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

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application 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

[0002] Hydrogen peroxide (H2O2) as a strong oxidant has been widely used in industrial and domestic fields, including wastewater treatment, chemical synthesis, industrial bleaching, energy storage, medical disinfection, and has become a very promising energy carrier in fuel cells. Under the background of green and sustainable development, the demand for hydrogen peroxide is increasing rapidly, and it is estimated that by 2027, the market share of H2O2 in the world will reach about 5.7 million tons, and its influence in the field of sustainable energy will be greater and greater. The traditional production method of H2O2 is mainly based on 2-ethylanthraquinone method, but it involves the introduction of hydrogen and the catalysis of noble metal catalysts in the preparation process. This leads to the difficulty in ensuring the safety of traditional processes, and it does not have green and sustainable development, which does not meet the development needs of today's society.

[0003] The photocatalytic production of H2O2 technology itself has the advantages of green, clean, low consumption, safety, stability, etc., which is to convert H2O or O2 into H2O2 using solar energy. In the process of photocatalytic production of H2O2, solar energy is used as the energy source, and green reactants are used as the substrate under the conditions of natural environment and pressure. It meets the current social demand for sustainable development, and is expected to become an ideal method to replace traditional processes.

[0004] However, the main reasons that limit the photocatalytic production of H2O2 technology to go on the industrial development include slow H2O2 production rate, poor stability of photocatalysts, and far from meeting the requirements of industrial production. The photocatalytic production rate of H2O2 of most materials stays at the level of μmol g -1 h -1 . Even in the presence of sacrificial agents, the photocatalytic production rate of H2O2 can only reach 0-10 mmol g -1 h -1 . At present, the material with the highest SCC value for photocatalytic production of H2O2 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 and high-efficiency production of H2O2. Therefore, to achieve low consumption, clean, safe and sustainable production of H2O2, it is still necessary to develop new high-efficiency and stable photocatalytic systems. SUMMARY

[0005] The application aims to provide an imine compound as a photocatalyst for photocatalytic production of hydrogen peroxide.

[0006] To achieve the aim, the application provides, in the first aspect, an imine compound as a photocatalyst for photocatalytic production of hydrogen peroxide.

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

[0008]

[0009] Wherein, R is any substituent at any position, and R can be selected from methyl, ethyl, methoxy, amino, hydroxyl, carboxyl, cyano, halogen substituent, benzene ring substituent, etc.

[0010] In the second aspect, the application provides a method for photocatalytic production of hydrogen peroxide, which comprises the following steps: in the presence of an imine compound as a catalyst, oxygen or air is introduced into a two-phase system composed of water (deionized water) and an organic solvent, and hydrogen peroxide is produced under light irradiation (the hydrogen peroxide is derived from the reduction of oxygen), the generated hydrogen peroxide is extracted in situ into the water phase, and the organic solvent in the organic phase is oxidized to generate a high-value-added product. The high-value-added product can be benzaldehyde, n-pentanal, benzoquinone, 2,5-diformylfuran, etc.

[0011] In the application, the hydrogen peroxide is derived from the reduction of oxygen, and oxygen or air is introduced into the reactor during the reaction process.

[0012] Further, the organic solvent and water are mixed in any volume ratio. The organic solvent and water are immiscible, and the organic solvent includes aromatic compounds and aliphatic compounds.

[0013] Preferably, the organic solvent includes, but is not limited to, the following types: high-molecular-weight aliphatic alcohols (butanol, pentanol, hexanol, etc.), halogen-substituted alkanes (dichloromethane, dichloroethane, etc.), aromatic alkanes (toluene, xylene, heavy aromatic hydrocarbon, etc.), aromatic alcohols (phenol, hydroquinone, benzyl alcohol, phenethyl alcohol, etc.), and aromatic amines (aniline, N,N-dimethylaniline, N-methyl-N-ethylaniline, etc.).

