Preparation method of a bonded lewis acid catalyst and application thereof in preparation of aromatic nitro compounds from nitrated aromatic compounds

Abstract

The application provides a preparation method of a bonded Lewis acid catalyst and application of the catalyst in preparation of aromatic nitro compounds from nitrated aromatic hydrocarbons. The catalyst is prepared by using sepiolite sequentially subjected to acid modification and silanization as a carrier, and bonding one or more active components, Lewis acids. The modification can improve the interaction between the carrier and the active acid component, and the stability of the catalyst is improved through the bonding mode of chemical bonds. The catalyst is applied to the nitration reaction of aromatic hydrocarbons. Meanwhile, the application is to use nitroxide compounds as a nitrating agent, and replace the traditional mixed acid system with the prepared modified sepiolite bonded with one or more Lewis acids as a catalyst. The method of the application belongs to green nitration, reduces the generation of waste acid and waste water, avoids the aggregation of mixed acid, and can be widely applied to the nitration reaction of various aromatic hydrocarbons.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a method for preparing bonded Lewis acid catalysts and their application in the preparation of aromatic nitro compounds from nitrated aromatic hydrocarbons. Background Technology

[0002] The nitration of aromatic hydrocarbons is an important type of organic substitution reaction, and the resulting nitroaromatic compounds play a crucial role in the synthesis of organic compounds. Aromatic nitro compounds can be widely used as raw materials or intermediates in the synthesis of pharmaceuticals, dyes, fragrances, fertilizers, plastics, and explosives. Therefore, researchers both domestically and internationally have conducted in-depth studies on the nitration reaction, both in its fundamental theoretical research and in its industrial production.

[0003] In traditional industry, the nitration of aromatics mainly uses nitration with a mixture of nitric and sulfuric acids, which is currently the most widely used method for producing nitroaromatic compounds both domestically and internationally. This technology has been applied in industrial production for over 160 years and is the most mature production process. However, it also has drawbacks such as poor atom economy, poor regioselectivity (occurrence of oxidation side reactions and over-nitration), generation of large amounts of waste acid, and environmental harm. Therefore, in recent years, to address these shortcomings, many researchers have devoted themselves to the research of novel green aromatic nitration reactions. Research work mainly focuses on improving nitrating agents and catalysts, in order to find greener nitrating agents and novel solid acid catalysts to replace sulfuric acid in aromatic nitration.

[0004] Currently, common nitrating agents include traditional nitric acid (HNO3)-sulfuric acid (H2SO4) mixed acid, nitric acid (HNO3)-sulfuric acid (H2SO4)-phosphoric acid (H3PO4), nitric acid and acetic anhydride, nitrate esters or nitrates, and nitrogen oxides. Among these, nitrogen oxides, when used as nitrating agents, can overcome the poor selectivity of the target product in the traditional nitric acid-sulfur mixed acid method, exhibiting good regioselectivity for the nitration reaction. Therefore, the selectivity of the target product among the nitration product isomers can be controlled by changing the reaction conditions. Furthermore, nitrogen oxide nitration is a non-acid nitration method. As a nitrating agent, it produces less waste acid and wastewater after the reaction, reducing subsequent treatment costs and saving costs. It is economical and has dual significance in terms of economic conservation and environmental protection, attracting the attention and research of researchers both domestically and internationally.

[0005] As for nitration catalysts, the main catalysts used include zeolite molecular sieve catalysts, clay catalysts, Lewis acid catalysts, metal oxides, rare earth metal salts, and ionic liquids.

[0006] Lewis acids are a type of acid-base theory proposed by American chemist Gilbert Newton Lewis. It states that any molecule, group, or ion that can accept an electron pair is an acid (and any molecule, group, or ion that can donate an electron pair is a base). Common Lewis acids include aluminum chloride, copper chloride, ferric chloride, zinc chloride, and boron trifluoride. Lewis acids are commonly used catalysts in organic reactions, exhibiting high catalytic activity in esterification, transesterification, Beckmann rearrangement, Friedel-Crafts alkylation, and oxidation. Kochi et al. studied the nitration of aromatic compounds using a series of Lewis acid catalysts and also speculated on the reaction mechanism of the nitration of aromatic compounds by NO2 catalyzed by Lewis acids. In the nitration of benzene at room temperature using dichloromethane as a solvent, the reaction time was 38–66 h, with a conversion rate of 21%. The Peng Xinhua research group at Nanjing University of Science and Technology studied the nitration of xylene catalyzed by a series of Lewis acids such as bismuth chloride, aluminum chloride, and zinc chloride, and concluded that bismuth chloride has a catalytic effect. Summary of the Invention

