A method for preparing chromium acetate from chromium hydroxide

Abstract

The application discloses a method for preparing chromium acetate from chromium hydroxide, which comprises the following steps: mixing chromium hydroxide wet filter cake with sulfonic acid group-chromium oxide composite mesoporous silica balls according to a proportion, adding glacial acetic acid, and then carrying out reaction, heating, separation, concentration crystallization and drying to obtain high-purity chromium acetate. The sulfonic acid group-chromium oxide composite mesoporous silica ball modified material is prepared by the following steps: first, synthesizing a mesoporous silica ball base by using a template agent, then loading chromium oxide and grafting a mercapto group by silanization, and finally oxidizing to obtain a sulfonic acid group functionalized material. The material can selectively adsorb impurity ions in situ in the reaction, so that the traditional complicated purification steps are simplified. The application has the advantages of simple operation, high product purity, and good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional materials technology, specifically to a method for preparing chromium acetate from chromium hydroxide. Background Technology

[0002] Chromium acetate, as an important chemical raw material and catalyst precursor, plays a crucial role in many industrial fields. Its conventional preparation route is usually based on the neutralization reaction of chromium hydroxide with acetic acid. However, this seemingly straightforward process faces significant purity challenges in actual industrial production. Industrial-grade chromium hydroxide raw materials often contain impurities such as sulfate, chloride, sodium, and various metal cations. If impurity-containing raw materials are used directly in the reaction, these impurity ions will inevitably enter the final product, severely affecting the quality of chromium acetate and its performance in downstream high-end applications, such as leading to reduced catalyst activity or substandard material performance. Therefore, how to economically and efficiently solve the impurity problem from the raw material end is a core issue in improving the quality of chromium acetate products.

[0003] To address the aforementioned purity challenges, existing technologies typically require complex pretreatment of chromium hydroxide feedstock. Common purification methods include alkaline washing to remove anionic impurities, but this introduces new sodium ion contamination, necessitating repeated washing with large amounts of deionized water—a lengthy process that generates significant wastewater. Another approach is to use quantitative acid displacement washing, which, while targeted, requires extremely stringent acidity control, easily leading to localized dissolution and loss of chromium hydroxide, and also suffers from the inefficiency caused by multi-stage washing. These traditional purification processes generally suffer from inherent drawbacks such as cumbersome steps, time-consuming and energy-intensive processes, reduced feedstock yield, and heavy wastewater treatment burdens. Developing a production process that simplifies pretreatment and achieves efficient in-situ purification is urgently needed to reduce production costs and enhance product competitiveness.

[0004] In recent years, advancements in materials science have provided new solutions for adsorption separation technologies, and the functional design of porous materials to selectively capture specific ions has become a research hotspot. However, the innovative application of this concept to the reaction system for preparing chromium acetate from chromium hydroxide, and the introduction of a composite modified material that can withstand strong acid environments and selectively adsorb impurities, has not yet been reported. In particular, the design of a composite material integrating a rigid framework, selective adsorption sites, and a structural stabilizer, enabling simultaneous deep removal of impurities during the acetic acid dissolution of chromium hydroxide, transforms the traditional multi-step process of "purifying raw materials first, then reacting and preparing" into a simple one-step process of "simultaneous reaction and purification," representing a significant technological breakthrough. This invention, based on this background, aims to provide a novel material and process solution to completely overcome the shortcomings of traditional methods. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing chromium acetate from chromium hydroxide, which solves the technical problems of existing traditional methods for preparing chromium acetate from impure chromium hydroxide, which requires cumbersome multi-step pretreatment of raw materials, resulting in long process flow, large raw material loss, large amount of wastewater, and difficulty in guaranteeing the purity of the final product.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing chromium acetate from chromium hydroxide includes the following steps:

[0008] S1, add chromium hydroxide wet filter cake and sulfonic acid-chromium oxide composite mesoporous silica balls into the reactor, and add glacial acetic acid under stirring to obtain a mixture;

[0009] S2, Heat the mixture to 60-80℃ and stir continuously to obtain the reaction mixture;

[0010] S3, the reaction mixture is cooled and centrifuged to obtain sulfonic acid-chromium oxide composite mesoporous silica spheres loaded with impurities and a chromium acetate solution;

[0011] S4. The chromium acetate solution obtained in step S3 is concentrated under reduced pressure at 70-90℃, then transferred to a crystallizer and allowed to stand at 0-10℃ for crystallization. After filtration, crystals are obtained, washed with anhydrous ethanol, and dried under vacuum at 40-50℃.

