Numerical simulation of the thermal destruction of some chlorinated C1 and C2 hydrocarbons

We have numerically modeled the breakdown of small quantities of several chlorinated hydrocarbons (CH3Cl, CH2Cl2, CHCl3, CCl4, C2H3Cl, and C2H5Cl) in a lean mixture of combustion products between 800 and 1480 K. This simulates the fate of poorly atomized waste in a liquid-injection incinerator. Kinetics calculations were performed using the CHEMKIN and SENKIN programs, with a reaction mechanism that was developed at Louisiana State University to model flat-flame burner experiments. A 99.99-percent destruction efficiency was attained in one second at temperatures ranging from 1280 to 960 K, with CCl4 requiring the highest temperature for destruction and C2H5Cl the lowest. For all compounds except C2H5Cl, there was a range of temperatures at which byproducts accounted for several percent of the elemental chlorine at the outlet. The more heavily chlorinated compounds formed more byproducts even though the amount of elemental chlorine was the same in all cases. The sensitivity of results to residence time, equivalence ratio, temperature profile, and the presence of additional chlorine, was examined for the case of CHCl3.     

Sources of airborne CC14

Atmospheric mixing ratios of chlorinated C₁ and C₂ hydrocarbons (CHCs) were measured at the mountain Wank (Garmisch-Partenkirchen, Bavarian Alps) in autumn 1992. The data lead to the assumption that at least part of the observed CC1₄ originates from a source different to the other CHCs measured (C₂HCL₃, C₂C1₄, CHCl₃ and CH₃CCl₃). The nature of this source is discussed.     

Release of iodine in the atmospheric oxidation of alkyl iodides and the fates of iodinated alkoxy radicals

This paper describes a study of the products of the Cl-atom-initiated oxidation of three alkyl iodides, RI=CH₃I, C₂H₅I, and 2-C₃H₇I, carried out in synthetic air at atmospheric pressure and at room temperature. Fourier-transform infrared spectroscopy was used to follow the decay of reactants and subsequent formation of products. The primary step proceeds via two channels, one of which yields HCl and an iodinated alkyl radical, and the other I atoms and an alkyl chloride. Quantitative analysis of the product yields, together with an assessment of the formation of HCl in secondary processes, allowed the fractional branching into the two channels to be calculated. The channel yielding HCl from RI constitutes a fraction 0.59, 0.93, and 0.68 for R=CH₃, C₂H₅, and 2-C₃H₇. The iodinated alkyl radical forms first a peroxy, and then an alkoxy, radical in the presence of air. The final products CH₂O, CH₃CHO, and CH₃COCH₃ were observed as expected for the decomposition of these radicals with RI=CH₃I, C₂H₅I, and 2-C₃H₇I, and the fractions of the alkoxy radicals fragmenting to the carbonyl compounds were 0.88, 0.57, and 0.86, respectively. Atomic iodine is formed concomitantly with the carbonyl species, so that these fractions also indicate the yield of I atoms in the secondary process. Alternative reaction pathways for the iodinated alkoxy radicals, in particular reaction with O₂, are evaluated and discussed. The yields of I atoms in the primary and secondary steps, taken in combination with kinetic data, make it possible to estimate the contribution of the Cl-initiated oxidation of the alkyl halides to I-atom production in the atmosphere (and, making certain assumptions, the analogous contribution from OH-initiated oxidation). Radical-initiated processes might augment the photolytic yield of I atoms from simple alkyl iodides: the maximum enhancements lie between 5% (CH₃I) and more than 30% (2-C₃H₇I).     

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.     

