Method and apparatus for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate

Abstract

This invention provides a method and apparatus for preparing monomers from polymethyl methacrylate (PMMA) through electromagnetic induction pyrolysis, belonging to the field of pyrolysis polymerization. The method includes: heating a metal catalyst heat carrier and a ceramic heat carrier in a rotating bed reactor to the depolymerization temperature of PMMA using electromagnetic induction; then adding crushed PMMA waste or raw materials, and the depolymerization reaction generates monomers. The apparatus is a rotating bed reactor, comprising a feeding system, a rotating reaction system with an electromagnetic induction heating system on its periphery, and a discharging system arranged sequentially. This invention utilizes electromagnetic induction heating technology, resulting in high heat transfer efficiency, good temperature control, and low heat loss; the improved rotating bed design ensures uniform temperature; and the combined use of a metal catalyst heat carrier and a ceramic heat carrier significantly shortens the heating time and improves the pyrolysis polymerization efficiency, enabling rapid and efficient pyrolysis polymerization of PMMA.

Description

Technical Field

[0001] This invention belongs to the field of pyrolysis polymerization, and particularly relates to a method and apparatus for preparing monomers from polymethyl methacrylate by electromagnetic induction pyrolysis. Background Technology

[0002] Polymethyl methacrylate (PMMA), commonly known as plexiglass, is widely used in automobiles, construction, aerospace, communications, multimedia, medical, and consumer applications. With rapid socio-economic development, my country's demand for PMMA is constantly increasing, but the large-scale use of discarded PMMA has caused soil and water pollution. The rational recycling of PMMA is crucial for environmental protection and resource conservation. Therefore, the pyrolysis of PMMA into methyl methacrylate monomers has significant commercial value and environmental protection implications.

[0003] Currently, the commonly used industrial method for the pyrolysis polymerization of polymethyl methacrylate (PMMA) is fixed-bed pyrolysis. Fixed-bed pyrolysis involves heating the bottom of the reactor using an open flame (coal or natural gas combustion) or an electric furnace. The monomer product leaves the top of the reactor and is then condensed and refined. This method has several drawbacks: low monomer yield (approximately 70%), severe coking, requiring shutdown for cleaning after a certain pyrolysis time, making it a semi-continuous production process; the reaction generates not only PMMA gas but also flammable gases such as methane, ethylene, and propylene, making operation under open flame conditions hazardous; and low heating efficiency, with a small effective volume and heating area within the reactor leading to uneven temperature distribution. Currently, the widely researched pyrolysis technology utilizes fluidized bed pyrolysis. The high-speed airflow within the fluidized bed ensures excellent mass transfer, resulting in uniform temperature and concentration within the reactor, and enabling continuous and efficient production. When applied to the depolymerization of PMMA, fluidized bed reactors achieve monomer yields exceeding 90%. However, this method has several drawbacks: high energy consumption, as fluidized beds require large amounts of inert gas (typically N2), and the heating and cooling of N2 results in significant energy consumption; external heating of the fluidized bed typically uses an electric heating mantle, which has low heating efficiency, effectively heating only the middle of the bed, and the electric heating speed is too slow to reach the required temperature quickly; furthermore, the high viscosity of the melted polymethyl methacrylate polymer causes the material to adhere to the fluidizing medium (typically sand), leading to bed collapse and forcing the pyrolysis reaction to stop. Based on the above analysis, fixed-bed reactors and fluidized-bed reactors have been used in the pyrolysis of polymethyl methacrylate, but both methods have insurmountable problems that limit their application. To solve these problems, it is necessary to develop new, highly efficient pyrolysis methods for the pyrolysis of polymethyl methacrylate. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for preparing monomers from polymethyl methacrylate by electromagnetic induction pyrolysis. The method utilizes electromagnetic induction heating technology, which has high heat transfer efficiency, good temperature control, and low heat loss. The improved rotating bed design ensures uniform temperature, and the combined use of a metal catalyst heat carrier and a ceramic heat carrier greatly shortens the heating time and improves the pyrolysis efficiency, enabling rapid and efficient pyrolysis of polymethyl methacrylate.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0006] A method for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate includes the following steps:

[0007] S1: The metal catalyst heat carrier and the ceramic heat carrier are added to the rotating bed reactor, and the metal catalyst heat carrier and the ceramic heat carrier are heated to the depolymerization temperature of polymethyl methacrylate using electromagnetic induction.

[0008] Furthermore, the heat carrier of the metal catalyst is an inductive medium.

