Process for the preparation of aromatic aldehydes by oxidation of aromatic hydrocarbons
By combining a fixed-bed photocatalytic reactor with a TiO2 surface-supported oxide catalyst, the problems of catalyst stability and separation difficulties in the existing technology are solved, and highly selective oxidation of aromatic hydrocarbons is achieved, which is suitable for the continuous production of aromatic aldehydes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2023-10-24
- Publication Date
- 2026-06-23
AI Technical Summary
Existing photocatalytic selective oxidation reactions are prone to over-oxidation of products under high conversion conditions, and the catalyst is difficult to separate from the reaction system, making it difficult to achieve long-term high-selectivity production.
A fixed-bed photocatalytic reactor is used, employing an oxide catalyst supported on the TiO2 surface. Through a combination of internal and external light sources, continuous photocatalytic selective oxidation of aromatic hydrocarbons is achieved. The catalyst is fixed in the inner and outer jacket layers, and the reaction is carried out using a mobile phase reactor.
It enables long-term, highly selective, continuous production. The catalyst is easy to separate from the reaction liquid, which improves reaction efficiency and inhibits excessive oxidation of the product, showing promise for industrial application.
Smart Images
Figure CN117567256B_ABST
Abstract
Description
Technical Field
[0001] This application relates to a method for preparing aromatic aldehydes by oxidizing aromatic hydrocarbons, belonging to the field of aromatic aldehyde preparation technology. Background Technology
[0002] Aromatic aldehydes are important intermediates in organic synthesis, widely used in pharmaceuticals, agrochemicals, fragrances, synthetic fibers, dyes, and polymers. Currently, there are two main industrial methods for preparing p-methylbenzaldehyde: one involves the Somley reaction, followed by photochlorination to produce benzyl chloride, which is then further acidified to yield the corresponding aromatic aldehyde. This process requires chlorine gas, strong acids, and produces numerous byproducts. The other method involves carbonylation, but this process requires highly corrosive liquids such as hydrofluoric acid.
[0003] The selective oxidation of aromatic hydrocarbons to aromatic aldehydes provides a simple and low-pollution reaction pathway. Solar energy is the most abundant clean energy source, and photocatalysis is not only environmentally friendly but can also be achieved at room temperature.
[0004] Currently, there are numerous reports on the selective oxidation of toluene. For example, patent CN112295576A discloses a Cs3Bi2Br9 / TiO2 perovskite heterostructure and its preparation method, which exhibits excellent performance in the oxidation of toluene to benzyl alcohol. However, perovskite materials generally suffer from stability issues, preventing their application in practical production. Patent CN115744987A discloses a method for preparing rare-earth-based oxide ultrafine nanowire materials and their application in photocatalytic toluene oxidation. This catalyst shows good selectivity for toluene oxidation, but the reaction rate is relatively low, and catalyst stability is not mentioned. Other photocatalytic oxidation reactions, such as p-BWO (Nat Catal 2018, 1, 704-710), Cl / BiOBr / TiO2 (Angew. Chem. Int. Ed. 2013, 52, 1035-1039), Ru / TiO2 (Angew. Chem. 2014, 126, 12813-12816), Pd / Bi2WO6 (Chinese Journal of Catalysis 2017, 38, 440-446), and BiOCl / TiO2 (J. Am. Chem. Soc. 2023, 10.1021 / jacs.3c05237), all exhibit excellent photocatalytic performance in the oxidation of toluene to benzaldehyde. However, a common problem reported above is that the reactions are all carried out in a batch reactor. High selectivity is essentially only achieved under low conversion conditions. Under high conversion conditions, subsequent oxidation of the product inevitably occurs preferentially, thus reducing the reaction activity and selectivity. Furthermore, batch reactors present post-processing issues such as catalyst separation from the reaction system for subsequent industrial applications. Summary of the Invention
[0005] To address the common problems in current photocatalytic selective oxidation, this application proposes a fixed-bed photocatalytic reaction method for selective oxidation, which can effectively overcome the problem of subsequent product oxidation over time and achieve a long-term high-selectivity reaction.
[0006] The purpose of this invention is to achieve the continuous photocatalytic selective oxidation of aromatic hydrocarbons to prepare aromatic aldehydes.
