Low-temperature Oxidation Reaction Research Articles

Experimental and kinetic modeling investigation on ethylcyclohexane low-temperature oxidation in a jet-stirred reactor

In this work, the oxidation of ethylcyclohexane was studied in a jet-stirred reactor at 780 Torr, 480–780 K and equivalence ratios of 0.5, 1.0 and 2.0. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used for the detection of oxidation products, including a series of reactive intermediates such as cycloalkylhydroperoxides, keto-hydroperoxides, alkenal-hydroperoxides and highly oxygenated molecules. Quantum chemistry calculations were performed to obtain ionization energies for the identification of some important intermediates and energy barriers of several important pathways. On the other hand, this work presents the first efforts on developing a low-temperature oxidation model of ethylcyclohexane. The present model can reasonably capture the low-temperature oxidation reactivities and negative temperature coefficient behaviors observed in both present and previous experimental work of ethylcyclohexane oxidation. Modeling analyses were performed to provide insight into the low-temperature oxidation chemistry of ethylcyclohexane. The two-stage O2 addition mechanism is concluded to dominate the chain-branching process in the low-temperature region. The concerted elimination reactions of cycloalkylperoxy radical and “formally direct” chemically activated reactions of cycloalkyl+O2 result in cycloalkenes and HO2 formation at the negative temperature coefficient region and serve as main chain-termination pathways. Compared with smaller cycloalkanes like cyclohexane and methylcyclohexane, the ethyl sidechain structure in ethylcyclohexane reduces the energy barriers of cycloalkylperoxy radical isomerization and facilitates the formation of keto-hydroperoxides which leads to more pronounced low-temperature oxidation reactivity of ethylcyclohexane.

Isomer-sensitive characterization of low temperature oxidation reaction products by coupling a jet-stirred reactor to an electron/ion coincidence spectrometer: case of n-pentane.

Through the use of tunable vacuum ultraviolet light generated by the DESIRS VUV synchrotron beamline, a jet-stirred reactor was coupled for the first time to an advanced photoionization mass spectrometer based upon a double imaging PhotoElectron PhotoIon COincidence (i2PEPICO) scheme. This new coupling was used to investigate the low-temperature oxidation of n-pentane, a prototype molecule for gasoline or diesel fuels. Experiments were performed under quasi-atmospheric pressure (1.1 bar) with a residence time of 3 s for two equivalence ratios (1/3 and 0.5) with a fuel initial mole fraction of 0.01. The measured time-of-flight mass spectra are in good agreement with those previously obtained with other photoionization mass spectrometers and, like those previous ones, display several m/z peaks for which the related species assignation is ambiguous. This paper shows how the analysis of the coincident mass-tagged Threshold PhotoElectron Spectra (TPES) together with first principle computations, consisting of the determination of the adiabatic ionization energies and the spectra of some products, may assist products' identification. The results mostly confirm those previously obtained by photoionization mass spectrometry and gas chromatography, but also allow a more accurate estimation of the 1-pentene/2-pentene mole fraction ratio. Our data also indicate a higher formation of acetone and methyl ethyl ketone than what is predicted by current models, as well as the presence of products that were not previously taken into account, such as methoxyacetylene, methyl vinyl ketone or furanone. The formation of three, four and five membered ring cyclic ethers is confirmed along with linear ketones: 2- and 3-pentanone. A significant general trend in indicating higher amounts of ketones than are indicated by gas chromatography is noted. Finally, TPES of alkenylhydroperoxides are also provided for the first time and constrains on the isomers identification are provided.

Possibilities of the Quantitative Comparison of Catalytic Capacity in Autocatalytic Processes of Palladium-Containing Nanocatalysts

When studying the nanocrystalline state, in some cases, an increase in functional activity is observed with an increase in the size of nanoparticles. In this case, the most active atoms are situated on the faces and have a higher coordination in comparison with the atoms on the tops and the edges. One of the explanations for this phenomenon is the formation of hypercycles due to the occurrence of autocatalytic processes. For oscillatory processes inherent in autocatalysis, when the parameters of a nonequilibrium process change over time, it is difficult to apply traditional methods of processing the results of analytical studies. In this regard, it is necessary to develop a methodology for a comparative study of short-term parameters of processes on the same scale, highlighting the main ones and eliminating insignificant and random ones, such as the phase shift at the beginning of self-oscillations or time-localized deviations from activity. This paper presents the results of such a study on the example of palladium-containing nanosystems in the reaction of low-temperature oxidation of CO. It is shown that the study of the behavior of nanocatalysts during the formation of hypercycles is informative using the calculated generalized parameters of the process

