10X molecular sieve catalyst based on calcium ion exchange as well as preparation method and application of 10X molecular sieve catalyst

Abstract

The invention provides a 10X molecular sieve catalyst based on calcium ion exchange and a preparation method and application thereof, in the preparation process of the 10X molecular sieve catalyst, through control of calcium exchange rate and collaborative optimization of citric acid modification, the prepared catalyst shows high activity (conversion rate gt; 98.5%) and high selectivity (gt; the molecular sieve prepared by the preparation method disclosed by the invention has the advantages that the crystallinity and the structural stability of the molecular sieve are better maintained while pore channel widening and acidity optimization are realized, the service life of the catalyst is longer, the acidity and the pore diameter of the catalyst can be continuously and accurately adjusted between typical properties of 10X and 13X, an optimal equilibrium point for a target reaction is found, and the molecular sieve is suitable for Friedel-Crafts acylation reaction. The whole preparation method is simple, raw materials are easy to obtain, strong corrosive chemicals are not needed in the preparation process, the catalyst can be easily separated and recycled for multiple times, the emission of three wastes is greatly reduced, the ultra-long stable operation capacity exceeding 500 hours is shown in continuous flow production, and the preparation method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and fine organic synthesis technology, specifically relating to a 10X molecular sieve catalyst based on calcium ion exchange, as well as the preparation method of the 10X molecular sieve catalyst and its application as a catalyst in Friedel-Crafts acylation reactions. Background Technology

[0002] Friedel-Crafts acylation is a core process in the synthesis of aromatic ketones, and its products, as key intermediates, are widely used in pharmaceuticals, pesticides, dyes, liquid crystal materials, and polymers. Among them, 4,4'-difluorobenzophenone, as a typical fluorinated aromatic ketone, plays an irreplaceable role in the synthesis of specialty engineering plastics such as polyetheretherketone (PEEK), liquid crystal display materials, and antifungal drugs due to the unique electronic effects and steric hindrance of the fluorine atom in its molecular structure, and its market demand continues to grow.

[0003] Current Friedel-Crafts acylation reactions commonly employ homogeneous Lewis acid catalysts such as anhydrous AlCl3 and FeCl3. While these catalysts achieve high reactant conversion rates, their industrial application suffers from several significant drawbacks: First, these catalysts are highly corrosive, necessitating the use of expensive titanium or Hastelloy materials in the reaction equipment, substantially increasing initial investment and long-term maintenance costs. Second, the reaction requires extensive quenching and hydrolysis with ice water, generating approximately 8-10 tons of aluminum-containing acidic wastewater for every ton of target product produced, resulting in challenging and costly environmental treatment. This places enormous environmental pressure on enterprises; thirdly, the catalyst easily forms stable complexes with the products, making it impossible to recover and reuse them through simple separation. This not only results in poor atom economy but also leads to a high raw material loss rate. In particular, for the reaction system of fluorobenzene and p-fluorobenzoyl chloride, the strong electron-withdrawing effect of fluorine atoms in the fluorobenzene molecule reduces the reactivity of the benzene ring. Currently, homogeneous Lewis acid catalysts are difficult to precisely control the regioselectivity, resulting in byproducts (such as 2,4'-difluorobenzophenone) content as high as 9% or more. This significantly increases the complexity and energy consumption of subsequent product separation and purification processes.

[0004] To address the aforementioned issues, the development of environmentally friendly, highly efficient, and stable solid acid catalysts has become a research hotspot in the industry. Zeolite molecular sieves, due to their regular pores, tunable acidity, and good thermal stability, are considered ideal alternative materials. Among them, X-type molecular sieves generally have large pore sizes. Of their two common subtypes, the 10X type (calcium type) is more acidic but has a slightly smaller pore size, while the 13X type (sodium type) has the largest pore size and mild acidity. Both have limitations when used for reactions with fluorobenzene, a low-activity substrate. The former is prone to decreased selectivity due to excessive acidity, while the latter often results in low conversion rates due to insufficient acidity.

