Sorption of carbon dioxide by zeolite X exchanged with Zn2+ and Cu2+

✍ Scribed by A Khelifa; Z Derriche; A Bengueddach

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 327 KB
• Volume: 32
• Category: Article
• ISSN: 1387-1811
• DOI: 10.1016/s1387-1811(99)00107-9

✦ Synopsis

The Gibbs energy change, isosteric heat and entropy of CO 2 , sorbed at intervals of approximately 30 K between 273 and 393 K in X-type zeolites exchanged with Zn2+ and Cu2+ cations to different degrees, are investigated. The best fit of sorption isotherm data is obtained with the Langmuir model. The NaX zeolite revealed the highest sorption affinity which decreases with increasing level of exchange. Analysis of the isosteric heat and differential entropy curves shows that the Zn(x)X samples present a heterogeneous profile, only at a greater extent of Zn2+ exchange and at low coverages. The most likely explanation of this is the appearance of Zn2+ in the supercages on sites II accessible to sorbed CO 2 . In contrast, the X zeolites containing Cu2+ cations do not exhibit an energetic heterogeneity at any exchange degree throughout the entire coverage range. Such a behaviour could be ascribed to the formation of inactive (CuMOMCu)2+ entities within zeolitic cavities. Furthermore, integral entropies of zeolitic CO 2 are less than the entropy of liquid CO 2 , suggesting reduced freedom in the sorbed phase.