Device and method for preparing graphene from waste plastics

Abstract

The invention discloses a device and a method for preparing graphene from waste plastics, and belongs to the technical field of treatment of waste plastics. The device comprises an automatic feeding module, a fixed bed pyrolysis module, a bubbling bed catalysis module and a product separation module, the automatic feeding module is used for inputting reaction raw materials into the fixed bed pyrolysis module, and the reaction raw materials comprise waste plastics; the fixed bed pyrolysis module is used for pyrolyzing the reaction raw materials to obtain a pyrolysis product; the bubbling bed catalysis module is used for carrying out catalytic reaction on the pyrolysis product in a bubbling form in the presence of a catalyst to obtain graphene and a gas product; and the product separation module is used for separating the gas product to obtain a gas product containing C2-C4 hydrocarbon. According to the method, the waste plastic can be fully converted into high-value graphene and C2-C4 hydrocarbon, and efficient recycling of the waste plastic is achieved.

Description

An apparatus and method for producing graphene from waste plastics Technical Field

[0001] This invention relates to an apparatus and method for producing graphene from waste plastics, belonging to the field of waste plastic treatment technology. Background Technology

[0002] With the rapid improvement of people's living standards and industrial development, the plastics industry is also developing rapidly, and global plastic production remains high. However, corresponding to this high production volume, plastic products often have a short lifespan, resulting in a daily increase in global waste plastics. On the one hand, waste plastics have a global and persistent impact on the environment and organisms, and on the other hand, most existing waste plastics originate from fossil fuels and are still valuable carbon resources. Currently, common recycling methods for waste plastics include landfill, incineration, chemical utilization, and physical recycling, with landfill and incineration still playing a dominant role. However, their ability to recover and utilize the chemical resources in waste plastics remains very limited.

[0003] Chemical utilization includes various pathways such as gasification, hydrolysis, pyrolysis, photocatalysis, electrocatalysis, and biodegradation. Among these, pyrolysis is a relatively mature technology with a simple process, making it an economically feasible and promising technology for large-scale disposal. Pyrolysis generally occurs in an inert atmosphere, breaking down plastics into small hydrocarbon molecules through high temperatures. Solid acid catalysis is commonly used, but it still faces challenges such as catalyst deactivation and regeneration. Furthermore, research on how to convert waste plastics into high-value graphene remains insufficient. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide an apparatus and method for producing graphene from waste plastics. This invention can effectively convert waste plastics into high-value graphene and C2-C4 hydrocarbons, achieving efficient recycling of waste plastics.

[0005] To achieve the above objectives, a first aspect of the present invention provides an apparatus for producing graphene from waste plastics, comprising: an automatic feeding module, a fixed-bed pyrolysis module, a bubbling-bed catalytic module, and a product separation module; the automatic feeding module is used to input reaction raw materials into the fixed-bed pyrolysis module, the reaction raw materials including waste plastics; the fixed-bed pyrolysis module is used to pyrolyze the reaction raw materials to obtain pyrolysis products; the bubbling-bed catalytic module is filled with a catalyst, the catalyst including a liquid alloy, the bubbling-bed catalytic module is used to catalyze the pyrolysis products in the presence of the catalyst in a bubbling manner to obtain graphene and gaseous products; the product separation module is used to separate the gaseous products obtained from the bubbling-bed catalytic module to obtain gaseous products containing C2-C4 hydrocarbons.

[0006] The second aspect of the present invention provides a method for producing graphene from waste plastics, the method being carried out using the aforementioned apparatus for producing graphene from waste plastics, the method comprising the following steps: (1) feeding the reaction raw materials into a fixed-bed pyrolysis module using an automatic feeding module, the reaction raw materials including waste plastics; (2) pyrolyzing the reaction raw materials using the fixed-bed pyrolysis module to obtain pyrolysis products; (3) catalyzing the pyrolysis products in the presence of a catalyst using a bubble bed catalytic module, the catalyst including a liquid alloy, to obtain graphene and gaseous products; (4) separating the gaseous products obtained from the bubble bed catalytic module using a product separation module to obtain gaseous products containing C2-C4 hydrocarbons.

[0007] This invention has at least the following beneficial effects: It can fully convert waste plastics into high-value graphene and C2-C4 hydrocarbons, achieving efficient recycling of waste plastics. The waste plastic conversion rate of this invention can reach >99%, and the selectivity of graphene can reach >20%. Furthermore, this invention also has the advantage of easy separation and collection of both gaseous and solid products. Attached Figure Description

[0008] Figure 1 is a schematic diagram of the device for producing graphene from waste plastics according to a specific embodiment of the present invention.

