Activated carbons with metal containing bentonite binders as adsorbents of hydrogen sulfide

Wood-based activated carbon was ground and mixed with 10% bentonite binders containing either iron, zinc or copper cations adsorbed within the interlayer space and/or on the external surface of bentonite flakes. To better understand the role of transition metals, carbon was also impregnated with iron, zinc and copper salts. The structure of materials after modification was determined using nitrogen adsorption. The modification resulted in a decrease in porosity, especially in micropore volume, as a result of combined mass dilution effect and adsorption/re-adsorption of metals in small pores. Introduction of bentonite binders containing adsorbed metal increased the capacity of carbon for hydrogen sulfide only in the case of material containing copper. Copper also significantly increases the performance of carbon as an H₂S adsorbent when impregnation is applied whereas the effects of other metals used in this study are much less pronounced. It is likely that copper present in the small pores acts as a catalyst for oxygen activation causing hydrogen sulfide oxidation. As a result of this process, elemental sulfur is formed which, when present in small pores, is oxidized to weakly adsorbed SO₂. The SO₂ is removed from the surface when continuous reaction with hydrogen sulfide occurs. Thus, even though binding carbon with spent bentonites after copper adsorption increases the capacity of carbon toward H₂S removal, the formation of SO₂, another undesirable pollutant, does detract somewhat from the procedure.     

A new strategy for hydrogen sulfide removal by amido-functionalized reduced graphene oxide as a novel metal-free and highly efficient nanoadsorbent

In this research, hydrogen sulfide is adsorbed on amido-functionalized reduced graphene oxide (AFRGO) as a nanoadsorbent. By the use of n-propylamine and allylamine, reduced graphene oxide (RGO) was amidated for the adsorption of hydrogen sulfide. The materials were characterized by adsorption of H₂S, potentiometric titration, scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The effect of the operational conditions of 4000–6000 h^?1 space velocities and 60,000?ppm H₂S feed concentrations were examined on adsorption capacity. The results show that H₂S feed concentration, space velocity, and functional groups of adsorbents have a major effect on H₂S adsorption. It was also found that the temperature in the range of 30–70°C had a significant effect on H₂S adsorption. The concentration of H₂S adsorbed in 3?h by AFRGO containing allyl substituent, AFRGO containing propyl substituent, graphene oxide (GO), and reduced graphene oxide (RGO) were reported as 59,710, 59,650, 59,600, and 59,500?ppm, respectively. Hydrogen sulfide adsorption analysis showed that nanoadsorbents increase adsorption capacity of H₂S.     

Removal of hydrogen sulfide from biogas on sludge-derived adsorbents

Desulfurization adsorbents were prepared from the mixtures of sewage sludge and metal sludge of various compositions and individual sludges by pyrolyses at 650, 800 and 950 °C. The resulting materials were used as adsorbents of hydrogen sulfide from simulated digester gas mixture. The adsorbents before and after H₂S removal were characterized using adsorption of nitrogen, elemental analysis, pH measurements, and thermal analysis. The behavior of materials as desulfurization media does not depend strongly on the humidification pretreatment. The pyrolysis temperature and composition of the mixture play a role in the development of final properties of adsorbents. When the content of sewage sludge is high the strong synergetic effect is noticed after high temperature of pyrolysis. Such factors as development of mesoporosity and new catalytic phases formed as a result of solid-state reactions contribute to this behavior. The removal of hydrogen sulfide on the materials obtained is complex due to the competition between H₂S and CO₂ for adsorption centers and deactivation of those centers by CO₂/H₂CO₃.     

H2S adsorption/oxidation on unmodified activated carbons: importance of prehumidification

Three microporous activated carbons supplied by Norit^® (of peat and bituminous coal origin) were used in this study as hydrogen sulfide adsorbents. Their surface properties were evaluated by means of nitrogen adsorption, Boehm titration, potentiometric titration, and thermal analysis. The results show that the carbons significantly differ in their pore structure and surface chemistry. This is reflected in their hydrogen sulfide breakthrough capacity. The breakthrough capacity is underestimated when not enough water is adsorbed on the carbon surface. The performance follows the expectations after extensive humidification of the sorbents’ surfaces. Moderately low pH in the acidic range of coal-based carbon, Vapure 612, promotes the oxidation of H₂S to sulfur oxides which is important from the point of view of water regeneration. The high pH of peat-based carbon, RB 4, results in H₂S oxidation to elemental sulfur.     

