N-heptane Oxidation Research Articles

Decoupling Analysis of Ignition Processes of Ammonia/N-Heptane Mixtures

Abstract: To further understand the influence of n-heptane on the ignition process of ammonia, an isotope labeling method was applied in the current investigation to decouple the influence of the chemical effect, the thermal effect, and the effect of O radical from the oxidation of n-heptane on the ignition delay times (IDTs) of ammonia. An analysis of the time evolution of fuel, analysis of the time evolution of temperature, rate of consumption and production (ROP) analysis, and sensitivity analysis were conducted to gain a further understanding of the mechanism of the influence of the chemical effect, the thermal effect, and the effect of O radical on the ignition of ammonia. The results showed that the negative temperature coefficient (NTC) behavior of n-heptane is mitigated by the blending of ammonia, and this mitigated effect of ammonia is mainly due to the chemical effect. The IDTs of ammonia under low and medium temperatures are significantly shortened by the chemical effect at a n-heptane mass fraction of 10%. The promoting effect of the chemical effect decreases when the n-heptane mass fraction increases. The time evolution of n-heptane for NC7H16/ND3-G can be classified into three stages at 800 K, and the rapid consumption stage is mitigated by an increase in temperature. The rapid consumption stage is suppressed by the chemical effect of ammonia, while O radical has a promoting effect on the rapid consumption stage. The chemical effect will enhance the sensitivities of reactions associated with ammonia. As the n-heptane mass fraction increases, the sensitivities of reactions associated with n-heptane are enhanced. Correspondingly, the effect of reactions associated with ammonia is weakened. When the n-heptane mass fraction is 30%, only reactions related to n-heptane have a great influence on the ignition of ammonia/n-heptane fuel blends under the thermal effect + the effect of O radical or only the thermal effect.

Effect of methanol-water mixtures on the oxidation of n-heptane at low to intermediate temperatures: Experimental and numerical study

Methanol is widely recognized as a carbon-neutral fuel. This work used synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) to study the oxidation process of water/methanol/n-heptane mixes in a jet-stirred reactor (JSR) at a pressure of 1 atm, equivalence ratios (ϕ) of 1 and a temperature range of 500–1100 K. The results of the experiment indicate that the inhibition of n-heptane's oxidation at low temperatures (500–740K) is the primary manifestation of the action of methanol/water mixtures on n-heptane oxidation. The strong interactions among the components of water/methanol/n-heptane mixtures at low temperatures are primarily between methanol and n-heptane. The higher the methanol content, the greater the strength of inhibition of n-heptane oxidation. This inhibitory effect primarily results from the competition of methanol with ˙OH radicals. It is noteworthy that the chemical kinetic interactions between methanol-water mixtures and n-heptane not only manifest changes in the ˙OH radical pools but are also associated with the intermolecular chemical kinetic interactions between peroxyalkyl radicals (ROO˙) and CH3OH.

Effects of different ammonia energy ratio on soot formation and oxidation in an ammonia diesel dual-fuel engine

Due to environmental pollution and energy crises, zero‑carbon fuel ammonia (NH3) has attracted extensive attention as an alternative fuel for engines. In this paper, the effects of ammonia energy ratio (AER) and injection strategy on particulate emission characteristics of an ammonia diesel dual-fuel engine were examined by merging experimental and simulation results; additionally, soot formation and oxidation mechanism were investigated. Results showed that the reduction in particulate emission was substantially higher than the increase in AER. When AER increased to 60 %, the reduction in particulate mass concentration reached 97.5 %. The initial soot formation area gradually moved to the bottom of the piston bowl with increasing AER. When the piston reached the top dead center, the high-soot-concentration area was shifted to the center of the piston bowl as AER increased. The contents of acetylene (C2H2) and methyl (CH3) reduced considerably, which restricted the formation of soot precursors. With AER increasing, the contents of nitric oxides (NOx) and other nitrogen-containing species increased and reacted with CH3 and other carbon-containing species, which effectively reduced the number of C in soot formation pathway, thereby lowering particulate emissions. As AER increased, hydroxyl (OH) involved in soot formation gradually decreased, and only 14 % of OH was involved in the oxidation of n-heptane at 60 % AER, which was favorable for reducing the soot formation rate. Furthermore, OH is a substantial species in soot oxidation. The introduction of ammonia caused an increase in OH, which facilitated the removal of soot. The decrease in hydrogenium (H) hindered the hydrogen–abstraction–acetylene–addition (HACA) reaction, further limiting the soot surface growth. By optimizing the injection timing and AER, particulate emission was lowered to 4.31 × 10−5 μg/cm3, and particle size was reduced by 64.2 % when AER was 60 %, injection timing was −20° CA ATDC, and injection pressure was 60 MPa.

Unveiling the crucial active sites responsible for CO, n-heptane, and toluene oxidation over Pt/ZrO2 catalyst

The surface Pt species and adsorbed oxygen on the Pt/ZrO2 catalyst were successfully modulated by altering the preparation methods, resulting in distinct catalytic behaviors for CO, n-heptane, and toluene oxidation. The Pt/ZrO2 catalyst was initially prepared via wetness impregnation and subsequently reduced in an H2 atmosphere to obtain the Pt/ZrO2-R catalyst. In contrast, the Pt/ZrO2-E catalyst was synthesized using ethanol solvent (also serving as a reducing agent) instead of water during wetness impregnation. Moreover, the pre-prepared Pt nanoparticles were loaded onto the ZrO2 surface using polyvinylpyrrolidine (as a protective and structure directing agent) dissolved in ethanol solvent to fabricate the Pt/ZrO2-EP catalyst. Among these catalysts, the Pt/ZrO2-R exhibits superior catalytic activity towards CO oxidation due to its abundant metallic Pt species. It is found that activity of Pt/ZrO2 catalyst for n-heptane oxidation is positively correlated with its surface adsorbed oxygen concentration, thus the highest activity is achieved over the Pt/ZrO2-EP catalyst possessing a higher concentration of surface adsorbed oxygen species. Unlike CO and n-heptane oxidation, toluene oxidation activity is affected by multiple factors, it is primarily promoted by synergistic catalysis between metallic Pt species (Pt0) and surface adsorbed oxygen species over the Pt/ZrO2-EP catalyst. Our preliminary findings underscore that precise modulation of sensitive active sites on surfaces plays a critical role in specific catalytic reactions.

Mechanism insights into low-temperature oxidation of n-heptane on CeO2 surface: A DFT study

The low-temperature oxidation (LTO) mechanism of n-heptane on CeO2 surfaces was investigated in this study employing density functional theory (DFT). Firstly, the adsorption conformations of relevant species were optimized, and the main reaction steps' energy barriers and reaction-rate coefficients were calculated. The results show that the hydroxyl groups of fuel radicals strengthen the adsorption of fuel radicals on CeO2 surfaces. Furthermore, the energy barriers associated with the low-temperature (LT) chain branching pathway of n-heptane on the CeO2 surface exhibit lower values compared to those observed in the gas phase. The presence of CeO2 is also observed to mitigate the detrimental impact of competing reactions on the low-temperature branching pathway of n-heptane. It should be noted that the energy barrier for the decomposition of H2O2 on the CeO2 surface is 32.575 kcal/mol, 33.2 % lower than that in the gas phase, which allows H2O2 to be decomposed much easier at low temperatures. The resultant OH radicals desorb to the intimated gas phase, accelerating the oxidation of fuel molecules in the gas phase. Therefore, n-heptane transitioned to high-temperature ignition more easily and rapidly in the presence of CeO2. The calculation's findings adequately explain the experimental finding that adding CeO2 improves diesel fuel combustion.

