Performance Characterization and Optimization of the AgNO3-Filter/FMA Fluorimetric Method for Atmospheric H2S Measurements

This sensitive, albeit precarious, method for measuring ppb-ppt (V/V) concentrations of H₂S was examined for various sources of potential error within the procedure. Filter preparation, filter storage, filter extraction, fluorimetric reagent stabilities, matrix differences between standards and samples, and possible interferences from other sulfur-containing compounds were separately studied for their effects on the analytical performance of the method. The overall method showed no Interference from SO₂, CS₂, COS, CH₃SH, CH₃SCH₃, and SO₄ ^-2. To minimize bias and obtain a reliable estimate of precision, the method should be calibrated with H₂S standards rather than liquid bisulfide standards. The measurement precision is a function of the quantity of H₂S collected as Ag₂S and/or AgSH on the impregnated filters. Because of the method’s linear dynamic range, sufficient air should be sampled to achieve filter loadings of 15 to 35 ng S/filter. A quality control method based on fluorescein mercuric acetate (FMA) is presented that ensures data quality while reducing the otherwise frequent need for fluori-metric calibration.     

A dynamic dilution system for the production of sub-ppb concentrations of reactive and labile species

A three-stage dynamic dilution system has been developed capable of generating calibration standards below 100 pptv using gravimetrically calibrated permeation tubes as a trace species source. Multistage dilution permits the use of equivalent one-step diluent flows approaching 1000 std 1 min ⁻¹. An allfluorocarbon flow path facilitates the handling of reactive and labile species. Accuracies of about ± 3 % have been demonstrated for several sulfur compounds including H₂S and SO₂ at mixing ratios below 200 ppt.     

Deodorization of Dimethyl Sulfide Using a Discharge Approach at Room Temperature

Abstract

The traditional technologies for odor removal of thiol usually create either secondary pollution for scrubbing, adsorption, and absorption processes, or sulfur (S) poisoning for catalytic incineration. This study applied a laboratory-scale radio-frequency plasma reactor to destructive percentage-grade concentrations of odorous dimethyl sulfide (CH₃SCH₃, or DMS). Odor was diminished effectively via reforming DMS into mainly carbon disulfide (CS₂) or sulfur dioxide (SO₂). The removal efficiencies of DMS elevated significantly with a lower feeding concentration of DMS or a higher applied rf power. A greater inlet oxygen (O₂)/DMS molar ratio slightly improved the removal efficiency. In an O₂-free environment, DMS was converted primarily to CS₂, methane (CH₄), acetylene (C₂H₂), ethylene (C₂H₄), and hydrogen (H₂), with traces of hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH), and dimethyl disulfide. In an O₂-containing environment, the species detected were SO₂, CS₂, carbonyl sulfide, carbon dioxide (CO₂), CH₄, C₂H₄, C₂H₂, H₂, formal-dehyde, and methanol. Differences in yield of products were functions of the amounts of added O₂ and the applied power. This study provided useful information for gaining insight into the reaction pathways for the DMS dissociation and the formation of products in the plasmolysis and conversion processes.     

Analysis of Kraft-Mill,Sulfur-Containing Gases with GLC lonization Detectors

The technique includes the use of two chromatographic columns in series to separate O₂, N₂, CO, CO₂, H₂O, H₂S, SO₂ and CH₃SH. Column 1, containing Triton 45 on Chromosorb, separates H₂O, H₂S, SO₂ and CH₃SH. Column 2, packed with Molecular Sieve, separates O₂, N₂, CO and CO₂. The conditions required to obtain adequate sensitivity and separation are discussed.     

