JPS6035288B2 - 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 wastewater. In particular, in hydroformylation and hydrocarboxylation reactions using homogeneous catalysts containing rhodium and organic neighboring compounds, most of the rhodium is separated and recovered from the catalyst liquid after the reaction products are separated from the reaction product liquid by distillation etc. In this case, it is advantageously applied when further rhodium is recovered from the collected rhodium-containing wastewater discharged from the separation and recovery process. 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 rusty catalyst can be recycled to the hydroformylation reaction process as a circulating catalyst liquid. This rhodium triarylphosphine-based collar having an organic phosphorus compound as a ligand is a known anchor formed from a rhodium compound such as rhodium nitrate, rhodium chloride, rhodium sulfate, rhodium acetate, etc. and an organic phosphorus compound such as phosphine. It can be easily prepared by this method.

Further, depending on the case, a rhodium compound and an organic phosphorus compound can be supplied to the reaction system to form a catalyst collar. Various phosphines or phosphites can be used as the organophosphorus compounds used to prepare the phosphatide. Preferably, triarylphosphines such as triphenylphosphine, tri-p-tolylphosphine, tri-m-tolylphosphine, trixylphosphine, tris(p-tolylphosphine) are preferred.
-ethylphenyl)phosphine, tris(p-methoxyphenyl)phosphine, etc. are used.

This complex is usually stabilized by allowing an excess of the organic phosphorus compound to coexist in the reaction system, and the excess organic phosphorus compound is several tens of times to more than rhodium in the reaction system. Several hundred times the molar amount may be used. The lead body is useful for various reactions such as hydrogenation of carbonyl compounds, olefins, aromatic compounds, etc., hydroformylation and hydrocarpoxylation of olefins.

However, in these reactions, various high-boiling 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 reality, a part of the reaction liquid, for example, the circulating catalyst liquid, is extracted from the system as waste catalyst liquid,
By removing high boiling point byproducts and recovering useful catalyst components from the waste catalyst liquid, the accumulation of harmful components as mentioned above is prevented, but the rhodium contained in the waste catalyst liquid is extremely expensive. Since it is a metal, it is extremely important industrially 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 strong acid, a strong acid (for example, sulfuric acid with a concentration of 6 W% or more) is added to the waste catalyst liquid, and the rhodium body is extracted with the 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 rhodium bodies from the acid aqueous solution. In this method, a portion of the rhodium collar body 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 peroxide.

After separating the aqueous phase containing the dium salt and decomposing the excess peroxide by heating, the aqueous phase is treated with monoxide under pressure in the presence of an organic solvent and an anchor compound-forming substance such as triphenylphosphine. This is a method of obtaining rhodium rust in an organic catalyst by treatment with carbon. Most of the rhodium complex obtained by this method is extracted into the solvent phase, but some of the converted 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 the combustion products generated by burning the waste catalyst liquid are introduced into water or other absorption medium, and the rhodium is converted into solid particles and the organic phosphorus compound is converted into phosphoric acid. Most of the rhodium solid particles dispersed in the absorption liquid can be recovered by heating, centrifugation, etc.
A portion of the rhodium remains dissolved in the phosphoric acid aqueous solution of the furnace fluid 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.

Since the rhodium present in the waste water is valuable and expensive, it is industrially very desirable to recover it as much as possible from the viewpoint of economics and prevention of pollution caused by waste water. 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 wastewater, and have found that if the pH of the wastewater is adjusted to a specific range in the presence of ferrous salts,
It was discovered that melted 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 wastewater, and the purpose is to add ferrous salts and a neutralizing agent to rhodium-containing wastewater to remove rhodium. pH of wastewater is 3.5-8.0 or 11.0
This can be easily achieved by adjusting the rhodium compound to 13.8 and separating the precipitated rhodium compound into solid and liquid.

Next, the present invention will be explained in detail.

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 process wastewater that is usually acidic (for example, acidic with phosphoric acid) that is drained 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 it is usually 2 to 30 plates pm, especially 2 to 50 plate pm.
The amount is approximately ppm, and the amount generally increases as the liquid of the wastewater becomes more acidic. In the method of the present invention, a ferrous salt and a neutralizing agent are added to the rhodium-containing wastewater to adjust the pH of the wastewater to 3.5-8.0 or 11.0-13.
8 and the rhodium dissolved in the waste water is precipitated as refractory compounds (mainly hydroxides).

Neutralizing agents used to adjust the pH of the wastewater include alkaline substances such as hydroxides or carbonates of alkali metals and alkali 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. Further, a ferrous salt is added to the wastewater together with an alkali, and examples of the ferrous salt include ferrous salts of inorganic acids such as ferrous sulfate and ferrous chloride.

