High-temperature Oxidation Reactions Research Articles

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

Oxidation Study and Mechanism Analysis of Desulfurization Ash in Dense-Phase Tower

Dense-phase-tower desulfurization technology is an emerging semi-dry flue-gas desulfurization ash process, i.e., the flue gas is allowed to enter the desulfurization tower from the bottom up and, at the same time, is sprayed with a desulfurizing agent that undergoes an acid–base reaction with the flue gas in the ascent process. The calcium sulfite and calcium sulfate produced by the reaction and the part of the desulfurization agent that is not involved in the reaction will enter the subsequent dust removal system, and what is retained is the by-product desulfurization ash. This desulfurization ash contains a large amount of calcium sulfite, which leads to its unstable nature; it is easily oxidized and expands in volume, and, if used in the field of building materials, it will lead to cracking and other problems, so it is difficult to effectively use it. In order to solve this problem, XRF, XRD, and iodometric and other analytical methods were used to determine the specific composition of desulfurization ash, and the muffle furnace and vertical tube furnace were used to study the thermal oxidative modification of calcium sulfite in desulfurization ash, to investigate the effects of the oxygen content, reaction temperature, medium flow rate, and chloride content on the oxidation of calcium sulfite, and to analyze the thermodynamics in the high-temperature oxidation reaction. The results showed that the oxidation rate of calcium sulfite increased with higher reaction temperatures. Increased oxygen content promoted the oxidation rate, particularly at low oxygen levels. The oxidation rate of calcium sulfite correlated positively with the medium flow rate until a rate of 75 mL·min− was reached. At a reaction temperature of 420 °C and a gas flow rate of 85 mL·min−1, the oxidation conversion efficiency exceeded 89%. Chloride content significantly reduced the oxidation rate of calcium sulfite, although this inhibition weakened at temperatures above 500 °C. Kinetic analysis suggested that the oxidation reaction of calcium sulfite predominantly occurred below 500 °C. These findings have both theoretical and practical implications for the thermal oxidation treatment and disposal of desulfurization ash.

Scaling up in situ combustion process for enhanced oil recovery in water-flooded light oil reservoirs from laboratory to field implementation

Aiming at low permeability, high water content light reservoir with a recovery rate higher than 20%, an improved air injection enhanced heat flooding technology is applied by combining the combustion reaction flow and flue gas flooding mechanism. The method involves the injection of air into the reservoir, which reacts with the crude oil at temperatures ranging from 220 to 300 °C. This reaction consumes part of the oil, enabling effective evaporation and flow of the remaining oil. This process combines combustion reaction flow with flue gas flooding, using high-temperature oxidation reactions to mobilize residual oil. Experimental results from combustion tube tests demonstrate stable reaction fronts, peak temperatures reaching up to 550 °C, and a significant increase in recovery rates, reaching 73.8% in some cases. Field applications of this technology require maintaining high air flux and burning rates in low-permeability zones to ensure effective heat-driven evaporation. The geological model of the well group shows that the recovery factor of the target block can be increased by more than 20% by air injection based on the water drive recovery factor of 28%–30%. The oil exchange ratio can be less than 4000 sm3/m3 by optimizing the air injection rate and oxygen content. The research results provide technical feasibility for heat flooding to significantly improve oil flow and recovery in low-permeability light oil reservoirs.

Bionic sweat high temperature self-lubricating coating based on ceramic precursor polysilazanes

Bionic sweat high temperature self-lubricating coating were prepared using ceramic precursor polysilazane and MoS2, Ag and BaF2 as fillers through high temperature chemical reaction to produce ceramic adhesive and molybdate solid lubricants. And the addition of active ZrB2 filler converted into ZrO2 and B2O3 through high temperature oxidation reaction not noly solved the cracking issues caused by the pyrolysis of polysilazane, but also enhances the tribology property due to the excellent fluidity and lubricity of the molten B2O3 through phase transition at high temperature through bionic sweat. Furthermore, the coating treated at 700 °C has the best lubrication performance at 500 °C, 2 N and 100 rpm that the friction coefficient was 0.223 and the wear rate was 1.53 × 10−4 mm3/N·m, respectively. Synergistic effect of solid lubricants and molten B2O3 leads to excellent lubrication property.

