AU654597B2 - Process for working up waste waters comprising rhodium compounds, derivatives or organic phosphines and other impurities in dissolved form - Google Patents

Description

P/00/011 26s/51o Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 654597

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT o r n o Application Number: Lodged: Invention Title: PROCESS FOR WORKING UP WASTE WATERS COMPRISING RHODIUM COMPOUNDS, DERIVATIVES OF ORGANIC PHOSPHINES AND OTHER IMPURITIES IN DISSOLVED FORM e The following statement Is a full description of this Invention, including the best method of performing it known to :-US Process for working up waste waters comprising rhodium compounds, derivatives of organic phosphines and other impurities in dissolved form The invention relates to a process for working up waste waters which comprise rhodium compounds, water-soluble derivatives of organic phosphines, furthermore arylsulfonates 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 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 courses or other receiving waters or can be recycled into chemical reactions as process water.

Waste waters which comprise, inter alia, rhodium compounds and organic phosphorus 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 20 ligands, form a water-soluble catalyst system, the solubility of which is based on the presence of sulfonated or also carboxylated aryl radicals in the organic phosphines. According to the process described in DE 26 27 354 Bl, the system is employed successfully for 25 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 30 EP 0 176 398 A to add cyclic amines onto conjugated 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 hydroformylation reaction, for example, this reduction in quality is due to catalyst poisons, such as iron 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 products of the aldehydes. The reduction in the concentration of the sulfonated phosphine employed in excess by oxidation to phosphine oxides, 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 :process greatly depends on keeping the rhodium losses as low as possible.

A process for the recovery of rhodium from aqueous .i 20 solutions comprising rhodium complex compounds and, if appropriate, excess complexing ligands is known from DE 26 26 536 Al. It comprises adding as water-soluble salt of a carboxylic acid having 7 to 22 carbon atoms in Segcess, based on the rhodium, to the solution, subsequently treating the solution with an oxidizing agent at 50 to 200°C, and separating off the rhodium precipitated as a compound which is sparingly soluble in water. About to 95% of the rhodium present in the solution can be recovered in this manner. Oxygen, air or hydrogen per- 30 oxide is used as the oxidizing agent.

A further development of the procedure outlined, above is described in DE 37 44 214 Al. 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 atoms. In the first stage, the solutions are reacted with oxygen or an oxygen-containing 3 gas at 80 to 140"C, and in the second stage they are reacted with hypochlorite at 50 to 140"C. The process allows about 95% of the rhodium present in the solutions to be recovered.

DE 38 33 427 Al also relates 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 excess, based on the rhodium. The aqueous solutions are treated, simultaneously or in succession, with hydrogen peroxide or a substance which forms hydrogen peroxide and with oxygen or an oxygen-containing gas.

94 to 98% of the rhodium originally present is separated :"off from the aqueous solutions by this route.

SIn the processes described above, the rhodium is obtained as a compound which is sparingly soluble in water and which can be extracted with an organic solvent. Residual amounts of rhodium, as well as water-soluble organic phosphorus compounds, the main proportion of which are *e sulfonated arylphosphine oxides, sulfonated arylphosphine sulfides and su 'onated arylphosphinic acids, and furthermore arylsulfonic acids and carboxylic acids 25 sen y still remain in the water. The above list of i impurities contained in the waste water is given merely by way of example and is in no way complete. Other watersoluble substances may be formed, depending on the ctants and the reaction conditions.

The object 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 can be introduced into conventional purification plants 4 or receiving waters or, for partial or complete avoidance of waste waters, can be recycled into chemical reactions.

Ac'-rding to the invention, the object is achieved by. a process for working up waste waters which comprise rhodium compounds, water-soluble derivatives of organic phosphines, furthermore arylsulfonates and/or carboxylates 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 (-S0 3 and/or carboxylate radicals (-COO) 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.