[0007] According to one aspect of this application, a method for preparing aromatic aldehydes by oxidation of aromatic hydrocarbons is provided, the method comprising:
[0008] In an oxygen-containing atmosphere, a solution containing aromatic hydrocarbons is contacted with a supported catalyst to react and obtain the aromatic aldehyde.
[0009] The reaction is carried out in a fixed-bed photocatalytic reactor;
[0010] The supported catalyst is a TiO2 surface supported oxide catalyst.
[0011] Optionally, the solid-bed photocatalytic reaction device includes an inner sleeve, an outer sleeve, an inner light source, and an outer light source; the inner sleeve is provided inside the outer sleeve.
[0012] The internal light source is disposed inside the inner sleeve;
[0013] The external light source surrounds the outer wall of the outer sleeve;
[0014] The supported catalyst is disposed between the inner sleeve and the outer sleeve.
[0015] Optionally, the wavelengths of the internal light source and the external light source are independently selected from 365 to 600 nm.
[0016] Optionally, the wavelengths of the internal light source and the external light source are independently selected from any value of 365nm, 400nm, 450nm, 500nm, 550nm, 600nm, or a range between any two of the above.
[0017] Optionally, the oxide in the TiO2 surface-supported oxide catalyst is selected from WO4. x BiO x NbO x VO x ZnO x CdO x NiO x FeO x CoO x At least one of them.
[0018] Optionally, the loading of oxides in the TiO2 surface-supported oxide catalyst is 5 wt% to 20 wt%.
[0019] Optionally, the loading of oxides in the TiO2 surface-supported oxide catalyst is independently selected from any value of 5 wt%, 10 wt%, 15 wt%, 20 wt%, or a range between any two of the above.
[0020] Optionally, the aromatic hydrocarbon is selected from at least one of toluene, 1,4-xylene, 1,2-xylene, 1,3-xylene, and halotoluene.
[0021] Optionally, the aromatic aldehyde is selected from at least one of benzaldehyde, p-methylbenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, and halogenated benzaldehyde.
[0022] Optionally, the oxygen content in the oxygen-containing atmosphere is 15% to 100%.
[0023] Optionally, the solvent in the aromatic hydrocarbon-containing solution is selected from at least one of ethyl acetate, acetonitrile, chloroform, 1,2-dichloroethane, diethyl ether, and n-octane.
[0024] Optionally, the mass-to-volume ratio of the supported catalyst to the solution containing aromatic hydrocarbons is 0.01–0.1 g / mL.
[0025] Optionally, the injection rate of the solution containing aromatic hydrocarbons is 0.5 to 5 mL / min.
[0026] Optionally, the injection rate of the oxygen-containing atmosphere is 0.5 to 5 mL / min.
[0027] Optionally, the method for preparing the TiO2 surface-supported oxide catalyst includes:
[0028] An equal volume of a mixture containing TiO2 and an oxide precursor is impregnated and calcined to obtain the TiO2 surface-supported oxide catalyst.
[0029] Optionally, the oxide precursor is selected from at least one of bismuth nitrate, ammonium tungstate, vanadium oxalate, niobium nitrate, zinc nitrate, cadmium nitrate, nickel nitrate, iron nitrate, and cobalt nitrate.
[0030] Optionally, the calcination temperature is 400–800°C, and the calcination time is 1–4 hours.
[0031] Optionally, BiO x / WO x The preparation methods of / TiO2 catalysts include:
[0032] 1) Take TiO2 powder, impregnate it with a certain amount of bismuth nitrate solution in equal volume, dry it, place it in a muffle furnace, heat it to 500℃, and keep it for 2 hours to obtain BiO2. x / TiO2 catalyst.
[0033] 2) Use the obtained BiO x A TiO2 catalyst was impregnated with an equal volume of ammonium tungstate solution, dried, and then placed in a muffle furnace. The temperature was raised to 500°C and maintained for 2 hours to obtain BiO2. x / WO x / TiO2.
[0034] Optionally, the preliminary preparation process of the supported catalyst in the fixed-bed photocatalytic reactor is as follows:
[0035] 1) Shape the powder photocatalyst into a pellet, and sieve it to a mesh size of 40-80 for later use;
[0036] 2) Depending on the reaction, mix the photocatalyst with glass beads (0.4-0.6 mm in diameter) in the required volume ratio.
[0037] 3) Fill the mixed material into the interlayer of the quartz tube.
