Desulfurization Sorbents Research Articles

High temperature gas desulfurization with elemental sulfur production

Preliminary results on the use of cerium oxide as a high-temperature desulfurization sorbent are presented. The primary advantage of cerium over current zinc-based sorbents is the potential to produce elemental sulfur during the regeneration phase of the process. Although CeO 2 is less effective for H 2S removal during sulfidation, the sulfided product, Ce 2O 2S, will react with SO 2 to produce elemental sulfur directly. Rapid and complete regeneration is possible over the range of 500 to 700°C, and only elemental sulfur is formed. Elemental sulfur concentrations (considered as S 2) as large as 20 mol% have been produced in the regeneration product. The sorbent has been subjected to ten sulfidation–regeneration cycles using a laboratory-scale fixed-bed reactor with negligible activity loss. Effectively complete conversion of CeO 2 to Ce 2O 2S during sulfidation and subsequent regeneration to CeO 2 was achieved in each cycle. A two-stage desulfurization process using CeO 2 for bulk H 2S removal followed by a zinc sorbent polishing step has been proposed to meet specifications of the integrated gasification combined cycle (IGCC) process. Economic comparison with a single-stage desulfurization process using zinc sorbent followed by elemental sulfur recovery using the direct sulfur recovery process (DSRP) shows that the two-stage cerium process may be less costly if the cerium sorbent is sufficiently durable.

Modification of ZnO−TiO2 High-Temperature Desulfurization Sorbent by ZrO2 Addition

To develop a highly reactive and easily regenerable zinc oxide high-temperature desulfurization sorbent, a modification of ZnO−TiO2 by addition of ZrO2 was studied. The metal oxides ZnO−TiO2−ZrO2 were prepared by a coprecipitation method: the amount of ZnO was a fixed 50 mol % of the sample. In this study, it was found that the addition of 5 or 10 mol % ZrO2 to 50 mol % ZnO−50 mol % TiO2 greatly improved the reactivity for H2S removal. Furthermore, the addition of ZrO2 improved its regenerability: the temperature for the regeneration of the sample was decreased to ca. 40 °C in the absence of H2O and ca. 75 °C in the presence of 10% H2O by the addition of 10% ZrO2.

Zeolite-Supported Metal Oxide Sorbents for Hot-Gas Desulfurization

This paper describes the results of the development of supported mixed-metal oxide sorbents for hot-gas desulfurization capable of withstanding multiple sulfidation/regeneration cycles at 871 °C (1600 °F). The sorbents consisted of various combinations of copper, molybdenum, and/or manganese oxides supported on a high silica-containing zeolite. These sorbents were tested in a fixed-bed reactor with simulated coal gas at 205 kPa (15 psig). The combination of all three metal oxides displayed synergism in enhancing efficiency for H2S removal and improved the crush strength on the pellets. Copper oxide was the most active component for reaction with H2S, while molybdenum and manganese oxides appeared to act as catalysts/promoters. During multicycle testing, this ternary metal oxide sorbent retained its reactivity and mechanical strength.

Preparation of Macroporous Lime from Natural Lime by Swelling Method with Acetic Acid for High-Temperature Desulfurization

To develop a highly active calcium oxide high-temperature desulfurization sorbent, a method of preparation of macroporous calcium oxides from lime was studied. This method is composed of two steps: swelling of the lime and calcination of the swelled sample. Swelling occurred when lime was exposed to the vapor of acetic acid. The swelling resulted from calcium acetate formation in the sample. The swelling rate was at a maximum in the presence of acetic acid and depressed by the presence of water vapor. The swelled sample was converted to macroporous calcium oxide by heating to 850 °C. The reactivity of the macroporous calcium oxide for the removal of SO2 or H2S in the presence of H2O vapor was higher than that of the calcined raw limestone. In particular, its SO2 removal capacity and the oxidative character of CaS to CaSO4 and CaO were greatly improved by this swelling method. These characteristics were also compared with those of a sample prepared from limestone by this swelling method.

