H2S Addition Research Articles

Experimental and kinetic study on laminar burning velocities of NH3/CH4/H2S/air flames

Recently, ammonia has been favored by scientists and engineers as a new type of carbon-free fuel for future carbon–neutral society. Before large-scale application, some existing drawbacks including extremely low reactivity need to be overcomed by enhancing combustion technology. Blending ammonia with sour gas, a type of natural gas resource containing amounts of H2S, can be a solution to enhance the combustion of ammonia as well as efficiently utilize natural gas resource. In this study, the laminar burning velocities of NH3/CH4/H2S/air flames were investigated using the Heat Flux method over a wide range of equivalence ratios and and mixing ratios. A kinetic model for NH3/CH4/H2S/air flames simulation was developed by integrating ammonia sub-mechanism with the mechanism of Han et al. and validated based on the experimental data. The experimental results show that the H2S addition has a negative effect on the flame speed, which reaches 13.36 % decrease at ϕ = 1.25 when the H2S mole fraction is 12 %. Kinetic analysis was performed for exploring the effect of H2S addition on the laminar flame propagation of NH3/CH4/H2S mixtures. The results show that the elevated H2S content significantly impacts the radicals pool in flame, where the mole fraction of H, OH radicals decreases while the S-containing species content increases obviously. Sensitivity analysis shows that the reactions involving S-containing species become important for laminar flame speed determination at high H2S content. Besides, the increament of NH3 ratio in the fuel significantly improves the concentration level of NH2 radical in the flame, leading to the increased importance of NH2 chemistry.

Hydrogen sulfide affects the performance of a methanogenic bioelectrochemical system used for biogas upgrading

Methanogenic bioelectrochemical systems (BESs) can convert carbon dioxide (CO2) to methane (CH4) and may be used for anaerobic digester biogas upgrading. However, the effect of hydrogen sulfide (H2S), a common biogas component, on BES performance is unknown. Thus, the objective of this study was to assess the effect of H2S addition to the cathode headspace on BES performance at a range of initial gas-phase H2S concentrations (0–6% v/v), as well as its effect on the anode and cathode microbial communities. As the initial cathode headspace H2S increased from 0 to 2% (v/v), biocathodic CH4 production increased by two-fold to 3.56 ± 0.36 mmol/L-d, due to dissolved H2S transport from the cathode to the anode where H2S was oxidized. Elemental sulfur and sulfate were H2S oxidation products detected in the anode. Above 3% initial cathode headspace H2S, biocathodic CH4 production declined due to inhibition. A phylotype most closely related to Methanobrevibacter arboriphilus dominated the cathode archaeal communities. In the sulfide-amended BES, a phylotype similar to the exoelectrogen Ochrobactrum anthropi was enriched in both the anode and cathode, whereas phylotypes related to sulfate-reducing and sulfur oxidizing Bacteria were detected in the bioanode. Thus, sulfide transport and oxidation in the anode play an important role in methanogenic BESs treating sulfide-bearing biogas.

A Heterogeneous Nanoscale Covalent Organic Framework Fluorescence Probe for Sensitive Detection of Hydrogen Sulfide

AbstractNew strategies for highly selective and sensitive detection of highly toxic environmental pollutants are still a pressing need. Here, through Cu2+ metalated porous nanoscale covalent organic framework (NCOF), a novel heterogeneous NCOF fluorescence probe has been synthesized for sensitive and selectivity detection of hydrogen sulfide (H2S). Upon H2S addition, the Cu2+ released from the CuCOF, accompanied by the fluorescence recovered of COF. As far as we know, NCOF has not been reported as fluorescence probe for H2S detection. The as‐prepared nano CuCOF displays an excellent sensitive response to H2S with a detection limit of 10 nM. In addition, such heterogeneous fluorescence probe exhibited high selectivity towards to H2S relative to other thiols and anionic species. Moreover, the detection of H2S was achieved successfully in different actual water samples.

