Removal of Hydrogen Sulfide From Various Industrial Gases: A Review of The Most Promising Adsorbing Materials

Pilot-Scale Experimental Study on the Coupling of Venturi-Bubbling Reactor to Promote the Absorption of Leaked H2S

Natural gas generates varying concentrations of H2S during natural formation and extraction, and H2S leak accidents are frequent, posing a significant threat to the safety of human life and the environment. Conventional treatment technology equipment is large and does not meet the emergency requirements of the complex topographical gas field. This study aimed to design a pilot-scale method coupling the venturi and bubbling reactors to reduce equipment size and improve emergency capabilities for the absorption of leaked H2S. It found that the ring system self-priming venturi reactor, which was suitable only for the coarse treatment of toxic gases, maintained an absorption efficiency of around 50% under most operating conditions, with substantial variations due to changes in process parameters, but that redundancy of the bubbling reactor was high. With the synergistic effect of venturi and bubbling, the coupling process had an extremely high absorption efficiency, basically more than 95%. The experiments also showed that the H2S concentration at the outlet of the venturi-bubbling reactor increased with increasing inlet gas concentration and gas volume. The absorption performance improved significantly on increasing Fe3+ concentration; it increased first and then remained constant, and the optimum Fe3+ concentration for the absorption of leaked H2S was 21 000 mg/m3. The absorption performance decreased with increasing submergence height and then remained stable after the size of the inlet approached 600 mm, whereas the overall absorption efficiency of the venturi-bubbling reactor remained constant. The optimum operating temperature range was 10 °C-50 °C. The experimental system kept the outlet concentration below the emergency discharge standard for a continuous period of 48 h following practical use in the gas field and resulting in significant enhancement in mass transfer performance, fully satisfying the emergency requirements.

Parametric investigation and RSM optimization of DBD plasma methods (direct & indirect) for H2S conversion in the air

Hydrogen sulfide (H2S) is known as a harmful pollutant for the environment and human health, and its emission control is a high priority. Non-thermal plasma is an effective technology in this field. In this study, for the first time, the performance of direct and indirect H2S plasma conversion methods was compared, optimized, and modeled with the CCD method. H2S was diluted in zero air, and the study investigated the effect of discharge power, relative humidity, total flow rate, initial H2S concentration, and their interactions. ANOVA results showed that the models for H2S conversion efficiency and energy yield were significant and efficient. The direct method achieved a maximum conversion efficiency of 56 % and energy yield of 3.43 g/kWh, while the indirect method produced 68 % conversion efficiency and 1.59 g/kWh energy yield. According to the process optimization results, the direct conversion method is more optimal than the indirect conversion method due to the presence of active species and high-energy electrons in the plasma treatment, and it is a better choice if there are suitable working conditions.

Review of Theoretical and Computational Studies of Bulk and Single Atom Catalysts for H2 S Catalytic Conversion

Catalytic conversion of hydrogen sulfide (H2 S) plays a vital role in environmental protection and safety production. In this review, recent theoretical advances for catalytic conversion of H2 S are systemically summarized. Firstly, different mechanisms of catalytic conversion of H2 S are elucidated. Secondly, theoretical studies of catalytic conversion of H2 S on surfaces of metals, metal compounds, and single-atom catalysts (SACs) are systematically reviewed. In the meantime, various strategies which have been adopted to improve the catalytic performance of catalysts in the catalytic conversion of H2 S are also reviewed, mainly including facet morphology control, doped heteroatoms, metal deposition, and defective engineering. Finally, new directions of catalytic conversion of H2 S are proposed and potential strategies to further promote conversion of H2 S are also suggested: including SACs, double atom catalysts (DACs), single cluster catalysts (SCCs), frustrated Lewis pairs (FLPs), etc. The present comprehensive review can provide an insight for the future development of new catalysts for the catalytic conversion of H2 S.

Solubility and Thermodynamic Parameters of H2S/CH4 in Ionic Liquids Determined by 1H NMR

Natural gas remains an important global source of energy. Usually, sour gas from the well or refinery stream contains H2S among other contaminants that should be removed to fulfill permissible standards of use. Despite the use of different gas-liquid sour gas upgrading technologies, ionic liquids (ILs) have been recognized as promising materials to remove H2S from sour gas. However, data concerned with thermodynamic solution functions of H2S in ILs have scarcely been reported in the literature. In this work, solution 1H NMR spectroscopy was employed for quantifying H2S soluble in [BMIM][Cl] and for gaining a better understanding of the H2S-IL interaction. Experiments were carried out in a Young-Tap NMR tube containing a saturated solution of H2S/CH4/[BMIM][Cl] and recording spectra from 298 to 333 K. The thermodynamic solution functions, determined from the Van't Hoff equation, showed that solubility of the H2S in the [BMIM][Cl] is an exothermic gas-liquid physisorption process (ΔsolH° = -66.13 kJmol-1) with a negative entropy change (ΔsolS° = -168.19 JK-1 mol-1). 1H NMR spectra of the H2S/[BMIM][Cl] solution show a feature of strong solute-solvent interactions. However, solubility enthalpy is a fifth of the H-S bond energy value. Results from 1H NMR spectroscopy also agree with those from the bench dynamic experiments.

Hydrogen Sulfide Removal via Sorption Process on Activated Carbon-Metal Oxide Composites Derived from Different Biomass Sources

Biomass exploitation is a global trend due to the circular economy and the environmentally friendly spirit. Numerous applications are now based on the use of biomass-derived products. Hydrogen sulfide (H2S) is a highly toxic and environmentally hazardous gas which is emitted from various processes. Thus, the efficient removal of this toxic hazardous gas following cost-effective processes is an essential requirement. In this study, we present the synthesis and characterization of biomass-derived activated carbon/zinc oxide (ZnO@AC) composites from different biomass sources as potential candidates for H2S sorption. The synthesis involved a facile method for activated carbon production via pyrolysis and chemical activation of biomass precursors (spent coffee, Aloe-Vera waste leaves, and corncob). Activated carbon production was followed by the incorporation of zinc oxide nanoparticles into the porous carbon matrix using a simple melt impregnation method. The synthesized ZnO@AC composites were characterized using X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and nitrogen porosimetry. The H2S removal performance of the ZnO@AC composites was evaluated through sorption experiments using a handmade apparatus. Our findings demonstrate that the Aloe-Vera-, spent coffee-, and corncob-derived composites exhibit superior H2S sorption capacity up to 106 mgH2S/gads., 66 mgH2S/gads., and 47 mgH2S/gads., respectively.