[0007] To address the technical problems of existing aromatic hydrocarbon nitration methods, such as the large amount of waste acid and wastewater generated by nitric acid or sulfuric acid and the difficulty in separating simple Lewis acid catalysts, this invention provides a method for preparing a bonded Lewis acid catalyst and its application in the preparation of aromatic nitro compounds from nitrated aromatic hydrocarbons. The method uses modified sepiolite bonded with one or more Lewis acids as the nitration catalyst, nitrogen oxides as the nitrating agent, and oxygen as the nitration activator. This catalytic nitration reaction of aromatic hydrocarbons prepares aromatic nitro compounds without the use of sulfuric acid, significantly reducing the generation of waste acid and wastewater. Furthermore, the catalyst is easily separated and can be reused.

[0008] The object of this invention is achieved by the following means: A method for preparing a bonded Lewis acid catalyst includes the following steps: S1. Sepiolite is first acid-treated, and then silanized with toluene and a silanizing agent in order to introduce amino groups; S2. Silanized sepiolite is chemically bonded to one or more Lewis acids through a chemical reaction between hydrogen in the amino group and chloride ions in the Lewis acid; S3. Calcination and activation yield modified sepiolite-bonded Lewis acids, i.e., bonded Lewis acid catalysts. This method can effectively immobilize stronger Lewis acids on sepiolite, increasing the acidity of the catalyst while significantly enhancing its catalytic performance stability in aromatic nitration.

[0009] Further, in S1, the silanizing agent is trimethoxysilane, triethoxysilane, or 3-aminopropyltriethoxy, more preferably 3-aminopropyltriethoxy, which can introduce amino groups to further increase the number of groups that can bond with Lewis acids. The mass ratio of the silanizing agent to sepiolite is 1 to 10, preferably 2 to 5. The solvent used in the silanization process is toluene, and the ratio of sepiolite to toluene is 1 g : 20 to 60 ml, preferably 1 g : 30 to 40 ml.

[0010] Further, S2 specifically involves dispersing silanized sepiolite in a solvent (such as ethanol), then adding one or more Lewis acid carbon tetrachloride solutions, stirring the mixture, and achieving chemical bonding.

[0011] Furthermore, the sepiolite treatment is performed using organic or inorganic acids, wherein the inorganic acid is one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, preferably nitric acid or hydrochloric acid; and the organic acid is one of oxalic acid, citric acid, and tartaric acid, preferably oxalic acid or citric acid.

[0012] Furthermore, the concentration of the organic or inorganic acid is 0.1-5 mol / L, preferably 1-2 mol / L; the acid treatment time is 1-6 h, preferably 2-4 h; and the ratio of sepiolite to acid is 1 g: 10-30 ml, preferably 1 g: 15-20 ml.

[0013] Furthermore, in S2, the Lewis acid is at least one of aluminum chloride, ferric chloride, zinc chloride, and titanium chloride, more preferably aluminum chloride or titanium chloride; the concentration of the Lewis acid solution is 0.02~2 mol / L, and the solid-liquid ratio of sepiolite to Lewis acid is 1:10~30.

[0014] Furthermore, in S3, the calcination activation temperature is 100~500℃, preferably 200~400℃; the activation time is 1~6h, preferably 2~4h.

[0015] The application of the above catalyst in the preparation of aromatic nitro compounds by nitration of aromatic hydrocarbons includes the following steps: using modified sepiolite bonded Lewis acid as a catalyst, aromatic hydrocarbons and nitrogen oxides are directly nitrated to prepare nitro aromatic compounds, the molar ratio of aromatic hydrocarbons to nitrogen oxides is 1:0.5~6, the reaction temperature is 0~80℃, the reaction time is 1~12 h, and the reaction oxygen pressure is 0~2 MPa.

[0016] Furthermore, the molar ratio of aromatics to nitrogen oxides is 1:1.5~3; the mass ratio of catalyst to aromatics is 1:5-25; the reaction temperature is 25~45℃; the reaction time is 2~5 h; the reaction oxygen pressure is 0.1~1 MPa, the concentration is 0.02~2 mol / L, and the solid-liquid ratio is 1:10~30.

[0017] Furthermore, aromatic hydrocarbons can be benzene, toluene, halobenzene, nitrobenzene, naphthalene, 1-nitronaphthalene, o-xylene, m-xylene, p-xylene, etc.

[0018] After the nitration reaction is completed, the mixture is cooled, filtered to separate the catalyst and reaction mixture, and a sample of the mixture is taken for gas chromatography analysis. The data are analyzed and the aromatic conversion rate and nitration product selectivity are calculated.

