Maximizing Anhydrosugar Production from Fast Pyrolysis of Eucalyptus Using Sulfuric Acid as an Ash Catalyst Inhibitor

• Main Authors: Dongyan Zhang, Yuyang Fan, Anqing Zheng, Zengli Zhao, Fengyun Wang, Haibin Li
• Format: Article
• Language: English
• Published: MDPI AG 2018-12-01
• Series: Catalysts
• Subjects: eucalyptus; fast pyrolysis; acid impregnation; H₂SO₄; inhibitor; anhydrosugar
• Online Access: https://www.mdpi.com/2073-4344/8/12/609

Anhydrosugars, such as levoglucosan (LG), are high value-added chemicals which are mainly derived from fast pyrolysis of pure cellulose. However, fast pyrolysis of raw lignocellulosic biomass usually produces a very low amount of levoglucosan, since alkali and alkaline earth metals (AAEM) present in the ash can serve as the catalysts to inhibit the formation of levoglucosan through accelerating the pyranose ring-opening reactions. In this study, eucalyptus was impregnated with H₂SO₄ solutions with varying concentrations (0.25⁻1.25%). The characteristics of ash derived from raw and H₂SO₄-impregnated eucalyptus were characterized by X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). The pyrolysis behaviors of raw and H₂SO₄-impregnated eucalyptus were performed on the thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TG analysis demonstrated that the H₂SO₄-impregnated eucalyptus produced less char than raw eucalyptus. Py-GC/MS analysis showed that even small amounts of H₂SO₄ can obviously improve the production of anhydrosugars and phenols and suppressed the formation of carboxylic acids, aldehydes, and ketones from fast pyrolysis of eucalyptus. The rank order of levoglucosan yield from raw and impregnated eucalyptus was raw < 1.25% H₂SO₄ < 1% H₂SO₄ < 0.75% H₂SO₄ < 0.25% H₂SO₄ < 0.5% H₂SO₄. The maximum yield of levoglucosan (21.3%) was obtained by fast pyrolysis of eucalyptus impregnated with 0.5% H₂SO₄, which was close to its theoretical yield based on the cellulose content. The results could be ascribed to that H₂SO₄ can react with AAEM (e.g., Na, K, Ca, and Mg) and lignin to form lignosulfonate, thus acting as an inhibitor to suppress the catalytic effects of AAEM during fast pyrolysis of eucalyptus.