Study of low temperature oxidation reaction of n-heptane by accurate mass measurement of oxidized products using high-resolution mass spectrometry

Study of low temperature oxidation reaction of n-heptane by accurate mass measurement of oxidized products using high-resolution mass spectrometry

THAI process: Determination of the quality of burning from gas composition taking into account the coke gasification and water-gas shift reactions

In the last 13 years, the Toe to Heel Air Injection (THAI) process has been piloted in six heavy oil reservoirs located in three countries.In the THAI process, the production of upgraded oil along with the production of hydrogen is a proven and constant feature. Unlike the conventional in-situ combustion (ISC) process, THAI has a very extended, long zone for the chemical reactions, displaying a considerably longer residence time. In addition to primary reactions like high temperature oxidation and pyrolysis, reactions among the products of primary reactions, like coke gasification and water-gas shift reactions (WGSR) take place. Both in conventional ISC and in THAI, estimate of the burning quality can be made by calculating the apparent hydrogen-carbon ratio (H/C) from the composition of the produced gas. However, in THAI process some of the produced CO2 is not due to oxidation process itself and, therefore, does not characterize the burning process; it is produced by coke gasification and WGSR.An evaluation of this non-burning CO2 is conducted, and a new method, taking into account this non-burning CO2, is developed. This evaluation is based on a correlation between hydrogen and CO2 generated by coke gasification and WGSR, in a simplified form. The method has been applied for the on-going Kerrobert THAI Project (in Saskatchewan, Canada), where CO% was close to zero, while H2% remained high (2–4%)H/C ratio calculated with the old methodology would provide a false impression of a better quality burning in the THAI process, sometimes resulting in unrealistically low H/C values. When using the new method, the calculated H/C ratio would slightly increase. Although slightly increased, it has never taken values higher than 2, confirming that in THAI process the intensity of low temperature oxidation reactions is considerably lower than that in the conventional ISC process.

Low-temperature oxidation reactions of crude oils using TGA–DSC techniques

In this research, combustion behaviour of three crude oils with different °API gravities was analysed. The thermogravimetric analyser (TGA) and differential scanning calorimeter (DSC) experiments were performed using three different heating rates (2, 5, and 10 °C min−1) under air atmosphere. The reaction regions, burn-out temperatures, and peak temperatures were determined accordingly. Two main reaction regions, particularly the low-temperature oxidation (LTO) and high-temperature oxidation (HTO) reactions, were figured out in TGA and DSC curves, which suggested exothermic behaviour. Kinetic parameters of the crude oils were determined using model free methods (Ozawa–Flynn–Wall, OFW, and Kissinger–Akahira–Sunose, KAS), which allows the calculation of kinetic properties at progressive conversion degrees without the requirement of any reaction models and f(α) estimations. The variation in activation energy with respect to the conversion degree pointed out that the LTO reaction stage can be subdivided into three subzones. The results indicated that the activation energies were changing depending on the conversion degree, which is an indication of complex reaction mechanisms. The change in activation energy with respect to conversion degree showed slight variation for heavy crude oil compared with that in light crude oil.

The synthesis of hollow In2O3 @ Pd-Co3O4 core/shell nanofibers with ultra-thin shell for the low-temperature CO oxidation reaction

In this paper, a series of hollow In2O3 @ Pd-Co3O4 core/shell nanofibers with ultra-thin shell about 20–30 nm have been successfully fabricated by coaxial electrospinning, which used in CO oxidation. Desirably, the In2O3 @ Pd-Co3O4 exhibited the higher CO activity with T90 = 56 °C and lower activation energy. Through some characterizations, it is verified that ultra-thin shell structures, stronger redox ability, structure defects, higher proportion of Pd2+ species and smaller proportion of Co3+ species and higher chemical adsorbed oxygen species of In2O3 @ Pd-Co3O4 were preponderant to the increase of CO activity. Therefore, the In2O3 @ Pd-Co3O4 catalyst could be considered a prospective candidate for the CO oxidation.

