Removal Of Organic Sulfur Research Articles

Enhanced degradation of methanethiol via operational pH regulation in biofilm reactor: Insight of sulfur metabolism pathways and microbial adaptation mechanism

Methanethiol (CH3SH), a typical organic sulfur pollutant, poses significant risks to both human health and ecological stability due to its high toxicity and corrosive properties. Membrane aerated biofilm reactor (MABR) has been regarded as a promising and eco-friendly solution for removing organic sulfur from wastewater. However, the oxidation of CH3SH might lead to spontaneous acidification, which might affect microbial metabolic activities to influence the CH3SH biotransformation in MABR system. This work demonstrated that operational pH regulation could effectively promote the complete conversion of CH3SH to SO42- in MABR, while the transformation efficiency was only 40.6% under uncontrolled pH condition. Meanwhile, operational pH regulation resulted in 35.2% reduction in the excessive secretion of extracellular polymeric substances, thereby building a stable biofilm structure with sufficient oxygen mass transfer to enhance the CH3SH transformation. Additionally, operational pH regulation favored the enrichment of sulfur-oxidizing microorganisms (e.g., Rhodanobacter and Rhodobacter), while the uncontrolled pH favored the proliferation of microorganisms in harsh environment (e.g., Chitinophagaceae sp. and Sphingobacteriales sp.). Moreover, operational pH regulation enhanced the expression of critical genes involved in sulfur metabolism (e.g., SELENBP1 and SoxA), accompanied with glycolysis (e.g., ppgK and pfkB) and pyruvate metabolism (e.g., ackA and aceE), which could provide sufficient energy and electron. Conversely, these gene expressions were down-regulated in pH unregulation reactor, while the microbial adaptation mechanism was activated through the enhancement of DNA replication, quorum sensing, and two-component system, enabling resistance to extreme acidic conditions. This study would provide the in-depth understanding of operational pH regulation on organic sulfur degradation and transformation in MABR system and offer novel guidance for organic sulfur removal.

ZnO enhanced molten Na2CO3-K2CO3 system for simulated waste resins treatment: Efficient conversion and fixation of organic sulfur and iron(III)

The radioactive spent resins from pressurized water nuclear power plant always contain a significant proportion of 55Fe, which invariably leads to the release of radionuclides and acidic gases if not treated promptly. Herein, an efficient ZnO enhanced molten salt oxidation (MSO) method was established for the removal and fixation of organic sulfur and Fe in simulated radioactive resins containing Fe3+ (Fe-CERs). The existence of Fe3+ facilitates the reaction with O2 to form Fe2O3, which contributes to the fracture of organic skeleton. The comparative study was conducted to explore the impact of ZnO on the oxidation behavior of Fe and S at 600–800 °C. The introduction of ZnO caused the continuous formation of ZnS at 600–700 °C, and the conversion of ZnO at 800 °C indirectly promotes the retention rate of S (85.42 %). The potential conversion of Zn0.73Fe0.27S to ZnS may occur within the temperature range of 700 °C to 800 °C. Additionally, the predominant presence of carbon in residues at approximately 700 °C could exert a stimulating effect on the sulfidation process of Fe2O3 and inhibit the formation of SO2. The coexistence of Fe2O3, carbon and ZnO effectively diminishes H2S and SO2 amounts while further enhancing the fixation of S and Fe. The increase generation of K2SO4, FeS and Fe3O4 leads to a high formation rate of SO42- (79.36 %) and a great retention efficiency of Fe (96.23 %) at 800 °C. The proposed novel MSO method holds promising potential for applications in the treatment of organic contaminants.

Catalytic hydrolysis of methyl mercaptan and methyl thioether on hydroxyl-modified ZrO2: a density functional theory study.

