Aluminum phosphate catalyst and its preparation method and application

Abstract

This invention provides an aluminum phosphate catalyst, its preparation method, and its application, belonging to the field of catalyst technology. The invention involves sequentially mixing boehmite and nitric acid solution in a solvent to obtain a boehmite gel. Anhydrous citric acid aqueous solution and a phosphorus-containing compound are then sequentially added to the boehmite gel, and the pH of the system is adjusted to 6-11 with ammonia to obtain a mixture. The mixture is then sequentially cooled, allowed to stand, dried, and calcined to obtain the aluminum phosphate catalyst. When the aluminum phosphate catalyst prepared by this invention is used for the gas-solid phase monoetherification of resorcinol with methanol to prepare 3-methoxyphenol, the catalyst exhibits high reactivity, few byproducts, and low byproduct selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to an aluminum phosphate catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] 3-Methoxyphenol, also known as m-hydroxyanisole or resorcinol monomethyl ether, has a molecular formula of C7H8O2 and a molecular weight of 124.14. Its structural formula is shown in Figure 1.1.

[0003]

[0004] Formula 1.1 Structural formula of 3-methoxyphenol

[0005] .1.1 3-methoxyphenol structural formula

[0006] 3-Methoxyphenol is a transparent pink to red liquid with a sweet, phenol-like odor. It is widely used as a chemical and pharmaceutical intermediate. In medicine, 3-methoxyphenol can be used to synthesize m-(alkylamino)alkoxyphenyl dimethylcarbamate, a major alternative ingredient in anesthetic awakening agents and widely used for postoperative anesthesia. Due to its unique aroma, 3-methoxyphenol can also be used directly as an insect repellent and attractant. Its unique properties of high inhibition and low stimulation make 3-methoxyphenol widely used in insect repellents and insect trapping. The aroma of 3-methoxyphenol can also be used to synthesize flavorings such as rue oil, celery seed oil, tobacco oil, orange leaf distillate, and castoreum, and is widely used in various foods, tobacco, toothpaste, perfumes, cosmetics, and daily chemicals. 3-Methoxyphenol is also widely used as a UV inhibitor, oil antioxidant, and polymerization inhibitor, and the market demand for 3-methoxyphenol is enormous.

[0007] However, the existing preparation methods of 3-methoxyphenol are difficult to industrialize, resulting in a large market gap for 3-methoxyphenol and high demand for industrialization.

[0008] At present, there are several main methods for preparing 3-methoxyphenol at home and abroad:

[0009] (1) 3-Methoxyphenol is extracted from natural plants.

[0010] 3-Methoxyphenol occurs naturally in oriental tobacco leaves and smoke. Smaller amounts are also found in rue oil, celery seed oil, tobacco oil, orange leaf distillate, and castoreum. Currently, there is no data demonstrating that 3-methoxyresorcinol can be extracted in large quantities from plants. Furthermore, 3-methoxyphenol is present in a variety of plant essential oils, but in low concentrations, depending on the extraction method and the plant's growth environment. Therefore, the 3-methoxyphenol currently sold on the market is synthesized through various methods.

[0011] (2) Resorcinol reacts with halogenated methyls (chloromethane, bromomethane, and iodomethane) to prepare 3-methoxyphenol.

[0012] The Williamson synthesis method is used to prepare 3-methoxyphenol by reacting resorcinol with methyl halides (methyl chloride, methyl bromide, and methyl iodide). Resorcinol and methyl halides are used as starting materials and undergo an O-alkylation reaction in an alkaline environment to form an ether. The other hydroxyl group is then replaced by an alkali metal to form an intermediate product. The hydroxyl group is then reduced with a large amount of strong acid to produce 3-methoxyphenol. The reaction flow diagram is shown in 1.3.

[0013]

[0014] Formula 1.3 Reaction of resorcinol and methyl halide to prepare 3-methoxyphenol

[0015] 1.3Preparation of 3-Methoxyphenol by Reaction of Resorcinol with Halomethane

[0016] This method has numerous drawbacks, primarily the use of large amounts of acid and base solutions, which produce significant amounts of waste salt and wastewater during the preparation of 3-methoxyresorcinol, contradicting the principles of green chemistry. Furthermore, the low boiling point of the methyl halides used as raw materials necessitates the use of an autoclave for the reaction, making continuous production impossible. Furthermore, the high price of methyl halides makes industrial application difficult.

