Molecular sieves, 4 ? is used to absorb molecules as large as butane. It is utilized for the separation of natural gas, liquified petroleum gas (LPG) and alkenes. It finds application in the refining and purification of liquid and gases. It is also used for drying and purification of air, inert gases and solvents. It is actively involved to remove methanol, carbon dioxide and ammonia from fluid streams. It plays a vital role to remove heavy metal ions available in water. It is also used as a soap forming agent and as a detergent auxiliary. It has been considered as a general-purpose drying agent in polar and non polar media.
Choosing a Molecular Sieve:
1. The preferential adsorption of one molecule over another depends upon pore diameter and mesh size.
2. The dynamic capacity of the silica gel for adsorbing a particular compound is governed by the internal surface area; the greater the surface area, the greater the dynamic capacity.
3. Rate of adsorption and sharpness of resolution are dependent chiefly on particle size and column packing; a fine particle size gives optimum sharpness of resolution.
4. Liquids are most readily adsorbed from solvents in which they are least soluble; a good solvent makes a good desorbing agent.
5. Highly polar liquids are readily adsorbed. Compounds having hydroxyl groups, or containing oxygen are strongly adsorbed.
6. For similar compounds, the higher the molecular weight the higher the selectivity.
7. For hydrocarbons of similar molecular weight, adsorptivity increases with the number of double bonds.
