Conversion Of SO2 Research Articles

Observation of chemical components of PM2.5 and secondary inorganic aerosol formation during haze and sandy haze days in Zhengzhou, China

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China. During this study, a haze episode (haze days) and a typical haze process mixed with sandstorm (sandy haze days) were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018. Concentrations of PM10 and crustal elements clearly increased in the sandy haze days. Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days. The sulfate concentrations, the sulfate fractions in PM2.5, and the sulfur oxidation ratios significantly increased in the sandy haze days. Heterogeneous reactions dominated the conversion of SO2 during the haze and sandy haze days. Enhanced SO2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity (RH) were in 30%–70%, and high O3 at certain time points. Gas-phase NO2 oxidation reactions were the main pathways for nitrate formation. In the sandy haze days, higher nitrogen oxidation ratio (NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate; higher NOR values at night may be attributed to the higher O3 concentrations, which promoted the formation of N2O5.

Uptake and surface chemistry of SO2 on natural volcanic dusts

V-dust (v-dust) is a highly variable source of natural particles in the atmosphere, and during the period of high volcanic activity it can provide a large surface for heterogeneous interactions with other atmospheric compounds. Icelandic v-dust was chosen as a case study due to frequency of volcanic eruptions and high aeolian activity in the area. In this study, we focus on the kinetics and mechanism of the reaction of sulfur dioxide (SO2) with natural v-dust samples under atmospheric conditions using coated wall flow tube reactor and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Steady state uptake coefficients determined are in the range of 10−9 to 10−8 depending on the considered v-dust. Concomitantly with SO2 uptake, both sulfites and sulfates are monitored on the surface of v-dust, with sulfates being the final oxidation product, attesting of SO2 surface reaction. Surface hydroxyl groups play a crucial role in the conversion of SO2 to sulfites as evidenced from both flow tube and DRIFTS experiments. Based on these experimental results, a mechanism for SO2 interaction with different surface sites of v-dust is proposed and discussed. This study provides original insights in the kinetics of SO2 uptake under simulated atmospheric conditions and its mechanism and transformation on volcanic material. To that regards, it brings an accurate perspective on SO2 heterogeneous sinks in the atmosphere.

Computational Fluid Dynamics Modeling of a Direct Solar Driven Sulfuric Acid Decomposition Reactor

A hydrogen economy requires primary sources to provide the power required to produce hydrogen from water, fossil fuels, biomass or similar compounds. Water-splitting processes are particularly attractive, since water is abundant around the planet, the unique products from water splitting are hydrogen and oxygen and a variety of primary energy sources can be used to produce the hydrogen. External electric power can be used to produce hydrogen by conventional water electrolysis [1], but it firstly requires the production of electricity to realize the electrochemical splitting of the water molecule. A more efficient and more cost-effective approach is to use thermal power to drive a thermochemical water splitting process. Such cycles break the hydrogen-oxygen bounds through a series of heat-driven chemical reactions, with recirculation of intermediate substances of different type. By this approach the external heat which drives the chemical reactions is converted into chemical energy of the hydrogen produced from water splitting. Among the various water splitting processes, the sulfur-based cycles and in particular the thermo-electrochemical Hybrid Sulfur (HyS) is one of the most appealing cycles. This process has only fluid reactants and is comprised of only two global reaction steps: a low temperature electrochemical exothermic section, operating at temperatures on the order of 100 °C, and a high temperature thermal section operating at max temperatures of about 800 °C. In the electrochemical section SO2 and H2O are combined together to produce electrochemically H2 at the electrolyzer cathode and H2SO4 at the electrolyzer anode. Sulfuric acid is recycled inside the plant, concentrated and decomposed, in the high temperature thermal section, into SO2, O2 and H2O. Oxygen is then separated from SO2 and water and extracted as byproduct of the process. Solar driven HyS process is being studied by the Greenway Energy and the University of South Carolina within the DOE HydroGEN program (part of the DOE Energy Material Network initiative) [2], partnering with the Idaho National Laboratory, the Savannah River National Laboratory and the National Renewable Energy Laboratory. The project focuses on the high temperature sulfuric acid thermal decomposition section, developing new optimized catalyst formulations (i.e. achieving higher activity, lower performance degradation and lower costs), to be integrated in novel solar reactor systems. A new bimetallic catalyst formulation has been developed and synthesized, based on novel composition and support. Compared with the current state of the art sulfuric acid decomposition catalysts, developed by Idaho National Laboratory during the DOE Nuclear Hydrogen Initiative [3], the proposed catalyst shows the potential for higher SO3 conversion yields and very limited sintering effects. Test results, under sulfuric acid environment and operating temperatures on the order of 800 °C, will be shown and discussed. The new catalyst will be placed in a novel solar reactor, being developed within the HydroGEN project. The proposed concept is based on a solar cavity receiver system, realizing the sulfuric acid decomposition and internal heat recovery in a single unit, directly heated by the incident solar radiation. This system, along with the actual H2SO4 decomposition into SO2, allows: (1) efficient internal heat recovery from the decomposition products and (2) connections with the metallic interfaced HyS equipment (e.g. tubing, valves etc) at low temperatures. A novel reactive computational fluid dynamic (CFD) model is presented, integrating mass, energy and momentum balance equations. A new kinetics expression has also been developed to model the behavior of the novel catalytic formulation. The model has been developed for both the high temperature catalytic decomposition process and for the vaporization/condensation of the sulfur mixture process. A novel two-phase model has been developed with the properties of the mixtures (SO2, SO3, H2O, H2SO4, O2) extracted from process models and integrated in the CFD code using numerical modeling approximations. Results are presented and discussed.

