Effect of Pore-Modifier Graphite on the Performance of a Zinc Titanate Sorbent in Hot Coal Gas Desulfurization

Abstract

The reactivity and performance of different zinc−titanium-based sorbent extrudates for desulfurization of coal gas at high temperature in successive sulfidation−regeneration cycles were studied in both a thermobalance and a fixed-bed reactor. The study showed that the sulfidation and the regeneration of these sorbents as cylindrical extrudates was mostly a diffusion-controlled process. In order to change the degree of dispersion of the active phase and porosity of the sorbent extrudates, some of them were prepared by coprecipitation and others by using graphite as a high-temperature pore-modifier additive. The study showed that the high degree of dispersion of the active phase achieved in the first stages of the coprecipitation process is practically destroyed during sorbent calcination at high temperature. Additionally, coprecipitation enhanced thermal sintering during preparation and the porosity of these fresh sorbents was low. Consequently, the reactivity in thermobalance tests was also low and performance in the reactor was very poor. On the contrary, graphite increased substantially the porosity of the fresh sorbent extrudates and, because it is eliminated at high temperature, this effect prevailed during calcination and successive sulfidation−regeneration cycles. Consequently, graphite notably improved the performance of zinc titanate extrudates as hot temperature sorbents which under the operation conditions used was clearly evidenced by an increase of the sorbent efficiency.

Role of Iron Oxide in the Promotion of Zn−Ti-Based Desulfurization Sorbents during Regeneration at Middle Temperatures

“…The importance of these structure changes during repeated sulfidation/regeneration cycles has already been mentioned by other researchers. [21][22][23][24] However, the relationship between the regeneration properties and the structure changes of sorbents has not been clearly defined. To support this relationship in our study, ZT and ZTF sorbents calcined at 1000 °C were prepared and their TPO experiments were established.…”

Performance and Recovering of a Zn-Doped Manganese Oxide as a Regenerable Sorbent for Hot Coal Gas Desulfurization

“…To increase the porosity of the fresh sorbent, the powder mixture was added with a 5 wt % of graphite as a pore-forming additive. During calcination at high temperature in oxidant atmosphere, graphite is eliminated as evolving CO 2 , while macropores of a size similar to those of the graphite particles used are formed in the solid . The effect of graphite addition enhancing the reactivity of different zinc-based sorbents has been evidenced through performance tests in a fixed bed reactor.…”

Performance of Mn and Cu Mixed Oxides as Regenerable Sorbents for Hot Coal Gas Desulfurization

“…This powder mixture was subsequently homogenized in a planetary ball mill and dispersed in water to form a paste of suitable viscosity to be extruded in a syringe to cylindrical shapes 2 mm diameter × 2 mm height. The extrudates were softly dried overnight at 50 °C and calcined at 950 °C for 6 h. During calcination in oxidant atmosphere, graphite was eliminated completely as CO 2 forming a permanent network of macropores that in zinc-based sorbents increased substantially the sorbent reactivity, at least in the most critical first two sulfidation−regeneration cycles, with minor detrimental effects on the mechanical strength . To enhance the formation of different potential mixed oxides, that could stabilize copper in the required oxidation states 2+ or 1+ under reducing conditions, sorbents were prepared using different concentrations of pure oxides.…”