[0009] Figure 2 is a schematic diagram of the process and mechanism of the method for producing graphene from waste plastics in a specific embodiment of the present invention.

[0010] Figure 3 is a transmission electron microscope image of the graphene prepared in Example 1.

[0011] Figure 4 shows the mass content distribution of solid and gaseous products of carbon materials prepared under different catalysts and at different catalytic reaction temperatures.

[0012] Figure 5 is a transmission electron microscope (TEM) image of the solid product obtained from the binary liquid alloy composed of 5 wt% Ni and 95 wt% Bi in Comparative Example 1 at a catalytic reaction temperature of 700 °C.

[0013] Figure 6 shows the mass content distribution of solid and gaseous products of carbon materials prepared from different reactants.

[0014] Figure 7 shows the degree of graphitization of solid carbon materials prepared from different reactants.

[0015] Reference numerals: 1-Automatic feeding module; 2-Fixed bed pyrolysis module; 3-Bubble bed catalysis module; 4-Product separation module; 101-Hopper; 102-Screw automatic feeder; 103-First air inlet pipe; 201-Pyrolysis reactor; 202-Second air inlet pipe; 203-Third air inlet pipe; 204-Fourth air inlet pipe; 301-Bubble reactor; 302-Insulation box; 401-Gas washing bottle; 402-Water bath. Detailed Implementation

[0016] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0017] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0019] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0020] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0023] According to a specific embodiment of the first aspect of the present invention, the present invention provides an apparatus for producing graphene from waste plastics, as shown in FIG1, comprising: an automatic feeding module 1, a fixed bed pyrolysis module 2, a bubbling bed catalytic module 3, and a product separation module 4; the automatic feeding module 1 is used to input the reaction raw materials into the fixed bed pyrolysis module 2, the reaction raw materials including waste plastics; the fixed bed pyrolysis module 2 is used to pyrolyze the reaction raw materials to obtain pyrolysis products; the bubbling bed catalytic module 3 is filled with a catalyst, the catalyst including a liquid alloy, the bubbling bed catalytic module 3 is used to catalyze the pyrolysis products in the presence of the catalyst in a bubbling form to obtain graphene and gaseous products; the product separation module 4 is used to separate the gaseous products obtained from the bubbling bed catalytic module 3 to obtain gaseous products containing C2-C4 hydrocarbons.

[0024] In some embodiments, the automatic feeding module 1 includes a hopper 101, a screw feeder 102, and a first air inlet pipe 103. The hopper 101 is filled with the reaction raw materials. The screw feeder 102 is connected to the hopper 101 and the fixed-bed pyrolysis module 2, and is used to input the reaction raw materials into the fixed-bed pyrolysis module 2. The first air inlet pipe 103 is connected to the hopper 101 and is used to provide a first protective gas to isolate oxygen from the screw feeder 102 during the input of the reaction raw materials. The screw feeder 102 is horizontally placed. By setting up the automatic feeding module 1, the reaction raw materials can be continuously fed into the fixed-bed pyrolysis module 2, which facilitates industrial operation.

[0025] In some embodiments, the fixed-bed pyrolysis module 2 includes a pyrolysis reactor 201.

[0026] In some embodiments, the pyrolysis reactor 201 is connected to a second gas inlet pipe 202, which is used to provide a second protective gas to the pyrolysis reactor 201 and the bubbling bed catalytic module 3.

[0027] In some embodiments, the pyrolysis reactor 201 is also connected to a third air inlet pipe 203 and a fourth air inlet pipe 204, which are used to supply reducing gas and oxidizing gas to the bubbling bed catalytic module 3, respectively, to treat the catalyst in the bubbling bed catalytic module 3.

[0028] In some embodiments, the fixed-bed pyrolysis module 2 further includes thermocouples and a control unit for detecting and controlling the pyrolysis temperature in the pyrolysis reactor 201.

[0029] In some embodiments, the pyrolysis reactor 201 is equipped with a sieve plate or a sand core, wherein the sieve plate has an aperture of 0.1 mm to 10 mm, and the sand core has a mesh size of 50 to 500 mesh. By setting the sieve plate or sand core, the flow pattern of the bubbles entering the bubbling bed catalytic module 3 can be adjusted, improving the heat and mass transfer effect, thereby increasing the conversion rate of waste plastics and the quality of graphene.