Stainless Steel Anti-Smog Mufflers—Cut Air Pollution

An automatic process gas chromatograph has been developed for use on the recovery furnace stack of a Kraft pulp mill. The instrument analyzes for widely varying concentrations of H₂S, SO₂, CH₃SH and higher order sulfur compounds. It is insensitive to the fixed gases and water vapor, and performs its analysis in approximately ten minutes. The instrument features a microcoulometric detector giving it sensitivity to H₂S as low as 0.1 ppm, and SO₂ and CH₃SH as low as 0.5 ppm. The major limit to even higher sensitivity at this stage of development lies with two problems: the background noise level in the detector and the sulfur compound absorption in the Porapak Q chromatograph column. At the reported sensitivity, a 40-ml gas sample was used. The instrument also contains a data analysis system supplementary to the usual strip chart recorder. This system is made up of a digital voltmeter, a digital translator, and a teletype and hence allows the transfer of the output data to a digital computer for processing. The processed data are usually presented in the form of ppm quantities of the component gases in the stack gas. The instrument has worked successfully on small furnace effluent for periods of 25 hr but has not been tried on recovery furnace stacks. It has also run on prepared samples for periods of up to seven days with no maintenance or attendance necessary.     

Photochemical oxidation and dispersion of gaseous sulfur compounds from natural and anthropogenic sources around a coastal location

The photochemical oxidation and dispersion of reduced sulfur compounds (RSCs: H₂S, CH₃SH, DMS, CS₂, and DMDS) emitted from anthropogenic (A) and natural (N) sources were evaluated based on a numerical modeling approach. The anthropogenic emission concentrations of RSCs were measured from several sampling sites at the Donghae landfill (D-LF) (i.e., source type A) in South Korea during a series of field campaigns (May through December 2004). The emissions of natural RSCs in a coastal study area near the D-LF (i.e., source type N) were estimated from sea surface DMS concentrations and transfer velocity during the same study period. These emission data were then used as input to the CALPUFF dispersion model, revised with 34 chemical reactions for RSCs. A significant fraction of sulfur dioxide (SO₂) was produced photochemically during the summer (about 34% of total SO₂ concentrations) followed by fall (21%), spring (15%), and winter (5%). Photochemical production of SO₂ was dominated by H₂S (about 55% of total contributions) and DMS (24%). The largest impact of RSCs from source type A on SO₂ concentrations occurred around the D-LF during summer. The total SO₂ concentrations produced from source type N around the D-LF during the summer (a mean SO₂ concentration of 7.4 ppbv) were significantly higher than those (≤0.3 ppbv) during the other seasons. This may be because of the high RSC and SO₂ emissions and their photochemistry along with the wind convergence.     

Measurement of Trace Levels of Atmospheric Sulfur Dioxide with a Gold Film Sensor

The mercury translation principle, wherein S(IV) reacts with Hg(l) to produce Hg(ll) and Hg(O), was utilized to measure trace levels of SO₂ with a conductometric gold film sensor. One approach involved impregnated glass fiber filters containing mercurous salts. The second and more successful approach utilized a porous membrane reactor where the reaction occurs in the interstitial liquid-gas interface as the sample gas flows inside and a dilute solution of Hg₂(NO₃)₂ flows outside the porous PTFE membrane tube. The first approach attained a LOD of 200 pptv SO₂(g), however, batch to batch reproducibility of the filters was poor and the filters could not be stored more than two days. The membrane reactor method provided better translation efficiency and highly reproducible results, with an LOD of 50 pptv SO₂(g). An intercomparlson of this method with an independent method relying on completely different chemistry showed good agreement for the measurement of subppbv levels of ambient SO₂. Both mercury translation methods were essentially unaffected by H₂S or CH₃SH.     

Ambient and Source SO2 Detector Based on a Fluorescence Method

The principle of this detector is based on the measurement of the intensity of the ultraviolet fluorescence of SO₂ produced by absorption of the Zn 2138 Å or Cd 2288 Å line. The fluorescence intensity was found to be linear from 0.1 to 500 ppm of SO₂ in air with the Zn lamp and from 0.1 to 1600 ppm with the Cd lamp. The detection limit at present is about 20 ppb. There is no detectable interference from O₃, H₂S, NO₂, CO₂, CO, or H₂, although the presence of a large concentration of CS₂ (500 times as much as SO₂) NO (500 times) or C₂H₄ (4000 times) interferes with the measurement. The presence of 2% H₂0 reduces the signal by 25%, while up to 1 % CH₄ has almost no effect.     