Thermal effect caused by low temperature oxidation of heavy crude oil and its in-situ combustion behavior

To investigate the thermal effect caused by low temperature oxidation (LTO) of one heavy crude oil in porous media, a combustion tube (CT) system coupled with a self-designed experimental scheme was adopted. Also, the in-situ combustion (ISC) performance of this heavy oil as well as alterations in oil properties before and after ISC was comprehensively evaluated. The results showed that there existed the apparent thermal effect induced by LTO within the researched ignition temperature (180–320 °C), and heat release became greater with the ignition temperature. It should be noted that the oxidation reaction rate of the heavy oil was rose remarkably releasing substantial heat when the ignition temperature was increased to 240 from 180 °C. The heavy oil was combusted under the ignition temperature of 350 °C, and the combustion front advanced sustainably. Some basic parameters during ISC, including apparent atomic H/C ratio, oxygen utilization, fuel consumption, etc., were determined, which made it accessible to predict field test performances. And the values of these parameters and post-mortem images of the CT test reflected the superior ISC performance of the heavy oil. The alterations in oil properties pre-ISC and post-ISC indicated that the produced oil encountered strong LTO reactions and thermal cracking reactions forming a considerable number of lighter oxygen-containing compounds. Comparison of differential scanning calorimetry (DSC) profiles of the crude oil and produced oil revealed that the ISC process made the heavy oil greatly upgrade.

Chemical kinetic study of triptane (2,2,3-trimethylbutane) as an anti-knock additive

2,2,3-Trimethylbutane (i.e., triptane) is a potential gasoline octane booster with a research octane number (RON) of 112. Recent studies showed that it can be catalytically produced with high selectivity from methanol (CH3OH) and dimethyl ether (DME), which presents a promising route for utilizing biomass derivatives as transportation fuels. Understanding the ignition properties of triptane at engine relevant conditions is crucial for its further evaluation.In this work, a detailed kinetic model for triptane combustion is developed and validated. The rate rules for the low-temperature oxidation reactions are evaluated based on quantum chemistry calculations from literature, and thermochemical properties of all the species are assessed based on new thermodynamic group values with careful treatment of gauche interactions. In addition, alternative isomerization pathways for peroxy-alkylhydroperoxide species (ȮOQOOH) are incorporated in the model.The model is validated against new ignition delay data from facilities at King Abdullah University of Science and Technology (KAUST): rapid compression machine (RCM) experiments at pressures of 20 and 40 bar, equivalence ratios of 0.5 and 1 and across a temperature range of 620 to 1015 K, and shock tube experiments at 2 and 5 bar, 0.5 and 1 equivalence ratio and over 1000–1400 K. Moreover, the model prediction of various species is compared against species profiles from jet stirred reactor experiments at three equivalence ratios (0.5, 1 and 2) at atmospheric pressure. Finally, triptane is compared with its less branched isomers, n-heptane and 2-methylhexane, to evaluate the effect of branching on fuel reactivity and importance of alternative isomerization pathway.

Effect of Zr Content on the Activity of 5%СuO/Ce1– xZrxO2 Catalysts in CO Oxidation by Oxygen in the Excess of Hydrogen

The article reports the synthesis of 5%CuO/Ce1– xZrxO2 catalysts based on CeO2, ZrO2 oxides and Ce1– xZrxO2 solid solutions with х = 0.2, 0.5, and 0.8. It is found that copper oxide is present in the catalysts in a highly dispersed form. In strong interaction with supports, it forms active oxygen, which participates in CO chemisorption and low-temperature oxidation of CO in the presence of hydrogen. In selective CO oxidation, the highest conversion (γmах = 100%) was obtained at temperatures of 120–160°С in the presence of 5%CuO/CeO2. In the modification of CeO2 by zirconium cations, the conversion on 5%Ce0.5Zr0.5O2 decreases to 92% at 160°С because oxygen binding strengthens on copper-containing sites. On the 5%CuO/ZrO2 sample, the maximum conversion is 67% at 180°С. The modification of ZrO2 by cerium cations leads to an increase in the conversion to 87% at 160°С on the 5%CuO/Ce0.2Zr0.8O2 sample as a result of increasing the amount of oxygen vacancies in the support. Taking into account the properties of CO complexes formed on copper-containing oxidation and adsorption sites, and the interaction of these complexes with adsorbed oxygen, their participation in the reaction of low-temperature CO oxidation by oxygen in excess of hydrogen on 5%CuO/CeO2 and 5%CuO/ZrO2 catalysts is considered.

