Complete exploitation of defatted Cynara cardunculus L. through an innovative biorefinery approach

Cynara cardunculus L. (cardoon) represents an interesting feedstock for the production of chemicals and fuels, being a perennial herbaceous crop able to grow on marginal lands. Up to now, the seeds of the cardoon flower have found applications for bio-diesel production, whilst the cardoon residues are generally pretreated by the steam explosion, which is mainly focused on cellulose exploitation leading to hemicellulose degradation and recovery of low-quality lignin. In this scenario, the present work proposes the effective one-pot fractionation of cardoon through the organosolv pretreatment to recover and valorize all the lignocellulosic fractions. For this purpose, the biphasic system 1-butanol/water acidified with H2SO4 was employed to solubilize the sugars deriving from hemicellulose hydrolysis in the aqueous phase and lignin in the organic one, recovering the enriched cellulosic residue as solid. The influence of temperature and acid loading was investigated and the highest lignin and hemicellulose solubilizations of 72 and 97 wt% were ascertained, respectively. Butanol was also employed for the alcoholysis of the recovered enriched cellulosic residue into butyl levulinate, a very promising bio-fuel, through a one-pot reaction catalyzed by H2SO4 reaching the highest yield of 46 mol%, higher than that reached starting from not pretreated defatted cardoon (36 mol%), thus proving the effectiveness of this pretreatment. On the other hand, the aqueous phase containing mainly xylose was directly exploited to produce furfural, one of the most important platform chemicals, achieving a yield of 52 mol%. Lastly, very pure lignin was recovered from the organic phase, as proven by FT-IR and elemental analysis characterizations. In conclusion, the complete exploitation of all the cardoon fractions to give a valuable bio-fuel, a platform chemical and lignin was successfully performed.