(417h) Thermocatalytic Fluidized Bed Co-Pyrolysis of Methane and Plastic Waste into Hydrogen and Carbon Nanotubes over a Multi-Metallic Catalyst

Production of hydrogen at a low cost without polluting the environment has gained prime attention nowadays due to its high energy potential, clean-burning properties. Among all the commercial processes for hydrogen production, the well-established steam methane reforming (SMR) process is a dominant process due to its high efficiency (~65%). However, thermo-catalytic decomposition of methane (TCD) has emerged as a novel alternate hydrogen production approach considering similar energy requirement as SMR along with no CO_x emission and valuable carbon byproducts. The rapidly increasing worldwide demand for plastics inevitably produces an enormous amount of waste plastics which needs to be utilized without polluting the environment. As hydrogen and carbon are the main building blocks of the majority type of plastics, they can be utilized in TCD process for increasing the yields of hydrogen and carbon.

In this context, decomposition of methane and plastics in a fixed bed, as well as fluidized bed reactor (FBR), were investigated. The catalyst used for the process is nickel-based copper-zinc promoted and alumina supported granular powder. By optimizing the concentration of promoters (i.e. copper and zinc), a specific metal crystal size range is obtained which ultimately lead to the high selectivity of the specific form of carbon i.e. carbon nanotubes (CNT). In the current work, the temperature is optimized for maximum hydrogen yield from methane and waste plastics. As the carbon is continuously depositing on the catalyst, the fluidized bed reactor is chosen for the reaction to accommodate spent catalyst regeneration and CNT separation. One of the challenges of the process is maintaining proper hydrodynamic condition in the fluidized bed reactor. The produced carbon is in the form of CNTs which is a valuable by-product which can help in improving the economy of the process. As waste plastic is a major source of carbon, its addition increases the yield of CNTs. At optimum reaction conditions, 75% methane conversion was observed along with the complete conversion of plastics to CNTs and Hydrogen. The obtained CNTs are multi-layered bamboo-shaped carbon nanotubes (Diameter: ~60 nm, Length: 2 microns).