Role Of Chlorine Research Articles

Impact of chlorine and acidification in the electrochemical treatment of tumours

Electrochemical treatment (EChT) of tumours offers considerable promise as a safe, simple and relatively noninvasive antitumour therapy. When platinum is used as electrode material, the major electrochemical reactions at the anode are chlorine and oxygen evolution. Conflicting opinions can be found in the literature over the role of chlorine in the underlying destruction mechanism behind EChT. In this present study, the impact of chlorine in EChT treatments is investigated by means of mathematical modelling. The analysis focuses on the tissue surrounding a spherical platinum anode when applying a constant current density. Tissue is modelled as an aqueous solution of sodium chloride containing a bicarbonate buffer system and organic constituents susceptible to reactions with chlorine. Except for the case of very low anode current densities, the simulations clearly show that it is the spreading of hydrogen ions – and not chlorine molecules – that determines the extent of tissue destruction around the anode. Moreover, it is found that the reactions of chlorine with tissue play important roles as generators of hydrogen ions. The contribution of these reactions to the acidification of tissue, surrounding the anode, is strongly dependent on the applied current density and increases with decreasing current density.

The Role of Chlorine in Dioxin Formation

There is poor correlation between total chlorine in waste streams and formation of polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/F) during waste combustion. This is because the active chlorine (Cl) species are strongly dependent upon combustion conditions. For homogeneous conditions, trace amounts of a hydrocarbon species (benzene) injected into the effluent from complete combustion of a mixed chlorocarbon fuel (ethylene and chloromethane) results in formation of stable, oxygenated and chlorinated compounds. This occurs over a broad range of temperatures (400–900°C), provided that a fraction of the system chlorine is in the Cl radical form. Cl is the only form in which chlorine can react, in gas-phase, with stable hydrocarbon species, and these reactions are very fast, even in the low temperature regime. Molecular chlorine (Cl2) may subsequently participate in reactions with carbon-based radicals, and these reactions are the primary source of chlorinated products. Hydrogen chloride (HC1)—the major chlorine species in the products—can react with oxidizing radicals (eg, OH) and promptly form significant amounts of Cl. Gas temperature has a great influence on the final distribution of products. At 800–900°C, practically all of the benzene which was attacked by Cl is converted to carbon monoxide and small unsaturated hydrocarbons by subsequent reactions with oxygen. At about 750°C, measurable concentrations of chlorobenzenes are formed. At lower temperatures (400–600°C), chlorophenols become a large fraction (up to 15%) of the total reacted benzene. Heterogeneous reactions result in the formation of Cl2 through catalyzed reactions (most actively by copper salts) and promotion of carbon-Cl bond formation. The latter is dependent on the ash surface species and type, ash adsorptive characteristics, temperature, and presence of regenerative Cl in the waste combustion products.

Use of XAFS Spectroscopy for Element Speciation in Environmentally Important Energy-Related Materials

The determination of element speciation in environmentally important materials is often critical for understanding (i) the threat to human health posed by a specific element, and (ii) the means to minimize the environmental impact of an element during processing or in waste disposal after processing. In this overview, the use of X-ray Absorption Fine Structure (XAFS) spectroscopy is described for speciation determinations of specific elements in complex solid materials of importance to various environmental and energy issues, viz. coal combustion byproducts (ash), carbon-based sorbents for mercury capture from combustion flue gases, and airborne fine particulate matter (PM). Among the topics discussed are: the occurrence of hexavalent chromium and other potentially hazardous elemental oxidation states in coal combustion ash ; the role of chlorine, sulfur, etc., in the sorption of mercury from flue gases on carbon-based sorbents; and the occurrence of various elements such as sulfur, chromium, arsenic, halogens, etc., in National Institute of Standards and Technology (NIST) Urban and Diesel particulate matter standard reference materials, SRM 1648 and SRM 1650, respectively.

