Study of adsorption kinetics by volumetric method

Abstract

There is a huge demand for cleaner energy to reduce the anthropogenic emissions of carbon dioxide into the atmosphere. With that in mind, a theoretical framework is proposed to study physical gas adsorption of carbon dioxide on activated carbon, “Maxsorb-III”, at isothermal conditions to establish its experimental fit with different isotherm models. The overarching study of gas adsorption in this report are twofold; firstly, adsorption at equilibrium conditions and secondly, adsorption kinetics.

Material characterisation techniques such as Scanning Electron Microscopy and Transmission Electron Microscopy were used to analyse the structures and features of the porous adsorbent, Maxsorb-III. For the preparatory phase of this study, the previous experimental apparatus were dismantled and volume calibration was performed, to use in the analysis. In addition, resistance temperature detectors and pressure transducers calibration were executed to ensure the precision and accuracy of these instruments.

Consequently, gas adsorption experiments (for study at equilibrium conditions) were conducted from 288.15 K to 328.15 K, for pressures up to 25 bar, to determine the equilibrium uptakes. The empirical parameters of Dubinin-Astakhov and Langmuir isotherm models used were obtained from the experimental data by means of regression analysis. The Langmuir isotherm proved to be the best fit providing a low RMSE of 0.788% and high RSQ of 99.735%. However, another isotherm model, namely A. isotherm, proposed by Chakraborty, A. (2012) which is yet to be published, has proved to be an even better fit and able to counter the limitations faced by both Langmuir and Dubinin-Astakhov isotherm models.

For the study on adsorption kinetics, adsorption experiments are conducted at 288.15 K and 298.15 K under high pressure. The experimental uptake data obtained was used to establish its experimental fit with the Linear Driving Force model. Both the Langmuir and Dubinin-Astakhov isotherm models were not used in adsorption kinetics experiments as it was imprecise in predicting gas uptake at rapid temperature transients. In conclusion, the Linear Driving Force model was found to be in good agreement with the experimental uptake data as a function of time.