Method for preparing benzaldehyde by oxidizing benzyl alcohol

Abstract

The invention relates to the field of heterogeneous catalysis, in particular to a method for preparing benzaldehyde by oxidizing benzyl alcohol. The method comprises the following steps: (A) mixing a benzyl alcohol solution and a TiO2 catalyst to obtain a mixed solution; wherein the TiO2 catalyst is TiO2 of which a {001} crystal face is exposed; (B) transferring the mixed solution into a reactor, introducing oxygen under a dark condition, and stirring until adsorption and desorption balance is achieved; and (C) irradiating ultraviolet light into the reactor, and carrying out photocatalytic oxidation reaction to form benzaldehyde. The method is a green and efficient catalytic method for effectively improving the selectivity of the benzyl alcohol oxidation reaction and increasing the yield of benzaldehyde by regulating and controlling the crystal face of the catalyst TiO2. The TiO2-{001} crystal face is used as the catalyst, the selectivity of benzaldehyde reaches 91.5%, the conversion rate of benzyl alcohol can reach 94.3%, and the selectivity of benzaldehyde is remarkably improved while the conversion rate is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of heterogeneous catalysis, and in particular to a method for preparing benzaldehyde by oxidizing benzyl alcohol. Background Art

[0002] As an important organic raw material, benzaldehyde is widely used in food, medicine, fragrance and chemical industries. my country has a large demand for benzaldehyde, and most high-quality benzaldehyde needs to be imported. In nature, benzaldehyde synthesis is mainly obtained from natural cinnamaldehyde. However, cinnamaldehyde is expensive and benzaldehyde selectivity is low, so this production method is costly.

[0003] There are three main methods for producing benzaldehyde in industry, namely: toluene air oxidation, toluene chlorination hydrolysis, and benzyl alcohol oxidation. However, these methods still have disadvantages. The first method is that toluene has a high cost and low economic benefit; although the second method has a large output, toluene chlorination hydrolysis will produce toxic byproducts, which will not only cause losses to the equipment, but also be limited in the pharmaceutical and perfume industries because the benzaldehyde produced by it contains chlorine compounds. Therefore, seeking a low-cost, chlorine-free and non-toxic green and efficient synthesis method for producing benzaldehyde has become a hot topic. The third method is simple to operate and has a low cost, but the oxidants used in industry are mostly toxic and corrosive substances such as dichromates and permanganates, so replacing these toxic and corrosive substances and seeking a non-toxic and harmless oxidant for the oxidation reaction of benzyl alcohol has attracted people's attention.

[0004] TiO2 has great development prospects because of its non-toxic, low-cost, and good stability. The selective photocatalytic oxidation of benzyl alcohol by titanium dioxide to prepare benzaldehyde can occur under mild conditions without other toxic byproducts. In recent years, due to the advancement of synthesis methods, the construction of different TiO2 nanostructures has also developed rapidly. The preparation of benzaldehyde by regulating the selective photocatalytic oxidation of benzyl alcohol by titanium dioxide has received widespread attention. However, the current research on regulating the oxidation of benzyl alcohol by regulating TiO2 is mostly focused on the conversion of benzyl alcohol, and there is little research on its influence on selectivity. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing benzaldehyde by oxidizing benzyl alcohol, which can effectively improve the oxidation selectivity of benzyl alcohol.

[0006] The present invention provides a method for preparing benzaldehyde by oxidizing benzyl alcohol, comprising the following steps:

[0007] (A) mixing a benzyl alcohol solution and a TiO2 catalyst to obtain a mixed solution;

[0008] Wherein, the TiO2 catalyst is TiO2 with exposed {001} crystal plane;

[0009] (B) transferring the mixed solution to a reactor, introducing oxygen in the dark, and stirring until adsorption-desorption equilibrium is reached;

[0010] (C) irradiating ultraviolet light into the reactor to perform a photocatalytic oxidation reaction to form benzaldehyde.

[0011] Preferably, in step (A), the benzyl alcohol solution is an acetonitrile solution of benzyl alcohol.

[0012] Preferably, in step (A), the concentration of the benzyl alcohol solution is 0.5 to 1 mM;

[0013] The dosage ratio of the benzyl alcohol solution to the TiO2 catalyst is 10 mL: (1-10) mg.

