Systems and methods for microwave-driven catalytic conversion of plastics into carbon black materials and gases

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 Fe2O3, Fe3O4, NiO, CoO, Co3O4, 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.