Effect of matrix on heterogeneous phase chlorine substitution reactions for dibenzo-p-dioxin and HCl in air

Five materials were used in gas-solid phase reactions between dibenzo-p- dioxin(DD) and HCl in order to determine the role of organic and inorganic components in fly ash on chlorine substitution reactions of chlorinated dioxins. The five solids were: granular activated carbon, silica gel, diatomaceous earth, Tenax-GC, and fly ash. Conditions for reactions were 10 min at 150°C with 5% HCl in air. Extent of chlorination was measured using GC/MS analyses of extracts of fly ash after treatment processes and was expressed as the ratio monochloroDD/original unreacted DD. These ratios were: fly ash, 1.082; silica gel, 0.059; activated carbon, 0.024; and Tenax-GC, 0.001. Measurement of similar behavior on diatomaceous earth was impossible since starting material and possible products were irreversibly adsorbed completely. The major chlorinated dioxin produced under these conditions was 2-chlorodibenzo-p- dioxin which is the isomer favored through an electrophilic substitution mechanism.     

Ozonation catalyzed by homogeneous and heterogeneous catalysts for degradation of DEHP in aqueous phase

Di-(2-ethyl hexyl) phthalate (DEHP), a recalcitrant and an endocrine disrupting chemical, was studied for its removal from wastewater by advanced oxidation process. The effects of pH, transition metal ions, and granular activated carbon (GAC) were investigated. Removal of DEHP increased with increase in pH and among metal ions Cr(III) was found to be the most active catalyst to remove DEHP. In the case of GAC, original carbon (G0) and GAC pre-ozonated in gas phase for 10 min (G10) were tested as catalysts in catalytic ozonation and found G0 to be more active than G10. This is because, during pre-ozonation, basic groups like chromene, pyrones and also graphene layers were oxidized to acidic surface oxygen groups. These basic surface groups are reported to be active catalytic centres for ozone decomposition into .OH which is a strong oxidant. According to kinetic manipulations, DEHP degradation rate constant due to .OH was affected by the catalyst while that due to direct ozonation is same in all cases with or without catalyst. G0 was doped with chromia gels (G0/CrA) to combine the benefits of homogeneous and heterogeneous catalysis. G0/CrA showed lower catalytic efficiency than that of only G0. This might be because of changes in surface structure of GAC caused by doping of chromia gel and changes in chemical nature of Cr(III) during formation of gel. A good correlation was found between the rate constants of ozone decay and DEHP degradation (R2=0.96). This correlation confirms that ozone decomposition into .OH is a critical factor for the activity of a catalyst during ozonation.     

Aromatic photonitration in homogeneous and heterogeneous aqueous systems

This work describes the nitration of aromatics upon near-UV photolysis of nitrate and nitrite in aqueous solution and upon photocatalytic oxidation of nitrite in TiO2 suspensions. Phenol is used in this work as a model aromatic molecule and as a probe for *NO2/N2O4. The photoinduced nitration of phenol in aqueous systems occurs upon the reaction between phenol and *NO2 or N2O4, and is enhanced by the photocatalytic oxidation of nitrite to *NO2 by TiO2. Aromatic photonitration in the liquid phase can play a relevant role in the formation of nitroaromatics in natural waters and atmospheric hydrometeors, thus being a potential pathway for the condensed-phase nitration of aromatics. Furthermore, the photoinduced oxidation of nitrite to nitrogen dioxide suggests a completely new role for nitrite in natural waters and atmospheric aerosols.     

