Decomposition of Chlorinated Hydrocarbons on Iron-Group Metals

The decomposition of 1,2-dichloroethane and chlorobenzene on nickel–alumina, cobalt–alumina, and iron–alumina catalysts at 400–600°C was studied. Thermodynamic calculations demonstrated that the susceptibility of metals to chlorination under exposure to HCl increases in the order Ni < Co < Fe. The addition of hydrogen to the reaction mixture was found to dramatically decrease the rate of carbon deposition in the decomposition of 1,2-dichloroethane because of the intense hydrogenation of intermediates that are graphite precursors. Two fundamentally different reaction paths were found in the degradation of 1,2-dichloroethane: decomposition via a carbide-cycle mechanism with the formation of carbon as the main product (under conditions of a deficiency of hydrogen) and 1,2-dichloroethane hydrodechlorination accompanied by methanation of the formed carbon (under conditions of an excess of hydrogen). The degradation of chlorobenzene diluted with hydrogen in a molar ratio of 1 : 50 was not accompanied by carbon formation on the catalyst. A comparison between the selectivity for reaction products on nickel–alumina and cobalt–alumina catalysts indicated that the former catalyst is more active in the rupture of C–C bonds and in the methanation reaction of deposited carbon, whereas the latter is more favorable for hydrodechlorination. The optimum conditions and thermal regime for efficient and stable operation of the catalysts were found.     

Distribution of Chlorinated Hydrocarbons in Different Ecosystems in Germany

Abstract

The German Environmental Specimen Bank (GESB) was established in 1985 as a permanent institution for the systematic collection, processing, characterization and storage of representative environmental samples from different ecosystems throughout Germany. Immediately after the reunification a special sampling campaign was performed in representative areas of the former GDR focusing on the assessment of the environmental pollution situation. These samples can be regarded as a basis for monitoring the development of spatial and temporal trends in Eastern Germany. Selected results about the determination of chlorinated hydrocarbons (CHC) in various bioindicators (earthworms, pigeon eggs, poplar leaves, pine shoots, breams) are presented. Particular emphasis is given to the comparsion of the CHC burden in East and West Germany with respect to different contamination sources.     

Determination of Nonpolar Chlorinated Hydrocarbons and PCB in Microsamples

Abstract

Analysis of small samples of fish eggs, rat brain sections and aquatic macro-invertebrates for 78 PCB congeners, hexachlorobenzene, octachlorostyrene, p, p′-DDE and mirex is described. With a gas chromatograph equipped with an Apiezon L coated glass capillary and electron capture detector capable of determining 10 ng/ml of analyte in hexane, a 10 mg sample may be analyzed with a precision of better than ±5% relative standard deviation.     

A Mid-Infrared Sensor for Monitoring of Chlorinated Hydrocarbons in the Marine Environment

Abstract

As part of the European research project SOFIE - “Spectroscopy using Optical Fibres in the Marine Environment”, a portable sensor system for chlorinated hydrocarbons in seawater is being developed. This novel analytical tool for real-time in-situ monitoring of a particularly important class of seawater pollutants consists of a robust, miniaturised FT-IR spectrometer in a sealed aluminium pressure vessel and a fibre optic sensor head. In a laboratory set-up using an ATR-crystal as a simplified sensor head, the effect of potentially interfering substances, both of natural and anthropogenic origin, on the sensor response was tested. It was found that the sensor readings for a specific analyte are not susceptible to aliphatic and aromatic components as well as other chlorinated hydrocarbons up to concentrations well above the average levels to be encountered in the oceans. The same applies for the parameters salinity and turbidity. Consequently, the proposed sensor system should be well suited for real-world sub-sea applications.     