[0009] Preferably, the heat carrier of the metal catalyst is made of one of iron, iron-nickel alloy, or iron-nickel-molybdenum alloy.

[0010] Preferably, the particle size of the metal catalyst heat carrier is 2 to 2.5 mm.

[0011] Preferably, the particle size of the ceramic heat transfer fluid is 2-3 mm.

[0012] The particle size of the metal catalyst heat carrier and the ceramic heat carrier affects the mixing effect of the two different particle types inside a rotating bed reactor. This application found that if the metal particles are too large, electromagnetic induction heating can only heat the surface of the particles and cannot penetrate deep into the interior. Smaller metal particles are easier to mix with larger-diameter ceramic particles, but if the metal particle size is too small, the metal particles will deposit at the bottom of the reactor, potentially causing stratification of the two types of particles, resulting in uneven mixing and making it difficult to achieve temperature equilibrium inside the reactor. Therefore, using a metal catalyst heat carrier with a ceramic heat carrier particle size that is slightly larger or comparable to the ceramic heat carrier can achieve better results.

[0013] Preferably, the volume ratio of the metal catalyst heat carrier to the ceramic heat carrier is 1:1 to 1:3. Selecting different volume ratios of the metal catalyst heat carrier and the ceramic heat carrier can alter the mixing effect of the two types of particles inside the reactor. Furthermore, the influence of the amount of inductive medium added on the reaction must be considered. As an inductive medium, the lower the relative content of the metal catalyst heat carrier in the two types of particles, the worse the electromagnetic induction heating effect, making it difficult to reach the temperature required for the pyrolysis reaction. Conversely, the higher the relative content of the metal catalyst heat carrier, the stronger the electromagnetic induction heating effect, making it difficult to maintain the required pyrolysis temperature. Therefore, an optimal balance needs to be achieved within the aforementioned volume ratio range.

[0014] Preferably, the total volume of the added metal catalyst heat carrier and ceramic heat carrier accounts for 8% to 25% of the total volume of the rotating bed reactor. The larger the volume of the metal catalyst heat carrier and ceramic heat carrier in the reactor, the smaller the cavity volume inside the reactor. However, if the volume of the two heat carriers in the reactor is too large, electromagnetic induction heating will have difficulty reaching the interior of the two particles, making it difficult for the reactor as a whole to reach the required pyrolysis temperature. Since polymethyl methacrylate (PMMA) generates gaseous products after pyrolysis, a smaller cavity volume inside the reactor results in a shorter residence time for the gaseous products, effectively reducing secondary reactions caused by excessive residence time and promoting the generation of more PMMA monomers.

[0015] Furthermore, the depolymerization temperature is 375–450°C.

[0016] Furthermore, the electromagnetic induction heating frequency is 20–1000 kHz; preferably, the metal catalyst heat carrier is electromagnetically induction heated by an electromagnetic induction coil outside the rotating bed reactor, thereby transferring heat to the ceramic heat carrier.

[0017] The depolymerization temperature is mainly controlled by the heating frequency, the type and amount of the metal catalyst heat carrier and the ceramic heat carrier. The heating frequency primarily affects the heating rate; a higher heating frequency results in a faster heating rate, making it easier for the metal catalyst heat carrier in the reactor to reach the required reaction temperature in a short time. However, excessively high heating frequencies increase heat loss and reduce thermal efficiency. Since the metal catalyst heat carrier is an inductive medium, a smaller amount of metal catalyst heat carrier results in a weaker electromagnetic induction heating effect. Therefore, different ratios of metal catalyst heat carrier and ceramic heat carrier affect the electromagnetic induction heating effect, thus affecting the thermal depolymerization reaction. It should be noted that in this application, the inductive heating carrier is not the reactor wall material, but rather the metal catalyst heat carrier and ceramic heat carrier within the reactor. The degree of mixing of the metal catalyst heat carrier and ceramic heat carrier determines the temperature uniformity inside the reactor. Therefore, controlling the type and amount of metal catalyst heat carrier and ceramic heat carrier, as well as the heating frequency, during reactor rotation to achieve a balance and maintain a relatively stable depolymerization temperature and time is a major technical problem solved by this application.

[0018] Preferably, the main body or inner wall material of the rotating bed reactor is ceramic, and the rotating bed reactor is externally wound with coils.

[0019] S2: Crushed polymethyl methacrylate waste or raw material is continuously added to the rotating bed reactor from the feed port. The polymethyl methacrylate undergoes a depolymerization reaction to generate monomers. The gaseous product containing monomers is discharged from the discharge port of the rotating bed reactor. The liquid product containing monomers is collected after condensation.

