LIQUID-PHASE RESISTANCE TO MASS-TRANSFER ON DISTILLATION TRAYS

The liquid-phase resistance to mass transfer was determined for the distillation of six binary mixtures. It was found that the liquid-phase resistance to mass transfer is significant, ranging from 20 to 55% of the total mass-transfer resistance. The results also indicated that the traditional assumption of theta(G) = theta(L) is not valid for distillation systems. If this assumption is applied, the fraction of liquid-phase resistance to mass transfer will be significantly underestimated. Tray efficiency models developed from data obtained from absorption and stripping systems (e.g., the AIChE method) were suggested to greatly overpredict the number of liquid-phase mass-transfer units for distillation systems. Thus, careful examination of the use of various efficiency models for tray design is required.