JPS583977B2 - Rhodium separation and recovery method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for separating and recovering rhodium.

Specifically, the present invention relates to a method for economically and efficiently recovering rhodium from rhodium-containing wastewater.

In particular, in hydroformylation and hydrocarboxylation reactions using a homogeneous catalyst containing rhodium and an organic phosphorus compound, most of the rhodium is separated from the catalyst liquid after the reaction product is separated from the reaction product liquid by distillation etc. When recovering rhodium, it is advantageously applied when further recovering rhodium from waste water containing a trace amount of rhodium discharged from the separation and recovery process.

In recent years, rhodium catalysts have been industrially advantageously used as catalysts for hydroformylation of olefins.

In particular, the rhodium-triarylphosphine complex catalyst is chemically extremely stable, so after separating the generated aldehyde from the hydroformylation reaction product liquid by distillation,
It has the great advantage that the residual liquid containing the complex catalyst can be recycled to the hydroformylation reaction process as a circulating catalyst liquid.

This rhodium triarylphosphine complex having an organophosphorus compound as a ligand is produced by a known complex formation method from a rhodium compound such as rhodium nitrate, rhodium chloride, rhodium sulfate, rhodium acetate, etc. and an organophosphorus compound such as phosphine. It can be easily prepared.

In some cases, a rhodium compound and an organic phosphorus compound can also be supplied to the reaction system to form a catalyst complex there.

The organophosphorus compounds used to prepare the complexes include various phosphines or phosphites.

Preferably triarylphosphines such as triphenylphosphine, tri-p-tolylphosphine, tri-m
-}Rylphosphine, tricylylphosphine, tris(p-ethylphenyl)phosphine, tris(p-methoxyphenyl)phosphine, etc. are used.

The complex is usually further stabilized by coexisting an excess of the organic phosphorus compound in the reaction system, and the excess organic phosphorus compound is several tens to several times larger than the rhodium in the reaction system. A hundredfold molar ratio may also be used.

The complexes are useful for a variety of reactions such as hydrogenation of carbonyl compounds, olefins, aromatics, etc., hydroformylation and hydrocarboxylation of olefins.

However, in these reactions, various high-boiling by-products are produced and the catalyst is deactivated.

Therefore, when these reactions are carried out continuously, high-boiling byproducts and deactivated catalysts accumulate in the reaction medium, so some of the reaction medium is continuously or intermittently removed from the reaction system. It is necessary to avoid excessive accumulation of high boiling by-products and deactivated catalyst in the medium.

In practice, a part of the reaction liquid, for example, the circulating catalyst liquid, is extracted from the system as a waste catalyst liquid, and high boiling point by-products are removed from the waste catalyst liquid, and useful catalyst components are recovered. Although it is possible to prevent the accumulation of harmful components such as
Since the rhodium contained in the waste catalyst liquid is an extremely expensive metal, it is extremely important industrially to efficiently recover it. Extraction methods using peroxides, decomposition methods using peroxides, combustion recovery methods, etc. are known.

In the extraction method using a strong acid, a strong acid (e.g. 60 wt%) is added to the waste catalyst liquid.
sulfuric acid) is added and the rhodium complex is extracted with strong acid.
This is a method of separating it from waste catalyst liquid.

When water is added to dilute the rhodium-containing acid solution obtained by phase separation, a rhodium complex precipitates, and this precipitate is extracted with a solvent to recover the rhodium complex from the aqueous nucleic acid solution.

In this method, a part of the rhodium complex remains dissolved in the acid aqueous solution and is not recovered, resulting in loss.

In the peroxide decomposition method, the waste catalyst liquid is treated with an acid aqueous solution such as nitric acid and a peroxide, the aqueous phase containing the rhodium salt is separated, the excess peroxide is decomposed by heating, and then the aqueous phase is separated. is treated with carbon monoxide under pressure in the presence of an organic solvent and a complex forming substance such as triphenylphosphine to obtain a rhodium complex in the organic solvent phase.

Most of the rhodium complex obtained by this method is extracted into the solvent phase, but a portion of the unconverted rhodium salt and rhodium complex remain dissolved in the aqueous phase and are not recovered and are lost.

