Evidence for isopentane adsorption in the pores of 5A zeolite

Adsorption of isopentane and n-pentane on 5A zeolite was investigated using a microbalance at temperatures between 50 and 420 degreesC (P-alkanes = 97 kPa). Analysis of the the adsorbed phase shows that, despite the well-know n geometric selectivity of 5A zeolite, isopentane enters the pores and rema ins trapped in the alpha cages. At saturation at 50 degreesC, all the alpha cages of the 5A zeolite are occupied by three isopentane molecules. Isopen tane molecules are completely removed from the zeolite pores by an adequate vacuum treatment at the adsorption temperature. At high temperature (T gre ater than or equal to 250 degreesC), trapped isopentane molecules ave trans formed into "coke" (oligomers and aromatic compounds) by successive reactio ns (cracking, polymerisation, cyclisation and hydrogen transfer) on the aci d sites of 5A zeolite. The "coke" molecules, blocked inside the alpha cages , limit the desorption of isopentane (and n-pentane).