Hot Coal Gas Research Articles

A review of sorbents for high-temperature hydrogen sulfide removal from hot coal gas

Integrated gasification combined cycle (IGCC) and solid oxide fuel cell (SOFC) systems are considered as the most promising clean coal technologies. Syngas derived from coal gasification is the major fuel sources for IGCC and SOFC power systems; however, large amounts of sulfur compounds, mainly in the form of hydrogen sulfide, are produced during gasification. Hydrogen sulfide has to be removed prior to syngas utilization to protect downstream equipment from high-temperature corrosion. Therefore, hydrogen sulfide removal from raw syngas plays a key role in successful application of IGCC and SOFC systems. Hot coal gas desulfurization using solid sorbents is a more efficient technique for hydrogen sulfide removal, compared with conventional cold coal gas desulfurization with amine solution. This article reviews solid sorbents for high-temperature desulfurization, e.g., transition metal oxides, rare-earth oxides, spinel oxides, perovskite oxides, nanoelemental metals and mesoporous desulfurizers. Composite oxides that combine the properties of diverse metal oxides are promising candidates for hot coal gas desulfurization. The extensive background knowledge and the state of the art on high-temperature sorbents for hydrogen sulfide removal in this review provides inspiration and guidance to develop new cost-effective sorbents.

High-sulfur capacity and regenerable Zn-based sorbents derived from layered double hydroxide for hot coal gas desulfurization.

The Zn-Al mixed metal oxide (ZnAl-MMO) with a plate-like structure was derived from Zn-Al layered double hydroxide. The ZnAl-MMO with a Zn/Al molar ratio of 3:1 exhibits superior absorption ability for H2S in a simulated coal gas at 600 ℃ due to the special structure of the ZnAl-MMO. Besides ZnS, elemental sulfur is also produced during the desulfurization process. The deactivation model could well simulate the absorption behavior of H2S. The sulfidation reaction over the sorbent shows large initial reaction rate constants (1110-5390 m3 min-1 kg-1) and low activation energy (29.5 kJ mol-1). The regeneration rate of the used sorbent can reach 99.8% under the optimum conditions. The regenerated sorbents still show high sulfur capacity (ca. 30%), implying its great application potential for industrial-scale desulfurization of the hot coal gas.

Ordered mesoporous Zn-based supported sorbent synthesized by a new method for high-efficiency desulfurization of hot coal gas

A new approach (microwave-hydrothermal plus oxidation) was proposed for the preparation of the Zn-based sorbents supported on the ordered mesoporous Si-based material. The hydrothermal synthesis and oxidation conditions of the sorbent precursor (ZnS/MCM41 mesophase) with Zn(AC)2 and thioacetamide (TAA) as the Zn and S sources, respectively, were optimized. The sorbents were evaluated in a fixed bed using the simulate gas of 2000 ppm H2S, 39% H2, 27% CO, 12% CO2, and N2 as balance gas. The structure of the sorbents was characterized by means of XRD, N2 adsoprtion, SEM, EDX, and TEM analysis. The results indicate that the optimal microwave-hydrothermal conditions are 400 W, 2.5 h, and 1:3 (the mole ratio of the Zn(AC)2 to TAA). The oxidation of ZnS in the sorbent precursor to ZnO is invalid at 550 °C due to unfavorable reaction kinetics. Both the fresh and used sorbents show ordered hexagonal mesoporous structure. It is confirmed that Zn2SiO4 present in the fresh and regenerated sorbents could be consumed during the desulfurization process via the reaction (Zn2SiO4 + 2H2S → 2ZnS + SiO2 + 2H2O), giving a positive effect on the desulfurization of the sorbents. The optimized Zn-based mesoporous sorbent (actual Zn content: 20.3%) exhibits superior (high breakthrough sulfur capacity: 5.4–5.7%) and stable desulfurization ability during five sulfidation/regeneration cycles. In addition, sulifidation reaction only leads to low-degree plugging of the pore structure of the regenerated sorbents, and the regeneration reaction could restore (at least mostly) the aforementioned changes in the pore properties.