[0020] Preferably, the particle size of the crushed polymethyl methacrylate waste or raw material is 2-20 mm.

[0021] Preferably, the method for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate may further include step S3: feeding the metal catalyst heat carrier containing carbon deposits generated by the long-term pyrolysis reaction in step S2 into a regeneration reactor, and introducing air to burn the carbon deposits to obtain a regenerated metal catalyst heat carrier.

[0022] The principle of electromagnetic induction heating is as follows: Based on Faraday's law of electromagnetic induction, alternating current (AC) is first rectified into direct current (DC) by a rectifier circuit. This DC is then converted into a high-frequency, high-voltage current. When this current passes through a coil, it generates an alternating magnetic field. The magnetic lines of force in this field, when passing through the metal heat carrier (inductive medium), produce strong eddy currents, causing the metal heat carrier to spontaneously and rapidly heat up, thus achieving rapid heating. The metal heat carrier then transfers its generated heat to the ceramic heat carrier used as the filling medium. As the reactor rotates clockwise or counterclockwise around a horizontal axis, these particles mix evenly, resulting in a uniform temperature. The reactor provides a reaction site for the pyrolysis polymerization reaction. During reactor rotation, the added materials mix evenly with the metal catalyst heat carrier and ceramic heat carrier inside the reactor, allowing the reaction to proceed under uniform temperature conditions. During the pyrolysis polymerization of polymethyl methacrylate (PMMA), the formation of PMMA monomers is mainly related to the stability of the side chain groups. During use, iron-based metal particles form iron oxide on their surface. Iron oxide catalyzes the depolymerization of polymethyl methacrylate (PMMA). Iron oxide bonds with the carbonyl oxygen of PMMA, weakening the conjugation effect of the ester group on free radicals and reducing the initial thermal degradation temperature and activation energy of waste plexiglass. On the other hand, the methyl and ester groups on the side chains of PMMA allow the generated monomers to exist more stably, improving the efficiency of the thermal depolymerization reaction and thus increasing the monomer yield.

[0023] The present invention also provides an apparatus for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate, the apparatus being a rotating bed reactor comprising a feeding system, a rotating reaction system, and a discharging system arranged sequentially; an electromagnetic induction heating system is provided on the outer periphery of the rotating reaction system.

[0024] Preferably, the electromagnetic induction heating system provided around the outer periphery of the rotary reaction system is specifically in the form of an electromagnetic induction coil surrounding the outer periphery of the rotary reaction system;

[0025] Preferably, the rotating reaction system may be provided with a plurality of baffles; further, the plurality of baffles may be 8 to 20, all of which are equidistantly distributed along the axis of rotation.

[0026] Furthermore, the electromagnetic induction heating system includes an insulating jacket surrounding the outer periphery of the rotating reaction system and an electromagnetic induction coil surrounding the outer periphery of the insulating jacket.

[0027] Preferably, the feeding system includes a screw feeder; the rotary reactor system includes a rotary reaction system, i.e., a rotating bed; and the discharge system includes a discharge port and a condenser located downstream of the discharge port.

[0028] Furthermore, the electromagnetic induction heating system includes a gas inlet, through which inert gas enters the reactor, preventing the product from remaining at the feed end for an extended period, reducing the occurrence of product side reactions, and thereby improving the product yield; in addition, it can maintain an inert atmosphere in the system (preventing air from entering).

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) Compared with fixed bed technology, the present invention uses electromagnetic induction heating technology to achieve rapid heating and increase heat exchange area.

[0031] (2) Compared with fluidized bed reactors, the polymethyl methacrylate polymer in the reactor of the present invention is not easy to adhere to the fluidizing medium to form large particles, and will not cause agglomeration or bed collapse and failure to fluidize, thereby making the entire pyrolysis polymerization process continuous; and it does not use electric heating, but generates heat through the self-heating of the inductive medium, which greatly improves the heating efficiency and also reduces the use of inert gas.

[0032] (3) Compared with fixed bed technology and fluidized bed reactor technology, the present invention uses iron oxide catalyst heat carrier to improve depolymerization efficiency and increase monomer yield. Attached Figure Description

[0033] To more clearly illustrate the background technology and the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings may only show some embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the apparatus for preparing monomers from polymethyl methacrylate by electromagnetic induction pyrolysis according to the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-Insulation jacket; 2-Rotating bed; 3-Driven gear; 4-Dynamic seal; 5-Screw feeder; 6-Gas inlet; 7-Motor; 8-Drive gear; 9-Rotating bed support plate; 10-Condenser; 11-Discharge port; 12-Electromagnetic induction coil. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" or "a number" means two or more, unless otherwise explicitly specified.

