DE102023106229A1 - Recovery of palladium from aqueous-organic solution - Google Patents

Abstract

The invention relates to a process for isolating and recovering palladium from a waste solution that originates from a catalyst process in an industrial process. The palladium is present in an aqueous-organic solution. Accompanying substances include catalyst residues and other potentially disruptive, partially complexing components.

Description

The invention relates to a method for isolating and recovering palladium from a waste solution that originates from a catalyst process in an industrial process. The palladium is present in an aqueous-organic solution. Accompanying substances include catalyst residues and other potentially disruptive, partially complexing components.

background

Due to the great importance of palladium in catalytic processes in homogeneous and heterogeneous phases, as well as its price, which sometimes fluctuates greatly at a high level, a large number of processes for the recovery of palladium are known and some are patented or have been patented.

In some cases, in addition to the recovery of the palladium, the recovery of the ligands or the palladium complex is in the foreground.

This is how it is EP000001834695A1 a process for recovering phosphine ligands from transition metal complexes used in homogeneously catalyzed reactions is described. The phosphine-containing ligands are obtained by contacting the reaction mixture remaining after completion of a homogeneously catalyzed reaction with an oxidizing agent, then extracting the reaction mixture with an organic solvent that is insoluble in the reaction mixture to separate the resulting transition oxide, and then isolating the oxidized phosphine ligand from the organic solvent separated from the reaction mixture.

The focus is on the recovery of the phosphine ligands, but oxidizing agents are used whose oxidation products must then be reduced again.

In US000007108839B2 describes the recovery of palladium bound to silica gel. The claimed process relates to heterogeneous catalysis or to palladium from homogeneous catalysis, which, however, must first be bound to silica gel.

Furthermore, processes are known in which activated carbon, which has previously been loaded with EDTA (ethylenediaminetetraacetic acid), binds palladium.

Some processes are described in which palladium is extracted using organic oximes.

Extractions with ion exchangers are described, but not all Pd is charged and too many impurities interfere, so that a yield of 100% is never achieved, but is often far below.

What these processes often have in common is that the palladium complex has to be destroyed through oxidation or intense heating. This is very complex in technical and energetic terms.

In US000004522760A A process for the extraction of palladium from homogeneous catalysis is described. The palladium or palladium complex is extracted using an alcoholic solution and an apolar, aliphatic, organic solvent.

The application is limited to cases of alcoholic palladium catalyst solutions that can be purified and separated using the solvents specified.

In US000004340570A discloses an extraction process for recovering rhodium, which is carried out with the aid of EDTA as the final extraction step. The process is complex and produces a number of different extracts, each of which contains disruptive secondary components that would hinder the actual extraction step.

In US000004013584A A process for the recovery of a spent palladium complex is presented, whereby the palladium is first released by oxidation with chlorine and recovered by various extraction processes and final evaporation.

In WO002022144338A1 A process is claimed in which palladium is bound under basic conditions by pH adjustment and binding via various bleaching earths, clays, diathomas earths (etc.).

WO002017198846A1 proposes a process for the aqueous extraction of palladium from organic solution using surfactants or dentrimers, i.e. essentially surface-active substances.

In WO002004106563A1 A process for the recovery of palladium from a heterogeneous catalytic process is presented, whereby the palladium is bound to activated carbon.

DE000001935169A claims a process for isolating dissolved palladium in aqueous solution by forming a precipitate in acidic conditions using thiocyanates.

In RU000002654818C1 An extraction process is presented that allows the extraction of palladium using organic oximes.

US000004319923A presents a process that precipitates palladium with potassium borohydride in a basic medium and can then be recovered by filtration. The process represents a series of reduction processes in which the charged palladium species are converted to Pd(0) and then precipitated or bound to activated carbon.

None of the methods presented is able to bind palladium in a simple manner with high yields from an aqueous organic solution, whereby the organic portion is freely miscible with both water and water-immiscible organic solvents and can thus act as an (undesirable) solubilizer.

The presented processes suffer from the fact that several complex process steps using expensive chemicals are always necessary, the yield is insufficient or an application to organic-aqueous systems containing an organic solvent such as THF or solvents with comparable mixing properties is not applicable.

Accompanying components such as catalyst residues, catalyst ligands, products, by-products, reactants, and/or auxiliary materials from the catalyst process or from the reprocessing of the respective process often interfere with recovery.

Due to the presence of THF as a solvent, which is freely miscible with water as well as with strongly non-polar organic solvents such as pentane, hexane, heptane, etc., a simple separation of interfering secondary components is not easily possible.