Application of signaling molecules in reducing metal accumulation in alfalfa and alleviating metal-induced phytotoxicity in Pb/Cd-contaminated soil

The utilization of forages grown on metal-contaminated soil can increase the risk of heavy metals entering the food chain and affecting human health because of elevated toxic metal concentrations. Meanwhile, hydrogen sulfide (H2S) and nitric oxide (NO) as signaling molecules are known to promote plant growth in metal-contaminated soils. However, the regulatory mechanisms of such molecules in plant physiology and soil biochemistry have not been well-documented. Hence, we investigate the role of the exogenous application of H2S and NO on alfalfa growth in lead/cadmium (Pb/Cd)-contaminated soil. Our results indicate that the signaling molecules increase the alfalfa chlorophyll and biomass content and improve alfalfa growth. Further, H2S and NO reduce the translocation and bioconcentration factors of Pb and Cd, potentially reducing the risk of heavy metals entering the food chain. These signaling molecules reduce metal-induced oxidative damage to alfalfa by mitigating reactive oxygen species accumulation and increasing antioxidant enzyme activities. Their exogenous application increases soil enzymatic activities, particularly of catalase and polyphenol oxidase, without significantly changing the composition and structure of rhizosphere bacterial communities. Interestingly, H2S addition enriches the abundance of plant-growth-promoting rhizobacteria in soil, including Nocardioides, Rhizobium, and Glycomyces. H2S is more effective than NO in improving alfalfa growth and reducing heavy-metal contamination of the food chain. These results provide new insights into the exogenous application of signaling molecules in alleviating metal-induced phytotoxicity, including an efficient strategy for the safe use of forages.

Palladium Coordination Polymers Nanosheets: New Strategy for Sensitive Photothermal Detection of H2S.

New strategies for portable detection of highly toxic environmental pollutants are still in urgent need. Here, through Pd2+ and methylene blue (MB) coordination, photothermal two-dimensional palladium coordination polymers nanosheets (2D PdCPsNSs) have been synthesized for sensitive photothermal detection of H2S. The sensing mechanism is based on the decomposing effect of H2S to 2D PdCPsNSs, accompanied by the decrease of PdCPsNSs concentration and the increase of MB concentration. Upon H2S addition, the heat released from the 2D PdCPsNSs under 808 nm lasers irradiation decreased, and the heat released from the MB increased under 650 nm lasers irradiation, respectively. Such temperature change signals could be easily detected by a portable thermometer. The 2D PdCPsNSs showed highly sensitive ratiometric response to H2S with a detection limit of 30 nM. In addition, such probe presents an excellent selective ratiometric response to H2S relative to other anionic species and thiols because of the specific interaction between Pd2+ and H2S. Moreover, the probe was suitable for the ratiometric determination of H2S in different actual water samples, providing a promising platform for convenient, stable, and universal analysis of H2S.

The role of H2S addition on Pt/Al2O3 catalyzed propane dehydrogenation: a mechanistic study

Effects of H2S addition on the Pt/Al2O3 catalyzed propane dehydrogenation.

Modeling the hydrogen sulfide binding to heme

The binding of hydrogen sulfide to a model heme compound is investigated by coupled-cluster singles-doubles augmented by a perturbative triple excitations, CCSD(T), and density functional theory, DFT. The minimum energy path for the H2S addition to an isolated heme center of the heme protein is evaluated by adopting as a model the heme compound FeP(Im) (P = porphyrin; Im = imidazole). The FeP(Im)-H2S aduct is bound by 13.7 kcal/mol at the CCSD(T) level of theory. Relaxed potential energy curves for the lowest lying spin states of the H2S to FeP(Im) binding using DFT reveal that the binding process is associated with a “double spin-crossover” reaction with the existence of long-distance van der Waals minima only 5–7 kcal/mol above the FeP(Im)-H2S ground state. The fact that the energy of the singlet ground state of FeP(Im)-H2S is so close in energy to the dissociation products FeP(Im) + H2S points towards the reversibility of the H2S adsorption/desorption process in biochemical reactions.

Hydrogen sulfide alleviates chlorobenzene toxicity in soybean seedlings

ABSTRACT: As a gas signaling molecule, endogenous hydrogen sulfide (H2S) plays a crucial role in the plant stress response. However, the role of H2S in the response to organic pollutants specifically has not been studied. Here, the effects of H2S addition on soybean (Glycine max) seedlings tolerance of 1,4-dichlorobenzene (1,4-DCB) were investigated. Under 1,4-DCB stress, the growth of soybean seedlings roots and stems was inhibited, while L-/D-cysteine desulfhydrase (LCD/DCD) activity was induced and endogenous H2S increased. When applied jointly with sodium hydrosulfide (NaHS), a H2S donor, root growth inhibition was effectively alleviated. Pre-treatment of seedlings with 0.4mmol L-1 NaHS reduced the malondialdehyde (MDA) and reactived oxygen species (ROS) content, mitigating root cell toxicity significantly. Further experiments confirmed that NaHS enhanced soybean seedlings peroxidase (POD) and superoxide dismutase (SOD) enzyme activities. In contrast, these effects were reversed by hypotaurine (HT), a H2S scavenger. Therefore, H2S alleviated 1,4-DCB toxicity in soybean seedlings by regulating antioxidant enzyme activity to reduce cell oxidative damage.

