Sulfur Retention Research Articles

Stable Long‐Term Cycling of Room‐Temperature Sodium‐Sulfur Batteries Based on Non‐Complex Sulfurised Polyacrylonitrile Cathodes

The cost‐effectiveness and high theoretical energy density make room‐temperature sodium‐sulfur batteries (RT Na–S batteries) an attractive technology for large‐scale applications. However, these batteries suffer from slow kinetics and polysulfide dissolution, resulting in poor electrochemical performance. Thus, the sulfurised polyacrylonitrile (SPAN) cathode is postulated as a suitable material due to the retention of sulfur through covalent bonds and the increase in the conductivity of sulfur. Furthermore, in this work the synthesis of SPAN has been carried out using simple synthesis methods, making it scalable, economical, and without the use of toxic compounds. The incorporation of the SPAN material helps mitigate the shuttle effect, reducing the capacity loss and improving both the efficiency and lifespan of Na–S batteries. The SPAN‐based cathode demonstrates that this RT Na–S battery configuration shows high stability, reaching 1000 cycles with a capacity loss per cycle of 0.11% and a satisfactory specific capacity of 400 mAh/gs at a high rate of 2C. This study demonstrates that the utilisation of SPAN derived from a non‐complex synthesis can be a viable alternative for enhancing the future of Na–S batteries technology.

Hydrothermal carbonization of sewage sludge for hydrochar valorization: Role of feedwater pH on sulfur removal and transformation

Adjusting the pH value is a useful method to improve the hydrochar properties during hydrothermal carbonization (HTC). The distribution of various sulfur species in hydrochar is considered as an important parameter affecting its further utilization. Nevertheless, the detailed effects of pH on the redistribution of different sulfur forms are still unknown. This study investigated the sulfur transformation pathways during HTC of sewage sludge with different feedwater pH (0–14) at 220 °C. Both acidic and alkaline feedwater facilitate the conversion of organic sulfur from the hydrochar into the stable species in aqueous products (i.e., sulfate-S). The latter especially leads to a decreased sulfur retention ratio of 31.97 % at pH=0 and 60.13 % at pH=14. Under acidic conditions, organic sulfur species such as sulfone-S and aliphatic-S undergo enhanced cyclization to form aromatic-S/thiophene-S in aqueous and hydrochar products; additionally, the oxidation of sulfone-S predominates the generation of sulfate-S in aqueous products at pH < 1. Under alkaline conditions, the aromatic-S/thiophene-S can be further oxidized into sulfate-S in aqueous products at pH>13. Furthermore, the interaction between water-soluble sulfate-S and hydrolytic intermediates (i.e., glucose, heterocyclic compounds) is intensified at pH=14, resulting in increased formation of sulfone-S and sulfite-S in aqueous products. The insights gained from this study can offer guidance for controlling sulfur distribution during HTC by adjusting the feedwater pH.

Pyrolysis char from waste tyres its characteristics, upgrading and application

The pyrolysis of waste tyres can recycle energy and produce reusable products (oil, char and gas). Although there are many reviews in the literature in regard to the pyrolysis characteristics of waste tyres, but this paper critically looked as pyrolysis char as one of the useful product. Its physical characteristics include pore diameter, pore volume, specific surface area, and composition. The common detection techniques of the physical characteristics include elemental analysis, proximate analysis, SEM, EDS, TGA, XRF, BET, and Raman spectroscopy. The chemical characteristics of tyre char mainly include calorific value, the surface functional groups (i.e phenols, alcohols, carboxylic acid and C-O/C-O-C chemical structures) which can be determined by FT-IR, XRD. The higher sulfur retention on the surface of tyre char is obtained at low temperature compared with that obtained at high temperature. Tyre char could also be directly used as a catalyst material to decrease the operational cost, and improve the quality of pyrolysis oil and gas. The modified tyre char with high specific surface area and lower ash content could be used as an activated carbon adsorbent material, catalyst and catalyst support, capacitor electrode to create higher commercial value, as an adsorbent, in batteries and so on. It is suggested that the recycling applications of tyre char should be developed, which can create a high level of potential economic prospects for the waste tyre pyrolysis industry.

Investigation of Polysulfide Adsorption on FeS2 Additive in Sulfur Cathode of Li–S Battery by Ex situ UV–Visible Spectroscopy

The performance of lithium–sulfur (Li–S) rechargeable batteries is strongly dependent on the entrapment of the higher‐order intermediate polysulfides at the sulfur cathode. An attracting way of preventing the polysulfide shuttle is by introducing a polar host which can form a Lewis acid–base complex with polysulfides. Herein, the Li–S battery by incorporating iron sulfides (FeS2) as a polar Lewis acid to entrap higher‐order polysulfides at the cathode center is investigated. FeS2/S cathode demonstrates largely improved retention of capacity compared to C/S cathode (capacity fading per cycle of 0.12% and 0.80% for FeS2/S and C/S respectively) and good rate performance in Li–S batteries compared to conventional carbon–sulfur (C/S) cathode. This is attributed to the decrease in polysulfide dissolution and better retention of active sulfur in the cathode during battery cycling which is due to the polar FeS2 additive that well anchors polysulfides. The effect of FeS2 in preventing the shuttle mechanism is demonstrated by ex situ UV–vis spectroscopy and ex situ Raman spectroscopy studies.

Advanced strategies for conversing and fixing sulfur during waste resins oxidation through Ca/Zn oxides enhanced Na2CO3-K2CO3 system

The effective reduction of sulfur pollutant emissions during the treatment of waste resins has always posed a challenge. This study put forward a solution to using the metallic oxide enhanced Na2CO3-K2CO3 system for the treatment of waste resins (CERs). Na2CO3-K2CO3 was used as a medium for heat transfer and desulfurization, while CaO or ZnO functioned as catalysts in the sulfur conversion process. The thermodynamic analysis substantiated the reliability of enhanced sulfur fixation by CaO and ZnO. H2S, SO2 and COS primarily generated during the destruction stage of -SO3H (280–500°C) and residues (∼700°C), which were largely absorbed through a vapor-liquid-solid reaction to generate CaCO3, ZnS and K2SO4. CaO improved the conversion of sulfur to sulfate and effectively mitigated the excessive emissions of CO2. SO2 generated by the oxidation of ZnS at about 800 °C could be further absorbed by molten Na2CO3-K2CO3 to form K2SO4. The proposed method exhibited in-situ desulfurization capability and effectively inhibited the sulfur migration to gaseous products. At 800°C, the sulfur retention rate, the formation rate of SO42- and the oxidation efficiency of CERs reached 91.39 %, 80.61 % and 99.99 %, respectively. The existence of CaO and ZnO facilitated the inorganic transformation of organic sulfur, and the efficient conversion of organic sulfur into inorganic compounds was achieved. This approach provides a new opportunity to improve the treatment efficiency of radioactive solid waste containing organic sulfur.

Effect of lignin, cellulose and hemicellulose from biomass on sulfur release behavior from dyeing sludge combustion

Co-combustion with biomass is recommended for treating dyeing sludge (DS) from the view of minimizing sulfur emissions. However, the sulfur emission from DS combustion depends on the lignin (L)/cellulose (C)/hemicellulose (H) ratio in the biomass, which is frequently overlooked. This study reveals the effect of biomass on the combustion characteristics and sulfur evolutions of DS combustion using triphenylmethyl mercaptan (TM) and L/C/H as model representative compounds of DS and biomass, respectively. Results indicated that the combustion behavior of the TM–biomass mixture was dominated by TM and secondarily by L/C/H. Although L/C/H brought forward the TM combustion, these biomass components (especially L) deteriorated the combustibility and burnout performances of the combustion. L/C/H promoted CH3SH and SO2 release at low temperatures but inhibited these emissions at high temperatures. The sulfur retention ratios of L, C, and H were 7.53 %, −5.75 %, and 0.17 %. TM–L interaction initially promoted and later inhibited the co-combustion process and the CH3SH and SO2 release. L/C/H addition reduced the E values of the mixtures and the co-combustion kinetics were dominated by Dn models. Residue analysis also indicated a dominant role of L in sulfur fixation, mainly because L additive created abundant adsorption sites in the co-combustion residue.