The object of the present invention was therefore to provide a process for recovering palladium from aqueous-organic solutions in high yields even in the presence of interfering accompanying substances.

The object is achieved by a method according to claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

1. a. Bereitstellen einer Palladium-haltigen wässrig-organischen Lösung,
2. b. Reduzierung des pH-Werts der Lösung aus a. bis zum Ausfällen von Palladium,
3. c. Isolieren des aus Schritt b. ausgefällten Palladiums durch Extraktion oder Filtration und Isolieren des nach der Extraktion oder Filtration verbleibenden Palladium-haltigen Filtrats,
4. d. Überführen des nach Schritt c. verbleibenden Palladium-haltigen Filtrats auf ein Palladium-absorbierendes Harz zur Absorption des restlichen Palladiums an dem Palladium-absorbierendem Harz,
5. e. Rückgewinnung des Palladiums von dem Palladium-absorbierendem Harz.

The present invention therefore provides a process for the recovery of palladium from aqueous-organic solution, comprising the steps

1. a. Providing a palladium-containing aqueous-organic solution,
2. b. Reducing the pH of the solution from a. until palladium precipitates,
3. c. isolating the palladium precipitated from step b. by extraction or filtration and isolating the palladium-containing filtrate remaining after extraction or filtration,
4. d. Transferring the palladium-containing filtrate remaining after step c. to a palladium-absorbing resin for absorption of the remaining palladium on the palladium-absorbing resin,
5. e. Recovery of palladium from the palladium absorbing resin.

The process described herein allows a simple and cost-efficient recovery of palladium from catalysis processes with palladium recovery yields of > 80%, preferably > 90% and especially > 95%.

The pH value of the aqueous-organic palladium-containing solution is reduced in the process according to the invention to a value at which part of the palladium precipitates as palladium salt or palladium complex (Pd acetate, phosphine, chloro or other complexes or salts). The precipitate is then isolated by filtration or extraction with an organic solvent and can be reused directly for recycling the originally active catalyst. Alternatively, the palladium can also be isolated from the precipitate by combustion.

After the pH has been adjusted again, the palladium-containing filtrate is brought into contact with a palladium-absorbing resin, which binds the remaining palladium. This process step can consist of a closed system, such as a stirred reactor, or (under dynamic conditions) in a fixed absorber bed through which the palladium-containing filtrate is pumped. For recovery, the resin can then be burned or eluted and regenerated using suitable methods. In the latter case, a concentrated palladium-containing solution is obtained.

Resins such as cation exchangers and selective ion exchangers are particularly suitable. However, due to the need to adjust the pH to 1.5-3, some absorbents that work well under neutral or basic conditions are not suitable in this case.

Preferably, in the process according to the invention, the pH of the palladium-containing aqueous-organic solution in step b. is adjusted to 1.5 - 3.

The palladium-absorbing resin preferably comprises a cation exchanger or selective ion exchanger. It is further preferred that the cation exchanger or selective ion exchanger comprises a polyamine, more preferably polyvinylamine.

It is further preferred that the palladium precipitated in step c. is isolated by combustion or can be recycled and used directly for catalytic processes. Combustion usually takes place at temperatures > 250 to > 400°C.

The palladium is also recovered from the palladium-absorbing resin by combustion. This means that the palladium that was still in the residue (effluent) after extraction or precipitation is bound to the resin, which is then preferably subjected to combustion. At a temperature of > 250 to > 400°C, the organic resin burns and the palladium can be recovered as oxide.

The palladium-containing aqueous-organic solution is preferably an aqueous THF solution. The aqueous THF solution can also comprise other organic solvents, for example linear or cyclic alkyl compounds, toluene, benzene, DMF, DMA, or other organic solvents and mixtures of the above.

The aqueous-organic solution can contain other ingredients, such as salts such as carbonates, halides, phosphates, sulfates, borates, etc. Furthermore, the aqueous-organic solution can contain complexing or non-complexing organic components from the catalyst process itself or other sources. These include in particular homo- or heterocyclic compounds, amino acids or their degradation products. Fluorine or fluorine compounds can also be included.

For the purposes of the invention, it is preferred if the palladium-absorbing resin is pH-stable in the range of pH 1.5-3. Many resins are therefore ruled out as alternatives.

As above for the recovery of palladium from the precipitation step, the recovery of palladium from step c. and step e. is carried out by combustion at a temperature > 400°C. This efficiently removes organic components.

