High concentration bioethanol production from corn stalk via enhanced pretreatment with ionic liquids.

• The [BHEM]mesy- glycol system had high pretreatment efficiency with 93% lignin removal rate. • The pretreated corn stalk was easy to enzymolysis with 91% cellulose and lower crystallinity. • The viscosity of enzymolysis materials was the key factors limiting the efficiency of enzymolysis by rheometer. • By feed-batch method, the glucose concentration reached 250 g/L with the yield of 100 %. The ethanol concentration is 93 g/L with the yield of 70 %. The transformation of lignocellulose into bioethanol is of great significance for energy security and environmental protection. Traditionally, the concentration of ethanol obtained by fermentation does not exceed 7 % (v/v), resulting in high cost of rectification (about 100 t water are needed to produce 1 t ethanol) and a large amount of wastewater, which is not suitable for industrial production. In this study, producting high concentration bioethanol from ionic liquid pretreated corn stalk integrated by feed-batch method was proposed. The cellulose content and the lignin removal rate of the corn stalk pretreated by [BHEM]mesy-ethylene glycol co-solvent system (rich-cellulose material) were 91 % and 93 %, respectively. The co-solvent system showed stable pretreatment efficiency after amplification of 20 times. Observably, the rich-cellulose material became easier to enzymolysis because the lower crystallinity from XRD, less lignin from CLSM and so on. The optimal enzymolysis conditions were 160 EGU/g cellulose, 50 ℃, pH = 4.8, 96 h, under which the yield of glucose could reach 90 %. The tolerance limit of Saccharomyces cerevisiae to glucose concentration is 0.3 g/L. The viscosity of enzymolysis materials was one of the main factors limiting the efficiency of enzymolysis by rheometer, and the 5 % concentration of materials was the most suitable for enzymolysis. Significantly, by feed-batch method, the glucose concentration reached 250 g/L with the yield of 100 %. The ethanol concentration is 93 g/L with the yield of 73 %. This study provided the possibility for industrialization of bioethanol production. [ABSTRACT FROM AUTHOR]