Application of supported alkali metal hydride as catalyst for hydrodealkylation reaction of aromatic hydrocarbon

Abstract

The invention provides an application of a supported alkali metal hydride as an aromatic hydrocarbon hydrodealkylation reaction catalyst. The catalyst is low in cost, can be repeatedly used, can catalyze the breakage of carbon-carbon bonds under mild conditions, realizes the hydrogenation dealkylation reaction of aromatic hydrocarbons, for example, can realize the hydrogenation dealkylation reaction of C8-C10 aromatic hydrocarbons at 200-250 DEG C, the conversion rate is higher than 45%, the reaction energy consumption is greatly reduced, and the catalyst has high activity and high selectivity.

Description

Technical Field

[0001] The invention belongs to the technical field of alkali metal hydrides and light aromatic hydrocarbons, and particularly relates to the application of supported alkali metal hydrides as aromatic hydrocarbon hydrodealkylation reaction catalysts. Background Art

[0002] Benzene, toluene, and xylene (BTX, or light aromatics) are important chemicals for producing value-added products such as polymers, solvents, paints, polishes, and pharmaceuticals. However, there is a huge imbalance between their supply and market demand. BTX is mainly derived from catalytic reforming of naphtha, cracking gas extraction, and C 9 + Aromatic hydrodealkylation reaction. Among them, the production of BTX by aromatic hydrodealkylation reaction has received increasing attention, especially with the increasing number of large-scale aromatic processes put into production, the production of aromatics will be greatly increased, providing abundant aromatic resources for this method. However, the aromatic hydrodealkylation reaction usually requires a high operating temperature of about 700℃-900℃, and the high energy consumption of the reaction leads to high process costs. Therefore, how to reduce the reaction temperature of the process and reduce the energy consumption of the reaction process has become one of the key issues in the efficient development of aromatic hydrodealkylation to prepare high-value chemicals such as BTX.

[0003] Compared with the non-catalytic hydrodealkylation method, the catalytic hydrodealkylation reaction method for preparing BTX has the advantages of low hydrogen consumption, high conversion rate and high selectivity. Therefore, the development of catalysts with high activity, high stability and low price under relatively mild conditions is crucial to reducing the energy consumption and cost of the process. As catalytic hydrodealkylation technology has received widespread attention from researchers, a variety of commercial processes such as TAC9, ZEOLYST / SK, and Detol have also been developed. Among them, taking the Houdry Detol process as an example, a multiphase catalyst containing chromium or molybdenum oxide, or a supported platinum catalyst (such as Pt / SiO 2 、Pt / Al 2 O 3 ), benzene is produced by the reaction of toluene and hydrogen, and the reaction temperature is usually 480℃-590℃, and the pressure range is 40bar-60bar. Since the hydrodealkylation process is exothermic, the reaction can also be carried out at lower temperatures, but low temperatures are often accompanied by catalyst deactivation. In addition, in most catalysts, precious metals such as Pt, Re and Pd are used as active ingredients, which undoubtedly increases production costs. In addition, many of the substrates studied are single model aromatic compounds such as toluene, rather than heavy aromatic compounds containing more C8-C10 components, which also limits the application of hydrodealkylation catalysts. Summary of the invention

[0004] In view of the above technical status, the inventors have discovered through extensive experimental exploration that supported alkali metal hydrides can be used as catalysts for the hydrodealkylation of aromatics, and have high catalytic activity and high stability under mild conditions.

[0005] In the supported alkali metal hydride, the alkali metal hydride is supported on a carrier.

[0006] The carrier includes carbon materials, two-dimensional materials, oxides, etc. Among them, the carbon material is not limited, including one or more of graphene, carbon nanotubes, nanodiamonds, etc.; the two-dimensional material is not limited, including hexagonal boron nitride, graphite phase carbon nitride (gC 3 N 4 ), one or more of two-dimensional transition metal carbon / nitride (i.e., two-dimensional transition metal carbide, nitride or carbonitride, denoted as MXene), etc.; oxides are not limited, including one or more of magnesium oxide, silicon oxide, rare earth oxides, etc.

