High-speed camera observation of cellulose fast pyrolysis under infrared irradiation

Fast pyrolysis using infrared irradiation is a method for converting cellulose into valuable chemicals. In the present study, the pyrolysis behavior of cellulose sheets (Whatman cellulose) and cellulose powder (Avicel cellulose) under infrared irradiation in a nitrogen flow was investigated using a high-speed camera. In the case of cellulose sheet, pyrolysis products, including levoglucosan and carbonized materials, were locally formed in the initial stage of the reaction. Subsequently, holes with a thin layer of pyrolysis products were formed, and pyrolysis proceeded as the hole expanded. For cellulose powder, pyrolysis occurred on the surface of the cellulose exposed to infrared irradiation, and droplets of pyrolysis products were formed. The droplets moved around, collecting the liquid products, and pyrolysis products volatilized from the droplets. This pyrolysis behavior continued into the unreacted cellulose powder below, resulting in the complete pyrolysis of all of the cellulose under fast pyrolysis conditions. Near-infrared (NIR) spectroscopy revealed that this characteristic pyrolysis behavior was due to the more efficient absorption of infrared radiation by the pyrolysis products, liquid and carbonized products, compared to the unreacted cellulose. It was also found that the addition of solid carbonized products efficiently promoted the fast pyrolysis reactions. These findings have important implications for the fast pyrolysis of cellulose under infrared irradiation. • Fast pyrolysis of cellulose under infrared was studied with a high-speed camera and UV-Vis-NIR spectroscopy. • In cellulose sheets, pyrolysis progresses as small hole formed locally and spread outward in concentric circles. • In cellulose powder, droplets formed, moved around, and volatilized while collecting the products. • These characteristics were due to pyrolysis products absorbing NIR more than original cellulose. • The addition of solid carbonized products with higher NIR absorptivity enhanced the rate of fast pyrolysis of cellulose.