Composition of gaseous combustion products of polymers

The gaseous products generated by the flaming combustion of ten kinds of synthetic polymers and a kind of wood (cedar) under the same conditions (sample weight, 0.1 g; temperature, 700°C air flow rates, 50 and 100 l./hr) were quantitatively analyzed by infrared spectrophotometry, gas chromatography, and colorimetric tube method. The main hydrocarbons generated were methane, ethylene, and acetylene. The amount of acetylene generated by the flaming combustion of polymers was much larger than the amount of acetylene formed by pyrolysis at 700°C in nitrogen. Acetylene increased in quantity with increasing air. For nitrogen compounds, hydrogen cyanide was generated from every polymer containing nitrogen used, but ammonia was detected only for nylon 66 and polyacrylamide. Nitrogen monoxide and nitrogen dioxide were detected only in small amounts. Nitrous oxide was detected in the gaseous products generated by the nonflaming combustion of urea resin and melamin resin. It was also found that about 70% of the nitrogen in N-66 and PAA was converted into nitrogen gas (N₂) by combustion under the conditions described above.     

Interferences in the determination of nitrogen dioxide in a chemiluminescent analyser

A commercial chemiluminescent nitrogen oxides analyzer performed well in its nitric oxide mode when applied to the combustion products of polyurethane materials, but when test gases were passed through a thermal converter prior to measurement of nitrogen dioxide, serious, interferences was encountered from hydrogen cyanide and other nitrogen compounds.     

Nitrogen-containing products from the thermal decomposition of flexible polyurethane foams

The thermal decomposition of a polyester and a polyether flexible foam in a nitrogen atmosphere has been studied by gas chromatography, mass spec-trometry and elemental ultramicroanalysis. It is shown that the decomposition behaviours of the two foams are similar. At low temperatures (200 to 300 °C) there is a rapid and complete loss of the tolylene diisocyanate unit of each foam as a volatile yellow smoke leaving a polyol residue. The smoke has been isolated as a yellow solid (common to both foams) which contains virtually all of the nitrogen of the original foams and, under the conditions of test, is stable at temperatures up to 750 °C. Nitrogen-containing products of low molecular weight (mainly hydrogen cyanide, acetonitrile, acrylonitrile, pyridine and benzonitrile) observed during the high temperature decomposition (over 800 °C) of the foams are shown to be derived from the yellow smokes. At 1000 °C, approximately 70% of the available nitrogen has been recovered as hydrogen cyanide.     

Conversion of fuels containing nitrogen to oxides of nitrogen in hydrogen and methane flames

Nitrogen-containing compounds such as hydrogen cyanide, acetonitrile, acrylonitrile, pyridine, benzonitrile, ammonia and methylamine, which are typical of the products likely to be encountered during the decomposition of nitrogen-containing polymers in fires, have been introduced into hydrogen and methane flames burning in oxygen-argon atmospheres. There is a complete conversion of fuel nitrogen in all cases to oxides of nitrogen and molecular nitrogen. The relative conversion to oxides of nitrogen (as NO_x/N₂) increases as the injection rate of nitrogen-containing fuels is decreased. The relative yields of oxides of nitrogen tend to be similar with methane and hydrogen premixed flames and markedly greater than observed with hydrogen diffusion flame. In all cases the yield of oxides of nitrogen-containing products such as hydrogen cyanide can also present a toxic risk during the burning of nitrogen-containing polymers, particularly when high temperature are involved. The combustion of these products in flame zones cannot be assumed to alleviate the additional toxic risk because of their conversion to oxides of nitrogen.     

Low NOx heavy fuel oil combustion with high temperature air

For an industrial-scale test furnace, the development and investigation of a heavy-oil-fired burner in a highly preheated air combustion system are discussed. The 1200 °C highly preheated combustion air was achieved by burners equipped with regenerators in high-cycle reciprocal firing. It was observed that the high-cycle reciprocal firing enhanced convective heat transfer to the furnace wall. Reduction of nitric oxide emissions was achieved by fuel directly injected into furnace (F2 mode) and mixed with combustion products. In previous studies of natural gas combustion in reciprocal firing, two injectors located at the burner quarl have been utilized to achieve low nitric oxide combustion. In this study, reduction of nitric oxide was investigated using single or paired atomizers located in the upper and lower position of burner quarl. It was found that buoyant forces were important for the mixing of fuel oil with high temperature air and for the resultant nitric oxide emission. Nitric oxide emission was found to be low with the paired atomizers in the F2 firing mode. Nitric oxide emission can be further reduced by use of a single atomizer rather than using paired atomizers.     