[0005] The core issue lies in the need for a catalyst that can precisely balance acidity and pore size. By controlling the degree of calcium ion exchange in NaX molecular sieves, materials with properties between 10X and 13X can be prepared, potentially yielding optimal performance for this reaction. However, determining the optimal calcium exchange level and employing suitable modification techniques to optimize its pore size and acidity distribution remains a challenge, lacking systematic research and feasible industrialization solutions. Summary of the Invention

[0006] The purpose of this invention is to address the problems of heavy pollution, difficulty in recovery, and poor selectivity of existing homogeneous catalysts, as well as the performance imbalance of existing solid acid catalysts, based on existing technologies. It provides a 10X molecular sieve catalyst based on calcium ion exchange, which exhibits excellent catalytic performance, high selectivity, good stability, and environmental friendliness. Through synergistic optimization of calcium exchange rate and citric acid modification, the resulting catalyst exhibits high activity (conversion >98.5%) and high selectivity (>97.5%). While achieving pore widening and acidity optimization, it better maintains the crystallinity and structural stability of the molecular sieve, resulting in a longer catalyst lifetime. This allows for continuous and precise adjustment of the catalyst's acidity and pore size between the typical properties of 10X and 13X, finding the optimal balance point for the target reaction. It is suitable for Friedel-Crafts acylation reactions, particularly for the highly selective synthesis of 4,4'-difluorobenzophenone in the Friedel-Crafts acylation reaction of fluorobenzene and p-fluorobenzoyl chloride.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned 10X molecular sieve catalyst based on calcium ion exchange. The entire preparation method is simple, the raw materials are readily available, the catalyst cost is controllable, no highly corrosive chemicals are required during the preparation process, the catalyst can be easily separated and regenerated multiple times, significantly reducing the emission of waste gas, wastewater, and solid waste, and exhibits an ultra-long stable operating capability of over 500 hours in continuous flow production, making it suitable for large-scale production.

[0008] A third objective of this invention is to provide the application of the above-mentioned calcium ion exchange-based 10X molecular sieve catalyst as a catalyst in Friedel-Crafts acylation reactions.

[0009] The technical solution of the present invention is as follows: The method for preparing a 10X molecular sieve catalyst based on calcium ion exchange provided by this invention includes the steps of calcium ion exchange, citric acid solution modification and washing, drying, and calcination activation. The specific steps are as follows: (1) Calcium ion exchange: NaX molecular sieve is subjected to ion exchange with calcium salt solution at an exchange temperature of 50-90℃, an exchange time of 1-6 hours, and 1-3 exchanges to obtain 10X molecular sieve intermediate with a calcium ion exchange rate of 15%-85%; wherein the molar ratio of SiO2 to Al2O3 in NaX molecular sieve is 2.0-3.0:1; (2) Citric acid modification: The 10X molecular sieve intermediate obtained in step (1) is mixed with citric acid solution and stirred for modification reaction at 60-95℃; (3) Post-processing: The modified solid product obtained in step (2) is filtered and separated, washed with deionized water until the filtrate is neutral, the washed product is dried at 100-120℃, and then the dried product is calcined in air at 450-550℃ for 3-6 hours to obtain 10X molecular sieve catalyst.

[0010] For the purposes of this invention, in step (1), the molar ratio of SiO2 to Al2O3 in the NaX molecular sieve is 2.0-3.0:1, which may be, but is not limited to, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1; in a preferred embodiment, the molar ratio of SiO2 to Al2O3 in the NaX molecular sieve is 2.4-2.6:1; in a more preferred embodiment, the molar ratio of SiO2 to Al2O3 in the NaX molecular sieve is 2.5:1.

[0011] For the purposes of this invention, in step (1), the calcium ion exchange rate of the 10X molecular sieve intermediate is 15%-85%, preferably 30%-80%; more preferably 50%-70%.

[0012] In this invention, during calcium ion exchange in step (1), the exchange temperature is 50-90°C; preferably, the exchange temperature is 75-85°C; more preferably, the exchange temperature is 80°C.