Role of Chlorine and Oxygen in the Photocatalytic Degradation of Trichloroethylene Vapor on TiO2 Films

The photocatalytic degradation of trichloroethylene (TCE) was investigated with ring-roughened annular reactors. Anatase titanium dioxide films were immobilized by chemical vapor deposition using titanium tetraisopropoxide as the source of titanium. Experimental variables included TCE concentration (0.1−10 parts per million by volume or ppmv), oxygen content (20−200 000 ppmv), residence time (2.46−9.57 s), and reactor length. In general, TCE conver sion increased with increasing values of all of these variables up to a maximum of 99.4% within the range investigated. Ten chlorinated organic intermediates/products were observed primarily at low oxygen concentrations. Among these compounds, carbon tetrachloride, chloroform, hexachloroethane, pentachloroethane, and tetrachloroethylene were present at quantifiable levels. Additional experiments revealed that pentachloroethane and tetrachloroethylene also decomposed with degradation efficiencies (up to 98 and 94%, respectively) being somewhat lower than that for TCE. Chloroform conversions were low (up to 30%), and no appreciable degradation of carbon tetrachloride was observed for the range of operating conditions investigated. Chlorinated organic intermediate/product formation was the result of various reactions involving chlorine and hydrogen atom extractions and additions. Chlorine atom attack reactions were inhibited in the presence of relatively high oxygen concentrations including that in ambient air due to the predominance of competing oxidation reactions involving unidentified reactive oxygen species.

The role of chlorine in high temperature corrosion in waste-to-energy plants

High temperature corrosion has been a serious problem in municipal solid waste (MSW) incinerators since the emergence of waste-to-energy (WTE) plants in the 1960s. Early researchers conjectured that corrosion was caused by sulfur compounds, but it soon became evident that the dominant corrosive species are chlorides, typically in combination with alkali metals (Na, K) and heavy metals (Pb, Zn). Yet, many uncertainties remain with respect to the complex interactions between metallic materials of construction and their corrosion products with aggressive species in the combustion atmosphere and in fireside deposits. Following a review of historical background, MSW incineration technology and refuse boiler materials/corrosion, this paper will examine the causes and mechanisms of high temperature corrosion in WTE plants, as well as the environmental and alloy-related factors affecting metal wastage. Attention will be called to remaining uncertainties regarding corrosion mechanisms, and to apparent incongruities and conflicting data on materials performance to help identify areas for further R&D.

On the Role of Chlorine in Selective Silicon Epitaxy by Chemical Vapor Deposition

Si thermal etching studies have been performed using pure in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor in the temperature range of 650–850°C and the flow rate range of 1–10 sccm which corresponds to a pressure range of 0.5–3.5 mTorr. The effects of temperature and flow were investigated with thermodynamic equilibrium calculations performed to determine possible reaction pathways. The effect of adding , up to 500 sccm, on Si etch rates at 800 and 850°C was also obtained experimentally. Thermodynamic equilibrium calculations were used to support the experimental results and determine the reaction by‐products. It is proposed that equilibrium partial pressure can be used as a means to compare the etching ability, thus the selectivity, of different selective Si processes. The results from the etching studies were used to explain the behavior of Si epitaxy growth rate from the and system in the 650–850°C, 22–24 mTorr processing regime. The implications of the etching studies for selective silicon epitaxy with the and chemistry are discussed and then extended to the based chemistry.

The Role of Chlorine in Stratospheric Chemistry

Abstract The chlorofluorocarbons (CFCs) are industrialchemicals used as solvents, refrigerants, plastic foam blowing agents,etc. These compounds are eventually released to the environment; theyslowly drift into the stratosphere, where they decompose, initiatinga catalytic process involving chlorine free radicals and leading toozone destruction. The stratospheric ozone layer is important for theearth's energy budget, and it shields the surface of the earth fromultraviolet radiation from the sun. Very significant depletion of theozone layer has been observed in the spring months over Antarctica duringthe last 10-15 years. Laboratory experiments, model calculations andfield measurements, which include several aircraft expeditions, haveyielded a wealth of information which clearly points to the CFCs asthe main cause of this depletion.

Assessment of chlorine exposure in swimmers during training.

