Sustainable exploitation of defatted Cynara cardunculus in an integrated biorefinery approach

Lignocellulosic biomass, such as Cynara cardunculus, offers a sustainable alternative to fossil fuels to produce value-added products. Nowadays, its seeds are used for biodiesel synthesis, whilst the defatted cardoon (DC) residue, rich in polysaccharides, remains underutilized. Thus, to turn this residue into a feedstock, this work develops an innovative microwave-assisted (MW-A) one-pot biorefinery process to convert DC into biofuels and high-value chemicals. For this purpose, an acidic biphasic organosolv pretreatment (water/n-butanol) was performed to isolate each biomass component: a solid cellulose-rich residue, an aqueous phase rich in xylose deriving from hemicellulose hydrolysis and an organic phase containing solubilized lignin. The organosolv pretreatment allowed the removal of 72 wt% of lignin and 97 wt% of hemicellulose, enriching the solid residue up to 74 wt% in cellulose. This latter was used as substrate in a MW-A one-pot butanolysis process catalyzed by H2SO4 to obtain n-butyl levulinate (BL), which up to now has been proposed as bio-blendstock for Diesel. Under optimized reaction conditions, a BL yield of 46 mol% was achieved, higher than that obtained from untreated biomass, proving the enhancement of cellulose accessibility and reactivity. The aqueous phase rich in xylose was further processed by MW heating to produce furfural, an important platform-chemical, via acid-catalyzed dehydration, reaching the highest yield of 52 mol%. The lignin solubilized in the organic phase was separated by butanol, allowing its possible reuse in the organosolv pretreatment or as solvent/reagent in the butanolysis step, while recovered lignin was characterized to prove its high purity. Lastly, BL was tested for the first time as a 10 vol% bio-blendstock with gasoline, showing that the engine performance was kept constant, as well as the pollutant emissions, proving the possibility of extending its application in gasoline engines.