Desulfurization Sorbents Research Articles

Regeneration Kinetics Study of Fe<sub>2</sub>O<sub>3</sub> Desulfurization Sorbents in SO<sub>2</sub> Atmosphere

The influences of the regeneration temperature and SO2volume fraction on regeneration kinetics behavior of Fe2O3 sorbent as a high-temperature desulfurization sorbent were researched by TGA (Thermos gravimetric analyzer) in this work. The main regeneration product of iron oxide desulfurization sorbent was Fe2O3 and sulfur in SO2 atmosphere which has an important practical significance for pollution control of H2Sandrecycleofsulfur. The results indicate that Fe2O3 desulfurization sorbent was completely regenerated at temperature of 725-775 °C and the higher regeneration temperature and volume fraction of SO2 is benefit to improve regeneration reaction rate. The regeneration reaction of Fe2O3 sorbent in SO2atmosphere can be first order reaction obtained by the equivalent grain model, and the controlling process of regeneration reaction is change from the chemical reaction control to the diffusion control in the whole regeneration process. The chemical reaction apparent activation energy and the corresponding frequency factor of chemical reaction are 145.31 kJ/mol and 0.0063 m/s, respectively. And that of diffusion are 50.73 kJ/mol and 4.38×10-3 m2/s, respectively.

New SiO2–NiO Aerogel Sorbents for Desulfurization by π-Complexation: Influence of Molar Ratio of Si/Ni

SiO2–NiO aerogels with different molar ratios of Si/Ni (n(Si/Ni)) were prepared by a sol–gel method and atmospheric pressure drying technology. The morphology and structure of SiO2–NiO aerogels were characterized by XRD, BET, XRF, and SEM methods. The equilibrium adsorption performance of thiophene or benzothiophene on the SiO2–NiO aerogels were studied at three different adsorption temperatures (298, 313, 333 K). The adsorption equilibrium data of thiophene on SiO2–NiO aerogels were more in line with the Temkin model at the lower temperature, while they were well fitted with both Langmuir and Temkin isotherms at the higher temperature. The maximum saturation adsorption capacities obtained by the Langmuir isotherms at different temperature decreased in the order qm(298 K) > qm(313 K) ≈ qm(333 K). The maximum saturation adsorption capacities of thiophene or benzothiophene on SiO2–NiO aerogels with different n(Si/Ni) values at 298 K decreased in the order SiO2–NiO-23 > SiO2–NiO-74 > SiO2–NiO-6. The maximum ...

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

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.

Application of CaO Sorbent for the Implementation and Characterization of an in Situ Desulfurization Steam-Blown Bubbling Fluidized-Bed Test Rig for Biomass Gasification

In this work, a test rig is presented that is suitable for investigations on the equilibrium of high-temperature in situ desulfurization sorbents under real process conditions of a fluidized-bed gasifier. Gasification was performed using wood pellets as fuel with addition of a defined amount of CS2 to raise the content of sulfur without significantly changing the composition of permanent gases. The conversion of CS2 to H2S under gasification conditions ensures a high sulfur content in the produced gas in the range of 1200 ppmv, representing a synthesis gas derived from gasification of low-grade residual biomass. This type of gas is suitable for investigating the equilibrium of the desulfurization reaction under real process conditions, as the initial sulfur content is high enough to observe a desulfurization effect upon addition of potentially suitable sorbents. Furthermore, the low ash content of wood pellets ensures long-term stable gasification conditions. Investigations using lime as a sulfur sorbent ...

Performance evaluation of porous sodium aluminate sorbent for halide removal process in oxy-fuel IGCC power generation plant

Integrated coal gasification combined cycle power generation that adopts oxy-fuel concept has potential to achieve thermal efficiency of 44% at lower heating value besides its CO2 separation ability. Halide control as well as dry gas sulfur removal is inescapable process to the proper operation of the plant. This study investigates performance of dry halide sorbents to establish suitable halide control procedure for the power plant. The most appropriate position of the process is considered to be in the upper stream of the dry sulfur removal process, where the process is able to prevent both corrosion of gas turbine and halogenation of zinc in the desulfurization sorbent. Preproduction sorbents for the dry-gas halide removal process were prepared as pellets containing sodium aluminate as a main ingredient. The sorbents could absorb stoichiometric amount of hydrogen chloride at 450 °C and 0.98 MPa absolute in a simulated coal derived gas environment. The fresh and spent sorbents were examined for dependence of kinetics of halide removal reaction on their pore structures. The results showed that the pore structure comprising of macropore peak at around 5.0 μm and smaller peaks at 1.0 μm or below was suitable to attain affordable kinetics on halide removal and sodium conversion of the sorbent.