98/04202 Effect of pore-modifier graphite on the performance of a zinc titanate sorbent in hot coal gas desulfurization

98/04202 Effect of pore-modifier graphite on the performance of a zinc titanate sorbent in hot coal gas desulfurization

98/02671 The effect of pore-modifier graphite on the performance of a zinc titanate sorbent in hot coal desulfurization: Pineda, M. et al DGMK Tagungsber, 1997, 9704, (Proceedings ICCS '97, Volume 3), 1739–1742.

98/02671 The effect of pore-modifier graphite on the performance of a zinc titanate sorbent in hot coal desulfurization: Pineda, M. et al DGMK Tagungsber, 1997, 9704, (Proceedings ICCS '97, Volume 3), 1739–1742.

98/02032 Reduction of spalling in mixed metal oxide desulfurization sorbents by addition of a large promoter metal oxide : Poston, J. A. U.S. US 5,693,588 (Cl. 502-400; B01J20/00), 2 Dec 1997, Appl. 689,634, 16 Aug 1996, 4 pp.

98/02032 Reduction of spalling in mixed metal oxide desulfurization sorbents by addition of a large promoter metal oxide : Poston, J. A. U.S. US 5,693,588 (Cl. 502-400; B01J20/00), 2 Dec 1997, Appl. 689,634, 16 Aug 1996, 4 pp.

Elemental sulfur production during the regeneration of iron oxide high-temperature desulfurization sorbent

The production of elemental sulfur instead of SO 2 during the regeneration of high temperature desulfurization sorbents will improve the efficiency of advanced power generation processes such as the integrated gasification combined cycle (IGCC). While much research is directed at developing zinc-based sorbents because of the favorable thermodynamics of the ZnO–H 2S reaction, SO 2 is the inevitable product from ZnS regeneration. Iron-based sorbents, although less efficient for H 2S removal, permit significant amounts of elemental sulfur to be formed during regeneration. A laboratory-scale fixed-bed reactor has been used to study the regeneration of FeS in steam-oxygen mixtures. The experimental results are interpreted on the basis of four simultaneous reactions. Oxygen reacts rapidly with FeS to produce SO 2 and Fe 2O 3. Steam reacts to give Fe 3O 4 and H 2S. Elemental sulfur is formed by the reaction between H 2S and SO 2, and additional O 2 is consumed in converting Fe 3O 4 to Fe 2O 3. The maximum yield of elemental sulfur, approximately 75% of theoretical, was achieved using a large H 2O-to-O 2 ratio (200-to-1) at the lowest feasible regeneration temperature (600°C), and using a small regeneration gas feed rate.

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

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.

In Situ Fourier Transform Infrared Characterization of Sulfur Species Resulting from the Reaction of Water Vapor and Oxygen with Zinc Sulfide

Steam is utilized as a diluent in the regeneration of zinc-based hot gas desulfurization sorbents used in fuel gas cleanup. Therefore, the effect of water vapor on the interaction of zinc sulfide (ZnS) with oxygen at 823, 873, and 923 K was studied using Fourier transform infrared (FTIR) spectroscopy. When ZnS at 823 K was exposed to oxygen, sulfate (SO42-) was the most prominent species observed at oxygen pressures greater than 5 × 10-2 Torr while sulfite (SO32-) was the major species observed during the water vapor exposures. When ZnS at 823 K was exposed to an equimolar mixture of water vapor and oxygen, sulfite and sulfate were the most prominent products but the intensity of the sulfite peak was more than that of the sulfate. The sulfur species formed during the water vapor and oxygen exposures at both 873 and 923K were similar to those at 823 K, but the relative intensities of the peaks corresponding to these sulfur species were different. At all three temperatures, the presence of water vapor enhan...

