Spinel-type composite oxide catalyst and preparation method thereof

Abstract

The present invention belongs to the technical field of fluorochemical industry, and specifically relates to a spinel-type composite oxide catalyst and a preparation method thereof. The general formula of the catalyst is AB2O4, and its preparation method includes: (1) mixing the raw materials at the A-site and the B-site, dissolving them in deionized water, adding citric acid monohydrate, and mixing and stirring to obtain a sol; (2) evaporating the sol to obtain a dry gel, then drying the dry gel, subsequently performing pretreatment on the dried dry gel, and performing calcination after pretreatment to obtain a spinel-type composite oxide catalyst; (3) placing the spinel-type composite oxide catalyst in a fixed-bed reactor, and simultaneously introducing N2 and HF for fluorination treatment. By using adjustable ion types and ratios at the A-site and the B-site to optimize the surface structure and active sites of the catalyst, combined with the citric acid-assisted sol-gel method and specific pretreatment, calcination, and fluorination treatment processes, the stability, catalytic activity, and selectivity of the catalyst are significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorochemical industry, and particularly relates to a spinel-type composite oxide catalyst and a preparation method thereof. Background Art

[0002] 3,3,3-Trifluoropropene (TFP) is an important compound with excellent properties such as low global warming potential (GWP), high energy efficiency, and low toxicity, and thus has received extensive attention and research. This compound is widely used in fields such as refrigerants, blowing agents, solvents, and polymerization monomers. Especially in the refrigeration industry, it is regarded as one of the ideal candidate materials to replace the refrigerant 1,1,1,2-tetrafluoroethane (HFC-134a) with a high GWP value. However, in its industrial production process, the selectivity and activity of the catalyst directly affect the quality and cost of the product. Therefore, developing an efficient and stable catalyst is of great significance for realizing the industrial production of 3,3,3-trifluoropropene. 1,1,3-Trichloropropene (TCP) is a key raw material for synthesizing 3,3,3-trifluoropropene. Under the action of a catalyst, the gas-phase fluorination reaction of TCP with hydrofluoric acid (HF) is a new method for preparing 3,3,3-trifluoropropene. The key to this reaction lies in the selection of the catalyst, because the activity, selectivity, and stability of the catalyst will directly affect the yield and purity of the product. Currently, the existing catalyst systems mainly include Cr-based catalysts, Al-based catalysts, and other composite oxide catalysts. However, these catalysts have exposed some problems in practical applications, such as easy deactivation of the catalyst, low selectivity, low conversion rate, and complex post-treatment. Therefore, developing a new catalyst to improve the conversion rate and selectivity of the reaction and optimize the stability of the catalyst has become a current research hotspot. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a spinel-type composite oxide catalyst, which optimizes the surface structure and active sites of the catalyst by using adjustable A and B site ion types and ratios, and combines the citric acid-assisted sol-gel method and specific pretreatment, calcination, and fluorination treatment processes, significantly improving the stability, catalytic activity, and selectivity of the catalyst.

[0004] Another purpose of the present invention is to provide a preparation method for a spinel-type composite oxide catalyst, with a simple process and easy for large-scale production.

[0005] The technical solution adopted by the present invention is as follows:

[0006] For the preparation method of the spinel-type composite oxide catalyst, the general formula of the spinel-type composite oxide catalyst is AB2O4, where A is one of Mg, Zn, or Ni, and B is Al or Cr;

[0007] The preparation method of the spinel-type composite oxide catalyst comprises the following steps:

[0008] (1) Mix the raw materials at the A-site and the B-site and dissolve them in deionized water. After adding citric acid monohydrate and mixing and stirring, a sol is obtained;

[0009] (2) After evaporating the sol to dryness to obtain a dry gel, then dry the dry gel, and subsequently perform pretreatment on the dried dry gel. After pretreatment, calcination is carried out at 500 - 800 °C, and a spinel-type composite oxide catalyst is obtained after calcination;

[0010] (3) Place the spinel-type composite oxide catalyst in a fixed-bed reactor, and simultaneously introduce N2 and HF for fluorination treatment. The steps of fluorination treatment are as follows: First, fluorinate at 200 - 400 °C for 12 - 48 h, and then raise the temperature to 450 - 650 °C and continue fluorination for 36 - 60 h.

