KR20060012657A - Process for recovery of palladium from spent catalyst - Google Patents

Abstract

The present invention relates to an improved process for the recovery of palladium from spent catalyst. The present invention particularly relates to a suitable method of catalyst recovery of precious metals from spent catalysts or inorganic waste and more specifically the process concerns with the recovery of palladium that is anchored on carbon and is used as catalyst for the hydrogenation of nitro aromatics or as a catalyst for many other organic transformations.

Description

Process for recovery of palladium from spent catalyst

The present invention relates to an improved process for recovering palladium from used catalysts. The present invention specifically relates to a suitable method for recovering catalysts of expensive metals from used catalysts or inorganic wastes, and more particularly, the method is a catalyst for the hydrogenation of nitro aromatics by recovering palladium fixed on carbon. Or as a catalyst for other organic conversion reactions.

Expensive transition metals and their coordination complexes may find their industrial use as supported catalysts and performance chemicals in the fine chemical industry. For example, metals such as Ag, Au, Pd, Pt, and Rh are variously used industrially as catalysts for oxidation, hydrogenation, and dehydrogenation reactions. Palladium salt catalysts are also widely used to catalyze reactions such as oxidation, dehydrogenation, hydrogenation, isomerization, and dimerization. Efficient recovery and purification of platinum group metals such as palladium and platinum from already used used catalysts is economically desirable. As a result, research has been conducted worldwide to develop a method for the complete recovery of such metals from used catalysts. Various polymeric materials, modified silicas, zeolites, and / or clay materials are used as support of such metals. Similarly, coordination metal complexes of Pd, Pt, Ru, and Rh are used as commercial catalysts in homogeneous conditions for hydroformylation and hydrogenation reactions. However, because it is difficult to separate metal complexes from product mixtures, there is an increasing need to develop heterogeneous catalysts in which coordinating metal complexes are supported in polymers or inorganic solid supports such as silica, carbon, zeolites, and alumina. Commercially, it is important to recover expensive metals to the maximum extent possible from the support once the catalyst is inactivated.

In some cases, the catalyst may be inactivated during or after the reaction cycle such that the reaction effluent may consist of various residues, for example complexes of various valence forms in the case of metal ions. In many cases, the presence of excess impurities reduces the recycling efficiency of the catalyst. However, the impurity, which is a problem associated with the decomposition of the catalyst due to repeated cycles, is due to side reactions, and the outflow of effective catalyst from the solid support is common in the case of heterogeneous catalysts. In view of the environmentally committed restrictions on the treatment of metal containing waste, the effective recovery of residual expensive metals from the reaction effluent is a very important way to grow environmentally suitable and economically.

Moreover, solvent recovery for separating expensive metals from each other and from non-metals that may be present is being used more widely while recovering expensive metals from ores or scraps containing used catalysts. Wet smelting methods used for the separation and recovery of platinum group metals (e.g. platinum, palladium, and rhodium) are typically some type of oxidative acid chloride leaching, with solvent extraction after treatment with aqua regia or hydrochloric acid / chlorine gas. acidic chloride leach).

According to U.S. Patent 4,705,896 (1987) to Van Der Puy et al., Extraction for palladium recovery using ortho alkoxy substituted phenyl oxime compounds useful for selectively separating and recovering palladium from aqueous compositions and mixtures containing palladium and other metals. Solvents are disclosed. In this patent, the oxime used for palladium extraction is hydroxyoxime and its derivatives, which is expensive for industrial application.

US Patent 4,654,145 to Demopoulos et al. Discloses the recovery of expensive metals, particularly gold and platinum group metals, from metal chloride solutions by solvent extraction and selective stripping / precipitation. The active extraction solvent used was in particular alkyl substituted 8-hydroxyquinoline. Gold is precipitated by hot water or hydrogen after a cold water wash. Palladium in the organic phase is precipitated by hydrogen reduction or stripped with inorganic acid. Platinum stripped into the aqueous solution may be recovered by hydrogen reduction. The organic phase does not decompose if the acid is washed and removed prior to hydrogen reduction and can be recycled. This method requires the removal of acid from the organic phase before the solvent is recovered and recycled, and requires several steps.

