Nano chromium oxyfluoride catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nano chromium oxyfluoride catalyst as well as a preparation method and application thereof, and the catalyst is prepared by taking a chromium source as a precursor, taking small molecular organic acid, a cationic surfactant and a nonionic surfactant as templates, adding a fluorine source and adopting a template agent guiding-solid phase thermal decomposition method. The preparation method comprises the following steps: grinding and mixing a chromium source precursor, a fluorine source and a template agent, reacting the mixture at 100-200 DEG C for 6-48 hours, centrifugally washing the reactant, drying, and sufficiently roasting the dried product in a muffle furnace to obtain the nano chromium oxyfluoride catalyst. The prepared nano chromium oxyfluoride catalyst has extremely high selectivity and stability when applied to a reaction for preparing fluorine-containing olefins (HFOs) through gas-phase HF removal of hydrofluoroalkanes (HFCs), the catalytic selectivity reaches up to 100% (the selectivity of a cis-product Z-HFO-1225ye reaches up to 98%), the catalytic conversion rate reaches 85% or above, and the nano chromium oxyfluoride catalyst has the advantages of being high in conversion rate, high in selectivity, good in stability and suitable for industrial production. The cost is low, and the operation is simple.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalyst technology, specifically relating to the preparation of a nano-chromium fluoride catalyst, its preparation method, and its application. Background Technology

[0002] Hydrofluorocarbons (HFCs), as an important class of fluorinated compounds, were once widely used in refrigeration, foaming, and aerosols to replace ozone-depleting chlorofluorocarbons (CFFCs) and hydrochlorofluorocarbons (HCFCs). However, HFCs have extremely high global warming potential (GWP), with a greenhouse effect thousands of times greater than that of carbon dioxide. Hydrofluoroolefins (HFOs), due to their low GWP, short atmospheric lifetime, and excellent thermodynamic properties, are considered key candidates for next-generation environmentally friendly refrigerants and functional chemicals.

[0003] Among the methods for synthesizing HFOs, the reaction of removing hydrogen fluoride (HF) from hydrofluoroalkanes to prepare hydrofluoroolefins (HFC→HFO+HF) is one of the most promising technical routes. This reaction achieves the reconstruction of CF through elimination reactions, which can utilize existing HFC production capacity, reduce raw material costs, and reduce environmental pollution from fluorine-containing waste.

[0004] Currently, this method faces many challenges. For example, the high bond energy of the CF bond (~485 kJ / mol) necessitates high-temperature conditions (>400℃) for traditional pyrolysis pathways, resulting in high energy consumption and a tendency to trigger side reactions (such as cracking and polymerization), thus reducing product selectivity. Secondly, during catalytic HF removal, the catalyst is prone to deactivation due to fluorination or coking, leading to insufficient stability. Furthermore, controlling the stereoselectivity of the reaction pathway is difficult, making it challenging to efficiently synthesize HFOs products with specific configurations (such as trans or cis). Therefore, developing a catalyst with anti-coking properties, high stability, and high selectivity is of great significance for the reaction.

[0005] This invention uses chromium nitrate as a precursor and employs different template agents and fluorine sources to prepare a nano-chromium fluoride oxyfluoride catalyst through solid-phase thermal decomposition at a certain temperature. Traditional chromium-based catalysts obtained by sol-gel and precipitation methods are mostly amorphous nanoparticles. During synthesis, due to the rapid hydrolysis and condensation rates of the precursor, it is difficult to control the grain size, and consequently, the final particle size. They also exhibit poor thermal stability, are prone to agglomeration leading to a decrease in specific surface area, and have underdeveloped porosity. This invention, by not using a solvent, avoids problems such as mesoporous structure collapse, oxide particle agglomeration, and poor thermal stability during template agent removal. Furthermore, the introduction of a fluorine source reduces the fluorination step of the catalyst, improving its catalytic efficiency. The catalyst prepared by this method has advantages such as high selectivity, high yield, low energy consumption, and simple operation. In the reaction of HFC-236ea deHF to prepare HFO-1225ye, the selectivity of Z-HFO-1225ye reaches as high as 98%. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, the present invention aims to provide a nano-chromium fluoride oxycatalyst, its preparation method, and its application. The catalyst of this invention possesses advantages such as being solvent-free, highly selective, having a high yield, low energy consumption, and simple operation. The application of the nano-chromium fluoride oxycatalyst in the catalytic deHF removal from 1,1,1,2,3,3-hexafluoropropane to prepare 1,2,3,3,3-pentafluoropropene exhibits advantages such as relatively low reaction temperature, high catalytic conversion rate, high catalytic selectivity, and good catalytic stability.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for preparing a nano-chromium fluoride catalyst, the specific preparation process includes the following steps:

