Production Of Carbon Oxides Research Articles

Oxidative dehydrogenation of ethane and propane at short contact time

Oxidative dehydrogenation of ethane and propane has been studied in the short contact time regime using Pt monolithic catalysts. Ignition/extinction behaviour of ethane/oxygen and propane/oxygen mixtures over the Pt catalyst has been investigated as well as the behaviour of ethane/propane mixtures during oxidative dehydrogenation in the same reactor configuration. Ignition/extinction behaviour of alkane/oxygen mixtures were observed at low furnace temperatures. Carbon oxides are the main products during ignition accompanied by a sharp increase of the reactor temperature. Olefins and methane are preferably produced at higher temperatures during oxidative dehydrogenation of ethane and propane. The results obtained on the Pt catalyst indicate that in the temperature range of this study heterogeneous reactions contribute to the production of carbon oxides and hydrogen, while olefins are produced via gas-phase reactions. The conversion of ethane is almost not influenced by the addition of propane, whereas ethane affects the conversion of propane. In mixtures of ethane, propane and oxygen, ethane and propane cannot be treated as if they were alone.

Emission-free fuel reformers for mobile and portable fuel cell applications

Conventional fuel reformers are complex, multi-component devices which produce large amounts of CO 2 emissions. The main objective of this work is to develop an efficient, compact and emission-free fuel reformer for mobile and portable fuel cell (FC) applications. The concept is based on single-stage catalytic pyrolysis of hydrocarbon fuels into hydrogen-rich gas and carbon products. This approach allows to eliminate the production of carbon oxides (CO and CO 2) and, consequently, the need for the water–gas shift (WGS) and gas separation stages which significantly simplifies the process. The paper presents the experimental results of CO 2-free production of hydrogen-rich gas via catalytic pyrolysis of hydrocarbon fuels (propane, methane and gasoline). The perspectives of CO 2-free fuel reformers for mobile and portable fuel cell applications are discussed in this paper.

Role of inherent water in low-temperature oxidation of coal

The role of water content in coal oxidation was studied using an isothermal flow reactor at atmospheric pressure and temperatures below 100°C. Transient rates of consumption of oxygen and production of CO 2 and CO were measured during oxidation experiments, by means of an online dual-column micro gas chromatograph and an oxygen analyzer. Experiments were carried out with a bituminous coal at three levels of initial water content, i.e., 0.8, 2.0, and 3.0%. Comparisons of the rates of production of carbon oxides during the oxidation experiments indicated that inherent water plays a roleinchemicalreactions occurring during coal oxidation. It was also found that the rateof oxygen consumption decreases with increasing water content of a sample. The current observations suggest that inherent water present in coal pores may react with carbonyl species to form carboxyl species during the oxidation process.

Kinetic modeling of low-temperature oxidation of coal

A kinetic model has been developed for determining the rate of oxygen consumption and production of carbon oxides during the oxidation of coal at low temperatures (i.e. <100°C), based on current understanding of the mechanism of coal oxidation. The chemical reactions considered in the model include two parallel sequences consuming oxygen and two thermal decomposition pathways producing carbon oxides. The resulting rate expressions reflect the contributions of various reactions consuming oxygen and producing carbon oxides and predict the effects of temperature, oxidation time and [O 2] in the gas phase. The general form of the rate expressions confirms that chemisorption is relatively fast, only playing an important rôle at the early stage of coal oxidation. With the formation of stable and unreactive oxygenated complexes in a coal’s structure, the oxidation of coal is dominated by thermal decomposition of oxygenated complexes.

Cone calorimeter study of high performance fibres—application to polybenzazole and p-aramid fibres

This work investigates the fire behaviour of high performance fibres. Poly-p-phenylenediamine-terephtalamide fibres (PPT) and poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibres as knitted fabrics are evaluated using the cone calorimeter as fire model. The investigation of the fire performance of the PPT and PBO fibres shows the excellent behaviour of PBO in comparison with PPT. The contribution to fire growth of PBO is very low whatever the external heat flux is. In comparison with PPT, smoke obscuration of PBO is dramatically reduced as well as the production of carbon oxides during the combustion of the materials.

