CN111423303A - Low-temperature aromatization method - Google Patents

Abstract

The invention belongs to the technical field of petrochemical industry, and particularly relates to a low-temperature aromatization method. In the present invention, Bronsted acid-Lewis acid diacid ionic liquid is used as catalyst, and cycloalkane containing tertiary carbon atoms is used as product distribution regulator. Under nitrogen or hydrogen atmosphere, aromatization reaction of light hydrocarbons is carried out to obtain aromatized products. The present invention utilizes the characteristics of low temperature and high activity of ionic liquid, and applies cycloalkane containing tertiary carbon atoms as an aromatization product regulator to the light hydrocarbon aromatization reaction for the first time, which is of great significance to the development of low temperature aromatization technology. and use value.

Description

A kind of low temperature aromatization method

technical field

The invention belongs to the field of petrochemical industry, and particularly relates to a low-temperature aromatization method.

Background technique

Aromatic hydrocarbons usually refer to Benzene (B for short), Toluene (T for short), and Xylene (X for short), which are important basic chemical raw materials and are also commonly used blending components to adjust the octane number of gasoline. In recent years, the demand for aromatic hydrocarbons in my country has grown rapidly, but the development of production capacity and output has been seriously lagging behind. Therefore, it is urgent to increase the production capacity of aromatic hydrocarbons and develop new technologies for aromatic hydrocarbons. Light hydrocarbon aromatization technology usually refers to the technology of preparing aromatic hydrocarbons from small molecular hydrocarbons through dehydrogenation, cracking, oligomerization, hydrogen transfer, cyclization and isomerization under the action of catalysts. The key to this technology is the research and development of catalysts and the development of catalytic processes.

In the existing literature and patents, the catalysts used for light hydrocarbon aromatization technology are generally solid catalysts such as molecular sieves, and the reaction temperature is relatively high. For example, the supported Pt/Al ₂ O ₃ and Pd/Al ₂ O ₃ catalysts developed by British Petroleum (BP) and UOP in the United States can convert alkanes into aromatics when the reaction temperature is higher than 550°C. This reaction is accompanied by Severe cracking side reactions, while Pt and Pd are precious metals, the cost is high (Csicsery S. Dehydrocyclodimerization of butanes oversupported platimun [J]. Journal of Catalysis, 1970, 17:207-215). The US Mobile company used HZSM-5 as a catalyst, although the aromatization reaction temperature was lowered to 425 ℃, but still serious carbon deposition occurred in the reaction process (Chen N, Yan Y. M2-forming-A process for aromatization of light hydrocarbons[J]. Industrial & Engineering Chemistry Process Design and Development, 1986, 25: 151-155). Wan Hai et al. (Wan Hai. Preparation and Reaction Study of Novel L Zeolite-Based Light Hydrocarbon Aromatization Catalysts [D]. 2015.) Using the Ga _1.0 -ZSM-5/Pt _0.6 -L composite molecular sieve prepared by classification as the catalyst, aromatic The reaction temperature is as high as 500 °C while the structural selectivity is improved. Most of these industrial catalysts mentioned above need to operate at higher temperature and hydrogen atmosphere, and are prone to the disadvantages of loss of active components, carbon deposition, and high energy consumption and cost. Therefore, the development of aromatization catalysts with low temperature and low consumption is the key to solving the bottleneck of aromatization technology.

Ionic liquids have broad and promising applications due to their numerous enhanced properties. At present, ionic liquid catalysts with Lewis acidity are widely used in alkane alkylation (Cui, P, Zhao G, Ren H, et al. Ionicliquid enhanced alkylation of iso-butane and 1-butene [J]. Catalysis Today, 2013 , 200: 30-35) and isomerization reactions (Zhang R, Meng X, Liu Z, et al. Isomerization ofn-pentane catalyzed by acidic chloroaluminate ionic liquids[J]. Industrial &Engineering Chemistry Research, 2008, 47: 8205- 8210). The present invention is the first to develop light hydrocarbon aromatization technology using Bronsted acid-Lewis acid double acid ionic liquid as catalyst and cycloalkane containing tertiary carbon atoms as product distribution regulator, which is of great significance to the development of aromatization technology and use value. In addition, the method of the invention has the advantages of simple preparation process, simple operation, low cost, and good economic benefit and industrialization potential.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems, the purpose of the present invention is to design a low-temperature aromatization method. Bronsted acid-Lewis acid diacid ionic liquid is used as catalyst, naphthenic hydrocarbon containing tertiary carbon atoms is used as product distribution regulator and light hydrocarbon raw material is placed in the reaction kettle, and aromatic hydrocarbons are obtained by low temperature reaction under the atmosphere.

