CHE368 - Absorption & Stripping

Study Notes

Absorption separates components in gas streams by transferring them to a non-volatile liquid solvent.
Three principal types of absorption processes:
- Physical Solution: Absorbate is more soluble, has reversible behavior based on gas partial pressure and temperature.
- Reversible Reaction: Absorbate chemically reacts, forming a compound with vapor pressure.
- Irreversible Reaction: Permanent reaction with no return.
Physical absorption is more suited for large gas quantities at high pressure; chemical absorption targets low concentrations at low partial pressures.

Conducted in equilibrium stages, with the gas mixture contacting the solvent in an absorber.
Simpler than distillation columns (no need for condensers or reboilers).
Process flow involves passing the gas through the absorber and then through a stripper to remove the absorbed components using a stripping gas.

Gas Absorber: Main unit for gas-liquid contact.
Pumps and Valves: Circulate solvent and control flow rates, maintaining efficiency.
Stripping Column: Removes components from liquid using a vapor stream, can operate in co-current or countercurrent flows.
Heat Exchangers: Optimize energy usage, enhancing system efficiency.

A process to remove a component from liquid mixtures by contacting it with a stripping agent gas.
Mass transfer dictates component movement between liquid and gas phases, relying on concentration gradients.

Stripping agents commonly include steam and air.
Key design considerations for stripping columns include height, diameter, packing type, and optimal operating conditions for temperature, pressure, and flow rates.

Governed by thermodynamic principles, such as Henry's Law and Raoult's Law, providing relationships between gas solubility and partial pressures.
Needs careful selection of operating conditions, considering three components: solute, carrier gas, and solvent.

Adsorption is the accumulation of molecules on a solid surface, differing from absorption, where substances enter a liquid.
Key terms: Adsorbate (substance being adsorbed) and Adsorbent (solid material).
Predominantly used adsorbent types include activated carbon, silica gel, and zeolites.

Several cycles are utilized in adsorption processes:
- Temperature-Swing Cycle: Energy-intensive, suitable for low adsorption concentrations.
- Inert-Purge Cycle: Uses non-adsorbing gas for rapid desorption.
- Displacement Purge Cycle: Employs a gas or liquid that adsorbs similarly to facilitate regeneration.
- Pressure-Swing Cycle: Effective in bulk-gas separations, rapidly lowers partial pressure.

Initial costs arise from equipment purchase, installation, and adsorbent materials.
Operational costs include adsorbent maintenance, energy, and spent adsorbent disposal, with adherence to environmental regulations being significant.

Extraction involves isolating components from mixtures by utilizing a solvent, influenced by differential solubility.
Critical factors include solvent selection, temperature, phase ratio, contact time, and mixing efficiency.

Various methods include spray extraction towers, packed towers, and continuous counter-flow contractors.
Different configurations balance efficiency, energy consumption, and extraction capacity.

Widely used in industries such as chemical metallurgy (e.g., hydrometallurgy, pyrometallurgy) and pharmaceuticals (e.g., maceration, Soxhlet extraction).