Upcycling lignocellulosic biomass using a radial-axial fixed-bed ex-situ catalytic pyrolysis reactor

The transition to green energy depends on the effective conversion of lignocellulosic biomass into a high-quality fossil-feedstock-compatible bio-oil, and catalytic pyrolysis is a promising approach. Here, we present a new design of a radial-axial fixed-bed ex-situ catalytic pyrolysis system to address the common issue of excessive pressure buildup in traditional fixed-bed reactors. This system includes a radial-flow pyrolysis reactor and an axial-flow catalytic pyrolysis-vapor upgrading reactor, thereby enabling the study of reaction parameters, mass balances, and three-phase product properties in ex-situ catalytic pyrolysis of biomass, as well as the stability and regenerability of the catalyst. As a demonstration, ex-situ catalytic pyrolysis of pinewood using Na₂CO₃/γ-Al₂O₃ catalyst was performed at 500 °C at different biomass-to-catalyst (B/C) ratios (of 2-16), and multiple reaction-regeneration cycles were conducted. Catalytic pyrolysis bio-oil at a B/C ratio of 2 exhibited high quality, with an oxygen content of 16.1 wt% and an HHV of 34.0 MJ kg^-1 over the fresh catalyst. However, it degraded during reaction-regeneration cycles, showing an oxygen content of 27.0 wt% and an HHV of 27.8 MJ kg^-1 over the 4th-time-regenerated catalyst. Comprehensive characterization revealed both reversible catalyst deactivation (due to coke deposition) and irreversible catalyst deactivation (related to the transformation of the active sites to NaAlO₂). This work emphasizes the development of novel catalysts with good stability and regenerability under harsh catalytic pyrolysis and regeneration conditions, and this new radial-axial fixed-bed ex-situ catalytic pyrolysis system provides an alternative reactor option.