CO2 Physisorption over an Industrial Molecular Sieve Zeolite: An Experimental and Theoretical Approach

The present work studies the adsorption of CO2 using a zeolitic industrial molecular sieve (IMS) with a high surface area. The effect of the CO2 feed concentration and the adsorption temperature in conjunction with multiple adsorption-desorption cycles was experimentally investigated. To assess the validity of the experimental results, theoretical calculations based on well-established equations were employed and the values of equilibrium, kinetic, and thermodynamic parameters are presented. Three additional column kinetic models were applied to the data obtained experimentally, in order to predict the breakthrough curves and thus facilitate process design. Results showed a negative correlation between temperature and adsorption capacity, indicating that physical adsorption takes place. Theoretical calculations revealed that the Langmuir isotherm, the Bangham kinetic model (i.e., pore diffusion is the rate-determining step), and the Thomas and Yoon-Nelson models were suitable to describe the CO2 adsorption process by the IMS. The IMS adsorbent material maintained its high CO2 adsorption capacity (>200 mg g-1) after multiple adsorption-desorption cycles, showing excellent regenerability and requiring only a mild desorption treatment (200 °C for 15 min) for regeneration.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

Determination of Total Sulfur Content in Fuels: A Comprehensive and Metrological Review Focusing on Compliance Assessment

Sulfur-containing compounds are naturally found in crude oil, and they can be partially removed during the refining process. The wide use of fossil fuels has a significant contribution to sulfur emissions into the atmosphere, and Governments are striving to reduce the amount of the fuels by environmental regulations. The reduction of sulfur levels in diesel and other transportation fuels is beneficial from economic and environmental points, but meeting this standard represents a major operational and economic challenge for the oil and gas industry. Quantitative measurement of the sulfur amount must be taken along the oil refining chains guided by standards of measurement and recommended analytical methods such as various American Society for Testing and Materials methods (ASTM D2622, ASTM D5453, ASTM D7039, and ASTM D7220). Advancement in the refining processes and environmental regulations also require reliable measurements and well-defined criteria for compliance assessment. This work presented a brief review of the ASTM Standards used in the laboratories of the Brazilian oil and gas industry to determine the total sulfur content in fuels. We also presented an approach based on the reproducibility of the measurement methods and the guard band concept to evaluate the conformity statement.

Adsorption of Hydrogen Sulfide on Activated Carbon Materials Derived from the Solid Fibrous Digestate

The goal of this work is to develop a sustainable value chain of carbonaceous adsorbents that can be produced from the solid fibrous digestate (SFD) of biogas plants and further applied in integrated desulfurization-upgrading (CO₂/CH₄ separation) processes of biogas to yield high-purity biomethane. For this purpose, physical and chemical activation of the SFD-derived BC was optimized to afford micro-mesoporous activated carbons (ACs) of high BET surface area (590-2300 m²g^-1) and enhanced pore volume (0.57-1.0 cm³g^-1). Gas breakthrough experiments from fixed bed columns of the obtained ACs, using real biogas mixture as feedstock, unveiled that the physical and chemical activation led to different types of ACs, which were sufficient for biogas upgrade and biogas desulfurization, respectively. Performing breakthrough experiments at three temperatures close to ambient, it was possible to define the optimum conditions for enhanced H₂S/CO₂ separation. It was also concluded that the H₂S adsorption capacity was significantly affected by the restriction to gas diffusion. Hence, the best performance was obtained at 50 °C, and the maximum observed in the H₂S adsorption capacity vs. the temperature was attributed to the counterbalance between adsorption and diffusion processes.

Carbon disulfide removal from gasoline fraction using zinc-carbon composite synthesized using microwave-assisted homogenous precipitation

Carbon disulfide (CS2) is one of the sulfur components that are naturally present in petroleum fractions. Its presence causes corrosion issues in the fuel facilities and deactivates the catalysts in the petrochemical processes. It is a hazardous component that negatively impacts the environment and public health due to its toxicity. This study used zinc-carbon (ZC) composite as a CS2 adsorbent from the gasoline fraction model component. The carbon is derived from date stone biomass. The ZC composite was prepared via a homogenous precipitation process by urea hydrolysis. The physicochemical properties of the prepared adsorbent are characterized using different techniques. The results confirm the loading of zinc oxide/hydroxide carbonate and urea-derived species on the carbon surface. The results were compared by the parent samples, raw carbon, and zinc hydroxide prepared by conventional and homogeneous precipitation. The CS2 adsorption process was performed using a batch system at atmospheric pressure. The effects of adsorbent dosage and adsorption temperatures have been examined. The results indicate that ZC has the highest CS2 adsorption capacity (124.3 mg.g-1 at 30 °C) compared to the parent adsorbents and the previously reported data. The kinetics and thermodynamic calculation results indicate the spontaneity and feasibility of the CS2 adsorption process.

