Complex effects of wax on ionic liquid pretreatment of oil palm empty fruit bunch

Wax plays an important role in oil palm as a protective barrier, but it reduces the efficiency of the pretreatments required when this biomass is used as a feedstock for bioethanol production. In this study, ionic liquid (IL) pretreatment and dewaxing were adopted to increase the enzymatic saccharification of the oil palm empty fruit bunch (OPEFB). The wax showed the complicated effects on IL pretreatment, because glucose yield was significantly improved when OPEFB was pretreated with the acetate-ILs after dewaxing. In contrast to that pretreatment of chloride-ILs did not improve the glucose yield. To elucidate this phenomenon, multiple dimension analyses including composition, cellulose crystallinity, morphology, cellulase accessibility were performed. It was found that the solubility of OPEFB in ILs was the main reason of complex effects of wax on glucose yield. Because, using 1-butyl-3-methylimidazolium acetate ([BMIM]Ac) which has higher potential solubilization property, removal of wax facilitated the significant rearrangement of internal structure and transformation of crystal cellulose to an amorphous one, resulting in better enzymatic hydrolysis. Whereas, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) with weak dissolution capacity only conferred a negligible structural change of OPEFB with or without the presence of wax. This study exhibits that dewaxing is necessary for wax-rich feedstocks to reach high glucose yield, especially when using ILs with strong solubilization.