Hunter William's British Patent A-2127001 discloses a method for recovering expensive metals, namely gold, palladium and platinum, from a solution in which at least one expensive metal compound is dissolved. This method involves adsorbing one expensive metal on activated carbon in the form of fibers. The loaded fiber form is treated with an aqueous cyanide solution to recover metal ions. The main limitation of this method is that the cyanide ligand must have a high affinity for the expensive metals to be recovered.

U.S. Patent 4,578,250 to Dimmit et al. Discloses palladium present in an aqueous solution by adjusting the pH of the solution to 0-5, and then treating the oxidized solution with ortho alkoxy substituted phenyl oxime using solvent extraction techniques, thereby providing Separation and purification together are disclosed. Examples of useful solvents are toluene, cyclohexane, xylene, chlorinated hydrocarbons, and aromatic, aliphatic, cyclo-aliphatic hydrocarbons such as kerosine and the like. The aqueous phase was separated from the organic phase and then palladium was stripped from the bond with the oxime compound in the organic phase by extraction with an aqueous ammonia solution. The disadvantage of this method is that it involves a multi-step process. Moreover, recovery of the solvent for further reuse further complicates this method.

Melka, Jr. U.S. Patent No. 4,435,258 discloses the recovery of palladium from an electroless catalyst bath that has already been used by dissolving palladium to produce a true solution and then electrolytic precipitation with a nickel anode or a nickel or copper cathode. This recovery method comprises the steps of: (a) dissolving colloidal palladium in a bath by adding an oxidant (eg, hydrogen peroxide) to form a true solution; (b) heating for a sufficient time to a predetermined temperature sufficient to essentially remove excess hydrogen peroxide; (c) adding the solution to an electrolysis cell having (i) a nickel anode and (ii) a negative electrode composed of a metal or metal surface that is readily removable from non-polluting or precipitated palladium; And (d) electromelting palladium from the solution on the cathode at a voltage that tends to minimize and substantially reduce tin precipitation.

On continued use, the catalyst bath is contaminated with copper from the copper cladding. If the bath is degraded to such a degree that performance or electroless plating exhibits less than expected stickiness, the waste should be discarded because it may not be suitable for commercial application.

U.S. Patent 4,105,742 to Edward et al. Discloses a process for separating platinum and / or palladium from a starting solution containing a chloro complex with other platinum group metals and / or nonmetals in a 0.01 to 2 M acid solution. Contacting the starting solution with a suitable extraction solvent (including a functional group of the formula R ₂ N-CH ₂ -COOH, wherein R is a long chain alkyl group, as an extraction solvent soluble in a water-insoluble solvent carried out in an organic phase), such as Separating the next two phases and recovering the extracted platinum or palladium or both from the loaded solvent extraction solvent. Such extraction solvents generally use very expensive and environmentally unfriendly organic solvents and are not suitable for industrial application.

Pauko Jan's C.S. Patent 251467 (1988) (Chemical Abstract 109 (24): 213964) discloses a method for recovering palladium from wastewater by adsorption on activated carbon pretreated with an alkali metal salt of ethylenediaminetetraacetic acid (EDTA). To recover expensive metals, it is necessary to acidify the wastewater to pH 3-7.5 before treating activated carbon with EDTA solution. However, this method is useful for homogeneous aqueous catalyst wastes but cannot be applied directly to non-aqueous systems.

Japanese Patent 54 9597 (1978) discloses a method for regenerating and recovering palladium from used residue obtained from a catalytic chemical process carried out under homogeneous conditions. This method is heated to about 550 ° C. to 600 ° C. to decompose the organic fragments and then acid treated to obtain the corresponding palladium salts. However, this invention is limited in its scope in that it is concerned only with the decomposition of metal complexes having lower aliphatic mono-carboxylic acids as organic moieties.

Shanton; Kenneth J. and Grant; In US Pat. No. 4,331,634 to Richard A, a strong acidic solution such as sulfuric acid, hydrochloric acid, perchloric acid or nitric acid is used as the stripping solvent for extracting palladium from an organic acidic solution containing oxime as extraction reagent. The organic phase may also contain an anionic phase transition metal or catalyst to assist the extraction process. In this patent, oximes used for palladium extraction are hydroxyoximes and derivatives thereof, but they are expensive for industrial application.

