Monolithic Zn–Co–Ti based sorbents for hot syngas desulfurization

Abstract

Charge of monolithic Zn–Co–Ti–O based sorbent was manufactured using natural clay as a binder and tested in model hot syngas desulfurization. Fresh and regenerated sorbent was characterized by XRD, SEM–EDX, XPS, mercury porosimetry, and TPRH2. After four cycles of desulfurization (at 540°C) and regeneration (540–650°C), monoliths retained the mechanical integrity and their geometry did not change. Monolithic sorbent captured 5.3gS/100g in the first cycle and 13.8gS/100g in the last one. Concentration of H2S in the treated gas was lowered from 6000ppmv to 3ppmv and the H2S removal efficiency was min. 99.6%. Fresh sorbent contains Zn2Ti3O8 (dominant phase), TiO2 and SiO2, while in the regenerated one always occurs: TiO2 (dominant phase), ZnTiO3, Zn2Ti3O8; SiO2; Zn2SiO4 and ZnAl2O4. Reducibility and the amount of sulfates formed in the used sorbent depend on its position in the bed. After tests, small amounts of free ZnO are present on the surface of the used monoliths. During regeneration the zinc oxide (from Zn–Ti–O mixed oxides) reacts with Al2O3 or SiO2 (clay components), and forms compounds more resistant to deactivation, such as Zn2SiO4 and ZnAl2O4.