Moisture effects on the phenanthrene adsorption capacity by carbonaceous materials

Considering that phenanthrene (Phe) is one of the main pollutants in the waste flue gases from organic material combustion, the aim of this paper is to examine the use of carbon materials to remove low concentrations of Phe from a hot exhaust gas stream as a function of its moisture content. Adsorption isotherms were measured with steam and Phe concentrations in the ranges of 0-20% and 0.02-3.2 ppmv, respectively. Three classic models [Langmuir, Freundlich, and Dubinin-Radushkevich (DR)] were applied and their parameters were then determined by regression analysis. It was found that all isotherms fitted the DR model. The determined parameters showed that, for a carbonaceous material, the higher the steam percentage (in volume) in the gas stream, the lower its Phe adsorption capacity. Results also showed that within the experimental conditions the Phe adsorption capacities of the carbonaceous materials in humid gas streams could be related to Phe concentration by the Langmuir model. The Freundlich model proved to be the most successful in describing the Phe adsorption behavior in dry gas streams. The effect of adsorbent characteristics on Phe adsorption from humid gas streams was determined from correlation coefficients between the adsorption capacities of sixteen carbonaceous materials and their textural parameters. The total micropore volume (pore size diameter < 2 nm) was the parameter that controlled the Phe adsorption both in humid and dry gas streams. Moreover, the difference, in percentage between adsorption capacities in dry and humid gas streams (10% steam percentage) was positively correlated with the narrow micropore volume (pore size diameter < 0.7 nm) with a statistical significance level higher than 99%.