Detailed Explanation Of The Working Principle Of Molecular Sieve

- Mar 20, 2019-

  Molecular sieves are used for the drying, purification and separation of gases and liquids. They work because they sift out molecules larger than their own pore size. The molecular sieve strongly adsorbs all polar molecules.


  Molecules such as water molecules and methanol molecules have positive and negative electrodes. These molecules with electrodes are firmly attracted by the molecular sieve. In contrast, electrodeless molecules, such as methane and ethane molecules, are much less attracted to the attraction. When a mixture of water (with electrodes) and methane (without electrodes) pass through the molecular sieve, although both are very small and easily pass through the pore size, only water is adsorbed.


  If the molecular sieve pore size is smaller than the methane molecule, but larger than the water molecule, the water can also be separated from the fluid with strong adsorption, such as methanol.


  When molecular sieves separate water molecules from industrial process streams, molecular sieves release heat. In most systems, the temperature of the industrial process stream rises only a few degrees. However, when a highly concentrated (greater than 0.5%) molecule with high attraction is adsorbed, the temperature rises above 100 °F (37.8 °C).


  At room temperature (less than 150 °F, or 65.5 °C), molecular sieves have a relatively high capacity for fluids such as water. However, at high temperatures (300-650 °F, 149-343 ° C), the capacity is very low. For this reason, when the molecular sieve is adsorbed and saturated, the molecular sieve can be heated by a gas stream of 300-650 °F (149-343 ° C) to desorb the adsorbed molecules. This operation is called "regeneration."


  After heating, the molecular sieves are cooled to operating temperature in a room temperature stream before the molecular sieves are returned to recycle. The operation can be continued using two or more containers, one or more of which are for regeneration and one or more for work. It is also possible to regenerate the molecular sieve by decompression.