Effect of sintering temperature on the transport properties of La2Ce2O7 ceramic materials

La₂Ce₂O₇ (LCO) based materials are of a paramount importance since they can be utilized for ammonium production, thermal barrier application, catalysts, hydrogen production and solid oxide fuel cells (SOFCs). In this work, a nano crystalline LCO powder was prepared using glycine-nitrate combustion method and then its properties were comprehensively characterized. The structural analysis of the synthesized LCO was carried out using conventional X-ray diffraction (XRD) and Raman spectroscopy. In a disordered phase, LCO is a biphasic mixture composed of C- and F-type phases. Densification studies were performed by sintering LCO pellets at different sintering temperatures. A densification of ≥95% was observed in all the samples with a very little variation. Sintering temperature had a marked effect on the electrical conductivity of LCO. The LCO sintered at 1100 °C showed the highest conductivity (3.68 mS/cm at 700 °C in air). The electrical conductivity was found to be decreasing with an increase in sintering temperature from 1100 to 1400 °C. To understand the behavior, the analysis of distribution function of relaxation times (DFRTs) utilized for correct separation of grain and grain boundary resistances. The presence of C- and F- type phases calculated from Raman spectra plays a crucial role in deciding conduction behavior of LCO. The results suggest a strong relationship between history of the ceramics preparation and their electrical properties.     

Phase changes in mineral matter of North Dakota lignites caused by heating to 1200 °C

Changes in structures of minerals taking place in lignitic coals during combustion were investigated by first concentrating the mineral matter in the coal by low-temperature ashing and then heating the mineral matter at 100 °C intervals from 200 °C–1200 °C and analysing the major mineral phases by X-ray powder diffraction. Samples of high and low sodium contents were analysed to determine differences in mineral phases with varying sodium contents. Quartz and bassanite were identified as major phases in the low-temperature mineral matter of all ten lignite samples, and pyrite and calcite were identified in eight of the ten samples. Kaolinite was the only clay mineral identified and appeared in nine of the ten samples. Those samples with a sodium oxide content of 8.56 wt % or greater, showed sodium nitrate as a major mineral phase in the low-temperature mineral matter. When the mineral matter was heated to higher temperatures, quartz was a major phase at 1200 °C in five of the samples, and was stable to 1000 °C in all of the samples. Anhydrite was a major mineral phase in all samples from 600 °C–800 °C, appearing in some of the samples as low as 200 °C, and persisting to 1100 °C in some samples. Hematite was found to be a major phase in seven of the ten samples, having an overall temperature range from 300 °C–1000 °C. Magnetite was detected in the range from 800 °C–1200 °C with hercynite forming as a major mineral phase, after magnetite, in two of the samples at 1200 °C. The solid solution series gehlenite-akermanite was found in all ten samples from 1100 °C–1200 °C although they appeared in some samples at 900 °C. Samples of high sodium content formed sodium sulphates at intermediate temperatures and sodium silicates at higher temperatures. Low Sodium samples formed bredigite, a calcium silicate, at higher temperatures.     

Comparison of hydrogenated shale oils with standard jet fuels

The characteristics of jet fuels obtained from typical U.S. shale oils (Geokinetics, Occidental, Paraho and Tosco II) were compared with standard petroleum jet fuels in order to study the possibility of using these shale oils as a substitute. The shale oil fractions distilling below 343°C were catalytically hydroprocessed at low, medium and high severities and fractionated to the jet fuel range (121–300°C). The hydroprocessed products and jet fuels were compared for composition and physical properties. High severity hydroprocessing of shale oils decreased the nitrogen, sulfur, olefin and aromatic content while increasing the hydrogen content. The nitrogen content in shale oil jet fuels was considerably higher even after the high severity treatment. The aromatic content, except in Paraho shale oil, was relatively higher and the hydrogen content was slightly lower. Sulfur and olefin contents were lower at all severities. The physical properties and heat of combustion, except the high freezing point of shale oil jet fuels, were comparable to those of standard petroleum jet fuels.     

