Photocatalytic water decomposition series hydrogenation reaction system and application thereof

Abstract

The invention relates to the technical field of hydrogenation reaction, in particular to a photocatalytic water decomposition series hydrogenation reaction system and application thereof. The photocatalytic water decomposition series hydrogenation reaction system comprises a photocatalytic water decomposition unit, a separation and purification unit and a hydrogenation unit which are connected in sequence; the photocatalytic water decomposition unit is used for photocatalytic water decomposition to produce hydrogen, the separation and purification unit is used for separating and purifying hydrogen, and the hydrogenation unit is used for hydrogenating carbon dioxide to produce methane or hydrogenating nitrogen to produce ammonia gas. The photocatalytic water decomposition reactor system and the hydrogenation reactor system are connected in series and used for hydrogenation reaction of carbon dioxide or nitrogen and the like, and the finally prepared target product is high in yield and selectivity and meets the standard of superior products. In the whole production process of the target product, no corrosive and toxic raw materials are introduced, and the method is green, economical, efficient and suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogenation reactions, and in particular to a photocatalytic water decomposition tandem hydrogenation reaction system and applications thereof. Background Art

[0002] The use of photocatalytic technology to convert carbon dioxide / nitrogen and water into chemicals such as methane and ammonia is considered to be one of the possible ways to alleviate energy depletion, global warming and hydrogen storage problems. However, carbon dioxide / nitrogen is a stable, chemically inert linear molecule, and the breaking of its chemical bonds requires extremely high energy. Conventional photocatalytic reactions are complex and usually have problems such as poor catalytic efficiency and difficult to control product selectivity.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] In order to solve the above problems in the prior art, the present invention provides a photocatalytic water splitting tandem hydrogenation reaction system and its application, so as to achieve high yield, high selectivity and high stability in producing industrial products such as methane or ammonia.

[0005] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a photocatalytic water splitting and tandem hydrogenation reaction system, comprising a photocatalytic water splitting unit, a separation and purification unit, and a hydrogenation unit connected in sequence; the photocatalytic water splitting unit is used to photocatalytically split water to produce hydrogen, the separation and purification unit is used to separate and purify hydrogen, and the hydrogenation unit is used to hydrogenate carbon dioxide to produce methane or hydrogenate nitrogen to produce ammonia.

[0006] In the prior art, in order to simplify the reaction process, methane or ammonia is usually prepared by a one-step reaction of water and carbon dioxide or nitrogen. However, there is still room for further improvement in the selectivity and yield of the products.

[0007] The present invention unexpectedly discovered that by first performing photocatalytic water decomposition to produce hydrogen, and then using the purified hydrogen as a reaction raw material to undergo a hydrogenation reaction with carbon dioxide or nitrogen to produce methane or ammonia, a lower energy barrier can be overcome, and the selectivity and yield of the product methane or ammonia can be significantly improved.

[0008] Preferably, the photocatalytic water splitting unit comprises a photocatalytic water splitting reactor, a water storage device and a first gas carrier; the photocatalytic water splitting reactor is used to carry out a photocatalytic water splitting reaction, the water storage device is used to store raw water, and the first gas carrier is used to transport an inert gas into the photocatalytic water splitting reactor. The photocatalytic water splitting reactor comprises a first feed port and a first discharge port, the water storage device comprises a second feed port, a third feed port, a second discharge port and a third discharge port, and the first gas carrier comprises a fourth feed port and a fourth discharge port. The first feed port and the first discharge port of the photocatalytic water splitting reactor, the second feed port and the second discharge port of the water storage device are connected in a pipeline circulation manner, and the fourth discharge port of the first gas carrier is connected to the third feed port of the water storage device through a pipeline.

