Method for preparing long-chain monoolefine through alkane dehydrogenation

Abstract

The invention discloses a method for preparing long-chain monoolefine through alkane dehydrogenation, which comprises the following steps: (1) adding a dehydrogenation catalyst, an activator and a solvent into a reactor, and stirring and dissolving to obtain a dissolved solution; and (2) adding long-chain alkane and a hydrogen acceptor into the dissolved solution, heating to react for a period of time, and cooling the reaction solution to obtain the long-chain monoolefine. According to the method, the reaction energy barrier and the reaction temperature can be greatly reduced, the dehydrogenation reaction can be carried out at the temperature lower than 200 DEG C, and the reaction mechanism is shown in figure 1; at the reaction temperature, the energy input by the system is far lower than the energy required by cracking and rearrangement side reactions, so that the side reactions are fundamentally avoided, the alkane conversion rate can be greater than 20%, and the monoene selectivity is greater than 79%.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a method for preparing long-chain monoolefins by dehydrogenating alkanes. Background Art

[0002] The dehydrogenation of long-chain alkanes to produce monoolefins can provide raw materials for high-value-added fine chemicals such as sodium dodecyl sulfonate (the main component of detergents). The platinum-based dehydrogenation catalysts commonly used in industry can achieve the dehydrogenation of long-chain alkanes under high temperature and hydrogen atmosphere (>450°C), but due to the high reaction temperature and reaction mechanism, side reactions such as cracking and rearrangement are difficult to avoid. At the same time, the higher reaction temperature requires more heat input, which seriously affects the economic benefits of alkane dehydrogenation to prepare fine chemicals. Therefore, under the premise of ensuring the alkane conversion rate and the selectivity of monoolefins, it is of great significance to the field to develop a milder dehydrogenation catalytic system. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing long-chain monoolefins by dehydrogenating alkanes. By adding an activator and a hydrogen acceptor to the catalytic system, the dehydrogenation reaction can be carried out at a temperature below 200°C, which greatly reduces the occurrence of side reactions.

[0004] The technical solution adopted by the present invention is: A method for preparing long-chain monoolefins by dehydrogenating alkanes comprises the following steps: (1) adding a dehydrogenation catalyst, an activator, and a solvent into a reactor, stirring and dissolving them to obtain a solution; (2) Add long-chain alkanes and hydrogen acceptors to the solvent, heat the reaction for a period of time, and then cool the reaction liquid to obtain long-chain monoolefins.

[0005] Preferably, the long-chain alkane is a straight-chain alkane having 10 to 20 carbon atoms.

[0006] Preferably, the dehydrogenation catalyst is p -MeO- tBu PCP-IrHCl catalyst and tBu At least one of POCOP-IrHCl.

[0007] Preferably, the activator is at least one of sodium tert-butoxide, potassium tert-butoxide or lithium tert-butoxide.

[0008] Preferably, the solvent is at least one of toluene, p-xylene and mesitylene.

[0009] Preferably, the hydrogen acceptor is at least one of styrene, tert-butylethylene and 4,4-dimethyl-1-pentene.

[0010] Preferably, the mass ratio of the dehydrogenation catalyst, the activator and dodecane is (4-6):1:(25-30), the mass ratio of the hydrogen acceptor to dodecane is 1:(2-3); and the mass volume ratio of the dehydrogenation catalyst to the solvent is 4-5:1 mg / ml.

[0011] Preferably, in step (1), the reactor is a reaction tube or a reaction kettle.

[0012] Preferably, in step (2), the heating reaction temperature is 155-165° C., and the reaction time is 15-30 minutes.

[0013] Preferably, in step (2), the cooling medium is ice water.

[0014] The beneficial effects of the present invention are: 1. By using a hydrogen acceptor to absorb the generated hydrogen, the reaction energy barrier and reaction temperature can be greatly reduced, so that the dehydrogenation reaction can be carried out at a temperature below 200°C. The reaction mechanism is as follows Figure 1 As shown; at this reaction temperature, the energy input into the system is far lower than the energy required for cracking and rearrangement side reactions, thereby fundamentally eliminating the occurrence of side reactions.

[0015] 2. The alkane conversion rate of the present invention can be greater than 20%, and the monoolefin selectivity can be greater than 79%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The reaction mechanism diagram of the present invention. 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 dehydrogenation catalyst used in the following examples is from the prior art, and its synthesis method is referred to known literature, doi: 10.1126 / science.add1088. Example 1

[0019] A method for preparing long-chain monoolefins by dehydrogenating dodecane, comprising: (1) Weigh the dehydrogenation catalyst tBu POCOP-IrHCl 4.8 mg, sodium tert-butoxide 1.2 mg, were added into the reaction tube, and then toluene 1 ml was added, and the mixture was stirred thoroughly to obtain a solution; (2) 34 mg of dodecane and 26 μL of tert-butylethylene (density 0.653 g / mL at 25 °C (lit.)) were added to the dissolved solution. The reaction tube was then placed in a preheated 155 °C oil bath. After heating for 30 minutes, the reaction tube was immediately cooled with ice water. The obtained product was analyzed by gas chromatography. The dodecane conversion was 20% and the monoolefin selectivity was 85%. Example 2