Upgrading coal-derived liquids to diesel fuel

Distilled fractions of a coal-derived liquid from the H-Coal process were upgraded to diesel fuel by catalytic hydrotreatment. The total hydrotreated products were distilled into naphtha (<180°C) and diesel fuel fractions (>180°C) and the diesel fractions were analysed for hydrocarbon-type composition, hydrogen content and some diesel fuel properties. GC—MS-analyses were carried out on the hydrocarbon-type fractions to identify individual chemical compounds. To investigate the effect of different distillation cut points on diesel fuel yield and properties, cut points for one hydrotreated product were varied. The diesel fuel cetane numbers were correlated with percentage hydrogen, total aromatics and saturates. Cetane numbers above 40 were obtained for diesel fuels containing (i) more than 75% saturates, (ii) less than 15% total aromatics and (iii) a hydrogen content above 12.8%. Compounds identified by GC—MS-analyses (in the diesel fractions) were typical aromatic and cycloparaffin compounds. Normal-and iso-paraffin compounds were not detected. By varying the distillation cut point from 135 to 180°C, the cetane number of the residual diesel fraction improved from 37 to 44. This increase is ascribed to the removal of aromatic compounds in the 135–180°C boiling point range.     

Combustion synthesis of graphene oxide–TiO2 hybrid materials for photodegradation of methyl orange

Graphene oxide (GO)–TiO₂ hybrid materials with enhanced photocatalytic properties were synthesized by a one-step combustion method using urea and titanyl nitrate as the fuel and oxidizer, respectively. During the synthesis procedure, the precursors containing GO, fuel, and oxidizer were maintained at different combustion temperatures (300–450 °C) for 10 min to ignite the combustion reaction. The effects of combustion temperatures on the weight loss, chemical status and photocatalytic properties were studied by thermogravimetry and differential scanning calorimetry, X-ray photoelectron spectroscopy, Raman, and photoluminescence. GO in the GO–TiO₂ hybrids were not oxidized, but thermally reduced by decomposition of partial oxygen-containing groups. Meantime, the nitrogen doping of GO was achieved. Compared to the neat TiO₂ obtained at same condition, GO–TiO₂ hybrid obtained at 350 °C exhibited enhanced photodegradation performance, which is attributed to the effective photo-generated electron transferring from TiO₂ to partially reduced GO, which confirmed by the photoluminescence quenching of TiO₂.     

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.     

Zur thermolyse von acrylnitril-vinylidenchlorid-copolymeren

The thermal degradation of random acrylonitrile-vinylidene chloride copolymers under nitrogen was studied at programmed temperature between 25 and 400°C. The following results were obtained: The initiation of dehydrochlorination, studied conductometrically, depends on the polymer composition and ranges from 70 (for copolymers with medium composition) to 130°C (for copolymers rich in acrylonitrile or vinylidene chloride). The total amount of hydrogen chloride evolved (up to 400°C, referred to the vinylidene chloride content) increases with the acrylonitrile content of the copolymers and is larger than that of polyvinylidene chloride. In the temperature range studied, the evolution of hydrogen chloride accounts for approx. 75% of the loss of weight, even with copolymers rich in acrylonitrile. Thc evolution of hydrogen cyanide, as detected by gas chromatography, starts between 150 and 190°C. The total amount of hydrogen cyanide evolved (up to 400°C, referred to the acrylonitrile content) increases with the vinylidene chloride content of the copolymers. Short oligomerized nitrile sequences were detected in the copolymers at 160°C by UV-spectroscopy. The results are discussed with respect to the sequence distribution obtained kinetically.     

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.     

