An oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, and its preparation method and application

Abstract

The present invention discloses an oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, a preparation method thereof, and an application thereof. The oxidation catalyst includes a Bi-modified alumina carrier and active components PdO, CuO, and ZrO2 supported on the carrier; the loading amounts of the active components in the carrier are respectively, PdO 0.1-3wt%, CuO 0.01-2wt%, and ZrO2 0.05-1wt%, based on 100wt% of the carrier weight. The oxidation catalyst provided by the present invention is used for the oxidation synthesis reaction of 3-methoxy-4-hydroxyphenylacetoic acid, and has the advantages of high activity, high reaction selectivity, and long-term stability.

Description

Technical Field

[0001] The present invention relates to an organic synthesis catalyst, in particular to an oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, and a preparation method and application thereof. Background Art

[0002] Vanillin, also known as vanillin or vanillic aldehyde, is typically a white or light yellow crystalline powder. Its chemical name is 3-methoxy-4-hydroxybenzaldehyde. It has the distinctive aroma of vanilla and a rich, milky flavor. It is the world's most produced synthetic fragrance, with a global production capacity of approximately 30,000 tons / year. It is also an important pharmaceutical intermediate. Currently, over 80% of vanillin is synthesized using the glyoxylic acid route, a process that includes condensation, oxidation, and decarboxylation. First, guaiacol and glyoxylic acid condense to produce 3-methoxy-4-hydroxymandelic acid, which is further oxidized to produce 3-methoxy-4-hydroxyphenylacetophenone acid, which is then decarboxylated to produce vanillin. The oxidation of 3-methoxy-4-hydroxymandelic acid to 3-methoxy-4-hydroxyphenylacetophenone acid is the most important step affecting vanillin yield.

[0003] Currently, the oxidation of 3-methoxy-4-hydroxymandelic acid mainly adopts catalytic oxidation process in industry, that is, the oxidation reaction is carried out in the presence of a catalyst using oxygen, hydrogen peroxide, etc. as an oxidant.

[0004] CN1258399C discloses a catalyst for the oxidation reaction of 3-methoxy-4-hydroxymandelic acid. The composition formula used to express the elements and their molar contents constituting the catalyst composition is: Mg 0～0.3 ·Mo 0～0.02 Fe 0.03～0.3 ·Cu 0.004～0.04 ·Zn 0.002～0.07 ·Al 0～0.7 ·K 0.009～0.4 ·Na 0～0.03 ·O 0.1～3.0 ·S 0.05～0.9 The disadvantages of this patent are that the catalyst composition and preparation process are complex and the cost is high. At the same time, the processing capacity of the catalyst is limited and can only ensure oxidation synthesis at a lower raw material concentration (only 7%), resulting in low production efficiency.

[0005] CN114345366A uses a ZrO2-loaded composite metal oxide of manganese, copper, lanthanum, and additives as a catalyst for the highly active and selective oxidation of 3-methoxy-4-hydroxymandelic acid to produce 3-methoxy-4-hydroxyphenylacetoacetic acid. However, the catalyst provided in this patent exhibits poor catalytic performance and can only meet oxidation production requirements at low feedstock concentrations. Furthermore, it requires high stirring conditions, which can easily lead to catalyst pulverization and difficulty in separation.

[0006] CN111359662A discloses a method for preparing 3-methoxy-4-hydroxyphenylacetophenone acid by catalyzing the oxidation of 3-methoxy-4-hydroxymandelic acid using a divalent copper ligand catalyst and a hydrogen peroxide oxidant. The patent has the following disadvantages: the preparation of the catalyst requires a relatively harsh reaction environment, such as an anhydrous and oxygen-free environment, resulting in a complex preparation process. Furthermore, the use of hydrogen peroxide increases production safety risks.

[0007] CN113828358A discloses a method for oxidizing 3-methoxy-4-hydroxymandelic acid using a metal ligand catalyst and an organic peroxide and / or oxygen. However, the disadvantage is that the preparation of the catalyst requires a relatively harsh reaction environment, such as an anhydrous and oxygen-free environment, and the preparation process is complex. Furthermore, the use of organic peroxides poses safety issues such as violent decomposition, overpressure, or explosion.