[0019] The beneficial effects of this invention are as follows: (1) The catalyst obtained in this invention can be used in the reaction system for the preparation of aromatic nitro compounds by nitrating aromatic hydrocarbons. It can not only achieve very good reaction results, but also significantly improve the stability of the catalyst. The catalyst is easy to separate and can be reused.

[0020] (2) The chemical bonding effect is significantly enhanced between the modified sepiolite and the specific Lewis acid, thereby significantly improving the activity and stability of the catalyst. Attached Figure Description

[0021] Figure 1 The figure shows the NH3-TPD diagrams of pristine sepiolite and bonded Lewis acid sepiolite (AlCl3-TiCl4-Sep-AS). The diagrams indicate that the acidity of sepiolite is significantly enhanced after the bonding of Lewis acids, especially the medium-strong acid sites are significantly enhanced, which is more conducive to the catalysis of toluene nitration.

[0022] Figure 2 The image shows the infrared spectrum of the original sepiolite and the bonded Lewis acid sepiolite (AlCl3-TiCl4-Sep-AS). The image shows that the basic structure of the sepiolite is maintained after bonding, and the characteristic peaks of Lewis acid are also displayed, indicating that the Lewis acid bonding was successful.

[0023] Figure 3 The figure shows a comparison of repeated experiments between silanized sepiolite-bonded Lewis acids (AlCl3-TiCl4-Sep-AS) and unsilanized sepiolite-supported Lewis acids (AlCl3-TiCl4-Sep). As can be seen from the figure, the unsilanized catalyst has poor stability, while the silanized and rebonded sample has good stability in the toluene nitration reaction because the introduction of amino groups allows for the bonding of Lewis acids and the effective immobilization of the active components. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0025] The modified sepiolite-bonded Lewis acid catalyst used below was first treated with hydrochloric acid, then silanized to bond with Lewis acids. The specific method was as follows: sepiolite was mixed with 1-2 mol / L hydrochloric acid at a ratio of 1 g: 15-20 ml. The resulting suspension was stirred at room temperature for 1-12 h, filtered, washed until neutral, and dried to obtain acid-treated sepiolite (Sep-A). Sep-A sample was added to toluene solution at a ratio of 1 g: 30-40 ml, stirred thoroughly, and then 2-5 g of the silanizing agent 3-aminopropyltriethoxysilane was added. The mixture was then stirred at 60 °C. o After reflux at 60 °C for 1–12 h, the sample was filtered, washed, and dried with toluene and methanol to obtain silanized sepiolite (Sep-AS). The Sep-AS sample was bonded to one or two solutions of 0.5–4 mol / L aluminum chloride, ferric chloride, zinc chloride, or titanium chloride at a ratio of 1 g: 15–20 ml. The mixture was refluxed and stirred at 60 °C for 1–12 h, filtered, dried, and then heated to 200–400 °C. o Activation was performed at C for 2–4 h, and different samples were labeled AlCl3-Sep-AS (bonded aluminum chloride), FeCl3-Sep-AS (bonded ferric chloride), and AlCl3-TiCl4-Sep-AS (bonded aluminum chloride and titanium chloride). Simultaneously, following the above method, the silanization step was omitted to prepare simple supported Lewis acid catalysts, such as those supported on aluminum chloride and titanium chloride, labeled AlCl3-TiCl4-Sep.

[0026] Example 1: 5.0 g chlorobenzene, 10.0 g acetic anhydride, and 2.5 g NO2 were weighed and placed in a 100 ml batch reactor. The oxygen pressure of the reaction was 0.5 MPa, and the reaction was carried out at 35°C. o After reacting at C for 4 h, the mixture was cooled, filtered to obtain a liquid mixture, and a sample was taken for gas phase analysis. The results showed that the conversion rate of chlorobenzene was 72.8% and the selectivity of p-nitrochlorobenzene was 62.5%.

[0027] Example 2: Except for changing 2.5 g NO2 to 5.0 g, the other operations were the same as in Example 1, and the chlorobenzene conversion rate was 80.1% and the selectivity for p-nitrochlorobenzene was 65.3%.

[0028] Example 3: Except for adding 0.1 g of AlCl3-Sep-AS catalyst to the reactor, the other operations were the same as in Example 1, and the conversion rate of chlorobenzene was 88.5%, and the selectivity of p-nitrochlorobenzene was 81.3%.