The amount of the ferrous salt added is such that the concentration of iron ions in the waste water is usually 1 pm or more, preferably 40 to 40 pm. 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 ferrous salt, and it may be added by any method such as adding it before adding the alkali, adding it at the same time as the alkali, or adding it after adding the alkali and adjusting the pH. be able to. Therefore, as typical embodiments of the method of the present invention, the following
■This can be mentioned. ■ After adding and mixing ferrous salt to the wastewater, a neutralizing agent is added to adjust the pH of the wastewater to 3.5-8.0 or 11.0-13.8 to solidify the precipitated rhodium compound. Separate the liquid.

(2) A ferrous salt and a neutralizing agent are simultaneously added to the waste water to adjust the pH of the waste water to 3.5 to 8.0 or 11.0 to 13.8, and the precipitated rhodium compound is separated into solid and liquid.

■ Add a neutralizing agent to the wastewater to adjust the pH of the wastewater to 3.5-8.
After adjusting to 0 or 11.0 to 13.8, ferrous salt is added and the rhodium compound emerging from the bush is separated into solid and liquid.

When adjusting the pH of wastewater to 3.5 to 8.0, there is almost no difference in the rhodium separation effect using any of these methods, so by selecting the conditions appropriately each time, Adopt one of the following methods.

When adjusting the pH of wastewater to 11.0 to 13.8,
Method (2) is advantageous because it has the greatest rhodium separation effect. The reason for this is not clear, but it is presumed that method (2) 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 ferrous salt and a neutralizing agent to the waste water as described above, when the waste water is aged while being incubated, rhodium is precipitated together with iron. Aging is carried out by stirring at a temperature of 10°C or higher, preferably 20 to 100°C, more preferably 50 to 100°C, for at least 1 minute, preferably 5 to 120 minutes. The slurry containing the rhodium precipitate (proliferatingly soluble rhodium compound) that has undergone the aging process is allowed to stand still as necessary, and then subjected to solid-liquid separation using ordinary solid-liquid separation methods, such as furnace filtration and centrifugation, to remove rhodium. Separate and collect the precipitate. Furthermore, it is preferable to use a furnace surface pre-coated with a furnace filter aid during the furnace separation, since this further improves the separation and recovery rate of rhodium. Examples of furnace auxiliary agents include Japanese bush earth, perlite, cellulose, asbestos, bone charcoal, and clean charcoal.
In particular, cellulose, bone char, and activated carbon (powdered activated carbon) are preferable in terms of ease of post-processing. The thickness of the precoat of the furnace auxiliary agent is usually 1 to 5 sides, preferably 1.5 to 3 sides. 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, ferrous salts and neutralizing agents are added to wastewater in this way,
Rhodium is precipitated by adjusting the specific pH, but the adjusted pH is
Figure 1 shows the relationship between the rhodium content and the residual rate of rhodium in wastewater.

The axis in Figure 1 is the pH of the adjusted wastewater, and the vertical axis is the pHI. 5
Ferrous salt (FeS04: Fe concentration in the liquid is 6 p
m) and an alkali were added, and after being heated for 3 minutes, the rhodium residual rate in the bottom liquid obtained by furnace filtration (=rhodium concentration in furnace liquid/rhodium concentration in waste water) is shown. As is clear from Figure 1, the rhodium separation effect is poor at pH 3.5 or lower. In addition, at pH 8.0 or higher, rhodium that had previously precipitated is redissolved, and pH. When it is 0 or more, the separation effect becomes better again. Therefore, the pH suitable for separating rhodium dissolved in the liquid is 3.5 to 8.0 or 11.0 to 13.8.
and preferably pH 4.0 to 7.0 or 11.4 to
13.0, especially PHIl. 6 to 12.6 is optimal.
The details of the effect of separating rhodium from wastewater by the method of the present invention are not clear, but synergistic effects such as precipitation of rhodium hydroxide due to pH adjustment and co-precipitation and adsorption of iron hydroxide in the liquid due to addition of ferrous salt are observed. This seems to be due to the effect.

As a result, in the method of the present invention, pH 3.5 to 8.0
In PHIl. 0 to 13.8, 90 to 99.0%, especially p
At H11.5-12.7, 97.5-99.0% can be precipitated and separated. 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, thereby preventing pollution caused by wastewater and recovering expensive rhodium. 3. Industrially and economically. Extremely advantageous.

Furthermore, by combining the method of the present invention with known rhodium recovery methods from waste catalyst liquids, such as the combustion recovery method, it is possible to recover rhodium from waste catalyst liquids at an extremely high rate. The various reactions used 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 body, triphenylphosphine, triphenylphosphine oxide, and a high-boiling point product obtained from an olefin hydroformylation reaction process was supplied to a submerged combustion device. and burned it.