[0007] The alkali metal hydride is not limited, and includes one or more of lithium hydride (LiH), sodium hydride (NaH), potassium hydride (KH), rubidium hydride (RbH), cesium hydride (CsH), etc.

[0008] In the supported alkali metal hydride, the mass percentage of the alkali metal hydride is preferably 1%-50%, more preferably 10%-50%.

[0009] In the supported alkali metal hydride, the mass percentage of the carrier is preferably 50%-99%, more preferably 50%-90%.

[0010] When the supported alkali metal hydride is used as a catalyst for the hydrogenation dealkylation reaction of aromatic hydrocarbons, the active component of the catalyst is the alkali metal hydride.

[0011] The preparation method of the supported alkali metal hydride is not limited, and can be prepared by the following method:

[0012] The alkali metal and the carrier are mixed in a high pressure reactor. 2 It is obtained by reacting under pressure of 1 bar to 100 bar and heating to 100°C to 300°C.

[0013] Preferably, the carrier is first calcined in nitrogen at a temperature of 200°C to 1200°C.

[0014] In the aromatic hydrocarbon hydrodealkylation reaction, the aromatic hydrocarbon is not limited, and is preferably a C8-C10 aromatic hydrocarbon, such as o-xylene, m-xylene, p-xylene, mesitylene, 1-trimethylbenzene, 2-trimethylbenzene, 6-trimethylbenzene, ethylbenzene, n-propylbenzene, isopropylbenzene, ethyltoluene, m-ethyltoluene, n-propyltoluene, isopropyltoluene, p-isopropyltoluene, naphthalene, tetralin, dimethylethylbenzene, 1-trimethylbenzene, 6 ...

[0015] The aromatic hydrocarbon hydrodealkylation reaction is carried out in a high-pressure reactor. The substrate aromatic hydrocarbon and the catalyst are added to the high-pressure reactor, and a certain volume of solvent is added. 2 Under the conditions of pressure and certain reaction temperature, the aromatic hydrocarbon undergoes a dealkylation reaction to obtain a reaction product. The solvent is not limited and includes one or a mixture of n-octane, n-pentane, n-hexane, etc.

[0016] The reaction products are toluene, benzene and other reaction products, and the other reaction products are different according to different substrates. Taking mesitylene as an example, the continuous hydrodealkylation reaction process is as follows:

[0017]

[0018] The aromatic reactants and reaction products in the aromatic hydrodealkylation reaction are analyzed online by gas chromatography-mass spectrometry (GC-MS) to obtain the conversion rate of the aromatic hydrodealkylation reaction and the yield of each reaction product. The conversion rate and the yield of each reaction product are defined as follows:

[0019] Conversion rate = (moles of reacted substrate / initial moles of substrate) × 100%

[0020] Yield of a reaction product = (number of moles of the reaction product generated / number of initial moles of substrate) × 100%

[0021] In the present invention, by adjusting H 2 The conversion rate of the aromatic hydrocarbon hydrodealkylation reaction and / or the yield of the reaction product can be adjusted by one or more of pressure, reaction temperature, reaction time, the mass percentage of alkali metal hydride in the supported alkali metal hydride, and the molar ratio of supported alkali metal hydride to aromatic hydrocarbon.

[0022] Preferably, the H 2 Pressurize to 1bar-80bar.

[0023] Preferably, the reaction temperature is 150°C-300°C, more preferably 200°C-250°C.

[0024] Preferably, the reaction time is 1 h-20 h.

[0025] Preferably, the molar ratio of the alkali metal hydride to the aromatic hydrocarbon in the catalyst is 1:100-1:1, more preferably 1:10-1:1.

