Low-temperature Oxidation Products Research Articles

Tracking the reaction networks of acetaldehyde oxide and glyoxal oxide Criegee intermediates in the ozone-assisted oxidation reaction of crotonaldehyde.

The reaction of unsaturated compounds with ozone (O3) is recognized to lead to the formation of Criegee intermediates (CIs), which play a key role in controlling the atmospheric budget of hydroxyl radicals and secondary organic aerosols. The reaction network of two CIs with different functionality, i.e. acetaldehyde oxide (CH3CHOO) and glyoxal oxide (CHOCHOO) formed in the ozone-assisted oxidation reaction of crotanaldehyde (CA), is investigated over a temperature range between 390 K and 840 K in an atmospheric pressure jet-stirred reactor (JSR) at a residence time of 1.3 s, stoichiometry of 0.5 with a mixture of 1% crotonaldehyde, 10% O2, at an fixed ozone concentration of 1000 ppm and 89% Ar dilution. Molecular-beam mass spectrometry in conjunction with single photon tunable synchrotron vacuum-ultraviolet (VUV) radiation is used to identify elusive intermediates by means of experimental photoionization energy scans and ab initio threshold energy calculations for isomer identification. Addition of ozone (1000 ppm) is observed to trigger the oxidation of CA already at 390 K, which is below the temperature where the oxidation reaction of CA was observed in the absence of ozone. The observed CA + O3 product, C4H6O4, is found to be linked to a ketohydroperoxide (2-hydroperoxy-3-oxobutanal) resulting from the isomerization of the primary ozonide. Products corresponding to the CIs uni- and bi-molecular reactions were observed and identified. A network of CI reactions is identified in the temperature region below 600 K, characterized by CIs bimolecular reactions with species like aldehydes, i.e., formaldehyde, acetaldehyde, and crotonaldehyde and alkenes, i.e., ethene and propene. The region below 600 K is also characterized by the formation of important amounts of typical low-temperature oxidation products, such as hydrogen peroxide (H2O2), methyl hydroperoxide (CH3OOH), and ethyl hydroperoxide (C2H5OOH). Detection of additional oxygenated species such as alcohols, ketene, and aldehydes are indicative of multiple active oxidation routes. This study provides important information about the initial step involved in the CIs assisted oligomerization reactions in complex reactive environments where CIs with different functionalities are reacting simultaneously. It provides new mechanistic insights into ozone-assisted oxidation reactions of unsaturated aldehydes, which is critical for the development of improved atmospheric and combustion kinetics models.

Molecular composition of low-temperature oxidation products of the heavy oil

Low-temperature oxidation (LTO) is the main reaction that affects fuel formation in the in-situ combustion process, which has important significance for the subsequent combustion propulsion and the successful extraction of crude oil. In this study, heavy oil was subjected to LTO reactions at different temperatures. Three types of reaction products with varying oxidation depths were characterized in terms of the number of oxygen atoms and the polarity of the molecule to reveal the low-temperature oxidation process of the heavy oil. Ketone compounds and acid polyoxides in the oil phase and deep oxidation products with a higher number of oxygen atoms in the coke were identified with increasing oxidation depth. The experimental results showed that the oxidation reaction of the heavy oil changed from kinetic-controlled to diffusion-controlled in the open oxidation system of the heavy oil as the oxidation depth increased. The oxidation reaction of the oil phase reached a maximum and stable value in oxygen content. The molecular compositions of the ketone compound and acid polyoxide did not change significantly with further increase in reaction temperature. The molecular compositions of the deep oxidation products with a higher number of oxygen atoms in the coke phase changed significantly. The coke precursor molecules with a lower oxygen content and condensation degree participated in the coke formation, and the oxidation reaction pathway and the complexity of the oxidation product component also increased.

