Application of imine compound as photocatalyst in photocatalytic production of hydrogen peroxide

Abstract

The invention discloses an application of an imine compound as a photocatalyst in photocatalytic production of hydrogen peroxide. The imine micromolecules are used as a photocatalyst for oxygen reduction reaction under illumination to generate hydrogen peroxide. The used system is a two-phase system composed of water and an organic solvent, the photocatalyst exists in an organic phase, generated hydrogen peroxide is extracted into a water phase in situ, and meanwhile, the organic solvent in the organic phase is oxidized to generate a high-added-value product. The photocatalytic reaction system has the excellent characteristics of simplicity in preparation, low cost, mild reaction conditions, high stability, high reaction rate and the like, and has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the field of photocatalytic preparation of hydrogen peroxide, in particular to the application of imine compounds as photocatalysts in photocatalytic production of hydrogen peroxide. Background Art

[0002] As a strong oxidant, hydrogen peroxide (H2O2) has been widely used in industrial and domestic fields, including wastewater treatment, chemical synthesis, industrial bleaching, energy storage, medical disinfection, etc., and has become a promising energy carrier in fuel cells. In the context of green and sustainable development, the demand for hydrogen peroxide is increasing rapidly. It is estimated that by 2027, the global market share of H2O2 will reach about 5.7 million tons, and its influence in the field of sustainable energy will become increasingly greater. The traditional production method of H2O2 is mainly based on the 2-ethylanthraquinone method, but its preparation process involves the introduction of hydrogen and the catalysis of precious metal catalysts. This makes it difficult to ensure the safety of traditional processes, and they are not green and sustainable, and do not meet the development needs of today's society.

[0003] The photocatalytic H2O2 production technology itself has the advantages of being green, clean, low-consumption, safe, and stable. Specifically, it uses solar energy to convert H2O or O2 into H2O2. In the process of photocatalytic H2O2 production, sunlight is used as an energy source and green reactants are used as substrates under mild conditions of natural environment and pressure. It meets the needs of sustainable development in the current society and is expected to become an ideal method to replace traditional processes.

[0004] However, the main reasons that limit the industrial development of photocatalytic H2O2 production technology include slow H2O2 production rate and poor stability of photocatalysts, which are far from meeting the requirements of industrial production. The photocatalytic H2O2 production rate of most materials remains at μmol g -1 h -1 Even in the presence of sacrificial agents, the photocatalytic H2O2 production rate can only reach 0-10 mmol g -1 h -1 At present, the material with the highest SCC value for photocatalytic H2O2 production is the phenolic resin prepared by Liu et al., which has an SCC value of 1.2% and a H2O2 production rate of 1820 μmol g -1 h -1 This is far from meeting the needs of industrial production. In addition, such materials usually have poor light stability and are not suitable for long-term high-efficiency production of H2O2. Therefore, in order to achieve low-consumption, clean, safe and sustainable H2O2 production, it is still necessary to develop a new type of efficient and stable photocatalytic system. Summary of the invention

[0005] The purpose of the present invention is to provide a scheme for using imine compounds as photocatalysts in photocatalytic production of hydrogen peroxide.

[0006] In order to achieve the purpose of the present invention, in a first aspect, the present invention provides the use of an imine compound as a photocatalyst in photocatalytic production of hydrogen peroxide.

[0007] The imine compound can be selected from pyridine, pyrazine, pyridazine, pyrimidine, phenazine, cinnoline, phenothiazine, phenoxazine small molecule compounds, and their structures are as follows:

[0008] Wherein, R is any substituent at any position, and R can be selected from methyl, ethyl, methoxy, amino, hydroxyl, carboxyl, cyano, halogen element substituent, benzene ring substituent, etc.

[0009] In the second aspect, the present invention provides a method for photocatalytically generating hydrogen peroxide from oxygen molecules, wherein oxygen or air is introduced into a two-phase system consisting of water (deionized water) and an organic solvent in the presence of a catalyst imine compound, and hydrogen peroxide (the hydrogen peroxide is derived from the reduction of oxygen) is generated under light conditions, and the generated hydrogen peroxide is extracted in situ into the water phase, while the organic solvent in the organic phase is oxidized to generate high value-added products, such as benzaldehyde, n-valeraldehyde, benzoquinone, 2,5-diformylfuran, etc.