Direct Partial Oxidation (dpo) of Methane to Higher Hydrocarbons by Modified h-Zsm5 Catalyst

The oxidation of methane has been studied in a flow system as a function of the chemical composition of zeolite catalyst using nitrous oxide as oxidant. It is concluded that methanol is a primary oxidation product which may undergo further oxidation to formaldehyde and to carbon oxides. However, it may also undergo conversion over the acidic catalyst to higher hydrocarbons. Reaction with nitrous oxide resulted in the production of carbon oxides, methanol, formaldehyde, C2 - C4 , C5 - C7 nonaromatics, and aromatics. The effect of Fe2 O3 and Al2 O3 , with or without, over HZSM5 on products was studied.

Approach for a novel control strategy for simultaneous nitrification/denitrification in activated sludge reactors

Biological nitrogen removal in activated sludge processes is conventionally obtained by a sequence of aerobic and anoxic processes. Kinetic mechanisms affecting the oxygen balance could trigger the production of total volatile organic carbon (TVOC) and nitric oxides (NO) under anoxic and anaerobic conditions. Measurements at a wastewater treatment pilot plant of capacity 1.6 m 3 wastewater show that the amount of TVOC and NO produced during the treatment process depends on carbon loading (low feed, balanced and overloaded) and aeration conditions. To confirm the results ORP, pH and dissolved oxygen (DO) are measured on-line and chemical parameters such as nitrate (NO 3-N), ammonium (NH 4-N) and TOC are measured in the wastewater. The ORP observed is in the range of −60 and +198 mV includes optimal setpoints for simultaneous nitrification and denitrification. From the pattern of NO emission plot, it can be assumed that a part of the produced NO 3-N is denitrified during the aeration period. NO emissions are especially high during denitrification conditions at low oxygen rates. The results suggest that both NO and TVOC emission concentrations in combination with ORP can be valuable parameters to control operation of a wastewater treatment plant. Continuous measurements of ORP and NO concentrations for estimation of NO emissions gauging the extent of nitrification or denitrification in the plant becomes possible.

Oxygen partial pressure effects on the oxidative dehydrogenation of propane

The effect of the gas-phase oxygen partial pressure for the oxidative dehydrogenation of propane over a V–Mg–O catalyst was investigated to explore reasons for improved propene yields when dehydrogenation was carried out under periodic operation. Steady-state experiments were performed in which the oxygen partial pressure was varied over a large range at constant propane partial pressures. In addition, the catalyst mass was varied to control the propane conversion so that selectivity and yield could be compared at a constant propane conversion. At the same propane conversion, propene selectivity increased as the partial pressure of oxygen decreased. Thus, propene yields can be improved at steady state by employing low oxygen partial pressures. It is likely that this is the reason for the higher propene yields observed under unsteady-state or periodic operation. It appears that the reaction mechanism must consist of more than one pathway for production of carbon oxides.

Alkene and Arene Combustion on Pd(111)

Oxidation reactions of ethene, propene, 1-butene, 1,3-butadiene, benzene, and toluene were studied on oxygen-precovered Pd(111) (0.25 ML–1.2 ML) using temperature-programmed reaction spectroscopy (TPRS). Combustion is the sole reaction pathway; no partial oxidation products are formed. Comparison of these results with those from Pd(100) demonstrates that the structure of the metal surface does not significantly affect the mechanism of catalytic oxidation of most of the olefins or aromatic hydrocarbons studied, although, in general, combustion occurs at higher temperatures on Pd(111). Only for benzene combustion is there an appreciable structure sensitivity. For all the hydrocarbons studied the CO2and CO yields are maximized for an oxygen precoverage of 0.34 oxygen atoms per surface palladium atom. Abrupt increases in carbon oxide production at specific oxygen coverages indicate that oxygen-induced surface reconstructions may play a role in the combustion activity.

