Multimodal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen and method for catalytically decomposing plastics to produce hydrogen

Abstract

The invention relates to a multi-modal solid-state source microwave catalytic system for decomposing waste plastics to produce hydrogen and a method for catalytically decomposing plastics to produce hydrogen. The invention aims to solve the problems of low hydrogen yield, insufficient reaction and long reaction time of the existing single-mode microwave hydrogen production technology based on magnetron. The multi-modal solid-state source microwave catalytic system of the invention comprises a feeding device, a microwave resonant cavity, waste plastics and a plurality of solid-state energy sources. The microwave resonant cavity is a regular polygonal prism, and an air inlet and an air outlet are respectively provided on the top of the microwave resonant cavity. A plurality of microwave energy interfaces are arranged on the side of the microwave resonant cavity, and a plurality of solid-state energy sources are arranged outside the microwave resonant cavity. The invention allows the existence of multiple frequency working modes by setting a microwave resonant cavity with a special shape, so that the energy distribution in the reaction cavity is more uniform. The multi-channel signal source provides microwave energy of multiple frequencies, effectively controls the phase change, and greatly improves the uniformity of microwave energy distribution.

Description

Technical Field

[0001] The invention belongs to the technical field of renewable energy, and in particular relates to a microwave catalytic hydrogen production system for waste plastic garbage and a method for producing hydrogen by decomposing plastic. Background Art

[0002] Microwave source refers to a device that can generate microwave energy. Different application requirements usually require microwave energy of different frequencies and powers. Currently, there are two most popular technologies: the first mainstream technology is the magnetron microwave source, which is widely used in food heating, industrial catalysis, electronic countermeasures and other fields due to its advantages such as high power and high efficiency; but the magnetron microwave source has the disadvantages of large size, poor output power stability, and difficulty in flexibly controlling microwave parameters such as frequency, phase, and power; the second mainstream technology is the semiconductor microwave source, also known as the solid-state microwave source, which has the advantages of small size, low operating voltage, and good stability. The disadvantage is that the output power is generally low. However, in recent years, with the application of new generation compound semiconductor technologies such as gallium nitride and silicon carbide, the competitiveness of solid-state microwave sources has been greatly improved.

[0003] Plastics are an indispensable part of my country's consumer market. While they bring convenience to people, they are also difficult to recycle due to their special chemical properties. Currently, the most commonly used recycling method is high-temperature decomposition and conversion, but due to its demanding reaction requirements, low efficiency, and low product selectivity, it not only leads to a large amount of energy waste, but also cannot achieve efficient reuse.

[0004] Existing technologies suitable for hydrogen production from plastic waste cracking can be divided into two categories:

[0005] The first type is the traditional high-temperature direct or indirect cracking, including one-step and two-step methods. The former is to directly heat the polymer to crack to obtain the product, and the latter is to first decompose it at a lower temperature, and then further crack the product of the initial cracking at high temperature, in this way to obtain a shorter reaction time and better product selectivity. The main advantages of this type of method are simple reactions and relatively mature industrial technology, but it also has many disadvantages: first, due to the use of direct heating, it is difficult to control the direction of the reaction, and the selectivity of the reaction product is poor; second, this type of reaction often requires a temperature of thousands of degrees Celsius, and requires complex catalysts and harsh reaction conditions; third, this type of reaction is slow, and it usually takes several hours to complete the reaction. Therefore, it is difficult for traditional high-temperature direct or indirect cracking to become an economical, fast, and environmentally friendly waste plastic recycling technology.

[0006] The second category is the emerging microwave hydrogen production technology. This type of technology is divided into microwave hydrogen production technology based on magnetron and microwave hydrogen production technology based on solid-state microwave source, and each microwave technology can adopt a single-mode or multi-mode working mode. Among them, magnetron has the advantages of high power and high efficiency, and is widely used in industrial heating, but it has the disadvantages of large size, poor output power stability, and difficulty in flexibly controlling microwave parameters such as frequency, phase, and power; while solid-state microwave source is becoming a new generation of microwave catalytic technology hotspot due to its small size, low operating voltage, good stability, and flexible control. For the two working modes, single-mode microwave hydrogen production technology mainly refers to the energy supply of the plastic cracking process by the electromagnetic wave mode of a single frequency and a single phase provided by the magnetron. This technology can significantly increase the production of hydrogen and accelerate the reaction rate, but the single-mode microwave hydrogen production technology based on magnetron has the characteristics of uneven energy distribution, which makes it impossible to fully utilize the thermal effect and non-thermal catalytic effect of microwave energy, ultimately resulting in low hydrogen yield, insufficient reaction, and long reaction time.

