 Also known as scrubbing  A unit operation that involves the diffusion of the solute from the gas phase through a stagnant liquid  There is a mass transfer of the component of the gas from the gas phase to the liquid phase  The solute transferred is said to be absorbed by the liquid

 The species transferred to the liquid phase are referred to as solutes or absorbate  No change in the chemical species present  Used to separate gas mixtures, remove impurities or recover valuable chemicals  The operation of removing the absorbed solute from the solvent is called stripping

 Common apparatus used is packed tower  Cylindrical column  Gas inlet and outlet  Liquid inlet and outlet  Tower packing  Tower packings:  Dumped at random  Stacked by hand  Ordered packings

 V = total gas flow rate, lb mole/hr  V`= inert gas flow rate, lb mole/hr  L = flow rate of solution, lb mole/hr  L`= flow rate of solvent, lb mole/ hr  Y = mole solute/ mole inert gas, mole ratio  y = mole fraction of solute in gas  X = mole solute/ mole solvent  x = mole fraction of solute in solution

 Common Solubility Data  See Fig for NH3-H2O  Table for SO2-H2O  Table for solubility as a function of temperature

 Ideal System (Ideal Gas, Raoult’s Law)  Vapor Pressure- Table 2-11  Pure Compounds as a function of tem Table 2-8 to 2-10  Dilute System (Ideal Gas, Henry’s Law)  H A- Tables and for various compounds in water

 d(Vy) = d(Lx)  differential equation of the operating curve, and its integral around the upper portion of the packing is the equation for the operating curve

N A is the mass-transfer flux [kmol/(s ⋅ m2)] a is the effective interfacialarea (m2/m3).

 Overall Mass Transfer Coefficients are introduced using a driving force based on difference between actual composition and equilibrium composition.  A capital symbol is used to represent the overall mass transfer coefficient N AG = Ky (y – y*) N AL = Kx (x* - x) where y* is based on x and x* on y

 Packings- solid materials used to provide contact between the gas and the liquid in the column  Common Types of Packings (See HB 14-54,55): a)Rings (Raschig, Pall) b)Saddles (Berl, Intalox) c)Tellerettes May also be random or structured (14-56)  Packing Characteristics a)Material b)Size c)Surface area per volume (a) d)Packing Factor (Fp)

 Flooding Velocity (GF) -is the mass velocity of the entering gas sufficient to cause liquid accumulation in the packed column which will lead to “flooding”. -the design of the column should be such that the mass velocity of the entering gas should be lower than the flooding velocity to avoid flooding.  Gv1= entering gass mass velocity  f= fraction, taken as 0.62 if not specified

 Procedure 1.Obtain liquid density ( ρ L ) and viscosity( μ L ), gas density( ρ G ) and packing factor(F P ) 2.Calculate the ratio of flow of entering liquid to entering gas (L/G) from problem data. 3.Calculate 4.Obtain CP from Fig /14-58 (HB) using FLG and pressure drop of 1.5 in Hg 5.Solve using appropriate units in the HB 6.

Procedure 1.Solve G v1 = f G F 2.Solve entering mass rate of gas (wV1) w V1 = V1 M V1 3.Cross Sectional Area S = w V1 /Gv1 4.Diameter = [4/ π S]^0.5

 A packed column (D = 40 cm) will treat 9000 L/min of a gas containing 15% NH 3, 85% air at 1.5 atm and 30°C. Pure water enters the top of the column. 95% recovery of NH 3 is desired using No. 1 plastic Intalox saddles. Find the height of packing if K G a = 80 kmols/hr-m 3 -atm using N OG evaluated by the Log- Mean Equation. Assume m =