Sulfur Release Research Articles

Experimental study on dynamic release and transformation of sulfur during pyrolysis of Shanxi high-sulfur anthracites based on MFBRA and XPS

Pyrolytic desulfurization of two Shanxi high-sulfur anthracites was investigated experimentally under hydrogen atmospheres using a micro fluidized bed reaction analyzer (MFBRA), the dynamic release behavior of sulfur-containing gas during pyrolysis was characterized by a rapid online gas analyzer, and the transformation between sulfur-containing components in the resultant char was analyzed based on morphological and XPS characterizations. The results show that the dynamic release of sulfur-containing gas features two intensity peaks at 530–560 °C and 812–830 °C, respectively, indicating that the sulfur release proceeds by two subsequent processes: the reduction reaction of pyrite and the organic sulfur decomposition. The migration from inorganic to organic sulfur occurs predominately at lower temperatures, while the transformation between different forms of organic sulfur components is dominant at higher temperatures. Overall, the anthracite coal with a higher organic sulfur content has a higher sulfur removal efficiency in the hydrogen atmosphere. The research results provide the essential data supporting the development of highly efficient pyrolysis desulfurization technology for clean and efficient utilization of high sulfur anthracite coal resources.

Transformation and Migrant Mechanism of Sulfur and Nitrogen during Chemical Looping Combustion with CuFe2O4

Chemical looping combustion (CLC) is a key technology for capturing CO2. Different types of oxygen carrier (OC) particles are used in coal CLC. The migration and transformation behaviors of sulfur and nitrogen are basically the same when CaFe2O4 and Fe2O3/Al2O3 are used as OC. CLC can be divided into two reaction stages: coal pyrolysis and char gasification; SO2 and NO show bimodal release characteristics, both of which show a basic trend of rising first and then falling down. The contents of H2S and NO2 increased rapidly at the beginning of the reaction and then decreased slowly at the stage of char gasification. H2S is released rapidly during coal pyrolysis and discharged from the reactor with flue gas, and then part of H2S is converted to SO2 during the char gasification stage by OC particles. NO can be oxidized by OC particles and form NO2. The increase in the reaction temperature and oxygen-to-carbon ratio (O/C) contributes to the release of sulfur and nitrogen and higher reaction temperature and O/C can inhibit the formation of metal sulfide. O2 released by CuFe2O4 significantly increases the contents of SO2, H2S, NO and NO2 in flue gas. This work is helpful for improving control strategies for pollutants.

Synthesis and Characterization of Nano-Sulfur and Its Impact on Growth, Yield, and Quality of Sunflower (Helianthus annuus L.)

ABSTRACT A laboratory study was undertaken to determine the response of sunflower to nano-sulfur application in comparison to conventional sulfatic fertilizer. Nano-sulfur particles were characterized using a particle size analyzer, zeta potential, UV-Spectroscopy, XRD, FT-IR, SEM, and TEM. After the complete characterization, the sulfur release pattern was studied in a percolation reactor system. Thereafter, response studies were carried out using sunflower (var. KBSH 42) crop. The stable and uniform nano-sulfur particles with a medium diameter of 35–45 nm are yielded by the aqueous precipitation method. The results showed that sulfur release from the nano-sulfur has prolonged for 42 days, while the sulfur release from the ordinary sulfur fertilizer (gypsum) ceased to exist within 35 days. Nano-sulfur fertilized plants had registered significantly higher dry matter production (11–12%), seed yield (15%), and oil content (14.7%) than gypsum fertilized plants. The data revealed that nano-sulfur assists in improving the available sulfur in soils.

