The following data were obtained from a single-solute isotherm experiment evalua

Question

The following data were obtained from a single-solute isotherm experiment evaluating the adsorption of methyl tert-butyl ether (MTBE) on an activated carbon: 4. Mass of activated carbon in isotherm bottle (mg) Aqueous-phase MTBE conc. at equilibrium (ug/L): 0 12.6 25.4 63.4 126.7 190.2 253.5 380.1 864 498 329 131 48.0 25.1 15.3 8.20 Each isotherm bottle was filled headspace-free with 254 mL of water and received the same mass of MTBE a) Prepare an isotherm plot and determine the Freundlich isotherm parameters Kf in units of (mglg)(L/m) and 1/n. Comment on this result. How do these results compare to published values? Does MTBE sorb strongly or weakly compared to other adsorbates? b)

Explanation / Answer

a) The Freundlich isotherm is given by

Qe = Kf Ce1/n

Taking logarithms on both sides, we get

Ln qe = lnKf + 1/n LnCe

Graphs are drawn between ln qe versus ln Ce ,slope is 1/n and intercept is LnKf

Ln qe= -0.812 ln Ce +0.7336

Comparing this equation with the Freundlich adsorption isotherm equation

Ln qe = ln Kf + 1/n ln Ce

Slope,1/ n = -0.812 & intercept, ln Kf = 0.7336

Kf (L/gm)

n

R2

2.08

-1.2315

0.8614

b) Actually the 1/n value should be between 0 and 1, but we got that as -0.812. order(n) cannot be negative. So this is a weak adsorption.

Kf (L/gm)

n

R2

2.08

-1.2315

0.8614

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