Normal butane oxidation: Measurements of autoxidation products in a jet-stirred reactor

The autoxidation of n-butane was studied experimentally in a jet-stirred reactor at 1 atm (560–720 K) and 10 atm (530–1030 K) for an equivalence ratio of 1. Samples of reacting mixtures were analysed in the gas phase by gas chromatography (GC) using several detectors (Flame ionization detector, thermal conductivity detector, quadrupole mass spectrometer), hydrogen peroxide analyser, and Fourier transform infrared spectroscopy. In addition to the fuel and oxygen, 37 products were quantified. Liquid phase samples were obtained by trapping the reacting mixtures in cooled acetonitrile (273 K). The liquid samples were analysed by high resolution mass spectrometry (HRMS Orbitrap Q-Exactive), either after flow injection or separation by high pressure liquid chromatography (HPLC). Besides stable species, several other low-temperature oxidation products, such as hydroperoxides and ketohydroperoxides, were detected. Products of third O2 addition on fuel’s radicals were also detected by high resolution mass spectrometry. To assess the presence of hydroxyl or hydroperoxyl groups in the products of oxidation we performed H/D exchange with D2O. Qualitative and quantitative results showed the same trends in terms of variation of mole fractions and signal intensities versus reacting temperature. Kinetic modelling was performed using a literature detailed kinetic reaction mechanism already used to simulate previous n-butane oxidation experiments in the cool-flame regime, showing that improvements are needed to better describe the oxidation of n-butane under the present conditions.

Ketones in Low-Temperature Oxidation Products of Crude Oil

Ketone compounds are oxidation products of crude oil in the in-situ combustion (ISC) process. Revealing the molecular composition of ketones can provide theoretical guidance for understanding the oxidation process of crude oil and valuable clues for studying the combustion state of crude oil in the reservoir. In this study, low-temperature oxidation (LTO) processes were simulated in thermal oxidation experiments to obtain thermally oxidized oil at different temperatures (170 °C, 220 °C, 270 °C, and 320 °C). A combination of chemical derivatization and positive-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to analyze the molecular composition of different kinds of ketones (fatty ketones, naphthenic ketones, and aromatic ketones) in the oxidized oils at different temperatures. The results showed that the concentration of aliphatic ketones and aliphatic cyclic ketones in the product oils decreased with the increase in temperature, while aromatic ketones increased with the increase in temperature. At the same oxidation temperature, the content of ketones follows this order: fatty ketones < cycloalkanes < aromatic ketones. The concentrations of ketones reached their maximum value at 170 °C and decreased at high temperatures due to over-oxidation. It was also found that nitrogen-containing compounds are more easily oxidized to ketone compounds than their hydrocarbon counterparts in the LTO process.

Ozone-assisted low-temperature oxidation of methane and ethane

Ozone addition is a promising way to control and monitor the combustion process, e.g., enhancing the low-temperature oxidation reaction. This paper studied the ozone-initiated low-temperature oxidation of methane and ethane in a jet-stirred reactor (JSR) at atmospheric pressure. For the first time, we observed that the low-temperature oxidation of methane and ethane started ca. 450 K. Dozens of low-temperature oxidation products, which are dominantly oxygenated species, were identified and quantified by synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). These data are valuable for evaluating the C1–C2 chemistry of base models. NUIGMech1.1 was used to simulate the experimental data in this work. The results reveal that the model can predict methane conversion, but a large deviation is observed for the intermediate species. In the case of ethane, NUIGMech1.1 overpredicts the low-temperature reactivity of ethane. We found that the reaction mechanism of the alkylperoxy radicals (CH3Ȯ2 and C2H5Ȯ2) is crucial in accurately predicting the low-temperature oxidation chemistry of methane and ethane. The bimolecular reactions of the alkylperoxy radicals with Ö atoms and ȮH and HȮ2 radicals, as well as the self and cross reactions of the alkylperoxy radicals, determine the balance of the radical pool of Ö, ȮH, and HȮ2, and subsequently the fuel reactivity and the formation of the oxidation intermediates. This work provides new insights into the reaction mechanism of the key intermediates in the base model for chemically sensitized low-temperature fuel oxidation that need to be thoroughly studied in the future.

