387498 Thermogravimetric Studies of Charcoal Formation from Cellulose Under Different Pyrolysis Conditions
Thermogravimetric studies of charcoal formation from cellulose under different pyrolysis conditions
Wang, L.a, Skreiberg, Ø.a, Grønli, M.b, Antal, M.J.c
a SINTEF Energy Research, Trondheim, Norway
b Dept. of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway
c Hawaii Natural Energy Institute, University of Hawaii, Honolulu, HI, United States
Charcoal formation from Avicel cellulose under different pyrolysis conditions has been studied by using thermogravimetric analyzers (TGAs). Evident differences in cellulose charcoal yields were obtained as cellulose was pyrolyzed in two thermogravimetric analyzers (TGAs) using crucible and pan with different geometries and depths. Deep crucibles restrained the egression of volatiles from the pyrolyzing solids and prolonged the vapor-phase residence time, enhancing cellulose charcoal yields. Confinement of pyrolysis volatiles by using crucible covers with and without pinholes significantly enhanced the cellulose charcoal yields. The charcoal yields in the open crucibles were 8-9% for heating rates of 5, 20 and 100 °C/min. When the pyrolysis experiments were conducted in capped crucibles with pinholes, the charcoal yields dramatically increased to respectively 18, 16 and 14% at the same heating rates. In order to maximize the confinement of pyrolysis volatiles, extra lids were put on the capped crucible covers to close the pinholes, and the cellulose charcoal yields further increased to 21 and 19%, as the samples were pyrolyzed from 25 to 500 °C at heating rates of 5 and 20 °C/min, respectively. Using deep crucibles and/or covering of the crucibles with lids prolongs vapor-phase residence time and increases the concentration of vapors in the carbonization process. This promotes secondary char forming reactions and attainment of high cellulose charcoal yields. On the other hand, for the experiments performed with open crucibles, lower heating rate alone was not sufficient to assure high cellulose charcoal yields. However, lower heating rate combined with considerable capture of pyrolysis volatiles through enhancement of secondary char forming reactions ensure higher cellulose charcoal yields, as observed in the present work.