Rare earth oxide doping and synthesis of spinel ZnMn2O4/KIT-1 with double gyroidal mesopores for desulfurization nature of hot coal gas

In this work, spinel ZnMn2O4/KIT-1 using KIT-1 with 3-dimensional wormhole-like channels as support was fabricated for hot coal gas desulfurization at high temperature via a sol-gel method. Effects of ZnMn2O4 contents, desulfurization temperature, rare earth oxide doping and steam volume on the desulfurization performances of ZnMn2O4/KIT-1 were investigated systematically. A superior sorbent of ZnMn(Ce)2O4/KIT-1 was obtained with the addition of 45%ZnMn2O4 and doping of CeO2, which was suitable for 550 °C desulfurization and endured a small impact of steam. Moreover, the crystal lattice replace between Ce3+ and Mn3+ facilitated the dispersion of active species and avoided Zn2+ converting to elemental Zn. The high sulfur capacity of ZnMn(Ce)2O4/KIT-1 was maintained after five consecutive desulfurization-regeneration cycles. The textural properties of sorbents were evaluated successively by means of XRD, BET, HRTEM, XPS, H2-TPR and TG/DSC techniques. Results revealed that the main active components in sorbent were robustly existed in form of ZnMn2O4 spinel which effectually prevented the vaporization of Zn in high temperature. Therefore, a low-cost sorbent of ZnMn(Ce)2O4/KIT-1 with the high BSC (171.7 mg S/g sorbent) has an excellent performance for H2S removal from hot coal gas.

Kinetic Analysis of H2S Removal over Mesoporous Cu–Mn Mixed Oxide/SBA-15 and La–Mn Mixed Oxide/KIT-6 Sorbents during Hot Coal Gas Desulfurization Using the Deactivation Kinetics Model

Kinetic analysis was investigated using the deactivation kinetics model, where the reaction order of each species based on the experimental data was estimated for H2S removal over mesoporous Cu–Mn mixed oxide/SBA-15 and La–Mn mixed oxide/KIT-6 sorbents during hot coal gas desulfurization in a fixed-bed reactor. The reaction orders, rate constants, apparent activation energy (Ea), and deactivation energy (Ed) were calculated as the kinetic parameters. The calculated reaction orders, α, β, and γ, were 1, 1, and 1 for Cu–Mn mixed oxide/SBA-15 and 0.6, 1.2, and 1 for La–Mn mixed oxide/KIT-6. The obtained Ea and Ed for Cu1Mn9 mixed oxide/SBA-15 were 33.02 and 46.34 kJ mol–1 and for La3Mn97 mixed oxide/KIT-6 were 48.98 and 56.10 kJ mol–1 , respectively. This model offered the H2S breakthrough curves for the whole duration of the desulfurization reaction, with errors less than 5% between calculated and experimental data.

Effect of preparation method of active component on the cycling performance of sorbents for hot coal gas clean‐up

AbstractHigh temperature gas desulphurization is an efficient environmentally friendly process for high efficiency technologies with syngas clean‐up. The present study investigated the impact of preparation methods on the behaviours of ZnO/red clay sorbent. The sorbents were prepared by the homogeneous precipitation method and solid‐state method, respectively. The surface and structural properties of the sorbents were characterized by thermogravimetric, X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscope‐elemental mapping, and N2 adsorption analysis. Successive desulphurization‐regeneration cycles were conducted to investigate the reusability of the sorbents. After four cycles of desulphurization‐regeneration experiments, the breakthrough times of the two kinds of regenerated sorbents plunged 18.17 % and 23.26 %, respectively. Attritions of sorbents have not been observed, meaning the regenerated sorbents still maintain a high mechanical strength. The sorbents prepared through the homogeneous precipitation method were found to exhibit a longer breakthrough time much greater than those prepared by the solid‐state method. The characterization data indicate that the homogeneous precipitation method results in more uniform distribution of active component sorbent with smaller particle size and better pore structure, which favours the chemical reaction and mass transfer processes.

High-temperature H2S removal performance over ordered mesoporous La-Mn-supported Al2O3-CaO sorbents

A series of La-Mn supported on ordered mesoporous Al2O3-CaO (OMA-2Ca) sorbents with various Mn/La molar ratio were first designed and synthesized for removal of H2S at 650–850°C. 40% 98Mn2La/OMA-2Ca exhibited satisfactory desulfurization performance at 800°C with a breakthrough sulfur capacity (BSC) of 16.15gS/100g sorbent. Elemental sulfur was formed during desulfurization as a result of synergistic catalysis of γ-Al2O3 and lanthanum oxysulfide at high temperature. The existence of high content steam in hot coal gas obviously reduced the sulfur capacity because of the formation of MnAl2O4. After five successive sulfidation-regeneration cycles, high BSC (about 90% of the initial BSC) was maintained. In addition, the characterization results indicated that the mesostructure of OMA-2Ca remained intact during sulfidation and regeneration except that the amorphous wall was converted to γ-Al2O3 phase, and active species were still well dispersed on support, which indicated the stability of Mn-La/OMA-2Ca sorbent.

