In situ high-temperature (HT) synchrotron X-ray powder diffraction (XRPD) was used in this study as a tool to understand the adsorption/desorption process features of methyl tert-butyl ether (MTBE)/toluene (TOL) and 1,2-dichloroethane (DCE)/MTBE binary mixtures adsorbed in organophilic ZSM-5 zeolite (SiO2/Al2O3 ~ 280), as well as framework structural modifications upon thermal treatment from room temperature to 600°C. The binary system was described by a competitive dual site Langmuir adsorption isotherm. The results achieved from the series of time-resolved Rietveld refinements allowed to highlight the out-of-equilibrium effects which govern desorption of ZSM-5 powders in dynamic conditions. The decomposition of TOL and MTBE in both systems starts at about 100°C and continuously proceeds up to ~250°C. As far as concerns DCE molecules, they are completely released from the cavities at ~350°C. Significant internal pressure is developed with the composition product diffusion, causing a corresponding transient distortion in the 10-ring channels. Above 500°C, the unit-cell volume contraction without any mass loss gives rise to a negative thermal expansion (NTE) process. Our results clearly demonstrated that ZSM-5 regeneration is effective when it is thermally treated at about 500°C. Above this temperature, when all the organic have been ejected, non-equilibrium distortions in the framework are relaxed and channel apertures become more circular, thus demonstrating the efficiency of thermal regeneration under mild conditions.

Kinetics and dynamic behaviour of VOCs desorption from binary aqueous mixtures on zeolite ZSM-5: a combined in situ high-temperature synchrotron powder X-ray diffraction and chromatographic study

RODEGHERO, Elisa;MARTUCCI, Annalisa;CRUCIANI, Giuseppe;SARTI, Elena;PASTI, Luisa
2016

Abstract

In situ high-temperature (HT) synchrotron X-ray powder diffraction (XRPD) was used in this study as a tool to understand the adsorption/desorption process features of methyl tert-butyl ether (MTBE)/toluene (TOL) and 1,2-dichloroethane (DCE)/MTBE binary mixtures adsorbed in organophilic ZSM-5 zeolite (SiO2/Al2O3 ~ 280), as well as framework structural modifications upon thermal treatment from room temperature to 600°C. The binary system was described by a competitive dual site Langmuir adsorption isotherm. The results achieved from the series of time-resolved Rietveld refinements allowed to highlight the out-of-equilibrium effects which govern desorption of ZSM-5 powders in dynamic conditions. The decomposition of TOL and MTBE in both systems starts at about 100°C and continuously proceeds up to ~250°C. As far as concerns DCE molecules, they are completely released from the cavities at ~350°C. Significant internal pressure is developed with the composition product diffusion, causing a corresponding transient distortion in the 10-ring channels. Above 500°C, the unit-cell volume contraction without any mass loss gives rise to a negative thermal expansion (NTE) process. Our results clearly demonstrated that ZSM-5 regeneration is effective when it is thermally treated at about 500°C. Above this temperature, when all the organic have been ejected, non-equilibrium distortions in the framework are relaxed and channel apertures become more circular, thus demonstrating the efficiency of thermal regeneration under mild conditions.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2369524
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact