Interaction of a phosphorus‐based FR,a nanoclay and PA6. Part 2 interaction of the complete PA6 polymer nanocomposites

Polyamide 6 (PA6) is modified with a nanoclay (NC), Cloisite 30B and/or a flame retardant (FR), OP1311. The thermal decomposition of pure PA6 and PA6 nanocomposites is done by thermogravimetric analysis (TGA). The decomposition products from TGA in nitrogen and air are analysed online by Fourier transform infrared (FTIR) spectroscopy in order to examine the time/temperature‐dependent thermal degradation processes and monitor the evolved gases online. The profiles of the evolved gases are compared with ε‐caprolactam spectra, which are the main species in the gas phase. Results show that the addition of the fire retardant decreases the degradation temperature, whereas the incorporation of NC (PA6+NC) contributes to increased residual mass and char formation. The evolved gases from TGA‐FTIR in nitrogen from pure PA6 and (PA6+NC) are hydrocarbons, carbon dioxide, water, ε‐caprolactam and ammonia. The (PA6+FR) and (PA6+NC+FR) evolve the same volatiles with an additional phosphorus‐containing species, namely diethylphosphinic acid. The thermo‐oxidative degradation of all these composites in air yields carbon monoxide with an increased production of carbon dioxide, water and hydrogen cyanide. Another important result is that the hydrogen cyanide does not increase when the phosphinate FR is used. Copyright © 2009 John Wiley & Sons, Ltd.     

Toxic products from the combustion and pyrolysis of polyurethane foams

Products from the thermal decomposition of four polyurethane foams heated to temperatures in the range 220 to 400 °C, in atmospheres of nitrogen, of 6% oxygen in nitrogen and of air were examined for some of the anticipated toxic materials. When phosphorus-containing inhibitors were added to or chemically incorporated in the foams, phosphorus compounds were evolved under most of the conditions employed. Other materials detected were hydrogen cyanide, isocyanate, urea, halogenated compounds and alkenes. A brief discussion is given of the hazard presented by polyurethane foams decomposing under these conditions.     

Reactions of coal with discharge-generated (excited) nitrogen species

Reaction between coal and nitrogen in a discharge furnishes hydrogen cyanide and smaller amounts of cyanogen, as well as some carbon monoxide and carbon dioxide; the cumulative yields of hydrogen cyanide and cyanogen depend upon rank. The apparent activation energies for formation of hydrogen cyanide and cyanogen are in the order of 2–4 kcal mol⁻¹ but increase sharply to ≈13–14 kcal mol⁻¹ at ≈200 °C (possibly coincident with incipient thermal decomposition of the coal). The cyanogen/hydrogen cyanide ratio increases with rank, and also depends upon the reaction temperature — falling with increasing temperature up to ≈200 °C, and thereafter rising progressively. Rate measurements and i.r. spectral changes accompanying the reaction suggest that hydrogen cyanide is mainly formed from non-aromatic carbon-hydrogen configurations in the coal, and that cyanogen derives for the most part from aromatic carbon — though some can also be generated from non-aromatic CH in competition with formation of hydrogen cyanide.     

Calculation of Decomposition Products from Components of Gunpowder by using ReaxFF Reactive Force Field Molecular Dynamics and Thermodynamic Calculations of Equilibrium Composition

The major combustion products from munitions containing nitro‐based propellants are water, carbon monoxide, carbon dioxide, hydrogen, and nitrogen. In addition, compounds including hydrogen cyanide, ammonia, methane, nitrogen oxides, benzene, acrylonitrile, toluene, furan, aromatic amines, benzopyrene, and various polycyclic aromatic hydrocarbons are detected in minor concentrations. The literature shows that the thermodynamic prediction of the major decomposition products agrees fairly well with the measurements. However, poor agreement is found for the minor species. We have studied the thermal decomposition products of the main gunpowder ingredients. Each of the components nitrocellulose, nitroglycerine, and the nitrate ester stabilizers diphenylamine and ethyl centralite were thermally decomposed with ReaxFF reactive force field molecular dynamics and equilibrium thermodynamics. The molecular dynamics results for the major decomposition products from nitrocellulose were partly consistent with measurements. Compared to the thermodynamic calculations, the molecular dynamics simulations agreed considerably better with experimental results for minor species like hydrogen cyanide. The nitrate ester stabilizers are the main sources for ammonia and aromatic combustion products, whereas hydrogen cyanide is produced from nitrocellulose as well as from the stabilizers when gunpowder is combusted.     