[0039] In this embodiment of the invention, gas chromatography was used to analyze the composition of the liquid product obtained from the reaction. The gas chromatograph used was a Shimadzu GC-2014 gas chromatograph, the chromatographic column was an HP-5 weakly polar column, and the detector was a flame ionization detector (FID). The determination method was the internal standard method, with ethanol as the solvent and dodecane as the internal standard. The determination conditions were: N2 as the carrier gas, vaporization chamber temperature 250°C, FID detector temperature 280°C, and the temperature program was: 40°C for 3 min, then increased to 180°C at a rate of 20°C / min, held for 1 min, then increased to 250°C at a rate of 40°C / min, held for 2 min; the analysis time was 14.75 min.

[0040] Example 1

[0041] A method for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate includes the following steps:

[0042] (1) Crush polymethyl methacrylate waste to 2-4 mm.

[0043] (2) Weigh 3000g of solid iron spheres as the heat carrier for the metal catalyst. The diameter of the solid iron spheres is 2-2.5mm. Weigh 2000g of ceramic heat carrier with a diameter of 2-3mm. The volume ratio of the solid iron spheres to the ceramic heat carrier is 1:1. Add them to the rotating bed reactor. The reactor volume filling rate is 25%. The rotating speed of the rotating bed reactor is 10rpm. The reactor is heated to the depolymerization temperature of 375℃ at a frequency of 100kHz and under a N2 atmosphere (20mL / min) using electromagnetic induction technology.

[0044] (3) 200g of waste polymethyl methacrylate was added to the rotating bed reactor in step (2) by a screw feeder at a feed rate of 10g / min. The pyrolysis reaction was carried out for 20min under normal pressure. The monomer gas was discharged from the outlet of the rotating bed reactor. After condensation, the liquid phase product was collected, and finally 190.9g of liquid oil was obtained.

[0045] The apparatus for preparing monomers from polymethyl methacrylate by electromagnetic induction pyrolysis in this embodiment is a rotating bed reactor, such as... Figure 1As shown, it includes an insulation jacket 1, a rotary bed 2, a driven gear 3, a dynamic seal 4, a screw feeder 5, a gas inlet 6, a motor 7, a drive gear 8, a rotary bed support plate 9, a condenser 10, a discharge port 11, and an electromagnetic induction coil 12, etc.

[0046] The rotary bed 2 is supported by a rotary bed support plate 9 and a support structure. The rotary bed support plate 9 is also equipped with a drive gear 8 driven by a motor 7. The drive gear 8 cooperates with the driven gear 3 on the rotary bed 2 to drive the rotary bed 2 to rotate. A screw feeder 5 is connected to the rotary bed 2, and a dynamic seal 4 is provided between them. The rotary bed 2 is also equipped with a gas inlet 6. An insulation jacket 1 is wrapped around the outer periphery of the rotary bed 2, and an electromagnetic induction coil 12 is surrounded by the insulation jacket 1. A condenser 10 and a discharge port 11 are located downstream of the rotary bed 2.

[0047] The rotating bed 2 has an internal diameter of 200 mm and a length of 300 mm, with eight 10 mm baffles evenly arranged along the axial direction. An electromagnetic induction coil 12 external to the insulation jacket 1 heats the rotating bed reactor. The driving gear 8 drives the driven gear 3 to rotate, causing the reactor body to rotate counterclockwise or clockwise around a horizontal axis. Waste polymethyl methacrylate polymer is added to the rotating bed 2 via a screw feeder 5, directly fed into the interior of the rotating bed 2. A small amount of N2 (20 mL / min) is continuously introduced through the gas inlet 6 to maintain an inert environment inside the reactor. The rotating bed support plate 9 supports the rotating bed 2. The mixed gas exiting from the outlet 11 is condensed by the condenser 10, and the liquid-phase monomer product is finally collected.

[0048] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.1%, and the mass yield of methyl methacrylate was 90.8%.

[0049] Example 2

[0050] The difference between this embodiment and Embodiment 1 is that the depolymerization temperature in step (2) is 400℃ and the reaction time is 18 min. After condensation, the liquid phase product is collected, and 193.2 g of liquid oil is finally obtained.

