A method for preparing benzyl alcohol

Abstract

The application discloses a preparation method of benzyl alcohol. The method is to use gaseous benzene and formaldehyde as raw materials, to carry out reaction in a fixed bed reactor filled with a supported catalyst, to separate and distill the obtained reaction product after condensation, and to obtain a benzyl alcohol product. The supported catalyst comprises an active metal and a beta molecular sieve carrier. The active metal is preferably one or more of iron, cobalt, nickel and zinc. The method can generate benzyl alcohol with high selectivity and high atomic economy, and avoids the problems of environmental pollution and product chlorine in a conventional route.

Description

Technical Field

[0001] This invention relates to a synthesis method, and more particularly to a method for preparing benzyl alcohol. Background Technology

[0002] Benzyl alcohol is an excellent solvent and an important intermediate in the synthesis of fragrances and pharmaceuticals, widely used in photosensitive materials, dyes, cosmetics, coatings, and inks. Benzyl alcohol offers numerous advantages as a diluent for epoxy resins, such as being non-toxic and non-volatile, exhibiting good compatibility with epoxy resins after curing without migration, promoting the reaction between epoxy resins and amines and accelerating the reaction rate, possessing excellent hydrophobic properties, significantly improving coating gloss, reducing birch whitening, and enhancing the toughness of cured products. With the development of related industries, the demand for benzyl alcohol is continuously increasing both domestically and internationally. Currently, the industrial preparation of benzyl alcohol mainly involves the hydrolysis of benzyl chloride, but this method is energy-intensive, polluting, and the chlorine content of the product affects its application in the food, pharmaceutical, and fragrance fields. Developing a new atom-economical route for the preparation of benzyl alcohol is of great significance.

[0003] The literature “Wu Xianchun, Shan Xilin, Dong Qun, et al. A new route for the synthesis of benzyl alcohol and methylene benzyl ether from benzene and formaldehyde on a shape-selective catalyst [J]. Fine Chemicals, 2001(2):114-116.” discloses a method for preparing benzyl alcohol and methylene benzyl ether from benzene and formaldehyde, but the conversion rate of benzene does not exceed 51.98% and the selectivity of benzyl alcohol does not exceed 53.1%, so there is still a lot of room for improvement. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for preparing benzyl alcohol. This method can generate benzyl alcohol with high selectivity and high atom economy, avoiding the environmental problems and chlorine content issues associated with conventional routes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing benzyl alcohol involves using benzene and formaldehyde in the gas phase as raw materials, reacting them in a fixed-bed reactor packed with a supported catalyst, and then separating the resulting reactants by condensation and distillation to obtain the benzyl alcohol product.

[0007] The supported catalyst comprises an active metal and a β-molecular sieve support; the active metal is preferably one or more of iron, cobalt, nickel, and zinc; preferably, the content of the active metal in the supported catalyst is 1-2 wt%.

[0008] This invention does not impose any restrictions on the preparation method of the supported catalyst; it can be obtained by referring to any known method for preparing supported catalysts, such as impregnation, precipitation, pyrolysis, ion exchange, vapor deposition, sol-gel method, electrochemical method, etc. Considering the simplicity of operation and the availability of readily available raw materials, impregnation and / or precipitation methods are preferred for preparation.

[0009] As a feasible example of the method for preparing the supported catalyst described in this invention, it includes the following steps:

[0010] a. First, calcine the β molecular sieve to remove impurities. The preferred calcination conditions are calcination at 400-650℃ for 1-5 hours.

[0011] b. Immerse the β molecular sieve in the active metal salt solution and mix thoroughly.

[0012] c. Separate the solid product of the catalyst precursor, dry it and then calcine it to obtain the supported catalyst; preferably, the calcination conditions are calcination at 500-800℃ for 1-5 hours.

[0013] In step c, the separation method of the catalyst precursor solid product is not limited to vacuum filtration, rotary evaporation, etc.

[0014] In some preferred examples, the average pore size of the β molecular sieve is 0.55-0.65 nm.

[0015] In some preferred examples, the molar ratio of benzene to formaldehyde is n(benzene):n(formaldehyde) = 0.95-1.05.