[0011] The raw material at the A-site is one of MgCl2·6H2O, Zn(NO3)2·6H2O or Ni(NO3)2·6H2O; the raw material at the B-site is Al(NO3)3·9H2O or CrCl3·6H2O.

[0012] The molar ratio of the raw materials at the A-site to the B-site is 1:(1 - 4); the mass ratio of the addition amount of citric acid monohydrate to the total amount of the raw materials at the A-site and the B-site is (0.9 - 1.5):1.

[0013] In the step (1), the temperature of mixing and stirring is room temperature, and the time is 1 - 2 h.

[0014] In the step (2), the temperature of evaporation to dryness is 60 - 90 °C; the temperature of drying is 90 - 110 °C.

[0015] In the step (2), the temperature of pretreatment is 180 - 220 °C, and the time is 30 - 60 min.

[0016] In the step (2), the temperature of calcination is 500 - 800 °C, and the time is 4 - 6 h.

[0017] In the step (3), the flow rate of N2 is 0.5 - 4 L / min, and the flow rate of HF is 10 - 30 g / h.

[0018] The spinel-type composite oxide catalyst is prepared by using the above preparation method of the spinel-type composite oxide catalyst.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention prepares a high-performance spinel-type composite oxide catalyst by substituting different elements at the A-site and B-site of spinel. Since the ions at the A-site and B-site can directly participate in the catalytic reaction as active components, it has high catalytic activity and selectivity. At the same time, when they form a spinel composite oxide, the number of oxygen vacancies on the catalyst surface increases, thus significantly enhancing the anti-coking ability of the catalyst and effectively extending the service life of the catalyst. Detailed implementation mode

[0021] The following further illustrates the present invention with reference to examples, but it does not limit the implementation of the present invention.

[0022] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are all conventional methods in the art unless otherwise specified.

[0023] Example 1

[0024] The general formula of the spinel-type composite oxide catalyst described is MgAl2O4, and its preparation method includes the following steps:

[0025] (1) Weigh 20.3 g of MgCl2·6H2O and 75 g of Al(NO3)3·9H2O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 2 h to fully dissolve and complex them to obtain a sol.

[0026] (2) Transfer the sol to a water bath at 60 °C and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to an oven at 90 °C and dry it overnight to fully expand it. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment. The pretreatment temperature is 180 °C and the time is 60 min. Then transfer the pretreated dry gel to a muffle furnace at 500 °C and calcine it for 6 h to obtain a spinel-type composite oxide catalyst.

[0027] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N2 and HF for fluorination treatment. The flow rate of N2 is 0.5 L / min, and the flow rate of HF is 10 g / h. The fluorination treatment steps are as follows: First, fluorinate at 200 °C for 48 h, and then raise the temperature to 450 °C and continue fluorination for 60 h. Keep it for use after fluorination.

[0028] Example 2

[0029] The general formula of the spinel-type composite oxide catalyst described is MgCr2O4, and its preparation method includes the following steps:

[0030] (1) Weigh 20.3 g of MgCl₂·6H₂O and 53.2 g of CrCl₃·6H₂O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 1.8 h to fully dissolve and complex them to obtain a sol.

[0031] (2) Transfer the sol to a water bath at 70 °C and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to an oven at 95 °C and dry it overnight to fully expand it. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment at a temperature of 190 °C for 55 min. Then transfer the pretreated dry gel to a muffle furnace at 550 °C and calcine it for 5.5 h to obtain a spinel-type composite oxide catalyst.

[0032] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N₂ and HF for fluorination treatment. The flow rate of N₂ is 1 L / min, and the flow rate of HF is 15 g / h. The steps of the fluorination treatment are as follows: First, fluorinate at 250 °C for 36 h, and then raise the temperature to 500 °C and continue fluorination for 54 h. After fluorination, it is ready for use.

[0033] Example 3

[0034] The general formula of the spinel-type composite oxide catalyst described above is ZnAl₂O₄, and its preparation method includes the following steps:

[0035] (1) Weigh 29.7 g of Zn(NO₃)₂·6H₂O and 75 g of Al(NO₃)₃·9H₂O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 1.5 h to fully dissolve and complex them to obtain a sol.

[0036] (2) Transfer the sol to a water bath at 75 °C and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to an oven at 100 °C and dry it overnight to fully expand it. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment at a temperature of 200 °C for 50 min. Then transfer the pretreated dry gel to a muffle furnace at 650 °C and calcine it for 5 h to obtain a spinel-type composite oxide catalyst.