Temporal evolution of submicron particles during extreme fireworks.

Evolution of submicron particles in terms of particle number concentration and mobility-equivalent diameter was measured during Diwali festival-specific intensive pyrotechnic displays in Varanasi over central Indo-Gangetic Plain (IGP). A scanning mobility particle sizer coupled with an optical particle sizer was used to fit in an overlapping size range, and particle number concentration was analyzed to have an insight into the new particle formation and subsequent evolution of particles from nucleation to accumulation mode. Further, variation in black carbon (BC) concentration and aerosol ionic composition was measured simultaneously. Frequent fluctuation in particle number concentration in and around Diwali festival was evidenced, primarily influenced by local emission sources and meteorology, with three distinct peaks in number concentrations (dN/dlogDp, 3.1-4.5 × 104 cm3) coinciding well with peak firework emission period (18:00-23:00 h). Submicron particle size distribution revealed a single peak covering a size range of 80-130 nm, and for all instances, number concentration maximum coincided with geometric mean minimum, indicating the emission primarily in the ultrafine range (< 0.1 μm). Interestingly, during peak firework emissions, besides rise in accumulation mode, an event of new particle formation was identified with increase in nucleation and small Aitken mode, before being dispersed to background aerosols. On an integral scale, a clear distinction was noted between a normal and an episodic event, with a definite shift in the formationof ultrafine particles compared with the accumulation mode. The BC diurnal profile was typical, with a prominent nocturnal peak (12.0 ± 3.9 μg m-3) corresponding to a decrease in the boundary layer height. A slight variation in maximum BC concentration(16.8 μg m-3) was noted in the night of the event coinciding well with firework emissions. An increase in some specific ionic species was also noted in combination with an increase in the overall cation to anion ratio, which was explained in terms of heterogeneous transformation of NOx and catalytic conversion of SO2. Graphical abstract Time-resolved evolution of particle size distribution during normal and episodic events.

