Method for photocatalytic oxidation desulfurization of fuel oil and defective carbon nitride photocatalyst

Abstract

The application discloses a kind of fuel system photocatalytic oxidation desulfurization method and catalyst, the desulfurization method includes the following steps: (1) under normal temperature and pressure conditions, using defective carbon nitride as photocatalyst, with oxygen or air as oxidant, under 300nm < λ < 1500nm wavelength, to the fuel catalytic desulfurization, while using extractant to extract the sulfur oxidation product generated in reaction.The desulfurization method realizes catalytic oxidation-extraction desulfurization coupling in one step, with excellent fuel desulfurization efficiency.Even in the case of complex components such as naphthenes, aromatics and other competitive oxidation, benzothiophene, dibenzothiophene and 4,6-dimethyl dibenzothiophene and other difficult to remove aromatic heterocyclic thiophene sulfides in simulated gasoline / diesel can still be selectively removed with high efficiency, and has good application prospect in the field of fuel catalytic oxidation desulfurization.

Description

TECHNICAL FIELD

[0001] The present application relates to a photocatalytic desulfurization method, more particularly to a fuel photocatalytic oxidation desulfurization method and a defective carbon nitride photocatalyst. BACKGROUND

[0002] Sulfur oxides (SOx) emitted by fuel combustion x)Sulfur in gasoline / diesel can cause acid rain and haze, and the sulfur content in gasoline / diesel should be less than 10 ppm according to the national VI standard. Therefore, future desulfurization will become an inevitable trend of fuel standard development. The most common desulfurization method in the petroleum refining industry is hydrodesulfurization (HDS). Compared with inorganic sulfur and alkyl sulfides, aromatic heterocyclic thiophene sulfides (including benzothiophene, dibenzothiophene, 4,6-dimethyl dibenzothiophene, etc.) are difficult to remove due to their conjugated structure and steric hindrance effect, which makes their HDS activity low. In the non-hydrodesulfurization process, the photocatalytic oxidation desulfurization technology uses hydrogen peroxide (H2O2) or oxygen (O2) as the oxidant, and the thiophene sulfur is oxidized to strong polarity sulfoxide or sulfone by the photocatalyst, and then separated from the oil phase by extraction. This is a new emerging desulfurization technology with mild reaction conditions, simple operation and green environmental protection, which can be expected to be applied to the efficient removal of aromatic heterocyclic thiophene sulfides. In the existing photocatalytic oxidation desulfurization technology, H2O2 is often used as the oxidant, but H2O2 has high cost and strong oxidation ability, which can easily cause side reactions and reduce the quality of fuel oil. Therefore, using cheap and environmentally friendly O2 as the oxidant to achieve efficient photocatalytic aerobic oxidation deep desulfurization has become an important technical breakthrough direction in the field of fuel desulfurization. However, the activity of the catalyst used in the photocatalytic aerobic oxidation desulfurization is generally low, and the catalyst is mostly metal oxides or polyoxometalates. The main problems that cause the low catalytic activity are: (1) the low activation efficiency of the catalyst for molecular oxygen, which leads to insufficient concentration of active oxygen species in the reaction process; (2) the weak adsorption capacity of inorganic catalysts for conjugated aromatic heterocyclic thiophene sulfides, which leads to low catalytic activity. Therefore, how to solve the above two problems in the process of photocatalytic oxidation desulfurization is the current key technical bottleneck. Although some existing literature reports and patent applications (such as patents CN201910369737.3, CN201910272345.5 and CN201510664884.5, and papers Energy Fuels, 2020, 34, 13588-13605; J. Photoch. Photobio. A, 2022, 433, 114162) disclose desulfurization catalysts containing g-C3N4, these desulfurization catalysts are composite catalysts such as Au-TiO2@C3N4, Ag2O / Na-g-C3N4 and Ti3C2 / g-C3N4 (Inorg. Chem. Front., 2020, 7, 1212-1219; Appl. Catal. B: Environ., 2020, 269, 118845; Appl. Catal. B: Environ., 2022, 316, 121614), which generally use the planar structure of g-C3N4 as the characteristic of the catalyst carrier, and other supports as the catalytically active unit. These composite catalysts containing g-C3N4 generally have complex components and complicated preparation processes.

[0003] Therefore, there is a need for a new method of photocatalytic oxidation desulfurization of fuel oil. SUMMARY

[0004] In view of the problems in the prior art of photocatalytic aerobic oxidation desulfurization, the present application provides a new method of photocatalytic oxidation desulfurization of fuel oil. The method uses a defective carbon nitride photocatalyst to remove aromatic heterocyclic thiophene sulfides in fuel oil through photocatalytic oxidation-extraction desulfurization technology in one step, thereby obtaining low-sulfur clean fuel oil. To achieve the purpose of the present application, the technical solutions of the present application are as follows:

[0005] A method of photocatalytic oxidation desulfurization of fuel oil, comprising the steps of: (1) under normal temperature and pressure conditions, using defective carbon nitride as a photocatalyst, oxygen or air as an oxidant, and a wavelength of 300 nm < λ < 1500 nm, photocatalytically desulfurizing the fuel oil, and simultaneously using an extractant to extract the sulfur-containing products generated in the reaction.

[0006] In another preferred embodiment of the present application, the defective carbon nitride photocatalyst has N 3C site nitrogen defects, and a morphology structure of ultrathin porous nanosheets.

[0007] In another preferred embodiment of the present application, the extractant is acetonitrile.