[0030] In some embodiments, the bubbling bed catalytic module 3 includes a bubbling reactor 301; the bubbling reactor 301 is filled with the catalyst; the catalyst includes a ternary liquid alloy, which comprises an active metal, a metal additive, and a metal solvent; the active metal includes one or more of iron, cobalt, nickel, copper, and zinc; the metal additive includes one or more of tungsten, molybdenum, and chromium; and the metal solvent includes one or more of bismuth, gallium, indium, and tin. Preferably, the active metal is nickel, the metal additive is molybdenum, and the metal solvent is bismuth, i.e., the catalyst includes a nickel-molybdenum-bismuth ternary liquid alloy. This invention has found that using the above-mentioned ternary liquid alloy as a catalyst is beneficial for improving the yield and quality of graphene, with the nickel-molybdenum-bismuth ternary liquid alloy exhibiting the best overall performance.

[0031] In some embodiments, based on the total mass of the ternary liquid alloy as 100%, the content of the active metal is 1-15%, the content of the metal additive is 1-5%, and the content of the metal solvent is 80-98%.

[0032] In some embodiments, the catalyst may selectively include a molten salt, wherein the mass ratio of the molten salt to the liquid alloy is (0-50):(100-50). Preferably, the molten salt includes one or more of alkali metal inorganic salts, alkaline earth metal inorganic salts, and transition metal inorganic salts. There are no particular limitations on the specific type of inorganic salt; for example, it may include one or more of halides, sulfates, nitrates, carbonates, and phosphates.

[0033] In some embodiments, the bubbling bed catalytic module 3 further includes an insulation box 302, which is connected to the bubbling reactor 301 and the fixed bed pyrolysis module 2, and is used to allow the pyrolysis products to enter the bubbling reactor through the insulation box 302.

[0034] In some embodiments, the bubbling bed catalytic module 3 also includes a thermocouple and a control unit for detecting and controlling the catalytic reaction temperature in the bubbling reactor 301.

[0035] In some embodiments, the product separation module 4 includes a gas washing bottle 401 and a water bath 402 disposed around the gas washing bottle 401.

[0036] According to a specific embodiment of the second aspect of the present invention, the present invention provides a method for producing graphene from waste plastics, the method being carried out using the above-mentioned apparatus for producing graphene from waste plastics, the method comprising the following steps: (1) feeding the reaction raw materials into a fixed bed pyrolysis module 2 using an automatic feeding module 1, the reaction raw materials including waste plastics; (2) pyrolyzing the reaction raw materials using the fixed bed pyrolysis module 2 to obtain pyrolysis products; (3) catalyzing the pyrolysis products in a bubbling form using a bubble bed catalytic module 3 in the presence of a catalyst, the catalyst including a liquid alloy, to obtain graphene and gaseous products; (4) separating the gaseous products obtained from the bubble bed catalytic module 3 using a product separation module 4 to obtain gaseous products containing C2-C4 hydrocarbons.

[0037] In some embodiments, in step (1), the waste plastic is in powder form and / or in the form of small spheres with a diameter of less than 3.5 mm.

[0038] In some embodiments, in step (1), the waste plastic includes waste polyethylene.

[0039] In some embodiments, in step (1), the automatic feeding module 1 includes a hopper 101, a screw automatic feeder 102, and a first air inlet pipe 103; the hopper 101 is filled with the reaction raw materials; the screw automatic feeder 102 is connected to the hopper 101 and the fixed-bed pyrolysis module 2, and is used to input the reaction raw materials into the fixed-bed pyrolysis module 2, the feeding rate of the screw automatic feeder 102 is 0.5-2 g / min; the first air inlet pipe 103 is connected to the hopper 101, and is used to provide a first protective gas to isolate oxygen during the input of the reaction raw materials by the screw automatic feeder 102, the flow rate of the first protective gas is 10-1000 mL / min. Specifically, the first protective gas includes one or more of nitrogen, helium, and argon. Specifically, the hopper 101 can be filled with 0.5-15 g of reaction raw materials at a time.