Effect of ferrocene as a combustion catalyst on the premixed combustion flame characteristics of Jatropha biodiesel

Fuel additives are widely used to optimize the combustion process, reduce the harmful emissions, and improve the performance of engines. Among the metal-based additives, ferrocene is soluble in most fuels, including biodiesel. Furthermore, it is easily available and has high stability, low toxicity, and high lipophilicity. It can evenly disperse in biodiesel without causing any change in the physicochemical properties. Therefore, it can serve as an effective combustion catalyst for biodiesel. In this study, the effect of ferrocene as a combustion catalyst on the pyrolysis and combustion performance of Jatropha biodiesel is investigated. The coupled technique of thermogravimetry-Fourier transform infrared spectroscopy-mass spectrometry (TG-FTIR-MS) is used to analyze the evolution characteristics of multicomponent gaseous products generated during the pyrolysis and high-temperature oxidation of Jatropha biodiesel (JB100) and Jatropha biodiesel + ferrocene (JBF). The laminar premixed combustion flame and pollutant emissions of JB100 and JBF are examined using a variety of techniques, including OH planar laser-induced fluorescence (OH-PLIF), flue gas analysis, spectral analysis, transmission electron microscopy, etc. The results reveal that after adding ferrocene, the activation energy for the pyrolysis reaction of JB100 decreases by 4.66 kJ/mol and the complete weight loss temperature decreases by 10 ℃. Further, the addition of ferrocene reduces the endothermic heat by 0.38 mW/mg during the initial stage of the high-temperature oxidation reaction of JB100, and the amounts of final products CO2 and H2O are increased. Compared with JB100, JBF shows an enhanced OH group intensity in the combustion flame and a lower soot spectral peak. Furthermore, compared with JB100, under JBF combustion, the pollutant PM2.5 emissions decrease by 13.3 %, PM10 emissions decrease by 13.2 %, PM> 10 particulate matter emissions decrease by 19.3 %, CO emissions decrease by 6.8 %, NOx emissions increase by 21.2 %, and the size of soot particles decreases by 20.8 %.

Effect of oxidation on the combustion flame characteristics of Jatropha biodiesel

This study investigated the effect of oxidation on the pyrolysis and combustion flame performance of Jatropha biodiesel. To analyze the escape characteristics of multi-component gas products during the pyrolysis and high-temperature oxidation processes of fresh and oxidized Jatropha biodiesel, the TG-FTIR-MS combined system was employed. In addition, various analytical equipment such as an OH-PLIF system, a flue gas analyzer, a spectral analyzer, and a transmission electron microscope were employed to examine the laminar premixed combustion flame and pollutant emissions of Jatropha biodiesel before and after oxidation. The results demonstrate that oxidation exhibits a nonlinear effect on the thermal decomposition of Jatropha biodiesel. Notably, the reaction activation energy exhibits an initial increase and followed by a decrease. Moreover, an increased oxidation degree led to a reduction in the activation energy of the high-temperature oxidation reaction of Jatropha biodiesel, without considerably affecting the total weight loss temperature. Furthermore, the peak temperatures of DTG and DSC exhibited a minor decrease. The production of C2, CH, and OH free radicals in the combustion flame of oxidized Jatropha biodiesel increased, along with an elevation in the spectral intensity of carbon smoke. With an increase in the degree of oxidation, the CO emission concentration from the combustion of Jatropha biodiesel decreased gradually from 75 mg/m3 to 36 mg/m3 after 6 h of oxidation. Additionally, NOx emissions gradually increased from 131 mg/m3 to 186 mg/m3 after 6 h of oxidation, and the particle size of carbon smoke exhibited a reduction of 28%.