[0008] In another preferred embodiment of the present application, the preparation method of the defective carbon nitride photocatalyst comprises the following steps:

[0009] (1) calcining a nitrogen and carbon-containing precursor at 400-600°C to obtain an intermediate product after first calcination, and grinding the obtained intermediate product,

[0010] The nitrogen and carbon-containing precursor is selected from a mixture of one or more of melamine, cyanamide, dicyandiamide, ammonium thiocyanate, urea, and thiourea;

[0011] (2) performing secondary calcination of the ground intermediate product at 400-600°C to obtain the defective carbon nitride photocatalyst.

[0012] In another more preferred embodiment of the present application, when the nitrogen and carbon-containing precursor is a mixture of multiple components in step (1), the nitrogen and carbon-containing precursor is first mixed with water, heated and stirred, and the water is evaporated to dryness, so that the different components are fully mixed and uniform, and then calcined.

[0013] In another more preferred embodiment of the present application, step (1) further comprises washing the ground intermediate product to remove impurities. In another more preferred embodiment of the present application, the washing method is to alternately wash with water and alcohol for 2-6 times. Preferably, the alcohol is ethanol.

[0014] In another more preferred embodiment of the present application, step (2) further comprises washing the product of the secondary calcination to remove impurities. In another more preferred embodiment of the present application, the washing is performed by alternately washing with water and alcohol for 2 to 6 times, preferably, the alcohol is ethanol.

[0015] In another more preferred embodiment of the present application, the carbon nitride precursor is selected from a mixture of melamine and urea, or a mixture of melamine and thiourea. In another preferred embodiment of the present application, the mass content of melamine in the mixture of melamine and urea and the mixture of melamine and thiourea is 20 to 50%. In another more preferred embodiment of the present application, the carbon nitride precursor is selected from a mixture of melamine and urea.

[0016] In another preferred embodiment of the present application, the calcination of step (1) is performed by heating from room temperature to 400 to 500°C at a heating rate of 1 to 10°C·min -1 , holding at 400 to 500°C for 2 to 5h; continuing to heat at a rate of 1 to 5°C·min -1 to 500 to 600°C, holding at 500 to 600°C for 2 to 5h, and then naturally cooling to room temperature.

[0017] In another preferred embodiment of the present application, the calcination of step (1) is performed by heating from room temperature to 400 to 500°C at a heating rate of 1 to 10°C·min -1 , holding at 400 to 500°C for 2 to 5h; continuing to heat at a rate of 1 to 5°C·min -1 to 500 to 550°C, holding at 500 to 550°C for 2 to 5h, and then naturally cooling to room temperature.

[0018] In another preferred embodiment of the present application, the calcination of step (2) is performed by heating from room temperature to 400 to 600°C at a heating rate of 1 to 5°C·min -1 , holding at 400 to 600°C for 2 to 3h, and then naturally cooling to room temperature.

[0019] In another more preferred embodiment of the present application, the calcination of step (2) is performed by heating from room temperature to 450 to 550°C at a heating rate of 1 to 5°C·min -1 , holding at 450 to 550°C for 2 to 3h, and then naturally cooling to room temperature.

[0020] In another preferred embodiment of the present application, the calcination of step (1) is performed in a closed container, and the calcination of step (2) is performed in an open container.

[0021] In another preferred embodiment of the present application, the fuel oil is selected from n-octane or dodecane simulated fuel oil, catalytic cracking gasoline or diesel oil system.

[0022] In another preferred embodiment of the present application, the sulfides contained in the fuel oil are selected from at least one of thiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT).

[0023] In another preferred embodiment of the present application, in the method for photocatalytic oxidative desulfurization of fuel oil, at least one of benzene, p-xylene, cyclohexene is added in the n-octane or dodecane simulated fuel oil as the unsaturated hydrocarbon in the simulated fuel oil.

[0024] In another preferred embodiment of the present application, in the method for photocatalytic oxidative desulfurization of fuel oil, the mass-volume ratio of the defective carbon nitride photocatalyst to the fuel oil is 0.01-2 g / L, preferably 0.5-1.5 g / L, more preferably 1.0 g / L.

[0025] In another preferred embodiment of the present application, in the method for photocatalytic oxidative desulfurization of fuel oil, the concentration of thiophene sulfides contained in the fuel oil is 100-1000 ppm.

[0026] In another preferred embodiment of the present application, in the method for photocatalytic oxidative desulfurization of fuel oil, the volume ratio of the fuel oil to the extractant is 1-10:1, preferably 1-5:1, more preferably 2:1.

[0027] The present application also provides a defective carbon nitride photocatalyst, and a preparation method of the defective carbon nitride photocatalyst comprises the following steps:

[0028] (1) calcining a nitrogen and carbon containing precursor at 400-600 ℃ to obtain a calcined intermediate product, and grinding the obtained intermediate product,

[0029] The nitrogen and carbon containing precursor is selected from a mixture of one or more of melamine, cyanamide, dicyandiamide, ammonium thiocyanate, urea and thiourea;

[0030] (2) secondary calcining the ground intermediate product at 400-600 ℃ to obtain the defective carbon nitride photocatalyst,

[0031] wherein the calcination method of step (1) is: heating from room temperature to 400-500 ℃ at a heating rate of 1-10 ℃·min-1, and keeping at 400-500 ℃ for 2-5 h; then heating to 450-550 ℃ at a heating rate of 1-5 ℃·min-1, and keeping at 450-550 ℃ for 2-5 h, and then naturally cooling to room temperature; the calcination method of step (2) is: heating from room temperature to 450-550 ℃ at a heating rate of 1-5 ℃·min-1, and keeping at 450-550 ℃ for 2-3 h, and then naturally cooling to room temperature, and

[0032] The roasting of step (1) is performed in a closed container, and the roasting of step (2) is performed in an open container.