[0040] In some embodiments, in step (2), the fixed-bed pyrolysis module 2 includes a pyrolysis reactor 201, and the pyrolysis temperature in the pyrolysis reactor 201 is 300-800 °C. Preferably, the heating rate in the pyrolysis reactor 201 is 5-30 °C / min. By controlling the pyrolysis temperature within the above range, it is beneficial to ensure that the pyrolysis products of waste plastic contain a higher content of long-chain hydrocarbon compounds. The pyrolysis products include wax phase, oil phase, and gas phase products. This invention has found that, compared with the prior art using small molecule hydrocarbons below C6 (such as methane) as carbon sources, this invention uses the pyrolysis products of waste plastic as carbon sources, which is more conducive to the synthesis of graphene, rather than amorphous carbon and other carbon materials, and is more conducive to improving the quality of graphene. Moreover, if the pyrolysis temperature is too high, carbon deposits are easily generated in the fixed-bed pyrolysis module 2, leading to a decrease in the yield and quality of graphene in the subsequent bubbling bed catalytic module 3.

[0041] In some embodiments, in step (2), the pyrolysis reactor 201 is connected to a second inlet pipe 202, which provides a second protective gas to the pyrolysis reactor 201 and the bubbling bed catalytic module 3. The flow rate of the second protective gas is 10-1000 mL / min. Specifically, the second protective gas includes one or more of nitrogen, helium, and argon. The second protective gas is used to provide a protective gas atmosphere in the pyrolysis reactor 201, maintain the gas flow rate in the pyrolysis reactor 201 and the bubbling reactor 301, and can be used to adjust the bubbling morphology in the bubbling reactor 301.

[0042] In some embodiments, the modules operate in a protective gas atmosphere, with the flow rate of the protective gas controlled at 10-1000 mL / min.

[0043] In some embodiments, in step (2), the pyrolysis reactor 201 is further connected to a third inlet pipe 203 and a fourth inlet pipe 204. The third inlet pipe 203 and the fourth inlet pipe 204 are respectively used to supply reducing gas and oxidizing gas to the bubbling bed catalytic module 3 to treat the catalyst in the bubbling bed catalytic module 3. The flow rates of the reducing gas and the oxidizing gas are 50-100 mL / min, respectively. Specifically, the reducing gas includes hydrogen, etc., and the oxidizing gas includes air, etc. The reducing gas can be used to regenerate the catalyst in the bubbling bed catalytic module 3, and the oxidizing gas can be used in the gasification reaction process in the bubbling bed catalytic module 3, that is, to participate in the reaction, thereby controlling the product distribution. The regeneration process can be carried out in accordance with conventional methods in the art, and the present invention does not impose any special limitations on it.

[0044] In some embodiments, in step (2), the pyrolysis reactor 201 is provided with a sieve plate or a sand core, wherein the sieve plate has a hole diameter of 0.1 mm-10 mm and the sand core has a mesh size of 50-500 mesh.

[0045] In some embodiments, in step (3), the bubbling bed catalytic module 3 includes a bubbling reactor 301; the bubbling reactor 301 is filled with the catalyst; the catalyst includes a ternary liquid alloy, which includes an active metal, a metal additive, and a metal solvent; the active metal includes one or more of iron, cobalt, nickel, copper, and zinc; the metal additive includes one or more of tungsten, molybdenum, and chromium; and the metal solvent includes one or more of bismuth, gallium, indium, and tin. Preferably, the active metal is nickel, the metal additive is molybdenum, and the metal solvent is bismuth, that is, the catalyst includes a nickel-molybdenum-bismuth ternary liquid alloy.

[0046] In some embodiments, in step (3), based on the total mass of the ternary liquid alloy as 100%, the content of the active metal is 1-15%, the content of the metal additive is 1-5%, and the content of the metal solvent is 80-98%.

[0047] In some embodiments, in step (3), the catalyst may selectively include a molten salt, wherein the mass ratio of the molten salt to the liquid alloy is (0-50):(100-50). Preferably, the molten salt includes one or more of alkali metal inorganic salts, alkaline earth metal inorganic salts, and transition metal inorganic salts. There are no special limitations on the specific type of inorganic salt; for example, it may include one or more of halides, sulfates, nitrates, carbonates, and phosphates.

[0048] In some embodiments, in step (3), the bubbling bed catalytic module 3 includes a bubbling reactor 301, and the catalytic reaction temperature in the bubbling reactor 301 is 700-1200 ℃. The bubbling reactor 301 is placed vertically.

[0049] In some embodiments, in step (3), in the bubbling reactor 301, the volume hourly space velocity of the pyrolysis products relative to the catalyst is 10-10000 h⁻¹. -1 The catalyst bed height in the bubbling reactor 301 can be 0.5-3 cm.