Quantification of n-heptane low temperature oxidation products by proton-transfer-reaction mass spectrometry

While studies on the low temperature oxidation of organic compounds have been in depth, fast and accurate quantitative analysis of oxidation products, especially for those without standard samples, remains challenging and requires analytical developments. This work studied n-heptane low temperature oxidation in a jet-stirred reactor (JSR) using proton-transfer-reaction mass spectrometry (PTR-MS). The oxidation products were also analyzed by a synchrotron vacuum ultraviolet radiation photoionization mass spectrometer (SVUV-PIMS) for comparison. The results showed that PTR-MS was able to measure most oxygenated intermediates compared to SVUV-PIMS. Furthermore, the method for the quantification of low temperature oxidation products was studied. By employing a series of calibration gases, the sensitivities of PTR-MS were confirmed to be linearly related to proton-transfer reaction rates, which were calculated using the trajectory parameterization theory. Mole fraction profiles of oxidation products measured by PTR-MS were compared to SVUV-PIMS and literature gas chromatography data, and in most cases, the results showed good consistency. Special attention is needed for some molecules, such as carboxylic acids, formaldehyde, and peroxides. The effect of the humidity of the reaction environment and the fragment on the quantification need to be considered. Overall, PTR-MS is a promising instrument for the quantitative analysis of combustion products and has the potential to measure the total mole fraction of complex isomers (could not distinguish isomers) and to predict the mole fraction of products without a standard sample.

Variable pressure JSR study of low temperature oxidation chemistry of n-heptane by synchrotron photoionization mass spectrometry

Low temperature oxidation chemistry is crucial in the auto-ignition process of internal combustion engines. The development of laboratory based reactors and diagnostic systems promotes understanding of the low temperature oxidation mechanism. This work develops a variable pressure jet-stirred reactor (VP-JSR) platform working from one to ten bar. Compared to previous high pressure studies which routinely use gas chromatography to analyze low temperature oxidation products, the difference in this work is the possibility of probing intermediates by synchrotron vacuum ultraviolet photoionization mass spectrometry via molecular beam sampling. The setup was validated by repeating n-heptane low temperature oxidation experiments at one and ten bar, respectively. Good agreement was observed between the data in this work and the data in the literature. A much more detailed species pool was probed compared to the literature study, including H2O2, carbonyl acids, alkylhydroperoxides, and keto-hydroperoxides. As a first demonstration of the usefulness of this design, the low temperature oxidation of n-heptane with initial fuel mole fraction of 0.005, residence time of 2 s, and equivalence ratio of 1.0 was studied at one, five, and ten bar. The preliminary results, including reactants, final products, and the initial low temperature oxidation intermediates, are discussed. The VP-JSR system developed in this work is valuable for study of the fuel chemistry from one to ten bar, to develop and examine chemical kinetic models, and to guide the development of the reaction system at even higher pressures, such as those in engine function and supercritical conditions.

Front Cover: Developing the Low‐Temperature Oxidation Mechanism of Cyclopentane: An Experimental and Theoretical Study (Chem. Eur. J. 8/2022)

Highly oxygenated intermediates play an important role in the low-temperature oxidation of fuels. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) is used to observe the low-temperature oxidation products, especially highly oxygenated intermediates like ketohydroperoxide (KHP), keto-dihydroperoxide (KDHP), olefinic hydroperoxides (OHP) and dione structure products. More information can be found in the Full Paper by S. Chen, J. Chen, Z. Tang, et al. (DOI: 10.1002/chem.202103546).

Molecular composition of low-temperature oxidation products in a simulated crude oil In-situ combustion

In-situ combustion (ISC) is a thermal enhanced oil recovery process in which energy is generated by the combustion of a portion of the oil within the reservoir. Low temperature oxidation (LTO) is one of the dominant mechanisms controlling fuel availability in ISC and affects the physical properties of the crude oil, thus the characterization of the crude oil and its LTO products are essential for a better understanding of the ISC process. In this study, a thermal oxidation experiment of a heavy crude oil was carried out to investigate the molecular changes associated to coke formation during ISC. More than half of the component was depleted by combustion or thermal pyrolyzed out, leaving a coke-like solid in the reactor with a yield of a quarter by weight of the crude oil. More than 90% of the coke-like solid is toluene soluble. Condensate oil expelled from the reactor was collected with a yield of about 15 wt% of the crude oil. Small-molecule oxidation products, such as ketones, fatty acids, phenolic compounds were identified in the condensate by GC–MS. High-resolution mass spectrometry results showed that the molecular composition of oxygen- and sulfur-containing compounds changed largely, with the generation of highly oxygenated compounds and sulfoxides. A substantial portion of large-molecule hydrocarbons were survived and enriched in the residue. The main components in the toluene insoluble substance, namely oxidation coke, are methanol soluble and composed of highly oxygenated compounds. The results indicate that oxidation and thermal cracking are both the important reaction in the simulated ISC, the molecular composition is instructive for the understanding of pyrolysis and oxidation behavior of coke formation from the crude oil.

