Microwave pyrolysis of cellulose at low temperature

• Bio-oil, biochar and gas can be easily produced from microwave pyrolysis of cellulose at low temperatures (200–280 °C).
• The highest bio-oil yield (45%) from microwave pyrolysis of cellulose was obtained at 260 °C.
• Water and activated carbon were used as microwave absorbers and had significant influences on product yields.
• Amorphous cellulose gave significantly higher amounts of levoglucosan than from microcrystalline cellulose.

Microwave pyrolysis of cellulose was successfully achieved at low temperature (200–280 °C) using a lab-scale microwave synthesis system. Both closed and open microwave setups were developed to measure yields of pyrolysis products and to characterize the bio-oil. The effect of temperature, type of cellulose (crystalline and amorphous), and microwave absorber were examined. Microwave-derived bio-oil compositions were compared to conventional pyrolysis (microfurnace pyrolyzer–GC/MS) under similar heating rates. Maximum bio-oil yield (45%) was obtained from amorphous cellulose at 260 °C using an open system. Addition of water significantly increased the bio-oil yield to 52% (amorphous) and to 47% (crystalline) while addition of activated carbon had the effect of increasing gaseous products. Microwave-derived bio-oil products varied in chemical nature and abundance depending on cellulose crystallinity and between open or closed microwave pyrolysis and showed significant differences from conventional pyrolysis bio-oil. High yields of levoglucosan were obtained from amorphous cellulose at 260 °C while conventional pyrolysis required a much higher temperature (400 °C).