[0008] CN101376622A discloses a method for preparing 3-methoxy-4-hydroxyphenylacetoacetic acid by oxidizing 3-methoxy-4-hydroxymandelic acid using a cuprous oxide catalyst and air. However, the patent has the disadvantages of requiring a large amount of catalyst, difficulty in filtering, and a limited number of recycling times.

[0009] In summary, the current industrial 3-methoxy-4-hydroxymandelic acid oxidation process has problems such as large catalyst dosage, easy pulverization, low activity and poor stability that still need to be solved. Summary of the Invention

[0010] To address the above technical problems, the present invention provides an oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, as well as its preparation method and application. The oxidation catalyst provided by the present invention is used in the oxidation reaction to synthesize 3-methoxy-4-hydroxyphenylacetoic acid, and has the advantages of high activity, high reaction selectivity, and long-term stability.

[0011] The present invention first proposes an oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid. The catalyst comprises a Bi-modified alumina support and loaded active components PdO, CuO, and ZrO2. The synergistic effect of the Bi-modified alumina support, prepared by a high-temperature solid-phase reaction, and the three active components imparts high activity, selectivity, and excellent stability to the catalyst. The catalyst, when used in the catalytic oxidation reaction of 3-methoxy-4-hydroxymandelic acid, achieves a feedstock conversion rate of 100%, a product selectivity exceeding 98.0%, and continuous, stable operation for over 1000 hours.

[0012] Based on the second aspect of the present invention, a method for preparing an oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid is also proposed. The method has a wide source of raw materials, is simple to operate, and has strong industrial applicability.

[0013] Based on the third aspect of the present invention, the use of an oxidation catalyst for the synthesis of 3-methoxy-4-hydroxyphenylacetoic acid is also provided. The oxidation catalyst of the present invention is applied to the oxidation reaction of 3-methoxy-4-hydroxymandelic acid to produce 3-methoxy-4-hydroxyphenylacetoic acid. The oxidation catalyst can maintain high reaction conversion and selectivity even under long run times and high substrate concentrations. The catalyst exhibits excellent catalyst stability and is therefore more suitable for the continuous production of 3-methoxy-4-hydroxyphenylacetoic acid, thereby improving reaction efficiency and reducing production costs.

[0014] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0015] An oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, comprising a Bi-modified alumina carrier and active components PdO, CuO and ZrO2 supported on the carrier;

[0016] The loading amounts of the active components in the carrier are respectively: PdO 0.1-3wt%, CuO 0.01-2wt%, and ZrO2 0.05-1wt%, based on 100wt% of the carrier weight.

[0017] As a preferred solution provided by the present invention, the loading amounts of the active components in the carrier are respectively PdO 0.5-2 wt%, CuO 0.1-1.5 wt%, and ZrO2 0.1-0.8 wt%, based on 100 wt% of the carrier weight.

[0018] As a preferred embodiment of the present invention, the Bi-modified alumina support is prepared by mixing a Bi precursor and alumina, followed by drying and calcining; preferably, the mixture is ground and sieved before drying;

[0019] Preferably, the amount of the Bi precursor and the aluminum oxide is calculated as a molar ratio of metal Bi to metal Al of (0.5-1):1;

[0020] Preferably, the drying conditions are: drying temperature is 100-150° C., preferably 120-140° C., and drying time is 2-10 h, preferably 4-8 h.

[0021] Preferably, the calcination conditions are: calcination temperature of 600-1500° C., preferably 900-1200° C., and calcination time of 8-20 h, preferably 10-15 h; a stable spinel-like multi-coordinate configuration structure is generated by high-temperature calcination to improve catalyst activity.

[0022] Preferably, the Bi precursor is one or more of bismuth nitrate, bismuth sulfate, bismuth hydroxide, bismuth oxalate, bismuth carbonate, and bismuth subcarbonate; the above raw material selections of Bi precursors are only limited examples of common bismuth-containing compounds on the market and do not serve as any limitation to the main protection scope of the present invention.

[0023] Preferably, after the Bi precursor and alumina are mixed, they are ground and mixed, then sieved to 100-200 mesh, and then dried and calcined.