[0007] The concept of microwave catalysis in the second type of technology has been a hot topic of research in domestic and foreign academic circles in recent years. The catalytic effect of microwaves on chemical reactions has been widely recognized by the academic community: the chemical catalytic effect of microwaves is mainly concentrated on 1. Thermal effect: through specific microwave absorbers, energy is efficiently absorbed, the temperature is quickly increased, and the reaction rate is accelerated; 2. Non-thermal effect: microwave energy excites plasma, so that chemical reactions obtain higher activation energy, molecular collisions are more intense, thereby accelerating the reaction rate and increasing production. Specific applications include the application number CN201610783373.X, the patent name is "A method for synthesizing alkali metal salts of hexaniobate by household microwave ovens", which modifies household microwave ovens to synthesize metal salts, and the application number CN202210478853.0, the patent name is "Air purification device for harmless treatment of VOCs and regeneration of activated carbon using household microwave ovens", which also uses household microwave ovens for air purification. These studies have paved the way for the application of microwave technology in chemical reactions. However, this type of technology has two obvious disadvantages. First, the magnetron microwave source in the microwave oven cannot conveniently control parameters such as frequency, phase, and power, and has disadvantages such as limited service life. Compared with magnetron microwave technology, the solid-state microwave source technology that is currently developing provides better performance: 1. It can flexibly control the frequency, phase, power and other parameters of the output electromagnetic field; 2. The semiconductor core device ensures its long service life; 3. It uses low-voltage DC power supply internally, which can maintain stable output in the case of unstable AC output voltage or low or high input voltage, and has high reliability and stability. Second, this type of single-mode microwave catalytic technology with a single frequency and a single phase is difficult to ensure uniform energy distribution, which leads to the inability to fully utilize microwave energy, low reaction yield, and slow reaction rate. Summary of the invention

[0008] The purpose of the present invention is to solve the problems of low hydrogen yield, insufficient reaction and long reaction time of the existing single-mode microwave hydrogen production technology based on magnetron, and to provide a multi-mode solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen and a method for catalytically decomposing plastics to produce hydrogen.

[0009] The multi-modal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen of the present invention comprises a feeding device, a microwave resonant cavity, waste plastics and a plurality of solid-state energy sources, wherein the microwave resonant cavity is a regular polygonal prism, a microwave absorbing catalyst is installed in the microwave resonant cavity, a feeding device is arranged on the upper part of the microwave resonant cavity, the feeding device is connected with the microwave resonant cavity through a feeding pipe, waste plastics are installed in the feeding device, an air inlet and an air outlet are respectively opened on the top of the microwave resonant cavity, a plurality of microwave energy interfaces are arranged on the side of the microwave resonant cavity, a plurality of solid-state energy sources are arranged outside the microwave resonant cavity, and the microwave energy interface on the microwave resonant cavity is connected with the solid-state energy source through a microwave transmission line.

[0010] In the multi-modal solid-state microwave catalytic system for waste plastic decomposition and hydrogen production of the present invention, a matching microwave energy interface is arranged on each side surface of the microwave heating cavity, each microwave energy interface is connected to the energy source through a matching microwave transmission line, and the frequency of each input port and the relative phase between the input ports are adjusted to feed energy into the microwave resonant cavity. The temperature sensor on the microwave resonant cavity and the gas detection flowmeter at the gas outlet are connected to the control unit, and the control unit controls the solid-state energy source according to the reaction situation.