[0013] In step (1), the calcium ion exchange takes 1-6 hours; preferably, the exchange time is 1.5-2.5 hours; more preferably, the exchange time is 2 hours. In step (1), the calcium ion exchange occurs 1-3 times; preferably, it occurs 2 times.

[0014] In this invention, in step (1), the calcium salt is one or more of calcium chloride, calcium nitrate or calcium acetate, preferably calcium chloride.

[0015] In step (1), the concentration of the calcium salt solution is 0.1-2.0 mol / L, preferably 0.2-1.0 mol / L. For example, the concentration of the calcium salt solution is 0.2 mol / L, 0.5 mol / L or 1.0 mol / L.

[0016] For the purposes of this invention, in step (1), during ion exchange, the mass-to-volume ratio (solid-to-liquid ratio) of NaX molecular sieve to calcium salt solution is 1:5-15 g / mL, which can be, but is not limited to, 1:5 g / mL, 1:6 g / mL, 1:7 g / mL, 1:8 g / mL, 1:9 g / mL, 1:10 g / mL, 1:11 g / mL, 1:12 g / mL, 1:13 g / mL, 1:14 g / mL or 1:15 g / mL; preferably, the mass-to-volume ratio (solid-to-liquid ratio) of NaX molecular sieve to calcium salt solution is 1:10 g / mL.

[0017] For the purposes of this invention, in step (2), the concentration of the citric acid solution is 0.05-1.5 mol / L, and may be, but is not limited to, 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, or 1.5 mol / L; preferably, the concentration of the citric acid solution is 0.3-0.8 mol / L; more preferably, the concentration of the citric acid solution is 0.5 mol / L.

[0018] For the purposes of this invention, in step (2), the mass-to-volume ratio of the 10X molecular sieve intermediate to the citric acid solution is 1:5-15 g / mL, which may be, but is not limited to, 1:5 g / mL, 1:6 g / mL, 1:7 g / mL, 1:8 g / mL, 1:9 g / mL, 1:10 g / mL, 1:11 g / mL, 1:12 g / mL, 1:13 g / mL, 1:14 g / mL or 1:15 g / mL; preferably, the mass-to-volume ratio of the 10X molecular sieve intermediate to the citric acid solution is 1:10 g / mL.

[0019] In this invention, in step (2), the 10X molecular sieve intermediate obtained in step (1) is mixed with citric acid solution and stirred for modification reaction at 60-95°C. The reaction temperature can be, but is not limited to, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C. Preferably, the reaction temperature is 75-85°C; more preferably, the reaction temperature is 80°C.

[0020] In step (2), the reaction time during the modification reaction is 4-6 hours, preferably 5 hours.

[0021] In this invention, in step (3), the washed product is dried at 100-120°C. The drying temperature can be, but is not limited to, 100°C, 105°C, 110°C, 115°C or 120°C. Preferably, the drying temperature is 105-115°C. More preferably, the drying temperature is 110°C.

[0022] In step (3), the drying time is 4-12 hours, preferably 10 hours.

[0023] In this invention, in step (3), the dried product is calcined in air at 450-550°C for 3-6 hours. The calcination temperature can be, but is not limited to, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, or 550°C. Preferably, the calcination temperature is 490-510°C. More preferably, the calcination temperature is 500°C.

[0024] Preferably, in step (3), the roasting time is 4 hours.

[0025] The design concept of the calcium ion exchange-based 10X molecular sieve catalyst provided by this invention is as follows: Starting with NaX molecular sieves, a series of 10X molecular sieves with different calcium ion exchange rates are prepared by controlling the calcium ion exchange rate. The calcium exchange rate directly regulates the acidity and pore size characteristics of the molecular sieve. When the calcium exchange rate is low, the properties tend to be close to 13X (Na⁺ predominant); when the calcium exchange rate is high, the properties tend to be close to existing 10X (Ca²⁺ predominant). This invention finds that controlling the calcium exchange rate in the intermediate range of 50%-70% allows the catalyst to obtain ideal acidity and pore size between existing 10X and 13X, adapting to the low activity characteristics of fluorobenzene and suitable for Friedel-Crafts acylation reactions, especially for the highly selective synthesis of 4,4'-difluorobenzophenone in the Friedel-Crafts acylation reaction of fluorobenzene and p-fluorobenzoyl chloride.