Y. Baba, K. Inoue, K. Yoshizuka, and T Furusawa (Industrial Engineering Chemistry Research, Volume 29, (19901), page 2111), dodecanal oxime, decanal oxime, octanal oxime for the extraction of palladium metals. And the use of unchelated oximes such as hexanol oxime. This method is disadvantageous in that the oxime used for extraction is expensive for industrial application.

According to the prior art, most metal recovery methods are applicable to homogeneous reaction mixtures and use chelating reagents to extract metal ions. Methods known in the art as for recovering metals from supported catalysts use inorganic acids and destroy the support structure without exception.

Purpose of the Invention

It is a primary object of the present invention to provide an improved process for recovering palladium from used catalysts that overcomes the disadvantages of the prior art.

It is another object of the present invention to recover palladium from used catalysts produced from hydrogenation plants used for the hydrogenation of nitro aromatic compounds.

Another object of the present invention is to recover 100% palladium having a purity of 99% or more.

Another object of the present invention is to recover carbon black as a value added product that can be recycled.

Summary of the Invention

It is an object of the present invention to provide an improved process for recovering 100% palladium having a purity of at least 99% from used catalysts. The used catalyst obtained in the hydrogenation plant is i) 0.1 to 0.2% Pd; Ii) 0.1 to 0.2% iron; Iii) 15-25% carbon; Vi) 60 to 80% moisture, and v) 3 to 6% tar of dinitrotoluene and used to recover expensive palladium as a palladium salt. The used catalyst is heat treated at about 500 ° C. to decompose the organic moiety, and then warmed in an inorganic acid for the required time to dissolve the palladium metal as the corresponding salt, and the carbon particles are separated by filtration. High purity solid palladium chloride was obtained by adjusting the pH of the filtrate. This product does not require further purification. Palladium recovered as a palladium salt can be used to load / fix onto a support material useful as a catalyst or catalyst support.

Therefore, the present invention

(Iii) thermally treating the finally separated used catalyst produced from the hydrogenation plant;

(Ii) cooling the used catalyst obtained in step (i) to room temperature in the range of 20-40 ° C. in air;

(Iii) warming the heat treated and cooled spent catalyst in an inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid;

(Iii) reacting the acid with the spent catalyst under continuous stirring;

(Iii) filtering the reaction mixture to separate the carbon particles from the liquid;

(Iii) precipitating palladium as a metal salt;

(Iii) providing a method for recovering palladium from used catalyst produced in a hydrogenation plant, comprising the step of drying a metal salt.

In one embodiment of the invention, the heat treatment of the used catalyst in step (i) is carried out for 4 to 6 hours at a temperature in the range from 350 to 450 ° C.

In another embodiment of the present invention, the palladium, iron, carbon, and moisture content in the used catalyst is 0.1 to 0.2, respectively; 0.1 to 0.2; 15 to 25%; And 60 to 80%.

In another embodiment of the invention, the heat treatment is carried out in an inert atmosphere or in air.

In another embodiment of the invention, the inert atmosphere is obtained using a gas selected from the group consisting of nitrogen, argon, and helium.

In another embodiment of the invention, the concentration of inorganic acid for warming is maintained in the range of 2 to 6 molarity.

In another embodiment of the invention, the temperature and time required for the acidic temperature needle are maintained in the range of 50 to 90 ° C. and 4 to 6 hours, respectively.

In another embodiment of the present invention, when the pH of the filtrate is in the range of 6 to 11, palladium is precipitated as a metal salt.

In another embodiment of the invention, the metal salts are dried in an air dried oven at a temperature in the range of 90 to 110 ° C.

In another embodiment of the invention, the recovery of palladium as metal salt is 100%.

In another embodiment of the invention, the carbon particles are recovered as by-products in the form of carbon black.

In another embodiment of the invention, the metal salt is palladium chloride.

