Production of phenols from pyrolysis of sugarcane bagasse lignin: Catalyst screening using thermogravimetric analysis – Thermal desorption – Gas chromatography – Mass spectroscopy

Abstract

The structural nature of lignin renders it suitable as a renewable source of phenolic compounds. The production of phenols from pyrolysis of sugarcane lignins with impregnated catalysts was investigated by screening of twelve catalysts (Al2O3, CaO, Fe2O3, TiO2, ZnO, MgO, CuO, MoO3, NiO, Ni/Al2O3-SiO2, NaOH, and KOH) at 1 wt.% content. Sugarcane bagasse lignins were isolated after soda-pulping (SD), soda-anthraquinone-pulping (SAQ) and steam explosion pre-treatment followed by enzymatic hydrolysis (SEH). Pyrolysis was conducted using a thermogravimetric analyser (TGA), and captured volatiles were quantified by thermal desorption (TD) gas chromatography–mass spectroscopy (GC–MS). The TGA results showed that the degradation profiles and char yields were influenced by the presence of catalysts, through modifications in conversion mechanisms. The highest increases in the total yield of phenols were obtained with KOH for SD lignin (+25.7%), CaO for SAQ lignin (+59.7%), and Fe2O3 for SEH lignin (+43.0%). Due to the enhancement of depolymerisation at low temperature (<350 °C), the yields of syringol, guaiacol, and vinylguaiacol increased by 41%, 32%, and 43% for SD lignin, 121%, 93%, and 84% for SAQ lignin, and 72%, 77%, and 54% for SEH lignin respectively. These significant increases in the yields of phenols using 1 wt.% compared to ≥10 wt.% reported in literatures demonstrated the effectiveness of impregnation method.