Date Published: January 11, 2016
Publisher: Springer Berlin Heidelberg
Author(s): Sasisanker Padmanabhan, Philippe Schwyter, Zhongguo Liu, Geoffrey Poon, Alexis T. Bell, John M. Prausnitz.
Pretreatment of miscanthus is essential for efficient enzymatic
production of cellulosic ethanol. This study reports a possible pretreatment method
for miscanthus using aqueous ethylenediamine (EDA) for 30 min at 180 °C with or
without ammonia. The mass ratio of miscanthus to EDA was varied from 1:3, 1:1, and
1:0.5, keeping the mass ratio of miscanthus to liquid (EDA + Water) constant at 1:8.
The ammonia-to-miscanthus ratio was 1:0.25. After pretreatment with a ratio of 1:3
miscanthus to EDA, about 75 % of the lignin was removed from the raw miscanthus with
90 % retention of cellulose and 50 % of hemicellulose in the recovered solid.
Enzymatic hydrolysis of the recovered solid miscanthus gave 63 % glucose and 62 %
xylose conversion after 72 h. EDA provides an effective pretreatment for miscanthus,
achieving good delignification and enhanced sugar yield by enzyme hydrolysis.
Results using aqueous EDA with or without ammonia are much better than those using
hot water and compare favorably with those using aqueous ammonia. The
delignification efficiency of EDA pretreatment is high compared to that for
hot-water pretreatment and is nearly as efficient as that obtained for
Economic and environmental concerns about the continued use of fossil
fuels have prompted a search for alternative fuels using sustainable lignocellulosic
biomass feedstock (Carroll and Somerville 2009). Conversion of abundant and renewable lignocellulosic biomass
to bioethanol as a transportation fuel provides a possible option to reduce
greenhouse gas emissions and fossil fuel consumption (Jordan et al. 2012). Miscanthus is a suitable biomass feedstock
because it has high carbohydrate density and low fertilizer requirements for growth
(Padmanabhan et al. 2012; de Vrije et
al. 2009; Carroll and Somerville
2009; Brosse et al. 2012).
EDA provides an effective pretreatment for miscanthus, leading to
good lignin removal and enhanced sugar yield by enzyme hydrolysis. Up to 75 % of
lignin is removed leading to a yield of 63 % glucose and 62 % xylose from the
recovered solid. The delignification efficiency of EDA pretreatment is high compared
to that for hot-water pretreatment and is nearly as efficient as that obtained for
aqueous-ammonia pretreatment. Addition of ammonia to EDA does not increase enzymatic
conversion to sugars despite more removal of lignin and hemicellulose. Increasing
EDA loading provides improved conversion of cellulose to sugars. Chemical
composition analysis shows that better lignin removal improves sugar yields. About
one-half of hemicellulose is removed from the solid during pretreatment; it is
dissolved in the liquid phase, where, following adjustments to lower pH, it can be
converted to xylose.