[0026] The present invention provides an innovative modification method for 10X molecular sieve catalysts based on calcium ion exchange: it abandons the commonly used modification with strong inorganic acids (hydrochloric acid, nitric acid, etc.) and instead uses citric acid, a weak organic acid, for modification. Citric acid has multiple carboxyl groups, and its chelating effect can more gently and selectively remove non-framework aluminum species. At the same time, by controlling the modification temperature (75-85℃) and time (4-6 hours), the dissolution of framework aluminum can be minimized. While widening the pores and optimizing the distribution of acidic sites, the framework structure of the molecular sieve is protected, avoiding excessive etching and structural collapse that may be caused by strong acids.

[0027] The calcium ion exchange-based 10X molecular sieve catalyst provided by this invention can be used as a catalyst in Friedel-Crafts acylation reactions, particularly for the highly selective synthesis of 4,4'-difluorobenzophenone in Friedel-Crafts acylation reactions using fluorobenzene as a substrate and p-fluorobenzoyl chloride as an acylation agent. The catalyst provided by this invention is applicable to both batch and fixed-bed continuous flow reaction modes in Friedel-Crafts acylation reactions, and offers optimized process parameters, demonstrating broad industrial application prospects.

[0028] For example, in a batch reaction mode of Friedel-Crafts acylation, the molar ratio of fluorobenzene to p-fluorobenzoyl chloride is 5-15:1, preferably 10:1; the reaction temperature is 70-150℃, preferably 80℃; the reaction time is 3-10 hours, preferably 6 hours; and the amount of catalyst is 1%-15% of the mass of p-fluorobenzoyl chloride, preferably 10%.

[0029] For example, in a Friedel-Crafts acylation reaction in a fixed-bed continuous flow reaction mode, the molar ratio of fluorobenzene to p-fluorobenzoyl chloride is 3-6:1, preferably 5:1; the reaction temperature is 80-140℃, preferably 120℃; and the mass hourly space velocity is 0.3-2.5 h⁻¹. -1 Preferably 1.0 h -1 .

[0030] The catalyst after the Friedel-Crafts acylation reaction can be recovered by solid-liquid separation, and after washing with organic solvents, drying, and calcination regeneration, it can be reused at least 4 times. For example, the catalyst after the Friedel-Crafts acylation reaction can be recovered by filtration, washed 3 times with acetone, dried at 110°C for 2 hours, and then calcined at 500°C for 3 hours to regenerate.

[0031] The advantages of using the technical solution of this invention are as follows: (1) Excellent catalytic performance: By controlling the calcium exchange rate at 50%-70% and synergistically optimizing the citric acid modification, the catalyst exhibits high activity (conversion rate >98.5%) and high selectivity (>97.5%), solving the problems of heavy pollution, difficulty in recovery, poor selectivity of existing homogeneous catalysts, and unbalanced performance of existing solid acid catalysts.

[0032] (2) Performance can be precisely controlled: Calcium exchange rate is a key control parameter, which allows the acidity and pore size of the prepared catalyst to be continuously and precisely adjusted between the typical properties of 10X and 13X, to find the best balance point for the target reaction. It is suitable for Friedel-Crafts acylation reaction, especially for the highly selective synthesis of 4,4'-difluorobenzophenone in the Friedel-Crafts acylation reaction of fluorobenzene and p-fluorobenzoyl chloride.

[0033] (3) The modification effect is mild and efficient: Citric acid modification is milder than inorganic acid modification such as hydrochloric acid and nitric acid. While achieving pore widening and acidity optimization, it better maintains the crystallinity and structural stability of molecular sieves, resulting in a longer catalyst life.

