H2S Removal Capacity Research Articles

Catalytic fixation of hydrogen sulfide over CuO-CaCO3 co-impregnated tea stalk-derived biochar

Effective treatment of hydrogen sulfide (H2S) is crucial for minimizing nuisance odors from intensive livestock and poultry operations. The development of high-performance desulfurizers holds practical significance in this context. Herein, a novel CuO-CaCO3 co-impregnated biochar desulfurizer (CuxCay/BCT) was synthesized by impregnation-pyrolysis method, using waste tea stalks and metal salts as raw materials, and it is intended for the treatment of H2S at room temperature. The optimized Cu0.75Ca0.25/BC800 shows an excellent H2S removal capacity of 182.67 mg/g, which is 31 times and 5.6 times that of inactivated biochar (BC800) and copper-oxide-impregnated biochar (Cu0.75/BC800). The desulfurization mechanism of Cu0.75Ca0.25/BC800 involves synergistic effect of reactive adsorption and catalytic oxidation. CaCO3’s alkaline adsorption sites and copper-mediated activation of superoxide radicals (∙O2-) were critical in this reaction. Besides, Cu0.75Ca0.25/BC800 demonstrated excellent reusability, retaining approximately 85 % of its initial H2S removal capacity after seven cycles of desulfurization and regeneration. This study aims to develop a metal oxide- and carbonate-impregnated biochar-based desulfurizer, with the goal of advancing the technology for catalytic removal of H2S in a more environmentally friendly and effective manner.

Cu-MOF-derived Cu nanoparticles decorated porous N-doped biochar for low-temperature H2S desulfurization

Hydrogen sulfide (H2S) is a highly toxic and corrosive gas that poses significant risks to human health and the environment. Therefore, the development of an adsorbent capable of efficiently purifying H2S at room temperature remains a challenging task. In this study, a novel composite adsorbent with a specific surface area of 434 m2·g−1 was fabricated by modifying porous N-doped biochar with Cu nanoparticles (Cu/NBC) derived from Cu-MOFs for low-temperature desulfurization of H2S. The effect of pyrolysis temperature and the doping ratio of Cu-MOFs to biochar on the desulfurization performance of H2S for the as-prepared Cu/NBC was comprehensively investigated. Experimental results indicated that the desulfurization capability of the optimized Cu/NBC-600-1 adsorbent (synthesized at a pyrolysis temperature of 600 °C and a doping ratio of 1:1) was significantly affected by the desulfurization conditions, and the optimal conditions were determined to be at 25 °C, with 20 % oxygen content and 70 % relative humidity. Under the optimized conditions, the Cu/NBC-600-1 adsorbent exhibited a high H2S removal capacity of 158.28 mg·g−1, which was about 3.8 times higher than that of the pristine N-doped biochar. The desulfurization mechanism of the Cu/NBC composite was demonstrated to involve reactive adsorption and catalytic oxidation, resulting in the formation of elemental sulfur and copper sulfides as the main products. This study not only provides a promising approach to modify porous biochar with MOF derivatives, but also offers an effective strategy to remove low concentration H2S at room temperature.

Bench and pilot scale assessment of 5A molecular sieves for tail gas treatment applications

The modified Claus Process stands out as the predominant method for sulfur recovery within natural gas and crude oil processing facilities. Over the past five decades, in a bid to mitigate the environmental consequences of SO2 emissions, the efficiencies of sulfur recovery units have been enhanced through the integration of tail gas treating units (TGTU). Globally, it is imperative that this sulfur recovery efficiency attains a minimum of 99.95%. This paper delves into both bench- and pilot-scale evaluations of utilizing commercial 5 A molecular sieves to extract H2S from specific tail gas streams, as part of scrutinizing the efficacy of a novel tail gas treatment process, delineated in Patent No. US 10662061 B1 (May 26, 2020). The evaluation revealed that employing a 5 A molecular sieve to remove H2S from dry tail gas treating presents distinct advantages. Notably, the CO2 adsorption capacity on 5 A molecular sieves, being several times that of H2S, did not substantially impair the physical stability and removal capacity of 99.95+% tail gas treating, even after 99 adsorption/desorption cycles. Furthermore, the evaluation demonstrated that extended regeneration at 300°C (as opposed to 250°C) following the 50th and 90th cycles could effectively reinstate the original removal capacity of the 5 A molecular sieves. Additionally, the gas emanating from the 5 A molecular sieve bed could be reused as regeneration gas for the second stage of the patented process. The H2S removal capacity of 5 A molecular sieves from dry tail gas, approximately 1.3 mmol/g, aligns with the reported capacities of other adsorbents, which range from 0.37 to 1.53 mmol/g. Given the cost-effectiveness of 5 A molecular sieves compared to AgY molecular sieves, and based on the evaluation outcomes, it is judicious to conclude that the use of 5 A molecular sieves will be a compelling option for future tail gas treating within sulfur recovery units.