[0050] In some embodiments, in step (3), the graphene has 3-10 layers (i.e., contains 3-10 layers of carbon atoms).

[0051] In this invention, the catalyst in the bubbling reactor 301 is loaded in a solid state. As the temperature inside the bubbling reactor 301 rises, the catalyst forms a homogeneous liquid state. The pyrolysis products undergo rapid heat and mass transfer with the liquid catalyst in a bubbling manner, reacting to generate solid and gaseous products during the process. The solid product is mainly graphene. Due to the density difference between graphene and the liquid catalyst, it floats on top of the liquid catalyst in the bubbling reactor 301, facilitating separation and preventing catalyst deactivation due to carbon buildup, thus significantly extending the catalyst's lifespan. The gaseous product enters the subsequent product separation module 4.

[0052] In some embodiments, in step (3), the bubbling bed catalytic module 3 further includes a heat preservation box 302, which is connected to the bubbling reactor 301 and the fixed bed pyrolysis module 2. The heat preservation box 302 is used to allow the pyrolysis products to enter the bubbling reactor 301 through the heat preservation box 302. The operating temperature of the heat preservation box 302 is 300-500 ℃. By setting the heat preservation box 302 and controlling its temperature within the above range, it can be ensured that the pyrolysis products will not condense into wax or other phases and solidify in the pipeline during the transportation process.

[0053] In some embodiments, in step (4), the product separation module 4 includes a gas washing bottle 401 and a water bath 402 disposed around the gas washing bottle 401, the temperature of the water bath 402 being 1-5 °C. The product separation module 4 is used to remove any liquid-solid products (e.g., liquid and wax phase products) that may remain in the gaseous product obtained from the bubble bed catalytic module 3, ultimately obtaining a gaseous product containing C2-C4 hydrocarbons, which can be subsequently collected by a gas bag or directly introduced into gas chromatography or other equipment for characterization and analysis. The gaseous product containing C2-C4 hydrocarbons is mainly a gaseous product containing C2-C4 olefins.

[0054] The reaction flow and reaction mechanism of steps (1) to (4) in some embodiments of the present invention are shown in Figure 2.

[0055] This invention can effectively convert waste plastics into high-value graphene and C2-C4 olefins, achieving efficient recycling of waste plastics. The waste plastic conversion rate of this invention can reach >99%, the selectivity of graphene can reach >20%, and the yield of C2-C4 olefins can reach >60%. Furthermore, this invention also has the advantage of easy separation and collection of both gaseous and solid products.

[0056] The technical solutions of the present invention are specifically illustrated below through embodiments, but the present invention is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of the present invention.

[0057] Calculation method: Conversion rate of waste plastics = Total mass of gas-liquid-solid three-phase products / Total mass of waste plastics fed in × 100%.

[0058] Selectivity of graphene = mass of graphene product / total mass of gas-liquid-solid three-phase products × 100%.

[0059] The yield of C2-C4 olefins = selectivity of C2-C4 olefin products × conversion rate of waste plastics. Wherein, selectivity of C2-C4 olefin products = mass of C2-C4 olefin products / total mass of gas-liquid-solid three-phase products.

[0060] Example 1

[0061] This embodiment provides a method for producing graphene from waste plastics, using the apparatus for producing graphene from waste plastics shown in Figure 1. Its structure has been described above and will not be repeated here.

[0062] The method of this embodiment includes the following steps: (1) 1 g of reaction raw material is put into the hopper 101 of the automatic feeding module 1, and nitrogen gas at 30 mL / min is introduced through the first air inlet pipe 103. The conveying rate of the screw automatic feeder 102 is set to 0.5 g / min. The screw automatic feeder 102 inputs the reaction raw material into the fixed bed pyrolysis module 2. The reaction raw material is waste plastic; (2) The reaction raw material is pyrolyzed using the pyrolysis reactor 201 of the fixed bed pyrolysis module 2. The pyrolysis reactor 201 is equipped with a sieve plate with a pore size of 1 mm. The pyrolysis temperature in the pyrolysis reactor 201 is 500 ℃, and the heating rate is 20 ℃ / min. At the same time, nitrogen gas at 70 mL / min is introduced through the second air inlet pipe 202 to obtain the pyrolysis product; (3) The pyrolysis product enters the heat preservation box 302 of the bubble bed catalytic module 3 along with the protective gas (i.e., nitrogen gas). The temperature of the heat preservation box 302 is 400 ℃. The catalyst is heated to 800 °C and then fed into a bubbling reactor 301, which contains a bed of catalyst with a height of 2 cm. The catalytic reaction takes place in a bubbling manner in the presence of the catalyst. The catalyst is a nickel-molybdenum-bismuth ternary liquid alloy, with a nickel content of 3.75 wt%, a molybdenum content of 1.25 wt%, and a bismuth content of 95 wt% by mass. The catalytic reaction temperature in the bubbling reactor 301 is 800 °C. The pyrolysis products are preheated to the catalytic reaction temperature at a heating rate of 20 °C / min before being introduced. The volume hourly space velocity (VHSV) of the pyrolysis products relative to the catalyst is 96 h⁻¹. -1 , to obtain graphene and gaseous products; (4) The gaseous products obtained from the bubble bed catalytic module 3 enter the gas washing bottle 401 of the product separation module 4 for separation. A flowing water bath 402 is set around the gas washing bottle 401. The temperature of the water bath 402 is 3 ℃, and gaseous products mainly composed of hydrogen and C2-C4 olefins are obtained.

