(67d) An Innovative Mixed Zinc Oxide Based Sorbent Regenerable At Low Temperature for the Desulfurization of Syngas in IGCC or XTL Processes

Integrated Gasification Combined Cycles (IGCC) and the second generation biofuels processes, and more generally Fischer-Tropsch based XTL processes, are attractive alternatives for future power production^1-3. In order to prevent the corrosion of the industrial units, especially the combustion turbine blade used in IGCC processes or, in the others processes, to avoid the Fischer-Tropsch catalysts poisoning, deep desulfurization of syngas is achieved with metal oxides according to the following reaction :    

MeO_(s) +  H₂S_(g)  →  MeS_(s) +  H₂O_(g)

 

The large amounts of solid wastes produced are one of the major disadvantages of the in-situ desulfurization of syngas. The in-situ regeneration of the sulfided sorbent, back to the oxide, during the process could resolve this problem.  From an industrial point of view, the oxidative regeneration is the simplest and most straightforward way to regenerate the sulfided sorbent, so it was mainly studied^4,5. However, this reaction presents several drawbacks. The first one is its high exothermicity that can cause the sintering of the particles and the loss of reactivity due to the alteration of the textural properties^6,7. Another drawback, which can be considered as the most important, is the formation of sulfates^5,8. These refractory phases require high temperature to decompose, which causes important modification of textural properties and decrease of reactivity due to the sintering of particles. Moreover, the resulting temperature increase will impose the use of expensive alloys to make the reactors and will affect the thermal efficiency of the process. The formation of sulfate has to be avoided in order to maintain the sorbent durability and the temperature of the in-situ oxidative regeneration must be as low as possible, ideally the closest to the desulfurization step, to improve the global efficiency of this process.

The main goal of this work is to bring a new insight on the phenomena involved during the oxidative regeneration of the sulfided solids. The methodology developed is based on the confrontation between a global theoretical approach based on thermochemical data and an experimental study. This work is divided into two parts. The first one is the evaluation and the classification of the behaviors observed during both sulfidation and oxidative regeneration of simple oxides, in particular ZnO. The second one is the evaluation of the mixed oxides, selected thanks to the results of the first part and by the anticipation of potential synergetic effects. The synergetic effects are expected to avoid the formation of refractory sulfates and the resulting increase of temperature.

The first part led to a classification of the simple oxides based on the stability of their sulfide and sulfate phases. This classification led to a selection of different simple oxides whose mixture could bring synergetic effect. Finally, this methodology led to an innovative material which composition allows a fast regeneration, at a temperature 150°C lower than ZnO regeneration temperature and without sulfates formation.

Reference List

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