Reduction of lignin heterogeneity using aqueous two-phase system: A facile and universal "one-step-three-fractions" approach.

As the most abundant aromatic biopolymer, lignin presents great potential to produce valuable materials and chemicals. However, its large-scale value-added application is still facing many practical challenges and one of them is the unstable properties caused by lignin heterogeneity. Herein, we developed a novel "one-step-three-fractions" fractionation strategy to reduce lignin heterogeneity using aqueous two-phase system (ATPS) composed of (NH 4) 2 SO 4 and ethanol. In contrast to conventional step-wise fractionation processes, the proposed process subdivided heterogeneous lignin into three homogeneous fractions in only one step: the first fraction (F1) dissolved in the ethanol-rich top layer; the second fraction (F2) dissolved in the salt-rich bottom layer and the last fraction (F3) insoluble in both two layers. F2 presented the lowest molecular weight followed by F1 while F3 showed the highest molecular weight. With the increase of molecular weight, the contents of guaiacyl unit and β-O-4 linkage increased while the content of hydrophilic groups (carboxyl and aromatic hydroxyl) decreased significantly. Moreover, the ATPS exhibited satisfactory recyclability and the fractionation approach could be applied to different types/sources of lignin. Consequently, the work indicates that ATPS is a novel and effective way to fractionate lignin and reduce its molecular weight polydispersity and structural heterogeneity in one step. [Display omitted] • Aqueous two-phase system (ATPS) consisting of (NH 4) 2 SO 4 and ethanol was used for lignin fractionation. • Enzymatic hydrolysis lignin was subdivided into three fractions in only one dissolution step. • The three fractions showed reduced heterogeneity in molecular weight and chemical structure. • The universal fractionation approach can be applied to different types/sources of lignin. • The fractionation using regenerated ATPS demonstrated the satisfactory recyclability. [ABSTRACT FROM AUTHOR]