Method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid

Abstract

The invention belongs to the technical field of inorganic chemical industry and material chemistry, and particularly relates to a method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid. The method comprises the following steps: uniformly mixing pretreated chromium trichloride hexahydrate and solid superacid in proportion in an inert atmosphere; placing the mixture in a tubular reactor, and carrying out temperature programming stepped dehydration in a flowing dry inert gas or vacuum environment; and after the reaction is finished, cooling to room temperature in inert gas flow, extracting and separating by using an organic solvent or screening and separating, and drying in vacuum to obtain the anhydrous chromium trichloride. According to the method, the solid acid is directly used as the main dehydrating agent and the catalyst, the chromium trichloride hexahydrate is efficiently converted into the high-purity anhydrous chromium trichloride through the one-step method, the technological process is simple, the conditions are mild and safe, and the product is high in purity and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical and materials chemistry, specifically relating to a method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid. Background Technology

[0002] Anhydrous chromium trichloride (CrCl3) is a crucial starting material in modern organometallic chemistry, catalysis industry, and materials science, and its activity directly determines the performance of subsequent complexes or catalysts.

[0003] Currently, the existing technologies for preparing anhydrous chromium trichloride have the following main defects: (1) They are highly toxic and dangerous. The traditional "chlorination dehydration method" (such as using CCl4) will produce highly toxic phosgene (COCl2). For example, the literature (Zhi Bingwen. Synthesis of anhydrous chromium trichloride [J]. Chemical Education, 1985, (03): 30-31. DOI: 10.13884 / j.1003-3807hxjy.1985030013.) poses a huge challenge to operational safety, environmental protection facilities and waste treatment. (2) Safety and environmental protection issues are prominent. The existing mainstream technologies all require the introduction of a second reaction component (such as SOCl2, NH3Cl, etc.) to bind water molecules. For example, (Journal of the American Chemical Society, 1996, 118(8): 1917-1930.), which inevitably produces corrosive, toxic tail gas or complex by-product separation problems. There are equipment corrosion and tail gas absorption pressure. (3) Efficiency and purity bottlenecks. Traditional methods (such as direct heating of hydrates and ammonium chloride dehydration) are slow. For example, (Gmelin Handbuch der Anorganischen Chemie, Gmelin Handbook: Cr: MVol.B, 100, page204-206) dehydration may be incomplete, which can easily lead to severe hydrolysis and oxidation of the product. The product contains chloride oxide impurities, has low activity, and poor batch stability.

[0004] Current technology still lacks a highly efficient method for converting high-purity anhydrous chromium trichloride that can directly and selectively remove water of crystallization without consuming or introducing impurity ions. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid. This method features a simple process flow, mild and safe conditions, high product purity, and is environmentally friendly.

[0006] The purpose of this invention is to provide a method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid, the method comprising the following steps: (1) The pretreated chromium trichloride hexahydrate and the solid superacid were mixed evenly under an inert atmosphere in a certain proportion; (2) Place the mixture in a tubular reactor and perform programmed temperature-step dehydration in a flowing dry inert gas or vacuum environment; (3) After the reaction was completed, the product was cooled to room temperature in an inert gas stream, extracted and separated by organic solvent, and the solid product was dried under vacuum to obtain anhydrous chromium trichloride.

[0007] This invention directly uses a solid superacid as the sole dehydration medium. By utilizing the adsorption, activation, and desorption of water of crystallization by its superprotic acid centers, a green synthesis of anhydrous chromium trichloride is achieved in a single step under mild conditions. The core of this method lies in upgrading the solid superacid from its traditional role as merely a catalyst to a dual role as both a reaction medium and a catalyst, achieving true solid-solid direct dehydration without a liquid phase or a secondary dehydrating agent. This preparation method features mild reaction conditions, no high-pressure conditions or highly toxic reagents, low energy consumption, safe production, and high purity and yield of anhydrous chromium trichloride.

[0008] The reaction mechanism is as follows: First, adsorption and protonation: Chromium trichloride crystal water molecules undergo chemical adsorption and protonation at strong acid sites on the surface of a solid superacid, forming unstable hydrated protons (H3O). + This greatly weakens the Cr-O coordination bond; Then, dehydration and dissociation: under heating conditions, activated water molecules desorb from the surface of the solid superacid in the form of water vapor and escape, while the solid superacid stabilizes the intermediate chromium species through the anionic framework after the release of protons. Finally, acid site regeneration: the desorbed acid sites can reactivate the next water molecule, and the process can be repeated without any consumption.

[0009] The overall reaction can be summarized as follows: CrCl3·6H2O + solid acid - H + → CrCl3 + 6 H2O↑ + solid acid - H + (Solid acid is recycled) Preferably, in step (1) of the above technical solution, the method for pretreatment of chromium trichloride hexahydrate is as follows: drying at 80°C and vacuum degree <10 Pa for 12-14 hours, and grinding through a 200-mesh sieve after drying; the solid superacid is activated under vacuum at 150°C for 3-4 hours before use.