Enhanced sulfur capacity of durable and regenerable mesoporous sorbents for the deep desulfurization of diesel

Abstract The adsorptive desulfurization of a mode diesel (300 ppmw S) and a commercial diesel (187.2 ppmw S) using the durable and regenerable Ag/Al-SBA-15, Ni/Al-SBA-15 and Ce/Al-SBA-15 sorbents was investigated in fixed-bed tests. The desulfurization capability of the sorbents was remarkably enhanced by elevating metal ion-exchanging temperature, increasing metal ion-exchanging number of times and using large pore SBA-15 (∼11.55 nm) as the support. Ni/ASL60-4 sorbent, which was prepared by exchanging Ni ions onto the aluminized large pore SBA-15 (∼11.55 nm) at 60 °C with 4 of times, exhibited the highest desulfurization capability. For the desulfurization of the model diesel, Ni/ASL60-4 can remove 0.228 mmol of total sulfur per gram at saturation. For desulfurization of commercial diesel, 7.0 ml of clean diesel (less than 1.0 ppmw S) can be produced over 1.0 g of Ni/ASL60-4. The desulfurization capability of Ni/ASL60-4 can be enhanced a total of 250% compared to Ni/AS20-1. The saturated Ni/ASL60-4 was regenerated in situ by heating in dry air at 350 °C. After generation, the desulfurization capability of Ni/ASL60-4 can be completely recovered even after 3 cycles. The NiO particles were not found on the fresh and regenerated Ni-based sorbents by XRD test. This showed that metal Ni was in the form of Ni ions after the desulfurization and regeneration. This was mainly because the Ni ions can be firmly anchored on the aluminized SBA-15 by ion-exchanging.

황화수소 정제용 아연계 분무건조 탈황제의 활성성분 함량 변경에 따른 물성 및 반응 특성

Gaseous sulfur compound such as <TEX>$H_2S$</TEX> or COS in coal- or biomass-derived hot syngas can be purified by solid sorbents at high temperatures. In this study, we investigated the physical properties and reactivity of solid regenerable desulfurization sorbents with 37.2, 41.9, and 46.5wt% ZnO to look into the ZnO content effect. The sorbents were produced by spray-drying method to apply to a fluidized-bed process. Sulfidation and regeneration reaction were carried out using a thermogravimetric analyzer. Sorbent prepared with 46.5wt% ZnO had physical properties suitable for a fluidized-bed process applications such as spherical shape, sufficient mechanical strength and density, high porosity and surface area. It showed high sulfur sorption capacity of 10.4wt% (ZnO utilization of 57%) at reaction temperatures of 500 and <TEX>$650^{\circ}C$</TEX> for sulfidation and regeneration, respectively. However, the sulfur sorption capacity and ZnO utilization were significantly reduced and dimple shape appeared when the ZnO content decreased to 37.2 and 41.9wt%. Sulfur sorption capacity and regenerability were improved as reaction temperature increased within the experimental temperatures used in this work. The reaction temperature zones of <TEX>$1500{\sim}550^{\circ}C$</TEX> and <TEX>$650{\sim}700^{\circ}C$</TEX> are recommended for sulfidation and regeneration, respectively, to lead best reaction performances of the ZnO-based spray-dried sorbents developed in this work.