Hydrogen sulfide improves colonic barrier integrity in DSS-induced inflammation in Caco-2 cells and mice

Intestinal barrier involves in the pathogeny of inflammatory bowel disease (IBD) and hydrogen sulfide (H2S) has been reported to improve intestinal barrier integrity. Thus, this study investigated the effects of GYY4137, a slow-release H2S donor, on DSS-induced inflammation and intestinal dysfunction. In vitro model, cellular permeability was significantly increased and expression of tight junctions (ZO-1, Cauldin4, and Occludin) was downregulated in Caco-2 cells. GYY4137 treatment markedly attenuated DSS-induced inflammation and barrier dysfunction. Cystathionine β-synthase (CBS)-siRNA transfection further demonstrated that endogenous H2S system involves in DSS-induced inflammation and mediates barrier function. In vivo model, DSS exposure caused colonic inflammation and injury in mice and GYY4137 injection alleviated inflammatory response and improved intestinal barrier via reducing intestinal permeability and upregulating of tight junctions. In conclusion, endogenous H2S system involves in DSS-induced inflammation and H2S addition alleviated inflammation and intestinal dysfunction in vitro and in vivo.

Study on the metabolites of isoalantolactone in vivo and in vitro by ultra performance liquid chromatography combined with Triple TOF mass spectrometry

Isoalantolactone (IAL) is an active sesquiterpene naturally present in many vegetables, condiments and medicinal plants. In this study, an efficient strategy was developed for the identification of metabolites following the in vivo metabolism and in vitro biotransformation of IAL with rat intestinal bacteria utilizing ultra performance liquid chromatography combined with Triple TOF mass spectrometry (UPLC-Triple TOF-MS/MS). As a result, 46 metabolites including 34 novel sulfur-containing products were identified. The results demonstrated that IAL could undergo general metabolic reactions, including oxidation, hydration, hydrogenation, demethylation, cysteine conjugation and N-acetylcysteine conjugation, but the most noticeable characteristic of IAL metabolism was the H2S addition to the double bond between C-11 and C-13 and subsequent reactions to produce a series of novel sulfur-containing dimers. This is the first study of IAL metabolism in vivo, whose results provide novel and useful data for a better understanding of the safety and efficacy of IAL.

The effects of pH and copper on the formation of volatile sulfur compounds in Chardonnay and Shiraz wines post-bottling

The effects of pH and Cu2+ treatment on the formation of volatile sulfur compounds (VSCs) were investigated in Chardonnay and Shiraz wine samples. Four VSCs were significantly affected by pH, with lower wine pH associated with decreased hydrogen sulfide (H2S), methanethiol, dimethyl sulfide, and carbon disulfide concentrations. The effects of pH and Cu2+ on H2S formation from known precursor compounds were subsequently studied in a model wine system. In samples treated with cysteine and glutathione lower pH produced less H2S. Nanoparticle tracking analysis was used to study the effects of variable pH concentrations in a model system containing Cu2+, tartaric acid, and H2S. Differences in Cu2+–tartrate complexes particle size and concentration were measured as a function of pH and H2S addition, suggesting the type of complexes formed may affect the binding sites of Cu2+ available to catalyse the formation of VSCs such as H2S.

Hydrogen sulfide deactivates common nitrobenzofurazan-based fluorescent thiol labeling reagents.

Sulfhydryl-containing compounds, including thiols and hydrogen sulfide (H2S), play important but differential roles in biological structure and function. One major challenge in separating the biological roles of thiols and H2S is developing tools to effectively separate the reactivity of these sulfhydryl-containing compounds. To address this challenge, we report the differential responses of common electrophilic fluorescent thiol labeling reagents, including nitrobenzofurazan-based scaffolds, maleimides, alkylating agents, and electrophilic aldehydes, toward cysteine and H2S. Although H2S reacted with all of the investigated scaffolds, the photophysical response to each scaffold was significantly different. Maleimide-based, alkylating, and aldehydic thiol labeling reagents provided a diminished fluorescence response when treated with H2S. By contrast, nitrobenzofurazan-based labeling reagents were deactivated by H2S addition. Furthermore, the addition of H2S to thiol-activated nitrobenzofurazan-based reagents reduced the fluorescence signal, thus establishing the incompatibility of nitrobenzofurazan-based thiol labeling reagents in the presence of H2S. Taken together, these studies highlight the differential reactivity of thiols and H2S toward common thiol-labeling reagents and suggest that sufficient care must be taken when labeling or measuring thiols in cellular environments that produce H2S due to the potential for both false-positive and eroded responses.

