Fast pyrolysis of cellulose with reactive methane gas in a single-pulse shock tube

A shock tube technique was employed to study the fast pyrolysis of cellulose with methane under conditions of high temperature, high heating rate, short reaction time, and rapid quenching. The effects of temperature, methane atmosphere, and reaction time are investigated. Experiments were carried out at temperatures between 700 and 2200°C in 1% methane (diluted in argon), and comparisons in the yields of major gas products are made with the results obtained in pure argon atmosphere. The total gas yield decreased about 25–30% in methane. The principal gas products—carbon monoxide, carbon dioxide, and acetylene, except ethylene—were significantly decreased in methane as compared to the yields in pure argon. An increase of about 25% in ethylene yield in methane over argon was observed. The onset of the decomposition of cellulose and the evolution of major pyrolysis products were changed with the reaction times, which also affected the amplitude and the distribution of the pyrolysis products. © 1994 John Wiley & Sons, Inc.     

Pyrolysis of methane in the presence of hydrogen

The kinetics of methane pyrolysis were studied in a tubular flow reactor in the temperature range 1200 to 1500°C at atmospheric pressure. To avoid excessive carbon formation the reaction time was short and the methane feed was diluted with hydrogen. Ethene, ethyne, benzene and hydrogen were the main gaseous products. Ethane was observed as a product at very low conversions of methane. More than 90% selectivity was obtained for C₂ products. The ratio of ethyne to ethene increased with increasing temperature. The yield of C₂ products is limited by gas-phase equilibrium at lower temperatures. Formation of carbon was strongly depressed by hydrogen at higher temperatures. The maximum yield of ethyne was found to increase from about 10% to about 50% when the temperature was increased from 1200 to 1500°C, with hydrogen dilution H₂: CH₄ = 2: 1. A mechanistic reaction model was used to simulate the pyrolysis of methane at the actual conditions. A sensitivity analysis was performed to evaluate the elementary reactions which influence the formation and consumption of the species in the model system.     

Cracking of propylene in a shock tube

The high-temperature decomposition of propylene has been investigated in a single-pulse shock tube in the temperature range 1160–1700 K. The stable products observed were hydrogen, methane, ethylene, acetylene, ethane, allene and propyne. The rate of evolution of the different products was found to have a similar concentration-dependence except for ethane, which was found to be dependent only on the third-body concentration. A computer model of the kinetics is presented, according to which the first step of the propylene decomposition has a rate constant (calorie units) of: $\text{k}{}_1\text{[}\text{Ar}\text{] (}\text{mol/cm}{}^3\text{s}\text{) = (10}{}^{\mathrm{13\; \pm \; 0.5}}\text{)}\text{exp}\text{[(?74 ± 1) /sx}\text{10}{}^3\text{RT}\text{]}$     

模拟输液器的热解特性

建立非化学计量平衡模型,根据Gibbs最小自由能原理对医疗垃圾中的典型组分输液器进行平衡分析,根据分析结果拟合出产物分布的计算公式。通过危险废物热解焚烧多功能试验台进行试验,试验结果验证了计算公式的可靠性,从而通过公式可直接预测医疗垃圾中典型组分输液器热解后的各产物百分含量。     

Interaction of a shock pulse with a contact discontinuity

Passing of a triangular moderate-intensity pulse through a constant discontinuity is considered. Decay of the shock wave that passed into the second gas is analyzed. Damping of the detonation wave after burnout of the combustible mixture is discussed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 102–107, July–August, 2007.     

Pyrolysis of methane and the role of surface area

A range of catalysts was screened for activity and product selectivities in the pyrolysis of methane. Experiments were performed in a flow reactor at 1125 °C and atmospheric pressure. It appears that the pyrolysis of methane is primarily affected by the specific surface area of the catalyst and not by the particular type of catalyst. The highest yields to gaseous and liquid products are obtained in an empty reactor tube, whereas high specific surface areas produce mainly graphitic coke and hydrogen. The results are compared with specific surface area effects in the catalytic oxidative dimerization of methane.     

