Investigation on the pretreatment process and mechanism of deep eutectic solvent synthesized from choline hydroxide and 1,3-propanediol: aiming to enhance the hydrogen production efficiency from corn straw

Pretreatment, as an upstream technology in biomass-based hydrogen production, determines the downstream process's production efficiency. To solve the problem of a high cellulose loss rate under acidic pretreatment conditions, an alkaline deep eutectic solvent (DES) with choline hydroxide solution ([Ch][OH]) and 1,3-propanediol solution (PDO) was synthesized and used for corn straw-derived hydrogen generation. The optimal pretreatment parameters were as follows: a mass-to-volume ratio of corn straw to DES of 1:47.1 (g:mL), a reaction temperature of 108.8 °C, and a reaction duration of 75.5 min. Within the corn straw lignocellulosic substrate, a portion of the β–O–4 bonds in lignin, some of the ester bonds in lignin-carbohydrate complexes, 45.13% of the hydrogen bonds connecting cellulose and lignin, and 26.31% hydrogen bonds connecting cellulose and hemicellulose were disrupted. Consequently, 78.52% of the lignin and 72.92% of the hemicellulose were eliminated. These structural alterations substantially enhanced the saccharification rate and hydrogen production yield of corn straw by 335.16% and 498.2%, respectively. The DES pretreatment method and the DES recycling strategy put forward in this study hold substantial positive implications for facilitating the application and promotion of DES in the fields of biological hydrogen production and biomass pretreatment.