[0051] A solid iron sphere containing carbon deposits, which is a heat carrier for metal catalysts generated by a long-term pyrolysis reaction, is fed into a regeneration reactor. Air is introduced to burn off the carbon deposits, resulting in a regenerated solid iron sphere for metal catalyst heat carriers.

[0052] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 96.2%, and the mass yield of methyl methacrylate was 92.9%.

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that the depolymerization temperature in step (2) is 450°C and the reaction time is 15 min. After condensation, the liquid phase product is collected, and 191.5 g of liquid oil is finally obtained.

[0055] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.5%, and the mass yield of methyl methacrylate was 91.4%.

[0056] Example 4

[0057] The difference between this embodiment and Embodiment 2 is that the reactor volume filling rate in step (2) is 5%, and the reaction time is 19 min. After condensation, the liquid phase product is collected, and 186.7 g of liquid oil is finally obtained.

[0058] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 90.3%, and the mass yield of methyl methacrylate was 84.3%.

[0059] Example 5

[0060] The difference between this embodiment and Embodiment 2 is that the reactor volume filling rate in step (2) is 15%, and the reaction time is 18 min. After condensation, the liquid phase product is collected, and 189.9 g of liquid oil is finally obtained.

[0061] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 92.5%, and the mass yield of methyl methacrylate was 87.8%.

[0062] Example 6

[0063] The difference between this embodiment and Embodiment 1 is that in step (2), 6000g of solid iron spheres are weighed as the heat carrier for the metal catalyst, with a diameter of 2-2.5mm; 1000g of ceramic heat carrier with a diameter of 2-3mm is weighed; the volume ratio of the solid iron spheres to the ceramic heat carrier is 2:1; the depolymerization temperature is 400℃; and the reaction time is 18min. After condensation, the liquid phase product is collected, ultimately yielding 191.6g of liquid oil.

[0064] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.6%, and the mass yield of methyl methacrylate was 91.6%.

[0065] Example 7

[0066] The difference between this embodiment and Embodiment 1 is that in step (2), 1500g of solid iron spheres are weighed as the heat carrier for the metal catalyst, with a diameter of 2-2.5mm; 4000g of ceramic heat carrier with a diameter of 2-3mm is weighed; the volume ratio of the solid iron spheres to the ceramic heat carrier is 1:2; the depolymerization temperature is 400℃; and the reaction time is 18min. After condensation, the liquid phase product is collected, ultimately yielding 192.4g of liquid oil.

[0067] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.8%, and the mass yield of methyl methacrylate was 92.1%.

[0068] Example 8

[0069] The difference between this embodiment and Embodiment 1 is that in step (2), the reactor rotation speed is 6 rpm, the depolymerization temperature is 400℃, and the reaction time is 16 min. After condensation, the liquid phase product is collected, and 191.3 g of liquid oil is finally obtained.

[0070] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 94.3%, and the mass yield of methyl methacrylate was 90.2%.

[0071] Example 9

[0072] The difference between this embodiment and Embodiment 1 is that in step (2), the reactor rotation speed is 2 rpm, the depolymerization temperature is 400℃, and the reaction time is 16 min. After condensation, the liquid phase product is collected, and 188.9 g of liquid oil is finally obtained.

[0073] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 93.4%, and the mass yield of methyl methacrylate was 88.2%.

[0074] Example 10

[0075] The difference between this embodiment and Embodiment 1 is that in step (2), the iron-nickel solid spheres serve as the heat carrier for the metal catalyst, the depolymerization temperature is 400℃, and the reaction time is 15 min. After condensation, the liquid phase product is collected, ultimately yielding 192.6 g of liquid oil.

[0076] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 96.1%, and the mass yield of methyl methacrylate was 92.5%.

[0077] Example 11

[0078] The difference between this embodiment and Embodiment 10 is that in step (2), the reaction is divided into two stages. In the first stage, the electromagnetic induction frequency is 600 kHz and the reaction time is 6 min; in the second stage, the electromagnetic induction frequency is 80 kHz and the reaction time is 2 min. After condensation, the liquid phase product is collected, and 193.5 g of liquid oil is finally obtained.

[0079] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 96.3%, and the mass yield of methyl methacrylate was 93.2%.

[0080] Example 12

[0081] The difference between this embodiment and Embodiment 1 is that in step (2), the reaction is divided into two stages. In the first stage, the electromagnetic induction frequency is 600 kHz and the reaction time is 5 min; in the second stage, the electromagnetic induction frequency is 100 kHz and the reaction time is 2 min. After condensation, the liquid phase product is collected, and 194.3 g of liquid oil is finally obtained.

