A method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics

Abstract

The present invention provides a method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics, which includes applying plasma to modify plastics to improve the polarity and hydrophilicity of the plastics, and then subjecting the modified plastics to a photoreforming reaction to directionally convert the plastics into high-value chemicals, while simultaneously coupling the water hydrogen production process at the photocathode to prepare hydrogen fuel. This method overcomes the problem of low photocatalytic reaction rate of non-polar plastics, improves the rate of hydrogen production by photoreforming of plastics, and is a green way to achieve high-value utilization of plastics in the context of energy shortages and serious plastic pollution.

Description

Technical Field

[0001] The present application relates to the field of plastic resource utilization, and in particular to a method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics. Background Art

[0002] There are currently two large-scale methods of plastic disposal: incineration and landfill. However, these two methods do not fully utilize the carbon resources of plastics. Instead, the microplastics, carbon dioxide and other products produced during the disposal process will have an adverse impact on the environment.

[0003] Therefore, the resource utilization of plastics is the main research direction of scientific researchers. The current mainstream methods for treating waste plastics include thermal catalysis, electrocatalysis, biodegradation, photocatalysis, etc.

[0004] Among them, photocatalytic conversion uses solar energy as energy input, consumes less energy during the conversion process, does not produce harmful substances, and can selectively break bonds and recombine specific products. It is a clean and green conversion path.

[0005] Photoreforming technology uses water and plastic as raw materials. Water is reduced by photogenerated electrons to produce hydrogen, and plastic is oxidized by photogenerated holes to produce high-value chemicals.

[0006] Compared with the traditional water decomposition process to produce hydrogen, plastic oxidation replaces water to decompose oxygen. The lower oxidation energy barrier accelerates the consumption of photogenerated holes, avoids the recombination of electron-hole pairs, improves hydrogen production efficiency, and realizes the high-value utilization of waste plastics.

[0007] However, most plastics, such as polyethylene, polypropylene, polyvinyl chloride, etc., are extremely hydrophobic and chemically inert, making it difficult for them to effectively come into contact with catalysts in aqueous solutions, and therefore it is impossible to achieve efficient photoreforming reactions.

[0008] Therefore, it is necessary to improve these properties of plastics through system design to achieve high-value conversion of plastics driven by solar energy. Summary of the invention

[0009] Technical problem to be solved by the present invention: The purpose of the present invention is to solve the deficiencies in the prior art. The present invention aims to provide a method for improving the polarity and hydrophilicity of plastics and realizing a plasma-photocatalytic conversion plastic coupled hydrogen production method driven by solar energy for high-value conversion of plastics.

[0010] Technical solution of the present invention: The present invention provides a method for producing hydrogen by coupling plastics through plasma-photocatalytic conversion, comprising the following steps: S1. applying plasma technology to treat plastic powder, grafting polar functional groups on the surface of the plastic, and improving the polarity and hydrophilicity of the plastic;

[0011] S2. Placing the plastic powder after plasma treatment in a photocatalytic reactor, adding semiconductor catalyst powder to carry out photoreforming reaction, converting the plastic into high-value chemicals, and at the same time reducing water to produce hydrogen.

[0012] Furthermore, in step S1, the plastic powder is processed by the plasma technology, including evenly spreading the plastic powder in a plasma reaction device, changing the atmosphere and gas pressure in the plasma reaction device through gas inlet and outlet, and adjusting the parameters of the plasma reaction device so that the power of the plasma reaction device is between 30W and 60W.

[0013] Furthermore, in the step S2, the photoreforming reaction includes adding the plastic powder and semiconductor catalyst powder processed in the step S1 into a photocatalytic reactor, passing nitrogen into the photocatalytic reactor, exhausting the original air, irradiating the photocatalytic reactor with a light source, and performing a photoreforming reaction;

[0014] Continuous magnetic stirring is applied during the photoreforming reaction process to convert plastics into high-value chemicals while water reduction is performed to produce hydrogen;

[0015] The high-value chemicals include CH4, C2H4 and HCOOH.

[0016] Furthermore, the semiconductor catalyst is a photocatalyst with a Pt loading of 1 wt%.

[0017] Furthermore, the semiconductor catalyst includes metal oxide semiconductor photocatalytic materials and carbon-based semiconductor photocatalytic materials, including TiO2, Fe2O3, ZnO, WO3, C3N4, and PI.

