Removal Of CH3SH Research Articles

Enhanced adsorption and regeneration performances for methyl mercaptan capture by a metal–organic framework incorporated in a mesoporous silica

Cu-modified adsorbent is widely used in removing S-containing odor pollutant, such as methyl-mercaptan (CH3SH). Increasing the dispersion of adsorptive sites and improving the regeneration cycle efficiency are two important problems. In this work, a copper metal–organic framework (MOF) was synthesized by in-situ growing the Cu-MOF on SBA-15. Micro-morphology characterizations revealed that the Cu-MOFs grew inside the SBA-15 mesopore channels and showed a good dispersion. When the hybrid (Cu-MOF in SBA-15) and the Cu-MOFs were compared for the CH3SH removal, the hybrid removed 1.70-mol CH3SH per mol of Cu in the adsorbent. This adsorbent capacity was far bigger than Cu-MOFs (0.70 mol·mol−1) and resulted from a better Cu-MOFs dispersion in SBA-15. Additionally, an easy and energy-saving hydrothermal method was put forward for the regeneration of the used adsorbent at 80 °C. The capacity of the regenerated material was higher than 70 % for at least 6 cycles. In addition, the regeneration temperature was far lower than that (> 350 °C) generally utilized in previous reports investigating cycled adsorption of CH3SH. The enhanced regeneration performances were attributed to the confinement effect of the SBA-15, which restrained the ligand around the Cu coordination centers. This work confirms the effective removal of odor-gas using a cost-effective regenerable adsorbent.

Biodegradation of organosulfur with extra carbon source: Insights into biofilm formation and bacterial metabolic processes

Organosulfur compounds are prevalent in wastewater, presenting challenges for biodegradation, particularly in low-carbon environments. Supplementing additional carbon sources not only provides essential nutrients for microbial growth but also serves as regulators, influencing adaptive changes in biofilm and enhancing the survival of microorganisms in organosulfur-induced stress bioreactors. This study aims to elucidate the biodegradation of organosulfur under varying carbon source levels, placing specific emphasis on functional bacteria and metabolic processes. It has been observed that higher levels of carbon supplementation led to significantly improved total sulfur (TS) removal efficiencies, exceeding 83 %, and achieve a high organosulfur CH3SH removal efficiency of ~100 %. However, in the reactor with no external carbon source added, the oxidation end-product SO42− accumulated significantly, surpassing 120 mEq/m2-day. Furthermore, the TB-EPS concentration consistently increasedwith the ascending glucose concentration. The analysis of bacterial community reveals the enrichment of functional bacteria involved in sulfur metabolism and biofilm formation (e.g. Ferruginibacter, Rhodopeudomonas, Gordonia, and Thiobacillus). Correspondingly, the gene expressions related to the pathway of organosulfur to SO42− were notably enhanced (e.g. MTO increased by 27.7 %). In contrast, extra carbon source facilitated the transfer of organosulfur into amino acids in sulfur metabolism and promoted assimilation. These metabolic insights, coupled with kinetic transformation results, further validate distinct sulfur pathways under different carbon source conditions. The intricate interplay between bacteria growth regulation, pollutant biodegradation, and microbial metabolites underscores a complex network relationship that significantly contributes to efficient operation of bioreactors.

Local microenvironment modulation of Pt0/Pt2+ nano-clusters inducing synchronous mass transfer effect to boost catalytic ozonation

Rational catalyst structure design is expected to solve the low O3 utilization and poor molecular mass transfer efficiency in heterogeneous catalytic ozonation (HCO). Herein, Pt/CMK-3 catalyst with confined space to enhance mass transfer was synthesized and employed for CH3SH removal. Unlike fully free diffusion in 0–2.0 wt% Pt/CMK-3 and bulk phase diffusion in 10.0 wt% Pt/CMK-3, removal efficiency of 5.0 wt% Pt/CMK-3 was significantly improved to 97.0%, which was attributed to the effective interfacial diffusion of O3 and CH3SH through local microenvironment modulation of Pt0/Pt2+ nanoclusters (NCs) inducing synchronous mass transfer. Experimental and DFT calculations confirmed the strong electronic interactions between O3 and Pt0 facilitated charge redistribution and preferential O3 activation. AIMD simulation demonstrated that the synchronous difference in mean-square displacements (MSD) and diffusion coefficient (Dc) of CH3SH (Dc=0.022) and O3 (Dc=0.0046) in the confined Pt/CMK-3 system could facilitate CH3SH migrate to Pt2+ through interfacial diffusion. Especially, the d-orbital electrons of Pt NCs interact sequentially with p-orbital electrons of CH3SH and O3 to maintain redox of Pt0/Pt2+. This study provides novel insights on effective mass transfer and kinetic properties of gaseous reaction between oxidant and pollutant by constructing unique interfacial diffusion behaviors.