Coal flash pyrolysis: 5. Pyrolysis in an atmosphere of methane

Flash pyrolysis of coal at temperatures above 700°C and in the presence of methane produces substantially more ethylene and other low molecular weight hydrocarbons than are produced by pyrolysis of coal in the presence of nitrogen alone. Evidence is presented to show that the increase is due to pyrolysis of the methane quite independently of the coal, except with the possible catalysis by the coal, coke or mineral matter in the coal ash. This is contrary to recent reports in the literature.     

Thermal decomposition and hydrogenation of coal dust in a shock tube

A vertical shock tube with fluidized coal particles prior to shocking was used for this investigation. The high heating and quenching rates together with the exceedingly short reaction times obtainable with the shock tube were shown to have a marked effect on the product distribution. Additions of iodine were shown to promote the reaction. The reaction conditions were varied over the following ranges: shock temperature, 600–1200 K; maximum reaction time, 1·29–1·89 ms; pressures in shock, 658–1546 kPa. Electron photomicrographs of shocked coal particles are also presented. The distribution of gaseous hydrocarbons produced from coal subjected to high heating rates and short reaction times during hydrogenation is found to differ considerably from that produced by long reaction times, the gases containing a greater proportion of unsaturates (acetylene, ethylene, and propylene). The presence of gaseous iodine has no effect upon the product distribution of the hydrocarbon gases formed, but permits a lower reaction temperature for a given degree of decomposition.     

单槽脉冲电沉积法制备FePt薄膜

以FeSO4.7H2O和H2PtCl6.6H2O分别作为Fe2+源和Pt4+源,以铂片为阳极,纯铜片为阴极,采用单槽脉冲电沉积法制备FePt薄膜,通过X-射线衍射仪(XRD)、带有能谱的场发射扫描电镜(FESEM-EDAX)、振动样品磁强计(VSM)分析手段对薄膜进行了表征。结果表明,新制备的FePt薄膜组成为Fe22Pt58O20,具有面心立方(fcc)结构,FePt薄膜的矫顽力为2.0 kA/m,饱和磁化强度为420 kA/m,具有软磁性。     

Ignition of magnesium particles near the end of a shock tube

Mathematical modeling is used to study the ignition of magnesium particles near the end of a shock tube by the action of the transmitted and reflected shock waves. A comparison with experimental data showed that the particle motion and the dependence of the system thermophysical parameters on the system state must be considered in determining the ignition delay time as a function of the temperature behind the shock front.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 139–142, November–December, 1991     

Pyrolysis of methane on oxide catalysts supported by resistive fechral and carborundum

Catalysts on resistive supports, namely, on the thermally stable metal alloy fechral (FeCrAl) and carborundum (silicon carbide SiC) were studied in the pyrolysis of methane into acetylene. The active components chosen for deposition on carborundum were oxides corresponding to those present on the surface of the heat-treated fechral alloy: iron, chromium, and aluminum oxides, as well as zirconium and silicon oxides. The deposition of oxides on carborundum leads to an increase in methane conversion compared to the starting carborundum. The maximum acetylene selectivity was obtained using the ZrO₂/SiC and Al₂O₃/SiC catalysts. In contrast, the deposition of the same oxides on fechral leads to a decrease in the activity and acetylene selectivity compared with those of the starting heat-treated fechral. On the other hand, the deposition of oxides on fechral results in an increase in the temperature range of the catalyst operation and its stability over time. In the case of carborundum, the deposition of oxides does not affect these characteristics. The study of the starting supports fechral and carborundum and supports with metal oxides showed that high acetylene selectivity correlates with the formation of carbon fibers on the catalyst surface. These fibers mainly form on the surface of alumina, zirconia, and silica.     

