Valorization of Cynara cardunculus crops by ethanol-water treatment Optimization of operating conditions

Ethanol-water (EW) process, an efficient and low energy consumption method for lignocellulose fractionation, has been applied to the valorization of Cynara cardunculus (cardoon) as an integrated biorefinery raw material. Cardoon is a perennial plant fully adapted to low fertility soils and could be a solution to improve the biomass supply in rural areas with marginal lands. The purpose of this study is to optimize the fractionation of cardoon biomass, maximizing glucose yield in the subsequent enzymatic saccharification. Operational conditions have been optimized using Taguchi statistical approach, being the responses: recovery of glucans, hydrolysis yield of xylans, delignification yield and enzymatic hydrolysis rate. The variables studied have been: time, temperature, liquid/solid (L/S) ratio and ethanol concentration; each variable was studied at three levels. The best treatment conditions are achieved at the maximum tested values for time, temperature and L/S ratio (120 min, 190 °C and 30 L/kg, respectively), and the intermediate level for the ethanol concentration (33%). Nevertheless, temperature is the most influential variable and, with a moderate energy input (60 min, 190 °C, 20 L/kg and 25% of ethanol), cardoon retains most of the glucans (> 97%), while significant amounts of xylans (> 68%) and lignin (> 58%) are removed, resulting in a a high glucose yield (c.a. 72%) in the subsequent enzymatic saccharification process. Therefore, EW treatment leads to similar glucose yields if compared to other pre-treatments, but at a fraction of the energy input.