Chlorinated Hydrocarbons: Pollutants or Indicators of Fish Stock Structure

Abstract

Chlorinated hydrocarbons are used in industry for many purposes. They are ubiquitous in the environment. Being soluble in lipids, they tend to accumulate in living organisms and consequently in the food chain. In an attempt to identify the herring stock units (Clupea harengus harengus) present in the St. Lawrence Estuary and the Chaleur Bay, we have measured the degree of contamination by some organochlorinated compounds, of herrings fished in both locations. The purpose of the study is to establish the presence of many discrete stocks units or of only one homogeneous stock brought about by large scale straying of individuals from one group to another. Adult herrings are thought to migrate to spawning areas in spring or autumn depending on whether they were born in spring or autumn. The juveniles are believed to remain close to where they were born for about three years before they join their parent stock migrations. If one area is contaminated by chlorinated pesticides, these products will accumulate in the herring fat and could possibly be used for fingerprinting if straying is negligible. The data obtained indicate that the populations studied are marked by their environment and that they probably have their own life cycle and their own migration pattern. A study of the genetic structure of these herring populations is being concurrently made.     

Determination of Chlorinated Hydrocarbons Using Sep-Pak Cartridges and Gas Chromatography

Methods are described for the determination of chlorinated hydrocarbons at levels of parts per billion in water and nonaqueous environmental samples by gas chromatography with electron-capture detection. C₁₈, Florisil, alumina N and silica Sep-Pak cartridges were compared to evaluate their cleanup ability. The accuracy of the results of this analytical technique was proved by the analysis of a certified reference material (lake sediment EC-2).     

Chlorinated Organic Compounds Decomposition in a Dielectric Barrier Discharge

The decomposition of chlorinated volatile organic compounds by non-thermal plasma generated in a dielectric barrier discharge was investigated. As model compounds trichloroethylene (TCE) and 1,2-dichloroethane (DCE) were chosen. It was found that TCE removal exceeds 95% for input energy densities above 0.2 eV/molecule, regardless of the initial concentration of TCE, in the range 100–750 ppm. On the other hand, DCE was more difficult to decompose, the removal rate reached a maximum of 60% at the highest input energy used. For both investigated compounds the selectivity towards carbon dioxide was significantly influenced by their initial concentration, increasing when low concentrations were used. The gas flow rate had also an effect on CO₂ selectivity, which is higher at low flow rate, due to the higher residence time of the gas in the plasma. The best values obtained in these experiments were around 80%.     

Specific Features of Alkylation of Organic Hydroperoxides with Chlorinated Hydrocarbons in Superbasic Media

Alkylation of organic hydroperoxides with chlorinated hydrocarbons in superbasic media (dipolar nonhydroxyl solvent-strong ionic base) was performed.     

Adsorption/Thermal Desorption with Tenax-GC for the Collection and Analysis of Polycyclic Aromatic Hydrocarbons and Chlorinated Compounds

A system for the determination of polycyclic aromatic hydrocarbons(PAHs) and chlorinated compounds in air by means of adsorption/thermal desorption(ATD) with small bed volume (0.1 g) Tenax cartridges, followed by cryogenic trap in a U-shaped stainless steel tube with liquid nitrogen as an appropriate concentration method prior to capillary gas chromatography is described. Recoveries were determined for the complete ATD method. Desorption recoveries near 100% were found for a variety of chlorinated compounds and polycyclic aromatic hydrocarbons.     

滑动弧电极放电等离子体作用甲烷制C2烃的工艺

采用刀片式不锈钢电极放电反应器,以Ar气为稀释气,研究了等离子体作用下甲烷转化制C2烃的工艺条件。考察了CH4流量、高频电源输入电压和电极间距等参数对甲烷转化率、C2烃选择性、收率和反应表观能耗的影响。结果表明,增加CH4流量,表观能耗随之降低;当输入电压和电极间距较小时,甲烷转化率随输入电压和电极间距的增大而增大,但输入电压和电极间距过大时,C2烃收率明显下降,积碳严重。在CH4流量14 mL/min、Ar气流量60 mL/min、高频电源输入电压22 V、电流0.44 A、电极间距4 mm的优化条件下,甲烷最高转化率为43.1%,C2烃收率、选择性和表观能耗分别为40.1%、93.2%和2.41 MJ/mol。C2烃中不饱和烃的体积分数可达95%以上。     

Comparative Analysis of the Dehydrogenation of Hydrocarbons and Alcohols in a Membrane Reactor

Kinetics and Catalysis - Membrane technologies are widely used in various modern technological processes. In the chemical industry, membranes are used to solve several problems from increasing the...     