[0024] As a preferred solution provided by the present invention, the oxidation catalyst is prepared by any one or more of the following methods including but not limited to: impregnation method, deposition precipitation method, sol-gel method, ion exchange method, preferably impregnation method, more preferably equal volume impregnation method.

[0025] For an example of a feasible preparation method, taking the impregnation method as an example, reference can be made to the general method for preparing supported catalysts by impregnation, for example:

[0026] The Bi-modified alumina support provided above is immersed in an aqueous solution containing soluble palladium salt, copper salt and zirconium salt, and after adsorption equilibrium is reached, it is dried and calcined to obtain the oxidation catalyst.

[0027] The relative amounts of the Bi-modified alumina carrier and the palladium salt, copper salt, and zirconium salt are based on the preparation of a catalyst with the expected theoretical composition.

[0028] Furthermore, the raw material selection of the palladium salt includes but is not limited to one or more of sulfate, nitrate, and organic acid salt of metallic palladium, preferably palladium nitrate;

[0029] Furthermore, the raw material selection of the copper salt includes but is not limited to one or more of sulfate, nitrate, and organic acid salt of metallic copper, preferably copper nitrate;

[0030] Furthermore, the raw material selection of the zirconium salt includes but is not limited to one or more of sulfate, nitrate and acetate of metallic zirconium, preferably zirconium acetate.

[0031] The present invention also provides a use of the oxidation catalyst as described above in the reaction of oxidizing 3-methoxy-4-hydroxymandelic acid to prepare 3-methoxy-4-hydroxyphenylacetoic acid.

[0032] In a specific method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, an alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is continuously passed through a fixed-bed reactor filled with the oxidation catalyst described above, and the reaction is carried out under conditions of oxygen-containing gas pressure to synthesize 3-methoxy-4-hydroxyphenylacetoic acid.

[0033] The oxygen-containing gas may be, for example, oxygen or air.

[0034] In the synthesis method provided by the present invention, as a preferred embodiment, the reaction conditions are: reaction temperature 70-120°C, preferably 80-100°C, reaction absolute pressure 0.1-1 MPa, preferably 0.3-0.7 MPa.

[0035] In the synthesis method provided by the present invention, as a preferred embodiment, the pH of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 9-13, preferably 10-12.

[0036] Preferably, the inorganic base used to provide the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is, for example, but not limited to, one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate, preferably sodium hydroxide or potassium hydroxide.

[0037] In the synthesis method provided by the present invention, as a preferred embodiment, the mass concentration of 3-methoxy-4-hydroxymandelic acid in the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 10-30 wt%, preferably 15-25 wt%.

[0038] In the synthesis method provided by the present invention, as a preferred embodiment, the space velocity of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 1-10 L / h / L·cat, preferably 3-7 L / h / L·cat.

[0039] The beneficial effects of the present invention are mainly reflected in the following points:

[0040] (1) Using Bi-modified alumina as a carrier for the active component can inhibit the pulverization problem of the catalyst in a strong alkaline environment, significantly improve the stability of the catalyst, and increase the concentration of lattice oxygen on the catalyst surface, which is beneficial to improving the reaction activity and selectivity.

[0041] (2) The synergistic effect of the active components PdO, CuO, and ZrO2 reduces the formation of reaction by-products and can simultaneously ensure a high reaction conversion rate and selectivity.

[0042] (3) The specific combination of the three active components is structurally designed and optimized from the perspective of synergistically reducing the reaction activation energy, improving the oxidation activity and the dispersion of the active components, the active surface area, and the anti-sintering performance, which comprehensively improves the reaction activity, helps shorten the reaction time, and thus increases the yield.

[0043] (4) The oxidation catalyst provided by the present invention has low metal loading, good anti-sintering performance, is not easy to pulverize in a strong alkaline environment, has a simple preparation process, is economical, and has good application prospects.

