STUDY OF TRACE CONTAMINANTS CO-ADSORPTION DYNAMICS ON A FIXED BED OF ACTIVATED CHARCOAL USING GAS CHROMATOGRAPHIC TECHNIQUE

[摘要] Trace contaminant adsorption on activated charcoal, Barnebey Cheney type 208, was studied using a gas chromatogram. Chromatograms were obtained experimentally by eluting pulses of different volumes through charcoal columns, using nitrogen as the carrier gas. Experimental data are reported for methanol, ethanol, 2-propanol, 1-butanol, toluene and trichloroethylene at 50, 100 and 150 C. For the alcohols and trichloroethylene, the following cases were considered: adsorption on (a) a clean bed, (b) a bed having the same compound adsorbed on it, and (c) a bed having toluene preadsorbed on it. All compounds were irreversibly adsorbed, the amount increasing with an increase in molecular weight and decreasing at higher temperatures.The elution curves have pronounced asymmetry, with a sharp leading edge and a long trailing edge. The average retention time varied with the pulse volume injected. The presence of toluene preadsorbed on the charcoal reduced the average retention time of each contaminant. The observed data are interpreted by a model that takes into account the nonlinearity of the adsorption isotherm at low surface coverages and axial dispersion. The adsorption isotherms are well represented by the Dubinin-Radushkevich-Stoeckli (DRS) characteristic curve equation. The micropore volume of charcoal was found to depend on the adsorbate used as a molecular probe. Effective axial dispersion coefficients were calculated from the first moments of the chromatographic peak. The effective axial dispersion coefficient was correlated with the superficial velocity and molecular diffusivity.The breakthrough times of toluene vapor at 100, 150 and 200(DEGREES)C were obtained by subjecting the charcoal column to an inlet containing a fixed vapor concentration. Up to c(,z)/c(,0) = 0.05, the breakthrough time varied linearly with {A + B ln(c(,z)/c(,0))}. The intercept A, obtained from a linear regression analysis, was found close to t(,0.5), the time to reach 50% of inlet concentration. The predicted values based on the absorption isotherm equation, compared well with those obtained experimentally, the maximum deviation being 30%. The pseudo first order rate constant was calculated from the slope B. This rate constant was correlated with superficial velocity and temperature.

[发布机构] Rice University

[效力级别] engineering