Direct Sulfur Recovery Process Research Articles

Catalytic reduction of SO2 under the regeneration of off-gas containing oxygen over Cu-Sn-Zr-based oxides for the hot coal gas desulfurization process

This study examined the activity of Cu-Sn-Zr-based catalysts for the direct sulfur recovery process under the regeneration gas containing oxygen, which consisted of sulfur dioxide and nitrogen as the main components. The catalytic reaction behavior was investigated with the addition of a copper promoter, and the reactive temperature for SO2 reduction was investigated according to the change in temperature by increasing and decreasing the temperature in the processes in stages. The catalytic reaction pathway changed with the catalysis of the promoter, and the activity of the reacted catalyst was higher than that of the fresh catalyst due to the sulfidation of the Cu-promoter. CuS leads to a COS intermediate mechanism, and prevents the deactivation of Cu-Sn-Zr-based by oxygen contained in the regeneration gas.

직접 황 회수 공정으로 유입되는 재생가스에 함유된 미량산소의 촉매활성저하 원인 규명

In order to regenerate the sulfidated desulfurization sorbent, oxygen is used as the oxidant agent on the regeneration process. The small amount of oxygen un-reacted in regeneration process is flowed into direct sulfur recovery process. However, the reactivity for SO2 reduction can be deteriorated with the un-reacted oxygen by various reasons. In this study, the deactivation effects of un-reacted oxygen contained in the off-gas of regeneration process flowed into direct sulfur recovery process of hot gas desulfurization system were investigated. Sn-Zr based catalysts were used as the catalyst for SO2 reduction. The contents of SO2 and O2 contained in the regenerator off-gas used as the reactants were fixed to 5.0 vol% and 4.0 vol%, respectively. The catalytic activity tests with a Sn-Zr based catalyst were for SO2 reduction performed at 300-450 ℃ and 1-20 atm. The un-reacted oxygen oxidized the elemental sulfur produced by SO2 catalytic reduction and the conversion of SO2 was reduced due to the production of SO2. However, the temperature for the oxidation of elemental sulfur increased with increasing pressure in the catalytic reactor. Therefore, it was concluded that the decrease of reactivity at high pressure is occurred by catalytic deactivation, which is the re-oxidation of lattice oxygen vacancy in Sn-Zr based catalyst with the un-reacted oxygen on the catalysis by redox mechanism. Meanwhile the un-reacted oxygen oxidized CO supplied as the reducing agent and the temperature in the catalyst packed bed also increased due to the combustion of CO. It was concluded that the rapidly increasing temperature in the packed bed can induce the catalytic deactivation such as the sintering of active components.

Effect of O2 on SO2 Reduction with CO or H2 over SnO2−ZrO2 Catalyst

To investigate the effect of the O2 content on the direct sulfur recovery process (DSRP) combined with the hot gas desulfurization (HGD) process with the unreacted O2 emitted from the regeneration process, either CO or H2 was used as a reducing agent for the reduction of SO2 over SnO2−ZrO2 catalyst with a Sn/Zr molar ratio of 2/1. Then, the reaction conditions, including temperature, CO (or H2)/SO2 molar ratio, and space velocity, were optimized to maximize the sulfur yield in the presence and absence of 1 vol % O2. The temperature, CO (or H2)/SO2 molar ratio, and space velocity were varied in the ranges of 300−600 °C, 1.0−4.0, and 1000−30000 h−1, respectively. In SO2 reduction using CO with 1 vol % O2, the temperature, CO/SO2 molar ratio, and space velocity for the maximum sulfur yield were 600 °C, 3.5, and 10000 h−1, respectively, in which case the SO2 conversion and sulfur yield were about 85% and 77%, respectively. In SO2 reduction using H2 with 1 vol % O2, the temperature, H2/SO2 molar ratio, and spa...

