Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass

A biorefinery scheme with separate processing of the two main carbohydrate streams (cellulose and hemicellulose-derived) was employed to the energy crop cardoon (Cynara cardunculus L.) to fractionate the whole stalk material. A high quality xylose-enriched substrate was obtained after selective one-step dilute sulfuric acid hydrolysis of hemicelluloses, yielding 18.1 g of xylose per 100 g of dry biomass. The xylan-free solid residue was delignified by sulfur-free organosolv pulping to produce dissolving grade pulps having 93.8% of α-cellulose (33.1 g per 100 g dry initial biomass) and 79.5% degree of crystallinity. About 76% of crop lignin (13.8 g per 100 g dry initial biomass) was recovered from the spent pulping liquor as a high purity reactive precipitated organosolv lignin. Response surface methodology was used for statistical modeling and optimization of the applied separation processes. The central composite rotatable design was applied to assess the effects of the principal technological parameters on the main reaction outputs.