Sulphur and particulate matter affecting on soil and underground plants

Environmental problems were faced, and one of them is the accumulation of Sulphur and its compounds in the atmosphere and through the atmosphere, it accumulates in the soil and then the underground plants. In the atmosphere Sulphur it is present in the form of aerosols and acid precipitation. Volatile Sulphur compounds are released by the combustion of fossil fuels and volcanic eruption also produces Sulphur oxides. Deficiency of Sulphur produces paling of plants and denaturing of some enzymes that are then fulfilled by using the fertilizers of Sulphur. Soil also has an adverse effect when particulate matter or Sulphur aggregates in the plants and their physiological and biological development is retarded. Most of the industrial processes contain Sulphur compounds like thiol, thiophene, oxides of Sulphur etc. Structural and chemical mutation occurs when particulate substances induce into the plants and productivity and efficiency of that plant is reduced. The impact of acid rain in places with high quantities of mixed air pollutants has yet to be determined. Acid inputs appear to be affecting several techniques in field soils. These must be measured in terms of plant output. SO2 enters the leaves via stomata and quickly dissolves in Apoplastic water, producing mostly Sulphite (SO3)-2, bisulphite (HSO-3), and H+ ions. SO2 phytotoxicity has been attributed to Sulphite and bisulphite ion interactions with different chemicals. If the quantities are not too high, most leaves can detoxify Sulphite and bisulphite by oxidizing them to less harmful Sulphate ions via a series of processes. SO2 absorbed by foliage may undergo reduction conversion, including absorption into organic Sulphur compounds and release from the leaves as H2S. The oxidizing or reducing route of SO2 in plants is determined by plant species, soil Sulphur content, SO2 amount and persistence, and plant growth conditions.

Numerical investigation on H2S formation characteristics in air-staging combustion of a tangentially coal-fired boiler

ABSTRACT Existing H2S generation models are mainly applied in laboratory-scale models and thoughtless about the fuel sulfur release characteristics in fuel-rich zone. So, a novel H2S generation model is proposed for describing the H2S formation characteristics of real-scale boilers in this work. It consists of two parts: fuel sulfur release and chemical reactions. The ratio of the gasification rate to the consumption rate for each char particle is calculated in coal combustion model through the user-defined function (UDF) approach, which is delivered to the H2S generation model for determining the proportions of char sulfur converted to COS and SO2. The numerical results show that the proportions of char sulfur converted to H2S are about 0.545 over the excess air coefficient range from 0.6 to 1.2. The strongly reducing atmosphere could just accelerate the H2S formation to a certain extent in the devolatilization stage. For a 600 MW tangentially coal-fired boiler, the H2S concentration over 400 mg∙kg−1 appears mainly in the zone below burner A and the zone between burner E and the separated over-fire air nozzle. This study is intended to guide for predicting possible corrosion zone and delivering targeted solutions for inhibiting metal corrosion.

Characterization of nitrogen and sulfur migration during pressurized coal pyrolysis and oxy-fuel combustion

In the present work, pressurized coal pyrolysis and oxy-fuel combustion experiments were carried out in a pressurized drop tube furnace to investigate the migration and transformation characteristics of nitrogen and sulfur. The pyrolysis experiments showed that high pyrolysis pressure inhibited the release of nitrogen and sulfur. The content of oxidized nitrogen (N-X), pyrite, sulfide, sulfoxide and sulfate in char decreased, while the content of pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q), thiophene and sulfone in char increased with the increase of pyrolysis pressure. The elevated pyrolysis temperature was conducive to the decomposition of nitrogen and sulfur-containing functional groups, and it also promoted the conversion of nitrogen and sulfur to functional groups with high stability such as N-Q and thiophene. The release of volatiles and the decomposition of nitrogen and sulfur-containing functional groups in coal were promoted by CO2 gasification. The increase of the total CO2 gasification pressure led to more nitrogen and sulfur remaining in char. During pressurized oxy-fuel combustion in O2/CO2 atmosphere, the emissions of NO, NO2 and SO2 were lower than those in air combustion. The emissions of NO, NO2 and SO2 gradually decreased with the increase of pressure at air and oxy-fuel atmospheres. The increase of temperature increased the emissions of NO and SO2 at different pressures, but the NO2 emission decreased at elevated temperature. In addition, the emissions of NO and NO2 increased, but the emission of SO2 decreased with the increase of oxygen concentration.

