In this paper, a study on the fractionation of pentosans and hexosans from poplar chips was performed using a circulation reactor. The study's methodology created kinetic models of both pentosan and hexosan hydrolysis/degradation to predict the fractionation yield of both substances. The conditions were varied to include a temperature range of 140-170 degrees C, a sulfuric acid concentration range of 0.1-0.9 wt %, and a constant liquor-to-wood ratio of 6:1. The yields of both substances were favored at high acid concentration and temperature, with pentosan being considerably more reactive. Under optimal conditions, 91% of pentosan (as monomers, oligmers, and degradation products) could be recovered, with more than 93% of hexosan retained in the solids. This study demonstrates that pentosans and hexosans may be fractionated from this biomass using acid hydrolysis, which will enable further processing of relatively homogeneous saccharide streams to create fuels or chemicals.