Evaluation Solvent Level Effect on Sugar Yield during Microwave-Assisted Pretreatment

An efficient pretreatment step is essential to ensure maximum and economical recovery of the fermentable sugar from enzymatic hydrolysis of lignocellulosic biomass. Microwave-assisted pretreatment was found to be a good alternative of conventional heating pretreatment of acid or alkali due to its direct heating of sample which reduce the energy consumption. The present study aims to evaluate the effect of using very diluted solvent (acid and alkali) on monomeric sugar yield during microwave-assisted pretreatment of lignocellulosic biomass (sago palm bark wastes). The changes of the surface structure of untreated and pretreated lignocellulosic biomass were detected using SEM analysis. Three solvents were employed at three concentrations (0.01, 0.05 and 0.1 N). The solvents that utilized in the microwave-assisted pretreatment were sulphuric acid (MA), sodium hydroxide (MH) and sodium bicarbonate (MB) and compared with distilled water (MW). Sago palm bark (SPB) was soaked in these solvents as a substrate at 5% w/v and subjected to microwave power at 800 W in a modified household microwave oven for 5 minutes. Immersing feedstock in distilled water and heating using microwave heating released 5.32 mg/g of monomeric sugar. Highest yield of monomeric sugar was found using 0.1N H₂SO₄ which yielded 10.28 mg/g during. Applying the pretreatment using the similar concentrations of NaOH and NaHCO₃ released 9.35 and 4.31 mg/g of monomeric sugar, respectively. Decreasing chemical solvent level from 0.1 to 0.05 and 0.01 N shows a negative influence on sugar yield for MA and MH pretreatment while MB pretreatment displays a positive effect by extracting some useful components such as xylose.