[0082] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 96.9%, and the mass yield of methyl methacrylate was 94.1%.

[0083] It can be seen that when electromagnetic induction heating is performed in stages using different frequencies, the reaction time can be shorter while the yield of methyl methacrylate is higher.

[0084] Example 13

[0085] The difference between this embodiment and Embodiment 1 is that in step (2), the iron-nickel-molybdenum solid spheres are used as the heat carrier for the metal catalyst, the depolymerization temperature is 400℃, and the reaction time is 17 min. After condensation, the liquid phase product is collected, and 191.8 g of liquid oil is finally obtained.

[0086] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.4%, and the mass yield of methyl methacrylate was 91.5%.

[0087] Example 14

[0088] The difference between this embodiment and Embodiment 1 is that in step (2), the depolymerization temperature is 400℃, the electromagnetic induction frequency is 20kHz, and the reaction time is 21min. After condensation, the liquid phase product is collected, and 189.3g of liquid oil is finally obtained.

[0089] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 94.5%, and the mass yield of methyl methacrylate was 89.5%.

[0090] Example 15

[0091] The difference between this embodiment and Embodiment 1 is that in step (2), the depolymerization temperature is 400℃, the electromagnetic induction frequency is 600kHz, and the reaction time is 17min. After condensation, the liquid phase product is collected, and 192.7g of liquid oil is finally obtained.

[0092] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 95.2%, and the mass yield of methyl methacrylate was 91.7%.

[0093] Example 16

[0094] The difference between this embodiment and Embodiment 1 is that in step (2), the depolymerization temperature is 400℃, and the nitrogen valve is closed. After condensation, the liquid phase product is collected, ultimately yielding 185.3g of liquid oil.

[0095] Gas chromatography analysis showed that the mass content of methyl methacrylate in the liquid product was 91.3%, and the mass yield of methyl methacrylate was 84.6%.

[0096] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing monomers by electromagnetic induction pyrolysis of polymethyl methacrylate, characterized in that, Includes the following steps: S1: Add the metal catalyst heat carrier and the ceramic heat carrier to the rotating bed reactor, and heat the metal catalyst heat carrier and the ceramic heat carrier to the depolymerization temperature of polymethyl methacrylate using electromagnetic induction. The metal catalyst heat carrier is heated by electromagnetic induction through an electromagnetic induction coil outside the rotating bed reactor, and the heat is then transferred to the ceramic heat carrier. The rotating bed reactor includes a feeding system, a rotating reaction system and a discharging system arranged in sequence; the rotating reaction system is surrounded by an electromagnetic induction coil; the feeding system includes a screw feeder (5); the rotating reactor system includes a rotating bed (2); and the discharging system includes a discharge port (11) and a condenser (10) located downstream of the discharge port (11). S2: Crushed polymethyl methacrylate waste or raw material is continuously added from the feed port of the rotating bed reactor. The polymethyl methacrylate undergoes a depolymerization reaction to generate monomers. The gaseous product containing monomers is discharged from the discharge port of the rotating bed reactor. After condensation, the liquid product containing monomers is collected. In step S1, the metal catalyst heat carrier is an inductive medium. The material of the metal catalyst heat carrier is one of iron, iron-nickel alloy or iron-nickel-molybdenum alloy. The particle size of the metal catalyst heat carrier is 2–2.5 mm. The particle size of the ceramic heat transfer fluid is 2-3 mm; The volume ratio of the metal catalyst heat carrier to the ceramic heat carrier is 1:1 to 1:

3. The total volume of the added metal catalyst heat carrier and ceramic heat carrier accounts for 8% to 25% of the total volume of the rotating bed reactor; the depolymerization temperature is 375 to 450°C.

2. The method according to claim 1, characterized in that, The electromagnetic induction heating frequency in step S1 is 20 to 1000 kHz.

3. The method according to claim 1, characterized in that, In step S1, the main body or inner wall material of the rotating bed reactor is ceramic, and the rotating bed reactor is externally wound with coils.

4. The method according to claim 1, characterized in that, In step S2, the particle size of the crushed polymethyl methacrylate waste or raw material is 2-20 mm.

5. The method according to claim 1, characterized in that, It also includes step S3: the metal catalyst heat carrier containing carbon deposits generated by the long-term pyrolysis reaction in step S2 is fed into the regeneration reactor, and air is introduced to burn the carbon deposits to obtain the regenerated metal catalyst heat carrier.

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