[0038] Optionally, in a fixed-bed photocatalytic reactor, the method for preparing aromatic aldehydes by oxidation of aromatic hydrocarbons specifically includes the following steps:
[0039] 1) After the granulated supported catalyst and glass beads are mixed evenly, they are loaded into the quartz tube jacket. The space between the clip and the quartz tube is filled with quartz wool. The function of the quartz wool at the inlet end is to guide the reaction gas and liquid to be evenly distributed in the quartz tube jacket, and the function of the quartz wool at the outlet end is to prevent catalyst particles from entering the pipeline with the liquid. After sealing with rubber rings and clips, it is connected to the back end of the peristaltic pump system and the gas injection system.
[0040] 2) Turn on the peristaltic pump and gas mass flow controller, and adjust to a suitable flow rate. The liquid and gas are mixed in the steel pipe before entering the quartz tube jacket. Turn on the fan for air cooling and turn on the LED light source to carry out photocatalytic reaction. Connect the PTFE hose to the reactor outlet end to facilitate observation of the situation inside the quartz sleeve. You can observe that the gas and liquid products are evenly distributed, and the liquid flows out in a segmented distribution pattern inside the tube.
[0041] As a specific implementation scheme, this application achieves its purpose through the following technical solution:
[0042] This application evaluates the photocatalytic selective oxidation performance in a mobile phase reactor. The reactor used is a sleeve-type fixed-bed reactor with dual internal and external light sources. The light sources are 365nm LED tubes (built-in) and 365nm LED strips (external). The catalyst has a large light-receiving area. The reaction system consists of a liquid peristaltic pump, an oxygen inlet device, and a quartz sleeve reactor.
[0043] The quartz-cased reactor consists of a 25mm thick quartz test tube as the inner tube and a 35mm thick quartz tube as the outer tube, with a sealing system consisting of a sealing ring and metal clips. The catalyst is granulated into 40-60 mesh particles, which are mixed evenly with glass beads of the same particle size and then filled into the interlayer between the two tubes. A 365nm LED tube is placed inside the inner quartz test tube, and a 365nm LED strip is wrapped around the outside of the outer quartz tube.
[0044] The liquid phase consists of acetonitrile solutions with varying contents of p-xylene, ranging from 1% to 10%; the gas phase consists of oxygen. The injection rates of the liquid and gas phases are controlled to ensure uniform distribution and flow of the liquid and gas within the reaction jacket, with intermittent outflow of gas and liquid at the outlet. The injection rate ranges from 0.5 mL / min to 5 mL / min.
[0045] The catalyst used in this application is a TiO2 surface-supported oxide. The oxide loading can effectively improve the photogenerated charge separation efficiency and inhibit product adsorption, thereby simultaneously improving the conversion rate and the selectivity of the target product.
[0046] This application employs photodeposition, impregnation, and high-temperature calcination methods to load oxides onto the TiO2 surface. The loaded oxides include WO3. x BiO x NbO x VO x ZnO x CdO x NiO x FeO x CoO x etc., with a load content of 5% to 20% by mass.
[0047] In the reaction of xylene oxidation to prepare p-methylbenzaldehyde, 1) in a batch reactor, the target reaction activity and product selectivity (selectivity, 92%) gradually decrease over time (selectivity, 82%), mainly due to subsequent over-oxidation of the product; while a fixed-bed photocatalytic reactor can maintain the target reaction activity and high product selectivity (conversion rate 18%, selectivity 92%) for a long time (at least 60h), effectively overcoming the problem of over-oxidation of the product; this preparation method can be extended to selective oxidation systems of other aromatic hydrocarbons.
[0048] The beneficial effects that this application can produce include:
[0049] 1) Compared with the traditional batch photocatalytic reaction, the method for preparing aromatic aldehydes in a fixed-bed photocatalytic reactor provided in this application uses a mobile phase reactor, where the catalyst is fixed and easily separated from the reaction liquid. At the same time, it can achieve long-term, highly selective, continuous production and has prospects for industrial application.
[0050] 2) Compared with the titanium dioxide catalyst, the supported catalyst used in this invention can not only improve the reaction efficiency, but also inhibit the formation of peroxidation products, thus greatly improving the selectivity of the product aldehyde.