Towards a Comprehensive Characterization of the Low-Temperature Autoxidation of Di-n-Butyl Ether.

In the present study, we investigated the oxidation of 2500 ppm of di-n-butyl ether under fuel-rich conditions (φ = 2) at low temperatures (460–780 K), a residence time of 1 s, and 10 atm. The experiments were carried out in a fused silica jet-stirred reactor. Oxidation products were identified and quantified in gas samples by gas chromatography and Fourier transform infrared spectrometry. Samples were also trapped through bubbling in cool acetonitrile for high-pressure liquid chromatography (HPLC) analyses. 2,4-dinitro-phenylhydrazine was used to derivatize carbonyl products and distinguish them from other isomers. HPLC coupled to high resolution mass spectrometry (Orbitrap Q-Exactive®) allowed for the detection of oxygenated species never observed before, i.e., low-temperature oxidation products (C8H12O4,6, C8H16O3,5,7, and C8H18O2,5) and species that are more specific products of atmospheric oxidation, i.e., C16H34O4, C11H24O3, C11H22O3, and C10H22O3. Flow injection analyses indicated the presence of high molecular weight oxygenated products (m/z > 550). These results highlight the strong similitude in terms of classes of oxidation products of combustion and atmospheric oxidation, and through autoxidation processes. A kinetic modeling of the present experiments indicated some discrepancies with the present data.

Comprehensive study of the low-temperature oxidation chemistry by synchrotron photoionization mass spectrometry and gas chromatography

Comprehensive analysis of the low-temperature oxidation intermediates, including the reactive intermediates and isomers, is crucial to develop the low-temperature oxidation models of the fuels. In this aim, the complementary analysis by different analytic methods is needed. Furthermore, the cross check by different analytic methods increases the fidelity of the experiment data. In this work, we developed a jet-stirred reactor (JSR) system that coupled to the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC) analysis. The JSR was designed to couple the SVUV-PIMS and GC, and the temperature homogeneity and mixing of the JSR was examined by a CFD simulation. The SVUV-PIMS system was developed to have a mass resolution of ca. 5000 at m/z 100. The GC system included a flame ionization detector (FID), thermal conductivity detector (TCD), and a mass spectrometer (MS). This newly developed setup was validated by repeating the oxidation data of n-heptane in the literature. A good agreement was observed between the two datasets. The low-temperature oxidation of n-butane was then studied to show the advantage of this setup, i.e., the simultaneous and comprehensive measurement of the low-temperature oxidation products. Specifically, the SVUV-PIMS enables the separation of the C/H/O composition of the intermediates, the measurement of formaldehyde and the peroxide intermediate, while the GC analysis gives a better separation of the oxygenated isomers and the quantification of the species that the SVUV-PIMS has difficult in quantifying. The experimental method developed in this work is valuable to study the fuel low-temperature oxidation chemistry, to reveal the species pool, and to provide reliable mole fraction data for the validation and development of combustion models.

DSC study on combustion behavior of tahe heavy oil and its low temperature oxidation products

In this study, the combustion behaviors of heavy oil and low temperature oxidation products were analyzed by differential scanning calorimetry (DSC) technique. The results elucidated that the coke formed after static oxidation showed the highest heat release (24.03 kJ/g), which was a positive signal for the in-situ combustion (ISC) process of Tahe heavy oil. The most abundant asphaltenes in heavy oil and residue contributed more fuel for high temperature oxidation (HTO), resulting the two samples to exhibit intense HTO reactions. In summary, activation energies of the samples in the low temperature oxidation (LTO) were higher than that in HTO region.