A new technique for collection,concentration and determination of gaseous tropospheric formaldehyde

This article describes an improved technique for making in situ measurements of gaseous tropospheric formaldehyde (CH₂O). The new technique is based on nebulization/reflux principles that have proved very effective in quantitatively scrubbing water soluble trace gases (e.g. CH₂O) into aqueous mediums, which are subsequently analyzed. Atmospheric formaldehyde extractions and analyses have been performed with the nebulization/reflux concentrator using an acidified dinitrophenylhydrazine solution that indicate that quantitative analysis of CH₂O at global background levels (∼ 0.1 ppbv) is feasible with 20-min extractions. Analysis of CH₂O, once concentrated, is accomplished using high performance liquid chromatography (HPLC) with ultraviolet photometric detection. The CH₂O-hydrazone derivative, produced by the reaction of 2,4-dinitrophenylhydrazine in H₂SO₄ acidified aqueous solution, is detected as CH₂O.     

酸碱改性对氧化铁脱硫剂脱硫性能影响的研究

通过酸碱改性制备了酸式和碱式2种不同表面性质的常温氧化铁脱硫剂,并采用FT-IR技术对其表面酸碱性质和净化硫化氢废气活性进行了研究.结果表明,表面酸碱件质不同的脱硫剂其脱硫反应行为也不同,在脱硫过程中硫化氢氧化生成的硫酸及亚硫酸会影响脱硫剂的表面酸碱性质,造成酸式脱硫剂的表面酸性更强,从而抑制了硫化氢分子在酸式脱硫剂表...     

Kinetics of Sulfur-Oxide Formation in Flames: II. Low Pressure H2S Flames

The microstructure of 1/10 and 1/20 atmosphere, lean H₂S—O₂—N₂ flames is developed using the mass-spectrometric flame-sampling technique. The flame mechanism developed is in agreement with that determined from an earlier study on 1-atm H₂S flames. The formation of SO₂ appears to be primarily related to the production of SH and the ensuing oxidation steps SH + O₂ = SO + OH and SO + O₂ = SO₂ + O. While there is some question whether SO₂ formation occurs via an SO or an S₂O intermediate, the present study does not give direct support to the role of S₂O in the oxidation mechanism. However, the presence of significant quantities of free sulfur in the pre-flame zone may be indicative of S₂O formation via SO + S → S₂O, and, possibly, via the disproportionation of SO, 3SO → S₂O + SO₂. Kinetic analyses of some of the pre-flame reactions indicate an apparent activation energy of 17,300 calories/mole for the decomposition of H₂S. The actual initiation process in the flame mechanism requires further examination. The specific rate for the reaction step H₂S + O = OH + SH is given by k ₆ = 1.45 × 10₁₅ exp ( – 6600/RT) cm³ mole^–1 sec^–1, and the specific rate for the oxidation of SO, SO + O₂ = SO₂ + O, is given by k ₅ = 5.2 × 10₁₄ exp (—19,300/RT) cm³ mole^–1 sec^–1.     

Removal of SO2 From Flue Gases Using Carbon at Elevated Temperatures

The interaction of a typical flue gas with active charcoal and bituminous coal char at temperatures between 600 and 800°C and atmospheric pressure has been studied. The SO₂ in the flue gas interacts with the carbon to form primarily H₂S, COS, and a carbon-sulfur surface complex. H₂S and COS break through the carbon bed much in advance of SO₂. At 800°C, sulfur retention on the bed exceeds at least 11% before SO₂ breakthrough occurs. The reaction of H₂S and COS with O₂ over active charcoal at 100–140°C to produce sulfur, which deposits on the carbon, has also been studied and found to be feasible. As a result of this study, a new process is outlined for the removal of SO₂ from flue gas, with the ultimate conversion     

Atmospheric methanethiol emitted from a pulp and paper plant on the shore of Lake Baikal

On-site measurement of methanethiol (CH₃SH) was performed for three years on ships and cars near a pulp and paper plant standing on the shore of Lake Baikal in Siberia, Russia, to investigate the behavior and impact of atmospheric CH₃SH emitted from a point source. Despite its strong odor, there are few reports on atmospheric CH₃SH, while many investigations have been carried out on dimethyl sulfide (DMS). In this work, CH₃SH and DMS were measured every 15 min by a recently developed automated instrument based on single column trapping/separation and chemiluminescence measurement. Hydrogen sulfide, sulfur dioxide and ozone were also measured simultaneously by individual instruments. Of these sulfur compounds, CH₃SH was dominant and its concentration sometimes reached several tens of ppbv. The concentration of CH₃SH was high at night, because of the lack of photodecomposition and local winds from the mountain to the lake. Such time variation was marked in the summer. The CH₃SH level decreased significantly downwind, while decreases in concentrations of other compounds such as DMS and SO₂ were relatively small. From these temporal and spatial variations, the behavior of CH₃SH is described in this paper. The impact of CH₃SH near the Siberian big sources is discussed with the presented data.     