The crack-healing and strength recovery mechanisms for the new developed Ti(C,N)-TiSi2-WC composite ceramic tool materials with crack-healing ability

Because the ceramic tool life will be reduced due to the crack growth, it is necessary to develop the new ceramic tools with crack-healing ability for improving the ceramic tool life. Ti(C,N)-TiSi2-WC composite ceramic tools were fabricated by vacuum hot pressing sintering technology. The Vickers hardness tester was used to prefabricate cracks with different lengths. The crack-healing abilities of materials were researched by air and vacuum heat treatments. The effects of different healing conditions on crack-healing behaviors were investigated based on the strength recovery and microstructure of crack morphology. The healing conditions included healing temperature, healing time, crack length and healing atmosphere. It could be found that the surface cracks were entirely healed after air heat treatment, but locally healed after vacuum heat treatment. After air heating at 800 °C for 90 min, the restoration ratio of flexural strength of the crack-healed samples returned to 109.02% compared to that of the smooth specimen. The strength of the crack-healed specimen would be fully recovered when the crack length was less than 400 μm. After vacuum heating at 1000 °C for 60 min, the recovery of the flexural strength of the crack-healed samples returned to 49.73%. X-ray diffraction and scanning electron microscope technology were used to analyze compositions and microstructure of crack-healed specimens. In the air atmosphere, the liquid filling of SiO2 and TiO2 and crack closure caused by WSi2 and MoSi2 were confirmed as the crack-healing mechanisms. SiO2 and TiO2 were produced by high temperature oxidation reaction of TiSi2 and WSi2. WiS2 and MoSi2 were new phases formed during sintering and heat treatment, and their formation could be explained by thermodynamically feasible reactions. In the vacuum atmosphere, local filling of the crack with silicide solid solutions such as WSi2, MoSi2 and NiSi was the main crack-healing mechanism.

Oxidation Kinetics Analysis of Crude Oils with Different Viscosities

In order to compare the oxidation kinetics parameters of crude oils with different properties in the process of crude oil oxidation, six different crude oil samples were selected to analyze the oxidation characteristics of crude oils with different properties. In order to study the oxidation of crude oil, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) synchronous analyzer were used for crude oil in the oxygen environment between 25 °C and 900 °C at a heating rate of 20 °C/min. The experimental results were based on crude oil oxidation using TGA and DTG experimental data to evaluate the oxidation mechanism of different crude oils, so as to better understand the situation in the oxidation reaction process. At the same time, the oxidation stage of crude oil was divided according to DSC data. Arrhenius method was used to analyze the oxidation kinetic parameters of crude oils with different properties, and the activation energies and pre-exponential factors of different crude oils were calculated. The experimental results show that the oxidation stage of crude oil can be divided into three stages: low-temperature oxidation, fuel deposition, and high-temperature oxidation. The low-temperature oxidation reaction begins at 280 °C, and the high-temperature oxidation reaction occurs at 400 °C. The low-temperature oxidation activation energy of an oil sample is 39.73–77.74 kJ/mol. The activation energy of the high-temperature oxidation is in the range of 106.27–264.47 kJ/mol. The activation energy of crude oil in the low-temperature oxidation stage increases with the increase of crude oil viscosity and decreases with the increase of crude oil viscosity in the high-temperature oxidation stage. Therefore, during the high-temperature oxidation stage, high-viscosity crude oil is more prone to reactions.

Kinetic modeling of NH3-selective catalytic reduction (SCR) over a mildly hydrothermally aged commercial Cu-SSZ-13 catalyst

Cu-SSZ-13 is often studied as a selective catalytic reduction (SCR) of NOx catalyst for diesel after-treatment systems. Mild hydrothermal aging (HTA) is commonly known to cause changes in catalyst performance. In this study, a kinetic model of SCR over a Cu-SSZ-13 catalyst that includes mild HTA and its impact on the SCR reaction was developed. The migration of Cu species during HTA, and how this change in Cu distribution affects low-temperature and high-temperature NH3 oxidation and SCR reaction mechanisms, were considered. Flow reactor test results were used for parameter estimation and verification. Different characterization techniques, including H2 temperature-programmed reduction (H2-TPR), NO + NH3-TPR, NH3 temperature-programmed desorption (NH3-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), were used to characterize and quantify catalyst site densities. The model can simulate the migration of Cu species and the NOx reduction performance changes during mild hydrothermal aging as a function of aging temperature and time.

