Inverse gas chromatography of chromia, Part I: Zero surface coverage

Abstract

The surface properties of the solid obtained from colloidal chromia were investigated by inverse gas chromatography (IGC), at zero surface coverage conditions. The solid samples I dried at 423 K and II heated at 1073 K in the amorphous and crystalline form, respectively, were studied in the temperature range 383-423 K. The dispersive components of the surface free energies, enthalpies, entropies, and the acid/base constants for the solids were calculated from the IGC measurements and compared with the data for a commercially available chromia (III). Significantly lower enthalpies and entropies were obtained for cyclohexane on solid II and chloroform, highly polar organic, on solid I. The dispersive contributions to the surface energy of solid II and III were similar, but much greater in the case of solid I. All the sorbents had a basic character, with the KD/KA ratio decreasing in the order I gt II gt III. The retention and resolution in the separation of a vapour mixture of C5-C8 n-alkanes on the three substrates were different. A rapid separation was observed on solid II and an enhanced retention on solid I. Generally, the heated chromia (II) exhibited diminished adsorption capacity, and enhanced homogeneity of the surface.

Ispitivana su površinska svojstva čvrste faze koloidnog hrom(III)-oksida metodom inverzne gasne hromatografije (IGC) pri nultoj prekrivenosti. Čvrsta faza sola sušena na 423 K (uzorak I) u amorfnoj, i žarena na 1073 K (uzorak II) u kristalnoj formi, je ispitivana u temperaturnom opsegu 383-423 K. Iz IGC merenja izračunate su vrednosti disperzivne komponente površinske slobodne energije, entalpije, entropije i kiselo/baznih konstanti, za uzorke I i II i upoređene sa vrednostima za komercijalni uzorak hrom(III)-oksida (III). Značajno manje entalpije i entropije su dobijene za cikloheksan na II, i za veoma polarnu supstancu, hloroform, na I. Doprinos disperzivne komponente površinske energije je sličan za II i III, a dosta je veći za I. Površine sva tri sorbenta pokazuju bazni karakter sa smanjenjem KD/KA odnosa u smeru I gt II gt III. Retencija i rezolucija kod razdvajanja smeše C5-C8 n-alkana su različite, sa brzom separacijom na II, i pojačanim zadržavanjem na I. Žareni uzorak je pokazao smanjeni adsorpcioni kapacitet i ima homogeniju površinu.