Carbon Disulfide and Hydrogen Sulfide Removal with a Peat Biofilter

ABSTRACT

Simultaneous removal of H₂S and CS₂ was studied with a peat biofilter inoculated with a Thiobacillus strain that oxidizes both compounds in an acidic environment. Both sulfurous gases at concentrations below 600 mg S/m³ were efficiently removed, and the removal efficiencies were similar, 99%, with an empty bed retention time (EBRT) of more than 60 sec. Concentrations greater than 1300-5000 mg S/m³ caused overloading of the filter material, resulting in high H₂SO₄ production, accumulation of elemental sulfur, and reduced removal efficiency. The highest sulfur removal rate achieved was 4500 g-S/day/m³ filter material. These results indicate that peat is suitable as a biofilter material for the removal of a mixture of H₂S and CS₂ when concentrations of gases to be purified are low (less than 600 mg/m³), but it is still odorous and toxic to the environment and humans.     

A Continuous Quantitative Detection Method for Total Mercaptans,Organic Sulphides,H2S,and CS2 for Odouriferous Emissions

A monitoring system enabling detection and determination of the nature of odour nuisance caused by industrial emissions of volatile organic sulphur compounds is presented. The system consists of two continuous, highly sensitive detectors for sulphur compounds at the ppb-level. One of the detectors is equipped with a SO_x-scrubber and measures the total amount of non-S0₂ sulphur compounds. By the use of a newly developed scrubber retaining S0₂, H₂S and CS₂ the second detector monitors the presence of odorous mercaptans and organic sulphides in ambient air. Both these continuous detection signals are fed to a data processor which triggers air collection for the determination of the individual compounds by gas chromatographic analysis in the laboratory. The concept and operation, as well as the practical possibilities and applications of the system are explained     

Mechanism of OH-initiated atmospheric photooxidation of the organophosphorus insecticide (C2H5O)3PS

O,O,O-triethyl phosphorothioate ((C₂H₅O)₃PS, TEPT) is a widely used organophosphorus insecticide. TEPT may be released into the atmosphere where it can undergo transport and chemical transformations, which include reactions with OH radicals, NO₃ radicals and O₃. The mechanism of the atmospheric reactions of TEPT has not been fully understood due to the short-lifetime of its oxidized radical intermediates, and the extreme difficulty in detection of these species experimentally. In this work, we carried out molecular orbital theory calculations for the OH radical-initiated atmospheric photooxidation of TEPT. The profile of the potential energy surface was constructed, and the possible channels involved in the reaction are discussed. The theoretical study shows that OH addition to the PS bond and H abstractions from the CH₃CH₂O moiety are energetically favorable reaction pathways. The dominant products TEP and SO₂ arise from the secondary reactions, the reactions of OH-TEPT adducts with O₂. The experimentally uncertain dominant product with molecular weight 170 is mostly due to (C₂H₅O)₂P(S)OH and not (C₂H₅O)₂P(O)SH.     