[0063] In this embodiment, the reaction raw material (i.e., waste plastic) is small spherical polyethylene with a diameter of 3 mm. The solid product of step (3) was characterized by transmission electron microscopy and verified to be graphene with 3-10 layers, as shown in Figure 3. The gaseous product of step (4) was characterized by gas chromatography and verified to be mainly composed of C2-C4 olefins. Calculations show that the conversion rate of waste plastic in this embodiment is 99.5%, the selectivity of graphene is 28%, and the yield of C2-C4 olefins is 67%.

[0064] Examples 2-3

[0065] Examples 2 and 3 are basically the same as Example 1, except that the catalyst in the bubbling reactor 301 is different. Everything else is the same as Example 1.

[0066] The catalyst in Example 2 was a ternary liquid alloy of iron, molybdenum, and bismuth, which contained 3.75 wt% iron, 1.25 wt% molybdenum, and 95 wt% bismuth by mass percentage.

[0067] The catalyst in Example 3 was a copper-molybdenum-bismuth ternary liquid alloy, which contained 3.75 wt% copper, 1.25 wt% molybdenum, and 95 wt% bismuth by mass percentage.

[0068] The solid products from step (3) of Examples 2 and 3 were characterized by transmission electron microscopy (TEM) to verify that they were graphene with 3-10 layers. The gaseous products from step (4) of Examples 2 and 3 were characterized by gas chromatography (GC) to verify that the gaseous products were mainly C2-C4 olefins. Calculations showed that the waste plastic conversion rate of Example 2 was 99%, the graphene selectivity was 16.6%, and the yield of C2-C4 olefins was 62.5%. The waste plastic conversion rate of Example 3 was 99%, the graphene selectivity was 13.2%, and the yield of C2-C4 olefins was 60.1%.

[0069] Comparative Example 1

[0070] This comparative example is basically the same as Example 1, except that the catalyst in the bubbling reactor 301 is pure bismuth liquid metal. Everything else is the same as in Example 1.

[0071] Transmission electron microscopy (TEM) characterization of the solid product from step (3) revealed it to be a layered amorphous carbon material. Gas chromatography (GC) characterization of the gaseous product from step (4) confirmed that it was predominantly composed of C2-C4 olefins. Calculations showed that the conversion rate of waste plastics in this comparative example was 92%, the yield of amorphous carbon material was less than 20%, the selectivity for graphene was 0%, and the yield of C2-C4 olefins was 61%.

[0072] Furthermore, this comparative example replaced the catalyst with other liquid metal or liquid alloy catalysts and varied the catalytic reaction temperature. The mass content distribution of solid and gaseous products of carbon materials prepared under different catalysts and catalytic reaction temperatures is shown in Figure 4. In Figure 4, numbers 1-5 represent the product distribution when pure bismuth liquid metal is used as a catalyst at different catalytic reaction temperatures. Numbers 6-10 represent the product distribution when binary liquid alloys composed of 5 wt% Fe, Co, Ni, Cu, or Zn and 95 wt% Bi are reacted at a catalytic reaction temperature of 700 °C. Additionally, Figure 5 shows the transmission electron microscopy (TEM) image of the solid product obtained from the binary liquid alloy composed of 5 wt% Ni and 95 wt% Bi at a catalytic reaction temperature of 700 °C, verifying that it is an amorphous carbon material.

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 1, except that the reaction raw material is methane. Everything else is the same as in Example 1.

