Steam Explosion as a Pretreatment of Cynara cardunculus Prior to Delignification

Cardoon (Cynara cardunculus) stalks were submitted to steam explosion (183 degrees C, 5 min) with a yield of 88% and a lignin loss of around 7%. Cardoon (C) and steam exploded cardoon (C-SE) were characterized by wet chemical analysis and Py-GC/MS. Total lignin and its S/G ratio were 21.6% and 1.3S in C and 22.4% and 1.40 in C-SE. These samples were delignified by kraft and organosolv processes. Cardoon pulps were obtained with different yields of 45.1% for kraft and 61.2% for organosolv. Kraft pulps yields were 45.1% and 50.9%, respectively, for C-k and CSE-K, corresponding to a lignin loss of 74.7% and 72.2%. The S/G ratio was similar 1.25 and 1.23. Organosolv pulps presented higher yields (61.2% vs 73.3%) and were less delignified (30.5% vs 13.8%), and the S/G ratio was 1.54 and 1.47, respectively, for C-org and CSE-org. Overall, the condition chosen for steam explosion allowed a low mass loss but did not promote delignification and neither enhanced lignin removal during kraft and organosolv processes.