Detailed Investigation of Thermal Regeneration of High-Silica ZSM-5 Zeolite through in Situ Synchrotron X-ray Powder Diffraction and Adsorption Studies

Abstract

Adsorption is important for many applications including catalysis and water remediation technology. To improve the performances of such applications, it is essential to have a deep understanding of adsorbent−adsorbate interactions, and of the dynamics involved in adsorption/desorption processes of porous adsorbent materials. In this study, the thermal desorption of high-silica (HS) ZSM-5 zeolite loaded with mixtures of organic compounds (namely, methyl tert-butyl ether/toluene, and methyl tert-butyl ether/1,2 dichloroethane) was investigated in real time using in situ high-temperature synchrotron X-ray powder diffraction (HT-XRPD). A picture of both kinetics and dynamic behavior of this adsorbent during thermal regeneration is presented, including the evolution of refined occupancies of the host molecules as a function of temperature. The adsorption enthalpy and entropy of the organic compound were also evaluated and compared with desorption temperature. It was found that configurational effects can affect the mobility of the molecules inside the framework, and in particular, the desorption temperature seems to be mainly related to the position of the molecule inside the porous structure.

Organic Guests within a Ferroelastic Host: The Case of High Silica Zeolite ZSM-5

“…As reported in previous works, ,,, within the stability field of the monoclinic phase (i.e., for T < T c ), no changes in the extraframework site occupancies are observed. Specifically, under the assumption of guest organic molecules exclusively localized within the host ZSM-5 zeolite framework, it has been observed that up to the transition temperature the number of guest molecules per unit cell is almost unchanged with respect to that found at RT.…”

“…According to those investigations, ,,, the first DTG peak can be ascribed to the desorption of species bounded to the sample surface (water molecules and/or embedded organic species). On the contrary, the desorption of guest molecules embedded in the ZSM-5 channels occurs at higher temperature, and their mobility inside the framework is controlled by configurational effects .…”

“…The concentration of the contaminants in the aqueous solution was analyzed before and after the contact with the zeolite by gas chromatography/mass spectroscopy. Details of the analytical methods are reported elsewhere . The procedure was repeated until the concentration of contaminants in the solution no longer decreased after contact with the zeolite.…”

“…High surface area, shape selectivity, and mechanical, thermal, biological, and chemical stability make ZSM-5 one of the most employed synthetic zeolites in the adsorption processes of organic contaminants for wastewater treatments. In particular, ZSM-5 turns out to well succeed in the removal of toluene (TOL), 1,2-dichloroethane (DCE), and methyl- tert -butyl-ether (MTBE) from waters, both as unary and binary mixtures. − The ZSM-5 zeolite (MFI framework topology) belongs to the pentasil zeolite family and it is characterized by a three-dimensional pore system formed by two intersecting sets of tubular channels: the so called straight channel parallel to the [010] direction and the sinusoidal channel parallel to the [100] direction. , Those channels have an opening defined by 10-membered rings of TO 4 tetrahedra with a free diameter which ranges from 5.4 to 5.6 Å and from 5.1 to 5.5 Å for the straight and the sinusoidal channel, respectively.…”

Adsorptive Removal of Methylene Blue from Aquatic Environments Using Thiourea-Modified Poly(Acrylonitrile-co-Acrylic Acid)

“…This phenomenon is further established with negative values of ΔGo. At higher temperature, Gibbs free energy changed from negative to positive, this suggested that desorption took place [63]. Besides, disorderliness at TA-poly(AN- co -AA) adsorbent-adsorbate solution interface decreases during adsorption process as indicated by the values of ΔS0.…”