Anaerobic oxidation of butane to butadiene over magnesium molybdate catalysts. I. Magnesia supported catalysts

A potential new process to styrene monomer from n-butane consists of oxidation of n-butane to butadiene followed by dimerization of butadiene to 4-vinylcyclohexene (VCH) and oxydehydrogenation of VCH to styrene. In this paper we report a catalyst which provides 40%–50% conversion of n-butane at 80% selectivity to butadiene and the n-butenes when exposed to 5–10 s pulses of n-butane followed by air regeneration. The optimum catalyst consists of 15%–25% MoO 3 dispersed on MgO. The addition of small amounts of alkali metal compounds are used to minimize the production of carbon oxides. Characterization of these catalysts by laser Raman spectroscopy and XANES indicates that octahedral polymolybdates and micro crystals of MgMoO 4 are initially the major species at molybdenum loadings corresponding to maximum activity on fresh catalyst. Designed experiments have resulted in models predicting the relationship of selectivity and conversion for various process conditions.

Denitrification in tillage and no tillage pampean soils: Relationships among soil water, available carbon, and nitrate and nitrous oxide production

Abstract The interactions among the denitrification (DN) regulating factors under no tillage (NT) and conventional tillage (CT) during the production of a wheat crop were studied. The usefulness of the water field pore space (WFPS) as an indicator of the magnitude of the nitrous oxide (N2O) losses under the two tillage methods was also analyzed. The N2O production, mineralizable carbon (MC), WFPS, and nitrate (NO3) content were measured in a typic argiudol. The NT system increased N2O losses by DN at the 0–10 cm sampling depth because of its action on the MC and WFPS. Denitrification correlated significantly with the WFPS (r = 0.6, p<0.01), MC (r = 0.69, p<0.01), and NO3 content (r = 0.37, p<0.05). The influence of these factors on denitrification explained 55% of the differences between tillage methods, and as a consequence, we would suggest another possible influence of other factors not considered in this investigation. The addition of fertilizer (urea) would result in an increase in DN losses with nei...

Promotion effects of various oxides on oxidation of benzene over vanadium pentoxide catalysts

The effect of promoters on the activity and selectivity of the active sites was investigated in the selective oxidation of benzene over vanadium pentoxide catalysts. The activity per surface area is increased by addition of MoO 3, WO 3, P 2O 5 and SnO 2, but the activity of each redox sites, i.e., turnover frequency (TF), was not. This indicates that the promoters enhanced the activity by increasing the redox sites, such as the surface V O species. The selectivity to maleic anhydride (MA) was improved by the addition of MoO 3, WO 3 and P 2O 5, while it was lowered by SnO 2. The effect on the selectivity was discussed in the light of the electronegativity of promoter cations. The additions of MoO 3, WO 3 and P 2O 5, of which the cations are more electronegative than V 5+, decreased TF of the production of carbon oxides more seriously than that of MA. On the other hand, the addition of less electronegative cation, i.e., Sn 4+, increased TF of the production of carbon oxides at the sacrifice of MA.

Oxydehydrogenation of ethylbenzene to styrene over metal pyrophosphates: 2. Microbalance studies of carbon deposition and burnoff

A flow microbalance was used to measure the deposition of carbon from styrene and ethylbenzene and also the burnoff of carbon in oxygen in order to determine the role of carbon in the Oxydehydrogenation of ethylbenzene. Small amounts of oxygen enhance the rate of carbon deposition from styrene and the rate approaches zero at a carbon loading which corresponds closely with a graphitic monolayer. On selective catalysts, carbon burns at the same rate as that of graphite, whereas on nonselective catalysts it burns significantly faster. In the presence of styrene vapor, the rate of production of carbon oxides increases with increasing carbon levels. Reaction models indicate that in the presence of styrene vapor, carbon itself does not burn readily, but it does catalyze the burning of styrene and is the actual catalyst for the Oxydehydrogenation of ethylbenzene.