Study on crack healing performance of Al2O3/SiCw/TiSi2 new ceramic tool material

In consideration of the crack sensitivity in ceramics, a new alumina-based ceramic material with excellent crack healing ability was successfully fabricated by adding SiC whiskers and TiSi2 particles. Different sizes of cracks were prefabricated on the surface of the material with the diamond indenter, and corresponding crack healing behavior was studied by high temperature oxidation experiments in a muffle furnace under air. The influences of healing temperature, healing time, and crack size on the surface morphology and flexural strength of the material were investigated in detail. When the crack width was 0.68 μm, the appropriate temperature and duration time for crack healing and full-strength recovery were 800 °C for 60 min or 1000 °C for 30 min, respectively. The maximum crack size capable for self-healing of the ceramic material was 2c = 250–300 μm and w = 0.68 μm, and the corresponding healing condition was of 800 °C/60 min. The crack healing of Al2O3/SiCw/TiSi2 ceramics was primarily driven by the high temperature oxidation reactions of Ti5Si3 and SiCw. Ti5Si3 was a new phase formed during sintering, and its formation could be described by thermodynamically feasible reactions. The new crack healing mechanism was revealed deeply, including both the local crack bridging generated by the in-situ development of TiO2 and the liquid phase filling of SiO2 intermediate oxides (Si2O3 and SiO). This research conclusion has great significance for the repairing and remanufacturing of ceramic materials with crack defects.

Apparent Heat of Reaction of Heavy Oil with Application of Accelerated Rate Calorimeter

Summary A series of accelerated rate calorimeter (ARC) experiments were conducted on heavy oil mixed with a carbonate core to study the thermal behavior and oxygen uptake operating at different air fluxes of 5.0, 2.5, and 1.25 (m3(ST)/(m2h)) referred to as Runs -1, -2 and -3, respectively. As a result, evaluation of the temperature rise per unit mass of oxygen was proposed as a new approach for identifying the main contributing mechanism during in-situ combustion (ISC). The obtained findings can be used for predicting the transition occurring between low- and high-temperature ranges (LTR and HTR). For Runs -2 and -3, such a transition occurred at 280°C, whereas for Run-1, operated at the highest air flux, LTR shifted to HTR at about 300°C. The overlapping curves of O2 to COx and O2 to low-temperature oxidation (LTO) plus water were interpreted as equal contributors to energy formation. The calculated maximum values varied between 4053 for LTO reactions and 13 420 dT(°C)dmO2(g) for high-temperature oxidation (HTO) reactions depending on the air flux. The measured self-heat rates (SHRs) and oxygen uptake, further used to obtain the apparent heat of reaction, were in general agreement with the values reported in the literature, 16 000 J/g O2 consumed. These values are typical for the HTO reactions; however, in this study, the heats of reaction when the oxidation reactions are operating in the oxygen addition or LTO mode were the main interest. Depending on the run, the apparent heats of LTO reactions varied between 4422 and 7101 J/g O2 consumed.

Integration of ramped temperature oxidation and combustion tube tests for kinetic modeling of heavy oil in-Situ combustion