The presence of a high prevalence of bronchial hyperresponsiveness and asthma-like symptoms in swimmers has been recently reported. Chlorine, a strong oxidizing agent, is an important toxic gas that the swimmer can breath during swimming. Measurements of the chlorine concentration at the breathing level (< 10 cm) were obtained randomly during five nonconsecutive days in four different swimming pool enclosures. The mean level in all the swimming pools was 0.42 +/- 0.24 mg.m-3, far below the threshold limited value (TLV) of 1.45 mg.m-3 for the work places for a day of work (8 h). The TLV could be reached and even exceeded if we consider the total amount of chlorine that a swimmer inhales in a daily training session of 2 h (4-6 g) compared with a worker during 8 h at the TLV (4-7 g). Low correlation was observed with the number of swimmers in the swimming pool during the measurements (0.446) and other variables as the water surface area of the pool, volume of the enclosure, and the chlorine-addition system in the swimming pool. A low turnover rate in the air with an increase of chlorine levels through the day (P < 0.05) was observed in all pools. The concentration of chlorine in the microenvironment where the swimmer is breathing is below the TLV concentration limit, but nevertheless results in a high total volume of chlorine inhaled by the swimmers in a given practice session. The possible role of chlorine in producing respiratory symptoms in swimmers needs further investigation.

The Role of Chlorine in Induction Periods During the Oxidation of Methane over Pd/SiO 21

The effect of chlorine elimination from Pt-Sn catalyst on the behavior of hydrocarbon reconstruction in propane dehydrogenation was investigated. The results showed that the chlorine elimination significantly affects multiple characteristics of the catalysts, the type of Pt active phases, and the behavior of hydrocarbon reconstruction. There was no apparent change in catalyst structure. In contrast, the acidity of the catalyst, its specific surface area, and pore volume remarkably decreased whereas its mean pore diameter increased under the same conditions. The degree of Pt sintering, which is disadvantageous to the reaction, was also aggravated. The chlorine elimination also influenced the behavior of hydrocarbon reconstruction in propane dehydrogenation and demonstrated a crucial function in determining selectivity as evidenced by coking experiments. In this work, a strong correlation was established to demonstrate the relation between the structure of Pt active phase and the behavior of hydrocarbon reconstruction in propane dehydrogenation. It is an optimum progress that the chlorine elimination conditions of the Pt active phases centered on the Pt(100) surfaces and the PtSnK/Al2O3 exhibited the best catalytic performance and a low coking rate. Finally, a new model was established to describe the influence of chlorine elimination on the interactions between Pt and SnOx.

The role of chlorine in methane coupling perovskite catalysts

ABO 3 perovskite ( A = Ca, Sr, Ba; B = Ti, Zr) has been prepared by a sol-gel method from oxygenated (I) or chlorinated (II) precursors. The difference in C 2-hydrocarbon selectivity depending on the preparation mode is ascribed to the presence of chlorine. To understand the effect of chlorine, the various catalysts have been characterized by XRD, BET, O 2 temperature programmed desorption. Addition of organic chlorinated compounds as probe molecules have been studied and compared on catalysts I and II.

A computational study of the role of chlorine in the partial oxidation of methane by MgO and Li/MgO

We investigate the surface defect chemistry of MgO and Li/MgO paying special attention to the effects of added chloride ions on the active sites in the materials when used as partial oxidation catalysts. We calculate that chloride ions will segregate to the surface of these materials and will be preferentially sited at low coordinate sites. The [LiCl] defect cluster is also calculated to be bound, both of which effects will have a major influence on catalytic properties. From our calculations we also comment on the siting and selectivities of the active sites in MgO and Li/MgO.