Evaluation of the effects and interactions of initial chlorine and sulphur contents on the release of potassium compounds during biomass combustion

In biomass combustion, understanding the effects of chlorine and sulphur release on the release of potassium compounds can help improve and predict the potassium release mechanisms. In this work, a kinetic model is applied to investigate the influences of S and Cl contents on the release of major potassium compounds during combustion. The results indicated that increasing the initial Cl from 3.8 × 10−5 mol/g biomass to 1.5 × 10−4 mol/g biomass promotes the maximum release of HCl and KCl by 518% and 273%, respectively, while inhibits the maximum release of KOH and K2SO4 by 99% and 68%, respectively. Cl in the biomass has directly influence the release of HCl, but indirectly impact the release of KCl; while its existence inhibits the formations of KOH and K2SO4 by adapting the contents of moisture, KO and KSO3. Raising the initial S from 2.7 × 10−5 mol/g biomass to 1.1 × 10−4 mol/g biomass only significantly affects the release of KOH and K2SO4 when temperature exceeds 1300 K, the maximum release of K2SO4 increased by 117%, while the release of KOH shifts from raise to decline. During combustion, S affects the formation and evaporation of K2SO4 by controlling the formations of intermediate S species. The results showed the model can accurately predict the major potassium compounds in various scenarios, and support the improvement of ash control technologies.

Structure evolution of lignite char in step pyrolysis and its combustion reactivity

Step pyrolysis was conducted in a laboratory-scale fixed bed reactor for char preparation. Characterization techniques such as volume solvent swelling, thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were applied to reveal char structure evolution during step pyrolysis. Combustion reactivities of the prepared chars were examined at a thermal gravimetric analyzer. Newly formed bond structures in char such as Cal-Cal and Car-Cal/O have been identified at the 1st stage of step pyrolysis, which evidences the occurrence of cross-linking reactions. As a result, step pyrolysis has higher char yield than direct pyrolysis. The char yield from step pyrolysis increases as the 1st stage pyrolysis temperature increases and reaches a maximum at 773 K. An index was put forward to assess the extent of cross-linking reactions during pyrolysis, which is well correlated with char production. The char from step pyrolysis has relatively high graphitization degree than from direct pyrolysis, and thus has lower combustion reactivity. Step pyrolysis can suppress sulfur and nitrogen release in comparison with direct pyrolysis owing to the formation of more stable sulfur and nitrogen species in char. The difference in nitrogen release varies within 8 percentage points and for sulfur release, it is within 5 percentage points under the examined experimental conditions.

Thermodynamic modelling of roasting of molybdenum sulphide concentrate with calcium hydroxide

This work aims to determine the conditions for the CaMoO4, CaSO4, Ca(ReO4)2 formation during oxidation of MoS2 and ReS2 in the presence of Ca(ОН)2. The concentrate from the Yuzhno-Shameyskoye deposit in the Sverdlovsk region, having 37% wt. Мо and 0.005% wt. Re, was selected as a feedstock for thermodynamic modelling of sweet roasting in the presence of Ca(OH)2. To determine the optimal amount of calcium-containing additives, the thermodynamic modelling was carried out using the following mass ratios: molybdenum concentrate: Ca(OH)2 = 1:0.8, 1:1, 1:1.2 and 1:1.5 in the temperature range of 100–800°С, with a step of 100°С, system pressure of 0.1 MPa in the air (molar ratio: molybdenum concentrate + Ca(OH)2: air = 1:5). The content of all sample components in moles was entered into the HSC 6.1 software package. The main reactions associated with the sweet roasting of molybdenum concentrate in the presence of calcium hydroxide were shown. It was established that the main phases formed as a result of roasting comprise CaSO4, CaSO3, MoO3, CaMoO4, CaMoO3 and CaReO4. The effect of temperature on the formation of the main gaseous products was studied under different mass ratios of molybdenum concentrate and Ca(OH)2. It was found that up to 600°C, with molybdenum concentrate to Ca(OH)2 ratio of 1:1, the concentrations of released sulphurous anhydride are lower than the maximum permissible concentrations. The calculated thermodynamic data was used for modelling the roasting process of molybdenum concentrate with calcium hydroxide. An optimal ratio necessary for the successful process operation was established: molybdenum concentrate: Ca(OH)2 = 1:1 by weight. Thermodynamic modelling showed that, in the temperature range of 100–600°С when using Ca(OH)2, no rhenium and molybdenum loss is observed, the release of sulfur is less than 10 mg/m3.