[0014] Further, the method comprises the following steps:

[0015] S1, dissolving the imine compound in the organic solvent, and ultrasonic treatment to ensure complete dissolution of the imine compound;

[0016] S2, adding water with the same volume as the organic solvent containing the imine compound to form a two-phase system of water-organic solvent containing the catalyst;

[0017] S3, transferring the prepared two-phase system to a light reaction container made of light-transmissive material (such as quartz) to ensure that the catalyst system can fully absorb light;

[0018] 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;

[0019] S5, adding light to drive the photocatalytic reaction in the light reactor, and continuously passing oxygen or air during the light irradiation, and controlling the temperature at 0-100℃;

[0020] S6, after a period of reaction, when the hydrogen peroxide in the water phase reaches the required concentration, separating the water phase from the organic phase to obtain pure hydrogen peroxide solution;

[0021] S7, re-adding water to the above organic phase to continue to produce hydrogen peroxide.

[0022] Further, in steps S4 and S5, the flow rate of oxygen or air is 100-1000 mL / min, and the reaction pressure is 1 atm.

[0023] Further, in step S5, the light is one or more of xenon lamp light, sunlight irradiation, and LED light, the wavelength of the light is 200-800 nm, and the intensity is 10-1000 mW / cm 2 .

[0024] In the present application, the catalyst can be recycled.

[0025] The present application 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 for the oxygen reduction reaction under light irradiation to produce hydrogen peroxide. The nitrogen atom in the imine structure small molecule acts as an active center for oxygen reduction to generate hydrogen peroxide. The imine small molecule is dissolved in an organic solvent and forms a two-phase system with water. While the hydrogen peroxide is generated by the reduction of oxygen under light irradiation, the organic solvent can be oxidized to generate higher value-added products. The generated hydrogen peroxide is extracted in situ into the water phase, increasing the rate of photocatalytic production of hydrogen peroxide and ensuring the stability of the catalyst.

[0026] By the above technical solution, the present application has at least the following advantages and beneficial effects:

[0027] (1) The photocatalytic reaction system of the present application is simple to prepare, low in cost, and mild in reaction conditions.

[0028] (II) The photocatalytic reaction system of the application has high stability and fast reaction rate for photocatalytic production of hydrogen peroxide.

[0029] (III) The photocatalytic reaction system of the application can simultaneously produce higher value-added oxidation products, and has higher economic value. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The figure is a curve of H2O2 concentration produced by the pyridine molecular catalyst in the water-n-pentanol two-phase system in the preferred embodiment of the application, and the horizontal axis represents time, and the vertical axis represents H2O2 concentration.

[0031] Figure 2 The figure is a curve of H2O2 concentration produced by the 1,6-dibromophenazine molecular catalyst in the water-toluene two-phase system in the preferred embodiment of the application, and the horizontal axis represents time, and the vertical axis represents H2O2 concentration.

[0032] Figure 3 The figure is a curve of H2O2 concentration produced by the dihydro-5,7,12,14-tetraazapentacene molecular catalyst in the water-o-xylene system in the preferred embodiment of the application, and the horizontal axis represents time, and the vertical axis represents H2O2 concentration.

[0033] Figure 4 The figure is a photograph of an outdoor flat plate test device of the water-o-xylene two-phase photocatalytic system of the benz[c]cinnoline molecular catalyst in the preferred embodiment of the application.

[0034] Figure 5 The figure is a curve of H2O2 concentration produced by the benz[c]cinnoline molecular catalyst in the water-o-xylene system in the preferred embodiment of the application, and the horizontal axis represents time, and the vertical axis represents H2O2 concentration. DETAILED DESCRIPTION

[0035] The application provides a novel imine small-molecule photocatalyst photocatalytic system for efficient photocatalytic production of hydrogen peroxide.

[0036] The application provides a novel molecular photocatalytic system for photocatalytic production of H2O2. The small molecule is a small molecule with an imine structure, including but not limited to a pyridine small molecule, a pyrazine small molecule, a pyridazine small molecule, a pyrimidine small molecule, a phenazine small molecule, a cinnoline small molecule, a phenothiazine small molecule, a phenoxazine small molecule, etc.