The process according to the invention ensures that the rhodium compounds, organic phosphorus compounds, furthermore salts of aromatic sulfonic acids and/or salts of carboxylic 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 25 water for chemical reactions.

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 individual 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.

=n ,ai esusit\-:!Cti \the waste waters employed according to the invention x the nature and 5 concentration of the substances dissolved th4-1 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 ie\,between 1 and 50 ppm by weight, in particular 3 and 30 ppm by weight, water-soluble phosphorus compounds, which aee present in a concentration of 0.5 to 1.5% by weight, in particular 0.7 to 1.2% by weight of phosphorus, sulfonic acids, which e 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 -ae>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 substances, the rhodium dissolved in the waste water is 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 waters comprise in total 200 to 350 g/l, in particular 230 to 290 g/l, of compounds which result in the COD value. The 25 COD value, the abbreviation COD represents chemical oxygen demand, is a parameter for the degree of contamination 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 standardized procedure. The determination is described, for example, in Ullmanns Encyclopadie der Technischen Chemie (Ullmann's Encyclopedia of Industrial Chemistry), 4th edition (1981), volumfe 6, page 375 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 6 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 excess 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 waste water. If free base is still present in the waste waters, in addition to sulfonates and/or carboxylates, the amount of hydrogen ions required to neutralize it is to be added to the amount of hydrogen ions to be used according to the invention.

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

The hydrogen ions 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 polybasic 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 stages. It can be 25 assumed that up to an acid constant of about 0.7 x 10"2, complete dissociation 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, as a dibasic acid and with n acid constant in the second dissociation stage of 1.2 x 10-2, gives two mol of hydrogen ions, while the tribasic phosphoric acid, corresponding to the acid 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 7 operating step with the aid of an amine which is sparingly soluble or insoluble in water. The amount of amine required also depends on the amount of sulfonate radicals and/or c^.oxylate 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 advantages.

Instead of first adding acid to the waste waters and then extracting the impurities with an amine, 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 case, the molar substance amounts of acid and amine used are of course the same.

Since the acid is always used in excess, based on dissolved 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 extraction. 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 salts must also be sparingly soluble in water, but on the other hand readily soluble in organic solvents. Another 25 mode of action of the amine is based on the purely physical 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 in particular 13 to 36, carbon atoms. Examples of such compounds are tri-n-hexylamine, tri-n-octylamine, 8 tri-isooctylamine, di-2-ethylhexylamine, tri-isononylamine (in the form of the isomer mixture), isotridecylamine (in the form of the isomer mixture), di-isononyl- 2-phenylpropylamine, isononyl-di-2-phenylpropylamine, tri-isotridecylamine (in the form of the isomer mixture), N,N-dimethyl-hexadecylamine and N,N-dimethyl-octadecylamine. Isotridecylamine, tri-n-octylamine and tri-isooctylamine have proved to be particularly suitable extraction agents.

The amines can in principle be employed in undiluted form for the extraction. However, it is more advantageous to use them as a solution in an organic solvent which is 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 solutions accordingly usually contain 10 to 50, preferably 15 to 35% by weight of amine. For selection of the solvent, its 20 physical properties are chiefly decisive. A low solubility 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 S. waters. Suitable solvents are kerosine-like fractions, Saromatic fractions, C 4

-C

2 ,-alcohols and C 8

-C

20 -ethers.

Kerosine-like fractions, i.e. hydrocarbons having boiling points of between 175 and 325 0 C, and toluene are pre- 30 ferred. The amine salts are always employed in the form of solutions, 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 conditions 9 which deviate from these, for example increased 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 solution of an inorganic base. Suitable compounds are the hydroxides of the alkali metals and alkaline earth metals, in particular sodium hydroxide, and in addition also the alkali metal carbonates. The base is employed as a 5 to 30% strength by weight solution and is preferably used in the stoichiometric 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 successfully used for working up the amine phase is its treat- 20 ment with steam. For this purpose, steam of at least 1.8 MPa is passed into the amine solution. Rhodium and the impurities pass into the aqueous phase here, which is separated from the amine phase, for example, by decanting.