Detailed description of the invention

The present invention

(Iii) heat treating the finally used used catalyst for 4 to 6 hours in the temperature range of 350 to 450 ° C;

(Ii) maintaining an inert atmosphere with a gas such as nitrogen, argon, helium, etc. during the heat treatment;

(Iii) cooling the used catalyst to room temperature (ie, 20-40 ° C.) in air;

(Iii) warming the calcined used catalyst in an inorganic acid selected from nitric acid, hydrochloric acid, or sulfuric acid in the range of 2 to 6 molar concentrations;

(Iii) reacting the acid with the used catalyst under continuous stirring for 4-6 hours at a temperature in the range of 50-90 ° C .;

(Iii) filtering the reaction mixture by known methods to separate carbon particles from the liquid;

(Iii) precipitating palladium as a metal salt in the range of pH 6-11;

(Iii) drying the metal salt in an air dried oven to a temperature range of 90 to 110 ° C. to provide an improved process for recovering palladium from used catalyst produced in the hydrogenation plant.

The catalyst produced in the hydrogenation plant comprises: i) Pd in the range of 0.1 to 0.2%; Ii) Fe in the range of 0.1 to 0.2%; Iii) carbon in the range of 15-25%; And v) tar in the range 60 to 80%, and v) 3 to 6% tar of dinitrotoluene, and can be used to recover the palladium metal.

The precisely separated used catalyst can be heat treated for 4 to 6 hours in the temperature range of 350 to 450 ° C. The heat treatment is preferably carried out in an inert atmosphere using a gas such as nitrogen, argon or helium. The calcined catalyst is preferably warmed in an inorganic acid such as nitric acid, hydrochloric acid, sulfuric acid or the like. The warming in the acid of the used catalyst is preferably carried out for 4 to 6 hours at a temperature in the range from 50 to 90 ° C. The concentration of acid used for warming may vary in the range of 2 to 6 molarity.

The pH of the filtrate can be varied in the range of 6 to 11 to precipitate the palladium as a metal salt such as palladium chloride.

Palladium is evaluated as a reddish brown complex, [PdI ₄ ] ^2-in an acidic aqueous solution. In an acid medium (hydrochloric acid, H ₂ SO ₄ ) containing excess iodide, palladium forms a reddish brown complex, [PdI ₄ ] ^2- . The molar absorption of the complex is 1.02 × 10 ⁻⁴ at λ _max = 410 nm (a = 0.096). Calibration curves are obtained by dissolving known amounts of palladium chloride and other reagents such as concentrated hydrochloric acid, ascorbic acid, and potassium iodide to produce a palladium iodide complex solution.

The volume / weight of the sample solution / solid containing less than 1 mg of Pd was accurately measured in a 100 mL bolometric flask. To this was added 10 mL of 6 N hydrochloric acid, 20 mL of potassium iodide 20% (w / v) solution, and 4 mL of ascorbic acid 1% (w / v) solution. Water was added to a 100 mL bolometric flask to fill the volume to 100 mL and the absorbance at 410 nm for water was measured.

The weight of palladium in the diluted solution can be obtained as follows:

Wt of Pd per 100 mL = (A / ε). (Mol.Wt of palladium)

A = absorbance at 410 nm of 100 mL solution

ε = extinction coefficient, 1.02ε ⁴ mol ^-1 cm ^-1 for [PdI ₄ ] ^2- species at 410 nm

Palladium was also spectroscopically evaluated using an ICP spectrometer. This is the most accurate way to evaluate metal ions at ppm / ppb levels. Calibration curves were obtained by dissolving known amounts of palladium chloride in hydrochloric acid and recording the intensity on an ICP spectrometer for palladium at 340.458 nm using a Perkin Elmer's Inductively Coupled Plasma Emission Spectrometer.

The process of the present invention thermally desorbs oligomerized nitro or amino organic compounds produced during the hydrogenation of nitro aromatic compounds and adsorbed onto active sites present on the surface of the catalyst and then relatively relatively in lower temperature air. Oxidation of carbon compounds having lower carbon numbers. The oxidation step, which is exothermic in nature, initiates the oxidation of the carbon support which causes the thermal chain reaction to oxidize the material which is entirely carbon present in the catalyst and is carried out without supplying additional heat. The calcined catalyst comprises an insoluble oxide of palladium, or other metal is dissolved by oxidation with an aqueous solution as a salt of the inorganic acid. The metal present in the aqueous solution is selectively precipitated by adjusting the pH of the solution.

