Method for generating p-methoxybenzaldehyde through catalytic oxidation and used catalyst

Abstract

The invention belongs to the field of compound preparation, and particularly relates to a method for generating p-methoxybenzaldehyde through catalytic oxidation and a used catalyst. The preparation method of the catalyst comprises the following steps: dissolving a mixed salt composed of a soluble cobalt salt, a soluble manganese salt and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution; dissolving sodium carbonate and sodium hydroxide in deionized water to obtain a mixed alkali solution; the mixed salt solution and the mixed alkali solution are mixed in a dropwise adding mode and then aged, then an aged product is subjected to suction filtration, an obtained catalyst precursor is roasted, and the catalyst for generating p-methoxybenzaldehyde through catalytic oxidation is obtained. The invention further provides a method for generating p-methoxybenzaldehyde through catalytic oxidation, p-methyl anisole is used as a raw material, and the obtained catalyst is utilized. According to the method for generating p-methoxybenzaldehyde through catalytic oxidation, a cocatalyst is not used, and the used catalyst can be repeatedly used.

Description

Technical Field

[0001] The invention belongs to the field of compound preparation, and specifically relates to a method for preparing p-methoxybenzaldehyde by catalytic oxidation of p-methylanisole (p-methoxytoluene) and a catalyst used therein. Background Art

[0002] p-Anisaldehyde is also known as anisaldehyde and anisealdehyde. Its molecular formula is C8H8O2. It is a colorless or light yellow liquid at room temperature. It has a lasting hawthorn aroma and is a high value-added spice. It is widely used in the preparation of flavor raw materials. p-Anisaldehyde is also an intermediate in the pharmaceutical industry and can be used to prepare drugs such as the antimicrobial drug amoxicillin, the vasodilator diltiazem hydrochloride, and the choleretic agent cholervita. p-Anisaldehyde is also used in polymer materials and can be used to prepare polyferrocene-p-methoxybenzaldehyde.

[0003] There are many methods for synthesizing p-methoxybenzaldehyde using p-methylanisole as raw material, as follows: 1. Electrochemical oxidation method: Electrochemical oxidation method is divided into direct and indirect electrochemical oxidation method. At present, domestic and foreign literature reports mostly use indirect electrochemical oxidation method. This method has high selectivity and yield, but the electrochemical method has high energy consumption and large equipment investment.

[0004] 2. Gas-phase catalytic oxidation method: This method mainly uses a supported catalyst to catalytically oxidize p-methylanisole to synthesize p-methoxybenzaldehyde at high temperature. However, this method has the disadvantages of too high reaction temperature (about 300°C) and excessive oxidation of raw materials to CO. x , the catalyst is easily deactivated and the preparation is complicated.

[0005] 3. Liquid phase catalytic oxidation method: This method is widely used and is one of the most common methods reported to prepare p-methoxybenzaldehyde.

[0006] This type of method uses p-methylanisole as a raw material and catalytically oxidizes to produce p-methoxybenzaldehyde. The main products are p-methoxybenzaldehyde and p-methoxybenzyl acetate, and also contain a small amount of p-methoxybenzyl alcohol as a by-product. The boiling points of p-methoxybenzaldehyde (248°C) and p-methoxybenzyl acetate (270°C) are quite different, so p-methoxybenzaldehyde can be easily distilled and purified from the reaction product (reaction mother liquor). p-Methoxybenzyl acetate is an important intermediate for industrial and pharmaceutical chemicals, and can also react with a strong base to obtain p-methoxybenzyl alcohol.

