Molecular mechanisms for the gas-phase conversion of intermediates during cellulose gasification under nitrogen and oxygen/nitrogen

Gas-phase conversions of volatile intermediates from cellulose (AvicelPH-101) were studied using a two-stage experimental setup and compared with those of levoglucosan (1,6-anhydro-b-D-glucopyranose). Under N2or 7% O2/N2flow, vapors produced from the pyrolysis zone (500°C) degraded in the secondary reaction zone at 400,500, 600 or 900°C (residence time:0.8-1.4 s). The 69.3% (C-based) of levoglucosan was obtained at 400°C under N2flow along with 1,6-anhydro-b-D-glucofuranose (8.3 %, C-based), indicating that these anhydrosugars are the major volatile intermediates from cellulose pyrolysis. Levoglucosan and other volatiles started to fragment at 600°C, and cellulose was completely gasified at 900°C. Most gas/tar formations are explained by gas-phase reactions of levoglucosan reported previously, except for some minor reactions originating from the molten-phase pyrolysis, which produced benzene, furans and 1,6-anhydro-b-D-glucofuranose. Synergetic effects of O2and volatiles accelerated fragmentation and cellulose gasification was completed at 600°C, which reduced benzene and hydrocarbon gas productions. The molecular mechanisms including the action of O2as a biradical are discussed. These lines of information provide insights into the development of tar-free clean gasification that maintains high efficiency