[0037] The catalytic system is a two-phase system composed of water and an organic solvent, the organic solvent and water are immiscible, which can be aromatic compounds or aliphatic compounds. Including but not limited to the following types of organic solvents: high molecular weight aliphatic alcohols (butanol, amyl alcohol, hexanol, etc.), halogen-substituted alkanes (dichloromethane, dichloroethane, etc.), aromatic alkanes (toluene, xylene, heavy aromatic hydrocarbon, etc.), aromatic alcohols (phenol, benzenediol, benzyl alcohol, phenethyl alcohol, etc.), and aromatic amines (aniline, N,N-dimethylaniline, N-methyl-N-ethyl aniline, etc.).

[0038] In the present application, the generation of hydrogen peroxide is driven under light conditions, which is one or more of xenon lamp illumination, sunlight irradiation, LED illumination, and the wavelength range of light is 200-800 nm. The intensity of the light is 10-1000 mW / cm 2 .

[0039] In the two-phase system described in the present application, the imine small molecule is dissolved and dispersed in the organic phase, which can reduce the oxygen dissolved in the organic solvent to H2O2 under light conditions, and the generated hydrogen peroxide is quickly extracted into the water phase. This process not only improves the production rate of H2O2, but also protects the small molecule catalyst and increases the light stability of the catalytic system.

[0040] In the two-phase system described in the present application, the imine small molecule catalyst not only reduces oxygen to generate H2O2, but also oxidizes the organic solvent to generate higher value 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.

[0041] When the photocatalytic production of H2O2 reaches the required concentration, H2O2 can be quickly separated, the reaction conditions are mild and the process is green and safe. And the organic phase system can be recycled and used in batch reaction.

[0042] The pyridine small molecule photocatalytic system photocatalytically produces H2O2 as follows:

[0043] S1, a certain amount of pyridine molecules are dissolved in an organic solvent that is immiscible with water, and ultrasonic is used to ensure that the pyridine molecules are completely dissolved.

[0044] S2, add a certain volume (such as equal volume) of aqueous solution to the above pyridine organic solvent to form a water-organic solvent two-phase system.

[0045] S3, transfer the prepared two-phase system catalytic liquid to a quartz light reaction container to ensure that the catalytic system can fully absorb light.

[0046] S4, oxygen or air is continuously introduced into the above-mentioned two-phase system for 10-30 min, so that the dissolved oxygen in the two-phase system reaches a saturated state.

[0047] S5, light-driven reaction is added in the photoreactor, the light is one or more of sunlight irradiation, xenon lamp irradiation, LED irradiation, the wavelength range of the light is 300-800 nm, the intensity of the light is 100-3000 mW / cm 2 During the irradiation process, oxygen or air is continuously introduced, and the temperature is controlled at 0-100℃.

[0048] S6, after a period of time of photocatalytic reaction, when the H2O2 in the aqueous phase reaches the required concentration, the aqueous phase is separated from the organic phase to obtain a pure H2O2 solution.

[0049] S7, after adding new pure water in the above-mentioned organic phase, the production of H2O2 can be continued.

[0050] The following examples are used to illustrate the present application, but not to limit the scope of the present application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art, and the raw materials used are commercially available.

[0051] Example 1

[0052] 0.80 g of pyridine was weighed and dissolved in 20 mL of n-pentanol solution by ultrasonic treatment.

[0053] 20 mL of deionized water was added to the above-mentioned n-pentanol solution of pyridine molecules to form a two-phase system of water-ortho-xylene or water-n-pentanol.

[0054] The above-mentioned two-phase reaction solution was transferred to a quartz glass photoreactor, and 80-100 mL min -1 of oxygen was continuously introduced at a flow rate of 80-100 mL min -2 for 30 min.

