CN114805225B - A kind of hydrogenation method of methylquinoxaline - Google Patents

Abstract

The invention discloses a hydrogenation method of methylquinoxaline. Using methylquinoxaline and hydrogen as raw materials, hydrogenation is carried out in the presence of a catalyst to obtain a hydrogenated product of methylquinoxaline, and the catalyst is selected from one or a combination of molybdenum carbide and tungsten carbide , the catalyst is an unsupported catalyst, the catalyst is a layered crystal, and the crystal is a hexagonal close-packed structure. The catalyst of the invention can realize the hydrogenation reaction of methyl quinoxaline at a lower temperature and under mild reaction conditions, the raw material conversion rate can be as high as 100%, and a high-quality percent perhydrogenation product can be obtained.

Description

A kind of hydrogenation method of methylquinoxaline

technical field

The present invention relates to a hydrogenation method of methylquinoxaline.

Background technique

At present, hydrogen energy storage and transportation are mainly carried out in the form of high-pressure hydrogen and liquid hydrogen. Among them, high-pressure hydrogen has low hydrogen storage density and poor safety performance; liquid hydrogen storage consumes a lot of energy, and needs to discharge hydrogen to relieve pressure, and its safety performance is not high enough. Liquid organic hydrogen storage can realize hydrogen storage and transportation at room temperature and pressure, which is safer and more convenient, and is an important development direction of hydrogen storage and transportation.

Nitrogen-containing fused heterocyclic aromatic compounds are widely used as hydrogen storage materials because of their mild hydrodehydrogenation process. Among them, methylquinoxaline has high mass hydrogen storage density and low hydrogenation temperature, and is a kind of preferred hydrogen storage and desorption material. However, the hydrogenation process of methylquinoxaline generally uses noble metal catalysts, such as Ru, Pt, Pd, etc. However, in the hydrogenation process of pure noble metal catalysts, the catalysts have poor resistance to toxicity and are prone to permanent poisoning and deactivation. Moreover, in the actual hydrogenation process, the industrially used methylquinoxaline may have certain impurities, which are easily adsorbed on the active site of the precious metal catalyst, and also aggravate the deactivation of the catalyst. In addition, the cost of noble metal catalysts is high. Chinese patent CN113753850A discloses the hydrogenation of monomethylquinoxaline in the presence of aluminum oxide or a carbon-supported noble metal catalyst, but the cost of the catalyst is still relatively high, and the hydrogenation catalysis efficiency needs to be further improved.

SUMMARY OF THE INVENTION

In view of the shortcomings and deficiencies of the prior art, the present invention provides an improved hydrogenation method for methylquinoxaline, which has high hydrogenation efficiency, mild hydrogenation conditions and low cost.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A kind of hydrogenation method of methylquinoxaline, take methylquinoxaline and hydrogen as raw materials, carry out hydrogenation reaction in the presence of a catalyst to obtain a hydrogenated product of methylquinoxaline, the catalyst is selected from molybdenum carbide A combination of one or two of tungsten carbide and tungsten carbide, the catalyst is an unsupported catalyst, the catalyst is a layered crystal, and the crystal is a hexagonal close-packed structure.

In some embodiments of the present invention, the specific surface area of the catalyst is 40-60 m ² /g, preferably 45-55 m ² /g, more preferably 55 m ² /g.

In some embodiments of the present invention, the sheet length of the layered structure is 20-40 nm, preferably 20-28 nm.

In some embodiments of the invention, the methylquinoxaline is selected from a combination of one or more of 2-methylquinoxaline, 5-methylquinoxaline, and 6-methylquinoxaline .

In some embodiments of the present invention, the mass ratio of the methylquinoxaline to the catalyst is 4-10:1.

In some embodiments of the present invention, the temperature of the hydrogenation reaction is 80-190° C., and the hydrogen pressure is 5-10 MPa.

In some embodiments of the present invention, the temperature of the hydrogenation reaction is 100-170° C., and the hydrogen pressure is 8-10 MPa.

Preferably, the temperature of the hydrogenation reaction is 120° C., and the hydrogen pressure is 8 MPa.

In some embodiments of the present invention, the time of the hydrogenation reaction is 5-10 hours.