Structural/surface characterization of transition metal element-doped H-ZSM-5 adsorbent for CH3SH removal: identification of active adsorption sites and deactivation mechanism.

CH3SH is a potential hazard to both chemical production and human health, so controlling its emissions is an urgent priority. In this work, a series of transition metal-loaded H-ZSM-5 adsorbents (Si/Al = 25) (Cu, Fe, Co, Ni, Mn, and Zn) were synthesized through the wet impregnation method and tested for CH3SH physicochemical adsorption at 60°C. It was shown that the Cu-modified H-ZSM-5 adsorbent was much more active for CH3SH removal due to its abundant strong acid sites than other transition metal-modified H-ZSM-5 adsorbents. The detailed physicochemical properties of various modified H-ZSM-5 adsorbents were characterized by SEM, XRD, N2 physisorption, XPS, H2-TPR, and NH3-TPD. The effects of metal loading mass ratio, calcination temperature, and acid or alkali modification on the performance of the adsorbent were also investigated, and finally 20% Cu/ZSM-5 was found to have the best adsorption capacity after calcined at 350°C. Additionally, the Cu/ZSM-5 adsorbent modified by sodium bicarbonate could expose more active components, which improved the adsorbent's stability. However, the consumption and reduction of the active component Cu2+ and the accumulation of sulfate during the adsorption process are the main reasons for the deactivation of the adsorbent. In addition, the simultaneous purging of N2 + O2 can effectively restore the adsorption capacity of the deactivated adsorbent and can be used as a potential strategy to regenerate the adsorbent.

Cation Substitution Induced d‐Band Center Modulation on Cobalt‐Based Spinel Oxides for Catalytic Ozonation

AbstractCo3O4 spinel is a promising transition metal oxide (TMO) catalyst for the catalytic ozonation of volatile organic compounds (VOCs). Herein, metal–organic frameworks (MOFs)‐derived Ni‐ and Mg‐ substituted Co3O4 catalysts retain similar spinel structures, but display improved and reduced ozonation performance of methyl mercaptan (CH3SH), respectively. Remarkably, the NiCo2O4 catalyst can still ≈90% removal of CH3SH after running for 20 h at room temperature under an initial concentration of 50 ppm CH3SH and 40 ppm O3, relative humidity of 60%, and space velocity of 300 000 mL h−1 g−1, exceeding the reported values. Experimental characterizations have unveiled that the substitution of Ni and Mg into the Co3O4 spinel altered surface acidity, oxygen species mobility, and Co2+/Co3+ ratio. The in situ Raman spectra reveal the dynamic formation Co(III)‐Oad* via the transformation of O3 into surface atomic oxygen (Oad*) and peroxide species (O2*). Theoretical calculations verify that Ni‐substitution increases nonuniform charges and Fermi density, leading to a moderate increase in d‐band center energy levels, thereby promoting O3 specific adsorption/activation to convert Oad*/O2* and •OH/1O2/•O2−, which contributes to eliminate CH3SH and prevent poisoning. The concept of tuning the d‐band center can provide valuable insights for the design of other catalysts for catalytic ozonation.

Construction of 2D/2D g-C3N4/Bi2WO6 heterostructure nanosheets for efficient visible-light-driven photocatalytic elimination of sulfur-containing VOCs

A simple hydrothermal method was applied to synthesize a 2D/2D g-C3N4/Bi2WO6 (CN/BWO) composite photocatalyst for the photocatalytic removal of gaseous methyl mercaptan (CH3SH). The layered structure of CN/BWO and the C-O-Bi bonds at the interlayer interface were confirmed by thorough characterization techniques. The C-O-Bi bonds were demonstrated to reduce interlayer charge transfer resistance and inhibit photogenerated electron/hole pairs recombination. Therefore, 0.1-CN/BWO exhibited the highest photocatalytic efficiency for CH3SH removal, which was 1.4 times higher than 0.1-CN/BWONF with nanoflower structure, and 5.1 and 1.9 times higher than that of pure g-C3N4 and Bi2WO6. The photocatalytic oxidation pathway and mechanism for CH3SH removal were revealed based on reactive species trapping, electron spin resonance (ESR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) tests. This work provides new insights into the design of photocatalysts with high photocatalytic performance and stability for the removal of volatile organic compounds (VOCs).