[0037] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N₂ and HF for fluorination treatment. The flow rate of N₂ is 2 L / min, and the flow rate of HF is 20 g / h. The steps of the fluorination treatment are as follows: First, fluorinate at 300 °C for 24 h, and then raise the temperature to 550 °C and continue fluorination for 48 h. After fluorination, it is ready for use.

[0038] Example 4

[0039] The general formula of the spinel-type composite oxide catalyst described is ZnCr2O4, and its preparation method includes the following steps:

[0040] (1) Weigh 29.7 g of Zn(NO3)2·6H2O and 53.2 g of CrCl3·6H2O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 1.2 h to fully dissolve and complex them to obtain a sol;

[0041] (2) Transfer the sol to an 80 °C water bath and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to a 105 °C oven and dry it overnight to fully expand it. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment at a temperature of 210 °C for 45 min. Then transfer the pretreated dry gel to a muffle furnace at 700 °C and calcine it for 4.8 h to obtain the spinel-type composite oxide catalyst;

[0042] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N2 and HF for fluorination treatment. The flow rate of N2 is 3 L / min, and the flow rate of HF is 22 g / h. The steps of the fluorination treatment are as follows: First, fluorinate at 350 °C for 18 h, and then raise the temperature to 600 °C and continue fluorination for 42 h. After fluorination, it is ready for use.

[0043] Example 5

[0044] The general formula of the spinel-type composite oxide catalyst described is NiAl2O4, and its preparation method includes the following steps:

[0045] (1) Weigh 29.1 g of Ni(NO3)2·6H2O and 75 g of Al(NO3)3·9H2O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 1 h to fully dissolve and complex them to obtain a sol;

[0046] (2) Transfer the sol to an 85 °C water bath and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to a 110 °C oven and dry it overnight to fully expand it. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment at a temperature of 215 °C for 40 min. Then transfer the pretreated dry gel to a muffle furnace at 750 °C and calcine it for 4.3 h to obtain the spinel-type composite oxide catalyst;

[0047] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N2 and HF for fluorination treatment. The flow rate of N2 is 3.5 L / min, and the flow rate of HF is 25 g / h. The steps of the fluorination treatment are as follows: First, fluorinate at 380 °C for 15 h, and then raise the temperature to 630 °C and continue fluorination for 40 h. After fluorination, it is ready for use.

[0048] Example 6

[0049] The general formula of the spinel-type composite oxide catalyst described is NiCr2O4, and its preparation method includes the following steps:

[0050] (1) Weigh 29.1 g of Ni(NO3)2·6H2O and 53.2 g of CrCl3·6H2O and dissolve them in deionized water. Then add 100 g of citric acid monohydrate and mix and stir at room temperature for 1.1 h to fully dissolve and complex them to obtain a sol;

[0051] (2) Transfer the sol to a water bath at 90 °C and evaporate it to dryness to obtain a compact dry gel. Then transfer the dry gel to an oven at 108 °C and dry it overnight to make it fully expand. Subsequently, transfer the dried dry gel to a muffle furnace for pretreatment. The pretreatment temperature is 220 °C and the time is 35 min. Then transfer the pretreated dry gel to a muffle furnace at 800 °C and calcine it for 4 h to obtain the spinel-type composite oxide catalyst;

[0052] (3) Take 50 mL of the spinel-type composite oxide catalyst and load it into a fixed-bed reactor. At the same time, introduce N2 and HF for fluorination treatment. The flow rate of N2 is 4 L / min, and the flow rate of HF is 28 g / h. The steps of the fluorination treatment are as follows: First, fluorinate at 400 °C for 12 h, and then raise the temperature to 650 °C and continue fluorination for 36 h. After fluorination, it is ready for use.

[0053] Comparative Example 1

[0054] The difference from Example 2 is that in step (2), the calcination temperature is 950 °C, and the others are the same as in Example 2.

[0055] Comparative Example 2

[0056] The difference from Example 2 is that 12.6 g of FeCl2·4H2O is used to replace MgCl2·6H2O in step (1), and the others are the same as in Example 2.