Ash melting behaviour of reed and woody fuels blends

Ash melting behaviour is an important issue regarding operation of boilers, for instance, to avoid the agglomeration of the fluidized bed. Previous studies have shown that ash melting behaviour of the blends could differ from that of single parent fuels. This study focuses on the melting behaviour of fuel ash blends of reed, pine wood pellets and Douglas fir wood chips. For that purpose, simultaneous thermal analysis, heating microscope and scanning electron microscopy with energy dispersive X-ray analysis, X-ray diffraction, and FactSage modelling were used. The ash sample was heated up to the final temperatures stepwise, and the morphology and composition of the ash samples were examined at different temperatures. The results revealed that the melting onset for reed and woody fuels blend ashes was related to KCl-K2SO4 eutectic. The melting started at 700 °C and chlorine was released. The decomposition of CaCO3 was observed for the ashes containing wood pellets. In the case of reed and wood pellet ash, both processes performed simultaneously. The second mass loss and sulphur release were observed at 1100 °C, which is related to decomposition of K2SO4. In reed and woody fuels blend ashes, the gas release was accompanied with the melting of other substances (e.g. Si-Ca or Si-Ca-K system) and the gases were trapped into melt. The feldspars abundant in Douglas fir wood chips, could cause the sluggish melting behaviour of ash material. The FactSage modelling indicated the melting onset at lower temperatures compared to the results obtained by the other methods applied.

Sulphur in Jharia and Raniganj coalfields: Chemical fractionation and its environmental implications

In coal, total sulphur content is not the only important factor for the industry, but also the forms of sulphur and their distributions should be considered before utilizing any coal for a particular use. In Jharia and Raniganj coalfields, sulphur is present in the forms of organic sulphur (OS), pyritic sulphur (PS), and sulphate sulphur (SS). In this perspective, the present study aims to know the different forms of sulphur in coking and non-coking coals of Jharia and Raniganj coalfields. Twenty samples were collected from both the mining areas. The total sulphur content in coking coals varied from 0.28% to 0.55% and in non-coking coals it varied from 0.33% to 0.54%. The distribution pattern of sulphur showed that PS and OS are dominating in both the coalfields. The OS in Jharia field varied from 0.13% to 0.47%, and in Raniganj coalfield it varied from 0.19% to 0.41%. This depicts that both the coalfields were formed under freshwater condition. Similarly, PS varied from 0.01% to 0.21% and from 0.06% to 0.29%, and SS varied from 0.0052% to 0.01% and 0.005%–0.02% in the above fields, respectively. It is noticed that the content of sulphate sulphur is less than 0.1 wt%, which is lower than other forms of sulphur. In the past two decades, sulphur emission has increased with the increase of thermal power plants due to more demand for power, which is one of the causes of global warming. During coal combustion, H2S and SOx, are produced and that can react with O2 and H2O to form H2SO3, H2SO4 or H2S. Thus, sulphur release can respond within the ecosystem in the form of acidic precipitation that may acidify and affect lakes and streams, sub-surface water and historical monuments. In India, coal consumption and ecological contaminations are increasing day by day due to the rapid energy consumption. Therefore, special attention should be given to adopt clean coal technologies though the coal contains less sulphur.

Preparation and Crystallization of Magnetic Glass-Ceramics from the Residues after Sulfur Release and Iron Recovery from Copper Ore Tailings with Varied CaO Content.

To comprehensively reuse copper ore tailings (COT), the fabrication of glass‐ceramics by the direct sintering method was investigated, where the residues after sulfur release and iron recovery from copper ore tailings were used as raw materials. The effect of the CaO added on the fabrication of glass‐ceramics was emphasized. After analysis of chemical composition and thermodynamics, crystallization kinetics were analyzed by Differential Scanning Calorimetry (DSC) and fitted to the Kissinger equation. The crystal phase and microstructure of sintered glass‐ceramics heated between 1080 °C and 1100 °C were estimated by X‐Ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM), respectively. Furthermore, the effects of the addition of CaO on the properties of the sintered glass‐ceramics have been discussed. The results showed that the magnetic glass‐ceramics were sintered by the residues successfully, the color of which was lighter than that of glass‐ceramics sintered by raw materials before iron recovery. According to the XRD analysis, hedenbergite, wollastonite and sekaninaite were formed with traces of maghemite and quartz. In terms of crystallization kinetics and sintering results, a decrease in the activation energies of crystallization and in sintering temperature were observed for an increase in the addition of CaO of up to 10 wt.%. Moreover, the properties of the sintered glass‐ceramics, including bulk density, linear shrinkage and flexural strength, were enhanced, while water absorption and true density were reduced with the increase of the amount of CaO added.

