We have extended our previous work on the modeling of geometry, liquid trickle flow, and pressure drop to study the mass-transfer process in a packed column. On the basis of the penetration theory and the detailed information of lateral and axial variations in packing geometry and fluid dynamics from our previous models, a predictive mass-transfer model has been developed on the scale much smaller than a packing particle in the case of random packings or a flow channel in the case of structured packings. Distillation experiments have been carried out with methanol/2-propanol and methanol/water for 16 mm metal Pall rings. The model has been validated with the experimental results and our previous data on a novel vertical-sheet structured packing. Simulations for uniform and uneven initial distributions have been carried out, which showed a strong influence of liquid-flow distribution on mass-transfer efficiency in a packed column.