[0026] In the present invention, aromatic hydrocarbons are aromatic hydrocarbons.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention finds that supported alkali metal hydrides can be used as catalysts for the hydrodealkylation reaction of aromatic hydrocarbons. This is attributed to the strong electron-donating ability of alkali metal hydrides. The electrons are transferred from alkali metals (Li, Na, K, Rb, Cs, etc.) to the unoccupied antibonding p-pπ* orbital of aromatic hydrocarbon molecules. This single electron transfer mode generates a free radical anion intermediate. The free radical can play a role in the reaction with aromatic compounds and initiate a free radical chain reaction. In addition, the catalyst can catalyze the breaking of carbon-carbon bonds under relatively mild conditions, and the high abundance and low price of alkali metals are conducive to reducing the preparation cost of the catalyst;

[0029] (2) The present invention can adjust H 2 One or more of the following: pressure, reaction temperature, reaction time, mass percentage of alkali metal hydride in supported alkali metal hydride, and molar ratio of supported alkali metal hydride to aromatic hydrocarbons to adjust the conversion rate of the aromatic hydrocarbon hydrodealkylation reaction and / or the yield of the reaction product;

[0030] (3) The present invention can realize the hydrodealkylation reaction of various aromatic hydrocarbons at 150°C-250°C, and can realize the hydrodealkylation reaction of C8-C10 aromatic hydrocarbons at a conversion rate of higher than 45% or even higher than 50% at 200°C-250°C. This temperature is lower than the reaction temperature of the current industrial process, greatly reducing energy consumption, and having both high activity and high selectivity;

[0031] (4) The supported alkali metal hydride of the present invention can be recycled and reused as a catalyst for the hydrogenation and dealkylation reaction of aromatic hydrocarbons without affecting the catalytic activity;

[0032] (5) When the supported alkali metal hydride of the present invention is used as a catalyst for the hydrogenation dealkylation reaction of aromatic hydrocarbons, the active component of the catalyst is the alkali metal hydride, and the carrier plays a high dispersion role. Both the alkali metal hydride and the carrier play an important role in the high activity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is SiO in Example 1 2 Schematic diagram of the hydrogenation reaction with alkali metal sodium in a high-pressure reactor. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention, and non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0035] The words “include”, “including” and the like used in the present invention should be interpreted as including rather than being exclusive or exhaustive; that is, the meaning is “including but not limited to”.

[0036] Embodiment 1:

[0037] Sodium hydride supported on silica (NaH / SiO 2 ) has a mass percentage of NaH of 30%, recorded as 30wt.%NaH / SiO 2 The 30wt.%NaH / SiO 2 , as follows:

[0038] Weigh 210 mg SiO 2 The carrier was in 30 mL / min N 2 The carrier was pre-treated by calcining at 550°C for 6 hours in air. 90 mg of alkali metal sodium was weighed, mixed with the carrier and placed in a high-pressure reactor at 110°C and 10 bar H 2 The hydrogenation reaction was carried out for 10 h. Figure 1 As shown, after the reaction, the mixture was cooled to room temperature and the remaining gas was discharged to obtain 30wt.% NaH / SiO 2 .

[0039] The 30wt.% NaH / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0040] o-xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h.

[0041] Embodiment 2:

[0042] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0043] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic meta-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0044] m-xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to m-xylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h.

[0045] Embodiment 3:

[0046] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0047] The prepared 30wt.% NaH / SiO 2 As a catalyst, a catalytic xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0048] Xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor with a molar ratio of NaH to xylene of 1:1, add n-octane, and heat at 80 bar H 2 React at 250℃ for 20h.

[0049] Embodiment 4:

[0050] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0051] The prepared 30wt.% NaH / SiO 2 As a catalyst, catalytic ethylbenzene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0052] Ethylbenzene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of 1:1 to ethylbenzene, and heat at 80 bar H 2 React at 250℃ for 20h.

[0053] Embodiment 5:

[0054] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0055] The prepared 30wt.% NaH / SiO 2 As a catalyst, a catalytic mesitylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0056] Mesitylene and 30wt.% NaH / SiO 2Place in a high pressure reactor, add n-octane at a molar ratio of NaH to mesitylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h.