Degradation of diclofenac by Fe(II)-activated bisulfite: Kinetics, mechanism and transformation products

As an emerging pollutant, Diclofenac (DCF) has potential threats to ecosystem and human health, and it can hardly be removed by conventional wastewater treatment processes. In this study, Fe(II)-activated bisulfite (BS), an advanced oxidation process, was used for rapid removal of DCF. The effect of initial pH, Fe(II) dosage, BS concentration, dissolved oxygen and reaction temperature on DCF removal and its degradation mechanism were investigated. Compared to Fe(II)/persulfate system, the removal efficiency of DCF was higher by Fe(II)/BS, and its degradation followed pseudo-first order kinetic model. Due to the morphology of Fe(II) and BS, the optimal pH for DCF degradation was 4.0. The increased initial Fe(II) or BS concentration promoted DCF degradation while excess Fe(II) or BS caused an inhibition effect as a SO4− scavenger. Dissolved oxygen was an essential factor inducing the conversion of SO3− to SO4−, while it had no effect on DCF removal in the range of 4.6–8.3 mg L−1. The activation energy of this reaction was calculated to be 120.75 ± 3.43 kJ mol−1 based on the improved DCF degradation with increasing temperature. According to the radical scavenging experiments, the contribution of SO4−, HO and the other reactive species to DCF degradation in Fe(II)/BS system were 71.1%, 24.6% and 4.3%, respectively. Nine transformation products were detected using UPLC-Q-TOF-MS. The potential degradation mechanism of DCF was thus proposed showing five reaction pathways including hydroxylation, decarboxylation, dehydration, dechlorination and formylation.

Three-dimensional electrochemical Bunsen reaction characteristics in the sulfur–iodine water splitting cycle for hydrogen production

Hydrogen production from the sulfur–iodine water splitting cycle integrated with solar or nuclear energy has been proposed as a promising technique. Bunsen reaction is one of the three main steps in the cycle and electrochemical method has been applied to this reaction. In present work, a three-dimensional numerical study of the electrochemical Bunsen reaction was conducted. A three-dimensional, steady state, laminar and isothermal mathematical model of electrolytic cell was developed and verified by experiments. The spatial maldistribution of species concentration was found between electrodes and proton exchange membrane (PEM). The electric power drives most H2SO4 and I2 to the anode and cathode surface, respectively, while the proton attraction contributes to HI enrichment on the surface of PEM. At the high inlet H2SO4 concentration of 50 wt%, the transformation of flow channel from single serpentine to single entry & double serpentine with the same inlet flow rate cannot solve the insufficient problem of SO2. But the increase of the overall inlet flow rate in the double entry & double serpentine flow channel make SO2 sufficient for anode reaction. Further decreasing the inlet H2SO4 concentration to 40 wt% and 30 wt% make the initial SO2 sufficient for overall reactions. The single serpentine channel gives the highest SO2 conversion rate, followed by the single entry & double serpentine and double entry & double serpentine flow channels. The single serpentine flow channel at the H2SO4 inlet concentration of 40 wt% is found optimal for achieving a high electrochemical Bunsen reaction performance.

Satellite-Derived Correlation of SO2, NO2, and Aerosol Optical Depth with Meteorological Conditions over East Asia from 2005 to 2015

Intense economic and industrial development in China has been accompanied by severe local air pollution, as well as in other downwind countries in East Asia. This study analyzes satellite observational data of sulfur dioxide (SO2), nitrogen dioxide (NO2), and aerosol optical depth (AOD) to explore the spatial distribution, long-term temporal variation, and correlation to meteorological conditions over this region over the period 2005–2015. SO2 and NO2 data are retrieved from the ozone monitoring instrument (OMI) onboard the National Aeronautics and Space Administration (NASA) Aura satellite, while AOD data are from the moderate-resolution imaging spectroradiometer (MODIS) onboard the NASA Aqua satellite. Spatial distributions of SO2, NO2, and AOD show the highest levels in the North China Plain (NCP), with hotspots also in Southeastern China (SC) and the Sichuan Basin (SB). Biomass burning also contributes to a high level of AOD in Southeast Asia in spring and in Equatorial Asia in fall. Considering the correlation of pollutant levels to meteorological conditions, monitoring data show that higher temperature and higher relative humidity (RH) favor the conversion of SO2 and NO2 to sulfate and nitrate aerosol, respectively. The impact of stronger lower tropospheric stability facilitates the accumulation of SO2 and NO2 in NCP and SC. Transport of SO2 and NO2 from intense source regions to relatively clean regions is highly influential over East Asia; such transport from the NCP leads to a considerable increase of pollutants in SC, SB, Taiwan Island (TW), and Taiwan Strait (TWS), particularly in winter. Aerosols generated by biomass burning in Southeast Asia and anthropogenic aerosol in SC are transported to TW and TWS and lead to the increase of AOD, with the highest levels of AOD in SC, TW, and TWS occurring in spring. Precipitation results in the removal of pollutants, especially in highly polluted regions, the effect of which is most significant in winter and spring.

