Alumina-loaded molecular alkane dehydrogenation catalyst and preparation method and application thereof

Abstract

The invention discloses an alumina-loaded molecular alkane dehydrogenation catalyst and a preparation method and application thereof. The preparation method comprises the following steps: (1) carrying out modification treatment on alumina balls; and (2) adding the modified alumina balls into a dissolved solution of a molecular catalyst, stirring, reacting until the supernatant is colorless, filtering, and drying to obtain the alumina-loaded molecular alkane dehydrogenation catalyst. The catalyst provided by the invention is used in a process for preparing olefin through dehydrogenation of straight-chain alkane, the alkane conversion rate can reach 21% or above, the catalyst is high in catalytic efficiency, good in selectivity and easy to recover, and the activity of the recovered catalyst is still high.

Description

Technical Field

[0001] The invention belongs to the technical field of dehydrogenation catalyst preparation, and specifically relates to an alumina-supported molecular alkane dehydrogenation catalyst and a preparation method and application thereof. Background Art

[0002] Heterogeneous alkane dehydrogenation catalysts are widely used in industry to convert low-value alkanes into high-value-added olefins; however, these catalysts require a high reaction temperature during the catalytic process and are accompanied by the generation of by-products such as cracking and rearrangement. Molecular alkane dehydrogenation catalysts have the characteristics of low reaction temperature and good selectivity. Taking the pincer iridium catalyst as an example, the reaction of catalytic transfer dehydrogenation of linear alkanes can be carried out at below 200°C without side reactions such as cracking and rearrangement. However, these molecular alkane dehydrogenation catalysts are soluble in the reaction solvent or alkane substrate, making it difficult to recycle the catalyst. Summary of the invention

[0003] The purpose of the present invention is to provide an alumina-supported molecular alkane dehydrogenation catalyst and a preparation method and application thereof.

[0004] The technical solution adopted by the present invention is: A method for preparing an alumina-supported molecular alkane dehydrogenation catalyst comprises the following steps: (1) Modification of alumina balls; (2) Add the modified alumina balls to the solution of the molecular catalyst, stir the reaction until the supernatant becomes colorless, then filter and dry to obtain an alumina-supported molecular alkane dehydrogenation catalyst.

[0005] Furthermore, the modification treatment method in step (1) comprises the following steps: (1.1) Add alumina balls to the modifier, stir until the water evaporates, filter out excess powder with a sieve, and dry for later use: (1.2) The dried alumina balls are calcined at high temperature under oxygen to obtain modified alumina balls.

[0006] Furthermore, in step (1.1), the modifier is an alkaline solution or salt solution of an alkali metal or an alkaline earth metal, the mass concentration of the alkaline solution or the salt solution is 2-3%, the mass ratio of the alumina ball to the alkali in the alkaline solution is 1:0.02-0.05, and the mass ratio of the alumina ball to the salt in the salt solution is 1:0.02-0.05.

[0007] Furthermore, the drying temperature in step (1.1) is 100-130° C., and the drying time is 10-15 hours; the calcination temperature in step (1.2) is 400-600° C., and the calcination time is 4-8 hours.

[0008] Furthermore, in step (1), the alumina balls are γ-alumina balls, and their diameter is 0.5 to 2.5 mm.

[0009] Furthermore, in step (2), the molecular catalyst is an iridium catalyst, and the iridium catalyst is p -MeO- tBu PCP-Ir(L n ).

[0010] Furthermore, in step (2), the solvent of the molecular catalyst is one of toluene, xylene or trimethylbenzene, and the mass ratio of the molecular catalyst to the solvent is 1:50-60.

[0011] Furthermore, in step (2), the mass ratio of alumina balls to molecular catalyst is 80 to 100:1.

[0012] Furthermore, in step (2), the pressure of the reduced pressure drying is <1 atm, the drying temperature is 30 to 60° C., and the drying time is 10 to 14 h.

[0013] A molecular alkane dehydrogenation catalyst supported by alumina prepared according to any one of the above preparation methods.