[0009] 1) Accurately weigh the chromium source, fluorine source and template agent, then grind and mix them. Transfer the uniformly ground mixture to the reaction vessel.

[0010] 2) After sealing the reactor, place it in a forced-air drying oven and crystallize it for 6 to 48 hours at a pyrolysis temperature of 100 to 200°C.

[0011] 3) After the reaction is completed, the product is cooled to room temperature, washed with deionized water and dried, and then calcined at high temperature in a muffle furnace. After calcination is completed, the product is cooled to room temperature to obtain nano-chromium fluoride catalyst.

[0012] Furthermore, the chromium source is selected from at least one of Cr(NO3)2·9H2O, CrCl3·6H2O, and chromium acetylacetone, preferably Cr(NO3)2·9H2O; the fluorine source is selected from at least one of ammonium fluoride, ammonium fluoroborate, and PTFE, preferably ammonium fluoride; the template agent is selected from at least one of citric acid (CA), hexadecyltrimethylammonium bromide (CTAB), and P123, preferably CTAB.

[0013] Furthermore, the molar ratio of the chromium source to the template agent is 0.5 to 2:1, preferably 1 to 1.5:1.

[0014] Furthermore, the molar ratio of the chromium source to the fluorine source is 1:1 to 5, preferably 1:3 to 4.

[0015] Furthermore, the pyrolysis temperature is 120–180℃, preferably 150–160℃, and the pyrolysis reaction time is 12–48 h, preferably 20–24 h.

[0016] Furthermore, the muffle furnace calcination temperature is set to 300–600℃, preferably 400–500℃, and the calcination time is 3–5 hours.

[0017] This invention also discloses the application of the aforementioned nano-chromium fluoride oxyfluoride catalyst in the catalytic gas-phase deHF removal of hydrofluoroalkanes to prepare fluorinated olefins. The application method is as follows: the catalyst is loaded into a fixed-bed reactor, and a mixed gas of N2 and hydrofluoroalkanes is introduced. The feed volume ratio of N2 to hydrofluoroalkanes is 1:0.5-2, preferably 1:0.5-1, and the total space velocity of the mixed gas of N2 and hydrofluoroalkanes is 300-800 h⁻¹. -1 Preferably 500-600h -1 The reaction temperature is 200–500℃, preferably 350–450℃, and the reaction produces pentafluoropropylene.

[0018] Furthermore, the hydrofluoroalkane is 1,1,1,2,3,3-hexafluoropropane, and the hydrofluoroolefin is 1,2,3,3,3-pentafluoropropene.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0020] (1) The nano-chromium oxyfluoride catalyst of the present invention is prepared by a template-guided solid-phase thermal decomposition reaction, overcoming the disadvantages of traditional wet catalyst preparation methods such as complex preparation, particle agglomeration, and environmental pollution. Using citric acid, cationic surfactant (CTAB), and nonionic surfactant (P123) as templates, and adding organic or inorganic fluorine sources, a layered mesoporous structure of chromium oxyfluoride is synthesized by solid-phase thermal decomposition of chromium nitrate precursor. The structure of the nano-chromium oxyfluoride material can be modulated by varying reaction factors such as surfactant type, pyrolysis temperature, crystallization time, and fluorine source ratio, thus preparing chromium oxyfluoride materials with amorphous or crystalline structures. Chromium nitrate, fluorine source, and templates work synergistically through electrostatic or hydrogen bonding, forming a layered structure through self-assembly, promoting the formation of chromium oxyfluoride molecular nuclei, and ultimately obtaining a stable mesoscopic structure.

