Reductive and oxidative combustion of polyethylene bags: Characterization of carbonaceous and nitrogenous species

This study aims to experimentally characterize the gaseous carbonaceous and nitrogenous species from the reductive and oxidant combustion of polyethylene plastic bags. The experimental device used is the tubular furnace, coupled to two gas analyzers: a Fourier transform infrared analyzer (FTIR) and a non dispersive infrared analyzer (NDIR). The gaseous products analyzed are: CO, CO₂, CH₄, C₃H₈, C₂H₄, C₂H₂, C₆H₆, HCN, N₂O, NO, NO₂ and NH₃. The experiments were conducted at temperatures ranging from 800 to 1000 °C. The results obtained allow us to note that carbonaceous compounds are mainly emitted as carbon oxides (CO and CO₂) whether you are reductive combustion or oxidative combustion.In addition:

• -Under reductive conditions, combustion is controlled by oxygen. The hydrocarbon most active in the formation of carbon monoxide is ethylene (C₂H₄) and to a lesser extent, from 900 °C, acetylene (C₂H₂). The extents we have made show that ammonia seem to be emitted during combustion with 10% of oxygen.
• -In an oxidative environment, there is production of C₆H₆ in substantial quantities, which partly explains the presence of soot and tar in the smoke exhaust ducts. The C₂H₄, CH₄ and C₂H₂ are hydrocarbons most active in the formation of CO and CO₂. Increasing of concentration of local oxygen from 10 to 21% for the combustion of plastic bags, favors an increase in efficiency of carbon conversion about 30%. About 99% of the carbon of the fuel is found to be converted to carbon oxides or hydrocarbons. Nitrogen monoxide (NO) is the major component among the gases measured with a conversion rate of nitrogen about 20%, three times larger than that obtained during the reductive combustion of plastic bags with 10% oxygen.

     

STUDY ON THE GASEOUS PRODUCTS OF HIGH TEMPERATURE PYROLYSIS OF ACRYLONITRILE POLYMERS BY ON-LINE FTIR METHOD

The gaseous products of high temperature pyrolysis (300℃ to 960℃) of aerylonitrile polymers were measured continuously under nitrogen atmosphere by on-line Fourier Transform Infrared Spectroscopic method (FTIR). From the variations of characteristic peaks it was found that the nitrogen of macromolecules evolved were mainly in the form of hydrogen cyanide and ammonia. During the pyrolysis amorphous carbonaceous element was formed, and crosslinked to form network structure. Three kinds of samples were used for comparison. The experimental results show that the gaseous products of volatile small molecules were HCN, NH_3, CH_4, C_2H_6 and cyanide. CO and CO_2 were also formed when copolymers of PAN were thermally pyrolyzed.     

Ion cyclotron resonance studies of some reactions of C+ ions

Product distributions and rate constants for the reaction of ground state C⁺ ions with O₂, NO, HCl, CO₂, H₂S, H₂O, HCN, NH₃, CH₄, H₂CO, CH₃OH, and CH₃NH₂ have been measured. Rate constants were obtained using ion cyclotron resonance trapped ion methods at JPL, and product distributions were obtained using a tandem (Dempster-ICR) mass spectrometer at the University of Utah. Rapid carbon isotope exchange has also been observed in C⁺-CO collisions.     

Multipole expansion of diatomic overlap

The systematic extension of Ruedenberg's expansion formula proposed in Part I [1] is applied to a series of diatomic and polyatomic molecules (BH, NH, HF, Be₂, C₂, F₂, CO, BH₃, CH₄, NH₃, H₂O, HCN and H₂CO). In general, good agreement with the results of full SCF calculations with the same minimum STO basis set is achieved. Thus, the errors due to this integral approximation scheme called MEDO (Multipole Expansion of Diatomic Overlap) are almost negligible compared to those introduced by basis set truncation.     

Synthese et caracterisation de fluorotellurates IV alcalins et d'ammonium partie II: Etude des fluorotellurates d'ammonium NH4TeF5 et (NH4)2TeF6

New methods of synthesis:

• •reaction of aqueous or anhydrous HF with TeO₂ and NH₄F or NH₄HF₂, with (NH₄)₂TeCl₆
• •reaction of TeF₄ with NH₄F or NH₄HF₂
• •reaction of NH₄HF₂ with TeO₂

have been investigated for NH₄TeF₅ and a new compound (NH₄)₂TeF₆. The resulting compounds have been analysed and characterized.     