Pyrolysis of brown coals. 3. Effect of cation content on the gaseous products containing oxygen from Yallourn coal

A study has been made of the evolution of water, carbon dioxide and carbon monoxide during the pyrolysis of Australian Yallourn brown coal, and of the way in which the evolution is influenced by exchange of the carboxyl groups in the coal with magnesium and barium cations. Virtually all the oxygen in the coal can be removed as carbon dioxide, water and carbon monoxide with the greatest rate of loss occurring at 300, 350 and 500 to 600 °C respectively. Increasing levels of cation alter the proportion of the volatile constituents but not the total amount of volatile matter evolved. Increased evolution of oxygen as carbon dioxide from a magnesium-form coal over that from acid-form coal is accompanied by a decrease in the amount evolved as water and carbon monoxide. Barium-form coals, however, show an increase in the amount of carbon monoxide evolved as the cation content increases. This is due in part to reactions involving the nitrogen gas used to provide a non-oxidizing atmosphere during pyrolysis. These reactions do not occur with magnesium-form coals. The amount of char formed by pyrolysis is the same for different levels of cation exchanged on the carboxyl groups. The results support conclusions that the carboxyl groups in a brown coal are associated with other oxygen groups, and that the mode of decomposition of the groups in this association (including carboxyl) is altered by the exchange of the carboxyl groups with cation.     

Chemical–analytical investigation of fire products in intermediate storages of recycling materials

Organic materials like paper, cardboard, textiles or plastics are mostly flammable. In intermediate storages for recycling products, these materials are stored in large amounts. If fire occurs in these stores, large emissions of smoke and other potentially harmful products are likely. In the present study, the gaseous products released from fires of such materials—for example, because of self‐ignition—were investigated. Different fractions (paper/cardboard, textiles and plastics) were crushed at low temperatures (about 80 K) and subsequently allowed to smoulder at different temperatures using the German standard Deutsches Institut für Normung 53436. The gases produced were sampled and analysed using Fourier transform infrared spectroscopy. The chemical composition of these gases differed considerably depending on fuel type. For flammable materials without heteroatom, the gases consisted predominantly of toxic compounds like carbon monoxide and carbon dioxide. Smouldering of materials containing heteroatoms showed, in addition to carbon monoxide, carbon dioxide and water vapour, further toxic components containing the heteroatom. Materials containing chlorine produced hydrogen chloride, and materials containing nitrogen produced ammonia and hydrogen cyanide. Copyright © 2011 John Wiley & Sons, Ltd.     

Reactions of coal with nitrogen/ hydrogen mixtures in a discharge

In-discharge reaction of coal with nitrogen/hydrogen mixtures rather than nitrogen alone raises rates of hydrogen cyanide generation by a factor of 10–50, and makes hydrogen cyanide account for ≈70–90% of the total product-gas volume. From these results and parallel tests with a pure carbon, it is concluded that enhanced formation of hydrogen cyanide is controlled by transient hydrogenation of aromatic carbon and consequent creation of additional (non-aromatic) reaction centres which can be abstracted by N^*.     

Studies on Thermal Decomposition of Energetic Nitrourea Salts

Thermal decomposition of nitrourea salts (K, Na, Ag, Ba) was studied in hydrogen atmosphere, helium atmosphere and vacuum by gas chromatography and mass spectrometry. The evolution of dinitrogen oxide, water, hydrazine, nitrogen dioxide and the formation of cyanate salts during thermodecomposition of nitrourea salts in helium and hydrogen were confirmed. In vacuum the evolved gaseous products changed to dinitrogen oxide, water, nitrogen monoxide, nitrogen gas indicating that interreaction between evolved gaseous products occurred. The same solid products – cyanate salts – are formed showing vacuum having no effects upon the decomposition mechanism.     

Reaction of coal with nitrogen in a microwave discharge

In a microwave discharge in nitrogen, high-volatile bituminous coal produces gaseous products, namely hydrogen cyanide, acetylene, small amounts of cyanogen and lowmolecular-weight hydrocarbon gases, and nitrogen-containing compounds, in addition to the usual hydrogen and carbon oxides. The reaction of coal in the nitrogen discharge occurs in two stages: interaction of active nitrogen with the coal molecule to cause rapid volatilization of gaseous products, and slow gasification of residual char by active nitrogen. Various factors influencing product type, yield, and distribution are examined. Under conditions where the gaseous products can be quickly quenched or removed, as by trapping at a very low temperature, more than 42% of carbon in the coal can be converted mainly to hydrogen cyanide and acetylene, which together constitute about 90% of the total products.     