[0075] The solid product from step (3) was characterized by transmission electron microscopy to verify that it is an amorphous carbon material. The gaseous product from step (4) was characterized by gas chromatography to verify that it is mainly composed of hydrogen and methane. Calculations showed that the methane conversion rate in this comparative example was 2%, the yield of the amorphous carbon material was less than 2%, the selectivity of graphene was 0%, and the yield of C2-C4 olefins was 0%.

[0076] In addition, the reactants in this comparative example were replaced with other hydrocarbon compounds. The mass content distribution of solid and gaseous carbon products prepared from different reactants is shown in Figure 6, and the degree of graphitization of solid products prepared from different reactants is shown in Figure 7.

[0077] Figure 7 was obtained through the following method: the solid carbon material product was subjected to temperature-programmed oxidation (TPO) using a chemisorption analyzer. The gas generated during the temperature-programmed oxidation process was analyzed by mass spectrometry, and the relative intensity curve of CO2 during the heating process was obtained, which is shown in Figure 7. As can be seen from Figure 7, when ethane is used as the reaction raw material, the oxidation peak appears at a lower temperature, corresponding to a disordered structure of carbon material, a low degree of graphitization, and amorphous carbon.

[0078] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An apparatus for producing graphene from waste plastics, comprising: The system comprises an automatic feeding module, a fixed-bed pyrolysis module, a bubbling-bed catalytic module, and a product separation module. The automatic feeding module feeds reactants into the fixed-bed pyrolysis module, the reactants including waste plastics. The fixed-bed pyrolysis module pyrolyzes the reactants to obtain pyrolysis products. The bubbling-bed catalytic module is filled with a catalyst, including a liquid alloy, which catalyzes the pyrolysis products in a bubbling manner in the presence of the catalyst to obtain graphene and gaseous products. The product separation module separates the gaseous products obtained from the bubbling-bed catalytic module to obtain gaseous products containing C2-C4 hydrocarbons.

2. The apparatus for producing graphene from waste plastics according to claim 1, wherein, The automatic feeding module includes a hopper, a screw automatic feeder, and a first air inlet pipe; the hopper is filled with the reaction raw materials; the screw automatic feeder is connected to the hopper and the fixed bed pyrolysis module, and is used to input the reaction raw materials into the fixed bed pyrolysis module; The first air inlet pipe is connected to the hopper and is used to provide a first protective gas so that the screw automatic feeder is isolated from oxygen during the input of the reaction raw materials.

3. The apparatus for producing graphene from waste plastics according to claim 1, wherein, The fixed-bed pyrolysis module includes a pyrolysis reactor.

4. The apparatus for producing graphene from waste plastics according to claim 3, wherein, The pyrolysis reactor is connected to a second gas inlet pipe, which is used to provide a second protective gas to the pyrolysis reactor and the bubbling bed catalytic module.

5. The apparatus for producing graphene from waste plastics according to claim 4, wherein, The pyrolysis reactor is also connected to a third air inlet pipe and a fourth air inlet pipe, which are used to supply reducing gas and oxidizing gas to the bubbling bed catalytic module, respectively, to treat the catalyst in the bubbling bed catalytic module.

6. The apparatus for producing graphene from waste plastics according to claim 3, wherein, The fixed-bed pyrolysis module also includes thermocouples and a control unit for detecting and controlling the pyrolysis temperature in the pyrolysis reactor.

7. The apparatus for producing graphene from waste plastics according to claim 3, wherein, The pyrolysis reactor is equipped with a sieve plate or a sand core. The sieve plate has an aperture of 0.1 mm to 10 mm, and the sand core has a mesh size of 50 to 500 mesh.

8. The apparatus for producing graphene from waste plastics according to claim 1, wherein, The bubbling bed catalytic module includes a bubbling reactor; the bubbling reactor is filled with the catalyst; the catalyst includes a ternary liquid alloy, the ternary liquid alloy includes an active metal, a metal additive, and a metal solvent; the active metal includes one or more of iron, cobalt, nickel, copper, and zinc; the metal additive includes one or more of tungsten, molybdenum, and chromium; the metal solvent includes one or more of bismuth, gallium, indium, and tin.

9. The apparatus for producing graphene from waste plastics according to claim 8, wherein, The active metal is nickel, the metal additive is molybdenum, and the metal solvent is bismuth.

