The effect of main chain length of 2-methylalkane on adsorption onto OH in the micropores of zeolite

Abstract

The adsorption of 2-methylalkanes (propane, butane and pentane) onto ferrierite zeolite was studied by infrared (IR) spectroscopy at temperatures below room temperature. It was found that 2-methylpropane molecules penetrate into micropores only partially, and that only a small fraction of the acidic OH groups available in the micropores interact with the alkyl groups of 2-methylpropane. The interaction is therefore considered to represent interaction between the methyl groups and OH groups located close to the entrance of the micropores. Increasing the carbon number of the main alkyl chain of 2-methylalkanes resulted in a proportional increase in the fraction of acidic OH groups interacting with alkyl groups. Infiltration of n-alkane molecules into the micropores of ferrierite therefore appears to be hindered by methylation of the carbon at the second position. In general, stability was achieved when the longest alkyl chain had entered the micropores of ferrierite, allowing the pore length of ferrierite to be estimated from the extrapolated length of the main alkyl chains. The estimated length of up to 30 nm is consistent with SEM observation.