JPS589129B2 - How to recover rhodium - Google Patents

Description

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

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

In particular, in hydroformation and hydrocarboxylation reactions using a homogeneous catalyst containing rhodium and an organic phosphorus compound, most of the rhodium is removed from the catalyst liquid after the reaction product is separated from the reaction product liquid by distillation or the like. This method is advantageously applied when further rhodium is to be recovered from the phosphoric acid acid wastewater containing a trace amount of rhodium discharged from the separation and recovery step.

In recent years, rhodium catalysts have been advantageously used industrially as catalysts for olefin hydroformylation reactions.

In particular, the rhodium triarylphosphine complex catalyst is chemically extremely stable, so after separating and obtaining the aldehyde produced 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 may be supplied to the reaction system to form a catalyst complex.

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

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

The complex is usually further stabilized by allowing an excess of the organic phosphorus compound to coexist 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 by-products and deactivated catalysts accumulate in the reaction medium, so a portion 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 reaction 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, high-boiling by-products are removed from the waste catalyst liquid, and useful catalyst components are recovered. However, since the rhodium contained in the waste catalyst liquid is an extremely expensive metal, it is industrially extremely important to efficiently recover it.

Conventionally, known methods for separating and recovering rhodium from waste catalyst liquid include an extraction method using a strong acid, a decomposition method using a peroxide, and a combustion recovery method.

In the extraction method using a strong acid, a strong acid (e.g. 60 wt%) is added to the waste catalyst liquid.
In this method, the rhodium complex is extracted with a strong acid by adding sulfuric acid (as described above) and separated from the 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 acid aqueous solution.

In this method, a portion 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., but a portion of the rhodium remains dissolved in the phosphoric acid aqueous solution of the filtrate and is not recovered, resulting in a loss.

As described above, most of the rhodium in the waste catalyst liquid is recovered by these separation and recovery methods, but some of it is not recovered during the separation and recovery operation but is dissolved in the waste water 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 present inventors have conducted intensive studies on a method for industrially advantageous recovery of rhodium dissolved in phosphoric acid wastewater, and as a result, the pH of the wastewater is adjusted to a specific range in the presence of a specific ferric salt. In this case, the present inventors discovered that dissolved rhodium effectively precipitates and precipitates, leading to the completion of the present invention.

That is, the purpose of the present invention is to provide a method for economically and efficiently recovering rhodium dissolved in phosphoric acid wastewater, and this purpose is to provide a method for economically and efficiently recovering rhodium dissolved in phosphoric acid acid wastewater, and this purpose is to provide a method for recovering rhodium dissolved in phosphoric acid acid wastewater containing rhodium. Ferric iron and a neutralizing agent are added to adjust the pH of the wastewater to 4-10 or 12.0-13.
This can be easily achieved by adjusting the rhodium compound to 8 and separating the precipitated rhodium compound into solid and liquid.

Next, the present invention will be explained in detail.

The rhodium-containing phosphoric acid acidic wastewater to be treated in the method of the present invention includes rhodium-containing phosphoric acid acidic process wastewater discharged from various factories, and especially, as mentioned above, phosphoric acid acidic process wastewater discharged from industrial processes using rhodium as a catalyst. Examples include phosphoric acid acidic process wastewater discharged when most of the rhodium is separated and recovered from the waste catalyst liquid.

The amount of rhodium dissolved in the waste water may vary greatly depending on the nature of the waste water, but it is usually 2 to 300 ppm, especially 2 to 3 ppm.
The amount is approximately 0 ppm, and the amount generally increases as the liquid quality of the wastewater becomes more acidic.

In the method of the present invention, ferric sulfate or ferric chloride and a neutralizing agent are added to the phosphoric acid acid wastewater containing rhodium to adjust the pH of the wastewater to 4-10 or 12.0-13.
8, and rhodium dissolved in the waste water is precipitated as a sparingly soluble compound (mainly hydroxide).

Neutralizing agents used to adjust the pH of the wastewater include alkaline substances such as hydroxides or carbonates of alkali metals and alkaline earth metals such as ammonia, caustic soda, caustic potash, slaked lime, and soda carbonate, or inorganic substances such as sulfuric acid and hydrochloric acid. Acid is used.