Ca-Cu/Al2O3 catalysts for H2S removal at near ambient temperature: Synthesis, characterization, DFT calculation, and mechanistic insights

A series of Ca-doped CuxO/Al2O3 catalysts were developed using the excessive impregnation method for H2S catalytic oxidation at near-ambient temperatures. Ca(NO3)-CuxO/Al2O3 catalyst with 2.5 wt% Ca exhibited optimal H2S desulfurization performance at 60 °C and RH 60%, achieving an H2S removal capacity of 401.34 mg/g. Experimental, characterization, and DFT calculation results demonstrate that during the catalytic oxidation of H2S, H2O can be catalytically convert into ·OH while simultaneously capturing and dissociating H2S. The ·OH and NO3- then catalyze the oxidation of HS-/S2- to elemental S. Moreover, the redundant OH adsorbed on the basic sites can buffer the pH and promote the dissociation of H2S. The above cyclic process could alleviate the deactivation of the Ca-Cu/Al2O3 catalyst. Therefore, a ·OH-induced desulfurization mechanism assisted with Ca2+ buffer the pH and NO3- cyclic oxidation of H2S has been proposed. This work contributes to the preparation of high-capacity mental-based catalysts for H2S oxidation.

Cu/TiO2 adsorbents modified by air plasma for adsorption–oxidation of H2S

In this study, non-thermal plasma (NTP) was employed to modify the Cu/TiO2 adsorbent to efficiently purify H2S in low-temperature and micro-oxygen environments. The effects of Cu loading amounts and atmospheres of NTP treatment on the adsorption-oxidation performance of the adsorbents were investigated. The NTP modification successfully boosted the H2S removal capacity to varying degrees, and the optimized adsorbent treated by air plasma (Cu/TiO2-Air) attained the best H2S breakthrough capacity of 113.29 mg H2S/gadsorbent, which was almost 5 times higher than that of the adsorbent without NTP modification. Further studies demonstrated that the superior performance of Cu/TiO2-Air was attributed to increased mesoporous volume, more exposure of active sites (CuO) and functional groups (amino groups and hydroxyl groups), enhanced Ti-O-Cu interaction, and the favorable ratio of active oxygen species. Additionally, the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicated the main reason for the deactivation was the consumption of the active components (CuO) and the agglomeration of reaction products (CuS and SO42−) occupying the active sites on the surface and the inner pores of the adsorbents.

Study on the essential features for MOFs to reversible adsorption of H2S at room temperature

Metal-organic frameworks (MOFs) have been extensively studied for hydrogen sulfide (H2S) capture. However, reversible adsorption of H2S by MOFs materials, which allow the adsorbents to be repeatedly used, remains challenging. To get a rational insight into the reversible H2S adsorption on MOFs, eight MOFs with different features were selected as representatives, and their behaviors of adsorption and desorption for H2S in three cycles were investigated in a fixed-bed reactor. X-ray diffraction and nitrogen adsorption-desorption characterization were used to confirm the reversibility based on the alterations in MOFs’ physical and chemical properties before and after H2S adsorption. The results indicated that only UiO-66, MOF-801, and Mg-MOF-74 exhibited reversibility among these selected MOFs. Nevertheless, their highest H2S capacity is only 3.81 mg/g, far away from the practical application. Calculation results of adsorption sites, the density of states, adsorption distance, and the heat of adsorption show that a weak interaction between MOFs and H2S, which is afforded by metal centers or/and organic ligands, is needed for reversible adsorption. However, it is difficult to get a satisfactory H2S removal capacity in such a situation. Introducing new adsorption sites into structurally stable MOFs is considered an efficient strategy for increasing their reversible adsorption capacity.

