Method for preparing benzaldehyde by catalyzing methyl benzoate with nano-ZnO

Abstract

The application provides a method for preparing benzaldehyde by catalyzing methyl benzoate hydrogenation with nano-ZnO, which is prepared by taking methyl benzoate as raw material and nano-ZnO as catalyst in a tubular reactor under the atmosphere of hydrogen. The preparation method of the nano-ZnO is as follows: dissolving zinc salt and a surfactant in water, adding an alkaline solution into the mixed solution of the zinc salt and the surfactant, stirring uniformly, reacting at a constant temperature of 100-150 DEG C for 10-15 h, washing, filtering, and calcining to obtain the nano-ZnO hydrogenation catalyst. The application selects the nano-ZnO as the hydrogenation catalyst, and the catalyst has good catalytic activity and high selectivity, and the yield of the benzaldehyde is high. The method improves the conversion rate of the methyl benzoate and the selectivity of the benzaldehyde, inhibits the generation of by-products, is simple in operation, has mild reaction conditions, has high product purity, and is simple in catalyst regeneration, and is suitable for the cyclic production of the benzaldehyde.

Description

Technical Field

[0001] This invention relates to a method for the hydrogenation of methyl benzoate to benzaldehyde catalyzed by nano-ZnO. Nano-ZnO is mainly used in the gas-solid phase continuous catalytic hydrogenation reduction of methyl benzoate to synthesize benzaldehyde, belonging to the fields of new catalytic materials and fine chemical technology. Background Technology

[0002] Benzaldehyde, also known as benzoaldehyde or benzaldehyde, has the molecular formula C7H6O. It resembles a bitter almond-smelling liquid, hence its alternative name, bitter almond oil. It is slightly soluble in water and miscible with organic solvents such as ethanol, chlorobenzene, and acetone. It has some irritant effect on the eyes and respiratory mucous membranes, but its volatility is too low to cause serious harm. Because the hydrogen on the benzene ring is replaced by an aldehyde group, it is relatively reactive and slowly oxidizes in air. Benzaldehyde has wide applications in the fine chemical industry and is an important raw material in the pharmaceutical, fragrance, fuel, and resin industries. In the pharmaceutical industry, it is used to prepare drugs such as phenylaminoacetic acid, benzaldehyde oxime, 2-phenylbenzimidazole, ephedrine, and chloramphenicol. Due to its unique aromatic odor, benzaldehyde is mainly used in the fragrance industry to blend food flavorings, and it can also be used to process other flavorings and produce lauraldehyde, cinnamic acid, and cinnamic green. As a dye intermediate, it is used to manufacture leuco malachite green, triphenylmethane dyes, and acridinone dyes. In other applications, benzaldehyde can be used to produce benzyl alcohol, aniline, pesticides, photographic chemicals, and electroplating additives.

[0003] The main methods for synthesizing benzaldehyde include benzyl alcohol oxidation, direct toluene oxidation, electro-oxidation of toluene, benzoic acid (methyl ester) reduction, styrene oxidation, benzene carbonylation, and indirect electro-synthesis of toluene. Large quantities of toluene are obtained during petroleum reforming, making direct toluene oxidation a primary research method for benzaldehyde production. However, the activation of the CH bonds in the toluene side chain is difficult, resulting in low catalytic oxidation activity. Furthermore, benzaldehyde is an intermediate oxidation product and is easily further oxidized to benzoic acid or carbon oxides, thus its selectivity is not high. Therefore, extensive research has been conducted to improve the selectivity of benzaldehyde, yielding many promising scientific results.