[0010] In the present invention, hydrogen peroxide comes from the reduction of oxygen, and oxygen or air needs to be introduced into the reactor during the reaction process.

[0011] Furthermore, the organic solvent and water are mixed in any volume ratio. The organic solvent is immiscible with water, and the organic solvent includes aromatic compounds and aliphatic compounds.

[0012] Preferably, the organic solvent includes but is not limited to the following categories: high molecular weight fatty alcohols (butanol, pentanol, hexanol, etc.), halogen element substituted alkanes (dichloromethane, dichloroethane, etc.), aromatic alkanes (toluene, xylene, heavy aromatics, etc.), aromatic alcohols (phenol, hydroquinone, benzyl alcohol, phenylethyl alcohol, etc.) and aromatic amines (aniline, N,N-dimethylaniline, N-methyl-N-ethylaniline, etc.).

[0013] Furthermore, the method comprises the following steps: S1, dissolving the imine compound in the organic solvent, and performing ultrasound to ensure that the imine compound is completely dissolved; S2, adding a certain volume (such as an equal volume) of water to the organic solvent containing the imine compound to form a two-phase system of water-organic solvent containing the catalyst; S3, transferring the configured two-phase system to a light reaction container made of a light-transmitting material (such as quartz) to ensure that the catalytic system can fully absorb light; S4, introducing oxygen or air into the above two-phase system for 10-30 min, so that the dissolved oxygen in the two-phase system reaches a saturated state; S5, adding light to the photoreactor to drive the photocatalytic reaction, during the light irradiation process, continuously introducing oxygen or air, and controlling the temperature at 0-100°C; S6. After a period of reaction, when the hydrogen peroxide in the aqueous phase reaches a desired concentration, the aqueous phase is separated from the organic phase to obtain a pure hydrogen peroxide solution; S7. Adding water again into the organic phase can continue to produce hydrogen peroxide.

[0014] Furthermore, in steps S4 and S5, the flow rate of oxygen or air is 100-1000 mL / min, and the reaction pressure is 1 atm.

[0015] Furthermore, in step S5, the illumination is one or more of xenon lamp illumination, sunlight irradiation, and LED illumination, and the wavelength of the light is 200-800 nm and the intensity is 10-1000 mW / cm 2 .

[0016] In the present invention, the catalyst can be recycled.

[0017] The present invention relates to the application of an imine small molecule photocatalytic system in the photocatalytic production of hydrogen peroxide. The imine small molecule is used as a photocatalyst to produce hydrogen peroxide by oxygen reduction reaction under light. The nitrogen atom in the imine structure small molecule acts as an active center for oxygen reduction to produce hydrogen peroxide by oxygen reduction. The imine small molecule is dissolved in an organic solvent and forms a two-phase system consisting of water-organic solvent with water. While light-induced oxygen reduction produces hydrogen peroxide, the organic solvent can be oxidized to produce a product with higher added value. The generated hydrogen peroxide is extracted in situ into the water phase, which increases the rate of photocatalytic production of hydrogen peroxide and ensures the stability of the catalyst.

[0018] By means of the above technical solution, the present invention has at least the following advantages and beneficial effects: (i) The photocatalytic reaction system of the present invention is simple to prepare, low in cost, and has mild reaction conditions.

[0019] (ii) The photocatalytic reaction system of the present invention has high stability and a fast reaction rate for photocatalytic production of hydrogen peroxide.

[0020] (III) The photocatalytic reaction system of the present invention can simultaneously prepare oxidation products with higher added value, thereby generating higher economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a curve diagram showing the change in H2O2 concentration over time by photocatalytic production of pyridine molecular catalyst in a water-n-pentanol two-phase system in a preferred embodiment of the present invention.

[0022] Figure 2 This is a curve diagram showing the change in H2O2 concentration over time by photocatalytic production of 1,6-dibromophenazine molecular catalyst in a water-toluene two-phase system in a preferred embodiment of the present invention.

[0023] Figure 3 This is a curve of the change in H2O2 concentration over time of the photocatalytic production of dihydro-5,7,12,14-tetraazapentacene molecular catalyst in a water-o-xylene system in a preferred embodiment of the present invention.