CaCO3-ZnO loaded scrap rice-derived biochar for H2S removal at room-temperature: Characterization, performance and mechanism

Metal oxide loaded carbon-based materials have attracted extensive attention as promising desulfurizers to solve the problem of H2S emission at room temperature. However, low desulfurization capacity, difficult regeneration and high economic cost are the main problems of metal oxide loaded carbon-based desulfurizers, which limit their industrial application. Herein, a novel and low-cost CaCO3-ZnO loaded biochar (RCZ) was synthesized by one-step pyrolysis of scrap rice and metal salts for highly efficient H2S removal at room-temperature. The optimized RCZ-1-1-1-800 sample showed an excellent H2S removal ability of 834.48 mg/g at the reaction temperature of 25 °C, oxygen content of 10%, and relative humidity of 70% as compared to 29.31 mg/g achieved by the inactivated biochar (prepared without activator). Such an RCZ-1-1-1-800 desulfurizer also delivered a high H2S removal ability under different desulfurization conditions. The associated desulfurization mechanism of RCZ was the coupling of reactive adsorption and catalytic oxidation with sulfur being the main desulfurization product. Moreover, the as-fabricated RCZ also exhibited a high reusability, retaining about 95% of the initial H2S removal capacity after five adsorption/regeneration cycles. This work provides a promising idea for the preparation of low-cost and high-capacity metal oxide- and carbonate-loaded carbon-based desulfurizers.

Photoautotrophic removal of hydrogen sulfide from biogas using purple and green sulfur bacteria.

Biogas desulfurization based on anoxygenic photosynthetic processes represents an alternative to physicochemical technologies, decreasing the risk of O2 and N2 contamination. This work aimed at assessing the potential of Allochromatium vinosum and Chlorobium limicola for biogas desulfurization under different light intensities (10 and 25 klx) and H2S concentrations (1 %, 1.5 % and 2 %) in batch photobioreactors. In addition, the influence of rising biogas flow rates (2.9, 5.8 and 11.5L d-1 in stage I, II and III, respectively) on the desulfurization performance in a 2.3L photobioreactor utilizing C. limicola under continuous mode was assessed. The light intensity of 25 klx negatively influenced the growth of A. vinosum and C. limicola, resulting in decreased H2S removal capacity. An increase in H2S concentrations resulted in higher volumetric H2S removal rates in C. limicola (2.9-5.3mgL-1 d-1) tests compared to A. vinosum (2.4-4.6mgL-1 d-1) tests. The continuous photobioreactor completely removed H2S from biogas in stage I and II. The highest flow rate in stage III induced a deterioration in the desulfurization activity of C. limicola. Overall, the high H2S tolerance of A. vinosum and C. limicola supports their use in H2S desulfurization from biogas.

The influencing mechanism of O2, H2O, and CO2 on the H2S removal of food waste digestate-derived biochar with abundant minerals

Hydrogen sulfide (H2S) removal has been a significant concern in various industries. In this study, food waste digestate-derived biochar (DFW-BC), a by-product of food waste treatment with abundant minerals, was assessed for removing H2S from different simulated biogas containing oxygen (O2) and carbon dioxide (CO2) and under different moisture (H2O) contents (0% and 20%) of biochar. The influencing mechanisms of the gas conditions combined with the moisture contents were also investigated. The results showed an H2S removal of 1.75 mg g−1 for dry biochar under pure H2S, 4.29 mg g−1 for dry biochar under H2S + O2, 5.29 mg g−1 for humid biochar under H2S, and 12.50 mg g−1 for humid biochar under H2S + O2. For dry DFW-BC, the high Fe content was responsible for the O2 enhancement. In contrast, O2 + H2O activated the catalytic H2S oxidation of the less reactive minerals (mainly Ca). The inhibition of CO2 on H2S adsorption was not obvious for dry DFW-BC; the specific pore structure may have provided a buffer against the physisorption competition of CO2. However, when H2O was present on DFW-BC, the changes in critical biochar properties and sulfur speciation as opposed to that without H2O implied an evident occurrence of CO2 chemisorption. This CO2 chemisorption partially hindered O2 + H2O enhancement, decreasing the H2S removal capacity from 12.50 to 8.88 mg g−1. The negative effect was ascribed to mineral carbonation of CO2, neutralizing the alkaline surface and immobilizing metal oxides, which thus reduced the acceleration in H2S dissociation and activation in catalytic H2S oxidation by O2 + H2O.Graphical

Ternary metal oxide nanocomposite for room temperature H2S and SO2 gas removal in wet conditions