[0033] In another more preferred embodiment of the present application, when the nitrogen and carbon containing precursor in step (1) is a mixture of multiple components, the nitrogen and carbon containing precursor is first mixed with water, heated and stirred, and the water is evaporated to dryness, so that the different components are mixed uniformly, and then roasting is performed.

[0034] In another more preferred embodiment of the present application, step (1) further comprises washing the ground intermediate product to remove impurities. In another more preferred embodiment of the present application, the washing is performed by alternately washing with water and alcohol for 2-6 times. Preferably, the alcohol is ethanol.

[0035] In another more preferred embodiment of the present application, step (2) further comprises washing the product of the second roasting to remove impurities. In another more preferred embodiment of the present application, the washing is performed by alternately washing with water and alcohol for 2-6 times. Preferably, the alcohol is ethanol.

[0036] In another preferred embodiment of the present application, the nitrogen and carbon containing precursor is selected from a mixture of melamine and urea, or a mixture of melamine and thiourea, wherein the mass content of melamine in the mixture of melamine and urea and the mixture of melamine and thiourea is 20-50%. In another more preferred embodiment of the present application, the nitrogen and carbon containing precursor is selected from a mixture of melamine and urea, wherein the mass content of melamine is 20-50%.

[0037] The present application also provides the use of the above-mentioned defective carbon nitride photocatalyst in the photocatalytic oxidation desulfurization of fuel oil. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 In the figures, the a figure, the b figure and the c figure are scanning electron microscope images, transmission electron microscope images and atomic force microscope images of the photocatalyst prepared in Example 1; the d figure, the e figure and the f figure are scanning electron microscope images, transmission electron microscope images and atomic force microscope images of the photocatalyst prepared in Example 3; the g figure, the h figure and the i figure are scanning electron microscope images, transmission electron microscope images and atomic force microscope images of the photocatalyst prepared in Example 5;

[0039] Figure 2 The BET figures of the carbon nitride nanosheets (photocatalyst) obtained in Examples 1, 2, 3, 4 and 5 of the present application.

[0040] Figure 3a , Figure 3b and Figure 3c are the C1s XPS figures, the N 1s XPS figures and the EPR figures of the carbon nitride nanosheets (photocatalyst) obtained in Examples 1, 2 and 3 of the present application, respectively.

[0041] Figure 4 The visible light current comparison diagrams are of the carbon nitride nanosheets (photocatalysts) obtained in Examples 1, 2, 3, 4 and 5 of this invention.

[0042] Figure 5a and Figure 5b The images show the reactive oxygen species radical maps obtained by EPR detection of carbon nitride nanosheets (photocatalysts) obtained in Examples 1, 2 and 3 of this invention, respectively.

[0043] Figure 6 The graph shows the desulfurization performance of different photocatalysts on simulated gasoline as measured in Example 6 of this invention.

[0044] Figure 7a This is a diagram showing the repeatability of the desulfurization experiment of the photocatalyst MUCN on simulated gasoline in Example 3 of the present invention. Figure 7b The images show the XRD patterns of the original photocatalyst MUCN and the photocatalyst MUCN after repeated desulfurization experiments.

[0045] Figure 8 The graph shows the simulated diesel desulfurization performance of different catalysts as measured in Example 7 of this invention.

[0046] Figure 9 The graph shows the desulfurization performance of the photocatalyst MUCN on different sulfur-containing substrates as measured in Example 8 of this invention.

[0047] Figure 10 The graph shows the desulfurization performance of the photocatalyst MUCN with different added interfering substances, as measured in Example 9 of this invention.

[0048] Figure 11 The graphs show the desulfurization performance of the photocatalyst MUCN on real gasoline (catalytic cracking gasoline) and real diesel (catalytic cracking diesel) as measured in Examples 10 and 11 of this invention. Detailed Implementation

[0049] Through in-depth research, the inventors of this application have developed a low-cost, easy-to-operate, and highly effective fuel photocatalytic oxidation desulfurization method, as well as the defective carbon nitride photocatalyst used in this invention.

[0050] Preparation of defective carbon nitride photocatalysts

[0051] In one specific embodiment of the present invention, the preparation method of the defective carbon nitride photocatalyst includes the following steps:

[0052] (1) The nitrogen- and carbon-containing precursors were calcined at 400–600 °C to obtain a single-calcination intermediate product, which was then ground.

[0053] the nitrogen and carbon containing precursor is selected from the group consisting of melamine, cyanamide, dicyanamide, ammonium thiocyanate, urea and thiourea, or a mixture of one or more thereof;

[0054] (2) performing secondary calcination on the ground intermediate product at 400-600°C to obtain the defective carbon nitride photocatalyst,

[0055] wherein the calcination of step (1) is performed by heating from room temperature to 400-500°C at a rate of 1-10°C / min -1 , holding at 400-500°C for 2-5h, and then continuing to heat at a rate of 1-5°C / min -1 to 500-600°C, more preferably 500-500°C, and holding at this temperature for 2-5h, and then naturally cooling to room temperature; the calcination of step (2) is performed by heating from room temperature to 400-600°C, more preferably 450-550°C, at a rate of 1-5°C / min -1 , holding at this temperature for 2-3h, and then naturally cooling to room temperature, and

[0056] wherein the calcination of step (1) is performed in a closed container, and the calcination of step (2) is performed in an open container.