[0024] Figure 4 This is a photo of an outdoor flat-plate test device for the benzo[c]cinnoline molecular catalyst in a water-o-xylene dual-phase photocatalytic system in a preferred embodiment of the present invention.

[0025] Figure 5 This is a graph showing the change in H2O2 concentration over time by the photocatalytic production of benzo[c]cinnoline molecular catalyst in a water-o-xylene system in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0026] The invention provides a novel photocatalytic system with imine small molecules as the main photocatalyst for efficient photocatalytic production of hydrogen peroxide.

[0027] The present invention provides a novel molecular photocatalytic system for photocatalytic H2O2 production. The small molecule is a small molecule with an imine structure, including but not limited to pyridine small molecules, pyrazine small molecules, pyridazine small molecules, pyrimidine small molecules, phenazine small molecules, cinnoline small molecules, phenothiazine small molecules, phenoxazine small molecules, etc.

[0028] The catalytic system is a two-phase system composed of water and an organic solvent. The organic solvent and water are immiscible, and the organic solvent can be an aromatic compound or an aliphatic compound, including but not limited to the following organic solvents: high molecular weight aliphatic alcohols (butanol, pentanol, hexanol, etc.), halogen element substituted alkanes (dichloromethane, dichloroethane, etc.), aromatic alkanes (toluene, xylene, heavy aromatics, etc.), aromatic alcohols (phenol, hydroquinone, benzyl alcohol, phenylethyl alcohol, etc.) and aromatic amines (aniline, N,N-dimethylaniline, N-methyl-N-ethylaniline, etc.).

[0029] In the present invention, the generation of hydrogen peroxide is driven under illumination conditions, wherein the illumination is one or more of xenon lamp illumination, sunlight irradiation, and LED illumination, and the wavelength of the light is in the range of 200 to 800 nm. The intensity of the illumination is 10 to 1000 mW / cm2 .

[0030] In the two-phase system described in the present invention, the imine small molecules are dissolved and dispersed in the organic phase. Under light conditions, they can reduce the oxygen dissolved in the organic solvent to H2O2. The subsequently produced hydrogen peroxide is quickly extracted into the aqueous phase. This process can not only increase the production rate of H2O2 but also protect the small molecule catalyst and increase the photostability of the catalytic system.

[0031] In the two-phase system described in the present invention, while the imine molecular catalyst reduces oxygen to generate H2O2, it may also oxidize the organic solvent to generate higher value-added products. This not only improves the rate of photocatalytic production of H2O2, but also reduces the cost of H2O2 and improves the value of the photocatalytic system.

[0032] When the H2O2 produced by photocatalysis reaches the required concentration, the H2O2 can be quickly separated. The reaction conditions are mild and the process is green and safe. In addition, the organic phase system can be recycled in intermittent batch reactions.

[0033] Among them, the process and steps of photocatalytic production of H2O2 by pyridine small molecule photocatalytic system are as follows: S1. Dissolve a certain amount of pyridine molecules in an organic solvent that is immiscible with water, and use ultrasound to ensure that the pyridine molecules are completely dissolved.

[0034] S2. Add a certain volume (such as equal volume) of aqueous solution to the above-mentioned pyridine molecule organic solvent to form a water-organic solvent two-phase system.

[0035] S3. Transfer the prepared two-phase system catalytic liquid to a quartz photoreaction container to ensure that the catalytic system can fully absorb light.

[0036] S4. Passing oxygen or air into the above two-phase system for 10-30 min to make the dissolved oxygen in the two-phase system reach a saturated state.

[0037] S5. Adding illumination to the photoreactor to drive the reaction, wherein the illumination is one or more of sunlight, xenon lamp illumination, and LED illumination, with a wavelength range of 300-800 nm and an intensity of 100-3000 mW / cm 2 During the illumination process, oxygen or air is continuously introduced and the temperature is controlled at 0~100℃.

[0038] S6. After a period of photocatalytic reaction, when the H2O2 in the water phase reaches the required concentration, the water phase and the organic phase are separated to obtain a pure H2O2 solution.

[0039] S7. After adding new pure water to the above organic phase, H2O2 can continue to be produced.

[0040] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products.

[0041] Example 1

[0042] Weigh 0.80 g of pyridine and place it in 20 mL of n-pentanol solution, and sonicate until the pyridine is completely dissolved.

