Pyrolysis of biomass components in a TGA and a fixed-bed reactor: Thermochemical behaviors, kinetics, and product characterization

The pyrolysis characteristics of three main components (hemicellulose, cellulose and lignin) of biomass were investigated using a thermogravimetric analyzer (TGA) and a fixed-bed reactor, respectively. In TGA, the pyrolysis of hemicellulose and cellulose occurred quickly with a weight loss from 210 to 370 °C for hemicellulose and from 260 to 410 °C for cellulose. Lignin decomposed over a wider range of temperature (from 200 to about 600 °C) and generated a high char yield. As the heating rate increased, TG and DTG curves shifted to the higher temperatures. The Flynn-Wall-Ozawa method was introduced to analyze the thermal reaction kinetics, and the activation energy (E) values of hemicellulose, cellulose and lignin pyrolysis are in correspondence with thermostability sequence of these three components. In the fixed-bed reactor, the pyrolysis of lignin generated remarkably high solid residue yield (61%) and very low liquid yield (0.5%) compared with cellulose and hemicellulose. The noncondensable gas mainly consisted of H₂, CH₄, CO₂ and CO. FTIR and GC-MS analysis of liquids showed that liquids from cellulose and hemicellulose pyrolysis included a range of light oxygenated compounds which was indicated that furans, aldehydes and ketones were the most prominent decomposition products. The depolymerization of lignin led to various phenols, including many methoxylated phenols. After pyrolysis, the carbon content in char increased while the hydrogen content decreased. All of the results and findings would help further understanding of thermal behavior of biomass and its thermo-chemical utilization for fuels and chemicals.