Intermediate Decomposition Products Research Articles

Analysis of low-temperature surface discharge plasma products from gaseous organic compounds

Nonequilibrium low-temperature discharge plasma decomposition products of 1000 ppm gaseous organic compounds contaminated in atmospheric pressure air, nitrogen, or oxygen, such as chlorofluorocarbon (CFC-113), organic chloride (trichloroethylene), and carbon tetrachloride, were studied for a better understanding of the decomposition mechanism of the plasma processing. A gas chromatograph-mass spectrometer was used as a main analyzing equipment. When the decomposition rate is not high (20-80%) for CFC-113, many various halogenated carbons or halogenated hydrocarbons are identified as intermediate products by the plasma processing. As the electric discharge power consumption increases, the decomposition rate of CFC-113 increases and intermediate products decrease. At the decomposition rate of more than 90%, some elemental products of hydrochloric acid, carbon dioxide, and nitrogen suboxide are recognized as final products. On the other hand, if the environmental gas is pure nitrogen without any oxygen and water vapor, the decomposition products are still intermediate with sufficient electric discharge power consumption, suggesting the existence of double decomposition mechanisms of nitrogen radicals and oxygen radicals. In the case of trichloroethylene decomposition, harmful intermediate decomposition products were observed when the decomposition rate was 20-90%.

Electron Beam Atmospheric Pressure Cold Plasma Decomposition of Carbon Tetrachloride and Trichloroethylene

The cold plasma decomposition of carbon tetrachloride (CCl 4 ) and trichloroethylene (C 2 HCl 3 ) at dilute concentrations in dry and wet air of atmospheric pressure was investigated. The cold plasma was generated in a tunable plasma reactor, where the electron concentration is controlled by an electron beam and the average electron energy is controlled by a superimposed sub-breakdown electric field. The energy expense for decomposition, i.e., the electron beam energy per molecule decomposed, as well as the intermediate and final decomposition products were determined. Moreover, likely reaction mechanisms for the decomposition of CCl 4 and C 2 HCl 3 are presented. These mechanisms are based on bimolecular dissociative electron attachment for both CCl 4 and C 2 -HCl 3 and additionally a chlorine chain reaction for C 2 HCl 3 . The present work provides a reference for the development of an advanced oxidation process on the basis of a tunable plasma reactor. Such a process would be especially suitable for the treatment of air contaminated with chemical compounds that dissociatively attach electrons.

Heterogeneous and homogeneous wastewater treatment — Comparison between photodegradation with TiO 2 and the photo-fenton reaction

The oxidative destruction of phenol, cyclohexanol (CyOH), and 4-nitroaniline (4-NA) in aqueous solution by the photo-Fenton reaction and TiO 2/UV-A is described and compared. The decomposition mechanisms were investigated by studying the intermediate products by HPLC and a photodiode array. The degradation of 4-NA was monitored by GC/MS to trace the decomposition products (nitrobenzene, p-benzoquinone, hydroquinone and resorcine). During the photochemical degradation of 4-NA nitrate ions were detected by an ion selective electrode. The degradation rates with the photo-Fenton reaction had the following order: Phenol > 4-NA >> CyOH, in contrast to the order CyOH > Phenol > 4-NA obtained with TiO 2/UV-A. The same intermediate decomposition products were obtained for each substrate by both methods.

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)](ClO) � 2DMF

The thermal decomposition process of the complex [Cu(NBOCTB)](ClO4)2 · 2DMF has been studied by the TG-DTG technique, and possible intermediate products of the thermal decomposition are conjectured. The results suggest that the decomposition of the complex can be divided into four steps: [Cu(NBOCTB)](CIO4)2 · 2DMF [Cu(NBOCTB)](ClO4)2 · DMF [Cu(NBOCTB)](ClO4 [Cu(OCTB)]ClO4 CuCl. The non-isothermal kinetics of steps 1 and 2 have been studied from the TG-DTG curves by means of the Achar et al. and Coats-Redfern methods. Steps 1 and 2 are both three-dimensional diffusion (spherical symmetry) and their kinetic equation can be expressed as dαdt = Ae−E/RT(32)(1 − α)(2/3)[1 − (1 − α)(1/3)]−1. The corresponding kinetic compensation effect expressions are found to be ln A = 0.2781E − 4.855 and ln A = 0.2403E − 3.758, respectively.