Multiphase flow and transport caused by spontaneous gas phase growth in the presence of dense non-aqueous phase liquid

Disconnected bubbles or ganglia of trapped gas may occur below the top of the capillary fringe through a number of mechanisms. In the presence of dense non-aqueous phase liquid (DNAPL), the disconnected gas phase experiences mass transfer of dissolved gases, including volatile components from the DNAPL. The properties of the gas phase interface can also change. This work shows for the first time that when seed gas bubbles exist spontaneous gas phase growth can be expected to occur and can significantly affect water-gas-DNAPL distributions, fluid flow, and mass transfer. Source zone behaviour was observed in three different experiments performed in a 2-dimensional flow cell. In each case, a DNAPL pool was created in a zone of larger glass beads over smaller glass beads, which served as a capillary barrier. In one experiment effluent water samples were analyzed to determine the vertical concentration profile of the plume above the pool. The experiments effectively demonstrated a) a cycle of spontaneous gas phase expansion and vertical advective mobilization of gas bubbles and ganglia above the DNAPL source zone, b) DNAPL redistribution caused by gas phase growth and mobilization, and c) that these processes can significantly affect mass transport from a NAPL source zone.     

Mechanism of the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans from chlorophenols in gas phase reactions

The pyrolysis of chlorinated phenates at a temperature of about 280 degrees C results in the formation of definite chlorinated dibenzodioxin (PCDD) congeners [1-3]. It is shown that in gas phase reactions chlorophenols react in the presence of oxygen above 340 degrees C not only to PCDD but also to chlorinated dibenzofurans (PCDF). The mechanism of this reaction of chlorophenols to PCDD and PCDF was elucidated. In a first step phenoxyradicals are formed which are capable of forming PCDDs and PCDFs. This is confirmed by the oxygen dependency of the reaction. In an argon atmosphere no dimerization of chlorophenols could be observed at 420 degrees C. By the identification of intermediates and by analyzing the PCDF isomers formed from individual chlorophenols the reaction pathway is elucidated. As intermediates in the formation of PCDFs polychlorinated dihydroxybiphenyls (DOHB) were identified. These are most likely formed by the dimerization of two phenoxy radicals at the hydrogen substituted carbons in ortho-positions under simultaneous movement of the hydrogen atoms to the phenolic oxygen PCDDs are formed in the gas phase via ortho-phenoxyphenols (POP) analogous to the pyrolysis of phenates, but due to the radical mechanism in the first condensation step to POPs not only a chlorine atom is capable for substitution but also the hydrogen atoms. The formation of the DOHBs and their condensation to PCDFs and hydroxylated PCDFs as well as the ratio of PCDD to PCDF formed show a strong dependency on the reaction temperature, the substitution pattern of the chlorophenols and the oxygen concentration.     

Transport of volatile compounds in porous media in the presence of a trapped gas phase

The presence of an immobile gaseous phase in an otherwise-saturated porous medium affects the transport of volatile compounds. The linear theory of partitioning tracers suggests that a volatile tracer introduced into such a system should be retarded with a constant retardation factor. Using high concentrations, however, the saturation of the gaseous phase will change as an effect of the tracer test itself. Competitive gas transfer among all volatile compounds and the change of saturation may lead to tracer concentrations that are temporarily higher than those injected. We analyze the system in the framework of the coherence theory by Helfferich [Soc. Pet. Eng. J. 21 (1) (1981) 51]. The governing equations are formulated as functions of total concentration, i.e., the mass of solutes in all phases per pore volume. Neglecting dispersion and mass-transfer kinetics, we derive the characteristic form of the resulting system of hyperbolic equations. In a system with N volatile compounds, a variation of the concentrations splits up into N waves, each traveling with its own characteristic velocity. If the presence of a gaseous phase is sustained, one wave will be a standing one. We perform numerical model calculations for tracers with various Henry's law coefficients and show that the results agree with the semi-analytical solution obtained by coherence theory.     