The purification and removal of organic sulfur from natural gas is conducive to increasing the added value of natural gas and reducing environmental pollution. In this study, the adsorption properties of methyl mercaptan (CH3SH), dimethyl sulfide (C2H6S) and H2O on the surface of hydroxyl-modified ZrO2 were investigated using density functional theory (DFT) calculations. Additionally, a reaction mechanism was proposed for hydroxyl-modified ZrO2 catalyzing the hydrolysis of CH3SH and C2H6S. The chemisorption of H2O molecules on the catalyst surface is attributed to H-O and H-Zr bonds. The chemisorption of CH3SH and C2H6S on the catalyst surface is attributed to Zr-S bonds. Competitive adsorption between the three gases exists only between CH3SH and C2H6S. It reveals the water-resistant properties of hydroxyl-modified ZrO2 in desulfurization. The adsorption energies of the three gas molecules on the hydroxyl-modified ZrO2 surface are in the order of CH3SH - (Zr) > C2H6S - (Zr) > H2O - (OH). The natural hydrolysis of CH3SH and C2H6S is a heat-absorbing process that cannot occur spontaneously. The rate-determining step for CH3SH catalytic hydrolysis is the formation of CH3O. The fracture of CH3SHO is the rate-determining step for C2H6S catalytic hydrolysis. The depletion of the surface hydroxyl groups can be replenished by the dissociation of H2O molecules. Hydroxyl-modified ZrO2 facilitated the hydrolysis process of CH3SH to a greater extent than that of C2H6S. This study provides theoretical guidance for industrial applications and the design of hydroxyl-containing hydrolysis catalysts.

Study on influencing factors of Coal Microbial Flotation Desulfurization

This study systematically investigates the influence of various factors on microbial flotation desulfurization of coal, with a particular focus on removing organic sulfur. The parameters examined encompass particle size, pretreatment time, bacteria species, bacterial concentration, forms of sulfur occurrence, ash yield, and coal rank. The study aims to develop a thorough understanding of the desulfurization process and establish a theoretical framework for advancing clean coal technology and efficient coal utilization. Stringent control was maintained over parameters such as particle size, pretreatment time, bacterial species, and bacterial concentration. Various forms of sulfur and coal rank were considered to evaluate their impact on desulfurization. Correlation analysis was conducted to investigate the relationship between ash yield reduction and the extent of desulfurization. Thiobacillus ferrooxidans and Rhodotorula mucilaginosa were employed in the experimental setup to assess their efficacy in microbial flotation desulfurization. The results demonstrate that microbial flotation desulfurization achieved the highest removal efficiency for organic sulfur, reaching 79.65%. Notably, the desulfurization of organic sulfur exhibited an increasing trend with decreasing coal rank. Correlation analysis reveals a positive correlation between ash yield and desulfurization, suggesting that high mineral matter content in coal facilitates microbial flotation desulfurization and enhances biological oxidation. Comparative analysis of single strain and mixed strain experiments revealed varying degrees of improvement in desulfurization extent, with the mixed-bacteria system exhibiting the most effective removal of organic sulfur, which suggests that Rhodotorula mucilaginosa can significantly enhance microbial flotation desulfurization. Overall, this research provides systematic insights into the influence of process conditions and geological factors on coal desulfurization. The study establishes a theoretical foundation for the development of clean coal technology and the efficient utilization of coal resources, contributing to the advancement of environmentally friendly practices in the coal industry.

The conversion of organic sulfur and strontium into inorganic compounds during the molten salt oxidation of mixed resin