[0044] (5) The oxidation catalyst has good stability and is particularly suitable for the oxidation reaction of 3-methoxy-4-hydroxymandelic acid using air or oxygen as an oxidant. 3-methoxy-4-hydroxyphenylacetophenone acid can be efficiently produced using a continuous fixed-bed process while maintaining a relatively high substrate concentration. Furthermore, the process has the advantages of simple operation, low cost, less waste, environmental protection, and high production efficiency. DETAILED DESCRIPTION

[0045] The present invention will be further described below through specific examples. The examples of the present invention are only for illustration of the present invention and do not limit the scope of the present invention.

[0046] The conversion rate was determined using liquid chromatography external standard curve analysis.

[0047] Liquid chromatography analysis conditions are as follows:

[0048] Instrument model: Shimadzu liquid chromatograph SPD-20A; column oven: CT0-10ASvp; column temperature: 30°C, chromatographic column: T3 column, mobile phase: water and acetonitrile, water / acetonitrile = 20:80 (vol / vol), total flow rate: 1 ml / min, residence time: 40 min, detector wavelength: 254 nm.

[0049] Catalyst performance can be measured by the conversion of the starting material, 3-methoxy-4-hydroxymandelic acid, and the selectivity for the target product, 3-methoxy-4-hydroxyphenylacetophenone. The conversion and selectivity are determined by calibrating the system with 3-methoxy-4-hydroxymandelic acid and 3-methoxy-4-hydroxyphenylacetophenone using an external standard.

[0050] The reactor in the embodiment is a fixed bed reactor.

[0051] The following Examples 1-5 and Comparative Examples 1-5 are used to provide oxidation catalysts with different compositions.

[0052] [Example 1]

[0053] Preparation of oxidation catalyst A:

[0054] 145.4 g of bismuth hydroxide and 28.5 g of aluminum oxide were added to a mortar and mixed evenly. After grinding and sieving, a 100-200 mesh mixture was obtained. Then, the mixture was transferred to a crucible, dried at 130°C for 6 h, and then calcined in air at 1200°C for 10 h (heating rate: 3°C / min) to obtain 150 g of white powder, which was then pressed into a 3*3 mm columnar carrier.

[0055] By using the equal volume impregnation method, 100 g of the above support was immersed in an aqueous solution containing 0.22 g of palladium nitrate dihydrate, 6.08 g of copper nitrate trihydrate and 2.66 g of anhydrous zirconium acetate. After adsorption equilibrium was reached, the support was dried and calcined in air at 300°C for 10 h to obtain oxidation catalyst A.

[0056] [Example 2]

[0057] Preparation of oxidation catalyst B:

[0058] 71.3 g of bismuth subcarbonate and 28.5 g of aluminum oxide were added to a mortar and mixed evenly. After grinding and sieving, a 100-200 mesh mixture was obtained. Then, the mixture was transferred to a crucible, dried at 120°C for 4 h, and then calcined in air at 900°C for 15 h (heating rate: 3°C / min) to obtain 140 g of white powder, which was then extruded to obtain a 3*3 mm strip carrier.

[0059] By using the equal volume impregnation method, 100 g of the above support was immersed in an aqueous solution containing 1.09 g of palladium nitrate dihydrate, 4.56 g of copper nitrate trihydrate and 1.33 g of anhydrous zirconium acetate. After adsorption equilibrium was reached, the support was dried and calcined in air at 400°C for 8 h to obtain oxidation catalyst B.

[0060] [Example 3]

[0061] 271.2 g of bismuth nitrate pentahydrate and 28.5 g of aluminum oxide were added to a mortar and mixed evenly. After grinding and sieving, a 100-200 mesh mixture was obtained. Then, the mixture was transferred to a crucible, dried at 140°C for 8 h, and then calcined in air at 600°C for 20 h (heating rate: 3°C / min) to obtain 145 g of white powder, which was then extruded into a 3*3 mm strip carrier.

[0062] By using the equal volume impregnation method, 100 g of the above support was immersed in an aqueous solution containing 3.27 g of palladium nitrate dihydrate, 3.04 g of copper nitrate trihydrate and 2.13 g of anhydrous zirconium acetate. After adsorption equilibrium was reached, the support was dried and calcined in air at 450°C for 6 h to obtain oxidation catalyst C.