[0057] Embodiment 6:

[0058] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0059] The prepared 30wt.% NaH / SiO 2 As a catalyst, catalytic cumene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0060] Cumene and 30wt.% NaH / SiO 2 Place in a high pressure reactor with a molar ratio of NaH to cumene of 1:1, add n-octane, and heat at 80 bar H 2 React at 250℃ for 20h.

[0061] Embodiment 7:

[0062] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0063] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic m-ethyltoluene hydrodealkylation reaction is carried out in a high-pressure reactor as follows:

[0064] m-Ethyltoluene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of 1:1 to m-ethyltoluene, and heat at 80 bar H 2 React at 250℃ for 20h.

[0065] Embodiment 8:

[0066] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0067] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic hydrodealkylation reaction of isopropylbenzene is carried out in a high-pressure reactor as follows:

[0068] p-Isopropylbenzene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of 1:1 to NaH and p-isopropyltoluene, and heat at 80 bar H 2React at 250℃ for 20h.

[0069] Embodiment 9:

[0070] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0071] The prepared 30wt.% NaH / SiO 2 As a catalyst, naphthalene hydrodealkylation reaction is carried out in a high pressure reactor as follows:

[0072] Naphthalene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to naphthalene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h.

[0073] Embodiment 10:

[0074] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0075] The prepared 30wt.% NaH / SiO 2 As a catalyst, a mixture of o-xylene, m-xylene, p-xylene and mesitylene is simultaneously catalyzed for hydrogenation and dealkylation in a high-pressure reactor, as follows:

[0076] o-xylene, m-xylene, p-xylene and mesitylene were mixed with 30 wt.% NaH / SiO 2 Put it into a high pressure reactor, the molar ratio of NaH, o-xylene, m-xylene, p-xylene and mesitylene (NaH: o-xylene: m-xylene: p-xylene: mesitylene) is 4:1:1:1:1, n-octane is added, and the mixture is heated at 80 barH. 2 React at 250℃ for 20h.

[0077] Comparative Example 1:

[0078] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0079] The prepared 30wt.% NaH / SiO 2 As a catalyst, naphthalene hydrodealkylation reaction is carried out in a high pressure reactor as follows:

[0080] Naphthalene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to naphthalene of 1:1, and heat at 10 bar H 2React at 250℃ for 20h.

[0081] Comparative Example 2:

[0082] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0083] The prepared 30wt.% NaH / SiO 2 As a catalyst, a catalytic tetralin hydrodealkylation reaction is carried out in a high pressure reactor, as follows:

[0084] Tetralin and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of 1:1 to tetrahydrofuran, and heat at 10 bar H 2 React at 250℃ for 20h.

[0085] Comparative Example 3:

[0086] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0087] The prepared 30wt.% NaH / SiO 2 As a catalyst, a catalytic tetralin hydrodealkylation reaction is carried out in a high pressure reactor, as follows:

[0088] Tetralin and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of 1:1 to tetrahydrofuran, and heat at 5 bar H 2 React at 250℃ for 20h.

[0089] Comparative Example 4:

[0090] Sodium supported on silica (Na / SiO 2 ) has a mass percentage of Na of 30%, recorded as 30wt.%Na / SiO 2 The 30wt.%Na / SiO 2 , as follows:

[0091] Weigh 210 mg SiO 2 The carrier was in 30 mL / min N 2 The carrier was pre-treated by calcining at 550°C for 6 hours in gas. 90 mg of alkali metal sodium was weighed, fully mixed with the carrier, and placed in a high-pressure reactor. The reaction was carried out at 110°C and 10 bar Ar for 10 hours. After the reaction, it was cooled to room temperature and the remaining gas was discharged to obtain 30 wt.% Na / SiO 2 .

[0092] The 30wt.% Na / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0093] o-xylene and 30wt.% Na / SiO 2 Put it into the autoclave, the molar ratio of Na to o-xylene is 1:1, add n-octane, and heat it at 80 bar H 2 React at 250℃ for 20h.