[0017] (3) Resorcinol and methyl p-toluenesulfonate / methanol are reacted to prepare 3-methoxyphenol.

[0018] The reaction of resorcinol and methyl p-toluenesulfonate to produce 3-methoxyphenol avoids the generation of large amounts of waste salt, but the high price of methyl p-toluenesulfonate makes it difficult to meet actual production needs. Later, improved processes based on this process flow, using methanol and methyl p-toluenesulfonate as raw materials, also suffer from high raw material prices and limitations on continuous production.

[0019] (4) Resorcinol is reacted with dimethyl sulfate / dimethyl carbonate to prepare 3-methylresorcinol.

[0020] The reaction of resorcinol and dimethyl sulfate to produce 3-methylresorcinol is a commonly used production process. In 1995, Chen Jingyuan et al. improved a foreign process for producing 3-methoxyresorcinol using resorcinol and dimethyl sulfate. However, dimethyl sulfate was still used as the raw material, resulting in a complex production process. The process also involved the use of strong bases, sodium hydroxide and hydrochloric acid, generating large amounts of waste salt and wastewater. The highly toxic dimethyl sulfate also caused significant environmental pollution. In 2012, Han Ying et al. reported an improved process using dimethyl sulfate and resorcinol as raw materials. This method achieved higher yields, but it still used large amounts of acid and base solutions to produce 3-methoxyphenol, generating significant amounts of waste salt. Furthermore, the toxicity of dimethyl sulfate remained unresolved. Subsequently, numerous studies have explored O-alkylation reactions using dimethyl carbonate as an alternative to dimethyl sulfate. Among them, Vijayaraj M et al. used resorcinol and dimethyl carbonate as raw materials and magnesium oxide as a catalyst to produce 3-methoxyphenol. This method avoids the generation of large amounts of waste salt and uses dimethyl carbonate instead of dimethyl sulfate, thus avoiding the environmental pollution caused by highly toxic substances. However, due to the high price of dimethyl carbonate, this method is difficult to apply to industrial production.

[0021] (5) Preparation of 3-methoxyphenol by hydrogenation reduction of complex aromatic hydrocarbons.

[0022] The synthesis of 3-methoxyresorcinol has been transformed from a synthesis reaction to a decomposition reaction. Sergeev AG et al. used catalytic decomposition of bis(3-methoxydiphenyl) ether to produce 3-methoxyphenol. This yield was high, but bis(3-methoxydiphenyl) ether was expensive and not a direct petrochemical product. It is a processed product with low production volume, making it unsuitable as a production raw material.

[0023] In summary, the existing methods for the industrial preparation of 3-methoxyphenol have certain difficulties, especially under the pressure of environmental protection, it is almost impossible to carry out industrial production.

[0024] Therefore, how to obtain a catalyst to achieve stable and highly selective catalytic synthesis of 3-methoxyphenol is a technical problem that needs to be solved at present. Summary of the Invention

[0025] The purpose of the present invention is to provide an aluminum phosphate catalyst and its preparation method and application, so as to solve the technical problems that 3-methoxyresorcinol cannot be synthesized industrially and the catalytic reaction selectivity is low.

[0026] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0027] The present invention provides a method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent, comprising the following steps:

[0028] 1) mixing pseudo-boehmite and nitric acid solution in a solvent in sequence to obtain pseudo-boehmite gel;

[0029] 2) adding an anhydrous citric acid aqueous solution and a phosphorus-containing compound to the pseudo-boehmite gel in sequence, and adjusting the pH of the system to 6 to 11 with aqueous ammonia to obtain a mixture;

[0030] 3) The mixture is cooled, allowed to stand, dried, and calcined in sequence to obtain an aluminum phosphate catalyst.

[0031] Furthermore, the mass volume ratio of the pseudo-boehmite, nitric acid solution and solvent is 1g:2-8mL:5-10mL; the concentration of the nitric acid solution is 30-35wt%; and the solvent contains water and / or ethanol.

[0032] Furthermore, in the step 1), the mixing is carried out under heating conditions, and the heating temperature is 50-90°C.

[0033] Furthermore, the molar ratio of citric acid in the anhydrous citric acid aqueous solution to aluminum atoms in pseudo-boehmite is 0.1 to 1.5:1.

[0034] Furthermore, the molar ratio of phosphorus atoms in the phosphorus-containing compound to aluminum atoms in the pseudo-boehmite is 0.75 to 1.50:1; and the phosphorus-containing compound comprises one or more of phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0035] Furthermore, the mass concentration of the anhydrous citric acid aqueous solution is 15-25 wt%, and the concentration of the ammonia water is 25-28 wt%.