Sulfur capture and release by ilmenite used as oxygen carrier in biomass combustor

Oxygen-Carrier-Aided Combustion (OCAC) is a promising technology for the combustion of solid heterogeneous fuels such as biomass and waste. However, a frequently encountered problem with biomass and waste is their high alkali contents, which can lead to the build-up of deposits on heat transfer surfaces, leading to corrosion and increased maintenance costs.The addition of elementary S is one of the options used in combustion processes to mitigate corrosion. Sulfation of KCl reduces the severity of corrosion on heat transfer surfaces due to the transformation of KCl into K2SO4, which is considered to be less corrosive. Even though many studies have been performed on the influence of sulfur on the corrosion process, there is to date little knowledge about the interaction of S with ilmenite used as an oxygen carrier (OC). Therefore, there is a need to understand the influence of S on both the properties of the ilmenite used as an OC and the morphologic development of the ilmenite particles. This study investigates the interactions between S and ilmenite as bed material, with the focus on the roles of ash layers in the capture and release of the added S under different combustion conditions.The present study focuses on bed material that was exposed in the Chalmers 12-MWth Circulating Fluidized Bed (CFB) combustor run with biomass as fuel and with the addition of elemental S. Calcined ilmenite without ash elements was used as a reference material and the collected bed material samples were tested for their abilities to capture S in a laboratory fluidized bed batch reactor run at 950 °C. Controlled SO2 exposures in an oxidizing environment were carried out, and the reversibility of the mechanisms for uptake and release of S was tested. Understanding the uptake and release of S components by ilmenite is of importance not only for the handling of bed materials, but also for developing new protocols for corrosion prevention in OCAC.In the present study, the ilmenite-sulfur interactions were followed using gas analysis, solid material characterization (SEM-EDX), and thermodynamic calculations (FactSage). The results suggest that SO2 is captured under oxidative conditions, preferentially by bed materials with developed ash layers, and released under reducing conditions. Mixed-sulfate-phase K2Ca2(SO4)3, K2SO4 and CaSO4 are found to be the main formed phases that can participate in S uptake and release.

Insights into in-situ sulfur retention by co-combustion of dyeing sludge and wood sawdust

Dyeing sludge (DS) incineration is a promising strategy to achieve waste reduction and waste-to-energy conversion efficiency; however, the poor-combustion performance and high-emission level of the gaseous sulfur of DS limit its applications. This study attempts to introduce wood sawdust (WS) to improve combustion performance and inhibit the sulfur emission during DS incineration. The combustion characteristics and release behavior of sulfur gas products of DS-WS mixtures were investigated using thermogravimetry and mass spectrometry (TG-MS), as well as the influence of WS on sulfur fate of DS and the in-situ retention mechanism to sulfur were revealed by ash analysis. Results indicated that WS addition restrained the devolatilization of light volatiles and facilitated the degradation of heavy volatiles and fixed carbon. WS addition improved the combustibility, burnout performance and combustion stability of DS. Organic sulfur species occupied most sulfur-containing compounds in DS, the thermal degradation of organic matter was responsible for emitting SO2, CH3SH, H2S, COS. SO2 contributed > 40% of sulfurous gas emissions. WS addition (30%) significantly reduced the normalized sulfur content from DS, and the in-situ retention ratio to sulfur reached 16.72%. The in-situ retention mechanism to sulfur was explained as potassium iron sulfate and calcium hydrogen sulfate jointly retained the release of sulfur. Moreover, Ca-based sulfate was more stable, indicating that the newly formed mineral contributed to preventing the re-emission of sulfur from incineration residue.