[0009] Preferably, the separation and purification unit includes a deoxygenator and a drying device. The deoxygenator is used to remove oxygen from the photocatalytic water decomposition product, and the drying device is used to remove moisture from the photocatalytic water decomposition product. The deoxygenator includes a fifth feed port and a fifth discharge port, and the drying device includes a sixth feed port and a sixth discharge port. The third discharge port of the water storage device is connected to the fifth feed port of the deoxygenator through a pipeline; the fifth discharge port of the deoxygenator is connected to the sixth feed port of the drying device through a pipeline.

[0010] Preferably, the hydrogenation unit comprises a hydrogenation reactor and a second gas carrier device; the hydrogenation reactor is used for carrying out hydrogenation reaction of carbon dioxide or nitrogen; the second gas carrier device is used for inputting carbon dioxide or nitrogen into the hydrogenation reactor; the hydrogenation reactor comprises a seventh feed port and a seventh discharge port, and the second gas carrier device comprises an eighth feed port and an eighth discharge port; the sixth discharge port of the drying device, the seventh feed port of the hydrogenation reactor and the eighth discharge port of the second gas carrier device are connected by a pipeline; the material at the seventh discharge port of the hydrogenation reactor is collected.

[0011] In the present invention, a rotor flowmeter, a pump, and a temperature and pressure sensor device etc. may be installed on the pipeline as required, which is not limited herein.

[0012] In the present invention, a liquid circulation metering device can be installed on the pipeline as needed, and the flow rate of the device is 0.1~4.5 L / min, but not limited to this.

[0013] In the present invention, the photocatalytic water splitting reactor can be a reactor type, a flat plate type, a continuous flow type, etc., but not limited thereto. Further, the hydrogenation reactor can be a reactor type, a fixed bed type, but not limited thereto.

[0014] In a second aspect, the present invention provides an application of the photocatalytic water splitting and tandem hydrogenation reaction system in preparing methane or ammonia.

[0015] In a third aspect, the present invention provides a method for preparing methane or ammonia by hydrogenation reduction, which comprises using the photocatalytic water decomposition tandem hydrogenation reaction system.

[0016] Preferably, the method for preparing methane or ammonia by hydrogenation reduction comprises: S1: mixing water and a first catalyst in a photocatalytic water splitting reactor, and performing a photocatalytic water splitting reaction under the irradiation of a light source and an atmosphere of an inert gas to produce hydrogen; S2: The hydrogen produced in S1 is passed into a deoxygenation device and a drying device in sequence to remove oxygen and water respectively; the deoxygenation device contains a deoxygenator, and the drying device contains a desiccant; S3: introducing the hydrogen and reaction gas separated and purified in S2 into a hydrogenation reactor, adding a second catalyst, and performing a hydrogenation reaction under the irradiation of a light source; the reaction gas is carbon dioxide or nitrogen.

[0017] Preferably, in S1, the intensity of the light source is 1.0-5.0 W / cm 2 .

[0018] Preferably, in S1, the first catalyst comprises one or more of titanium dioxide, ruthenium-loaded titanium dioxide (loading amount is 10~15wt%), cadmium sulfide and zinc indium sulfide; and / or, in S3, the second catalyst comprises one or more of ruthenium, cadmium sulfide and indium oxide.

[0019] More preferably, in S2, the deoxidizer includes one or more of sodium sulfite, hydrazine or dimethyl ketoxime; and / or the desiccant includes one or more of calcium sulfate, calcium chloride, silica gel and activated alumina.

[0020] Preferably, in S1, the pressure of the photocatalytic water splitting reaction is 0-40 kPa, and the temperature of the photocatalytic water splitting reaction is 278-333 K; and / or, in S3, the space velocity of the hydrogenation reaction is 0-1500 L g -1 h -1 The temperature of the hydrogenation reaction is 373~648 K; the light intensity of the hydrogenation reaction is 0.4~3.0 W / cm 2 ; and / or, in S3, the flow rate ratio of the carbon dioxide to the hydrogen is 1:2~4; the flow rate ratio of the nitrogen to the hydrogen is 1:3~5.