Catalytic reduction of sulfur dioxide with carbon monoxide over tin dioxide for direct sulfur recovery process

SO 2 reduction by CO over SnO 2 catalyst was studied in this work. The parameters were the reaction temperature, space velocity (GHSV) and [CO]/[SO 2] molar ratio. The optimal temperature, GHSV and [CO]/[SO 2] molar ratio were 550 °C, 8000 h −1 and 2.0, respectively. Under these conditions, the SO 2 conversion and sulfur selectivity were about 78% and 68%, respectively. The following reaction pathway involving two mechanisms was proposed in SO 2 reduction by CO over SnO 2 catalyst: in the first step involving Redox mechanism, the elemental sulfur was produced by the mobility of the lattice oxygen between SO 2 and SnO 2 surface. In the second step, COS was formed by the side reaction between elemental sulfur and CO or metal sulfide and CO. In the third step involving COS intermediate mechanism, the abundant elemental sulfur was produced by the SO 2 reduction by COS which was produced in the second step and was more effective reducing agent than CO.

Direct Reduction of Sulfur Dioxide to Elemental Sulfur with Hydrogen over Sn−Zr-Based Catalysts

We conducted the SO2 reduction with H2 over Sn−Zr-based catalysts for the direct sulfur recovery process. The reaction temperature was varied from 250 to 550 °C while using SnO2-only, ZrO2-only, and SnO2−ZrO2 (Sn/Zr = 2/1) catalysts. The highest reactivity was obtained using the SnO2−ZrO2 (Sn/Zr = 2/1) catalyst at 550 °C, for which the SO2 conversion and sulfur selectivity were 98 and 55%, respectively. Also, the following mechanistic pathway was suggested: (1) The elemental sulfur is produced by the direct conversion of SO2 according to the redox mechanism (SO2 + 2H2 → S + 2H2O). (2) The produced sulfur is partially converted into H2S with the hydrogenation (H2 + S → H2S). (3) Finally, the Claus reaction proceeds through Lewis and Brönsted acidic sites (SO2 + 2H2S → 3S + 2H2O). It was estimated that the lattice oxygen vacancies might be active sites for the redox mechanism and the Lewis and Brönsted acidic sites might be related to the pathway of the Claus reaction.

Investigation of Catalytic Reduction of Sulfur Dioxide with Carbon Monoxide over Zirconium Dioxide Catalyst for Selective Sulfur Recovery

In this work, a ZrO2 catalyst was used to reduce SO2 using CO for the direct sulfur recovery process (DSRP), and a mechanistic investigation was performed. ZrO2 catalyst was prepared by a precipitation method. It was supposed that ZrO2 catalysts exhibit high activity in the SO2 reduction by CO at relatively high temperature because of their Lewis acidic sites and Bronsted acidic sites. In addition, the following mechanistic pathway could be suggested: (1) In the first step initialized by the redox mechanism, the ZrO2 catalyst was reduced by CO and then sulfate groups, which have the effect of improving the Lewis acidic sites and Bronsted acidic sites, were formed on the surface. (2) In the second step, elemental sulfur was produced by the movement of lattice oxygen between SO2 and the lattice oxygen vacancies of the ZrO2 catalyst having redox catalytic properties. (3) In the third step, COS was formed by the reaction of S + CO → COS. (4) In the fourth step, SO2 and COS were adsorbed and reacted on the su...

Catalytic reduction of sulfur dioxide using hydrogen or carbon monoxide over Ce 1− xZr xO 2 catalysts for the recovery of elemental sulfur