Effect of adsorbent composition on H2S removal on sewage sludge-based materials enriched with carbonaceous phase

In order to improve the carbonaceous phase content in sewage sludge derived adsorbents, dewatered sludge was physically mixed with polystyrene sulfonic acid-co maleic acid sodium salt with the following ratios of polymer to sludge: 10:90, 30:70, 50:50 and 70:30. The samples, along with the pure precursors, were carbonized at 950 °C and then washed in water to remove the excess of sodium salt/hydroxide. The performance of materials as H₂S adsorbents was tested using a home-developed dynamic breakthrough test. The samples, before and after adsorption process, were characterized by adsorption of nitrogen, potentiometric titration, thermal analysis and SEM. Differences in the performance were linked to the surface properties. It was found that mixing polymer with sludge increases the amount of H₂S adsorbed/oxidized in comparison with the adsorbents obtained from pure precursors (sludge or polymer). Sewage sludge provides the catalytic centers for hydrogen sulfide oxidation whereas a carbonaceous phase contributes to an increase in the dispersion of catalytic centers and provides more “storage space” in its micropores. There is an optimal ratio in the composition of the precursors for which the best performance is achieved. When the content of the polymer is too high, the “buffering capacity” of the sludge-derived phase is not enough to neutralize the suppressing effect of acidic surface groups of a carbonaceous phase.     

Effect of H2S on the CO2 corrosion of carbon steel in acidic solutions

The objective of this study is to evaluate the effect of low-level hydrogen sulfide (H₂S) on carbon dioxide (CO₂) corrosion of carbon steel in acidic solutions, and to investigate the mechanism of iron sulfide scale formation in CO₂/H₂S environments. Corrosion tests were conducted using 1018 carbon steel in 1 wt.% NaCl solution (25 °C) at pH of 3 and 4, and under atmospheric pressure. The test solution was saturated with flowing gases that change with increasing time from CO₂ (stage 1) to CO₂/100 ppm H₂S (stage 2) and back to CO₂ (stage 3). Corrosion rate and behavior were investigated using linear polarization resistance (LPR) technique. Electrochemical impedance spectroscopy (EIS) and potentiodynamic tests were performed at the end of each stage. The morphology and compositions of surface corrosion products were analyzed using scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the addition of 100 ppm H₂S to CO₂ induced rapid reduction in the corrosion rate at both pHs 3 and 4. This H₂S inhibition effect is attributed to the formation of thin FeS film (tarnish) on the steel surface that suppressed the anodic dissolution reaction. The study results suggested that the precipitation of iron sulfide as well as iron carbonate film is possible in the acidic solutions due to the local supersaturation in regions immediately above the steel surface, and these films provide corrosion protection in the acidic solutions.     

Selective oxidation of H<Subscript>2</Subscript>S to sulfur over CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> catalyst

The catalytic oxidation of hydrogen sulfide (H₂S) to elemental sulfur was studied over CeO₂-TiO₂ catalysts. The synthesized catalysts were characterized by various techniques such as X-ray diffraction, BET, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia, and scanning electron microscopy (SEM). Catalytic performance studies of the CeO₂-TiO₂ catalysts showed that H₂S was successfully converted to elemental sulfur without considerable emission of sulfur dioxide. CeO₂-TiO₂ catalysts with Ce/Ti=1/5 and 1/3 exhibited the highest H₂S conversion, possibly due to the uniform dispersion of metal oxides, high surface area, and high amount of acid sites.     

Hydrogen sulfide removal by copper sulfate circulation method

Although copper sulfate (CuSO₄) as a valuable desulfurizer is commonly used in the laboratory, it is not applied in industry due to its high cost and lack of practical regeneration method. In this study, a method for regeneration of the absorption product copper sulfide (CuS) under mild conditions is put forward. In the presence of sodium chloride (NaCl), CuSO₄ could be regenerated smoothly in acid solution and be recycled for the absorption of hydrogen sulfide (H₂S). Specifically, under the conditions of 0.30 mol/L chloride ion (Cl^?), 1.8% acidity at 323 K, for 5.5 h, the regeneration efficiency will be higher than 99%. Moreover, extensive experimental studies showed that the addition of Cl^? would not observably influence the absorption efficiency of H₂S. These results reveal the potential for developing a novel, efficient and low-cost desulfurization technology.     

Low-cost metal oxide activated carbon prepared and modified by microwave heating method for hydrogen storage

Novel microporous activated carbon (MAC) with high surface area and pore volume has been synthesized by microwave heating. Iron oxide nanoparticles were loaded into MAC by using Fe(NO₃)₃·9H₂O followed by microwave irradiation for up to five minutes. The surface modified microporous activated carbon was characterized by BET, XRD, SEM and thermogravimetric examinations. Adsorption data of H₂ on the unmodified and modified MACs were collected with PCT method for a pressure range up to 120 bar at 303 K. Greater hydrogen adsorption was observed on the carbon adsorbents doped with 1.45 wt% of iron oxide nanoparticle loaded due to the joint properties of hydrogen adsorption on the carbon surface and the spill-over of hydrogen molecules into carbon structures.     