High performance of Fe nanoparticles/carbon aerogel sorbents for H2S Removal

To solve the effect of the strong reduction gas, sintering problem and improve the desulfurization activity. Fe nanoparticles (NPs) into carbon aerogel desulfurizers were fabricated with by 50%Fe/C700 precursor and their performance for H2S removal in hot coal gas was studied. The Fe nanoparticles loading in mesoporous carbon aerogels with larger specific surface area and pore volume sorbent were designed and firstly applied to remove H2S with high efficiency in hot coal gas. The H2S removal experiments were conducted in the temperature range of 500–650°C using hot coal gas containing 0.2vol% H2S. We explored the optimum temperature conditions and the influence of textural parameters of carbon aerogels and tested the Fe nanoparticles desulfurizers with 10–20% H2 and 10–20% CO. The fresh, used, regenerated samples were characterized by N2 adsorption, X-ray diffraction, high-resolution scanning electron microscope techniques (HRSEM) and high resolution transmission electron microscopy (HRTEM). The results confirmed that Fe nanoparticle sorbent had high desulfurization performance. This work could provide a new direction and new field in hot coal gas desulfurization and would be important to research on the development sector of the coal industry.

High H2O-resistance CaO-MnOx/MSU-H sorbents for hot coal gas desulfurization

A series of xMnyCa/MSU-H sorbents with various Mn/Ca molar ratio were first designed and synthesized with a sol-gel method. The desulfurization performance of the new sorbent was investigated at 600–800°C in hot coal gas. 90Mn10Ca/MSU-H exhibited better desulfurization performance at 750°C with a breakthrough sulfur capacity (BSC) of 18.69g S/100g sorbent compared to other supported Mn-based sorbents (13.2g S/100g sorbent) in similar desulfurization condition, and strong durability in multiple sulfidation-regeneration cycles using oxidation/reduction regeneration method which resolved the scientific issue of that CaSO4 is hardly decomposed to CaO. The introduction of Ca species effectively promoted the dispersion of active constituents, which improved the desulfurization activity. More importantly, 90Mn10Ca/MSU-H showed excellent H2O-resistance ability due to the fact that CaO enhanced the sorption of H2O. Moreover, the utilization of MSU-H with large pore size and excellent thermal stability effectively assured fast mass-transfer and confined the migration of active particles, which led to long lifetime stability of sorbents.

Study of molybdenum–nickel alumina based catal-sorbents to simultaneously remove of H2S and NH3 from hot coal gas

Molybdenum–nickel-based catal-sorbents were prepared with gamma-alumina (γ-Al2O3) via an impregnation (MNAI30) method, and tested for the simultaneous removal of H2S and NH3 gases in a fixed-bed reactor system. The NH3 and H2S breakthrough times of the MNAI30 catal-sorbents were 200 and 225 min, respectively. The NH3 breakthrough time was shorter than that of H2S because the NH3 decomposition ability was decreased when α- and β-NiMoO4, NiO, and MoO3 were converted into Ni3S2 and MoS2, which were ineffective in decomposing NH3 in the presence of H2 gas. NiAl2O4 was also observed in the MNAI30 catal-sorbent and was reduced during the decomposition of NH3 at a low temperature, a phenomenon that improved the NH3 decomposition ability of the catal-sorbent during the H2S absorption process.

Performance of rare earth oxide doped Mn-based sorbent on various silica supports for hot coal gas desulfurization

A Mn-based sorbent with high desulfurization efficiency were fabricated using various mesoporous silica as support and doping rare earth oxides, and their physical properties were characterized by means of XRD, BET, H2-TPR, CO2-TPD, O2-TPD and UV–Vis techniques. The results indicated that Mn/MCF exhibited the highest desulfurization performance among Mn/MCM-41, Mn/SBA-15, Mn/MCM-48 and Mn/MCF due to the 3-D ultra-large mesopores and excellent thermal stability of MCF at 700°C. Doping rare earth oxides into Mn/MCF can make the high dispersion of active particles. But the breakthrough sulfur capacities (BSCs) over 95Mn5Ce/MCF, 95Mn5La/MCF and 95Mn5Sm/MCF sorbents are lower than Mn/MCF sorbent due to the lower BSCs of CeO2, Sm2O3 and La2O3 themselves and the lower SBET and VT. The desulfurization efficiency and precision further declined with increasing steam content for Mn/MCF sorbent. The high sulfur capacity over the Mn/MCF sorbent was maintained during the five consecutive desulfurization/regeneration cycles.

