436 / 2018-09-01 16:57:29

Kinetic Modeling of the Effects of Cellulose Crystallinity on Cellulose Pyrolysis

全体主题 > 生物质多联产

The main objective of this study is to propose a new kinetic mechanism that includes the effects of crystallinity on cellulose pyrolysis. The thermogravimetric analysis of two kinds of cellulose with different crystallinity indexes (CI = 45% and 0, respectively) was conducted at different heating rates. Furthermore, two samples were also introduced in a Pyrolysis - Gas Chromatographer - Mass Spectrometry (Py-GC-MS) for volatiles analysis during pyrolysis at different final temperatures and heating rates. With the thermogravimetric (TG) curves, the isoconversional method originated an almost constant activation energy (~171 kJ/mol) for CI-45 cellulose at different conversions (α), and a rapid increasing activation energy for cellulose CI-00 from 146 kJ/mol at α = 0.1 to 171 kJ/mol at α = 0.2. The proposed kinetic mechanism, shown in Figure 1, is based on the cellulose kinetic sub-mechanism of the Bio-PoliMi. It considers the decomposition of the crystalline and amorphous regions of cellulose through different pathways. The unavailable kinetic parameters and reaction coefficients of the introduced reactions were fitted to the TG results using a two-step fitting procedure. The TG results show that a lower crystallinity index can advance the decomposition of cellulose and promote the formation of the char yield. The Py-GC-MS results show that lower crystallinity can promote the formation of small oxygenates and furan compounds at the expense of anhydro-sugars, while these effects may be weakened at higher heating rates. The kinetic mechanism proposed in the present study can accurately predict the pyrolysis behaviour as well as the total product yields of char, gas and tar of cellulose with different crystallinity indexes. In addition, it is able to predict the effects of crystallinity on the generation of reaction intermediates and volatiles distribution