In order to achieve the above object, the present invention adopts the following technical solutions:

A low-temperature aromatization method, specifically comprising the following steps:

(1) Synthesis of Bronsted acid-Lewis acid double acid ionic liquid catalyst: The ionic liquids used in the present invention can be prepared by known prior art methods known to those skilled in the art.

(2) Low-temperature aromatization process: weigh the above-mentioned ionic liquid catalyst, cycloalkanes containing tertiary carbon atoms and light hydrocarbons and mix them uniformly in a high pressure reaction kettle. The mass ratio of ionic liquid catalyst to light hydrocarbons is 0.01-10, and The mass ratio of cycloalkanes to tertiary carbon atoms is 0.01-0.1. In the atmosphere, the low temperature reaction yields aromatic hydrocarbons.

Wherein, the raw material light hydrocarbons are C ₁ -C ₈ alkanes or alkenes, and the tertiary carbon atom cycloalkane product distribution regulator is methylcyclohexane, methylcyclopentane, (ortho, meta, para) dimethylcyclohexane Any of the monocyclic or bicyclic alkanes of alkane and 2,2,6-trimethylcycloheptane.

Wherein, the Bronsted acid-Lewis acid diacid ionic liquid is any one of imidazole, pyridine, quaternary ammonium type or quaternary phosphine type ionic liquid, which is a compound represented by the following specific structural formula:

；

;

In the formula, X- is one or more of AlCl ₄ ^- , Al ₂ Cl ₇ ^- , CuAlCl ₅ ^- , AlBr ₄ ^- ; R is any one of C ₁ -C ₈ linear alkyl groups; R ` is none, any one of C ₁ -C ₈ straight chain alkyl, COOH, -PO ₄ H ₂ or -SO ₃ H acid radical; n=1-6.

Further, the reaction pressure is 0-1 MPa, the reaction temperature is 0-120° C., the catalytic reaction time is 0.5-60 h, and the gas atmosphere is one or both of nitrogen and hydrogen.

The advantages of the present invention are:

The above-mentioned light hydrocarbon aromatization method provided by the present invention, compared with the existing molecular sieve catalyst, uses tertiary carbon atom cycloalkane as the product regulator to synthesize aromatic hydrocarbon products with high yield at low temperature. Has the following advantages:

(1) The ionic liquid catalyst has the advantages of good solubility, low volatility, high thermal stability, wide temperature range of liquid existence, designability and repeatability;

(2) The operating pressure and temperature of the experimental process are greatly reduced, which overcomes the harsh conditions of the high reaction temperature of the existing molecular sieve catalyst aromatization process, reduces the energy consumption, and reduces the overall cost of the application of this technology. The addition of the alkane product distribution regulator significantly improves the yield of aromatic hydrocarbons, and has good economic benefits and industrialization potential.

Description of drawings

Fig. 1 Speculated reaction mechanism of aromatization of n-hexane on ionic liquids.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the following embodiments will describe the present invention more comprehensively, but should not be construed as limiting the scope of the present invention.

The ionic liquid catalysts used in the following examples were synthesized according to conventional methods.

Example 1

Ionic liquid catalyst A ([HO ₃ SC ₃ NEt ₃ ]Cl-5AlCl ₃ ) with a mass ratio of 0.2:1 (based on 10 g of n-hexane) (for the preparation method, refer to Industrial & Engineering Chemistry Research, 2008, 47:8205- 8210) and n-hexane were added to the autoclave, nitrogen was introduced into the autoclave, the initial pressure was controlled to be 0.1 MPa, the stirring speed was 500 rpm, the reaction temperature was controlled at 20 °C, and the reaction was carried out for 3 h to obtain a total content of aromatics of 0.888. The obtained aromatics included benzene, Toluene and xylene, see Table 1 for specific data.

The presumed reaction mechanism for aromatization of n-hexane on ionic liquids is shown in Figure 1:

First, n-hexane forms carbocation intermediates at the acid position of L acid, then forms olefin intermediates, dimer intermediates, and cyclization intermediates at the acid position of B, and finally dehydrogenates at the L acid position to generate aromatic hydrocarbons. The addition of cycloalkanes containing tertiary carbon atoms in this process stabilizes the carbocation and induces the production of cycloalkane intermediates, thereby increasing the yield of aromatics.