SIMULATION OF THE KINETICS OF HETEROGENEOUS OXIDATION OF N-HEPTANE BY OXYGEN

The catalytic reaction of n-heptane (n-C7H16) oxidation with molecular oxygen has been studied. Various compositions of the polymer catalyst Mn-P4VP/MBAA (where Mn-P4VP is manganese-immobilised poly-4-vinylpyridine and MBAA is N,N′-methylene-bis-acrylamide) containing 2-5 wt% Mn were prepared and tested. The concentration of manganese in the catalyst based on immobilized metal-polymer complexes is within the range of 2-5 wt% Mn. The oxidation reaction was carried out at a ratio of components n-C7H16/O2/polymer catalyst with Mn = 1 : 3.38 : 0.003 and time 6 h within the temperature range 303-383 K. The data on the yield of the major products of n-heptane oxidation are presented, taking into account the initial components, catalyst composition, temperature and the time of oxygen contact with the reacting components. It has been established that during the oxidation of n-C7H16 (303-383 K), the yield of alcohols is higher than the yield of other oxidation products. The oxidative conversion of n-heptane increases from 45 to 75 mol% with an increase in temperature in the range of 303-383 K. For the multistage oxidation of n-heptane with oxygen, a kinetic model was selected and considered. On the basis of this model, the reaction rate constants were calculated in the range of 303-383 K considering the degree of heptane conversion. The activation energy of n-heptane oxidation was estimated, taking into account the method of choosing the most plausible parameter and experimental data on n-heptane convection.

A Data-Based Hybrid Chemistry Acceleration Framework for the Low-Temperature Oxidation of Complex Fuels

The oxidation of complex hydrocarbons is a computationally expensive process involving detailed mechanisms with hundreds of chemical species and thousands of reactions. For low-temperature oxidation, an accurate account of the fuel-specific species is required to correctly describe the pyrolysis stage of oxidation. In this study, we develop a hybrid chemistry framework to model and accelerate the low-temperature oxidation of complex hydrocarbon fuels. The framework is based on a selection of representative species that capture the different stages of ignition, heat release, and final products. These species are selected using a two-step principal component analysis of the reaction rates of simulation data. Artificial neural networks (ANNs) are used to model the source terms of the representative species during the pyrolysis stage up to the transition time. This ANN-based model is coupled with C0–C4 foundational chemistry, which is used to model the remaining species up to the transition time and all species beyond the transition time. Coupled with the USC II mechanism as foundational chemistry, this framework is demonstrated using simple reactor homogeneous chemistry and perfectly stirred reactor (PSR) calculations for n-heptane oxidation over a range of composition and thermodynamic conditions. The hybrid chemistry framework accurately captures correct physical behavior and reproduces the results obtained using detailed chemistry at a fraction of the computational cost.

Investigation of the NH3 consumption and H2O/NO formation during the oxidation of n-heptane and iso-octane blended with ammonia

Adding highly active fuels with ammonia is a compromising way to increase the mixture's reactivity. However, there are very few studies blending ammonia with large hydrocarbons, such as n-heptane and isooctane. In this study, the NH3, NO, and H2O time-histories were simultaneously measured during the oxidation of ammonia/n-heptane and ammonia/isooctane mixtures (equivalence ratio ϕ ∼ 1.2) in a shock tube. For the ammonia/n-heptane mixture, a reduced kinetics model, the Wang 2023 model, shows the best predictions in terms of the mixture reactivity and the H2O production but underpredicts the NO plateau. For the ammonia/isooctane mixture, the CRECK_TPRF_Alcohols_NOx (CRECK) model is the only available kinetics model containing ammonia and isooctane mechanisms. The CRECK model captures the H2O plateau but underpredicts the ammonia/isooctane mixture reactivity and the NO plateau. Detailed analyses are conducted based on the Wang 2023 and CRECK models. Rate-of-production (ROP) analyses reveal that: the consumption or formation pathways of the three species in the two models are basically the same but the magnitudes of the ROPs are quite different, especially for the NO formation; the reaction of ethylene or propylene with NH2 radical in the Wang 2023 model also contributes significantly to the NH3 consumption but they are not considered in the CRECK model. Sensitivity analyses show that: H + O2 = O + OH is the most promoting reaction for both mixtures and models; however, several reactions show strong effects in one mixture while having little effect in another mixture, or even playing an opposite effect. After modifying or adding some key reactions, the Wang 2023 and CRECK models get significantly improved in predicting the species' time-history during the oxidation of the ammonia/n-heptane or ammonia/isooctane mixture.

