters an inorganic acid in an amount such that at least 1.1 mol of hydrogen ions are present per mol of sulfonate radicals (-SO3-) and/or carboxylate radicals (-C00~) present in solution, subse-quently extracting the mixture with at least one mol of an amine which is sparingly soluble or insoluble in water per mol of dissolved sulfonate radicals and~or carboxy-late radicals, separating the organic and aqueous phasefrom one another and further processing the organic phase.

The process according to the invention ensures that the rhodium compounds, organic phosphorus compounds, further-more salts of aromatic sulfonic acids and~or salts ofcarboxylic acids and other organic impurities dissolved in the waste water, which overall result in the COD
value, are largely removed. The purified waste waters do not pollute the environment and can be used as process water for chemical reactionY.

The process according to the invention starts from waste waters which are obtained when rhodium and water-soluble organic phosphine derivatives are separated off from aqueous solutions used as a catalyst phase. It is of no importance which separation process is used in an indivi-dual case. The processes mentioned in the context of outlining the prior art are given merely as examples, and other separation and working up processes are possible.
An e~sential featura of the waste waters employed according to the invention is the nature and 2 ~ 2 r ~

concentration of the ~ubstances dissolved in them.
Because of their economic value or their influence on the environment, substances which are important are, in particular, rhodium, the concentration of which in typical waste waters is between 1 and 50 ppm by weight, in particular 3 and 30 ppm by weight, water-soluble phosphorus compounds, which are present in a concentra-tion of O.S to 1.5% by weight, in particular 0.7 to 1.2~
by weight of phosphorus, ~ulfonic acids, which are present in a concentration of 1.0 to 2.5% by weight, in particular 1.4 to 2.0% by weight, and carboxylic acids, which are present in a concentration of 2.0 to 4.0~ by weight, in particular 2.5 to 3.5% by weight. In terms of the ~ubstances, the rhodium dissolved in the waste water i~ in the form of rhodium salts; the phosphorus compounds are mainly sulfonated or carboxylated arylphosphine oxides and arylphosphine sulfides; the sulfonic acids are chiefly obtained by cleavage of sulfonated arylphosphines and are accordingly arylsulfonates; and the content of carboxylic acids is essentially based on the addition of carboxylates during the prior recovery of rhodium.
Including the abovementioned substances, the waste water~
comprise in total 200 to 350 g/l, in particular 230 to 290 g/l, of compounds which result in the COD value. The COD value, the abbreviation COD represents chemical oxygen demand, i~ a parameter for the degree of con-tamination of waste waters. It is the amount of potassium dichromate, expressed as oxygen equivalents, consumed by the oxidizing contents of one liter of water. The COD
value is determined by a standsrdized procedure~ The determination i~ described, for example, in Ullmanns Encyclopadie der Technischen Chemie (Ullmann's Encyclo-pedia of Industrial Chemistry), 4th edition (1981), volume 6, page 376 et seq.

The waste waters to be worked up by the novel process are first acidified. For this purpose, according to the invention, an inorganic acid is added in an amount such 2 ~ ,C,,~ ,~

that at least 1.1 mol, in particular 1.2 to 3.5 mol, of hydrogen ions are present per mol of sulfonate radicals and/or carboxylate radicals present in the solution. A
higher exces of acid does no harm, but it is not necessary, for example, for economic reasons, but in particular also to avoid unnecessary pollution of the wa~te water. If free ba3e is still present in the waste waters, in addition to sulfonates and/or carboxylates, - the amount of hydrogen ions required to neutralize it i~
to be added to the amount of hydrogen ions to be used according to the invention.

The ~ulfonate radicals can be determined, for example, by high pre~sure liquid chromatography (HPLC). Carboxylates can be determined, for example, potentiometrically with mineral acids, or, after conversion into the free acid~
and extraction, by gas chromatography.

The hydrogen ion3 are added to the waste waters in the form of strong inorganic acids, such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.
Sulfuric acid and phosphoric acid are particularly suitable. If polyba~ic acids, such as sulfuric acid or phosphoric acid, are used, the amount of hydrogen ions introduced into the waste water depends on the acid constant of the individual dissociation stage~. It can be as3u~ed that up to an acid constant of about 0.7 x 10-2, complete dis~ociation of the hydrogen ions takes place, that is to say one mol of acid produces one mol of hydrogen ions. Accordingly, one mol of sulfuric acid, a6 a dibasic acid and with an acid constant in the second dissociatio~ stage of 1.2 x 10-2, gives two mol of hydro-gen ions, while the tribasic phosphoric acid, correspond-ing to the a~ d constant in the first dissociation stage of 0.75 x 10-2, produces only one mol of hydrogen ions.