In some embodiments of the present invention, the hydrogenated product of methylquinoxaline includes a perhydrogenated product of methylquinoxaline and a tetrahydrogenated product of methylquinoxaline, the perhydrogenated product of methylquinoxaline The mass of the product accounts for more than 85% of the mass of the hydrogenated product of methylquinoxaline.

Preferably, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 92% of the mass of the hydrogenation product of methylquinoxaline. Further preferably, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 95% of the mass of the hydrogenation product of methylquinoxaline. Particularly preferably, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 98% of the mass of the hydrogenation product of methylquinoxaline.

In some embodiments of the present invention, the hydrogenated product of methylquinoxaline includes a perhydrogenated product of methylquinoxaline, a hexahydrogenated product of methylquinoxaline, and a tetrahydrogenated product of methylquinoxaline, The mass of the perhydrogenation product of methylquinoxaline accounts for more than 62% of the mass of the hydrogenation product of methylquinoxaline.

Preferably, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 65% of the mass of the hydrogenation product of methylquinoxaline. Further preferably, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 95% of the mass of the hydrogenation product of methylquinoxaline.

The inventor found through research that when one or two unsupported tungsten carbide or molybdenum carbide are used as the catalyst for the hydrogenation reaction of methylquinoxaline, and the catalyst is controlled to be a layered crystal, the crystal When the unit cell configuration is a hexagonal close-packed structure, the efficient hydrogenation of methylquinoxaline can be achieved under mild hydrogenation reaction conditions. Using the catalyst for hydrogenation, the conversion rate of raw materials is high, and a high-quality percentage of fully hydrogenated products can be obtained, and technical-grade methylquinoxaline containing a certain impurity content can be used as a hydrogenation raw material, and the hydrogenation reaction can be carried out stably .

In some embodiments of the present invention, the method for hydrogenating methylquinoxaline specifically includes the following steps: mixing the catalyst and the methylquinoxaline, adding an organic solvent to obtain a reaction mixture, and mixing the catalyst with the methylquinoxaline. The reaction mixture is placed in a reactor, and the hydrogenation reaction is carried out at a temperature of 80 to 180° C. and a hydrogen pressure of 5 to 10 MPa.

In some embodiments of the present invention, the organic solvent is selected from a combination of one or more of 1,4-dioxane, cyclohexane, and methylcyclohexane.

In some embodiments of the present invention, the mass ratio of the organic solvent to the methylquinoxaline is 1.5-4:1.

In some embodiments of the present invention, the method for hydrogenating methylquinoxaline further comprises, after the hydrogenation reaction is completed, reducing the temperature and pressure to hydrogenate the catalyst and the methylquinoxaline The product is isolated.

Compared with the prior art, the present invention has the following advantages:

(1) The catalyst of the present invention can realize the hydrogenation reaction of methylquinoxaline at lower temperature and mild reaction conditions, the conversion rate of raw materials is high, which can be as high as 100%, and a high percentage of perhydrogenation products can be obtained.

(2) When the catalyst of the present invention is used for the hydrogenation reaction of analytically pure methylquinoxaline, it can be recycled for many times, and the catalyst activity will not be significantly reduced after repeated use; the catalyst of the present invention can be applied to industrial grades containing certain impurities In the hydrogenation reaction of methyl quinoxaline, the catalyst activity will not be significantly reduced, and the catalyst has strong anti-toxicity stability.

(3) By controlling the temperature and hydrogen pressure of the hydrogenation reaction, the mass percentage of the fully hydrogenated product in the hydrogenated product of methylquinoxaline can be further increased. The mass percentage of the fully hydrogenated product in the hydrogenated product of methylquinoxaline can be as high as 98%.

(4) The catalyst of the present invention is non-supported, simple to prepare, non-precious metal, and low cost.

Description of drawings

FIG. 1 is a TEM spectrum of the molybdenum carbide catalyst in Example 1.

Detailed ways

The present invention will be further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions adopted in the examples can be further adjusted according to different requirements of specific use, and the unremarked implementation conditions are the conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

Example 1

The present embodiment provides a kind of hydrogenation method of 2-methylquinoxaline:

Among them, the catalyst is unsupported molybdenum carbide, the molybdenum carbide is a crystal with a layered structure, the sheet length of the layered structure is 20 nm, the specific surface area is 50 m ² /g, and the unit cell structure of the crystal is a hexagonal close-packed structure. . The TEM image of the catalyst is shown in Figure 1, and it can be seen that the catalyst has a layered structure. 2-Methylquinoxaline was analytically pure.