This study focuses on the direct sulfur recovery process (DSRP), in which SO 2 can be directly converted into elemental sulfur using a variety of reducing agents over Ce 1− x Zr x O 2 catalysts. Ce 1− x Zr x O 2 catalysts (where x = 0.2, 0.5, and 0.8) were prepared by a citric complexation method. The experimental conditions used for SO 2 reduction were as follow: the space velocity (GHSV) was 30,000 ml/g -cat h and the ratio of [CO (or H 2, H 2 + CO)]/[SO 2] was 2.0. It was found that the catalyst and reducing agent providing the best performance were the Ce 0.5Zr 0.5O 2 catalyst and CO, respectively. In this case, the SO 2 conversion was about 92% and the sulfur yield was about 90% at 550 °C. Also, a higher efficiency of SO 2 removal and elemental sulfur recovery was achieved in the reduction of SO 2 with CO as a reducing agent than that with H 2. In the reduction of SO 2 by H 2 over the Ce 0.5Zr 0.5O 2 catalyst, SO 2 conversion and sulfur yield were about 92.7% and 73%, respectively, at 800 °C. Also, the reduction of SO 2 using synthetic gas with various [CO]/[H 2] molar ratios over the Ce 0.5Zr 0.5O 2 catalyst was performed, in order to investigate the possibility of using coal-derived gas as a reducing agent in the DSRP. It was found that the reactivity of the SO 2 reduction using the synthetic gas with various [CO]/[H 2] molar ratios was increased with increasing CO content of the synthetic gas. Therefore, it was found that the Ce 1− x Zr x O 2 catalysts are applicable to the DSRP using coal-derived gas, which contains a larger percentage of CO than H 2.

A study on the characteristics of the SO 2 reduction using coal gas over SnO 2-ZrO 2 catalysts

SO 2, which is an air pollutant causing acid rain and smog, can be converted into elemental sulfur in direct sulfur recovery process (DSRP). SO 2 reduction was performed over catalyst in DSRP. In this study, SnO 2-ZrO 2 catalysts were prepared by a co-precipitation method, and CO and coal gas, which contains H 2, CO, CO 2 and H 2O, were used as reductants. The reactivity profile of the SO 2 reduction over the catalysts was investigated at the various reaction conditions as follows: reaction temperature of 300–550 °C, space velocity of 5000–30,000 cm 3/g -cat. h, [reductant]/[SO 2] molar ratio of 1.0–4.0 and Sn/Zr molar ratio of SnO 2-ZrO 2 catalysts 0/1, 2/8, 3/5, 5/5, 2/1, 3/1, 4/1 and 1/0. SnO 2-ZrO 2 (Sn/Zr = 2/1) catalyst showed the best performance for the SO 2 reduction in DSRP on the basis of our experimental results. The optimized reaction temperature and space velocity were 325 °C and 10,000 cm 3/g -cat. h, respectively. The optimal molar ratio of [reductant]/[SO 2] varied with the reductants, that is, 2.0 for CO and 2.5 for coal gas. SO 2 conversion of 98% and sulfur yield of 78% were achieved with the coal gas.

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.

The direct sulfur recovery process

AbstractThe Research Triangle Institute under contract to the U.S. Department of Energy, Morgantown Energy Technology Center, is developing the Direct Sulfur Recovery Process (DSRP) for converting either reduced or oxidized sulfur gases directly to elemental sulfur. Laboratory tests were conducted to evaluate the effects of stoichiometry, pressure, temperature, space velocity and steam content. Pressure was found to be the most important variable. Increasing pressure from 1.5 atm to 20 atm quadrupled the sulfur recovery at equivalent space velocity. Sulfur recoveries from dilute SO2 streams were greater than 96% in tests simulating the first stage of reaction. In the first stage of reaction, SO2 is directly reduced to elemental sulfur by coal gas or other reducing gases at high temperature and high pressure. Under second‐stage reaction conditions, recoveries ranged from 80 to 98% depending on operating conditions. Combined with a first‐stage conversion of 96%, this translates into overall conversions of 99.2 to 99.9%. Preliminary economic comparisons with conventional processes that could be used for treating dilute SO2 tail gases showed a decisive cost advantage for the new catalytic process. The effectiveness of the high‐pressure, high‐temperature DSRP on H2S containing gases has also been demonstrated. Direct conversions of H2S to elemental sulfur ranged to 98% in a single stage of reaction using near stoichiometric amounts of air or oxygen. Bench‐scale development is ongoing to investigate a variety of reactor types and configurations.