[0012] In this invention, during the preparation of chromium acetate, the sulfonic acid-chromium oxide composite mesoporous silica spheres perform a dual function: on the one hand, the densely distributed sulfonic acid groups on their surface act as the sole ion exchange active centers, efficiently capturing free high-valence impurity cations such as sodium, iron, and aluminum under specific acetic acid concentrations and acidic pH conditions in the reaction system through strong electrostatic interactions; on the other hand, the chromium trioxide nanoparticles generated in situ within the pores do not directly participate in adsorption but serve as structural anchoring points, stabilizing the spatial distribution of sulfonic acid groups and enhancing the thermochemical stability of the mesoporous framework, ensuring the material remains intact during reaction and regeneration cycles. Simultaneously, chromium hydroxide gradually dissolves under excess glacial acetic acid and moderate heating conditions, and the resulting trivalent chromium ions rapidly self-assemble in the acetic acid medium into low-charge polynuclear cluster complexes, such as trinuclear oxygen-bridged chromium acetate cations. Because the overall charge density of these complexes is much lower than that of the free trivalent impurity ions, the electrostatic attraction between them and the sulfonic acid groups is significantly weakened, thus they are almost not adsorbed. This adsorption selectivity based on the difference in ion morphology allows the target product to remain in solution, while impurities are efficiently retained on the solid-phase material. After the reaction, solid-liquid separation can be achieved by simple centrifugation. The resulting pure chromium acetate solution is concentrated, crystallized at low temperature, and dried to finally obtain high-purity blue-purple chromium acetate hexahydrate crystals. The entire process couples the reaction and purification without the need for additional precipitants or extractants, demonstrating the technological advantages of being green, efficient, and atom-economical.

[0013] According to a preferred embodiment of the present invention, in step S1, the mass ratio of chromium hydroxide wet filter cake to sulfonic acid-chromium oxide composite mesoporous silica balls is 100:1-5.

[0014] According to a preferred embodiment of the present invention, in step S2, the reaction is continuously stirred for 2-4 hours.

[0015] According to a preferred embodiment of the present invention, in step S3, the reaction mixture is cooled to 24-26°C.

[0016] According to a preferred embodiment of the present invention, in step S4, the time for static crystallization at 0-10°C is 6-12 hours.

[0017] According to a preferred embodiment of the present invention, the preparation steps of the sulfonic acid-chromium oxide composite mesoporous silica spheres include:

[0018] A1, by weight, adds 0.15-0.25 parts of hexadecyltrimethylammonium bromide to a mixture of 20-30 parts of anhydrous ethanol, 3-5 parts of deionized water, and 0.5-0.8 parts of concentrated ammonia, and stirs at 24-26°C; then adds a mixture of 1.0-1.5 parts of tetraethyl orthosilicate and 5-10 parts of anhydrous ethanol, and continues stirring at 28-32°C. The solid is collected by centrifugation, washed and dried, and then calcined at 545-555°C in air to obtain a mesoporous silica sphere substrate.

[0019] A2, the mesoporous silica sphere substrate is immersed in 8-12 parts of chromium nitrate aqueous solution, filtered and dried, and then calcined at 395-405℃ under nitrogen atmosphere to obtain chromium oxide supported mesoporous silica spheres.

[0020] A3. Chromium oxide-supported mesoporous silica spheres were dispersed in anhydrous toluene, and 0.8-1.2 parts of 3-(mercaptopropyl)trimethoxysilane were added. The mixture was refluxed at 108-112℃ under nitrogen protection. After the reaction was completed, the mixture was filtered, washed, and dried to obtain mercapto-functionalized chromium oxide-mesoporous silica spheres.

[0021] A4. The mercapto-functionalized chromium oxide-mesoporous silica spheres were dispersed in a mixed oxidizing solution composed of deionized water and hydrogen peroxide, and stirred in a water bath at 48-52℃. After the reaction was completed, the mixture was filtered to obtain a solid product. The solid product was washed with deionized water and dried at 78-82℃.

[0022] In this invention, the construction of sulfonic acid-chromium oxide composite mesoporous silica spheres follows an "inorganic-then-organic" synthesis strategy to ensure the structural integrity and chemical stability of the functional components. First, using hexadecyltrimethylammonium bromide as a template agent, silica microspheres with a highly ordered mesoporous structure are formed through controlled hydrolysis and condensation of tetraethyl orthosilicate in an alkaline ethanol-water system. Subsequently, the template agent is removed by high-temperature calcination, yielding a high specific surface area and thermally stable mesoporous silica sphere substrate. Based on this, the silica spheres are impregnated with a chromium nitrate solution and calcined at medium temperature in an inert nitrogen atmosphere, causing the chromium precursor to be converted in situ into amorphous chromium trioxide nanoparticles, which are firmly anchored to the inner walls of the pores, forming chromium oxide-supported mesoporous silica spheres that possess both high dispersibility and skeletal reinforcement. The key to this step is avoiding the use of an air atmosphere to prevent trivalent chromium from being oxidized to toxic and soluble hexavalent chromium, thereby ensuring the environmental safety and structural stability of the material. Subsequently, in anhydrous toluene system, the material surface was covalently modified using a mercaptosilane coupling agent to introduce mercapto functional groups. Finally, under weakly acidic conditions, hydrogen peroxide was used to quantitatively oxidize the mercapto groups to strongly acidic sulfonic acid groups. The entire oxidation process did not require the addition of any strong acid, relying solely on the weakly acidic environment of the hydrogen peroxide aqueous solution itself, effectively preventing the acid dissolution loss of the already formed chromium trioxide structure. Ultimately, a composite mesoporous adsorbent material synergistically integrating sulfonic acid groups and chromium oxide was obtained.