Benzene and toluene influence with or without nitrogen dioxide on inorganic pigments of works of art—Part II

Air pollution has a great impact on the social and economic aspects all over the world. In order to account the human interaction with the atmospheric environment, a suitable scientific basis is needed.That is why six physicochemical quantities have been determined in a previous work for each one heterogeneous system between organic volatile pollutants and oxide-pigments of works of art. This investigation is extended in order to determine experimentally five new ones. Thus, a more precise contribution to the elucidation of the mechanism of the deterioration of various works of art in museums is achieved. These physicochemical quantities are: (1) local adsorption energies, (2) local monolayer capacities, (3) local adsorption isotherms, (4) density probability function, and (5) pollutant concentration on the oxide-pigment at equilibrium. All these adsorption parameters mentioned above have been calculated as a function of experimental time for the systems: C₆H₆/TiO_2, C₆H₆/NO₂/TiO_2, C₆H₆/Cr₂O_3, C₆H₆/NO₂/Cr₂O_3, C₆H₅CH₃/TiO_2, C₆H₅CH₃/NO₂/TiO_2, C₆H₅CH₃/Cr₂O_3, C₆H₅CH₃/NO₂/Cr₂O_3, C₆H₆/PbO, C₆H₆/NO₂/PbO, C₆H₅CH₃/PbO, and C₆H₅CH₃/NO₂/PbO for the first time. Thus, in this work we shall stress the recent new aspect of Reversed Flow-(Inverse) Gas Chromatography (RF-GC or RF-IGC), i.e. the time-resolved chromatography related to the evaluation of some important adsorption parameters. Gas Chromatography is a promising meeting place of surface science and atmospheric chemistry.     

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.     

Thermal analysis of polyethylene glycol: evolved gas analysis with ion attachment mass spectrometry

The thermal decomposition of polyethylene glycol was investigated by using a technique combining evolved gas analysis (time-resolved pyrolysis) with ion-attachment mass spectrometry. This technique allows the detection of intact pyrolysis products and, therefore, offers the opportunity for direct real-time monitoring of thermal by-products. Unstable products can thus be detected; for instance, many highly reactive organic peroxides, such as CH₃OOH and HOCH₂OOH, were found in this study. Classification analysis revealed 10 major compositional formulas among the product species: C_nH_2n+2O, C_nH_2n+2O₂, C_nH_2n+2O₃, C_nH_2n+2O₄, C_nH_2n+2O₅, C_nH_2n+2O₆, C_nH_2n+2O₇, C_nH_2nO, C_nH_2nO₂, and HO(CH₂CH₂O)_nH ethylene glycol oligomers. The Li⁺ ion adduct mass spectra showed a characteristic profile in terms of both the appearance of unique components and the distribution of pyrolysis products. Among the products of the thermal decomposition of PEG, formaldehyde (HCHO) and organic peroxides were particularly interesting. Formaldehyde, one of the 10 most abundant products, is a known human carcinogen. The detection of peroxides suggests that they may form during the incineration of PEG, which may have important environmental implications. The existence of peroxide products may have implications for chemical evolution in incinerator systems.     

Hg Reactions in the Presence of Chlorine Species: Homogeneous Gas Phase and Heterogeneous Gas-Solid Phase

Abstract

The kinetics of Hg chlorination (with HCl) was studied using a flow reactor system with an online Hg analyzer, and speciation sampling using a set of impingers. Kinetic parameters, such as reaction order (α), overall rate constant (k′ ), and activation energy (E _a), were estimated based on the simple overall reaction pathway. The reaction order with respect to C _Hg, k′, and E _a were found to be 1.55, 5.07 x 10^-2exp(-1939.68/T) [(μg/m³)^-0.55(s)^-1], and 16.13 [kJ/mol], respectively. The effect of chlorine species (HCl, CH₂Cl₂) on the in situ Hg capture method previously de-veloped²⁸ was also investigated. The efficiency of capture of Hg by this in situ method was higher than 98% in the presence of chlorine species. Furthermore, under certain conditions, the presence of chlorine enhanced the removal of elemental Hg by additional gas-phase oxidation.     