In-situ combustion (ISC) has been applied as a follow-up process after steam injection-based technologies to improve heavy oil recovery and lower operating costs. Comprehensive understanding of the oxidation behavior and reliable prediction of the ISC performance are of great importance in the design of a ISC process. In this work, a calibration workflow was proposed to investigate the oxidation behavior and then establish a reaction kinetics model. A Ramped Temperature Oxidation (RTO) experiment was firstly conducted to capture the detailed oxidation behavior at elevated temperature conditions. Subsequently, a Combustion Tube (CT) test was performed to further evaluate the overall performance of ISC. Based on the integration of RTO and CT results, a comprehensive reaction kinetics model was developed to predict the ISC performance within a wide temperature range, including Low Temperature Oxidation (LTO), Negative Temperature Gradient Region (NTGR), and High Temperature Oxidation (HTO) reactions. It is found that the NGTR of heavy oil with high saturate and low asphaltene exhibits a narrow temperature range. The combustion front velocity in the RTO is comparable with that in the CT. In a stable HTO region, the CO2 concentrations in the RTO experiment and CT test were kept around 17% and 14%, respectively. The existence of LTO reactions in the RTO experiment caused the deviation of CO2 concentration. With the incorporation of the reaction model into simulation, a good agreement between measured and predicted results was obtained. This demonstrates that the established reaction model is capable of capturing the key oxidation mechanisms. In addition, the proposed workflow also helps upscale the oxidation behavior from a RTO experiment to a CT test and provide benchmarks for field operations.

Experimental Study of Oxygen-Rich in Situ Combustion for Heavy Oil Recovery

The in-situ combustion method is the commonly used method for heavy oil production with high recovery rate and low cost. However, the characteristics of the oil oxidation reaction during in-situ combustion are still not clearly understood so far. In this study, the thermal oxidation experiment was carried out for the in-situ combustion process based on the heavy oil from Du 66 block. The results show that: the fired oil zone can be divided into the combustion zone, the coking zone, the condensation zone, the movable oil zone, etc. When the combustion front is formed, the CO2 and CO contents rise to 10% and 20%, respectively. In the expansion phase of the combustion front, the oxygen utilization rate is 83.93%, and the H/C atomic ratio is 1.413, indicating that the high temperature oxidation reaction plays the leading role. Sustained gas injection with enough intensity can ensure that the combustion front moves forward continuously, and the combustion front can drive the crude oil forward in the form of snowballing due to the extremely high oil displacement efficiency. The pressure increases as the combustion front and the movable oil zone advance, but the movable oil zone begins to decrease as it advances to the production well. Through this study, it is concluded that effective combustion front and movement of combustion front are the foundation for the formation of movable oil zone. And the movable oil zone pressurization is an important mechanism for in-situ combustion. The findings of this study can help for better understanding of the in-situ combustion oxidation mechanism and can improve the production design for heavy oil reservoirs.

Athabasca Toe-to-Heel Air Injection Pilot: Evaluation of the Spontaneous Ignition Based on Apparent Atomic Hydrogen-Carbon Ratio Variation

Summary An in-depth analysis was performed to determine the ignition delay via the enhanced spontaneous ignition (ESI) method on three well pairs (each pair constituted by one vertical injector and one horizontal producer) belonging to the Toe-To-Heel Air Injection (THAI) pilot in Athabasca. ESI consisted of preheating of the surroundings of injection wells by injecting a steam slug for 3 to 4 months just before starting air injection. At first, the ignition delay had been determined based on both the oil production and on the bottomhole temperatures (BHTs) recorded in the observation wells as well as at the toe of the horizontal producer. For the purposes of this paper, a more rigorous evaluation was carried out based on the variation in time of the apparent atomic hydrogen-carbon ratio (AAHCR) calculated from detailed gas analyses for a long period of time. AAHCR is a very strong synthetic parameter giving a direct indication of the peak temperature value before, during, and after the in-situ combustion (ISC) front is generated. Therefore, it provides complete information on the occurrence of high-temperature oxidation and low-temperature oxidation (LTO) reactions. Using the variation of the AAHCR, it was found that the ignition time was shorter than those determined by the previously mentioned methods. In the case of first well pair, ignition took 3 weeks as compared to the 1 month determined by the previous methods. The second well pair ignited in 1 month as compared to the previously calculated 2 months, and for the third well pair, ignition time was approximately 2 months in both cases. As an additional and complementary approach, estimation of the ignition time was also based on the variation of individual components of the produced gas. This allowed for the discovery of a new method for ignition time determination. This was possible in the THAI process, unlike conventional ISC processes, significant concentrations of hydrogen (H2) are produced, and the interpretation of its variation can give an indication of the ignition time. The new method is very simple to use, as the percentage of hydrogen in the produced gas starts to take off only after the full establishment of an ISC front, as hydrogen production is associated with high-temperature bond scission reactions in the ISC front. In general, the ignition delay is overestimated to some degree when using this method.