Evaluation of the Iron-o-Phenanthroline Procedure For Determining S02 in Turbine Exhaust Gases

Several wet chemical methods have been used or suggested for the determination of SO₂ concentrations in air pollution work. These include the iron-O-phenanthroline procedure reported by Stephens and Lindstrom, the Scaringelli-modified West-Gaeke method and the Schulze method. This paper describes a laboratory study to evaluate the usefulness of the iron-o-phenanthroline procedure and is directed to individuals concerned with the analysis of gases from the exhaust of gas turbine engines and other combustion processes, including stationary power plants. The variables considered were: range of usefulness in terms of concentration of SO₂, efficiency of collection, effect of contaminants, specifically oxides of nitrogen, olefin and aldehyde and effect of storage prior to spectrophctometric measurement. The Stephens-Lindstrom method was found to be suitable for measuring higher levels of SO₂ concentrations. It can accurately measure amounts totalling 6000 µl of SO₂ and above whereas the other mentioned methods are generally used for lower levels. Collection efficiency was satisfactory. Contaminants, particularly oxides of nitrogen, are a problem only at low levels of SO₂. NO₂ interference may be eliminated by absorption of the NO₂ on Ultraport S impregnated with ANEDA/H₂SO₄ solution. Temperature control during SO₂ addition is necessary. Storage of exposed reagents prior to measurement produce only small errors if stored at 0°C or at room temperature.     

Sulfuric odorous compounds emitted from pig-feeding operations

The objective of the study was to quantify the concentration and emission levels of sulfuric odorous compounds emitted from pig-feeding operations. Five types of pig-housing rooms were studied: gestation, farrowing, nursery, growing and fattening rooms. The concentration range of sulfuric odorous compounds in these pig-housing rooms were 30–200 ppb for hydrogen sulfide (H₂S), 2.5–20 ppb for methyl mercaptan (CH₃SH), 1.5–12 ppb for dimethyl sulfide (DMS; CH₃SCH₃) and 0.5–7 ppb for dimethyl disulfide (DMDS; CH₃S₂CH₃), respectively. The emission rates of H₂S, CH₃SH, DMS and DMDS were estimated by multiplying the average concentration (mg m⁻³) measured near the air outlet by the mean ventilation rate (m³ h⁻¹) and expressed either per area (mg m⁻² h⁻¹) or animal unit (AU; liveweight of the pig, 500 kg) (mg pig⁻¹ h⁻¹). As a result, the emission rates of H₂S, CH₃SH, DMS and DMDS in the pig-housing rooms were 14–64, 0.8–7.3, 0.4–3.4 and 0.2–1.9 mg m⁻² h⁻¹, respectively, based on pig's activity space and 310–723, 18–80, 9–39 and 5–22 mg AU⁻¹ h⁻¹, respectively, based on pig's liveweight, which indicates that their emission rates were similar, whether based upon the pig's activity space or liveweight. In conclusion, the concentrations and emission rates of H₂S were highest in the fattening room followed by the growing, nursery, farrowing and gestation rooms whereas those of CH₃SH, DMS and DMDS concentrations were largest in the growing room followed by the nursery, gestation and farrowing rooms.     

An on-line analysis of reduced sulfur gases in the ambient air surrounding a large industrial complex

In this study, the concentrations of reduced sulfur compounds (RSC: H₂S, CH₃SH, DMS, and DMDS) were continuously measured from an odor monitoring station over a 4-month period (August–November 2005) using an on-line GC system. The hourly measurement data of RSC, collected along with some major aromatic VOCs (benzene, toluene, xylene, etc.), approached the sum of 1500; the mean for all hourly H₂S was computed to be 295 ppt, while those of the others were seen at 7 (DMS), 1 (CH₃SH), and 0.4 ppt (DMDS). When these RSC data were compared across two seasons and on a 24 h scale basis, the values for either the summer or nighttime periods were generally high relative to their counterparts in the fall and daytime. Analysis of these RSC data generally suggests that most RSCs occur at some ppt concentration ranges and that their values frequently fall below detection limits (DL) values (except for H₂S). If the total number of effective data sets (i.e., above DL values) are compared to each other, the results tend to differ significantly between H₂S and the others: the proportion of effective number was as high as 75% for H₂S, while the others were very low (6% of DMS and even less than that for the others). The distributions of RSC were hence clearly distinguished from those of VOCs in that the determination of the latter was scarcely limited by the instrumental detectability. According to the present study, the H₂S data exhibit strong potential as the malodor tracers, while those of the other RSCs are unlikely due to the limited detectability. The overall results of this study hence suggest that several factors which include the selection of target compounds, the location of the monitoring points, and the scale (or number) of total monitoring points should be considered simultaneously to effectively track down the odor occurrence patterns in areas near strong source processes.