Applications of zeolites

The principal applications of zeolites are discussed below.

 

1. Catalysts and catalyst supports
   
   Acidity and shape –selective properties of zeolites play major roles in their use as catalysts to produce premium quality fuels and chemicals. Zeolites b ecause of their acidity find applications in catalytic cracking, isomerization, alkylation and aromatization reactions. Fluidized catalytic cracking is the largest and oldest application of zeolite catalysts. Medium pore zeolites are being widely used in conversion of light hydrocarbons to monocyclic aromatics, because of their ability to selectively perform these reactions, while minimizing coke formation. For same reactions, when small pore zeolites are used, no aromatics are produced and severe operating conditions are required, whereas large pore zeolites produce heavy aromatics and deactivate rapidly. The major advantage of large pore molecular sieves, developed recently, is their ability to crack larger molecules, such as present in heavy petroleum residue, more efficiently. Major commercial catalytic processes using zeolites are summarized in Table 2.
   
   Table 2. Commercial catalytic processes using zeolite catalysts
   
   
   
   

   In addition to the well established commercial processes some other new applications of zeolites are being developed. Conversion of n-hexane and n-heptane to benzene and toluene is carried out on a PtBa/Zeolite L catalyst while, isomerization of C₅/C₆ is done with Pt/mordenite /alumina catalyst. For ZSM-5 catalysts various applications are developed. For example, alkylation of benzene and toluene to form high octane alkyl aromatics, methanol to gasoline, methanol to alkene, toluene disproportionation to p-xylene, or selective catalytic reduction of NO has been reported with ZSM-5 or modified ZSM- 5 catalysts.
   

2. Selective adsorbents and drying agents
   
   Zeolites have unique ability to adsorb water while rejecting larger molecules. For many applications they are the best available drying agents. Used in drying air, natural gas, organic solvents and refrigerants .
   
   
3. Separation and purification of gasses and liquids
   
   Zeolites are used in purification of gases and hydrocarbon liquids. The 5A (CaA) and 13X(NaX) zeolites have been the most commonly used sorbents for air separation. The typical commercial 5A used for air separation is made by exchanging ~70% of the Na⁺ in NaA by Ca²⁺ ions. The nitrogen is preferentially adsorbed on the zeolite.