Prominent Role of Sulfate Reduction in Considerable Sulfur Retention in a Subtropical Soil

AbstractThe sulfur biogeochemical cycle controls the sulfur dynamics in the soil. In contrast to almost all deposited sulfur leaching out in temperate catchments, approximately 80% of the deposited S is retained in the catchments in subtropical regions. However, the mechanisms for sulfur retention were unclear, hindering the understanding of potential threats of legacy sulfur with environmental changes. Here, we demonstrated that sulfate reduction (as sulfide fixed in soil) was a prominent yet overlooked mechanism for sulfur retention in addition to the widely recognized sulfate adsorption in soil, based on a study on soil sulfur storage and stable isotope signatures within entire soil profiles in a typical subtropical catchment in China. Using a dual‐isotopic model, the sulfate reduction flux was further determined to be 30% of the S deposition. Due to a lot of deposited sulfur fixed via sulfate reduction, the release of soil legacy sulfur would be less in response to decreasing sulfur deposition compared to the projections only considering adsorption. However, the remobilization of large amounts of reduced S should be regarded as a threat to the environment under climate change in the future.

The effect of spray nozzles failure on SO2 removal efficiency

ABSTRACT This study was carried out on an absorber in the body of flue gas desulphurization system (FGD) of a coal-fired power plant. In this study, efficiency losses caused by the clogging or breaking of the spray nozzles were examined. These abovementioned problems of spray nozzles are the most common among the many factors affecting the sulfur retention efficiency. Although energy and exergy analysis is very common to optimize the system efficiency of FGD units, failure of spray nozzles in absorbers might be the main reason in terms of low FGD units efficiency and low SO2 removal rates. In this study, firstly locations of clogged or damaged nozzles are determined by examining a total of 240 nozzles (3 × 80). After the replacement of the broken spray nozzles, increase in the efficiency of A-B, B-C, A-C and A-B-C spray lines were observed as 9.14%, 3.77%, 10.56%, 9.72%, respectively. Depending on the washing zone of the nozzles, if one nozzle is damaged, it causes the efficiency to decrease between 0.24% and 0.36%.

Unveiling the polysulfide-PPY interaction for enhanced lithium–sulfur battery performance

Understanding the processes in lithium–sulfur (Li–S) batteries is critical to advancing this promising energy storage technology. To this end, a 3D polypyrrole-based sponge (PPY) was synthesized as a sulfur host for positive electrodes in (Li–S). Through optimization, the PPY:S8 composite showed interesting electrochemical performance, including a cycle lifetime of over 200 cycles and remarkable specific capacitances at 0.2 A g−1. Electrochemical impedance spectroscopy (EIS) data provided valuable insights. In addition to the unchanged solution resistance indicating a minimal shuttle effect, the capacitance of the PPY film remains robust due to its bipolaronic state and shows strong sulfur retention, especially at the LiPSs/S8 potential. Operando Raman spectroscopy revealed the stability of the bipolaronic state and the “neutralization” of the lithium polysulfides (LiPSs) by the incorporation of sulfur. Moreover, UV–vis analysis confirmed the efficient absorption of LiPS within the PPY matrix. These results highlight the potential of PPY as an effective sulfur host that minimizes the shuttle effect and improves the charge storage capability of Li–S batteries. This research contributes to the development of advanced materials for energy storage systems and highlights the importance of using positively charged materials as carriers for sulfur in Li–S batteries.

Co-hydrothermal carbonization of sludge and food waste for hydrochar valorization: Effect of mutual interaction on sulfur transformation