[0011] The method for producing hydrogen by decomposing plastics by multi-mode microwave catalysis based on a solid-state microwave source is implemented according to the following steps:

[0012] 1. Add waste plastics and microwave absorbing catalyst into the microwave resonant cavity and stir evenly;

[0013] Second, multiple solid-state energy sources are turned on, and the multiple solid-state energy sources provide output signals of different frequencies. The multiple output signals form multiple working modes. The phase of one of the output signals is used as the reference phase, and the difference between the phase of the other output signals and the reference phase is adjusted. The complementary frequency mode of the heating area is selected through frequency scanning, and the input phase difference with uniform standing wave energy distribution is selected through phase scanning to perform multi-mode microwave catalytic decomposition;

[0014] 3. Collect hydrogen from the outlet of the microwave resonant cavity.

[0015] The complementary frequency modes in step 2 of the present invention refer to different main distribution areas of energy of different frequencies. Here, multiple frequency modes that can be superimposed together and completely and evenly cover the entire cavity are selected to form complementary modes.

[0016] The method for producing hydrogen by catalytic decomposition of plastics of the present invention integrates solid-state microwave source technology and multi-modal microwave hydrogen production, thereby realizing the utilization of waste plastics and the preparation of hydrogen.

[0017] The present invention discloses a multi-mode solid-state microwave source system for microwave catalytic decomposition of plastics to produce hydrogen. By setting a microwave resonant cavity with a special shape, it allows multiple frequency working modes to exist, and strengthens reflection to make the energy distribution in the reaction cavity more uniform. The multi-channel signal source provides microwave energy of multiple frequencies, effectively controls phase changes, greatly improves the distribution uniformity of microwave energy, enables plastic reactants and catalysts to absorb microwave energy to the greatest extent, and ultimately greatly improves both thermal and non-thermal effects.

[0018] The multimodal solid-source microwave catalytic system for waste plastic decomposition to produce hydrogen and the method for catalytic decomposition of plastic to produce hydrogen of the present invention can firstly solve the shortcomings of existing plastic waste recycling and reuse, such as high energy consumption, low efficiency, complex products and poor selectivity; secondly, solve the shortcomings of magnetron-based microwave catalytic technology, such as difficulty in flexible control and short equipment service life; thirdly, solve the shortcomings of single-frequency, single-phase single-modal microwave catalytic technology, such as uneven energy distribution and incomplete reaction. More importantly, the microwave catalytic method provided by the present invention can be widely used in organic synthesis, catalyst preparation, sewage treatment and other fields, such as water cracking to produce hydrogen. The present invention proposes for the first time a microwave catalysis method based on a multi-modal solid-state microwave source. For general industrial microwave catalysis, 800-1000W of power is generally required, so magnetron technology is used. The present invention uses multiple modes to work in parallel, and the total power is shared by the solid-state microwave source of each frequency mode, which reduces the output power required by a single solid-state microwave source, thereby reducing the design requirements of the solid-state microwave source and making up for the disadvantage that the power of a single solid-state microwave source is lower than that of a magnetron; through the special design of the resonant cavity: first, the size is increased to allow multiple frequency modes to exist at the same time; second, a multi-prism structure is used to enhance reflection, so that energy distribution is uniform, and the rate and efficiency of hydrogen production are improved. After adopting the microwave catalysis system and hydrogen production method of the present invention, the recycling of waste plastics has advantages that other technologies cannot match, such as low consumption, fast reaction, low temperature requirements, and high utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of a multi-modal solid-state source microwave catalytic system for decomposing waste plastics to produce hydrogen according to the present invention;

[0020] Figure 2 The top surface schematic diagram of the microwave resonant cavity is a regular octagonal prism;

[0021] Figure 3 This is a comparison chart of energy consumption of various green hydrogen production methods, in kWh / kg;

[0022] Figure 4 This is a comparison chart of the product composition of the multimodal solid-state source microwave catalytic decomposition and the traditional thermal cracking plastic in the embodiment, the unit is mmol / g polypropylene plastic, where A represents gas products, B represents solid products, and C represents oil products (hydrocarbons);

