In this Demonstration, a trayed absorption column is used to remove an impurity solute (chloroform) from a gas feed by absorbing the impurity in a liquid solvent. The number of trays/stages needed to obtain an outlet solute mole ratio of ppm in the gas stream (set with a slider) is calculated. A stage is a plate that contacts the liquid solvent and the gas to promote mass transfer. Use a slider to set the solute mole ratio of the liquid feed stream. When a partial stage is calculated, the number of stages is rounded down to the nearest full stage. Use sliders to change the pressure and temperature in the column, the solvent flow rate and the solute mole ratio in the gas feed, . The slope of the pink operating line, , is shown on the column on the right. Checking the "" box shows the minimum slope for the operating line; the desired separation would require an infinite number of stages at a lower slope. The equilibrium line is orange. Check "show diagram with 5 stages" to set conditions that require 5 stages and display the mole ratios entering and leaving each stage. Move your mouse over the pink and orange lines on the diagram to see their labels.