[0034] (4) Green and environmentally friendly: The entire preparation and use process does not require strong corrosive chemicals, and the catalyst can be easily separated and regenerated multiple times, greatly reducing the emission of waste.

[0035] (5) Great potential for industrial application: The preparation method is simple, the raw materials are readily available, and the catalyst cost is controllable. It can be used to synthesize 4,4'-difluorobenzophenone with high selectivity in the Friedel-Crafts acylation reaction of fluorobenzene and p-fluorobenzoyl chloride. For example, the conversion rate of p-fluorobenzoyl chloride can reach 99.8% in batch process and can be stably operated for more than 500 hours in fixed bed continuous flow process. The selectivity of 4,4'-difluorobenzophenone is always higher than 98%. It also has the advantages of being environmentally friendly, having no equipment corrosion, and being easy to separate and regenerate (it can be reused 4 times and still maintain a conversion rate of more than 95%), making it suitable for large-scale production. Attached Figure Description

[0036] Figure 1 These are the NH3-TPD diagrams of CaX-60 molecular sieves before and after citric acid modification in Example 1; Figure 2 XRD patterns of CaX-60 molecular sieve before and after modification with citric acid, hydrochloric acid and nitric acid in Example 2; Figure 3 BET diagrams of CaX-60 molecular sieves before and after modification with citric acid, hydrochloric acid and nitric acid in Example 2. Detailed Implementation

[0037] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0038] Example 1: Preparation and citric acid modification of 10X molecular sieves with different calcium exchange rates (1) Take several portions of NaX molecular sieve raw powder with a molar ratio of SiO2 to Al2O3 of 2.5, each portion being 10g; and carry out ion exchange with 100mL CaCl2 solution of different concentrations (0.2, 0.5, 1.0 mol / L) respectively. The exchange temperature is 80℃, the number of exchanges is 2, and the exchange time is 2 hours each time (the mass-volume ratio of NaX molecular sieve to calcium salt solution (solid-liquid ratio) is 1:10 g / mL). 10X molecular sieve intermediates with calcium exchange rates of 30%, 60%, and 80% are prepared and are denoted as CaX-30, CaX-60, and CaX-80.

[0039] (2) Take 5g of each of the three different 10X molecular sieve intermediates obtained in step (1), mix them with 50 mL of 0.5 mol / L citric acid solution, and carry out the modification reaction at 80℃ for 5 hours. The mass-volume ratio (solid-liquid ratio) of the 10X molecular sieve intermediate to the citric acid solution is 1:10 g / mL.

[0040] (3) The three different solid products obtained in step (2) were filtered and separated, washed with deionized water until the filtrate was neutral, and the washed products were dried at 110°C for 10 hours. The dried products were then calcined in air at 500°C for 4 hours to obtain three different 10X molecular sieve catalysts, labeled as Cat-CaX-30-CA, Cat-CaX-60-CA, and Cat-CaX-80-CA, respectively.

[0041] Example 2: Comparison of the effects of different acid modifications Take three portions of the 10X molecular sieve intermediate CaX-60 prepared in Example 1, 5g each.

[0042] One sample was mixed with 50 mL of 0.5 mol / L hydrochloric acid solution and stirred at 80 °C for 5 hours for modification. The resulting modified solid product was filtered and separated, washed with deionized water until the filtrate was neutral, and the washed product was dried at 110 °C for 10 hours. The dried product was then calcined in air at 500 °C for 4 hours to obtain the 10X molecular sieve catalyst (comparative sample, Cat-CaX-60-HCl).

[0043] One sample was mixed with 50 mL of 0.5 mol / L nitric acid solution and stirred at 80 °C for 5 hours for modification. The resulting modified solid product was filtered and separated, washed with deionized water until the filtrate was neutral, and the washed product was dried at 110 °C for 10 hours. The dried product was then calcined in air at 500 °C for 4 hours to obtain 10X molecular sieve catalyst (comparative sample, Cat-CaX-60-HNO3).