[0020] A method for preparing long-chain monoolefins by dehydrogenating dodecane, comprising: (1) Weigh the dehydrogenation catalyst p -MeO- tBu 5.2 mg of PCP-IrHCl catalyst and 1.2 mg of potassium tert-butoxide were added to the reaction tube, and then 1 mL of p-xylene was added and stirred thoroughly to dissolve; (2) Add 34 mg of dodecane and 24 μL of styrene to the solution. Then place the reaction tube in a preheated oil bath at 155°C. After heating for 30 minutes, immediately cool the reaction tube with ice water. The obtained product is analyzed by gas chromatography. The conversion rate of dodecane is 21%, and the selectivity of monoolefins is 84%. Example 3

[0021] A method for preparing long-chain monoolefins by dehydrogenation of decane, comprising: (1) Weigh the dehydrogenation catalyst p -MeO- tBu 5.2 mg of PCP-IrHCl catalyst and 0.9 mg of lithium tert-butoxide were added to the reaction tube, followed by 1 mL of mesitylene, and stirred thoroughly to dissolve; (2) 34 mg of decane and 25 μL of 4,4-dimethyl-1-pentene (density: 0.683 g / mL at 25°C (lit.) were added to the solution; the reaction tube was placed in a preheated 165°C oil bath and heated for 15 minutes, and then immediately cooled with ice water; the reaction solution was analyzed by gas chromatography. The decane conversion was 23% and the monoolefin selectivity was 79%.

[0022] Comparative Example 1

[0023] A method for preparing long-chain monoolefins by dehydrogenating dodecane, comprising: (1) Weigh the dehydrogenation catalyst tBu POCOP-IrHCl 4.8 mg, sodium tert-butoxide 1.2 mg, were added into the reaction tube, and then toluene 1 ml was added, and the mixture was stirred thoroughly to obtain a solution; (2) 34 mg of dodecane was added to the solution, and the reaction tube was then placed in a preheated 155°C oil bath. After heating for 30 minutes, the reaction tube was immediately cooled with ice water. The obtained product was analyzed by gas chromatography, and the dodecane conversion rate was 0.

[0024] Comparative Example 2

[0025] A method for preparing long-chain monoolefins by dehydrogenating dodecane, comprising: (1) Weigh the dehydrogenation catalyst tBu POCOP-IrHCl 4.8 mg was added into the reaction tube, and then 1 ml of toluene was added and stirred thoroughly to obtain a solution; (2) Add 34 mg of dodecane and 26 μL of tert-butylethylene (density 0.653 g / mL at 25 °C (lit.)) to the dissolved solution; then place the reaction tube in a preheated 155 °C oil bath. After heating for 30 minutes, immediately cool the reaction tube with ice water. The obtained product is analyzed by gas chromatography. The dodecane conversion rate is 0.

[0026] It can be seen from Comparative Example 1 and Example 1 that the catalytic system without adding a hydrogen acceptor has no catalytic dodecane dehydrogenation activity under the same reaction conditions.

[0027] It can be seen from Comparative Example 2 and Example 1 that the catalyst system without an activator has no catalytic dodecane dehydrogenation activity under the same reaction conditions.

[0028] 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 long-chain monoolefins by dehydrogenation of alkanes, characterized in that: The following steps are involved: (1) adding a dehydrogenation catalyst, an activator, and a solvent into a reactor, stirring and dissolving them to obtain a solution; (2) Add long-chain alkanes and hydrogen acceptors to the solvent, heat the reaction for a period of time, and then cool the reaction liquid to obtain long-chain monoolefins.

2. The method for preparing long-chain carbon monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The long-chain alkane is a straight-chain alkane having 10 to 20 carbon atoms.

3. The method for preparing long-chain carbon monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The dehydrogenation catalyst is p -MeO- tBu PCP-IrHCl catalyst and tBu At least one of POCOP-IrHCl.

4. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The activator is at least one of sodium tert-butoxide, potassium tert-butoxide or lithium tert-butoxide.

5. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The solvent is at least one of toluene, p-xylene and mesitylene.

6. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The hydrogen acceptor is at least one of styrene, tert-butylethylene and 4,4-dimethyl-1-pentene.

7. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: The mass ratio of the dehydrogenation catalyst, the activator and dodecane is (4-6):1:(25-30), the mass ratio of the hydrogen acceptor and dodecane is 1:(2-3); the mass volume ratio of the dehydrogenation catalyst and the solvent is 4-5:1 mg / ml.

8. The method for preparing long-chain monoolefins by dehydrogenating alkanes according to claim 1, characterized in that: In step (1), the reactor is a reaction tube or a reaction kettle.

9. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: In step (2), the heating reaction temperature is 155 to 165° C., and the reaction time is 15 to 30 minutes.

10. The method for preparing long-chain monoolefins by dehydrogenation of alkanes according to claim 1, characterized in that: In step (2), the cooling medium is ice water.

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