Effect of ash – ZnO heat carrier on sulfur migration behavior during pyrolysis of coal

In this paper, the effects of ash heat carrier (AHC) and ash-ZnO heat carrier (A-ZHC) on the release and transformation of sulfur during the pyrolysis of Yuandatan (YDT) high-sulfur bituminous coal were studied. The samples were pyrolyzed in a fixed-bed reactor, the composition of sulfur in char, crystal structure of inorganic sulfur, and species of sulfur in pyrolysis gas were analyzed by XPS, XRD and GC. Compared with AHC, the A-ZHC can better inhibit sulfur migration to tar and gas during coal pyrolysis so as to obtain more pure volatile products. Both the AHC and A-ZHC promote the formation of CaS and FeS. The presence of ZnO in the A-ZHC promotes the formation of ZnS, and the interaction between ZnS and FeS can produce solid solutions (Zn,Fe)S, which further reduces the release of H2S and COS and advances the increase of sulfide sulfur content. In addition, the catalytic effect of ZnO in A-ZHC promotes the conversion of thiophene sulfur to sulfide sulfur in char at high temperature. The catalytic effect of ZnO also promotes the conversion of tar sulfur to sulfide and sulfone sulfur in char by reacting with metal-oxides and oxygen-containing groups during the secondary reaction stage.

Thermodynamic research on the effect of H2O on transformation of organic sulphur during coal pyrolysis under CO2 atmosphere

This study investigates the effect of H2O on transformation of organic sulphur in coal during CO2 atmospheres by thermodynamic equilibrium calculation by HSC Chemistry. The effect of water vapour on the release of sulphur containing compounds was studied. Detailed S distribution between 200-1400°C was explored. The results show that CO2 not only promotes the formation of inorganic compounds, but also moves the peak of released less complicated organic compounds such as Thiophene, Methylthiophene, Dimethylthiophene, etc. to a much lower temperature. The ranking of the sulphur release in CO2 atmosphere by HSC is: SO2 > Methyl thiophene > Dimethyl thiophene > Ethyl thiophene > dimethyl sulfone. Temperature affects the transformation of sulphur greatly during pyrolysis in CO2 atmosphere. Below 700 °C, COS and H2S are two major sulphur containing compounds formed during pyrolysis in CO2. Above 700 °C, SO2 plays the main role. H2O at different temperature range during heating also reacts with organic sulphur compounds, leading to a further decomposition. Since more organic S stays in inert gas, water promotes the decomposition of organic S compounds more intense than that in CO2 atmosphere. Besides, the effect of water vapour on S distribution depends on the amount of H2O in the reaction.

Mineralization of Farm Manures and Slurries under Aerobic and Anaerobic Conditions for Subsequent Release of Phosphorus and Sulphur in Soil

A good understanding of nutrient release from manure or compost after application through mineralization is important to assure meeting the nutrient demand of crops, to secure timely fertilizer application and to enhance nutrient use efficiency. The current study was done to evaluate phosphorus (P) and sulphur (S) release patterns from different types of manures viz. cow dung, cow dung slurry, tricho-compost, vermicompost, poultry manure, poultry manure slurry and mungbean residues. The mineralization study was performed under aerobic (field capacity) and anaerobic (waterlogging) conditions for 180 days at 25 ± 1 °C in the laboratory. The release of P and S showed the highest values within 75–180 and 75–150 days, respectively, and was always higher in aerobic conditions than in anaerobic conditions. The first-order kinetic cumulative model was a good fit for mineralization, which was significantly influenced by manure type, soil moisture level and incubation period. Poultry manure slurry exerted the highest P and S release under both moisture conditions. Both slurries showed higher potential mineralization, with a lower rate constant for these elements compared to that in their manure states. Hence, appropriate manures should be chosen and applied in the proper quantity to provide exact amounts of nutrients, to increase crops nutrient use efficiency and to formulate correct fertilizer recommendations.

Reduction Characteristic of CaSO4-CuO Combined Oxygen Carrier Under CO Atmosphere