Co-hydrothermal carbonization of sludge and food waste is a promising method for hydrochar valorization. The sulfur content and form of hydrochar are the key parameters that determine its further utilization. However, the effect of the chemical composition of food waste on sulfur redistribution remains unknown. Herein, the sulfur transformation behavior during the co-hydrothermal carbonization of sludge and model compounds (cellulose, starch, xylan, and palmitic acid) of food waste was investigated, with focus on the detailed reaction pathways from inorganic-S/organic-S media in aqueous to hydrochar. The added model compounds, particularly the starch and xylan, increased the sulfur retention ratio from 41.0 to 44.7– 49.2 % in hydrochar. Among them, starch and xylan can react with aliphatic-S in aqueous via cyclization and oxidization to form the thiophene-S/aromatic-S and sulfone-S and can react with SO42−-S to form sulfone-S via sulfonate reaction. These formed organic-S can polymerize with hydrolyzed intermediates (i.e., 5 hydroxymethyl-furfural, glucose, and xylose) from model compounds to transform into hydrochar. Cellulose enhanced the formation of sulfone-S in hydrochar via the reactions between the water-insoluble partial hydrolysate and SO42− in the aqueous. Additionally, palmitic acid hydrolysate provided an acidic environment that facilitated the polymerization of thiophene-S/aromatic-S from aqueous to hydrochar. Generally, the chemical composition of food waste largely affects the redistribution behavior of sulfur during co-hydrothermal carbonization, and this occurs primarily due to the differences in the hydrolysate and degree of hydrolysis for various model compounds. The results can provide guidance for preparing sludge-based hydrochar possessing different sulfur content and species, that can be used as clean fuel or carbon material.

The influence of clinkering conditions and cooling rate on the phase composition of Belite-Ye’elimite-Ferrite (BYF) clinker

BYF cements are a promising alternative to Portland cement due to their lower carbon dioxide (CO2) emissions and reduced energy requirements. BYF clinkers can generally be produced at lower firing temperatures, and their main clinker phases (belite, ye’elimite, and ferrite) have lower lime content and require less energy for their formation. The formation of these phases, their relative proportions, and polymorphism, which determines their reactivity, strongly depend on clinker synthesis parameters. Therefore, assessing the influence of the raw meal composition, burning conditions, and cooling rate on the BYF clinker phase composition is essential. This study was carried out in order to examine the influence of raw materials proportioning, retention time, and cooling rate on the mineralogy and microstructure of the BYF clinker. Raw meals with different contents of sulfate (SO3) were calculated, and laboratory clinkers were produced in a high-temperature electrical furnace. The burning temperature of the clinkers was set at 1350 °C. The influence of retention time at the maximum temperature was investigated starting at 15 min and including 30, 60, and up to 120 min. The effect of different cooling rates on phase composition and polymorphism of main clinker phases was studied. The resulting mineral composition of the clinkers was examined by X-ray powder diffraction (XRD) with Rietveld refinement for quantitative phase analysis. The experimental results of this study indicate that the retention time of 30 min, excess SO3, and rapid cooling with forced air flow were the most beneficial for obtaining the desired clinker phase composition with the most reactive polymorphs of belite and ye’elimite. It was demonstrated that sulfur content and retention time had a greater effect on clinker mineral composition and polymorphism of belite and ye’elimite than the cooling rate. These results emphasize the importance of optimizing the technological parameters of clinker production to achieve the desired clinker composition.

Influence of Radioactive Sludge Content on Vitrification of High-Level Liquid Waste

The radioactive sludges formed at the bottom of high-level liquid waste (HLW) storage tanks pose challenges when the HLWs are vitrified. This study aims to determine the influence of the sludge content (enriched in Na2O, Al2O3, NiO, Fe2O3, and BaSO4) on the structure and properties of waste glasses in order to find the optimal ratio of sludges to HLW during vitrification. In the experiments, the simulated sludge and simulated HLW were mixed at different ratios from 0:8 to 4:4, with an overall waste content of 16 wt %, in a borosilicate glass wasteform. It is found that the glass density, molar volume, sulfur retention, and glass transition temperature changed little when increasing the sludge content of the glasses, while the viscosity, chemical durability, and crystallization features of the glasses varied notably. The crystals formed in the glasses during the thermal treatment were exclusively Fe-substituted diopside (Ca, Mg, Fe)2Si2O6. An increase in the Al2O3 and NiO content of the glasses may have been responsible for the increased crystallinity at high temperatures. The leaching rate of Si, B, Na, and Cs from the glasses declined with the increasing addition of sludge to the glasses. Although all the glasses fulfilled the requirements for vitrification processing and glass-product performance, it is recommended that the sludge content of the whole waste should not exceed 25 wt %. This study guides further research on the immobilization of high-level sludges.

