Effect of Sulfidity and Anthraquinone on Modified Batch Pulping Processes, 1999 Pulping Conference Proceedings

S. Chivukula, Hasan Jameel, H-m Chang, Wolfgang Wizani

Modified batch pulping processes recycle the black liquor from the end of the cook to absorb the sulfur preferentially onto the chips. This absorbtion of sulfur, minimizes the soda type reactions during kraft pulping. The objective of this study was to study the impact of varying the sulfidity in a modified batch process from 15 to 45%. In a conventional kraft cook sulfidity has a significant impact on yield and pulping rates up to about 15% sulfidity. Beyond 25% sulfidity the impact the kraft process was found to be minimal. In this study, the impact of sulfidity was evaluated since the amount of sulfur being recycled in the process is different than for a conventional kraft process. Increasing the sulfidity leads to faster delignification rates with substantial yield increases even at low kappa numbers. As the sulfidity was increased from 15 –45% a yield improvement was observed in all cases, as compared to conventional kraft pulps where yield improvements were minimal above 25% sulfidity. The amount of yield increase, decreased as the sulfidity of the cook was increased over 35%. About 2% higher yield was observed at kappa 20 when the sulfidity was increased from 15 to 24%. A lower impact of sulfidity was expected, with modified batch pulping systems since a large amount of the sulfur was being recycled in the process but the impact of sulfidity was actually higher. The viscosity of the pulps was also higher at 35% sulfidity. The impact of using AQ at the different sulfidities were also studied, since it was known that in conventional kraft pulping AQ is more effective at the lower sulfidity. It was also found for the modified batch pulping process that the impact of using AQ is higher at the lower sulfidity. The increase in yield with AQ at 15 % sulfidity was 2.7% vs 0.7% yield increase at 45% sulfidity. The optimum sulfidity with AQ was found to be 24%. The pulps with 45% sulfidity and 0.1% had the highest viscosity.