A method for recovering valuable metal elements from acrylonitrile catalysts

Abstract

This invention relates to a method for recovering valuable metal elements from acrylonitrile catalysts. It uses an environmentally friendly, low-volatility, and recyclable eutectic solvent as a leaching agent to dissolve metal oxides, replacing highly corrosive inorganic acids and alkalis that easily pollute the environment, thus achieving efficient recovery of valuable metal elements from acrylonitrile catalysts. The eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond acceptor is a quaternary ammonium salt compound, and the hydrogen bond donor is selected from C2-C8 hydroxycarboxylic acids, with a carboxyl group functionality of 1-2 and a hydroxyl group functionality of 1.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and in particular to a method for recovering valuable metal elements from acrylonitrile catalysts. Background Technology

[0002] Currently, acrylonitrile is mainly produced using the propylene ammoxidation process. In this process, most industrial catalysts are molybdenum-bismuth-based multi-metal oxides supported on silica, with multi-component catalysts based on the molybdenum-bismuth-iron-nickel system being the most mature and widely used. Acrylonitrile catalysts deactivate over long-term use due to factors such as carbon poisoning, element loss, and pore collapse, with a lifespan generally around 5 years. Directly treating deactivated spent catalysts as solid waste not only wastes a large amount of valuable metal resources but also causes serious heavy metal pollution. Therefore, it is necessary to recover and reuse the valuable metal elements from spent acrylonitrile catalysts.

[0003] Existing processes for recovering valuable metals from spent acrylonitrile catalysts typically involve high-temperature roasting (roasting temperature ≥250℃) with concentrated acid and / or alkali to leach these metals. This process is energy-intensive and produces significant pollution from the acid and / or alkali wastewater. For example, patent CN102912132A describes a method for recovering valuable metals from spent acrylonitrile catalysts. This method involves mixing spent acrylonitrile catalyst powder with solid sodium hydroxide, roasting the mixture at 250–350℃ for 2–5 hours, then leaching the roasted material with hot water at 75–95℃. Finally, a co-precipitation method is used to recover valuable metals such as molybdenum and bismuth from the spent acrylonitrile catalyst. Patent application CN 117305590 A discloses a method for recovering valuable elements from waste metal catalysts. This method involves a multi-step recovery process, including roasting at 400℃–800℃ followed by alkali leaching, acid leaching, ion exchange, evaporation crystallization, extraction, and back-extraction. This process boasts high recovery rates, high selectivity, and high product purity for Bi, Ni, and Mg metals. However, it requires excessive amounts of acid, alkali, and extractant, and also generates large quantities of saline wastewater. All of these hydrometallurgical processes suffer from high energy consumption, high pollution, and high cost.