[0063] [Example 4]

[0064] 71.3 g of bismuth subcarbonate and 28.5 g of aluminum oxide were added to a mortar and mixed evenly. After grinding and sieving, a 100-200 mesh mixture was obtained. Then, the mixture was transferred to a crucible, dried at 150°C for 2 h, and then calcined in air at 1500°C for 8 h (heating rate: 3°C / min) to obtain 142 g of white powder, which was then pressed into a 3*3 mm columnar carrier.

[0065] By using the equal volume impregnation method, 100 g of the above support was immersed in an aqueous solution containing 4.35 g of palladium nitrate dihydrate, 0.3 g of copper nitrate trihydrate and 0.27 g of anhydrous zirconium acetate. After adsorption equilibrium was reached, the support was dried and calcined in air at 500°C for 4 h to obtain oxidation catalyst D.

[0066] [Example 5]

[0067] 145.4 g of bismuth hydroxide and 28.5 g of aluminum oxide were added to a mortar and mixed evenly. After grinding and sieving, a 100-200 mesh mixture was obtained. Then, the mixture was transferred to a crucible, dried at 100°C for 10 h, and then calcined in air at 1000°C for 12 h (heating rate: 3°C / min) to obtain 147 g of white powder, which was then extruded to obtain a 3*3 mm strip carrier.

[0068] By using the equal volume impregnation method, 100 g of the above support was immersed in an aqueous solution containing 6.35 g of palladium nitrate dihydrate, 0.03 g of copper nitrate trihydrate and 0.13 g of anhydrous zirconium acetate. After adsorption equilibrium was reached, the support was dried and calcined in air at 600°C for 2 h to obtain oxidation catalyst E.

[0069] [Comparative Example 1]

[0070] The catalyst was prepared by referring to a method substantially the same as that in Example 1, and was recorded as oxidation catalyst F, with the only difference being that during the equal volume impregnation process, the support was replaced with commercially available alumina.

[0071] [Comparative Example 2]

[0072] The catalyst was prepared by referring to a method substantially the same as that in Example 1, and was recorded as oxidation catalyst G, except that copper nitrate trihydrate was not added during the equal volume impregnation process.

[0073] [Comparative Example 3]

[0074] The catalyst was prepared by referring to a method substantially the same as that in Example 1, and was designated as oxidation catalyst H, except that anhydrous zirconium acetate was not added during the equal volume impregnation process.

[0075] [Comparative Example 4]

[0076] The catalyst was prepared by referring to a method substantially the same as that in Example 1, and was designated as Oxidation Catalyst I, except that copper nitrate trihydrate and anhydrous zirconium acetate were not added during the equal volume impregnation process.

[0077] [Comparative Example 5]

[0078] The catalyst was prepared by referring to a method substantially the same as that in Example 1, and was recorded as oxidation catalyst J, except that palladium nitrate dihydrate was not added during the equal volume impregnation process.

[0079] The following Examples 6-10 and Comparative Examples 6-10 were used to oxidatively synthesize 3-methoxy-4-hydroxyphenylacetoic acid to evaluate the catalyst performance.

[0080] [Example 6]

[0081] A reactor was filled with 50 ml of oxidation catalyst A, heated to 70° C., and oxygen was introduced to raise the system pressure to 1.0 MPa. After the system stabilized, a 15% alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid (pH 9) was pumped into the reactor at a space velocity of 5 L / h / L·cat. After 10 hours of reaction, liquid chromatography analysis showed a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.5%. After 1100 hours of continuous operation, the catalyst was sampled and analyzed, revealing a feedstock conversion of 99.6% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.2%.

[0082] [Example 7]

[0083] A reactor was filled with 50 ml of oxidation catalyst B, heated to 80° C., and oxygen was introduced to raise the system pressure to 0.7 MPa. After the system stabilized, a 10% alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid (pH 10) was pumped into the reactor at a space velocity of 3 L / h / L·cat. After 15 hours of reaction, liquid chromatography analysis showed a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.6%. After 1200 hours of continuous operation, the catalyst was sampled and analyzed, revealing a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.4%.

