Laboratory-scale apparatus for the characterization of gas-phase dioxin adsorption

Zeolites are reported as selective adsorbents for the preconcentration of dioxin congeners for emission monitoring at stationary sources. This article involves the development of a laboratory-scale apparatus to characterize gas-phase dioxin adsorption on zeolites and thermal desorption. The laboratory-scale apparatus prepared stable levels of dioxin in a nitrogen flow and in-line adsorption/thermal desorption coupled to a gas chromatograph-mass spectrometer. The apparatus takes into account the low-volatility of the dioxins for their transport in the carrier gas and the possible high temperatures used for zeolite desorption. The apparatus functionalities, such as in-line concentration measurement by a sampling loop and gas chromatograph-mass spectrometer and breakthrough measurement during in-line adsorption, were validated. The generator delivers a stable 2,3-dichlorodibenzo-p-dioxin concentration of 304 +/- 6 mu g/m(3) over 20 days. Two methods, weighing a vial and mass analysis of the sampling loop, were employed for measuring the concentration provided results that were in good agreement. Preliminary gas-phase adsorption experiments have been carried out without any memoryw effects in the valves and transfer lines. The dioxin concentration generated and large diameter of the beads led to low adsorption efficiency of dioxin on FAU13X Na-type zeolites due to a low micropore accessibility.