[0023] According to a preferred embodiment of the present invention, in step A1, the calcination time at 545-555°C is 6-8 hours.

[0024] According to a preferred embodiment of the present invention, in step A2, the calcination time at 395-405°C is 3-6 hours; the concentration of the chromium nitrate aqueous solution is 0.15-0.25 mol / L.

[0025] According to a preferred embodiment of the present invention, in step A3, the reflux reaction at 108-112°C is carried out for 24-30 hours.

[0026] According to a preferred embodiment of the present invention, in step A4, the stirring reaction in a water bath at 48-52°C is carried out for 12-14 hours.

[0027] The beneficial effects of this invention are as follows:

[0028] The technical solution provided by this invention, by introducing a composite modified material and optimizing the process route, produces a series of significant and synergistic technical effects in the preparation of chromium acetate, fundamentally overcoming many bottlenecks of traditional production methods.

[0029] First, the core effect of this invention lies in achieving extreme simplification of the process flow and a revolutionary improvement in production efficiency. Specially formulated sulfonic acid-based chromium oxide composite mesoporous silica spheres are directly blended with chromium hydroxide raw materials and glacial acetic acid, simultaneously completing the generation of chromium acetate and the in-situ deep purification of the reaction system within a single reactor. This integrated "one-pot" process combines previously discrete multi-unit operations into four continuous steps, significantly shortening the production cycle and reducing equipment footprint and investment costs. Simultaneously, by avoiding the loss of chromium hydroxide colloids due to repeated washing, the effective conversion rate of raw materials is significantly improved, enhancing production economics from the source.

[0030] Secondly, this invention achieves product purity and quality stability that are difficult to attain using traditional methods. The key lies in the unique dual-functional design of the composite mesoporous silica spheres: the sulfonic acid groups grafted onto the surface act as strong acidic ion exchange sites, efficiently capturing monovalent cation impurities such as sodium and potassium; while the embedded chromium oxide nanoparticles not only act as structural stabilizers, but their surface properties also exhibit a specific affinity for trivalent metal impurity ions such as iron and aluminum in acidic environments. More importantly, in the concentrated acetic acid reaction system, the target product chromium ions mainly exist as polynuclear clusters with very low charge density, and their interaction with the modified material is far weaker than that of impurity ions in a free hydrated state. This highly selective adsorption mechanism, based on the difference between the ion's existing form and the material's surface properties, enables precise removal of impurity ions, thereby ensuring that the resulting chromium acetate solution has extremely high purity. After crystallization, the content of key impurities in the product is reduced to the parts per million level, meeting the stringent standards of high-end applications.

[0031] Finally, this invention demonstrates excellent comprehensive benefits and green environmental characteristics, possessing strong potential for industrial-scale promotion. The entire process operates under mild conditions, with moderate main reaction temperatures, ensuring safe and controllable operation. All chemical raw materials used, from basic chromium hydroxide and glacial acetic acid to silicon sources, template agents, chromium salts, and silane coupling agents required for modified material preparation, are commercially available bulk or conventional fine chemicals, ensuring a stable supply chain and eliminating raw material acquisition barriers. The modified material itself can be reused within a certain period through simple acid washing regeneration, reducing unit consumption costs and solid waste generation. Furthermore, this process completely eliminates the large amounts of chromium-containing wastewater generated by traditional multi-step water washing, solving the environmental problem of heavy metal wastewater treatment at its source, demonstrating outstanding environmental friendliness. In summary, this invention, through material innovation and process reform, constitutes a complete technological advantage loop in improving product quality, reducing production costs, and achieving clean production, providing a novel solution for the high-quality, high-efficiency industrial production of chromium acetate. Detailed Implementation

[0032] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0033] Example 1

[0034] Preparation of sulfonic acid-chromium oxide composite mesoporous silica spheres:

[0035] A1. Preparation of mesoporous silica sphere substrate: In a 500 mL three-necked round-bottom flask, 25.0 g of anhydrous ethanol, 4.0 g of deionized water, 0.6 g of concentrated ammonia (28% by mass), and 0.2 g of hexadecyltrimethylammonium bromide were added sequentially. The flask was placed in a 25 °C constant temperature water bath and mechanically stirred at 300 rpm for 20 min. Subsequently, 1.2 g of tetraethyl orthosilicate was mixed with 8.0 g of anhydrous ethanol and added dropwise to the three-necked flask at a rate of approximately 0.5 mL / min using a constant pressure dropping funnel. After the addition was complete, the water bath temperature was adjusted to 30 °C and maintained at this temperature while continuously stirring for 24 h. After the reaction was completed, the resulting white suspension was centrifuged at 8000 rpm for 5 min, and the supernatant was discarded. The collected solid was washed three times each with 40 mL of deionized water and 40 mL of anhydrous ethanol by centrifugation. The solid was then dried in an 80 °C forced-air drying oven for 12 h. Subsequently, the dried powder was placed in an alumina ceramic boat in a tube furnace, and the temperature was programmed to rise to 550°C at a rate of 2°C / min under static air atmosphere, and then calcined at this temperature for 7 hours. After calcination, the powder was allowed to cool naturally to room temperature in the furnace to obtain a mesoporous silica sphere substrate.

[0036] A2, Chromium Oxide Nanoparticle Loading: Accurately weigh 3.00 g of the mesoporous silica sphere substrate prepared in step A1 above and place it in a 100 mL beaker. Measure 10.0 g of a 0.20 mol / L chromium nitrate aqueous solution and pour it into the beaker, ensuring complete immersion of the solid. Place the beaker in an ultrasonic cleaner and sonicate at 40 kHz for 30 min, then allow it to stand at 25 °C for 12 h. After immersion, filter using a Buchner funnel and 0.45 μm pore size filter paper. Rinse the filter cake twice with 10 mL of deionized water and then transfer it to a 100 °C oven to dry for 6 h. Grind the dried solid, place it in a porcelain boat, and center it in a tube furnace. Purge the furnace with 99.999% high-purity nitrogen at a flow rate of 100 mL / min for 30 min, then begin heating. Increase the temperature to 400 °C at a rate of 5 °C / min and calcine at this temperature under a continuously flowing nitrogen atmosphere for 4 h. After calcination, the chromium oxide-supported mesoporous silica spheres were cooled to below 50°C under nitrogen protection and removed.

[0037] A3, Thiol-functionalization: Accurately weigh 5.00 g of the chromium oxide-supported mesoporous silica spheres prepared in step A2 above and place them in a 250 mL three-necked flask equipped with a reflux condenser. Add 20.0 g of anhydrous toluene to the flask and sonicate for 10 min. Then, accurately add 1.00 g of 3-(mercaptopropyl)trimethoxysilane using a pipette. Set up the apparatus, turn on the cooling water, and continuously purge the system with nitrogen as a protective gas. Start the mechanical stirrer at 400 rpm. Heat the reaction oil bath to 110 °C and maintain the solution under gentle reflux for 26 h. After the reaction is complete, stop heating and allow it to cool naturally to room temperature. Filter the reaction mixture, and wash the resulting solid three times each with 20 mL of toluene, 20 mL of acetone, and 20 mL of anhydrous ethanol. Transfer the washed solid to a vacuum drying oven and dry at 60 °C for 10 h to obtain thiol-functionalized chromium oxide-mesoporous silica spheres.

[0038] A4, Oxidation Preparation of Sulfonic Acid Groups: Accurately weigh 4.00 g of the mercapto-functionalized chromium oxide-mesoporous silica spheres prepared in step A3 above and place them in a 250 mL single-necked flask. Add 16.0 g of deionized water and 4.00 g of a 30% (w / w) hydrogen peroxide aqueous solution sequentially. Place the flask in a 50 °C constant temperature water bath and magnetically stir at 500 rpm for 13 h. After the reaction is complete, filter the mixture and wash the filter cake with approximately 200 mL of deionized water until the filtrate is neutral as determined by pH paper. Spread the filter cake evenly on a watch glass and dry it in an 80 °C forced-air drying oven for 8 h to finally obtain sulfonic acid-chromium oxide composite mesoporous silica sphere powder.

[0039] Method for preparing chromium acetate from chromium hydroxide:

[0040] S1, Mixing and Acidification: In a dry 250mL three-necked flask, add 100.0g of wet chromium hydroxide filter cake (40% moisture content) and 3.00g of the sulfonic acid-chromium oxide composite mesoporous silica spheres prepared above. Install a mechanical stirrer and mix at 300rpm for 5min. Then, using a constant pressure dropping funnel, slowly add 290.0g of glacial acetic acid (purity ≥99.5%) to the flask, controlling the dropping rate to keep the reaction system temperature below 50℃, and the addition time is approximately 30min.

[0041] S2, Heating to Promote Solubility and In-situ Purification: After the addition of materials is complete, the reaction oil bath temperature is set to 70℃. After the reaction mixture reaches 70℃, the stirring speed is adjusted to 400 rpm, and the timer is started. The reaction is continued to be stirred at this temperature for 3 hours.

[0042] S3, Solid-Liquid Separation: After the reaction is complete, remove the oil bath and allow the reaction mixture to cool naturally to 25°C. Transfer the cooled mixture to a 50 mL centrifuge tube and centrifuge at 10,000 rpm for 10 min. The supernatant is a deep blue chromium acetate solution; carefully decant and collect. The solid at the bottom is the modified material loaded with impurities.