[0057] When the nitrogen and carbon containing precursor is a single component in step (1), it does not need to be mixed with water, and can be directly calcined. When the nitrogen and carbon containing precursor is a mixture of multiple components, the nitrogen and carbon containing precursor is first mixed with water, heated and stirred, and the water is evaporated to dryness, so that the different components are fully mixed and uniform, and then calcined. The amount of water is not particularly limited, and the purpose of mixing the nitrogen and carbon containing precursor with water is to fully mix the different components in the mixture. Preferably, the weight / volume ratio of the nitrogen and carbon containing precursor to water is 1g / 5-15mL. In step (1), the temperature during heating and stirring, and evaporation of water to dryness is not particularly limited, and is preferably 60-100°C, more preferably 70-90°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C. Step (1) further comprises washing the ground intermediate product to remove impurities, and the washing method is to alternately wash with water and alcohol 2-6 times, preferably the alcohol is ethanol.

[0058] In one embodiment, step (1) further comprises grinding the intermediate product after cooling to room temperature, and then washing with deionized water and anhydrous ethanol alternately. Preferably, the cooling is natural cooling. The purpose of grinding the solid is to grind the caked sample into powder so as to achieve better washing effect in the subsequent washing process, and the grinding is to a completely loose powder. The purpose of washing with deionized water and anhydrous ethanol alternately is to remove the impurities contained in the calcined catalyst. In the process of washing with deionized water and anhydrous ethanol alternately, the amount of deionized water and anhydrous ethanol is not particularly limited, for example, 3-4 g of the precursor raw material after the first calcination is washed with 20-40 mL of deionized water and 20-40 mL of anhydrous ethanol alternately for 2-6 times.

[0059] In one embodiment, step (2) further comprises washing the product after the second calcination after cooling to room temperature to remove the impurities contained in the catalyst. The washing method is to wash with water and alcohol alternately for 2-6 times, and preferably the alcohol is ethanol. In the process of washing with deionized water and anhydrous ethanol alternately, the amount of deionized water and anhydrous ethanol is not particularly limited, for example, 3-4 g of the precursor raw material after the second calcination is washed with 20-40 mL of deionized water and 20-40 mL of anhydrous ethanol alternately for 2-6 times.

[0060] The container for preparing the defective carbon nitride photocatalyst can be a crucible, and the calcination reaction can be carried out in a muffle furnace or a tube furnace.

[0061] The calcination of step (1) is carried out in a closed container to reduce the volatilization loss of carbon and nitrogen precursors, so as to better occur the thermal polymerization process of the precursors to generate carbon nitride in the closed container. The calcination of step (2) is carried out in an open container to promote the pyrolysis process of the blocky carbon nitride after the first calcination. The carbon nitride obtained after the first calcination is mostly blocky material with large morphology and size, and when the second calcination is carried out in an open container, the carbon nitride reacts with oxygen to release NH3, CO2 and other gases containing carbon / nitrogen components, and weaken the interlayer van der Waals force of the blocky carbon nitride, so as to form defects and the structure of ultra-thin porous nanosheets in the final carbon nitride product.

[0062] Method for photocatalytic oxidative desulfurization of fuel oil

[0063] In one embodiment of the present application, the method for photocatalytic oxidation desulfurization of fuel oil comprises the steps of: (1) under normal temperature and pressure conditions, using defective carbon nitride as a photocatalyst, using oxygen or air as an oxidant, and using a wavelength of 300 nm<λ<1500 nm, the fuel oil is subjected to photocatalytic desulfurization, and an extractant is used to extract the sulfur-containing products generated in the reaction.

[0064] Preferably, the wavelength is 300 nm<λ<780 nm.

[0065] In this invention, the desulfurization reaction can be carried out directly in an air atmosphere; or the air in the reactor can be removed by evacuation and then oxygen can be introduced to carry out the reaction in an oxygen atmosphere; or air or oxygen can be continuously introduced into the reaction liquid through a gas pipeline.

[0066] In the description of this invention, "room temperature" refers to 4 to 40°C, preferably 15 to 35°C.

[0067] In the description of this invention, "atmospheric pressure" refers to approximately 0.1 MPa.

[0068] In the description of this invention, "multiple" refers to two or more types, and "many" refers to two or more types.

[0069] In the description of this invention, "water" can be deionized water or distilled water.

[0070] In the description of this invention, the thickness of the "ultrathin porous nanosheet" is 0.1 to 1 nm, for example 0.2 to 1 nm, 0.4 to 1 nm, or 0.6 to 1 nm.

[0071] The N of the present invention 3C The mechanism of photocatalytic oxidation-extraction desulfurization of defective carbon nitride lies in the following: the extractant first partially extracts aromatic heterocyclic thiophene sulfides (such as BT, DBT, 4,6-DMDBT) into the extractant, which can be rapidly adsorbed and activated by the unsaturated heptaazine ring conjugated structure of defective carbon nitride. At the same time, the NC=N site of defective carbon nitride can activate dissolved O2 to form superoxide radicals (·O2). - ) and singlet oxygen ( 1 O2) active oxide species, thereby oxidizing thiophene sulfur to sulfone. Since sulfone has stronger polarity, it can selectively dissolve in the extractant. The reduction of thiophene sulfur in the extractant will cause thiophene sulfur in the oil phase to continuously transfer to the extractant and be catalytically oxidized by defective carbon nitride, thereby promoting the continuous progress of the oxidation forward reaction (i.e., the reaction proceeds in the direction of oxide formation) until the thiophene sulfur in the oil phase is completely extracted and oxidized, achieving the efficiency of deep desulfurization.

