Dual Role of Gluconic Acid in the Cascading Saccharification of Hemicellulose and Cellulose from Various Lignocellulosic Stuff

Gluconic acid (GA) was used for lignocellulose pretreatment as a systematic self-providing and recyclable acid-catalyst. GA presented good dual roles to degrade and selectively separate hemicellulose and lignin during the solo GA pretreatment and the hydrogen peroxide-assisted GA pretreatment. The continuous removal of hemicellulose and lignin by two-step GA-based pretreatments achieved an effective and cascading saccharification of hemicellulose and cellulose by acidic and enzymatic hydrolysis in three main sorts of lignocellulosic biomasses such as poplar sawdust, Chinese fir, and rice straw. By the comparison of varied procedure integrations with GA-based pretreatments, a two-pot and two-step process (TPTS) was developed for the coproduction of xylo-oligosaccharides, xylose, and glucose with the highest sugar yields, in which 8.1, 1.8, and 9.4 g of xylo-oligosaccharides as well as 38.9, 37.7, and 34.5 g of glucose were obtained, respectively, from 100 g of poplar sawdust, Chinese fir, and rice straw. This pretreatment method provided a novel green and economical approach to achieve nearly complete enzymatic saccharification of cellulose from both herbaceous and woody biomass.