Odour impact assessment using kinetics and optimization: case studies on removal of multiple volatile organo-sulphur compounds from sewage wastewater using porous functional materials.

Expanding industries and booming population have led to the increase in the installation of wastewater and sewer systems, even in close proximity to residential areas. Emissions from these installations particularly volatile organo-sulphur compounds (VOSCs) such as methyl mercaptan (CH3SH), ethyl mercaptan (C2H5SH), dimethyl sulphide (CH3SCH3) and carbon disulphide (CS2) are a nuisance to people even when present in small concentration. Strategies for removal involve addition of chemicals or other chemical processes which are generally expensive. Biofilters, on the other hand, consume large amount of energy and wash waters. Hence keeping commercialization in mind, it is important to develop a strategy which would be cost-effective and at the same time be effective to remove most of the odorous compounds present in these systems. In the present research work, granular activated carbons (GAC) are functionalized with alkali solution to improve the adsorption capacity. Liquid phase batch adsorption is performed with GAC and various functionalized activated carbons (FACs) with the help of raw sewage water from a local sewage water treatment plant. Concentration of odour was evaluated by two methods-olfactometry-based analysis for sensory measurement and GCMS-based analysis for analytical estimation of a specific odorous compound. The adsorption capacities of the functionalized GACs are higher primarily because of complex formation at the surface of modified GACs. Pseudo-second-order kinetic model agreed well with experimental results with the rate constant being 0.0191mg/l min and 0.0153mg/l min for methyl and ethyl mercaptan adsorption onto FAC-NH3. Boyd's film diffusion along with rate kinetic model supported that chemical adsorption forms the rate-limiting step. Response surface methodology (RSM) was used to optimize the removal of VOSCs with respect to different process parameters like adsorbent amount and time. The olfactometry removal of overall odour was also optimized taking 6 factors in the Box Behnken design. Variance of analysis results indicated that all the models displayed considerable goodness of fit with R2 values close to 1. Methyl mercaptan turned out to be the highest contributor to the overall odour as confirmed both from experimental and optimization study. The optimized olfactometry odour removal (77.4%) along with CH3SH removal (80.34%), C2H5SH removal (59.16%), CH3SCH3 removal (63.21%) and CS2 removal (71.95%) was found at optimum process conditions, with amount of adsorbent of 10.29g, adsorption time of 2.92h. This result indicates that methyl mercaptan (CH3SH) is the highest odour contributing component out of the studied VOSCs. The results show promising potential for the use of activated carbon as an adsorbent for removal of odorous compounds from STPs.

Electron Transfer Trade-offs in MOF-Derived Cobalt-Embedded Nitrogen-Doped Carbon Nanotubes Boost Catalytic Ozonation for Gaseous Sulfur-Containing VOC Elimination

High-performance and robust catalysts act as core drivers for catalytic ozonation to eliminate gaseous sulfur-containing volatile organic compounds (VOCs). Herein, nitrogen-doped carbon nanotubes embedded with Co species (Co@NCNT) are synthesized by thermolysis of a ZIF-67/melamine mixture. The carbon-confinement effects in Co@NCNT not only improve the stability of Co species but also regulate the electronic structure of Co─C bonds, consequently synergistically improving the catalytic ozonation performance. The experimental results indicate that the Co@NCNT catalyst could still remove ∼86% of odorous methyl mercaptan (CH3SH) after running for 60 h at 25 °C under an initial concentration of 50 ppm CH3SH and 40 ppm ozone, relative humidity of 60%, and space velocity of 600,000 mL h–1 g–1, outdistancing reported values under comparable reaction conditions. Detailed characterization and theoretical simulations reveal that the electronic metal–support interaction of Co─C bonds in Co@NCNT significantly adjusts the electronic structure of Co species, thereby promoting ozone-specific adsorption/activation to convert the surface atomic oxygen (*Oad) and ·OH/1O2/·O2–. Also, the electrons obtained from CH3SH in the electron-poor center transferred through the C─Co bond bridge to maintain the redox cycle of ≡Co0/2+ → ≡Co3+ → ≡Co0/2+ and realize the efficient and stable removal of CH3SH into CO2/SO42–/H2O. This work demonstrates that MOF-derived materials with tunable electronic structures achieve the stable removal efficiency for gaseous sulfur-containing VOCs via electron transfer trade-offs and provide potential candidate catalysts for the application of air purification.

