Molecular sieve properties of the carbonaceous products prepared by chemical dehydrohalogenation of polyvinylidene chloride

Abstract

The molecular sieve properties of the carbonaceous products prepared by chemical dehydrohalogenation of polyvinylidene chloride (hereafter referred to as “carbons”) have been investigated by a heat of immersion study, using the immersional liquid as a molecular probe. Dehydrohalogenation reaction time has been found to play an important role in the carbons' molecular sieve properties. Characterization of the carbons by low temperature nitrogen adsorption was found in some cases to be limited by activated diffusion so the study was supplemented by measuring the adsorption of carbon dioxide at –78 and 0°C. A marked transition was observed in the molecular sieve properties as reaction time during dehydrohalogenation was varied. This was clearly illustrated by a sudden drop in surface area, as measured by low temperature nitrogen adsorption, when entrance into the pores by nitrogen is prevented by an activated diffusion mechanism. The carbons prepared using a small reaction time are shown to have 4–5 A molecular sieve properties which can separate straight and branched chain hydrocarbons. Carbons prepared by longer reaction periods were found to have 3 A molecular sieve properties. These carbons have also been contrasted to the properties of carbons prepared by pyrolysing polyvinylidene chloride.