[0021] (2) The nano-chromium fluoride catalyst obtained in this invention is used in the catalytic deHF removal of 1,1,1,2,3,3-hexafluoropropane to prepare 1,2,3,3,3-pentafluoropropene. It has the advantages of relatively low reaction temperature, high catalytic conversion rate, high catalytic selectivity, good catalytic stability and low catalyst cost. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0023] Example 1

[0024] Weigh out 0.05 mol of Cr(NO3)3·9H2O, 0.15 mol of NH4F, and 0.05 mol of CTAB, mix and grind them evenly. Place the mixed solid sample into a reaction vessel, then seal the reaction vessel and place it in a forced-air drying oven. React at a pyrolysis temperature of 150℃ for 24 h. After the reaction, cool to room temperature, wash the product with a large amount of deionized water, dry the washed product, place it in a graphite crucible, and put it in a muffle furnace. Under an air atmosphere, heat the product from room temperature to 500℃ at a rate of 5℃ / min, and then calcine it at 500℃ for 3 h. After calcination, allow it to cool naturally to room temperature in the muffle furnace to obtain the nano-chromium oxide catalyst. Press the obtained catalyst sample into tablets at 10–20 MPa, crush them, and sieve them using a 20–40 mesh sieve.

[0025] The nano-chromium oxide catalyst prepared above was used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye), as shown in the following reaction formula:

[0026]

[0027] The catalytic reaction conditions were as follows: the catalyst was loaded into a fixed-bed reactor at a loading rate of 1 ml; a mixture of N2 and HFC-236ea was introduced, with the N2 flow rate controlled at 5 ml / min and the HFC-236ea flow rate at 5 ml / min; and the total space velocity of the mixed gas was 600 h⁻¹. -1 The reaction temperature was 350℃, and the reaction was carried out at atmospheric pressure for 30 hours. The evaluation results are shown in Table 1.

[0028] Example 2

[0029] Example 2 The preparation steps of the catalyst are the same as in Example 1, except that the pyrolysis temperature is 120°C, and other conditions remain unchanged.

[0030] Example 3

[0031] Example 3 The preparation steps of the catalyst are the same as in Example 1, except that the pyrolysis temperature is 180°C, and other conditions remain unchanged.

[0032] The catalysts used in Examples 2 and 3 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropylene (HFO-1225ye). The catalytic reaction conditions were the same as in Example 1, with the reaction under normal pressure for 30 h. The evaluation results are shown in Table 1.

[0033] Table 1. Catalytic activity of catalysts at different pyrolysis temperatures for HFC-236ea cracking.

[0034]

[0035] Example 4

[0036] The preparation steps of the catalyst in Example 4 were the same as in Example 1, except that the crystallization time was 12 hours, while other conditions remained unchanged.

[0037] Example 5

[0038] The preparation steps of the catalyst in Example 5 were the same as in Example 1, except that the crystallization time was 48 hours, while other conditions remained unchanged.

[0039] The catalysts used in Examples 4 and 5 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropylene (HFO-1225ye). The catalytic reaction conditions were the same as in Example 1, with the reaction under atmospheric pressure for 30 h. The evaluation results are shown in Table 2.

[0040] Table 2 Catalytic activity of catalysts at different crystallization times for HFC-236ea cracking

[0041]

[0042] Example 6

[0043] Example 6 The catalyst preparation steps are the same as in Example 1, except that "0.05 mol of CTAB is replaced with an equal amount of citric acid", and other conditions remain unchanged.

[0044] Example 7

[0045] Example 7 The catalyst preparation steps are the same as in Example 1, except that "0.05 mol of CTAB is replaced with surfactant P123 and the amount of P123 is 0.001 mol", and other conditions remain unchanged.

[0046] The catalysts of Examples 6 and 7 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic reaction conditions were the same as in Example 1, and the reaction was carried out at atmospheric pressure for 30 h. The evaluation results are shown in Table 3.

[0047] Table 3: Catalytic activity of catalysts for HFC-236ea cracking under different template agent conditions

[0048]

[0049] Example 8

[0050] The preparation steps of the catalyst in Example 8 were the same as in Example 1, except that the fluorine source was replaced with an equal molar amount of NH4BF4, while other conditions remained unchanged.