Hydrogen sulfide removal from normal heptane using zinc oxide, silicon dioxide and zeolite 13X: adsorption capacity, kinetics, selectivity, breakthrough and regeneration

This article focuses on the H2S adsorption from normal heptane (nC7) as synthetic natural gas liquids (NGL) using ZnO, SiO2 and zeolite 13X in static mode. Results of the isotherm and kinetics of the investigated adsorbents for H2S adsorption under ambient condition showed that ZnO had the highest H2S adsorption capacity between 260 and 700 mgH2S.g-1 in the initial concentration range of 2500 and 7500 ppmH2S with an equilibrium time of less than 30 minutes. Additionally, the ZnO selectivity was greater than 3.16. In continued, H2S removal from nC7 with ZnO was examined in dynamic mode. The H2S breakthrough time for ZnO reduced from 210 to 25 minutes as weight hourly space velocity (WHSV) was increased from 5 to 20 h-1 at 30 bar. Also, the breakthrough time at 30 bar was about 2.5 times greater than that at atmospheric pressure. Furthermore, H2S/CO2 mixture (i.e., 1000 ppmH2S + 1000 ppmCO2) caused the H2S breakthrough time to increase approximately by 1.11-fold. Alternatively, the ZnO regeneration conditions with hot stagnant air were optimized at different initial H2S concentrations (1000 ~ 3000 ppmH2S) using the Box-Behnken design. For instance, ZnO contaminated with 1000 ppmH2S was regenerated with an efficiency of more than 98 % for 160 minutes at 285 °C.

Anchoring Cu-N active sites on functionalized polyacrylonitrile fibers for highly selective H2S/CO2 separation

As an essential part of clean energy, natural gas is often mixed with varying degrees of H₂S and CO₂, which poses a serious environmental hazard and reduces the fuel's calorific value. However, technology for selective H₂S removal from CO₂-containing gas streams is still not fully established. Herein, we synthesized functional polyacrylonitrile fibers with Cu-N coordination structure (PANF_EDA-Cu) by an amination-ligand reaction. The results showed that PANF_EDA-Cu exhibited a remarkable adsorption capacity (143 mg/g) for H₂S at ambient temperature, even in the presence of water vapor, and showed a good separation of H₂S/CO₂. X-ray absorption spectroscopy results confirmed the Cu-N active sites in as-prepared PANF_EDA-Cu and the formed S-Cu-N coordination structures after H₂S adsorption. The active Cu-N sites on the fiber surface and the strong interaction between highly reactive Cu atoms and S are the main reasons for the selective removal of H₂S. Additionally, a possible mechanism for the selective adsorption/removal of H₂S is proposed based on experimental and characterization results. This work will pave the way for the design of highly efficient and low-cost materials for gas separation.

Adsorptive Desulfurization of Condensate Contains Aromatic Compounds Using a Commercial Molecular Sieve

This study is undertaken to evaluate the potential of a commercial molecular sieve to remove diverse sulfur compounds from condensate with high aromatic on an industrial scale. For the first part of this study, the adsorbent is characterized in detail using inductively coupled plasma optical emission spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, and Brunauer-Emmett-Teller analysis. For the second part, dynamic breakthrough experiments on an industrial scale are performed to assess the dynamic adsorption performance of a commercial molecular sieve. Dynamic experiments show that the adsorbent effectively removes the sulfur compound from condensate that has approximately 900 ppmw S. In more detail, this commercial molecular sieve selectively desulfurizes condensate to about 12 ppmw S, and this is achieved when the concentration of non-sulfur aromatic is greater than 15 times higher than the total sulfur. As regeneration is a crucial part of the continuous adsorption-regeneration cycling process, the final part of this study is focused on finding a desorption method to avoid a sulfur concentration peak in tail gas.

Development of microwave-assisted nitrogen-modified activated carbon for efficient biogas desulfurization: a practical approach

Removal of H₂S (hydrogen sulfide) from biogas is anticipated for higher energy conversion of methane (CH₄), while reducing the detrimental impacts of corroding the metal parts in the plant and its hazardous effect on humans and the environment. The introduction of microwave (MW) heating and nitrogen-modification could generate superior adsorbent features, contributing to high H₂S removal. Up to date, there is no work reported on the influence of physicochemical characteristics of nitrogen-modified carbon synthesized via MW and conventional heating (TH) methods and their performance in H₂S removal. Palm shell activated carbon (PSAC) was functionalized with nitrogen groups via urea impregnation, followed by the synthesis of MW and TH at 950 °C, 500 ml/min of N₂ flow rate and 30 min of heating time. MW and TH heating effects on the modified PSAC adsorbent were analysed and compared towards hydrogen sulfide (H₂S) removal. PSAC with nitrogen functionalization produced using MW heating (PSAC-MW) demonstrates superior performance, with an adsorption capacity of 356.94 mg/g. The adsorbent sample generated using MW heating exhibited notable properties, including a large surface area and a sponge-like structure, with new pores developed within the current pores. Instead of that, there was an observation of 'hot spot' appearance during the MW heating process, which is believed to be responsible for the development of physical and chemical characteristics of the adsorbent. Thus, it is believed that MW heating was assisted in the development of the adsorbent's properties and at the same time contributed to the high removal of H₂S at low adsorption temperature. The utilization of biomass-based adsorbent (PSAC) for H₂S removal can address the lignocellulosic waste disposal problem, while mitigating the H₂S release from the biogas production plants thus has several environmental merits. This indirectly contributed to zero-waste generation, while overcoming the adverse effects of H₂S.

Templated Synthesis of SiO2 Nanotubes for Lithium-Ion Battery Applications: An In Situ (Scanning) Transmission Electron Microscopy Study

One of the weaknesses of silicon-based batteries is the rapid deterioration of the charge-storage capacity with increasing cycle numbers. Pure silicon anodes tend to suffer from poor cycling ability due to the pulverization of the crystal structure after repeated charge and discharge cycles. In this work, we present the synthesis of a hollow nanostructured SiO₂ material for lithium-ion anode applications to counter this drawback. To improve the understanding of the synthesis route, the crucial synthesis step of removing the ZnO template core is shown using an in situ closed gas-cell sample holder for transmission electron microscopy. A direct visual observation of the removal of the ZnO template from the SiO₂ shell is yet to be reported in the literature and is a critical step in understanding the mechanism by which these hollow nanostructures form from their core-shell precursors for future electrode material design. Using this unique technique, observation of dynamic phenomena at the individual particle scale is possible with simultaneous heating in a reactive gas environment. The electrochemical benefits of the hollow morphology are demonstrated with exceptional cycling performance, with capacity increasing with subsequent charge-discharge cycles. This demonstrates the criticality of nanostructured battery materials for the development of next-generation Li⁺-ion batteries.