10. The apparatus for producing graphene from waste plastics according to claim 8, wherein, Based on the total mass of the ternary liquid alloy as 100%, the content of the active metal is 1-15%, the content of the metal additive is 1-5%, and the content of the metal solvent is 80-98%.

11. The apparatus for producing graphene from waste plastics according to claim 1, wherein, The catalyst also selectively includes a molten salt, wherein the mass ratio of the molten salt to the liquid alloy is (0-50):(100-50).

12. The apparatus for producing graphene from waste plastics according to claim 8, wherein, The bubbling bed catalytic module further includes an insulation box connected to the bubbling reactor and the fixed bed pyrolysis module, for allowing the pyrolysis products to enter the bubbling reactor through the insulation box; and / or, the bubbling bed catalytic module further includes a thermocouple and a control unit for detecting and controlling the catalytic reaction temperature in the bubbling reactor.

13. The apparatus for producing graphene from waste plastics according to claim 1, wherein, The product separation module includes a gas washing bottle and a water bath disposed around the gas washing bottle.

14. A method for producing graphene from waste plastics, said method being carried out using the apparatus for producing graphene from waste plastics according to any one of claims 1-13, said method comprising the following steps: (1) The reaction raw materials are fed into the fixed bed pyrolysis module using an automatic feeding module. The reaction raw materials include waste plastics. (2) The reaction raw materials are pyrolyzed using the fixed bed pyrolysis module to obtain pyrolysis products. (3) The pyrolysis products are catalyzed in the presence of a catalyst in the form of bubbles using a bubble bed catalysis module. The catalyst includes liquid alloys to obtain graphene and gaseous products. (4) The gaseous products obtained by the bubble bed catalysis module are separated using a product separation module to obtain gaseous products containing hydrocarbons of C2-C4.

15. The method for producing graphene from waste plastics according to claim 14, wherein, In step (1), the waste plastic is in powder form and / or in the form of small spheres with a diameter of less than 3.5 mm; and / or, in step (1), the waste plastic includes waste polyethylene; and / or, in step (1), the automatic feeding module includes a hopper, a screw automatic feeder, and a first air inlet pipe; the hopper is filled with the reaction raw material; the screw automatic feeder is connected to the hopper and the fixed bed pyrolysis module, and is used to input the reaction raw material into the fixed bed pyrolysis module, the feeding rate of the screw automatic feeder is 0.5-2 g / min; the first air inlet pipe is connected to the hopper, and is used to provide a first protective gas so that the screw automatic feeder isolates oxygen during the input of the reaction raw material, the flow rate of the first protective gas is 10-1000 mL / min.

16. The method for producing graphene from waste plastics according to claim 14, wherein, In step (2), the fixed-bed pyrolysis module includes a pyrolysis reactor, and the pyrolysis temperature in the pyrolysis reactor is 300-800 ℃.

17. The method for producing graphene from waste plastics according to claim 16, wherein, In step (2), the pyrolysis reactor is connected to a second gas inlet pipe, which is used to provide a second protective gas to the pyrolysis reactor and the bubble bed catalytic module. The flow rate of the second protective gas is 10-1000 mL / min.

18. The method for producing graphene from waste plastics according to claim 17, wherein, In step (2), the pyrolysis reactor is also connected to a third gas inlet pipe and a fourth gas inlet pipe. The third gas inlet pipe and the fourth gas inlet pipe are respectively used to provide reducing gas and oxidizing gas to the bubbling bed catalytic module to treat the catalyst in the bubbling bed catalytic module. The flow rates of the reducing gas and the oxidizing gas are 50-100 mL / min, respectively.

19. The method for producing graphene from waste plastics according to claim 14, wherein, In step (3), the bubble bed catalytic module includes a bubble reactor, and the catalytic reaction temperature in the bubble reactor is 700-1200 ℃.

20. The method for producing graphene from waste plastics according to claim 19, wherein, In step (3), in the bubbling reactor, the volume hourly space velocity of the pyrolysis products relative to the catalyst is 10-10000 h⁻¹. -1 ; and / or, in step (3), the bubbling bed catalytic module further includes a heat preservation box, which is connected to the bubbling reactor and the fixed bed pyrolysis module, for allowing the pyrolysis products to enter the bubbling reactor through the heat preservation box, and the working temperature of the heat preservation box is 300-500 ℃.

21. The method for producing graphene from waste plastics according to claim 14, wherein, In step (4), the product separation module includes a gas washing bottle and a water bath disposed around the gas washing bottle, the temperature of which is 1-5 ℃.

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