Estimating the standard free energy of formation of zeolites using the polymer model

• Published in: Microporous and mesoporous materials Vol. 27; no. 1; pp. 41 - 47
• Main Authors: Mattigod, S.V., McGrail, B.P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-01-1999; Elsevier
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; Polymer model; Standard free energy of formation; Surface physical chemistry; Thermodynamics of zeolite; Zeolites: preparations and properties; Polymer model; Standard free energy of formation; Thermodynamics of zeolite; Thermodynamic model; Theoretical study; Formation free energy; Zeolite; Thermodynamic properties; Heat of formation; Molecular sieve
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(98)00228-5

The standard free energies of formation of a number of zeolites were estimated using the polymer model developed previously for smectites by Sposito. The estimates made with the polymer model were on average within 19
kJ
mol
−1 (0.28%) of the experimental values for zeolites; this compares with the values estimated by the methods of LaIglesia and Aznar and of Chermak and Rimstidt which differed from the experimental values on average by approximately 27
kJ
mol
−1 (0.40%) and 32
kJ
mol
−1 (0.47%) respectively. The values predicted by the polymer model for dehydrated zeolites were within 28
kJ
mol
−1 (0.3%) of the experimental values, whereas the other two methods generate estimates of free energies of formation values that differed on average by 89
kJ
mol
−1 (1.28%) and 107
kJ
mol
−1 (1.59%) from the experimental values. These comparisons indicate that the polymer model, formulated specifically for a class of silicate minerals such as zeolites, always typically provides a better estimate of the standard free energy values than general models for all silicate minerals which contain a number of ad hoc assumptions. Better estimates provided by the polymer model can be attributed to the principle that the free energy changes associated with the formation of condensation polymers, such as zeolites, are related principally with the free energy changes associated with the relative change in coordination of exchangeable cations as they transfer from reactant hydroxide sites to exchangeable sites.