Catalytic and biocatalytic cascade conversion of giant reed and cardoon residues to glucose, levulinic acid, and long-chain fatty acid methyl esters

Giant reed was hydrolysed by the green salt FeCl 3 under microwave irradiation. Differently, cardoon residues were pretreated by steam explosion and hydrolysed by the same catalyst. Each pretreatment showed efficient biomass fractionation, with xylan hydrolysis reaching 99 mol% for giant reed and 70 mol% for cardoon. Then, glucose yields of 55 and 30 mol% were obtained for giant reed and cardoon, respectively, under mild reaction conditions (34 min, 150 °C, biomass loading 9 wt%, FeCl 3 2.7 wt%). Sugars-rich hydrolysates were fermented by the yeasts L. starkeyi and L. tetrasporus to produce triglycerides. L. starkeyi achieved a lipid yield of 13.5 wt% from giant reed hydrolysate and 14.2 wt% from cardoon hydrolysate. L. tetrasporus reached a lipid yield of 16.0 and 17.6 wt% from giant reed and cardoon hydrolysate, respectively. Moreover, both yeasts were able to convert cardoon hemicellulose into triglycerides, reaching at pH 5.5 a lipid yield of 13.9 wt% ( L. starkeyi ) and 19.4 wt% ( L. tetrasporus ). These oils were converted to long-chain fatty acids methyl esters. The final valorisation of unconverted glucan in solid residues resulted in the FeCl 3 -catalysed production of levulinic acid and formic acid to close the biorefinery cycle of both biomasses.