Experimental and kinetic modeling study of n-hexane oxidation. Detection of complex low-temperature products using high-resolution mass spectrometry

This study concerns the oxidation of n-hexane. It was conducted in continuous flow fused-silica jet-stirred reactor (JSR) at 10 atm and an equivalence ratio of 0.5. n-Hexane initial concentrations were (i) 2500 ppm with a mean residence time of 1.5 s and (ii) 1000 ppm with a mean residence time of 0.7 s; we operated in the cool-flame regime for temperatures ranging from 540 to 720 K and 530 to 800 K, respectively. Products were analyzed and quantified in the gas phase using gas chromatography (with flame ionization, thermal conductivity, and quadrupole mass spectrometry) and Fourier transform infrared spectrometry. Products of low-temperature oxidation were sampled in the JSR and trapped in acetonitrile for characterization using an Orbitrap Q-Exactive®. Flow injection analyses (FIA) and ultra-high pressure liquid chromatography (UHPLC) coupled with atmospheric pressure chemical ionization (APCI +/- modes)- high resolution mass spectrometry (HRMS) analyses were used to characterize hydroperoxides (C6H14O2), keto-hydroperoxides (C6H12O3, C3H6O3, C4H8O3, and C5H10O3), cyclic ethers (C6H12O), carboxylic acids (C2 to C6), ketones (C3 to C6), diones (C6H10O2), unsaturated ketones (C6H10O and C6H8O), unsaturated diones (C6H8O2), and highly oxygenated molecules (C6H12O4-8) produced by addition of three and four oxygen molecules on fuel's radicals. To confirm the presence of hydroxyl or hydroperoxyl groups in the oxidation products we used H/D exchange with D2O. 2,4-Dinitrophenylhydrazine (2,4-DNPH) derivatization was used to characterize and confirm the presence of different carbonyls which can be formed during the low temperature oxidation of n-hexane. An available kinetic reaction mechanism including 3rd O2 addition on fuel's radicals was used to simulate the formation of the presently detected keto-hydroperoxides (KHP) and highly oxygenated molecules (HOMs).

Experimental Characterization of Tetrahydrofuran Low-Temperature Oxidation Products Including Ketohydroperoxides and Highly Oxygenated Molecules

The oxidation of tetrahydrofuran (THF) was carried out in a continuously jet-stirred tank reactor (JSR) at a total pressure of 10 atm, in fuel-lean conditions (equivalence ratio = 0.5), an initial fuel mole fraction of 5000 ppm, at a mean residence time of 2 s, and for temperatures ranging from 550 to 620 K. High-resolution mass spectrometry analyses was used to characterize low-temperature oxidation products of THF. MS analyses were performed using atmospheric pressure chemical ionizations in positive and negative modes. Both flow injection analyses and ultra-high-pressure liquid chromatography-MS/MS allowed characterizing a large set of chemicals including hydroperoxides and diols (C 4 H 8 O 3), ketohydroperoxides (C 4 H 6 O 4), and more oxygenated molecules (up to C 4 H 8 O 7) resulting from up to three oxygen molecules addition of on α and β THF radicals. The existence of-OH or-OOH groups in the products was confirmed by hydrogen-deuterium exchange using D 2 O. We detected 24 products with molecular weight of 40-168, not reported in previous studies. Simulations using the latest THF oxidation chemical kinetic reaction mechanism available from the literature were compared to the present measurements of ketohydroperoxides and other products of THF cool flame. The kinetic scheme represented well the present qualitative data.