Performance of a highly reactive impregnated Fe2O3/Al2O3 oxygen carrier with CH4 and H2S in a 500 Wth CLC unit

A synthetic Fe-based oxygen carrier prepared by impregnation using γ-Al2O3 as support, successfully tested for gas CLC combustion, has been now evaluated with respect to gas combustion in a 500Wth CLC continuous unit when the fuel, CH4, contained variable amounts of H2S.Full gas combustion was reached at oxygen carrier-to-fuel ratio values higher than 1.5. The presence of sulfur in the fuel gas hardly affected the reactivity and combustion efficiency of the oxygen carrier, independently of the amount of sulfur in the gas stream. All the sulfur introduced as H2S in the fuel reactor (FR) was released in the same reactor as SO2. Furthermore, oxygen carrier particles extracted from the CLC unit after the experimental tests with H2S addition were characterized by means of different techniques and no sulfur was detected in any case. The impregnated Fe-based oxygen carrier was highly reactive and sulfur resistant, and can be considered as a suitable material for CLC with gaseous fuels that contain sulfur.

An empirical investigation of the influence of sulfur additives on the catalytic rate of coke deposition and CO formation in the steam cracking of LPG over Incoloy 600 and stainless steel

In the current paper, the influence of sulfur additives in the steam cracking of LPG (liquefied petroleum gas), as an industrial feedstock, has been investigated. The effect of hydrogen sulfide (H2S) and dimethyl disulfide (DMDS) on the rate of catalytic coke deposition and CO formation have been examined over Incoloy 600, and stainless steel. The impact of sulfur concentration, temperature, and residence time on the rate of catalytic coke formation over each metal, and the CO formation have been investigated using the central composite design (CCD) technique for designing the experiments. Furthermore, the empirical models of the coke deposition rate and CO formation have been proposed for Incoloy and stainless steel individually, based on the statistical analysis of the experimental results. Then, the performance of DMDS was compared with H2S at some of the selected conditions observed for the H2S addition.

Effects of H2S addition on hydrogen ignition behind reflected shock waves: Experiments and modeling

Hydrogen sulfide is a common impurity that can greatly change the combustion properties of fuels, even when present in small concentrations. However, the combustion chemistry of H2S is still poorly understood, and this lack of understanding subsequently leads to difficulties in the design of emission-control and energy-production processes. During this study, ignition delay times were measured behind reflected shock waves for mixtures of 1% H2/1% O2 diluted in Ar and doped with various concentration of H2S (100, 400, and 1600ppm) over large pressure (around 1.6, 13, and 33atm) and temperature (1045–1860K) ranges. Results typically showed a significant increase in the ignition delay time due to the addition of H2S, in some cases by a factor of 4 or more over the baseline mixtures with no H2S. The magnitude of the increase is highly dependent on the temperature and pressure. A detailed chemical kinetics model was developed using recent, up-to-date detailed-kinetics mechanisms from the literature and by changing a few reaction rates within their reported error factor. This updated model predicts well the experimental data obtained during this study and from the shock-tube literature. However, flow reactor data from the literature were poorly predicted when H2S was a reactant. This study highlights the need for a better estimation of several reaction rates to better predict H2S oxidation chemistry and its effect on fuel combustion. Using the kinetics model for sensitivity analyses, it was determined that the decrease in reactivity in the presence of H2S is because H2S initially reacts before the H2 fuel does, mainly through the reaction H2S+H⇄SH+H2, thus taking H atoms away from the main branching reaction H+O2⇄OH+O and inhibiting the ignition process.

Poisoning of cobalt catalyst used for Fischer–Tropsch synthesis

Sulfur in the form of H2S has been added at various concentration levels during cobalt Fischer–Tropsch synthesis. A steady-state FTS conversion was established prior to adding H2S. At low levels (<500ppb) H2S addition does not cause a detectable decrease in activity during 5–10 days of exposure to H2S. Above the threshold limit of about 500ppb, the rate of decrease in CO conversion is linearly related to the H2S concentration in the gas feed. At H2S levels in the 500–1000ppb range, it appears that the poisoning effect is reversible so that catalytic activity is recovered when the addition of H2S is terminated.