Adsorption-Desorption Behavior of Hydrogen Sulfide Capture on a Modified Activated Carbon Surface

Metal-based adsorbents with varying active phase loadings were synthesized to capture hydrogen sulfide (H₂S) from a biogas mimic system. The adsorption-desorption cycles were implemented to ascertain the H₂S captured. All prepared adsorbents were evaluated by nitrogen adsorption, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. From the results, modified adsorbents, dual chemical mixture (DCM) and a core-shell (CS) had the highest H₂S adsorption performance with a range of 0.92-1.80 mg H₂S/g. After several cycles of heat/N₂ regeneration, the total H₂S adsorption capacity of the DCM adsorbent decreased by 62.1%, whereas the CS adsorbent decreased by only 25%. Meanwhile, the proposed behavioral model for H₂S adsorption-desorption was validated effectively using various analyses throughout the three cycles of adsorption-desorption samples. Moreover, as in this case, the ZnAc₂/ZnO/CAC_OS adsorbents show outstanding performances with 30 cycles of adsorption-desorption compared to only 12 cycles of ZnAc₂/ZnO/CAC_DCM. Thus, this research paper will provide fresh insights into adsorption-desorption behavior through the best adsorbents' development and the adsorbents' capability at the highest number of adsorption-desorption cycles.

A state-of-the-art review on capture and separation of hazardous hydrogen sulfide (H2S): Recent advances, challenges and outlook

Hydrogen sulfide (H₂S) is a flammable, corrosive and lethal gas even at low concentrations (ppm levels). Hence, the capture and removal of H₂S from various emitting sources (such as oil and gas processing facilities, natural emissions, sewage treatment plants, landfills and other industrial plants) is necessary to prevent and mitigate its adverse effects on human (causing respiratory failure and asphyxiation), environment (creating highly flammable and explosive environment), and facilities (resulting in corrosion of industrial equipment and pipelines). In this review, the state-of-the-art technologies for H₂S capture and removal are reviewed and discussed. In particular, the recent technologies for H₂S removal such as membrane, adsorption, absorption and membrane contactor are extensively reviewed. To date, adsorption using metal oxide-based sorbents is by far the most established technology in commercial scale for the fine removal of H₂S, while solvent absorption is also industrially matured for bulk removal of CO₂ and H₂S simultaneously. In addition, the strengths, limitations, technological gaps and way forward for each technology are also outlined. Furthermore, the comparison of established carbon capture technologies in simultaneous and selective removal of H₂S-CO₂ is also comprehensively discussed and presented. It was found that the existing carbon capture technologies are not adequate for the selective removal of H₂S from CO₂ due to their similar characteristics, and thus extensive research is still needed in this area.

Permeation of Ternary Mixture Containing H2S, CO2 and CH4 in Aquivion® Perfluorosulfonic Acid (PFSA) Ionomer Membranes

Aquivion^® E87-12S Perfluorosulfonated acid ionomer material (PFSA) has been studied as a membrane technology for natural gas sweetening from CO₂, H₂S due to its interesting chemical and mechanical stability and good separation performance for polar compounds in humid environments. In the present work, permeation of the H₂S/CO₂/CH₄ ternary mixture in this short-side PFSA chain was investigated at pressures up to 10 bar, temperatures up to 50 °C, and in a range of relative humidity (RH) from 20% to 90%. The results obtained confirm the strong dependence of Aquivion^® on water activity and temperature, and its ability to separate gases based on their water solubility without substantial differences between pure and mixed gas experiments. Indeed, even when tested in ternary mixture, the permeation behavior remains similar to that observed for pure components and binary mixtures. In particular, the permeability of H₂S is higher than that of CO₂ and methane CH₄, reaching values of 500 Barrer at 50 °C and 80% RH, against 450 and 23 Barrer for the other two gases respectively. Additionally, when tested at higher pressures of up to 10 bar under humid conditions, the membrane properties remained largely unchanged, thus confirming the overall stability and durability of Aquivion^® E87-12S in acid environments.

Effect of Bimetallic-Activated Carbon Impregnation on Adsorption-Desorption Performance for Hydrogen Sulfide (H2S) Capture

This study reports on the impregnation of bi-metallic adsorbents based on commercial coconut activated carbon (CAC), surface-modified with metal acetate (ZnAc₂), metal oxide (ZnO and TiO₂), and the basic compound potassium hydroxide (KOH). The morphology of the adsorbents was then characterized with SEM-EDX, the microporosity was determined using Brunauer-Emmett-Teller (BET) analysis, the thermal stability was investigated via thermogravity analysis (TGA), and functional group analysis was undertaken with Fourier-transform infrared (FTIR) spectroscopy. These modified adsorbents were subjected to a real adsorption test for H₂S capture using a 1 L adsorber with 5000 ppm H₂S balanced for N₂, with temperature and pressure maintained at an ambient condition. Adsorption-desorption was carried out in three cycles with the blower temperature varied from 50 °C to 150 °C as the desorption condition. Characterization results revealed that the impregnated solution homogeneously covered the adsorbent surface, effecting the morphology and properties. Based on this study, it was found that ZnAc₂/TiO₂/CAC_DCM showed a significant increase in adsorption capacity with the different temperatures applied for the desorption in the second cycle: 1.67 mg H₂S/g at 50 °C, 1.84 mg H₂S/g at 100 °C, and 1.96 mg H₂S/g at 150 °C. ZnAc₂/ZnO/CAC_DCM seemed to produce the lowest percentage of degradation in the three cycles for all the temperatures used in the adsorption-desorption process. Therefore, ZnAc₂/ZnO/CAC_DCM has the potential to be used and commercialized for biogas purification for H₂S removal.

