Simultaneous production of aromatics-rich bio-oil and carbon nanomaterials from catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas

Abstract

An integrated process that includes catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas were conducted to simultaneously produce aromatics-rich bio-oil and carbon nanotubes (CNTs). The influences of feedstocks blending ratio on the characteristics of bio-oil and CNTs were established. The reaction mechanism of carbon deposition during the system was also probed. The results showed that co-feeding plastic to biomass siginificantly enhanced the selectivity of monoaromatics (benzene, toluene, and xylene) from 5.6% for pure biomass to the maximum yield of 44.4% for 75.0% plastic ratio, and decreased naphthalene and its derivates from 85.9 to 41.7% correspondingly. The most synergistic effect on BTX selectivity occurred at 25% of plastic ratio. The multi-walled CNTs were successfully synethsized on Ni catalyst by utilizing prolysis gas as feedstocks. For pure biomass, the least CNTs yield with ultrafine diameters of 3.9–8.5 nm was generated via disproportionation reaction of CO which was derived from decarboxylation and decarbonylation of oxygenates on the ZSM-5 acid sites. With the rise of plastic ratio, sufficient hydrocarbons were produced for CNTs growth, endowing CNTs with long and straight tube walls, along with uniform diameters (~16 nm). The CNTs yield increased as high as 139 mg/g-cata. In addition, the decreased CO2 inhibited dry reforming with C1-C4 hydrocarbons and deposited carbon, avoiding excessive etching of CNTs. Thereby, high-purity CNTs with less defects were fabricated when plastic ratio was beyond 50% in the feedstock. The strategy is expected to improve the sustainability and economic viability of biomass pyrolysis.