[0036] Furthermore, the drying temperature is 80-120° C., and the drying time is 12-48 hours.

[0037] Furthermore, the calcination temperature is 400-800° C., and the calcination time is 5-24 hours.

[0038] The present invention provides an aluminum phosphate catalyst.

[0039] The present invention also provides an application of an aluminum phosphate catalyst in the gas-solid phase monoetherification of resorcinol and methanol to prepare 3-methoxyphenol.

[0040] Beneficial effects of the present invention:

[0041] The catalyst prepared by the present invention has a widely adjustable phosphorus-aluminum molar ratio. The complexation with citric acid not only protects the mesoporous structure of the catalyst but also enables the catalyst to maintain an amorphous structure, thereby being able to prepare an aluminum phosphate catalyst with a high phosphorus-aluminum ratio. The catalyst is suitable for the gas-solid phase preparation of 3-methoxyphenol from resorcinol and methanol.

[0042] The present invention will significantly improve the industrial preparation process of 3-methoxyphenol.

[0043] The invention meets the requirements of green chemistry and can prepare 3-methoxyphenol with cheap and readily available raw materials, resorcinol and methanol.

[0044] The present invention provides an aluminum phosphate catalyst prepared by the above preparation method. When the aluminum phosphate catalyst is used for gas-solid phase monoetherification of resorcinol and methanol to prepare 3-methoxyphenol, the catalyst has high reaction activity, few by-products and low by-product selectivity.

[0045] The catalyst provided by the present invention has good stability. The activity of the catalyst provided by the present invention does not show a significant decrease after 200 hours of reaction. The resorcinol conversion rate can be maintained at more than 75%, the 3-methoxyphenol selectivity can be maintained at more than 60%, and the selectivity of other by-products is about 35%. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a graph showing the activity stability results of the catalyst obtained in Example 1 of the present invention;

[0047] Figure 2 This is a SEM image of the catalyst prepared in Example 1 of the present invention;

[0048] Figure 3 This is the XRD pattern of the catalyst prepared in Example 1 of the present invention;

[0049] Figure 4 This is a nitrogen adsorption-desorption isotherm diagram of the catalyst prepared in Example 1 of the present invention;

[0050] Figure 5 This is the pore size distribution diagram of the catalyst prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The present invention provides a method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent, comprising the following steps:

[0052] 1) mixing pseudo-boehmite and nitric acid solution in a solvent in sequence to obtain pseudo-boehmite gel;

[0053] 2) adding an anhydrous citric acid aqueous solution and a phosphorus-containing compound to the pseudo-boehmite gel in sequence, and adjusting the pH of the system to 6 to 11 with aqueous ammonia to obtain a mixture;

[0054] 3) The mixture is cooled, allowed to stand, dried, and calcined in sequence to obtain an aluminum phosphate catalyst.

[0055] In the present invention, the mass volume ratio of the pseudo-boehmite, nitric acid solution and solvent is 1g:2~8mL:5~10mL, preferably 1g:3~5mL:8~10mL, and further preferably 1g:4.5mL:10mL; the concentration of the nitric acid solution is 30~35wt%, preferably 33wt%; the solvent contains water and / or ethanol, preferably water.

[0056] In the present invention, the standing time is 1 to 4 hours, preferably 2 hours.

[0057] In the present invention, in step 1), the mixing is performed under heating conditions, and the heating temperature is 50 to 90°C, preferably 60 to 80°C, and more preferably 65 to 75°C.

[0058] In the present invention, the molar ratio of citric acid in the anhydrous citric acid aqueous solution to aluminum atoms in pseudo-boehmite is 0.1 to 1.5:1, preferably 0.35 to 1.2:1, and more preferably 0.5:1.

[0059] In the present invention, the molar ratio of phosphorus atoms in the phosphorus-containing compound to aluminum atoms in the pseudo-boehmite is 0.75 to 1.50:1, preferably 0.8 to 1.35:1, and more preferably 1.10 to 1.25:1; the phosphorus-containing compound comprises one or more of phosphoric acid, diammonium hydrogen phosphate and ammonium dihydrogen phosphate, preferably phosphoric acid.

[0060] In the present invention, the mass concentration of the anhydrous citric acid aqueous solution is 15-25wt%, preferably 18-22wt%, more preferably 20wt%; the concentration of the ammonia water is 25-28wt%, preferably 26-28wt%, more preferably 28wt%.