Molten salt oxidation (MSO) has the ability to capture sulfur and metal ions from radioactive mixed resin (MR). Nevertheless, the chemical conversion of sulfur (S) and strontium (Sr) in molten carbonate remains to be further investigated. Herein, MR doped with Sr2+ (Sr-MR) was used to replace spent mix resin containing radioactive 90Sr. The oxidation behaviors of MR and Sr-MR in ternary carbonate (Li2CO3-Na2CO3-K2CO3) were comparatively studied. Sr2+ could react with sulfur-containing species to form corresponding compounds in addition to the adsorption of SO2 by molten carbonate. The content of SO2 drops to 0 ppm at 800 °C, which indicates that the complete decomposition of sulfur-containing structures in Sr-MR and the efficient adsorption of SO2 by molten carbonate. Besides, Sr2+ could significantly promote the removal of organic sulfur, and the existence forms of strontium in molten salt are strontium sulfide (SrS, 350 °C), strontium oxide (SrO, 450 °C) and strontium carbonate (SrCO3, ≥ 550 °C). The presence of quaternary ammonium group (-N+(CH3)3) in Sr-MR indirectly stimulated the formation of sulfates from sulfur-containing compounds. The residual amounts of S and C in Sr-MR decreased to 1.44 % and 6.89 % at 650 °C, which were lower than that of pure MR under the same conditions. The proposed MSO system had excellent retention effects of Sr (98.51 %) and S (47.66 %) at 800 °C for 2.0 h, which provides a new perspective on the disposal of organic wastes containing sulfur radioactive metal ions.

Optimization Studies of Coal Organic Sulfur Removal using Potassium Carbonate and Ethylene Glycol as a Deep Eutectic Solvent

Optimization Studies of Coal Organic Sulfur Removal using Potassium Carbonate and Ethylene Glycol as a Deep Eutectic Solvent

Experimental investigation on sulfur transformation during coal steam gasification with Ca-based absorbent

To investigate the effects of temperature, Ca-based absorbent (CaO) and atmosphere on the sulfur transformation characteristics in coal steam gasification, experiments were conducted in a fixed-bed reactor. As temperature increased from 600 °C to 750 °C, H2S-S (sulfur in H2S) was elevated by 21.86% and absorbent-S decreased by 7.66%. More gaseous sulfur was captured by organic groups to form organic sulfur in char at higher temperature. CaO promoted the sulfur conversion, and played the role of gaseous sulfur absorbent at the same time, and showed an ability of organic sulfur removal. CaO slowed down the H2S release by reacting with it to form CaS, resulting in that the peak concentration of H2S without CaO reached 1026.7 ppm, which decreased to 426.3 ppm with CaO. The increase in Ca/C promoted the sulfur conversion slightly and reduced the sulfate content in char. Compared with inert atmosphere, H2S-S in the steam atmosphere increased by 35.07%, while absorbent-S decreased by 23.42%. The solid–solid reaction mechanism is more suitable for the sulfate transformation in inert atmosphere, while the gas–solid reaction mechanism is more suitable in steam atmosphere. The sulfur conversion in inert atmosphere was lower, but sulfate had a higher decomposition rate.

Adsorptive desulfurization of model and real fuel via wire-, rod-, and flower-like Fe3O4@MnO2@activated carbon made from palm kernel shells as newly designed magnetic nanoadsorbents

The removal of organic sulphur from liquid fuel via applicable and cheap processes is one of the most challenging energy issues worldwide. Adsorptive desulfurization (ADS) processes can address this issue if highly effective magnetic nanoadsorbents with favourable textural properties are used. In this work, activated carbon produced from palm kernel shells was decorated with wire-, rod- and flower-like magnetic MnO2 by a hydrothermal route to produce reusable magnetic nanoadsorbents with tunable pore volume and pore diameter. The magnetic nanoadsorbents labelled Fe3O4@MnO2-w@AC, Fe3O4@MnO2-r@AC and Fe3O4@MnO2-f@AC were characterized using state-of-the-art spectroscopic techniques and used for sulphur removal from model and real fuels. The results revealed that the prepared magnetic nanoadsorbents had suitable oxygen functionalities, porous morphology and specific surface area of 480 for wire, 312 for rod, and 340 m2/g for flower-like magnetic nanoadsorbents. The newly-designed magnetic nanoadsorbents exhibited superior sulphur removal efficiency at 100 min contact time, 35 °C adsorption temperature, and 0.4 g adsorbent dose per 40 mL of model or real fuel. Among them, a wire-like magnetic nanoadsorbent showed 99 % sulphur removal from model fuel with 530 ppm sulphur content as DBT, 97.6 % and 90 % sulphur removal from commercial kerosene and diesel fuels with 430 and 1050 ppm sulphur content, respectively. The adsorption kinetics, isotherms and thermodynamics disclosed that adsorption of organic sulphur follows the pseudo first-order kinetic model, was an exothermic, and diffusion-controlled process. The magnetic properties enabled the nanoadsorbents to be recovered more easily and reused at least five times.

