A method for synthesizing maleic acid by photocatalytic oxidation of furfural

Abstract

The present invention belongs to the field of photocatalysis and bio-based chemicals, and discloses a method for synthesizing maleic acid by photocatalytic oxidation of furfural, comprising the following steps: (1) adding furfural, eosin Y, and H2O2 to a mixed solvent consisting of methanol and a buffer solution; the furfural concentration is 20 to 50 mM; the H2O2 amount is 15 to 110 times the molar concentration of the furfural; the buffer solution concentration is 50 to 150 mM, and the pH is 6.0 to 8.0; the volume ratio of the methanol to the buffer solution is 9:2 to 6:5; and (2) performing an illumination reaction using green light at a reaction temperature of 15-37°C to obtain maleic acid. The advantages of the present invention are that the raw materials used are widely available, the reaction conditions are mild, the process is environmentally friendly, the yield is high, the process is simple, and industrial production can be easily achieved.

Description

Technical Field

[0001] The invention belongs to the field of photocatalysis and bio-based chemicals, and particularly relates to a method for synthesizing maleic acid by utilizing photocatalytic conversion of furfural. Background Art

[0002] Furfural is an important furan platform compound derived from biomass. It is usually prepared in industry by acid-catalyzed hemicellulose hydrolysis / dehydration reaction. Furfural molecules contain highly active formyl and furan rings, so they can be converted into high-value-added chemical intermediates such as 2-furoic acid, 5-hydroxy-2(5H)-furanone (HFO) and maleic acid (MA) through oxidation, reduction and other reactions; these intermediates are widely used in food, chemical and pharmaceutical fields. Maleic acid (MA), also known as maleic acid, is one of the important C4 intermediates in the chemical industry and is widely used in the synthesis of unsaturated polyester resins, surface coatings, pesticides and pharmaceuticals (Molecular Catalysis 2021, 504, 484).

[0003] At present, maleic acid is mainly obtained by gas-phase oxidation of benzene or butane / butene in industry, using vanadium oxide as catalyst, O2 as oxidant, although the method has been applied for many years, but CO2 and CO and other by-products are produced during the reaction, and the reaction conditions are fierce (Sustainable Chemical Processes, 2015, 3, 9). With the depletion of petroleum resources and the increasing severity of environmental problems, in recent years, many researchers have begun to pay attention to the preparation of MA (Green Chemistry, 2011, 3, 554) from renewable biomass-derived chemicals such as levulinic acid, 5-hydroxymethylfurfural, furfural, etc. In these biomass-derived platform chemicals, furfural has attracted more and more attention, because furfural is a kind of industrial raw material (Chemical Society Reviews, 2020, 13, 4273) produced with a production capacity of about 300,000 tons per year by lignocellulose as raw material.

[0004] Photocatalysis is a green catalytic technology driven by sunlight or artificial lighting, and has broad application prospects in organic synthesis. Eosin Y (EY) is a widely used non-metallic organic dye photocatalyst with a maximum ultraviolet absorption wavelength of 532nm. Compared with the precious metal and its complex catalysts used in the past, this photosensitizer is cheaper and more environmentally friendly. At present, there are usually two approaches to synthesize the final product MA using furfural as a substrate. One is to use furfural as a raw material, first convert furfural into HFO by photocatalytic oxidation, and then convert HFO into MA by chemical methods, biocatalysis or chemical / biocatalysis; the intermediate product HFO needs to be separated and purified in the entire synthesis route, and the reaction steps are relatively many (ACS Sustainable Chemistry & Engineering, 2020, 8, 10626). Another method is to directly synthesize MA in one step using furfural as a substrate. Usually, a heterogeneous solid catalyst or high-frequency ultrasonic radiation is used and H2O2 is used as an oxidant for the reaction. However, there are problems such as harsh reaction conditions and low MA yield (J.Phys.Chem.C 2011,115,17516; Inorg.Chem.Commun.2021,129,108637;Green Chem.2017,19,98;Green Chemistry,2022,24,4164). Summary of the Invention

