Overcoming major challenges in lignocellulose catalytic pyrolysis by combination of low-temperature thermal decomposition and co-processing with vegetable oils over ZSM-5 zeolite: boosted production of aromatic hydrocarbons and prolonged catalyst lifetime

The current study addresses the major challenges of lignocellulose catalytic pyrolysis over zeolites: the low hydrocarbon yields and the fast catalyst deactivation. The results here reported demonstrate how these hindrances can be sharply improved by the combination of low-temperature lignocellulose pyrolysis and catalytic co-processing with vegetable oils. This strategy has been successfully applied here to different combinations of lignocellulose (oak woodchips and acid-washed wheat straw) and vegetable oils (camelina and jatropha). The experiments were carried out in an ex-situ fixed-bed reactor with continuous feeding systems for both substrates, enabling the evaluation of the catalyst performance over time on stream. A nanocrystalline ZSM-5 zeolite was used as a catalyst. In comparison with conventional catalytic pyrolysis, the combination of low-temperature pyrolysis (350 °C) followed by catalytic co-processing resulted in a sharp enhancement of both the production of aromatic hydrocarbons (AR) and catalyst lifetime. Thus, the AR yield was boosted in the co-processing tests, reaching values of c.a. 22 wt% (≈40% carbon yield) at the beginning of the reaction (1 h of time on stream). Simultaneously, the deactivation kinetic constant (first order model) was reduced by a factor of about eight by combining low-temperature lignocellulose pyrolysis and vegetable oil co-processing, substantially improving catalyst stability. A preliminary comparative economic analysis was carried out to determine the product revenues that could be obtained, whereas an assessment of the CO 2 carbon sequestration potential was also performed. In both analyses, the proposed low-temperature lignocellulose pyrolysis and vegetable oil co-processing approach outperformed clearly the other considered cases.