[0072] The fuel photocatalytic oxidation desulfurization method of the present application is a catalytic oxidation-extraction synergistic desulfurization process under the condition of using molecular oxygen at normal temperature and pressure, which has the advantages of green and clean, mild and low consumption. This method has very high requirements for the performance of the catalyst, which requires the catalyst to have good hydrophilicity to disperse in the extraction phase (to avoid pollution of the oil phase and catalyst poisoning), and also requires the catalyst to have excellent oxygen activation ability and aromatic heterocyclic thiophene sulfide adsorption ability in the extraction phase. In the reported photocatalytic oxidation desulfurization processes, H2O2 is required as an oxidant (Mol. Catal., 2023, 536, 112916; J. Clean. Prod., 2022, 380, 134968; CN201911249876.9), or additional heating is required, or a process step of oxidation first and extraction later is adopted (Fuel, 2018, 224, 261-270; CN201911371323.0; CN201911155208.X, in which the catalyst is easy to be poisoned and the oil phase is easy to be polluted), or an emulsifying desulfurization is used by using an emulsifier for oxidation-extraction (Langmuir 2019, 35, 3963-3971; Appl. Catal. A General, 2023, 656, 119133), which requires the use of emulsifiers and demulsifiers, which will pollute the oil phase to some extent.

[0073] The existing g-C3N4-containing desulfurization catalysts are basically composite catalysts, and the carbon nitride morphology is mostly micron-sized block structure, which lacks effective surface active sites, so the single desulfurization activity is poor. Therefore, in the prior art, the g-C3N4 planar structure is often used as a catalyst carrier, and metal oxides or noble metals and other active components are loaded thereon for catalytic oxidation desulfurization. Compared with the prior art, the present application uses at least one precursor to perform multiple pyrolysis, in which process, not only a large amount of heat and gas released in the pyrolysis reaction is used to obtain an ultrathin porous carbon nitride structure with a large specific surface area to provide more active sites for the reaction, but also a unique N 3c site defect is formed in the carbon nitride molecular structure by co-pyrolysis, which can effectively enhance the adsorption and activation of O2 by the catalyst, and the unsaturated heptazine ring conjugated structure formed by the defect structure will also enhance the π-π interaction with aromatic heterocyclic thiophene sulfides, thereby promoting the adsorption capacity of the catalyst for sulfides. The catalyst prepared by the present application has a special composition and structure, so it can directly exhibit excellent photocatalytic oxidation desulfurization performance without any metal catalyst.

[0074] Therefore, compared with the prior art, the present application has the following advantages:

[0075] 1.The defective carbon nitride obtained by pyrolysis of at least one precursor has large specific surface area and ultra-thin porous structure characteristics, the raw material is cheap, easy to mass-produce, and stable, only needs pyrolysis operation, and has simple process and low cost.

[0076] 2.The N 3C The defects can effectively promote the activation of molecular oxygen in the catalytic reaction and the adsorption of aromatic heterocyclic thiophene sulfides, so that the defective carbon nitride has high photocatalytic oxidation-extraction desulfurization activity.

[0077] 3.The method used in the present application can exhibit high desulfurization performance for simulated fuel and actual fuel containing unsaturated hydrocarbons under the conditions of normal temperature and pressure and using oxygen or air as an oxidant.

[0078] The present application will be further described below in conjunction with specific examples, which should not be limited to the following examples in practical application.

[0079] Example 1

[0080] The preparation method of the defective carbon nitride comprises the following steps:

[0081] Melamine (3 g) was dissolved in a certain amount of deionized water (20 mL), stirred at 80℃ until the liquid was evaporated, then placed in an oven and dried at 80℃ for 12 h, heated to 420℃ at a heating rate of 8℃ / min in a muffle furnace, and kept at this temperature for 3 h (covered), then heated to 520℃ at a heating rate of 2℃ / min, and kept at this temperature for 2 h (covered), then ground the solid, washed with deionized water (20 mL) and anhydrous ethanol (20 mL) alternately for 4 times, and dried at 80℃, then heated to 500℃ at a heating rate of 2℃ / min in a muffle furnace, and calcined at this temperature for 2 h (without cover), then naturally cooled to room temperature, and repeated the above washing steps (i.e., washed with deionized water (20 mL) and anhydrous ethanol (20 mL) alternately for 4 times), and then dried at 80℃ to obtain the photocatalyst MCN.

[0082] Example 2

[0083] Urea (10 g) was heated in a muffle furnace at a ramping rate of 6 °C / min to 500 °C and kept at this temperature for 2 h (covered), then heated at a ramping rate of 3 °C / min to 520 °C and kept at this temperature for 3 h (covered), after cooling to room temperature the solid was ground and washed with deionized water (40 mL) and absolute ethanol (40 mL) alternately for 6 times, the sample dried at 90 °C was heated in a muffle furnace at a ramping rate of 4 °C / min to 550 °C and calcined at this temperature for 3 h (without covering), after natural cooling to room temperature the above washing step was repeated (i.e. washed with deionized water (40 mL) and absolute ethanol (40 mL) alternately for 6 times), after drying at 90 °C the photocatalyst UCN was obtained.

[0084] Example 3

[0085] Melamine (1 g) and urea (3 g) were dissolved in deionized water (30 mL) according to a mass ratio of 1 :3, stirred at 80 °C until the liquid was evaporated, then put into an oven and dried at 80 °C for 12 h, heated in a muffle furnace at a ramping rate of 5 °C / min to 500 °C and kept at this temperature for 4 h (covered), then heated at a ramping rate of 3 °C / min to 550 °C and kept at this temperature for 2 h (covered), after cooling to room temperature the solid was ground and washed with deionized water (30 mL) and absolute ethanol (30 mL) alternately for 4 times, the dried sample was again heated in a muffle furnace at a ramping rate of 4 °C / min to 580 °C and calcined at this temperature for 2 h (without covering), after natural cooling to room temperature the above washing step was repeated (i.e. washed with deionized water (30 mL) and absolute ethanol (30 mL) alternately for 4 times), after drying the photocatalyst MUCN was obtained.