Desulfurization in co-firing of sewage sludge and wooden biomass in a bubbling fluidized bed combustor under air and oxy-fuel conditions

This work presents results of an experimental investigation of a direct addition of Ca-based sorbent for SO2 capture in a bubbling fluidized bed combustion. The fuel of interest was secondary biomass represented by a dried sewage sludge, which was mixed with primary biomass represented by wooden pellets in a weight ratio of 30:70. The performance of this SO2 capture approach is compared in air and oxy-fuel combustion conditions, since the different gas environment in the bed significantly affects the SO2 capture process. The experiments were carried out in an experimental bubbling fluidized bed combustor with a power load of about 30 kW.Sewage sludge is typical for its high ash content and has sufficient dimensions and attrition resistance to create the fluidized bed without the support of external bed materials. However, it typically consists of S-containing organic substances, resulting in the presence of SOX in the off-gas. A reference case was initially conducted without any sorbent addition in order to investigate the effect of sulfur self-retention in the fuel ash. The sulfur retention in the ash reached almost 45 % in air- and up to 55 % under oxy-combustion.In the next phase, the performance of Ca-based sorbents in sulfur capture was evaluated. The sorbents were represented by two types of limestone with diverse CaCO3 content produced at different locations. The experiments were carried out with three Ca/S mole ratios (1.5, 3, and 4.5). The effect of the fluidized bed temperature was also investigated as the most important parameter.The SO2 capture ratio (used as a performance indicator) was calculated based on emission factors, due to the different specific volumes of flue gas in the air and oxy-fuel modes. The results show in general a significantly higher SO2 capture ratio under oxy-fuel conditions. The differences are more significant in lower Ca/S ratios, where the SO2 capture ratio increased from 46 % under air conditions to 75 % under oxy-fuel for Ca/S = 1.5. In the case of the highest Ca/S ratio examined (Ca/S = 4.5), the increase in SO2 capture was from 90 % to 95 %.

Salinization of coastal saline-alkali soil might enhance H2S release by affecting H2S-related bacterial communities

Bacterial metabolism can result in the production and release of hydrogen sulfide (H2S), a reductive gas, in soils. Hydrogen sulfide-releasing bacteria (HSRB) assimilate organic sulfur or dissimilate sulfate to generate and release H2S, whereas H2S-oxidizing bacteria (HSOB) oxidize H2S generated by themselves or other bacteria to soluble sulfate resulting in sulfur retention in soil. However, the effects environmental factors such as electrical conductivity on both these bacterial groups and H2S release remain unclear; some key processes such as H2S oxidation also remain underexplored. In this study, we found that high electrical conductivity in coastal saline-alkali soil affects these bacterial communities, especially HSRB, potentially enhancing H2S release. The “sink” of H2S gas, represented by sulfidic sulfur (concentration, 0.2–3.4 nmol/g) in coastal saline-alkali and inland soils, was determined using the methylene blue method, and found to be positively correlated with soil electrical conductivity, suggesting that more H2S gas potentially volatilized from salinized soil. We then revealed that the proportion of HSRB clones was correlated positively and significantly with the electrical conductivity and sulfidic sulfur of soil, but not with the pH or sulfur source. Further, 16S rRNA gene sequence comparison indicated significantly reduced richness and diversity of bacterial communities and considerably altered the composition of dominant bacterial populations in coastal saline-alkali soil. The phyla Proteobacteria, Bacteroidetes, and Gemmatimonadetes accounted for 38 %, 30.1 %, and 11.1 % and for 28 %, 12.9 %, and 2.5 % of the bacterial populations in coastal saline-alkali and inland soil, respectively. PICRUSt analysis showed that the richness of genes encoding the key H2S oxidation enzymes, sulfide:quinone reductase and sulfate hydrolase, was decreased significantly and negatively correlated with the detected sulfidic sulfur. These enzymes are usually expressed by HSOB in coastal saline-alkali soil, implying a low sulfide oxidation capacity. These results indicate that the number of HSRB is increased whereas the ability of H2S oxidation is decreased in coastal saline-alkali soil, which might lead to enhanced H2S release. Overall, this study provides new insights for understanding the sulfur biological cycle in saline-alkali soils.