[0021] The photocatalytic water splitting and hydrogenation reaction system provided by the present invention and its application are designed to be connected in series with the photocatalytic water splitting and hydrogenation reactor systems for hydrogenation reactions of carbon dioxide or nitrogen, etc., and the target product finally prepared has high yield and selectivity, and meets the standard of superior products. In the production process of the entire target product, the present invention does not introduce corrosive and toxic raw materials, is green, economical, efficient, and suitable for industrial scale-up production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the process of the photocatalytic water decomposition and tandem hydrogenation reaction system provided by the present invention.

[0024] Description of the drawings: 1 hydrogen evolution reactor, 2 water storage device, 3 deoxygenation device, 4 drying device, 5 hydrogenation reactor. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the various raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0027] Example 1

[0028] This embodiment provides a photocatalytic water splitting tandem hydrogenation reaction system (see the schematic diagram of the process Figure 1 ), comprising a photocatalytic water splitting unit, a separation and purification unit and a hydrogenation unit connected in sequence; the photocatalytic water splitting unit is used for photocatalytic water splitting to produce hydrogen, the separation and purification unit is used for separating and purifying hydrogen, and the hydrogenation unit is used for hydrogenating carbon dioxide to produce methane or hydrogenating nitrogen to produce ammonia.

[0029] The photocatalytic water splitting unit comprises a photocatalytic water splitting reactor 1, a water storage device 2 and a first gas carrier; the photocatalytic water splitting reactor 1 is used to perform a photocatalytic water splitting reaction, the water storage device 2 is used to store raw water, and the first gas carrier is used to transport an inert gas into the photocatalytic water splitting reactor 1; The photocatalytic water splitting reactor 1 includes a first feed port and a first discharge port, the water storage device 2 includes a second feed port, a third feed port, a second discharge port and a third discharge port, and the first gas carrier device includes a fourth feed port and a fourth discharge port; the first feed port and the first discharge port of the photocatalytic water splitting reactor 1, the second feed port and the second discharge port of the water storage device 2 are connected in a pipeline circulation manner, and the fourth discharge port of the first gas carrier device is connected to the third feed port of the water storage device 2 through a pipeline.

[0030] The separation and purification unit includes a deoxygenator 3 and a drying device 4; the deoxygenator 3 is used to remove oxygen from the photocatalytic water decomposition product, and the drying device 4 is used to remove moisture from the photocatalytic water decomposition product; the deoxygenator 3 includes a fifth feed port and a fifth discharge port, and the drying device 4 includes a sixth feed port and a sixth discharge port; the third discharge port of the water storage device 2 is connected to the fifth feed port of the deoxygenator 3 through a pipeline; the fifth discharge port of the deoxygenator 3 is connected to the sixth feed port of the drying device 4 through a pipeline. The deoxygenator 3 contains a deoxygenator, which is sodium sulfite; the drying device 4 contains a desiccant, which is silica gel.

[0031] The hydrogenation unit includes a hydrogenation reactor 5 and a second gas carrier device; the hydrogenation reactor 5 is used for hydrogenation reaction of carbon dioxide or nitrogen; the second gas carrier device is used for inputting carbon dioxide or nitrogen into the hydrogenation reactor 5; the hydrogenation reactor 5 includes a seventh feed port and a seventh discharge port, and the second gas carrier device includes an eighth feed port and an eighth discharge port; the sixth discharge port of the drying device 4, the seventh feed port of the hydrogenation reactor 5 and the eighth discharge port of the second gas carrier device are connected by a pipeline; the material at the seventh discharge port of the hydrogenation reactor 5 is collected.