煤热解过程中含氮气相产物转化规律的实验研究

为了研究煤在热解过程中含氮气相产物的生成规律,在滴管炉反应系统中对四种原煤以及两种脱除矿物质煤样分别在500℃、700℃、900℃和1100℃进行了实验研究。结果表明,随着温度的升高,作为NO前驱物的HCN和NH3的收率随之增加,N2的收率也增加。煤种对含氮气相产物的生成规律也有着较大的影响,煤化程度比较低的煤在热解过程中,燃料氮向气相含氮产物的转化率较高;煤化程度比较高的煤转化率则偏低,大部分的氮缩聚在多环芳香结构中,成为焦炭氮。煤中的矿物质对燃料氮向N2的转化起到了促进作用,而对燃料氮向HCN和NH3的转化起到了抑制作用。     

Cooperative effect of Fe and Ti species over Fe–Ti–Ox catalysts on the catalytic hydrolysis performance of hydrogen cyanide

FeO_x, TiO₂, and Fe–Ti–O_x catalysts were synthesized and used in the catalytic hydrolysis of hydrogen cyanide (HCN). Nearly 100% HCN conversion was achieved at 250 °C over the Fe–Ti–O_x catalyst. TiO₂ rutile was detected over TiO₂, but not over Fe–Ti–O_x, which suggested that the interaction between Fe and Ti species could inhibit the TiO₂ phase transition. Furthermore, the interaction between Fe and Ti species over Fe–Ti–O_x could promote the selectivity of NH₃ and CO. The mechanism of hydrolysis of HCN over FeO_x, TiO₂, and Fe–Ti–O_x can be given as follows: HCN + H₂O → methanamide → ammonium formate → formic acid → H₂O + CO.     

TG–MS analysis of thermal behavior and gaseous emissions during co-combustion of straw with municipal sewage sludge

The thermal behavior and gas product distribution during combustion of straw (wheat straw, corn stalks, and cotton stalks), municipal sewage sludge (MSS), and their blends were investigated by thermogravimetry–mass spectroscopy. The experiments were conducted with various blending ratios and temperatures ranging from 323 to 1,173 K. Addition of MSS decreased the combustion performance of the straw. The reactions between wheat straw and corn stalks with MSS proceeded more easily than that of cotton stalks. Significant interactions were observed between the straw and MSS at the char combustion stage. Gaseous species (CO₂, SO₂, NH₃, HCN, and NO) were mainly produced at temperatures of 523–873 K at which most of the mass loss occurred. Higher MSS proportions in the blends resulted in lower emissions peaks for CO₂, NH₃, HCN, and NO except for SO₂. To ensure combustion performance and mitigate problematic gaseous emissions, the proportion of MSS added to the blends should be <30 mass%.     

Dipole moment derivatives from MINDO/3 semi-empirical MO calculations

Dipole moment derivatives for CO, NO, CO₂, H₂O, HCN, BF₃, CH₄, C₂H₄, C₂H₆, CH₃F, F₂CO and H₂CO molecules have been evaluated using MINDO/3 MO calculations. The values are compared with those obtained by other semi-empirical MO methods.     

Basis set and correlation effects on computed proton affinities of some oxygen and nitrogen bases

Basis set expansion and correlation effects on the computed proton affinities of the oxygen and nitrogen bases CH₃OH, H₂CO, CO, CH₃NH₂, CH₂NH, and HCN have been evaluated. Basis set enhancements lead to systematic changes in computed proton affinities. These effects appear to be additive, and are greater for correlated proton affinities than for Hartree-Fock energies. Inclusion of correlation decreases proton affinities, with fourth-order Møller-Plesset energies bracketed by second and third order energies.     

Extended Koopmans' theorem: Approximate ionization energies from MCSCF wave functions

The extended Koopmans' theorem has been implemented using multiconfigurational self-consistent field wave functions calculated with the GAMESS, HONDO, and SIRIUS programs. The results of illustrative calculations are presented for the molecules HF, H₂O, NH₃, CH₄, N₂, CO, HNC, HCN, C₂H₂, H₂CO, and B₂H₆. The lowest extended Koopmans' theorem ionization potentials agree well within the experimental values and the ionization potentials representing excited states of the ions show some improvements over the Koopmans' theorem values in most cases. The extended Koopmans' theorem is easily implemented and the time required to calculate the ionization energies is insignificant compared to the time required to calculate the wave function of the un-ionized molecule. © 1992 by John Wiley & Sons, Inc.     

The multiconfigurational spin tensor electron propagator method (MCSTEP): Comparison with extended Koopmans' theorem results

Summary We applied the multiconfigurational spin tensor electron propagator method (MCSTEP) for determining the lowest few (in energy) vertical ionization potentials (IPs) of HF, H₂O, NH₃, CH₄, N₂, CO, HNC, HCN, C₂H₂, H₂CO, and B₂H₆. We chose these molecules so that we could compare MCSTEP IPs with recently reported extended Koopmans' theorem (EKT) IPs on the same molecules. Using standard Dunning core-valence basis sets with relatively small complete active spaces, MCSTEP results are in very good to excellent agreement with experiment. These MCSTEP IPs are obtained using matrices no larger than 400 × 400. EKT matrices are even smaller; however, to obtain similar but generally slightly worse agreement with experiment, fairly large active spaces are required with EKT.     