The combustion recovery method is a method in which combustion products generated by burning waste catalyst liquid are introduced into an absorption liquid such as water, and rhodium is captured as solid particles and organic phosphorus compounds as phosphoric acid.

Most of the rhodium solid particles dispersed in the absorption liquid are recovered by filtration, centrifugation, etc., or a portion of the rhodium remains dissolved in the phosphoric acid aqueous solution of the p liquid and is not recovered and is lost.

As described above, although most of the rhodium in the waste catalyst liquid is recovered by these separation and recovery methods, some of it is not recovered during the separation and recovery operation and is dissolved in the wastewater and becomes a loss. .

Although the amount of rhodium dissolved in the wastewater is very small, it is expensive, so it is industrially very desirable to recover as much as possible from the viewpoint of economy and prevention of pollution caused by wastewater.

Conventionally, there is no known method for effectively recovering rhodium dissolved in wastewater.

The inventors of the present invention have conducted intensive studies on an industrially advantageous method for recovering rhodium dissolved in wastewater, and have found that if the pH of the wastewater is adjusted to a specific range, dissolved rhodium can be effectively precipitated. The purpose of the present invention is to provide a method for economically and efficiently recovering rhodium dissolved in wastewater. , by adding alkali to rhodium-containing wastewater to adjust the pH of the wastewater to 12 to 13.
．． This can be easily achieved by adjusting the rhodium compound to 5 and separating the precipitated rhodium compound into solid and liquid.

The present invention will be explained in detail below.

The rhodium-containing wastewater to be treated in the method of the present invention is mostly rhodium-containing process wastewater discharged from various factories, especially waste catalyst liquid discharged from industrial processes that use rhodium as a catalyst, as described above. Examples include normally acidic (for example, phosphoric acid acidic) process wastewater that is discharged when separating and recovering rhodium.

The amount of rhodium dissolved in the waste water may vary greatly depending on the nature of the waste water, but generally 2 to 300 ppm, especially 2 to 300 ppm.
The amount is approximately 30 ppm, and the amount generally increases as the liquid quality of the wastewater becomes more acidic.

In the method of the present invention, an alkali is added to the rhodium-containing wastewater to adjust the pH of the wastewater to 12 to 13.5, and the rhodium dissolved in the wastewater is converted into a poorly soluble compound (
precipitates mainly as hydroxide).

Examples of the alkali used to adjust the pH of the wastewater include ammonia, caustic soda, caustic potash, slaked lime, soda carbonate, and other alkali metal hydroxides or carbonates.

These alkaline substances do not need to be pure products, and may be mixtures thereof or waste alkalis discharged from various processes.

After adjusting the pH of the waste water by adding alkali to the waste water in this way, when the waste water is aged, rhodium dissolved in the liquid will precipitate as a compound.

Aging is carried out at a temperature of 10 to 100°C, but since there is almost no difference in the precipitation rate of rhodium within this temperature range, it is usually preferable to carry out the aging at the same temperature as the waste water.

The maturing time is usually 2~2 to 30 minutes if the wastewater is allowed to stand after pH adjustment.
When stirring for 3 hours, the stirring time is usually from several minutes to about 1 hour.

After aging, the slurry containing rhodium precipitates (poorly soluble rhodium compounds) is allowed to stand still as necessary, and then subjected to solid-liquid separation using ordinary solid-liquid separation methods, such as P filtration and centrifugation, to remove the rhodium precipitates. Separate and collect.

In addition, it is preferable to use a filtration surface pre-coated with a p-filtering aid during the offshore filtration separation, since this further improves the separation and recovery rate of rhodium.

Examples of the P superimposition agent include diatomaceous earth, perlite, cellulose, asbestos, bone charcoal, activated carbon, etc., and cellulose, bone charcoal, activated carbon (powdered activated carbon), etc. are particularly preferred in terms of ease of post-treatment.

The thickness of the precoat of the Oki filter aid is usually 1 to 5 mm, preferably 1.5 to 3 mm.

The recovered rhodium can be reused as a rhodium catalyst after being subjected to normal purification treatments such as roasting.

