Effect of hardwood species in mixture during kraft cooking: Modelling and experimental results

摘要: In this work six hardwoods species were studied pure and in mixtures (binaries and ternaries) for their kraft cooking behaviour and results were confronted to existing kraft pulping simulator. It was shown that the general model structure combining three-phase kinetics and mass transfer equations fitted well but required some adjustments of parameters. For most of the species, the H-factor model activation energy (132 kJ/mol) was found underestimated. Other parameters such as extent of initial delignification, rate constants and lignin/polysaccharides removal ratios during the bulk phase were the most influencing ones. Then, an existing pulping simulator, originally conceived for softwoods, was adapted to hardwoods taking in consideration the measurements obtained in the first part, namely the linear-bulk delignification transition points, the polysaccharide versus lignin removal ratio and lignin/polysaccharide removal stoichiometry, the kinetic rate and the activation energies. Very good agreement was obtained for the different hardwoods, but no unique set of data was found for all hardwoods. Three groups were observed to be statistically different: Birch; chestnut and oak; poplar, eucalyptus and beech.