[0061] In the present invention, the drying temperature is 80-120° C., preferably 100° C.; the drying time is 12-48 hours, preferably 24 hours.

[0062] In the present invention, the calcination temperature is 400-800° C., preferably 500-700° C., more preferably 600° C.; the calcination time is 5-24 h, preferably 10-20 h, more preferably 15 h.

[0063] The present invention provides an aluminum phosphate catalyst.

[0064] The present invention also provides an application of an aluminum phosphate catalyst in the gas-solid phase monoetherification of resorcinol and methanol to prepare 3-methoxyphenol.

[0065] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0066] Example 1

[0067] 10 g of pseudo-boehmite and 100 mL of deionized water were mixed and continuously stirred at 80° C. and hydrothermally refluxed; after the mixture was stirred evenly, 45 mL of 33 wt % nitric acid was added and stirred evenly to obtain pseudo-boehmite gel;

[0068] A 20 wt% aqueous solution of anhydrous citric acid, wherein the molar ratio of citric acid to aluminum is 0.5:1, is added to pseudo-boehmite gel. After stirring for 2 hours, phosphoric acid is added, wherein the atomic molar ratio of phosphorus to aluminum is 1.25:1. The pH value is adjusted to 8 with 28 wt% aqueous ammonia to obtain a mixture. The mixture obtained in the above step is continuously stirred for 2 hours and then allowed to stand for 2 hours. The mixture is heated until the water is evaporated and dried in a drying oven at 100°C for 24 hours to obtain a solid material. The solid material is then calcined at 500°C for 24 hours to obtain an aluminum phosphate catalyst.

[0069] Example 2

[0070] The preparation of the catalyst was the same as in Example 1, except that the atomic molar ratio of citric acid to aluminum was 1:1.

[0071] Example 3

[0072] The preparation of the catalyst was the same as in Example 1, except that the atomic molar ratio of citric acid to aluminum was 0.35:1.

[0073] Example 4

[0074] The preparation of the catalyst was the same as in Example 1, except that the pH value was adjusted to 7 with aqueous ammonia.

[0075] Example 5

[0076] The preparation of the catalyst was the same as in Example 1, except that the pH value was adjusted to 9 with aqueous ammonia.

[0077] Example 6

[0078] The preparation of the catalyst was the same as in Example 1, except that the atomic molar ratio of phosphorus to aluminum was 0.75:1.

[0079] Example 7

[0080] The preparation of the catalyst was the same as in Example 1, except that the atomic molar ratio of phosphorus to aluminum was 1.00:1.

[0081] Example 8

[0082] The preparation of the catalyst was the same as in Example 1, except that the ratio of nitric acid (mL) to pseudo-boehmite (g) was 5:1.

[0083] Comparative Example 1

[0084] The preparation of the catalyst was the same as in Example 1, except that the atomic molar ratio of citric acid to aluminum was 0:1.

[0085] Comparative Example 2

[0086] The preparation of the catalyst was the same as in Example 1, except that the pH value of the system did not need to be adjusted.

[0087] Application Example 1

[0088] The catalysts prepared in Examples 1 to 8 and Comparative Examples 1 to 2 were used in the gas-solid phase monoetherification of resorcinol and methanol to prepare 3-methoxyphenol. The reaction was carried out on a fixed bed apparatus under the following reaction conditions: a molar ratio of resorcinol to methanol of 1:6, a reaction temperature of 280°C, and a reaction space velocity of 2 mL·g -1 ·h -1 .

[0089] The conversion rate of resorcinol, the selectivity of 3-methoxyphenol, the selectivity of 2-methylresorcinol, the selectivity of 4-methylresorcinol and the selectivity of other by-products were calculated, and the results are shown in Table 1.

[0090] Table 1 Application results of Examples 1 to 8 and Comparative Examples 1 to 2 in catalytic synthesis of 3-methoxyphenol

[0091]

[0092]

[0093] Application Example 2

[0094] The catalysts prepared in Example 1 and Comparative Example 2 were used in the gas-solid phase monoetherification of resorcinol and methanol to prepare 3-methoxyphenol. The reaction was carried out on a fixed bed apparatus under the following conditions: a molar ratio of resorcinol to methanol of 1:6, a reaction temperature of 280°C, and a reaction space velocity of 2 mL·g -1 ·h -1 .

