Two-stage microwave/chemical pretreatment process of napier grass for monomeric sugar production

Abstract

Disruption of the lignocellulosic structure of biomass by pretreatment plays a key role in producing bioethanol from lignocelluloses. A microwave pretreatment method using different catalysts, H2SO4, H3PO4, NH4OH, and NaOH, was investigated. The pretreatment was performed at (0.5, 1, 2, 3, 4, and 5) % w/v concentrations while temperatures were studied in ranges of 40°C to 160 °C for alkaline pretreatment and 60°C to 160 °C for acid pretreatment. Pretreatment times were also performed at 5 min to 60 min. Three different liquid-to-solid ratios (15:1, 30:1 and 45:1) were also studied in the pretreatment. Napier grass was used as a raw material. Each catalyst provided different optimal conditions to produce amounts of monomeric sugars (30.93, 24.99, 6.19 and 6.15 g/100 g biomass) when treated with H2SO4, H3PO4, NH4OH, and NaOH, respectively. In addition, optimal conditions for two-stage pretreatment provided the high total monomeric sugar yields 40.16 and 45.28 for microwave-assisted NH4OH followed by H2SO4 and microwave-assisted NaOH followed by H2SO4, respectively. The structural change of the pretreated Napier grass was elucidated using Fourier transform infrared spectroscopy.