[0043] S4, Crystallization and Drying: Pour all the chromium acetate solution obtained in step S3 into a 250 mL round-bottom flask and connect it to a rotary evaporator. Set the water bath temperature to 85 °C and concentrate under reduced pressure at a vacuum of -0.09 MPa (gauge pressure) until the solution volume is approximately 30 mL and a distinct crystalline film appears on the inner wall. Quickly pour the concentrate into a 100 mL crystallizing dish and transfer it to a low-temperature incubator set to 5 °C, allowing it to crystallize for 10 h. After crystallization, rapidly filter the solution using a Buchner funnel to obtain blue-purple needle-like crystals. Wash the crystals twice with 10.0 g of anhydrous ethanol pre-cooled to 5 °C. Finally, transfer the crystals to a watch glass and dry them in a vacuum drying oven at 45 °C for 6 h to obtain the chromium acetate hexahydrate product.

[0044] Example 2

[0045] The specific implementation method is the same as in Example 1, except that the sulfonic acid-chromium oxide composite mesoporous silica spheres are prepared as follows:

[0046] A1. Preparation of mesoporous silica sphere substrate: In a 500 mL three-necked flask, 22.0 g of anhydrous ethanol, 3.5 g of deionized water, 0.55 g of concentrated ammonia, and 0.18 g of hexadecyltrimethylammonium bromide were added sequentially, and the mixture was stirred at 25 °C for 20 min. 1.1 g of tetraethyl orthosilicate was mixed with 6.0 g of anhydrous ethanol and added dropwise to the flask, and the mixture was stirred at 29 °C for 22 h. The solid was collected by centrifugation, washed, and dried at 80 °C for 12 h. The solid was then calcined in air at a rate of 2 °C / min to 548 °C for 6.5 h to obtain the mesoporous silica sphere substrate.

[0047] A2, Chromium oxide nanoparticle support: 3.00 g of mesoporous silica sphere substrate was weighed and immersed in 9.0 g of 0.18 mol / L chromium nitrate aqueous solution. After sonication for 30 min, it was allowed to stand for 12 h. After filtration and drying, it was calcined at 398 °C at 5 °C / min under a nitrogen atmosphere for 3.5 h to obtain chromium oxide supported mesoporous silica spheres;

[0048] A3, Thiol-functionalized: 5.00 g of chromium oxide-supported mesoporous silica spheres were weighed and dispersed in 18.0 g of anhydrous toluene. 0.90 g of 3-(mercaptopropyl)trimethoxysilane was added, and the mixture was refluxed at 109 °C for 25 h under nitrogen protection. After filtration and washing, the mixture was dried under vacuum at 60 °C for 10 h to obtain thiol-functionalized chromium oxide-mesoporous silica spheres.

[0049] A4. Oxidation preparation of sulfonic acid groups: Weigh 4.00 g of mercapto-functionalized chromium oxide-mesoporous silica spheres and disperse them in a mixture of 15.0 g of deionized water and 3.5 g of 30% hydrogen peroxide. Stir the mixture in a water bath at 49 °C for 12.5 h. Filter, wash with water until neutral, and dry at 80 °C for 8 h to obtain sulfonic acid-chromium oxide composite mesoporous silica spheres.

[0050] Method for preparing chromium acetate from chromium hydroxide:

[0051] S1, Mixing and Acidification: Add 100.0g of wet chromium hydroxide filter cake and 1.50g of modified material to a 250mL flask, and slowly add 260.0g of glacial acetic acid while stirring;

[0052] S2, Heating to promote dissolution and in-situ purification: The mixture was heated to 65°C and stirred continuously for 3.5 hours;

[0053] S3, solid-liquid separation: After the reaction solution is cooled to 24°C, it is centrifuged at 10,000 rpm for 10 min to separate the chromium acetate solution.

[0054] S4, Crystallization and Drying: The solution was concentrated at 80℃ and -0.09MPa, and then allowed to crystallize at 1℃ for 8 hours. After filtration, the crystals were washed with 8.0g of anhydrous ethanol and dried under vacuum at 42℃ for 6 hours.

[0055] Example 3

[0056] The specific implementation method is the same as in Example 1, except that the sulfonic acid-chromium oxide composite mesoporous silica spheres are prepared as follows:

[0057] A1. Preparation of mesoporous silica sphere substrate: In a 500 mL three-necked flask, 28.0 g of anhydrous ethanol, 4.5 g of deionized water, 0.70 g of concentrated ammonia, and 0.22 g of cetyltrimethylammonium bromide were added sequentially, and the mixture was stirred at 25 °C for 20 min. 1.4 g of tetraethyl orthosilicate was mixed with 9.0 g of anhydrous ethanol and added dropwise to the flask, and the mixture was stirred at 31 °C for 26 h. The solid was collected by centrifugation, washed, and dried at 80 °C for 12 h. The solid was then calcined in air at a rate of 2 °C / min to 552 °C for 7.5 h to obtain the mesoporous silica sphere substrate.