[0051] 3) Compared with traditional routes such as photochlorination, organic amination, and acid hydrolysis, the method for preparing aromatic aldehydes by the oxidation of aromatic hydrocarbons provided in this application has the advantages of high atom economy and environmental friendliness, and is a green production route for p-methylbenzaldehyde and its homologues. Attached Figure Description
[0052] Figure 1 This is a schematic diagram of the fixed-bed photocatalytic mobile phase reactor in Example 1 of this application.
[0053] Figure 2 BiO in Embodiment 4 and Comparative Example 1 of this application x / WO x Comparison of the catalytic performance of TiO2 catalyst in mobile phase reactor and batch reactor.
[0054] Figure 3 This is an activity diagram of the photocatalytic selective oxidation of toluene in Example 5 of this application.
[0055] Figure 4 For comparison of the reaction activity of the catalyst in Comparative Example 2 of this application, BiO2 reacted within the same reaction time. x / WO x The activity of the / TiO2 catalyst is twice that of the TiO2 catalyst.
[0056] Figure 5 For the selectivity comparison of the catalyst in Comparative Example 2 of this application, compared with unsupported TiO2, BiO2 at the same conversion rate... x / WO x The selectivity of p-methylbenzaldehyde is about 10% higher with the / TiO2 catalyst.
[0057] Figure 6 BiO in Embodiment 2 of this application x / WO x XRD pattern of TiO2 catalyst.
[0058] Figure 7 BiO in Embodiment 3 of this application x / WO x The morphology of the TiO2 catalyst (a) is BiO2. x / WO x (a) Dark-field transmission electron microscopy image of TiO2 catalyst, scale bar 5 nm; (b) BiO2 catalyst. x / WO x (a) Bright-field high-resolution transmission electron microscopy image of the TiO2 catalyst, scale bar 5 nm; (b) Dark-field image, scale bar 10 nm; (c) Scanned elemental distribution map.
[0059] Figure 1 In the middle, 1. Inner sleeve; 2. Outer sleeve. Detailed Implementation
[0060] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.
[0061] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.
[0062] The prepared catalyst was characterized using a SmartLab X-ray diffractometer and a FEIQuanta 200FEG transmission electron microscope. The reaction products were analyzed in liquid phase using an Agilent gas chromatography-mass spectrometry (GC) column with Ar carrier gas, and in gas phase using a TCD detector with a TDX-102 column with H2 carrier gas.
[0063] Conversion rate = Sum of all product moles / Initial moles of aromatic hydrocarbons;
[0064] Selectivity = number of moles of aldehyde product / sum of moles of all products;
[0065] Yield = Conversion rate × Selectivity
[0066] Example 1
[0067] like Figure 1As shown, the fixed-bed photocatalytic reaction device includes an inner sleeve 1 and an outer sleeve 2; the inner sleeve 1 and the outer sleeve 2 are made of quartz tubing, and the fixed-bed photocatalytic reaction device consists of two quartz tubings of different diameters forming the main body, with a sealing system consisting of sealing rings and buckles; the supported photocatalyst is fixed in the interlayer between the inner sleeve 1 and the outer sleeve 2, the inner sleeve 1 is equipped with an internal light source, and the outer light source surrounds the outer wall of the outer sleeve 2, adopting a dual-lighting method; the fixed-bed photocatalytic reaction device also includes a reactant inlet, an oxygen gas inlet, a product outlet, and an air cooling system; the light source is an LED light strip, with a 365nm LED tube placed inside the inner quartz tube and the 365nm LED light strip wrapped around the outside of the outer quartz tube.
[0068] When using a fixed-bed photocatalytic reactor, the powder photocatalyst is first shaped, granulated, and screened to 40-80 mesh for later use; then, depending on the reaction conditions, the photocatalyst is mixed with glass beads (particle size 0.4-0.6 mm) in the required volume ratio, and the mixed material is filled into the interlayer formed by the inner sleeve 1 and the outer sleeve 2.
[0069] Example 2:
[0070] 10% BiO x -7.5% WO x -Preparation of TiO2 catalyst:
[0071] Take 1g of TiO2 powder, impregnate it with 1mL of bismuth nitrate solution, dry it at 60℃ for 5h, then place it in a muffle furnace, heat it to 500℃, and hold it for 2h to obtain BiO2. x / TiO2 catalyst.
