A sustainable and cost-effective method to simultaneously produce carbon nanomaterials and syngas from lignite and banana waste

A novel approach was adopted to generate carbon nanomaterials from the syngas, originating from the co-gasification of lignite and banana as a biomass waste. Aiming at that, cobalt and an industrial solid waste (ISW)-based sustainable catalyst was synthesized by following the co-precipitation route, where the support substrate was obtained from a coal-processing industrial unit. The carbon nanotubes (CNTs) were generated in a fixed-bed catalytic reactor at around 400 °C owing to thermocatalytic reactions of first-stage product syngas. The product syngas fed to the second-stage reactor system was produced in a fluidized-bed gasifier at 800 °C, operating in a bubbling fluidization regime at around 0.5–0.7 MPa. The integrated reactor system with the novel catalyst substrate generated CNTs of varying lengths up to a few microns, with an outer diameter of 30 – 60 nm and inner diameters below 10 nm. The carbon yield varied between 0.92 ± 0.09 gCarbon/gCatalyst and 0.99 ± 0.21 gCarbon/gCatalyst for the repeated number of experiments between 400 °C and 600 °C temperature of the second stage reactor. The high-crystallinity and graphitization degree of the solid carbon product were deciphered by applying various analytical techniques of X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray (EDX) analysis, etc. Due to a strong active metal-support interaction, the role of alloy structures consisting of Co and support-induced Si, Al, and Fe oxide phases was identified towards the CNT growth steps following the base-growth mechanism. The current investigation represented a sustainable way of value-upgrading industrial solid waste as a catalyst for continuously producing high-value carbon nanomaterials from steam-gasified conventional and renewable carbonaceous substrates. • A novel study to directly convert carbonaceous feed to carbon nanomaterials. • An integrated fluidized bed gasification and catalytic fixed bed reactor system. • Production of highly crystalline and graphitic carbon nanostructures. • Base-growth mechanism over active Co-industrial solid waste-supported catalyst. • A comprehensive analysis of CNTs applying XRD, FTIR, and HRTEM-EDX techniques.