Extraction of hemicellulose from South African eucalyptus grandis using weak white liquor activation technology and its impact on kraft pulping efficiency

Abstract

This work summarises the findings of our research on the activation of woodchips using weak white liquor as an alternative mill self-generated alkaline solvent. The ultimate goal was to gain a better understanding on: the effectiveness of the weak white liquor in terms of wood loss, pH and concentration of the hemicellulose in the resulting extract, kraft pulping efficiency, and critical pulp and paper properties. It appears that in order to minimise wood loss and to maintain the pH of the extract, near neutral pH during woodchips activation, a short wood activation time (15 min), and weak white liquor to water ratio of 20:80 is required. The concentration of hemicelluloses in the extract was approximately 2.0 g/L. During kraft pulping, weak white liquor activated woodchips responds much faster than the control. To maintain the same kappa number as the control pulps, a 20% reduction in pulping chemicals and improvement in pulp washing efficiency of 6% are achievable. Critical pulp and hand-sheet properties of the pre-activated woodchip’s pulp samples were comparable to those of the control pulp samples. Therefore, the most attractive benefits that could be obtained from the weak white liquor woodchip activation technology are decreased mill energy demands, reduction in kraft pulping chemicals, and additional revenues from new value chains from the hemicellulose stream.