[0007] For example, the following scenarios are included: Chinese patent CN111253227A reported that a solution containing p-methylanisole was passed into a capillary column loaded with active components. This method has high selectivity, but there are problems such as low conversion rate, troublesome preparation of capillary columns with active components, and difficulty in recovery after deactivation. Hong Long's research group used metal porphyrin / metal salt catalysts to catalytically oxidize p-methylanisole to prepare p-methoxybenzaldehyde (Guangdong Chemical Industry, 2015, 42, 9-10). This method has a low conversion rate, and the use of homogeneous catalysts cannot be repeated. Catalytic oxidation generates a large amount of p-methoxybenzyl alcohol byproducts, whose boiling point is close to that of p-methoxybenzaldehyde and is difficult to separate and purify. Du Xi's research group used copper acetate and cobalt acetate as catalysts, potassium bromide and sodium carbonate as co-catalysts, and hydrogen peroxide as an oxygen source to catalytically oxidize p-methylanisole to prepare p-methoxybenzaldehyde (Anhui Agricultural Sciences, 2010, 38, 18657-18660). This method has high selectivity, but the main catalyst and co-catalyst are homogeneous catalysts and cannot be reused, and a lot of three wastes are generated after the reaction.

[0008] The invention of CN115850044B "A method for synthesizing p-methoxybenzaldehyde" states: p-hydroxybenzaldehyde and dimethyl carbonate are used as raw materials, and a methylation reaction is carried out in the presence of a catalyst to generate p-methoxybenzaldehyde. The catalyst is a supported catalyst, including a support and a metal oxide supported on the support; the metal oxide is selected from a combination of one or more of zinc oxide, manganese oxide, magnesium oxide, barium oxide, calcium oxide, lithium oxide, sodium oxide, potassium oxide and rubidium oxide. The supported catalysts are respectively recorded as Mg-Na2CO3-0.05-H3BO3 / Y, K-NaOH-0.05-H3BO3 / Y, Ba-NaOH-0.05-H3BO3 / Y, Cu-NaOH-0.05-H3BO3 / Y, Fe-NaOH-0.05-H3BO3 / Y, Ag-NaOH-0.05-H3BO3 / Y, Ca-NaOH-0.05-H3BO3 / Y, and Co-NaOH-0.05-H3BO3 / Y. The price of the raw material p-hydroxybenzaldehyde used in CN115850044B is relatively high, usually 15000-25000 yuan / ton higher than the market price of p-methyl anisole, and the economic efficiency of preparing p-methoxybenzaldehyde with p-hydroxybenzaldehyde is relatively poor; and the reaction pressure is high, reaching 2MPa.

[0009] The invention of CN109456152B, "A method for preparing p-methoxybenzaldehyde by catalytic oxidation of p-methoxytoluene", states: p-methoxytoluene (i.e., p-methyl anisole) is used as a substrate, and transition metal salts and nitrogen-containing ligands are used as catalysts to catalytically selectively oxidize p-methoxybenzaldehyde under mild conditions. The transition metal salts used are cobalt nitrate, cobalt acetate, cobalt chloride, cobalt sulfate, cobalt acetylacetonate, cobalt isooctanoate, cobalt oleate, cobalt neodecanoate, copper nitrate, copper acetate, copper chloride, copper sulfate, copper acetylacetonate, copper isooctanoate, copper oleate, copper neodecanoate, manganese nitrate, manganese acetate, manganese chloride, manganese sulfate, manganese acetylacetonate, manganese isooctanoate, manganese oleate, and manganese neodecanoate. CN109456152B uses a homogeneous catalyst, and the catalyst is difficult to reuse; the conversion rate of p-methyl anisole is low (no more than 50%).