[0004] Using benzoic acid or its esters as raw materials has become a hot topic in benzaldehyde preparation. The process involves oxidizing toluene to obtain benzoic acid, which is then esterified with methanol under the catalysis of concentrated sulfuric acid to produce methyl benzoate. Benzaldehyde is then obtained by hydrogenation reduction of the benzoic acid (methyl benzoate). This method produces high-quality benzaldehyde, is chlorine-free, has a high yield, low environmental pollution, and a relatively simple process. Commonly used catalysts include ZrO2 series, Y2O3 series, Cu-Cr series, and γ-Al2O3 series. Copper-based materials are prone to deactivation due to agglomeration at high temperatures, and Cr can easily cause environmental pollution. Patent CN03142119.9 designed a catalyst using M / Mn / Al hydrotalcite as a precursor and applied it to the gas-phase synthesis of benzaldehyde from benzoic acid or methyl benzoate. Methyl benzoate showed good conversion, but the selectivity for benzaldehyde was poor. Patent CN201611055790.9 utilizes a Cr-Zr catalyst, exhibiting good methyl benzoate conversion and benzaldehyde selectivity. However, the use of Cr causes environmental pollution, hindering the development of such catalysts. Patent CN201710233585.5 designs a Mn-ZrO2 catalyst, which possesses high selectivity, high activity, and high stability. However, this catalyst uses chromium oxide during molding, also posing environmental risks. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO. The method uses methyl benzoate as a raw material and directly obtains benzaldehyde through hydrogenation catalysis with a nano-ZnO catalyst. This preparation method improves the conversion rate of methyl benzoate and the selectivity of benzaldehyde, suppresses the generation of by-products, and is simple to operate, with mild reaction conditions and high product purity.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO involves using methyl benzoate as a raw material and nano-ZnO as a catalyst in a tubular reactor under a hydrogen atmosphere. The reaction temperature is 400-500℃, the reaction pressure is 0.2-1.5 MPa, the reaction time is 10-100 h, the molar ratio of hydrogen to methyl benzoate is 5-20, and the volume hourly space velocity (VHSV) of the liquid-phase methyl benzoate feed is 0.1-2 h⁻¹. -1 .

[0007] Preparation method of nano ZnO: Dissolve zinc salt and surfactant in water, then add alkaline solution to the mixed solution of zinc salt and surfactant, stir evenly, react at a constant temperature of 100~150℃ for 10~15h, wash, filter, and calcine to obtain nano ZnO hydrogenation catalyst.

[0008] The zinc salt is one or a mixture of zinc nitrate, zinc acetate, and zinc chloride. The surfactant is at least one of P123, CTAB, urea, and sodium citrate. The alkaline solution is one or more of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, or ammonia water. The calcination temperature is 400-600℃, and the time is 2-10 hours. The molar ratio of zinc salt to surfactant is (20-1):1.

[0009] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to a method for the selective preparation of benzaldehyde using methyl benzoate as a raw material. Methyl benzoate is selected as the raw material, and nano-ZnO is used as the hydrogenation catalyst, exhibiting good catalytic activity and selectivity, resulting in a high yield of benzaldehyde. This preparation method improves the conversion rate of methyl benzoate and the selectivity of benzaldehyde, suppresses the generation of byproducts, is simple to operate, has mild reaction conditions, produces high-purity products, and the catalyst regeneration is simple, making it suitable for the cyclical production of benzaldehyde. Attached Figure Description

[0010] Figure 1 a-d are scanning electron microscope (SEM) images (a), thermogravimetric (TGA) images (b), XRD phase before reaction (c), and XRD phase after reaction (d) of ZnO prepared in Example 1, respectively.

[0011] Figure 2 a-2d are scanning electron microscope (SEM) images (a), high-resolution transmission electron microscope (HEM) images (b), transmission electron microscope (TEM) images (c), and adsorption-desorption curves (d) of ZnO prepared in Example 2, respectively.

[0012] Figure 3 a-3c are scanning electron microscope (SEM) images (a), transmission electron microscope (TEM) images (b), and X-ray photoelectron spectroscopy (XPS) images (c) of ZnO prepared in Example 3, respectively.

[0013] Figure 4 a-4d are scanning electron microscope images of ZnO prepared in Examples 4, 5, 6, and 7, respectively. Detailed Implementation

[0014] The preparation and application of the nano-ZnO catalyst of the present invention will be further illustrated below through specific embodiments.

[0015] Example 1 Weigh 15 mmol Zn(OAc)₂·2H₂O and 1.7 mmol urea and dissolve them in 50 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue stirring magnetically and slowly add 50 mL of 2 mol / L KOH. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor with a 100 mL PTFE liner and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 120 °C for 12 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 500 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to obtain nano-ZnO material.

[0016] Figure 1 a-d are scanning electron microscope (SEM) images, thermogravimetric analysis (TGA) images, XRD patterns before and after the reaction of the ZnO prepared in Example 1, respectively. As can be seen from the figures, the obtained ZnO has a plate-like structure, and the sample remains relatively stable at 800℃ without decomposition.

[0017] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the aforementioned ZnO catalyst was weighed and loaded into the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be reduced at 500℃ for 8 hours. A micro-syringe was used to pump the methyl benzoate feedstock solution into the reactor, mixed with H2 for continuous hydrogenation. The reaction temperature was set at 400℃, the reaction pressure at 1.0 MPa, and the hydrogen-to-ester molar ratio at 1:2. The methyl benzoate was added at a rate of 0.1 h / min. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0018] Example 2 Weigh 10 mmol Zn(NO3)2·6H2O, 10 mmol Zn(OAc)2·2H2O, and 1.7 mmol sodium citrate dihydrate and dissolve them in 50 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue stirring magnetically and slowly add 50 mL of 2 mol / L NaOH. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor with a 100 mL polytetrafluoroethylene liner and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 120 °C for 12 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 500 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to obtain nano-ZnO material.

