کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4907202 | 1426197 | 2018 | 10 صفحه PDF | دانلود رایگان |
- Adsorption of lead(II) and phenol on carbons at 303Â K, 333Â K and 353Â K was studied.
- Difference between calculated enthalpies and direct calorimetric data was found.
- Calorimetric enthalpies correspond better to mean isosteric enthalpies.
Comparison among adsorption enthalpies of thermodynamic analysis and these of direct calorimetric measurements is reported for sorption of lead(II) and phenol on natural coals and activated carbon. Thermodynamic calculations came out from developments of equilibrium adsorption isotherms recorded at 303 K, 333 K and 353 K. Standard adsorption enthalpies ÎH0 were calculated from temperature dependences of equilibrium constants of adsorption Ka, with values of Ka being evaluated directly from experimental data and from fitted courses of the Langmuir and Freundlich isotherms. In addition, dependences of isosteric enthalpy on surface coverage were evaluated. Values of the exothermic enthalpies (ranging from â6 kJ molâ1 to â50 kJ molâ1) were obtained, however exclusive endothermic effect for lead(II) adsorption on a sample of natural coal (24 kJ molâ1) was also ascertained. Direct calorimetric measurements using flow and immersion techniques then proved that all the studied adsorptions proceed with exothermic effects from â2 kJ molâ1 to â42 kJ molâ1. It was found that experimental adsorption enthalpies correspond better to mean isosteric enthalpies in the interval 0-1 mol kgâ1 of the surface coverages than to the standard adsorption enthalpies ÎH0 of the thermodynamic calculations.
Journal: The Journal of Chemical Thermodynamics - Volume 116, January 2018, Pages 97-106