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Molecular Sieves & Zeolites

 

Molecular Sieves

SiliaDry molecular sieve and zeolites

A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecules small enough to pass through are adsorbed, while larger molecules are not. It is different from a common filter in that it operates on a molecular level. Molecular sieves are mostly used in the petroleum industry, for the purification of gas streams.

Molecular sieves come in many different forms: as microporous, mesoporous or macroporous cavities.

> see molecular sieves product range and prices

 

Zeolites

Zeolites are a microporous form of molecular sieves, with aluminosilicates as a skeletal composition and pore diameters less than 2 nm (or 20 Å).

They are capable of adsorbing nearly 22 % of their weight in water and are largely used for gas drying applications.

When developing applications for Zeolites, one must keep in mind that there are nearly 40 different types of Zeolites with different physical specifications, chemical properties and composition.

Particle density, molecular pore size, crystal structures are only few differences that can discriminate one type of Zeolite from another.

It is imperative to specifically know what type of Zeolite is needed for one’s application.

 

Most Popular Applications of Zeolites

Pore Diameter Most Popular Applications
Type 3 Å [see 3 Ångström molecular sieves]
  • Nominal Pore Diameter: 3 Å
  • Molecules Excluded: > 3 Å effective diameter (e.g.: C2H6)
  • Base: Alumina - Silicate
  • Cation: Potassium (K+)
  • Type 3 Å will adsorb molecules having a critical pore diameter of less than 3 Å. e.g.: Helium (He), Hydrogen (H) and Carbon Monoxide (CO).
  • Preferred adsorbent for the commercial dehydration of unsaturated hydrocarbon streams such as cracked gas, propylene, butadiene and acetylene.
  • Essential for storing Electron Microscopy specimen stubs (SEM, TEM, REM, STEM).
  • Recommended for drying unsaturated hydrocarbons and highly polar compounds such as methanol and ethanol.
  • Particularly effective in dehydrating the inner space of insulating glass windows as well as refrigerant gases.
  • Potassium form of Zeolite.
Type 4 Å [see 4 Ångström molecular sieves]
  • Nominal Pore Diameter: 4 Å
  • Molecules Excluded: > 4 Å effective diameter (e.g.: C3H8)
  • Base: Alumina - Silicate
  • Cation: Sodium (Na+)
  • Preferred adsorbent for static dehydration in a closed gas or liquid system. Will adsorb molecules having a critical pore diameter of less than 4 Å. (e.g.: Methanol, Ethane and Propane).
  • Typically used in regenerable drying systems to remove water vapor or contaminants that have a smaller critical diameter than 4 Å.
  • Used as a static desiccant in household refrigerating systems, packaging of drugs, electronic components, perishable chemicals and as a water scavenger in paint and plastic systems.
  • Also used commercially in drying saturated hydrocarbon streams (Ethane, Butane).
  • Sodium form of Zeolite.
Type 5 Å [see 5 Ångström molecular sieves]
  • Nominal Pore Diameter: 5 Å
  • Molecules Excluded: > 5 Å effective diameter
  • Base: Alumina - Silicate
  • Cation: Calcium (Ca+)
  • Typically used to separate isomeric alkanes (less than 5 carbons) from branched-chain and cyclic hydrocarbons through a selective adsorption process.
  • Will adsorb those molecules having a critical pore diameter of less than 5 Å (e.g.: Methanol, Ethane and Propane).
  • Calcium form of Zeolite.
Type 10 Å & 13 Å [see 10 Ångström molecular sieves and 13 Ångström molecular sieves]
  • Nominal Pore Diameter: 10 - 13 Å
  • Molecules Excluded: > 10 - 13 Å effective diameter
  • Base: Alumina - Silicate
  • Cation: Sodium (Na+)
  • Preferred molecular sieve adsorbent for dynamic dehydration in a closed gas or liquid system.
  • Used commercially for general gas drying, air plan feed purification (simultaneous removal of H2O and CO2) and liquid hydrocarbon (C5+) and natural gas sweetening (H2S and mercaptan removal).
  • Ensure dryness of medical and air compressor systems.
  • All molecules which can be adsorbed on Molecular Sieves 3 Å, 4 Å and 5 Å can be adsorbed on type 13 X. In addition, 13 X can adsorb molecules of larger critical diameters, such as aromatics and branched-chain hydrocarbons.
  • A modified sodium form of Zeolite.