Experimental study on the mechanism of enhanced oil recovery by air-assisted cyclic steam stimulation process in extra-heavy oil reservoirs

ABSTRACTWith the increasing demand of energy, extra-heavy oil has attracted more and more attention at present. Cyclic steam stimulation (CSS) process is one of the main methods to produce extra-heavy oil, however with the increase of stimulation cycle, the periodic oil production of well decreases obviously and the water cut increases significantly. As non-condensable gas, surfactant, high-temperature foam, horizontal well technology, and other assisted CSS methods have been applied in heavy oil reservoirs, it indicates that CSS process has been developing toward diversification. Air-assisted cyclic steam stimulation (AACSS) process has become a more and more popular technique for developing extra-heavy oil due to its abundant sources and low cost. In this paper, static oxidative experiments were carried out to study the mechanism of low-temperature oxidation (LTO) reaction of extra-heavy oil and the effect of temperature, pressure, and catalyst on the LTO reaction. In addition, four groups of CSS experiments were conducted to compare the development performance of different stimulation methods, such as conventional CSS, first-injection AACSS, simultaneous-injection AACSS, and later-injection AACSS. The results show that the system pressure and O2 content decreased, but carbon oxides increased after LTO reaction. The residue O2 content decreased from 21% to below 12% under the safety risk of explosion caused by the mixture of O2 and hydrocarbon gases. During LTO process, both cracking reaction and polymerization reaction of molecule occurred in the extra-heavy oil, which increased the content of saturates and aromatics, while decreased the content of heavy components. LTO reaction also increased the oil viscosity because of the increase of asphaltene content. But pyrolysis reaction would upgrade the extra-heavy oil and decrease the asphaltene content of extra-heavy oil under high-temperature condition. Besides, the higher the reaction temperature and pressure, the faster the reaction and the lower the O2 content. Moreover, the catalyst could enhance the LTO reaction and O2 consumption. Based on the larger scale sand pack experiments, the results indicate that AACSS could effectively improve the oil recovery compared with conventional CSS, and air injection after injecting steam during each cycle could achieve the highest recovery.

Catalytic Effect of Cobalt Additive on the Low Temperature Oxidation Characteristics of Changqing Tight Oil and Its SARA Fractions

Air flooding is a potential enhanced oil recovery (EOR) method to economically and efficiently develop a tight oil reservoir due to its sufficient gas source and low operational costs, during which low temperature oxidation (LTO) is the key to ensuring the success of air flooding. In addition to inefficiency of conventional LTO, air flooding has seen its limited applications due to the prolonged reaction time and safety constraints. In this paper, a novel air injection technique based on the catalyst-activated low temperature oxidation (CLTO) is developed to improve the operational safety together with its oil recovery in tight oil reservoirs. Experimentally, static oxidation experiments are conducted to examine the influence of the catalyst on the LTO reaction kinetics of Changqing tight oil and its fractions. The catalytic oxidation characteristics are identified by applying a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR) with respect to tight oil and its SARA (i.e., saturates, aromatics, resins, and asphaltenes) fractions. Accordingly, the catalyst can obviously decrease the LTO reaction activation energy of the Changqing tight oil and its SARA fraction. Cobalt additive can change the LTO reaction pathways of the SARA fractions, i.e., promoting the formation of hydroxyl-containing oxides and CO2 from the oxidation of saturates, aromatics and resins, while inhibiting the formation of ethers from the oxidation of aromatics and resins. The LTO of each SARA fraction contains both oxygen addition reaction and bond scission reaction that can be effectively promoted with the cobalt additive. The catalytic effect on the bond scission reaction is continuously enhanced and becomes gradually stronger than that on the oxygen addition reaction as the reaction proceeds.

