Abstract
The chromatographic properties and thermal stability are investigated for the polymeric stationary phase based on the norbornene polymer. It was shown that without additional cross-linking, poly(3-(tributoxysilyl)tricyclononene-7) demonstrates properties similar to liquid chromatographic stationary phases. It was also found to be more thermally stable than previously studied trimethylsilyl- and trimethoxysilyl- derivatives. The long-term heating at 170 °C resulted in an increase of mass transfer rate between stationary and mobile phases which could be observed as a decrease of parameter C of Van Deemter equation. This effect is rather unusual, as the polymeric stationary phases tend in decrease of the layer volume and porosity while ageing. Additionally, the values of thermodynamic parameters of sorption are calculated for the polymeric stationary phase: enthalpy of sorption varied −28 to −37 kJ/mol, entropy change was −41 to −51 J/mol K. The compensation curves were plotted for the alkanes, arenes, and alcohols, and the parameters of compensation plot were calculated, demonstrating the different sorption mechanisms both for hydrocarbons and oxygen-containing compounds, and different classes of organic compounds.
Highlights
Over the past decades, membrane technologies for the separation of vapors and gases have attracted more and more attention: they are used to remove carbon dioxide from flue gases, purify hydrogen in modern power plants, and many papers are devoted to the separation of light hydrocarbons
It is known that the transport of gases in thin polymer layers is often described using the gas permeability value P, which includes both the thermodynamic component and the kinetic component
There is no consensus in the literature on the approaches to determining the thermal stability of chromatographic phases, but all researchers agree that with any method it is important to record such general properties of chromatographic stationary phases, as the values of potential and kinetic efficiency, selectivity, and thermodynamic parameters of sorption of compounds of various classes
Summary
Membrane technologies for the separation of vapors and gases have attracted more and more attention: they are used to remove carbon dioxide from flue gases, purify hydrogen in modern power plants, and many papers are devoted to the separation of light hydrocarbons. During the chromatographic investigation of polymeric stationary phases [10,11,12,13,14] of different natures with similar membrane properties an increase in the retention coefficient k was observed for several samples with sterically hindered structures of polymers such as PIM-1 (see Figure 1) after accelerated thermal ageing. This phenomenon indicates an increase in Henry’s constants and, in solubility of sorbates in the stationary phases. Thermal ageing induces rearrangements of polymer chains, creating more adapted sites for solutes retention and, in turn, changes the number of solute/stationary phase interactions
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