Pearl millet (Pennisetum glaucum) as a sustainable feedstock for bioethanol production by catalytic downflow liquid contact reactor

Abstract

Future transportation liquid fuels are mainly focused on biological sources due to the scope of carbon-neutral nature. The Government has mandated the blending of 10% ethanol in fuel but right now only around 6% ethanol is being added to the fuel, the IOC source said. This was mainly due to low ethanol production in the country. Nearly 4bn litres of ethanol will be required to achieve the 10% ethanol blending ratio. Among the biological sources, lignocellulosic feedstocks are a good candidate for bioethanol production if adequately pre-treated for lignin removal. The main aim of this study to assess the effectiveness of the combined process (oxidative lime pre-treatment) used in a catalytic reactor to pre-treat the pearl millet straw. To optimize the combined pretreatment process parameters, three levels of three independent parameters viz., lime loading (8, 10 and 12%), reaction time (5, 20 and 60 min.) and reactor column height (0.6, 0.9 and 1.2 m) were selected and analysed via central composite design of experiments with response surface methodology approach. Results of the output responses like percentage reduction in lignin, hemicellulose, cellulose increase and total reducing sugars were discussed. X-Ray diffraction (XRD) analysis supports and confirms these results. The highest lignin reduction and total reducing sugars were achieved as 69% and 155 mg/g, respectively via optimal conditions (lime: 12%, reactor column height: 1.2 m and reaction period: 60 min.). Enzymatic saccharification studies show the highest reducing sugar yield was 40.6±0.6 mg/g in 96 h at 40 FPU/g. Determination of specific reducing sugars: arabinose, xylose, fructose, mannose, galactose and glucose were performed by HPLC RI using COL-AMINO 150×4.6mm column. This innovative pre-treatment reactor was more effective for lignin removal.