Low-temperature catalytic decomposition of hydrogen sulfide on metal catalysts under layer of solvent

When hydrogen sulfide decomposition {2 H₂S ? 2 H₂?+?S₂^(gas)} is carried out in the flow regime at room temperature on metal catalysts placed in a liquid capable of dissolving H₂S and sulfur, the reaction equilibrium can be significantly (up to 100%) shifted to the right yielding the desired product – hydrogen. The process efficiency was demonstrated using aqueous solutions of monoethanolamine (MEA), sodium carbonate, which is widely used in industry for H₂S absorption from tail gases, and aqueous hydrazine as examples. IR and Raman spectroscopy data demonstrated that sulfur obtained in the solutions is in the form of diatomic molecules. DFT calculations showed that diatomic sulfur forms weakly bound coordinative complexes with solvent molecules. Some problems related to sulfur accumulation and recovery from the solvents are discussed.     

Effects of exchanged ammonium cations on structure characteristics and CO2 adsorption capacities of bentonite clay

Different alkali and alkaline earth cation forms of bentonite clay were exchanged with protonated mono-, di- and triethanolamine compounds, to study the effect of the exchanged ammonium cations on the structure characteristics, thermal behavior, surface properties and CO₂ adsorption capacities of bentonite clay. The revolution of the interlayer structure characteristics, thermal properties, the specific surface area and elemental analysis were characterized by XRD, FTIR, TGA, BET and CHNS techniques respectively, while the CO₂ adsorption capacities were gravimetrically measured by using magnetic suspension balance (MSB) equipment. It was found that the intercalation of ammonium cations into the interlayer space of bentonite clay induced a step change in its basal spacing, depending on their molar mass and the interlayer molecular arrangement. The presence of the characteristic IR peaks of amine compounds in the spectra of bentonite clay adsorbents modified by amines was qualitatively supported by the incorporation of ammonium cations in the interlayer space of bentonite, while the presence of C, H and N elements using CHNS technique was quantitatively confirmed by the intercalation process of amine compounds. It was also found that the molar mass of amines has an inverse effect on the amount of the adsorbed water (intensity), its desorption temperature (position) and the specific surface area of the synthesized materials. The CO₂ adsorption capacities on all the studied bentonite clay adsorbents modified by amines were found to increase between 2.68 and 3.15 mmol/g, compared to 0.93 mmol/g for untreated bentonite at the studied temperature and pressure. As expected, bentonite clay modified with di- and triethanolammonium cations showed lower CO₂ adsorption capacities than that treated with monoethanolammonium cations, due to their low specific surface area.     

Adsorptive desulfurization of model gasoline by using modified bentonite

This work involved the investigation on the removal of organic sulfur compounds from the model liquid fuels by using adsorption desulfurization (ADS) method. For this purpose, removal of 4-methyl dibenzothiophene (4-MDBT) in model gasoline streams with raw bentonite, nanobentonite and nanobentonite modified by nanomagnetite, active carbon and Ni(NO₃)₂.9H₂O was considered. Various factors influencing the desulfurization capability, including loading and baking temperature were investigated. Thermo-gravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) showed that the ability of modified bentonite to adsorb 4-MDBT depends strongly on surface chemistry, particularly on the presence of basic oxygen-containing groups and acid content. The adsorbents tested for desulfurization capacity at breakthrough followed the order: 30wt% Fe₃O₄/30wt% Active carbon/40% Na -Nanobentonite?>?30wt% Fe₃O₄/30wt% Active carbon/40% Ca – Nanobentonite > 30wt % Fe₃O₄/70% Ca-Nanobentonite?>?15wt % Fe₃O₄/15wt% Ni/70% Ca– Nanobentonite. The results of preliminary tests for raw bentonite and nanobentonite were not significant in comparison with the modified nanobentonites: a, b, c, d samples, (about 40% lower than the four sample models). The optimum calcination temperature was 800°C. The multivariate methods were used for optimization of acceptance parameters. A Plackett–Burman design (PBD) was chosen as a screening method to estimate the relative influence of the factors that can be affected on the analytical response. Results show that surface area, pore size and pore volume of the bentonite can be increased several times using the impregnation method by 30wt% Fe₃O₄/30% active carbon. Also, the surface morphology of the bentonite is changed with this modification.     