Integrative Investigation of Low-Temperature Oxidation Characteristics and Mechanisms of Heavy Crude Oil

During an in situ combustion (ISC) process, low-temperature oxidation (LTO) is of vital significance for the follow-up oxidation reactions and oil recovery. Herein, this work is intended to carry out in-depth investigations regarding LTO of heavy crude oil. Alterations of evolved gas compositions and oil properties caused by LTO were first examined. Then the particular focus was placed on the analyses of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) of oxidized oil samples. The results indicated that the LTO degree was intensified with the oxidation temperature, during which produced gas compositions and the contents of element, saturates–aromatics–resins–asphaltenes (SARA) fractions, free radicals, and hydrogen groups of oils changed obviously. Furthermore, part of the main LTO reactions are given in this paper. On the basis of these reactions and experimental results obtained, some aspects of LTO mechanisms of the oil are stated, which were highly valuable for ISC field appl...

Oxidation kinetic evaluation of the low temperature oxidized products of Tahe heavy oil characterized by the distributed activation energy model

In view of the significance of low temperature oxidation (LTO) for in-situ combustion (ISC) of heavy crude oil and to provide further data for Tahe ISC numerical simulation, this research aimed to investigate the non-isothermal oxidation behavior of heavy oil after static LTO reactions. Thermogravimetric (TG) and differential scanning calorimetry (DSC) techniques were used to characterize oxidation behavior, and distributed activation energy method (DAEM) was used to calculate kinetic parameters. The results showed that the non-isothermal oxidation process of static LTO oxidized oil was the result of the interaction between residue and coke, and coke can significantly reduce the activation energy of oxidized oil. Only one HTO region was identified for the coke from DTG/DSC curves, and it had the lowest activation energy (114.57 kJ/mol) and the highest heat enthalpy (24.3 kJ/g), indicating high oxidative activity with maximum heat release potential. A satisfactory corresponding relation between DTG and DSC curves was presented for all samples in FD and HTO regions, which indicated that the sequential reaction mechanisms, fuel deposition and combustion, were undergone. In LTO region, there was a temperature difference between the peaks of the mass loss and heat flow, indicating that the LTO process was more complex with a multi-step control mechanism should be considered to analyze and simulate the LTO stage.

EFFECT OF DURATION OF THE BENTONITE ACID MODIFICATION ON THE ACTIVITY OF PD(II)-CU(II) CATALYTIC COMPOSITIONS IN THE REACTION OF CARBON MONOXIDE OXIDATION

The effect of duration of the bentonite acid modification on its physicochemical and structural parameters and also on the catalytic properties of bentonite anchored palladium-copper complexes in the reaction of low-temperature carbon monoxide oxidation with air oxygen has been studied. For all acid modified bentonite samples, 1H-Bent-τ (τ = 0.5, 1.0, 3.0, 4.0, and 6.0 h), some regularities of changes as compared with natural bentonite, N-Bent, in the bentonite phase composition and X-ray spectral parameters of montmorillonite that is a samples, regardless a contact time, τ, the montmorillonite crystalline structure does not change however its aluminosilicate layers constrict for both bentonite acid modified samples and Pd(II)-Cu(II)/1H-Bent-τ compositions. After acid treatment, the number and positions of IR bands characterizing structural groups Al-Al-OH, Al-Fe 3+ -OH, Si-O-Si, and Si-O-Al of Mont phase do not change however their intensities, except for Si-O-Si, decrease pointing to the loss of Al 3+ and Fe 3+ cations. Palladium-copper complexes can be anchored not only on Mont structural groups but also on surfaces of quarts, amorphous SiO 2 , and calcite if any. It has been found that the changes in physicochemical and structural parameters of the bentonite samples result in alterations in the catalytic activity of Pd(II)-Cu(II)/S— compositions (S— is N-Bent or 1H-Bent-τ) in the reaction of carbon monoxide oxidation with air oxygen. The composition based on 1Н-Бент-0.5 characterizing by the minimum pH value of its aqueous suspension shows the maximum catalytic activity: CO conversion is 78 %.