[0014] Preferably, in step (A), the mixing method is ultrasonic treatment.

[0015] Preferably, in step (C), a xenon lamp equipped with a 350 nm ultraviolet bandpass filter is used to irradiate ultraviolet light into the reactor by top illumination.

[0016] Preferably, the xenon lamp is a 300W xenon lamp.

[0017] Preferably, in step (C), the reaction time is 4.5 to 15 hours.

[0018] Preferably, in step (C), after the reaction is completed, the following post-treatment is further performed: the reaction solution obtained after the reaction is centrifuged using a centrifuge, and the supernatant is filtered to obtain a benzaldehyde product.

[0019] Preferably, in step (B), the reactor is a reactor.

[0020] Preferably, the TiO2 exposing the {001} crystal plane is prepared by the following preparation method:

[0021] S1, mixing tetrabutyl titanate and hydrofluoric acid solution, heating for reaction; then, washing, drying, and grinding the obtained white solid into powder to obtain solid powder;

[0022] S2. Mixing the solid powder with an alkaline solution for reaction, and then washing and drying to obtain a TiO2 product with exposed {001} crystal plane.

[0023] The present invention provides a method for preparing benzaldehyde by oxidation of benzyl alcohol, comprising: irradiating an acetonitrile solution of benzyl alcohol with ultraviolet light under normal temperature and pressure with oxygen as an oxygen source, and effectively regulating the oxidation selectivity of benzyl alcohol by changing different crystal faces of TiO2. The present invention is a green and efficient catalytic method for effectively improving the selectivity of benzyl alcohol oxidation reaction and increasing the yield of benzaldehyde by regulating the crystal face of catalyst TiO2 under ultraviolet light irradiation. The present invention uses TiO2-{001} crystal face as a catalyst, and the benzaldehyde selectivity reaches 91.5%, and the benzyl alcohol conversion rate can reach 94.3%, which significantly improves the selectivity of benzaldehyde while ensuring the conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 This is a diagram showing the reaction activity of photocatalytic oxidation of benzyl alcohol by three TiO2 with different crystal faces. DETAILED DESCRIPTION

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0027] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0028] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0029] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0030] In this article, when referring to the units of a data range, if only the right endpoint is followed by a unit, it means that the units of the left and right endpoints are the same.

[0031] A method for preparing benzaldehyde by oxidation of benzyl alcohol comprises the following steps:

[0032] (A) mixing a benzyl alcohol solution and a TiO2 catalyst to obtain a mixed solution;

[0033] Wherein, the TiO2 catalyst is TiO2 with exposed {001} crystal plane;

[0034] (B) transferring the mixed solution to a reactor, introducing oxygen in the dark, and stirring until adsorption-desorption equilibrium is reached;

[0035] (C) irradiating ultraviolet light into the reactor to perform a photocatalytic oxidation reaction to form benzaldehyde.

[0036] Regarding step (A):

[0037] (A) A benzyl alcohol solution and a TiO2 catalyst are mixed to obtain a mixed solution.

[0038] In the present invention, the benzyl alcohol solution is a solution formed by dissolving benzaldehyde in a solvent. The solvent is preferably acetonitrile, that is, the benzyl alcohol solution is preferably an acetonitrile solution of benzyl alcohol. In the present invention, the concentration of the benzyl alcohol solution is preferably 0.5 to 1 mM, more preferably 1 mM.

[0039] In the present invention, the TiO2 catalyst is TiO2 with exposed {001} crystal plane. By using the catalyst, the selectivity to benzaldehyde can be effectively improved while ensuring the conversion rate of benzaldehyde.

[0040] In the present invention, the usage ratio of the benzyl alcohol solution to the TiO2 catalyst is preferably 10 mL: (1-10) mg, more preferably 10 mL: 5 mg.

[0041] In the present invention, the method of mixing the benzyl alcohol solution and the TiO2 catalyst is preferably ultrasonic treatment, and the catalyst is uniformly dispersed in the benzyl alcohol solution by ultrasonic treatment to obtain a mixed solution. There is no special restriction on the conditions of the ultrasonic treatment, as long as the above materials can be uniformly mixed.

