Hydrothermal depolymerization of spent biomass for production of lactic acid and small aromatics

Abstract

Lactic acid synthesis from lignocelluloses can respond to the environmental concerns associated with producing this important commodity chemical for various applications, e.g., food, cosmetics, pharmaceuticals, etc. Pretreatment of palmarosa (Cymbopogon martinii) biomass with 1.0 % HNO₃ solution at 121 °C temperature and 1.03 bar pressure for 60 min under an autoclave conditions demonstrated a highly selective conversion of biomass contained hemicellulose to xylose in ∼17 wt % yield. A further hydrolytic depolymerization of pretreated biomass to liquid products was carried out via processing in the presence of anthraquinone (5 wt % loading) as a catalyst under temperature (250 °C) and pressure (15–16 bar, where, 1 bar = 10⁵ Pa) in dilute NaOH (1.5 M) solution for 60 min to afford a hydrolysate rich in carboxylic acids and small aromatics. Solvent extraction method was applied successfully to separate the aromatic compounds from the aqueous phase. The carboxylic acids were formed as the product of cellulose oxidation with good selectivity (>45 %) towards the DL-lactic acid (∼14 wt % yield with respect to substrate biomass). Small aromatics, predominantly phenol was identified as the product of depolymerized lignin.