The dried and sieved biomass of 7e10 g (precision to 0.1 mg)
was filled in the sample holder. After the sample holder was placed
in the pathway of microwave, the quartz tube was sealed tightly. In
order to maintain anoxic circumstances, Nitrogen gas was purged
into the system with a flow rate of 50 mL/min and controlled by
buoy flow meter. After purging N2 for 30 min, anoxic atmosphere
can be reached. Then the microwave power was turned on to the
designated microwave power level for the designated processing
time. Reflection microwave power was adjusted to be below 10% of
incident microwave power during the whole experimental period.
After reaching the designated processing time, the microwave
generator was shut down. The carrier gas kept purging until solid
residues were cooled down to 80 C before removing to desiccators.
In this study, four parameters, including microwave power level,
processing time, water content of biomass, and particle size were
varied to optimize the process. The detailed operating conditions
are depicted in Table 2.