Efficient integrated production of bioethanol and lignin from oil palm empty fruit bunch biomass using chemical steam explosion method

Abstract

Indonesia as the world’s largest palm oil producer produces large amounts of waste during palm oil processing, one of which is oil palm empty fruit bunches (OPEFB). OPEFB can be converted into biochemicals, bioethanol, and lignin. This study aims to produce bioethanol from OPEFB using response surface method (RSM) analysis with the addition of the bleaching process and Cellic® Ctec2 and Cellic® Ctec3 enzymes used in the saccharification process. In addition, lignin was isolated from black liquor in the pretreatment process with the CO₂ bubbling method. Bioethanol production begins with pulp production by the alkaline (NaOH) steam explosion of OPEFB followed by bleaching. Subsequently, enzymatic saccharification with three parameters: enzyme concentration, solid loading, and temperature, was carried out. Saccharomyces cerevisiae was used in the fermentation to produce ethanol. Meanwhile, the lignin isolation was carried out by injecting CO₂ gas 2 L/min into the black liquor solution with variations in time. The results showed that the bleaching processes significantly increased cellulose content and reduced lignin content in OPEFB, with pulp yields reaching 91% and 89% for the first and second stages of bleaching, respectively, demonstrating high efficiency in preparing materials for sugar recovery. Optimal conditions were achieved using RSM analysis at an enzyme concentration of 30 FPU, solid loading of 20% (w/v), and temperature of 50 °C with a sugar content of 12.63% and ethanol of 2.14%. The implication of the bleaching process showed a lower concentration of 1.2% ethanol when compared to only unbleached pulp which produced 2.42% ethanol. In addition, the use of Cellic® Ctec3 enzyme produced higher sugar and ethanol content with 14.04% sugar and 4.42% ethanol compared to Cellic® Ctec2. On the other hand, the largest lignin isolation result was obtained at a processing time of 2 h with a yield of 1.16% and purity of 96.94%.

Graphical Abstract