Single Component Absorption Example Carbon disulfide, CS2, used as a solvent in a chemical plant, is evaporated from the product in a drier into an inert gas (essentially N2) in order to avoid an explosion hazard. The vapor-N2 mixture is to be scrubbed with an absorbent hydrocarbon oil, which will be subsequently steam-stripped to recover the CS2. The CS2-N2 mixture has a partial pressure of CS2 equal to 50 mmHg at 24º C (75ºF) and is to be blown into the absorber at essentially standard atmospheric pressure at the expected rate of 0.40m3/s (50,000 ft3/h). The vapor content of the gas is to be reduced to 0.5%. The absorption oil has av mol wt 180, viscosity 2 cP, and sp gr 0.81 at 24ºC. The oil enters the absorber essentially stripped of all CS2, and solutions of oil and CS2, while not actually ideal, follow Raoult’s law [see Ewell et al.: Ind. Eng. Chem., 36, 871 (1944)]. The vapor pressure of CS2 at 24º C=346 mmHg. Assume isothermal operation.

(a) Determine the minimum liquid/gas ratio. (b) For a liquid/gas ratio of 1.5 times the minimum, determine the kilograms of oil to

enter the absorber per hour. (c) Determine the number of theoretical trays required, both graphically and analytically.