97/05071 Development of advanced sorbents for hot gas desulfurization: Abbasian, J. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 602–607

Integrated Gasification Combined-Cycle (IGCC) processes are among the leading contenders for the production of electricity from coal. Coal gas desulfurization to sufficiently low levels at elevated temperatures (T > 350 C) is now recognized as crucial to efficient and economic coal utilization in advanced IGCC processes. The implementation of hot coal gas desulfurization relies heavily on the development of regenerable sorbent materials which can efficiently reduce H{sub 2}S from several thousand ppmv levels down to a few ppmv over many cycles of sulfidation/regeneration. Zinc-based sorbents, such as zinc titanate, are currently the leading candidate sorbents, however, they have been shown to suffer from zinc volatilization at elevated temperatures leading to sorbent deterioration, increasing sorbent replacement costs, and the overall cost of hot gas cleanup. This paper discusses the results obtained in an ongoing investigation geared towards developing advanced mixed-metal oxide sorbents for desulfurization of coal-derived fuel gases in the temperature range of 350 to 550 C. The paper focuses on the study related to the development of durable sorbents and addresses thermodynamic considerations, sulfidation kinetics, regenerability, and long term durability of a number of novel sorbents.

A study on regeneration of zinc titanate sorbents for H2S removal

In this study the regeneration of used zinc titanate sorbents for high temperature desulfurization of fuel gases was investigated. Zinc titanate sorbents with Zn/Ti molar ratio of 1.5 were prepared and the regeneration was carried out in quartz fixed-bed reactor of 1 cm diameter. Regeneration of zinc titanate sorbents at high temperature is exothermic reaction that brings about deterioration of sorbents. So far experimental parameters such as reaction temperature, concentration of oxygen, flow rate and steam content have been considered to obtain suitable regeneration conditions. H2S and SO2 breakthrough curves were obtained during desulfurization-regeneration. Also, properties of the sorbents before and after regeneration were analyzed using SEM, XRD, Hg-porpsimetry and BET method. From such results, we obtained the most suitable regeneration conditions including 650 ‡ C of regenerating temperature, 5 % of oxygen content and 10 % of steam in the gas stream.

97/05096 An innovative approach to the regeneration of hot gas desulfurization sorbents: White, J. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 620–625

97/05096 An innovative approach to the regeneration of hot gas desulfurization sorbents: White, J. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 620–625

97/03730 Development of regenerable copper-based sorbents for hot gas desulfurization

The implementation of hot gas cleanup systems heavily depends on the development of regenerable sorbents for removal of sulfur-containing species (mainly H{sub 2}S) from the fuel gas stream at elevated temperatures (i.e., >350 C) from levels of several thousand ppm down to a few ppm, over many sulfidation/regeneration cycles. In addition, these sorbents must have high sulfur capacity, good sulfidation kinetics, good mechanical strength, and good chemical and structural stability over multicycle testing. Zinc-based sorbents, such as zinc titanates, are the leading contenders for hot gas desulfurization. However, these sorbents have been shown to suffer from zinc volatilization at elevated temperatures, resulting in sorbent deterioration and losses through attrition, loss of reactivity, leading to increasing sorbent replacement costs and overall cost of electricity. Copper-based sorbents do not suffer from volatilization problems due to the high melting point of the metal. However, bulk copper oxide is easily reduced to elemental copper in a reducing fuel gas environment, which in turn results in insufficient level of desulfurization. Fortunately, the sorbent desulfurization performance can be greatly enhanced by combining copper oxide with other oxides to minimize or prevent sorbent reduction during the sulfidation stage. This paper reports on research conducted to-date on themore » development of copper-based sorbents for hot coal gas desulfurization. The results of packed-bed experiments carried out for the determination of optimum operating conditions and for the evaluation of the long-term durability and regenerability of selected copper chromite sorbents are presented and discussed.« less

