VAPOR-PRESSURE AND BOILING-POINT ELEVATION OF SLASH PINE BLACK LIQUORS - PREDICTIVE MODELS WITH STATISTICAL APPROACH

Vapor-liquid equilibria and boiling point elevation of slash pine kraf t black liquors over a wide range of solid concentrations (up to 85% s olids) has been studied. The liquors are from a statistically designed pulping experiment for pulping slash pine in a pilot scale digester w ith four cooking variables of effective alkali, sulfidity, cooking tim e, and cooking temperature. It was found that boiling point elevation of black liquors is pressure dependent, and this dependency is more si gnificant at higher solids concentrations. The boiling point elevation data at different solids contents (at a fixed pressure) were correlat ed to the dissolved solids (S/(1 - S)) in black liquor. Due to the sol ubility limit of some of the salts in black liquor, a change in the sl ope of the boiling point elevation as a function of the dissolved soli ds was observed at a concentration of around 65% solids. An empirical method was developed to describe the boiling point elevation of each l iquor as a function of pressure and solids mass fraction. The boiling point elevation of slash pine black liquors was correlated quantitativ ely to the pulping variables, using different statistical procedures. These predictive models can be applied to determine the boiling point rise (and boiling point) of slash pine black liquors at processing con ditions from the knowledge of pulping variables. The results are prese nted, and their utility is discussed.