[0084] [Example 8]

[0085] A reactor was filled with 50 ml of oxidation catalyst C, heated to 90° C., and oxygen was introduced to raise the system pressure to 0.5 MPa. After the system stabilized, a 20% alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid (pH 11) was pumped into the reactor at a space velocity of 7 L / h / L·cat. After 20 hours of reaction, liquid chromatography analysis showed a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.4%. After 1150 hours of continuous operation, the catalyst was sampled and analyzed, revealing a feedstock conversion of 99.4% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.3%.

[0086] [Example 9]

[0087] A reactor was filled with 50 ml of oxidation catalyst D, heated to 100° C., and oxygen was introduced to raise the system pressure to 0.3 MPa. After the system stabilized, a 25% mass concentration of 3-methoxy-4-hydroxymandelic acid alkaline aqueous solution (pH 12) was pumped into the reactor at a space velocity of 1 L / h / L·cat. After 12 hours of reaction, liquid chromatography analysis showed a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.8%. After 1300 hours of continuous operation, the catalyst was sampled and analyzed, revealing a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.7%.

[0088] [Example 10]

[0089] A reactor was filled with 50 ml of oxidation catalyst E, heated to 120° C., and oxygen was introduced to raise the system pressure to 0.1 MPa. After the system stabilized, a 30% alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid (pH 13) was pumped into the reactor at a space velocity of 10 L / h / L·cat. After 15 hours of reaction, liquid chromatography analysis showed a feedstock conversion of 100.0% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.1%. After 1400 hours of continuous operation, the catalyst was sampled and analyzed, revealing a feedstock conversion of 99.5% and a selectivity for 3-methoxy-4-hydroxyphenylacetoic acid of 99.3%.

[0090] [Comparative Example 6]

[0091] The oxidation synthesis reaction was carried out in substantially the same manner as in Example 6, except that the oxidation catalyst A was replaced by the oxidation catalyst F.

[0092] After 10 hours of reaction, liquid chromatography analysis showed that the raw material conversion rate was 90.0% and the selectivity for 3-methoxy-4-hydroxyphenylacetoic acid was 95.5%. After 500 hours of continuous operation of the catalyst, sampling analysis showed that the raw material conversion rate was 70.5% and the selectivity for 3-methoxy-4-hydroxyphenylacetoic acid was 82.5%.

[0093] [Comparative Example 7]

[0094] The oxidation synthesis reaction was carried out in substantially the same manner as in Example 6, except that the oxidation catalyst A was replaced by the oxidation catalyst G.

[0095] After 10 hours of reaction, liquid chromatography analysis showed a feed conversion of 93.2% and a selectivity of 94.0% for 3-methoxy-4-hydroxyphenylacetoic acid. After 400 hours of continuous operation, sampling and analysis showed a feed conversion of 86.7% and a selectivity of 96.4% for 3-methoxy-4-hydroxyphenylacetoic acid.

[0096] [Comparative Example 8]

[0097] The oxidation synthesis reaction was carried out in substantially the same manner as in Example 6, except that the oxidation catalyst A was replaced by the oxidation catalyst H.

[0098] After 10 hours of reaction, liquid chromatography analysis showed that the raw material conversion rate was 95.0% and the selectivity of 3-methoxy-4-hydroxyphenylacetoic acid was 96.5%. After 500 hours of continuous operation of the catalyst, sampling analysis showed that the raw material conversion rate was 90.5% and the selectivity of 3-methoxy-4-hydroxyphenylacetoic acid was 97.3%.

[0099] [Comparative Example 9]

[0100] The oxidation synthesis reaction was carried out in substantially the same manner as in Example 6, except that the oxidation catalyst A was replaced by the oxidation catalyst I.

[0101] After 10 hours of reaction, liquid chromatography analysis showed that the raw material conversion rate was 85.4% and the selectivity of 3-methoxy-4-hydroxyphenylacetoic acid was 92.3%. After 500 hours of continuous operation of the catalyst, sampling analysis showed that the raw material conversion rate was 80.5% and the selectivity of 3-methoxy-4-hydroxyphenylacetoic acid was 95.1%.

[0102] [Comparative Example 10]

[0103] The oxidation synthesis reaction was carried out in substantially the same manner as in Example 6, except that the oxidation catalyst A was replaced by the oxidation catalyst J.