Catalysts for gaseous organic sulfur removal.

Organic sulfur gases (COS, CS2 and CH3SH) are widely present in reducing industrial off-gases, and these substances pose difficulties for the recovery of carbon monoxide and other gases. The reaction pathways and reaction mechanisms of organic sulfur on different catalyst surfaces have yet to be fully summarized. The literature shows that many factors, such as catalyst synthesis method, loaded metal composition, number of surface hydroxyl groups, number of acid-base sites and methods of surface modification, have important effects on the catalytic performance of metal catalysts. Therefore, this paper presents a comprehensive review of the research on the application of catalysts such as zeolites, metal oxides, carbon-based materials, and hydrotalcite-like derivatives in the field of organic sulfur removal. Future research prospects are summarized, more in situ characterization experiments and theoretical calculations are needed for the catalytic decomposition of methanethiol to analyze the coke generation pathways at the microscopic level, while the simultaneous removal of multiple organic sulfur gases needs to be focused on. Based on previous catalyst research, we propose possible innovations in catalyst design, desulfurization technology and organic sulfur resource utilization technology.

Non-thermal effect of microwave on organic sulfur removal from coal by microwave with peroxyacetic acid

This work investigated the non-thermal microwave effect during organic sulfur removal from coal by microwave irradiation combined with oxidation assistants. XANES was used to analyze the change of sulfur forms in the desulfurization process of high organic sulfur coal under microwave heating and conventional heating conditions. The effects of microwave fields on the molecular properties, bond strength and reaction kinetic of organic sulfur-containing groups were studied by quantum chemical calculation. Results showed that the desulfurization rate with microwave heating improved by 26% at the same temperature compared with conventional heating. The XANES analysis indicated that microwave radiation promoted the transformation of low-valence sulfur into high-valence sulfur, which resulted in the sulfur in the treated coal mainly existing as heterocyclic sulfur and oxidized sulfur. For the theoretical calculation, it is observed that the nucleophilic reaction activity of sulfur-containing groups could be improved and the strength of CS bands could be reduced under the extra electric fields due to the non-thermal microwave effect. Besides, the reaction activation energy was reduced and the reaction rate was increased under the same extra electric fields, promoting the formation of oxidized sulfur in coal. Therefore, there was a competitive relationship between sulfur-containing bond dissociation and group oxidation under the action of microwave non-thermal effect, which provided a reference for coal desulfurization research.

A novel method for the desulfurization of medium–high sulfur coking coal

The presence of sulfur affects the clean utilization of coking coal. Inorganic sulfur in coal, which exists mainly in the form of pyrite, inherently pollutes clean coal during flotation, while organic sulfur, on the other hand, can only be effectively removed by chemical means. Here, the combined methods of flotation and oxidation were adopted for desulfurization, and the desulfurization mechanisms were analyzed via XPS (X-ray photoelectron spectrometer), SEM (Scanning electron microscopy), MD (Molecular Dynamics), etc. Results showed that the removal of inorganic sulfur was preferred compared to the removal of organic sulfur. The sulfur and ash contents in coal were reduced from 2.55% and 46.16% to 1.33% and 13.41%, respectively, via flotation-oxidation (FO) method. During the oxidation-flotation (OF) method, however, Fe2O3 was observed to form on the surface of pyrite, while the content of oxygen-containing functional groups, adsorption capacity of water molecules and hydrophilicity were observed to increase. MD simulation was in agreement with experimental results, in which the diffusion coefficient of water molecules on the surface of oxidized coal was found to be lower than that of raw coal. As such, the oxidation process reduced the hydrophobicity of coal, resulting in a lower recovery of the products obtained via OF as compared to FO method.

