Impact of surfactant-aided subcritical water pretreatment process conditions on the reducing sugar production from oil palm empty fruit bunch

Oil palm empty fruit bunch (OPEFB), waste produced from the palm oil mills, has not been intensely utilized while its abundant availability in tropical countries such as Indonesia. It is one of the potential lignocellulosic material sources which can be utilized to produce sugar. The subcritical water process has been known as a promising lignocellulose-to-sugar conversion process. This study examined the effects of temperature, surfactant types, and concentrations on the sugar yield from OPEFB through the subcritical water process. In this research, the subcritical water process was conducted at a varied temperature of 140-180 °C, constant pressure and time of 60 bar, and 60 minutes, respectively. The types of surfactants studied were non-ionic, anionic, and cationic (Tween 80, SDS, and CTAB). Reducing sugar concentration analyses and solid characterizations using SEM, XRD, FTIR, and TGA were carried out in this research to evaluate the impact of the subcritical water process variables. The experiments showed that Tween 80 addition to the subcritical water process produced significant sugar yields at temperature 140 °C. The addition of CTAB to the subcritical water process shows adverse effects, while that of SDS showed support in the sugar production yields. This may be caused by hydrophobic and hydrophilic interactions between functional groups of the lignin unit and the hydrophobic and ionic groups of the surfactants. The subcritical water process run at a temperature of 180 °C assisted by SDS is the best scenario to produce the highest reducing sugar yield of 4.034%.