The effect of inert gases on the yield and morphology of carbon deposits resulting from methane pyrolysis on fechral catalyst under direct current resistive heating

The effect of the inert component nature (argon, helium) in a gas mixture on the morphology and the amount of carbon deposits formed upon methane pyrolysis on a resistive fechral wire catalyst heated by direct current was studied. The carbon deposits had a similar morphology with fibrous texture in all cases. By varying the gas medium composition, one can obtain either fibers with up to 150 μm length and 2–3 μm diameter or short fibers of 8–10 μm length formed from a dense surface carbon layer. In the presence of helium, the amount of carbon deposited on the surface was virtually proportional to the methane content in the gas mixture, while in argon medium, the carbon formation was markedly retarded.     

Pyrolysis of methane on a heat-treated FeCrAl coil heated with electric current

We studied methane pyrolysis of at 750 to 1100°C on a heat-treated FeCrAl wire heated by electric current both in the absence of oxygen and at CH₄ : O₂ = 15 : 1 and 9 : 1. The process proceeds in two temperature ranges differing in pyrolysis product selectivity. In the transition region, intensive carbon deposition occurs on the wire surface. The presence of oxygen shifts the methane conversion versus temperature and product selectivity versus temperature curves to higher temperatures. We believe that the existence of two process regions is due to the coking of the catalyst surface.     

Kinetics of nonstationary condensation of methane on a perovskite catalyst

The interaction of methane with the oxidized surface of the KNaSrCoO_3−x is first order in methane with respect to formation of higher hydrocarbons and zero order with respect to formation of CO₂. At the initial stage the rate of formation of the reaction products is independent of the amount of oxygen from the catalyst consumed (up to 5–7 monolayers of oxygen), after which the rate of the reaction falls linearly. The overall amount of oxygen consumed in the reaction reaches 30 monolayers. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 182–187, May–June, 2000.     

Kinetics of methane steam reforming on a Ni on alumina-titania catalyst

The kinetics of methane steam reforming on a nickel on alumina-titania catalyst, was studied in the range of 773–873 K. A Hougen-Watson type model gives good agreement with the experimental rates.     

A high coking-resistance catalyst for methane aromatization

Steaming-dealuminated HZSM-5-supported molybdenum catalysts have been found to be high coking-resistance catalysts for methane aromatization reactions; compared with conventional catalysts, they give a much higher selectivity towards aromatics.     

Catalytic pyrolysis of atmospheric residue on a fluid catalytic cracking catalyst for the production of light olefins

Catalytic pyrolysis of Chinese Daqing atmospheric residue on a commercial fluid catalytic cracking (FCC) catalyst was investigated in a confined fluidized bed reactor. The results show that the commercial FCC catalyst has good capability of cracking atmospheric residue to light olefins. The analysis of gas samples shows that the content of total light olefins in cracked gas is above 80%. The analysis of liquid samples shows that the content of aromatics in liquid samples ranges from 60% to 80%, and it increases with the enhancement of reaction temperature. The yield of total light olefins shows a maximum with the increase of reaction temperature, the weight ratios of catalyst-to-oil and steam-to-oil, respectively. The optimal reaction temperature, the weight ratios of catalyst-to-oil and steam-to-oil are about 650℃, 15 and 0.75, respectively.     

The preparation of hydrogen by the catalytic pyrolysis of ethanol on a nickel catalyst

High efficiency of a nickel catalyst on the SiO₂ support in low-temperature ethanol conversion as a method for the preparation of hydrogen was demonstrated. One mole of the alcohol was found to yield one mole of hydrogen. The catalyst studied did not stimulate the methanation and shift reactions.     

Reaction space organization effect on propane pyrolysis in the presence of a nickel-copper catalyst

Propane pyrolysis at atmospheric pressures and temperatures of 500–700°C in the presence of a bimetallic catalyst containing 50 wt % Ni, 40 wt % Cu, and a silicon dioxide textural promoter has been investigated. It has been established experimentally that the reactor geometry and the way the reactants are let in and out exert an effect on the catalytic pyrolysis. The overall process rate is mainly determined by the heterogeneous reaction occurring on the catalyst surface. The homogeneous constituent of the process has an effect on the propane conversion at the early stages of the reaction.     

铜基催化剂上甲烷催化燃烧反应动力学特性研究

采用固定床微分反应器,在常压、450~500℃、甲烷体积分数10%~35%条件下,进行铜基催化剂上甲烷催化燃烧动力学特性研究。研究表明,甲烷分压对反应速率影响显著,而氧气分压的影响可以忽略。采用最小二乘法进行动力学模型参数估计,建立的反应动力学模型为-rCH4=1.61×107×e-108 000/RT×pCH40.5。检验结果表明,所建模型与实验数据良好相容,是适宜和可信的。根据实验结果推断甲烷催化燃烧分两步进行,首先氧气快速与铜基催化剂上活性空位点反应,形成吸附氧气分子;随后吸附氧气分子和甲烷分子反应,生成二氧化碳和水。     

Formation of compaction products in methane dry reforming on a Ni-containing catalyst

The formation of compaction products and their morphological features in the process of methane dry reforming on a Ni₃Al catalyst were studied. It was shown that the initial porous structure of a sample was retained in the course of reaction, and the formation of carbon deposits did not decrease the catalytic activity of Ni₃Al over a long period of time.     