Insights into in-situ upgrading of bitumen in the hybrid of steam and combustion process: From experimental analysis aspects

In situ combustion (ISC) has been evaluated as a follow up process in the steam injection process for heavy oil and bitumen recovery. Except for providing energy or heat to reduce bitumen viscosity, in situ upgrading of bitumen is another advantage of ISC process. In situ upgrading of bitumen through co-injection of steam and oxygen is evaluated in this work. Three different types of laboratory experiments, including one static thermal cracking experiment, one ramped temperature oxidation (RTO) experiment, and one combustion tube test, were performed to examine the produced oil properties and the potential of bitumen in situ upgrading. A comprehensive analysis of produced oil properties and gas composition was performed. Bitumen was significantly upgraded in the thermal cracking experiment at a temperature of 430 °C, in which Saturates fraction increased to 56%, while Resin and Asphaltene fractions reduced to 6.7% and 6.8%, respectively. The thermal cracking of Resin and Asphaltene contribute to the production of the light oil and gases, leading to the upgrading of the bitumen. Dynamic properties of produced oil were measured in the RTO and combustion tube test in terms of produced oil viscosity, density, boiling point temperature distribution, and produced oil compositions, etc. In the RTO test, the extent of bitumen upgrading is greater with the increase of temperature, further proving that the high temperature generated by the combustion front is able to effectively crack the bitumen. Furthermore, the lack of light hydrocarbon in the produced oil indicates light hydrocarbon participates in the high temperature oxidation reactions. Different from thermal cracking experiment and RTO test results, combustion tube test results indicated that the bitumen was slightly upgraded in late stage of the combustion tube test and most produced bitumen are similar with original bitumen. By examining the temperature distribution along the combustion tube, it is found that upgraded bitumen cannot be effectively displaced to the producer. This implies the limitation of in situ upgrading in the conventional in situ combustion process. Proper well configuration was recommended for the future field application of the hybrid steam and combustion process to achieve the high oil recovery factor and partial in situ upgrading of bitumen.

Enhancing CO2 separation performance of mixed matrix membranes by incorporation of L-cysteine-functionalized MoS2

The incorporation of lamellar materials into polymer matrix can improve the gas separation performance of mixed matrix membranes (MMMs), which have great potential in chemical separation process. However, few intrinsic selectivity sites on MoS2 sheets suppress further employment in the membrane separation. In this work, the vacancies and defects-containing MoS2 sheets were prepared by high temperature oxidation and hydrothermal reaction in NaOH solution, and then L-cysteine-functionalized MoS2 (Cys-MoS2) was synthesized by a thiol-click chemistry reaction between S vacancies and thiol groups as confirmed by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 absorption. After blending with polyether-block-amide (Pebax), the as-prepared MMMs showed outstanding mechanical properties as a result of the homogeneous dispersion of Cys-MoS2 and hydrogen bonding between two phases as evidenced by attenuated total reflectance-FTIR, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The highest permeability of 297 Barrer accompanied with a CO2/N2 selectivity of 120 was obtained for MMMs loaded with 1.5 wt% Cys-MoS2, which were enhanced by 206.2 % and 124.7 % over the pristine Pebax membrane, respectively. Meanwhile, this value was superior to that of the previously reported Pebax-based MMMs, transcending 2019 upper bound. The enhanced gas separation performance is due to the improved CO2 adsorption selectivity by the vacancies and defects of Cys-MoS2, while the amine groups carrier enhanced CO2 reactivity selectivity.