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)](CIO 4) 2 · 2DMF

The thermal decomposition process of the complex [Cu(NBOCTB)](ClO 4) 2 · 2DMF has been studied by the TG-DTG technique, and possible intermediate products of the thermal decomposition are conjectured. The results suggest that the decomposition of the complex can be divided into four steps: [Cu(NBOCTB)](CIO 4) 2 · 2DMF ▪ [Cu(NBOCTB)](ClO 4) 2 · DMF [Cu(NBOCTB)](ClO 4 [Cu(OCTB)]ClO 4 CuCl. The non-isothermal kinetics of steps 1 and 2 have been studied from the TG-DTG curves by means of the Achar et al. and Coats-Redfern methods. Steps 1 and 2 are both three-dimensional diffusion (spherical symmetry) and their kinetic equation can be expressed as dα dt = A e −E/RT( 3 2 )(1 − α) (2/3)[1 − (1 − α) (1/3)] −1 . The corresponding kinetic compensation effect expressions are found to be ln A = 0.2781 E − 4.855 and ln A = 0.2403 E − 3.758, respectively.

Aspects of emergency relief design for reactive systems

AbstractAn approach is presented to accurately design emergency relief systems for even the most complex chemical reactions. Two examples illustrate how large differences in relief requirements can result if small, but important, aspects of the calorimetry data are overlooked. Although both simple and rigorous kinetic models may seem to predict calorimetry data reasonably well, these examples demonstrate the importance of well‐designed experiments, optimization algorithms, rigorous kinetic modeling, correct physical properties, and dynamic simulations.The first example shows how the inclusion of a subtle equilibrium reaction in the kinetic model will allow venting of an intermediate species, decreasing the reactant available for the highly exothermic irreversible reaction. The second example emphasizes the importance of a rigorous model for the decomposition of a large molecule where bond cleavage can occur between repetitive groups.This example takes advantage of the tempering effect of intermediate decomposition products which are accounted forwith the rigorous model.

Ionic conduction of Ba 3Y 4O 9

The compound Ba 3Y 4O 9 is stable in dry air. However, in moist air it decomposes below 1200°C into Y 2 O 3+ BaCO 3. The fast ionic conduction observed in the range 370°C< T<600°C is shown to occur in an immobilized-liquid state of an intermediate decomposition product Ba( OH) 2− BaO 2− x and/or a eutectic Ba( OH) 2−11 w/o BaCO 3.

Effect of Ni-EDTA on production of methane and decomposition of volatile fatty acids in paddy soil

Abstract In flooded soil, volatile fatty acids (VFAs) which are intermediate products of organic matter decomposition are toxic to rice plant. The VFAs consist mainly of acetic acid (CH3COOH), and methane (CH4)-producing bacteria (MPBs) decompose them into CH4 and carbon dioxide (CO2).

Thermal dehydration and decomposition of nickel chloride hydrate (NiCl2·xH2O)

The dehydration and decomposition characteristics of an undried and a partly dried sample of NiCl2·xH2O have been investigated by isothermal and non-isothermal (TG and DTA) methods in static air as well as flowing nitrogen environment. While the isothermal weight loss method fails to distinguish between different steps of reaction, TG curves upto 800°C reveal as many as five steps in static air and four steps in nitrogen atmosphere. However, both methods indicate that NiCl2 is stable upto 400°C above which dehydrochlorination takes place in presence of water vapour. The intermediate products of dehydration and decomposition at different temperatures have been characterized by chemical analysis, X-ray diffraction, infrared and diffuse reflectance spectroscopy. All these methods reveal the presence of water in samples calcined at even 400°–600°C. Thermodynamic functions for different steps of dehydration have been calculated and discussed in the light of the possible structural changes occurring in the partially dehydrated products.