Effectiveness of gases in desulphurization of coal

The effect of air, steam and hydrogen on the desulphurization of 10 U.S. high-volatile bituminous coals was investigated. Air treatment was most effective at 450 °C where an average of 38% total sulphur, comprising 51% of the inorganic sulphur and 20% of the organic sulphur, was removed. With steam at 600 °C, 61% of the total sulphur, 87% of inorganic and 25% of organic was lost. Hydrogen was not effective below 850 °C, but at 900 °C 86% of the total sulphur was dispelled, i.e. 94% of the inorganic and 76% of the organic sulphur. Without oxidative pretreatment the sulphur was much more difficult to remove; after oxidative pretreatment at 300 °C for 10 min followed by treatment with hydrogen at 900 °C, as much sulphur was removed in 4 min as in 60 min without the pretreatment. With raw coal, heating under nitrogen ‘cooked-in’ or fixed some of the sulphur making it more difficult to remove with hydrogen; whereas following oxidative pretreatment, heating for up to 1 h did not lessen the reduction of sulphur with hydrogen. For temperature-swelling coals with large quantities of organic sulphur, heating at 300 °C in air followed by reduction with hydrogen at 900 °C appears to permit rapid discharge (3–10 min) of the organic as well as the inorganic sulphur, to produce a smokeless product with a CV (per unit of product) similar to the fuel value of the untreated coal.     

The pyrolysis behaviors of ternary copolyimide derived from aromatic dianhydride and aromatic diisocyanates

A polyimide (PI) based on benzophenone‐3,3′,4,4′‐tetracarboxylic acid dianhydride, toluene diisocyanate (TDI), and 4,4′‐methylenebis (phenyl isocyanate) (MDI) has been synthesized via a one‐step polycondensation procedure. The resulting PI possessed excellent thermal stability with the glass transition temperature (T_g) 316°C, the 5% weight loss temperature (T_5%) in air and nitrogen 440.4°C and 448.0°C, respectively. The pyrolysis behaviors were investigated with dynamic thermogravimetric analysis (TGA), TGA coupled with Fourier transform infrared spectrometry (TGA–FTIR) and TGA coupled with mass spectrometry (TGA–MS) under air atmosphere. The results of TGA–FTIR and TGA–MS indicated that the main decomposition products were carbon dioxide (CO₂), carbonic oxide (CO), water (H₂O), ammonia (NH₃), nitric oxide (NO), hydrogen cyanide (HCN), benzene (C₆H₆), and compounds containing NH₂, C?N, N?C?O or phenyl groups. The activation energy (E_a) of the solid‐state process was estimated using Ozawa–Flynn–Wall (OFW) method which resulted to be 143.8 and 87.8 kJ/mol for the first and second stage. The pre‐exponential factor (A) and empirical order of decomposition (n) were determined by Friedman method. The activation energies of different mechanism models were calculated from Coats–Redfern method. Compared with the activation energy values obtained from the OFW method, the actual reaction followed a random nucleation mechanism with the integral form g(α) = ?ln(1 ? α). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40163.     

Factors influencing the reduction of barium sulphate

The reduction of pure barium sulphate and of barytes to barium sulphide and soluble barium compounds has been carried out in an indirectly heated tube furnace using carbon as the reducing agent. Increasing the reduction temperature increases the yield of barium compounds. The best yield is obtained with a reduction period of 1–2 h at 850–1100°C, while excluding air during the reduction and subsequent cooling process. The influence of ferric oxide and silica impurities on the yield of soluble barium products has been studied at a reduction temperature of 1000°C. Both reduce the yield of soluble barium products, ferric oxide having a much greater effect. The effect of these two impurities is not additive, silica minimizing the effect of ferric oxide.     

Simultaneous SO x /NO x removal in a fluidized bed reactor using natural manganese ore

In this experiment, the simultaneous removal of SO₂ and NO from flue gases was investigated through the use of natural manganese ore as a sorbent‐catalyst in a fluidized bed reactor. Selective catalytic reduction behavior was determined as a function of the sulfation degree within the temperature range from 100 °C to 500 °C. The natural manganese ore showed a high activity in the production of nitrogen and water by the reaction of nitric oxide with ammonia and oxygen up to around 200 °C. At higher temperatures, the nitric oxide removal efficiency decreased due to the oxidation of ammonia by oxygen. With the increase of sulfation degree, the temperature at which the maximum selective catalytic reduction of nitric oxide appears gradually increased, however the maximum nitric oxide removal efficiency decreased. Additionally, we investigated the removal efficiency of sulfur dioxide and nitric oxide with reaction time in a batch fluidized bed reactor within a temperature range of 350 °C to 500 °C. As the reaction temperature increased, the adsorption capacity of sulfur dioxide increased, but the nitric oxide removal efficiency decreased. © 2001 Society of Chemical Industry     

