Pyrolysis behavior and kinetics of biomass derived materials

Abstract

From previous biomass decomposition studies, it is well established that thermolysis generally occurs between 200 and 400 °C. For most materials, this temperature range constitutes up to 95% of total degradation; nonetheless, secondary decomposition reactions continue to occur in the solid matrix above 400 °C. The extent of these reactions, as indicated by the material loss above 400 °C, is small, and in the past has been either ignored or included in the primary degradative step. However, this latter step (reactions above 400 °C) exhibits many unique characteristics that differentiate it from the primary pyrolysis step and therefore needs to be treated separately. Additionally, it is widely accepted that primary decomposition of biomass material (<400 °C) consists of a degradative process, whereas the secondary thermolysis (>400 °C) involves an aromatization process. In this study, It is shown that the latter step can be deconvoluted from the primary decomposition step, particularly for materials with limited aromaticity, such as cellulose and other carbohydrates. A thermogravimetric analyzer (TGA) coupled with a differential scanning calorimeter (DSC) and mass spectrometer (MS) was used to pyrolyze materials such as cellulose, xylan and other carbohydrates; and a pyroprobe interfaced with a gas chromatograph (GC) and mass spectrometer for product identification. In addition to monitoring the major products for each step, one also monitored and compared the temperatures corresponding to the maximum rate. From this analysis, the DTG results at 20 °C min −1 heating rate show that the temperature differences between the peak temperatures of the two decomposition steps are approximately 70, 190, and 200 °C for cellulose, pectin, and xylan, respectively. Furthermore, TGA data were used to calculate sets of biomass-specific kinetic parameters for these two steps.