Adsorption Isotherm Measurement and Correlation of Toluene and n-Hexane on Activated Carbon in an Aqueous Solution

Thenumber of hazardous waste disposals reported has increased in recentyearsdue to improper
management of chemical generated by chemical and petrochemical industries. Volatile organic
compounds are one of the major pollutants to the environment. Two of the volatile organics
compounds selected for this study are toluene and n-hexane are The adsorption measurement in
aqueous solutions has been carried out by using batch system at 35°C, 55°C and 65°C with the
range of initial concentration between 10 to 200ppm. There are three types of activated carbon
that have been used, which are Granular Activated Carbon (GAC) 2.5mm, Granular Activated
Carbon 0.25mm, and Powder Activated Carbon.
The objectives of this study are to determine the adsorption isotherms of toluene and n-hexane
on activated carbon through the adsorption process, to investigate the effect of temperature on
the adsorption capacity of toluene and n-hexane, and to model the experimental adsorption
isotherm databy using the established adsorption isotherm equations on activated carbon.
The equilibrium concentrations have been analyzed using UV-Vis Spectrophotometer and Gas
Chromatography with Purge and Trap after the solutions were adsorbed for 24 hours.
The toluene adsorption isotherm has the S-shaped form and of type V isotherm based on the
classification of Brunaeur, Deming, Deming and Teller (BDDT). Among the three temperature
conditions, it is found that the adsorption favors the lowest temperature (35°C). This indicates
that adsorption process is exothermic, lower the temperature will shift the adsorption
equilibrium to adsorption rather than desorption. GAC 2.5 mm is found to have the highest
adsorption capacityamongthe others. It is impossible to carry out the experimentwith n-hexane
due to its high volatility. The amount of n-hexane is considered negligible in aqueous solution
and adsorption process does not require.
Freundlich isotherm is the most popular model which is widely used in the correlation of liquid
adsorption. Sips isotherm which is the combination between Langmuirand Freundlichequation
is an alternative model. However, the techniques were not successful with toluene isotherm
measurement.