The forgotten potential of sulphite-based processes

The current production of sulphite pulps, including paper-grade and semi-chemical pulps, accounts for approximately 5% of the world wood pulp production, and the capacity is predicted to increase. The advantages of sulphite processes include the versatility of process and a high flexibility in pulp yields, facilitating the production of specialized fibre products and the isolation of lignocellulosic materials from the spent liquors for conversion to various value-added products. Sulphite pulping at neutral or slightly alkaline pH is commonly known as a pre-treatment process of high yield semi-chemical (NSSC) pulp production for corrugating medium. However, the research on the utilization of NSSC spent liquors is still very limited. Extending the cooking at neutral pH chemical pulps with high yields of carbohydrates can be produced. The higher amounts of dissolved lignocellulosic materials in the spent liquors of extended neutral sulphite cooks can be utilized in the production of value-added by-products. The aim of this work is to examine the potential of forest biorefinery, based on neutral sulphite process for the production of tailored fibres, with simultaneous isolation of value-added by-products. The preliminary results show the significant glucomannan yield and the content of acidic groups in the produced pine sulphite pulps. Further research is needed to evaluate the potential of fibres in various applications and to define the most valuable materials to be isolated from the spent liquor.