SULPHIDITY REDUCTION IN A KRAFT PROCESS

The main object of this study was to reduce the sulphidity in a kraft process by tile addition of small quantities of methanol. Using a cent ral composite design (CCD) approach, the methanol concentration, the l evel of sulphidity and the H-factor were optimized in order to determi ne if the chosen operating conditions were equivalent or if better pul ps were produced when compared with the kraft process. As dependent pa rameters, the kappa number, the yield and the viscosity as well as mec hanical and optical properties were evaluated. White birch (Betula Pap yrifera) was used. Using a methanol concentration of 15% and a reduced sulphidity level of 12.5%, it is possible, for a given I-I-factor, to produce pulps with properties comparable to the kraft process at 25% sulphidity in terms of kappa number, yield and viscosity. For a given kappa number the yield was four units superior using methanol. With th e KLS-MeOH process (kraft low sulphidity methanol) it is possible to p roduce pulp having higher tear but lower breaking length when compared with a standard kraft process. However, the addition of methanol in t he kraft process allows the reduction of the sulphidity.