[0010] Preferably, in step (1) of the above technical solution, the chromium trichloride hexahydrate and the solid superacid are mixed in a chromium-to-acid molar ratio of 1:0.5-3; the solid superacid is phosphotungstic acid (H3PW). 12 O 40 ), silicotungstic acid (H4SiW)12 O 40 ) or supported superacids (such as SO4) 2- (ZrO2). This invention uses a solid superacid as a dehydrating agent, with an acidity more than a hundred times that of concentrated sulfuric acid. Its surface possesses extremely strong Brønsted and / or Lewis acid sites, which can deeply polarize and activate water molecules. Furthermore, its thermal stability is higher than the dehydration temperature, resulting in no loss. Simultaneously, by controlling the molar ratio of acid to chromium, sufficient acid sites are ensured to cover and activate all water of crystallization; too low a ratio leads to incomplete dehydration, while too high a ratio is uneconomical.

[0011] Preferably, in step (2) of the above technical solution, the flow rate of the inert gas is 100-120 mL / min. Using flowing inert gas can promptly remove the separated moisture.

[0012] Preferably, in step (2) of the above technical solution, the programmed heating method is as follows: increase to 120-150℃ at 2℃ / min and hold for 2 hours; then increase to 180-220℃ at 2℃ / min and hold for 2 hours; finally increase to 230-250℃ at 1℃ / min and hold for 3 hours. The gradient heating method of this invention can avoid sudden large-scale loss of moisture causing material splashing and makes dehydration more thorough.

[0013] Preferably, in step (3) of the above technical solution, the organic solvent is anhydrous ethanol, the extraction temperature is 50-60℃, and the extraction time is 20-24h. This invention selects anhydrous ethanol, which has significantly different physical properties, as the extraction solvent, enabling efficient and non-destructive separation of the solid superacid from the product, and allowing for recycling.

[0014] Preferably, in step (3) of the above technical solution, the vacuum drying temperature is 120±5℃ and the time is 4-5h.

[0015] Preferably, in step (3) of the above technical solution, the separated organic solvent is recovered as ethanol by rotary evaporation, and the remaining solid after evaporation is recovered as solid superacid after vacuum activation at 150-200℃. Recycling the solid superacid results in low single-use loss, low long-term operating costs, and is economical and environmentally friendly.

[0016] Preferably, in the above technical solution, the inert gas is high-purity nitrogen or argon. The entire process of this invention uses inert gas protection, which effectively prevents product oxidation, and the flowing inert gas can promptly remove water vapor, pushing the reaction equilibrium to the right and achieving efficient purification of chromium trichloride.

[0017] Advantages compared to existing technologies: Compared with existing technologies, this invention uses solid superacid as the sole dehydration medium, avoiding the risks of impurities such as chlorine, ammonia, and silicon introduced by a second dehydrating agent, resulting in higher product purity. The only gaseous byproduct of the reaction is water vapor, eliminating the need to treat corrosive or toxic gases (such as HCl, SO2, NH3), resulting in significant environmental benefits. Furthermore, the invention eliminates the need for the introduction, metering, and recovery of a second dehydrating agent (such as NH4Cl), reducing process steps and operational complexity. The solid superacid dehydrating agent is recyclable and can be reused multiple times, with low single-use losses and long-term operating costs far lower than consumable dehydrating agents. The main dehydration temperature range is lower than traditional methods, reducing energy consumption, and the absence of high-pressure conditions or highly toxic reagents ensures high production safety. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for preparing anhydrous chromium trichloride based on the direct dehydration method of solid superacid according to the present invention. Detailed Implementation

[0019] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products and can be purchased from the market.

[0021] The present invention will be further described in detail below with reference to embodiments: Example 1 The process flow diagram for preparing anhydrous chromium trichloride based on the direct dehydration method of phosphotungstic acid is as follows: Figure 1 As shown, it includes the following steps: (1) Raw material preparation: Chromium trichloride hexahydrate was dried at 80℃ and <10 Pa vacuum for 12h and ground through a 200 mesh sieve; phosphotungstic acid was activated under vacuum at 150℃ for 3h for later use.

[0022] (2) Mixing: In a glove box filled with argon, weigh 10.00g (0.038mol) of dried CrCl3·6H2O powder and 35.00g (about 0.012mol) of activated phosphotungstic acid, and grind and mix them in an agate mortar for 30min until uniform.

[0023] (3) Dehydration reaction: The mixture was transferred to a quartz tube reactor and dry argon gas was introduced at a flow rate of 100 mL / min. The temperature was increased according to the following program: the temperature was increased to 120℃ at 2℃ / min and held for 2 hours; then the temperature was increased to 200℃ at 2℃ / min and held for 2 hours; finally the temperature was increased to 250℃ at 1℃ / min and held for 3 hours.

