A Zn-Offretite for the adsorption of thiophenic species under fluidized catalytic cracking conditions. Synthesis, characterization and reactivity

Abstract

A zinc-containing offretite (Zn-OFF) was synthesized using a hydrothermal method. The goal was to prepare a Zn-OFF zeolite with adsorption properties for selective removal of thiophenic chemical species in gasoline. It was expected that this new sorbent would perform favorably under the conditions close to the ones of FCC units. Following the Zn-OFF synthesis, several characterization techniques were used such as: a) temperature programmed desorption (TPD), b) temperature programmed reduction (TPR), c) temperature programmed oxidization (TPO), d) X-ray diffraction, e) N2 isotherm, f) UV–vis spectra, g) Scanning Electron Microscopy (SEM) and h) Fourier Transform Infrared Spectroscopy (FTIR). In addition, chemical characterization was developed using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and X-Ray Fluorescence (XRF). It was proven on this basis, that zinc species are most likely included in the zeolite framework. Regarding the influence of Zn on the OFF zeolites, it was shown that Zn considerably increases (doubles) the weak acidity measured by TPD as well as shifts the TPD peak towards a higher temperature range. Additionally, FTIR pyridine adsorption also showed in the case of the Zn-OFF in comparison with the OFF, a 2.5 times higher abundance of Lewis acid sites versus Brönsted sites. It is speculated on this basis, that the Zn in the OFF structure increases species adsorption, changing the adsorption bonding strengths. Regarding the Zn-OFF performance, it was proven in a CREC Riser Simulator unit that one can achieve 37wt% of 2-methylthiophene removal with less than 1.3wt% being converted into coke.