Effect of microwave irradiation on the preparation of iron oxide/arenaceous clay sorbent for hot coal gas desulfurization

For applications in the high temperature coal gas desulfurization process, iron oxide/arenaceous clay sorbents were prepared by microwave irradiation and conventional heating, respectively. The desulfurization performances of sorbents were evaluated using a fixed-bed reactor with simulated coal gas. The effects of calcination temperature and microwave heating time on the properties of sorbents were also investigated. The microwave-irradiated sorbents exhibit sulfur capacity and reactivity greater than those prepared by conventional heating. X-ray diffraction, X-ray photoelectron spectroscopy, a scanning electron microscope, a transmission electron microscope and N2 adsorption were used to characterize the physical and structural properties of the sorbents. Several benefits have been observed using microwave heating rather than conventional heating for the preparation of sorbents. The results indicate that microwave irradiation leads to better inner structure of sorbent and more uniform distribution of the active component with smaller particle size, which facilitate chemical reaction and mass transfer. Microwave irradiation also results in greater outer layer electron density and higher contents of surface metal element, both of which are beneficial to the increase of absorption efficiency and desulfurization reactivity. Then the microwave-irradiated sorbents were tested for three successive sulfurization–regeneration cycles, the 3rd regenerated sorbent still performed well with no apparent deterioration, it proved that the sorbent has good regenerability and is suitable for hot gas desulfurization.

Effects of microwave irradiation on H2S removal activity from hot coal gas by modified semicoke-supported ZnO sorbents

To improve the desulfurization performance of sorbents at a low cost, modified semicoke-supported zinc oxide sorbents were prepared for hot coal gas by calcining the precursors using microwave and conventional heating. The desulfurization performances of these sorbents were evaluated over a fixed-bed reactor. The effects of microwave-assisted calcination temperature and time on the properties of sorbents were also investigated. These sorbents were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption. The results show that the sorbents calcined by microwave exhibited a much higher sorbent utilization and desulfurization efficiency than those heated by conventional method. Compared to conventional heating, even and rapid heating of microwave led to smaller crystal size and better dispersion of active species. The Brunauer–Emmett–Teller results confirm that microwave irradiation modified the microstructure improved the pore structure (an increase in the specific surface area and pore volume), thus facilitating the gas–solid interactions during the desulfurization processes. A higher concentration of elements Zn and O was observed on the surface of sorbents by XPS analysis, facilitating the reaction of active species with H2S. The performance of the sorbents heated by microwave irradiation appeared to be stable over multiple sulfidation–regeneration cycles.

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.

Performance of Zn–Fe–Mn/MCM-48 sorbents for high temperature H2S removal and analysis of regeneration process

MCM-48 was synthesized using a rapid and facile process at room temperature. A series of 50%Zn–Fe–Mn/MCM-48 sorbents were prepared and their performance of hot coal gas desulfurization was investigated. High breakthrough sulfur capacity (13.2g-S/100g sorbent) and utilization (66.1%) of 50%1Zn2Fe2Mn/MCM-48 sorbent at 550°C was achieved. The characterization results of XRD, BET, TPR and FT-IR revealed that MCM-48 had excellent thermal stability at less than 700°C, ZnMn2O4 and (Mn, Zn)Fe2O4 were mainly active particles in fresh sorbents which were highly dispersed on support. The MCM-48 mesoporous structure remained intact after eight successive desulfurization/regeneration cycles. The regeneration process of 50%1Zn2Fe2Mn/MCM-48 sorbent was analyzed, it indicated that the breakthrough sulfur capacity decline of sorbent was due to the migration of Zn onto the sorbent surface and Zn accumulated on the surface and vaporized to the exterior from the surface. In the TPO test, the oxidation of Zn was different for 50%Zn/MCM-48 at 700°C. It revealed that the temperature of regeneration for ZnO sorbent should be higher than 700°C.