[0032] Example 2

[0033] This embodiment provides a method for synthesizing methane by adding water to carbon dioxide in a photocatalytic water splitting and hydrogenation reactor in series, using the system of embodiment 1, including the following steps: 50 mg CuPt-loaded TiO2 catalyst (loading amount of 12 wt%) was uniformly dispersed in 500 mL aqueous solution, ultrasonicated and stirred. The dispersion was then transferred to a photocatalytic water splitting reactor and reacted at 293 K and 20 kPa. At the same time, 5 mg of nano-Ru catalyst was uniformly coated on the front of the glass fiber (1*1 cm), and then placed on the bracket in the hydrogenation reactor. The reactor system was sealed and CO2 reaction gas was introduced until the gas filled the reactor system, and the reaction was carried out at 573 K. The flow rate ratio of carbon dioxide to purified hydrogen was 1:4. Both photocatalytic water splitting and hydrogenation reactions were carried out at a light intensity of 3000 mW / cm 2 The reaction was carried out under xenon light source for 3 h. After the reaction was completed, the methane production was quantitatively measured using a gas chromatograph.

[0034] The yield of methane produced by this cascade reaction system can reach 1.1 mmol g -1 h -1 , the selectivity can reach 95%, which meets the standards of superior products.

[0035] Example 3

[0036] This embodiment provides a method for synthesizing ammonia by adding nitrogen to water in a photocatalytic water splitting and hydrogenation reactor connected in series, using the system of Embodiment 1, which differs from Embodiment 2 only in that carbon dioxide is replaced by nitrogen, and the flow rate ratio of nitrogen to purified hydrogen is 1:3.

[0037] The yield of ammonia produced by this cascade reaction system can reach 0.5 mmol g -1 h -1 , the selectivity can reach 90%, which meets the standards of superior products.

[0038] Comparative Example 1

[0039] This comparative example provides a method for synthesizing methane by adding carbon dioxide to water. The photocatalytic reaction of adding carbon dioxide to water is carried out at room temperature and pressure. The specific test operation is as follows: weigh 3 mg TiO 2-x -Au was placed in a centrifuge tube, 300 μL of ultrapure water was added to it, and then it was evenly dispersed with an ultrasonic machine, and the solution was drop-coated on the surface of a 1×1 cm glass fiber, dried completely at 50 °C overnight, and then transferred to a photocatalytic gas-solid reactor, and 400 μL was placed at the bottom of the tube, and then CO2 gas was introduced and the reactor was closed. The reactor was placed in front of a 300 W xenon light source for irradiation to allow the sample surface to react. After the reaction was completed, the gas was extracted from the quartz tube by a syringe, and a gas chromatograph (GC-7890A, Agilent) equipped with a nickel converter (methanation), a TCD detector, and a FID detector was used to detect methane and carbon monoxide in the gas product.

[0040] The yield of methane produced can reach 0.003 mmol g -1 h -1 , the selectivity can reach 25%.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photocatalytic water splitting and tandem hydrogenation reaction system, characterized in that: It comprises a photocatalytic water splitting unit, a separation and purification unit and a hydrogenation unit which are connected in sequence; the photocatalytic water splitting unit is used for photocatalytic water splitting to produce hydrogen, the separation and purification unit is used for separating and purifying hydrogen, and the hydrogenation unit is used for hydrogenating carbon dioxide to produce methane or hydrogenating nitrogen to produce ammonia.

2. The photocatalytic water splitting and tandem hydrogenation reaction system according to claim 1, characterized in that: The photocatalytic water splitting unit comprises a photocatalytic water splitting reactor, a water storage device and a first gas carrier; the photocatalytic water splitting reactor is used to perform a photocatalytic water splitting reaction, the water storage device is used to store raw water, and the first gas carrier is used to transport an inert gas to the photocatalytic water splitting reactor; The photocatalytic water splitting reactor comprises a first feed inlet and a first discharge port, the water storage device comprises a second feed inlet, a third feed inlet, a second discharge port and a third discharge port, and the first gas carrier comprises a fourth feed inlet and a fourth discharge port; The first feed port and the first discharge port of the photocatalytic water splitting reactor, the second feed port and the second discharge port of the water storage device are connected in a pipeline circulation manner, and the fourth discharge port of the first gas carrier device is connected to the third feed port of the water storage device through a pipeline.