惯性管盘绕方式对脉管制冷机性能的影响

为了研究惯性管盘绕方式对脉管制冷机性能的影响,揭示不同盘绕结构时惯性管调相能力及制冷机性能变化规律,为实际应用提供必要的实验数据或理论支持,结合湍流因素影响,计算了不同盘绕惯性管的压降损失,分析对调相能力的影响。研究发现,绕圈数越多,压降越大,惯性管调相能力越小。最后,选用了不同盘绕方式的惯性管进行了实验研究,实验结果显示随着惯性管盘绕圈数增加,压缩机效率略微减小,相同冷量下制冷机输入功率显著增大。对惯性管型脉管制冷机盘管方式的实际应用具有重要指导意义。     

Mathematical modeling of dispersion of a compressed burning monofuel gas suspension in a shock tube

Mathematical modeling of shock-wave discharge of a mixture of gas and burning particles of a monofuel from a high-pressure chamber to a low-pressure chamber is realized within the framework of the equations of two-velocity, two-temperature motion of a reacting gas suspension. The influence of particle burning as well as of the parameters of the dispersed phase and the pressure at which the diaphragm ruptures on the dynamics of dispersion of the gas suspension is studied numerically. It is found that, depending on the initial conditions of dispersion of the burning gas suspension, the pressure behind the shock wave front in the low-pressure chamber can either exceed or be equal to the pressure at which the diaphragm ruptures.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 85–93, January–February, 1996.     

Ignition performance of TiO2 coated boron particles using a shock tube

This study coated the surface of irregularly shaped 5-μm boron particles with TiO₂ nanoparticles to improve the ignition performance of the boron. A simple and inexpensive chemical method was used to coat the surface of boron with TiO₂. Five different samples of boron coated with TiO₂ nanoparticles were obtained by varying the concentration of Ti precursor. Surface structures were analyzed using different characterization techniques, which showed the formation of nanocrystalline TiO₂ nanoparticles over the boron surface. The nanoparticles of TiO₂ were well dispersed over the boron surface, and exhibited strong interfacial contact with the boron. The oxidation of boron and boron coated with TiO₂ was analyzed by thermogravimetric technique in an air atmosphere from room temperature to 1000 °C. Results revealed that the oxidation of boron started at a temperature approximately 162 °C lower after coating with TiO₂. The ignition behavior of the boron and boron coated with TiO₂ particles was studied using a shock tube. The results of the shock tube experiments demonstrated the TiO₂ coated boron had a shorter ignition delay time than the bare boron. An approximate 35% reduction was observed in the ignition delay time of boron after coating with TiO₂ nanoparticles, showing its potential value in high energy density fuels.     

Catalytic combustion of methane on palladium single crystals

Catalytic methane combustion was studied over the palladium single crystals Pd(1 1 1), Pd(1 0 0) and Pd(1 1 0). Under lean reaction conditions at 600 K (O₂:CH₄ = 10:1), stoichiometric palladium oxide was formed with an increase in surface area by a factor of approximately two. The oxide phase formed a “cauliflower-like” surface structure composed of approximately 4 nm sized semispherical oxide agglomerates. This oxide structure was independent of the original metal single crystal orientation. The turnover rates over the oxide structure starting with metal single crystals were 0.7 s⁻¹ on Pd(1 1 1), 0.9 s⁻¹ on Pd(1 0 0) and 0.9 s⁻¹ on Pd(1 1 0) at 600 K, 160 Torr O₂, 16 Torr CH₄, 1 Torr H₂O and N₂ balance to 800 Torr, suggesting that the methane combustion reaction is independent of the initial structure of the catalyst. Methane combustion on palladium single crystals experienced an activation period in which the initial turnover rates based on the initial Pd surface area were about 1/8–1/4 of the steady-state rates determined based on the oxide surface area. This activation period was caused by the slow oxidation of palladium single crystals and concomitant surface area increase during reaction. The increase in surface area happened mostly in the first 10 min of reaction. Carbon dissolution into the crystal was not found during methane combustion under reaction conditions in excess oxygen.