[0010] The invention of CN103936568B "a method for preparing p-methoxybenzyl alcohol from p-methoxytoluene" informs: p-methoxytoluene, catalyst I and solvent are added to an oxidation reactor, oxygen is passed through at a certain temperature, and the reaction is stopped after a certain time of reaction. Catalyst I is a transition metal salt, preferably acetate, such as cobalt acetate, manganese acetate, nickel acetate, cerium acetate, chromium acetate, zinc acetate, iron acetate, acetic acid ketone, cobalt nitrate, manganese nitrate, nitrate ketone, cobalt chloride, cobalt bromide, cobalt acetylacetonate, iron acetylacetonate, cobalt stearate, manganese stearate, cobalt naphthenate, palladium acetate, palladium chloride, etc., or several catalysts thereof are pressed into a composite catalyst of a certain molar ratio, preferably cobalt acetate, manganese acetate, chromium acetate, cerium acetate, palladium acetate, iron acetate, copper acetate, etc., or they are pressed into a composite catalyst of a certain molar ratio. Although CN103936568B uses a homogeneous catalyst to achieve catalyst repetition, the application step is cumbersome. According to the environmental impact report of the 2015 fine chemicals production (Phase III) technical transformation project of Kos Chemical, the recovery and application of the catalyst is to distill at 140°C to evaporate most of the acetic acid and water, then add 10 times the amount of water as the catalyst to the bottom of the distillation to wash and separate the liquid, and wash the water-soluble catalyst (cobalt acetate, chromium acetate, cerium acetate) from the organic matter; then filter the water phase containing the catalyst to filter out the organic solid waste, and heat the filtrate to 105~112°C under normal pressure to distill out the water vapor containing acetic acid, and the bottom of the distillation is the catalyst; finally, add acetic acid to the catalyst at the bottom of the distillation to dissolve it at 70~90°C, and reuse it after dissolution. The recovery and application of the patented homogeneous catalyst consumes a lot of energy, and it is inevitable that some catalysts, raw materials and products will be lost during the liquid separation, water washing and distillation stages. Summary of the invention

[0011] The technical problem to be solved by the present invention is to provide a method for generating p-methoxybenzaldehyde by catalytic oxidation using a heterogeneous catalyst.

[0012] In order to solve the above technical problems, the present invention provides a method for preparing a catalyst (high-efficiency catalyst) for catalytic oxidation to generate p-methoxybenzaldehyde, comprising the following steps: 1) Dissolve a mixed salt consisting of a soluble cobalt salt (divalent), a soluble manganese salt (divalent) and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution (solution A); (Cobalt + Manganese): trivalent metal = (4 ± 0.1): 0.8~2 molar ratio; Cobalt: manganese = (1~3): (3~1) molar ratio; The trivalent metal is aluminum or cerium; 2) Sodium carbonate and sodium hydroxide are dissolved in deionized water to obtain a mixed alkaline solution (solution B); in the mixed alkaline solution, the total concentration of sodium ions is 2.8±0.2 mol / L, and the molar ratio of sodium hydroxide: sodium carbonate is (3±0.2):1; 3) Control the temperature in the reaction container to 50-70°C (preferably 60±5°C), add the mixed salt solution dropwise to the reaction container under stirring for 20-50 minutes (preferably 30-40 minutes), and simultaneously add the mixed alkali solution dropwise to the reaction container during the process of adding the mixed salt solution (forming a reaction system), thereby controlling the pH of the reaction system in the reaction container to 8.5-9.0; After the mixed salt solution is added dropwise, the mixed alkali solution is continued to be added dropwise into the reaction container (still maintaining the temperature and stirring conditions of 50-70° C.) until the pH of the reaction system in the reaction container is 9.5-10; then the temperature in the reaction container is increased to 75-90° C. (preferably 80±5° C.), and the product is aged for 22-26 hours under stirring conditions to obtain an aged product; Description: During the simultaneous dropwise addition of the mixed salt solution and the mixed alkali solution, the reaction system in the reaction container undergoes coprecipitation to obtain a layered metal hydroxide (with a hydrotalcite structure); 4) Filter the aged product obtained in step 3) by suction, and wash the filter cake with water (deionized water) until the filter cake is neutral after washing, and then dry the washed filter cake (place it in an oven for drying) to obtain a catalyst precursor (cobalt manganese aluminum catalyst precursor or cobalt manganese cerium catalyst precursor); 5) The catalyst precursor obtained in step 4) is heated to 350-450°C at a rate of 10-20°C per minute, and then calcined for 3-5 hours (preferably calcined at 400±50°C for 4 hours), and then naturally cooled to room temperature to obtain a catalyst (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide) for catalytic oxidation to produce p-methoxybenzaldehyde.

[0013] The above calcination can be carried out in a muffle furnace.

[0014] As an improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: In the mixed salt solution, the sum of the concentrations of cobalt, manganese and trivalent metal is 0.7 to 1.2 mol / L (preferably 0.8 to 1 mol / L).