The roles of chlorine and sulfur in bimetallic Pt-Re/Al 2O 3 reforming catalyst

Factors affecting rhenium reduction and the degree of bimetallic cluster formation were studied for Pt-Re/Al 2O 3catalysts. Temperature programmed reduction (TPR) and X-ray absorption near edge structure (XANES) were used to examine Pt catalyzed reduction of Re following a series of thermal pretreatments and suggest that chloride on the Al 2O 3 support plays a major role in Pt-Re alloying during reduction. A critical review of published data on the role of chloride and sulfur and their interaction with both the precursors and metal cluster to form an active reforming catalyst is also presented. To minimize yield-octane loss via hydrocracking, hydrogenolysis and low activity, the active metal sites of Pt-Re/Al 2O 3 catalysts must be carefully constructed so as to maximize the number of well-dispersed Pt-Re alloy clusters and essentially eliminate the presence of isolated Re atoms. Alloy clusters are formed by the catalytic reduction of Re species by immobile Pt°, and the Re species must be mobile on the alumina surface. Two mobile Re species are believed to exist, a hydrous Re oxide and a Re oxychloride. Pt°-catalyzed reduction of hydrous Re oxide, a wet reduction, is undesirable for two reasons. Water strips chloride from the alumina and can remove Re from Pt-Re alloy clusters. For the preferred dry reduction of a Re oxychloride to be successful, it is critically important that there be adequate Cl to provide Re mobility. Experimental data generated by TPR and XANES support this reasoning. The function of the S added to Pt-Re/Al 2O 3 catalyst is to confine activity of the Pt to hydrogenation- dehydrogenation. It is shown that the amount of irreversibly adsorbed sulfur, S (irr) is an equilibrium value dependent on temperature and H 2S partial pressure. However, there must be enough S (irr) present to sulfide all the Re and about 10%of the Pt at the stoichiometry of Pt 2S and Re 2S. If the S (irr) is too low, either through undersulfiding or overstripping, catalyst performance suffers. Reversibly adsorbed sulfur, S (rev), is also an equilibrium value dependent on temperature and H 2S partial pressure. Activity maintenance of Pt-Re/Al 2O 3 catalysts is decreased by S (rev). As the Re to Pt atomic ratio increases, adverse sensitivity of the catalyst to S (rev) also increases.

ChemInform Abstract: The Role of Chlorine in the Partial Oxidation of Methane to Ethene on MgO Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Role of Chlorine in Oxygen Adsorption on Ag(111)

The effect of chlorine adsorption on oxygen adsorption on Ag(111) was studied with HREELS and TPD. Oxygen adsorption on Ag(111) and Ag(111) exposed to a low chlorine dose produces mainly atomic oxygen species at 170 K and room temperature. On Ag(111) exposed to a high chlorine dose and a surface with the same chlorine adsorption conditions, but followed by removal of chlorine, a molecular oxygen species was the only product of oxygen adsorption at 170 K or room temperature. The altered behavior of oxygen adsorption is due to surface defects created via chlorine adsorption. It was also found that these surface defects increase the adsorption rate of oxygen and promote the diffusion of oxygen into the subsurface.

The role of chlorine in chlorine-promoted methane coupling catalysts

Methane coupling catalysts which contain Ba or Sr, a non-basic metal oxide, and chloride on the catalyst and/or in the feed gas appear to operate by the commonly accepted heterogeneous - homogeneous mechanism, give very high ethylene to ethane product ratios, and are significantly more stable than reported literature catalysts. The best supports are acidic for high ethylene to ethane product ratios. Chlorine, added in the form of parts per million of ethyl chloride to the reaction feed, is proposed to serve three functions in these catalysts. It increases the rate of methane conversion, probably by increasing the number of active sites on the catalyst. It decreases the rate of carbon dioxide formation, which is proposed to result from a slow catalyst change. Finally, it is responsible for the high ethylene to ethane product ratios observed using these catalysts. This is proposed to result from an interaction of chlorine with the support in which chlorine radicals are released from the surface of the catalyst into the gas phase, where they initiate free radical reactions resulting in conversion of ethane to ethylene.

The role of chlorine in the loss of 238U decay chain nuclides and 232Th from a basaltic rock

Volatilization experiments on U decay chain nuclides and Th involving the addition of CaCl2 to a basanite and heating sequentially at 1300°C were performed. The results indicate loss of 210Pb with Na and K at low Cl concentrations and 226Ra with Fe at considerably higher Cl concentrations. 238U, 230Th and 232Th were not lost by volatilization even at the highest Cl concentrations.

