Comparison between diffusional and first-order kinetic model, and modeling the adsorption kinetics of pyridine onto granular activated carbon

Abstract

In this work, a surface diffusion model (SDM) obtained in a previous work was verified in a wide range of experimental conditions to predict the adsorption kinetics of pyridine on activated carbon. Moreover, the predictions of SDM model were compared with that obtained by using the first-order kinetic model. The results showed that the first-order model adjusted satisfactorily the experimental data. The effect of the stirring speed, mass of pyridine adsorbed, (q_e), and temperature on the rate constant of the first-order model, (k₁), was analyzed and equations were proposed to correlate k₁ as functions of q_e and temperature. Nevertheless, the dependence of k₁ regarding the temperature, stirring speed, and q_e cannot be accurately correlated, indicating that the overall adsorption rate of pyridine on activated carbon is controlled by the intraparticle diffusion. Moreover, it was shown that the rate of adsorption on active site is not controlling the overall adsorption rate. On the other hand, the SDM model provided a much better prediction than the first-order kinetic model. The surface diffusion coefficient can be readily estimated from a correlation recommended in this work, whereas the value of k₁ could not be predicted for some of the experimental conditions studied in this work.

Keywords:

• Activated carbon
• Adsorption rate
• Diffusional model
• Kinetic model
• Pyridine

Acknowledgment

This work was funded by Consejo Nacional de Ciencia y Tecnologia, CONACyT, Mexico, through grant numbers INFR-2012-01-188381, CB-2012-02-182779, and MOD-ORD-12-2013PCI-0721113.