[0055] A 100 W xenon lamp with a light density of 100 mW cm -2 and a 420 nm filter was used as a light source to continuously irradiate the reaction system in the photoreactor, and oxygen was continuously introduced during the irradiation process, and the reaction temperature was controlled at 25℃.

[0056] The H2O2 concentration in the aqueous solution of the two-phase system was tested at different reaction time points.

[0057] When the H2O2 concentration in the aqueous phase reaches the required concentration, the oxygen is turned off, the light source is turned off, and the organic solvent and the hydrogen peroxide solution are separated, then the H2O2 solution is taken out, and then new deionized water is added to produce the next batch of H2O2.

[0058] In this embodiment, the high value-added product generated in the organic phase is n-pentanal.

[0059] The plot of the concentration of H2O2 produced by the pyridine molecular catalyst in the water-n-pentanol two-phase system versus time is shown in Figure 1. Figure 1 .

[0060] Embodiment 2

[0061] This embodiment provides a method for producing H2O2 using a photo-catalytic system constructed using 1,6-dibromophenazine as a photo-catalyst, and the process is as follows:

[0062] 2.27 g of 1,6-dibromophenazine was placed in 100 mL of toluene and ultrasonicated until the 1,6-dibromophenazine was completely dissolved.

[0063] 100 mL of deionized water was added to the above toluene solution of 1,6-dibromophenazine to form a water-toluene two-phase system.

[0064] The above two-phase reaction solution was transferred to a 2 L beaker, and air was continuously introduced at a flow rate of 800-1000 mL / min under the liquid surface for 30 min. -1

[0065] The system was continuously irradiated with outdoor sunlight as the light source, and air was continuously introduced during the irradiation process.

[0066] The concentration of H2O2 in the aqueous solution of the two-phase system was tested at different reaction times.

[0067] When the concentration of H2O2 in the aqueous phase reached the required value, the air was turned off, and after the organic solvent and hydrogen peroxide solution were separated, the H2O2 solution was removed, and then new deionized water was added to produce the next batch of H2O2.

[0068] In this embodiment, the high value-added product generated in the organic phase is benzaldehyde.

[0069] The plot of the concentration of H2O2 produced by the 1,6-dibromophenazine molecular catalyst in the water-toluene two-phase system versus time is shown in Figure 2. Figure 2 .

[0070] Embodiment 3

[0071] This embodiment provides a method for producing H2O2 using a photo-catalytic system constructed using dihydro-5,7,12,14-tetranaphthoquinone (DHQP) as a photo-catalyst, and the process is as follows:

[0072] ​Take 0.285 g DHQP and place it in 20 mL o-xylene solution, and ultrasonic until DHQP is completely dissolved.

[0073] Add 20 mL deionized water to the above DHQP o-xylene solution to form a water-dichloromethane two-phase system.

[0074] Transfer the above two-phase reaction solution to a quartz glass photo-reactor, and continuously pass 80-100 mL / min of air under the liquid surface for 30 min. -1 The flow rate of the oxygen gas is 80-100 mL / min.

[0075] Use a 100 W xenon lamp with a light density of 100 mW cm -2 , and a 420 nm filter as the light source to continuously illuminate the reaction system in the photo-reactor. The oxygen gas is continuously passed during the illumination process, and the reaction temperature is controlled at 25°C.

[0076] Test the H2O2 concentration in the aqueous solution in the two-phase system at different reaction time points.

[0077] When the H2O2 concentration in the aqueous phase reaches the required value, turn off the oxygen and light source, and let the organic solvent and hydrogen peroxide solution separate. Then take out the H2O2 solution, and add new deionized water to produce the next batch of H2O2.

[0078] In this example, the high-value product generated in the organic phase is phthalic anhydride.

[0079] The H2O2 concentration produced by the DHQP molecular catalyst in the water-o-xylene system changes with time, as shown in the graph Figure 3 .

