Hot water treatment of hardwood kraft pulp produces high-purity cellulose and polymeric xylan

Abstract

Hot water treatments (HWTs) of unbleached hardwood kraft pulps under various process conditions were conducted to extract the xylan and thus produce a high-purity cellulosic pulp that could be used in dissolving applications. Increasing treatment temperature up to 240°C increased the removal of xylan over the degradation of cellulose in birch pulp, but this effect was minor at higher temperatures. Addition of acetic acid lowered the treatment intensity needed to reach a certain degree of pulp purity, but did not improve the selectivity in xylan removal compared to water-only experiments. HWTs of eucalyptus pulp, with lower xylan content than birch pulp, produced cellulosic fibers with higher degree of polymerization at a given pulp purity. Under selected operational conditions (240°C for 10 min) in a flow-through reactor, and provided that the HWTs were applied before bleaching, the chemical and macromolecular properties of water-treated pulps may be suitable for their conversion to viscose. Moreover, at high flow rates (200-400 mL/min), the extracted xylan was recovered from the aqueous hydrolysate in high yield and with relatively high molar mass (*10 kDa). Based on the results of this study, HWTs of hardwood kraft pulp are suggested as a simple and green method to produce high-purity cellulose and polymeric xylan for high value-added applications.

Birch wood pre-hydrolysis vs pulp post-hydrolysis for the production of xylan-based compounds and cellulose for viscose application

“…The pulp Kraft_240.10, i.e., the kraft pulp after post-hydrolysis at 240 ºC for 10 min, had a xylan content of about 7% and a viscosity of about 300 mL/g. In agreement with our previous results Borrega, Concha-Carrasco, Pranovich, & Sixta, 2017), it appears that water post-hydrolysis of kraft pulp cannot lower the hemicelluloses content below 7% without compromising the pulp quality by extensive degradation of the cellulose fraction.…”

“…The unbleached kraft and PHK pulps were then subjected to water post-hydrolysis to extract the residual xylan fraction. The operational conditions for the post-hydrolysis were selected based on the results of our previous study (Borrega, Concha-Carrasco, Pranovich, & Sixta, 2017). In all pulps, the hemicelluloses (xylan) content decreased with increasing post-hydrolysis time, while the cellulose yield decreased only slightly (Fig.…”

“…that of commercial PHK pulps for viscose application (Borrega et al, 2017). Nonetheless, the most important quality parameter of any dissolving pulp is probably its so-called reactivity.…”

“…Modern pulp mills (biorefineries) are regarded as one of the cornerstones for the development of biobased economies. Within this context, water post-hydrolysis of pulp is of interest because, if applied in a flow-through system, the extracted hemicelluloses may be recovered from the aqueous hydrolysate in high yield and relatively high molar mass, depending on the flow rate Borrega, Concha-Carrasco, Pranovich, & Sixta, 2017).…”

Characterisation of cellulose pulps isolated from Miscanthus using a low-cost acidic ionic liquid

“…For example, acetylation can yield cellulose acetate which is spun into textile fibres (Edgar et al 2001). Abundance, lowcost and desirable material properties such as high strength, biodegradability and biocompatibility have made isolated cellulose fibres and their derivatives attractive in industries ranging from paper, packaging and hygiene products to textiles, pharmaceuticals and optics (Berg and Lingqvist 2017;Edgar et al 2001;Osong et al 2016;Shatkin et al 2014).…”