Example 2

The ionic liquid catalyst A ([HO ₃ SC ₃ NEt ₃ ]Cl-5AlCl ₃ ), methylcyclohexane and n-hexane with a mass ratio of 0.1:0.02:1 (based on 10 g of n-hexane) were added into the autoclave, Nitrogen was introduced, the initial pressure was controlled at 0.1 MPa, the stirring speed was controlled at 500 rpm, the reaction temperature was controlled at 20 °C, and the reaction was carried out for 3 h to obtain a total content of aromatics of 0.888. The obtained aromatics included benzene, toluene and xylene. The specific data are shown in Table 1. .

Example 3

The ionic liquid catalyst A ([HO ₃ SC ₃ NEt ₃ ]Cl-5AlCl ₃ ) with a mass ratio of 0.1:0.05:1 (based on 10 g of n-hexane), methylcyclohexane and n-hexane were added to the autoclave, Nitrogen was introduced, the initial pressure was controlled at 0.5 MPa, the stirring speed was controlled at 500 rpm, the reaction temperature was controlled at 30 °C, and the reaction was carried out for 3 h to obtain a total content of aromatics of 1.256. The obtained aromatics included benzene, toluene and xylene. The specific data are shown in Table 1. .

Example 4

The ionic liquid catalyst B ([HO ₃ SC ₃ NEt ₃ ]Br-5AlBr ₃ ) (the compound is a self-made compound), methylcyclopentane and n-hexane was added into the autoclave, nitrogen was introduced, the initial pressure was controlled to be 0.5 MPa, the stirring speed was 500 rpm, the reaction temperature was controlled at 30 °C, and the reaction was carried out for 3 h. The total content of aromatics was 1.256, and the obtained aromatics included benzene, toluene and dimethicone. Toluene, see Table 1 for specific data.

Example 5

Ionic liquid catalyst C ([HO ₃ SC ₃ NEt ₃ ]Cl -5AlCl ₃ -0.67CuCl) with a mass ratio of 1:2 (based on n-hexane 10 g), methylcyclopentane and n-hexane (both The mass ratio of 0.01-0.1) was added into the autoclave, nitrogen was introduced into the autoclave, the initial pressure was controlled to 1 MPa, the stirring speed was 500 rpm, the reaction temperature was controlled at 40 °C, and the reaction was performed for 3 h. The total content of aromatics was 1.619. The obtained aromatics include Benzene, toluene and xylene, the specific data are shown in Table 1.

Example 6

Ionic liquid catalyst C ([HO ₃ SC ₃ NEt ₃ ]Cl -5AlCl ₃ -0.67CuCl), p-dimethylcyclohexane and n-hexane with a mass ratio of 0.2:0.1:2 (based on n-hexane 10 g) It was put into the autoclave, nitrogen was introduced, the initial pressure was controlled to be 1 MPa, the stirring speed was 500 rpm, the reaction temperature was controlled to 40 °C, and the reaction was carried out for 3 h, the total content of aromatics was 1.619, and the obtained aromatics included benzene, toluene and xylene, The specific data are shown in Table 1.

Example 7

The ionic liquid catalyst A ([HO ₃ SC ₃ NEt ₃ ]Cl-5AlCl ₃ ) with a mass ratio of 1:1 (based on n-pentene 10 g) and n-pentene were added to the autoclave, and nitrogen was introduced into the autoclave. The gas was closed by the valve, the initial pressure was controlled as room pressure, the stirring speed was controlled at 500 rpm, the reaction temperature was controlled at 100 °C, and the reaction was performed for 3 h. The total content of aromatics was 3.990. The obtained aromatics included benzene, toluene and xylene. The specific data are shown in Table 1. .

Example 8

The ionic liquid catalyst A ([HO ₃ SC ₃ NEt ₃ ]Cl-5AlCl ₃ ) with a mass ratio of 0.01:0.1:1 (based on n-pentene 10 g), methylcyclohexane and n-pentene were added to the autoclave Inside, nitrogen was introduced, and then the air was released and the valve closed, the initial pressure was controlled to be room pressure, the stirring speed was 500 rpm, the reaction temperature was controlled at 100 °C, and the reaction was carried out for 3 h to obtain a total content of aromatics of 6.698. The obtained aromatics included benzene, toluene and Xylene, the specific data are shown in Table 1.

