Purification of cellulosic pulp by hot water extraction

Hot water extraction (HWE) of pulp in a flow-through reactor was evaluated as a method to purify paper-grade pulps. About 50–80 % of the xylan and up to 50 % of the lignin in unbleached birch Kraft pulp was extracted by the HWE without losses in cellulose yield. The residual xylan content in the extracted pulps was predominantly too high for dissolving-grade applications, but some of the pulps with a xylan content of 5–7 % might still be suitable as rayon-grade pulps. Increasing extraction temperature lowered the xylan content at which cellulose yield started to decrease. Furthermore, at any given xylan content, increasing extraction temperature resulted in cellulosic pulp with higher degree of polymerization. The extracted xylan was recovered almost quantitatively as xylo-oligosaccharides. The results suggest that HWEs at elevated temperatures may be applied to purify cellulosic pulps, preferably containing a low xylan content, and to recover the extracted sugars.Finnish Bioeconomy Cluster FIBIC OyTechnology Development Centre (Finland

Wood biorefinery based on γ-valerolactone/water fractionation

A novel biorefinery concept based on the fractionation of woody biomass in a γ-valerolactone (GVL)/water binary mixture is introduced. Under optimal GVL/water ratio, Eucalyptus globulus wood was effectively fractionated in a single step into its principal components. The pulp fraction, characterized by high yield, high cellulose purity and high bleachability, was directly spun to produce regenerated cellulosic fibers with mechanical properties comparable to the best man-made fibers currently available in the market. Most of the hemicelluloses and lignin in wood were extracted and dissolved into the spent liquor. The dissolved hemicellulose-based fraction may be upgraded to furanic platform chemicals in subsequent catalytic conversion processes. About 50–60% of the extracted lignin was precipitated by the addition of water, an anti-solvent. The precipitated lignin was characterized by low carbohydrate and ash contamination, high phenolic content, relatively low polydispersity and low molecular mass. The lignin extracted by GVL/water fractionation may thus be suitable for a wide range of energy, material or chemical applications.Peer reviewe