Innovative low temperature regenerable zinc based mixed oxide sorbents for synthesis gas desulfurization

Zinc oxide-based materials are commonly used for the final desulfurization of synthesis gas in IGCC and Fischer–Tropsch based XTL processes. The formation of large amount of solid waste is the major issue of this process. In-situ oxidative regeneration is a promising way to reduce this waste formation and enhance desulfurization process efficiency and economics. However, previous studies showed that one of the major drawbacks of oxidative regeneration of sulfided oxides relies in the high operating temperature range required to overcome the formation of inhibitory sulfate phases. A preliminary work of the authors focused on single oxides identified that regeneration temperature of zinc oxide-based sorbent could be reduced through the addition of molybdenum oxide. Two composites oxides – a single oxides mixture (ZnO and MoO3) and a mixed oxide (ZnMoO4) – were synthesized and characterized. Their sulfidation and oxidative regeneration properties were investigated through thermogravimetry and in-situ characterizations. Sulfidation of the single oxides mixture was shown to be similar to the combination of the sulfidation of both independent single oxides. Mixed oxide sulfidation leads to ZnMoO4 phase demixing into ZnS, MoS2 and ZnMoO3. The oxidative regenerations of the sulfided single oxide mixtures and mixed oxide are initiated, respectively, at 350°C and 300°C. These temperatures are 250°C and 300°C lower than the regeneration temperature of a pure ZnS. For the sulfided mixed oxide regeneration is even complete at 500°C under isothermal conditions. Regeneration of sulfided oxides mixture and mixed oxide was thus shown to exhibit synergetic effects, resulting from exothermic oxidative reactions of molybdenum phases. Heat energy released during these reactions is assumed to enhance ZnS oxidation kinetics at a temperature lower than the previously measured one.

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.

Microwave-Assisted Hydrothermal Synthesis of α-MnO2: Lattice Expansion via Rapid Temperature Ramping and Framework Substitution

Cobalt-doped cryptomelane-type manganese oxide (K-OMS-2) microwires have been successfully synthesized and characterized. Their catalytic activity was tested in an oxidation reaction with benzyl alcohol as the substrate, and the cobalt-doped OMS-2 materials showed 100% selectivity toward benzyl aldehyde with a conversion of 55%. The cobalt-doped OMS-2 materials were also investigated as a desulfurization sorbent in a fixed bed reactor at 250 °C where high sulfur sorption capacities (49.4 g of sulfur/100 g of sorbent) were observed. Here, structure-controlled synthesis was performed using a facile one-step microwave-assisted hydrothermal method (MWHY) associated with a rapid temperature ramping (200 °C/min). The structural effects induced by the compositional control of transition metal dopants on the cryptomelane (space group I4/m) body centered tetragonal structure were identified with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD and TEM results showed that the systematic v...

Deactivation Kinetics Model of H2S Removal over Mesoporous LaFeO3/MCM-41 Sorbent during Hot Coal Gas Desulfurization

The improved deactivation kinetic model over mesoporous LaFeO3/MCM-41 sorbents for hot coal gas desulfurization was established with mass-transfer correlation based on elementary stoichiometric equation, which consisted of both the spatial and the time partial differential equations. MATLAB software was used to solve partial differential equations by means of forward finite differential method and to estimate kinetic parameters via nonlinear least-squares fitting. The rate constants ka and kd were obtained via aforementioned kinetic model over different LaFeO3/MCM-41 sorbents. The calculated results were in accordance with experimental data under various operating conditions. The kinetic model can be used successfully to predict the distributions of H2S concentration at different times and spatial positions within fixed-bed layers, compared to unreacted shrinking core model, random pore model, or grain model. It is of very great significance to obtain basical chemical engineering data for the design of ne...

The regeneration mechanisms of sulfurized α-Fe2O3 surfaces under O2 atmosphere: A density functional theory study

The regeneration mechanisms of sulfurized α-Fe2O3 desulfurization sorbent under O2 atmosphere are systematically studied by density functional theory (DFT) slab calculation. The regeneration pathways are proposed for two sulfurized surfaces, “S-contained surface” and “S-adsorbed surface”, which are derived from the substitution of surface O atom by S atom and the adsorption of S atom on the surface Fe atom, respectively. Our results show that two competitive regeneration pathways exist on each sulfurized surface. For the regeneration on the S-contained surface and the S-adsorbed surface, the rate-determining step is the dissociation of O2 with the energy barriers of 136.7 and 227.3kJ·mol−1, respectively, suggesting that the regeneration on the S-contained surface is easier than that on the S-adsorbed surface. Then, the O vacancy on the α-Fe2O3(0001) surface can be repaired under O2 atmosphere, and the reparation mechanism demonstrates that the dissociation of O2 on the O-vacancy α-Fe2O3(0001) surface only needs to overcome a lower energy barrier of 49.8kJ·mol−1 than those (136.7 and 227.3kJ·mol−1) on two sulfurized surfaces. As a result, the presence of O vacancy on the α-Fe2O3(0001) surface can accelerate the dissociation of O2, which is favorable to the regeneration of sulfurized surfaces.

