Adsorption kinetics and performance of packed bed adsorber for phenol removal using activated carbon from dates' stones

Kinetic studies of phenol adsorption on activated carbon (AC) produced from waste dates' stone (DS) were performed using four different AC particle sizes (1.47, 0.8, 0.45 and 0.225 mm) and initial concentration of phenol of 200 and 400 ppm. Breakthrough data for phenol removal using a packed bed of AC produced from DS were collected over a wide range of operating conditions: bed height = 5, 10, 15, 20, and 25 cm, initial phenol concentration = 50, 100 and 150 ppm, flow rate = 23.3-141.5 ml/min and particle size = 0.45, 0.8, and 1.50 mm. It was found that adsorption kinetics of phenol can be very well represented by the pseudo-second order equation. The initial rate of adsorption (h) predicted from the pseudo-second order model, decreased with increasing particle diameter (d(p)) as a result of higher interfacial surface area provided by particles with smaller d(p). The obtained breakthrough curves were very well fitted using an axial dispersion model (correlation coefficient of 0.997 or better), which enabled the determination of the axial dispersion coefficient and Peclet number (Pe). Additionally, breakthrough data were analyzed using the Equivalent Length of Unused Bed (LUB) approach. Defining the Fractional Equivalent Length of Unused Bed (FLUB) as LUB divided by the bed height it was found that FLUB can be correlated with Pe with fairly good accuracy using the relation: FLUB = e(-0.0713(Pe)) for the whole range of experimental parameters explored. It was also shown that the film mass transfer coefficient obtained from the analysis of breakthrough curves for small particle size and short bed at applicable conditions agreed fairly well with that obtained from mass transfer correlation available in literature. (C) 2009 Elsevier B.V. All rights reserved.