Advances in the process of the present invention include: (i) removing the oligomerized organic compound in an inert atmosphere prior to oxidation of the carbon compound, (ii) oxidizing the carbon compound having a low carbon number compound at about 500 ° C. and oxidizing the carbon support. The use of the thermal energy produced to initiate, (i) the metal present in the calcined contents is dissolved by infiltration with an inorganic acid, and the metal salt is selectively precipitated by adjusting the pH of the solution.

The method of the present invention is advantageous in that it does not include incineration using very high temperatures to recover expensive metals. Due to the selective precipitation of the metal salts, the metal salts are recovered in very high purity. Such products do not require additional purification steps, solvent extraction techniques, and the use of expensive organic complexing ligands such as oximes, hydroxyoximes, derivatives thereof and the like for metal recovery.

The following examples are intended to further illustrate the invention and are not intended to limit the scope of the invention.

Example  One

715 g of a used catalyst containing 0.15% of palladium, 0.15% of iron, 5% of m-dinitrotoluene, 20% of carbon, and the rest of water were placed in an electric muffle and dried at 150 ° C. for 3 hours. The dried used catalyst containing Pd, Fe, and organic compounds was burned for 5 hours at elevated temperatures below 400 ° C. The burned product of the powder was obtained. The weight of ash containing all burned carbon and expensive metals was found to be 4.3 g, and the brown burned mixture thus obtained was incubated at 90 ° C. for 5 hours in 2M hydrochloric acid solution. It was cooled to ambient temperature and then filtered with a Buckner funnel. The pH of the filtrate containing palladium was raised to 6 and then the precipitate formed was filtered to remove impurities, especially iron and other metals. The precipitate was collected and then dried. The pH of the filtrate obtained at pH 6 was raised to 9.5, and the precipitate was collected and dried.

The precipitates obtained at pH 6 and pH 9.5 were analyzed for palladium content. 0.745 g of a precipitate was obtained at pH 6, which contained no palladium. At pH 9.5, 1.026 g of precipitate was collected, which contained 0.59 g of palladium as measured spectroscopically. The total palladium content adsorbed on carbon based on the initial palladium injected into the carbon was 0.605 g, indicating a 98% recovery by this method.

Example  2

566 g of the used catalyst was dried in an electric furnace at 150 ° C. for 3 hours and then calcined at 400 ° C. for 5 hours. The brown mixture thus obtained was incubated for 3 hours while maintaining the temperature of 80 ° C. with continuous stirring in 2M hydrochloric acid solution. The reaction mixture was filtered to separate ash and dissolved material. The pH of the filtrate thus obtained was initially raised to 6 and then the precipitate of iron chloride was removed by filtration. The pH of the second filtrate was raised to 9.5 and then the precipitate was collected and dried. As a result of spectroscopic measurement, 0.882 g of precipitate was determined to contain 0.65 g of palladium, indicating 100% recovery of palladium as palladium chloride.

Example  3

566 g of the used catalyst was dried in an electric furnace at 150 ° C. for 3 hours and then calcined at 400 ° C. for 3 hours. The brown mixture thus obtained was incubated for 3 hours while maintaining the temperature of 80 ° C. with continuous stirring in 2M hydrochloric acid solution. The reaction mixture was filtered to separate ash and dissolved material. The pH of the filtrate thus obtained was initially raised to 6 and then the precipitate of iron chloride was removed by filtration. The pH of the second filtrate was raised to 9.5 again, the precipitate was collected and dried, and the recovered PdCl ₂ was evaluated by gravimetric analysis using dimethylglyoxime as a complexing agent. 25 mg of the separated solid (solid at pH = 9.5) are dissolved in 25.0 mL (6M HCl), to which 20 mL of dimethylglyoxime solution (prepared in ethanol, 250 mg / 25 mL) is added and the mixture Was stirred and maintained for 1 hour. It was filtered in a pre-weighed G-3 crucible and then washed with cold and hot water, and the precipitate thus obtained was dried at 110 ° C. The weight of Pd (dmg) ₂ was 0.0476 g, which is equivalent to 25 mg of PdCl ₂ . From these results, both methods showed the same result and also indicate that the recovered PdCl ₂ is 100% pure.