3. The photocatalytic water splitting and tandem hydrogenation reaction system according to claim 1, characterized in that: The separation and purification unit includes a deoxygenation device and a drying device; The deoxygenation device is used to remove oxygen from the photocatalytic water decomposition product, and the drying device is used to remove water from the photocatalytic water decomposition product; The deoxygenation device comprises a fifth feed inlet and a fifth discharge port, and the drying device comprises a sixth feed inlet and a sixth discharge port; The third discharge port of the water storage device is connected to the fifth feed port of the deoxygenation device through a pipeline; the fifth discharge port of the deoxygenation device is connected to the sixth feed port of the drying device through a pipeline.

4. The photocatalytic water splitting and tandem hydrogenation reaction system according to claim 1, characterized in that: The hydrogenation unit includes a hydrogenation reactor and a second gas carrier; The hydrogenation reactor is used for hydrogenation reaction of carbon dioxide or nitrogen; the second gas carrier is used for inputting carbon dioxide or nitrogen into the hydrogenation reactor; The hydrogenation reactor comprises a seventh feed port and a seventh discharge port, and the second gas carrier comprises an eighth feed port and an eighth discharge port; The sixth discharge port of the drying device, the seventh feed port of the hydrogenation reactor and the eighth discharge port of the second gas carrier device are connected through a pipeline; the material at the seventh discharge port of the hydrogenation reactor is collected.

5. Use of the photocatalytic water splitting and tandem hydrogenation reaction system according to any one of claims 1 to 4 in the preparation of methane or ammonia.

6. A method for preparing methane or ammonia by hydrogenation reduction, characterized in that: The method is realized by using the photocatalytic water splitting and tandem hydrogenation reaction system described in any one of claims 1 to 4.

7. The method for preparing methane or ammonia by hydrogenation reduction according to claim 6, characterized in that: include: S1: mixing water and a first catalyst in a photocatalytic water splitting reactor, and performing a photocatalytic water splitting reaction under the irradiation of a light source and an atmosphere of an inert gas to produce hydrogen; S2: The hydrogen produced in S1 is passed into a deoxygenation device and a drying device in sequence to remove oxygen and water respectively; the deoxygenation device contains a deoxygenator, and the drying device contains a desiccant; S3: introducing the hydrogen and reaction gas separated and purified in S2 into a hydrogenation reactor, adding a second catalyst, and performing a hydrogenation reaction under the irradiation of a light source; the reaction gas is carbon dioxide or nitrogen.

8. The method for preparing methane or ammonia by hydrogenation reduction according to claim 8, characterized in that: In S1, the intensity of the light source is 1.0~5.0 W / cm 2 .

9. The method for preparing methane or ammonia by hydrogenation reduction according to claim 8, characterized in that: In S1, the first catalyst includes one or more of titanium dioxide, ruthenium-loaded titanium dioxide, cadmium sulfide and zinc indium sulfide; and / or, in S3, the second catalyst includes one or more of ruthenium, cadmium sulfide and indium oxide; Preferably, in S2, the deoxidizer includes one or more of sodium sulfite, hydrazine or dimethyl ketoxime; and / or the desiccant includes one or more of calcium sulfate, calcium chloride, silica gel and activated alumina.

10. The method for preparing methane or ammonia by hydrogenation reduction according to claim 8, characterized in that: In S1, the pressure of the photocatalytic water splitting reaction is 0-40 kPa, and the temperature of the photocatalytic water splitting reaction is 278-333 K; And / or, in S3, the space velocity of the hydrogenation reaction is 0 to 1500 L g -1 h -1 ; The temperature of the hydrogenation reaction is 373~648K; The light intensity of the hydrogenation reaction is 0.4~3.0 W / cm 2 ; And / or, in S3, the flow rate ratio of the carbon dioxide to the hydrogen is 1:2-4; the flow rate ratio of the nitrogen to the hydrogen is 1:3-5.

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