[0004] Deep eutectic solvents (DESs) are eutectic mixtures with a hydrogen bond network structure formed by mixing hydrogen bond acceptors and hydrogen bond donors in a certain stoichiometric ratio. They are commonly used as reaction media or electrolytes, and can also be used for gas absorption or liquid-phase extraction. Due to their superior properties such as environmental friendliness, biodegradability, low volatility, and recyclability, they are widely used. Eutectic solvents are highly suitable alternatives to traditional inorganic acids and bases as solvents for dissolving metal oxides. Currently, eutectic solvents are increasingly used in the recycling of valuable metals such as lithium and manganese in lithium-ion battery electrode materials. In this field, the binding strength between metal elements and electrode materials is low, and their metal compounds have high solubility in acidic solvents, making leaching relatively easy. However, for complex spent acrylonitrile catalysts, the metal components are tightly bound to the silica support, making leaching difficult. Furthermore, multi-metal oxides can form solid solutions or composite oxides (such as bismuth molybdate, nickel molybdate, and nickel ferrite) at high temperatures or during synthesis. Ordinary acid leaching methods are unlikely to destroy this stable crystal lattice; there are no reports of efficient eutectic solvents being used to recover valuable metal elements from spent acrylonitrile catalysts. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and shortcomings of existing processes for recovering valuable metal elements from spent acrylonitrile catalysts, and to provide a method for recovering valuable metal elements from acrylonitrile catalysts. This method uses an environmentally friendly, low-volatility, and recyclable eutectic solvent as a leaching agent to dissolve metal oxides, replacing highly corrosive inorganic acids and alkalis that easily pollute the environment, thereby achieving efficient recovery of valuable metal elements from acrylonitrile catalysts.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a method for recovering valuable metal elements from acrylonitrile catalysts, comprising the following steps: S1, the acrylonitrile catalyst is immersed in the eutectic solvent and heated at 80-160°C for leaching treatment. After solid-liquid separation, the leachate is obtained. The acrylonitrile catalyst is a molybdenum-bismuth-based multi-metal oxide supported on a silica support. S2, the valuable metal elements in the leachate are precipitated and recovered; The eutectic solvent is a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:(1-3); The hydrogen bond acceptor is a quaternary ammonium salt compound, and its chemical structural formula is shown below: (Formula I) In the formula, R1, R2, R3 and R4 are independently selected from C1-C4 alkyl groups; R5 is selected from H, carboxyl, and hydroxyl groups; X - Selected from bromide ions, hydrogen sulfate ions, and dihydrogen phosphate ions; The hydrogen bond donor is selected from C2-C8 hydroxycarboxylic acids, and the functionality of the carboxyl group is 1-2 and the functionality of the hydroxyl group is 1.

[0007] In some embodiments, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(1.5-2.5).

[0008] In some embodiments, the hydrogen bond acceptor is at least one of choline bromide, choline bisulfate, choline dihydrogen phosphate, tetraethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium bisulfate, and betaine bisulfate.

[0009] In some embodiments, the hydrogen bond donor is at least one of glyceric acid, glycolic acid, 3-hydroxypropionic acid, and 2-hydroxyadipic acid.

[0010] In some embodiments, the molybdenum-bismuth-based multi-metal oxide is a molybdenum-bismuth-iron-nickel multi-metal oxide.

[0011] Optionally, the acrylonitrile catalyst has the following metal element composition by mass fraction: 15-25% molybdenum, 3-10% nickel, 1-4% bismuth, 1-4% iron, with the balance being silicon dioxide and unavoidable impurities.

[0012] In some embodiments, the valuable metal element is at least one of molybdenum, bismuth, or nickel.

[0013] In some embodiments, in step S1, the leaching temperature of the heated leaching treatment is 110~150℃, and the leaching time is ≥1 h.

[0014] In some embodiments, the leaching temperature is 110~130°C; more preferably, the leaching temperature is 115~125°C.

[0015] Preferably, the leaching time is ≥10 h, more preferably 10-24 h.

[0016] In some embodiments, in step S1, the solid-liquid ratio of the acrylonitrile catalyst and the eutectic solvent is 1~100 g / L, preferably 15~75 g / L.

[0017] In some embodiments, in step S2, the precipitation recovery process is a coprecipitation method and / or an electrodeposition method.

[0018] The co-precipitation method of this invention involves adding a precipitant to the leachate in stages and adjusting the pH of the solution, followed by precipitation and filtration separation, so that bismuth, molybdenum, and nickel form insoluble precipitates respectively, thereby achieving the separation and recovery of bismuth, nickel, and molybdenum. The electrodeposition method utilizes the significant differences in the standard reduction potentials of molybdenum, bismuth, and nickel, and achieves stepwise recovery through controlled potential electrolysis.

[0019] Specifically, when co-precipitation is used for precipitation recovery in step S2, it includes: (1) Add ammonia to the leachate to adjust the pH to 2-4, so that the bismuth salt precipitates, and then filter to recover the bismuth; (2) Add oxalic acid solution to the filtrate obtained in step (1) to adjust the pH to between 1 and 2, so that nickel salt precipitates, and then filter to recover nickel; (3) Add an excess of ammonium sulfide solution to the filtrate obtained in step (2) to precipitate molybdenum salt, and then filter to recover molybdenum.