[0058] A2, Chromium oxide nanoparticle support: 3.00 g of mesoporous silica sphere substrate was weighed and immersed in 11.0 g of 0.22 mol / L chromium nitrate aqueous solution. After sonication for 30 min, it was allowed to stand for 12 h. After filtration and drying, it was calcined at 402 °C at a rate of 5 °C / min under a nitrogen atmosphere for 5 h to obtain chromium oxide supported mesoporous silica spheres;

[0059] A3, Thiol-functionalized: 5.00 g of chromium oxide-supported mesoporous silica spheres were weighed and dispersed in 22.0 g of anhydrous toluene. 1.10 g of 3-(mercaptopropyl)trimethoxysilane was added, and the mixture was refluxed at 111 °C for 28 h under nitrogen protection. After filtration and washing, the mixture was dried under vacuum at 60 °C for 10 h to obtain thiol-functionalized chromium oxide-mesoporous silica spheres.

[0060] A4. Oxidation preparation of sulfonic acid groups: Weigh 4.00 g of mercapto-functionalized chromium oxide-mesoporous silica spheres and disperse them in a mixture of 18.0 g of deionized water and 4.5 g of 30% hydrogen peroxide. Stir the mixture in a water bath at 51 °C for 13.5 h. Filter, wash with water until neutral, and dry at 80 °C for 8 h to obtain sulfonic acid-chromium oxide composite mesoporous silica spheres.

[0061] Method for preparing chromium acetate from chromium hydroxide:

[0062] S1, Mixing and Acidification: Add 100.0g of wet chromium hydroxide filter cake and 4.50g of modified material to a 250mL flask, and slowly add 320.0g of glacial acetic acid while stirring;

[0063] S2, Heating to promote dissolution and in-situ purification: The mixture was heated to 75°C and stirred continuously for 2.5 hours.

[0064] S3, solid-liquid separation: After the reaction solution is cooled to 26°C, it is centrifuged at 10000 rpm for 10 min to separate the chromium acetate solution.

[0065] S4, Crystallization and Drying: The solution was concentrated at 88℃ and -0.09MPa, and then allowed to crystallize at 8℃ for 11 hours. After filtration, the crystals were washed with 12.0g of anhydrous ethanol and dried under vacuum at 48℃ for 6 hours.

[0066] Comparative Example 1

[0067] The specific implementation method is the same as in Example 1, except that this comparative example does not add sulfonic acid-chromium oxide composite mesoporous silica balls.

[0068] S1, Mixing and Acidification: In a 250mL three-necked flask, add 100.0g of wet filter cake of chromium hydroxide (same batch as in Example 1), and slowly add 290.0g of glacial acetic acid while stirring.

[0069] S2, Heating to promote dissolution and in-situ purification: Heat the mixture to 70°C and stir continuously for 3 hours.

[0070] S3, Solid-liquid separation: After the reaction solution is cooled to 25°C, it is directly filtered using a Buchner funnel and filter paper (without centrifugation) to separate chromium acetate solution and a small amount of insoluble residue.

[0071] S4, Crystallization and Drying: The conditions and operations for the subsequent concentration, crystallization, washing and drying steps are exactly the same as in Example 1.

[0072] Comparative Example 2

[0073] The specific implementation method is the same as in Example 1, except that this comparative example uses an unfunctionalized mesoporous silicon sphere substrate. The preparation of this material is only carried out up to the end of step A1 in Example 1 to obtain the mesoporous silicon sphere substrate.

[0074] S1, Mixing and Acidification: In a 250mL three-necked flask, add 100.0g of wet filter cake of chromium hydroxide and 3.00g of the above-mentioned pure mesoporous silica balls, and slowly add 290.0g of glacial acetic acid while stirring.

[0075] S2, Heating to promote dissolution and in-situ purification: Heat the mixture to 70°C and stir continuously for 3 hours.

[0076] S3, Solid-liquid separation: After the reaction solution is cooled to 25°C, it is centrifuged at 10,000 rpm for 10 min to separate the chromium acetate solution and the solid.

[0077] S4, Crystallization and Drying: The subsequent steps are exactly the same as in Example 1.

[0078] Comparative Example 3

[0079] The specific implementation method is the same as in Example 1, except that this comparative example uses mesoporous silica spheres that are functionalized with only sulfonic acid groups but not loaded with chromium oxide. The preparation process of this material is as follows: take the mesoporous silica sphere substrate obtained in step A1 of Example 1, skip step A2, and directly perform the same thiolation and oxidation treatment as steps A3 and A4 in Example 1.

