Valorization of lignocellulosic platform products based on biorefinery schemes through sequential pretreatments

Abstract

Pretreatments have been identified as the core of lignocellulosic biorefinery design due to biomass fractionation and the influence on subsequent reaction and downstream processes. However, most pretreatments are described as single-step, maximizing the valorization of a side stream. Therefore, sequential pretreatments could better describe the integral valorization of lignocellulosic biomass to obtain platform products that can be further used for value-added products. This work experimentally analyzed the sequential pretreatments for the fractionation of rice husks to obtain individual lignocellulosic fractions. It was demonstrated that the dilute acid-wet air oxidation (DA-WAO) sequence is suitable for biorefinery designs since it is possible to solubilize up to 80% of hemicellulose during the first stage and subsequently fractionate almost 90% of lignin after the second stage, obtaining a pretreated solid with high cellulose content. The isolated lignocellulosic fractions were used as platform products to obtain furfural, levulinic acid, and phenolic compounds. As a main result, yields and conversions were improved when valorizing the cellulose platform based on sequential pretreatment. In contrast, valorizing the black liquor after a combination scheme decreased aldehyde yields such as vanillin and syringaldehyde by 4.8–11.9%. The findings indicate that from the biorefinery approach, sequential pretreatments improve the yield of platform products. Despite the decrease of phenolic compounds, levulinic acid and furfural production is significantly enhanced.