An experimental and kinetic modeling study on low-temperature oxidation of gasoline and diesel/polyoxymethylene dimethyl ether (OME3) blends

In this work, the low-temperature oxidation of polyoxymethylene dimethyl ether (OME3) with multi-component surrogates for diesel (DS:60%n-heptane/20%cyclohexane/20%toluene) and gasoline (GS:20%n-heptane/60%iso-octane/20%toluene) blends was investigated respectively using a jet-stirred reactor (JSR) with a temperature range of 500–950 K, constant fuel fraction of 0.008, residence time (τ) of 2 s and near atmospheric pressure. Two detailed multi-component kinetic mechanisms were established to describe the low-temperature oxidation characteristics and the interaction of blended fuels. Generally, the oxidation process of highly-reactive OME3 and n-heptane is inhibited, while that of inactive fuels, including iso-octane, cyclohexane and toluene, are triggered and enhanced in various degrees in the blends. The OH radical acts as a bridge between high and low reactivity components. It is of interest that n-heptane reveals a quite different low-temperature oxidation behavior in diesel (DS) and gasoline (GS) surrogate respectively. In GS, the low-temperature oxidation of n-heptane is significantly inhibited, while in DS, the inhibition is mild, mainly due to the much different low-temperature oxidation characteristics of iso-octane and cyclohexane. As for OME3, it mainly improves the reactivity of the blends in the negative temperature coefficient (NTC) process. As for low-reactivity fuels of iso-octane and toluene, their low-temperature oxidations are completely triggered and dominated by highly-reactive fuels due to their weak OH build-up ability. On the contrary, when the low-temperature oxidation of cyclohexane is triggered, its self-enhancement also plays a crucial role in addition to the promoting effect from highly-reactive fuels. Therefore, cyclohexane reveals a promoting-ignition effect on the blended fuels, while iso-octane and toluene act as an inhibiting-ignition factor in blends.

Impacts of NO on low-temperature oxidation of n-heptane in a jet-stirred reactor

Low-temperature (low-T) oxidation experiments of n-heptane –with and without NO addition– were experimentally and numerically investigated at stoichiometric conditions in a jet-stirred reactor. Experiments were performed at atmospheric pressure over a temperature range of 500–800 K. Reactants, intermediates, and products, were measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A detailed kinetic model was developed to gain insight into the chemical effect of NO on low-T oxidation chemistry of n-heptane. Taking 650 K as the transition temperature, the results revealed that NO addition exhibited an inhibiting effect on fuel reactivity below 650 K and a promoting effect above 650 K. The reactions of ROO + NO = RO + NO2 and HO2 + NO = OH + NO2 at different temperature regions were responsible for the inhibition and promotion effects, respectively. Evidence gathered from both experimental measurements and kinetic model predictions indicated that NO addition had a significant inhibitory effect on the formation of cool flame species during the low-T oxidation process. NO suppressed low-T oxidation via the reaction of ROO + NO = RO + NO2, which impeded the subsequent isomerization, O2 addition, OH-, and HO2-elimination reaction, and influenced product distribution of the cool flame species. The experimental observations provided detailed information about these reactive intermediates, which offered new insights into low-T oxidation phenomena and clarified the importance of NO reactions which prevent the formation of cool flame products during low-T oxidation.

Oxidation of Methane/n-Heptane Mixtures in a High-Pressure Flow Reactor

To evaluate the use of diesel as a pilot fuel in natural gas combustion in two-stroke maritime engines, research on high-pressure oxidation of methane/n-heptane mixtures is of interest. In this study, laminar flow reactor experiments were conducted at pressures of 21 and 100 bar, temperatures in the range 450–900 K, and under stoichiometric and fuel-lean conditions. For all conditions, the n-heptane conversion starts below 600 K. A pronounced negative temperature coefficient region was observed at 21 bar. The n-heptane was depleted at all conditions before reaching 900 K. Methane oxidation was initiated once n-heptane was consumed. Compared to the oxidation of pure n-heptane and NH3/n-heptane mixtures, the presence of methane promoted n-heptane oxidation in the full temperature range. The model from Zhang et al. provided overall a good agreement with the experimental data. However, the low-temperature conversion of n-heptane at 21 bar and stoichiometric conditions is underpredicted, possibly because some chemical coupling between n-heptane and methane is missing in the model.