[0095] The conversion rate of resorcinol and the selectivity of by-products were calculated. The results obtained in Example 1 are as follows: Figure 1 As shown, it can be clearly observed that the conversion rate does not decrease significantly after the catalyst participates in the reaction for 200 hours, and the selectivity of 3-methoxyphenol is maintained at above 60%, indicating that the catalyst prepared by the preparation method provided by the present invention has good stability.

[0096] Figure 2 This is an SEM image of the catalyst prepared in Example 1. It can be seen from the figure that the catalyst has a short rod-like morphology, good particle dispersion, obvious pore structure can be seen in the gaps between the catalysts, and no obvious impurity crystals are observed;

[0097] Figure 3 This is the XRD pattern of the catalyst prepared in Example 1. It can be seen from the figure that the XRD curve of the sample has four diffraction peaks near 2θ = 20.4°, 21.6°, 23.2° and 35.8°, respectively. The diffraction peaks at 2θ = 20.4°, 21.6° and 23.2° correspond to the (020), (211) and (212) crystal planes of the phosphotyrite type AlPO4; the diffraction peak at 2θ = 35.8° corresponds to the (260) crystal plane of the α-cristobalite type AlPO4, indicating that the catalyst has two different AlPO4 crystal forms. In all the catalysts tested, no characteristic diffraction peaks of other oxides such as Al2O3 and P2O5 were detected, indicating that the prepared Al-PO catalyst is not a simple mixture of Al2O3 and P2O5. The bun peak and diffraction peak appearing at 20-25° indicate that the catalyst is mainly an amorphous aluminum phosphate, which contains a small amount of aluminum phosphate crystals.

[0098] Figure 4 The nitrogen adsorption-desorption isotherms of the catalysts prepared in Example 1 are shown in FIG. As can be seen from the figure, the adsorption-desorption isotherms of the catalysts all exhibit typical IV type and have H1 type hysteresis loops, indicating that the catalysts are all typical mesoporous materials.

[0099] Figure 5 This is the pore size distribution diagram of the catalyst prepared in Example 1. It can be seen from the figure that the pore size of the catalyst is about 8 nm and the pore size distribution is uniform.

[0100] As can be seen from the above examples, the present invention provides an aluminum phosphate catalyst, its preparation method, and application. The aluminum phosphate catalyst prepared by the preparation method provided by the present invention has high catalytic activity, good selectivity for 3-methoxyphenol, and good stability. It has broad application prospects in the monoetherification reaction of resorcinol and methanol to prepare 3-methoxyphenol.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent, characterized in that: The following steps are involved: 1) mixing pseudo-boehmite and nitric acid solution in a solvent in sequence to obtain pseudo-boehmite gel; 2) adding anhydrous citric acid aqueous solution and a phosphorus-containing compound to the pseudo-boehmite gel in sequence, and adjusting the pH of the system to 6-11 with aqueous ammonia to obtain a mixture; 3) cooling, standing, drying and calcining the mixture in sequence to obtain an aluminum phosphate catalyst; The mass volume ratio of the pseudo-boehmite, nitric acid solution and solvent is 1g:2-8mL:5-10mL; the concentration of the nitric acid solution is 30-35wt%; The mass concentration of the anhydrous citric acid aqueous solution is 15-25wt%, and the mass concentration of the ammonia water is 25-28wt%.

2. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to claim 1, characterized in that: The solvent comprises water and / or ethanol.

3. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to claim 2, characterized in that: In the step 1), the mixing is performed under heating conditions, and the heating temperature is 50-90°C.

4. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to any one of claims 1 to 3, characterized in that: The molar ratio of citric acid in the anhydrous citric acid aqueous solution to aluminum atoms in pseudo-boehmite is 0.1-1.5:

1.

5. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to claim 4, characterized in that: The molar ratio of phosphorus atoms in the phosphorus-containing compound to aluminum atoms in the pseudo-boehmite is 0.75-1.50:1; the phosphorus-containing compound comprises one or more of phosphoric acid, diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

6. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to claim 5, characterized in that: The drying temperature is 80-120° C., and the drying time is 12-48 hours.

7. The method for preparing an aluminum phosphate catalyst using citric acid as a complexing agent according to claim 1, 2, 5 or 6, characterized in that: The calcination temperature is 400-800° C., and the calcination time is 5-24 hours.

8. The aluminum phosphate catalyst obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the aluminum phosphate catalyst according to claim 8 in the preparation of 3-methoxyphenol by gas-solid phase monoetherification of resorcinol and methanol.

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