[0015] As a further improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: The molar ratio of cobalt: manganese: trivalent metal = 1:3:1.9.

[0016] As a further improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: The soluble cobalt salt is Co(NO3)2·6H2O; the soluble manganese salt is Mn(NO3)2·4H2O; The soluble trivalent metal salts are Al(NO3)3·9H2O and Ce(NO3)3·6H2O.

[0017] As a further improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: The drying in step 4) is carried out at a temperature of 90 to 110° C. and for 6 to 10 hours.

[0018] As a further improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: The stirring speed of step 3) is 400-800 rpm.

[0019] As a further improvement of the preparation method of the catalyst for catalytic oxidation to produce p-methoxybenzaldehyde of the present invention: In the step 4), the catalyst precursor is obtained by drying and then crushing (passing through a 100-mesh sieve).

[0020] The present invention also provides a method for generating p-methoxybenzaldehyde by catalytic oxidation, using p-methylanisole as a raw material and using a catalyst (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide) prepared by any of the above methods, comprising the following steps: A catalyst, acetic acid as a solvent, and p-methylanisole as a raw material are loaded into a gas-connected reactor, oxygen as a reaction gas is introduced into the reactor, and the reaction pressure of the reactor is controlled to be 0.2-0.4 Mpa (the reaction pressure can be controlled by controlling the opening of an oxygen pressure reducing valve, preferably 0.3 Mpa). Under the catalytic action of the catalyst, p-methylanisole and oxygen react, the reaction temperature is 90-120° C. (preferably 110±10° C.), and the reaction time is 4-8 hours; thereby preparing p-methoxybenzaldehyde; Catalyst: p-methylanisole = 0.15~0.38g / 1ml, the amount of acetic acid used is 4~20 times the volume of p-methylanisole.

[0021] The reaction equation is: .

[0022] Note: After the reaction is completed, the reaction product in the reactor consists of solvent, catalyst, p-methoxybenzaldehyde as the main product and by-products; The reaction product is filtered / centrifuged, and the solid obtained by filtration / centrifugation is a recoverable catalyst that can be reused (the recovered catalyst can be directly reused. In order to exclude other substances from affecting the content detection, the catalyst is washed before repeated application experiments); The liquid obtained by filtration / centrifugation contains p-methoxybenzaldehyde as the main product. The product content can be measured by gas phase, and p-methoxybenzaldehyde can be obtained by conventional distillation. This distillation method is common knowledge in this industry and will not be elaborated in detail.

[0023] In the method of catalytic oxidation to produce p-methoxybenzaldehyde of the present invention, since the catalyst (cobalt-manganese-aluminum composite metal oxide or cobalt-manganese-cerium composite metal oxide) is insoluble in the reaction system, it is a heterogeneous catalyst, and the catalytic reaction occurs on the surface of the catalyst. Therefore, the catalyst can be easily separated after the reaction is completed, thereby achieving reuse.

[0024] The catalyst of the present invention has the technical advantages of high activity, strong selectivity and reusability, and the solvent used in the present invention is cheap and easily available acetic acid. In the existing similar technologies, the catalyst used is a homogeneous catalyst that cannot be reused, and most of the existing similar technologies use relatively expensive solvents.

[0025] The method for generating p-methoxybenzaldehyde by catalytic oxidation of the present invention does not use a co-catalyst, and the catalyst used can be repeatedly used. The method for generating p-methoxybenzaldehyde by catalytic oxidation of the present invention has a fast reaction rate and a high conversion rate, and the obtained p-methylbenzaldehyde has a high yield and is easy to separate. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto: Example 1-1: Preparation of Co-Mn-Al composite metal oxide as a catalyst, the following steps are performed in sequence: 1) Prepare mixed salt: The mixed salt Co-Mn-Al is composed of 0.02 mol (5.82 g) of Co(NO3)2·6H2O, 0.06 mol (14.70 g) of Mn(NO3)2·4H2O, and 0.017 mol (6.38 g) of Al(NO3)3·9H2O. The mixed salt Co-Mn-Al was dissolved in 120 mL of deionized water to obtain a mixed salt solution (solution A). In the mixed salt solution, the sum of the concentrations of the three metal elements Co, Mn and Al was 0.81 mol / L.