[0023] Figure 5 This is a comparison chart of unit hydrogen production of different cracking hydrogen production methods in the embodiment, the unit is mmol / g polypropylene plastic;

[0024] Figure 6 This is a comparison chart of the reaction completion time of different cracking hydrogen production methods in the embodiment, the unit is minutes;

[0025] Figure 7 This is a comparison chart of the reaction temperature requirements of different cracking hydrogen production methods in the examples, in °C;

[0026] Figure 8 This is a comparison diagram of the effects of different resonant cavity shapes on hydrogen production efficiency in the embodiments, in which a pentagonal prism is used as a comparison;

[0027] Fig. 9 The energy distribution diagram formed by different working modes in the microwave resonance cavity in the embodiment;

[0028] Fig.10 This is a test diagram of the effect of different energy distribution uniformities on hydrogen production efficiency in the embodiments, in which the normalized efficiency value of the single-mode system is compared. DETAILED DESCRIPTION

[0029] Specific implementation method 1: In this implementation method, the multimodal solid-state source microwave catalytic system for decomposing waste plastics to produce hydrogen includes a feeding device 8, a microwave resonant cavity 4, waste plastics 6 and multiple solid-state energy sources 3. The microwave resonant cavity 4 is a regular polygonal prism. The microwave resonant cavity 4 is equipped with a microwave absorbing catalyst. A feeding device 8 is arranged on the upper part of the microwave resonant cavity 4. The feeding device 8 is connected to the microwave resonant cavity 4 through a feed pipe. The feeding device 8 is equipped with waste plastics 6. An air inlet 11 and an air outlet 1 are respectively opened on the top of the microwave resonant cavity 4. Multiple microwave energy interfaces are arranged on the side of the microwave resonant cavity 4. Multiple solid-state energy sources 3 are arranged outside the microwave resonant cavity 4. The microwave energy interface on the microwave resonant cavity 4 is connected to the solid-state energy source 3 through a microwave transmission line.

[0030] The multi-modal microwave hydrogen production technology proposed in this embodiment not only has multiple operating frequency modes, but also has the function of adjusting the relative phases of multiple microwave energy sources, so that the microwave energy is more evenly distributed in the cavity, further improving the microwave thermal effect and non-thermal effect, significantly increasing the hydrogen production and the reaction speed.

[0031] In this embodiment, the height and the side length of the bottom surface of the microwave resonant cavity are greater than one working wavelength, thereby allowing multiple frequency working modes to exist.

[0032] Specific embodiment 2: The difference between this embodiment and specific embodiment 2 is that the microwave resonance cavity 4 is a regular pentagonal prism, a regular hexagonal prism, a regular heptagonal prism or a regular octagonal prism.

[0033] In this embodiment, the microwave resonant cavity is preferably a regular octagonal prism.

[0034] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the microwave resonant cavity 4 is placed on the pressure sensor 12 .

[0035] Specific embodiment 4: This embodiment is different from any one of specific embodiments 1 to 3 in that a temperature sensor 5 and a stirrer 10 are further provided in the microwave resonance cavity 4 .

[0036] Specific implementation method five: This implementation method is different from specific implementation methods one to four in that a gas detection flow meter 2 is provided on the gas outlet 1 .

[0037] Specific embodiment six: This embodiment is different from any one of specific embodiments one to five in that the solid-state energy source 3 adopts a gallium nitride-based RF power amplifier, a gallium oxide-based RF power amplifier or a diamond-based RF power amplifier.

[0038] Specific embodiment 7: This embodiment is different from any one of specific embodiments 1 to 6 in that the microwave absorption catalyst is a mixture of one or more of iron-based metal oxides, aluminum-based metal oxides, and cobalt-based metal oxides.

[0039] In this embodiment, the microwave absorbing catalyst is preferably an aluminum oxide iron mixture, ferrosoferric oxide or cobalt oxide.

[0040] Specific implementation eight: This implementation is different from any one of specific implementations one to eight in that the waste plastic 6 is made of thermoplastic plastic or thermosetting plastic.

[0041] Common plastics such as polyethylene plastic, polypropylene plastic or polystyrene plastic can be used in this embodiment.