Formulation of heterometallic ZIF-8@Cu/Ni/ZnO@CNTs heterostructure photocatalyst for Ultra-Deep desulphurization of coal and fuels

Developing efficient methods for deep desulphurization of commercial fuel is critical because of the requirements to limit sulphur concentrations below 10 ppm. Among various methods, recently photocatalytic oxidative desulphurization (PODS) has attracted great attention as it does not require high temperature and pressure. Herein, we report a novel heterostructure h-ZIF-8@Cu/Ni/ZnO@CNTs, having heterometallic ZIF-8 (h-ZIF-8) coated on Cu/Ni/ZnO (h-ZIF-8@Cu/Ni/ZnO), supported over carbon nanotubes (CNTs) sponge for selective PODS of both coal and fuel. The Cu/Ni/ZnO-based ternary hybrid metal oxide was first stabilized on a CNTs sponge followed by a surface reaction of metal particles with 2-methyl imidazole to in-situ form h-ZIF-8 shell on the surface of Cu/Ni/ZnO. The resulting h-ZIF-8@Cu/Ni/ZnO@CNTs exhibited high surface area (1283.47 m2/g), meso/microporous backbone, narrow bandgap (2.52 eV), and a large number of available active sites. Owing to these characteristics, the h-ZIF-8@Cu/Ni/ZnO@CNTs exhibited excellent photocatalytic response for the removal of organic sulphur with a removal rate of 0.76 Kg m−3 day−1 compared to control ZIF-8@ZnO@CNTs (0.4 Kg m−3 day−1). The removal rate was further enhanced to 3.3 Kg m−3 day−1 for dibenzothiophene, confirming the higher PODS potential of the designed photocatalyst for refractory organic sulphur. In summary, the h-ZIF-8@Cu/Ni/ZnO@CNTs possess promising characteristics to be applied for the desulphurization of commercial fuels.

Evaluation of the microwave-assisted organic acid separation of organic sulfur from high-sulfur coal

To explore the feasibility of organic sulfur removal using organic acids, oxalic acid, citric acid and ascorbic acid were selected as desulfurization reagents. Combined with microwave irradiation technology, desulfurization experiments of high-sulfur coal treated with nitric acid were conducted. The orthogonal experimental results showed that the microwave synergistic citric acid desulfurization had a better desulfurization effect. The removal efficiency of organic sulfur was 55.47% when the operating conditions of the reaction were 1 mol/L, 90 °C and 1000 W for 7 min. The desulfurization efficiency of oxalic acid and ascorbic acid was low, and their organic sulfur removal efficiencies were 32.35% and 21.37%, respectively. Fourier transform infrared spectroscopy showed that sulfones and sulfoxides were partially reduced and the removal effect of thiophene was poor. X-ray photoelectron spectroscopy showed that the mercapto group in the mercaptan combined with hydrogen ions and escaped in the form of H2S. The content of aromatic thioether and aromatic thiol in the coal treated with microwave irradiation was only 0.1%. Research indicates that organic sulfur in coal can be easily reduced to sulfur-containing compounds under microwave heat and acid environment of citric acid. The outcomes provide helpful references for further studies on organic desulfurization reagents.

Study on the Non-Thermal Microwave Effect of Organic Sulfur Removal from Coal by Microwave with Peroxyacetic Acid

Study on the Non-Thermal Microwave Effect of Organic Sulfur Removal from Coal by Microwave with Peroxyacetic Acid

Desulfurization of sour crude oil using an invasive weed adsorbent: An efficient, eco-friendly, and ultra-low-cost option