The combustion products were immediately quenched by introduction into water. In this absorption liquid, the produced phosphorus pentoxide was phosphoric acid, and the rhodium was dispersed in the water in the form of solid particles. The absorption liquid was filtered through a filter with a pore size of 0.2 m to separate solid and liquid, and the rhodium dispersed in the liquid was separated and recovered as solid particles. Furnace liquid is rhodium 20. Nakapm and 2% phosphoric acid
containing pHI. This was an acidic aqueous solution of No. 5 (hereinafter referred to as the test solution). While sacrificing 1000 minutes of this sample solution, 0.3 hours of ferrous sulfate (FeS04, 7 days 20) was added to make the Fe concentration in the solution 60 ppm, and then 1
While adding 0% caustic soda, the pH of the sample solution is increased.
H was adjusted to 12.0.

Thereafter, this was aged for 60 minutes while being stirred at a temperature of 60o○ to precipitate the rhodium compound, and then the pore size was 0.
．． The filter surface of a 2-m filter is pre-coated with powdered activated carbon to a thickness of 2 feet. The precipitate of the Dium compound was separated and collected. The rhodium concentration dissolved in the furnace liquid was analyzed, and the rhodium (Rh) recovery rate was determined from the following formula. The results are shown in Table 1. Rh recovery rate = Rh concentration in the test solution - Rh concentration in the sap solution Rh concentration in the test solution Note that rhodium was analyzed using an atomic absorption spectrometer.

Examples 2 to 7 The treatment was carried out under the same conditions as in Example 1, except that the pH of the test solution was adjusted to 11.0, 13.0, 13.5, 4.0, 6.0, and 7.0, respectively. .

The results are shown in Table 1. Example 8 The treatment was carried out under the same conditions as in Example 1 except that ferrous salt was added after pH adjustment.

The results are shown in Table 1. Example 9 The treatment was carried out under the same conditions as in Example 1 except that the pH of the test solution was adjusted to 6.0 and then ferrous salt was added.

The results are shown in Table 1. Example 10 In Example 1, ferrous chloride (F
Adding 0.22 t of e○ evening 2nd and 4th 20)
The treatment was carried out under the same conditions except that the concentration was 60 ppm.

The results are shown in Table 1. Example 11 In Example 1, ferrous chloride (F
Fe in the liquid was
The treatment was carried out under the same conditions except that the concentration was increased to 60 ppm' and the pH of the test solution was adjusted to 6.0.

The results are shown in Table 1. Comparative Shark Examples 1 to 5 * In Example 1, the pH was adjusted to 2.0, 3.
Except for adjusting to 0, 9.0, 10.0 and 10.5,
The treatment was carried out under the same conditions.

The results are shown in Table 2. Comparative Example 6 Except for not adding ferrous sulfate in Example 1,
The treatment was carried out under the same conditions.

The results are shown in Table 2. Comparative Examples 7 to 11 In Comparative Example 6, the pH of the test solution was set to 4.0 and 6.0, respectively.
Processing was carried out under the same conditions except that the values were adjusted to 0, 10.0, and 13.0.

The results are shown in Table 2. Table 1

[Brief explanation of the drawing]

Figure 1 shows how ferrous salt and neutralizing agent are added to wastewater to achieve a specific pH level.
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. Figure l

Claims (1)

[Claims] 1. Adding a ferrous salt and a neutralizing agent to rhodium-containing wastewater to adjust the pH of the wastewater to 3.5 to 8.0 or 11.0.
A method for recovering rhodium, which comprises adjusting the rhodium concentration to 13.8 to 13.8, and separating the precipitated rhodium compound into solid and liquid. 2. The rhodium recovery method according to claim 1, which comprises adjusting the pH of the wastewater to 11.0 to 13.8. 3. The rhodium recovery method according to claim 1, which comprises adjusting the pH of the wastewater to 3.5 to 8.0. 4. The method for recovering rhodium according to claim 2, which comprises adjusting the pH of the waste water to 11.4 to 13.0. 5. A method for recovering rhodium according to any one of claims 1 to 4, characterized in that a neutralizing agent is added after the ferrous salt is added to the waste water. 6. The rhodium recovery method according to any one of claims 1 to 4, characterized in that the ferrous salt is added after the pH is adjusted by adding a neutralizing agent to the waste water. How to do it. 7 Claims 1 to 6
The method for recovering rhodium according to any one of Items 1 to 3, wherein the waste water is acidic waste water. 8. The method for recovering rhodium according to claim 7, wherein the waste water is phosphoric acid acid waste water. 9. A method for recovering rhodium according to any one of claims 1 to 8, characterized in that precipitation of a rhodium compound occurs in the presence of activated carbon. 10 Any one of claims 1 to 9
The method for recovering rhodium as described in 1., wherein the solid-liquid separation is carried out using a filter surface pre-coated with a filter aid.