After the acidification, rhodium and the impurities contained in the waste waters are extracted in a second 2 ~

operating step with the aid of an amine which i8 sparingly ~oluble or insoluble in water. The amount of amine required also depends on the amount of sulfonate radicals and/or carboxylate radicals contained in the waste water. At least one mol of amine is added to the waste water per mol of sulfonate radicals and/or carboxylate radicals present in the solution. It is possible to use excess amine, but this results in no advantageR .

Instead of first adding acid to the waste waters and then extracting the impurities with an amina, in a particular embodiment of the process according to the invention the amount of acid and amine required can be added in the form of an amine salt. In this ca3e, the molar substance amounts of acid and amine used are of course the same.
Since the acid is always used in excess, based on dis-solved sulfonate and/or carboxylate, an amine excess is then also always present.

The amine used for the extraction is advantageously liquid under the conditions of the extractionr Its action is based, inter alia, on the fact that it reacts with the acid content of the waste water to form salts. The amine salt~ must al80 be ~paringly soluble in water, but on the other hand readily soluble in organic solvent~. Another mode of action of the amine is based on the purely phy~ical solution of impurities contained in the waste waters.

Possible amines which form, with acids, salts which are sparingly soluble in water but lipophilic are acyclic or cyclic aliphatic, aromatic, araliphatic and heterocyclic primary, secondary or tertiary, preferably secondary or tertiary, amines. Preferred amines are acyclic, branched or unbranched aliphatic amines having a total of 10 to 60, in particular 13 to 36, carbon atoms. Examples of such compounds are tri-n-hexylamine, tri-n-octylamine, ~0~'3~

tri-i~ooctylamine, di-2-ethylhexylamine, tri-i~ononyl-amine (in the form of the isomer mixture), isotridecyl-amine (in the form of the i30mer mixture), di-isononyl-2-phenylpropylamine, isononyl-di-2-phenylpropylamine, S tri-isotridecylamine (in the form of the i~omer mixture), N,N-dimethyl-hexadecylamine and N,N-dimethyl-octadecyl-amine. Isotridecylamine, tri-n-octylamine and tri-iso-octylamine have proved to be particularly suitable extraction agents.

The amines can in principle be employed in undiluted form for the extraction. However, it i8 more advantageous to use them as a ~olution in an organic solvent which i8 immiscible or only slightly miscible with water. The concentration of the amine in the solution can extend over a wide range. It is essentially limited by the solubility of the amine salts in the solvent and by the viscosity of the salt solution obtained. The solution~
accordingly usually contain 10 to 50, preferably 15 to 35% by weight of amine. For selection of the solvent, its physical properties are chiefly decisive. A low solubil-ity in water, low evaporation and little or no tendency to form emulsions are desirable. The solvent moreover should be inert, non-toxic and inexpensive, display good hydrodynamic properties and also have a good extraction capacity for other impurities dissolved in the waste water~. Suitable solvents are kerosine-like fractions, aromatic fractions, C4-C20-alcohols and Ca-C20-ether~.
Rerosine-like f-ractions, i.e. hydrocarbons having boiling points of between 175 and 325C, and toluene are pre-ferred. The amine salts are always employed in the formof solution~, the same solvents as for the amines being used. The concentration of the salts in the solution is likewise usually 10 to 50, preferably 15 to 35% by weight.

The extraction is as a rule carried out at normal temperature and under normal pressure, but condition~

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_ 9 _ which deviate from these, for example increa~ed pressure, are not excluded.