A review on sensitivity of operating parameters on biogas catalysts for selective oxidation of Hydrogen Sulfide to elemental sulfur

Hydrogen sulfide (H₂S) is a critical problem for biogas applications, such as electricity and heat generation, or the production of different chemical compounds, due to corrosion and toxic effluent gases. The selective catalytic oxidation of H₂S to S is the most promising way to eliminate H₂S from biogas due to the lack of effluents, therefore can be considered a green technology. The most extensively used catalysts for H₂S selective oxidation can be classified in two groups: metal oxide-based catalysts, including vanadium and iron oxides, and carbon-based catalysts. Numerous studies have been devoted to studying their different catalytic performances. For industrial applications, the most suitable catalysts should be less sensitive to the operating parameters like the temperature, O₂/H₂S ratio, and H₂O content. More specifically, for metal oxides and carbon-based catalysts, the temperature and O₂/H₂S ratio have a similar effect on the conversion and selectivity, but carbon-based catalysts are less sensitive to water in all operating conditions.

Recent Attempts on the Removal of H2S from Various Gas Mixtures Using Zeolites and Waste-Based Adsorbents

Natural gas, biogas, and refinery gas all include H2S, which has adverse effects not only on the environment and human health but also on the equipment and catalysts that are employed in the relevant processes. H2S is removed from the aforementioned gases using a variety of techniques in order to fulfill the necessary sales criteria and for reasons of safety. The adsorption method stands out among various other approaches due to its straightforward operation, high level of efficiency, and low overall cost. This technique makes use of a variety of adsorbents, such as metal-organic frameworks (MOFs), activated carbon, and zeolites. The use of zeolite-based adsorbents is by far the most common of these various types. This is due to the specific properties of zeolite-based adsorbents, which include a high adsorption capacity, the ability to be regenerated, a high temperature stability, a diversity of types, the possibility of modification, high efficiency, and low cost. In addition, research is being done on adsorbents that are made from inexpensive raw materials in order to remove H2S. This article focuses on zeolites, zeolite modifications, and wastes as an adsorbent for the removal of H2S, all of which have been investigated fruitfully in recent years, as well as the promising applications of zeolites.

Technologies for Deep Biogas Purification and Use in Zero-Emission Fuel Cells Systems

A proper exploitation of biogas is key to recovering energy from biowaste in the framework of a circular economy and environmental sustainability of the energy sector. The main obstacle to widespread and efficient utilization of biogas is posed by some trace compounds (mainly sulfides and siloxanes), which can have a detrimental effect on downstream gas users (e.g., combustion engines, fuel cells, upgrading, and grid injection). Several purification technologies have been designed throughout the years. The following work reviews the main commercially available technologies along with the new concepts of cryogenic separation. This analysis aims to define a summary of the main technological aspects of the clean-up and upgrading technologies. Therefore, the work highlights which benefits and criticalities can emerge according to the intended final biogas application, and how they can be mitigated according to boundary conditions specific to the plant site (e.g., freshwater availability in WWTPs or energy recovery).

Efficiently Integrated Desulfurization from Natural Gas over Zn-ZIF-Derived Hierarchical Lamellar Carbon Frameworks

Selective removal of carbonyl sulfide (COS) and hydrogen sulfide (H₂S) is the key step for natural gas desulfurization due to the highly toxic and corrosive features of these gaseous sulfides, and efficient and stable desulfurizers are urgently needed in the industry. Herein, we report a class of nitrogen-functionalized, hierarchically lamellar carbon frameworks (N-HLCF-xs), which are obtained from the structural transformation of Zn zeolitic imidazolate frameworks via controllable carbonization. The N-HLCF-xs possess the desirable characteristics of large Brunauer-Emmett-Teller surface areas (645-923 m²/g), combined primary three-dimensional microporosity and secondary two-dimensional lamellar microstructure, and high density of nitrogen base sites with enhanced pyridine ratio (17.52 wt %, 59.91%). The anchored nitrogen base sites in N-HLCF-xs show improved accessibility, which boosts their interaction with acidic COS and H₂S. As expected, N-HLCF-xs can be employed as multifunctional and efficient desulfurizers for selective removal of COS and H₂S from natural gas. COS was first transformed into H₂S via catalytic hydrolysis, and the produced H₂S was then captured and separated and catalyzed oxidation into elemental sulfur. The above continuous processes can be achieved with solo N-HLCF-xs, giving extremely high efficiencies and reusability. Their integrated desulfurization performance was better than many desulfurizers used in the area, such as activated carbon, β zeolite, MIL-101(Fe), K₂CO₃/γ-Al₂O₃, and FeO_x/TiO₂.

Steel Manufacturing EAF Dust as a Potential Adsorbent for Hydrogen Sulfide Removal

Electric arc furnace dust (EAFD) is a high-volume steel manufacturing byproduct with currently limited value-added applications. EAFD contains metal oxides that can react with H₂S to form stable sulfides. Hence, the valorization potential of EAFD as an adsorbent material for syngas H₂S removal was investigated. EAFD from European steel plants was characterized and tested in dynamic H₂S breakthrough tests and benchmarked against a commercial ZnO-based adsorbent. For this, the EAFD was first processed into adsorbents by simple milling and granulation steps. The EAFD samples exhibited sulfur capture capacities at 400 °C and an SV of 17,000 h^-1 that correlated with the sample milling times and Zn concentrations. It was verified that only zinc participated in sulfur capture. Yet, both ZnO and the zinc in ZnFe₂O₄ were found to be active in sulfidation. At higher temperatures (500 and 600 °C), EAFD sample performance drastically improved and even exceeded the reference zinc oxide performance. The high-zinc (48% by mass) EAFD-B sample exhibited the highest tested performance at 500 °C, with a sulfur capture capacity of 234 mg g^-1. The results indicate that sufficiently high-zinc-content EAFD could serve as a viable sulfur capture material.