[0072] The 1g BiO obtained x TiO2 catalyst was impregnated with an equal volume of 0.75 mL of ammonium tungstate solution, dried at 60 °C for 5 h, and then placed in a muffle furnace. The temperature was raised to 500 °C and held for 2 h to obtain BiO2 catalyst. x / TiO2 catalyst yields 10% BiO x -7.5% WO x -TiO2.
[0073] Figure 6 For this application BiO x / WO x XRD pattern of TiO2 catalyst, from Figure 6 It can be observed that bismuth tungstate has not formed; only TiO2 diffraction peaks are present, proving that the supported BiO2... x Ox exhibits good dispersibility on the TiO2 surface.
[0074] Example 3:
[0075] 20% BiO x -10%WO x -Preparation of TiO2 catalyst:
[0076] Take 1g of TiO2 powder, impregnate it with 2mL of bismuth nitrate solution, dry it at 60℃ for 5h, then place it in a muffle furnace, heat it to 500℃, and hold it for 2h to obtain BiO2. x / TiO2 catalyst.
[0077] The 1g BiO obtained x TiO2 catalyst was impregnated with 1 mL of ammonium tungstate solution by equal volume, dried at 60 °C for 5 h, and then placed in a muffle furnace. The temperature was raised to 500 °C and held for 2 h to obtain BiO2 catalyst. x / TiO2 catalyst yields 20% BiO x -10%WO x -TiO2.
[0078] from Figure 6 The XRD pattern shows that when the loading concentration is 20% BiO x and 10%WO x At that time, BiO can be observed 2-x Phase diffraction peaks demonstrate that as the loading increases, BiO x There will be family reunions.
[0079] Figure 7 (a) is BiO x / WO x The image shows a dark-field transmission electron microscope image of the TiO2 catalyst. It can be seen from the image that two sizes of particles are uniformly distributed on the TiO2 surface, with particle sizes of about 1 nm and 5 nm, respectively. Figure 7 (b) is BiO x / WO x The bright-field high-resolution transmission electron microscope (HRTEM) image of the TiO2 catalyst shows obvious lattice fringes of the TiO2 {101} crystal plane, but not lattice fringes of tungsten oxide and bismuth oxide. Therefore, tungsten oxide and bismuth oxide are uniformly distributed amorphously on the TiO2 surface. The dark-field image... Figure 7 (c) and its corresponding scan element distribution Figure 7 From (d), it can be determined that W is uniformly distributed on the TiO2 surface without obvious aggregation, while Bi is also uniformly distributed on the TiO2 surface but aggregates in small island-like patterns. Therefore, tungsten oxide has better dispersion on the titanium dioxide surface than bismuth oxide. The approximately 1 nm particles distributed on the TiO2 surface are mainly WO3. x Particles around 5nm are mainly BiO x .
[0080] Example 4
[0081] The 10% BiO prepared in Example 2 x -7.5% WO x - TiO2 catalyst was used in the preparation of p-methylbenzaldehyde. The reaction was carried out using a mobile phase fixed-bed photocatalytic reactor, and the activity selectivity of the reaction was detected.
[0082] Take 10g of 10% BiO x -7.5% WO x TiO2 catalyst was compressed, crushed, and granulated into 40-80 mesh particles. Glass beads of the same size were taken, with a volume three times that of the granulated catalyst. The mixture was shaken to ensure uniform mixing of the catalyst particles and glass beads, and then packed into the quartz jacket of a fixed-bed reactor. The quartz tube was sealed with a clamp and rubber ring before oxidation to prepare aromatic aldehydes. A mixture of p-xylene and acetonitrile (volume ratio 1:100) was introduced into the fixed-bed photocatalytic reactor. The injection rate of the p-xylene-containing liquid was 1 mL / min, and the oxygen injection rate was 2 mL / min. The selectivity of the reaction products was calculated using an Agilent gas chromatography-mass spectrometry (GC) FID detector. The column used was an HP-INNOWAX. Comparative Example 1:
[0083] The 10% BiO prepared in Example 2 x -7.5% WO x - TiO2 catalyst was used for the preparation of p-methylbenzaldehyde, and the reaction was carried out in a batch reactor under the following specific reaction conditions:
[0084] Take 20mg of 10% BiO x -7.5% WO x -TiO2(BiO x / WO x The TiO2 catalyst was placed in a quartz autoclave, and 4 mL of a reaction solution with a volume ratio of p-xylene and acetonitrile of 1:100 was added. After oxygen treatment for 15 minutes, the reaction was carried out under stirring and irradiated with a xenon lamp.