Catalysis with palladium deposited on rare earth oxides: influence of the support on reforming and syngas activity and selectivity

The influence of the support has been tested on the reactivity of Pd/rare earth oxides catalysts (La{sub 2}O{sub 3}, CeO{sub 2}, Pr{sub 6}O{sub 11}, Nd{sub 2}O{sub 3}, Tb{sub 4}O{sub 7}). According to BET surface area, chemisorption, temperature-programmed reduction (TPR) and oxidation (TPO), x-ray diffraction (XRD) and x-ray photoemission (XPS) characterizations, these catalysts have been classified into three classes according to their ability to create anion vacancies: (i) oxides of the type Re{sub 2}O{sub 3} which are unreducible, (ii) CeO{sub 2} where anion vacancies can be created extrinsically by the reduction process, and (iii) Pr{sub 6}O{sub 11} and Tb{sub 4}O{sub 7} where anion vacancies exist due to the nonstoichiometric nature of these oxides. The authors emphasize also the role of chlorine, coming from the palladium precursor salt, which reacts with the support to form a stable oxychloride phase surrounding the metallic particle and interacting with it. Concerning the catalytic activity, (i) the active site is purely metallic in methylcyclopentane hydrogenolysis, with small selectivity changes on fluorite oxides as compared to Pd/Al{sub 2}O{sub 3} catalysts due to some electronic interaction with the support, but (ii) the mechanism is found to be partly bifunctional in 3-methylhexane aromatization with a large increase in aromatizationmore » on Pr{sub 6}O{sub 11} and Tb{sub 4}O{sub 7} supports, and (iii) in syngas conversion, production of high alcohols occurs at the metal-support interface and is favored by the presence of intrinsic anion vacancies on Pr{sub 6}O{sub 11} and Tb{sub 4}O{sub 7} supports.« less

The role of halides in selective oxidation reactions

The role of chlorine, in various chemical forms, in the methane activation reaction has been investigated. It has been found that although there is a release of methyl chloride and HCl from the surface of chloride-containing catalysts during the methane coupling reaction very little ethene is produced from ethane in the post catalyst volume. However, depending on the experimental conditions used, it is possible to envisage an important contribution from gas phase reactions in the catalyst bed.

Effects of additives on CO hydrogenation over chlorine-containing magnetite catalysts in slurry phase.

Effects of metal oxide addition on hydrogenation of carbon monoxide were investigated over chlorinecontaining magnetite (Cl/Fe3O4) catalysts in the slurry phases at 325°C, under 10atm, and with H2/CO=1. By addition of various metal oxides, the crystal size of magnetite and the XPS binding energy of the surface Fe decreased. A linear relationship between methane selectivity, or the ratio (P/O) of paraffin to olefin in the C2-C4 products, and electronegativity of M in the additives (MOx) was obtained. These results suggest that the added acidic oxides keep Fe of the catalysts in a low oxidation state and increase the hydrogenation activity of the catalysts. Thus, the role of chlorine in such catalysts with low P/O ratios was not explained in terms of its acidity, but in terms of its oxidative effect, maintaining the high oxidation state of Fe in the catalyst.

Role of chlorine in improving selectivity in the oxidative coupling of methane to ethylene

Samarium, magnesium and manganese oxide and alkali-promoted oxide catalysts have been prepared and tested for the oxidative coupling of methane. The results show that alkali-promoted oxides inhibit total oxidation and have a higher selectivity for the formation of C 2 products than the undoped metal oxides. These catalysts have been promoted by injecting pulses of gaseous chlorinated compounds (dichloromethane and chloroform) during the reaction. It has been found that these chlorinated compounds markedly increase the selectivity for the formation of C 2 products for all the MnO 2-based catalysts and for lithium-doped MgO and Sm 2O 3 catalysts. The effect is greatest in MnO 2-based catalysts. When dichloromethane is added to a pure, unpromoted MnO 2 catalyst the selectivity for the formation of carbon dioxide decreases from 82.6% to 4.1% and the selectivity for the formation of C 2H 4 increases from virtually zero to 56.3%. The highest C 2 selectivity observed after promotion of pure MnO 2 by dichloromethane is about 93%. Promotion of these pure oxide catalysts by gaseous chlorinated compounds provides an alternative to alkali promotion as a method of inhibiting total oxidation and of increasing ethylene production.