Phosphogypsum pyrolysis with mineralization agent under weak reducing atmosphere

Batch experiments of phosphogypsum (PG) pyrolysis were carried out under weak reducing atmosphere, adding coke as reductant and CaF2 as mineralization agent. As 3 wt% CaF2 was added to the mixture, the optimal parameters of PG decomposition were mole ratio (C: CaSO4) 0.7, reaction temperature 950 °C, pyrolysis time 60 min, and 1.9-2.2% oxygen content of inlet gas. Under this condition, the decomposition ratio of CaSO4 was up to 90.6%, the SO2 conversion was 70.4%, and the average volume concentration of SO2 was 11.9%. With the aid of CaF2, the pyrolysis temperature of CaSO4 decreased significantly. The surface structure and morphology analysis revealed that CaF2 was beneficial to the pyrolysis efficiency of CaSO4. TG curve, XRD analysis and kinetic process have proved that the generation of intermediate substance CaS is the first stage for thermal decomposition of CaSO4, and CaO is the end product of CaSO4 pyrolysis under weak reducing atmosphere.

The effects of surfactants on the heterogeneous uptake of sulfur dioxide on hematite

Surfactants are often found to be associated with atmospheric particles. They can change the physicochemical properties of these particles, and thereby impact their chemical reactivity. However, their influences on heterogeneous reactions of atmospheric trace gases have not been paid much attention. In this study, the impacts of different surfactants on the heterogeneous conversion of SO2 on hematite were investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), including cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS) and nonionic polyethylene glycol tert-octylphenyl ether (Triton X-100). Results indicated that heterogeneous reactivities of hematite-surfactant mixtures were significantly different due to the presence of different surfactants. Under dry conditions, heterogeneous reactivities decreased with the increase of their concentrations, but the higher reactivities were observed at an appropriate concentration range of CTAB and SDS when compared to pure hematite, showing their promoting effects at this concentration range. Under the condition of 58% relative humidity, the heterogeneous reactivities increased first and then decreased with the increasing mass fractions of CTAB and SDS, but pure hematite showed the highest reactivity. While the mixtures containing Triton X-100 had stronger ability to suppress sulfate formation under 58% RH than under dry condition, though these mixtures under 58% RH presented same trend as under dry condition. Water molecules can renew surface reactive sites and promote sulfate formation at an appropriate mass fraction of CTAB or SDS, water molecules can also promote the adsorption mode transition of Triton X-100 from adsorption through terminal OH groups to adsorption through ethoxyl groups, resulting in more surface active sites being covered and a drastically decrease in the reactivity. A possible mechanism for the impact of surfactants on the heterogeneous conversion of SO2 on hematite is proposed, and atmospheric implications based on these results are discussed.

Simulation Study of an Oxy-Biomass-Based Boiler for Nearly Zero Emission Using Aspen Plus

