Pyrolysis of α-cellulose using a multimode microwave oven

• Pyrolysis of cellulose was run using a multimode microwave oven.
• High yield of bio-oil was reached with iron as MW absorber.
• Large gasification was obtained using carbon as MW absorber.
• High char production was realized with alumina as MW absorber.
• Water was formed in low amount using silica as MW absorber.

α-Cellulose was pyrolyzed using a multimode microwave oven, different microwave absorbers and experimental set ups. The microwave absorber showed a strong influence: carbon gave a large gasification of cellulose (yield of gas up to 53.8%) while Al2O3 gave a high yield of bio-char (64.1%) and a low gas production (3.0%). Bio-oil was obtained with the highest yield (37.6%) using iron as microwave absorber and a condenser between the oven and the collecting system. Dark brown bio-oils having low density and viscosity due to the presence of large amount of furanosidic compounds were collected. Bio-oils were characterized through GC–MS, FT-IR, NMR, The GC–MS analysis was employed to evaluate the composition of bio-oils using calculated retention factors. A high concentration of levoglucosan (133.9 mg/mL) together with acetic acid, acetic anhydride, 1-hydroxy-2-propanone, formic acid and furfural were obtained using graphite as microwave absorber. A mechanisms was proposed to rationalize the formation of aromatic compounds present in bio-oils. Water contents in bio-oils were affected by all parameters of the process, mainly by the microwave absorber. The use of silica has proved to be a promising way to obtain bio-oil with low water content (13%), while pyrolysis in the presence of carbon gave a large amount of water (46%).