Insights into the different catalytic behavior between Ce and Cr modified MCM-41 catalysts: Cr2S3 as new active species for CH3SH decomposition

High sulfur resistance and high stability of catalysts are crucial for the catalytic decomposition of sulfur-containing volatile organic compounds. In this work, compared to 5Ce-MCM-41, the 5Cr-MCM-41 catalyst exhibited ultra-stability (no activity loss at 600 h) and higher sulfur resistance. The physical structure and chemical characteristics of the catalysts were analyzed by XRD, H2-TPR, NH3-TPD, CO2-TPD, XPS, and TEM. Combining the characterization results, we found that the 5Cr-MCM-41 catalyst presented outstanding catalytic performance due to superior reducibility and appropriate acidity, which results in the conversion of most of the C and S elements in the CH3SH to the gas-phase coke- and sulfur-containing products rather than accumulating on the catalyst surface. Meanwhile, the catalytic performance, reaction path, and deactivation mechanism of rare earth metal (Ce) and transition metal (Cr) modified MCM-41 catalysts were systematically investigated by in situ DRIFTS and DFT calculations. Additionally, a new active phase (sulfide state Cr2S3) was proposed and proved via accurately designed experiments, which plays a significant role in the collaborative removal of CH3SH with hexavalent chromium (Cr(VI)). These findings are beneficial for designing high sulfur resistance catalysts for the removal of CH3SH and other sulfur-containing products.

Enhanced Catalytic Ozonation for Eliminating CH3SH via Graphene-Supported Positively Charged Atomic Pt Undergoing Pt2+/Pt4+ Redox Cycle.

Constructing catalysts with electronic metal-support interaction (EMSI) is promising for catalytic reactions. Herein, graphene-supported positively charged (Pt2+/Pt4+) atomically dispersed Pt catalysts (AD-Pt-G) with PtxC3 (x = 1, 2, and 4)-based EMSI coordination structures are achieved for boosting the catalytic ozonation for odorous CH3SH removal. A CH3SH removal efficiency of 91.5% can be obtained during catalytic ozonation using optimum 0.5AD-Pt-G within 12 h under a gas hourly space velocity of 60,000 mL h-1 g-1, whereas that of pure graphene is 40.4%. Proton transfer reaction time-of-flight mass spectrometry, in situ diffuse reflectance infrared Fourier transform spectroscopy/Raman, and electron spin resonance verify that the PtxC3 coordination structure with atomic Pt2+ sites on AD-Pt-G can activate O2 to generate peroxide species (*O2) for partial oxidation of CH3SH during the adsorption period and trigger O3 into surface atomic oxygen (*Oad), *O2, and superoxide radicals (·O2-) to accomplish a stable, high-efficiency, and deeper oxidation of CH3SH during the catalytic ozonation stage. Moreover, the results of XPS and DFT calculation imply the occurrence of Pt2+ → Pt4+ → Pt2+ recirculation on PtxC3 for AD-Pt-G to maintain the continuous catalytic ozonation for 12 h, i.e., Pt2+ species devote electrons in 5d-orbitals to activate O3, while Pt4+ species can be reduced back to Pt2+ via capturing electrons from CH3SH. This study can provide novel insights into the development of atomically dispersed Pt catalysts with a strong EMSI effect to realize excellent catalytic ozonation for air purification.

The role of H2O in the removal of methane mercaptan (CH3SH) on Cu/C-PAN catalyst

Methane mercaptan (CH3SH) is a common organic sulfur in smelting flue gas, which has significant harm to the environment, industrial production and human health. Therefore, research on the purification of CH3SH has received extensive attention. Herein, we focused on the role of H2O in the removal of CH3SH, and revealed that H2O promotes the adsorption of CH3SH at low temperature and promotes its hydrolysis at high temperature, which significantly improves the removal of CH3SH. In this study, the polyacrylonitrile-based activated carbon fiber was prepared by electrospinning, with the diameter of about 300~400 nm. Cu, Fe and Mn were loaded by impregnation method, and the CH3SH removal efficiency were compared. The combination of characterization results by HR-TEM, XRD, XPS, NH3-TPD and activity evaluation as well as DFT calculation results finally revealed the removal mechanism of CH3SH with the participation of H2O.

