Chemical pulping

The b.p. rise (elevation) of aq. industrial solns. is often of significant importance for the design of process conditions, equipment, heat balances, etc. However, few rigorous methods exist for predicting b.p. elevation in complex, multicomponent, electrolyte solns. An example of such a soln. is the black liquor obtained in kraft pulp prodn.: a complex mixt. of org. and inorg. ions including Na+, K+, OH-, HS-, CO32-, SO42-, S2O32-, CH3COO-, various phenolates and many more. This work shows one application of the semi-empirical Pitzer method to the theor. prediction of the b.p. rise in industrial black liquor solns. The values of the b.p. elevation were measured in two series of black liquors from representative Swedish mills, including both the original and lignin-lean black liquor at different solid contents. The results show a good agreement between exptl. and predicted values at low to moderate solid content, and good qual. prediction at high solid content.