Thermal dehydration and decomposition of cobalt chloride hydrate (CoCl2·xH2O)

Dehydration and decomposition of an undried and a partly dried sample of hydrated CoCl2 have been investigated by using both isothermal and non-isothermal weight loss methods. The intermediate products of dehydration and decomposition at different temperatures have been characterized by chemical analysis, X-ray diffraction, microscopy, infrared and diffuse reflectance spectroscopy. Though XRD failed to identify clearly the formation of basic salt, infrared spectra reveal the occurrence of hydrogen bonded OH groups in the samples heated at even 500°–600°C. This is further supported from the diffuse reflectance spectra of “dehydrated” samples which indicate tetragonally distorted co-ordination structures due to the presence of H2O. Thermodynamic functions for different steps of dehydration have been calculated and discussed in the light of structural changes taking place in the dehydrated salts.

Intermediate phases and products of thermal decomposition of the compound Tl 2Pb[Cu(NO 2) 6

The stoichiometry of the thermal decomposition of the compound Tl 2Pb[Cu(NO 2) 6] has been studied. It is shown that the composition of the intermediate phases depends on the atmosphere in the reaction space, the composition of the intermediate phases being different when the decomposition is carried out in nitrogen or in air. As intermediate phases produced during decomposition under a nitrogen atmosphere, Cu 2O and Pb(NO 3) 2 were formed at 280°C. At the same temperature in an air atmosphere there were identified TlNO 3, Pb 6O 5(NO 3) 2 and TL 5.1PbO 9.15 as intermediates. Further heating of this system led to the subsequent crystallization of Tl 2O 3, CuO and, probably, Tl 6Pb 2O 5 (520°C). As the final product of the decomposition a mixture of CuO, Tl 2O and PbO was identified.

Vibrational spectroscopic investigation of the goethite thermal decomposition products

Goethite, hematite and intermediate products of goetite thermal decomposition were studied by IR and Raman spectroscopy to identify these products used as catalysts of some chemical reactions. The presence of a small number of OH-groups in the products of the decomposition up to 900–1000° C was supposed to hinder the formation of perfect hematite structure. The hypothesis concerning C3v6space group of protohematite indistinguishable from D3d6space group of hematite by X-Ray diffraction was suggested. This hypothesis explains both the additional lines in IR and Raman spectra compared to hematite spectra and the same position of peaks in X-Ray diffraction picture.

Investigation of the ozonolysis of ethylenebisdithiocarbamate-fungicides in model solutions

A study of the effectiveness of ozonation for the removal of nabam (disodium ethylenebisdithiocarbamate) from aqueous solutions was carried out. Nabam is the parent compound of a commonly used group of fungicides. The process of nabam degradation was followed in terms of several parameters such as nabam concentration, chemical oxygen demand (COD), sulphate ion concentration as a measure of the relative degree of mineralization of nabam, and the pH value of the solution. Ozonation accelerates the decomposition of nabam with the formation of sulphates and nitrates as final products. The intermediate decomposition products of nabam are more resistant to degradation by ozone than the parent compound. The amounts of ozone which are used in wastewater treatment plants for disinfection may be sufficient to remove both nabam and its decomposition products, at a low level of contamination, but if the concentration of nabam is too high the intermediate decomposition products can still be present. Lowering the pH of the medium favours the oxidation of nabam.

Thermal decomposition of cobalt(II) acetate tetrahydrate studied with time-resolved neutron diffraction and thermogravimetric analysis

The thermal decomposition of cobalt acetate tetrahydrate has been studied using time-resolved powder neutron diffraction. By using selectively deuterated samples, the loss of water or the breakdown of the acetate group can be identified by following the decrease in the incoherent background of the diffraction pattern as the hydrogen atoms are lost. The results suggest that by 150 °C dehydration is complete and a glass-like phase is formed. Crystallization of this anhydrous acetate occurs at 200 °C. Further heating initiates a two-stage decomposition of the anhydrous acetate terminated by the formation between 275–310 °C of a tetrahedrally co-ordinated cubic zinc blende form of CoO. This transforms at 310 °C to a rock-salt structure. The neutron diffraction data have been complemented by thermogravimetric and chemical analyses from which we have been able to propose some possible intermediate decomposition products and suggest an explanation for the formation of the unusual zinc blende form of CoO.