Example  4

250 g of used catalyst was placed in an electric muffle and first dried at 150 ° C. for 3 hours. After nitrogen gas was introduced into the muffle at a rate of 200 Nl / hr, the residue was heated at a temperature of 400 ° C. over 2-4 hours to remove organic residues (tar, nitro aromatic compounds, and aromatic amines). The used catalyst thus obtained was incubated in 2500 mL of 3M hydrochloric acid solution for 8 hours. It was cooled to ambient temperature, then filtered through a Buckner funnel, washed with dilute hydrochloric acid and then dried at 100 ° C. in an oven. The filtrate raised the pH to about 6 and the formed precipitate was filtered to remove impurities, especially iron and other metals. The precipitate was collected and dried. Then, the pH of the filtrate was raised to 9 or more, the precipitate was collected and then dried.

The precipitate obtained at about pH 6 and the precipitate obtained at about pH 9.5 were analyzed for palladium content. At about pH 6, 0.2 g of a precipitate was obtained, which contained no palladium. Above pH 9, 1.1 g of precipitate was collected, and the precipitate contained 0.052 g of palladium as spectroscopically measured, indicating that the recovery by the method was 8%. The precipitate obtained was further purified to yield 0.087 g of 100% PdCl ₂ .

Example  5

200 g of used catalyst was placed in an electric muffle and first dried at 150 ° C. for 3 hours. After nitrogen gas was introduced into the muffle at a rate of 200 Nl / hr, the residue was heated at a temperature of 400 ° C. over 5 hours to remove organic residues (tar, nitro aromatic compounds, and aromatic amines). The used residue thus obtained was warmed in 2000 mL of 50% hydrochloric acid solution for 7 hours. It was cooled to ambient temperature, then filtered through a Buckner funnel, washed with 5M aqueous hydrochloric acid solution, and the carbon thus obtained was dried at 100 ° C. in an oven. The pH of the filtrate containing palladium was raised to about 6 and the precipitate formed was filtered to remove impurities, especially iron and other metals, if present. The precipitate was collected and dried. Then, the pH of the filtrate obtained at pH 6 was raised to 9.5, and the precipitate was collected and dried.

1.05 g of the precipitate collected at pH 9.5 contained 0.163 g of palladium as measured spectroscopically, indicating a 98% recovery by this method. The precipitate obtained was further purified to yield 0.16 g of 100% PdCl ₂ .

Claims (12)

(Iii) thermally treating the finally separated used catalyst produced from the hydrogenation plant; (Ii) cooling the used catalyst obtained in step (i) to room temperature in the range of 20-40 ° C. in air; (Iii) warming the heat treated and cooled spent catalyst in an inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid; (Iii) reacting the acid with the spent catalyst under continuous stirring; (Iii) filtering the reaction mixture to separate the carbon particles from the liquid; (Iii) precipitating palladium as a metal salt from the filtrate; (Iii) a method for recovering palladium from used catalyst produced in a hydrogenation plant, comprising drying the metal salt. The method of claim 1, wherein the heat treatment of the used catalyst in step (i) is carried out for 4 to 6 hours at a temperature in the range of 350 to 450 ℃. The method of claim 1, wherein the palladium, iron, carbon, and moisture content in the used catalyst is 0.1 to 0.2, respectively; 0.1 to 0.2; 15 to 25%; And 60 to 80%. The method of claim 1 wherein the heat treatment is carried out in an inert atmosphere or in air. The method of claim 4 wherein the inert atmosphere is obtained using a gas selected from the group consisting of nitrogen, argon, and helium. The method of claim 1, wherein the concentration of the inorganic acid for warming is maintained in the range of 2 to 6 molarity. The method of claim 1, wherein the temperature and time required for acidic warming are maintained in the range of 50-90 ° C. and 4-6 hours, respectively. The method of claim 1, wherein palladium is precipitated as a metal salt by maintaining the pH of the filtrate in the range of 6-11. The method of claim 1 wherein the metal salt is dried in an air dried oven at a temperature in the range of 90 to 110 ° C. The method of claim 1 wherein the recovery of palladium as a metal salt is 100%. The method of claim 1 wherein the carbon particles are recovered as by-products in the form of carbon black. The method of claim 1 wherein the metal salt is palladium chloride.