A ternary Mn–Zn–Fe oxide nanocomposite was fabricated by a one-step coprecipitation method for the remotion of H2S and SO2 gases at room temperature. The nanocomposite has ZnO, MnO2, and ferrites with a surface area of 21.03 m2 g−1. The adsorbent was effective in mineralizing acidic sulfurous gases better in wet conditions. The material exhibited a maximum H2S and SO2 removal capacity of 1.31 and 0.49 mmol g−1, respectively, in the optimized experimental conditions. The spectroscopic analyses confirmed the formation of sulfide, sulfur, and sulfite as the mineralized products of H2S. Additionally, the nanocomposite could convert SO2 to sulfate as the sole oxidation by-product. The oxidation of these toxic gases was driven by the dissolution and dissociation of gas molecules in surface adsorbed water, followed by the redox behaviour of transition metal ions in the presence of molecular oxygen and water. Thus, the study presented a potential nanocomposite adsorbent for deep desulfurization applications.

Removal of H2S in an extremely acidic-biotrickling filter: Evaluation of removal performance and characterization of microbial communities

A cost-efficient, environmentally friendly, and extremely acidic biotrickling filter is essential for desulfurization to recover elemental sulfur and sulfate for extensively remediating H2S. The present study investigated the H2S removal capacity, accumulation of desulfurization products, sulfur balance, microbial community, and the H2S biodegradation kinetics. The results showed that when the empty bed retention time (EBRT) decreased from 180 s to 60 s, the removal efficiency of H2S decreased from 100% to 95.4%, and the elimination capacity increased from 18.0 ± 1.3–51.5 ± 3.2 gH2S m–3 h–1. Furthermore, with the increase of EBRT, the proportion of SO42–-S in the biodesulfurization products gradually decreased from 74.83% to 38.71%, whereas that of S0-S increased from 16.04% to 53.30%. The content of polysaccharide (PS), protein (PN), and the change of PN/PS values during the H2S removal process were studied. Moreover, 16 S rRNA high-throughput sequencing analysis showed that Acidithiobacillus, Thiobacillus, Sulfuricurvum, and Sulfobacillus were the main genera in the removal of H2S, and their total abundance was higher than 68.00%. In addition, the system viability and robustness were proved by shock loads and starvation regimes.

Evaluation of H2S gas removal by a biotrickling filter: Effect of oxygen dose on the performance and microbial communities

A cost-efficient and environmentally friendly biofiltration system is essential for desulfurization to recover elemental sulfur and sulfate for extensively remediating H2S. This work investigated the H2S removal capacity, accumulation of desulfurization products, sulfur balance, microbial community, and the pathway for sulfide oxidation under different O2 doses (1%, 3%, 5%, and 10%). The results showed that the removal efficiency of H2S increased from 94.1% to 100.0% with the increase of O2 dose. At 1% O2, the elimination capacity (EC) was 5.72 ± 0.33 gH2S m–3 h–1, and about 78.13% of S0-S was generated. However, with stepwise increase of O2 concentration to 10%, the EC became 6.00 ± 0.35 gH2S m–3 h–1, and SO42–-S was the dominant product at 80.39%. Furthermore, the sulfur balance was verified by calculating the proportion of sulfur compounds (S0-S, SO42−-S, and SO32−-S) and comparing the microstructure of packing material in the biotrickling filter. Moreover, 16 S rRNA high-throughput sequencing analysis showed that the cooperation of sulfur-oxidizing bacteria in the biofiltration system was the key to the stable and efficient removal of H2S. In addition, possible reaction pathways in which H2S was transformed to S0 and SO42− were proposed.

Insight into the influence of Ni2+ doping on the room temperature desulfurization/regeneration performance of ZnO supported MCM-41 adsorbents

Ni2+ doped ZnO/MCM-41 adsorbents with various doping content were prepared by melt infiltration method and its effect on the room temperature desulfurization and regeneration performance of ZnO adsorbents were systemically investigated. The experimental results indicated that the H2S removal capacity of the adsorbents first increased and then decreased with increasing the Ni2+ doping content, its value reaches the highest of 72.5 mg/g when the Ni2+ doping content is 3 at.%. The improved desulfurization performance was attributed to the decreased grain sizes of ZnO nanoparticles and the increased numbers of Lewis acid sites on its surface, the former affords more active sites towards H2S removal and the latter promoted the dissociation of H2S through acid-base reaction. It also found that Ni2+ doping has a negative effect on the regeneration performance of ZnO adsorbents. The incomplete regeneration of ZnS plus the collapse of adsorbents’ framework structure and the formation of sulfates during the regeneration process are responsible for its inferior regeneration performance.

