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Efficient Biogas and Ethanol Production from Safflower Straw Using Sodium Carbonate Pretreatment

Hashemi, Seyed Sajad, Karimi, Keikhosro, Nosratpour, Mohammad Javad, Sárvári Horváth, Ilona
Energy & Fuels 2016 v.30 no.12 pp. 10592-10601
Carthamus tinctorius, alkali treatment, biogas, biotransformation, cellulose, ethanol, ethanol production, gasoline, glucose, methane, methane production, sodium carbonate, straw
Safflower straw, an agricultural lignocellulosic waste, was used for biogas and bioethanol production. Prior to bioconversion, the straw was pretreated with 0.5 and 1 mol/L sodium carbonate (Na₂CO₃) at 120, 150, and 180 °C for 1–5 h, resulting in a liquid fraction containing hemicellulosic sugars and a solid fraction mainly containing cellulose. Two scenarios were followed: (I) subjecting both solid and liquid fractions to biogas production and (II) subjecting the solid fraction to bioethanol production and the liquid fraction to biogas production. The highest yield of glucose was 91.4%, achieved after pretreatment at 180 °C with 0.5 mol/L Na₂CO₃ for 5 h, as compared to that of 22.1% for the untreated substrate. The ethanol yield of untreated straw was 11.1%, and it was improved to 58.1% after alkali pretreatment at 180 °C with 1 mol/L Na₂CO₃ for 2 h. The highest methane yield obtained was 139.6 N mL/g of volatile solids (VS) after pretreatment at 120 °C with 0.5 mol/L Na₂CO₃ for 1 h, while that from the untreated straw was only 92.1 N mL/g of VS. On the other hand, from the liquid fraction, a maximum of 88.2 N mL/g of VS of methane was produced after pretreatment with 0.5 mol/L Na₂CO₃ at 180 °C for 2 h. The highest equivalent gasoline (on the basis of 1 ton of safflower straw) for scenario I was 113.9 L, obtained by pretreatment at 120 °C with 0.5 mol/L Na₂CO₃ for 1 h. This value for scenario II was 100.0 L, observed after pretreatment at 180 °C with 1 mol/L Na₂CO₃ for 2 h. The equivalent gasoline for untreated straw for scenarios I and II was 93.6 and 17.1 L, respectively.