Investigation of Primary Reactions and Secondary Effects from the Pyrolysis of Different Celluloses

The primary reactions and secondary effects resulting from cellulose fast pyrolysis were investigated using a micropyrolyzer system by changing sample weight and length scale. To exclude the catalytic effects from metal ions, all cellulose samples were demineralized prior to pyrolysis. Heat transfer calculations estimated the characteristic time scale for heat transfer to be 1 order of magnitude smaller than the pyrolysis reaction time when the sample weight was less than 800 mu g. It was found that mass transfer limitations existed when the sample weight of the powder cellulose was larger than 800 mu g or when the cellulose particles were pyrolyzed at a larger characteristic length scale. The mass transfer limited system led to secondary reactions including secondary char and gas formation from volatile products and decomposition/dehydration of levoglucosan into low molecular weight products, furans, and dehydrated pyranose. The secondary reactions were found to be catalyzed by the char from cellulose pyrolysis. The pyrolysis of powder celluloses of differing crystallinity, degree of polymerization, and feedstock type were studied. Over 87 wt % mass balance closure was achieved for each type of cellulose. Similar product distributions were obtained for all of the different celluloses, implying that the primary products from cellulose were not influenced by these factors.