Molecular sieves can be defined as 3D structure of crystalline metal aluminosilicates which mostly perform on size exclusion principle. Molecular sieves are used as adsorbent for gases and liquids and often function as desiccant. Generally they are of many types 3A, 4A, 5A, 10X, 13X and used accordingly in different industries depending on adsorption efficiency and adsorbent requirements. Moleular sieves are available in different forms- beads, pellets and powder. Though pellets have bigger surface area but beads are readily used due to less breakage and less dust. Because of the high efficiency of molecular sieves, they are widely used in petroleum and chemical industry to remove moisture. It is also used in API and pharma companies for packaging because of its excellent drying property.
In petroleum industry main impurities are carbon dioxide, hydrogen sulphide, carbon dioxide, water and mercaptan. For removal of mercaptan normally 13X molecular sieve is used at a high temperature of 200C to 315C. The petroleum product is passed through a bed of zeolite for a certain time period and contaminants are removed effectively. After heating, a cooling period is required to reduce the temperature of molecular sieve.
13X composes 1 Na2O: 1 Al2O3 : 2.8 ± 0.2 SiO2 : xH2O; which has crystal form and has more effective pore opening and adsorption efficiency than A type sieves. LPG, natural gas and other liquid hydrocarbons contain high amount of mercaptans which is necessary to remove to obtain pure product. 13X has application in gas drying, desulphurization, air plant feed purification and natural gas sweetening.
Molecular Sieves 