Effect of alkaline pretreatment on chemical composition of lignocellulosic biomass using radio frequency heating

• Alkaline pretreatment of barley straw grind using radio frequency technique.
• The effect of the pretreatment was evaluated through chemical composition analysis.
• Ratio of biomass:NaOH solution played a vital role in the breakdown of the matrix.
• This resulted in lower acid insoluble and higher total acid soluble lignin moieties.
• Trade off exists between matrix breakdown and degradation of energy potentials.

The very nature of lignocellulosic biomass presents resistance and recalcitrance to biological and chemical degradation during enzymatic hydrolysis and the subsequent fermentation process. This leads to a very low conversion rate, which makes the process economically unfeasible. In this study, alkaline (NaOH) pretreatment was applied on barley straw, using radio-frequency-based dielectric heating to enhance accessibility and digestibility during the subsequent stage of enzymatic hydrolysis. Three levels of temperature (70, 80, and 90 °C), five levels of biomass:NaOH solution ratio (1:4, 1:5, 1:6, 1:7, and 1:8), 1 h equilibration time, screen size of 1.6 mm, 1% w/v NaOH concentration, and 20 min residence time were used for the pretreatment. The effect of the alkaline pretreatment was evaluated through chemical composition analysis of the pretreated and non-treated biomass samples. The use of NaOH solution and the biomass:NaOH solution ratio played a vital role in the breakdown of the lignified matrix. The ratio 1:6 at the four temperatures studied was determined to be the optimal treatment conditions. Radio frequency-assisted alkaline pretreatment resulted in lower acid insoluble lignin and higher total acid soluble lignin moieties. Based on the obtained data, we predict that this pretreatment will decrease the required amount and cost of enzymes by up to 64% compared to using non-treated biomass.