Fast pyrolysis in a novel wire-mesh reactor: Design and initial results

Pyrolysis is known to occur by decomposition processes followed by vapour phase reactions. The goal of this research is to develop a novel device to study the initial decomposition processes. For this, a novel wire-mesh reactor was constructed. A small sample (<0.1 g) was clamped between two meshes that were heated fast (up to 10 000 °C/s, ΔTmesh ±35 °C) by an electrical current. The mesh/feedstock was placed inside a vacumized (P < 0.3 mbar), liquid nitrogen cooled vessel (Twall < −80 °C). These two last features were proven to result in a low vapour life time (<15–25 ms versus ∼2 s in typical pyrolysis). The vapour residence time and temperature could be increased by increasing the pressure inside the reactor and by removing of the liquid nitrogen cooling. Reproducible results concerning yields (mass balance closures 90–110 wt%) and analysis were obtained (oil by SEC and NMR, gas by GC, char by FTIR). The yields and oil composition were changing with loading from 0.05 g to 0.1 g, despite the small sample amounts. Compared to more “conventional” pyrolysis processes, high oil yields (84 wt%), very low char yields (5 wt%) and low gas yields (8 wt%) were obtained. Using a high speed camera, movies were made and together with accompanying pressure profiles, it was possible to estimate the conversion rate. At 500 °C the conversion process was finished within 0.8 s which is faster than previously reported in the literature. Especially an increase in gas yield (+14 wt%, mainly CO) was observed in absence of cooling (Pvac/No Cooling), while both the gas (+4 wt%) and char yield (+3 wt%) increased under atmospheric pressure (Patm/Cooling), all at the expense of oil yield. Compared to more “conventional” pyrolysis oil, the oil did contain: (i) heavier molecules and (ii) a sugar fraction.

► Initial decomposition processes in the fast pyrolysis of pine wood.
► A novel wire-mesh reactor was successfully introduced.
► Vapour residence times were proven to be only 15–25 ms.
► Biomass conversion was finished faster than can be derived from kinetic expressions in the literature.
► High oil yields (over 80 wt%) and very low char yields (5 wt%) were obtained.