[0086] Example 4

[0087] 4 g of thiourea was put into an oven and dried at 80 °C for 12 h, heated in a muffle furnace at a ramping rate of 6 °C / min to 460 °C and kept at this temperature for 8 h (covered), then heated at a ramping rate of 2 °C / min to 540 °C and kept at this temperature for 3 h (covered), after cooling to room temperature the solid was ground and washed with deionized water (35 mL) and absolute ethanol (35 mL) alternately for 4 times, the dried sample was again heated in a muffle furnace at a ramping rate of 4 °C / min to 480 °C and calcined at this temperature for 3 h (without covering), after natural cooling to room temperature the above washing step was repeated (washed with deionized water (35 mL) and absolute ethanol (35 mL) alternately for 4 times), after drying the photocatalyst TCN was obtained.

[0088] Example 5

[0089] Melamine (1.5 g) and thiourea (1.5 g) were dissolved in deionized water at a mass ratio of 1:1, stirred at 80°C until the liquid (water) was evaporated, then placed in an oven at 80°C for 12 h, heated to 450°C at a heating rate of 4°C / min in a muffle furnace, and kept at this temperature for 5 h (covered), then heated to 550°C at a heating rate of 2°C / min, and kept at this temperature for 2 h (covered), after cooling to room temperature, the solid was ground, washed with deionized water (30 mL) and anhydrous ethanol (30 mL) alternately for 4 times, the dried sample was heated to 480°C at a heating rate of 3°C / min in a muffle furnace, and calcined at this temperature for 3 h (without covering), after natural cooling to room temperature, the above washing step was repeated (i.e., washed with deionized water (30 mL) and anhydrous ethanol (30 mL) alternately for 4 times), and the photocatalyst MTCN was obtained after drying.

[0090] The photocatalysts obtained in Examples 1, 3 and 5 were observed by scanning electron microscopy (JEOL JSM-6700), transmission electron microscopy (JEOL JEM-2100F) and atomic force microscopy (Brruker Dimension ICON), respectively, and the results are shown in FIGS. a-i of Figure 1 From FIGS. a-i of Figure 1 , it can be seen that the photocatalyst MCN sample prepared from melamine presents a large block structure. The gas released and decomposed during the thermal polycondensation process further promotes the formation of a porous structure by the copolymerization of the precursors. The photocatalyst MUCN sample prepared from the mixture of melamine and urea presents a large number of pore structures, and the photocatalyst MTCN sample prepared from the mixture of melamine and thiourea has a small number of pores on the surface. Transmission electron microscopy further shows that the prepared samples are all ultrathin porous nanosheets, the photocatalyst MCN has a relatively complete surface, and the photocatalysts MUCN and MTCN have edge curling due to more pore structures and thinner layers. In addition, atomic force microscopy tests confirm that the thickness of the prepared nanosheets is less than 1 nm, showing the characteristics of ultrathin single-layer nanosheets.

[0091] The BET tests of the photocatalysts prepared in Examples 1, 2, 3, 4 and 5 were performed using a full-automatic specific surface area analyzer of Micromeritics APS P2460 model, and the results are shown in FIG. Figure 2 , and Figure 2 From the N2 adsorption-desorption curve of the sample, it can be seen that the specific surface area of the prepared photocatalyst gradually increases with the increase of the type of precursor, and the specific surface area of the photocatalyst MUCN sample can reach 127.4 m 2 ·g -1 .

[0092] X-ray photoelectron spectroscopy (XPS) was performed using a Kratos AXISNOVA spectrometer to study the evolution of surface functional groups after the co-pyrolysis of melamine and urea. The results are shown in [reference needed]. Figures 3a to 3c Through the analysis of Figure 3a Comparative analysis of peak areas of different carbon-containing functional groups in the fine C1s spectrum showed that the NC=N / CC ratio of the photocatalyst MUCN was significantly higher than that of the photocatalysts MCN and UCN; Figure 3b In the N1s fine spectrum, the peak area ratio of the CN=C / N-(C)3 functional group in the photocatalyst MUCN is 5.47, which is greater than that of the photocatalyst MCN (3.89) and the photocatalyst UCN (2.48). This change is mainly due to the formation of more N in the photocatalyst MUCN. 3C Defects, thus making N 3c The relative content of sites decreased, while the relative content of NC=N increased. Further testing of the nitrogen defect concentration of different photocatalysts using electron paramagnetic resonance (EPR, Bruker A300) spectroscopy revealed that the nitrogen defect concentration of photocatalyst MUCN was significantly higher than that of photocatalysts MCN and UCN. (See [link to relevant documentation]). Figure 3c .

[0093] The photocurrent of the carbon nitride catalysts obtained in Examples 1, 2, 3, 4, and 5 was measured using a KOSTER CS310M electrochemical workstation. The results are shown in [Figure number missing]. Figure 4 . Figure 4 The visible photocurrent spectra of the samples show that all samples exhibit good photoelectric response performance. Among them, the photocatalysts MUCN and MTCN, which are prepared from precursors composed of two components, have stronger photocurrent intensity than the photocatalysts prepared from their respective single-component precursors, indicating that they have better photogenerated carrier separation efficiency.

[0094] In-situ EPR (Bruker A300) analysis of reactive oxygen species was performed on the carbon nitride photocatalysts obtained in Examples 1, 2, and 3, revealing that all samples formed superoxide radicals (·O2). - ) and singlet oxygen ( 1 O2) active oxide species, see [link] Figure 5a and Figure 5b Furthermore, the MUCN photocatalyst sample was found to have the highest concentration of active oxygen species, indicating that the catalyst has good molecular oxygen activation ability, which can generate a large number of active oxygen species in the desulfurization process and accelerate the efficiency of photocatalytic oxidation desulfurization.