[0094] Comparative Example 5:

[0095] 90 mg of commercial NaH was used as a catalyst to carry out the catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor as follows:

[0096] o-Xylene and NaH were placed in a high pressure reactor with a molar ratio of NaH to o-Xylene of 1:1. n-Octane was added and heated at 80 bar H 2 React at 250℃ for 20h.

[0097] Comparative Example 6:

[0098] 225 mg SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0099] o-xylene and SiO 2 Put into the high pressure reactor, SiO 2 The molar ratio of n-octane to o-xylene was 1:1, and n-octane was added at 80 bar H 2 React at 250℃ for 20h.

[0100] Comparative Example 7:

[0101] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0102] 300 mg of 30 wt.% NaH / SiO 2 As a catalyst, it catalyzes the hydrodealkylation reaction of o-xylene in a high-pressure reactor, as follows:

[0103] (1) o-xylene and 30 wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h;

[0104] (2) 30wt.%NaH / SiO after reaction 2 The cyclic catalytic o-xylene hydrodealkylation reaction is carried out by adding the same volume of o-xylene into the autoclave again to carry out the catalytic o-xylene hydrodealkylation reaction at 80 bar H 2 React at 250℃ for 20h.

[0105] Comparative Example 8:

[0106] 50wt.%NaH / SiO was prepared by melt impregnation method 2 , as follows:

[0107] Weigh 150 mg SiO 2 The carrier was in 30 mL / min N 2 The carrier was pre-treated by calcining at 550°C for 6 hours in air. 150 mg of alkali metal sodium was weighed, mixed with the carrier and placed in a high-pressure reactor at 110°C and 10 barH 2 The hydrogenation reaction was carried out for 10 h. Figure 1 As shown, after the reaction, the mixture is cooled to room temperature and the remaining gas is discharged to obtain 50wt.% NaH / SiO 2 .

[0108] The prepared 50wt.% NaH / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0109] o-xylene and 50wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 20h.

[0110] Comparative Example 9:

[0111] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0112] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0113] o-xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:10, and heat at 80 bar H 2 React at 250℃ for 20h.

[0114] Comparative Example 10:

[0115] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0116] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0117] o-xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:1, and heat at 80 bar H 2 React at 150℃ for 20h.

[0118] Comparative Example 11:

[0119] 30wt.%NaH / SiO 2 The preparation method is the same as that of Example 1.

[0120] The prepared 30wt.% NaH / SiO 2 As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0121] o-xylene and 30wt.% NaH / SiO 2 Place in a high pressure reactor, add n-octane at a molar ratio of NaH to o-xylene of 1:1, and heat at 80 bar H 2 React at 250℃ for 10h.

[0122] Comparative Example 12:

[0123] 30wt.%KH / SiO was prepared by melt impregnation method 2 , as follows:

[0124] Weigh 210 mg SiO 2 The carrier was in 30 mL / min N 2 The carrier was pre-treated by calcining at 550°C for 6 hours in air. 90 mg of alkali metal potassium was weighed, mixed with the carrier and placed in a high-pressure reactor at 110°C and 10 bar H 2 The hydrogenation reaction was carried out for 10 h under the condition of 40 °C. After the reaction, the remaining gas was discharged after cooling to room temperature to obtain 30 wt.% KH / SiO 2 .

[0125] The prepared 30wt.% KH / SiO 2As a catalyst, the catalytic o-xylene hydrodealkylation reaction is carried out in a high-pressure reactor, as follows:

[0126] o-xylene and 30wt.% KH / SiO 2 Put it into the autoclave, the molar ratio of KH to o-xylene is 1:1, add n-octane, and heat it at 80 bar H 2 React at 250℃ for 20h.

[0127] Comparative Example 13:

[0128] 30 wt.% NaH / MXene was prepared by melt impregnation method as follows:

[0129] 210 mg of MXene carrier was weighed and stirred at 30 mL / min N 2 The carrier was pre-treated by calcining at 550°C for 6 hours in air. 90 mg of alkali metal sodium was weighed, mixed with the carrier and placed in a high-pressure reactor at 110°C and 10 barH 2 The mixture was hydrogenated for 10 h under 400 °C. After the reaction, the mixture was cooled to room temperature and the remaining gas was discharged to obtain 30 wt.% NaH / MXene.