[0016] In some preferred examples, the feed mass hourly space velocity (WHSV) for the benzene and formaldehyde reaction is 0.2-1 h⁻¹. -1 Preferably 0.3-0.5h -1 .

[0017] In some preferred examples, the reaction temperature of benzene and formaldehyde is 180-250°C, preferably 200-220°C; and / or, the reaction pressure is atmospheric pressure.

[0018] In this invention, the source of formaldehyde is not restricted in any way. It can be purchased directly from commercial products or obtained by depolymerization of trioxymethylene using conventional methods. Preferably, the depolymerization temperature is 190-220℃, and more preferably 200-210℃.

[0019] This invention uses β-molecular sieves as catalyst supports, which can exhibit good shape selectivity through their "confined" effect, avoiding excessive reaction of benzyl alcohol to generate large molecules such as diphenylmethane. Furthermore, the reaction selectivity is further improved through active metal modification. Compared with the prior art, the present invention can improve the selectivity of benzyl alcohol to over 90%. Detailed Implementation

[0020] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0021] Unless otherwise specified, the raw materials and reagents used in the embodiments and comparative examples of this invention were all purchased from commercially available sources. Among them:

[0022] β-zeolite-1: average pore size 0.6 nm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0023] β-zeolite-2: average pore size 0.65 nm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0024] β-zeolite-3: average pore size 0.55 nm, purchased from Beijing Innocare Technology Co., Ltd.

[0025] Trimethylformaldehyde: Purchased from Beijing Innoka Technology Co., Ltd.

[0026] Product content test method:

[0027] High performance liquid chromatography: Shimadzu LC-20AT, operating conditions: column: Waters XSelect HSS T3 5μm×4.6mm×250mm, detection wavelength: 233nm, mobile phase: acetonitrile / water (containing 0.1% phosphoric acid) = 35 / 65, elution mode: isocratic elution, flow rate: 1.0mL / min, column temperature: 30℃, injection volume: 10μL.

[0028] [Preparation Example 1] Co / β molecular sieve catalyst

[0029] First, β-zeolite-1 was calcined in a muffle furnace at 550℃ for 2 hours to remove impurities. 98g of the calcined β-zeolite was then impregnated in 200g of a deionized aqueous solution containing 4.94g of cobalt nitrate hexahydrate, and thoroughly mixed. The resulting mixture was then placed in a rotary evaporator and evaporated at room temperature and negative pressure (1kPaA) for 2 hours. The resulting catalyst precursor was dried in a forced-air drying oven at 120℃ for 2 hours, and finally calcined in a muffle furnace at 550℃ for 2 hours to obtain Co / β-zeolite catalyst 1 with a Co loading of 1wt%.

[0030] [Preparation Example 2] Fe / β molecular sieve catalyst

[0031] First, β-zeolite-2 was calcined in a muffle furnace at 550℃ for 2 hours to remove impurities. 98g of the calcined β-zeolite was then impregnated in 200g of a deionized aqueous solution containing 8.6g of ferric nitrate, and thoroughly mixed. The resulting mixture was then placed in a rotary evaporator and evaporated at room temperature and negative pressure (1kPaA) for 2 hours. The resulting catalyst precursor was dried in a forced-air drying oven at 120℃ for 2 hours, and finally calcined in a muffle furnace at 550℃ for 2 hours to obtain Fe / β-zeolite catalyst 2 with a 2wt% Fe loading.

[0032] [Preparation Example 3] Ni / β Molecular Sieves Catalyst

[0033] First, β-zeolite-3 was calcined in a muffle furnace at 550℃ for 2 hours to remove impurities. 98g of the calcined β-zeolite was then impregnated in 200g of deionized water containing 7.425g of nickel nitrate, and the mixture was thoroughly stirred. The stirred mixture was then placed in a rotary evaporator and evaporated at room temperature and negative pressure (1kPaA) for 2 hours. The resulting catalyst precursor was dried in a forced-air drying oven at 120℃ for 2 hours, and finally calcined in a muffle furnace at 550℃ for 2 hours to obtain Ni / β-zeolite catalyst 3 with a Ni loading of 1.5wt%.