[0027] 2) Prepare alkaline solution: Dissolve 0.2 mol of NaOH and 0.067 mol of Na2CO3 in 120 mL of deionized water to prepare a mixed alkaline solution; in the mixed alkaline solution, the total concentration of sodium ions is 2.78 mol / L. The molar ratio of NaOH:Na2CO3 is ≈3:1.

[0028] 3) Place the mixed salt solution (Solution A) and the mixed alkali solution (Solution B) into a 200 mL constant pressure funnel respectively, and place the constant pressure funnel on a four-necked flask; simultaneously drop Solution A and Solution B into the four-necked flask, as follows: The temperature in the four-necked flask is controlled at 60° C. Under stirring conditions, solution A is uniformly dropped into the four-necked flask within 30 to 40 minutes. During the dropping process of solution A, solution B is simultaneously dropped into the four-necked flask, thereby controlling the pH of the reaction system in the four-necked flask to be 8.5 to 9.0. After the dropping of solution A is completed, solution B is continuously dropped under stirring conditions until the pH of the reaction system in the four-necked flask is controlled to be 9.5 to 10; then the temperature is increased to 80° C., and the product is aged for 24 hours under stirring conditions to obtain an aged product.

[0029] The stirring speed during the dropping process and the stirring speed during the aging process are both 600 to 800 rpm.

[0030] Note: During the simultaneous dropwise addition of the mixed salt solution and the mixed alkali solution, coprecipitation occurs in the reaction system in the reaction container.

[0031] 4) The aged product obtained in step 3) is filtered, and the filter cake (precipitate) obtained by filtration is washed with deionized water until it is neutral. The washed filter cake is placed in an oven and dried at 100° C. for 8 hours, and ground into powder (passed through a 100-mesh sieve) to obtain a Co-Mn-Al catalyst precursor.

[0032] 5) The Co-Mn-Al catalyst precursor was placed in a programmed temperature muffle furnace, heated from room temperature to 400°C at a heating rate of 15°C per minute, and then calcined at 400°C for 4 hours.

[0033] Then, it was naturally cooled to room temperature in a muffle furnace to obtain a composite metal oxide named Co-Mn-Al0.85, where 0.85 is the molar ratio of Al to Co.

[0034] Example 1-2 to Example 1-4: Compared with Example 1-1, the amount of Al(NO3)3·9H2O in step 1) was changed (as described in Table 1 below), and the rest was the same as Example 1-1. Thus, Co-Mn-Al composite metal oxides (Co-Mn-Al1, Co-Mn-Al1.4, Co-Mn-Al1.9) were obtained.

[0035] Table 1

[0036] Example 2-1: Preparation of Co-Mn-Ce composite metal oxide as a catalyst, with the following changes compared to Example 1-1: 1) Prepare mixed salt: The mixed salt Co-Mn-Ce is composed of 0.02 mol (5.82 g) of Co(NO3)2·6H2O, 0.06 mol (14.70 g) of Mn(NO3)2·4H2O, and 0.017 mol (7.38 g) of Ce(NO3)3·6H2O.

[0037] The mixed salt Co-Mn-Ce was dissolved in 120 mL of deionized water, thereby obtaining a mixed salt solution (solution A) accordingly; in the mixed salt solution, the sum of the concentrations of the three metal elements Co, Mn, and Ce was 0.81 mol / L; The rest is the same as Example 1-1.

[0038] In this Example 2-1, the product obtained in step 4) is named Co-Mn-Ce catalyst precursor; the product obtained in step 5) is named Co-Mn-Ce0.85 composite metal oxide, where 0.85 is the molar ratio of Ce to Co.