[0005] In view of the problems existing in the existing methods, the purpose of the present invention is to provide a green and efficient method for synthesizing maleic acid by catalyzing the oxidation and ring opening of furfural under mild conditions using furfural as a substrate.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for synthesizing maleic acid comprises the following steps:

[0008] (1) Furfural, eosin Y, and H2O2 are added to a mixed solvent consisting of methanol and a buffer solution; the concentration of the furfural is 20 to 50 mM; the amount of the H2O2 is 15 to 110 times the molar concentration of the furfural; the concentration of the buffer solution is 50 to 150 mM, and the pH is 6.0 to 8.0; the volume ratio of the methanol to the buffer solution is 9:2 to 6:5;

[0009] (2) Using green light for illumination reaction at a reaction temperature of 15-37°C to obtain maleic acid.

[0010] Preferably, the concentration of furfural is 20-30 mM.

[0011] Preferably, the amount of Eosin Y is 1% to 10% of the molar concentration of furfural.

[0012] Preferably, the amount of H2O2 is 50 to 110 times the molar concentration of furfural.

[0013] Preferably, the buffer is one or both of citrate buffer and phosphate buffer.

[0014] Preferably, the volume ratio of methanol to buffer is 9:2 to 7:4.

[0015] Preferably, the reaction conditions are temperature 25-35° C., rotation speed 150±50 rpm, and time 48±12 h.

[0016] Preferably, the light source of the illumination is a 530nm-540nm LED lamp with a power of 30±20W.

[0017] Compared with the existing methods, the present invention has the following advantages:

[0018] 1) The present invention utilizes non-metallic organic dye Eosin Y as a photocatalyst, air and H2O2 as oxidants, and a mixed solution of methanol and buffer as a reaction medium. The entire reaction system is environmentally friendly.

[0019] 2) The present invention has mild reaction conditions, high yield, simple reaction process, and easy scale-up. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a liquid chromatogram of the sample analysis of Example 5; furfural, 5-hydroxy-2(5H)-furanone (HFO), and maleic acid (MA).

[0021] Figure 2 It is the structural formula of furfural, 5-hydroxy-2(5H)-furanone, and maleic acid. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0023] Furfural, 5-hydroxy-2(5H)-furanone and Eosin Y were purchased from MacLean Biochemical Technology Co., Ltd.

[0024] Example 1

[0025] 200 μL of pH 6.0, 85 mM citrate buffer was added to 900 μL of methanol to a final concentration of 20 mM furfural, 1 mol% EY (1% of the molar concentration of furfural), and 110 equiv. H2O2 (110 times the molar concentration of furfural). After thorough mixing, the mixture was placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. The reaction was monitored by liquid chromatography ( Figure 1 After 48 hours of reaction, the yield of maleic acid was 77%.

[0026] Example 2

[0027] 200 μL of pH 6.0, 85 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 110 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 87%.

[0028] Example 3

[0029] To 900 μL of methanol, 200 μL of 100 mM phosphate buffer (pH 6.0) was added (final concentration: 20 mM furfural, 10 mol% EY, 10 equiv. H₂O₂) and mixed thoroughly. The mixture was then placed in a photoreactor equipped with a 30 W 530-540 nm green LED light source to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 55%.

[0030] Example 4

[0031] 200 μL of pH 6.0, 100 mM phosphate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 73%.

[0032] Example 5

[0033] 200 μL of pH 6.0, 100 mM phosphate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 110 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 63%.

[0034] Example 6

[0035] 200 μL of pH 8.0, 100 mM phosphate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 69%.

[0036] Example 7

[0037] 200 μL of pH 6.0, 20 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 34%.

[0038] Example 8

[0039] 200 μL of pH 6.0, 50 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 65%.