[0042] In the present invention, the TiO2 with exposed {001} crystal plane can be prepared by the following preparation method:

[0043] S1, mixing tetrabutyl titanate and hydrofluoric acid solution, heating for reaction; then, washing, drying, and grinding the obtained white solid into powder to obtain solid powder;

[0044] S2. Mixing the solid powder with an alkaline solution for reaction, and then washing and drying to obtain a TiO2 product with exposed {001} crystal plane.

[0045] In step S1:

[0046] The mass fraction of the hydrofluoric acid solution (i.e., an aqueous solution of hydrofluoric acid gas) is preferably 40%. The volume ratio of tetrabutyl titanate and hydrofluoric acid solution is preferably 25:3. There is no special restriction on the way of mixing tetrabutyl titanate and hydrofluoric acid solution, and the two can be mixed evenly, such as stirring and mixing. After the two are mixed evenly, heat the reaction. The heating temperature is preferably 180°C. The heating reaction time is preferably 24h. After the reaction, a white solid is formed in the system, which is washed. The washing is preferably washed with deionized water. The washing or solid is dried. The drying temperature is preferably 70°C. The drying time is preferably 12h. After drying, grind into a white powder.

[0047] In step S2:

[0048] The alkaline solution is an aqueous solution of an alkaline substance. The alkaline substance is preferably NaOH. The concentration of the alkaline solution is preferably 0.1M. The amount of the alkaline solution is in excess, that is, it can completely immerse the white powder obtained in the previous step. The solid powder is mixed with the alkaline solution and stirred for reaction. The temperature of the stirring reaction is not particularly limited and can be carried out at room temperature. The stirring reaction time is preferably 24 to 36 hours, more preferably 24 hours. After the above reaction, washing is performed, preferably washing the obtained white powder with deionized water; the washing method is preferably centrifugal washing; washing until the pH of the supernatant is 7.0. After the above washing, drying is performed. The drying temperature is preferably 23 to 70°C, more preferably 70°C. The drying time is preferably 24 to 36 hours. After drying, a white powder is obtained, which is a TiO2 product with exposed {001} crystal planes, recorded as TiO2-{001}.

[0049] In one embodiment, the TiO2 with exposed {001} crystal plane is prepared by the following preparation method: 25 mL of tetrabutyl titanate and 3 mL of hydrofluoric acid solution (mass fraction of 40%) are added to a stainless steel sleeve with a polytetrafluoroethylene liner, stirred until uniform, and the stainless steel sleeve is placed in an oven at 180°C for reaction for 24 hours. After the reaction, the obtained white solid is washed with deionized water, and the washed solid is placed in an oven at 70°C for drying for 12 hours and ground into a white powder. Then, it is placed in a beaker containing 1L of NaOH solution with a concentration of 0.1M and stirred for 24 hours. The white powder is then centrifuged and washed with deionized water until the pH of the supernatant is 7.0, and then placed in an oven at 70°C for drying to obtain TiO2-{001}.

[0050] Regarding step (B):

[0051] (B) transferring the mixed solution into a reactor, introducing oxygen in the dark, and stirring until adsorption-desorption equilibrium is reached.

[0052] In the present invention, the reactor is preferably a reactor. In the present invention, oxygen is introduced into the reactor under dark conditions and stirred. The stirring time is preferably 20 to 40 minutes, specifically 20 minutes, 30 minutes, 40 minutes, and more preferably 30 minutes, until the adsorption-desorption equilibrium is reached.

[0053] Regarding step (C):

[0054] (C) irradiating ultraviolet light into the reactor to perform a photocatalytic oxidation reaction to form benzaldehyde.

[0055] In the present invention, in step (C), it is preferred to maintain an oxygen environment and perform ultraviolet light irradiation to perform a photocatalytic oxidation reaction. The pressure of the oxygen environment is preferably 1 to 2 bar, more preferably 1 bar.

[0056] In the present invention, preferably, a xenon lamp equipped with a 350nm ultraviolet bandpass filter is used to irradiate ultraviolet light into the reactor through top illumination. The xenon lamp is preferably a 300W xenon lamp. The photocatalytic oxidation reaction is carried out under ultraviolet light irradiation, and the reaction time is preferably 4.5 to 15 hours, more preferably 13.5 hours.

