Innovative combined dry fractionation technologies for rice straw valorization to biofuels
The separation of lignocellulose into its major components (cellulose, hemicelluloses and lignin) is a key step in lignocellulosic biorefineries. Most pretreatments of lignocellulosic biomass into chemicals or biofuels are currently based on expensive chemical and energy consuming processes, which entail significant resource consumption (e.g. water) and generate a number of residual streams. In this work, two innovative dry fractionation technologies (physical fractionation: turbo- and electrostatic separation of lignocellulose particles) have been developed for rice straw “RS” fractionation and bioconversion to sugars and biofuels. Turbo-fractionation technology (TF-T) comprises particle separation according to their size and density, whereas electrostatic fractionation technology (EF-T) is based on the separation of particles according to their surface properties (chemical composition and charges). TF-T and EF-T are suitable for producing lignocellulose fractions displaying very different structures, biochemical compositions and reactive surfaces without extensively damaging the raw fibers as well as minimizing waste generation (E-factor: 0.7–0.75). The produced fractions could be hydrolyzed, being able to produce large quantities of glucose (250–280 g kg−1 RS) after 72 h of hydrolysis and subsequently ethanol (130–150 g kg−1 RS) after fermentation. TF-T and EF-T can therefore improve the economic feasibility by low energy consumption and produce reactive lignocellulose particles with different physicochemical structures in a short time, which can be easily converted to biofuels, minimizing waste (no effluent generation).