Hybrid Silsesquioxane/Benzoate Cu7-Complexes: Synthesis, Unique Cage Structure, and Catalytic Activity

A series of phenylsilsesquioxane-benzoate heptacopper complexes 1-3 were synthesized and characterized by X-ray crystallography. Two parallel routes of toluene spontaneous oxidation (into benzyl alcohol and benzoate) assisted the formation of the cagelike structure 1. A unique multi-ligation of copper ions (from (i) silsesquioxane, (ii) benzoate, (iii) benzyl alcohol, (iv) pyridine, (v) dimethyl-formamide and (vi) water ligands) was found in 1. Directed self-assembly using benzoic acid as a reactant afforded complexes 2-3 with the same main structural features as for 1, namely heptanuclear core coordinated by (i) two distorted pentameric cyclic silsesquioxane and (ii) four benzoate ligands, but featuring other solvate surroundings. Complex 3 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with hydrogen peroxide and tert-butyl hydroperoxide, respectively, at 50 °C in acetonitrile. The maximum yield of cyclohexane oxidation products as high as 32% was attained. The oxidation reaction results in a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone. Upon the addition of triphenylphosphine, the cyclohexyl hydroperoxide is completely converted to cyclohexanol. The specific regio- and chemoselectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicate the involvement of of hydroxyl radicals. Complex 3 exhibits a high activity in the oxidation of alcohols.

An experimental and modeling study on the oxidation of ammonia and n-heptane with JSR

The oxidation of neat ammonia, n-heptane, and ammonia/n-heptane blends was investigated both experimentally and numerically. Experiments were carried out in a fused silica jet-stirred reactor (JSR) under atmospheric pressure and lean conditions covering a temperature range of T=500–1200 K. Mole fraction profiles of 28 species were obtained with online SVUV-PIMS and GC techniques. A detailed analysis of reaction products and intermediates was performed, and the results were interpreted with an improved kinetic model, describing the oxidation of ammonia and n-heptane, as well as fuel interaction and NOx formation. The measurements indicate that ammonia reactivity is promoted by n-heptane addition at wide-ranging temperatures, while ammonia addition can also accelerate the oxidation process of n-heptane, especially at intermediate temperatures, manifesting mutual reinforcement in oxidation reactivity. Kinetic analysis shows that the low-temperature reaction of n-heptane generates reactive species that initiate and interact with the oxidation of ammonia along the pathway of NH2→H2NO/HNO→NO→NO2 at low temperatures. As the reaction pathway changes with increasing temperature, n-heptane oxidation likely provides the radical pool necessary to trigger ammonia oxidation through H2O2 decomposition at an intermediate temperature; while ammonia oxidation in turn accelerates the generation of hydroxyl radicals via NOx chemistry as a more direct pathway. As such, a self-reinforcing looping cycle could be formed, leading to the rapid oxidation of ammonia/n-heptane blends at intermediate temperatures. It is noted that despite the good overall performance, the kinetic model under-predicts NOx concentration and only qualitatively captures the rapid oxidation behavior. More kinetic modeling work is necessary in order to better understand the co-oxidation mechanism of ammonia and large hydrocarbons at wide-ranging operating conditions.

Numerical and experimental studies on minimum ignition energies in primary reference fuel/air mixtures

Understanding flame initiation is of great interests to combustion research. For induced ignition, a minimum ignition energy (MIE) must be provided by an external ignition source for the formation of a flame kernel. In this paper, the minimum ignition energy in lean primary reference fuel (PRF) /air mixtures is investigated by simulations and experiments. The simulations feature a detailed treatment of chemical kinetics and molecular transport to solve the conservation equations for a flame evolving from an ignition source. In the experiments, a cruciform burner is used for the ignition of the fuel/air mixture. After applying the heat source, three qualitatively different types of evolution are observed: ignition failure, flame kernel formation with subsequent flame extinction, and flame propagation. We define two kinds of MIEs: one for flame initiation, and one for flame propagation. The dependence of MIE for flame propagation on the research octane number (RON) in both experiments and simulations exhibits an upturn at a certain RON: Below this RON, the MIE for flame propagation increases weakly, and above this RON, the MIE for flame propagation increases rapidly with increasing RON. The existence of the upturn can be explained by different reaction pathways of the n-heptane and iso-octane flame. At smaller RON, the massive production of C2H5 during the oxidation of n-heptane helps to sustain the critical early phase of flame with strong diffusion. The results in this study highlight the importance of the interaction between chemical reactions and transport for understanding behaviours of practical ignition processes.