[0044] One sample was mixed with 50 mL of 0.5 mol / L citric acid solution and stirred at 80 °C for 5 hours for modification. The resulting modified solid product was filtered and separated, washed with deionized water until the filtrate was neutral, and the washed product was dried at 110 °C for 10 hours. The dried product was then calcined in air at 500 °C for 4 hours to obtain a 10X molecular sieve catalyst (sample in Example 1 of this invention, Cat-CaX-60-CA).

[0045] Example 3: Evaluation of catalytic performance in batch reactor mode 50 mmol of fluorobenzene, 5 mmol of p-fluorobenzoyl chloride, and a catalyst (0.088 g of different catalysts prepared in Examples 1 and 2, accounting for 10% of the mass of p-fluorobenzoyl chloride) were added to a 100 mL three-necked flask. The mixture was stirred in an oil bath at 80 °C for 6 hours under N2 protection. After cooling, the resulting reaction solution was filtered, and the filtrate was analyzed by gas chromatography. The conversion and selectivity (4,4'-difluorobenzophenone) were calculated, and the results are shown in Table 1.

[0046] Table 1 Performance evaluation of different catalysts in batch reactor mode

[0047] As shown in Table 1, the citric acid-modified catalyst (Cat-CaX-60-CA) with a calcium exchange rate of 60% exhibits the best performance. Its activity and selectivity are higher than those of samples with high or low exchange rates, and also superior to inorganic acid-modified samples with the same exchange rate, thus verifying the correctness of the design concept of this invention.

[0048] Example 4: Catalyst Reuse and Regeneration Performance (Batch Reactor Mode) The Cat-CaX-60-CA catalyst recovered after the reaction in Example 3 was filtered, washed three times with acetone, dried at 110°C for 2 hours, and then calcined at 500°C for 3 hours to regenerate. The reaction was repeated under the same conditions, and the results are shown in Figure 2.

[0049] Table 2 Reuse performance of Cat-CaX-60-CA catalyst

[0050] As shown in Table 2, after regenerating the Cat-CaX-60-CA catalyst after the reaction in Example 3, it can be reused 4 times and still maintain a conversion rate of over 95%.

[0051] Example 5 Performance evaluation of fixed-bed continuous flow reaction mode The Cat-CaX-60-CA catalyst was compressed into tablets (10 MPa), sieved to obtain 20-40 mesh particles (0.45-0.90 mm in diameter), and packed into a fixed-bed reactor (stainless steel, 10 mm inner diameter, 300 mm length) at a loading of 2.0 g. The catalyst bed was fixed by filling the top and bottom with quartz sand. A dual-plunger metering pump (flow accuracy ±0.1 mL / h) was used to deliver the raw materials. Fluorobenzene and p-fluorobenzoyl chloride were mixed at a molar ratio of 5:1 and continuously fed. The reaction temperature was controlled at 120℃, and the mass hourly space velocity (WHSV) was 1.0 h⁻¹. -14,4'-Difluorobenzophenone was synthesized via Friedel-Crafts acylation in a fixed-bed continuous flow reaction mode. Sampling was initiated after 2 hours of stable system operation, and samples were taken every 20 hours for GC analysis.

[0052] The results showed that within 100 hours of continuous operation, the average conversion rate of p-fluorobenzoyl chloride was 92.5%, the average selectivity of 4,4'-difluorobenzophenone remained above 97.8%, no obvious carbon precursors were detected in the product, and the pressure drop of the catalyst bed remained stable below 0.15 MPa, demonstrating excellent stability for industrial applications.

[0053] Example 6: Long-term stability test of fixed bed To verify the catalyst's long-term industrial operation capability, a stability experiment was conducted under enhanced conditions (compared to the conventional conditions in Example 5: reducing the molar ratio of fluorobenzene to p-fluorobenzoyl chloride and increasing the mass hourly space velocity to increase the catalyst loading). The catalyst loading was 10 mL (20-40 mesh), the reaction temperature was 130℃, and the mass hourly space velocity was 1.8 h⁻¹. -1 The molar ratio of fluorobenzene to p-fluorobenzoyl chloride was 4:1. Samples were taken for analysis every 12 hours during a 500-hour continuous operation.