[0057] Comparative Example 3

[0058] The difference from Example 2 is that in step (3), the steps of the fluorination treatment are as follows: First, fluorinate at 250 °C for 36 h, and then raise the temperature to 800 °C and continue fluorination for 54 h, and the others are the same as in Example 2.

[0059] Respectively take 50 mL of the fluorinated catalysts prepared in Examples 1-6 and Comparative Examples 1-3 and load them into a fixed-bed reactor. Introduce TCP and HF, and set the reaction temperatures to 300 °C and 350 °C respectively. Control the molar ratio of HF to TCP to be 10:1, and the space velocity is 250 h -1 , and TFP is prepared.

[0060] Calculate the TCP conversion rate (%) and TFP selectivity (%) of each reaction respectively.

[0061] The test results are shown in Table 1.

[0062] Table 1 Performance test results

[0063]

[0064] It can be seen from the test data in Table 1 that due to the differences in elements used, calcination temperature and other conditions, the catalysts prepared in Examples 1-6 exhibit different catalytic performances. Among them, the catalyst prepared from two elements, Mg and Cr, in Example 2 has the best catalytic effect.

[0065] Compared with Example 2, in Comparative Example 1, increasing the calcination temperature led to a sharp drop in the specific surface area of the catalyst, so the activity and selectivity of the catalyst both decreased.

[0066] Compared with Example 2, in Comparative Example 2, replacing the raw material Mg with Fe led to a decrease in the catalyst activity, which also indicates that the presence of Mg is more beneficial to the activity of the catalyst. Since Mg is an alkaline earth metal element, the catalyst has more basic centers, so the anti-coking ability is stronger.

[0067] Compared with Example 2, in Comparative Example 3, increasing the fluorination temperature of the catalyst led to over-fluorination of the catalyst, resulting in a decrease in the catalyst activity.

Claims

1. A preparation method of a spinel-type composite oxide catalyst, characterized in that, The general formula of the spinel-type composite oxide catalyst is AB2O4, where A is one of Mg, Zn or Ni, and B is Al or Cr; The raw material at the A site is one of MgCl2·6H2O, Zn(NO3)2·6H2O or Ni(NO3)2·6H2O; the raw material at the B site is Al(NO3)3·9H2O or CrCl3·6H2O; The preparation method of the spinel-type composite oxide catalyst includes the following steps: (1) Mix the raw materials at the A site and the B site and dissolve them in deionized water. After adding citric acid monohydrate and mixing and stirring, a sol is obtained; (2) After evaporating the sol to obtain a dry gel, then dry the dry gel, and then perform pretreatment on the dried dry gel. The pretreatment temperature is 180-220°C. After pretreatment, calcine at 500-800°C to obtain a spinel-type composite oxide catalyst; (3) Place the spinel-type composite oxide catalyst in a fixed-bed reactor and simultaneously introduce N2 and HF for fluorination treatment. The steps of fluorination treatment are: first fluorinate at 200-400°C for 12-48h, and then raise the temperature to 450-650°C and continue fluorination for 36-60h.

2. The preparation method of the spinel-type composite oxide catalyst according to claim 1, characterized in that, The molar ratio of the raw materials at the A site to the B site is 1:(1-4); the mass ratio of the addition amount of citric acid monohydrate to the total amount of the raw materials at the A site and the B site is (0.9-1.5):

1.

3. The preparation method of the spinel-type composite oxide catalyst according to claim 1, characterized in that, In the step (1), the mixing and stirring temperature is room temperature and the time is 1-2h.

4. The preparation method of the spinel-type composite oxide catalyst according to claim 1, characterized in that, In the step (2), the evaporation temperature is 60-90°C; the drying temperature is 90-110°C.

5. The preparation method of the spinel-type composite oxide catalyst according to claim 1, characterized in that, In the step (2), the pretreatment time is 30-60min.

6. The preparation method of the spinel-type composite oxide catalyst according to claim 1, wherein In the step (2), the calcination time is 4-6h.

7. The preparation method of the spinel-type composite oxide catalyst according to claim 1, characterized in that, In the step (3), the flow rate of N2 is 0.5-4L / min.

8. The preparation method of the spinel-type composite oxide catalyst according to claim 1, wherein, In the step (3), the flow rate of HF is 10-30g / h.

9. A spinel-type composite oxide catalyst, characterized in that, It is prepared by using the preparation method of the spinel-type composite oxide catalyst described in any one of claims 1-8.

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