Secondary Reactions of Levoglucosan and Char in the Fast Pyrolysis of Cellulose

摘要

In fast pyrolysis of cellulose, levoglucosan is often reported as the most abundant primary decomposition product. Char, the solid residue of pyrolysis is thought to catalyze secondary reactions that decompose levoglucosan into water and additional, secondary char. A CDS Analytical Pyroprobe 5200 was used to pyrolyze pure cellulose to levoglucosan and the generated vapors were passed through a temperature-controlled tubular reactor filled with material to be tested for catalytic activity and then to a GC-FID for analysis. Carbonaceous materials included as-received and acid-washed char derived from pyrolysis of red oak and, pure graphite. Acid-washed red oak char and pure graphite had little effect on levoglucosan decomposition compared with the empty tubular reactor for the range of tubular reactor temperatures studied (200-400°C). In contrast, unwashed red oak char significantly reduced the amount of levoglucosan when the tubular reactor was operated above 300° C. These results suggest that metals—which are removed through the procedure of acid washing—rather than the fixed carbon in the char, catalyze the decomposition of levoglucosan in the vapor phase.