[0080] S1, Mixing and Acidification: In a 250mL three-necked flask, add 100.0g of wet filter cake of chromium hydroxide and 3.00g of the above-mentioned sulfonated mesoporous silica balls, and slowly add 290.0g of glacial acetic acid while stirring.

[0081] S2, Heating to promote dissolution and in-situ purification: Heat the mixture to 70°C and stir continuously for 3 hours.

[0082] S3, Solid-liquid separation: After the reaction solution is cooled to 25°C, it is centrifuged at 10,000 rpm for 10 min to separate the chromium acetate solution and the solid.

[0083] S4, Crystallization and Drying: The subsequent steps are exactly the same as in Example 1.

[0084] Performance testing

[0085] The chromium acetate prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following method, which included the following steps:

[0086] Accurately weigh 5.00 g of the chromium acetate crystals obtained after final drying in each example and comparative example, place them in a 50 mL polytetrafluoroethylene digestion vessel, add 10 mL of analytical grade concentrated nitric acid, seal the vessel, and place it in a microwave digester at 180 °C for 30 min. After the program is completed, wait for the digestion vessel to cool to room temperature, transfer all the digestion solution to a 50 mL volumetric flask, wash the inner wall of the digestion vessel several times with ultrapure water and combine the washings, finally dilute to the mark, shake well, and obtain the test solution A, which is used for the analysis of metal cation impurity content. The iron, aluminum, and sodium content in solution A was analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES). Fe (238.204 nm), Al (396.152 nm), and Na (589.592 nm) were used as analytical spectral lines. Calibration curves were established using mixed standard solutions with concentrations of 0 mg / L, 0.5 mg / L, 1.0 mg / L, 5.0 mg / L, and 10.0 mg / L. The instrument's nebulizer gas flow rate was 0.70 L / min, plasma gas flow rate was 12.0 L / min, auxiliary gas flow rate was 1.0 L / min, RF power was 1.30 kW, and sample rise rate was 1.5 mL / min. Each sample was measured in triplicate, and the average value was taken.

[0087] Separately, accurately weigh 1.00 g of chromium acetate product, dissolve it in ultrapure water, and dilute to a 100 mL volumetric flask to obtain solution B, which was used for anion impurity analysis. The sulfate and chloride ion contents in solution B were analyzed using an ion chromatograph equipped with an anion exchange column: a mixed solution of 3.2 mmol / L sodium carbonate and 1.0 mmol / L sodium bicarbonate was used as the eluent, the flow rate was 1.0 mL / min, the suppressor current was 25 mA, and the column temperature was 30 °C. A calibration curve was established using mixed anion standard solutions with concentrations of 0 mg / L, 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, and 5.0 mg / L for quantitative analysis.

[0088] The purity of chromium acetate products is calculated by the difference method, that is, by subtracting the sum of the percentages of all measured impurities such as iron, aluminum, sodium, sulfate, and chloride from 100%.

[0089] Test results:

[0090] Table 1: Test results of each embodiment and comparative example

[0091] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Product purity (%) 99.73 99.65 99.70 98.05 98.88 99.21 Fe content (ppm) 8.5 10.2 9.1 825.4 760.8 105.7 Al content (ppm) 12.1 14.8 13.5 310.6 295.4 95.8 Na content (ppm) 15.3 18.7 16.9 2050.7 1980.5 55.4 <![CDATA[SO4 2- Content (ppm) <10 <10 <10 450.2 420.5 <10 <![CDATA[Cl - Content (ppm) <10 <10 <10 320.8 305.4 <10

[0092] As can be seen from Table 1, the methods of the present invention represented by Examples 1-3, compared with the traditional or partially improved methods represented by Comparative Examples 1-3, comprehensively and effectively solve the core technical problems in the traditional process.

[0093] First, regarding the core indicator of product purity, the purity of the products in Examples 1-3 remained consistently at a high level of 99.65-99.73%, while the purity of Comparative Example 1 (without any modified materials) and Comparative Example 2 (using only physical adsorption carriers) was only 98.05% and 98.88%, respectively. This directly proves that by introducing composite modified materials with specific functions, the present invention can achieve a qualitative leap in the purity of the final product without the need for cumbersome pretreatment of raw materials, thus completely solving the problem of "difficulty in guaranteeing product purity".

[0094] Secondly, regarding impurity removal efficiency, the examples demonstrate particularly outstanding removal capabilities for key metal impurity ions. The iron, aluminum, and sodium contents in the products are only 8.5-10.2 ppm, 12.1-14.8 ppm, and 15.3-18.7 ppm, respectively, while the contents of these impurities in Comparative Examples 1 and 2 are tens to hundreds of times higher. For example, the iron content exceeds 760 ppm, and the sodium content reaches approximately 2000 ppm. Simultaneously, the sulfate and chloride ion contents in the examples are both below 10 ppm, far lower than the levels exceeding 300 ppm in Comparative Examples 1 and 2. This data comparison strongly confirms the synergistic effect of sulfonic acid groups and chromium oxide in the modified material of this invention, enabling in-situ, efficient, and selective adsorption and removal of various anionic and cationic impurities with minimal interference to the target product chromium ions. This "one-step" in-situ purification technology completely eliminates the multi-step pretreatment processes such as alkali washing, acid washing, and repeated water washing that are necessary in traditional processes to remove these impurities. This shortens the process flow at the source, avoids the loss of chromium hydroxide raw materials caused by multiple washing and filtration, and greatly reduces the amount of process wastewater generated.