Influence of Regeneration Condition on Physical and Chemical Properties of High Temperature Coal Gas Desulfurization Sorbent

Physical and chemical properties are closely related to desulfurization, regeneration performance and cycle stability for high temperature coal gas desulfurizer. This review focuses on influence rules of changes in regeneration atmosphere, temperature and space velocity on physical and chemical properties. A large number of experimental researches have shown that regeneration atmosphere, regeneration temperature, space velocity have an important influence on mechanical strength, active component and texture change for high temperature coal gas desulfurizer. The different regeneration atmosphere obviously results in different active ingredients for desulfurization sorbent after regeneration, and regeneration at a higher regeneration temperature will easily cause desulfurizer sintering, as well as small regeneration space velocity can lead to the formation of sulfates. In order to make the circulatory system of sulfidation-regeneration-sulfidation need to the requirements in industrial application, the further research of influence rules of regeneration condition on physical and chemical properties will be crucial.

Influence Rules of Texture on the Stability of High Temperature Coal Gas Desulfurization Sorbent

Pulverizing problem, low mechanical strength and poor wear resistance of desulfurization sorbent limit the further development and industrialization of hot coal gas desulfurization technology. The present paper highlighted on the recent progress of hot gas desulfurization researches and gave a fully detailed introduction on physical parameters that reflect the texture of desulfurizer: specific surface area, pore volume, pore size and its distribution, porosity, fractal dimension and so on. Different from the traditional physical parameters, fractal dimension, as a comprehensive physical parameter describing a fractal structure, reflects the regularity degree of a porous structure. With the increase of sorbent fractal dimension, the complexity of pore spatial geometrical features increases, and the porosity and average diameter for pore decrease. The specific surface area also increased consequentially with the increase of micro-pore. Besides, this paper also investigated the proper texture of desulfurization sorbent that is favorable for desulfurization process on the basis of desulfurization mechanism for fuel gas.

New nanostructured sorbents for desulfurization of natural gas

Desulfurization of natural gas is achieved commercially by absorption with liquid amine solutions. Adsorption technology could potentially replace the solvent extraction process, particularly for the emerging shale gas wells with production rates that are generally lower than that from the large conventional reservoirs, if a superior adsorbent (sorbent) is developed. In this review, we focus our discussion on three types of sorbents: metal-oxide based sorbents, Cu/Ag-based and other commercial sorbents, and amine-grafted silicas. The advantages and disadvantages of each type are analyzed. Possible approaches for future developments to further improve these sorbents are suggested, particularly for the most promising amine-grafted silicas.

18O2 label mechanism of sulfur generation and characterization in properties over mesoporous Sm-based sorbents for hot coal gas desulfurization

Using a sol–gel method, SmMeOx/MCM-41 or SBA-15 (Me=Fe, Co and Zn) and corresponding unsupported sorbents were prepared. The desulfurization performance of these sorbents was evaluated over a fixed-bed reactor and the effects of reaction temperature, feed and sorbent composition on desulfurization performance were studied. Samarium-based sorbents used to remove H2S from hot coal gas were reported for the first time. The results of successive sulfidation/regeneration cycles revealed that SmFeO3/SBA-15 sorbent was suitable for desulfurization of hot coal gas in the chemical industry. The formation of elemental sulfur during both sulfidation and regeneration processes depended strongly on the catalytic action of Sm2O2S species, which was confirmed for the first time via high sensitive time of flight mass spectrometer (TOF-MS) using 6%vol18O2/Ar regeneration gas and can reduce markedly procedural complexity. The sorbents were characterized using N2-adsorption, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), temperature-programmed reduction of H2 (H2-TPR), thermogravimetry (TG) and time-of-flight mass spectrometry (TOF-MS) techniques.