[0042] Specific embodiment 9: This embodiment is different from any one of specific embodiments 1 to 8 in that the air inlet 11 is connected to a nitrogen source.

[0043] Specific embodiment 10: The method for producing hydrogen by decomposing plastics using multi-mode microwave catalysis based on a solid-state microwave source is implemented according to the following steps:

[0044] 1. Add waste plastic 6 and microwave absorbing catalyst into the microwave resonant cavity 4 and stir evenly;

[0045] Second, the multi-channel solid-state energy source 3 is turned on, and the multi-channel solid-state energy source 3 provides output signals of different frequencies, and the multi-channel output signals form multiple working modes (one channel output signal corresponds to one working mode). The phase of one channel output signal is used as the reference phase, and the difference between the phase of the other channels output signal and the reference phase is adjusted. The complementary frequency mode of the heating area is selected through frequency scanning, and the input phase difference with uniform standing wave energy distribution is selected through phase scanning to perform multi-mode microwave catalytic decomposition;

[0046] 3. Collect hydrogen from the gas outlet 1 on the microwave resonant cavity 4.

[0047] Specific embodiment 12: The difference between this embodiment and specific embodiment 11 is that in step 1, the mass ratio of the waste plastic 6 and the microwave absorbing catalyst is (1-5):1.

[0048] Specific implementation thirteen: The difference between this implementation and specific implementation eleven or twelve is that the number of working modes in step two is n, forming n-1 step-change phases, and the step-change value of the phase is (360 / n)°.

[0049] Specific implementation fourteen: The difference between this implementation and any one of specific implementations eleven to thirteen is that the number of working modes in step two is 8, and the microwave frequencies of the 8 working modes are 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, 2.4489 GHz, 2.4517 GHz, 2.4578 GHz, 2.4621 GHz and 2.4701 GHz respectively.

[0050] Specific embodiment 15: This embodiment is different from any one of specific embodiments 11 to 14 in that the method for adjusting the output power of the solid-state energy source 3 in step 2 is: according to the formula ,in is the output power of the solid-state energy source after feedback regulation, is the target output power of the system without feedback regulation, It is the error between the actual hydrogen production rate detected in real time by the gas detection flow meter during the reaction and the set target yield. The optimal input power of the microwave energy currently required for the reaction is obtained through real-time feedback, and then the solid-state microwave source is controlled by the control unit for real-time and precise adjustment.

[0051] Embodiment: The multimodal solid-state source microwave catalytic system for decomposing waste plastics to produce hydrogen in this embodiment includes a feeding device 8, a microwave resonant cavity 4, a microwave absorption catalyst, multiple solid-state energy sources 3 and a control unit 7. The microwave resonant cavity 4 is a regular octagonal prism. The microwave resonant cavity 4 is equipped with a microwave absorption catalyst. A feeding device 8 is arranged on the upper part of the microwave resonant cavity 4. The feeding device 8 is connected to the microwave resonant cavity 4 through a feed pipe. The feeding device 8 is equipped with waste plastic 6. An air inlet 11 and an air outlet 1 are respectively opened on the top of the microwave resonant cavity 4. A temperature sensor 5 and an agitator 10 are arranged in the microwave resonant cavity 4. A gas detection flowmeter 2 is arranged on the air outlet 1. Multiple microwave energy interfaces are arranged on the side of the microwave resonant cavity 4. Multiple solid-state energy sources 3 are arranged outside the microwave resonant cavity 4. The microwave energy interface on the microwave resonant cavity 4 is connected to the solid-state energy source 3 through a microwave transmission line. The control unit 7 is connected to the temperature sensor 5, the gas detection flowmeter 2 and the solid-state energy source 3 through a wire.