[0095] Example 6

[0096] Photocatalytic oxidation desulfurization of fuel systems

[0097] In this embodiment, the simulated oil was prepared as follows: 500 ppm DBT was weighed as a sulfur-containing compound, and 50 mL of n-octane was added as simulated gasoline. 50 mg of the photocatalyst from Examples 1-5 was weighed, and 25 mL of acetonitrile was added as an extractant. A magnetic stirrer was turned on, and circulating water was introduced to ensure a homogeneous and sealed system during the reaction, maintaining the reaction temperature at room temperature. The mixture was stirred in the dark for 30 min to achieve adsorption-desorption equilibrium between the catalyst and reactant molecules, as well as extraction equilibrium of dibenzothiophene by the extractant. A 300W xenon lamp was used as a simulated sunlight source, and the reaction was carried out under illumination for 2 h. After the reaction, the acetonitrile and n-octane phases were centrifuged and filtered, and the changes in the content of dibenzothiophene in the n-octane phase and the oxidation product dibenzothiophene sulfone in the acetonitrile phase were tested by gas chromatography.

[0098] See test data results Figure 6 .from Figure 6 It can be seen that the photocatalysts prepared in Examples 1-5 all have good desulfurization efficiency. The carbon nitride photocatalyst prepared by co-pyrolysis of two precursors has better performance. Among them, MUCN shows the best desulfurization activity, with a desulfurization rate of up to 97.1%.

[0099] The photocatalyst MUCN was recovered after the desulfurization reaction, and multiple repeated desulfurization experiments were conducted. The data results are available in [link to relevant documentation]. Figure 7a Its catalytic oxidation desulfurization activity is very stable, exhibiting excellent activity stability. Furthermore, the XRD patterns of the photocatalyst MUCN after the initial and repeated experiments (using a Shimadzu XRD-7000 powder diffractometer) are compared; the test data results can be found in [link to relevant documentation]. Figure 7b The diffraction peaks were completely consistent, indicating that the photocatalyst MUCN has good structural stability.

[0100] Example 7

[0101] The difference between this embodiment and Embodiment 6 above lies in the preparation of the simulated oil. 500 ppm DBT is weighed as a sulfur-containing compound, and 50 ml of n-dodecane is added as simulated diesel oil.

[0102] The photocatalysts of Examples 1-5 were subjected to activity testing, and the test data results are shown below. Figure 8 .from Figure 8 It can be seen that the photocatalyst MUCN obtained by co-pyrolysis of the two precursors can remove dibenzothiophene from simulated diesel to less than 10 ppm after reacting for 2 hours under suitable reaction conditions, with a desulfurization rate of 99.6%.

[0103] Example 8

[0104] The difference between this embodiment and Embodiment 6 above lies in the preparation of the simulated oil. BT, DBT, and 4,6-DMDBT are used as sulfur-containing compounds, and 50 mL of n-octane is added to simulate gasoline.

[0105] The photocatalyst of Example 3 was subjected to activity test, and the test data are shown in Table 1. Figure 9 The test data are shown in Table 2. Figure 8 As shown in Table 2, the photocatalyst MUCN has good desulfurization activity for various thiophene-containing sulfur substrates.

[0106] Example 9

[0107] The difference between this example and Example 6 described above is the preparation of simulated oil. DBT is selected as the sulfur-containing compound, n-octane is selected as the simulated gasoline, and benzene, p-xylene and cyclohexene (the addition amount is 10% of the mass of DBT) are added respectively to prepare the simulated oil mixture.

[0108] The photocatalyst prepared in Example 3 was subjected to activity test. As shown in Table 3, the addition of interference has little effect on the desulfurization activity of the catalyst, and the catalyst shows excellent desulfurization selectivity. Figure 10

[0109] Example 10

[0110] In order to test the desulfurization activity of real oil, the difference between this example and Example 6 described above is that real catalytic cracking gasoline is selected as the oil to be desulfurized (50 mL in volume and 540 ppm in sulfur content), and no other sulfur-containing pollutants are added, and 100 mg of photocatalyst is added. Figure 11 As shown in Table 4, the photocatalytic reaction is carried out for 3 h, and the desulfurization activity is 98.8%.

[0111] Example 11

[0112] The difference between this example and Example 10 described above is that real catalytic cracking diesel is selected as the oil to be desulfurized (50 mL in volume and 890 ppm in sulfur content), and no other sulfur-containing pollutants are added, and 100 mg of photocatalyst is added.

[0113] The photocatalyst of Example 3 was subjected to activity test. As shown in Table 5, the photocatalytic reaction is carried out for 6 h, and the desulfurization activity is 96%. Figure 11 The data obtained in the above examples show that the high specific surface area defect type carbon nitride prepared by co-pyrolysis has higher photocatalytic activity. When it is used for photocatalytic desulfurization of fuel oil, catalytic oxidation-extraction desulfurization coupling can be realized in one step, and the fuel oil has excellent desulfurization efficiency. And in the case of competition oxidation of complex components such as naphthenes and aromatics, benzothiophene, dibenzothiophene and 4,6-dimethyldibenzothiophene and other difficult-to-remove aromatic heterocyclic thiophene sulfides in simulated gasoline / diesel can be removed with high efficiency and selectivity.