[0043] 20 mL of deionized water was added to the above n-pentanol solution of pyridine molecules to form a two-phase system of water-o-xylene or water-n-pentanol.

[0044] The above two-phase reaction solution was transferred to a quartz glass photoreactor and passed 80-100 mL min -1 Oxygen was continuously introduced at a flow rate of 30 min.

[0045] The light intensity is 100 mW cm -2 A 100 W xenon lamp equipped with a 420 nm filter was used as the light source to continuously illuminate the reaction system in the photoreactor. Oxygen was continuously introduced during the illumination process, and the reaction temperature was controlled at 25°C.

[0046] The H2O2 concentration of the aqueous solution in the two-phase system was tested at different reaction time points.

[0047] When the H2O2 concentration in the water phase reaches the required level, turn off the oxygen and light source, let the organic solvent and hydrogen peroxide solution stand for separation, take out the H2O2 solution, and then add new deionized water to produce the next batch of H2O2.

[0048] In this embodiment, the high value-added product generated in the organic phase is n-valeraldehyde.

[0049] The curve of H2O2 concentration produced by photocatalysis of pyridine molecular catalyst in water-n-pentanol two-phase system over time is shown in Figure 1 .

[0050] Example 2

[0051] This embodiment provides a method for producing H2O2 using a photocatalytic system constructed with 1,6-dibromophenazine as a photocatalyst, and the process is as follows: 2.27 g of 1,6-dibromophenazine was placed in 100 mL of toluene and ultrasonicated until 1,6-dibromophenazine was completely dissolved.

[0052] 100 mL of deionized water was added to the above 1,6-dibromophenazine toluene solution to form a water-toluene two-phase system; Transfer the above two-phase reaction solution to a 2 L beaker and pass 800-1000 mL min -1 Air was continuously passed through the chamber at a flow rate of 1.5 % for 30 min.

[0053] The system is continuously illuminated by adding outdoor sunlight as the light source, and air is continuously ventilated during the illumination process.

[0054] The H2O2 concentration of the aqueous solution in the two-phase system was tested at different reaction time points.

[0055] When the H2O2 concentration in the water phase reaches the required level, turn off the air, let the organic solvent and hydrogen peroxide solution stand for separation, take out the H2O2 solution, and then add new deionized water to produce the next batch of H2O2.

[0056] In this embodiment, the high value-added product generated in the organic phase is benzaldehyde.

[0057] The curve of H2O2 concentration produced by photocatalysis of 1,6-dibromophenazine molecular catalyst in water-toluene two-phase system over time is shown in Figure 2 .

[0058] Example 3

[0059] This embodiment provides a method for producing H2O2 using a photocatalytic system constructed with dihydro-5,7,12,14-tetraazapentacene (DHQP) as a photocatalyst, and the overall process is as follows: Weigh 0.285 g of DHQP and place it in 20 mL of o-xylene solution, and sonicate until DHQP is completely dissolved.

[0060] 20 mL of deionized water was added to the above DHQP o-xylene solution to form a water-dichloromethane two-phase system; The above two-phase reaction solution was transferred to a quartz glass photoreactor and passed 80-100 mL min -1 Oxygen was continuously introduced at a flow rate of 30 min.

[0061] The light intensity is 100 mW cm -2 A 100 W xenon lamp equipped with a 420 nm filter was used as the light source to continuously illuminate the reaction system in the photoreactor. Oxygen was continuously introduced during the illumination process, and the reaction temperature was controlled at 25 °C.

[0062] The H2O2 concentration of the aqueous solution in the two-phase system was tested at different reaction time points.

[0063] When the H2O2 concentration in the water phase reaches the required level, turn off the oxygen and light source, let the organic solvent and hydrogen peroxide solution stand for separation, take out the H2O2 solution, and then add new deionized water to produce the next batch of H2O2.

[0064] In this embodiment, the high value-added product generated in the organic phase is phthalic anhydride.

[0065] The curve of H2O2 concentration produced by photocatalysis of DHQP molecular catalyst in water-o-xylene system over time is shown in Figure 3 .

[0066] Example 4

[0067] This embodiment provides a method for producing H2O2 using a photocatalytic system constructed with benzo[c]cinnoline as a photocatalyst, and the overall process is as follows: Weigh 10.0 g of benzo[c]cinnoline and place it in 1000 mL of benzyl alcohol solution. Ultrasonicate until the benzo[c]cinnoline is completely dissolved.