[0019] Figure 2 Images a-2d are scanning electron microscope (SEM) images, high-resolution transmission electron microscope (HTEM) images, transmission electron microscope (TEM) images, and adsorption-desorption curves of ZnO prepared in Example 2, respectively. The ZnO obtained using this method exhibits a columnar flower morphology. It has good crystallinity and a lattice size of 0.253 nm. The nitrogen adsorption-desorption isotherm of the ZnO shows that the obtained sample has a typical Type IV isotherm. The specific surface area was calculated using the BET method, and the specific surface area of ​​the sample was 9.96 m². 2 / g.

[0020] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the aforementioned ZnO catalyst was weighed and loaded into the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be 500℃ for 8 hours for reduction. The feed solution was injected using a microsyringe, and mixed with H2, the hydrogenation reaction was continuously carried out in the reactor. The reaction temperature was set at 430℃, the reaction pressure at 0.5MPa, the hydrogen-to-ester molar ratio at 15, and the methyl benzoate was added at a rate of 0.2 h. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0021] Example 3 10 mmol Zn(NO3)2·6H2O and 1.0 mmol CTAB were weighed and dissolved in 50 mL of water. The mixture was magnetically stirred for 30 min to obtain a mixed solution. Then, 5 mL of concentrated ammonia was slowly added dropwise while still magnetically stirring. After stirring magnetically for another 30 min, the mixture was transferred to a stainless steel hydrothermal reactor with a 100 mL PTFE liner and sealed. The volume of the mixed solution was controlled to be 70 mL, and the reactor was placed in an oven at 120 °C for 12 h. After the reactor cooled naturally, the supernatant was removed, the mixture was centrifuged, and washed with deionized water and anhydrous ethanol until neutral. The mixture was then dried overnight in an oven at 120 °C. The dried sample was then heated to 400 °C at a rate of 3 °C / min and held at this temperature for 4 h to obtain nano-ZnO material.

[0022] Figure 3 a-3c are scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, and X-ray photoelectron spectroscopy (XPS) images of ZnO prepared in Example 3, respectively. This preparation method can produce uniformly shaped spherical ZnO particles. XPS analysis shows that the sample contains Zn in an oxidized state.

[0023] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the aforementioned ZnO catalyst was weighed and placed in the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be 500℃ for 8 hours for reduction. The feed solution was injected using a microsyringe, and mixed with H2, the hydrogenation reaction was continuously carried out in the reactor. The reaction temperature was set at 450℃, the reaction pressure at 0.2MPa, the hydrogen-to-ester molar ratio at 10, and the methyl benzoate was added at a rate of 0.5 h. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0024] Example 4 Weigh 2.0 mmol ZnCl and 0.5 mmol P123 and dissolve them in 100 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue to slowly add 2 M Na2CO3 dropwise under magnetic stirring until the pH reaches 10. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor with a 100 mL PTFE liner and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 150 °C for 5 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 600 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to finally obtain nano-ZnO material.

[0025] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the ZnO catalyst was weighed and placed in the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be 500℃ for 8 hours for reduction. A microsyringe was used to inject the feed solution, mixed with H2, into the reactor for continuous hydrogenation. The reaction temperature was set at 400℃, the reaction pressure at 0.2MPa, and the hydrogen-to-ester molar ratio at 20. The reaction was carried out at a rate of methyl benzoate for 2 hours. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0026] Example 5 Weigh 2.0 mmol Zn(OAc)₂·2H₂O, 1.0 mmol ZnCl, and 0.5 mmol sodium citrate dihydrate and dissolve them in 67 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue stirring magnetically and slowly add 2 M NaHCO₃ until the pH reaches 8. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor with a 100 mL PTFE liner and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 150 °C for 5 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 500 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to obtain nano-ZnO material.