Effect of pressure and temperature on the reaction of coal with alcohol-alkali

The ethanol-NaOH reaction of Taiheiyo coal (C, 77.5; H, 6.3 wt%) was examined under a pressure of 0.1–8 MPa nitrogen or hydrogen, at 300 °C for 1 h. Almost all of the products are extracted with pyridine for the entire pressure range and the extraction yield with ethanol increases with pressure, even under nitrogen. The yield of the products extracted with ethanol is higher when the coal is reacted under hydrogen than when reacted under nitrogen. The explanation for these results is that, under pressure, the hydrogen produced from the reaction of alcohol and NaOH is enclosed for a longer period in the solvent, thus accelerating the hydrogenation reaction of the coal, also under hydrogen pressure, the reaction is particularly accelerated because the hydrogenation takes place with the hydrogen gas. At 300 °C, the ethanol-extraction yield is much higher than the benzene-extraction yield, but the latter increases rapidly and approaches that of the ethanol-extraction yield as the temperature rises to 400 °C. This is because the polar groups, e.g. as hydroxyl groups which are rich in the low-temperature products, decrease with the temperature rise.     

The thermal decomposition of some polyurethane foams

Polyurethanes exposed to fire conditions might generate decomposition products which would be responsible for a significant part of the toxicity of the fire gases. Polyurethanes have been prepared from a commercial mixture of tolylene-2, 4- and 2,6-di-isocyanates, pure tolylene-2,4-di-isocyanate, pure tolylene-2,6-di-isocyanate and pure m-phenylene di-isocyanate. All polymers except that prepared from tolylene-2,6-di-isocyanate were obtained as flexible foams. When each polyurethane was heated at 300°C in a stream of nitrogen, a sublimate was obtained. The sublimates were all apparently polymers derived from the di-isocyanate rather than from the diol constituents of the polyurethanes. Pyrolysis of these materials at high temperatures (800–1000°C) led to similar mixtures of volatile products: at 1000°C the most abundant nitrogenous product, in each case, was hydrogen cyanide.     

Sulphur transformation and removal for Western Kentucky coals

Inhibition isotherms were measured for Western Kentucky No.9 coal. Crushed and sieved coal (?25 + 140 U.S. mesh) was fluidized in 10-g batches in a 22-mm i.d. quartz reactor up to a temperature of 870 °C. The release of hydrogen sulphide during heatup under nitrogen and at the run temperature (usually 1–2 h) under the same gas (pyrolysis), hydrogen, or hydrogen/hydrogen sulphide mixtures was followed by gas chromatography. The residue or char was analysed for pyritic, organic, sulphide, sulphate, and total sulphur. Inhibition isotherms, which are pseudo-equilibria between sulphur in the char and gaseous hydrogen sulphide, were measured at 600 and 870 °C. At the lower temperature the isotherm was found to be independent of the hydrogen sulphide concentration in the gas stream and the char sulphur content remained constant at 2.6%. At 870 °C the sulphur content of the char was greater than that of the original coal when gas mixtures of 1, 3, and 6% hydrogen sulphide in hydrogen were used, indicating the necessity of maintaining low hydrogen sulphide concentration for sulphur removal. In pure hydrogen, sulphur removal increased continuously from 47% at 600 °C to 84% at 870 °C. For pyrolysis under nitrogen, sulphur removal was 40% at 600 °C and increased to 59% at 740 °C. No further removal occurred above this temperature up to 870 °C. In addition to the inhibition isotherms, sulphur-form transformation diagrams were constructed for coal treated with nitrogen, hydrogen, and hydrogen/hydrogen sulphide mixtures. Pyritic sulphur, which comprised 40% of the sulphur in the original coal, was completely converted to ferrous sulphide at 600 °C in hydrogen and 740 °C in nitrogen. At 870 °C the sulphur content of the char produced under hydrogen was 1.1% made up of 48.4% ferrous sulphide, 43.4% organic sulphur, and 8.2% sulphate.