[0014] The above-mentioned alumina-supported molecular alkane dehydrogenation catalyst is used in the dehydrogenation process of long-chain alkanes with a carbon number of 10 to 20.

[0015] The beneficial effects of the present invention are: 1. The present invention uses alumina balls as carriers to load iridium catalysts. When used in fixed bed reactors, compared with commonly used powdered alumina, alumina balls, especially γ-alumina balls, have a larger diameter and produce a lower pressure drop. At the same time, there is less mass loss during the catalyst recovery process, which is more convenient for recovery.

[0016] 2. Compared with untreated alumina carrier, the catalytic efficiency and selectivity of the dehydrogenation catalyst can be further improved by loading the iridium catalyst on the modified alumina. The catalyst of the present invention is used in the process of dehydrogenating long-chain alkanes with carbon numbers of 10 to 20 to prepare olefins, and the alkane conversion rate can reach more than 21%, and the olefin selectivity can reach more than 90%. DETAILED DESCRIPTION

[0017] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0018] The alumina balls used in the examples and comparative examples were purchased from SASOL.

[0019] The synthesis of iridium catalysts was referred to known literature, doi: 10.1126 / science.add1088. Example 1

[0020] The preparation method of the molecular alkane dehydrogenation catalyst A supported by γ-alumina is as follows: (1) Weigh 0.47 g of potassium carbonate, add 20 mL of distilled water, stir thoroughly to form a 2.29% potassium carbonate aqueous solution, add 10 g of γ-alumina balls with a diameter of 1 mm to the potassium carbonate aqueous solution; stir carefully at room temperature, and after the water evaporates, place the γ-alumina balls in a 120°C oven to dry for 12 hours, and use a sieve to sieve out alumina powder with a diameter of less than 1 mm; then place the sieved γ-alumina balls in an oxygen flow and calcine at 550°C for 5 hours. After cooling, alkali-treated γ-alumina balls are obtained.

[0021] (2) 0.048 g of iridium catalyst p -MeO- tBu PCP-Ir(L n ) was added to 3 ml of toluene to dissolve, and then 4 g of the γ-alumina balls treated with alkali in step (1) were added, and the mixture was carefully stirred until the supernatant became colorless and then filtered. The residual solvent was dried under reduced pressure to obtain a γ-alumina-supported molecular alkane dehydrogenation catalyst A. Example 2

[0022] The preparation method of the molecular alkane dehydrogenation catalyst B supported by γ-alumina is as follows: (1) Weigh 0.3 g of potassium hydroxide, add 13 mL of distilled water, stir thoroughly to form a 2.25% potassium hydroxide aqueous solution, add 6.5 g of γ-alumina balls with a diameter of 0.5 mm to the potassium hydroxide aqueous solution; stir carefully at room temperature, and after the water evaporates, place the γ-alumina balls in a 100°C oven to dry for 14 hours, and use a sieve to sieve out alumina powder with a diameter of less than 0.5 mm; then place the sieved γ-alumina balls in an oxygen flow and calcine at 580°C for 4.5 hours. After cooling, alkali-treated γ-alumina balls are obtained.

[0023] (2) 0.01 g of iridium catalyst p -MeO- tBu PCP-Ir(L n ) was added into 0.6 ml of xylene to dissolve, and then 0.85 g of the γ-alumina balls treated with alkali in step (1) was added, and the mixture was carefully stirred until the supernatant became colorless and then filtered. The residual solvent was dried under reduced pressure to obtain a γ-alumina-supported molecular alkane dehydrogenation catalyst B. Example 3

[0024] The preparation method of the molecular alkane dehydrogenation catalyst C supported by γ-alumina is as follows: (1) Weigh 0.3 g of sodium bicarbonate, add 12 mL of distilled water, stir thoroughly to form a 2.4% sodium bicarbonate aqueous solution, add 7.5 g of γ-alumina balls with a diameter of 2.5 mm to the sodium bicarbonate aqueous solution; stir carefully at room temperature, and after the water evaporates, place the γ-alumina balls in a 110°C oven to dry for 13 hours, and use a sieve to sieve out alumina powder with a diameter of less than 1.5 mm; then place the sieved γ-alumina balls in an oxygen flow and calcine at 500°C for 6 hours. After cooling, alkali-treated γ-alumina balls are obtained.