[0068] 500 mL of deionized water was added to the benzyl alcohol solution of benzo[c]cinnoline to form a water-benzyl alcohol biphasic system; The above two-phase reaction solution was transferred to a flat outdoor photoreactor and a flow rate of 800-1000 mL / min was passed under the liquid surface. -1 Air was continuously passed through the chamber at a flow rate of 1.5 % for 30 min.

[0069] The system is continuously illuminated by adding outdoor sunlight as the light source, and air is continuously ventilated during the illumination process.

[0070] The H2O2 concentration of the aqueous solution in the two-phase system was tested at different reaction time points.

[0071] When the H2O2 concentration in the water phase reaches the required level, turn off the air, let the organic solvent and hydrogen peroxide solution stand for separation, take out the H2O2 solution, and then add new deionized water to produce the next batch of H2O2.

[0072] In this embodiment, the high value-added product generated in the organic phase is benzaldehyde.

[0073] Figure 4 This is a photo of the outdoor flat-plate test device of benzo[c]cinnoline molecular catalyst in the water-o-xylene dual-phase photocatalytic system.

[0074] The curve of H2O2 concentration produced by photocatalysis of benzo[c]cinnoline molecular catalyst in water-o-xylene system over time is shown in Figure 5 .

[0075] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. Application of imine compounds as photocatalysts in photocatalytic production of hydrogen peroxide; The imine compound is selected from pyridine, pyrazine, pyridazine, pyrimidine, phenazine, cinnoline, phenothiazine, phenoxazine small molecule compounds, and their structures are as follows: in, R is any substituent at any position, and R is selected from methyl, ethyl, methoxy, amino, hydroxyl, carboxyl, cyano, halogen element substituent, and benzene ring substituent.

2. A method for photocatalytically generating hydrogen peroxide from oxygen molecules, characterized in that: In the presence of a catalyst imine compound, oxygen or air is introduced into a two-phase system consisting of water and an organic solvent, hydrogen peroxide is generated under light conditions, and the generated hydrogen peroxide is extracted in situ into the water phase, while the organic solvent in the organic phase is oxidized to generate a high value-added product; The imine compound is the same as that described in claim 1.

3. The method according to claim 2, characterized in that The organic solvent and water are mixed in any volume ratio.

4. The method according to claim 2, characterized in that: The organic solvent is immiscible with water, and the organic solvent includes aromatic compounds and aliphatic compounds; Preferably, the organic solvent is selected from one or more of butanol, pentanol, hexanol, dichloromethane, dichloroethane, toluene, xylene, heavy aromatics, benzyl alcohol, and phenylethyl alcohol.

5. The method according to claim 2, characterized in that: The following steps are involved: S1, dissolving the imine compound in the organic solvent, and performing ultrasound to ensure that the imine compound is completely dissolved; S2, adding a certain volume of water to the organic solvent containing the imine compound to form an organic solvent-water two-phase system containing a catalyst; S3, transferring the configured two-phase system to a light reaction container made of a light-transmitting material to ensure that the catalytic system can fully absorb light; S4, introducing oxygen or air into the above two-phase system for 10-30 min, so that the dissolved oxygen in the two-phase system reaches a saturated state; S5, adding light to the photoreactor to drive the photocatalytic reaction, during the light irradiation process, continuously introducing oxygen or air, and controlling the temperature at 0-100°C; S6. After a period of reaction, when the hydrogen peroxide in the aqueous phase reaches a desired concentration, the aqueous phase is separated from the organic phase to obtain a pure hydrogen peroxide solution; S7. Adding water again into the organic phase can continue to produce hydrogen peroxide.

6. The method according to claim 5, characterized in that In steps S4 and S5, the flow rate of oxygen or air is 100-1000 mL / min, and the reaction pressure is 1 atm.

7. The method according to claim 5, characterized in that In step S5, the illumination is one or more of xenon lamp illumination, sunlight irradiation, and LED illumination, the wavelength of the light is 200-800 nm, and the intensity of the illumination is 10-1000 mW / cm 2 .

8. The method according to any one of claims 2 to 7, characterized in that: The catalyst can be recycled.

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