[0029] Example 4: Except that the catalyst was changed to FeCl3-Sep-AS catalyst and the reaction substrate was changed to toluene instead of chlorobenzene, the rest of the operation was the same as in Example 3. The conversion rate of toluene was 75.6% and the selectivity of p-nitrotoluene was 61.3%.

[0030] Example 5: Except for changing the catalyst to AlCl3-TiCl4-Sep-AS, the other operations were the same as in Example 3, and the yield of mononitrotoluene was 98%.

[0031] Example 6: Except for changing the catalyst to AlCl3-TiCl4-Sep-AS which can be used for five cycles, the other operations were the same as in Example 3, and the yield of mononitrotoluene was 97%, with its activity remaining basically unchanged.

[0032] Example 7: Except for changing the catalyst to AlCl3-TiCl4-Sep, the other operations were the same as in Example 3, and the yield of mononitrotoluene was 86%.

[0033] Example 8: Except for changing the catalyst to AlCl3-TiCl4-Sep which is used for five cycles, the rest of the operation was the same as in Example 3. The yield of nitrotoluene was 61%, and its activity was significantly reduced. Example 9: Except for changing the amount of catalyst to 0.3 g, the rest of the operation was the same as in Example 3. The conversion rate of chlorobenzene was 96.2%, and the selectivity for p-nitrotoluene was 87.2%.

[0034] Example 10: Except for replacing the reaction substrate with benzene instead of toluene, the other operating conditions were the same as in Example 5, and the conversion rate of benzene was 99% and the selectivity of nitrobenzene was 99%.

[0035] Example 11: Except for replacing the reaction substrate with toluene, the other operating conditions were the same as in Example 5, and the conversion rate of toluene was 83.6%, and the selectivity of p-nitrotoluene was 63.5%.

[0036] Example 12: Except for replacing the reaction substrate with naphthalene instead of toluene, the other operating conditions were the same as in Example 5, and the conversion rate of naphthalene was 100%, and the selectivity of 1,5-dinitronaphthalene was 42.6%.

Claims

1. A method for preparing a bonded Lewis acid catalyst, characterized in that, Includes the following steps: S1. Sepiolite is first acid-treated, and then silanized using a silanizing agent. The acid treatment of sepiolite uses organic or inorganic acids, wherein the inorganic acid is one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid; and the organic acid is one of oxalic acid, citric acid, and tartaric acid. S2. Disperse the silanized sepiolite in a solvent, then add one or more Lewis acid carbon tetrachloride solutions dropwise, stir the reaction, and achieve chemical bonding; S3. Calcination and activation yield modified sepiolite-bonded Lewis acid, i.e., bonded Lewis acid catalyst; In S1, the concentration of the organic or inorganic acid is 0.1~5 mol / L; the acid treatment time is 1~6 h; and the ratio of sepiolite to acid is 1g:10~30 ml. In S1, the silanizing agent is 3-aminopropyltriethoxy, the mass ratio of the silanizing agent to sepiolite is 1~10, the solvent used is toluene, and the volume ratio of sepiolite to toluene is 1 g : 20~60 ml. In S2, the Lewis acid is at least one of aluminum chloride, ferric chloride, zinc chloride, and titanium chloride; the concentration of the Lewis acid carbon tetrachloride solution is 0.02~2 mol / L, and the solid-liquid ratio of sepiolite to the Lewis acid carbon tetrachloride solution is 1:10~30 g / ml.

2. The method for preparing the bonded Lewis acid catalyst according to claim 1, characterized in that, In S3, the calcination activation temperature is 100~500℃; the activation time is 1~6 h.

3. The application of the catalyst obtained by the preparation method according to claim 1 or 2 in the preparation of aromatic nitro compounds from nitrated aromatic hydrocarbons, characterized in that, The process includes the following steps: using modified sepiolite-bonded Lewis acid as a catalyst, aromatic hydrocarbons and nitrogen oxides are directly nitrated to prepare nitro aromatic compounds. The molar ratio of aromatic hydrocarbons to nitrogen oxides is 1:0.5~6, the reaction temperature is 0~80℃, the reaction time is 1~12 h, and the reaction oxygen pressure is 0~2 MPa.

4. The application according to claim 3, characterized in that, The molar ratio of aromatic hydrocarbons to nitrogen oxides is 1:1.5~3; the reaction temperature is 25~45℃, the reaction time is 2~5 h, and the reaction oxygen pressure is 0.1~1 MPa.

5. The application according to claim 3, characterized in that, The aromatic hydrocarbons mentioned are benzene, toluene, halobenzene, nitrobenzene, naphthalene, 1-nitronaphthalene, o-xylene, m-xylene, or p-xylene.

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