CaSO4 oxygen carrier is considered to be a potential oxygen carrier (OC) for Chemical Looping Combustion because of its high oxygen capacity and low price. But its reactivity is lower than the main metal oxide oxygen carriers, and it deactivates due to sulfur loss as well as sintering at high reaction temperatures above 920 ℃. To improve the performance of CaSO4-based oxygen carrier, small amounts of CuO particles were mixed mechanistically with CaSO4 particles to use as combined oxygen carrier in this work. The reduction reactions of CaSO4 oxygen carrier, CuO oxygen carrier and CaSO4-CuO combined oxygen carrier under CO atmosphere were investigated. The effects of reaction factors including reaction temperature, the oxygen-carrying ratio of CuO to CaSO4 and mass of oxygen carrier, on the reductions have been investigated in this study. XRD, SEM-EDS, BET and gas analyses were performed to investigate the variations of solid phase, element compositions in solid residual and sulfur release with reaction time. The results show that the addition of CuO increases the reactivity of the CaSO4-based oxygen carrier while also suppressing the release of the gas sulfur. For the individual reduction of CaSO4 by CO, with the increase of CaSO4 mass (500 - 1200 mg), CO2 yield also increases until 1000 mg stops and SO2 released rises remarkably; An increase in the reaction temperature aggravated the SO2 emission. The carbon dioxide generation efficiency also increases with an increase in temperature, but decreases when the temperature exceeds 950 ℃ due to sintering of the oxygen carrier particles; With respect to the reaction of CuO with CO, CO2 yield does not change significantly with increasing temperature, due to the sintering of the CuO oxygen carrier in a high temperature reaction environment;For the combined oxygen carrier: a.As the reduction reaction temperature increases, the reduction reaction performance of the combined oxygen carrier is enhanced within the reaction temperature range of 750~900℃. b. CaO the use of CuO additives not only improves the CO conversion rate, but also inhibits the release of gas sulfide. As the oxygen carrying fraction of CuO increases, SO2 released is reduced and the SO2 release time is delayed. What� more, the solid products after reduction reaction mainly contain CaS, CaO, CuO, Cu2O and CaSO4, and no copper sulfide is detected. c. When the oxygen-carrying ratio of CuO to CaSO4 is increasing from 15% to 20%, CO2 yield increases greatly.

Interplay of mechanics and chemistry governs wear of diamond-like carbon coatings interacting with ZDDP-additivated lubricants

Friction and wear reduction by diamond-like carbon (DLC) in automotive applications can be affected by zinc-dialkyldithiophosphate (ZDDP), which is widely used in engine oils. Our experiments show that DLC’s tribological behaviour in ZDDP-additivated oils can be optimised by tailoring its stiffness, surface nano-topography and hydrogen content. An optimal combination of ultralow friction and negligible wear is achieved using hydrogen-free tetrahedral amorphous carbon (ta-C) with moderate hardness. Softer coatings exhibit similarly low wear and thin ZDDP-derived patchy tribofilms but higher friction. Conversely, harder ta-Cs undergo severe wear and sub-surface sulphur contamination. Contact-mechanics and quantum-chemical simulations reveal that shear combined with the high local contact pressure caused by the contact stiffness and average surface slope of hard ta-Cs favour ZDDP fragmentation and sulphur release. In absence of hydrogen, this is followed by local surface cold welding and sub-surface mechanical mixing of sulphur resulting in a decrease of yield stress and wear.

Global climate disruption and regional climate shelters after the Toba supereruption

The Toba eruption ∼74,000 y ago was the largest volcanic eruption since the start of the Pleistocene and represents an important test case for understanding the effects of large explosive eruptions on climate and ecosystems. However, the magnitude and repercussions of climatic changes driven by the eruption are strongly debated. High-resolution paleoclimate and archaeological records from Africa find little evidence for the disruption of climate or human activity in the wake of the eruption in contrast with a controversial link with a bottleneck in human evolution and climate model simulations predicting strong volcanic cooling for up to a decade after a Toba-scale eruption. Here, we use a large ensemble of high-resolution Community Earth System Model (CESM1.3) simulations to reconcile climate model predictions with paleoclimate records, accounting for uncertainties in the magnitude of Toba sulfur emissions with high and low emission scenarios. We find a near-zero probability of annual mean surface temperature anomalies exceeding 4 °C in most of Africa in contrast with near 100% probabilities of cooling this severe in Asia and North America for the high sulfur emission case. The likelihood of strong decreases in precipitation is low in most of Africa. Therefore, even Toba sulfur release at the upper range of plausible estimates remains consistent with the muted response in Africa indicated by paleoclimate proxies. Our results provide a probabilistic view of the uneven patterns of volcanic climate disruption during a crucial interval in human evolution, with implications for understanding the range of environmental impacts from past and future supereruptions.