Effects of Sulfur Dioxide and Nitric Oxide on Mercury Oxidation and Reduction under Homogeneous Conditions

Abstract

This paper is particularly related to elemental mercury (Hg⁰) oxidation and divalent mercury (Hg²⁺) reduction under simulated flue gas conditions in the presence of nitric oxide (NO) and sulfur dioxide (SO₂). As a powerful oxidant and chlorinating reagent, Cl₂ has the potential for Hg oxidation. However, the detailed mechanism for the interactions, especially among chlorine (Cl)-containing species, SO₂, NO, as well as H₂O, remains ambiguous. Research described in this paper therefore focused on the impacts of SO₂ and NO on Hg⁰ oxidation and Hg²⁺ reduction with the intent of unraveling unrecognized interactions among Cl species, SO₂, and NO most importantly in the presence of H₂O. The experimental results demonstrated that SO₂ and NO had pronounced inhibitory effects on Hg⁰ oxidation at high temperatures when H₂O was also present in the gas blend. Such a demonstration was further confirmed by the reduction of Hg²⁺ back into its elemental form. Data revealed that SO₂ and NO were capable of promoting homogeneous reduction of Hg²⁺ to Hg⁰ with H₂O being present. However, the above inhibition or promotion disappeared under homogeneous conditions when H₂O was removed from the gas blend.     

Experimental research of oily sawdust air gasification

This article shows oily sawdust gasification research on countercurrent installation. Experimental research was on a laboratory scale. The main purpose of the experiment was combustible gas production with higher CH₄ concentration. Gas concentrations like CO, CO₂, CH₄, H₂, and C_nH_m determine syngas composition. The technological parameter’s value defines experimental conditions. Value of this was fuel to air ratio. With fuel to air ratio change, syngas composition was a differential phenomenon where it depended on the process parameters like temperature. Additionally, evaluation of methane formation from CO, H₂, and CO₂ was done. Methanization coefficients were based on CO and CO₂ hydrogenation reactions. Component’s activity was in analogs way to syngas components changed.

     

Variability of SO2, CO,and light hydrocarbons over a megacity in Eastern India: effects of emissions and transport

The Indo-Gangetic plain (IGP) has received extensive attention of the global scientific community due to higher levels of trace gases and aerosols over this region. Satellite retrievals and model simulations show that, in particular, the eastern part IGP is highly polluted. Despite this attention, in situ measurements of trace gases are very limited over this region. This paper presents measurements of SO₂, CO, CH₄, and C₂–C₅ NMHCs during March 2012–February 2013 over Kolkata, a megacity in the eastern IGP, with a focus on processes impacting their levels. The mean SO₂ and C₂H₆ concentrations during winter and post-monsoon periods were eight and three times higher compared to pre-monsoon and monsoon. Early morning enhancements in SO₂ and several NMHCs during winter connote boundary layer effects. Daytime elevations in SO₂ during pre-monsoon and monsoon suggest impacts of photo-oxidation. Inter-species correlations and trajectory analysis evince transport of SO₂ from regional combustion sources (e.g., coal burning in power plants, industries) along the east of the Indo-Gangetic plain impacting SO₂ levels at the site. However, C₂H₂ to CO ratio over Kolkata, which are comparable to other urban regions in India, show impacts of local biofuel combustions. Further, high levels of C₃H₈ and C₄H₁₀ evince the dominance of LPG/petrochemicals over the study location. The suite of trace gases measured during this study helps to decipher between impacts of local emissions and influence of transport on their levels.     