Harmful by-products in selective catalytic reduction of nitrogen oxides by olefins over alumina

The selective reduction of nitrogen dioxide and nitrogen monoxide by olefins (ethene, propene) has been studied over two different -aluminium oxides in the temperature range 473–873 K. Nitrogen dioxide was reduced more effectively than nitrogen monoxide with both, ethene and propene, as a reductant. At temperatures exceeding 700 K, ammonia was formed as a by-product over one type of alumina. Concentrations in the range 30–40 ppm were determined for propene in combination with both, NO and NO₂, while no ammonia was produced with ethene as a reductant. In addition, significant formation of hydrogen cyanide up to 70 ppm was observed with propene over both aluminium oxides starting from either NO or NO₂. In contrast, hydrogen cyanide formation remained below 10 ppm with ethene as a reductant. Nitrous oxide formation did not exceed 10 ppm for all investigations. The results show that for alumina catalysts ethene is a more suitable reductant than propene due to its lower tendency to form undesired by-products.     

Gaseous products formed by γ-irradiation of bisphenol-A polycarbonate

Summary Bisphenol-A polycarbonate (PC) was γ-irradiated under vacuum at doses from 125 to 1000 kGy. Gases formed were analyzed by gas chromatography - mass spectrometry, and their radiation-chemical yields (G) were calculated. The total G value of gases was equal to 1.00 molec/100 eV, and main products of PC radiolysis were carbon monoxide and hydrogen, their G = 0.87 and 0.08, respectively. Traces of methane, carbon dioxide, acetaldehyde and acetone were detected at doses above 300 kGy. It has been found that acetaldehyde and acetone were produced practically by radiolysis of carbon monoxide - hydrogen mixture evolved from the irradiated PC. Mechanism of gaseous products formation by the PC irradiation has been discussed. Received: 5 July 2000/Accepted: 22 September 2000     

新型变压吸附技术的开发和应用

简要介绍了新型两段法变压吸附高效气体分离技术开发的背景及意义，详细介绍了该技术在脱碳、提氢、提纯CO、制氧领域中的应用。该技术的开发成功，极大地简化了工艺流程，既节省动力设备购置费、运行费和设备维护费，又大幅提高了装置稳定性、安全性和可靠性。     

High-resolution FTIR analysis of coal gas

Coal gas samples collected from a laboratory scale gasifier have been analysed using high-resolution (0.125 cm^?1) Fourier transform infrared spectrometry (FTIR). The gas samples were introduced into an evacuated 8.76 m path-length gas cell and backfilled with nitrogen to 1 atm. Carbonyl sulphide and ammonia were quantified in samples with concentrations ranging from trace to 370 ppm, and non-detectable to 25 ppm, respectively. Other compounds identified in the coal gas samples include: methane, ethane, ethylene, ?C₃ hydrocarbons, acetylene, carbon monoxide, carbon dioxide, ethylene oxide, methane thiol, hydrogen cyanide, formaldehyde, cyanogen (?), ethane thiol (?), methanol, and nitric acid (?). Several compounds were sought but were not present in detectable quantities (less than ≈ 1 ppm). These include: nickel carbonyl, arsine, benzene, methyl chloride, methylamine, HCI, nitrogen oxides, and phosgene. Selected compounds, e.g. ammonia, were quantified by calibration with a standard gas. High resolution FTIR, a nearly universal detector, is especially useful for determining presence or absence of specific pollutants or interest which are not easily determined by routine gas chromatographie methods.     

The relative hydrogen saturation factor and its use for material balance analysis of underground coal gasification

Steady oxygen and hydrogen conservation relationships for an underground coal gasification reactor were combined with a simple model for the evolution of oxygen and hydrogen within the gasifier to yield a relationship for the fraction of evolved carbon originating from char gasification. This relationship is independent of the flow terms due to injection and production of water, whether the gas which leaks from the gasifier is like injected gas or produced gas. The relationship is a function of a dimensionless parameter called the relative hydrogen saturation factor of the evolved gas. Equations based on the concept of the relative hydrogen saturation factor are given for the carbon recovery efficiency and the fraction of exploited coal which has been completely gasified. Data from two field experiments were analysed. Results indicate that the relative hydrogen saturation factor is a valuable monitor of the relative importance of char gasification. The carbon recovery efficiency predicted by the analysis compares fairly well with the value measured from an excavation of a gasification site. The fraction of evolved carbon originating from char gasification, the carbon recovery efficiency, and the fraction of exploited coal which has been completely gasified are given for each field test.     

A shock tube study of the high temperature reactions of nitrogen with hydrocarbons

A single pulse shock tube has been used to study the reactions of nitrogen with methane, ethane and acetylene at 1400°-6000°K. Reactants heated by the reflected shock for about 1–1.5 milliseconds are cooled by rarefaction waves, and samples obtained through a quick-opening check valve are analyzed by gas chromatography. The effect of nitrogen on hydrocarbon pyrolysis appears to be negligible below about 2000°K. At higher temperatures, vibrationally excited nitrogen molecules react with free radicals and produce hydrogen cyanide. Activation energies in the range 23 to 54 Kcal/mole are calculated for the formation of hydrogen cyanide.     