Catalytic Steam Methane Reforming Over Ir/Ce0.9Gd0.1O2–x: Resistance to Coke Formation and Sulfur Poisoning

AbstractThis work investigates the catalytic properties of Ir/Ce0.9Gd0.1O2–x (Ir/CGO) catalyst and CGO support in steam reforming of methane in the absence or presence of H2S (50 ppm) for further application in a solid oxide fuel cell (SOFC) working under methane at intermediate temperatures and integrating a gradual internal reforming concept. The catalytic activity was measured at 750 °C by using a 50 mol.% CH4/5 mol.% H2O/45 mol.% N2 mixture and a 10 mol.% CH4/90 mol.% N2 mixture. The addition of Ir to CGO improves the catalytic activity in hydrogen production by two orders of magnitude with respect to that of CGO alone. Temperature programmed oxidation experiments were performed after reaction in both types of mixtures to study the eventual formation of carbon deposits. Over Ir/CGO, carbon formed in little amounts (even in the absence of H2O in the feed), being highly reactive toward O2. Upon H2S addition, the CGO support exhibited surprisingly an improved catalytic activity on the contrary to Ir/CGO which partly deactivated. Upon suppression of H2S in the feed the initial catalytic activity was fully restored for both catalysts. The catalytic behavior of CGO in the presence of H2S was discussed, based upon temperature programmed reaction of CH4.

Experimental examination of flame chemistry in hydrogen sulfide-based flames

Spectroscopic examination of the emission spectra of excited species in hydrogen/air flames both without and with H2S addition and in hydrogen sulfide/oxygen flame are conducted. The baseline case of hydrogen/air flame showed one distinct global peak of OH* at 309.13nm. However, higher resolution spectrum analysis showed the presence of three major OH* peaks at 306.13, 309.09, and 312.9nm. The addition of hydrogen sulfide to hydrogen/air flame resulted in the presence of a bluish cone located at inner regions of the flame. The spectrum of the blue cone showed group of peaks in the 350–470nm spectral range. The addition of H2S drastically reduced the peak value of OH* due to extensive consumption of the hydroxyl group during H2S combustion. The group of peaks in the blue cone spectrum can be divided into three major bands. The first band is formed by SO* within 320–350nm, the second band is attributed to SO3∗ within 350–400nm, and the third band is caused by H* within 400–470nm. However, the distinction of SO3∗ band and H* band around 400nm is an issue that requires further examination. Absorption bands of SH were observed at 324.03nm and 328.62nm. The effect of sulfur dioxide on the spectrum was observed by neither emission bands nor absorption bands because of its reaction with elemental oxygen to produce excited sulfur trioxide. Gas chromatography analysis showed that combustion products did not contain any SO2. The spectra of H2S/O2 flame have also been examined under lean conditions (at Φ=0.5). In contrast to H2/air/H2S flames, the spectra of H2S/O2 showed strong absorption bands of SO2 within 280–310nm. Strong continuum was observed between 280 and 460nm with distinct group of peaks superimposed in the spectra. The continuum is attributed to the afterglow of singlet and triplet SO2. The superimposed peaks are attributed to SO3∗ and H*.

H2S Effects in Base-Metal-Catalyzed Hydrocracking of Fischer−Tropsch Wax

The effect of H2S on catalyst activity and product selectivity during hydrocracking of Fischer−Tropsch (FT) wax was studied using sulfided silica−alumina-supported NiMo and NiW catalysts. FT wax, which is sulfur free was hydrocracked at various H2S concentrations by addition of dimethyl disulfide (DMDS). Conversion and selectivity were affected by the reaction temperature and H2S concentration. On the basis of the classical hydrocracking mechanism, the observed variations in product selectivity were attributed to the change in the ratio of metal to acid sites, which was affected by H2S addition. Catalyst deactivation in commercial practice is compensated by increasing the operating temperature, but higher reaction temperatures create more unsulfided metal sites, which on the other hand result in catalyst selectivity changes. This effect has to be balanced by adjusting the H2S concentration accordingly.

The Effect of Sulfur on ZrO2-Based Biomass Gasification Gas Clean-Up Catalysts

The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm H2S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results revealed that the sulfur addition affected positively on the catalyst properties mainly at 600 and 700 °C: over Y2O3–ZrO2 and ZrO2 sulfur addition improved naphthalene and ammonia conversion. However, over SiO2–ZrO2 no clear effect with H2S addition was observed. The effect of sulfur addition on the catalyst properties was connected to the formation of SO2 from H2S when oxygen was available. The intensity of the sulfur effect increased with the Lewis basicity strength of the catalysts. This indicates that the sulfur adsorption has a role in generating new type of active sites and/or plays role in changing the redox properties of the zirconia. Since the biomass gasification gas contains usually significant amounts of H2S the sulfur tolerance of the zirconia based catalysts is a remarkable benefit.