Molecular sieves, 3 Å

Molecular sieves are crystalline metal aluminosilicates having a 3-dimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size. The 3A form is made by substituting potassium cations for the inherent sodium ions of the 4A structure, reducing the effective pore size to ~3Å, excluding diameter >3Å, e.g., ethane. The 4 to 8-mesh type is normally used in gas-phase applications. Molecular sieves are considered a universal drying agent in polar and nonpolar media.

Molecular sieves have been used for the drying of dimethyl sulfoxide.
They may also be used in the following:

• Synthesis of ecteinascidin 743 (a potential marine-derived antitumor agent).
• Preparation of vanillyl nonanoate (a model capsinoid compound).
• Highly enantioselective Friedel-Crafts alkylation of indoles with nitroalkenes.

Molecular sieves, 3 Å may be used in the following processes:

• As a general-purpose drying agent in polar and nonpolar media.
• Commercial dehydration of unsaturated hydrocarbon streams, including cracked gas, propylene, butadiene, acetylene
• Drying polar liquids such as methanol and ethanol.
• Adsorption of molecules such as NH₃ and H₂O from a N₂/H₂ flow.