This article presents the results of a correlation that accurately estimates the adsorption capacity of activated carbon for removing oxygenated petrochemicals in water. Adsorption on activated carbon is an effective method for water purification.
Results use the Freundlich equation for adsorption capacity as a function of the compound concentration in aqueous liquid. The correlation constants are presented in a tabular format, which makes for rapid engineering use. Correlation and experimental results agree favorably.
Previous articles (OGJ, May 5, 2003, p. 80; Apr. 12, 2004, p. 66) developed correlations for the adsorption capacity of activated carbon for alkyl benzenes in water and chlorinated petrochemicals in water.
Background
Physical and thermodynamic property data for oxygenated petrochemicals are especially helpful to engineers and scientists in industry. In particular, capacity data for adsorption of oxygenated petrochemicals on activated carbon are increasingly important in engineering and environmental studies because of more stringent environmental regulations involving water.
The results in this article are suitable for engineering and environmental analyses. Capacity data from the correlation, for example, are useful in the engineering design of carbon-adsorption systems to remove oxygenated petrochemicals from water.
Correlation
The correlation for adsorption capacity of activated carbon (Calgon Carbon Corp.'s Filtrasorb 400) as a function of the compound concentration in water is based on the Freundlich equation (see equations box).
Table 1 shows the correlation constants, K and 1/n, for various oxygenated petrochemicals. The tabulation is based on both experimental and estimated values. Table 1 is arranged by carbon number to make it easy to use for quickly locating data using the chemical formula.
Table 1 shows the adsorption capacity at concentrations of x minimum, 10 ppm (wt), and x maximum in water.
Fig. 1 shows a comparison of correlation and experimental data for a representative compound, 3-heptanone. Adsorption capacity is at typical conditions encountered in water pollution control. The graph shows a favorable agreement between correlation and experimental data.
Estimation equation
In preparing the correlation, we conducted a literature search to identify source publications relative to experimental data and property values for estimates.1-4 We used appropriate data to create a database of adsorption-capacity values at different concentrations for which experimental data are available. The database also served as a basis to check the accuracy of the correlation.
After data collection, we estimated adsorption capacity for the remaining compounds. For oxygenated petrochemicals(alkyl alcohols, aldehydes, acetates, and ketones), we used Equation 2, which is a modified version of an equation originally developed by Arbuckle,1 for estimates.
For Equation 2, the data for density, liquid molar volume, and solubility in water are from data compilations by Yaws.3 4
Fig. 2 shows adsorption capacity as a function of the adjusted adsorption potential (Polyani theory) for oxygenated petrochemicals. The graph is based on data for alkyl alcohols, aldehydes, acetates, and ketones. The equation agrees favorably with experimental data.
In general, the literature only contains limited experimental data for adsorption capacity of activated carbon for organic compounds in water at concentrations of several hundred ppm. Arbuckle did present concentrations in the range of several hundred ppm for 22 oxygenated petrochemicals.1
Due to the limited experimental data, estimates in Table 1 are rough approximations useful for initial analyses. If initial feasibility studies using the tabulated values are favorable, we recommend a follow-up experimental determination of equilibrium adsorption capacity.
Example calculation
Water from an industrial process contains 110.2 ppm (wt) of ethyl butyl ketone (3-heptanone); estimate the adsorption capacity of activated carbon for removing the compound from water at ambient conditions.
Substitution of the coefficients from Table 1 and concentration into the correlation equation yields:
log10 Q = log10 (7.25) + 0.30 log10 (110.2) = 1.473
Q = 101.473
Q = 29.72 g ethyl butyl ketone/100 g carbon.
References
1. Arbuckle, W.B., Environmental Science & Technology, Vol. 15 (1981), No. 7, p. 812.
2. Sontheimer, H., Crittenden, J.C., and Summers, R.S., Activated carbon for water treatment, 2nd Edition, Deutsche Vereinigung des Gas und Wasserfaches-Forschungsstelle, Engler-Bunte-Institut, University of Karlsruhe, Germany, 1988.
3. Yaws, C.L., Chemical Properties Handbook, New York: McGraw-Hill Cos., 1999.
4. Yaws, C.L., Yaws handbook of thermodynamic and physical properties of chemical compounds, electronic edition, www.knovel.com, Knovel Corp., Norwich, NY, 2003.
The authors
Carl L. Yaws (yawscl@ HAL.LAMAR.EDU) is professor of chemical engineering at Lamar University, Beaumont, Tex. His research interests include technology development, thermodynamic and transport property data, environmental engineering, and process simulation. Yaws holds a BS in chemical engineering from Texas A&I University, Kingsville, and an MS and PhD in chemical engineering from the University of Houston. He is a registered professional engineer in Texas.
Rafael Tadmor is assistant professor of chemical engineering at Lamar University, Beaumont, Tex. His research interests include technology of surfaces, chemical engineering, environmental engineering, and bioengineering. Tadmor holds a BS and MS from Technicon-Israel Institute of Technology, Haifa, and a PhD from Weizmann Institute of Science, Rehovot, Israel, all in chemical engineering.
Prasad K. Narasimhan is graduate student in chemical engineering at Lamar University. His research interests include thermodynamics, environmental engineering, and process simulation. He holds a BS in chemical engineering from Siddaganga Institute of Technology, India