Evaluation of lignocellulose degradation and ethanol production via dilute acid and alkali pretreatment of hybrid Pennisetum

Abstract

Chemically pretreating lignocellulose has been widely used in the production of clean energy. An energy grass called hybrid Pennisetum was pretreated with different H2SO4 and NaOH concentrations to analyse the effects of an acid and alkali pretreatment on the degradation of hybrid Pennisetum lignocellulose. The chemical composition, hydrolyzed sugar yield, and microstructure were determined. The results showed that a NaOH pretreatment retained more cellulose and removed more lignins, while a H2SO4 pretreatment significantly inhibited the removal of lignins and increased hemicellulose degradation. X-ray diffraction analysis indicated that increasing the concentration of NaOH or H2SO4 could intensify the cellulose polymerization; this effect was stronger with NaOH compared to H2SO4. Scanning electron microscopy images showed that the cellulose bundles pretreated with H2SO4 were arranged tightly, while the cellulose bundles pretreated with NaOH were loose. Fourier transform infrared spectroscopy exhibited that the ether/ester bond between lignins and carbohydrates was broken by the H2SO4 pretreatment. The NaOH pretreatment increased the number of carbonyl and hydroxyl groups, resulting in more hydrophilic lignins, enabling greater facile degradation. Although the two methods are different in terms of destroying the structure of lignocellulose, the NaOH pretreatment can retain more cellulose, which is beneficial to subsequent ethanol production.