Weigh 10 g of molybdenum carbide catalyst, 50 g of 2-methylquinoxaline, and 100 g of organic solvent 1,4-dioxane. First, the molybdenum carbide catalyst and 2-methylquinoxaline are mixed, stirred evenly, then 1,4-dioxane is added, and the hydrogenation reaction is carried out in a reaction kettle. The conditions of the hydrogenation reaction are: the heating temperature is 120°C, the hydrogen pressure is 8MPa, and the reaction time is 7h. After the reaction is completed, the temperature is lowered and the pressure is relieved, the hydrogenated product of 2-methylquinoxaline and the molybdenum carbide catalyst are separated, and the hydrogenated product of 2-methylquinoxaline is collected for use.

Example 2-5

Embodiment 2-5 provides a kind of hydrogenation method of methylquinoxaline, and the technology of this hydrogenation method is basically the same as that of embodiment 1, and the difference is only: changing the lamella length and specific surface area of catalyst molybdenum carbide, changing methylquinoxaline The type of oxaline, or technical-grade methylquinoxaline is selected as the raw material, as shown in Table 1 below.

Using the online sampling method, the sampled organic matter was analyzed and detected by gas chromatography-mass spectrometry, the type and content of the hydrogenated products of methylquinoxaline in Examples 1-5 were analyzed, and the conversion rate of the hydrogenation reaction was calculated. , the results are shown in Table 2 below, wherein the 4H product refers to the tetrahydrogenation product, and the 6H product refers to the hexahydrogenation product.

It can be seen from the above Table 2 that the molybdenum carbide catalyst of the present invention can achieve high conversion hydrogenation of 2-methylquinoxaline, 5-methylquinoxaline or 6-methylquinoxaline, and in the hydrogenation product, perhydrogenation The mass percentage of the product can be as high as 98%. In addition, the molybdenum carbide catalyst of the present invention can be used for the hydrogenation of industrially pure methylquinoxaline, the catalyst is not easily poisoned by impurities, and has good stability.

Example 6

The present embodiment provides a kind of hydrogenation method of 2-methylquinoxaline:

Among them, the catalyst is unsupported tungsten carbide, the tungsten carbide is a layered crystal, the sheet length of the layered structure is 20 nm, the specific surface area is 50 m ² /g, and the unit cell structure of the crystal is a hexagonal close-packed structure. . 2-Methylquinoxaline was analytically pure.

Weigh 10g of tungsten carbide catalyst, 50g of 2-methylquinoxaline, and 100g of organic solvent 1,4-dioxane. First, the tungsten carbide catalyst and 2-methylquinoxaline are mixed, stirred evenly, then 1,4-dioxane is added, and the hydrogenation reaction is carried out in a reaction kettle. The conditions of the hydrogenation reaction are: the heating temperature is 150°C, the hydrogen pressure is 8MPa, and the reaction time is 7h. After the reaction is completed, the temperature is lowered and the pressure is relieved, the hydrogenation product of 2-methylquinoxaline and the tungsten carbide catalyst are separated, and the hydrogenation product of 2-methylquinoxaline is collected for subsequent use.

Examples 7-10

Embodiment 7-10 provides a kind of hydrogenation method of methylquinoxaline, and the technique of this hydrogenation method is basically the same as that of embodiment 6, and the difference is only: changing the sheet length and specific surface area of the catalyst tungsten carbide, changing the methylquinoxaline The type of oxaline, or technical-grade methylquinoxaline is selected as the raw material, as shown in Table 3 below.

The on-line sampling method was adopted, and the sampled organic matter was analyzed and detected by gas chromatography-mass spectrometry, the type and content of the hydrogenated products of methylquinoxaline in Examples 6-10 were analyzed, and the conversion rate of the hydrogenation reaction was calculated. , the results are shown in Table 4 below, wherein the 4H product refers to the tetrahydrogenation product, and the 6H product refers to the hexahydrogenation product.