Experimental characterization of n-heptane low-temperature oxidation products including keto-hydroperoxides and highly oxygenated organic molecules (HOMs)

The oxidation of n-heptane was performed in a jet-stirred reactor (JSR) at 10 atm, an equivalence ratio of 0.5, and an initial fuel concentration of 1000 ppm at a residence time of 1 s in the temperature range 580–790 K (from cool-flame, negative temperature coefficient NTC, to intermediate temperature oxidation regime), and with 5000 ppm of fuel at 647 K and a residence time of 1.5 s. Low-temperature products formed in JSR were characterized using high-resolution mass spectrometry analyses (HRMS). Atmospheric pressure chemical ionizations (APCI) was used in positive and negative modes for MS analyses. Both flow injection analyses (FIA) or ultra-high-pressure liquid chromatography-OrbitrapⓇ coupling were used to characterize hydroperoxides (C7H16O2), keto-hydroperoxides (C7H14O3), cyclic ethers (C7H14O), carboxylic acids (C2H4O2, C3H6O2, C4H8O2), ketones (C3–5H6–10O), diones (C7H12O2), and highly oxygenated molecules (C7H14O5, C7H14O7, C7H14O9, C7H14O11) resulting from the addition of up to six O2 molecules on fuel radicals. H/D exchange with D2O was used to confirm the presence of –OH or –OOH groups in the products. Several available kinetic reaction mechanisms were tested against the present measurements of keto-hydroperoxides showing significant discrepancies.

Quantification of low‐temperature oxidation of light oil and its SAR fractions with TG‐DSC and TG‐FTIR analysis

AbstractThe oxidation reaction is the key to determining the success of air flooding. In this paper, experimental and theoretical techniques have been developed to identify the low‐temperature oxidation (LTO) mechanisms for light oil during air flooding by comprehensively analyzing thermal stability and oxidation process of the crude oil and its SAR (ie, saturates, aromatics, and resins) fractions. Experimentally, both a thermogravimetric analyzer coupled with differential scanning calorimetry (TG‐DSC) and a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG‐FTIR) are employed to quantify the LTO process of crude oil and each SAR fraction as well as the corresponding oxidation properties. Theoretically, reaction models have been developed to reproduce the experimentally identified reactions. The results show that the oxygen addition reaction and the bond scission reaction occur simultaneously. The former can be initiated when temperature is higher than 50°C, and it is gradually shifted to the latter with the continuous increase in reservoir temperature. The LTO products of light oil include H2O, CO2, carboxylic acids, alcohols, phenols, and ethers. Saturates, aromatics, and resins are all the sources of H2O, CO2, alcohols, and carboxylic acids, whereas ethers are mainly derived from aromatics and resins. At the beginning of an air flooding process, heat is mainly generated from the oxidation of aromatics and resins. Subsequently, oxidizing saturates gradually dominates the air flooding process with an increase in the reservoir temperature.

Non-isothermal pyrolysis and combustion kinetics of heavy oil and its low temperature oxidation products by thermal analyses

The focus of this work was to investigate the pyrolysis and combustion behaviors of heavy oil and its low temperature oxidation products by TG/DSC techniques. The results indicated that coke had similar reaction paths and sequences during pyrolysis and combustion process. The pyrolysis of samples mainly showed endothermic effect, while two major exothermic stages (LTO and HTO) were obviously identified on the combustion DSC curves. The magnitudes difference of the remaining mass and activation energy of the samples revealed the difference in the types of substances involved and molecular reactive sites during the pyrolysis and combustion processes.

Water and aromatics fraction interaction at elevated temperature and their impact on reaction kinetics of in-situ combustion