Cyclic In-Situ Combustion Process for Improved Heavy Oil Recovery after Cyclic Steam Stimulation

Summary Cyclic in-situ combustion (ISC) is a novel process with great potential for thermal enhanced oil recovery (EOR). In this study, a 3D physical simulation experiment of cyclic ISC after cyclic steam stimulation (CSS) was carried out for the first time. The mass loss during heavy oil oxidation was studied by thermogravimetry (TG) and the preheating temperature of sandpack was determined by differential scanning calorimeter (DSC). The oxidation process of heavy oil in a porous medium was investigated by a heavy oil static oxidation experiment. The development characteristics and EOR mechanism of cyclic ISC after CSS were studied through 3D physical simulation experiments and the characteristics of the coking zone was studied by scanning electron microscope (SEM) and computed tomography (CT). The results of the thermal analysis indicate that three different regions were observed with increasing temperature: low-temperature oxidation zone (LTO), fuel deposition zone (FD), and high-temperature oxidation zone (HTO). When the temperature reaches 480°C, the mixed oil sand has the most exothermic effect and the high-temperature oxidation reaction is the most vigorous. The results of the 3D physical simulation show that steam channeling and steam overlay in CSS reduced the swept volume of steam and heat usage rate. During the cyclic ISC, the oil bank can overcome the heterogeneity of the oil reservoir caused by steam channeling and steam overlay, which makes the combustion front move forward smoothly. Cyclic ISC can greatly increase the temperature of the zone near the well, and upgrade the crude oil through cracking to reduce the viscosity of heavy oil. The foaming oil formed by the dissolution of flue gas improves the fluidity of the crude oil. The oil recovery of CSS is 19.3%, and the oil recovery of cyclic ISC increased by 13.2%. SEM and CT show that flake black solid coke was attached to the surface of the sand at the coking zone. The coking zone is a porous medium structure with a porosity of 35.14%, which has little effect on the oil recovery in the process of cyclic ISC.

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.

Catalytic effects of Al2O3 nano-particles on thermal cracking of heavy oil during in-situ combustion process

In-situ combustion (ISC) is regarded as one of the most promising and economic alternative in the development of heavy oil reservoir. Maintaining high temperature oxidation (HTO) reaction with a high cracking efficiency at relatively low fuel consumption is deemed particularly crucial for the success of ISC process. In this work, Al2O3 nano-particles as a catalyst for achieving this during ISC is investigated in three parts. First, kinetic cell experiments with ramped temperature oxidation (RTO) process were conducted on the heaviest fraction of crude oil (residue) to obtain the apparent activation energy (Ea) fingerprints for oil-oxygen reactions with and without Al2O3. Second, thermogravimetric analysis-mass spectrometry-differential scanning calorimetry (TGA-MS-DSC) was used to detect pyrolysis products from the residue and characterize its dynamic change during the process, with SEM and EDS employed to observe the morphology and verify the condition of nano-particles afterwards. Third, combustion tube experiments were performed on the whole crude to analyze the distinction between combustion behavior with and without Al2O3. The results showed addition of Al2O3 catalyst resulted in: Ea decreased and oscillated visibly, temperature of fire front increased by 60.3–83.6 °C, speed of propagation was enhanced by 37.3%, residual coke remains in the quartz sand at the end of combustion tube experiment decreased by 24.8%, production efficiency increased by 13–64% with the reduction of COx production (12.3%) and oxygen consumption (26.9%). This shows a higher ultimate oil recovery is possible with higher upgraded oil percentage during a catalyst-assisted ISC process, which bodes well for future field application.

High temperature oxidation behavior of disordered (Ti0.5Zr0.5)2AlC MAX phase via a Machine Learning-Augmented DFT approach

The Zr-based MAX phases have attracted considerable attention for their outstanding irradiation behavior and high neutron transparency relevant to nuclear power generation technologies. In spite of increased understanding of physical behavior crystalline MAX phases, the high-temperature oxidation behavior and reaction mechanism of disordered MAX phases both from theory and experiments are not well understood due to increased system complexity. Here, we present a detailed comparative assessment of high-temperature thermodynamic-stability and oxidation behavior (reaction-products and chemical activity) of ordered Ti2AlC and disordered (Ti0.5Zr0.5)2AlC. We believe that the new insights will enhance our understanding of oxidation process in disordered MAX phases.