25 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 be purified from time to time, for example by distillation, as can the solvent.

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

10 The process according to the invention is carried out discontinuously or, preferably, continuously, the apparatuses 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 describe 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, sulfuric acid (29.9% by weight, based on ago**: 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 succession 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 20 with aqueous NaOH solution for 30 minutes. The aqueous phase obtained after the phase separation comprises virtually all the impurities of the waste water in S.concentrated form, and the amine phase can be used again S. as the extraction agent. The reaction conditions and the 25 results of the working up of the waste water are summarized in Table 2'.

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

S S

S

S Table 1 T-aste ,water

COD

subs tances 1 (g/1) Rh P Phosphorusfree (ppm by (ppm by Carboxylate Sulfonate weight) weight) radicals radicals by by weight) weight) P-sulfonates 2 (g equivalents/kg of waste water) A 238 5.26 7100 2.7 1.46 0.60 B 269 5.33 8200 3.0 1.72 0.80 C 267 4.783 7500 2.9 1.51 0.71 D 285 5,37 8900 2.5 1.94 0.85 1)Contents measured in the form of the COD value Sulfonated arylphosphines, -phosphine o:-,t:ides, -phosphine sulfides ~0* 0 0 0 0 *0 a. S Table 2 Example Waste HSQ0 (Mol) water sulfonate and carboxylate radicals (mol) Amine (mol)_ sulfonate, and carboxylate radicals 'mol) Purified waste water (decrease in the content in based on the untreated waste water) Rh P COD value 1.58 0.71 0.87 0.70 0.70 0.52 3.28 1.19 1.30 1.41 2.38 0.74 98.2 98.5 97.8 93.1 98.1 63.9 99.0 98.0 98.8 99.2 97.8 82.2 99.4 98.8 99.1 99.4 98.2 86.5 (comparison) 7 (Cornparison) 0.50 1.20 65.2 75A8 82.9 I I 13 Examples 8 to Examples 8 to 10 were carried out in the same manner as Examples 1 to 7, but using salts of tri-isooctylamine (Example 8: sulfate; Example 9: hydrogen sulfate; Example 10: dihydrogen phosphate) instead of acid and amine. They were used as a solution in toluene (about 20% by weight of salt, based on the solution).

9 9 9* 9*

C

C

Table 3 Example Waste Acid (mol) water sulfonate and carboxylate radicals (mol) Amine (mol) sulfonate and carboxylate radicals (mol) Purified waste water (decrease in the contents in based on the untreated waste water) Rh P COD value 8 D 0.60 1.20 90.7 96.0 98.3 9 D 1.20 1.20 93.4 96.0 98.2 D 1.20 1.20 95.0 98.0 97.8

Claims (2)

1. 3.5 mol of hydrogen ions are present in the waste water per mol of dissolved sulfonate radicals and/or carboxylate radicals. The process as claimed in claim 1 or 2, wherein sulfuric acid or phosphoric acid is employed as the inorganic acid. o 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. The process as claimed in claim 4, wherein tri-iso- octylamine is employed as the amine. 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. 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. The process as claimed in claim 7, wherein the amine or the amine salt is dissolved in a kerosine-like fraction or in toluene. 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.
2. 10.) The process as claimed in claim 1, wherein the organic phase is further processed by treatment with 15 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. *e *e DATED this 3rd day of December 1992. 9 HOECHST AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS "THE ATRIUM" 290 BURWOOD ROAD HAWTHORN. VIC. 3122. I p Frankfurt, 02.12.1991 PAT/rcht-sei HOE 91/Y011 Hoechst Aktiengesellschaft, Frankfurt am Main 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 10 particular embodiment, the inorganic acid is used in the form of a salt of the amine used as the extraction agent. 9*