IN-SITU PRODUCTION OF POLYSULFIDE LIQUOR IN A KRAFT MILLS CAUSTICIZERS .1. PILOT-PLANT TRIALS

Batch and continuous pilot plant trials at two kraft mills confirmed t he technical feasibility of partial and selective oxidation of a porti on of the sulphide in white liquor to polysulphide, using lime mud as the primary oxidation catalyst. Use of a disc impeller, to maximize ga s-liquid mixing, and the addition of small amounts of manganese dioxid e (MnO2) were found necessary to improve reaction selectivity and redu ce retention time requirements. Using oxygen, with MnO2 addition, a co oking liquor with polysulphide concentrations >6 g/L (as sulphur) and with selectivities >70%, suitable for pulping, was-produced with react ion times of 70 to 90 minutes. Using air, reaction times of about 130 minutes were required.