separation

CHAPTER 6
MECHANICAL-PHYSICAL
SEPARATION PROCESSES

Introduction
Separation Processes
Many chemical processes materials and biological substances occur as mixtures of different components in the gas, liquid, or solid phase. In order to separate or remove one or more of the component from its original mixture, it must be contacted with another phase.
The two-phase pair can be gas-liquid, gas-solid, liquid, or liquid-solid.
Absorption
When the two contacting phases are a gas and a liquid. A solute A or several solutes are absorbed from the gas phase into a solid phase.
Distillation
A volatile vapor phase and a liquid phase that vaporizes are involved.
Liquid-liquid Extraction

When the two phases are liquids, where a solute or solutes are removed from one liquid phase to another liquid phase
Leaching (extraction)
If a fluid is being used to extract a solute from a solid.
Crystallization
Solute components soluble in a solution can be removed from the solution by adjusting the conditions such as temperature or concentration.
Adsorption
One or more components of a liquid or gas stream are absorbed on the surface or in the pores of a solid adsorbent. Membrane Processing
The relatively thin, solid membrane controls the rate of movement of molecules between two phases.

Physical-Chemical vs. Mechanical-Physical
Physical-chemical
Based on physical-chemical differences in the molecules themselves and on mass transfer of the molecules
Individual molecules are separated into two phases because of these molecular differences
 Examples : Absorption, distillation, extraction, crystallization, membrane processing. Mechanical-Physical
Separation is not accomplished on a molecular scale nor is it due to the differences among the various molecules.
Separation will be accomplished using mechanical-physical forces and not molecular or chemical forces and diffusion.
Examples :

Filtration
In filtration a pressure difference