Bioenergy integrated CO2 capture is considered to be one of the viable options to reduce the carbon footprint in the atmosphere, as well as to lower dependability on the usage of fossil fuels. The present simulation-based study comprises the oxy bio-CCS technique with the objective of bringing about cleaner thermal energy production with nearly zero emissions, CO2 capture and purification, and with the ability to remove NOx and SO2 from the flue gas and to generate valuable byproducts, i.e., HNO3 and H2SO4. In the present work, a simulation on utilization of biomass resources by applying the oxy combustion technique was carried out, and CO2 sequestration through pressurized reactive distillation column (PRDC) was integrated into the boiler. Based on our proposed laboratory scale bio-CCS plant with oxy combustion technique, the designed thermal load was kept at 20 kWth using maize stalk as primary fuel. With the objective of achieving cleaner production with near zero emissions, CO2 rich flue gas and moisture generated during oxy combustion were hauled in PRDC for NOx and SO2 absorption and CO2 purification. The oxy combustion technique is unique due to its characteristic low output of NO sourced by fuel inherent nitrogen. The respective mechanisms of fuel inherent nitrogen conversion to NOx, and later, the conversion of NOx and SO2 to HNO3 and H2SO4 respectively, involve complex chemistry with the involvement of N–S intermediate species. Based on the flue gas composition generated by oxy biomass combustion, the focus was given to the fuel NOx, whereby different rates of NO formation from fuel inherent nitrogen were studied to investigate the optimum rates of conversion of NOx during conversion reactions. The rate of conversion of NOx and SO2 were studied under fixed temperature and pressure. The factors affecting the rate of conversion were optimized through sensitivity analysiês to get the best possible operational parameters. These variable factors include ratios of liquid to gas feed flow, vapor-liquid holdups and bottom recycling. The results obtained through optimizing the various factors of the proposed system have shown great potential in terms of maximizing productivity. Around 88.91% of the 20 kWth boiler’s efficiency was obtained. The rate of conversion of NOx and SO2 were recorded at 98.05% and 87.42% respectively under parameters of 30 °C temperature, 3 MPa pressure, 10% feed stream holdup, liquid/gaseous feed stream ratio of 0.04 and a recycling rate of the bottom product of 20%. During the simulation process, production of around four kilograms per hour of CO2 with 94.13% purity was achieved.

Influence of cerium and cesium promoters on vanadium catalyst for sulfur dioxide oxidation

We studied the catalytic performance of vanadium catalyst promoted with cerium and cesium for sulfur dioxide oxidation. The catalyst samples were characterized by FT-IR, Raman, XRD, SEM, BET and XPS. The results showed that the properties of the catalyst promoted with 4 wt% CeO2 and 7 wt% Cs2SO4 were superior to the commercial V2O5-K2SO4/SiO2 and V2O5-K2SO4-Cs2SO4/SiO2 catalysts, in terms of low temperature activity, thermal stability, SO2 oxidation efficiency and ignition temperature. The FT-IR, Raman, XRD and XPS results evidenced the formation of V2O5-Cs2S2O7 pyrosulfate, CeVO4 and CeO2 crystalline phase in V2O5-K2SO4-Cs2SO4-CeO2/SiO2 catalyst These crystalline phases play an important role in redox reaction at low temperature and can increase the available oxygen for the redox reaction. The characterization results also showed that cerium can promote the formation of pyrosulfate, increase the proportion of large macropores, and improve stability of VV at high temperature. Due to its excellent low-temperature and high-temperature activity, the V2O5-K2SO4-Cs2SO4-CeO2 /SiO2 catalyst appears to be more efficient for the conversion of SO2 in a larger concentration range.

Influence of relative humidity on SO2 oxidation by O3 and NO2 on the surface of TiO2 particles: Potential for formation of secondary sulfate aerosol.

The heterogeneous reactions of SO2/O3 and SO2/NO2 with TiO2 particles were studied as a function of relative humidities (RHs). An in situ microscopic Fourier transform infrared (micro-FTIR) spectrometer was used to monitor the reaction kinetics. Rapid conversion of SO2 to sulfate occurs on the surface of TiO2 particles in the presence of O3 or NO2, which is sensitive to RHs. For unreacted (fresh) particles, the uptake coefficients for SO2 in initial stage are both obviously enhanced over four times with the increasing RH from ~4% to ~85%. Moreover, the uptake coefficient in the system of SO2/O3 is about 40% higher than that of SO2/NO2 on TiO2 particles at the similar RH conditions. For TiO2 after exposure to SO2/O3 or SO2/NO2 (sulfated) particles, the uptake coefficients for SO2 in moisture absorption stage are all higher than that on fresh particles in initial stage at the similar RH, indicating rapid mixture gases adsorption with particle hygroscopic growth. The high production of the secondary sulfate for heterogeneous reaction of mixture gases on TiO2 surface from arid region to humid region provides new insights for better understanding the severe haze under the humid condition.

