Enzymatic hydrolysates of corn stover pretreated by a N-methylpyrrolidone–ionic liquid solution for microbial lipid production

In this study, we reported a novel N-methylpyrrolidone (NMP)–1-ethyl-3-methyl imidazolium acetate (EmimAc) mixed solvent (XILs = 0.2, mole fraction of ionic liquids (ILs) in the mixed solution) that can dissolve up to 10 wt% corn stover at 140 °C in 60 min. Physiochemical analysis showed major differences in terms of cellulose crystallinity, compositional distribution and surface morphology between raw corn stover samples and the regenerated materials, indicating that dissolution in the NMP–EmimAc system followed by regeneration with anti-solvents could be used as an effective pretreatment technology. Enzymatic saccharification of the regenerated corn stover afforded an 82.9% total reducing sugars yield and a 60.8% glucose yield within 24 h. The hydrolysates were used, without detoxification, as the carbon sources for the cultivation of Rhodosporidium Toruloides Y4 for lipid production. Glucose and xylose in the hydrolysates were both consumed in our process. In a word, our study reported a novel dissolution pretreatment technology for biomass utilization with outstanding advantages compared with traditional pure ionic liquid processes, such as (I) minimal use of expensive ILs in NMP, and commercially available EmimAc and NMP can be used directly without any further dry purification; (II) high cellulose and hemicellulose regeneration; (III) high enzymatic hydrolysis efficiency of the pretreated sample with full conversion of carbohydrates in less than 24 h; (IV) air-dried corn stover can be used directly (water content = ∼5%); (V) the hydrolysates can be used for further bioconversion and on inhibitory effect was observed. We believe that all of these advantages determine its potential for practical applications.