Mononuclear Oxidovanadium(IV) Complexes with BIAN Ligands: Synthesis and Catalytic Activity in the Oxidation of Hydrocarbons and Alcohols with Peroxides

Reactions of VCl3 with 1,2-Bis[(4-methylphenyl)imino]acenaphthene (4-Me-C6H4-bian) or 1,2-Bis[(2-methylphenyl)imino]acenaphthene (2-Me-C6H4-bian) in air lead to the formation of [VOCl2(R-bian)(H2O)] (R = 4-Me-C6H4 (1), 2-Me-C6H4 (2)). Thes complexes were characterized by IR and EPR spectroscopy as well as elemental analysis. Complexes 1 and 2 have high catalytic activity in the oxidation of hydrocarbons with hydrogen peroxide and alcohols with tert-butyl hydroperoxide in acetonitrile at 50 °С. The product yields are up to 40% for cyclohexane. Of particular importance is the addition of 2-pyrazinecarboxylic acid (PCA) as a co-catalyst. Oxidation proceeds mainly with the participation of free hydroxyl radicals, as evidenced by taking into account the regio- and bond-selectivity in the oxidation of n-heptane and methylcyclohexane, as well as the dependence of the reaction rate on the initial concentration of cyclohexane.

Experimental and kinetic modeling studies on oxidation of n-heptane under oxygen enrichment in a jet-stirred reactor

Oxygen-enriched combustion can improve thermal efficiency and reduce CO, unburned hydrocarbons and soot emissions in internal combustion engines. There are significant differences in the combustion process and pollutant emissions between oxygen-enriched and air condition. In order to develop an improved understanding of the effect of oxygen concentration on n-heptane oxidation, the jet-stirred reactor oxidation characteristics of n-heptane were experimentally tested at temperatures of 450–950 K and pressures of 1.03 atm with the residence time (τ) of 2 s, under the condition of oxygen mole fractions from 0.055 to 0.6. Meantime, the simulations were performed on CHEMKIN. Results show that, firstly, with the increase of oxygen concentration, the NTC (Negative Temperature Coefficient) effect is weakened, mainly due to the strengthening of low-temperature reaction path, which is also the reason for the improvement of ignition stability in cold-start condition of engines. Secondly, the activity of the reaction system improves with the increase of oxygen concentration. Within 500–750 K, it is due to enhancement of the low-temperature reaction path. When the temperature is higher than 750 K, the improvement is due to the enhancement of decomposition of H2O2 and addition reaction of H and O2. Thirdly, with the increase of oxygen concentration, both the generation and consumption of CO are strengthened, which leads to the tip of the diesel spray flame changing from soot area under air condition to the CO chemiluminescence.

Synthesis of ultra-thin 2D MnO2 nanosheets rich in oxygen vacancy defects and the catalytic oxidation of n-heptane

N-heptane (C7H16) is a kind of VOCs from a wide range of sources, which harm to the atmosphere and human health. So far, most of the researches on C7H16 have focused on catalytic cracking rather than its low temperature degradation. As a kind of long straight carbon chain alkanes, the study of catalytic oxidation of C7H16 has a certain guiding value for the degradation and mechanism analysis of complex organic compounds. In our study, 2D birnessite-MnO2 nanosheet with the thickness of 1.7–2.5 nm was successfully prepared and it can achieve complete conversion of C7H16 at 252.31 °C, which is better than the bulk catalyst. The characterization (such as TEM, XRD, etc.) and kinetic experiments results showed that it has good catalytic oxidation performance due to its ultra-thin, large specific surface, abundant oxygen vacancies and excellent electron transfer efficiency, which not only exposes more surface atoms, but also absorbs more gaseous O2 and rapidly transforms into reactive oxygen species (ROS) that can participate in catalytic oxidation. Surface reactive oxygen species play an important role in catalytic oxidation due to the formation of surface oxygen vacancies.