[0054] The results showed that the conversion rate of p-fluorobenzoyl chloride remained above 90%, the selectivity of 4,4'-difluorobenzophenone remained stable above 97.5%, and the catalyst bed pressure drop slowly increased from the initial 0.12 MPa to 0.18 MPa without obvious deactivation.

[0055] Comparative Example 1: Performance Evaluation of Existing AlCl3 Catalysts Under the reaction conditions of Example 3, the catalyst was replaced with 2 molar amounts (relative to p-fluorobenzoyl chloride) of anhydrous AlCl3 (1.33 g). After the reaction was completed, the reaction mixture was slowly poured into 100 g of ice water to quench it, and the organic phase was extracted with dichloromethane (50 mL × 3 times). After washing with water, drying, and concentration, the mixture was subjected to GC analysis.

[0056] The results showed that the conversion rate of p-fluorobenzoyl chloride was >99%, but the selectivity of 4,4'-difluorobenzophenone was only 91%, and the main byproduct was 2,4'-difluorobenzophenone (content was 7.2%). At the same time, 80 mL of aluminum-containing acidic wastewater (pH=1-2) was generated, the catalyst could not be recovered, and the subsequent wastewater treatment cost was high.

[0057] Comparative Example 2: Unmodified CaX-60 The CaX-60 intermediate was directly calcined (calcined at 500°C for 4 hours in air atmosphere) without citric acid modification and used in the same batch reaction mode as in Example 3.

[0058] The results showed that the conversion rate of p-fluorobenzoyl chloride was 88.5%, and the selectivity for 4,4'-difluorobenzophenone was 96.2%. This indicates that citric acid modification plays a key role in improving activity (pore expansion and acidity optimization).

[0059] Comparative Example 3: Comparison of the exchange effects of different calcium sources To illustrate the effect of calcium salt selection, intermediates with an exchange rate of 60% were prepared using different calcium salts.

[0060] Three portions of NaX molecular sieve with a SiO2 to Al2O3 molar ratio of 2.5 were subjected to ion exchange with calcium salt solutions of equal calcium ion molar concentrations (0.75 mol / L CaCl2, 0.75 mol / L Ca(NO3)2, and 1.5 mol / L Ca(CH3COO)2) under the same conditions (exchange temperature 80℃, two exchanges, and two hours per exchange). During ion exchange, the mass-to-volume ratio (solid-to-liquid ratio) of the NaX molecular sieve to the calcium salt solution was 1:10 g / mL. The calcium exchange rates of the 10X molecular sieve intermediates were determined to be 61%, 59%, and 58%, respectively.

[0061] The three different 10X molecular sieves were mixed with 0.5 mol / L citric acid solution and subjected to a stirring modification reaction at 80℃ for 5 hours. The mass-to-volume ratio (solid-to-liquid ratio) of the 10X molecular sieve intermediate to the citric acid solution was 1:10 g / mL. The three different modified solid products were separated by filtration, washed with deionized water until the filtrate was neutral, and dried at 110℃ for 10 hours. The dried products were then calcined in air at 500℃ for 4 hours to obtain three different 10X molecular sieve catalysts.

[0062] The catalytic performance of the three different 10X molecular sieve catalysts was evaluated under the reaction conditions described in Example 3. The batch reaction test results showed that the performance of the three catalysts was extremely similar (conversion of p-fluorobenzoyl chloride was 98.5%-98.8%, and selectivity for 4,4'-difluorobenzophenone was 97.7%-98.0%), indicating that calcium salt anions have no significant impact on the catalytic performance of this invention and that it has wide process adaptability.