[0040] Example 9

[0041] 200 μL of pH 6.0, 150 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 85%.

[0042] Example 10

[0043] 200 μL of pH 6.0, 85 mM citrate buffer, a final concentration of 20 mM furfural, 5.5 mol% EY, and 15 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 87%.

[0044] Example 11

[0045] 200 μL of pH 6.0, 85 mM citrate buffer, a final concentration of 50 mM furfural, 5.5 mol% EY, and 15 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 55%.

[0046] Example 12

[0047] 200 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 35°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 90%.

[0048] Example 13

[0049] 200 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 15°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 67%.

[0050] Example 14

[0051] 1000 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 100 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 15°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 56%.

[0052] Example 15

[0053] 400 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 700 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 15°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 72%.

[0054] Example 16

[0055] 600 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 500 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 15°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 58%.

[0056] Comparative Example 1

[0057] Furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 1.1 mL of methanol to a final concentration of 20 mM. The mixture was thoroughly mixed and placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 11%.

[0058] Comparative Example 2

[0059] To 1.1 mL of pH 6.0, 100 mM citrate buffer, furfural at a final concentration of 20 mM, 10 mol% EY, and 50 equiv. H2O2 were added. After thorough mixing, the mixture was placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 58%.

[0060] Comparative Example 3

[0061] 200 μL of pH 4.0, 100 mM acetate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 25%.

[0062] Comparative Example 4

[0063] 200 μL of pH 6.0, 85 mM citrate buffer, a final concentration of 75 mM furfural, 5.5 mol% EY, and 15 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 39%.

[0064] Comparative Example 5

[0065] 200 μL of pH 6.0, 85 mM citrate buffer, a final concentration of 150 mM furfural, 5.5 mol% EY, and 15 equiv. H2O2 were added to 900 μL of methanol. After thorough mixing, the mixture was placed in a photoreactor equipped with 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 25°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 36%.

[0066] Comparative Example 6

[0067] To 1000 μL of methanol, 100 μL of pH 6.0, 100 mM citrate buffer, a final concentration of 20 mM furfural, 10 mol% EY, and 50 equiv. H2O2 were added. After thorough mixing, the mixture was placed in a photoreactor equipped with a 30 W 530 nm-540 nm green light (LED lamp) to initiate the reaction. The reaction was carried out at 15°C and 150 rpm. After 48 hours of reaction, the yield of maleic acid was 38%.

Claims

1. A method for synthesizing maleic acid by photocatalytic oxidation of furfural, characterized in that: The following steps are involved: (1) Furfural, eosin Y, and H2O2 are added to a mixed solvent consisting of methanol and a buffer solution; the concentration of the furfural is 20 to 50 mM; the amount of the H2O2 is 15 to 110 times the molar concentration of the furfural; the concentration of the buffer solution is 50 to 150 mM, and the pH is 6.0 to 8.0; the volume ratio of the methanol to the buffer solution is 9:2 to 6:5; and the buffer solution is one or both of a citrate buffer solution and a phosphate buffer solution; (2) Use green light for illumination reaction at a reaction temperature of 15-37°C to obtain maleic acid.

2. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to claim 1, wherein: The concentration of furfural is 20-30 mM.

3. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to claim 2, wherein: The amount of Eosin Y used is 1% to 10% of the molar concentration of furfural.

4. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to claim 3, wherein: The amount of H2O2 used is 50 to 110 times the molar concentration of furfural.

5. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to claim 4, wherein: The volume ratio of the methanol to the buffer solution is 9:2-7:

4.

6. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to claim 5, characterized in that: The reaction conditions are as follows: temperature 25-35° C., rotation speed 150±50 rpm, and time 48±12 h.

7. The method for synthesizing maleic acid by photocatalytic oxidation of furfural according to any one of claims 1 to 6, wherein: The conditions for the light reaction are: the light source is a 530 nm-540 nm LED lamp with a power of 30±20W.

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