8-31: Sugar production from dilute acid pretreated sunflower stalks

Sunflower stalks are left behind on fields after seed harvesting and are usually eliminated by burning, with associated economical costs and environmental concerns. As an alternative, their conversion into ethanol and other chemicals has been proposed. For this conversion to be attained, a key step is the pretreatment, by which sugars are released from the lignocellulosic matrix.

The objective of this work is to determine the optimal conditions of dilute acid pretreatment of sunflower stalks, based on sugar release both from cellulose and hemicellulose fractions. Temperature (in the range 150-200ºC), and acid concentration (1.5-2% w/v) were selected as operation variables. After pretreatment, solids were further enzymatically hydrolyzed at standard conditions for sugar release using commercial enzyme complex. Monomeric sugars in the liquid fraction were also determined.

Results show that 16.3 g glucose/100 g raw material can be obtained from enzymatic hydrolysis of solids when pretreating at 155ºC and 2% sulphuric acid concentration; at the same time, liquids issued from pretreatment contain also 13.3 g xylose (and 4.4 g glucose) per 100 g sunflower stalks. This amount is equivalent to near 70% of sugars present in the raw material.