Inverse Gas Chromatography Study of n-Alkane and 1-Alkene Adsorption on Pure-silica LTA (ITQ-29) and CHA

Inverse gas chromatography was used to investigate the Henry adsorption constants, adsorption enthalpies, and entropies of n-alkanes and 1-alkenes up to C12 on the small-pore pure-silica zeolites LTA (ITQ-29) and CHA (Si-CHA). Small hydrocarbons with two adjacent single bonds (such as propane and 1-butene) are shown to experience strong mass transfer limitations due to the small pore window of these zeolites. In contrast, these mass transfer limitations were absent for hydrocarbons with alternating single- and double bonds (such as propylene and butadiene). The extent of this effect decreases with increasing carbon numbers on both zeolites. For Si-LTA, a typical monotonous increase in Henry constant with carbon number is observed for both n-alkanes and 1-alkenes. In contrast, a nonmonotonous increase in Henry constants with carbon number, so-called cage (nestling) effect, is observed for Si-CHA. This effect is observed experimentally for 1-alkenes for the first time. Overall, our study sheds light on remarkable mass transfer limitations and cage effects that affect n-alkanes and 1-alkenes adsorption in these small-pore zeolites.