[0052] Application Example: The method for producing hydrogen by decomposing plastics through multi-modal microwave catalysis using the multi-modal solid-state microwave catalytic system is implemented according to the following steps:

[0053] 1. First, open the valve of the feeding device and pour the (crushed) polypropylene plastic waste into the microwave resonance cavity through the valve. The microwave resonance cavity is a regular octagonal prism. After the feeding is completed, close the valve of the feeding device to stop feeding. Use the agitator to mix the polypropylene plastic particles and the microwave absorbing catalyst (the catalyst is a mixture of aluminum oxide and iron oxide in a mass ratio of 1:1) evenly. Open the air inlet and outlet, and pass nitrogen to exhaust the air. After the gas detection flowmeter detects that the air is exhausted, stop adding nitrogen and close the air inlet.

[0054] Second, 8 frequency modes with complementary energy distribution are selected. The microwave frequencies of the 8 working modes are 2.4312GHz, 2.4384GHz, 2.4436GHz, 2.4489GHz, 2.4517GHz, 2.4578GHz, 2.4621GHz and 2.4701GHz respectively. The microwave power is turned on and adjusted (the power of a single input port is 80-100W, using an octagonal prism, about 640-800W). According to the gas production rate detected by the gas detection flowmeter, the relative phase of the 8 microwave energy input ports is controlled (using a phase shift circuit). With 45° as a phase gradient, 8 phase steps are set, that is, the difference between the phase of the output signal of other channels and the reference phase is 45°, 90°, 135°, 180°, 225°, 270° and 315° respectively. The gas production rate fed back by the gas detection flowmeter and the temperature of the reaction system fed back by the thermometer are used.

[0055] 3. When the reaction no longer produces gas, turn off the microwave energy source, open the air inlet, introduce nitrogen, and exhaust the remaining hydrogen. When the gas detection flow meter detects that the hydrogen in the exhaust gas is exhausted, stop introducing nitrogen;

[0056] 4. Clean the carbon attached to the catalyst surface: After the reaction gas is emptied, continue to introduce carbon dioxide into the microwave resonant cavity through the air inlet, turn on the microwave energy source and adjust the power to a high level. At this time, the carbon deposited on the surface of the microwave absorbing catalyst reacts with carbon dioxide to generate carbon monoxide. At the same time, read the readings of the pressure sensor and the gas detection flowmeter. After the pressure sensor detects that the mass of the resonant cavity (including the resonant cavity itself and the microwave absorbing catalyst) has recovered to the same level as before this reaction and the gas detection flowmeter detects that no carbon monoxide is generated in the reaction system, stop introducing carbon dioxide, and then introduce nitrogen to exhaust carbon dioxide and carbon monoxide.

[0057] 5. The gas mixture discharged from the gas outlet is further pressurized and liquefied to obtain pure hydrogen and carbon monoxide. The separated nitrogen and carbon dioxide can be reused.

[0058] 6. After the wave-absorbing catalyst is cleaned and the gas atmosphere is re-formed, close the air inlet, open the valve of the feeding device, continue to feed (crushed) polypropylene plastic waste into it, then close the valve of the feeding device, and repeat the above steps to achieve continuous hydrogen production.

[0059] The multimodal microwave catalytic process optimized in this embodiment is as follows: the microwave frequencies of the eight working modes are 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, 2.4489 GHz, 2.4517 GHz, 2.4578 GHz, 2.4621 GHz and 2.4701 GHz, respectively; the power of a single output port is 80-100 W; the reaction temperature is 350-500 ° C; and the reaction time is within 40-80 s.

[0060] In this embodiment, a production cycle is generally 6-8 hours of continuous hydrogen production. After each production cycle, the reaction chamber is cleaned with chemical reagents to remove hydrocarbon by-products attached to the inner wall of the microwave resonance chamber and the surface of the catalyst, followed by drying. The feeding device is then filled with plastic particles required for one cycle to start the next production cycle.

[0061] The energy consumption comparison of existing green hydrogen production methods is shown in the figure below: Figure 3 As shown in the figure, the energy consumption comparison of the multi-modal microwave catalytic decomposition of plastic hydrogen production method based on solid source and the existing green hydrogen production methods (under the same experimental platform). From the experimental results, it can be seen that the multi-modal microwave catalytic decomposition of plastic hydrogen production method based on solid source has the advantage of low energy consumption compared with the existing various green hydrogen production methods.