Findings on the use of a Ca-based sorbent as an oxygen carrier precursor in a Chemical Looping Combustion unit

Limestone Chemical Looping Combustion (L-CLCTM) is a novel process to burn sulfurous fuels with intrinsic desulfurization and CO2 capture. L-CLCTM is based on using calcium-based sorbents as precursors for CaSO4 formation, which is used as an oxygen carrier. Its principle lies in the in-situ sulfur retention process performed in fluidized bed combustors burning solid fuels with high sulfur content. The target redox pair for the oxygen transference to the fuel is CaSO4/CaS. In this research work, experimental tests burning CH4, syngas and H2 with a moderate H2S concentration were conducted in a continuous CLC unit. This experimental campaign is first in a kind as there is hardly information about the CaSO4/CaS pair for the L-CLCTM process. High combustion efficiencies were achieved at moderate temperatures (800–850 °C) when burning H2 and syngas (∼96–99 %). Likewise, low CH4 combustion efficiency (∼59 %) was found even operating at a temperature as high as 945 °C. Additionally, experimental tests at different Ca/S molar ratios were performed. They revealed that it was possible to reach suitable sulfur retention values (∼82 %) by using a Ca/S molar ratio of 2.25. This value resulted in a very feasible ratio since it is commonly used in fluidized bed combustors.

Products distribution and sulfur fixation during the pyrolysis of CaO conditioned textile dyeing sludge: Effects of pyrolysis temperature and heating rate

Textile dyeing sludge (TDS) is a typical industrial solid waste whose amount surged with the textile industry's development. Pyrolysis treatment is a promising technique for TDS to realize harmless disposal and resource reuse. However, the high content of organic compounds would cause sulfurous pollutants emission, reducing the economic feasibility during pyrolysis. This study aimed to fill the knowledge gaps about the thermal behavior, products distribution, kinetics, and sulfur transformation during TDS pyrolysis in 350–575 ℃ with the heating rate of 60, 600, and 6000 ℃/min, then investigate the sulfur fixation effect of CaO under representative conditions (350 ℃, 650 ℃ with 60 ℃/min, 6000 ℃/min). The primary decomposition stage of TDS is observed in 127–557 ℃, following the Avrami-Erofeev (n = 3) model, while the activation energy presents a convergent tendency with the increased heating rate. The pyrolysis temperature and heating rates impact the cracking of organic compounds, while a weakening effect is found for the sulfur distribution. CaO addition could efficiently realize sulfur fixation in char by absorbing sulfurous gas products, but SO2 escape appeared with the increased CaO fraction. Pyrolysis condition at 650 ℃-60 ℃/min with 10 wt% CaO addition is recommended to achieve high sulfur retention, and the sulfur transformation mechanism in char during the TDS pyrolysis with and without CaO is proposed. Our findings provide novel and fundamental insights into the efficient disposal and pollution control during TDS pyrolysis.

Sulphur retention and in-situ preparation of metal sulphide catalysts during activation of petroleum coke

Petroleum coke (petcoke) containing sulphur has limited direct applications, but stockpiling the material creates an environmental issue. Although chemical activation can be used to valorise the petcoke to activated carbon, sulphur is released creating alternative environmental problems. In this study, a new activation method for high sulphur content (∼6.5 wt%) petcoke was developed to retain sulphur and prepare transition metal sulphide catalysts simultaneously. Petcoke was mixed with tungsten and nickel precursors and then activated by KOH at 600 °C in the presence of steam. After washing, the activated petcoke had a sulphur content of 5.1 wt%, which was much higher than that in the absence of steam during activation (0.4 wt%). Sulphur was also retained (>4 wt% of sulphur) when other transition metals including molybdenum and cobalt were used. Characterization by XRD, XPS, and SEM-EDS suggested that sulphur was retained on the activated petcoke in the form of metal sulphides. Further thermodynamic analysis of the system revealed that in the presence of steam an H2S/H2 mixture was generated, and this mixture promoted the formation of the metal sulphide species when metal precursors were introduced. The prepared metal sulphide catalysts were active for several reactions including the photoreduction of CO2. Overall, this study provided an effective method to prepare metal sulphide catalysts from sulphur containing carbonaceous waste.