两相均流板对弯管中气固两相运动分布特征的影响

针对燃煤电厂烟气污染物脱除系统设备入口弯管内的气固两相分布不均的问题,提出一种两相均流板,采用CFD数值模拟的方法对比分析了安装两相均流板与常规导流装置的弯道内气流速度分布、颗粒质量浓度分布以及弯管进出口压差变化特征。结果表明：在弯管内安装两相均流板较安装导流板/三角翼挡板更优,既可以使气固两相均匀分布又可以有效降低系统的压阻,克服了常规均流装置气固两相均流效果不佳、阻力大等缺点,在较低的压阻下解决燃煤电厂烟气污染物脱除系统入口气固两相混合不均匀的问题,有效提高污染物脱除效率。     

Combustion and thermal destruction of hexanes in the presence of inorganic and organic chlorine

Hexane was burned in an atmosphere containing an equal molar quantity of hydrogen chloride. Combustion characteristics and partial combustion products were compared to the combustion of pure 1-chlorohexane in air. The product distribution and burning properties were nearly identical.     

Degradation of some biorecalcitrant pesticides by homogeneous and heterogeneous photocatalytic ozonation

Photo-Fenton/ozone (PhFO) and TiO2-photocatalysis/ozone (PhCO) coupled systems are used as advanced oxidation processes for the degradation of the following biorecalcitrant pesticides: alachlor, atrazine, chlorfenvinfos, diuron, isoproturon and pentachlorophenol. These organic compounds are considered Priority Hazardous Substances by the Water Framework Directive of the European Commission. The degradation process of the different pesticides, that occurs through oxidation of the organic molecules by means of their reaction with generated OH radical, follows a first and zero-order kinetics, when PhFO and PhCO are applied, respectively. These two Advanced Oxidation Processes, together with the traditional ozone+UV, have been used to investigate TOC reduction of the different pesticide aqueous solutions. The best results of pesticide mineralization are obtained when PhFO is applied; with the use of this advanced oxidation process the aqueous pesticide solutions become detoxyfied except in the case of atrazine and alachlor aqueous solutions for which no detoxification is achieved at the experimental conditions used in the work, at least after 2 and 3 h of treatment, respectively.     

Homogeneous and heterogeneous reactions of phenanthrene with ozone

The reactions of gas-phase phenanthrene and suspended phenanthrene particles with ozone were conducted in a 200l chamber. The secondary organic aerosol formation was observed in the reaction of gas-phase phenanthrene with ozone and simultaneously the size distribution of the secondary organic aerosol was monitored with a scanning mobility particle sizer during the formation process. The particulate ozonation products from both reactions were analyzed with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. 2,2′-Diformylbiphenyl was identified as the dominant product in both homogeneous and heterogeneous reactions of phenanthrene with ozone. GC/MS analysis of ozonation products of phenanthrene in glacial acetic acid was carried out for assigning time-of-flight mass spectra of reaction products formed in the homogeneous and heterogeneous reactions of phenanthrene with ozone.     

Oxidative degradation of 2,4-xylidine by photosensitization with 2,4,6-triphenylpyrylium: homogeneous and heterogeneous catalysis

The possibility of using zeolites containing the 2,4,6-triphenylpyrylium cation as photocatalysts for the degradation of pollutants has been tested on aqueous xylidine (2,4-dimethylaniline) solutions as models for contaminated wastewaters. The influence of the photocatalyst and substrate concentrations on xylidine oxidation has been investigated in homogeneous solution, by performing a series of experiments chosen according to the experimental design methodology (Doehlert uniform array). The empirical models and the corresponding response surfaces obtained from data analysis have been used for simulating and predicting degradation efficiency. The results have shown that conversion increases with increasing amounts of photocatalyst and decreasing concentration of the model pollutant. The fluorescence of 2,4,6-triphenylpyrylium was quenched by xylidine with a rate constant k(q) of 3.1x10(9)M(-1)s(-1). This result suggests a direct electron transfer between the excited pyrylium salt and xylidine. Because of the limited stability of the photocatalyst in homogeneous media, a pyrylium containing Y-zeolite has been tested for the photocatalytic oxidation of xylidine under heterogeneous conditions. The results suggest that the supported catalyst has a much improved stability and that xylidine oxidation rates remain nearly constant during the whole reaction time. An additional advantage of the pyrylium containing zeolite photocatalyst is that it can be recycled and used for further experiments.     