[0062] like Figure 4 The figure shows the comparison of the reaction product composition between the multi-modal microwave catalytic decomposition of plastics to produce hydrogen based on solid sources and the traditional high-temperature cracking of plastics to produce hydrogen. From the experimental results, it can be seen that the multi-modal microwave catalytic decomposition of plastics to produce hydrogen based on solid sources has higher reaction selectivity, in which more than 98% of the gaseous substances are hydrogen, more than 98% of the solid substances are carbon, and the content of oily substances is greatly reduced.

[0063] like Figure 5-Figure 7 As shown, it is a comparison chart of hydrogen production, reaction time, and reaction required temperature of a multi-modal microwave catalytic decomposition method for hydrogen production from plastics based on a solid-state microwave source and a traditional high-temperature cracking method for hydrogen production from plastics, a two-step method for hydrogen production from plastics, and a single-mode microwave catalytic decomposition method for hydrogen production from plastics. The hydrogen yield of the multi-modal microwave catalytic decomposition method for hydrogen production from plastics in this embodiment is 71.4mmol / g, and the reaction completion time is 40~80s. From the experimental results, it can be seen that the multi-modal microwave catalytic decomposition method for hydrogen production from plastics based on a solid-state source has obvious advantages in hydrogen production, reaction time, and reaction required temperature compared with the above-mentioned other methods, and provides an efficient hydrogen production method with high yield, fast reaction, low consumption, and low temperature requirement. In the figure, traditional high-temperature cracking: requires a catalyst, a high-temperature reactor, and a temperature ranging from 1000℃ to 2000℃, and a complex separation process is required after the reaction. Two-step method: requires a catalyst, a high-temperature reactor, a temperature of 900℃-1200℃, requires two-step reaction, and the separation process is easier than traditional high-temperature cracking. Single-mode microwave catalysis: requires a catalyst, reaction temperature 500℃-600℃, no high-temperature reactor, no complicated separation process. Multi-mode microwave catalysis: requires a catalyst, reaction temperature 300℃-500℃, no high-temperature reactor, no complicated separation process.

[0064] like Figure 8 As shown in the figure, it is a comparison chart of the effects of different resonant cavity shapes on hydrogen production efficiency. From the experimental results, it can be seen that within a certain range, the more sides the polygonal column cavity has, the greater the hydrogen production efficiency, but when the number of sides is large enough, the hydrogen production efficiency gradually remains unchanged or even decreases, so the present invention selects several cavity structures with higher efficiency.

[0065] like Fig. 9 As shown in the figure, it is an energy distribution diagram formed by different working modes in the microwave resonant cavity. From the simulation results, it can be seen that different working modes will form different energy distribution concentration areas in the cavity. The present invention adopts multiple complementary working modes, which can make the energy distribution more uniform by means of the superposition effect.

[0066] The influence of different working mode numbers and modal phase differences on energy distribution uniformity is shown in Table 1. The 4 frequency points in Table 1 are: 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, and 2.4489 GHz. 6 frequency points: 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, 2.4489 GHz, 2.4517 GHz, and 2.4578 GHz. 8 frequency points: 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, 2.4489 GHz, 2.4517 GHz, 2.4578 GHz, 2.4621 GHz, and 2.4701 GHz.

[0067] Table 1

[0068] The number of working modes of the resonant cavity Phase difference of each mode (uniform distribution) Energy distribution mean square error 4 0° 124 4 90° 284 4 180° 234 6 0° 98 6 60° 245 6 120° 201 6 180° 222 8 0° 72 8 45° 189 8 90° 177 8 135° 165 8 180° 172

[0069] like Fig.10 The figure shows the influence of different energy distribution uniformity on hydrogen production efficiency. The experimental results show that the higher the energy distribution uniformity, the higher the hydrogen production efficiency. The present invention adopts multiple working modes and multiple phase differences to greatly improve the energy uniformity inside the cavity, thereby achieving efficient and continuous microwave hydrogen production.

