Hydrothermal pre-treatment and enzymatic hydrolysis of sunflower stalks

► Sunflower stalks as source of renewable fermentable sugars. ► Hydrothermal pre-treatment and enzymatic hydrolysis was applied. ► Results compared favorably with other pre-treatments, other biomasses. ► Ninety percentage of glucose in pretreated material was released. ► Up to 18g ethanol/100g sunflower stalks could be obtained in ideal conditions. The production of fermentable sugars by biochemical conversion of pretreated sunflower stalks is studied in this work. Liquid hot water pre-treatment, in a temperature range from 180 to 230°C was used. After pre-treatment, solid residue and liquid fractions are separated by filtration. Pretreated solids are further submitted to enzymatic hydrolysis for glucose release using a commercial enzyme preparation. Enzymatic hydrolysis yields show that 90% glucose conversion can be obtained after 72h enzyme action on pretreated sunflower stalks at 220°C. Nevertheless, under such pre-treatment conditions most of the hemicellulosic sugars are lost due to solubilisation and degradation reactions. Taking into account all sugars that can be obtained from this agricultural residue, the best results in terms of potential ethanol production is found when pretreating sunflower stalks at 190°C. The characterization of hydrolysate composition is also discussed as inhibitor compounds are also found in liquid fractions issued from pre-treatment.