Kinetics of zinc titanate desulfurization at high temperature

Sulfur compounds in coal gas must be removed before gas processing or burning to meet the chemical synthesis and environmental law. The developments of desulfurization sorbent and technologies at high temperature have been attracting world wide attention because of its importance to the advanced coal based power generation (e.g. IGCC). The existing problems for coal gas desulfurization technology at high temperature are the loss of effective component and the powdering of desulfurizer which considerably hinder the industrial application. Zinc titanate desulfurizer is regarded as a promising sorbent for its good chemical and mechanical performance. The effect of the concentration of H_2S and desulfurization temperature on the desulfurization beheavior of zinc titanate (Zn_2TiO_4)sorbent and the kinetic model validation were investigated in a fixed bed reactor under atmospheric pressure. The results show that the sorbent has a very good desulfurization performance. The desulfuization rate of the sorbent increases with raising the sulfidation temperature in the range of 400 ℃ ～600 ℃ and the H_2S concentration of inlet gas in the range of 3 g/m3～10 g/m3. Model tests show that the desulfurization process can be fitted by the equivalent grain model with the diffusion controlling in the product layer. The calculated values of diffusion activation energy and corresponding frequency factor are 61.4 kJ/mol and 4.4×10 -5 m2/min, respectively. It suggests that the desulfurization process is controlled by solid grain diffusion instead of pore diffusion. It is found that specific surface area and pore volume of the sulfided sample decrease considerably and there are many congregating grains formed on the surface of sulfided sorbent by means of N_2 adsorption analysis and SEM photos of surface morphology, which further validates that the desulfurization of Zn_2TiO_4 sorbent is controlled by the solid grain diffusion.