Utilizing N,N-dimethylbutylammonium hydrogen sulfate for the pretreatment of lignin-rich waste, argan nut shells

Abstract Argan nut shells (ANSs), a lignin-rich residue (40 wt-%) from the argan plant, have seen limited use for energy and material-based applications so far. To explore the potential of this industrial crop waste for prospective applications, fractionation of ANS with the protic ionic liquid (PIL), N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO 4 ]) was performed at different operating conditions for enzymatic saccharification of cellulose. At 140 °C for 5 h, [DMBA][HSO 4 ] extracted 73% of the lignin revealing cellulose-enriched biomass with 75% cellulose content. Recovered cellulose-enriched pulp showed morphological and crystallinity changes consistent with its composition, including the emergence of fibrous structures and an increase in the crystallinity index. Cellulose-enriched pulp was enzymatically converted into reducing sugars, achieving approximately 70% saccharification yield. Characterization of lignin precipitates from the pretreatment slurries using FTIR and TGA confirmed the absence of carbohydrates, indicating high-quality lignin. Additionally, humin formation as evident from the spherical forms observed on the recovered pulp following pretreatment at 160 °C for 5 h highlights the importance of the severity of pretreatment conditions. This study helps to understand the interaction between ANS and a PIL and raises the question of whether the cellulose- and lignin-rich fractions obtained after pretreatment can potentially be utilized; however, further evaluation is required to determine their suitability for energy and material generation.