Molecular Sieves

What is Adsorption ?
Adsorption is a surface phenomenon. Molecules in gas or in liquid are attracted to the internal surface of a solid ’s pores. Trivially, adsorption can be seen as a condensation phenomenon, where a vapor tends to condense when it meets a cold surface.

What are Zeolites?
Zeolites are a group of alumino-silicate minerals, with a solid crystalline structure, that may occur either in nature or are manufactured synthetically. Zeolite crystals, defined above, are porous. And are composed of a three-dimensional network of channels (pores). For a given zeolite formulation and structure, the pores have the unique characteristic of being all the same size. The diameter of these pores can be as small as a very tiny molecule such as water.
  
What are Molecular Sieves?
The term “Molecular Sieve” was originated by W.W. McBain in 1932. Molecular Sieves are a certain kind of zeolites, which for their pore size and chemical composition have particularly developed adsorption properties, which means they are capable of separating or removing one substance from another on a molecular scale. While the properties of natural zeolites are fixed, synthetic zeolites can be tailored to meet industrial specifications. Therefore, synthetic zeolites dominate the Molecular Sieve market among which the "A" and "X" structures are the most commonly used.

  
Why is pore size important ?
Thanks to the Molecular Sieve’s very precise and uniform pore opening, certain molecules can be trapped (adsorbed), while others are not. The size of the opening (typically ranging between 3 Angstrom to 10 Angstrom) determines the size of the molecules, which can be adsorbed or released.
 
 What is the difference between “A” structure and "X" structure ?

 “A” Structure

4Å opening is obtained with a sodium cation.
3Å opening is obtained with a potassium cation.
5Å opening is obtained with a calcium cation.
 
“X” Structure

(different arrangement and proportion of the ions)
10Å opening is obtained with a sodium cation.
  
What is the optimized selectivity per market ?
Molecular Sieves SILIPORITE® with a small pore diameter provide greater selectivity than those having a bigger pore diameter.

Different types of Molecular Sieves are used for different applications:

3A is used mainly for the dehydration of unsaturated hydrocarbon streams such as cracked gas, propylene, butadiene, and acetylene. It is also used for methanol and ethanol drying. As a static desiccant, it is used in the manufacturing of insulated glass, refrigeration systems and as scavenger in paint.

4A is typically used for saturated hydro carbons streams drying and natural gas. As static desiccant in household refrigeration systems; in packaging of drugs, electronic components and perishable chemicals, and as water scavenger in paint and plastic systems. It is also used for saturated hydrocarbon streams drying.

5A is used for N- and Iso-paraffin separations, for Hydrogen purification and hydrocarbon streams sweetening.

10A is commercially used for air separation plant feed purification and liquid hydrocarbon and natural gas sweetening.

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