[0095] In summary, the test data objectively verified, from the two dimensions of final product purity and impurity control level, that this invention, through material and process innovation, simultaneously achieves high product purification and green production through a simple and efficient path, successfully overcoming the comprehensive technical challenges inherent in traditional methods, such as lengthy processes, high water and material consumption, and poor purity.

[0096] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing chromium acetate from chromium hydroxide, characterized in that, Includes the following steps: S1, add chromium hydroxide wet filter cake and sulfonic acid-chromium oxide composite mesoporous silica balls into the reactor, and add glacial acetic acid under stirring to obtain a mixture; S2, Heat the mixture to 60-80℃ and stir continuously to obtain the reaction mixture; S3, the reaction mixture is cooled and centrifuged to obtain sulfonic acid-chromium oxide composite mesoporous silica spheres loaded with impurities and a chromium acetate solution; S4. The chromium acetate solution obtained in step S3 is concentrated under reduced pressure at 70-90℃, then transferred to a crystallizer and allowed to stand at 0-10℃ for crystallization. After filtration, crystals are obtained, washed with anhydrous ethanol, and dried under vacuum at 40-50℃.

2. The method for preparing chromium acetate from chromium hydroxide according to claim 1, characterized in that, In step S1, the mass ratio of wet chromium hydroxide filter cake to sulfonic acid-chromium oxide composite mesoporous silica spheres is 100:1-5.

3. The method for preparing chromium acetate from chromium hydroxide according to claim 1, characterized in that, In step S2, the reaction is continuously stirred for 2-4 hours.

4. The method for preparing chromium acetate from chromium hydroxide according to claim 1, characterized in that, In step S3, the reaction mixture is cooled to 24-26°C.

5. The method for preparing chromium acetate from chromium hydroxide according to claim 1, characterized in that, In step S4, the time for crystallization at 0-10℃ is 6-12 hours.

6. The method for preparing chromium acetate from chromium hydroxide according to any one of claims 1-5, characterized in that, The preparation steps of the sulfonic acid-chromium oxide composite mesoporous silica spheres include: A1, by weight, adds 0.15-0.25 parts of hexadecyltrimethylammonium bromide to a mixture of 20-30 parts of anhydrous ethanol, 3-5 parts of deionized water, and 0.5-0.8 parts of concentrated ammonia, and stirs at 24-26°C; then adds a mixture of 1.0-1.5 parts of tetraethyl orthosilicate and 5-10 parts of anhydrous ethanol, and continues stirring at 28-32°C. The solid is collected by centrifugation, washed and dried, and then calcined at 545-555°C in air to obtain a mesoporous silica sphere substrate. A2, the mesoporous silica sphere substrate is immersed in 8-12 parts of chromium nitrate aqueous solution, filtered and dried, and then calcined at 395-405℃ under nitrogen atmosphere to obtain chromium oxide supported mesoporous silica spheres. A3. Chromium oxide-supported mesoporous silica spheres were dispersed in anhydrous toluene, and 0.8-1.2 parts of 3-(mercaptopropyl)trimethoxysilane were added. The mixture was refluxed at 108-112℃ under nitrogen protection. After the reaction was completed, the mixture was filtered, washed, and dried to obtain mercapto-functionalized chromium oxide-mesoporous silica spheres. A4. The mercapto-functionalized chromium oxide-mesoporous silica spheres were dispersed in a mixed oxidizing solution composed of deionized water and hydrogen peroxide, and stirred in a water bath at 48-52℃. After the reaction was completed, the mixture was filtered to obtain a solid product. The solid product was washed with deionized water and dried at 78-82℃.

7. The method for preparing chromium acetate from chromium hydroxide according to claim 6, characterized in that, In step A1, the calcination time at 545-555℃ is 6-8 hours.

8. The method for preparing chromium acetate from chromium hydroxide according to claim 6, characterized in that, In step A2, the calcination time at 395-405℃ is 3-6 hours; the concentration of the chromium nitrate aqueous solution is 0.15-0.25 mol / L.

9. The method for preparing chromium acetate from chromium hydroxide according to claim 6, characterized in that, In step A3, the reflux reaction at 108-112℃ takes 24-30 hours.

10. The method for preparing chromium acetate from chromium hydroxide according to claim 6, characterized in that, In step A4, the reaction is carried out in a water bath at 48-52℃ for 12-14 hours with stirring.