Insight into the effect of alkali treatment on enhancing adsorptivity of activated carbon for HCl removal in H2 feedstock

The removal of contaminated HCl gas in the petrochemical plants is essential to prevent corrosion problems, catalysts poisoning, and downstream contamination. Alkali-treated activated carbon (AC) was proposed as an effective adsorbent for HCl removal. Understanding the underlying mechanism of HCl adsorption on modified AC is key to design promising strategies for removal of HCl and other chlorinated hydrocarbon gases in the H2 feedstock. Here, a combined experimental and computational approach was used to study the role of alkali treatment on the adsorption behavior of HCl on the AC surfaces. We find that an interplay between alkali ions and oxygen-containing functional groups on the AC surface plays a crucial role in stabilizing the adsorbed HCl. The origin of such stable adsorbed configurations can be attributed to the dissociative adsorption of HCl leading to a formation of low energy species such as water, OH– and Cl– anions. These anions are electrostatically stabilized by the alkali ions resulting in a strong adsorption of −3.61 eV and −3.69 eV for Na+ and K+, respectively. Close investigation on charge analysis reveals that the epoxy functional group facilitates adsorbent-surface charge transfer where O and Cl atoms gain more charges of 0.37 e and 0.58 e which is in good correlation with the improved adsorption strength. The calculated results are consistence with the experimental observations that the Langmuir adsorptivity has been enhanced upon alkali modification. The maximum adsorption capacity of AC has been improved approximately by 4 times from 78.9 to 188.9 mg/g upon treatment.

Insights on Cryogenic Distillation Technology for Simultaneous CO2 and H2S Removal for Sour Gas Fields

Natural gas demand has dramatically increased due to the emerging growth of the world economy and industry. Presently, CO2 and H2S content in gas fields accounts for up to 90% and 15%, respectively. Apart from fulfilling the market demand, CO2 and H2S removal from natural gas is critical due to their corrosive natures, the low heating value of natural gas and the greenhouse gas effect. To date, several gas fields have remained unexplored due to limited technologies to monetize the highly sour natural gas. A variety of conventional technologies have been implemented to purify natural gas such as absorption, adsorption and membrane and cryogenic separation. The application of these technologies in natural gas upgrading are also presented. Among these commercial technologies, cryogenic technology has advanced rapidly in gas separation and proven ideally suitable for bulk CO2 removal due to its independence from absorbents or adsorbents, which require a larger footprint, weight and energy. Present work comprehensively reviews the mechanisms and potential of the advanced nonconventional cryogenic separation technologies for processing of natural gas streams with high CO2 and H2S content. Moreover, the prospects of emerging cryogenic technologies for future commercialization exploitation are highlighted.

Core Shell Nanostructure: Impregnated Activated Carbon as Adsorbent for Hydrogen Sulfide Adsorption

This study focuses on the synthesis, characterization, and evaluation of the performance of core shell nanostructure adsorbent for hydrogen sulfide (H₂S) capture. Commercial coconut shell activated carbon (CAC) and commercial mixed gas of 5000 ppm H₂S balanced N₂ were used. With different preparation techniques, the CAC was modified by core shell impregnation with zinc oxide (ZnO), titanium oxide (TiO₂), potassium hydroxide (KOH), and zinc acetate (ZnAC₂). The core structure was prepared with CAC impregnated by single chemical and double chemical labelled with ZnAC₂-CAC (single chemical), ZnAC₂/KOH-CAC, ZnAC₂/ZnO-CAC, and ZnAC₂/TiO₂-CAC. Then, the prepared core was layered either with KOH, TiO₂, NH₃, or TEOS for the shell. The synthesized adsorbents were characterized in physical and chemical characterization through scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analyzers. Operation of the adsorber column takes place at ambient temperature, with absolute pressure at 1.5 bar. The H₂S gas was fed into the column at 5.5 L/min and the loaded adsorbents were 150 g. The performance of synthesized adsorbent was analyzed through the adsorbent’s capability in capturing H₂S gas. Based on the results, ZnAc₂/ZnO/CAC_WOS shows a better adsorption capacity with 1.17 mg H₂S/g and a 53% increment compared to raw CAC. However, the degradation of the adsorbents was higher compared to ZnAc₂/ZnO/CAC_OS and to ZnAc₂/ZnO/CAC_WS ZnAc₂/ZnO/CAC_OS. The presence of silica as a shell has potentially increased the adsorbent’s stability in several cycles of adsorption-desorption.

Hydrogen sulphide management in anaerobic digestion: A critical review on input control, process regulation, and post-treatment

Hydrogen sulphide (H₂S) in biogas is a problematic impurity that can inhibit methanogenesis and cause equipment corrosion. This review discusses technologies to remove H₂S during anaerobic digestion (AD) via: input control, process regulation, and post-treatment. Post-treatment technologies (e.g. biotrickling filters and scrubbers) are mature with >95% removal efficiency but they do not mitigate H₂S toxicity to methanogens within the AD. Input control (i.e. substrate pretreatment via chemical addition) reduces sulphur input into AD via sulphur precipitation. However, available results showed <75% of H₂S removal efficiency. Microaeration to regulate AD condition is a promising alternative for controlling H₂S formation. Microaeration, or the use of oxygen to regulate the redox potential at around -250 mV, has been demonstrated at pilot and full scale with >95% H₂S reduction, stable methane production, and low operational cost. Further adaptation of microaeration relies on a comprehensive design framework and exchange operational experience for eliminating the risk of over-aeration.

