Fermentation and pyrolysis of Finger millet straw: Significance of hydrolysate composition for ethanol production and characterization of bio-oil

Abstract

This study investigates the biorefinery approach to utilize Finger millet straw (FMS) for bioethanol, bio-oil and char production through fermentation and pyrolysis for the first time. The FMS was pretreated with sulphuric acid along with autoclaving and then detoxified. The detoxified hydrolysate (DH) was fermented in the absence and presence of additional supplements except xylose using Pichia stipitis NCIM-3497 at 30 °C, pH 5.0 and 150 rpm for 96 h. The presence of additional supplements in DH enhanced the ethanol production by 35% as compared the only DH. The pyrolysis of pretreated solid residue resulted in 42% (w/w) bio-oil and 27.2% (w/w) char. The pH of bio-oil was 3.5 with a density of 1.1 g/mL. The bio-oil contained 50% (v/v) aromatics, 13.7% (v/v) heterocyclics and 12% (v/v) non–aromatic compounds. The upgradation of obtained bio-oil is required to refine the valuable compounds such as furfural, 1-(2-hydroxy-5-methylphenyl)-ethanone and 4-allyl syringol.