The effect of ZnFe2O4/activated carbon adsorbent photocatalytic activity on gas-phase desulfurization

The effects of light exposure on the gas phase desulfurization of a reactive adsorbent consisting of ZnFe2O4 dispersed onto activated carbon (ZnFe2O4/AC) were investigated in both moist and dry conditions. The porosity and surface chemistry of the materials before and after the exposure to H2S were evaluated in details. The experimental results demonstrated that visible light irradiation has a negative effect on the H2S removal capacity. In moist conditions and under light, the photogenerated electron-hole pairs of ZnFe2O4 resulted in the formation of •OH, a strong oxidizer that directly oxidized H2S into H2SO3/H2SO4, which resulted in the deactivation of the adsorbent. In dry conditions, the photogenerated holes led to the oxidation of H2S to SO2, with the help of O2, and SO2 was released in the outlet. These findings provide an insight on the rational designing and practical applications of efficient H2S removal adsorbents, which might differ in the performance depending on the conditions of their usage.

Effective removal of hydrogen sulfide using Mn-based recovered oxides from recycled batteries

The use of clean and environmentally friendly renewable energy as well as the minimization of waste disposal are fundamental aspects to be considered nowadays in a circular economy approach. In this way, the development of efficient systems for sulfur removal in biomass and waste gasification is of key relevance and the use of recycled materials will provide an opportunity to combine the reduction of waste‘s production and the application of circular economy principles.Sorbents from waste powder of recycled batteries have been prepared at laboratory scale. Subsequently, their potential application to syngas cleaning is evaluated specifically for H2S removal. Lab-scale tests at 400°C, 10 bar and space velocity of 3500 h−1 were carried out using first a simplified gas mixture of 0.9% H2S in N2 and then a more complex one consisting of 20% H2, 40% CO and 0.45% H2S/N2 to investigate the effect of reducing components, CO and H2 co-existing with H2S in any syngas. Sorbent utilization values as high as 80% (w/w, %) were obtained when tested under realistic syngas composition. XRF, XRD, XPS, TEM and textural characterization results of fresh and sulfided samples showed that those materials with higher Mn contents showed higher H2S removal capacity although the Mn/Zn ratio demonstrated to play a crucial role in their selectivity to form sulfides. Additionally, plausible mechanisms for H2S removal are discussed where the influence of composition, structure and morphology of the recovered binary metal oxides on sulfur removal efficiency is analysed.

Carbon-Dioxide and Hydrogen-Sulfide Removal from Simulated Landfill Gas Using Steel Slag

Municipal solid waste landfills are a source of major greenhouse gases such as methane (CH4) and carbon dioxide (CO2) and emit a trace amount of hydrogen sulfide (H2S). Recently, steel slag has extensively been used for mineral CO2 sequestration to minimize the CO2 releases to the atmosphere. This study explores the potential of basic oxygen furnace (BOF) steel slag to simultaneously remove CO2 and H2S from landfill gas (LFG). Various batch and column tests were conducted to evaluate the CO2 and H2S removal potential of the BOF slag under various conditions such as moisture content and particle size of the BOF slag. The three different particle sizes of BOF slag (coarse, as-is, and fine) were exposed to continuous flow of a synthetic LFG [50% CO2, 48.25% CH4, and 1.75% H2S by volume (v/v)] in a column reactor to evaluate the effect of particle size on CO2 and H2S removal capacity of the slag. Similarly, the BOF slag was exposed to synthetic LFG as well as 20% (v/v) of H2S alone in batch reactors at varying moisture contents (10%–30% by weight) to evaluate the effect of moisture content on the CO2 and H2S removal capacity of the slag. A significant H2S removal of 27 g H2S kg−1 BOF slag and CO2 removal of 76 g CO2 kg−1 BOF slag were obtained in the batch reactor. The fine BOF slag (<0.106 mm) showed the maximum CO2 removal (300 g CO2 kg−1 BOF slag) and H2S removal (38 g H2S kg−1 BOF slag) upon exposure to continuous synthetic LFG flow in the column reactor. The quantitative X-ray diffraction (QXRD) analysis showed the highest increase in carbon (77.5 g C kg−1 BOF slag) and sulfur (28 g S kg−1 BOF slag) contents in the fine BOF slag, which was consistent with the mass balance of carbon and sulfur from CO2 and H2S uptake in column tests. The major reaction product with H2S was elemental sulfur depicted by the significant increase in the sulfur content in the X-ray fluorescence analysis. The key minerals involved in carbonation reactions were lime, portlandite, and larnite, as these minerals showed significant reduction in weight percentage (100%, 82%, and 80%, respectively) in the QXRD analysis. Overall, BOF slag showed promising results in mitigating CO2 and H2S from LFG.