OXIDATION OF N-HEPTANE IN THE PRESENCE OF MANGANESE-POLYMER CATALYST AND THE KINETICS OF THE OXIDATION PROCESS

Catalysts with manganese nanoparticles (5 and 10 wt %) immobilized on poly-4-vinylpyridine were prepared. These catalyst compositions have been used to oxidize n-heptane with pure oxygen to give alcohols, aldehydes and ketones. Oxidation of n-heptane was carried out in the temperature range 303-383 K, molar ratios of heptane:oxygen = 1:3.38, and at atmospheric pressure. It has been found that the non-crosslinked (MnP4VP polymer poly-4-vinylpyridine) and N,N- methylene-bisacrylamide-crosslinked MnP4VP/MBAA metal-polymer catalyst containing 5 wt % Mn2+ exhibits the highest activity in n-heptane oxidation reactions. The kinetic parameters of the reaction of n-heptane oxidation with oxygen at low temperatures were studied using a kinetic model based on the heptane conversion data.

Revisiting low temperature oxidation chemistry of n-heptane

Benefitting from the rapid development of instrumental analysis methods, intermediate products that were difficult to probe in the past can now be measured and quantified in complex reaction systems. To understand low temperature reactions of interest for combustion applications, and reduce the deviations between model predictions and experimental measurements, constant advancement in understanding low temperature oxidation process is necessary. This work examines the oxidation of n-heptane in jet-stirred reactors at atmospheric pressure, with an initial n-heptane mole fraction of 0.005, equivalence ratio of 0.5, a residence time of 1s, and over a temperature range of 500-800 K. Reaction products were analyzed using synchrotron ultra-violet photoionization mass spectrometry, gas chromatography, and Fourier-transform infrared spectroscopy. Ignition delay times of n-heptane/O2/CO2 mixture were measured in a rapid compression machine at 20 and 40 bar over a 600-673 K temperature range. Based on the experimental results, a comprehensive kinetic model of n-heptane low temperature oxidation was developed by considering the sub-mechanisms of keto-hydroperoxide, cyclic ether, heptene isomers, and the third O2 addition reaction, and by updating the rate constants of keto-hydroperoxide decomposition and second oxygen addition reactions. The combination of reaction mechanism development and evaluation of the rate constants of key reactions enabled the model to effectively predict the species concentrations and ignition delay times of n-heptane low temperature oxidation, providing additional insight into alkane low temperature oxidation chemistry.

EFFECT OF THE COMPOSITION OF A MANGANESE-CONTAINING POLYMER CATALYST ON THE KINETICS OF THE OXIDATION REACTION OF N-HEPTANE WITH MOLECULAR OXYGEN

Catalysts with manganese nanoparticles (5 and 10 wt %) immobilized on poly-4-vinylpyridine were prepared. When interacting with molecular oxygen, the catalyst forms active oxygen, which is involved in the low-temperature oxidation of n-heptane. These catalyst compositions have been used to oxidize n-heptane with pure oxygen to give alcohols, aldehydes and ketones. Oxidation of n-heptane was carried out in the temperature range 303-383 K, molar ratios of heptane:oxygen = 1:3.38, and at atmospheric pressure. It has been found that the non-crosslinked (MnP4VP polymer poly-4-vinylpyridine) and N,N-methylene-bis-acrylamide-crosslinked MnP4VP/MBAA metal-polymer catalyst containing 5 wt % Mn2+ exhibits the highest activity in n-heptane oxidation reactions. The kinetic parameters of the reaction of n-heptane oxidation with oxygen at low temperatures were studied using a kinetic model based on the heptane conversion data. The kinetic model was compiled on the basis of experimental data: heptane:oxygen = 1:3.38 at atmospheric pressure using Mn (wt. 5%) P4VP/MBAA in the temperature range 303-383 K. Within the framework of the chosen kinetic model effective rate constants of the oxidation reaction with the formation of alcohols was calculated