A novel design for mass production of multi-walled carbon nanotubes using Co-Mo/MgO catalyst via pyrolysis of polypropylene waste: effect of operating conditions

Abstract

A two-stage process was employed for high yield production of multi-walled carbon nanotubes (MWCNTs) via pyrolysis of polypropylene (PP) waste. In the first stage, a new design was used for the pyrolysis of PP waste at 500 °C to form a mixture of condensable hydrocarbons (≥C₆) and non-condensable gases (C₁–C₅) inside a vertical reactor closed from the bottom and connected directly to a vertical condenser at the top. This pyrolysis technique permitted to form a large amount of non-condensable hydrocarbon gases, which were used in the second stage as a carbon source for the production of MWCNTs over Co-Mo/MgO catalyst. The influences of growth temperature (700–850 °C) and carrier gas flow rate of N₂ (50–110 sccm) on the yield and morphology of as-deposited MWCNTs have been investigated. The fresh Co-Mo/MgO catalyst and the as-deposited carbon were characterized by XRD, FTIR, TPR, BET surface properties, TEM, Raman spectroscopy and TGA. The results demonstrated that the adjustment of growth temperature and N₂ flow-rate caused a marked impact on the yield, type and quality of as-grown MWCNTs. The optimum MWCNTs yields of 32.6 and 38.3 g/g_catalyst have been achieved at the growth temperature of 800 °C and the carrier gas flow rate of 90 sccm, respectively. TEM images illustrated the formation of pure MWCNTs at the growth temperature range of 700–800 °C, whereas mixed materials of MWCNTs and graphene nanosheets (GNSs) were obtained at the growth temperature of 850 °C. Raman spectroscopy illustrated that highly graphitized and crystalline MWCNTs were produced at all operating conditions. TGA proved that all MWCNTs samples exhibited higher thermal stability.

Keywords:

• Two-stage process
• polypropylene waste
• pyrolysis
• Co-Mo/MgO catalyst
• multi-walled carbon nanotubes

Acknowledgments

This research work was funded by the Science and Technology Development Fund (STDF) of Egypt under project contract number 15114, basic and applied grant. The authors greatly acknowledge this support.