The objective of this study was to elucidate primary and secondary reactions of cellulose pyrolysis, which was accomplished by comparing results from a micro-pyrolyzer coupled to a GC-MS/FID system and a 100 g/hr bench scale fluidized bed reactor system. The residence time of vapors in the micro-pyrolyzer was only 15-20 ms, which precluded significant secondary reactions. The fluidized bed reactor had a vapor residence time of 1-2 s, which is similar to full-scale pyrolysis systems and is long enough for secondary reactions to occur. Products from the fluidized bed pyrolyzer reactor were analyzed using a combination of micro-GC, GC-MS/FID, LC-MS and IC techniques. Comparison between the products from the two reactor systems revealed that the oligomerization of leglucosan and decomposition of primary products such as 5-hydroxymethyl furfural, anhydro xylopyranose and 2-furaldehyde were the major secondary reactions occurring in the fluidized bed reactor. This study can be used to build more descriptive pyrolysis models that can predict yield of specific compounds. (C) 2011 Elsevier Ltd. All rights reserved.