97/04278 A new approach to coal/air flow balancing

Kinetic studies in thermobalance carried out by several authors previously have shown that small concentrations of TiO2 or CuO can increase substantially the overall sulfidation rate of zinc ferrites, as regenerable sorbents for hot coal gas desulfurization. These oxides modify the textural properties of both the fresh or regenerated and the sulfided sorbent, modifying consequently the sulfidation rate because it is a partially diffusion-controlled process. However, by using grain models it is shown that most of the observed changes are due to changes in the intrinsic reactivity of the sorbent. Detailed studies of characterization in previous papers using different techniques have failed in revealing differential chemical changes that could be associated with a different behavior. In fact, the only significant changes observed in these studies were an apparent disappearance in fresh sorbents calcined at very high temperatures of the Raman effect, and a slight shift of the XPS binding energy of Fe levels, indicating a probable site migration and/or a change of the oxidation state. These characterization results, however, were not completely conclusive and additional efforts should be undertaken.In this paper more sensitive techniques such as Mössbauer spectroscopy (MS), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDX), have been used for the characterization of fresh, regenerated and sulfided sorbents. The study shows that the addition of TiO2 or CuO induce substantial structural changes in zinc ferrites that can explain their apparent enhancing effect on the overall sulfidation reactivity. Additionally, this effect is decreased as the number of sulfidation-regeneration cycles increases, probably explaining the performance decay exhibited by these sorbents in multicycle tests in a fixed bed reactor.

Novel Preparation Method of Macroporous Lime from Limestone for High-Temperature Desulfurization

In order to develop a highly active calcium oxide high-temperature desulfurization sorbent, macroporous calcium oxides were directly prepared from limestone. This method is composed of two steps: swelling of the limestone in the gas phase followed by drying and calcination of the swelled samples. The swelling was found when limestone was exposed to a vapor of aqueous acetic acid. The swelling of the sample resulted from an increase of calcium acetate formation in the sample. It was then converted to macroporous calcium oxides by heating the sample to 850 °C. The reactivity of the macroporous calcium oxide for the removal of SO2 or H2S under coexisting H2O vapor was higher than that of the calcined raw limestone. In particular, its SO2 removal capacity and oxidative character of CaS to CaSO4 and CaO were greatly improved by the swelling method.

Modelling of performance of zinc ferrites as high-temperature desulfurizing sorbents in a fixed-bed reactor

The performance of zinc ferrites as desulfurization sorbents at high temperature was evaluated. Sorbents were prepared by calcination, at 650 and 1100°C, of mixtures of bulk oxides in three different stoichiometries. To calculate the global reaction rate of sulfidation in a thermogravimetric experiment, a grain model with variable properties was developed. The predicted and experimental results were in good agreement. Under the test conditions, the intrinsic reactivity and the diffusion of the reactant gas across the sulfide film on the particle were rate-limiting. These results were confirmed by SEM-EDX analysis of sulfur over a particle cross-section. The calculated global reaction rates of sulfidation were used in a simple model to predict the breakthrough curves at different space velocities in a fixed-bed reactor. The theoretical and experimental results were largely in agreement.

97/01821 Comparison of calcium-based sorbents for coal gas desulfurization

97/01821 Comparison of calcium-based sorbents for coal gas desulfurization

97/01836 Regenerable sorbents for low temperature desulfurization of coal gas

97/01836 Regenerable sorbents for low temperature desulfurization of coal gas

97/01837 Removal of hydrogen chloride from hot coal gas streams

During gasification, chloride species in coal are converted to HCl, a reactive, corrosive, and toxic gas that must be removed to meet environmental regulations, to protect power generation equipment, and to minimize deterioration of hot coal gas desulfurization sorbents. Thermochemical calculations indicated that sodium-based sorbents are capable of reducing HCl vapor to less than 1 ppm in coal gas streams up to a temperature of 650 C, but they are not easily regenerable. The mineral nahcolite (NaHCO{sub 3}) was used to make inexpensive sorbents suitable for fixed- and fluidized-bed reactors. Bench-scale tests confirmed that these sorbents have >50 wt% chloride capacity. The reaction of HCl with the sorbent was rapid and followed overall first-order kinetics.