Thermal decomposition of silver chromate complex with 1, 10 phenanthroline, Ag2(phen)2CrO4

The decomposition of silver chromate complex with 1, 10 phenanthroline has been studied by TG/DTG/DTA method and X-ray diffraction analysis. Intermediate decomposition products have been isolated and characterized. The thermolysis of Ag2(phen)2CrO4 occurs in the two major stages: Ag2(phen)x“CrO4” as a product of the first stage and various mixtures of silver, silver chromate and silver metachromite as the final residue. The comparison of the decomposition process of the complex with that of parent Ag2CrO4 indicates that the presence of ligand changes thermal behaviour of the latter.

Isolation and identification of an aerobic γ-HCH-decomposing bacterium from soil

We succeeded in isolating an aerobic bacterium, which utilizes γ-HCH as a sole carbon source and can rapidly and completely decompose this substance. This bacterium was isolated from a γ-HCH plot of a long-term experimental upland field where the applied γ-HCH disappeared rapidly within I month. The bacterium was identified as Pseudomonas paucimobilis. It was suggested that the rapid loss of the applied γ-HCH in the upland field was closely related to the presence of the bacterium. In addition, P. paucimobilis had the ability to decompose the applied γ-HCH even in other soils where γ-HCH had never been applied. The pathway of γ-HCH decomposition by P. paucimobilis was found to be rather exceptional in that some chlorophenols were identified as the intermediate products of γ-HCH decomposition.

Organic lead compounds in vehicle exhaust

AbstractSpecies‐specific measurements of the five tetraalkyllead compounds used in gasoline and their intermediate decomposition products, the tri‐ and di‐alkyllead species, have been made in vehicle exhaust fumes. Under normal engine running conditions 0.3–3% of the lead emitted in exhaust is as an organic compound, but cold, choked engines emit proportionally much larger amounts of alkyllead. Alkyllead is emitted in both the gas and the aerosol phases.

A thermal analysis study of lanthanide adipate hydrates

The multi-step dehydration and decomposition of trivalent lanthanide adipate hydrates has been investigated by TG, DTG and DTA, together with infrared study of these compounds and the corresponding intermediate decomposition products. X-ray diffraction data for adipate complexes of general stoichiometry Ln2(C6H8O4)3· 10H2O, where Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are also reported.

Lignosulfonate polymerization: Effect of cross‐linking agents

AbstractFactors affecting the thermosetting properties of spray‐ or freeze‐dried, ammonium‐based spent sulfite liquor, a material rich in lignosulfonates, were investigated. It was found that purified lignosulfonates did not thermoset readily, unless either monomeric wood sugars or formaldehyde were present. Under the conditions employed, the monosaccharides were more effective than formaldehyde as thermoset accelerators. This may be due to the greater functionality of the intermediate decomposition products of the carbohydrates, which would create more reactive sites for intermolecular bonding with lignin. In contrast to previous findings, it was found that lignosulfonates (of mol wt ≥ 10,000) underwent polymerization, and subsequent thermosetting, more rapidly than their lower molecular weight counterparts. This was established by HPLC size exclusion elution chromatography of each sample following thermal treatment. It was also observed that wood did not affect the rate of thermosetting.

Thermal reactions of leadhillite Pb4SO4(CO3)2(OH)2

AbstractReactions undergone by leadhillite from the type locality on heating to 1000°C have been followed by DTA, TG, DSC, evolved gas analysis, continuous-heating XRD and IR, and hot-stage microscopy. Intermediate decomposition products were identified by X-ray powder photography. At 80°C, biaxial leadhillite inverts to a uniaxial phase with properties similar to those of susannite, a naturally occurring polymorph of leadhillite, but this higher-temperature modification only partially reverts to the original structure on cooling (up to 24 hours at room temperature is required for complete reversion). Between 250 and 600°C the mineral undergoes two decomposition reactions: PbO.PbCO3 and PbO.PbSO4 form during the first reaction (PbCO3 may form in the initial stages) and 4PbO.PbSO4 during the second. α-2PbO.PbSO4 appears at 650°C due to solid-state reaction between the other lead oxysulphate products. Melting occurs above 850°C. The reaction products are discussed in relation to the phase diagrams for the systems PbO-CO2 and PbO-PbSO4.