[0039] Example 2-2 to Example 2-4: Compared with Example 2-1, the amount of Ce(NO3)3·6H2O in step 1) was changed (as described in Table 2 below), and the rest was the same as Example 2-1. Thus, Co-Mn-Ce composite metal oxides (Co-Mn-Ce1, Co-Mn-Ce1.4, Co-Mn-Ce1.9) were obtained.

[0040] Table 2

[0041] In the Example 3 series, relative to the Example 1-2, the molar amount of Al(NO3)3·9H2O is kept unchanged at 0.02 mol, and the total molar amount of Co(NO3)2·6H2O and Mn(NO3)2·4H2O is kept unchanged at 0.08 mol. Only the molar ratio of Co(NO3)2·6H2O and Mn(NO3)2·4H2O is changed, as described in the following Table 3; the rest is the same as the Example 1-2.

[0042] Table 3

[0043] In Example 4 series, relative to Example 2-2, the molar amount of Ce(NO3)3·6H2O is kept unchanged at 0.02 mol, and the total molar amount of Co(NO3)2·6H2O and Mn(NO3)2·4H2O is kept unchanged at 0.08 mol. Only the molar ratio of Co(NO3)2·6H2O and Mn(NO3)2·4H2O is changed, as described in Table 4 below; the rest is the same as Example 2-2.

[0044] Table 4

[0045] Experimental series 1, a method for preparing p-methoxybenzaldehyde from p-methylanisole (for catalyst performance evaluation): The Co-Mn-Al and Co-Mn-Ce composite metal oxides obtained in Example 1 and Example 2 were respectively subjected to the following operations: 0.75g of Co-Mn-Al or Co-Mn-Ce composite metal oxide as a catalyst was placed in a 300mL gas-connected reactor, followed by the addition of 2mL of p-methylanisole and 40mL of acetic acid. The reactor was connected to an oxygen cylinder, and the gas pressure of the reactor was controlled at 0.3MPa. Under the catalytic action of the catalyst, p-methylanisole and oxygen reacted at a reaction temperature of 110°C for 4h.

[0046] After the reaction is completed, the reaction product in the reactor is placed in a centrifuge for centrifugation (rotation speed is 8000 rpm, and the centrifugation time is 5 minutes). The solid obtained by centrifugation is a reusable catalyst.

[0047] The liquid obtained by centrifugation was tested for component content using the gas phase area normalization method, and the reaction results are shown in Table 5. Among them, the conversion rates of Co-Mn-Al 1.9 and Co-Mn-Ce 1.9 were high, and the yield of p-methoxybenzaldehyde was also high.

[0048] It should be noted that the Co—Mn—Al and Co—Mn—Ce composite metal oxides of Example 1 series to Example 2 series will not dissolve in the reaction system of Experiment 1 above.

[0049] Table 5 Comparison of catalytic oxidation effects of catalysts with different Al and Ce contents

[0050] Note: The present invention adopts the gas phase area normalization method to obtain the conversion rate and selectivity.

[0051] p-Methylanisole conversion rate (%) = 100-peak area percentage of p-methylanisole; p-Anisaldehyde yield (%) = peak area percentage of p-Anisaldehyde; p-Methoxybenzyl alcohol yield (%) = peak area percentage of p-methoxybenzyl alcohol; Yield of p-methoxybenzyl acetate (%) = peak area percentage of p-methoxybenzyl acetate.

[0052] Experiment 2 series: Compared with Experiment 1, the catalysts obtained from Example 3 and Example 4 were used to investigate the effects of different Co and Mn contents on the catalytic performance; the rest was the same as Experiment 1.

[0053] The comparison of the reaction results with those of Co-Mn-Al 1 (i.e., Co1-Mn3-Al1) and Co-Mn-Ce1 (i.e., Co1-Mn3-Ce1) in Experiment 1 is shown in Table 6. According to Table 6, Co1-Mn3-Al1 is the catalyst with the second highest conversion rate among the Co-Mn-Al1 series catalysts, but the highest yield of p-methoxybenzaldehyde. Co1-Mn3-Ce1 is the catalyst with the highest conversion rate and p-methoxybenzaldehyde yield among the Co-Mn-Ce1 catalysts.