Promoted adsorption of methyl mercaptan by γ-Al2O3 catalyst loaded with Cu/Mn

This paper describes the effect of loaded metal(including Fe, Cu, Mn, and Co) on catalytic performance of γ-Al2O3 catalysts for the removal of CH3SH. The catalysts are synthesized by the method of impregnation, and used in room temperature to absorb CH3SH. The experiment investigated the effect of components, loading and calcination temperature for the catalytic activity. The results showed that metal-modified γ-Al2O3 can enhance removal effect of CH3SH. CH3SH removal capacity of various metal-reforming catalysts decline as follows: Cu–Mn/γ-Al2O3> Cu–Co/γ-Al2O3≈ Cu/γ-Al2O3> Cu–Fe/γ-Al2O3> Co/γ-Al2O3> Mn/γ-Al2O3> Fe/γ-Al2O3. Among these samples the γ-Al2O3 catalyst loaded with 15% Cu and 5% Mn has the best removal rate and stability, which could reach a 100% removal rate of CH3SH in about 85 min. The catalysts were characterized by XRD, N2-adsorption/desorption techniques, CO2-TPD and FT-IR. It indicated that CuO was the mainly active ingredient on γ-Al2O3 carrier. Meanwhile, as the second elements, MnOx was in favor of diffusion of CuO on the carrier and improved activity of catalyst.

Kinetics and removal formula of methyl mercaptan by ethanol absorption without neglecting solute accumulation

The wet scrubbing process is commonly adopted for organic odor treatment. In this study, methyl mercaptan (CH3SH) was selected as a representative hydrophobic organic odorant which was treated using an ethanol solution in a scrubbing tower. Results showed that the ethanol solution can retain the ideal CH3SH removal effect for 2.0 h. The following experimental conditions were set: intake load of 4,700 m3 m−2 h−1, spraying load of 5,100 L m−2 h−1, and volume ratio of ethanol/water at 1:5. The solute accumulation of CH3SH in the scrubbing liquid exceeded 3.01 × 10−4 kmol CH3SH/kmol ethanol when the scrubbing tower operated for more than 2.0 h. The mathematical formula which neglected solute accumulation in the ethanol solution exhibited poor adaptability to the removal effect of CH3SH by ethanol absorption. The CH3SH removal effect of solute accumulation in the ethanol solution was explored in long-term operation. Meanwhile, the CH3SH removal rate formula which considered solute accumulation in the ethanol solution could be calculated as η = a′-b′X2/Y1. The kinetic parameters of the formula fitting results were phase equilibrium constant m 0.0076, and overall mass transfer coefficient KY 4.98 kmol m−2 h−1 in the scrubbing tower. These findings can serve as a reference for engineering design and operation for the removal of CH3SH by ethanol absorption.

Enhanced Performance and Conversion Pathway for Catalytic Ozonation of Methyl Mercaptan on Single-Atom Ag Deposited Three-Dimensional Ordered Mesoporous MnO2.

In this study, Ag deposited three-dimensional MnO2 porous hollow microspheres (Ag/MnO2 PHMSs) with high dispersion of the atom level Ag species are first prepared by a novel method of redox precipitation. Due to the highly efficient utilization of downsized Ag nanoparticles, the optimal 0.3% Ag/MnO2 PHMSs can completely degrade 70 ppm CH3SH within 600 s, much higher than that of MnO2 PHMSs (79%). Additionally, the catalyst retains long-term stability and can be regenerated to its initial activity through regeneration with ethanol and HCl. The results of characterization of Ag/MnO2 PHMSs and catalytic performance tests clearly demonstrate that the proper amount of Ag incorporation not only facilitates the chemi-adsorption but also induces more formation of vacancy oxygen (Ov) and lattice oxygen (OL) in MnO2 as well as Ag species as activation sites to collectively favor the catalytic ozonation of CH3SH. Ag/MnO2 PHMSs can efficiently transform CH3SH into CH3SAg/CH3S-SCH3 and then oxidize them into SO42- and CO2 as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy. Meanwhile, electron paramagnetic resonance and scavenger tests indicate that •OH and 1O2 are the primary reactive species rather than surface atomic oxygen species contributing to CH3SH removal over Ag/MnO2 PHMSs. This work presents an efficient catalyst of single atom Ag incorporated MnO2 PHMSs to control air pollution.

