M.-S. Chou and J.-H. Chiou (J. Envir. Engrg., ASCE, 123, 437(1997)) have studied the

Chapter 25, Problem 25.34

(choose chapter or problem)

M.-S. Chou and J.-H. Chiou (J. Envir. Engrg., ASCE, 123, 437(1997)) have studied the effect of moisture content on the adsorption capacities of granular activated carbon (GAC, Norit PK 13) for the volatile organic compounds (VOCs) normal hexane and cyclohexane in air streams. The following table shows the adsorption capacities (qwater = mwater /mGAC) of GAC for pure water from moist air streams as a function of relative humidity (RH) in the absence of VOCs at 41.5C. RH 0.00 0.26 0.49 0.57 0.80 1.00 qwater 0.00 0.026 0.072 0.091 0.161 0.229 The authors conclude that the data at this and other temperatures obey a Freundlich type isotherm, qwater = k(RH)1/n. (a) Test this hypothesis for their data at 41.5C and determine the constants k and n. (b) Why might VOCs obey the Langmuir model, but water the Freundlich model? (c) When both water vapour and cyclohexane were present in the stream the values given in the table below were determined for the ratio rVOC = qVOC/qVOC, RH=0 at 41.5C. RH 0.00 0.10 0.25 0.40 0.53 0.76 0.81 rVOC 1.00 0.98 0.91 0.84 0.79 0.67 0.61 The authors propose that these data fit the equation rVOC = 1 qwater. Test their proposal and determine values for k and n and compare to those obtained in part (b) for pure water. Suggest reasons for any differences.