Influence of Pyrolysis Temperature on Characteristics and Aromatics Adsorption Capability of Magnetic Biochars Derived from Rice Straw Pyrolysis Oil Distillation Residue

Influence of pyrolysis temperature on characteristics and aromatics adsorption capability of magnetic biochars derived from rice straw pyrolysis oil distillation residue

Hao Li, Shuqian Xia*, Peisheng Ma

Key Laboratory for Green Chemical Technology of State Education Ministry, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin, PR China

The bio-oil, derived from rice straw fast pyrolysis, deservedly offers an opportunity as alternatives to replace fossil fuels due to its renewable characteristics. Unfortunately, pyrolysis oil is an unstable product and the physical and chemical properties are changing during storage, which limit its application. Distillation as an effective method for upgrading biomass fast pyrolysis oil has been gained great attention. Although the high-value chemicals or high-quality fuel were obtained from the pyrolysis oil distillation, the distillate yield did not reach 100% and a fraction of solid residue was formed after pyrolysis oil distillation. In this work, the magnetic biochars were synthesized by pyrolyzing the ditillation residue derived from rice straw pyrolysis oil at different temperature of 400, 600 and 800 ºC. The effects of pyrolysis temperature on the physicochemical and morphological properties of magnetic biochars were investigated. The experimental results of TGA, FTIR, SEM and XRD indicated that the increase in pyrolysis temperature led to the formation of magnetic biochar with a stable aromatic carbon structure. When the pyrolysis temperature was increased up to 600 ºC, the surface area and pore volume of magnetic biochar were enhanced, while a further increase in the pyrolysis temperature lowered the value of surface area and pore volume due to pores widening or blocked pores in the magnetic biochar during pyrolysis. Experimental studies related to the adsorption behaviors of the different magnetic biochars toward various aromatic contaminants (i.e., anisole, phenol and guaiacol), key affecting factors and the underlying mechanisms proposed to explain the adsorption behaviors, have been investigated. The Freundlich adsorption model could describe successfully the adsorption performance and the used magnetic biochars could be easily separated from the aqueous solutions by an outer magnet. An analysis of adsorption mechanisms suggests that the specific surface area and pore volume were the dominant mechanism for adsorption of anisole and phenol on the magnetic biochars while the adsorption of guaiacol on the magnetic biochars were controlled by the ¦Ð-¦Ð electron donor¨Cacceptor (EDA) interaction. Furthermore, compared with phenol and guaiacol, the higher adsorption capacity of anisole can be attributed to the high hydrophobicity (or low polarity) of magnetic biochars.