Fractionating pretreatment of sugarcane bagasse by aqueous formic acid with direct recycle of spent liquor to increase cellulose digestibility–the Formiline process

A lignocellulose pretreatment process was developed with formic acid delignification (FAD) followed by alkaline deformylation (AD), which was termed as Formiline process. In FAD, more than 80% of lignin and hemicellulose were removed, but cellulose formylation also happened. Formic acid concentration (FAC) was the most important factor affecting delignification and cellulose formylation. Increasing FAC could enhance degree of delignification but also increased cellulose formylation. The presence of formyl group could inhibit the enzymatic hydrolysis of cellulose; however, removing formyl group with a small loading of alkali well recovered cellulose digestibility. The spent liquor could be directly recycled for delignification thus significantly decreasing energy consumption in solvent recovery. The Formiline-pretreated substrates showed an excellent enzymatic digestibility and could be very well converted to ethanol by simultaneous saccharafication and fermentation (SSF). The final ethanol concentrations were 55.4 and 80.1 g/L respectively at initial solid consistencies of 15% and 20%.