[0018] Furthermore, the plastic is a non-polar plastic, including polyethylene, polypropylene, polyvinyl chloride, and polystyrene.

[0019] Furthermore, a quartz window that is permeable to light is provided on the top of the photocatalytic reactor.

[0020] Furthermore, in step S2, the mass ratio of the plastic powder to the semiconductor catalyst powder is (1±0.1).

[0021] Furthermore, the plasma reaction device includes a plasma generator connection port, an upper electrode, a quartz upper cover, a quartz reactor, a lower electrode and a gas inlet and outlet;

[0022] Placing the plastic powder in the quartz reactor, covering it with the quartz upper cover, and introducing the reaction gas into the quartz reactor through the built-in gas inlet and outlet;

[0023] The plasma generator connection port is connected to a plasma reaction device to generate high voltage at the upper electrode; the lower electrode is grounded, and the voltage difference between the upper electrode and the lower electrode excites plasma in the reactor to react with the plastic powder.

[0024] Furthermore, the photocatalytic reactor comprises a gas valve, a liquid inlet and a gas inlet;

[0025] In the step S2, the plastic after the reaction is transferred into the photocatalytic reactor, and the aqueous solution and semiconductor photocatalyst required for the reaction are added at the same time, and the gas valve is opened to introduce inert gas nitrogen into the photocatalytic reactor and then the valve is closed;

[0026] After the light source irradiates and reacts, the reacted liquid is obtained from the liquid taking port, and the reacted gas is obtained from the gas taking port.

[0027] Beneficial effects:

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. Combining plasma technology with photoreforming reaction can solve the problem that existing plastics are difficult to effectively contact with catalysts in aqueous solution; using plasma to modify plastic powder, converting non-polar plastics into polar plastics by attaching polar functional groups on the plastic surface; after treatment, the hydrophilicity of the plastic is enhanced, the interaction between the plastic and the catalyst is increased, and the photoreforming activity is greatly improved.

[0030] 2. During the photoreforming process, the qualitative transformation of waste plastics can be achieved through the energy band regulation and active site design of the catalyst, and the plastics can be oxidized to produce high-value chemicals.

[0031] 3. Compared with existing plastic recycling methods, the method proposed in the present invention has low energy consumption, less pollution, and high selectivity of the obtained products. It realizes the high-value utilization of waste through a green and clean approach, and realizes the preparation of green hydrogen by coupling the water decomposition reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for preparing high-value chemicals coupled with hydrogen production using waste polyethylene in an embodiment of the present invention;

[0033] Figure 2 It is a plasma reaction device and a photocatalytic reaction device in the embodiment of the present invention;

[0034] Figure 3 This is a comparison chart of hydrogen production of different plastics after using this method in the embodiments of the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0036] The plasma-photocatalytic conversion plastic coupling hydrogen production method in this application, such as Figure 1-2 As shown, according to the plasma reaction device and the photocatalytic reaction device of the embodiment of the present invention, during the implementation of the method,

[0037] It includes a plasma reaction device and a photocatalytic reactor 8; wherein the plasma reaction device includes a plasma generator connection port 1, an upper electrode 2, a quartz upper cover 3, a quartz reactor 4, a lower electrode 5 and a gas inlet and outlet 6; the photocatalytic reactor 8 includes a gas valve 7, a liquid inlet 9 and a gas inlet 10.

[0038] The plastic powder is placed in a quartz reactor 4 with an inner diameter of 60 mm and a depth of 8 mm. The reactor is covered with a quartz upper cover 3 and the reaction gas is introduced into the reactor through the built-in gas inlet and outlet 6 .

[0039] The plasma reaction device is connected at 1, high voltage is generated at electrode 2, electrode 5 is grounded, and the voltage difference between electrodes 2 and 5 excites plasma in the reactor to react with the plastic powder.

[0040] The reacted plastic is transferred to the photocatalytic reactor 8, and the aqueous solution and semiconductor photocatalyst required for the reaction are added at the same time. The gas valve 7 is opened to introduce inert gas nitrogen into the reactor and then the valve is closed. After simulating the light source irradiation reaction, the reacted liquid is obtained from the liquid intake port 9, and the reacted gas is obtained from the gas intake port 10.

