Pyrolysis of Maize Stalk on the Characterization of Chars Formed under Different Devolatilization Conditions

Abstract

In this context, the work dealt with the characterization of chars obtained by the pyrolysis of maize stalk and the effects of pyrolysis temperature and heating rate on the char properties. The pyrolysis was performed at atmospheric pressure and temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rate (HHR) conditions. The chars were characterized by ultimate analysis, X-ray diffraction (XRD), helium density measurement, N2 isothermal adsorption/desorption method, and Fourier transform infrared spectroscopy (FTIR). The results indicated that the char characteristics markedly depended upon pyrolysis conditions, particularly temperature. The char yield decreased from 22 to 16.3% with increasing temperature from 600 to 900 °C. The decrease in H/C was more than twice that in O/C. As the temperature increased, maize stalk chars had a slightly less amorphous structure and less aliphatic side chains and became more aromatic and ordered. At a HHR, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum development of micro- and mesopores appeared at 900 °C. The surface area of char reached a maximum of 81.6 m2/g at 900 °C and decreased slightly at higher temperatures. Over 900 °C, structural ordering, pore widening, and/or the coalescence of neighboring pores led to the decrease in the surface area values, resulting in thermal deactivation of the chars. The influence of the heating rate on the surface area was not significant. FTIR analysis showed that the hydroxyl, aliphatic C−H, and carbonyl and olefinic C═C groups were lost at high temperatures. The loss of ether groups led to a more ordered carbon structure.