Prediction of alkaline pulping yield: equation derivation and validation

Abstract

A method is described which allows prediction of alkaline pulp yield. It is based on an equation which relates the pulp yield to the cellulose content and cellulose degree of polymerization of the alkaline pulp. From the slope and intercept of this linear equation, the lignin-free pulp yield, ${\text{Y}}_{\text{T}}^{{\prime }}$, of a pulp sample can be calculated when the lignin-free cellulose content (${\text{G}}^{{\prime }}$) and the cellulose degree of polymerization (DP) of the pulp fiber are determined by sugar analysis and viscosimetry, respectively. In this paper the yield prediction equation is derived and validated using model celluloses and hemicelluloses. As part of the yield prediction method, a new equation was developed which corrects the cellulose degree of polymerisation obtained from the pulp intrinsic viscosity for the hemicellulose content of the pulp. The approach was successfully validated by cooking of cotton at different temperatures (160–180 °C), alkalinities (1.30–2.60 mol/L, the equivalent to an effective alkali (as Na₂O) charge of 12–24 % at a L/W ratio of 4.0 L/kg), sulfidities (15 and 30 %) and anthraquinone charges (0, 0.05 and 0.1 %). The cellulose protecting effect of AQ was confirmed by the lower number of glucose units removed by alkaline peeling compared to that removed during conventional alkaline or kraft cooking.