Biorefinery of Energy Crop Cardoon(Cynara cardunculus l.)-Hydrolytic Xylose Production as Entry Point to Complex Fractionation Scheme

Abstract

Response surface methodol. (RSM) was employed for statistical modeling and optimization of low temp. dil. sulfuric acid hydrolysis of hemicellulose fraction of energy agro-crop cardoon (Cynara cardunculus L.), as an entry point to complex biorefinery scheme. The 23 central composite rotatable design (CCRD) was used to assess the effect of the principal independent process variables (reaction time, temp. and acid concn.) on efficiency and selectivity of heteroxylan conversion to xylose. The second-order polynomial model was fitted to exptl. data to find optimal reaction conditions of xylan-to-xylose hydrolysis by multiple regression anal. The effect of acid concn. (linear and quadratic) was found as a more significant (p = 0.001-0.007) for monomeric xylose recovery in soln. The maximal xylose yield of ca. 86% (18.08 g/100 g biomass) was achieved after cardoon hydrolysis at 138.5°C in 1.28% sulfuric acid soln. for 52 min, vs. 87% predicted by model. The resulting xylose-enriched substrate revealed low concn. of toxic substances (1.04% furfural, 0.33% 5-hydroxymethylfurfural, 2.03% glucose), providing required quality for subsequent xylose (bio)conversion to final products (e.g. to xylitol). The enzymic saccharification/digestibility of insol. residue after hemicellulose removal was improved in four times, resulting in cellulose conversion to fermentable glucose by 76% vs. 19% for unhydrolyzed cardoon. [on SciFinder(R)]