A chemical and kinetic study of cellulose and biomass pyrolysis at high heating rates

A molecular beam mass spectrometer has been interfaced with an entrained flow reactor to study the pyrolytic decomposition of biomass. The system operates in a fast/flash pyrolysis regime, with peak heating rates on the order of 104-K/s. Detailed particle models suggest pyrolysis of sub-50-μm biomass particles is possible in a kinetically controlled regime with this reaction system. Cellulose pyrolysis has been examined both by mass spectrometry and by sampling the pyrolysis residues. Pyrolysis data conform well to the weight loss pyrolysis rates from the literature that involve an activation energy of ∼140-kJ/mol. A rate is calculated for the thermal destruction of the primary vapors of cellulose. Pyrolysis experiments were performed for a standard set of biomass materials. Results from factor analysis of biomass pyrolysis vapor mass spectra and qualitative observations suggest that current biomass models are inadequate for modeling the fast pyrolysis of biomass. At the temperatures of this reaction system, evolution of the polysaccharide and lignin constituents was relatively concurrent, but in varying relative proportion. Data comparison with more traditional batch reactor experiments highlights surprising spectral differences that can be attributed to heating rate effects and char-tar interactions. Several parameters that may drive complex interactions in the formation of char and the destruction of the tars are identified.