These neutralizing agents do not necessarily have to be pure products, and may be mixtures thereof or waste alkalis or waste acids discharged from various processes.

The amount of ferric sulfate or ferric chloride added as a ferric salt is usually 20 pp as iron ion concentration to the wastewater.
m or more, preferably within the range of 40 to 400 ppm.

If the amount added is too small, there is no effect of the addition, and if it is too large, there is no difference in the effect of the addition, and the cost increases, which is not industrially advantageous.

There is no particular restriction on the timing of addition of the ferric salt, and the ferric salt can be added by any of the following methods: before adding the alkali, at the same time as the alkali, or after adding the alkali and adjusting the pH. be able to.

Therefore, typical embodiments of the method of the present invention include the following (1) to (3).

(1) After adding ferric salt to the wastewater and mixing, add a neutralizing agent to adjust the pH of the wastewater to 4-10 or 12.0-13.8.
The precipitated rhodium compound is separated into solid and liquid.

(2) A ferric salt and a neutralizing agent are simultaneously added to the waste water to adjust the pH of the waste water to 4 to 10 or 12.0 to 13.8, and the precipitated rhodium compound is separated into solid and liquid.

(3) After adding a neutralizing agent to the waste water to adjust the pH of the waste water to 4 to 10 or 12.0 to 13.8, ferric salt is added to separate the precipitated rhodium compound into solid and liquid.

When adjusting the pH of wastewater to 4 to 10, there is almost no difference in the rhodium separation effect using any of these methods, so by selecting the conditions appropriately each time (1) to (3) Adopt one of the following methods.

When adjusting the pH of wastewater to 12.0 to 13.8,
Method (1) is advantageous because it has the greatest rhodium separation effect.

Although the reason for this is not clear, it is presumed that method (1) produces particularly uniform precipitation of fine particles of iron compounds in the liquid.

In addition, in order to further improve the rhodium recovery effect in the method of the present invention, activated carbon may be added to the wastewater to adjust the pH and precipitate rhodium.

After adjusting the pH of the waste water by adding ferric salt and a neutralizing agent to the waste water as described above, when the waste water is aged with stirring, rhodium is precipitated together with iron.

Aging is carried out at a temperature of 10 to 100°C, preferably at the same temperature as the wastewater for at least 1 minute, preferably 5 to 3
This is carried out by stirring for 0 minutes.

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

Further, during filtration and separation, it is preferable to perform filtration using a filtration surface coated with a filter aid, since this further improves the separation and recovery rate of rhodium.

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

The thickness of the filter aid precoat 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 a conventional purification treatment.

In the method of the present invention, a ferric salt and a neutralizing agent are added to wastewater in this way, and the pH is adjusted to a specific value to precipitate rhodium. As shown in the figure.

The horizontal axis in Figure 1 is the pH of the adjusted wastewater, and the vertical axis is pH 1.5.
Ferric salt (FeCl3; Fe concentration in the liquid is 62p)
pm) and an alkali, stirred for 30 minutes, and filtered to obtain a rhodium residual rate in the filtrate (=rhodium concentration in filtrate/rhodium concentration in waste water).

As is clear from FIG. 1, the rhodium separation effect is small at pH 4 or lower.

Moreover, at pH 10 or higher, rhodium that has precipitated once is redissolved, and at pH 12 or higher, the separation effect becomes good again.

Therefore, the pH is suitable for separating rhodium dissolved in the liquid.
is from 4 to 10 or from 12.0 to 13.8, preferably from pH 5 to 7 or from 12.5 to 13.5, particularly around pH 13.

The details of the effect of separating rhodium from phosphoric acid wastewater by the method of the present invention are not clear, but precipitation of rhodium hydroxide by pH adjustment and co-precipitation and adsorption of iron hydroxide in the liquid by addition of ferric salt. This seems to be due to the synergistic effect of these factors.

As a result, in the method of the present invention, 55 to 83% of the rhodium dissolved in the waste water at pH 4 to 10, and 55 to 83% of the rhodium dissolved in waste water at pH 1
2.0 to 13.8, 55 to 68%, especially pH 12.5
~13.5, 80-90% can be precipitated and separated.

As described in detail above, according to the method of the present invention, rhodium dissolved in phosphoric acid wastewater can be efficiently recovered in a simple manner. And it is extremely advantageous economically.