Greener reactants, renewable energies and environmental impact mitigation strategies in pyrometallurgical processes: A review

Abstract

Metals and alloys are among the most technologically important materials for our industrialized societies. They are the most common structural materials used in cars, airplanes and buildings, and constitute the technological core of most electronic devices. They allow the transportation of energy over great distances and are exploited in critical parts of renewable energy technologies. Even though primary metal production industries are mature and operate optimized pyrometallurgical processes, they extensively rely on cheap and abundant carbonaceous reactants (fossil fuels, coke), require high power heating units (which are also typically powered by fossil fuels) to calcine, roast, smelt and refine, and they generate many output streams with high residual energy content. Many unit operations also generate hazardous gaseous species on top of large CO₂ emissions which require gas-scrubbing and capture strategies for the future. Therefore, there are still many opportunities to lower the environmental footprint of key pyrometallurgical operations. This paper explores the possibility to use greener reactants such as bio-fuels, bio-char, hydrogen and ammonia in different pyrometallurgical units. It also identifies all recycled streams that are available (such as steel and aluminum scraps, electronic waste and Li-ion batteries) as well as the technological challenges associated with their integration in primary metal processes. A complete discussion about the alternatives to carbon-based reduction is constructed around the use of hydrogen, metallo-reduction as well as inert anode electrometallurgy. The review work is completed with an overview of the different approaches to use renewable energies and valorize residual heat in pyrometallurgical units. Finally, strategies to mitigate environmental impacts of pyrometallurgical operations such as CO₂ capture utilization and storage as well as gas scrubbing technologies are detailed. This original review paper brings together for the first time all potential strategies and efforts that could be deployed in the future to decrease the environmental footprint of the pyrometallurgical industry. It is primarily intended to favour collaborative work and establish synergies between academia, the pyrometallurgical industry, decision-makers and equipment providers.

Graphical abstract

Highlights

A more sustainable production of metals using greener reactants, green electricity or carbon capture is possible and sometimes already underway. More investments and pressure are required to hasten change.

Discussion

Is there enough pressure on the aluminum and steel industries to meet the set climate targets?The greenhouse gas emissions of existing facilities can often be partly mitigated by retrofitting them with green technologies, should we close plants prematurely to build new plants using greener technologies?Since green or renewable resources presently have limited availability, in which sector should we use them to maximize their benefits?

Recent Progress in the Steam Reforming of Bio-Oil for Hydrogen Production: A Review of Operating Parameters, Catalytic Systems and Technological Innovations

The present review focuses on the production of renewable hydrogen through the catalytic steam reforming of bio-oil, the liquid product of the fast pyrolysis of biomass. Although in theory the process is capable of producing high yields of hydrogen, in practice, certain technological issues require radical improvements before its commercialization. Herein, we illustrate the fundamental knowledge behind the technology of the steam reforming of bio-oil and critically discuss the major factors influencing the reforming process such as the feedstock composition, the reactor design, the reaction temperature and pressure, the steam to carbon ratio and the hour space velocity. We also emphasize the latest research for the best suited reforming catalysts among the specific groups of noble metal, transition metal, bimetallic and perovskite type catalysts. The effect of the catalyst preparation method and the technological obstacle of catalytic deactivation due to coke deposition, metal sintering, metal oxidation and sulfur poisoning are addressed. Finally, various novel modified steam reforming techniques which are under development are discussed, such as the in-line two-stage pyrolysis and steam reforming, the sorption enhanced steam reforming (SESR) and the chemical looping steam reforming (CLSR). Moreover, we argue that while the majority of research studies examine hydrogen generation using different model compounds, much work must be done to optimally treat the raw or aqueous bio-oil mixtures for efficient practical use. Moreover, further research is also required on the reaction mechanisms and kinetics of the process, as these have not yet been fully understood.

Transforming Plastic Waste into Porous Carbon for Capturing Carbon Dioxide: A Review

Plastic waste generation has increased dramatically every day. Indiscriminate disposal of plastic wastes can lead to several negative impacts on the environment, such as a significant increase in greenhouse gas emissions and water pollution. Therefore, it is wise to think of other alternatives to reduce plastic wastes without affecting the environment, including converting them into valuable products using effective methods such as pyrolysis. Products from the pyrolysis process encompassing of liquid, gas, and solid residues (char) can be turned into beneficial products, as the liquid product can be used as a commercial fuel and char can function as an excellent adsorbent. The char produced from plastic wastes could be modified to enhance carbon dioxide (CO2) adsorption performance. Therefore, this review attempts to compile relevant knowledge on the potential of adsorbents derived from waste plastic to capture CO2. This review was performed in accordance with PRISMA guidelines. The plastic-waste-derived activated carbon, as an adsorbent, could provide a promising method to solve the two environmental issues (CO2 emission and solid management) simultaneously. In addition, the future perspective on char derived from waste plastics is highlighted.

Experimental and Computational Approaches for the Structural Study of Novel Ca-Rich Zeolites from Incense Stick Ash and Their Application for Wastewater Treatment

At present, chemical Si/Al sources are mainly used as precursor materials for the manufacturing of zeolites. Such precursor materials are quite expensive for commercial synthesis. Here, we have reported the synthesis of Ca-based zeolite from incense stick ash waste by the alkali-treatment method for the first time. Incense stick ash (ISA) was used as a precursor material for the synthesis of low Si zeolites by the alkali-treatment method. The as-synthesized zeolites were characterized by various instruments like particle size analyzer (PSA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). FTIR and XRD helped in the identification of the microstructure and crystalline nature of the zeolites and also confirmed the synthesis of Ca-based zeolite with two thetas at 25.7°. The microscopic analysis by FESEM and TEM exhibited that the size of synthesized Ca-rich zeolites varies from 200 to 700 nm and they are aggregated and cuboidal in shape. Additionally, structural, electronic, and density of states’ characteristics of gismondine (Ca2Al4Si4O16·9H2O) structures were evaluated by computational simulations (first principle, density functional theorem). The structural optimization of structures was carried out in the first stage under the lowest condition of total energy and forces acting on atoms for the lattice constant, as well as the available experimental and theoretical findings. The present research approach predicted the transformation of ISA waste into a value-added mineral, i.e., zeolite, which was further used for the removal of both heavy metals and alkali metals from fly ash-based wastewater using inductively coupled plasma-optical emission spectroscopy (ICP-OES).