[0051] Example 9

[0052] Example 8 The preparation steps of the catalyst are the same as in Example 1, except that the fluorine source is replaced with an equal molar amount of PTFE, and other conditions remain unchanged.

[0053] The catalysts of Examples 8 and 9 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic reaction conditions were the same as in Example 1, and the reaction was carried out at atmospheric pressure for 30 h. The evaluation results are shown in Table 4.

[0054] Table 4: Catalytic activity of catalysts for HFC-236ea cracking under different fluorine sources

[0055]

[0056] Example 10

[0057] Example 10 The preparation steps of the catalyst are the same as in Example 1, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of CTAB is replaced with 0.025 mol", while other conditions remain unchanged.

[0058] Example 11

[0059] Example 11 The catalyst preparation steps are the same as in Example 1, except that the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol and the amount of CTAB is replaced with 0.1 mol, while other conditions remain unchanged.

[0060] Example 12

[0061] Example 12 The catalyst preparation steps are the same as in Example 6, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of citric acid is replaced with 0.025 mol", while other conditions remain unchanged.

[0062] Example 13

[0063] Example 13 The preparation steps of the catalyst are the same as in Example 6, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of citric acid is replaced with 0.1 mol", while other conditions remain unchanged.

[0064] Example 14

[0065] Example 14 The preparation steps of the catalyst are the same as in Example 7, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of P123 is replaced with 0.005 mol", while other conditions remain unchanged.

[0066] Example 15

[0067] Example 15 The catalyst preparation steps are the same as in Example 7, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of P123 is replaced with 0.025 mol", while other conditions remain unchanged.

[0068] The catalysts in Examples 10-15 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic reaction conditions were repeated in Example 1, and the reaction was carried out at atmospheric pressure for 30 h. The evaluation results are shown in Table 5.

[0069] Table 5: Catalytic activity of catalysts for HFC-236ea cracking under different surfactant contents

[0070]

[0071] Example 16

[0072] Example 16 The preparation steps of the catalyst are the same as in Example 1, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of NH4F is replaced with 0.05 mol", while other conditions remain unchanged.

[0073] Example 17

[0074] Example 17 The catalyst preparation steps are the same as in Example 1, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of NH4F is replaced with 0.25 mol", while other conditions remain unchanged.

[0075] Example 18

[0076] Example 18 The preparation steps of the catalyst are the same as in Example 8, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of NH4BF4 is replaced with 0.05 mol", while other conditions remain unchanged.

[0077] Example 19

[0078] Example 19 The preparation steps of the catalyst are the same as in Example 8, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of NH4BF4 is replaced with 0.25 mol", while other conditions remain unchanged.

[0079] Example 20

[0080] Example 20 The preparation steps of the catalyst are the same as in Example 9, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of PTFE is replaced with 0.05 mol", while other conditions remain unchanged.

[0081] Example 21

[0082] Example 21 The preparation steps of the catalyst are the same as in Example 9, except that "the amount of Cr(NO3)3·9H2O remains unchanged at 0.05 mol, and the amount of PTFE is replaced with 0.25 mol", while other conditions remain unchanged.

[0083] The catalysts of Examples 16-21 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic reaction conditions were repeated in Example 1, and the reaction was carried out at atmospheric pressure for 30 h. The evaluation results are shown in Table 6.

[0084] Table 6: Catalyst activity for HFC-236ea cracking under different fluorine sources and dosages

[0085]

[0086] Example 22

[0087] Example 22 The catalyst preparation steps are the same as in Example 1, except that "the amount of CTAB is replaced with 0 mmol", and other conditions remain unchanged.

[0088] Example 23

[0089] Example 23 The catalyst preparation steps are the same as in Example 1, except that "the amount of NH4F is replaced with 0 mmol", and other conditions remain unchanged.

[0090] Example 24

[0091] Example 24 The catalyst preparation steps are the same as in Example 1, except that "0.15 mol NH4F is replaced with 0.075 mol NH4F and 0.075 mol PTFE", and other conditions remain unchanged.

[0092] The catalysts used in Examples 22-24 were used to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic reaction conditions were the same as in Example 1, with the reaction under normal pressure for 30 h. The evaluation results are shown in Table 7.