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

EXAMPLES Next, the present invention will be specifically explained using examples, but the present invention is not limited to the following examples unless the gist of the invention is exceeded.

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

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 filtered 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.

The solution was an acidic aqueous solution (hereinafter referred to as test solution) with a pH of 1.5 containing 10.5 ppm of rhodium and 2% of phosphoric acid.

While stirring 1000 g of this test solution, ferric chloride (F
After adding 0.3 g of eCl3.6H2O) to make a mixed solution with an Fe concentration of 62 ppm, 10% caustic soda was further added with stirring to bring the pH of the test solution to 13.0.
Adjusted to.

Thereafter, this was aged for 5 minutes while stirring in a room 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 filtrate was analyzed, and the rhodium (Rh) recovery rate was determined from the rhodium concentration using the following formula.

The results are shown in Table-1. Note that rhodium was analyzed using an atomic absorption spectrometer.

Examples-2 to 7 In Example-1, the pH of the test solution was 12.5,
Processing was carried out under the same conditions except that the values were adjusted to 13.5, 13.8, 5.0, 7.0, and 9.0.

The results are shown in Table-1.

Example-8 The treatment was carried out under the same conditions as in Example-1 except that ferric chloride was added after adjusting the pH.

The results are shown in Table-1.

Example-9 The test solution was treated under the same conditions as in Example-1 except that ferric chloride was added after adjusting the pH of the test solution to 5.0.

The results are shown in Table-1. Example-10 In Example-1, ferric chloride (FeCl3.6H2O
) instead of ferric sulfate (Fe2(SO4)3.9H2
The treatment was carried out under the same conditions except that 0.3 g of O) was added to make the Fe concentration in the liquid 60 ppm.

The results are shown in Table-1. Example-11 In Example-1, ferric chloride (FeCl3.6H2O
) instead of ferric sulfate (Fe2(SO4)3.9H2
The treatment was carried out under the same conditions except that 0.3 g of O) was added to make the Fe concentration in the solution 60 ppm, and the pH of the test solution was adjusted to 5.0.

The results are shown in Table-1.

Comparative Examples-1 to 3 In Example-1, the pH was adjusted to 2.0 and 3.0, respectively.
The process was carried out under the same conditions except for adjustment 1 to 11.0.

The results are shown in Table-2. Comparative Example-4 The treatment was carried out under the same conditions as in Example-1 except that ferric chloride was not added.

The results are shown in Table-2.

Comparative Example-5 The treatment was carried out under the same conditions as in Comparative Example-4 except that the pH of the test solution was adjusted to 5.0.

The results are shown in Table-2.

[Brief explanation of drawings]

Figure 1 shows how ferric salts and neutralizing agents are added to wastewater to achieve a specific pH.
It is a graph which shows the relationship between the adjusted pH and the rhodium residual rate in waste water when rhodium is precipitated by adjusting to pH.

Claims (1)

[Claims] 1. Ferric sulfate or ferric chloride and a neutralizing agent are added to phosphoric acid acidic wastewater containing rhodium to reduce the pn of the wastewater to 4.
10 or 12.0 to 13.8, and solid-liquid separation of precipitated rhodium compounds. 2. The method for recovering rhodium according to claim 1, which comprises adjusting the pH of the wastewater to 12.0 to 13.8. 3. The method for recovering rhodium according to claim 1, which comprises adjusting the pH of the wastewater to 4 to 10. 4. The rhodium recovery method according to claim 2, which comprises adjusting the pH of the wastewater to 12.5 to 13.5. 5. The rhodium recovery method according to any one of claims 1 to 4, characterized in that a neutralizing agent is added after ferric sulfate or ferric chloride is added to the waste water. how to. 6. In the method for recovering rhodium according to any one of claims 1 to 4, ferric sulfate or ferric chloride is added after adjusting the pH by adding a neutralizing agent to the waste water. A method characterized by: 7. A method for recovering rhodium according to any one of claims 1 to 6, characterized in that precipitation of a rhodium compound occurs in the presence of activated carbon. 8. A method for recovering rhodium according to any one of claims 1 to 7, characterized in that solid-liquid separation is performed using a filtration surface pre-coated with a filter aid.