Pyrolytic characteristics and kinetics of Guanzhong wheat straw and its components for high-value products

Abstract

Wheat straw produced annually in the Shaanxi Guanzhong region is a potential biomass feedstock for the production of transportation fuels and specialized chemicals through combustion, pyrolysis, or gasification. In this work, the pyrolytic characteristics, evolved gas products, and kinetics of Guanzhong wheat straw and its components were first investigated with a thermogravimetry-Fourier infrared spectroscopy (TG-FTIR) system. A comparative kinetic study was conducted using different model-free methods of Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Kissinger, and the Coats-Redfern methods. The main pyrolysis products identified by FTIR include H2O, CH4, CO2, and CO as well as aromatics, acids, ketones, and aldehydes. Kinetic results showed that the pyrolytic apparent activation energy of the straw is approximately 200 kJ/mol obtained via FWO and KAS methods at the conversion range of 0.4 to 0.75, which was 30 kJ/mol higher than the value 171.1 kJ/mol obtained by the Kissinger method. The apparent activation energy of cellulose in its main pyrolysis region is 135.5 kJ/mol and is about three times larger than that of hemicellulose (49.5 kJ/mol). The apparent activation energy of lignin at the temperature range of 45 to 116 °C was 34.5 kJ/mol, while that value at the temperature range of 120 to 252 °C was 6.64 kJ/mol.

Pyrolysis Mechanism of Wheat Straw Based on ReaxFF Molecular Dynamics Simulations

“…Biomass pyrolytic kinetics is routinely considered to be based on a single reaction. , Here, the time-dependent number of the C–C bonds is used to represent the degree of thermal decomposition due to its importance in organic matters . Biomass decomposition is assumed to follow a first-order reaction which has been widely applied in previous works. ,,− The rate constant can be described for each temperature by the following equation where k is the rate constant.…”

“… 4 − 6 Among these processes, pyrolysis is a promising method, during which biomass can be converted into biochar, bio-oil, biogas, or other high-quality products. 7 …”

“…4−6 Among these processes, pyrolysis is a promising method, during which biomass can be converted into biochar, bio-oil, biogas, or other high-quality products. 7 To comprehend the pyrolytic behavior of biomass, numerous experimental measurements have been carried out under different conditions. Greenhalf et al 8 and Zuo et al 9 investigated the impact of biomass type on pyrolysis behavior.…”

“…Among different biomass types, lignocellulosic biomass is one of the most abundant resources, and its components include cellulose, hemicellulose, lignin, and a small amount of extractives . The main thermochemical transformation processes of biomass are pyrolysis, gasification, combustion, and liquefaction. − Among these processes, pyrolysis is a promising method, during which biomass can be converted into biochar, bio-oil, biogas, or other high-quality products …”

Effect of Potassium Salts on Biochar Pyrolysis

“…In the last stage (0.8 < α < 0.95), the values of activation energy showed a significant increase at elevated temperatures. According to the previous phenomena, this is resulted from the chemical alteration of biomass to form different derivatives [34].…”