In the method of the present invention, rhodium is precipitated by adding an alkali to the wastewater to adjust the pH to a specific value, and the relationship between the pH to be adjusted and the residual rate of rhodium in the wastewater is shown in FIG.

The horizontal axis in Figure 1 is the pH of the adjusted wastewater, and the vertical axis is pH 1.4.
Rhodium residual rate in P solution obtained by adding alkali to waste water, stirring for 30 minutes, and filtering (Rh concentration in Ninohe solution/
(Rh concentration in wastewater).

As is clear from FIG. 1, when the pH is less than 12, the rhodium separation effect is small, and when the pH exceeds 13.5, the rhodium that was once precipitated and separated begins to dissolve again.

Therefore, rhodium dissolved in wastewater can be separated at pH 12.
It is preferable to adjust the pH to a range of ~13.5, and a pH of around 13 is most effective.

As detailed above, according to the method of the present invention, rhodium dissolved in wastewater, especially acidic wastewater, can be efficiently recovered in a simple manner, so that it can be used for industrial purposes such as prevention of pollution caused by wastewater and recovery of expensive narodium. And it is extremely advantageous economically.

Furthermore, by combining the known method of recovering rhodium from waste catalyst liquid, such as the combustion recovery method, with the method of the present invention, it is possible to recover rhodium from waste catalyst liquid at an extremely high rate. Various reactions can be carried out with industrial advantage.

EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example-1 A submerged combustion device for a waste catalyst liquid containing a rhodium triphenylphosphine complex, triphenylphosphine, triphenylphosphine oxide, and high-boiling byproducts obtained from the olefin hydroformylation reaction process. was supplied and burned.

The combustion products were immediately quenched by introduction into water.

In this absorption liquid, the generated phosphorus pentoxide became phosphoric acid, and rhodium was dispersed in the water in the form of solid particles.

The absorbed liquid was passed through a filter with a pore size of 0.2 μm to separate solid and liquid, and the rhodium dispersed in the liquid was separated and recovered as solid particles.

P solution contains 10 ppm rhodium and 2% phosphoric acid.
1.4 acidic aqueous solution (hereinafter referred to as test solution).

10% caustic soda was added to 1000 g of this test solution with stirring to adjust the pH to 13.

Thereafter, this was aged at room temperature for 10 minutes with stirring to precipitate a rhodium compound, and then filtered through a filter with a pore size of 0.2 μm to separate and collect the precipitate of a rhodium compound.

The rhodium concentration dissolved in the P solution was analyzed, and the rhodium (Rh) recovery rate was determined using the following formula.

The results are shown in Table-1.

Note that rhodium was analyzed using an atomic absorption spectrometer.

Examples-2 to 3 In Example-1, the pH of the test solution was set to 12 and 1, respectively.
The treatment was carried out under the same conditions except that the temperature was adjusted to 35.

The results are shown in Table-1. Comparative Examples-1 to 3 In Example-1, the pH of the test solution was set to 7 and 1 l, respectively.
The process was carried out under the same conditions except that it was adjusted to 13.8.

The results are shown in Table-1. Leprosy Examples 4 to 6 Leprosy Examples 1 to 3 were treated under the same conditions except that a filter pre-coated with powdered activated carbon to a thickness of 3 mm was used on the p-filtration surface of the filter.

The results are shown in Table-1.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the adjusted pH and the residual rate of rhodium in the waste water when rhodium is precipitated by adding alkali to the waste water and adjusting the pH to a specific pH.

Claims (1)

[Claims] 1. A method for separating and recovering rhodium, which comprises adding an alkali to rhodium-containing wastewater, adjusting the pH of the wastewater to 12 to 13.5, and separating precipitated rhodium compounds from solid to liquid. . 2. The method for separating and recovering rhodium according to claim 1, wherein the waste water is acid waste water. 3. The method for separating and recovering rhodium according to claim 2, characterized in that the waste water is phosphoric acid acid waste water. 4. A method for separating and recovering rhodium according to any one of claims 1 to 3, characterized in that solid-liquid separation is carried out using an F filtration surface pre-coated with a filtration aid.