[0085] from Figure 2 As can be seen, although the conversion rate gradually increases over time in the batch reactor, the selectivity gradually decreases. After 6 hours of reaction, the selectivity for p-methylbenzaldehyde drops from 92% to 82%, failing to maintain high selectivity for an extended period, and the reaction volume processed per batch is very small. In contrast, the fixed-bed photocatalytic mobile phase reactor can maintain the reaction conversion rate at around 18%, ensuring that the selectivity for p-methylbenzaldehyde remains at around 92%, enabling long-term, continuous, large-scale, high-selectivity production.
[0086] Example 5
[0087] The BiO prepared in Example 2 x / WOx TiO2 catalyst was used in the preparation of benzaldehyde, and the reaction was carried out in a mobile phase fixed-bed photocatalytic reactor. The activity selectivity of the reaction was detected.
[0088] The raw materials, toluene and acetonitrile in a volume ratio of 1:100, were fed into a fixed-bed photocatalytic reactor. The injection rate of the toluene-containing liquid was 1 mL / min, and the injection rate of oxygen was 2 mL / min. The selectivity of the reaction products was calculated by analyzing them using an Agilent gas chromatography-FID detector. The chromatographic column used was HP-INNOWAX.
[0089] like Figure 3 As shown in the figure, benzaldehyde is prepared using toluene as a reactant. It can be seen from the figure that, in a fixed-bed photocatalytic reactor, the preparation of benzaldehyde using toluene as a raw material can achieve highly selective and continuous production, similar to the preparation of p-methylbenzaldehyde. Therefore, the fixed-bed photocatalytic mobile phase reactor of this application is also suitable for the selective oxidation of toluene and its homologues.
[0090] Example 6
[0091] The BiO prepared in Example 2 x / WO x TiO2 catalyst was used in the preparation of p-methylbenzaldehyde, and the reaction was carried out in a mobile phase fixed-bed photocatalytic reactor. The activity selectivity of the reaction was detected.
[0092] Take 10g BiO x / WO x The TiO2 catalyst was compressed, crushed, and granulated into 40-80 mesh particles. Glass beads of the same size were taken, with a volume three times that of the granulated catalyst. The mixture was shaken to ensure uniform mixing of the catalyst particles and glass beads, and then packed into the quartz jacket of a fixed-bed reactor. The quartz tube was sealed with a clamp and rubber ring before oxidation to prepare aromatic aldehydes. A raw material of p-xylene and acetonitrile at a volume ratio of 1:100 was introduced into the fixed-bed photocatalytic reactor. The liquid containing p-xylene was introduced at a rate of 1 mL / min. The reaction was carried out according to the oxygen flow rates in Table 1 to study the effect of oxygen quantity on the reaction. The specific reaction results are shown in Table 1.
[0093] Table 1: Effect of oxygen content on the preparation of aromatic aldehydes
[0094] <![CDATA[O2 flow rate / mL min -1 > p-Xylene conversion rate / % p-Toluene Selectivity / % 0.5 5.1 91.9 1.5 12.0 94.4 2.5 18.2 93.1 3.5 15.0 92.7
[0095] As can be seen from Table 1, the selectivity of p-methylbenzaldehyde does not change much with the increase of oxygen injection rate. The conversion rate first increases and then decreases. Therefore, the O2 flow rate should not be too high in order to achieve a suitable yield.
[0096] Example 7
[0097] The BiO prepared in Example 2 x / WO x TiO2 catalyst was used in the preparation of p-methylbenzaldehyde, and the reaction was carried out in a mobile phase fixed-bed photocatalytic reactor. The activity selectivity of the reaction was detected.
[0098] Take 10g BiO x / WO x The TiO2 catalyst was compressed, crushed, and granulated into 40-80 mesh particles. Glass beads of the same size were taken, with a volume three times that of the granulated catalyst. The mixture was shaken to ensure uniform mixing of the catalyst particles and glass beads, and then packed into the quartz jacket of a fixed-bed reactor. The quartz tube was sealed with a clamp and rubber ring before oxidation to prepare aromatic aldehydes. Acetonitrile solutions containing different concentrations of p-xylene were passed into the fixed-bed photocatalytic reactor. The injection rate of the p-xylene-containing liquid was 1 mL / min, and the oxygen injection rate was 2 mL / min. The effect of aromatic hydrocarbon concentration on the reaction was studied, and the specific reaction results are shown in Table 2.
