γ-Fe₂O₃ For Hydrogen Sulfide Capture At Low Temperature

The basic condition of energy in our country is lack of oil and gas, rich of coal. Coal-based co-production is one of the important ways to solve the problem of energy, energy efficiency, environmental problems. The coal gas desulfurization purification is a very important step in the process of coal-based co-production. Owing to such advantages as moderately-priced easy, high sulfur capacity, and easy regeneration, the iron oxide desulfurizer have been widely used in sulfur removal. However, commercially available iron oxide fine desulfurizer is poor reactivity and use low airspeed. In addition, iron oxide has a variety of crystal type, mostly can be used for desulfurization under different temperature, but the desulfurization behavior of gamma iron oxide is rarely reported. Explore the gamma iron oxide desulfurization performance at low temperature, the method to improve desulfurization activity and use of airspeed is of great significance to the iron oxide desulfurization at low temperature.In this study, the reagent gamma ferric oxide(R-γ-Fe2O3) and iron silicon adsorbents as the research subjects, the iron silicon adsorbents refer to the three-dimensional macroporous (3DOM) γ-Fe2O3/SiO2 composites with different Fe/Si ratio prepared by colloidal crystal template method. Then scanning electron microscopy (SEM), X-ray diffraction (XRD), FTIR and X-ray photoelectron spectroscopy (XPS) were used for characterization.Scanning electron microscopy (SEM) images showed that the as-prepared (3DOM) iron oxide sorbent had three-dimensionally ordered macroporous which were arrayed highly periodically and interconnected through windows. X-ray diffraction (XRD), XPS, TEM identified that the main polymorph of Fe2O3 in 3DOM iron silicon composites is γ-Fe2O3. But as the less silicon dioxide content in the desulfurizer, the bigger iron oxide grain is and partially conversation of crystalline phase occurs, lead to appearance of α-Fe2O3. Silica existed as amorphous form. The role of silicon in two aspects, namely the dispersion of the active ingredient, to reduce its particle size and increase the surface area; second is to help the formation of stable γ-Fe2O3, to prevent the transfer of steady state α-Fe2O3.The desulfurization of R-γ-Fe2O3 is investigated on a fixed bed reactor under different temperatures (20-80℃). The desulfurization evaluation results found that γ-Fe2O3 often has certain desulfurization activity in low temperature, and increases with temperature rise. With the condition of different iron silicon proportion of 3DOM iron silicon compound desulfurizer at 80 ℃, the desulfurization studies show that the desulfurization effect of desulfur with iron silicon mole ratio of 8:1 FS-8 is best,once desulfurization sulfur capacity reached 40.61%, far higher than the sulfur capacity of γ-Fe2O3 (10.58%).By XRD, XPS characterization results before and after the FS-8 desulfurization, H2S and gamma Fe2O3 in first reaction, normal and low temperature, often generate Fe2S3 and H2O, SiO2 was not involved in the desulfurization. Part of the Fe2S3 decomposed into FeS2 and Fe3S4; Under aerobic conditions, Fe2S3 regenerated into Fe2O3 and elemental sulfur, FeS2 react with oxygen and water vapor into ferric sulfate. The study also found, if keep the right amount of moisture in the atmosphere, maintain the alkalinity of the surface of the desulfurizer (PH≈8) has a positive influence on the desulfurization of 3DOM iron silicon compound desulfurizer, high water content and alkalinity inhibit the desulfurization of iron oxide desulfurizer instead. In addition,3DOM iron silicon compound desulfurizer can not only removing hydrogen sulfide, also has good desulfurization activity for ethanethiol, FS-8 once penetrating sulfur capacity reached 24.5%.Research of the regeneration performance of samples after the desulfurization found that natural regeneration is very slow under the normal temperature. After regeneration with 5% oxygen, in above 80℃,200℃ and 300 ℃, there are more a-Fe2O3 in the samples, and in secondary sulfide has a great reduction of sulfur capacity compared with the first sulfide.Under the condition of 80℃, the desulfurization with the method of continuous desulfurization regeneration (import atmosphere contains 5% oxygen) of 3DOM iron silicon composite desulfurizer FS-8 has received a better effect, the desulfurization through sulfur capacity up to 79.1%, higher than the sum of twice sulfur capacity of the intermittent sulfide (60%), and the reaction product has no α-Fe2O3 with poor desulfurization activity.