It has further been found that advantageously in step d. the pH is adjusted to a pH of 2-3 before the remaining palladium-containing filtrate is transferred to a palladium-absorbing resin for absorption of the remaining palladium on the palladium-absorbing resin. This improves the absorption on the palladium-absorbing resin.

The invention will now be explained in more detail using exemplary embodiments, although these are not to be viewed as limiting the scope of protection of the invention, but merely serve to improve understanding.

Example 1:

The pH value of an aqueous-organic solution containing palladium is adjusted to a pH value between 1.75 and 2.5 using 35% HCl while stirring vigorously. The precipitate is filtered off. The proportion of palladium in the precipitate to the total amount of dissolved palladium is 68%.

Example 2:

The pH of the filtrate (40 ml) from Example 1 is adjusted to a pH between 2 and 3 using 5 M sodium hydroxide solution. The palladium-containing aqueous-organic solution is then mixed with 2 g of T425, a palladium-complexing absorber resin, and shaken for 30 minutes. The pH of the solution is kept at a value between 2-3 by adding further 35% HCl or 5 M NaOH if necessary.

The absorber resin is filtered off. The bound amount of palladium from the filtrate is >90%.

Example 3:

The palladium is recovered from the palladium-containing filtration residue from Example 1 and the palladium-containing absorber resin from Example 2 by combustion at temperatures >400°C.

Example 4:

The pH value of the filtrate from Example 1 is adjusted to a value between 2 and 3 and then pumped through a cartridge containing a palladium-complexing absorber resin until it breaks through. The effluent is collected and analyzed for palladium.

The palladium-containing absorber resin is then burned to isolate the palladium.

The invention represents a simple and effective process for isolating palladium from an aqueous-organic solution, whereby only simple and inexpensive chemicals and absorbers are used using established process steps. Both the palladium and the catalytically active complex can be isolated in this way. None of the known processes can isolate palladium from aqueous-organic solutions according to the known state of the art, in which the organic component is freely miscible with both water and non-polar organic solvents.

The method presented here is a simple process for recovering palladium from an aqueous-organic solution in the presence of a large number of interfering components. By selecting the conditions appropriate to the palladium-containing solution, palladium can be recovered in high yield using simple chemicals and low energy consumption. In the process presented, interfering components are either precipitated or inactivated by selecting the pH value, whereby the bond to absorber resins is not or not significantly disturbed.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP 000001834695 A1 [0004]
• US 000007108839 B2 [0006]
• US 000004522760 A [0011]
• US 000004340570 A [0013]
• US 000004013584 A [0014]
• WO 002022144338 A1 [0015]
• WO 002017198846 A1 [0016]
• WO 002004106563 A1 [0017]
• DE 000001935169 A [0018]
• RU 000002654818 C1 [0019]
• US 000004319923 A [0020]

Claims (10)

Process for recovering palladium from an aqueous-organic solution comprising the steps a. providing a palladium-containing aqueous-organic solution, b. reducing the pH of the solution from a. until palladium precipitates, c. isolating the palladium precipitated from step b. by extraction or filtration and isolating the palladium-containing filtrate remaining after the extraction or filtration, d. transferring the palladium-containing filtrate remaining after step c. to a palladium-absorbing resin for absorption of the remaining palladium on the palladium-absorbing resin, e. recovering the palladium from the palladium-absorbing resin. Procedure according to Claim 1 , wherein the pH of the palladium-containing aqueous-organic solution in step b. is adjusted to 1.5 -3. Procedure according to Claim 1 or 2 wherein the palladium-absorbing resin comprises a cation exchanger or selective ion exchanger. Process according to one of the preceding claims, wherein the palladium precipitated in step c. is isolated by combustion or can be used directly for catalytic processes via recycling. A process according to any preceding claim, wherein the recovery of palladium from the palladium-absorbing resin is carried out by combustion. A process according to any one of the preceding claims, wherein the palladium-containing aqueous-organic solution comprises an aqueous THF solution. Procedure according to Claim 6 , wherein the aqueous THF solution comprises further organic solvents selected from the group comprising linear or cyclic alkyl compounds, toluene, benzene, DMF, DMA and mixtures thereof. A process according to any preceding claim, wherein the palladium-absorbing resin is pH stable in the range of pH 1.5-3. Process according to one of the preceding claims, wherein the recovery of the palladium from step c. and step e. is carried out by combustion at a temperature > 250 to > 400°C. A process according to any one of the preceding claims, wherein in step d. the pH is adjusted to a pH of 2-3 prior to transferring the remaining palladium-containing filtrate to a palladium-absorbing resin for absorption of the remaining palladium on the palladium-absorbing resin.

Images