[0020] The leaching agent after recovering molybdenum, bismuth, and nickel is recycled after removing impurity ammonium ions and replenishing lost components through a hydrogen-type cation exchange resin.

[0021] Specifically, when step S2 uses electrodeposition for precipitation recovery, it includes: An electrolysis system is constructed using leachate as electrolyte, stainless steel sheet as cathode material, and inert electrode as anode material.

[0022] The cathode potential was controlled between -0.1 V and -0.3 V (vs. SCE), and the mixture was gently stirred while monitoring the change in current over time. When the current dropped to a stable value, a bismuth metal coating was obtained on the cathode. By controlling the cathode potential between -0.8 V and -1.0 V (vs. SCE), a metallic nickel plating layer is obtained on the cathode; By controlling the cathode potential to be less than -1.2 V (vs. SCE), a molybdenum coating is obtained on the cathode.

[0023] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for recovering valuable metal elements from acrylonitrile catalysts. It uses an environmentally friendly, low-volatility, and recyclable eutectic solvent as a leaching agent to dissolve metal oxides, replacing highly corrosive inorganic acids and alkalis that easily pollute the environment, thereby achieving efficient recovery of valuable metal elements from acrylonitrile catalysts. Attached Figure Description

[0024] Figure 1 These are comparative images of the catalyst before and after leaching with the eutectic solvent in Example 1 of this invention. The left image is before leaching, and the right image is after leaching. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way.

[0026] Example 1 A method for recovering valuable metal elements from acrylonitrile catalysts includes the following steps: S1, Take the waste acrylonitrile catalyst and mechanically crush it to obtain catalyst powder with an average particle size of 1~10 μm; Then, 10 mL of a eutectic solvent was taken, and the catalyst powder was added to the eutectic solvent at a solid-liquid ratio of 15 g / L for leaching treatment. The leaching temperature was 120℃, and the leaching time was 20 h. After centrifugation, a leachate rich in the target metal element was obtained. The eutectic solvent was a choline bisulfate-glyceric acid mixture with a molar ratio of 1:2. The results are as follows: Figure 1 As shown.

[0027] The spent acrylonitrile catalyst is a molybdenum-bismuth-iron-nickel multi-metal oxide supported on a silica carrier. By mass fraction, the metal element composition of the spent acrylonitrile catalyst is: molybdenum 23%, nickel 8%, bismuth 3%, iron 3%, with the remainder being silica and unavoidable impurities. The testing methods are inductively coupled plasma atomic emission spectrometry (ICP-OES) and X-ray fluorescence spectrometry (XRF).

[0028] S2, valuable metal elements in the leachate are precipitated and recovered by co-precipitation method; The co-precipitation method is specifically as follows: (1) Add ammonia to the leachate to adjust the pH to 3, so that the bismuth salt precipitates and the bismuth element is recovered by filtration; (2) Add oxalic acid solution to the filtrate obtained in step (1) to adjust the pH value to 1.5, so that the nickel salt precipitates and the nickel element is recovered by filtration; (3) Add an excess of ammonium sulfide solution to the filtrate obtained in step (2) to precipitate molybdenum salt and then filter to recover molybdenum.

[0029] After recovering molybdenum, bismuth, and nickel, the leaching agent is regenerated by removing impurity ammonium ions through a hydrogen-type cation exchange resin, replenishing the lost components, and then recycled back to step S2.

[0030] Example 2 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 1 in that: in step S2 of this example, the solid-liquid ratio of the catalyst powder and the eutectic solvent is 40 g / L.

[0031] Example 3 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 1 in that: in step S2 of this example, the solid-liquid ratio of the catalyst powder and the eutectic solvent is 75 g / L.

[0032] Example 4 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 1 in that the leaching temperature in step S2 of this example is 90°C.

[0033] Example 5 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 1 in that the leaching temperature in step S2 of this example is 150°C.