Synergistic effects of liquid and gas phase discharges using pulsed high voltage for dyes degradation in the presence of oxygen

The technology of combined liquid and gas phase discharges (LGD) using pulsed high voltage for dyes degradation was developed in this study. Apparent synergistic effects for Acid orange II (AO) degradation in the presence of oxygen were observed. The enhancement of AO degradation rate was around 302%. Furthermore, higher energy efficiency was obtained comparing with individual liquid phase discharge (LD) or gas phase discharge process (GD). The AO degradation in the presence of oxygen by LGD proceeded through the direct ozone oxidation and the ozone decomposition induced by LD. Important operating parameters such as electrode distance, applied voltage, pulse repetition rate, and types of dyes were further investigated.     

贵州地区大气汞污染及湿法脱硫装置除汞效果的初步评价

2004年冬季在贵州地区对大气中气态元素汞进行了大范围的流动监测调查,重点监测电厂分布地区及东部汞采冶加工地区,结果表明,气态元素汞浓度的高值出现在汞化工区和金矿区;在广大农村地区和小县城附近,大气汞浓度大都在100 ng/m3范围内.同期还进行了大气颗粒物汞的采样和分析,结果表明,监测到的大气颗粒物的汞浓度水平＜3 ng/m3,与国内其他一些城市相当;细颗粒物中汞的富集度高,粒径＜2.2 μm的颗粒物汞占60%～80%.此外,实测了采用石灰-石膏法脱硫电厂的燃煤汞平衡,评价了汞去除效果,结果表明,燃煤中的汞大约20%留在灰渣中,石灰-石膏脱去约20%,约59%的汞通过烟气排放到空气中.     

气体二氧化氯对图书馆空间环境的消毒研究

选用高纯气体二氧化氯作为杀菌消毒剂,以中北大学图书馆阅览室作为研究对象,采用五点梅花法对空气中细菌进行采样,平板涂布法对采集到的细菌进行计数.通过研究不同气体二氧化氯浓度和杀菌时间条件下,气体二氧化氯对图书馆阅览室的杀菌效果,得出气体二氧化氯在低浓度下灭活细菌的最佳条件,即气体二氧化氯质量浓度为0.3 mg/m3、杀菌...     

Modeling heterogeneous ClNO2 formation,chloride availability,and chlorine cycling in Southeast Texas

Nitryl Chloride (ClNO₂) mixing ratios above 1 ppbv have been measured off the coast of Southeast Texas. ClNO₂ formation, the result of heterogeneous N₂O₅ uptake on chloride-containing aerosols, has a significant impact on oxidant formation for the Houston area. This work reports on the modeling of ClNO₂ formation and describes the sensitivity of ClNO₂ formation to key parameters. Model sensitivity analyses found that: (1) Chloride availability limits the formation of nitryl chloride at ground level but not aloft; (2) When excess particulate chloride was assumed to be present at ground level through sea salt, ClNO₂ concentrations increased in some locations by a factor of 13, as compared to cases where sea salt chloride was assumed to be limited; (3) Inland formation of ClNO₂ seems feasible based on chloride availability and could have a large impact on total ClNO₂ formed in the region; and (4) ClNO₂ formation is quite sensitive to the assumed yield of ClNO₂ from N₂O₅ uptake. These results demonstrate that there is a need for further field studies to better understand the geographic extent of ClNO₂ formation and the atmospheric conditions which control partitioning of chloride into the particle phase. In addition, this work examined the role of ClNO₂ in the cycling of chlorine between chloride and reactive chlorine radicals. The modeling indicated that the majority of reactive chlorine in Texas along the Gulf coast is cycled through ClNO₂, demonstrating the importance of including ClNO₂ into photochemical models for this region.     

