Influence of the process conditions on the kinetic behaviour of zinc orthotitanate for syngasclean-up

In this study, high-temperature removal of hydrogen sulphide was investigated in a fixed bed reactor using zinc orthotitanate as adsorbent material. The effect of external mass transfer limitation was examined, where no effect on the desulphurization process was observed within the studied flow rate range. The relationship between the product layer diffusion resistance and the reaction temperature was also revealed for the temperature range 450–750 °C. Additionaly, the influence of the reaction atmosphere (reduction, oxidation and gasification) at 750 °C on the desulphurization rate was investigated. The physicochemical changes of the adsorbent during the reaction were interrelated with its desulphurization behaviour through the characterization methods, namely XRD, SEM/EDS and TEM. The study revealed that the product layer formation created a significant resistance and slowed down the desulphurization kinetics. Increasing the temperature within the thermodynamic boundaries was a way of recovering the kinetics. In both the gasification and the H₂ atmosphere, reduction of zinc titanate occurred and this caused losses in desulphurization activity. Water vapor caused poisoning of the active sites and this led to a steady loss of desulphurization activity. The study showed that desulphurization performance of Zn₂TiO₄ was less influenced by mass transfer limitations compared to its alternatives, which suggests that zinc titanate has great potential for industrial-scale hot desulphurization applications.