Multiscale Applications of Two Online-Coupled Meteorology-Chemistry Models during Recent Field Campaigns in Australia, Part I: Model Description and WRF/Chem-ROMS Evaluation Using Surface and Satellite Data and Sensitivity to Spatial Grid Resolutions

Air pollution and associated human exposure are important research areas in Greater Sydney, Australia. Several field campaigns were conducted to characterize the pollution sources and their impacts on ambient air quality including the Sydney Particle Study Stages 1 and 2 (SPS1 and SPS2), and the Measurements of Urban, Marine, and Biogenic Air (MUMBA). In this work, the Weather Research and Forecasting model with chemistry (WRF/Chem) and the coupled WRF/Chem with the Regional Ocean Model System (ROMS) (WRF/Chem-ROMS) are applied during these field campaigns to assess the models’ capability in reproducing atmospheric observations. The model simulations are performed over quadruple-nested domains at grid resolutions of 81-, 27-, 9-, and 3-km over Australia, an area in southeastern Australia, an area in New South Wales, and the Greater Sydney area, respectively. A comprehensive model evaluation is conducted using surface observations from these field campaigns, satellite retrievals, and other data. This paper evaluates the performance of WRF/Chem-ROMS and its sensitivity to spatial grid resolutions. The model generally performs well at 3-, 9-, and 27-km resolutions for sea-surface temperature and boundary layer meteorology in terms of performance statistics, seasonality, and daily variation. Moderate biases occur for temperature at 2-m and wind speed at 10-m in the mornings and evenings due to the inaccurate representation of the nocturnal boundary layer and surface heat fluxes. Larger underpredictions occur for total precipitation due to the limitations of the cloud microphysics scheme or cumulus parameterization. The model performs well at 3-, 9-, and 27-km resolutions for surface O3 in terms of statistics, spatial distributions, and diurnal and daily variations. The model underpredicts PM2.5 and PM10 during SPS1 and MUMBA but overpredicts PM2.5 and underpredicts PM10 during SPS2. These biases are attributed to inaccurate meteorology, precursor emissions, insufficient SO2 conversion to sulfate, inadequate dispersion at finer grid resolutions, and underprediction in secondary organic aerosol. The model gives moderate biases for net shortwave radiation and cloud condensation nuclei but large biases for other radiative and cloud variables. The performance of aerosol optical depth and latent/sensible heat flux varies for different simulation periods. Among all variables evaluated, wind speed at 10-m, precipitation, surface concentrations of CO, NO, NO2, SO2, O3, PM2.5, and PM10, aerosol optical depth, cloud optical thickness, cloud condensation nuclei, and column NO2 show moderate-to-strong sensitivity to spatial grid resolutions. The use of finer grid resolutions (3- or 9-km) can generally improve the performance for those variables. While the performance for most of these variables is consistent with that over the U.S. and East Asia, several differences along with future work are identified to pinpoint reasons for such differences.

Catalytic Role of Process Dust in SO2-to-SO3 Conversion in Flash Smelting Heat Recovery Boilers

The aim of this work is to examine the catalytic role of copper smelter, copper converter, and nickel smelter process dusts in SO2-to-SO3 conversion at 750°C. To clarify the role of specific oxides in greater detail, synthetic dusts containing varying concentrations of either CuO or Fe3O4 were also studied. All studied dusts catalyzed SO3 conversion. Among the industrial flue dusts, the highest concentration of SO3 formed in the presence of copper smelter dust. Comparing individual oxides, CuO had a greater impact on the SO3 formation. Such catalytic effects of smelter dusts may lead to SO3 concentrations in the process gas so high that sulfuric acid dew point corrosion may occur.