[0054] It should be noted that the Co—Mn—Al and Co—Mn—Ce composite metal oxides of Example 3 series to Example 4 series will not dissolve in the reaction system of Experiment 2 above.

[0055] Table 6 Effect of different Co and Mn contents on catalytic performance

[0056] Experiment 3 series: Compared with the catalyst of "Co-Mn-Al1.9, Co-Mn-Ce1.9" in Experiment 1, the amount of catalyst used, the amount of p-methylanisole added, and the reaction time were changed; the amount of acetic acid solvent was kept unchanged, and the rest was the same as Experiment 1.

[0057] The details are as follows: 1g / 1.5g of Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst was placed in a 300mL gas-connected reactor, followed by 4mL / 8mL of p-methylanisole and 40mL of acetic acid. The reactor was connected to an oxygen cylinder, the gas pressure was controlled at 0.3MPa, the reaction temperature was 110℃, the reaction was continued for 8h, and the reaction results are shown in Table 7.

[0058] It should be noted that the catalysts used in the Experiment 3 series will not dissolve during the reaction.

[0059] Table 7 Effect of increasing the amount of p-methylanisole on the catalytic reaction

[0060] Experiment 4 series: Catalyst repeated application experiment: First time (i.e., 0 times of application): 1.5g of Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst was placed in a 300mL gas-connected reactor, followed by 8mL of p-methylanisole and 40mL of acetic acid. The reactor was connected to an oxygen cylinder (oxygen was introduced into the reactor as a reaction gas), the gas pressure was controlled at 0.3MPa, the reaction temperature was 110°C, and the reaction was carried out for 8h. After the reaction was completed, the reaction product was placed in a centrifuge for centrifugation (speed of 8000rpm, centrifugation time of 5 minutes), and the solid obtained by centrifugation was washed 3 times with ethanol and dried at 100°C to constant weight, which was a recyclable catalyst (about 1.2-1.4g).

[0061] The number of applications is 1: using the above-recovered catalyst and adding fresh Co-Mn-Al1.9 or Co-Mn-Ce1.9 catalyst accordingly, until the total amount of the catalyst is still 1.5g; repeating the above reaction; And so on, we can obtain cases with different application times, as shown in Table 8 below.

[0062] The catalytic activity of Co-Mn-Al1.9 decreased with the increase of repeated applications. However, the catalytic activity of Co-Mn-Ce1.9 did not decrease significantly with the increase of the number of applications. After repeated applications for 3 times, the conversion rate was still above 70% and the yield of p-methoxybenzaldehyde was above 23%.

[0063] Table 8 Catalyst repeated application test results

[0064] Comparative experiment 1: The trivalent metals Al and Ce in Example 1-2 "Co-Mn-Al1 (Co1-Mn3-Al1)" and Example 2-2 "Co-Mn-Ce1 (Co1-Mn3-Ce1)" were replaced with Cr and Fe, and other catalyst preparation conditions were similar; thereby obtaining Co1-Mn3-Cr1 or Co1-Mn3-Fe1, respectively.

[0065] 0.75 g of Co1-Mn3-Cr1 or Co1-Mn3-Fe1 was tested according to the method described in Experiment 1. The reaction results are shown in Table 9. It can be seen that when the trivalent metals are replaced by Fe and Cr, the catalyst conversion rate and product yield both drop significantly.

[0066] Table 9 Effects of different trivalent metals on the catalytic activity of catalysts

[0067] Comparative experiment 2: Relative to Example 1-2, Mn is replaced with one or more metal element combinations of Ce, Cr, and Mn (the amounts remain unchanged), and other catalyst preparation conditions are similar to those of Example 1-2; thereby obtaining Co1-Ce3-Al1, Co1-Ce2-Cr1-Al1, and Co1-Mn2-Ce1-Al1, respectively.