[0057] In the present invention, after the reaction is completed, the following post-treatment is preferably performed: the reaction solution obtained after the reaction is centrifuged using a centrifuge, and the supernatant is filtered to obtain a benzaldehyde product.

[0058] The present invention provides a method for preparing benzaldehyde by oxidation of benzyl alcohol, comprising: irradiating an acetonitrile solution of benzyl alcohol with ultraviolet light under normal temperature and pressure with oxygen as an oxygen source, and effectively regulating the oxidation selectivity of benzyl alcohol by changing different crystal faces of TiO2. The present invention effectively improves the selectivity of the oxidation reaction of benzyl alcohol by regulating the crystal face of catalyst TiO2 under ultraviolet light irradiation, using non-toxic and highly stable TiO2 as a catalyst, molecular oxygen as an oxygen source, and ultraviolet light as an energy source, and the reaction process is green and environmentally friendly. The benzaldehyde selectivity of the TiO2-{001} crystal face reaches 91.5%, and the benzyl alcohol conversion rate can reach 94.3%. The reaction has high selectivity, good activity, and high application value.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The present invention can efficiently change the selectivity of the benzyl alcohol oxidation reaction by regulating the crystal surface of TiO2, thereby achieving effective regulation of the benzyl alcohol oxidation reaction.

[0061] (2) The catalyst TiO2 used in the present invention is green and non-toxic, has good stability and low cost.

[0062] (3) The reaction process of the present invention uses oxygen as the oxygen source, avoiding the use of toxic oxidants such as dichromate and permanganate, and no other toxic byproducts are generated, which is green and pollution-free.

[0063] (4) The reaction conditions of the present invention are ultraviolet irradiation, and the reaction conditions are mild, which avoids harsh conditions such as high temperature and high pressure, and reduces energy consumption. This embodiment has high oxidation activity for benzyl alcohol. The selectivity and conversion rate of benzaldehyde on the TiO2-{001} crystal surface can reach more than 90%, with high reaction selectivity, good activity, and high application value.

[0064] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0065] Preparatory Example

[0066] 1. Preparation of TiO2-{101} and TiO2-{100}:

[0067] Adjust the cold trap temperature to 0°C, add 6.6 mL of titanium tetrachloride to 10 mL of 0.43 M hydrochloric acid solution at 0°C, stir magnetically for a period of time, then add 10 mL of 0.43 M hydrochloric acid solution to obtain a clear mixed solution. Add the mixed solution dropwise into 50 mL of 5.5 wt% ammonia solution, then adjust the pH of the solution to 6-7 with 4 wt% ammonia solution, and stir for 2 hours. Wash with deionized water and dry at room temperature to obtain the precursor Ti(OH)4. Take 2 g of Ti(OH)4 precursor in a polytetrafluoroethylene liner, add 0.2 g of NH4Cl (for the synthesis of TiO2-{101}) or 0.5 g of (NH4)2·SO4 (for the synthesis of TiO2-{100}), add 15 mL of water and 15 mL of isopropanol, stir for 20 minutes, ultrasonicate for 20 minutes, transfer to a stainless steel sleeve, react at 180°C for 24 hours, wash and dry after the reaction, and obtain TiO2-{101} and TiO2-{100}, respectively.

[0068] 2. Preparation of TiO2-{001}:

[0069] 25mL of tetrabutyl titanate and 3mL of hydrofluoric acid solution (mass fraction of 40%) were added to a stainless steel sleeve with a polytetrafluoroethylene liner, stirred until uniform, and the stainless steel sleeve was placed in an oven at 180°C for 24 hours. After the reaction, the obtained white solid was washed with deionized water, and the washed solid was placed in an oven at 70°C for 12 hours and ground into a white powder. Then, it was placed in a beaker containing 1L of a 0.1M NaOH solution and stirred for 24 hours. Subsequently, the white powder was centrifuged and washed with deionized water until the pH of the supernatant was 7.0, and dried in an oven at 70°C to obtain TiO2-{001}.

[0070] Example 1

[0071] (A) 10 mL of 1 mM benzyl alcohol in acetonitrile solution was placed in a 100 mL quartz cup, and then 5 mg of TiO2 catalyst was added. The catalyst was evenly dispersed in the solution by ultrasound to obtain a mixed solution.