It can be seen from the above Table 4 that the tungsten carbide catalyst of the present invention can achieve high conversion hydrogenation of 2-methylquinoxaline, 5-methylquinoxaline or 6-methylquinoxaline, and in the hydrogenation product, perhydrogenation The mass percentage of the product can be as high as 96%. In addition, the tungsten carbide catalyst of the present invention can be used for the hydrogenation of industrially pure methylquinoxaline, the catalyst is not easily poisoned by impurities, and has good stability.

Examples 11-15

Embodiment 11-15 provides a kind of hydrogenation method of 2-methylquinoxaline. The process of this hydrogenation method is basically the same as that of embodiment 1, that is, a molybdenum carbide catalyst is used, and the difference is only that the temperature of the hydrogenation reaction and the hydrogen gas are changed. pressure. The specific conditions of Examples 11-15, the conversion rate of the hydrogenation reaction, the type and mass percentage of hydrogenation products are shown in Table 5 below.

Example 16

Embodiment 16 provides a hydrogenation method of 2-methylquinoxaline, and the process of the hydrogenation method is basically the same as that of embodiment 1, except that the temperature of the hydrogenation reaction is 190° C. and the hydrogen pressure is 5 MPa. Results The conversion rate of hydrogenation reaction was 100%, the mass percentage of perhydrogenation product in the hydrogenation product of 2-methylquinoxaline was 85%, and the other products were ring-breaking products.

It can be seen from Examples 11-16 that when the hydrogen pressure is kept constant, increasing the hydrogenation reaction temperature within a certain range helps to improve the conversion rate of the hydrogenation reaction and the mass percentage of the fully hydrogenated product in the hydrogenated product. However, when the temperature is too high, the ring of the hydrogenated product may be broken, and the mass percentage of the perhydrogenated product may be reduced instead.

Comparative Example 1

Comparative example 1 provides a kind of hydrogenation method of 4,6-dimethyldibenzothiophene, and the technique of this hydrogenation method is basically the same as that of embodiment 1, and the difference is only: replace 2-methylquinoxaline with 4, 6-Dimethyldibenzothiophene. After testing, it can be seen that the conversion rate of the hydrogenation reaction is 32%, and the hydrogenation products have ring breakage. The hydrogenation products specifically include hexahydrogenated products, toluene and methylcyclohexane.

Comparative Example 2

Comparative Example 2 provides a hydrogenation method of 2-methylthiophene, and the process of the hydrogenation method is basically the same as that of Example 1, except that 2-methylquinoxaline is replaced with 2-methylthiophene. After testing, it was found that the hydrogenation reaction could not actually proceed, and no hydrogenation product was obtained.

Comparative Example 3

Comparative example 3 provides a kind of hydrogenation method of benzofuran, and the technique of this hydrogenation method is basically the same as that of embodiment 1, and the difference is only that: 2-methylquinoxaline is replaced with benzofuran. After testing, it can be seen that the conversion rate of the hydrogenation reaction is 17%, and the hydrogenation products include dihydrogenated products, no perhydrogenated products, and no ring-breaking products.

As can be seen from Comparative Examples 1-3, the tungsten carbide and molybdenum carbide catalysts of the present invention either cannot catalyze the hydrogenation of monoheterocyclic, oxo- or thia-containing hetero-fused rings or polycyclic rings, or although they can catalyze their hydrogenation. reaction, but the conversion rate is low, the hydrogenation product has ring breakage, and the content of the perhydrogenation product is low. The inventors have found through research that the catalyst of the present invention is suitable for the hydrogenation reaction of methylquinoxaline, and can efficiently obtain a perhydrogenation product, which is then used in the hydrogenation reaction of a specific methylquinoxaline.

Comparative Example 4

Comparative example 4 provides a kind of hydrogenation method of 2-methylquinoxaline, the process of this hydrogenation method is basically the same as that of embodiment 1, the difference is only: the catalyst is replaced with Ni/Al ₂ O with a load mass percentage of 20% ₃ catalysts. After testing, it can be seen that the conversion rate of the hydrogenation reaction is 95%, the hydrogenation products include hexahydrogenation products and a large number of ring-breaking products, and no perhydrogenation products are detected. In the hydrogenation process of the supported nickel catalyst, the selectivity of the target product is poor, and it can only hydrogenate the benzene ring part of 2-methylquinoxaline, and the heterocyclic part is easy to break the ring and generate by-products.

