Choline chloride-based deep eutectic solvent for corn straw pretreatment: enhancing biohydrogen production and elucidating underlying mechanisms

Hydrogen is a clean energy source with a high calorific value. Using crop straw, an agricultural by-product, for biological hydrogen production is a very promising way to convert biomass energy. This study investigated how deep eutectic solvent (DES) pretreatment altered the physical and chemical structures of corn straw and optimized key process parameters. In the DES system, choline chloride and p-toluenesulfonic acid act as hydrogen bond acceptors and donors, respectively. The performance is best at a mass-to-volume ratio of 0.06 g: 1 mL. After pretreatment, the hydrogen production reached 106.97 mL H₂/g TS, a 469.29% increase over the untreated sample. 70.98% of the lignin was effectively removed, while 86.63% of the cellulose was retained. In addition, 61.73% of the hydrogen bonds between cellulose and hemicellulose, along with 39.70% of the hydrogen bonds between cellulose and lignin, were disrupted. These chemical components and the structural changes of lignocellulose are regarded as the main factors for the increase in hydrogen production of corn straw. It is worth noting that DES maintained a stable catalytic efficiency in the fifth regeneration cycle, indicating its potential for sustainable application in biological hydrogen production.