Preparation method effect on the physicochemical and catalytic properties of a methane dehydroaromatization catalyst

The molybdenum precursor effect on the physicochemical properties of the Мо/ZSM-5 catalyst and on its catalytic properties in nonoxidative methane conversion into aromatic hydrocarbons has been investigated. The textural characteristics of molybdenum catalysts have been determined by low-temperature nitrogen adsorption, and their acidity has been measured by temperature-programmed ammonia desorption. The microstructure and composition of Mo/ZSM-5 samples have been determined by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The activity and on-stream stability of the Мо-containing zeolite catalyst in the nonoxidative conversion of methane depend on the type of molybdenum compound that was used in catalyst preparation.     

Kinetics of growth of carbon fibers on an iron catalyst in methane pyrolysis: A measurement procedure with the use of an optical microscope

A procedure was developed for measuring the kinetic parameters of growth of carbon fibers in the catalytic pyrolysis of hydrocarbons. In this procedure, the dependence of the averaged length of grown fibers on growth time is constructed based on the measurements of fiber lengths with an optical microscope. The procedure proposed allowed us to reliably determine the Arrhenius parameters of the rate of fiber growth and the induction period of fiber nucleation in the measurement of carbon fibers 100 nm or more in diameter. The kinetics of growth of carbon fibers from methane-hydrogen mixtures on an iron catalyst was measured over a temperature range of 950–1050°C. It was found that the rate of fiber growth as a function of methane activity in the gas phase exhibited a maximum in the activity range 200–300; the value of this maximum depends on the contribution of the products of gas-phase methane pyrolysis to the growth of fibers. It was also found that the rate of fiber growth dramatically increased as the critical concentration of pyrolysis products in the mixture was reached. This increase was interpreted as a change from one growth mechanism (growth from methane) to another growth mechanism (growth from acetylene). The experimental data explained the high sensitivity of the process of carbon fiber growth from methane to temperature and the residence time of the gas in the reactor.     

Growth of unusual carbon nanofilaments in methane pyrolysis

Two types of carbon nanofilaments (nanotubes) differing markedly in morphology and growth rate grow on substrate plates containing a supported catalyst in a methane atmosphere at ～1050°C. According to provisional estimates, nanofilaments of one of these types grow at a rate of 5–10 μm/s, which is 50–100 times as high as the growth rate observed for ordinary catalytic filaments (tubes). These filaments are as long as several millimeters, being 50 to 100 nm in diameter. A preliminary examination of their structure has demonstrated that there is no catalyst particle at the filament end and that the filament is likely a carbon-rich polymer. A possible mechanism of the growth of these carbon filaments is discussed.     

Electrical conductivity of magnesium oxide as a catalyst for radical chain hydrocarbon pyrolysis reactions

The electrical conductivity of polycrystalline MgO between 350 and 750°C is determined by the transport of surface electronic and hole defects and depends on the applied voltage. Near 620°C at low applied voltages, the conductivity decreases by 1–2 orders of magnitude in a narrow temperature range (ΔT = 75°C), and this is accompanied by a change of the sign of the surface charge carriers. The “ignition” of the catalytic activity of magnesium oxide in free radical generation in radical chain hydrocarbon pyrolysis is observed in the same temperature range. It is assumed that the change of the sign of the charge carriers is due to the existence of an isoelectric temperature T _i and that, at T > T _i , O_O^· defects come out to the magnesium oxide surface.     

Influence of chemical nature and concentration of the catalyst on hydrocarbon pyrolysis

The dependence of pyrolysis rate of hydrocarbons on the concentrations of catalysts of various chemical nature has been studied. Substances active in pyrolysis can be divided into three groups: inhibiting the reaction and enhancing either its homogeneous or heterogeneous components.

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Zeolite-supported Ni catalyst for methane reforming with carbon dioxide

In the present work, we compare the catalytic behaviour, in the dry reforming of methane, of Ni-based Silicalite-1 type catalyst obtained by different post-synthesis treatments. The Silicalite-1 type material, used as Ni-support, has been treated in order to observe the role of the silanol groups on the Ni impregnation, and then on the overall catalyst performance. Among the applied treatments (ionic-exchange, calcinations and silylation), the silylation is the one that allows the formation of smaller and more reducible Ni-oxide species that not only improve the methane conversion but also reduce the deactivation of the catalyst, due to the coke deposition.     

Influence of FCC catalyst steaming on HDPE pyrolysis product distribution

A commercial FCC catalyst based on a zeolite active phase has been used in the catalytic pyrolysis of HDPE. The experimental runs have been carried out in a conical spouted bed reactor provided with a feeding system for continuous operation. Different treatments have been applied to the catalyst to improve its behaviour. This paper deals with the optimization of catalyst steaming and pyrolysis temperature in order to maximize the production of diesel-oil fraction. The performance of the fresh catalyst has been firstly studied at 500 °C. This catalyst gives way to 52 wt% gas yield, 35 wt% light liquid fraction and a low yield of C₁₀⁺ fraction (13 wt%). After mild steaming (5 h at 760 °C) the results show a significant improvement in product distribution. Thus, gas yield decreases to 22 wt%, the yield of light liquid is similar to that of the fresh one (38 wt%), whereas the yield of the desired C₁₀⁺ fraction increases to 38 wt%. Nevertheless, the best results have been obtained when a severe steaming is applied to the catalyst (8 h at 816 °C) and pyrolysis temperature is reduced to 475 °C. There is a significant reduction in the gaseous fraction (8 wt%). The light liquid fraction has also been reduced to 22 wt%, but the yield of diesel fraction increases to 69 wt%. Moreover, the deactivation of the catalyst has also been studied under the optimum conditions.