Desulfurization is a technology commonly used by refineries to mitigate the environmental burden caused by toxic gas emissions from hydrocarbon fuels. Expanding global population will increase liquid fuel demand by 20% between 2018 and 2050, with a total consumption of 240 quadrillion British thermal units (Btu) in 2050. Conventional catalytic Hydrodesulfurization (HDS) accounts for high cost and severe operating conditions (high temperature, pressure, catalyst poisoning and H2S safety). While studies have shown that adsorptive desulfurization (ADS) is highly effective in the removal of organic sulfur, limitations in the regeneration of adsorbent and selection of adsorbent with suitable structure to remove organic sulfur compounds exist. On the other hand, Prosopis juliflora, the world's most threatening invasive weed causes multifaceted environmental problems. The present study offers a novel solution that addresses both these issues contributing to climate change. Desulfurization of sour crude oil sample is performed using chemical-free, non-activated charcoal obtained from invasive weed species as adsorbent. XRD analysis showed amorphous structure and FTIR analysis confirmed the presence of CC bending functional group of the adsorbent. Adsorption-desorption isotherm showed presence of mesopores with pore diameter of 2.718 ​nm. Kinetic study findings reported 46% removal of total sulfur. GCMS findings showed efficient removal of some organic sulfur, including 100% removal of dibenzothiophene 4-methyl -. The equilibrium data is best represented by Freundlich isotherm. ICP-OES tests indicate the removal of toxic elements as well. The cost of the adsorbent is USD 0.12628 per kg, the lowest among all the adsorbents known thus far. The present study describes a novel, ultra-low cost, efficient, eco-friendly, desulfurization process that implements a chemical-free, non-activated adsorbent, achieves synergy, and offers multi-dimensional benefits to the environmental development. To our knowledge, this is the first study to characterize desulfurization of sour crude oil using an invasive weed.

An effective method to remove organic sulfur in coal: Effects on the physicochemical properties and combustion kinetics

The present work investigated an effective method to remove organic sulfur in coal utilizing different microorganisms (Nocardia mangyaensis and Pseudomonas putida). The most obvious finding to emerge from the sulfur forms analysis is that the organic sulfur removal of these two bacterial strains on Yunnan bumuga high-sulfur coal were 61.58% and 54.19%, respectively. This result may be confirmed by the Fourier transform infrared spectroscopy (FTIR) analyses that there were obvious decreases of intensity after biotreatment in the CS bond. Besides, the results of X-ray diffraction and X-ray photoelectron spectroscopy showed that major mineralogical phases in the forms of kaolinite and pyrite exist in raw coal. And more than 80% of thiophene and sulfoxide in the raw coal were removed by N. mangyaensis and P. putida. In addition, the results of the thermogravimetric analysis indicated that the combustion performance of biotreated coal samples was better than that of raw coal, and the most probable models to describe the combustion kinetics for biotreated coal and raw coal at different stages were obtained by the Arrhenius method and Coats–Redfern method.

Modeling CO2, H2S, COS, and CH3SH Simultaneous Removal Using Aqueous Sulfolane–MDEA Solution

In this study, a rate-based absorption model coupled with an improved thermodynamic model was developed to characterize the removal of acid components (CO2 and H2S) and organic sulfur (COS and CH3SH) from natural gas with an aqueous sulfolane–MDEA solution. First, the accuracy of the thermodynamic model was validated by comparing the calculated partial pressure of CO2, H2S, and CH3SH with those of the experimental data reported in the literature. Then, the industrial test data were employed to validate the absorption model and the simulation results agreed well with the experimental data. The average relative errors of the removal rates of CO2, COS, and CH3SH are 3.3%, 3.0%, 4.1%, respectively. Based on the validated coupled model, the total mass transfer coefficient and mass transfer resistance of each solute component at different column positions were analyzed. The effects of the gas–liquid ratio, overflow weir height, and absorption pressure on the absorption performance of each component were studied, and the influence of the acid component concentration in the feed gas on the removal efficiency of methyl mercaptan (CH3SH) was also discussed. It is found that the improved absorption model can better characterize the absorption performance and be conducive to the optimal design of the absorber column.