Activation of persulfate by CuO-sludge-derived carbon dispersed on silicon carbide foams for odorous methyl mercaptan elimination: identification of reactive oxygen species.

In this work, sludge-derived carbon (SC) was innovatively integrated with copper oxide (CuO) on macroporous silicon carbide foams to construct a distinctive catalyst (CuO/SC) with strong catalytic activity, which can effectively activate persulfate (PS) for the removal of methyl mercaptan (CH3SH). The structure and morphology of CuO/SC were investigated by means of XRD, SEM, and EDS. The effects of initial pH values, copper contents, PS dosages, and flow rates on CH3SH removal were also investigated. Under optimal condition, more than 90% of CH3SH was removed by CuO/SC-PS combined system within 10-min reaction due to the synergistic function of CuO and SC. More importantly, on the basis of reactive species trapping and ESR spectroscopy, it is revealed that the responsible reactive species for catalytic CH3SH composition were ·SO4-, ·OH, 1O2, and ·O2- in CuO/SC-PS system. Finally, the possible PS activation scheme of CuO/SC samples was proposed.

Highly Efficient Performance and Conversion Pathway of Photocatalytic CH3SH Oxidation on Self-Stabilized Indirect Z-Scheme g-C3N4/I3--BiOI.

A self-stabilized Z-scheme porous g-C3N4/I3--containing BiOI ultrathin nanosheets (g-C3N4/I3--BiOI) heterojunction photocatalyst with I3-/I- redox mediator was successfully synthesized by a facile solvothermal method coupling with light illumination. The structure and optical properties of g-C3N4/I3--BiOI composites were systematically characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, X-ray photoelectron spectroscopy, N2 adsorption/desorption, UV-vis diffuse reflectance spectrum, and photoluminescence. The g-C3N4/I3--BiOI composites, with a heterojunction between porous g-C3N4 and BiOI ultrathin nanosheets, were first applied for the photocatalytic elimination of ppm-leveled CH3SH under light-emitting diode visible light illumination. The g-C3N4/I3--BiOI heterojunction with 10% g-C3N4 showed a dramatically enhanced photocatalytic activity in the removal of CH3SH compared with pure BiOI and g-C3N4 due to its effective interfacial charge transfer and separation. The adsorption and photocatalytic oxidation of CH3SH over g-C3N4/I3--BiOI were deeply explored by in situ diffuse reflectance infrared Fourier transform spectroscopy, and the intermediates and conversion pathways were elucidated and compared. Furthermore, on the basis of reactive species trapping, electron spin resonance and Mott-Schottky experiments, it was revealed that the responsible reactive species for catalytic CH3SH composition were h+, •O2-, and 1O2; thus, the g-C3N4/I3--BiOI heterojunction followed an indirect all-solid state Z-scheme charge-transfer mode with self-stabilized I3-/I- pairs as redox mediator, which could accelerate the separation of photogenerated charge and enhance the redox reaction power of charged carriers simultaneously.

Deep Removal of Methyl Mercaptan in Biogas

For a distributed PEMFC power station utilizing biogas as a source to produce hydrogen, deep desulfurization of the biogas is important. ZnO/γ-Al2O3 and CuO/γ-Al2O3 were prepared by an impregnation method, and their performances on CH3SH removal in the biogas have been studied. Results showed that CuO/γ-Al2O3 is able to remove CH3SH to below 10 ppb at 250-400 °C and has a sulfur capacity of 0.056 mmol g-1 at 300 °C. Regarding to the desulfurization mechanism, it has been confirmed that the removal of CH3SH with CuO/γ-Al2O3 is based on chemical adsorption. In the desulfurization, CH4s dry reforming took place at above 250 °C, and the generated H2 and CO reduced CuO to Cu2O and Cu. Further, it was supposed that H2S generates through the hydrogenation of CH3SH at the presence of H2.

Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters

Hydrogen sulfide (H2S) and methylmercaptan (CH3SH) are the most common sulfur compounds found in biogas. The simultaneous removal of H2S and CH3SH was tested at neutral pH in two biotrickling filters, one operated under aerobic conditions and the other one under anoxic conditions. Both reactors were run for several months treating a H2S concentration of around 2000ppmv. Then, the effect of CH3SH loading rate (LR) on H2S and CH3SH removal was investigated in both reactors maintaining a constant H2S LR of 53–63gS-H2Sm−3h−1, depending on the reactor. Initially, CH3SH concentration was stepwise increased from 0 to 75–90ppmv. Maximum elimination capacities (ECs) of around 1.8gS-CH3SHm−3h−1 were found. After that, the CH3SH LR was increased by testing different empty bed residence times (EBRTs) between 180 and 30s. Significantly lower ECs were found at short EBRTs, indicating that the systems were mostly mass transfer limited. Finally, EBRT was stepwise reduced from 180 to 30s at variable CH3SH and H2S loads. Maximum H2S ECs found for both reactors were between 100 and 140gS-H2Sm−3h−1. A negative influence was found in the ECs of CH3SH by the presence of high H2S LR in both biotrickling filters. However, sulfur mass balances in both reactors and batch tests under aerobic and anoxic conditions showed that CH3SH chemically reacts with elemental sulfur at neutral pH, enhancing the overall reactors performance by reducing the impact of sulfur accumulation. Also, both reactors were able to treat CH3SH without prior inoculation because of the already existing sulfide-oxidizing microorganisms grown in the reactors during H2S treatment. Co-treatment of H2S and CH3SH under aerobic and anoxic conditions was considered as a feasible operation for concentrations commonly found in biogas (2000ppmv of H2S and below 20ppmv of CH3SH).

Water absorption and photocatalytic activity of TiO2 in a scrubber system for odor control at varying pH

The water absorption and photocatalytic activity of TiO2 in a novel scrubber system for odor control using CH3SH gas as target compound was investigated. It was found that the amount of absorbed CH3SH in water increased with increasing initial pH of water, especially in basic water, which was approximately four times than those in acid and neutral water. Adding TiO2 into water had little influence on the dissolved property of CH3SH in water with different pH. TiO2 exhibited excellent photocatalytic activity in the scrubber system for CH3SH removal and reaction solution with high pH facilitated the photocatalytic degradation of CH3SH. In basic TiO2 suspensions, 96.3% of dissolved CH3SH was degraded and the pseudo-first-order kinetic constant was roughly 1.5 and 2.7 times of those obtained in neutral and acid TiO2 suspensions, respectively. Role of TiO2 on CH3SH degradation in water was also discussed. Furthermore, the outlet concentrations of CH3SH all decreased to nearly zero after 60min of UV light irradiation in TiO2 suspensions with different pH. Varieties in the pH of water and TiO2 suspended solution after absorption and degradation process were measured. The absorption capacity of basic water with addition of TiO2 was relatively stable and TiO2 kept high photocatalytic activity for a long time (900min). This study provided helpful information on expanding the photocatalytic scrubber system for practical odor treatment.

Oxidation of CH3SH by in situ generation of ferrate(VI) in aqueous alkaline solution for odour treatment

This study demonstrated a new approach of odorous gas treatment in a wet scrubbing-oxidation system with in situ generation of ferrate(VI), in which gaseous CH3SH can be quickly absorbed by aqueous alkaline solution and rapidly oxidized by liquid ferrate(VI) generated through electrochemical synthesis in situ. In this study, the electrochemical generation of ferrate(VI) in aqueous NaOH solution was studied and the experiments demonstrated that a maximum current efficiency to generate ferrate(VI) occurred at 14M NaOH concentration, while an applied current density of 14.06mAcm−2 was applied. Then the self-decomposition of ferrate(VI) in such strong alkaline solutions was studied, and the results showed that ferrate(VI) behaved more stable in the stronger alkaline solution. Furthermore, the reactivity of ferrate(VI) with CH3SH in this highly-concentrated NaOH solution was investigated under different reaction conditions as the first time. The experimental results confirmed that CH3SH can be fully oxidized by ferrate(VI) to sulphate ion as a final product. The second-order reaction model is suitable to describe the kinetics of CH3SH reaction with ferrate(VI) in the strong alkaline solution. Meanwhile, stoichiometry of ferrate(VI) reaction with CH3SH in aqueous solution was determined with a minimum molar ratio of 2.20:1 (Fe(VI):CH3SH) to destruct CH3SH effectively and a higher molar ratio of 4.53:1 to convert CH3SH to sulphate ion completely. The experiments also demonstrated that the NaOH concentration in aqueous solution would be a key parameter and the best performance of CH3SH removal was achieved at the optimum NaOH concentration of 6M under our experimental conditions due to an optimum balance between the oxidation potential of ferrate(VI) and its generation rate in this wet scrubbing-oxidation system.