Abstract
BackgroundDue to the unsustainable consumption of fossil resources, great efforts have been made to convert lignocellulose into bioethanol and commodity organic compounds through biological methods. The conversion of cellulose is impeded by the compactness of plant cell wall matrix and crystalline structure of the native cellulose. Therefore, appropriate pretreatment and even post-treatment are indispensable to overcome this problem. Additionally, an adequate utilization of coproduct lignin will be important for improving the economic viability of modern biorefinery industries.ResultsThe effectiveness of moderate alkaline ethanol post-treatment on the bioconversion efficiency of cellulose in the acid-steam-exploded corn stover was investigated in this study. Results showed that an increase of the alcoholic sodium hydroxide (NaOH) concentration from 0.05 to 4% led to a decrease in the lignin content in the post-treated samples from 32.8 to 10.7%, while the cellulose digestibility consequently increased. The cellulose conversion of the 4% alcoholic NaOH integrally treated corn stover reached up to 99.3% after 72 h, which was significantly higher than that of the acid steam exploded corn stover without post-treatment (57.3%). In addition to the decrease in lignin content, an expansion of cellulose I lattice induced by the 4% alcoholic NaOH post-treatment played a significant role in promoting the enzymatic hydrolysis of corn stover. More importantly, the lignin fraction (AL) released during the 4% alcoholic NaOH post-treatment and the lignin-rich residue (EHR) remained after the enzymatic hydrolysis of the 4% alcoholic NaOH post-treated acid-steam-exploded corn stover were employed to synthesize lignin-phenol-formaldehyde (LPF) resins. The plywoods prepared with the resins exhibit satisfactory performances.ConclusionsAn alkaline ethanol system with an appropriate NaOH concentration could improve the removal of lignin and modification of the crystalline structure of cellulose in acid-steam-exploded corn stover, and consequently significantly improve the conversion of cellulose through enzymatic hydrolysis for biofuel production. The lignin fractions obtained as byproducts could be applied in high performance LPF resin preparation. The proposed model for the integral valorization of corn stover in this study is worth of popularization.
Highlights
Due to the unsustainable consumption of fossil resources, great efforts have been made to convert lignocellulose into bioethanol and commodity organic compounds through biological methods
Compositional analysis The acid-steam-exploded corn stover was post-treated with alkaline ethanol with different sodium hydroxide (NaOH) concentrations, and an acid sodium chlorite post-treated acid-steamexploded corn stover was obtained as a comparison
The corresponding lignin contents of Samples 1–3 and 5 were 32.8, 19.1, 15.9, and 3.0%, respectively. These results indicated that the efficiency of enzymatic hydrolysis was significantly affected by the remaining lignin content, and it increased as the lignin content decreased
Summary
Due to the unsustainable consumption of fossil resources, great efforts have been made to convert lignocellulose into bioethanol and commodity organic compounds through biological methods. Due to compactness of lignocellulose matrix and the crystalline structure of the native cellulose [5, 6], pretreatment is necessary to disrupt the recalcitrant matrix to make the cellulose more accessible to the enzymes, which convert carbohydrate polymers into fermentable sugars [7]. These pretreatment technologies can be classified into biological, physical, chemical, and physicochemical methods, including dilute acid, steam explosion, hot-compressed water, organosolv, ammonia fiber explosion, and aqueous lime or alkali pretreatments [8,9,10,11,12,13]. All of the pretreatment methods have limitations; the synergistic benefits of combined methods should be considered [14]
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