The Inhibition of Photochemical Smog

Additional inhibitors for the conversion of NO to NO₂ in C3H6—NO—0₂ irradiated mixtures have been tested at 25°C. These mixtures initially contained 16 mTorr C₃H₆, 8 mTorr NO, 0.012 mTorr NO₂, additive, and enough O₂ to bring the total pressure to 100 Torr. The NO₂ pressure was monitored photometrically. In the absence of additive, the NO₂ pressure first increases with irradiation time reaching a maximum conversion at about 15 minutes. As the irradiation time increases beyond 15 min, the NO₂ pressure drops. Before adding the inhibitors, runs were done with 10 Torr of CO added, and in these runs the conversion was speeded so that the maximum in NO₂ pressure occurred at 10 min. This enhancement in conversion rate is considered to be diagnostic for the presence of HO radicals. Next 10-min irradiations were done with various amounts of hexafluorobenzene (C₆F₆), nitrobenzene (C₆H₅NO₂), or naphtha lene (C₁₀H₈) added. The NO₂ pressure was reduced to one-half its value in the absence of inhibitor with 270 mTorr C₆F₆’, 220 mTorr C₆H₅N0₂, or 4 mTorr C₁₀Hg. The C₁₀H₈ is a very efficient inhibitor, but additions of up to 1 8.5 mTorr C₁₀H₈ did not reduce the N0₂ pressure to zero. Studies of the percent conversion of NO to NO₂ vs. irradiation time were done with either 4.2 mTorr C₁₀H₈ or 40 mTorr 2,6-di-ferf-butyl-4-methylphenol (Ph) added. In the former case the peak conversion was delayed from 15 to 22 min, while in the latter case no delay occurred. However, with the Ph added, there appeared to be some reduction in the maximum value of percent conversion.     

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.     

Nonthermal Plasma Chemical Processing of Bromomethane

ABSTRACT

Nonthermal plasma chemical decomposition of bromomethane (CH₃Br) was investigated with a coaxial type packed-bed plasma reactor. It has been demonstrated that plasma chemical processing is an effective approach to decompose CH₃Br in a wide concentration range. It has been shown that CH₃Br decomposition reactivity depends on reactor operating factors such as background gas, O₂ concentration, and humidification. Higher decomposition efficiencies can be obtained in dry N₂. However, organic byproducts such as BrCN are concurrently produced under deaerated conditions. Water suppresses CH₃Br decomposition and also affects the yields of CO_x (CO and CO₂) and organic byproducts due to the involvement of some active species generated from water. The presence of O₂ retards CH₃Br decomposition by quenching high-energy electrons, while it suppresses organic byproducts and improves CO_x yield. The reacted carbons in CH₃Br are recovered as CO_x almost quantitatively in air. Higher CO₂ selectivities cannot be achieved by increasing O₂ concentration. NO_x formation, which is accompanied by CH₃Br decomposition, can be effectively suppressed by decreasing O₂ concentration down to 2%. Furthermore, reaction mechanisms are discussed by comparing the reactivities of CH₃Br and its congeners.     

Methyl chloride emissions from halophyte leaf litter: dependence on temperature and chloride content

Methyl chloride (CH₃Cl) is the most abundant natural chlorine containing compound in the atmosphere, and responsible for a significant fraction of stratospheric ozone destruction. Understanding the global CH₃Cl budget is therefore of great importance. However, the strength of the individual sources and sinks is still uncertain. Leaf litter is a potentially important source of methyl chloride, but factors controlling the emissions are unclear. This study investigated CH₃Cl emissions from leaf litter of twelve halophyte species. The emissions were not due to biological activity, and emission rates varied between halophyte species up to two orders of magnitude. For all species, the CH₃Cl emission rates increased with temperature following the Arrhenius relation. Activation energies were similar for all investigated plant species, indicating that even though emissions vary largely between plant species, their response to changing temperatures is similar. The chloride and methoxyl group contents of the leaf litter samples were determined, but those parameters were not significantly correlated to the CH₃Cl emission rate.     

Rate Constants for the Reaction of OH with Halocarbons in the Presence of O2 + N2

Rates of CO₂ production in the reaction CO + OH and CO + OH + halocarbon have been used to determine rate constants for some OH + halocarbon reactions at 29.5°C relative to that of k(CO + OH) = 2.69 × 10^?13 cm³ molecule^?1 sec^?1. The following rate constants were obtained: k(OH + CH₃Cl) = 3.1 ± 0.8, k(OH + CH₂Cl₂) = 2.7 ± 1.0, k(OH + C₂H₅Cl) = 44.0 ± 25, k(OH + CICH₂CH₂CI) = 6.5, (<29) and k(OH + CH₃CCl₃) = 2.1 (<5.7) cm³ molecule^?1 sec^?1 × 10^?14. The k values, CH₂Cl₂ excepted, are in substantial agreement with determinations made in nonoxygen environments. The present results for CH₂Cl₂ are almost certainly in error due to difficulties with the competitive approach used.     

