Removal of fuel-based compounds from natural water is of considerable interest due to their harmful effects on the environment, even at very low concentration. Toluene (TOL), 1,2-dichloroethane (DCE) and methyl-tert-butyl-ether (MTBE) are of special relevance since they are toxic and commonly found in surface and ground water. Recently, high-silica zeolites, have been shown to be environmental friendly materials able to efficiently adsorb from water fuel based pollutants[1]. Moreover, zeolites can be easily thermally regenerated at low cost without changing their initial adsorption [2]. In this work, the in situ high-temperature (HT) synchrotron X-ray powder diffraction (XRPD), is used as a key to continuous monitoring the DCE, MTBE and DCE-MTBE mixture decomposition process as well as the structural modifications undergoing on ZSM-5 upon a temperature-programmed thermal treatment. Kinetics and adsorption isotherm batch data were obtained via Headspace Solid Phase Microextraction-GC. Thermal analyses were performed in air up to 900°C at 10°C/min. HT-XRPD data (temperature range 30°-600°C) were collected on the ID31 beamline (ESRF, Grenoble). Rietveld refinements demonstrated that regeneration of ZSM-5 is effective when thermally treating the adsorbent in mild conditions (~300°C). Once regenerated and reloaded, thermogravimetric, chromatographic (Figure 1) and diffractometric analyses (Figure 2) indicates that both organics location and content remain substantially unchanged thus highlighting ZSM-5 is able to re-adsorb the selected pollutants in amounts comparable to that adsorbed in the first cycle. XRD analysis demonstrates that the regenerated and reloaded zeolite does not show any significant crystallinity loss, as well as perfectly regains the crystallographic features of fresh material (Figure 2). The regeneration/adsorption process also occurs without any significant deformations in the channel apertures. In conclusion, the use of this adsorbent with unchanged adsorption performances after thermal regeneration under mild conditions appears very promising also over several cycles of the adsorption/desorption process.
Desorption mechanism of toluene into an organophilic zeolite ZSM-5: an "in situ" time resolved synchrotron powder diffraction study
RODEGHERO, Elisa;MARTUCCI, Annalisa;CRUCIANI, Giuseppe;PASTI, Luisa
2014
Abstract
Removal of fuel-based compounds from natural water is of considerable interest due to their harmful effects on the environment, even at very low concentration. Toluene (TOL), 1,2-dichloroethane (DCE) and methyl-tert-butyl-ether (MTBE) are of special relevance since they are toxic and commonly found in surface and ground water. Recently, high-silica zeolites, have been shown to be environmental friendly materials able to efficiently adsorb from water fuel based pollutants[1]. Moreover, zeolites can be easily thermally regenerated at low cost without changing their initial adsorption [2]. In this work, the in situ high-temperature (HT) synchrotron X-ray powder diffraction (XRPD), is used as a key to continuous monitoring the DCE, MTBE and DCE-MTBE mixture decomposition process as well as the structural modifications undergoing on ZSM-5 upon a temperature-programmed thermal treatment. Kinetics and adsorption isotherm batch data were obtained via Headspace Solid Phase Microextraction-GC. Thermal analyses were performed in air up to 900°C at 10°C/min. HT-XRPD data (temperature range 30°-600°C) were collected on the ID31 beamline (ESRF, Grenoble). Rietveld refinements demonstrated that regeneration of ZSM-5 is effective when thermally treating the adsorbent in mild conditions (~300°C). Once regenerated and reloaded, thermogravimetric, chromatographic (Figure 1) and diffractometric analyses (Figure 2) indicates that both organics location and content remain substantially unchanged thus highlighting ZSM-5 is able to re-adsorb the selected pollutants in amounts comparable to that adsorbed in the first cycle. XRD analysis demonstrates that the regenerated and reloaded zeolite does not show any significant crystallinity loss, as well as perfectly regains the crystallographic features of fresh material (Figure 2). The regeneration/adsorption process also occurs without any significant deformations in the channel apertures. In conclusion, the use of this adsorbent with unchanged adsorption performances after thermal regeneration under mild conditions appears very promising also over several cycles of the adsorption/desorption process.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