[0024] (4) Separation and recovery: After the reaction is completed, the product is cooled to room temperature in an argon gas flow and transferred to a Soxhlet extractor. It is continuously extracted with anhydrous ethanol at 60°C for 24 hours. The phosphotungstic acid is partially dissolved in ethanol and enters the flask, while the anhydrous CrCl3 remains insoluble in the extraction sleeve.

[0025] (5) Post-processing: The purple solid in the sleeve was vacuum dried at 120°C for 4 h to obtain 5.25 g of purple flake-like anhydrous chromium trichloride, with a yield of 87.0% and a purity of 98.5%. The ethanol solution in the extraction flask was rotary evaporated, and the remaining solid was vacuum activated at 150°C to recover phosphotungstic acid, with a recovery rate of >95%.

[0026] Example 2 The method for preparing anhydrous chromium trichloride based on the direct dehydration of silicotungstic acid includes the following steps: (1) Raw material preparation: Chromium trichloride hexahydrate was dried at 80℃ and <10 Pa vacuum for 13h and ground through a 200 mesh sieve; silicotungstic acid was activated under vacuum at 150℃ for 4h for later use.

[0027] (2) Mixing: In a glove box filled with argon, weigh 10.00g (0.038mol) of dried CrCl3·6H2O powder and 34.50g (about 0.012mol) of activated silicotungstic acid, and grind and mix them in an agate mortar for 30min until uniform.

[0028] (3) Dehydration reaction: The mixture was transferred to a quartz tube reactor and dry argon gas was introduced at a flow rate of 110 mL / min. The temperature was increased according to the following program: the temperature was increased to 130℃ at 2℃ / min and held for 2 hours; then the temperature was increased to 190℃ at 2℃ / min and held for 2 hours; finally the temperature was increased to 240℃ at 1℃ / min and held for 3 hours.

[0029] (4) Separation and recovery: After the reaction is completed, the product is cooled to room temperature in an argon gas flow and transferred to a Soxhlet extractor. It is continuously extracted with anhydrous ethanol at 55°C for 22 hours. Silicotungstic acid is partially dissolved in ethanol and enters the flask, while anhydrous CrCl3 remains insoluble in the extraction sleeve.

[0030] (5) Post-processing: The purple solid in the sleeve was vacuum dried at 120℃ for 4h to obtain 5.41 g of purple flake-like anhydrous chromium trichloride, with a yield of 90.0% and a purity of 98.8%. The ethanol solution in the extraction bottle was rotary evaporated, and the remaining solid was vacuum activated at 200℃ to recover silicotungstic acid, with a recovery rate of >95%.

[0031] Example 3 A method for preparing anhydrous chromium trichloride based on direct dehydration using supported superacids includes the following steps: (1) Raw material preparation: Chromium trichloride hexahydrate was dried at 80℃ and <10 Pa vacuum for 14h and ground through a 200-mesh sieve; solid H2[ZrO(SO4)2] was activated under vacuum at 150℃ for 3h for later use.

[0032] (2) Mixing: In a glove box filled with argon, weigh 10.00g (0.038mol) of dried CrCl3·6H2O powder and 11.50g (about 0.038mol) of activated solid H2 [ZrO(SO4)2] and grind and mix them in an agate mortar for 30min until uniform.

[0033] (3) Dehydration reaction: The mixture was transferred to a quartz tube reactor and dry argon gas was introduced at a flow rate of 120 mL / min. The temperature was increased according to the following program: the temperature was increased to 150℃ at 2℃ / min and held for 2 hours; then the temperature was increased to 220℃ at 2℃ / min and held for 2 hours; finally the temperature was increased to 250℃ at 1℃ / min and held for 3 hours.

[0034] (4) Separation and recovery: After the reaction is completed, the product is cooled to room temperature in an argon gas flow and transferred to a Soxhlet extractor. It is continuously extracted with anhydrous ethanol at 50°C for 24 hours. H2[ZrO(SO4)2] partially dissolves in ethanol and enters the flask, while anhydrous CrCl3 remains insoluble in the extraction sleeve.

[0035] (5) Post-processing: The purple solid in the sleeve was vacuum dried at 120℃ for 4h to obtain 5.47 g of purple flake-like anhydrous chromium trichloride, with a yield of 91.0% and a purity of 98.9%. The ethanol solution in the extraction flask was rotary evaporated, and the remaining solid was activated under vacuum at 200℃ to recover H2 [ZrO(SO4)2], with a recovery rate of >95%.

[0036] Comparative Example 1 The method for preparing anhydrous chromium trichloride based on the direct dehydration of phosphotungstic acid differs from Example 1 in that the amount of phosphotungstic acid added in step (2) is 21.89 g (approximately 0.0076 mol), while the rest is the same as in Example 1.

