1. Sizing a permanent contact column with parallel currents (piston model)

• Consider the transfer of a single solute from phase 1 to phase 2.

• The volume flow rates of both phases are assumed to be constant. This is the case in liquid-liquid extraction for immiscible solvents and trace solutes, and in the absorption of trace constituents. We can reason in terms of molar flow rates, if these are constant in the apparatus, or in terms of molar fractions (in the case of constant molar flow distillation).

• $c_i^j$ denotes the concentration of the solute in phase i at level j with j ≥ 0 for phase 1 inlet (z ≥ 0) and j ≥ 1 for phase 1 outlet (z ≥ Z ), and c _i represents the concentration of...