Systems and methods for microwave-driven catalytic conversion of plastics into carbon black materials and gases
A system for microwave-assisted catalytic conversion of plastics into carbonaceous materials and gases includes a materials sorter to sort and remove metals from a batch of plastics; a metal detector to detect metals in the batch of plastics; a mixer configured to receive the batch of plastics and a corresponding batch of micro or nano-scale metal oxides, and further configured to produce a mixture of the plastics and the metal oxides to achieve an essentially uniform distribution of the metal oxides in the plastics; and a rotary microwave oven in communication with a microwave generator and configured to receive microwaves to heat contents of the rotary microwave oven. The rotary microwave oven receives the mixture; and a processor executing a program of instructions controls operation of the rotary microwave oven to convert the plastics to produce one or more carbonaceous materials and one or more gases.
1 . A system for microwave-assisted catalytic conversion of plastics into carbonaceous materials and gases, comprising:
a materials sorter configured to sort and remove metals from a batch of plastic materials;
a metal detector configured to detect metals in the batch of plastic materials;
a mixer configured to receive the batch of plastic materials and to receive a corresponding batch of metal oxides, and further configured to produce a mixture comprising the plastic materials and the metal oxides to achieve an essentially uniform distribution of the metal oxides in the plastic materials;
a rotary microwave oven in communication with a microwave generator and configured to receive microwaves to heat contents of the rotary microwave oven, wherein the rotary microwave oven receives the mixture; and
a processor executing a program of instructions stored on a non-transitory, computer readable storage medium to control operation of the rotary microwave oven, wherein the heating heats the metal oxides, wherein heated metal oxides transfer heat to the plastic materials, wherein the heat transfer vaporizes the plastic materials, wherein the vaporized plastic materials produce one or more types of carbonaceous materials and one or more gases.
2 . The system of claim 1 , wherein metal-oxide particles are chosen from the group consisting of Fe 2 O 3 , Fe 3 O 4 , NiO, CoO, Co 3 O 4 , mixed ferrites, and combinations thereof.
3 . The system of claim 1 , further comprising a metal-oxide fabrication facility, the facility comprising: one or more pH-controlled stirred reactors; a filter press; a spray dryer; and a muffle or rotary kiln.
4 . The system of claim 1 , wherein the rotary microwave oven is operated under an inert atmosphere and comprises a direct gas take-off configured to continuously remove pyrolysis vapors and permanent gases during operation.
5 . The system of claim 1 , wherein localized catalyst-particle surface temperatures reach up to about 2000° F. while a bulk reactor temperature is controlled between about 800° C. and about 1200° C.
6 . The system of claim 1 , wherein the one or more gases comprise hydrogen and syngas.
7 . The system of claim 1 , wherein the processor is further configured to execute a recipe specifying at least one of: rotation speed, microwave power profile, temperature ramp rate, maximum temperature and hold time, inert sweep flow rate, and gas take-off timing.
8 . The system of claim 1 , wherein the mixer and rotary microwave oven are instrumented with sensors configured to provide signals to the processor, and the processor is configured to adjust operation based on the signals.
9 . The system of claim 1 , wherein metal-oxide particles comprise microspheres having D50 between about 10 μm and about 100 μm formed by spray drying and calcination.
10 . The system of claim 1 , wherein the carbonaceous materials comprise at least one of amorphous carbon black, graphitic carbon, graphene, carbon nanotubes, and iron carbide.
11 . The system of claim 1 , wherein the materials sorter and metal detector are part of a multi-stage metals-removal subsystem comprising:
a primary shredder configured to reduce feedstock to particles of about 50-100 mm and liberate embedded metals;
an overband magnet and a magnetic head pulley for bulk ferrous removal;
an eddy-current separator for removal of non-ferrous metals;
an inductive all-metal sensor sorter with an air-jet array for removal of stainless steel and embedded metallic fragments; and
a fines treatment stage comprising a rare-earth drum magnet and a gravity free-fall all-metal separator.
12 . The system of claim 1 , wherein the processor is configured to reject or divert a feedstock batch when a detected total metal content exceeds a predetermined threshold.
13 . The system of claim 1 , wherein a particle-size distribution of metal-oxide particles is selected based on microwave penetration depth at both cold-start and elevated operating temperatures, such that a Dmax is no greater than about 150 μm at 2.45 GHz to ensure uniform heating.
14 . The system of claim 1 , wherein penetration depth of metal-oxide particles at operating temperature is at least twice a mean particle diameter.
15 . The system of claim 1 , wherein the processor is configured to integrate real-time sensor data from the reactor stage, mixing stage, and gas take-off stage into a feedback control loop that adjusts at least one of microwave power, rotation speed, sweep-gas flow, or gas take-off rate.
16 . The system of claim 1 , wherein the processor is further configured to execute predictive maintenance algorithms trained on historical sensor data to schedule maintenance before component failure.
17 . A system for microwave-assisted catalytic production of solid carbonaceous products including carbon nanotubes and few-layer graphene from plastic materials, comprising:
a materials sorter configured to sort and remove metals from a batch of plastic materials;
a metal detector configured to detect metals in the batch of plastic materials;
a mixer configured to receive the batch of plastic materials and to receive a corresponding batch of metal-oxide particles comprising at least one transition-metal oxide selected from the group consisting of Fe 2 O 3 , Fe 3 O 4 , NiO, CoO, Co 3 O 4 , and mixed ferrites, the metal-oxide particles having an average particle size between about 50 nm and about 150 μm, the particle size selected based on microwave penetration depth at both cold-start and elevated operating temperatures;
a rotary microwave oven in communication with a microwave generator and configured to receive microwaves to heat contents of the rotary microwave oven under an inert atmosphere, wherein the rotary microwave oven receives a mixture of the metal oxide particles and the plastic materials; and
a processor executing a program of instructions stored on a non-transitory, computer-readable storage medium to control operation of the rotary microwave oven,
wherein the microwaves heat the metal-oxide particles,
wherein the heated metal-oxide particles transfer heat to the plastic materials to induce pyrolysis and vaporization,
wherein the processor controls at least carbon activity, hydrogen partial pressure, pyrolysis vapor residence time, and catalyst surface morphology to promote carbon nanotube or few-layer graphene growth on catalyst surfaces,
wherein recovered solid carbonaceous products comprise:
for carbon nanotube production, at least 10% by mass carbon nanotubes having an average outer diameter between about 5 nm and about 50 nm; and
for few-layer graphene production, graphene sheets having fewer than 10 layers and a lateral dimension greater than 1 μm comprising at least 10% by mass of the solid carbonaceous products.