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.

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 CO 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.