Alkaline Pretreatment Severity Leads to Different Lignin Applications in Sugar Cane Biorefineries

Lignin, a multifunctional major biomass component, has a prominent potential as feedstock to be converted into high value-added products. Lignin is available in high amounts as side streams during cellulosic ethanol production, and within the biorefinery context, it is important to assess its structural characteristics in order to explore its potential to replace some petroleum-based reactants. In this study, some important features were evaluated for different lignins such as lignin purity and the amounts of syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units. Four alkaline lignins, generated from a pilot-scale pretreatment of sugar cane bagasse (NaOH 1.5%, 30 min), were evaluated according to the severity of the alkaline pretreatment (130 or 170 °C, with or without the addition of anthraquinone). The different pretreatments produced lignins with different chemical characteristics that can be used for different purposes in sugar cane biorefineries. As the severity of alkaline pretreatment increased, the recovered lignins presented higher amounts of H- and lower amounts of S-lignin units. In particular, the lignin obtained at 170 °C with the addition of anthraquinone presented the highest content of H- and the lowest content of S-lignin units, which would present higher reactivity toward formaldehyde in phenolic resins.