[0068] 0.75 g of Co1-Ce3-Al1, Co1-Ce2-Cr1-Al1, and Co1-Mn2-Ce1-Al1 were tested according to the method described in Experiment 1. The reaction results are shown in Table 10. When Mn was replaced by Ce or a combination of Ce and Cr, the catalytic oxidation effect was poor. If Mn was replaced by Mn and Ce to form Co1-Mn2-Ce1-Al1 catalyst, although the conversion rate of p-methyl anisole was high, the yield of p-methoxybenzaldehyde was low.

[0069] Table 10 Effect of different catalyst combinations on the catalytic effect of catalysts

[0070] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing a catalyst for catalytic oxidation to generate p-methoxybenzaldehyde, characterized in that The steps include: 1) Dissolving a mixed salt consisting of a soluble cobalt salt, a soluble manganese salt and a soluble trivalent metal salt in deionized water to obtain a mixed salt solution; (Cobalt + Manganese): trivalent metal = (4 ± 0.1): 0.8~2 molar ratio; Cobalt: manganese = (1~3): (3~1) molar ratio; The trivalent metal is aluminum or cerium; 2) Sodium carbonate and sodium hydroxide are dissolved in deionized water to obtain a mixed alkaline solution; in the mixed alkaline solution, the total concentration of sodium ions is 2.8±0.2 mol / L, and the molar ratio of sodium hydroxide: sodium carbonate is (3±0.2):1; 3) Control the temperature in the reaction container to 50-70°C, and under stirring, drip the mixed salt solution into the reaction container for 20-50 minutes. During the dripping of the mixed salt solution, drip the mixed alkali solution into the reaction container, thereby controlling the pH of the reaction system in the reaction container to 8.5-9.0; After the mixed salt solution is added dropwise, the mixed alkali solution is continued to be added dropwise into the reaction container until the pH of the reaction system in the reaction container is 9.5-10; then the temperature in the reaction container is increased to 75-90° C., and the mixture is aged for 22-26 hours under stirring conditions to obtain an aged product; 4) Filter the aged product obtained in step 3) by suction, and wash the filter cake with water until the filter cake is neutral after washing, and then dry the washed filter cake to obtain a catalyst precursor; 5) The catalyst precursor obtained in step 4) is heated to 350-450° C. at a rate of 10-20° C. per minute, and then calcined for 3-5 hours, and then naturally cooled to room temperature to obtain a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde.

2. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to claim 1, characterized in that: In the mixed salt solution, the sum of the concentrations of cobalt, manganese and trivalent metals is 0.7~1.2 mol / L.

3. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to claim 2, characterized in that: The molar ratio of cobalt: manganese: trivalent metal = 1:3:1.

9.

4. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to any one of claims 1 to 3, characterized in that: The soluble cobalt salt is Co(NO3)2·6H2O; the soluble manganese salt is Mn(NO3)2·4H2O; The soluble trivalent metal salts are Al(NO3)3·9H2O and Ce(NO3)3·6H2O.

5. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to claim 4, characterized in that: The drying in step 4) is carried out at a temperature of 90 to 110° C. and for 6 to 10 hours.

6. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to claim 5, characterized in that: The stirring speed in step 3) is 400-800 rpm.

7. The method for preparing a catalyst for catalytic oxidation to produce p-methoxybenzaldehyde according to claim 6, characterized in that In the step 4), the catalyst precursor is obtained by drying and then crushing.

8. A method for producing p-methoxybenzaldehyde by catalytic oxidation, using p-methylanisole as a raw material, characterized in that: The catalyst prepared by any one of the methods of claims 1 to 7 comprises the following steps: A catalyst, acetic acid as a solvent, and p-methylanisole as a raw material are loaded into a gas-connected reactor, oxygen as a reaction gas is introduced into the reactor, and the reaction pressure of the reactor is controlled to be 0.2-0.4 MPa. Under the catalytic action of the catalyst, p-methylanisole and oxygen react with each other at a reaction temperature of 90-120° C. and a reaction time of 4-8 hours; thereby p-methoxybenzaldehyde is prepared; Catalyst: p-methylanisole = 0.15~0.38g / 1ml, the amount of acetic acid used is 4~20 times the volume of p-methylanisole.

Images