Pollution Characteristics and Source Apportionment of PM2.5 in Heating and Non-heating Periods in Shenyang

To study the atmospheric PM2.5 pollution characteristics and sources in heating and non-heating periods in Shenyang, 113 groups of effective PM2.5 samples were collected from January 29, 2015 to January 26, 2016, and the water-soluble ions, carbon constituents and elements in PM2.5 were tested. The results indicated that the average PM2.5 mass concentration in Shenyang during the sampling period was 66 μg·m-3. Among the sampled PM2.5 concentrations, 31.0% exceeded the daily value of the secondary standard limit of the Chinese National Ambient Air Quality Standard (75 μg·m-3). The average concentration and over-standard rate of PM2.5 in the heating period (90 μg·m-3, 68.6%) was higher than that of the non-heating period (51 μg·m-3, 31.4%). The concentrations of the 21 elements (except Mg, Ti, Ca, Fe, and Si), water-soluble ions (except Ca2+), OC, and EC were all higher in the heating period than in the non-heating period. The ratio of[NO3-]/[SO42-]showed that the influence of moving source increased obviously in the non-heating period, and fixed source was still the main contributor in the heating period. The water-soluble ions were the result of the interaction of fixed source and moving source. The NOR and SOR analyses showed that the secondary conversion of NOx was weak, and the secondary conversion of SO2 was obvious, especially in the non-heating period. The enrichment factor showed that the elements with high EF value mainly came from coal burning, traffic pollution, and industrial emissions. The reconstructed PM2.5 masses were highly correlated with the measured ones. The main constituents of PM2.5 in both heating and non-heating seasons were organic matter (28.0%, 23.1%), mineral dust (14.5%, 26.0%), and sulfate (15.1%, 19.9%), and PM2.5 was mainly affected by the secondary particles, combustion sources and dust sources.

Catalytic Activity and Molecular Behavior of Lanthanum Modified CoSx/γ-Al2O3 Catalysts for the Reduction of SO2 to Sulfur in Smelter Off-Gas Using CO-H2 Mixture as Reductant

In this study, a series of three-component CoSx/γ-Al2O3 catalysts were developed for the reduction of high-content SO2 to sulfur in smelter off-gas. The introduction of a small amount of lanthanum additive greatly improved the catalytic activity and stability of Co-Cu/γ-Al2O3 catalysts using coal gas as reductant. The catalysts were characterized by XRD, XPS, BET, and SEM techniques. H2/CO-TPR was recorded to study redox properties of catalysts. With the use of a CO-H2 mixture with different proportions, a series of parallel experiments were performed to investigate the mutual impact and relation of CO and H2. Under optimum conditions, SO2 conversion of 99% and sulfur selectivity of 99% were obtained. The catalyst remained highly active after a long run of 200 h. Process simulation was used to investigate the molecular behavior of catalyst. Combined with in situ infrared characterization, the catalytic mechanism was put forward and verified.

Study of MoO3-γAl2O3 catalysts behavior in selective catalytic reduction of SO2 toxic gas to sulfur with CH4.

In the present study, a detailed investigation was carried out on MoO3 alumina-supported catalysts behavior in selective catalytic reduction of SO2 to sulfur with CH4. At first, four different molybdenum catalysts with weight rates of 0, 5, 10, and 15 were impregnated on γ-alumina to be characterized using XRD, SEM, BET, BJH, and N2 adsorption. Then, to find the most active catalyst, temperature dependency test was performed on all of the prepared catalysts and the result representing Al2O3-Mo10 as the best catalyst. In next step, the effects of feed gas composition, space velocity, and long-term activity, as an important industrial factor, were tested on Al2O3-Mo10. It was revealed instantaneously from the beginning, MoO3 specie started to convert mainly into MoS2 and MoO2, and a minor part into Mo2C, which is terminated after 750min achieving a stable condition. Thereafter, SO2 conversion and sulfur selectivity increased from 85.8 to 89.4% and 99.4 to 99.7%, respectively. XRD graph of the used catalyst and TPO thermogravimetric/mass-spectra proved possible happening of the proposed mechanism in long-term activity. At the end, mean activation energy was determined based on Arrhenius model in temperature range of 550 to 800°C, with a value of 0.33eV for Al2O3-Mo10.