[0104] After 10 hours of reaction, the feed conversion was 91.5% and the selectivity for 3-methoxy-4-hydroxyphenylacetoic acid was 97.2%. After 600 hours of continuous operation, the catalyst was sampled and analyzed, and the feed conversion was 83.7% and the selectivity for 3-methoxy-4-hydroxyphenylacetoic acid was 98.4%.

[0105] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be considered within the scope of protection of the present invention.

Claims

1. An oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, characterized in that: The invention comprises a Bi-modified alumina carrier and active components PdO, CuO and ZrO2 loaded on the carrier; The loading amounts of the active components in the carrier are respectively: PdO 0.1-3wt%, CuO 0.01-2wt%, and ZrO2 0.05-1wt%, based on 100wt% of the carrier weight.

2. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 1, characterized in that The loading amounts of the active components in the carrier are respectively: PdO 0.5-2wt%, CuO 0.1-1.5wt%, and ZrO2 0.1-0.8wt%, based on 100wt% of the carrier weight.

3. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 1, characterized in that The Bi-modified alumina carrier is prepared by mixing a Bi precursor and alumina, followed by drying and calcining.

4. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 3, characterized in that The Bi-modified alumina carrier is prepared by mixing a Bi precursor and alumina, grinding, screening, drying and calcining.

5. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 3, characterized in that The amounts of the Bi precursor and aluminum oxide used are calculated based on the molar ratio of metal Bi to metal Al, which is (0.5-1):

1.

6. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 3, characterized in that The calcination conditions are as follows: calcination temperature is 600-1500° C., and calcination time is 8-20 hours.

7. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 6, characterized in that The calcination conditions are: calcination temperature of 900-1200° C., and calcination time of 10-15 hours.

8. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 3, characterized in that The Bi precursor is one or more of bismuth nitrate, bismuth sulfate, bismuth hydroxide, bismuth oxalate, bismuth carbonate, and bismuth subcarbonate.

9. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 3, characterized in that After the Bi precursor and alumina are mixed, they are ground and mixed, sieved to 100-200 meshes, and then dried and calcined.

10. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to any one of claims 1 to 9, characterized in that The oxidation catalyst is prepared by any one or more of an impregnation method, a deposition precipitation method, a sol-gel method, and an ion exchange method.

11. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 10, characterized in that: The oxidation catalyst is prepared by an impregnation method.

12. The oxidation catalyst for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 10, characterized in that: The oxidation catalyst was prepared by an equal volume impregnation method.

13. Use of the oxidation catalyst according to any one of claims 1 to 12 in the oxidation of 3-methoxy-4-hydroxymandelic acid to produce 3-methoxy-4-hydroxyphenylacetoic acid.

14. A method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid, characterized in that: An alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is continuously passed through a fixed-bed reactor filled with the oxidation catalyst according to any one of claims 1 to 12, and reacted under pressure of an oxygen-containing gas to synthesize 3-methoxy-4-hydroxyphenylacetophenone acid.

15. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 14, characterized in that: The reaction conditions are: reaction temperature 70-120° C., reaction absolute pressure 0.1-1 MPa.

16. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 15, characterized in that: The reaction conditions are: reaction temperature 80-100° C., reaction absolute pressure 0.3-0.7 MPa.

17. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to any one of claims 14 to 16, characterized in that: The pH of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 9-13.

18. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 17, characterized in that: The pH of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 10-12.

19. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to any one of claims 14 to 16, characterized in that: In the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid, the mass concentration of 3-methoxy-4-hydroxymandelic acid is 10-30 wt %.

20. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 19, characterized in that: In the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid, the mass concentration of 3-methoxy-4-hydroxymandelic acid is 15-25 wt %.

21. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to any one of claims 14 to 16, characterized in that: The space velocity of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 1-10 L / h / L·cat.

22. The method for synthesizing 3-methoxy-4-hydroxyphenylacetoic acid according to claim 21, characterized in that: The space velocity of the alkaline aqueous solution of 3-methoxy-4-hydroxymandelic acid is 3-7 L / h / L·cat.