[0099] Table 2: Effect of xylene concentration on the preparation of aromatic aldehydes
[0100]
[0101] As can be seen from Table 2, the effect of aromatic hydrocarbon concentration on the reaction is mainly reflected in the conversion rate. As the aromatic hydrocarbon concentration increases, the conversion rate decreases, but it has little effect on the reaction selectivity, and the overall yield of the product shows an upward trend.
[0102] Comparative Example 2:
[0103] Catalyst performance comparison:
[0104] TiO2 catalyst was used to prepare p-methylbenzaldehyde. The reaction was carried out using a batch-type photocatalytic reactor, and the activity selectivity of the reaction was detected.
[0105] Take 20mg TiO2 or BiO x / WO x The TiO2 catalyst was placed in a quartz still reactor, and 4 mL of a reaction solution with a volume ratio of 1:100 for p-xylene and acetonitrile was added. After oxygen treatment for 15 minutes, the reaction was carried out under stirring and irradiated with a xenon lamp.
[0106] like Figure 4 and Figure 5 As shown, TiO2 and BiO x / WO x A comparison of the reaction conversion and selectivity of TiO2 catalyst. It can be seen that within the same time period, BiO2... x / WO xThe conversion rate of the / TiO2 catalyst is about twice that of the TiO2 catalyst, and the selectivity for methylbenzaldehyde is about 10% higher.
[0107] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A method for preparing aromatic aldehydes by oxidation of aromatic hydrocarbons, characterized in that, The preparation method includes: In an oxygen-containing atmosphere, a solution containing aromatic hydrocarbons is contacted with a supported catalyst to react and obtain the aromatic aldehyde. The reaction is carried out in a fixed-bed photocatalytic reactor; The supported catalyst is a TiO2 surface-supported oxide catalyst, and the oxide is WO3. x and BiO x ; The solid-bed photocatalytic reaction device includes an inner sleeve, an outer sleeve, an inner light source, and an outer light source; the inner sleeve is installed inside the outer sleeve. The internal light source is disposed inside the inner sleeve; The external light source surrounds the outer wall of the outer sleeve; The supported catalyst is disposed between the inner sleeve and the outer sleeve.
2. The preparation method according to claim 1, characterized in that, The wavelengths of the internal and external light sources can be independently selected from 365 nm to 600 nm according to the reaction requirements.
3. The preparation method according to claim 1, characterized in that, In the TiO2 surface supported oxide catalyst, WO x The loading amount is 5wt%~20wt%, BiO x The load is 5wt%~20wt%.
4. The preparation method according to claim 1, characterized in that, The aromatic hydrocarbon is selected from at least one of toluene, 1,4-xylene, 1,2-xylene, 1,3-xylene, and halotoluene; The aromatic aldehyde is selected from at least one of benzaldehyde, p-methylbenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, and halogenated benzaldehyde; The oxygen content in the oxygen-containing atmosphere is 15% to 100%. The solvent in the solution containing aromatic hydrocarbons is selected from at least one of ethyl acetate, acetonitrile, chloroform, 1,2-dichloroethane, diethyl ether, and n-octane.
5. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the supported catalyst to the solution containing aromatic hydrocarbons is 0.01~0.1 g / mL; The injection rate of the solution containing aromatic hydrocarbons is 0.5~5 mL / min.
6. The preparation method according to claim 1, characterized in that, The injection rate of the oxygen-containing atmosphere is 0.5~5 mL / min.
7. The preparation method according to claim 1, characterized in that, The preparation method of the TiO2 surface supported oxide catalyst includes: TiO2 is impregnated with BiO2 in equal volume x Precursor salts, WO3 x The precursor salt is calcined to obtain the TiO2 surface-supported oxide catalyst.
8. The preparation method according to claim 7, characterized in that, The BiO x The precursor salt is bismuth nitrate, and the WO x The precursor salt is ammonium tungstate.
9. The preparation method according to claim 8, characterized in that, The roasting temperature is 400~800℃, and the roasting time is 1~4h.