Effect of oxalic acid and sodium hydroxide on the desulfurization of coal using UV–H2O2 oxidation system

To research the efficient and economical desulfurization of Lingshi high sulfur coal (LS), the influence of acid and alkaline additives on an ultraviolet (UV) light oxidation desulfurization system was assessed. Sodium hydroxide (NaOH) and oxalic acid (OA) were selected as the alkaline and acid additives, respectively, to investigate whether acid and alkaline additives could promote oxidative desulfurization in the UV–H2O2 system. The coal samples were investigated via scanning electron microscopy (SEM), Brannuer–Emmett–Teller analysis (BET), contact angle analysis (CA), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the desulfurization mechanism, including sulfur removal, sulfur conversion, and change of coal surface morphology on the reaction, was investigated. The results demonstrated that the surface morphology and the pore structure in coal improved; the wettability and oxygen-containing functional groups increased after the action of NaOH and OA, which indicated that the oxidation was enhanced during the reaction. This study proved that strong oxidation promoted the efficient removal of sulfur from coal samples, where NaOH reacted strongly with pyrite, and OA influenced the removal of organic sulfur, which played a directional desulfurization effect.

Coal desulfurization by photocatalytic oxidation in the presence of [HO2MMim][HSO4] and H2O2

Photocatalytic oxidation has been widely used in sulfur oxidation due to its mild reaction conditions. In order to improve the efficiency of removing sulfur from coal, especially the organic sulfur, TiO2, SiO2 and modified SiO2 were used as photocatalysts under UV lamp irradiation in the presence of 1-carboxymethyl-3-methylimidazole bisulfite ([HO2MMim][HSO4]) and hydrogen peroxide (H2O2). The results show that the photocatalysts played important roles in coal desulfurization. The desulfurization rate of [HO2MMim][HSO4]–H2O2 (1:10) treatment on coal was only 16.89%, while after adding TiO2, e.g. [HO2MMim][HSO4]–H2O2-TiO2 (1:10:4), it increases to 38.46% and the removing rate of organic sulfur approached 20.17% under normal temperature and pressure on a basis of photocatalysis. According to FTIR and XPS measurements, it is found that the catalytic oxidation can be accelerated in the presence of photocatalysts under ultraviolet irradiation, and the thiophene conversion can be enhanced significantly. Generally, TiO2 is more efficient in organic sulfur removal than SiO2 during photocatalytic oxidation. The results of quantum chemistry calculation indicates that thiophene sulfone could be produced much easier than the thiophene ring-cleaved reaction when thiophene was oxidized in the presence of hydroxyl radicals. In addition, compared to the traditional methods, the photocatalytic desulfurization only show a slight reduction of combustion heat value according to TG-DSC-DDSC measurements.

Synergistic mechanisms of mechanochemical activation on the mild oxidative desulfurization of superfine pulverized coal

Exploiting efficient and low-cost oxidative desulfurization methods is urgently needed for promoting the development of novel desulfurization technologies. In this work, the sulfur speciation in the mechanochemically activated and H2O2 oxidized coals was quantitatively characterized through X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The influences of H2O2 concentration and particle size on the sulfur transformation were discussed. In addition, the synergistic mechanisms of mechanochemical activation and H2O2 oxidation on the removal of organic sulfur were focused. Finally, combined with the sulfur speciation and deconvolution analysis, the main SO2 precursors during the pyrolysis were elucidated. The results indicate that mechanochemical activation can promote the conversion from organic to inorganic sulfur by reducing the strength of C-S bond and accelerating the oxidation of thiophene and sulfide, which is beneficial to remove organic sulfur. On the other hand, the dissolution amount of sulfate in small particles decreases due to the decreased macropore volumes, complicated pore structure, and increased mass transfer resistance. Then, an optimal particle size around 20 μm (i.e., HN_23.9 and NMG_18.7) is observed for the studied coals, where the reduced amplitude of SO2 after the chemical oxidation reaches the maximum. Besides, a dilute oxidant concentration is needed for low-rank coal during the chemical removal of sulfur, which is conducive to reduce the cost. The findings shed light on elucidating the origination of sulfur oxides from a molecular level and further exploiting the new efficient and low-cost desulfurization technologies.