Elsevier

Chemical Engineering Journal

Volume 165, Issue 1, 15 November 2010, Pages 133-141
Chemical Engineering Journal

Modeling adsorption rate of pyridine onto granular activated carbon

https://doi.org/10.1016/j.cej.2010.09.002Get rights and content

Abstract

The overall adsorption rate of pyridine on a granular activated carbon (GAC) is modeled in this work. The concentration decay curves for pyridine adsorption on GAC were obtained in a rotating basket adsorber. The experimental data were interpreted using a diffusional model that considered external mass transport, intraparticle diffusion, and adsorption on an active site; intraparticle diffusion could be due to both pore volume and surface diffusion. Results showed that the surface diffusion represented more than 93.5% of total intraparticle diffusion, confirming that surface diffusion was the mechanism controlling the overall adsorption rate. The model considering that surface diffusion was the controlling diffusion mechanism, interpreted reasonably well the concentration decay data for pyridine adsorption at different experimental conditions. Results showed that the surface diffusion coefficient increased while raising the temperature and mass of pyridine adsorbed at equilibrium, and was independent on the particle diameter. The external mass transport did not affect the overall rate of pyridine adsorption on GAC.

Introduction

Pyridine is a colorless, volatile, flammable, and toxic organic liquid that gives off an unpleasant odor when present in wastewater. Pyridine is widely used as a solvent in paints and an intermediate in the manufacture of insecticides, herbicides, textiles, fuels, drugs, vitamins, colorants, and adhesives. Due to its wide range of applications, its presence in wastewater has increased over the past years [1], [2], [3]. Pyridine and its derivatives are very toxic for aquatic and human life [2], and their removal is of great consequence to prevent diseases and avoid environmental pollution.

The most common methods for removal of pyridine from aqueous solution encompass biological degradation [4], [5], [6], photocatalysis [7], ozonation [8], membrane separation [9], and adsorption [3], [10], [11], [12], [13]. Adsorption on activated carbon has been widely applied to remove organic compounds from water effluents.

It has been shown that pyridine can be considerably adsorbed on activated carbon from an aqueous solution. Lataye et al. [11] investigated the adsorption of pyridine on rice husk ash and commercial granular activated carbon (GAC) and found that the percentage removal of pyridine was dependent on the solution pH, the maximum percentage removal happened at pH 6.5 with a carbon mass to solution volume ratio of 30 g/L, adsorption equilibrium was attained in 12 h and the adsorption process was endothermic.

Few works have been focused in the overall adsorption rate of pyridine on GAC and in the mass transport mechanisms controlling it. Mohan et al. [3] studied the adsorption kinetics of pyridine on activated carbons manufactured from agricultural waste and reported that the first-order kinetic model satisfactorily fitted the kinetic data.

The main aim of the present work was to study the overall adsorption rate of pyridine from aqueous solution on GAC and to develop a diffusional model to satisfactorily interpret the overall rate of adsorption. Furthermore, the effect of impeller speed, temperature, mass of adsorbent and initial concentration of pyridine upon the overall adsorption rate was analyzed in detail.

Section snippets

Diffusional model

It is well documented that the overall rate of adsorption rate on a porous solid includes the following three simultaneous steps: external mass transport, intraparticle diffusion, and adsorption on an active site; intraparticle diffusion may be due to pore volume diffusion, surface diffusion, or a combination of both mechanisms [14], [15], [16].

In this work, the diffusional model was derived by assuming the following: (i) intraparticle diffusion occurs by pore volume diffusion (Fick's

Adsorbent

The granular activated carbon (GAC) used in this work was manufactured from a bituminous carbon by Calgon, Inc. (Pittsburgh, PA) and is commercially available as F-400. The GAC was sieved to an average particle diameter of 1.02 mm, washed several times with deionized water, dried in an oven at 110 °C for 24 h and stored in a plastic container.

The surface area, pore volume and average pore diameter of GAC, determined by the N2-BET method using a Micromeritics, model ASAP 2010, physisorption

Adsorption isotherm of pyridine on GAC

The effect of pH upon the adsorption of pyridine on activated carbon was investigated by evaluating the adsorption capacity of the GAC at an initial concentration of pyridine of 100 mg/L, T = 25 °C and the pH values ranging from 4 to 12. The pyridine adsorption capacity of the GAC was 16.5, 28.3, 30.3, 31.0, 32.2, 28.8 and 27.7 mg/g at the pH values of 4, 6, 8, 9, 10, 11 and 12, respectively. The maximum capacity of GAC for adsorbing pyridine took place at pH 10; however, the variation of the

Conclusions

In a rotating basket adsorber, the external mass transport did not affect the overall adsorption rate of pyridine on GAC for rotating speeds above 150 rpm.

The PVDM model considering that pore volume diffusion was the controlling mechanism and surface diffusion was negligible, was reasonably well fitted to the experimental concentration decay data. However, Dep values were much greater than the molecular diffusion coefficient of pyridine in water. Hence, the Dep values assessed with the PVDM

Acknowledgements

This study was funded by CONACyT through grant No. CB-2007-01-83375. In addition, FOMIX San Luis Potosi (FMSLP-2008-C02-106795) granted a fellowship to Mr. Raul Ocampo Perez to pursue a research internship in the Department of Inorganic Chemistry, University of Granada, Spain.

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