Ion-exchange Modification of Zeolite LTA

In the unit cell there are 12 sodium cations, of which 8 are located at the eight 6-rings, and the remaining four cations are near the three 8-ring windows. That is, one of the 8-membered rings is possibly occupied by two sodium cations. 

In the dehydrated 5A zeolite, four of the eight 6-membered rings are occupied by Na+ ions whereas the other four are occupied by Ca2+ cations. The Ca2+ cations are located on the plane of the 6-ring, and the Na+ cation is about 0.4 A above the 6-ring plane, pointing toward the a-cage. This phenomenon indicates that, under there circumstances, the variation of the zeolite pore size depends on the exchange of Na+ by Ca2+. 

From these results, it is concluded that, after exchange with Ca2+, zejolite LTA can selectively adsorb n-butanol and higher normal alcohols, n-butene and higher normal alkenes, propane and C4 Ci4 normal alkanes, and cyclopropane, etc., which cannot be adsorbed by zeolite 4A. On the other hand, the presence of divalent Ca2+ promotes the adsorption selectivity of 5A zeolite for polar molecules and other unsaturated compounds. 

Pore size is not the only parameter that affects adsorption. Molecules containing polar groups such as -OH, CO, -NH2 and polarizable groups such as CO=CO and C6H5- strongly interact with the surface of zeolites the cations in the zeolites generate 

Adsorbate Temperature/°C Pressure (mmHg) 5A Silica gel Active carbon 

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