[0093] Table 7: Catalytic activity of catalyst for HFC-236ea cracking under varying surfactant and fluorine source conditions

[0094]

[0095] Example 25

[0096] Example 25 describes an experiment using the catalyst from Example 1 to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic evaluation process was repeated in Example 1, except that the reaction time at atmospheric pressure was 50 h. All other conditions remained the same. The evaluation results are shown in Table 8.

[0097] Example 26

[0098] Example 26 describes an experiment using the catalyst from Example 1 to catalyze the cracking of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to prepare 1,2,3,3,3-pentafluoropropene (HFO-1225ye). The catalytic evaluation process was repeated in Example 1, except that the reaction time at atmospheric pressure was 100 h. All other conditions remained the same. The evaluation results are shown in Table 8.

[0099] Table 8: Catalytic activity of catalysts at different reaction times for HFC-236ea cracking

[0100]

[0101] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a nano-chromium fluoride catalyst, characterized in that... A fluorine source and a template agent are added to a chromium source, ground and mixed evenly, and then the solid sample is loaded into a reaction vessel. After the reaction vessel is sealed, it is transferred to a forced-air drying oven and subjected to solid-phase pyrolysis reaction at 100~200℃ for 6~48h. After the reaction is completed, the sample is cooled to room temperature, washed and dried, and finally calcined at high temperature in a muffle furnace to obtain the nano-fluorine oxychromium catalyst.

2. The method for preparing a nano-chromium oxyfluoride catalyst as described in claim 1, characterized in that... The chromium source is selected from at least one of Cr(NO3)2·9H2O, CrCl3·6H2O, and chromium acetylacetone, preferably Cr(NO3)2·9H2O; the fluorine source is selected from at least one of ammonium fluoride, ammonium fluoroborate, and PTFE, preferably ammonium fluoride; the template agent is selected from at least one of citric acid (CA), hexadecyltrimethylammonium bromide (CTAB), and surfactant P123, preferably CTAB.

3. The method for preparing a nano-chromium fluoride catalyst as described in claim 1, characterized in that... The molar ratio of chromium source to template agent is 0.5~2:1, preferably 1~1.5:

1.

4. The method for preparing a nano-chromium fluoride catalyst as described in claim 1, characterized in that... The molar ratio of chromium source to fluorine source is 1:1 to 5, preferably 1:3 to 4.

5. The method for preparing a nano-chromium fluoride catalyst as described in claim 1, characterized in that... The pyrolysis temperature is 120~180℃, preferably 150-160℃, and the pyrolysis reaction time is 12~48h, preferably 20-24h.

6. The method for preparing a nano-chromium fluoride catalyst as described in claim 1, characterized in that... The muffle furnace calcination temperature is set to 300~600℃, preferably 400~500℃, and the calcination time is 3~5h.

7. A nano-chromium fluoride catalyst prepared by the method described in any one of claims 1-6.

8. The application of the nano-chromium fluoride catalyst as described in claim 1 in the catalytic gas-phase deHF removal of hydrofluoroalkane to prepare fluorinated olefins.

9. The application of the nano-chromium fluoride catalyst as described in claim 8 in the catalytic gas-phase deHF removal of hydrofluoroalkanes to prepare fluorinated olefins, characterized in that, The catalyst is loaded into a fixed-bed reactor, and a mixture of N2 and hydrofluoroalkane is introduced. The feed volume ratio of N2 to hydrofluoroalkane is 1:0.5~2, preferably 1:0.5~1, and the total space velocity of the N2 and hydrofluoroalkane mixture is 300~800 h⁻¹. -1 Preferably 500~600 h -1 The reaction temperature is 200~500 ℃, preferably 350~450 ℃, and the reaction produces pentafluoropropylene.

10. The application of the nano-chromium fluoride catalyst as described in claim 8 in the catalytic gas-phase deHF removal of hydrofluoroalkanes to prepare fluorinated olefins, characterized in that, The hydrofluoroalkane is 1,1,1,2,3,3-hexafluoropropane, and the hydrofluoroolefin is 1,2,3,3,3-pentafluoropropene.

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