[0041] Embodiment 1:

[0042] 0.1 g of polyethylene powder was placed in a plasma reaction device and evenly spread on the bottom of a quartz reactor 4. The voltage and frequency of the plasma reaction device were adjusted, and the voltage and current changes were observed by an oscilloscope. The peak voltage at both ends of the electrode in this embodiment was 40 kV, the total power was 45 W, the treatment time was 30 min, and 100 mL / min of air was passed during the treatment.

[0043] The contact angle of the treated sample was measured, and the water contact angle of the treated polyethylene was 86.3°.

[0044] 25 μL of chloroplatinic acid solution, 0.5 g of P25-TiO2 powder and 3 mL of methanol solution were added to 27 ml of water. After stirring at room temperature for 30 min, the mixture was irradiated under a xenon lamp for 2 h. The obtained precipitate was washed and dried to obtain a Pt-loaded TiO2 catalyst.

[0045] 0.03 g of plasma pretreated polyethylene powder and 0.03 g of Pt|TiO2 catalyst were added to the photocatalytic reactor 8, and 30 ml of deionized water was added. Nitrogen was passed into the reactor to expel the original air. A xenon lamp was used as a simulated sunlight source to illuminate the reactor. The reaction system was stirred by magnetrons. The hydrogen production rate within 4 h of reaction was 107.64 μmol g - 1 h -1 .

[0046] After the reaction was completed, the air above the reactor was taken for testing, and hydrocarbons such as CH4, C2H2, and C2H4 were detected.

[0047] Comparative Example 1:

[0048] The difference from Example 1 is that the plasma treatment time is changed to 10 min and 60 min respectively, and the photoreforming hydrogen production rates obtained are 66.53 μmol g -1 h -1 and 49.72 μmol g -1 h -1 .

[0049] Comparative Example 2:

[0050] The difference from Example 1 is that the voltage of the plasma treatment is changed, and the raw material is subjected to plasma treatment at a voltage of 20 kV, and the photoreforming hydrogen production rate obtained is 38.54 μmol g -1 h -1 .

[0051] Comparative Example 3:

[0052] The difference from Example 1 is that the type of plastic used is changed, and the method is applied to convert polypropylene and polyvinyl chloride respectively, and the obtained photoreforming hydrogen production rates are 54.49 μmol g -1 h -1 and 68.70 μmol g -1 h -1 .

[0053] Embodiment 2:

[0054] 0.1 g of polyethylene powder was placed in a quartz reactor. The peak voltage at both ends of the electrodes of the plasma reaction device was 40 kV, the total power was 45 W, the treatment time was 30 min, and air was passed through at 100 mL / min during the treatment process.

[0055] The contact angle of the treated powder was measured, and the water contact angle of the treated polyethylene was 86.3°.

[0056] 0.3 g of melamine was heated to 550°C at a rate of 7°C / min and kept at this temperature for 4 h. The solid obtained after calcination was ground into powder, washed with water, filtered and dried to obtain a g-C3N4 sample.

[0057] 25 μL of chloroplatinic acid solution, 0.5 g of g-C3N4 powder and 3 mL of methanol solution were added to 27 ml of water. After stirring at room temperature for 30 min, the mixture was irradiated under a xenon lamp for 2 h. The obtained precipitate was washed and dried to obtain a g-C3N4 catalyst loaded with Pt.

[0058] 0.03 g of plasma-pretreated polyethylene powder and 0.03 g of Ni2P|g-C3N4 catalyst were added to the photocatalytic reactor. Nitrogen was passed into the reactor to expel the original air. A xenon lamp was used as a simulated sunlight source to illuminate the reactor. The reaction system was stirred by magnetrons. The hydrogen production rate within 4 h was 8.92 μmol g -1 h -1 .

[0059] Results and Discussion:

[0060] In order to explore the effects of voltage, time and plastic type on the reaction activity during dielectric barrier discharge plasma treatment, comparative examples 1, 2 and 3 were designed respectively, and the reaction activity was measured by the hydrogen production rate.

[0061] It can be seen from Example 1 and Comparative Example 1 that as the plasma treatment time increases, the photoreforming reaction activity increases. However, when the plasma treatment time exceeds 30 min, the photoreforming activity decreases.