[0025] (2) 0.03 g of iridium catalyst p -MeO- tBu PCP-Ir(L n ) was added into 2 ml of trimethylbenzene to dissolve, and then 2.7 g of the γ-alumina balls treated with alkali in step (1) were added, and the mixture was carefully stirred until the supernatant became colorless and then filtered. The residual solvent was dried under reduced pressure to obtain a γ-alumina-supported molecular alkane dehydrogenation catalyst C.

[0026] Catalyst performance evaluation: 200 mg of the dehydrogenation catalyst of Examples 1-3 were respectively added to the reactor, and 68 μl of dodecane, 39 μl of tert-butylethylene, and 1 ml of toluene were added. The reaction temperature was 200° C. After reacting at normal pressure for 1 hour, the supernatant was taken and the alkane conversion rate was determined by gas chromatography, as shown in Table 1.

[0027] Evaluation of recovery performance of dehydrogenation catalyst: The reaction solution of Example 1 was recovered and filtered to obtain a γ-alumina-supported molecular alkane dehydrogenation catalyst A. The quality test showed that the catalyst was not lost. The recovered catalyst was used to continue the dodecane dehydrogenation reaction under the same conditions. After the reaction was completed, the supernatant was removed to determine the alkane conversion rate. The olefin selectivity is shown in Table 1.

[0028]

[0029] It can be seen from Table 1 that the dehydrogenation catalyst of the present invention has high catalytic efficiency and good selectivity. After being reused seven times, the seventh alkane conversion rate is 18%, and it still has good activity after recycling.

[0030] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications are also within the protection scope of the present invention.

Claims

1. A method for preparing an alumina-supported molecular alkane dehydrogenation catalyst, characterized in that: The following steps are involved: (1) Modification of alumina balls; (2) Add the modified alumina balls to the solution of the molecular catalyst, stir the reaction until the supernatant becomes colorless, then filter and dry to obtain an alumina-supported molecular alkane dehydrogenation catalyst.

2. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: The modification treatment method comprises the following steps: (1.1) Add alumina balls to the modifier, stir until the water evaporates, filter out excess powder with a sieve, and dry for later use: (1.2) The dried alumina balls are calcined at high temperature under oxygen to obtain modified alumina balls.

3. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 2, characterized in that: The modifier is an alkaline solution or salt solution of an alkali metal or an alkaline earth metal, the mass concentration of the alkaline solution or the salt solution is 2-3%, the mass ratio of the alumina ball to the alkali in the alkaline solution is 1:0.02-0.05; the mass ratio of the alumina ball to the salt in the salt solution is 1:0.02-0.

05.

4. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 2, characterized in that: The drying temperature is 100-130°C, and the drying time is 10-15 hours; the roasting temperature is 400-600°C, and the roasting time is 4-8 hours.

5. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: The alumina balls are γ-alumina balls with a diameter of 0.5 to 2.5 mm.

6. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: The molecular catalyst is an iridium catalyst, and the iridium catalyst is p -MeO- tBu PCP-Ir(L n ).

7. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: The solvent of the molecular catalyst is one of toluene, xylene or trimethylbenzene, and the mass ratio of the molecular catalyst to the solvent is 1:50-60.

8. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: In step (2), the mass ratio of alumina balls to molecular catalyst is 80 to 100:

1.

9. The method for preparing an alumina-supported molecular alkane dehydrogenation catalyst according to claim 1, characterized in that: In step (2), the pressure of the reduced pressure drying is less than 1 atm, the drying temperature is 30 to 60° C., and the drying time is 10 to 14 h.

10. An alumina-supported molecular alkane dehydrogenation catalyst prepared according to the preparation method according to any one of claims 1 to 9.

11. Use of the alumina-supported molecular alkane dehydrogenation catalyst according to claim 10 in the dehydrogenation process of long-chain alkanes having a carbon number of 10 to 20.

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