Hemicellulose extraction and its effect on pulping and bleaching

A potential biorefinery is envisioned to use the hemicellulose portion of biomass to create transportation fuels or chemicals and the cellulose portion for fiber to be used in papermaking. To understand the effect on hemicellulose removal to pulpability and bleachability, a liquid hot water extraction was performed on two types of biomass with high hemicellulose content: poplar and miscanthus. The resulting materials were pulped using either a soda anthraquinone or kraft process. The pulps were then oxygen delignified and bleached with an elemental chlorine free sequence. The results demonstrate that a significant portion of hemicellulose can be extracted using liquid hot water extraction conditions of 170°C, 60 min, and a 6:1 ratio, with minimal glucan degradation. These low hemicellulose-content pulps delignified similarly to the control pulp, but had lower oxidative demand because of the absence of hemicellulose degradation products. Oxygen delignification of the low hemicellulose-content pulps was enhanced, but so was cellulose degradation. The delignification gains resulted in higher brightness ceilings for the pulps when a D(EP)D sequence was used. Measured fiber morphology did not change significantly from extracting the hemicellulose. Overall, hemicellulose extraction before pulping improved the efficiency of pulping and bleaching materials to a high brightness, but increased cellulose degradation.