Effect of sucrose on technetium and rhenium retention during vitrification of low‐activity wastes

AbstractSucrose (C12H22O11) has been used in low‐activity waste (LAW) melter feeds containing large fractions of nitrates, nitrites, or both because it facilitates foam suppression and denitration. This study focused on the effect of sucrose in LAW feeds on technetium (Tc) and rhenium (Re) retention. The amount of sucrose added in feeds was varied to differentiate the carbon‐to‐nitrogen mole ratio (C/N ratio). The results show that larger sucrose addition (higher C/N ratio) enhances Tc and Re retention. Reducing conditions induced by sucrose decomposition and early chemical reactions between sucrose and NaNO3/NaNO2 are expected to increase Tc and Re retention. However, high sucrose addition decreased sulfur (S) retention slightly because sodium sulfate decomposes in reducing conditions at lower temperature. This early sulfate decomposition can affect Tc and Re retention partly because these species can be soluble in sulfate phases. This correlation indicates that the decrease of sulfate phases in the glass by early decomposition can reduce the solubility of Tc and Re in the sulfate phases, which may increase Tc and Re retention in the glass. In addition, continuous gas evolution and vigorous foaming at the foaming temperature range of 700–900°C may influence Tc and Re retention process interrupting retention or facilitating volatilization.

Ca-based sorbents as precursors of oxygen carriers in chemical looping combustion of sulfurous fuels

Limestone Chemical Looping Combustion process (LCL-C™) patented by Alstom Power Inc. proposes the formation of a CaSO4 oxygen carrier via sulfur retention process when supplying a Ca-based sorbent together with sulfurous fuels in the fuel reactor. In the present research work, four Ca-based sorbents, three limestones and one dolomite with different physico-chemical characteristics, have been evaluated as oxygen carrier precursors during consecutive redox cycles by thermogravimetric analysis. 5% H2 and 3000 vppm H2S (N2 to balance) and 10% O2 (N2 to balance) were selected as reducing and oxidizing gases, respectively. Additionally, an anhydrite ore has also been studied for comparison purpose. Results from SEM-EDX characterization of the sorbent particles revealed the existence of three different sulfation patterns: (1) uniform distribution, (2) core–shell structure and (3) high sulfur content with high limitation to be converted into CaSO4. All sorbents exhibited high oxygen transport capacity (Roc = 13.3–20.8%), except for the material showing pattern (3) (Roc = 2.6%). Likewise, the materials presented high reactivity with rate index values ranged between 11.0 and 18.8%/min. Therefore, the Ca-based sorbents herein assessed can be considered suitable precursors for the formation of CaSO4 based oxygen carriers to be used in CLC systems burning sulfurous fuels.

Tuning functional two-dimensional MXene nanosheets to enable efficient sulfur utilization in lithium-sulfur batteries

Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti 3 C 2 T z -MXene via one-step surface functionalization using di(hydrogenated tallow)benzylmethyl ammonium chloride (DHT). The latter renders the Ti 3 C 2 T z surface hydrophobic, making it readily dispersible in sulfur dissolved in a carbon disulfide (CS 2 ) solvent. By evaporating the solvent, we conformally coat the DHT-Ti 3 C 2 T z (DMX) with sulfur. The developed composite, with higher available active area, enables effective trapping of lithium polysulfides (LiPs) on the electroactive sites within the cathode, leading to improvement in electrochemical performance at higher sulfur loadings. The DMX/S cathodes function with high sulfur loading of ∼10.7 mg·cm −2 and deliver a stable areal capacity of ∼7 mAh·cm −2 for 150 cycles. Moreover, a DMX/S cathode in a pouch-cell configuration retains ∼770 mAh·g −1 after ∼200 cycles at 0.2C (85.5% retention). Ex situ studies elucidate the nature of the LiPs-MXene interaction and the effect of surface functionalization towards improved performance. DHT functionalized hydrophobic MXenes (DMX) form a stable colloidal solution in CS 2 Atomically thin, metallically conductive DMX improves sulfur utilization in composites DMX/S cathode delivers good cycling stability at a high sulfur loading of 10.7 mg·cm −2 Emphasis on cathode development, pouch-cell performance, and nature of the interactions Rechargeable lithium-sulfur (Li-S) batteries have the potential to replace lithium-ion batteries because of their higher specific energy. Pai et al. report a surface fictionalization strategy to enable maximum sheet-surface area use of 2D-MXenes in Li-S batteries, which enables high sulfur loading, capacity retention, and long cycle life.