[0130] The prepared 30 wt.% NaH / MXene was used as a catalyst to carry out a catalytic o-xylene hydrodealkylation reaction in a high-pressure reactor as follows:

[0131] o-Xylene and 30 wt.% NaH / MXene were placed in a high pressure reactor with a molar ratio of NaH to o-Xylene of 1:1. n-Octane was added and heated at 80 bar H 2 React at 250℃ for 20h.

[0132] The aromatic hydrocarbon reactants and reaction products in Examples 1-10 and Comparative Examples 1-13 were analyzed online qualitatively and quantitatively using a gas chromatograph-mass spectrometer (GC-MS). The conversion rates and yields obtained are shown in Table 1 below.

[0133] Table 1: Aromatic conversion and yield in Examples 1-10 and Comparative Examples 1-13

[0134]

[0135]

[0136]

[0137] Note: Product 1 is the main reaction product besides toluene and benzene, and varies depending on the substrate.

[0138] From Table 1, we can conclude that:

[0139] (1) Catalyst 30wt.%NaH / SiO 2 It has good catalytic activity for the hydrodealkylation of different C8-C10 aromatics under mild catalytic conditions;

[0140] For example, in Examples 1-10, at 250°C and 80 bar H 2 Under the above conditions, the conversion rate after 20 hours of reaction is above 45%. Except for isopropylbenzene, the conversion rates of other aromatics are all above 50%, especially the conversion rates of mesitylene and naphthalene are above 90%, and the conversion rate of naphthalene even reaches 100%.

[0141] (2) Other reaction conditions are the same, when H 2 When the pressure decreases, the conversion rate of aromatic dealkylation will decrease, but the selectivity of dealkylation products will increase. Therefore, it is important to determine the appropriate H in the hydrodealkylation reaction. 2 The pressure range is also quite critical;

[0142] For example, in Comparative Examples 2 and 3, when H 2 When the pressure is reduced, the conversion rate of aromatic dealkylation will decrease, but the selectivity of dealkylation products will increase. Comparing Example 9 with Comparative Example 1, the same rule can be obtained.

[0143] (3) When supported alkali metal hydride is used as a catalyst, both the alkali metal hydride and the carrier play an important role in the high activity of the catalyst;

[0144] For example, compared with the NaH / SiO 2 As a catalyst, compared with the comparative example 4, Na / SiO 2 As a catalyst for catalytic o-xylene hydrodealkylation, the activity test results showed that the yield of product 2 (toluene) was reduced by about 20 times;

[0145] As in Example 1, NaH / SiO 2 As compared with the comparative example 5, in which NaH was used as a catalyst for catalytic hydrodealkylation of o-xylene, the activity test results showed that the yield of product 2 (toluene) was reduced by about 20 times.

[0146] (4) It can be seen from Comparative Example 7 that the supported alkali metal hydride can be recovered and recycled as a catalyst for the hydrodealkylation reaction of aromatic hydrocarbons after the reaction without affecting the catalytic activity, and there is no obvious loss in the yield of the dealkylation product.

[0147] (5) Ethyl toluene in Example 7 and p-isopropyl toluene in Example 8 in NaH / SiO 2The hydrodealkylation reaction catalyzed by NaH / SiO 2 Methyl groups are more easily hydrodealkylated than ethyl or isopropyl groups under catalysis due to the increased "steric effect" of ethyl and isopropyl groups relative to methyl groups.

