Hydrothermal pretreatment with sulfonated bentonite catalyst enhances potassium removal and bioconversion of oil palm empty fruit bunch to sugar and biohydrogen

Oil palm empty fruit bunch (EFB), a rich of polysaccharide and element as potassium, is being recognized as one of the most potential kinds of lignocellulosic biomass for bioenergy and biochemical production. In this study, EFB was subjected to hydrothermal pretreatment in the absence (HT) and presence of a sulfonated bentonite catalyst (HT_cat). The effect of pretreatment on enzymatic hydrolysis and anaerobic digestion was investigated. The hydrothermal pretreatments were conducted at 160–200 °C for 5–25 min, while the effect of catalytic HT_cat pretreatment of EFB was studied at 180–200 °C for 25 min. The results showed that temperature and catalyst in HT_cat pretreatment were the main factors that could enhance both production of glucose and biohydrogen up to 1.04–1.14- and 3.32–4.36-fold, respectively, compared with those pretreated by HT at 180–200 °C for 25 min without catalyst. The catalyst specifically enhanced hemicellulose and lignin removal from EFB. During HT pretreatment, disruption of EFB cell wall also facilitated over 70% potassium dissolution from EFB to the liquid residue at 160–190 °C for 25 min, while poorer dissolution of potassium was found at 200 °C without or with catalyst addition. The HT pretreatment successfully improved the removal of potassium from EFB and its bioconversion yield. However, the potassium forms a sticky compound with other elements and soluble organic compound, and further study is required for the valorization of the potassium and liquid residue.