Co-production of carbon nanotubes and hydrogen from waste plastic gasification in a two-stage fluidized catalytic bed

Abstract

This study aims to develop a two-stage fluidized catalytic bed reactor system for continuous co-production of carbon nanotubes (CNTs) and hydrogen from waste plastics gasification. Ni/Al-SBA-15 and Ni–Cu/CaO–SiO 2 catalysts have been synthesized and granulated for CNTs synthesis and hydrogen production in the first- and second-stage reactor, respectively. The operating parameters, including reaction temperature and equivalence ratio (ER), were investigated to confirm the feasibility for CNTs and hydrogen production of this system. The Ni/Al-SBA-15 added in the first-stage reactor enhanced the waste plastics degradation to produce CH 4 and C 2 –C 5 hydrocarbons with increasing temperature, which could be used as the source for CNTs synthesis. Lowering the ER promoted the catalytic thermal cracking and reforming of hydrocarbons that contributed to the CNTs and hydrogen production. Nevertheless, the H 2 production rate showed a significant increase to 857.6 mmol/h-g catalyst with the assistance of Ni–Cu/CaO–SiO 2 in the second-stage reactor. The produced smaller-molecule hydrocarbons from the second-stage reactor with higher temperatures could benefit the co-production of CNTs and hydrogen. The two-stage fluidized catalytic bed gasification system exhibited an optimal performance of high fraction CNTs and H 2 when temperatures of first- and second-stage reactor were controlled at 600 and 800 °C, respectively, with 0.1 ER. • A two-stage fluidized catalytic bed is developed to produce carbon nanotubes and H 2 . • Ni/Al-SBA-15 and Ni–Cu/CaO–SiO 2 were granulation to use in the pilot-scale system. • Ni/Al-SBA-15 and Ni–Cu/CaO–SiO 2 highly enhanced carbon nanotubes and H 2 production. • Operating parameters of the fluidized bed were evaluated for catalytic performance. • The system gave 857.6 mmol H 2 /h-g catalyst and carbon nanotubes fraction of 48.0%.