Optimization of diluted acid and lime pretreatments in bioethanol production from switchgrass (Panicum virgatum L.) and determination of ethanol yields of some genotypes

In this study, optimization of bioethanol production was performed by diluted acid and lime pretreatments from switchgrass (Panicum virgatum L.) which is known as an energy crop type. Firstly, biomass was hydrolyzed with 3 different enzyme (Novozymes Cellic CTec2) dosages for 7 days so that optimum dosage and time was determined. According to results, optimum enzyme dosage was 0.06 mL/g biomass and hydrolysis time was 3 days. For pyrolysis optimisation, switchgrass was pyrolyzed with two different chemicals (sulphuric acid and lime) in two different concentrations (0.5% and 1.0% (w/w) sulphuric acid or 0.05 and 0.10 g lime/biomass) at various temperatures (120,140 and 180 °C) for three different process time (10, 60, 90 min). According to the obtained results, the maximum total fermentable sugar was found to be 50.58 g/100 g biomass, optimum pyrolysis condition was 120 °C, 0.5% of sulphuric acid treatment for 90 minutes. Additionally, the maximum total fermentable sugar was found to be 44.76 g/100 g biomass at 120 °C, 0.1 g lime/biomass for 60 minutes. In order to determinate optimum fermentation conditions, fermentation was carried out by Saccharomyces cerevisiae at two temperatures (25 and 30 °C) and two mediums (control and 4 gL-1 YE additions). The maximum ethanol yield was obtained at 25 °C and 4 gL-1 YE added medium and the yield was found to be 0.0966 g ethanol/100 g biomass. The results showed that the bioethanol yields from 10 genotypes ranged between 0.0842 and 0.1220 g/100 g biomass.