[0034] [Preparation Example 4] Fe-Co / β molecular sieve catalyst

[0035] First, β-zeolite-1 was calcined in a muffle furnace at 550℃ for 2 hours to remove impurities. 98g of the calcined β-zeolite was then impregnated in 200g of deionized water containing 4.94g of cobalt nitrate hexahydrate and 4.3g of ferric nitrate. The mixture was thoroughly stirred and then placed in a rotary evaporator for rotary evaporation at room temperature and negative pressure (1kPaA) for 2 hours. The resulting catalyst precursor was dried in a forced-air drying oven at 120℃ for 2 hours, and finally calcined in a muffle furnace at 550℃ for 2 hours to obtain Fe-Co / β-zeolite catalyst 4 with 1wt% Co and 1wt% Fe loading.

[0036]

Examples 1-4

[0037] (1) Trioxymethylene solid powder was first heated to 70°C in a glass bottle using an oil bath to melt it into a liquid. Then, it was quantitatively pumped into a cracking reaction tube (empty tube, no catalyst, temperature controlled by an electric heating mantle) using a horizontal flow pump to crack and generate formaldehyde. The cracking reaction conditions are shown in Table 1.

[0038] (2) Benzene was pumped into a continuous fixed-bed reactor containing 100g of catalyst. Formaldehyde gas generated from the cracking of paraformaldehyde was introduced into the fixed-bed reactor and reacted with benzene at atmospheric pressure. The reaction conditions are shown in Table 1. After the reactants were cooled by a condenser, samples were taken for analysis of the reaction conversion rate and selectivity. The results are shown in Table 2.

[0039] Table 1

[0040]

[0041]

[0042] Table 2

[0043] Example 1 Example 2 Example 3 Example 4 benzene conversion rate 52.2％ 49.2％ 54.4％ 53.9％ Benzyl alcohol selectivity 90.4％ 91.3％ 90.9％ 91.1％

[0044] Comparative Example 1

[0045] Benzene and formaldehyde were subjected to a batch reaction in a three-necked round-bottom flask. 100 g of benzene, 110 g of a 35% aqueous formaldehyde solution, and 4.2 g of p-toluenesulfonic acid were added to the flask. The mixture was stirred, heated to 200 °C, and reacted for 3 hours. Analysis of the samples showed a benzene conversion rate of 61.2%, a benzyl alcohol selectivity of 0.38%, and a diphenylmethane selectivity of 93.5%.

[0046] Comparative Example 2

[0047] The reaction was carried out in essentially the same manner as in Example 1, except that supported catalyst 1 was replaced with β-zeolite-1. Sample analysis of the reactants showed a benzene conversion of 51.1% and a benzyl alcohol selectivity of 80.6%.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing benzyl alcohol, characterized in that, It uses benzene and formaldehyde in the gas phase as raw materials, and the reaction is carried out in a fixed-bed reactor packed with a supported catalyst. The resulting reactants are condensed and then separated by distillation to obtain benzyl alcohol product. The supported catalyst comprises an active metal and a β-zeolite support; the active metal is one or more of iron, cobalt, nickel, and zinc; the content of the active metal in the supported catalyst is 1-2 wt%.

2. The method for preparing benzyl alcohol according to claim 1, characterized in that, The molar ratio of benzene to formaldehyde is n(benzene):n(formaldehyde) = 0.95-1.

05.

3. The method for preparing benzyl alcohol according to claim 1, characterized in that, The feed mass hourly space velocity (MHSV) for the benzene and formaldehyde reaction is 0.2-1 h⁻¹. -1 .

4. The method for preparing benzyl alcohol according to claim 3, characterized in that, The feed mass hourly space velocity (WHSV) for the benzene and formaldehyde reaction is 0.3-0.5 h⁻¹. -1 .

5. The method for preparing benzyl alcohol according to any one of claims 1-4, characterized in that, The reaction temperature of benzene and formaldehyde is 180-250℃; and / or, the reaction pressure is atmospheric pressure.

6. The method for preparing benzyl alcohol according to claim 5, characterized in that, The reaction temperature of benzene and formaldehyde is 200-220℃.

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