H2 S Dosimetry by CuO: Towards Stable Sensors by Unravelling the Underlying Solid-State Chemistry

The precise detection of the toxic gas H₂S requires reliable sensitivity and specificity of sensors even at minute concentrations of as low as 10 ppm, the value corresponding to typical exposure limits. CuO can be used for H₂S dosimetry, based on the formation of conductive CuS and the concomitant significant increase in conductance. In theory, at elevated temperature the reaction is reversed and CuO is formed, ideally enabling repeated and long‐term use of one sensor. Yet, the performance of CuO tends to drop upon cycling. Utilizing defined CuO nanorods we thoroughly elucidated the associated detrimental chemical changes directly on the sensors, by Raman and electron microscopy analysis of each step during sensing (CuO→CuS) and regeneration (CuS→CuO) cycles. We find the decrease in the sensing performance is mainly caused by the irreversible formation of CuSO₄ during regeneration. The findings allowed us to develop strategies to reduce CuSO₄ formation and thus to substantially maintain the sensing stability even for repeated cycles. We achieved CuO‐based dosimeters possessing a response time of a few minutes only, even for 10 ppm H₂S, and prolonged life‐time.

Metal-Free Phosphated Mesoporous SiO2 as Catalyst for the Low-Temperature Conversion of SO2 to H2S in Hydrogen

Highly active metal-free mesoporous phosphated silica was synthesized by a two-step process and used as a SO2 hydrogenation catalyst. With the assistance of a microwave, MCM-41 was obtained within a 10 min heating process at 180 °C, then a low ratio of P precursor was incorporated into the mesoporous silica matrix by a phosphorization step, which was accomplished in oleylamine with trioctylphosphine at 350 °C for 2 h. For benchmarking, the SiO2 sample without P precursor insertion and the sample with P precursor insertion into the calcined SiO2 were also prepared. From the microstructural analysis, it was found that the presence of CTAB surfactant was important for the incorporation of active P species, thus forming a highly dispersed, ultrafine (uf) phosphate silica, (Si-P) catalyst. The above approach led to the promising catalytic performance of uf-P@meso-SiO2 in the selective hydrogenation of SO2 to H2S; the latter reaction is very important in sulfur-containing gas purification. In particular, uf-P@meso-SiO2 exhibited activity at the temperature range between 150 and 280 °C, especially SO2 conversion of 94% and H2S selectivity of 52% at 220 °C. The importance of the CTAB surfactant can be found in stabilizing the high dispersion of ultrafine P-related species (phosphates). Intrinsic characteristics of the materials were studied using XRD, FTIR, EDX, N2 adsorption/desorption, TEM, and XPS to reveal the structure of the above catalysts.

Shrinking-Core Model Integrating to the Fluid-Dynamic Analysis of Fixed-Bed Adsorption Towers for H2S Removal from Natural Gas

Natural gas sweetening is an essential process within hydrocarbon processing operations, enabling compliance with product quality specifications, avoiding corrosion problems, and enabling environmental care. This process aims to remove hydrogen sulfide (H2S), carbon dioxide, or both contaminants. It can be carried out in fixed-bed adsorption towers, where iron oxide-based solid sorbent reacts with the H2S to produce iron sulfides. This study is set out to develop a fluid-dynamic model that allows calculating the pressure drop in the H2S adsorption towers with the novelty to integrate reactivity aspects, through an iron sulfide layer formation on the solid particles’ external skin. As a result of the layer formation, changes in the particle diameter and the bed void fraction of the solid sorbent tend to increase the pressure drop. The shrinking-core model and the H2S adsorption front variation in time support the model development. Experimental data on pressure drop at the laboratory scale and industrial scale allowed validating the proposed model. Moreover, the model estimates the bed replacement frequency, i.e., the time required to saturate the fixed bed, requiring its replacement or regeneration. The model can be used to design and formulate new solid sorbents, analyze adsorption towers already installed, and help maintenance-planning operations.

A novel one-step synthesis of Ce/Mn/Fe mixed metal oxide nanocomposites for oxidative removal of hydrogen sulfide at room temperature

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions. The microscopic images confirmed polyhedral nanocrystals of 10–20 nm size, clustered to form nanospheres. The elemental mapping confirmed the uniform distribution of transition metal oxides in the CeO₂ matrix. The X-ray diffraction analysis confirmed the phase purity of metal oxides in nanocomposites. The surface area of nanocomposites was in the range of 16–21 m² g⁻¹. X-ray photoelectron spectroscopy confirmed 25–28% of Ce³⁺ ions in the CeO₂ of nanocomposites. These nanocomposites were tested for the removal of hydrogen sulfide gas at room temperature. The maximum adsorption capacity of 28.3 mg g⁻¹ was recorded for CeO₂/Mn₂O₃/Fe₂O₃ with 500 ppm of H₂S gas and 0.2 L min⁻¹ of flow rate. The adsorption mechanism probed by X-ray photoelectron spectroscopy showed the presence of sulfate as the only species formed from the oxidation of H₂S, which was further confirmed by ion chromatography. Thus, the study reports room-temperature oxidation of H₂S over mixed metal composites, which were synthesized by a novel one-step approach.

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions.

Adsorption of Hydrogen Sulfide at Low Temperatures Using an Industrial Molecular Sieve: An Experimental and Theoretical Study

In the work presented herein, a joint experimental and theoretical approach has been carried out to obtain an insight into the desulfurization performance of an industrial molecular sieve (IMS), resembling a zeolitic structure with a morphology of cubic crystallites and a high surface area of 590 m² g^-1, with a view to removing H₂S from biogas. The impact of temperature, H₂S inlet concentration, gas matrix, and regeneration cycles on the desulfurization performance of the IMS was thoroughly probed. The adsorption equilibrium, sorption kinetics, and thermodynamics were also examined. Experimental results showed that the relationship between H₂S uptake and temperature increase was inversely proportional. Higher H₂S initial concentrations led to lower breakpoints. The presence of CO₂ negatively affected the desulfurization performance. The IMS was fully regenerated after 15 adsorption/desorption cycles. Theoretical studies revealed that the Langmuir isotherm better described the sorption behavior, pore diffusion was the controlling step of the process (Bangham model), and that the activation energy was 42.7 kJ mol^-1 (physisorption). Finally, the thermodynamic studies confirmed that physisorption predominated.