Comparative Example 5

Comparative example 5 provides a kind of hydrogenation method of 2-methylquinoxaline, the process of this hydrogenation method is basically the same as that of embodiment 1, the difference is only: the molybdenum carbide catalyst is supported on the alumina carrier with a mass percentage of 40% . After testing, it can be seen that the conversion rate of the hydrogenation reaction is 48%, and the hydrogenation reaction products include perhydrogenation products, hexahydrogenation products and tetrahydrogenation products, wherein the mass percentage of perhydrogenation products is 33%. It can be seen that when the catalyst is supported, the conversion rate of the hydrogenation reaction is reduced, and it is not conducive to the formation of perhydrogenation products.

The above-mentioned embodiments are only intended to illustrate the technical concept and characteristics of the present invention, and the purpose thereof is to enable those who are familiar with the art to understand the content of the present invention and implement them accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included within the protection scope of the present invention.

The endpoints of the ranges disclosed herein and any values are not limited to the precise ranges or values, which are to be understood to include values near those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

Claims (9)

1. a hydrogenation method of methyl quinoxaline, taking methyl quinoxaline and hydrogen as raw materials, carrying out hydrogenation reaction in the presence of a catalyst, obtaining the hydrogenation product of methyl quinoxaline, it is characterized in that: The catalyst is selected from one or a combination of molybdenum carbide and tungsten carbide, the catalyst is an unsupported catalyst, the catalyst is a layered crystal, and the crystal is a hexagonal close-packed structure; the catalyst The specific surface area is 40-60 m ² /g; the sheet length of the layered structure is 20-40 nm. 2. The hydrogenation method of methylquinoxaline according to claim 1, wherein the methylquinoxaline is selected from 2-methylquinoxaline, 5-methylquinoxaline and 6-methylquinoxaline A combination of one or more of methylquinoxaline; and/or, the mass ratio of the methylquinoxaline to the catalyst is 4 to 10:1. 3. the hydrogenation method of methylquinoxaline according to claim 1, is characterized in that: the temperature of described hydrogenation reaction is 80～190 ℃, and the hydrogen pressure is 5～10MPa; The hydrogen reaction time is 5 to 10 hours. 4. The hydrogenation method of methylquinoxaline according to claim 1, characterized in that: the temperature of the hydrogenation reaction is 100～170° C., and the hydrogen pressure is 8～10MPa. 5. The hydrogenation method of methylquinoxaline according to claim 1, wherein the hydrogenation product of the methylquinoxaline comprises the perhydrogenation product of methylquinoxaline and the hydrogenation product of methylquinoxaline. The tetrahydrogenation product, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 85% of the mass of the hydrogenation product of methylquinoxaline. 6. The hydrogenation method of methylquinoxaline according to claim 1, wherein the hydrogenation product of the methylquinoxaline comprises a perhydrogenation product of methylquinoxaline, a methylquinoxaline Hexahydrogenation product and tetrahydrogenation product of methylquinoxaline, the mass of the perhydrogenation product of methylquinoxaline accounts for more than 62% of the mass of the hydrogenation product of methylquinoxaline. 7. The hydrogenation method of methylquinoxaline according to claim 1, characterized in that: the hydrogenation method of the methylquinoxaline specifically comprises the following steps: combining the catalyst with the methylquinoxaline The reaction mixture is placed in a reaction kettle, and the hydrogenation reaction is carried out at a temperature of 80 to 180° C. and a hydrogen pressure of 5 to 10 MPa. 8. The hydrogenation method of methylquinoxaline according to claim 7, wherein the organic solvent is selected from one of 1,4-dioxane, cyclohexane and methylcyclohexane One or more combinations; and/or, the mass ratio of the organic solvent to the methylquinoxaline is 1.5 to 4:1. 9. The hydrogenation method of methylquinoxaline according to claim 1, characterized in that: the hydrogenation method of methylquinoxaline further comprises, after the hydrogenation reaction is completed, reducing temperature and pressure, The catalyst and the hydrogenated product of methylquinoxaline are separated.

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