Effects of ultrasound on the desulfurization performance of hot coal gas over Zn-Mn-Cu supported on semi-coke sorbent prepared by high-pressure impregnation method

Zn-Mn-Cu/SC(U) sorbent was hydrothermally synthesized by ultrasound-assisted high-pressure impregnation method with semi-coke (SC) as support and the mixed solution of zinc nitrate, manganese nitrate and copper nitrate as active component precursors. The desulfurization performances of hot coal gas on the prepared sorbent at a mid-temperature of 500 °C were tested in fixed-bed reactor. Morphology and pore structure of the prepared sorbent were also characterized by TEM, N2 adsorption/desorption isotherms and XRD. For comparison, the sorbent of Zn-Mn-Cu/SC prepared by conventional high-pressure impregnation was also evaluated and characterized in order to study the effects of ultrasound treatment. Zn-Mn-Cu/SC(U) sorbent prepared by high-pressure impregnation under ultrasound-assisted condition showed a better desulfurization performance than Zn-Mn-Cu/SC. It could remove H2S from 1000×10−6 m3/m3 to 0.1×10−6 m3/m3 at 500 °C and maintained for 12.5 h with the sulfur capacity of 7.74%, in which both the breakthrough time and sulfur capacity were about 32% and 51% higher than those of Zn-Mn-Cu/SC sorbent. The introduction of ultrasound during high-pressure impregnation process greatly improved the morphology and pore structure of the sorbent. The ultrasonic treatment made particle size of active components smaller and made them more evenly disperse on semi-coke support, which provided more opportunities to contact with H2S in coal-based gases. However, there were no any difference in compositions and existing forms of active components on the Zn-Mn-Cu/SC and Zn-Mn-Cu/SC(U) sorbents.

High-temperature desulfurization of hot coal gas on Mo modified Mn/KIT-1 sorbents

The MnxMoy/KIT-1 sorbents with different Mn/Mo molar ratio were prepared by a sol–gel method. The structural properties of these sorbents were investigated by XRD, N2-adsorption, H2-TPR, TEM, SEM, XPS and TG/DSC techniques. It revealed that the mixed metal oxides were highly dispersed in the wormlike-hole channels of KIT-1 support and there is high surface area and large pore volume for MnxMoy/KIT-1 expect for Mn50Mo50/KIT-1. The effects of the Mn/Mo molar ratio, desulfurization temperature and steam content on the desulfurization performance were investigated. The addition of small amount of Mo in Mn/KIT-1 sorbents can improve significantly sulfur capacity (168.4mgS/g sorbent) of sorbent due to the synergetic effects of Mn–Mo oxides. The results of five successive desulfurization-regeneration cycles verified that high sulfur capacity of sorbent was maintained.

Feasibility Application of Cu-Contaminated Soil on the Removal of H<sub>2</sub>S from Hot Coal Gas

In this study Cu-contaminated soils were chosen as a candidate material for the removal of hydrogen sulfide (H2S) from hot coal gas. Experimental results showed that the H2S was significantly reduced below 10ppm when the Cu-contaminated soils were reacted with H2S. The optimal removal temperature of H2S was found to be at 923K in the operating conditions. In addition to Cu species, free Fe oxides in the contaminated soils also performed an active species to react with H2S and enhanced the overall sulfur capacity. Through the XPS analysis, Fe sulfide (FeS) and Cu sulfide (Cu2S) were the major products after removal experiments. Regeneration experimental results also indicated that the Cu-contaminated soils can be regenerated by pass air and thus be reused for many times. [doi:10.2320/matertrans.M2014393]

Synthesis of functional xLayMn/KIT-6 and features in hot coal gas desulphurization.

To enhance the stability of sorbents during continuous desulphurization-regeneration cycles, KIT-6 with 3D pore channels was used as a support for the sorbents. A series of mesoporous xLayMn/KIT-6 sorbents with different La/Mn atomic ratios were fabricated using a sol-gel method and their desulphurization properties of hot coal gas were investigated at 700-850 °C. 3La97Mn/KIT-6 performed the best at 800 °C with a breakthrough sulphur capacity of 11.56 g sulphur per 100 g sorbent. The eight successive desulphurization (800 °C)-regeneration (600 °C) cycles revealed that 3La97Mn/KIT-6 with endurable regeneration abilities could retain 80% of the initial sulphur capacity. It indicated a better desulphurization performance compared to pure 3La97Mn and 3La97Mn/MCM-41. The fresh and used xLayMn/KIT-6 sorbents were characterized by means of BET, XRD, HRTEM, XPS and H2-TPR techniques. The XRD patterns and HRTEM images of fresh and used 3La97Mn/KIT-6 verified that the utilization of KIT-6 effectively suppressed the aggregation of Mn2O3 particles and improved the stability of the sorbent.

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...