Further processing of the organic phase in a third operating step for recovery of the rhodium, conversion of the impurities into a concentrated aqueous solution and regeneration of the amine can be carried out in various ways. It has thus proved appropriate to reextract the amine phase with the aqueous ~olution of an inorganic base. Suitable compounds are the hydroxides of the alkali metals and alkaline earth metals, in particular ~odium hydroxide, and in addition also the alkali metal car-bonates. The base is employed as a 5 to 30~ strength by weight solution and is preferably used in the stoichio-metric amount, based on the amine, and if appropriate in an excess of up to 20%. A larger excess of base adds another undesirable solution constituent to the aqueous solution comprising the impurities in concentrated form, and should therefore be avoided. Another process success-fully used for working up the amine phase i8 its treat-ment with steam. For this purpose, steam of at least1.8 MPa is passed into the amine solution. Rhodium and the impurities pas~ into the aqueous phase here, which i8 separ~ted from the amine phase, for example, by decanting.

The amine recovered after treatment with a base or with steam can be employed again, together with the solvent employed if appropriate, for extractive treatment of waste waters by the process according to the invention.
It can b0 purified from time to time, for example by di~tillation, as can the solvent.

The rhodium is separated off from the aqueous ~olution by known processes, for example as a sparingly soluble carboxylic acid ~alt, and the aqueou~ solution comprising the impurities in concentrated form is disposed of.

20~40s."j The proce~s according to the in~ention iB carried out discontinuou~ly or, pre~erably, continuously, the appar-atuses customary for extractive substance separations, such as extraction columns and mixer-settlers, being used. It can be carried out in one or more stages.

The following examples de~cribe the invention, but do not limit it to these specific embodiments.

Examples 1 to 7 Waste waters A, B, C and D, the contents of which are summarized in Table 1, are employed in the following examples.

The waste water, 3ulfuric acid (29.9% by weight, based on the aqueous solution) and a solution of tri-isooctylamine in toluene ~about 20% by weight, based on the solution), as the extraction agent, are introduced in succesæion into a stirred reactor. The mixture is stirred at room temperature for 30 minutes, and the aqueous phase, i.e.
the purified waste water, is then separated from the amine phase. The amine phase is reextracted by stirring with aqueous NaOH solution for 30 minutes. The aqueous phase obtained after the phase separation comprise~
virtually all the impurities of the waste water in concentrated form, and the amine phase can be used again as ths extraction agent. The reaction conditions and the results of the working up of the waste water are summarized in Table 2.

Examples 1 to 5 de~cribe the novel process, and Examples 6 and 7 were carried out under conditions which do not correspond to those of the invention.

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Claims

1.) A process for working up a waste water comprising rhodium compounds, water-soluble derivatives of organic phosphines, furthermore arylsulfonates and/or carboxylates and, if appropriate, other organic impurities in dissolved form, which com-prises adding to the waste water an inorganic acid in an amount such that at least 1.1 mol of hydrogen ions are present per mol of sulfonate radicals (-S03-) and/or carboxylate radicals (-C00-) present in solution, subsequently extracting the mixture with at least one mol of an amine which is sparingly soluble or insoluble in water per mol of dissolved sulfonate radicals and/or carboxylate radicals, separating the organic and aqueous phase from one another and further processing the organic phase.

2.) The process as claimed in claim 1, wherein 1.2 to

3.5 mol of hydrogen ions are present in the waste water per mol of dissolved sulfonate radicals and/or carboxylate radicals.

3.) The process as claimed in claim 1 or 2, wherein sulfuric acid or phosphoric acid is employed as the inorganic acid.

4.) The process as claimed in one or more of claims 1 to 3, wherein the extraction is carried out with an acyclic branched or unbranched, secondary or ter-tiary aliphatic amine having a total of 10 to 60, in particular 13 to 36, carbon atoms.

5.) The process as claimed in claim 4, wherein tri-iso-octylamine is employed as the amine.

6.) The process as claimed in claim 1, wherein the inor-ganic acid and amine are added to the waste water in _ 16 -the form of an amine salt.

7.) The process as claimed in one or more of claims 1 and 4 to 6, wherein the amine or the amine salt are dissolved in an organic solvent.

8.) The process as claimed in claim 7, wherein the amine or the amine salt is dissolved in a kerosine-like fraction or in toluene.

9.) The process as claimed in one or more of claims 1 and 4 to 8, wherein the concentration of the amine or of the amine salt in the solvent is 10 to 50, in particular 15 to 35% by weight, based on the solution.

10.) The process as claimed in claim 1, wherein the organic phase is further processed by treatment with an alkali metal hydroxide or alkaline earth metal hydroxide or an alkali metal carbonate or by treat-ment with steam of at least 1.8 MPa.