Improved modified krafi cooking Part 3: Modified vapor-phase polysulfide cooking

摘要

An improved modified krafi cooking process (1) consists of an initial vapor-phase stage followed by a liquor-phase stage. All sulfide is charged at the beginning of the vapor-phase stage, while alkali is divided between the two stages. Using this cooking technique, the effect of added polysulfide was studied. The increase in yield at a given kappa number was found to be univocally determined by the concentration of polysulfide in the initial phase of the cook. Consequently, at the same polysulfide concentration, the yield increase for a conventional polysulfide cook is nearly the same as that for a modified vapor-phase polysulfide cook. The increase in viscosity at a given kappa number was clearly related to the sulfide concentration in the initial phase of the cook. Consequently, at the same sulfur charge, a modified vapor-phase polysulfide pulp has somewhat lower viscosity than a modified vapor-phase krafi pulp, due to the lower sulfide concentration that resulted from the decomposition of polysulfide into the nonreactive thiosulfate in the polysulfide cook.