In situ and downstream sulfidation reactivity of PbO and ZnO during pyrolysis and hydrogenation of a high-sulfur lignite

Üner, Deniz
Economical valorization of low quality, high sulfur feedstocks is an important challenge. Most of the valorization processes start from pyrolysis, with a significant amount of evolution of sulfur containing compounds. This study addresses in situ and downstream sulfur capture ability of lead oxide (PbO) in comparison to zinc oxide (ZnO) during the pyrolysis of high-sulfur Tuncbilek lignite. In order to assess the role of hydrogen in sulfur capture, hydrogenation experiments were also performed. Sulfidation reaction thermodynamics of PbO and ZnO was compared to most commonly used metal oxides for sulfur capture i.e., FeO, MnO, and CaO. The equilibrium conversions indicated superior performance of PbO and ZnO towards sulfidation reactions at high temperatures. Thermodynamic superiority of PbO sulfidation encouraged us to investigate the PbO as a new sulfur sorbent for hot gas desulfurization. The experimental verification of the high temperature sulfidation ability of PbO and ZnO was performed using high-sulfur Tuncbilek lignite under semibatch conditions. The final compounds formed after each process were observed by X-ray diffractometer (XRD) and Diffuse Reflectance Infrared Fourier Transformation Spectroscopy (DRIFTS). Experiments revealed that PbO can be promising candidate as hot gas sulfur trap during pyrolysis and hydrogenation processes, while ZnO can hold up sulfur only in the presence of hydrogen. Furthermore, both PbO and ZnO show the superior sulfur capture performance in the presence of hydrogen when they were used as adsorbents located after the reactor (downstream) at ambient conditions. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.