Performance predictions of the In-Situ Combustion (ISC) process is a challenge as it involves complicated chemical reactions, fluids movement, phase changes, and heat and mass transfer. This study investigates how oil type and water presence can affect the ISC performance, based on using a combination of combustion tube and Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA/DSC) experiments.Combustion tube experiments were conducted with two different crude oil without water (Swi = 0%) and with the presence of water (Swi = 34%). Experimental conditions were kept constant (3 L/min air injection rate and 100 psig pack pressure) for all four experiments conducted with two different oil samples.To determine the chemical reactions that occurred during combustion tube experiments, the initial crude oil samples and their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions were subjected to TGA/DSC experiments under air injection at two constant heating rates with and without water addition. Because two heating rates were observed during combustion tube experiments, 5 °C/min was used to represent the slow heating region (Steam Plateau, Evaporation and Visbreaking) and 20 °C/min was used to mimic the rapid heating region (Cracking Region and Combustion Zone).To better understand the complicated mutual interactions of functional groups in crude oil, TGA/DSC experiments were repeated on normal-decane (an alkane), decanal (an aldehyde), decanone (a ketone), and decanol (an alcohol) which represent the low temperature oxidation (LTO) products. Note that these chemicals have a constant carbon number (C10).The combustion tube experiments showed that Oil 1 was able to burn for both conditions (with and without water), while Oil 2 could only sustain combustion with water. To determine the reason for this difference, the burning behavior of the crude oils and their individual SARA fractions with and without water additions was studied through TGA/DSC experiments. At the high heating rate (20 °C/min), heat generation does not vary for both crude oil samples. However, at the low heating rate (5 °C/min), Oil 1 generates a higher amount of energy at high temperature oxidation (HTO) zone. We observed similarities between the decanone (a ketone) burning behaviors with aromatics fractions for Oil 1 which indicates that the aromatics fraction may contain ketone functional groups as LTO products. Upon burning, ketones generate higher energy than any LTO products. Therefore, Oil 1 may have functional groups in its structure more like ketones which promotes its combustion more than Oil 2. While presence of water does not change the burning behavior of Oil 1, we observed that the aromatics fraction of Oil 2 in the presence of water generates components similar to decanol (an alcohol) burning behavior. Note that alcohols generate more heat than aldehydes upon burning which explains the enhancement of Oil 2 burning behavior in the presence of water. However, aldehydes produced less energy than ketones. As a result, the combustion performance of Oil 2 was poorer than Oil 1. These results suggest that the chemical structure of the aromatics fraction is critical for the success of ISC. Water and aromatics fraction interaction at elevated temperature favors ISC reactions.

A study of the low-temperature oxidation of a long chain aldehyde: n-hexanal

Large aldehydes are important species among the oxygenated products formed during the oxidation of fuels (e.g. alkanes or alkenes) and biofuels (e.g. long chain alcohols), but their oxidation chemistry has been scarcely studied up to now. In this work, a study of the oxidation of hexanal has been performed in a jet-stirred reactor over the temperature range 475–1100K, at a residence time of 2s, a pressure of 106.7kPa, an inlet fuel mole fraction of 0.005 and at three equivalence ratios (0.25, 1 and 2). Reaction products were quantified using two analytical methods: gas chromatography and cw-cavity ring-down spectroscopy. In addition to species usually measured during oxidation study (such as CO, CO2, water, H2O2 and C1-C3 olefins, aldehydes and ketones), specific low temperature oxidation species were also observed: C6 species, such as δ- and γ-caprolactones and hexanoic acid, but also C5 species, such as 2-methyl-tetrahydrofuran and pentanal which are typical reaction products detected during the oxidation of n-pentane. A detailed kinetic model has been developed using an automatic generation software. This model was used to highlight the specificities of the oxidation chemistry of long chain aldehydes and to understand the formation routes of the C5 and C6 low-temperature oxidation products. Simulations indicate that the low energy of the aldehyde CH bond has a significant effect on the fuel reactivity and on the distribution of reaction products.

The composition of gaseous products of low-temperature oxidation of coal mass and biomass depending on temperature

Coal and biomass emit gases during storage. The composition and quantity of these gases is dependent on many factors. This study deals with gaseous products that are released during coal and sawdust heating to find how the composition of gaseous products varies in dependence on temperature changes and how these changes can be used to indicate the condition of the stored materials. Samples were examined in a furnace, being placed in a cube-shaped basket whose side measured 5 cm. The samples were heated in the temperature range of 50–200 °C with increments of 50 °C for 180 min. Qualitative and quantitative analysis of the generated gases was performed using a FTIR spectrometer and a gas analyzer. The analysis indicated that these gaseous products primarily contain water vapour, carbon oxides and aliphatic hydrocarbons. At 200 °C, methanol appeared in the gaseous products released by the wood material. The measured results show that the amount of CO2, CO and CH4 increases with heating temperature. It has also been found that the CO/CO2 ratio is temperature - dependent in coal while this dependence is not so clear for sawdust. The results are useful for assessing the impact of temperature on the amount of gaseous products polluting the working and living environment and can help in selecting appropriate security measures.