Comparative Example 1

This comparative example uses an unmodified ZSM-5 molecular sieve as a catalyst for comparison with Example 1.

The ZSM-5 molecular sieve catalyst and n-hexane with a mass ratio of 1:3 (based on 10 g of n-hexane) were added to the autoclave, nitrogen was introduced, the initial pressure was controlled to be 1 MPa, the stirring speed was 500 rpm, and the reaction temperature was controlled at 20 °C, the reaction was carried out for 3 h.

Comparative Example 2

This comparative example uses an unmodified ZSM-5 molecular sieve as a catalyst for comparison with Example 1.

The ZSM-5 molecular sieve catalyst and n-hexane with a mass ratio of 1:3 (based on 10 g of n-hexane) were added to the autoclave, nitrogen was introduced, the initial pressure was controlled to be 1 MPa, the stirring speed was 500 rpm, and the reaction temperature was controlled at 50 °C, the reaction was carried out for 3 h.

Comparative Example 3

This comparative example uses an unmodified ZSM-5 molecular sieve as a catalyst for comparison with Example 1.

The ZSM-5 molecular sieve catalyst and n-hexane with a mass ratio of 1:3 (based on 10 g of n-hexane) were added to the autoclave, nitrogen was introduced, the initial pressure was controlled to be 1 MPa, the stirring speed was 500 rpm, and the reaction temperature was controlled at 100 ° C, the reaction 24 h.

Table 1 List of light hydrocarbon aromatization results

It can be seen from the data in Table 1 that the ionic liquid catalyst of the present invention has obvious aromatization reaction activity, so it has the ability of light hydrocarbon aromatization reaction. And compared with the comparative example, the traditional molecular sieve catalyst has a catalytic activity for the aromatization of light hydrocarbons at low temperature. Therefore, the ionic liquid catalyst of the present invention has the ability to catalyze the conversion of light hydrocarbons into aromatic hydrocarbons at low temperature, has simple operation, low cost, good economic benefits and industrialization potential.

Obviously, the above-mentioned embodiments are only examples for clear illustration, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. It is also not possible to exhaust all implementations here. The obvious changes or changes that are not extended are still within the protection scope of the present invention.

Claims (9)

1. A low temperature aromatization process characterized by: the method comprises the steps of taking Bronsted acid-Lewis acid diacid ionic liquid as a catalyst, taking cycloalkane containing a tertiary carbon atom as a product distribution regulator, placing the ionic liquid, the cycloalkane containing the tertiary carbon atom and a light hydrocarbon raw material in a reaction kettle in a gas atmosphere, uniformly mixing and reacting to obtain the aromatic hydrocarbon.

2. The low temperature aromatization process of claim 1 wherein: the Bronsted acid-Lewis acid diacid ionic liquid is any one of imidazole, pyridine, quaternary ammonium type or quaternary phosphine type diacid ionic liquid, and is a compound represented by the following specific structural formula:

in the formula, X-is AlCl₄ ^-, Al₂Cl₆Br^-, GaCl₄ ^-, Al₂Cl₇ ^-, CuAlCl₅ ^-, AlBr₄ ^-One or more of; r is C₁-C₈Any one of the linear alkyl groups of (a); r' is nothing, C₁-C₈Any one of linear alkyl, -COOH and-PO₄H₂or-SO₃H acid radical; n = 1-6.

3. The low temperature aromatization process of claim 1 wherein: the tertiary carbon atom-containing cycloparaffin product distribution regulator is any one of monocyclic or bicycloalkane of methylcyclohexane, methylcyclopentane, (o-, m-, p-) dimethylcyclohexane and 2, 2, 6-trimethylcycloheptane.

4. The low temperature aromatization process of claim 1 wherein: the light hydrocarbon raw material is C₁-C₈An alkane or an alkene of (a).

5. The low temperature aromatization process of claim 1 wherein: the mass ratio of the tertiary carbon atom naphthenic product distribution regulator to the light hydrocarbon raw material is 0.01-0.1.

6. The low temperature aromatization process of claim 1 wherein: the mass ratio of the ionic liquid to the light hydrocarbon raw material is 0.01-10.

7. The low temperature aromatization process of claim 1 wherein: the reaction temperature is 0-120 ℃, and the reaction pressure is 0-1 MPa.

8. The low temperature aromatization process of claim 1 wherein: the gas atmosphere is one or two of nitrogen and hydrogen.

9. The low temperature aromatization process of claim 1 wherein: the reaction time is 0.5-60 h.

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