[0063] In summary, this invention controls the calcium ion exchange rate (preferably 50%-70%) to keep the acidity of the 10X molecular sieve within an "optimal range," and further optimizes the pore and acidic site distribution by mild citric acid modification while protecting the framework. The synergistic effect of these two methods enables the catalyst to achieve a balance of high conversion rate, high selectivity, and high stability in the Friedel-Crafts acylation reaction of fluorobenzene and p-fluorobenzoyl chloride, demonstrating significant industrial application value.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications may still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions may be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a 10X molecular sieve catalyst based on calcium ion exchange, characterized in that, Includes the following steps: (1) Calcium ion exchange: NaX molecular sieve is subjected to ion exchange with calcium salt solution at an exchange temperature of 50-90℃, an exchange time of 1-6 hours, and 1-3 exchanges to obtain 10X molecular sieve intermediate with a calcium ion exchange rate of 15%-85%; wherein the molar ratio of SiO2 to Al2O3 in NaX molecular sieve is 2.0-3.0:1; (2) Citric acid modification: The 10X molecular sieve intermediate obtained in step (1) is mixed with citric acid solution and stirred for modification reaction at 60-95℃; (3) Post-processing: The modified solid product obtained in step (2) is filtered and separated, washed with deionized water until the filtrate is neutral, the washed product is dried at 100-120℃, and then the dried product is calcined in air at 450-550℃ for 3-6 hours to obtain 10X molecular sieve catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the calcium ion exchange rate is 30%-80%, preferably 50%-70%; the molar ratio of SiO2 to Al2O3 in the NaX molecular sieve is 2.4-2.6:1, preferably 2.5:

1.

3. The preparation method according to claim 2, characterized in that, In step (1), the exchange temperature is 75-85℃, preferably 80℃; the exchange time is 1.5-2.5 hours, preferably 2 hours; and the number of exchanges is 2.

4. The preparation method according to claim 3, characterized in that, In step (1), the calcium salt is one or more of calcium chloride, calcium nitrate or calcium acetate, preferably calcium chloride; the concentration of the calcium salt solution is 0.1-2.0 mol / L, preferably 0.2-1.0 mol / L; during ion exchange, the mass-to-volume ratio of NaX molecular sieve to calcium salt solution is 1:5-15 g / mL, preferably 1:10 g / mL.

5. The preparation method according to claim 4, characterized in that, In step (2), the concentration of the citric acid solution is 0.05-1.5 mol / L, preferably 0.3-0.8 mol / L, more preferably 0.5 mol / L; the mass-to-volume ratio of the 10X molecular sieve intermediate to the citric acid solution is 1:5-15 g / mL, preferably 1:10 g / mL; the reaction temperature during the modification reaction is 75-85℃, preferably 80℃; and the reaction time is 4-6 hours, preferably 5 hours.

6. The preparation method according to claim 5, characterized in that, In step (3), the drying temperature is 105-115℃, preferably 110℃; the drying time is 4-12 hours, preferably 10 hours; the calcination temperature is 490-510℃, preferably 500℃; and the calcination time is 4 hours.

7. A 10X molecular sieve catalyst based on calcium ion exchange obtained by the preparation method of claims 1-6.

8. The application of the calcium ion exchange-based 10X molecular sieve catalyst of claim 1 as a catalyst in Friedel-Crafts acylation reactions; particularly as a catalyst in Friedel-Crafts acylation reactions using fluorobenzene as a substrate and p-fluorobenzoyl chloride as an acylation agent.

9. The application according to claim 8, characterized in that, In the Friedel-Crafts acylation reaction in batch reaction mode, the molar ratio of fluorobenzene to p-fluorobenzoyl chloride is 5-15:1, preferably 10:1; the reaction temperature is 70-150℃, preferably 80℃; the reaction time is 3-10 hours, preferably 6 hours; and the amount of catalyst is 1%-15% of the mass of p-fluorobenzoyl chloride, preferably 10%.

10. The application according to claim 8, characterized in that, In the Friedel-Crafts acylation reaction in a fixed-bed continuous flow reaction mode, the molar ratio of fluorobenzene to p-fluorobenzoyl chloride is 3-6:1, preferably 5:1; the reaction temperature is 80-140℃, preferably 120℃; and the mass hourly space velocity is 0.3-2.5 h⁻¹. -1 Preferably 1.0 h -1 .

Images