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.     

Effect of ethanol addition on soot precursors emissions during benzene oxidation in a jet-stirred reactor

A constant volume reactor model (PSR) was used to investigate the effect of ethanol addition on the formation of some pollutants during benzene oxidation in a jet-stirred reactor. The blended fuels were formed by incrementally adding 4 % wt of oxygen (ethanol) to the neat benzene fuel and by keeping the inert mole fraction (nitrogen) and the equivalence ratio constants. The main objective of this work was to obtain fundamental understanding of the mechanisms through which the oxygenate compound affects soot precursor amounts. The modeling results showed that C₂H₂, C₅H₅, and C₃H₃ mole fractions decreased upon increasing the ethanol percentage in the fuel mixture.     

Application of Computer Controlled High Resolution Mass Spectrometry to the Analysis of Air Pollutants

An AEI-MS9 high resolution mass spectrometer interfaced with a PDP-12 digital computer has been adapted for the multicomponent analysis of air pollutants. Air sampling techniques for particulate and gaseous pollutants have been developed which are compatible with the mass spectrometric system. A single stage impactor has been designed for sampling particulate matter of particle diameters greater than 1–2 μm. The remainder of the particulate matter is collected on a glass fiber filter. Gaseous pollutants are collected on a styrene-divinylbenzene copolymer (Chromosorb 102).

The particulate samples are introduced directly into the mass spectrometer utilizing a temperature programed insertion probe. Gaseous pollutants are desorbed from the copolymer directly into the mass spectrometer by heating. Analysis of composite mass spectral data is facilitated through the use of a digital computer utilizing newly developed computer programs. Final computer output yields qualitative and quantitative results for up to 300 pollutants. Organic pollutants identified in particulate matter include polycyclic aromatic compounds, alkyl chlorides, polychlorinated aromatics, substituted benzenes and organic acids. Composite quantitative results are reported for alkanes and alkenes in the following groups: C₁₅-C₃₀, C₃₀-C₅₀ and Cso-polymeric. Inorganic pollutants identified include As₄O₆, H₂SO_4/ (NH₄)₂SO₄, (NH₄)₂SO₃, NaHSO₄, NH₄NO_3/ NaNO₃, NH₄CI, SeO₂, I₂, elemental sulfur, and elemental cadmium.     

The Inhibition of Photochemical Smog I. Inhibition by Phenol,Benzaldehyde, and Aniline

In urban atmospheres hydrocarbons promote the conversion of NO to NO₂ under the influence of sunlight, ultimately giving rise to photochemical smog. The conversion results from a long chain process with HO radicals as the chain carrier. If this chain could be interrupted by suitable radical traps, the formation of photochemical smog would be inhibited. In this paper we report the results of studies using phenol, benzaldehyde, and aniline as inhibitors. Mixtures containing 16 mTorr C₃H₆, 8 mTorr NO, ～85 Torr 0₂, and the addi tives were irradiated at 25°C. The NO₂ pressure was monitored photometrically. In the absence of additive, the NO2 pressure first increases with irradiation time reaching a maximum conversion corresponding to 70% of the NO at 1 2 minutes. As the radiation time is lengthened, the NO₂ pressure drops. With the additive present, the formation of NO₂ is delayed. The time to reach the maximum percent conversion of NO to N0₂ becomes 20, 22, 31, and 40 minutes respectively, for 13 mTorr C₆H₅OH, 2 mTorr C₆H₅CHO, 8 mTorr C₆H₅CHO, and 4.1 mTorr C₆H₅NH₂ added. The problems and possibilities of adding inhibitors to the atmosphere to control air pollution are discussed.