A FUNDAMENTAL ANALYSIS OF THE ISOTHERM FOR THE ADSORPTION OF PHENOLIC-COMPOUNDS ON ACTIVATED CARBON

The Freundlich isotherm has been widely used in the design of activate d-carbon adsorption processes. The isotherm is easy to use and is appl icable to a wide spectrum of organic compounds and adsorbents. The mai n drawback for the isotherm is that it is an empirical formula requiri ng experiments to determine its coefficients. To alleviate this drawba ck, a procedure is developed in this study to correlate the Freundlich coefficients-with the basic properties of three components involved i n adsorption (adsorbate, adsorbent and solvent). Chloro-and nitropheno ls were used as the test adsorbates, and granular activated carbon (GA G) was used as the adsorbent. The isotherm data showed that the percen tage of the GAC pore surface covered by phenolic molecules was a bette r measurement for the amount adsorbed than the traditional mass-based solid concentration. A solution concentration normalized with respect to the solubility of the phenolics was used to account for the effects of phenol-water interactions. Isotherms of surface coverage versus no rmalized concentration conformed very well to a modified Freundlich mo del. The modified Freundlich exponent (l/n') was found to have an inve rse linear relationship with the electron density of phenolics calcula ted from molecular orbital theory. The correlation will allow the pred iction a priori of l/n' from the molecular structures of the adsorbate and adsorbent. (C) 1997 Elsevier Science B.V.