The Effect of K Salts on SO2–SO3 Conversion and Denitration Behavior over V2O5–WO3/TiO2 Catalysts

A series of V2O5–WO3/TiO2 catalysts treated by KCl or K2SO4 were prepared using the equal volume impregnation method. The effects of adding these K salts on SO2–SO3 conversion and on denitration behavior over the catalyst were studied, using reactor trials and various characterization methods, including NH3-TPD, H2-TPR, ICP, BET, XRD, SEM, FT-IR and XPS. The results of catalytic activity evaluation tests show that adding K salts decreases the denitration efficiency, while SO2 enhances the activity of the KCl-poisoned catalyst to an extent. The presence of K salts also improves the SO3 formation rate, such that the SO3 formation rate for the K2SO4-poisoned catalyst is as high as 1.53% at 410 °C (compared with 0.60% for the fresh catalyst). The characterization data indicate that K salts aggregate on the catalyst surface, blocking the pores of the catalyst. The reduction ability of the catalyst is decreased slightly and new weakly acidic sites appear. In addition, the concentration of strongly acidic sites declines. SO2 can increase the surface acidity of the catalyst. K salts increase the number of V5+=O bonds and weakly acidic sites, but consume oxygen atoms along with V and W species. Importantly, the strength of the V5+=O bonds, the concentration of surface chemically adsorbed oxygen and the V4+/V5+ ratio all played vital roles in improving the conversion of SO2–SO3 and in enhancing the NO reduction.

Contrary Role of H2O and O2 in the Kinetics of Heterogeneous Photochemical Reactions of SO2 on TiO2.

Although the heterogeneous conversion of SO2 on TiO2 has been considered a potential source of sulfate in the troposphere, little is known about the kinetics of SO2 uptake on TiO2 under ambient conditions. In this study, heterogeneous reactions of SO2 on a TiO2 surface at 298 K were investigated by a coated-wall flow tube reactor and in situ diffuse reflectance Fourier transformed infrared spectroscopy (DRIFTS). The effect of UV irradiation, relative humidity (RH), and O2 on the uptake coefficients and adsorption amount of SO2 have been analyzed comprehensively. UV irradiation exhibits a slight effect on the initial uptake coefficient (γBET), which increases from 1.23 × 10-6 to 1.48 × 10-6 in air conditions and 5.89 × 10-7 to 6.42 × 10-7 in a N2 stream under dry conditions. Surface water exhibits a competition effect on the adsorption of SO2 on TiO2. An increase in RH (in the range of 0-75%) led to a decrease in the γBET and adsorption amount of SO2 both in the dark and the light reaction. In contrast, oxygen plays an important role in the uptake of SO2. Both the uptake coefficients and adsorption amount of SO2 on TiO2 decreased in the N2 stream compared to those in air conditions. Only sulfite was formed during the adsorption of SO2 in dark and dry conditions. The presence of UV irradiation was found to promote the conversion of SO2 to sulfate and the adsorption amount of sulfur species on the TiO2 surface. These results suggest that heterogeneous reaction on TiO2 as a sink for SO2 is not important in the atmosphere.

Simultaneous terpolymerization of CO2/SO2 with epoxide and mechanistic understanding

CO2 and SO2 appear simultaneously in most industrial cases and have caused serious environmental and health issues, however, the simultaneous conversion of SO2 and CO2 has not been reported until now. This work describes an alternating terpolymerization of SO2/CO2 with cyclohexene oxide using SalenCrIIICl as catalyst and bis(triphenylphosphine)iminium chloride as cocatalyst, and a novel poly(cyclohexene carbonate sulfite) was obtained. The terpolymers were characterized by nuclear magnetic resonance spectroscopy, infrared spectroscopy, and gel permeation chromatography, and effects of the different reaction conditions on the structures of the terpolymers (carbonate content and sulfite content in the block copolymer) were investigated. In experiments, we found that SO2 not only acts as reactant, but also exhibits a nucleophilicity to promote the ability embedding of SO2 in the terpolymers. According to the study of mechanism that proposed by predecessors and experiment, the possible terpolymerization mechanisms are recommended. The results proved that the terpolymerization of CO2/SO2 with epoxides may be considered as an effective approach to simultaneously convert CO2 and SO2, and improve efficiency of the CO2/SO2 utilization.