Molecular sieves are crystalline metal aluminosilicates having a threedimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed this network by heating to produce uniform cavities which ively adsorb molecules of a specific size. A 4 to 8-mesh sieve is normally used in gasphase applications, while the 8 to 12-mesh type is common in liquidphase applications. The powder forms of the 3A, 4A, 5A and10X, 13X sieves are suitable for specialized applications. Long known for their drying capacity (even to 90癈), molecular sieves have recently demonstrated utility in synthetic organic procedures, frequently allowing isolation of desired products condensation reactions that are governed by generally unfavorable equilibria. These synthetic zeolites have been shown to remove water, alcohols (including methanol and ethanol), and HCl such systems as ketimine and enamine syntheses, ester condensations, and the conversion of unsaturated aldehydes to polyenals. Specifications: 1) 3A (0.6 K2O: 0.40 Na2O: 1 Al2O3: 2.0?.1 SiO2: x H2O) Major applications: 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 a N2/H2 flow; considered as a general-purpose drying agent in polar and nonpolar media 2) 4A (1 Na2O: 1 Al2O3: 2.0?.1 SiO2: x H2O) Major applications: preferred for static dehydration in closed liquid or gas systems, such as in packaging of drugs, electric components and perishable chemicals; water scavenging in printing and plastics systems and drying saturated hydrocarbon streams; adsorbed species include SO2, CO2, H2S, C2H4, C2H6, and C3H6; generally considered as a universal drying agent in polar and nonpolar media 3) 5A (0.80 CaO: 0.20 Na2O: 1 Al2O3: 2.0?.1 SiO2: x H2O) Major applications: separation of normal paraffins branched-chain and cyclic hydrocarbons; removal of H2S, CO2 and mercaptans natural gas; molecules adsorbed include nC4H10, nC4H9OH, C3H8 to C22H46, and dichlorodifluoro-methane (Freon 12? 4) 13X (1 Na2O: 1 Al2O3: 2.8?.2 SiO2: xH2O) Major application