Tetraalkylammonium Salts of Platinum Nitrato Complexes: Isolation, Structure, and Relevance to the Preparation of PtOx/CeO2 Catalysts for Low-Temperature CO Oxidation

A series of tetraalkylammonium salts with anionic platinum nitrato complexes (Me4N)2[Pt2(μ-OH)2(NO3)8] (1), (Et4N)2[Pt2(μ-OH)2(NO3)8] (2), ( n-Pr4N)2[Pt2(μ-OH)2(NO3)8] (3b), ( n-Pr4N)2[Pt(NO3)6] (3a), and ( n-Bu4N)2[Pt(NO3)6] (4) were isolated from nitric acid solutions of [Pt(H2O)2(OH)4] in high yield. The structures of salts 2, 3a, 3b, and 4, prepared for the first time, were characterized by X-ray diffraction. The sorption of [Pt(NO3)6]2- and [Pt2(μ-OH)2(NO3)8]2- complexes onto the ceria surface from acetone solutions of salts 4 and 1 was examined. The dimeric anion was shown to quickly and irreversibly chemisorb onto the CeO2 carrier, selectively transforming into Pt(II) centers after thermal treatment, becoming active in the low-temperature CO oxidation reaction ( T50% = 110 °C at a space velocity of 240 000 h-1). By contrast, the homoleptic complex [Pt(NO3)6]2- did not interact with the ceria, which may be attributed to the substitutional inertness of the [Pt(NO3)6]2- anion. We believe that the strategy based on the sorption of polynuclear platinum nitrato complexes is an effective route to prepare ionic platinum species uniformly distributed on an oxide carrier for various catalytic applications.

Thermal Behavior and Kinetic Triplets of Heavy Crude Oil and Its SARA Fractions during Combustion by High-Pressure Differential Scanning Calorimetry

In situ combustion (ISC) has been regarded as an efficient technique for the exploitation of heavy oil reserves. In this work, the thermal behavior of one heavy crude oil and the fractions of its saturates, aromatics, resins, and asphaltenes (SARA) during combustion was thoroughly investigated using high-pressure differential scanning calorimetry. Two typical isoconversional methods were adopted to determine the variation of activation energy (E) and frequency factor (Ar) versus conversion degree in the course of the reaction, followed by the evaluation of the reaction model, f(α), via the master plot method. The results indicated that the heavy oil encountered larger thermal release caused by low-temperature oxidation (LTO) reactions rather than high-temperature oxidation (HTO) reactions, suggesting that appreciable heat could be available within the low-temperature range. Saturates showed a notably apparent heat release in the LTO reactions. For aromatics, the exothermic effect at the LTO stage was appa...

Controlled synthesis of Pd/CoOx–InOx nanofibers for low-temperature CO oxidation reaction

Herein, we report a series of Pd/CoOx–InOx nanofibers with different morphologies (such as nanofibers, porous nanofibers and bead-like nanofibers) via electrospinning, annealing and impregnation methods.

Flame Propagation Enhancement by Dielectric Barrier Discharge-Generated Intermediate Species

ABSTRACT The interaction between nonthermal plasma (NTP) and fuel-air mixtures was studied both experimentally and by means of simulations, to elucidate their promotional effect on flame propagation. A promotional effect on flame propagation velocity was experimentally observed by generating a dielectric barrier discharge (DBD), prior to spark plug ignition of an n-heptane mixture in a high-pressure and -temperature environment, using a rapid compression and expansion machine (RCEM). A novel method of concentration calibration for mass-spectral analysis was conducted, to determine the intermediate species in the fuel-air mixtures passing through the DBD plasma. The effect of the intermediate chemical species on flame propagation was examined numerically using the PREMIX code, with the observed species being considered as initial additives in the calculations. The promotional effect was reproduced numerically with the addition of alkyl hydroperoxide to an n-heptane/air mixture; and the higher the temperature and leaner the mixture in the parameter region, the more pronounced was the effect. The promotional behavior was examined using reaction path analysis, on the basis of which enhanced low-temperature oxidation reactions, due to the dissociation of the alkyl hydroperoxide, were determined in pre-flame region.

No.1-6 湿潤雰囲気における石炭の低温酸化反応性評価

No.1-6 湿潤雰囲気における石炭の低温酸化反応性評価