Claims

1. A multi-modal solid-source microwave catalytic system for hydrogen production by decomposing waste plastics, characterized in that The multi-modal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen comprises a feeding device (8), a microwave resonant cavity (4), waste plastics (6), and a plurality of solid-state energy sources (3). The microwave resonant cavity (4) is a regular polygonal prism. A microwave absorbing catalyst is contained in the microwave resonant cavity (4). A feeding device (8) is arranged on the upper part of the microwave resonant cavity (4). The feeding device (8) is connected to the microwave resonant cavity (4) through a feeding pipe. The waste plastics (6) are contained in the feeding device (8). An air inlet (11) and an air outlet (1) are respectively provided on the top of the microwave resonant cavity (4). Sides of the microwave resonant cavity (4) are provided with a plurality of solid-state energy sources (3). A plurality of microwave energy interfaces are arranged on the surface, a plurality of solid-state energy sources (3) are arranged outside the microwave resonant cavity (4), and the microwave energy interfaces on the microwave resonant cavity (4) are connected to the solid-state energy sources (3) via microwave transmission lines; the plurality of solid-state energy sources (3) provide output signals of different frequencies, and the multi-channel output signals form multiple working modes, and the phase of one of the output signals is used as a reference phase, and the difference between the phase of the other output signals and the reference phase is adjusted, and the frequency mode complementary to the heating area is selected through frequency scanning, and the input phase difference with uniform standing wave energy distribution is selected through phase scanning, so as to perform multi-mode microwave catalytic decomposition.

2. The multi-modal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen according to claim 1, characterized in that The microwave resonant cavity (4) is a regular pentagonal prism, a regular hexagonal prism, a regular heptagonal prism or a regular octagonal prism.

3. The multimodal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen according to claim 1, characterized in that The microwave resonant cavity (4) is placed on the pressure sensor (12).

4. The multi-modal solid-source microwave catalytic system for hydrogen production by decomposing waste plastics according to claim 1 is characterized in that A temperature sensor (5) and a stirrer (10) are also provided in the microwave resonance cavity (4).

5. The multi-modal solid-source microwave catalytic system for hydrogen production by decomposing waste plastics according to claim 1, characterized in that A gas detection flow meter (2) is provided on the gas outlet (1).

6. The multi-modal solid-source microwave catalytic system for decomposing waste plastics to produce hydrogen according to claim 1, characterized in that The microwave absorbing catalyst is a mixture of one or more of iron-based metal oxides, aluminum-based metal oxides and cobalt-based metal oxides.

7. A method for producing hydrogen from plastics by multi-modal microwave catalytic decomposition based on a solid-state microwave source, characterized in that The method for producing hydrogen by microwave catalytic decomposition of plastics is implemented according to the following steps:

1. Adding waste plastic (6) and a microwave absorbing catalyst into a microwave resonant cavity (4), wherein the microwave resonant cavity (4) is a regular polygonal prism, and stirring evenly; 2. Turning on the multiple solid-state energy sources (3), the multiple solid-state energy sources (3) provide output signals of different frequencies, the multiple output signals form multiple working modes, taking the phase of one of the output signals as the reference phase, adjusting the difference between the phase of the other output signals and the reference phase, selecting the complementary frequency mode of the heating area through frequency scanning, selecting the input phase difference with uniform standing wave energy distribution through phase scanning, and performing multi-mode microwave catalytic decomposition; 3. collecting hydrogen from the gas outlet (1) on the microwave resonant cavity (4); The number of working modes in step 2 is n, forming n-1 step-change phases, and the step-change value of the phase is (360 / n)°.

8. The method for producing hydrogen from plastics by multi-modal microwave catalytic decomposition based on a solid-state microwave source according to claim 7, characterized in that In step 1, the mass ratio of the waste plastic (6) to the microwave absorbing catalyst is (1-5):

1.

9. The method for producing hydrogen by multi-modal microwave catalytic decomposition of plastics based on a solid-state microwave source according to claim 7, characterized in that In step 2, the number of working modes is 8, and the microwave frequencies of the 8 working modes are 2.4312 GHz, 2.4384 GHz, 2.4436 GHz, 2.4489 GHz, 2.4517 GHz, 2.4578 GHz, 2.4621 GHz and 2.4701 GHz respectively.

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