[0062] It can be seen from Example 1 and Comparative Example 2 that as the voltage increases during the plasma treatment process, the reaction activity increases.

[0063] like Figure 3 As shown, it can be seen from Example 1 and Comparative Example 3 that for different plastics, the improvement of photoreforming activity by plasma treatment is different, and the improvement effect on polyethylene is higher than that on polypropylene and polyvinyl chloride.

[0064] In order to explore the application of different photocatalysts in this system, Example 2 was designed. It can be seen from Examples 1 and 2 that under full irradiation, the reaction activity of carbon-based photocatalysis is lower than that of commercial titanium dioxide.

[0065] In general, the plasma-photocatalytic reaction system can effectively improve the activity of plastic photoreforming reaction. Factors such as voltage and time during plasma treatment will affect the reaction activity.

[0066] After plasma treatment, polar functional groups are grafted onto the plastic surface, and non-polar plastics show good hydrophilicity. Through the plasma-photocatalytic reaction system, plastics can eventually be converted into high-value hydrocarbons.

[0067] The basic principles, main features and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics, characterized in that: The method comprises the following steps: S1. applying plasma technology to treat plastic powder, grafting polar functional groups on the plastic surface, and improving the polarity and hydrophilicity of the plastic; In the step S1, the plastic powder is processed by the plasma technology, including evenly spreading the plastic powder in a plasma reaction device, changing the atmosphere and gas pressure in the plasma reaction device through a gas inlet and outlet, and adjusting the parameters of the plasma reaction device so that the power of the plasma reaction device is between 30 W and 60 W; S2. Placing the plasma-treated plastic powder in a photocatalytic reactor (8), adding semiconductor catalyst powder to carry out a photoreforming reaction, converting the plastic into high-value chemicals, and simultaneously reducing water to produce hydrogen; In the step S2, the photoreforming reaction comprises adding the plastic powder and semiconductor catalyst powder processed in the step S1 into a photocatalytic reaction kettle (8), passing nitrogen into the photocatalytic reaction kettle (8), exhausting the original air, irradiating the photocatalytic reaction kettle (8) with a light source, and performing a photoreforming reaction; Continuous magnetic stirring is applied during the photoreforming reaction process to convert plastics into high-value chemicals while water reduction is performed to produce hydrogen; The high-value chemicals include CH4 and C2H4; The semiconductor catalyst is a titanium dioxide catalyst loaded with Pt, wherein the loading amount of Pt is 1wt%; The plastic is a non-polar plastic, including polyethylene, polypropylene, and polyvinyl chloride; The plasma reaction device comprises a plasma generator connection port (1), an upper electrode (2), a quartz upper cover (3), a quartz reaction kettle (4), a lower electrode (5) and a gas inlet and outlet (6); The plastic powder is placed in the quartz reaction kettle (4), covered with the quartz upper cover (3), and the reaction gas air is introduced into the quartz reaction kettle (4) through the built-in gas inlet and outlet (6); The plasma generator connection port (1) is connected to a plasma reaction device to generate high voltage at the upper electrode (2); the lower electrode (5) is grounded, and the voltage difference between the upper electrode (2) and the lower electrode (5) excites plasma in the reactor to react with the plastic powder.

2. The method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics according to claim 1, characterized in that: The top of the photocatalytic reaction kettle (8) is provided with a quartz window that is permeable to light.

3. The method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics according to claim 1, characterized in that: In the step S2, the mass ratio of the plastic powder to the semiconductor catalyst powder is 0.9-1.1:

1.

4. The method for producing hydrogen by coupling plasma-photocatalytic conversion of plastics according to claim 1, characterized in that: The photocatalytic reaction kettle (8) comprises a gas valve (7), a liquid intake port (9) and a gas intake port (10); In the step S2, the plastic after the reaction is transferred into the photocatalytic reaction kettle (8), and the aqueous solution and semiconductor photocatalyst required for the reaction are added at the same time, and the gas valve (7) is opened to pass inert gas nitrogen into the photocatalytic reaction kettle (8), and then the valve is closed; After the light source irradiates the reaction, the liquid after the reaction is obtained from the liquid taking port (9), and the gas after the reaction is obtained from the gas taking port (10).

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