Enthalpy–entropy compensation effect on adsorption of light hydrocarbons on monolithic stationary phases

Abstract

Enthalpy and entropy of adsorption of light hydrocarbons C1-C4 have been measured for three monoliths of different polarity and for five different carrier gases: helium, hydrogen, nitrogen, carbon dioxide and dinitrogen oxide. Using carrier gas helium the highest values of enthalpy and entropy were observed for monolith based on ethylenedimethacrylate and the lowest values were observed for monolith based on silica, while monolith based on divinylbenzene demonstrated intermediate values. Entropy-enthalpy correlations were observed with carrier gas helium for all thee monoliths and possess similar slope indicating similar adsorption mechanism on all monoliths studied. Comparing different carrier gases entropy-enthalpy correlations within a homological series of solutes were observed for light carrier gases (He, H2 and N2) and were not observed for heavy carrier gases (CO2 and N2O). Instead, entropy-enthalpy correlations for heavy carrier gases were observed with pressure as variable and the higher the carrier gas pressure the lower the values of enthalpy and entropy observed. The observed changes in entropy-enthalpy correlations were explained by competitive adsorption of heavy carrier gas on monoliths.

Enthalpy–entropy compensation for isosteric state adsorption at near ambient temperatures

“…Studies have shown that EEC also occurs during the adsorption of low molecular weight gases on active surfaces (Burevski et al 1991;Fletcher and Thomas 2000;Garrone et al 2008;Korolev et al 2011;Hercigonja and Rakić 2013;Pera-Titus 2016;Zukal et al 2009;Kelut et al 2014), wherein the dependence isn't necessarily linear, as Eq. (1) in unequivocal manner (Fletcher and Thomas 2000;Garrone et al 2008).…”

Fabrication of zeolitic imidazolate framework-8-methacrylate monolith composite capillary columns for fast gas chromatographic separation of small molecules

“…= 34.6 • C, dipole moment = 1.15 D) was the first eluent, followed by . The BuMA-co-EDMA monolith is mainly apolar, but it is more polar than silicate stationary phases [28][29][30], which led to a faster elution of the more polar acetone than the less polar dichloromethane, despite the lower b.p. of the latter.…”

Trace Adsorption of Light Hydrocarbons at Low Temperatures: Influence of Carrier Gas Coadsorption

“…The influence of carrier gases on separation processes in general has been discussed in some publications. − Joseph et al investigated the adsorption of propane, butane, and Freon-12 on an activated carbon from the carrier gases helium, nitrogen, and carbon dioxide at 17.4 °C and ambient pressure . The data show that with increasing adsorption of the carrier gas, a significantly lower loading of the target component is achieved (He < N 2 < CO 2 ).…”

“…Under the assumption that helium hardly adsorbs, Joseph et al described the isotherms from the carrier gas helium as pure component isotherms. Korolev et al determined increasing adsorption enthalpies for a series of carrier gases on a silicalite in the order H 2 > He > N 2 > CO 2 > N 2 O, and helium was selected as the quasi-ideal, best possible carrier gas …”

“…Korolev et al determined increasing adsorption enthalpies for a series of carrier gases on a silicalite in the order H 2 > He > N 2 > CO 2 > N 2 O, and helium was selected as the quasi-ideal, best possible carrier gas. 10 Rufford et al investigated the separation of equimolar mixtures of methane and nitrogen on a microporous activated carbon at −30 and +30 °C. 13 Temperature reduction increased the selectivity of methane over nitrogen, yet significant amounts of nitrogen were adsorbed (0.68 mol/kg at −30 °C and 110 kPa).…”