A Reactive Molecular Dynamics Study of Chlorinated Organic Compounds. Part II: A ChemTraYzer Study of Chlorinated Dibenzofuran Formation and Decomposition Processes

In our two-paper series, we first present the development of ReaxFF CHOCl parameters using the recently published ParAMS parametrization tool. In this second part, we update the reactive Molecular Dynamics – Quantum Mechanics coupling scheme ChemTraYzer and combine it with our new ReaxFF parameters from Part I to study formation and decomposition processes of chlorinated dibenzofurans. We introduce a self-learning method for recovering failed transition-state searches that improves the overall ChemTraYzer transition-state search success rate by 10 percentage points to a total of 48 %. With ChemTraYzer, we automatically find and quantify more than 500 reactions using transition state theory and DFT. Among the discovered chlorinated dibenzofuran reactions are numerous reactions that are new to the literature. In three case studies, we discuss the set of reactions that are most relevant to the dibenzofuran literature: (i) bimolecular reactions of the chlorinated-dibenzofuran precursors phenoxy radical and 1,3,5-trichlorobenzene, (ii) dibenzofuran chlorination and pyrolysis, and (iii) oxidation of chlorinated dibenzofurans.     

Decomposition of Benzene in Air in a Plasma Reactor: Effect of Reactor Type and Operating Conditions

The decomposition of benzene was carried out in two types of plasma reactors packed with BaTiO₃ pellets: one reactor had two stainless steel electrodes (SUS reactor), and the other reactor had a glass layer between two concentric electrodes (GL reactor). The decomposition efficiency and the suppression of formation of N₂O and NO_x were greater in the GL reactor than in the SUS reactor. In contrast, the suppression of O₃ formation and the oxidation to CO_x in the SUS reactor were superior to those in the GL reactor. The effect of wa eform and frequency of applied ac power was in estigated for each reactor.     

固定床反应器中Ti-MWW催化H2O2分解

在固定床反应器中,H2O2与Ti-MWW分子筛的接触时间越长,其分解率越高.结果表明,分子筛骨架Ti和其拥有的酸性位是造成H2O2在分子筛上分解的主要原因,非骨架Ti对H2O2分解的影响弱于骨架Ti.H2O2的无效分解直接影响反应物的转化效率.了解H2O2无效分解的原因,有利于设计出高活性钛硅分子筛.同时在固定床中研究钛硅分子筛催化分解H2O2的反应有可能成为一种评价钛硅分子筛催化活性的新方法.     

Laboratory Reactor for Visual Examination of Formation/Decomposition of Gas Hydrates in Water-Oil Systems

Russian Journal of Applied Chemistry - Design of an installation for studying the formation and decomposition of gas hydrates in water-oil systems via visual examination and video recording under...     

Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor

The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO ₃ pellets. Lattice oxygen species in BaTiO ₃ play an important role in the formation of N ₂ O and the oxidation of CH ₄ . The oxidation products such as CO and CO ₂ were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N ₂ O and NO _x were independently formed in the N ₂–O ₂ reaction, suggesting that different oxygen species give N ₂ O and NO _x. N ₂ O was produced by the oxidation of molecular nitrogen with lattice oxygen species.     

共沉淀镍催化剂用于膜反应器中高碳烃类燃料水蒸气重整反应

 采用共沉淀法制备了NiO/La-Al2O3催化剂,利用低温N2物理吸附、程序升温还原、 H2-O2化学吸附和X射线衍射对催化剂进行了表征,并将该催化剂应用于Pd膜反应器中高碳烃类燃料水蒸气重整反应. 结果表明,催化剂中NiO与载体间存在较强的相互作用. 与常规固定床反应器相比,在膜反应器中,由于高渗透性能的Pd金属复合膜能选择分离氢气,结果氢气产率得到了明显的提高,甲烷的生成得到了有效抑制,并且在接近实用的反应条件下,依然能够得到高的氢气产率和回收率. 高碳烃类燃料水蒸气重整反应制氢的过程可以在一个膜反应器中,利用一种催化剂在反应温度低于823 K的温和条件下实现.