Calorimetric study of reactions occurring between impregnated activated fibres and hydrogen sulphide

Activated carbon fibres, which exhibit high specific area and numerous active surface sites constitute very powerful adsorbents and are widely used in filtration to eliminate pollutants from liquid or gaseous effluents. The fibres studied in this work are devoted to the filtration of gaseous effluents containing very small amounts (few vpm) of hydrogen sulphide. To improve their fixation capacity towards H₂S the activated fibres are impregnated in an aqueous solution of potassium hydroxide and then thermally treated. The treatment leads to the deposition of crystallites of K₂CO₃ showing a great activity for H₂S gas in the presence of water vapour. The H₂S fixation mechanism proposed can be summarised as follow: K₂CO₃ and H₂S dissolve in a liquid aqueous solution formed on the fibre surface. Then carbonate ions and H₂S molecules react together almost completely to yield HS⁻ species. This mechanism has been validated and completed by the study of the thermal effects induced when the treated fibres are in contact with H₂S together with water vapour. The study has been carried out using a calorimetric method. The variations of standard enthalpy of reactions involved in the fixation mechanism are measured and compared to the data given by the thermodynamic tables for bulk solutions.     

Electrocatalytic reduction of hydrogen peroxide at nanostructured copper modified electrode

The electrocatalytic reduction of hydrogen peroxide (H₂O₂) has been studied at nanostructured copper (Cu_nano) modified glassy carbon (GC/Cu_nano) electrode in phosphate buffer (pH 7.2). The electrical properties of GC/Cu_nano modified electrodes were studied by electrochemical impedance spectroscopy (EIS). Surface and electrochemical characterization were carried out by using atomic force microscopy (AFM) and cyclic voltammetry. A well-defined H₂O₂ reduction signal, which is due to mediation of a surface active site redox transition exhibits at the GC/Cu_nano electrode. The Cu_nano is acting as a bridge without the aid of any other electron mediator, which enables the direct electron transfer between the modified electrode and the substrate. The results are compared with bulk copper macroelectrode and emphasized the efficiency of the Cu_nano modified electrode. Systematic investigations were made to optimize the experimental parameter, such as applied potential (E_app) for copper electrodeposition. The calibration curve obtained from chronoamperometric studies was found to be linear in the range 0.5 to 8.0 μM H₂O₂ with a detection limit of ca.10 nM (S/N = 3) at the GC/Cu_nano electrode. The modified electrode is stable for 1 week in phosphate buffer after repetitive measurements.     

Nanoclays as nano adsorbent for oxidation of H<Subscript>2</Subscript>S into elemental sulfur

Modified bentonites were used for the oxidation of H₂S into elemental sulfur. Active phases such as iron and cobalt sulfide were added to supports Cloisite 30B and 15A. The produced nano adsorbents were characterized by X-Ray diffraction, ICP, BET surface area and SEM. Selective oxidation of H₂S was carried out over the nano adsorbent in the experimental setup. The tests were performed at 70 and 180 °C, under atmospheric pressure and in the presence of 5,000 ppm of H₂S in the inlet gas stream. The results confirmed the increase in the distribution of active metals and activity of Cloisite 30B, in comparison with Cloisite 15A. Cobalt-containing support showed significant improvement in the capacity of H₂S removal, and in the outlet stream less than 50 ppm of H₂S was detected.     

Polyol Mediated Solvothermal Synthesis and Characterization of CuIn<Subscript>(1−x)</Subscript>Ga<Subscript>x</Subscript>S<Subscript>2</Subscript> Nanocrystals

Gallium-substituted copper indium sulfide (CuIn_(1?x)Ga_xS₂) nanoparticles have been synthesized by a convenient solvothermal method without usage of surfactants or toxic reductants such as hydrazine. Thiourea, sodium hydroxide, CuCl₂·2H₂O, InCl₃ and GaCl₃ were used as starting materials and ethylene glycol as solvent and reducing agent. The reactions were performed at 200 °C for 16 h. Effect of sodium hydroxide on the reaction products is analyzed. The powders are mainly characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, BET surface area measurements and UV–Vis absorption spectroscopy. The results show that the gallium is successfully incorporated into the chalcopyrite crystal structure. The homogeneous powders obtained are constituted of nanoparticles with sizes in the range 20–30 nm and exhibit a specific surface area close to 65 m²/g. Further, the possible mechanism for the formation of CuIn_(1?x)Ga_xS₂ nanocrystals is explained. The optical band gap energies of the nanoparticles were in the range 1.48–1.75 eV.     