[0072] (B) The quartz cup was placed in a reactor, oxygen was introduced in the dark, and magnetic stirring was applied for 30 minutes to achieve adsorption-desorption equilibrium.

[0073] (C) maintaining an oxygen environment of 1 bar, irradiating ultraviolet light into the reactor through top illumination using a 300W xenon lamp equipped with a 350nm ultraviolet bandpass filter, and reacting for 13.5 hours. Then, the resulting reaction solution was centrifuged, and the supernatant was filtered to obtain a benzaldehyde product.

[0074] Three kinds of TiO2 catalysts, TiO2-{101}, TiO2-{100} and TiO2-{001}, were used to carry out the above-mentioned photocatalytic oxidation reaction.

[0075] test:

[0076] After obtaining the product, the conversion rate and selectivity of the reaction were analyzed by Agilent 1260 liquid chromatography. The detection wavelengths of ultraviolet light of the high performance liquid chromatography were 210nm, 254nm, and 228nm, respectively, for detecting benzyl alcohol, benzaldehyde, and benzoic acid. The mobile phase was a mixture of acetonitrile and 0.1% phosphoric acid aqueous solution in a volume ratio of 35:65; the detection time was 13min.

[0077] Test results see Figure 1It can be seen that the conversion rates of benzyl alcohol are similar among TiO2-{101}, TiO2-{100} and TiO2-{001} under the same illumination time, but the selectivity to the target product benzaldehyde is significantly different. TiO2-{001} has a high selectivity of 91.5% for benzaldehyde, while the selectivity of TiO2-{101} and TiO2-{100} for benzaldehyde is only 34.4% and 40.6%, respectively, which is less than half of TiO2-{001}. Therefore, the present invention can effectively control the selectivity of the benzyl alcohol oxidation reaction by regulating the crystal surface of TiO2, thereby changing the selectivity of the benzyl alcohol oxidation reaction in a green and efficient manner.

[0078] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing benzaldehyde by oxidation of benzyl alcohol, characterized in that: The following steps are involved: (A) mixing a benzyl alcohol solution and a TiO2 catalyst to obtain a mixed solution; Wherein, the TiO2 catalyst is TiO2 with exposed {001} crystal plane; (B) transferring the mixed solution to a reactor, introducing oxygen in the dark, and stirring until adsorption-desorption equilibrium is reached; (C) irradiating ultraviolet light into the reactor to perform a photocatalytic oxidation reaction to form benzaldehyde.

2. The preparation method according to claim 1, characterized in that: In step (A), the benzyl alcohol solution is an acetonitrile solution of benzyl alcohol.

3. The preparation method according to claim 1, characterized in that: In step (A), the concentration of the benzyl alcohol solution is 0.5-1 mM; The dosage ratio of the benzyl alcohol solution to the TiO2 catalyst is 10 mL: (1-10) mg.

4. The preparation method according to claim 1, characterized in that: In step (A), the mixing method is ultrasonic treatment.

5. The preparation method according to claim 1, characterized in that: In step (C), a xenon lamp equipped with a 350 nm ultraviolet bandpass filter is used to irradiate ultraviolet light into the reactor through top illumination.

6. The preparation method according to claim 5, characterized in that: The xenon lamp is a 300W xenon lamp.

7. The preparation method according to claim 1, characterized in that: In step (C), the reaction time is 4.5 to 15 hours.

8. The preparation method according to claim 1, characterized in that: In step (C), after the reaction is completed, the following post-treatment is further performed: the reaction solution obtained after the reaction is centrifuged using a centrifuge, and the supernatant is filtered to obtain a benzaldehyde product.

9. The preparation method according to claim 1, characterized in that: In step (B), the reactor is a reactor.

10. The preparation method according to claim 1, characterized in that: The TiO2 with exposed {001} crystal plane is prepared by the following preparation method: S1. Mix tetrabutyl titanate and hydrofluoric acid solution, and heat to react; then, wash, dry, and grind the obtained white solid into powder to obtain a solid powder; S2. Mixing the solid powder with an alkaline solution for reaction, and then washing and drying to obtain a TiO2 product with exposed {001} crystal plane.

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