[0114]

[0115] ​​In summary, this invention develops modified nitrogen-deficient carbon nitride (g-C3N4) as a catalyst, establishing a novel method for deep desulfurization of fuel oil through photocatalytic oxidation-extraction. First, by co-pyrolyzing various precursor raw materials and utilizing the large amount of heat and gas released during the polymerization reaction, an ultrathin porous carbon nitride structure with a large specific surface area is prepared, which is beneficial for providing numerous active sites for the reaction and promoting the adsorption of reactants. Second, the N2O3 formed in the carbon nitride molecular structure during the co-pyrolysis process... 3C Site defects can optimize the catalyst's adsorption and activation ability for O2, enabling it to generate more superoxide radicals (·O2). - ) and singlet oxygen ( 1 O2) active oxide species. Furthermore, this nitrogen defect can form numerous coordinatingly unsaturated heptaazine ring conjugated structures within the g-C3N4 polymer plane, thereby strengthening the π-π interaction with aromatic heterocyclic thiophene sulfides and promoting their adsorption capacity. Combining these three points comprehensively solves the bottleneck problem limiting oxidative desulfurization, thus achieving highly efficient photocatalytic oxidative desulfurization.

[0116] Obviously, the above embodiments of the present invention are merely simple applications of defective carbon nitride in improving the activity of photocatalysts, and are examples given to clearly illustrate the broadness of the present invention, rather than limiting the application field and implementation methods of the present invention. For specific applications of various photocatalysts, other variations should be made according to specific circumstances. It is neither necessary nor possible to exhaustively list all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for photocatalytic oxidation desulfurization of fuel oil, characterized in that, The desulfurization method comprises the following steps: using a defective carbon nitride as a photocatalyst, using oxygen or air as an oxidant, and performing photocatalytic desulfurization on the fuel under the condition of normal temperature and pressure and under the wavelength of 300 nm < λ < 1500 nm, and simultaneously using an extractant to extract the sulfur-containing product generated in the reaction, The defective carbon nitride photocatalyst has N 3C site nitrogen defects, and has a morphology of super-thin porous nanosheets. The preparation method of the defective carbon nitride photocatalyst comprises the following steps: (1) roasting a nitrogen and carbon-containing precursor at 400-600 DEG C to obtain an intermediate product after first roasting, and grinding the obtained intermediate product, The nitrogen and carbon-containing precursor is selected from a mixture of melamine and urea or a mixture of melamine and thiourea; (2) performing second roasting on the ground intermediate product at 400-600 DEG C to obtain the defective carbon nitride photocatalyst, The roasting in step (1) is performed in a closed container, and the roasting in step (2) is performed in an open container.

2. The method according to claim 1, wherein the photocatalytic oxidation desulfurization method is a method for removing sulfur compounds in fuel oil. The extractant is acetonitrile.

3. The method of photocatalytic oxidation of fuel oil desulfurization according to claim 1, characterized in that, In step (1), the nitrogen and carbon-containing precursor is first mixed with water, heated and stirred, and the water is evaporated to dryness, so that the different components in the mixture are fully mixed and uniform, and then roasting is performed, and / or Step (1) further comprises washing the ground intermediate product to remove impurities, and / or Step (2) further comprises washing the product after second roasting to remove impurities.

4. The method of photocatalytic oxidation of fuel oil desulfurization according to claim 1, characterized in that, The mass content of melamine in the mixture of melamine and urea and the mixture of melamine and thiourea is 20-50%.

5. The method of photocatalytic oxidation of fuel oil desulfurization according to claim 1, characterized in that, The roasting method of step (1) is: from room temperature to 400-500°C, the heating rate is 1-10°C / min -1 , and the temperature is kept at 400-500°C for 2-5h; then heated to 500-600°C at a rate of 1-5°C / min -1 , and kept at 500-600°C for 2-5h, and then naturally cooled to room temperature; and / or The roasting method of step (2) is: from room temperature to 400~600℃, the heating rate is 1~5℃·min -1 and isothermal at 400~600℃ for 2~3 h, and then naturally cooled to room temperature.

6. The method of photocatalytic oxidation of fuel oil desulfurization according to claim 1, characterized in that, The desulfurization method has one or more of the following characteristics: (i) the fuel is selected from n-octane or dodecane simulated fuel, catalytic cracking gasoline or catalytic cracking diesel, (ii) the sulfides contained in the fuel are selected from at least one of benzothiophene, dibenzothiophene and 4,6-dimethyl dibenzothiophene, (iii) the mass-volume ratio of the defective carbon nitride photocatalyst to the fuel is 0.01-2 g / L, (iv) the concentration of thiophene sulfides contained in the fuel is 100-1000 ppm, (v) the volume ratio of the fuel to the extractant is 1-10:

1.

7. The method according to claim 6, wherein the photocatalyst is Ti02. The desulfurization method has one or two of the following characteristics: The mass-volume ratio of the defective carbon nitride photocatalyst to the fuel is 0.5-1.5 g / L, The volume ratio of the fuel to the extractant is 1-5:

1.

8. A defective carbon nitride photocatalyst, characterized by, The preparation method of the defective carbon nitride photocatalyst comprises the following steps: (1) roasting a nitrogen and carbon-containing precursor at 400-600 DEG C to obtain an intermediate product after first roasting, and grinding the obtained intermediate product, The nitrogen and carbon-containing precursor is selected from a mixture of melamine and urea or a mixture of melamine and thiourea; (2) performing second roasting on the ground intermediate product at 400-600 DEG C to obtain the defective carbon nitride photocatalyst, The roasting in step (1) is performed in a closed container, and the roasting in step (2) is performed in an open container.

9. The use of the defective carbon nitride photocatalyst in claim 8 in the photocatalytic oxidative desulfurization of fuel.

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