[0027] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the ZnO catalyst was weighed and loaded into the middle of the reaction tube, with both ends secured with quartz wool. The reaction was pre-programmed to a temperature of 550℃ for 8 hours for reduction. A microsyringe was used to inject the feed solution, mixed with H2, into the reactor for continuous hydrogenation. The reaction temperature was set at 420℃, the reaction pressure at 0.5MPa, the hydrogen-to-ester molar ratio at 8, and the methyl benzoate was added at a rate of 0.8 h. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0028] Example 6 Weigh 1.0 mmol Zn(OAc)₂·2H₂O, 1.0 mmol Zn(NO₃)₂·6H₂O, and 0.5 mmol P₁₂₃ and dissolve them in 100 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue to slowly add a mixture of 2 M Na₂CO₃ and 2 M NaHCO₃ under magnetic stirring until the pH reaches 9. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor lined with 100 mL of polytetrafluoroethylene and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 180 °C for 15 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 500 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to finally obtain nano-ZnO material.

[0029] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the aforementioned ZnO catalyst was weighed and loaded into the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be 550℃ for 8 hours for reduction. The feed solution was injected using a microsyringe, and mixed with H2, the hydrogenation reaction was continuously carried out in the reactor. The reaction temperature was set at 450℃, the reaction pressure at 1.0 MPa, the hydrogen-to-ester molar ratio at 1:2, and the methyl benzoate was added at a rate of 1.0 h. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0030] Example 7 Weigh 1.0 mmol Zn(OAc)₂·2H₂O and 1.0 mmol Zn(NO₃)₂·6H₂O, and 0.5 mmol CTAB and dissolve them in 100 mL of water. Stir magnetically for 30 min to obtain a mixed solution. Then, continue stirring magnetically and slowly add concentrated ammonia until the pH reaches 9. After stirring magnetically for another 30 min, transfer the mixture to a stainless steel hydrothermal reactor with a 100 mL PTFE liner and seal it. Control the volume of the mixed solution to 70 mL and place it in an oven at 180 °C for 15 h. After the reactor cools naturally, remove the supernatant, centrifuge, and wash with deionized water and anhydrous ethanol until neutral. Dry the sample overnight in an oven at 120 °C. Then, heat the dried sample to 500 °C at a rate of 3 °C / min and hold it at this temperature for 4 h to obtain nano-ZnO material.

[0031] The hydrogenation of methyl benzoate to benzaldehyde was carried out in a fixed-bed microreactor. 2g of the aforementioned ZnO catalyst was weighed and loaded into the middle of the reaction tube, with both ends secured with quartz wool. Before the reaction, the temperature was programmed to be 550℃ for 8 hours for reduction. The feed solution was injected using a microsyringe, and mixed with H2, the hydrogenation reaction was continuously carried out in the reactor. The reaction temperature was set at 400℃, the reaction pressure at 0.1MPa, the hydrogen-to-ester molar ratio at 10, and the methyl benzoate was added at a rate of 0.2 h. -1 Space velocity feed. The reaction solution was collected in a cold trap and analyzed offline using gas chromatography (GC-2014, Shimadzu).

[0032] Figure 4 Images a-4d are scanning electron microscope (SEM) images of ZnO prepared in Examples 4, 5, 6, and 7, respectively. The images show different morphologies of ZnO obtained under different zinc sources, alkali sources, and hydrothermal temperatures. 4a shows a disc-shaped morphology, 4b a bread-like morphology, 4c a short cubic morphology, and 4d a cubic morphology with a length greater than 400 nm.

Claims

1. A method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO, characterized in that: Benzaldehyde was obtained by reacting methyl benzoate as a raw material and nano-ZnO as a catalyst in a tubular reactor under a hydrogen atmosphere at 400-500℃ and 0.2-1.5MPa. The preparation method of nano-ZnO is as follows: zinc salt and surfactant are dissolved in water, and then an alkaline solution is added to the mixed solution of zinc salt and surfactant. After stirring evenly, the mixture is reacted at a constant temperature of 100-150℃ for 10-15h. After washing, filtering, and calcination, nano-ZnO hydrogenation catalyst is obtained. The calcination is carried out at 400-600℃ for 2-10h. The surfactant is at least one of P123, CTAB, urea, and sodium citrate. The molar ratio of zinc salt to surfactant is (20-1):

1.

2. The method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO according to claim 1, characterized in that: The molar ratio of hydrogen to methyl benzoate is 5-20, and the volume hourly space velocity (VHSV) of the methyl benzoate liquid feed is 0.1-2 h⁻¹. -1 .

3. The method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO according to claim 1, characterized in that: The zinc salt is one or a mixture of zinc nitrate, zinc acetate, and zinc chloride.

4. The method for preparing benzaldehyde by hydrogenation of methyl benzoate catalyzed by nano-ZnO according to claim 1, characterized in that: The alkaline solution is one or more of an alkali metal hydroxide, an alkali metal carbonate, an alkali metal bicarbonate, or ammonia water.

Images