[0034] Example 6 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 1 in that the leaching time in step S2 of this example is 24 hours.

[0035] Example 7 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 6 in that: in step S2 of this example, the valuable metal elements in the leachate are recovered by precipitation using an electrodeposition method.

[0036] The electrodeposition method specifically involves using the leachate as the electrolyte, stainless steel sheets as the cathode material, and an inert electrode as the anode material to electrolytically recover the metal elements in the leachate.

[0037] The cathode potential is controlled between -0.1 V and -0.3 V (vs. SCE), with gentle stirring to ensure mass transfer and prevent concentration polarization. The current is monitored over time; when the current drops to a very small, stable value, it indicates that bismuth has been largely deposited, resulting in a bismuth plating on the cathode. This plating is then scraped off, cleaned, and dried for recovery. Similarly, the cathode potential is controlled between -0.8 V and -1.0 V (vs. SCE), and less than -1.2 V (vs. SCE) to deposit and recover nickel and molybdenum, respectively. The leaching agent after recovering molybdenum, bismuth, and nickel is recycled after replenishing the lost components.

[0038] Example 8 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 7 in that: in step S2 of this example, the valuable metal elements in the leachate are recovered by a combination of electrodeposition and co-precipitation.

[0039] The combined treatment of electrodeposition and coprecipitation methods is as follows: Using the leachate as the electrolyte, copper sheet as the cathode material, and graphite electrode as the anode material, bismuth and nickel in the leachate are electrolytically recovered by electrodeposition. Bismuth is recovered by deposition when the cathode potential is controlled between -0.1 V and -0.3 V (vs. SCE), and nickel is recovered by deposition when the cathode potential is controlled between -0.8 V and -1.0 V (vs. SCE).

[0040] Ammonium sulfide solution is added to the electrolyzed solution to precipitate molybdenum salt, and molybdenum is recovered by filtration. The leaching agent after recovering molybdenum, bismuth, and nickel is recycled after removing impurity ammonium ions and replenishing lost components through a hydrogen-form cation exchange resin.

[0041] Examples 9-14 This embodiment provides a series of methods for recovering valuable metal elements from acrylonitrile catalysts. The difference from Example 8 is that the composition of the eutectic solvent in this embodiment is shown in Table 1.

[0042] Table 1. Components of eutectic solvents

[0043] Comparative Example 1 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent of this comparative example is 1:4.

[0044] Comparative Example 2 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent of this comparative example is 1:0.5.

[0045] Comparative Example 3 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that the leaching temperature in this comparative example is 60 °C.

[0046] Comparative Example 4 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that the leaching temperature in this comparative example is 180 °C.

[0047] Comparative Example 5 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that the eutectic solvent in this comparative example is choline chloride-urea in a molar ratio of 1:2.

[0048] Comparative Example 6 A method for recovering valuable metal elements from an acrylonitrile catalyst, which differs from Example 9 in that: the hydrogen bond acceptor in this comparative example is choline chloride, and the hydrogen bond donor is citric acid.

[0049] Performance testing The acrylonitrile catalyst was treated using the methods described in the above examples and comparative examples, and the metal components of the leachate during the treatment process were determined.

[0050] 1. The concentrations of molybdenum, bismuth, and nickel ions in the leachate were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The leaching rate was calculated as (metal concentration in the leachate × volume of the leachate) / mass of metal in the catalyst before leaching.

[0051] The mass percentage of metal M in the catalyst before leaching was determined by inductively coupled plasma atomic emission spectrometry (ICP-OES) and X-ray fluorescence spectrometry (XRF).

[0052] Table 2

[0053] As shown in Table 2, the recovery method of the present invention can efficiently recover valuable metal elements from acrylonitrile catalysts, and the leaching agent used is an environmentally friendly, low-volatility, recyclable eutectic solvent; the leaching solution of the present invention has a Mo leaching rate ≥92.1%, a Bi leaching rate ≥85.2%, and a Ni leaching rate ≥80.5%.