Basis set and correlation effects on computed lithium ion affinities of some oxygen and nitrogen bases

Basis set expansion and correlation effects on computed lithium cation affinities have been evaluated for the oxygen and nitrogen bases CH₃OH, H₂CO, CO, CH₃NH₂, CH₂NH, and HCN. The presence of diffuse functions on nonhydrogen atoms is found to be the most important single enhancement of double- and triple-split valence plus polarization basis sets. With the triple-split basis, enhancement effects are nearly additive. Correlation usually decreases computed lithium ion affinities, with the second order Møller-Plesset correlation term being the dominant term.     

Thermal degradation and evolved gas analysis of thiourea-formaldehyde resin (TFR) during pyrolysis and combustion

Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH₃, CS₂, CO, HCN, HNCS, and NH₂CN. The main products in the second stage are NH₃ CO₂, CS₂, SO₂, and H₂O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO₂ is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH₃, and CO when compared with combustion in similar conditions.     

The mass spectrometry of some aromatic azides

Bromophenyl azides provide the only exceptions to the observation that nitrogen (N₂) is eliminated from the molecular ions. Splitting out of HCN, C₂H₂ and (in the case of acyl or o-nitroaryl azides) CO are important processes.     

Scaling in pseudopotential theory

Simple Gaussian nonlocal pseudopotentials are determined for K shells. Extrapolation formulas are derived for the parameters as functions of the reduced atomic number. Small hydrids are used for the basis function analysis. Comparison is made with the set of molecules in the book by Snyder and Basch, and detailed results are presented for the molecules BH₃, CH₄, NH₃, H₂O, HF, N₂, CO, BF, CH₃F, C₂H₂, HCN, CHONH₂, and CHOOH. Results on energy levels, total energy, total valence energy and dipolmoment and in a few cases some geometry predictions are made.     

A density functional study of pseudotetrahedral metal–nitrosyl complexes

Local and nonlocal density functional computations have been carried out to study the electronic structure and the equilibrium geometry of the isoelectronic series Cr(NC)₄, Mn(NO)₃(CO), Fe(NO)₂(CO)₂, and Co(NO)(CO)₃ and model compounds Fe(NO)₂L₂ (L = Cl, HCN, NH₃, PH₃, and C₂H₄). The structure of Fe(NO)₂(C₄H₆) is also described. The discussion is focused on structural modifications through a change of ligand, in particular those concerning the metal-nitrosyl conformation (linear vs. bent). Though this is a preliminary study of metal–nitrosyl properties by DFT methods and more computations are required to analyze the mechanism of homogeneous catalysis processes, our results support the hypothesis that structural reorganization from linear to bent metal–nitrosyl plays a key role in some reactions, such as in butadiene dimerization. © 1994 John Wiley & Sons, Inc.     

Decomposition of Acetaldehyde in Atmospheric Pressure Filamentary Nitrogen Plasma

The removal of 500?ppm acetaldehyde in nitrogen at 1?bar is characterized in a pulse dielectric barrier discharge generating a spatial random distribution of plasma filaments. The identification and the quantification of numerous by-products are performed. At 20?°C, CH₃CHO is efficiently dissociated, probably owing to quenching of N₂ metastable states. The most abundant by-products are CO, H₂, and CH₄, in consistency with the three important exit channels for the quenching of the N₂(A³?? _u ⁺ ) state by CH₃CHO proposed by Faider et al. (2011). In order of importance, other products are HCN, C₂H₆, CH₃CN, HNCO, CO₂, CH₃COCH₃, C₂H₄, C₂H₅CN, NH₃, C₂H₂, and a group of nitriles and of ketones. An increase of the temperature from 20?°C up to 300?°C induces a strong decrease of the removal characteristic energy, but the by-products types remain unchanged. Probably the reaction of H with CH₃CHO plays a role in the removal of the molecule at 300?°C.     

Average dipole polarizabilities from the unsold approximation and ab initio data

An approximate static dipole polarizability equation is developed on the basis of the Unsold approximation, and is cast in closed shell LCAO MO SCF formalism. A brief study is made of the use of Koopmans' theorem as a means of obtaining an average ionization energy, necessary in the polarizability equation presented. Average polarizabilities for the systems He, Ne, H₂, HF, H₂O, NH₂, CH₄, HCN, N₂, C₂H₂, C₂H₄, C₂H₆, C₆H₆, and C₆H₅F are calculated from the dipole polarizability expression developed using a small 4-31G basis set level. Results show good agreement with experimental data.     

Geometry optimization in ab initio SCF calculations. VII. Proton affinities and ion structures calculated with floating orbital geometry optimization (FOGO)

The FOGO method is used to calculate absolute proton affinities of the molecules H₂, HF, NH₃, H₂O, CH₃OH, C₂H₅OH, H₂O₂, CH₂O, CO, and CH₂CO. Comparison with experimental values demonstrates that the geometrical and energetical data resulting from this type of ab initio calculation are of chemical accuracy. Predictive data for higher energy isomers, such as hydroxymethylene and ethynol are given as possible aid for the identification of these species.