Supercritical adsorption of ‘permanent’ gases under corresponding states on various carbons

Adsorption isotherms at 298 K have been measured on four different carbons for six gases: argon, carbon monoxide, hydrogen, methane, nitrogen and oxygen at pressures up to 7 MPa. For all the carbons, methane, on a molar basis, was adsorbed to a greater extent than all the other gases and hydrogen the least. These same gases were then adsorbed using the same carbons at temperatures corresponding to a reduced temperature of 2.36 up to reduced pressures of about 1.0. Under those conditions, five gases presented very similar uptakes on any given carbon although the porous nature of these carbons was very different. The exceptional gas was hydrogen. For every carbon, hydrogen was adsorbed to a much greater extent than the other gases. In all cases, the isotherms were reversible suggesting that only physisorption was involved. It would appear that hydrogen can penetrate into pores within the structure of carbons that go undetected by conventional pore or surface characterisation techniques. The carbon with the highest 77 K N₂ D-R micropore volume, AX-21, still showed the greatest hydrogen uptake under these reduced conditions.     

Pyrolysis of brown coals. 2. Decomposition of acidic groups on heating in the range 100–900 °C

The pyrolysis of a Yallourn brown coal in the acid form and several different cation forms has been studied at temperatures up to 900 °C, in regard to the decomposition of acid groups, the relation between oxygen products evolved and these groups, and the fate of cations. The exchange of carboxyl groups changes the amounts of both carbon dioxide and water evolved on pyrolysis, indicating that oxygen-containing groups other than carboxyl are affected by the exchange. The total acid-group content of the acid-form coal heated at different temperatures can be related to the sum of the acid group content of the residual char, and carbon dioxide and carbon monoxide evolved during pyrolysis. The results, in general, confirm the conclusion reached previously in regard to pyrolysis carried out at temperatures up to 300 °C. Pyrolysis in nitrogen at 900 °C releases all oxygen from the acid-form coal. In cation coals the amount of oxygen retained in the char in combination with the cation depends on the type of cation and the extent of reaction with nitrogen in the pyrolysis atmosphere.     

Pyrolysis of brown coals. 4. Relation between acidic groups and evolved carbon oxides

A comparison has been made between the total acid-group contents of a number of low-rank coals as determined by ion exchange with barium hydroxide and by the determination of carbon dioxide and carbon monoxide evolved on pyrolysis. The latter determination was based on the assumption that on pyrolysis carboxylic and phenolic groups decompose to carbon dioxide and carbon monoxide. The results obtained by the two methods agreed well for 17 of the 20 coals examined.     

Relative thermophysical properties of some polyimides

A comparative thermogravimetric study of ten polyimide films of varying composition revealed that thermal and thermo-oxidative stability of the polymers increases directly with increasing imide content. Films degraded more rapidly in air than in vacuo; the insertion of connecting groups within the polymer repeat unit decreased stability in both environments. The effect of inserting “ladder-like” segments in the polymer structure did not enhance resistance to oxidation; but under vacuum, those segments probably operated beneficially in promoting the retention of the carbon-like residue. Infrared spectral measurements showed little loss of imide bands with progressive weight loss in air, indicating unit-by-unit degradation. Conversely, infrared spectra of films heated under vacuum conditions showed that progressive loss of imide bands occurred simultaneously with an increasing development of bands related to carbon–nitrogen double bonds. Dynamic heating under vacuum developed singularly uniform weight loss curves; however, concurrent mass-spectrographic analyses indicated two distinct reactions. Gaseous carbon monoxide and carbon dioxide species accounted for the major weight change, and their periods of maximum evolution occurred at different temperatures for each film. A subsequent minor weight loss period was associated with the liberation of hydrogen cyanide which maximized at the same temperature for all ten films.     

A kinetic study of methanol decomposition catalyzed over plate-type palladium catalyst

A kinetic study of the catalytic methanol decomposition to carbon monoxide and hydrogen has been carried out in the pressure range of methanol up to 8 atm at 200 and 250°C over a palladium catalyst supported on an oxidized aluminum plate. The reaction pathway can be proposed as (i) dissociative adsorption of methanol to methoxyl groups and hydrogen adsorbed on palladium sites, (ii) decomposition of the methoxyl groups to carbon monoxide and hydrogen adsorbed, and (iii) desorption of the surface carbon monoxide and hydrogen species. It is suggested that the second step is rate-determining and the surface hydrogen species enhance the decomposition of the methoxyl groups. This revised version was published online in July 2006 with corrections to the Cover Date.