Separations analysis fundamentals - Principles of Chemical Separations with Environmental Applications - page 50

Table 3.1 Selected values of the Langmuir-isotherm parameters (Equation 3.14) for adsorption
of various organic compounds on PAC [8].

Compound a (mmol / g) K (L / mmol) Compound a (mg / mg) K (L / mg)

i-propanol 0.79 0.123 Aniline 0.108 0.177

n-propanol 0.92 0.158 Benzyl alcohol 0.158 0.176

i-butanol 1.04 0.482 Benzaldehyde 0.210 0.170

n-butanol 1.06 0.954 2-naphthol 0.345 0.643

n-pentanol 2.85 0.858 o -toluidine 0.186 0.256

n-hexanol 3.21 1.35 p -toluidine 0.186 0.256

Propionaldehyde 1.21 0.107 o -anisidine 0.240 0.417

Butyraldehyde 1.19 0.745 m -anisidine 0.185 0.338

Ethyl acetate 1.54 0.531 p -anisidine 0.248 0.505

i-propyl acetate 1.66 0.954 Anisaldehyde 0.305 0.468

Propyl acetate 7.13 0.153 Salicylaldehyde 0.240 0.417

Butyl acetate 10.7 0.166 Vanillin 0.375 1.110

Methyl ethyl ketone 1.00 0.526 Pyridine 0.055 0.154

Diethyl ketone 1.67 0.911 2-methylpyridine 0.106 0.262

Methyl i-butyl ketone 1.95 1.44 o -cresol 0.240 0.417

2-chlorophenol 0.272 0.405

Nitrobenzene 0.310 0.230

o -methoxyphenol 0.296 0.400

Quinaldine 0.296 0.400

Pyrrole 0.030 0.152

Indole 0.240 0.417

The Langmuir isotherm is based on the following assumptions:
1 The adsorbent surface has a fixed number of identical individual “spaces” in which an
adsorbate molecule can reside.
2 The adsorbent surface will accumulate only one layer of adsorbate molecules.
3 Reversible chemical equilibrium is assumed to exist.
When KC e 1, the Langmuir isotherm reduces to a linear form analogous to Henry's

Law. Sorbate-sorbent pairs that display a Type I isotherm can use the Langmuir equation.

Example 3.2: determining Langmuir-isotherm constants

Problem:
Laboratory tests were conducted on an aqueous stream containing 50 mg L phenol.

Various amounts of powdered activated carbon (PAC) were added to four containers
each containing 1 liter of the wastewater. When equilibrium was reached, the phenol
concentration in each container was measured and is tabulated below. Determine
the Langmuir-isotherm constants for this system and calculate the amount (mass of
carbon required) required to reduce the phenol concentration to 0.10 mg

/

/ L for a

1-liter sample.