Characterization of Biomass Chars Formed under Different Devolatilization Conditions: Differences between Rice Husk and Eucalyptus

Abstract

A comparison between the properties of chars produced by pyrolysis of rice husk and eucalyptus at different temperatures and heating rates has been performed. Low heating rate (LHR) devolatilization experiments were conducted in a fixed bed reactor at temperatures ranging from 600 to 900 °C, while a fluidized bed reactor was used for preparing chars at high heating rate (HHR) and temperatures of 800 and 900 °C. The morphological changes in carbonaceous solids produced in the different thermal treatments were observed by scanning electron microscopy (SEM). X-ray diffraction (XRD) and Raman spectra were obtained to evaluate the degree of char structural order. The chars were characterized by their ultimate analysis, oxygen functional group content, and CO 2 adsorption at 0 °C using the Dubinin-Radushkevich method. The results obtained from the different techniques were contrasted to give an overview of the chemical and physical properties of the biomass char samples studied. The influence of the parent material and char properties on char reactivity toward O 2 and NO reduction was further investigated. It was found that, though rice husk chars have a greater reactivity toward oxygen, the NO reduction ability was significantly higher for the eucalyptus chars.

Comparison of high temperature chars of wheat straw and rice husk with respect to chemistry, morphology and reactivity

“…This hypothesis was examined and verified by 29 Si NMR by Freitas et al [9]. Guerrero et al [15] reported no major morphological changes of rice husk under fast heating, and ascribed this observation to a high thermal resistance of rice husk ash, containing mostly silicon compounds. Pottmaier et al [11] concluded that rice husk is less reactive than wheat straw, prepared at temperatures (300e1300 C) under slow and fast heating, and related differences in reactivity to the higher contents of lignin and silicon in the rice husk.…”

The effect of char properties on gasification reactivity

“…Similarly, due to the lower ash content, black wattle biochar showed higher surface area (241 g/m 2 ) than vineyard (92 g/m 2 ) [29]. Guerrero et al also observed that chars from rice husk devolatilization have lower surface areas compared with those from eucalyptus obtained under similar conditions [30]. On the other hand, the demineralization with acid washing slightly affected surface characteristics of chars, leading to less increase.…”

A Comprehensive Review on Biomass Torrefaction

“…In addition to this, the higher heating rate also affects the morphological structure of the solid product. More round pores are formed during the pyrolysis when the temperature increased from 600 °C to 800 °C (Guerrero et al, 2008). This establishes a larger internal cavity and more open structures.…”