MB IN ADSORPTION & ABSORPTION

What is Adsorption?

- Adsorption is a separation of mixture of liquids or gases based on affinity into solid adsorbent.

Steps to solve the material balance:

Read and understand the process description
Draw flowchart
Write down all variables with labels
Assign algebraic letters to unknown
DOF analysis
Assign basis and write mass balance equation
Solve the equations

Example:

Wet air containing 4.0 mol% water vapor is passed through an adsorption column containing calcium chloride pellets. The pellets adsorb 97.0% of the water and none of the other constituents of the air. The column packing was initially dry and had a mass of 3.40 kg. Following 5.0 hours of operation, the pellets are re-weigh and found to have a mass of 3.54 kg. Calculate the molar flow rate (mol/h) of the feed gas and mole fraction of water vapor in the product gas.

DOF ANALYSIS

4 unknowns :

3 independent equations

DoF = Unknowns. - Independent Equations

= 4 – 3

DoF = + 1

Overall mass balance

INPUT=OUTPUT + ACCUMULATION (water in pellets - CaCl2)

Absorption Unit:

- separation of mixture of gases based on gas solubility in liquid solvent

Steps to solve the material balance:

Read and understand the process description
Draw flowchart
Write down all variables with labels
Assign algebraic letters to unknown
DOF analysis
Assign basis and write mass balance equation
Solve the equations

Example:

Gas absorption of gas scrubbing is a commonly used method for removing environmentally undesired species from waste gases in chemical manufacturing and combustion processes. A waste gas containing 10 mol% SO2 (a precursor of acid rain) and several other species (collectively as A) is fed to scrubbing tower where it contacts a solvent (B) that absorbs SO2. The ratio of liquid stream to gas stream fed to the column is 5. The solvent feed rate to the tower is 1000 mol/min. The absorption unit has an efficiency of 98%. Assume that the absorption of A and evaporation of B in the scrubbing can be neglected, calculate the mole fraction of SO2 in the liquid and gas streams.