Factors Affecting Delignification of Oil Palm Empty Fruit Bunch by Microwave-assisted Dilute Acid/Alkali Pretreatment

Abstract

Microwave-assisted dilute acid/alkali pretreatment is an efficient and rapid method of removing lignin and hemicellulose, however, the optimized parameters for the maximum efficiency have to date not been presented in the literature. The purpose of this study was to determine those conditions by examining the effects of three factors: microwave power, temperature, and time on delignification in microwave-assisted dilute acid/alkali pretreatment. For the control condition of conventional pretreatment (CP), empty fruit bunches (EFBs) were soaked in 2.5 M NaOH for two hours in the autoclave. In the experimental condition, EFB were first soaked in dilute sulfuric acid with conventional autoclave heating, which removed 90% of their hemicellulose. The acid-treated EFBs were then soaked in 2.5 M NaOH solution and microwaved at different conditions: microwave power (700 - 100 watts), time (60 - 90 min), and temperature (80 -110 °C). The amount of acid-insoluble lignin was determined by Klason method. Microwave-Alkali (Mw-A) pretreatment was modeled until it attained maximum delignification. More than twice the rate of delignification that is, 71.9% was attained with microwave-assisted alkali/acid pretreatment of 900 W microwave power at 110 °C for 80 min compared to 34.6% with conventional pretreatment.

Keywords

• Microwave-alkali (Mw-A)
• Microwave-assisted dilute acid/alkali pretreatment
• Oil palm biomass
• Empty fruit bunches (EFB)
• Cellulose
• Hemicellulose
• Lignin