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: $\text{k}{}_1\text{[}\text{Ar}\text{] (}\text{mol/cm}{}^3\text{s}\text{) = (10}{}^{\mathrm{13\; \pm \; 0.5}}\text{)}\text{exp}\text{[(?74 ± 1) /sx}\text{10}{}^3\text{RT}\text{]}$     

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。     

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.     

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     

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.     

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.     

振荡管内消除反射激波技术的研究

分析了振荡管内激波的行为及反射激波对制冷效应的影响。对几种消除反射激波技术进行了评述 ,分析了其效果及优缺点 ,指出了消波技术发展的方向。     

单筒冷却机中的新型扬料装置

〕本文介绍了洪堡公司在单筒冷却机内部装置上所作的改进，其新型弧形扬料装置提高了单冷机的热效率及运转可靠性，这对于我国单冷机的改进与发展有借鉴意义。     

Principal characteristics of turbulent gas-particulate flow in the vicinity of single tube and tube bundle structure

In this paper the particle rebounding characteristics of a gas-particle flow over a cylindrical body and an in-line tube bundle arrangement is investigated. With the aid of both experimental and numerical approaches, the mean particulate flow patterns, comprising both incident and rebound particles resulting from the impact of particles on solid walls, are examined. In the experimental investigation, a two-dimensional laser-Doppler anemometry (LDA) technique is used in the immediate vicinity of the body surface to measure the instantaneous incident and rebound particle velocities. The Reynolds-averaging Navier-Stokes equations are solved for the continuum gas phase and the results are used in conjunction with a Lagrangian trajectory model to predict the particle-rebound characteristics. For the single tube model, the experimental observations, also confirmed through computations, reveal a particle rebound zone where the mean particulate flow pattern is significantly modified due to the contribution of the rebound particles during the process of particle-wall impact interaction. This particle rebound zone is found to be a function of mainly the Stokes number (particle inertia), and to a lesser extent on the fluid Reynolds number (gas flow condition) except for high gas flow velocities. For the in-line tube bundle model, particles being rebounded from the first row of tubes at upstream migrated downstream and impinged the other tubes in an extremely complex and random disposition. Detailed measurements on the flow and turbulent characteristics within the subset containing two cylindrical tubes representing the flow over the first and second row tubes in the tube bundle configuration revealed that the heavier particles possessed higher axial and transverse velocity fluctuations than the gas and lighter particles. A means of quantifying the erosion rate using a semi-empirical relationship and CFD approach is presented. The erosion distributions were found to be significantly different between the lighter and heavier particles. Analysis of the effect of the above-mentioned parameters on the rebounding particle flow characteristics and their interrelationship has provided a better understanding on the behaviour of particulate flow impinging on a solid wall body or series of solid bodies. The usefulness of employing the experimental and computational approaches to quantify the particle-wall impact interaction phenomena in this study provides the basis for additional investigations to be undertaken to better comprehend the particulate behaviour in tube bundle structure, for example staggered tube arrangement commonly found in many commercial heat exchangers.