[0037] The yield of anhydrous chromium trichloride was 62.3%, and the purity was 98.3%.

[0038] Comparative Example 2 The method for preparing anhydrous chromium trichloride based on the direct dehydration of phosphotungstic acid differs from Example 1 in that the amount of phosphotungstic acid added in step (2) is 437.73 g (approximately 0.152 mol), while the rest is the same as in Example 1.

[0039] The yield of anhydrous chromium trichloride was 87.1%, and the purity was 98.4%.

[0040] Comparative Example 3 The method for preparing anhydrous chromium trichloride differs from that in Example 1 in that phosphotungstic acid in step (2) is replaced with an equimolar amount of boric acid, while the rest is the same as in Example 1.

[0041] The yield of anhydrous chromium trichloride was 45.6%, and the purity was 97.2%.

[0042] Comparative Example 4 The method for preparing anhydrous chromium trichloride based on the direct dehydration method of phosphotungstic acid differs from Example 1 in that the dehydration reaction in step (3) is carried out at a fixed temperature of 200°C for 7 hours, while the rest is the same as in Example 1.

[0043] The yield of anhydrous chromium trichloride was 80.1%, and the purity was 98.6%.

[0044] Comparative Example 5 The method for preparing anhydrous chromium trichloride based on the direct dehydration method of phosphotungstic acid differs from Example 1 in that the dehydration reaction in step (3) is carried out at a fixed temperature of 250°C for 7 hours, while the rest is the same as in Example 1.

[0045] The yield of anhydrous chromium trichloride was 82.0%, and the purity was 98.6%.

[0046] The results above show that this invention uses solid superacid as the sole dehydration medium, eliminating the risk of introducing secondary impurities. By carrying out the dehydration reaction under flowing inert gas and mild conditions, the resulting anhydrous chromium trichloride has high purity (above 98.5%) and a yield of over 87%. It is safe, environmentally friendly, and low in cost. Furthermore, the solid superacid used can be recycled and reused, resulting in low long-term operating costs. This preparation method has broad application prospects.

[0047] In Comparative Example 1, too little solid superacid was used, resulting in too few acid sites and insufficient coverage to activate all the water of crystallization, leading to incomplete dehydration and a low yield of anhydrous chromium trichloride. In Comparative Example 2, excessive use of solid superacid, while not affecting the final result, was uneconomical. In Comparative Example 3, a solid weak acid was used, which could not achieve the goal of activating water molecules and completely dehydrating the water. In Comparative Examples 4 and 5, a fixed temperature dehydration method was used, and even though the temperatures were relatively high, the yield was not as high as that of the gradient temperature dehydration method of this invention, indicating that gradient dehydration, first at a low temperature and then at a high temperature, is more thorough.

[0048] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid, characterized in that, The method includes the following steps: (1) The pretreated chromium trichloride hexahydrate and the solid superacid were mixed evenly under an inert atmosphere in a certain proportion; (2) Place the mixture in a tubular reactor and perform programmed temperature-step dehydration in a flowing dry inert gas or vacuum environment; (3) After the reaction is completed, the product is cooled to room temperature in an inert gas stream, extracted and separated by organic solvent, and the solid product is dried under vacuum to obtain anhydrous chromium trichloride.

2. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (1), the pretreatment method for chromium trichloride hexahydrate is as follows: dry it for 12-14 hours in a vacuum environment of 80°C and vacuum degree <10 Pa, and then grind it through a 200-mesh sieve; the solid superacid is activated in a vacuum at 150°C for 3-4 hours before use.

3. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (1), the chromium trichloride hexahydrate and the solid superacid are mixed in a ratio of 1:0.5-3 (chromium to acid molar ratio); the solid superacid is phosphotungstic acid, silicotungstic acid or a supported superacid.

4. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (2), the flow rate of the inert gas is 100-120 mL / min.

5. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (2), the temperature program is as follows: raise the temperature to 120-150℃ at 2℃ / min and hold for 2 hours; raise the temperature to 180-220℃ at 2℃ / min and hold for 2 hours; and finally raise the temperature to 230-250℃ at 1℃ / min and hold for 3 hours.

6. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (3), the organic solvent is anhydrous ethanol, the extraction temperature is 50-60℃, and the extraction time is 20-24h.

7. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, In step (3), the vacuum drying temperature is 120±5℃ and the time is 4-5h.

8. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, The organic solvent separated in step (3) is used to recover ethanol by rotary evaporation. The remaining solid after evaporation is then activated under vacuum at 150-200℃ to recover solid superacid.

9. The method for preparing high-purity anhydrous chromium trichloride based on direct dehydration of solid acid according to claim 1, characterized in that, The inert gas is high-purity nitrogen or argon.

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