Bituminous coal-based activated carbons modified with nitrogen as adsorbents of hydrogen sulfide

Bituminous coal-based activated carbon was modified by impregnation with melamine and heat treatment at 850 °C. Another sample was impregnated with melamine and urea and heat treated at 650 and 850 °C. Chemical and physical properties of the materials were determined using Boehm titration, thermal analysis, sorption of nitrogen and SEM with EDX. Then the H₂S breakthrough capacity tests were carried out and the sorption capacity was calculated. The results revealed that carbons modified with nitrogen-containing species and heat-treated at 850 °C have a hydrogen sulfide removal capacity exceeding more then 10 times the capacity of unmodified sample. H₂S on the surface of these materials is oxidized to sulfuric acid and elemental sulfur and stored in the pore system. New carbons are hypothesized to act as catalytic reactors promoting two different pathways of hydrogen sulfide oxidation in two different locations. In small micropores, where water is present, hydrogen sulfide dissociate to HS⁻ ions and those ions are oxidized to sulfur radicals and sulfur dioxide leading to the formation of sulfuric acid. In larger pores with incorporated nitrogen, basic sites promote dissociation and formation of sulfur polymers, which are resistant to further oxidation.     

Hydrogen Sulfide-Resistant Bifunctional Catalysts for the Steam Reforming of Methane: Activity and Structural Evolution

Results are presented from studying an iron–nickel catalyst for the steam reforming of methane, synthesized by epitaxial coating on the surface of spherical pellets of commercial γ-Al₂O₃. It is shown the catalyst is resistant to the presence of hydrogen sulfide in a steam–gas mixture. The degree of conversion of methane during reforming is close to equilibrium at a pressure of 2.0 MPa, a temperature of 800°C, a ratio of Н₂О: СН4 = 2: 1, a feedstock hourly space velocity (FHSV) of 6000 h^?1, and a H₂S concentration of 30 ppm. The structural evolution and phase state of the active components of the system are studied via X-ray diffraction analysis, transmission electron microscopy (TEM), and Mössbauer spectroscopy. The formation of paramagnetic iron oxide clusters tightly bound to the structure of the support, and of FeNi₃ iron–nickel alloy particles on the surface of the catalyst, is responsible for the polyfunctional properties of the catalyst, which displays high activity in both the steam reforming of methane and the oxidative decomposition of hydrogen sulfide to elemental sulfur.     

Electrospun polyacrylonitrile/zinc chloride composite nanofibers and their response to hydrogen sulfide

In this work, we explore the electrospinning of polyacrylonitrile (PAN)/zinc(II) chloride (ZnCl₂) composite nanofibers and the response of these nanofibers to hydrogen sulfide (H₂S). Solution properties, including surface tension, viscosity, and conductivity, have been measured and integrated with the results of a variety of other analytical techniques to investigate the effects of ZnCl₂ salt on the structure and thermal properties of electrospun nanofibers. It is found that the addition of ZnCl₂ reduces the diameter and inhibits the instantaneous cyclization reaction of these nanofibers. Additionally, exposing PAN/ZnCl₂ fibers to H₂S leads to the formation of PAN/zinc sulfide (ZnS) composite nanofibers that contain ZnS crystals on the surface. These results indicate that PAN/ZnCl₂ composite nanofibers could find applications in H₂S sensing and removal, or as precursors for semiconductor ZnS-coated polymer nanofibers.     

Spectroscopic investigation,cage occupancy,and gas storage capacity of hydroquinone clathrates formed with H<Subscript>2</Subscript>S-N<Subscript>2</Subscript> and COS-N<Subscript>2</Subscript> binary gas mixtures

The objective of this investigation was to determine whether hydroquinone (HQ) can form clathrate compounds with two sulfides (hydrogen sulfide (H₂S) and carbonyl sulfide (COS)) at their diluted concentrations. Hydroquinone samples obtained at ambient temperature and at two pressures (40 and 80 bar) for binary gas mixtures consisting of H₂S-N₂ and COS-N₂, were analyzed using solid-state ¹³C NMR and Raman spectroscopy. An elemental analyzer was also used to obtain quantitative information regarding the kind and amount of gas captured in the solid samples. Results show that H₂S can be concentrated within the solid clathrate from H₂S-containing gas, while COS is little captured after reaction with the COS-containing gas. This suggests that the HQ clathrate can be used to remove H₂S, and that selective separation can be achieved when two sulfides of H₂S and COS coexist. On the basis of the calculated cage occupancies of the gas components in the solid clathrate, the enclathration preference of the gas components used in this research was found to be the order of H₂S>N₂>COS.