Thermal decomposition of energetic materials 11. Condensed phase structural characteristics and high rate thermolysis of di- and trinitroaliphatic carboxylic acids and carbonates

IR spectra of 3,3,3-trinitrobutyric acid, 1, 3,3-dinitrovaleric acid, 2, bis(2,2,2-trinitroethyl)carbonate, 3, and bis(2,2-dinitropropyl)carbonate, 4, were analyzed from 163K to the decomposition temperature. Below the decomposition temperature most of the structural alterations involve the COOH group. Once decomposition begins, the spectral changes also involve the CNO 2 groups. The backbone of the gem-dinitroalkyl compounds degrades more readily than the gem-trinitro compounds. Concentration-time profiles of the gas products from high-rate thermolysis (>75K s −1) show that NO 2 is the predominant initial decomposition product while CO 2 is initially important only from 2. NO is a major initial product of the gem-dinitro series but not the gem-trinitro series. Through the duration of observation, the concentration of the carbon oxidation products increases while [NO 2] decreases, suggesting that NO 2 is the principal oxidizing agent. The decomposition-to-deflagration transition occurs in the gem-trinitro compounds but not the gem-dinitro compounds under these experimental conditions.

Oxidation of methane over H-ZSM5 and other catalysts

The oxidation of methane has been studied in a flow system over an H-ZSM5 catalyst, using dioxygen and nitrous oxide as oxidants. Reaction with dioxygen gave only carbon dioxide product over a wide range of experimental conditions. However, reaction with nitrous oxide resulted in the production of carbon oxides, methanol, formaldehyde, lower olefins (ethylene and propylene) and C 6 C 12 aromatics. It is concluded that methanol is a primary oxidation product which may undergo further oxidation to formaldehyde and to carbon oxides, but which may also undergo conversion over the acidic catalyst to olefins and aromatics. Methane oxidation has also been examined over a range of other catalysts, some of which have been reported in the literature to yield partial oxidation products, but all gave only carbon oxide products.

Products from rapid heating of a brown coal in the temperature range 400–2300 °C

The devolatilisation behaviour of Yallourn brown coal was investigated under rapid heating conditions using two different flash pyrolysers: a fluid-bed reactor giving coal particle heating rates of 10 4 °Cs −1 with a gas residence time of about 0.5 s and a shock tube which generated heating rates of the order of 10 7 °Cs −1 and a 1 ms reaction time. Yields of products are reported covering pyrolysis temperatures in the range 400–2300 °C. Hydrocarbon gas yields reached maximum values which were remarkably similar for both reactors although occurring at different temperatures. Carbon oxide production was also similar for both reactors with CO yields reaching 30% wt/wt daf coal. These high yields of CO are very different from those reported for slow heating conditions. It appears that on flash heating, coal decomposition pathways change in a manner which increases CO yields at the expense of H 20 and to a lesser extent C0 2, resulting in the volatilisation of additional carbon from the coal.

Low-temperature atmospheric oxidation of mixtures of titanium and carbon black or boron

This article reports on the thermogravimetric investigation of mixtures of titanium no. 2 and carbon black with various mass carbon contents. Adding carbon black (as opposed to boron) to titanium leads to an increase in the rate of heat release of the oxidation reaction. An attempt is made to clarify the low-temperature oxidation mechanism of titanium mixtures in air. An x-ray phase and chemical (for bound carbon) analysis of specimens of a stoichiometric Ti + C mixture after heating in air to a temperature of 650/sup 0/C at the rate of 10/sup 0//min was conducted. The results indicate that the oxidation of the titanium-carbon mixture probably proceeds according to a more complex mechanism associated with the transport of the gaseous carbon oxidation products and their participation in the titanium oxidation.