(277e) Rigorous Modeling of Chlorine Drying Using Sulfuric Acid

Sulfuric acid absorption is used to dry chlorine manufactured by chloralkali processes to very low levels, and packed columns are customarily the column internal of choice. Pumparounds are usually used for temperature control and because the feed rate of sulfuric acid is relatively low. Design of this process requires both an accurate vapor-liquid equilibrium (VLE) correlation and a rate-based model to evaluate the effects of column height, packing type, pumparound rates, etc. Development of the VLE correlation is challenging since the sulfuric acid concentration varies from about 98 wt% at the top of the column to about 50 wt% in the bottom of the column, and the system is a complex electrolytic mixture. We have developed an accurate VLE correlation using correct speciation and the Electrolyte NRTL model. The process model is often simplified to one using ideal stages and HETP (height equivalent of a theoretical plate), but this simplification renders the model inadequate to evaluate the effect of column height, pumparound rates and packing types. We demonstrate that the rate-based model in Aspen Plus enables reliable estimates of these variations, and therefore of capital and operating costs.