[0080] Example 4

[0081] This example provides a method for producing H2O2 using a photo-catalytic system constructed with benz[c]cinnoline as a photo-catalyst. The process is as follows:

[0082] Take 10.0 g of benz[c]cinnoline and place it in 1000 mL of benzyl alcohol solution, and ultrasonic until the benz[c]cinnoline is completely dissolved.

[0083] Add 500 mL of deionized water to the above benz[c]cinnoline benzyl alcohol solution to form a water-benzyl alcohol two-phase system.

[0084] Transfer the above two-phase reaction solution to a flat-plate outdoor photo-reactor, and continuously pass 800-1000 mL / min of air under the liquid surface for 30 min. -1 The flow rate of the oxygen gas is 80-100 mL / min.

[0085] The system is continuously lighted by adding outdoor sunlight as light source, and air is continuously introduced during the light process.

[0086] The H2O2 concentration of the aqueous solution in the two-phase system is tested at different reaction time points.

[0087] When the H2O2 concentration in the aqueous phase reaches the required value, the air is turned off, and the organic solvent and the hydrogen peroxide solution are separated. Then, the H2O2 solution is taken out, and the production of the next batch of H2O2 can be carried out by adding new deionized water.

[0088] In this embodiment, the high-value-added product generated in the organic phase is benzaldehyde.

[0089] Figure 4 The photo of the outdoor flat test device of the benz[c]cumene molecular catalyst in the water-o-xylene two-phase photocatalytic system.

[0090] The curve of the H2O2 concentration produced by the benz[c]cumene molecular catalyst in the water-o-xylene system with time is shown in Figure 5 .

[0091] Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of the present application claimed.

Claims

1. A method for photocatalytically producing hydrogen peroxide from oxygen molecules, characterized in that, In the presence of a catalyst, oxygen or air is introduced into a two-phase system consisting of water and organic solvent. Hydrogen peroxide is generated under light irradiation. The generated hydrogen peroxide is extracted in situ into the aqueous phase, while the organic solvent in the organic phase is oxidized to generate high-value-added products. The catalyst is a pyridine compound with the following structure: ； Wherein, R is any substituent at any position, and R is selected from methyl, ethyl, methoxy, amino, hydroxy, carboxyl, cyano, halogen substituents, and benzene ring substituents; or, The catalyst is dihydro-5,7,12,14-tetraazapentabenzene.

2. The method according to claim 1, characterized in that, The organic solvent and water are mixed in any volume ratio.

3. The method according to claim 1, characterized in that, The organic solvent is immiscible with water; The organic solvent is selected from one or more of butanol, pentanol, hexanol, dichloromethane, dichloroethane, toluene, xylene, benzyl alcohol, and phenethyl alcohol.

4. The method according to claim 1, characterized in that, Includes the following steps: S1. Dissolve the catalyst in the organic solvent and sonicate to ensure complete dissolution of the catalyst; S2. Add a certain volume of water to the above-mentioned organic solvent containing the catalyst to form a catalyst-water biphase system. S3. Transfer the prepared two-phase system to a photoreaction container made of a light-transmitting material to ensure that the catalytic system fully absorbs light. S4. Introduce oxygen or air into the above two-phase system for 10-30 minutes to saturate the dissolved oxygen in the two-phase system. S5. Light is added to the photoreactor to drive the photocatalytic reaction. During the light irradiation process, oxygen or air is continuously introduced and the temperature is controlled at 0~100℃. S6. After the reaction has proceeded for a period of time, when the hydrogen peroxide in the aqueous phase reaches the required concentration, the aqueous phase and the organic phase are separated to obtain a pure hydrogen peroxide solution. S7. Water is added back to the above organic phase to continue the production of hydrogen peroxide.

5. The method according to claim 4, 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.

6. The method according to claim 4, characterized in that, In step S5, the illumination is one or more of xenon lamp illumination, solar irradiation, and LED illumination, with a wavelength of 200~800 nm and an intensity of 10~1000 mW / cm². 2 .

7. The method according to any one of claims 1-6, characterized in that, The catalyst is recycled.

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