[0148] (6) By comparing Example 1 with Comparative Example 8, it can be seen that when other conditions are the same, the conversion rate and yield can be adjusted by adjusting the mass percentage of the alkali metal hydride;

[0149] By comparing Example 1 with Comparative Example 9, it can be seen that when other conditions are the same, the conversion rate and yield can be adjusted by adjusting the molar ratio of the supported alkali metal hydride to the aromatic hydrocarbon;

[0150] By comparing Example 1 with Comparative Examples 10 and 11, it can be seen that when other conditions are the same, the conversion rate and yield can be adjusted by adjusting the reaction temperature or reaction time.

[0151] The above-described embodiments provide a detailed description of the technical solutions of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of supported alkali metal hydrides as catalysts for the hydrodealkylation of aromatics.

2. The use according to claim 1, characterized in that: In the supported alkali metal hydride, the alkali metal hydride is supported on a carrier; The carrier includes carbon materials, two-dimensional materials, and oxides; Preferably, the carbon material includes one or more of graphene, carbon nanotubes, and nanodiamonds; Preferably, the two-dimensional material includes one or more of hexagonal boron nitride, graphite carbon nitride, and two-dimensional transition metal carbon / nitride; Preferably, the oxide includes one or more of magnesium oxide, silicon oxide, and rare earth oxide.

3. The use according to claim 1, characterized in that: The alkali metal hydride includes one or more of lithium hydride, sodium hydride, potassium hydride, rubidium hydride, and cesium hydride.

4. The use according to claim 1, characterized in that: In the supported alkali metal hydride, the mass percentage of the alkali metal hydride is 1%-50%, and the mass percentage of the carrier is 50%-99%.

5. The use according to claim 1, characterized in that: The preparation method of the supported alkali metal hydride comprises mixing the alkali metal and the carrier in a high-pressure reactor, pressurizing H2 to 1 bar-100 bar, and heating to 100° C.-300° C. to react to obtain the supported alkali metal hydride; Preferably, the support is first calcined in nitrogen; Preferably, the calcination temperature is 200°C-1200°C.

6. The use according to claim 1, characterized in that: The aromatic hydrocarbon is a C8-C10 aromatic hydrocarbon; Preferably, the aromatic hydrocarbon is one or a mixture of o-xylene, m-xylene, p-xylene, mesitylene, 3-trimethylbenzene, 6-trimethylbenzene, 2-trimethylbenzene, ethylbenzene, n-propylbenzene, isopropylbenzene, ethyltoluene, m-ethyltoluene, n-propyltoluene, isopropyltoluene, p-isopropyltoluene, naphthalene, tetralin, dimethylethylbenzene, 3-trimethylbenzene, 2-trimethylbenzene, 2-trimethylbenzene, 1-methylpropylbenzene, butylbenzene and diethylbenzene.

7. The use according to claim 1, characterized in that: Adding the substrate aromatic hydrocarbon and the catalyst into a high-pressure reactor, adding a solvent, and causing the aromatic hydrocarbon to undergo a dealkylation reaction under H2 pressure and a certain reaction temperature to obtain a reaction product; Preferably, the reaction product comprises toluene and / or benzene; Preferably, the solvent includes one or more of n-octane, n-pentane and n-hexane.

8. The use according to claim 7, characterized in that: The conversion rate of the aromatic hydrocarbon hydrodealkylation reaction and / or the yield of the reaction product are adjusted by adjusting one or more of the following: H2 pressure, reaction temperature, reaction time, the mass percentage of alkali metal hydride in the supported alkali metal hydride, and the molar ratio of the supported alkali metal hydride to aromatic hydrocarbons.

9. The use according to claim 7, characterized in that: The reaction temperature is 150°C-300°C, more preferably 200°C-250°C; Preferably, H2 is pressurized to 1 bar-80 bar; Preferably, the reaction time is 1h-20h; Preferably, the molar ratio of the alkali metal hydride to the aromatic hydrocarbon in the catalyst is 1:100-1:1, more preferably 1:10-1:

1.

10. The use according to any one of claims 1 to 9, characterized in that: The reaction temperature is 200°C-250°C, and the conversion rate of the C8-C10 aromatic hydrocarbon hydrodealkylation reaction is higher than 45%, preferably higher than 50%.

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