Carbonaceous aerosol in jet engine exhaust: emission characteristics and implications for heterogeneous chemical reactions

Characteristic parameters of black carbon aerosol (BC) emitted from jet engine were measured during ground tests and in-flight behind the same aircraft. Size distribution features were a primary BC mode at a modal diameter D≈0.045 μm, and a BC agglomeration mode at D<0.2 μm. The total BC number concentration at the engine exit was 2.9×10⁷ cm^-3 with good agreement between model results and in-flight measured number concentrations of non-volatile particles with D⩾0.014 μm. A comparison between total number concentration of BC particles and the non-volatile fraction of the total aerosol at the exit plane suggests that the non-volatile fraction of jet engine exhaust aerosol consists almost completely of BC. In-flight BC mass emission indices ranged from 0.11 to 0.15 g BC (kg fuel)^-1. The measured in-flight particle emission value was 1.75±0.15×10¹⁵ kg^-1 with corresponding ground test values of 1.0–8.7×10¹⁴ kg^-1. Both size distribution properties and mass emission indices can be scaled from ground test to in-flight conditions. Implications for atmospheric BC loading, BC and cirrus interaction and the potential of BC for perturbation of atmospheric chemistry are briefly outlined.     

Modeling solute transport in one-dimensional homogeneous and heterogeneous soil columns with continuous time random walk

In this paper, we used the continuous time random walk (CTRW) framework to characterize the transport process in 1250-cm long one-dimensional homogenous and heterogeneous soil columns at the experiments conducted by Huang et al. [Huang, K., Toride, N., van Genuchten, M.Th., 1995. Experimental investigation of solute transport in large, homogeneous and heterogeneous, saturated soil columns. Trans. Porous Media. 18, 283-302]. The transport process was also simulated by using the advection-dispersion equation (ADE) and the spatial fractional advection-dispersion equation (FADE) for comparison. In the homogeneous soil column, the non-Fickian behavior is found at the distances less than 1000cm with beta values larger than 1.60, but less than 2, and Fickian form transport is obtained at distances larger than 1000cm with beta values larger than 2. In the heterogeneous soil column, we found the most anomalous behavior at distances from 200cm to 700cm with beta values ranging from 0.894 to 0.958, and non-Fickian transport process is observed at distances larger than 800cm with beta values in the range between 1 and 1.3. More significant non-Fickian behavior is found for transport in the heterogeneous soil column than that in the homogeneous soil column. The CTRW fits to the breakthrough curves (BTCs) have lower values of root mean square error (RMSE) and higher values of determination coefficient (r(2)), with respect to the fits of ADE and FADE. The CTRW model also is better captures the full evolution of BTCs, and especially their tails.     

Influence of permeability on nanoscale zero-valent iron particle transport in saturated homogeneous and heterogeneous porous media

Environmental Science and Pollution Research - Nanoscale zero-valent iron (NZVI) particles can be used for in situ groundwater remediation. The spatial particle distribution plays a very important...     

Decarboxylation and alkaline colour fading reactions in presence of humic substances

Humic substances (HSs) can substantially influence velocity of reactions in the environment as shown on example of decarboxylation and alkaline colour (e.g., malachite green and crystal violet) fading reactions. In colour fading and decarboxylation reactions of 6-nitrobenzisoxazole-3-carboxylic acid HS act as inhibitors, but additions of surfactants change the pattern of reaction. The inhibitory activity of HSs much depends on their origin. The velocity of studied reactions depends also on pH, temperature and concentration of HS used. Possible micellar catalysis mechanism has been suggested.     

Gas phase ozonolysis of camphene in the presence of SO2

Gas phase ozonolysis of camphene in air results in a 1:1 mixture of camphenilone and 6,6-dimethyl-ϵ-caprolactone-2,5-methylene. In the presence of SO₂ (0.4 mg/10 ℓ), the product ratio rises to 8:1. This seems to indicate that the Criegee diradical oxidizes SO₂ to SO₃ prior to cyclization to dioxirane.