Chars from wood gasification for removing H2S from biogas

Biomass gasification is a mature thermochemical process used to produce a gaseous fuel to run burners, engines, and gas turbines. One of the byproducts of biomass gasification is char, which is a residue with low value and sometimes this material is even considered waste. Therefore, options for using gasification chars are required. On the other hand, there is a necessity of making biogas production and use more attractive by employing cheap materials for the biogas cleaning process. One of the promising options for using gasification chars is for cleaning biogas produced via anaerobic digestion (AD). The objective of this work was to assess the use of residual gasification chars from fast growing wood species (Eucalyptus Grandis-EG and Pinus Patula-PP) to remove hydrogen sulfide (H2S) from biogas produced via AD. Gasification chars were produced employing a laboratory scale downdraft gasifier. EG char (EG-C30) was produced by gasification of EG using a 30 L min−1 airflow, whereas the PP chars (PP–C20 and PP-C40) were produced from PP using 20 and 40 L min−1 airflow. Results show that these three chars offer potential for biogas cleaning, although PP-derived chars produced at higher airflow rates are more effective. The H2S removal capacity of the chars is ascribed to their large apparent surface area (up to 517 m2 g−1) and the presence of minerals and metals (e.g., Ca, K, and Fe) in the chars’ ash.

Chemistry of H2S over the surface of Common solid sorbents in industrial natural gas desulfurization

The chemistry on sorptive H2S removal in industrial natural gas desulfurization was reviewed on mechanistic aspects of H2S adsorption/sorption over the surface of activated carbon, zeolite/molecular sieve, zinc oxide, copper oxide, and iron oxide as representative industrial common sorbents. H2S removal of natural gas underwent through weak chemisorption over the surface of activated carbon and zeolite/molecular sieve and dissociative chemisorption over the surface of ZnO, CuO, and Fe2O3 at ambient or relatively low temperature. Dissociative chemisorption over the oxides concomitantly occurred with lattice oxygen replacement by sulfur migration into bulk of oxides, which contributes to higher H2S removal capacity. The infrared spectroscopy and X-ray photoelectron spectroscopy studies elucidated the influence of the presence of impurities, such as CO2 or H2O on H2S removal over each surface. The advantages and disadvantages of industrially preferred H2S removal sorbents, CuO and Fe2O3, were highlighted especially on the role of oxidation state. At last, the discussion of spent sulfided sorbents was extended to the environmental and safety aspect.

Bifunctional ZnO-MgO/activated carbon adsorbents boost H2S room temperature adsorption and catalytic oxidation

A series of bifunctional ZnO-MgO/activated carbon adsorbents (denoted as MgxZn1-x/AC) were synthesized. The molar ratio of Mg/(Mg + Zn) was optimized maintaining a 20 wt. % total content of oxides. The materials were characterized using adsorption of nitrogen, TEM-EDS, XPS, XRD, FT-IR, TG and CO2-TPD. On them an H2S breakthrough capacity was measured in moist and dry conditions in the absence of oxygen in a gas stream. The best adsorbent retained 113.4 mg/g at moist conditions and 96.5 mg/g at dry conditions. Besides a large surface area and pore volume, and a high dispersion of ZnO, the high H2S removal capacity was attributed to MgO, which, owing to its basicity and limited solubility in water, continuously promoted the formation of HS− important for reactive adsorption and then for catalytic oxidation. The detected surface reaction/catalytic oxidation products were ZnS, elemental sulfur and sulfates. Based on the results obtained, plausible desulfurization mechanisms were proposed.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H2S, but it’s difficult to remove high concentration of H2S in biogas efficiently due to the mass transfer limitation of H2S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H2S (about 5000 ppmv) from biogas. The removal efficiency of H2S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H2S loading was 143.1 ± 4.5 g/(m3·h). Moreover, the removal capacity of H2S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m3·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O2 and H2S from gas to liquid through gas reflux.