[0054] Compared to Example 8, in Comparative Examples 1-2, the leaching rates of Mo, Bi, and Ni were lower when the molar ratio of hydrogen bond acceptors to hydrogen bond donors in the eutectic solvent was too small or too large.

[0055] In Comparative Examples 3-4, when the leaching temperature was too low or too high, the leaching rates of Mo, Bi, and Ni decreased.

[0056] In Comparative Example 5, when the eutectic solvent was choline chloride-urea, the leaching rate of Bi and Ni elements was extremely low.

[0057] In Comparative Example 6, when choline chloride-citric acid was used as the eutectic solvent, the leaching effect on sparingly soluble metal ions such as Bi and Ni was poor.

[0058] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering valuable metal elements from acrylonitrile catalysts, characterized in that, Includes the following steps: S1, the acrylonitrile catalyst is immersed in a eutectic solvent and heated at 80-160°C for leaching treatment. After solid-liquid separation, the leachate is obtained. The acrylonitrile catalyst is a molybdenum-bismuth-based multi-metal oxide supported on a silica support. S2, the valuable metal elements in the leachate are precipitated and recovered; The eutectic solvent is a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:(1-3); The hydrogen bond acceptor is a quaternary ammonium salt compound, and its chemical structural formula is shown below: (Formula I) In the formula, R1, R2, R3 and R4 are independently selected from C1-C4 alkyl groups; R5 is selected from H, carboxyl, and hydroxyl groups; X - Selected from bromide ions, hydrogen sulfate ions, and dihydrogen phosphate ions; The hydrogen bond donor is selected from C2-C8 hydroxycarboxylic acids, and the functionality of the carboxyl group is 1-2 and the functionality of the hydroxyl group is 1.

2. The method for recovering valuable metal elements from acrylonitrile catalyst according to claim 1, characterized in that, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:(1.5-2.5).

3. The method for recovering valuable metal elements from acrylonitrile catalyst according to claim 1, characterized in that, The hydrogen bond acceptor is at least one of choline bromide, choline hydrogen sulfate, choline dihydrogen phosphate, tetraethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium hydrogen sulfate, and betaine hydrogen sulfate.

4. The method for recovering valuable metal elements from acrylonitrile catalyst according to claim 1, characterized in that, The hydrogen bond donor is at least one of glyceric acid, glycolic acid, 3-hydroxypropionic acid, and 2-hydroxyadipic acid.

5. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 1, characterized in that, The molybdenum-bismuth-based multi-metal oxide is a molybdenum-bismuth-iron-nickel multi-metal oxide.

6. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 1, characterized in that, The valuable metal element is at least one of molybdenum, bismuth, or nickel.

7. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 1, characterized in that, In step S1, the leaching temperature of the heating leaching treatment is 110~150℃, and the leaching time is ≥1h.

8. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 1, characterized in that, In step S1, the solid-liquid ratio of the acrylonitrile catalyst and the eutectic solvent is 1~100 g / L, preferably 15~75 g / L.

9. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 1, characterized in that, In step S2, the precipitation recovery treatment is a co-precipitation method and / or an electrodeposition method.

10. The method for recovering valuable metal elements from an acrylonitrile catalyst according to claim 9, characterized in that, The co-precipitation method is as follows: a precipitant is added to the leachate and the pH of the solution is adjusted to 2-4 to separate bismuth salts; the pH of the solution is adjusted to 1-2 to separate nickel salts; and ammonium sulfide is added to separate molybdenum salts, thereby achieving the separation and recovery of bismuth, nickel, and molybdenum. The electrodeposition method is as follows: in an electrolytic system, the cathode potential is controlled between -0.1V and -0.3V to obtain a bismuth metal coating on the cathode; the cathode potential is controlled between -0.8V and -1.0V to obtain a nickel metal coating on the cathode; and the cathode potential is controlled to be less than -1.2V to obtain a molybdenum metal coating on the cathode.

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