The Recovery of Sulfur Resource during Regeneration Process for the Hot Gas Desulfurization Sorbent

Recovery of sulfur source is an important goal of industrialization regeneration for hot coal gas desulfurization sorbent. The different sulfide forms of sulfur produced in regeneration atmosphere and the method for recovering of sulfur source are discussed in this paper. The regeneration exhausted gas of high temperature desulfurization sorbent mainly has several forms of sulfides: sulfur dioxide, hydrosulfide and elemental sulfur, sulfide form and regeneration atmosphere have a direct relationship. Recovering sulfur dioxide utilize the reduction of CO or ammonia, and recovering hydrosulfide use selective catalytic oxidation which is the desulfurization method for achieve prospects of industrialization, but there is catalyst poisoning in these methods. We point out that the direct recovery of elemental sulfur from different forms of sulfide will be the focus of future research.

Development of High-efficiency Oxy-fuel IGCC System

CO2 emission control is a significant issue as a countermeasure for a global warming problem. Carbon dioxide capture and storage technology is regarded as one of the methods of reducing CO2 emission, but it leads to a drop in a thermal efficiency. It is important to maintain thermal efficiency as high as possible for an efficient use of limited fossil fuel resources. CRIEPI started a joint project with Kyushu university to develop “High-efficiency oxy-fuel IGCC”, a high thermal efficiency integrated coal gasification combined cycle power generating system with CO2 capture, which can keep its efficiency more than 40% (HHV). This system gasifies coal with mixed gas of O2 and recirculated exhaust gas mainly composed by CO2, just as oxy-fuel combustion boiler. This paper is to introduce latest achievements done by CRIEPI on this project by quoting latest papers. In order to clarify the effect of CO2 enrichment on coal gasification reaction, coal gasification experiments were executed using pressurized entrained flow coal gasifier whose fuel capacity is 3TPD. And in order to evaluate characteristics of O2- CO2 gasifier by numerical simulation, pressurized drop tube experiments were performed to obtain reaction data necessary for constructing high precision reaction model for numerical simulation code. The data clarified difference between O2 gasification and CO2 gasification on soot behaviour. When we start this project, this system had a problem to be solved. That is carbon deposition on the surface of hot gas clean-up sorbent, installed to improve thermal efficiency. As CO concentration of syngas is so high that carbon particles are supposed to deposit on desulfurization sorbent. But fundamental experiments showed an appropriate countermeasure for carbon deposition, whose impact on thermal efficiency is quite small. Now it is time for us to summarize achievements and propose the next steps toward realization of this system.

A Study of the Zn-based Desulfurization Sorbents for H2S Removal in the IGCC

The various Zn-based sorbents were prepared by physical mixing method and co-precipitation method. The sulfur removing capacity and regeneration properties of the various sorbents were measured in fixed bed reactor at middle temperature condition (sulfidation process 480 °C, regeneration process 580 °C). The sulfur removing capacities of the sorbents were depended on the physical properties such as pore volume, surface area and particle size. The Zn-based sorbents prepared by co-precipitation method were higher pore volume, surface area and smaller particle size resulting in the higher capacities than those prepared by the physical mixing method. To improve the regeneration properties of the sorbents, the various promoters such as cobalt, iron, nickel and cerium were added to the sorbents. The promoters have various roles with the kind of promoter. The roles of promoters could be explained by heat effect and catalytic effect of the promoters. Also, the alloyed structure like spinel structure (ZnTi2O4) has been proposed to explain the superior regeneration properties compared to the single ZnO structure. In addition, the simultaneous removals of the H2S and NH3 over the Zn–Al-based sorbents were tested at 650 °C. So, the new process for simultaneous removal using the developed Zn-based sorbents could be proposed. The role of promoters, effect of hydrogen potential pressure and the deactivation mechanism including the sulfidation of metal oxide to metal sulfide were also discussed.

A Review on Research of Carbonaceous and Carbon-Supported Sorbents for Flue Gas Desulfurization

The development of flue gas desulphurization technologies and the control and reduction of SO2 pollution from coal combustion have become a hot research topic due to environmental concerns. Carbonaceous and carbon supported desulfurizing sorbents have highly porous structures, large specific surface area and low production costs and can be widely used as desulfurizer. This paper provides a comprehensive review of carbonaceous and carbon-based desulfurizing sorbents, including active components, compositions of raw gas and effects of process operation conditions. It can be concluded that the use of char supported metal desulfurizing sorbents for removing sulfur dioxide from flue gas is a promising technology. Different aspects of applications of carbonaceous and carbon-supported desulfurization sorbents are discussed in detail.