Initial Reaction Temperature Research Articles

On the oxy-combustion of blends of coal and agro-waste biomass under dry and wet conditions

Integrating bioenergy into carbon capture and storage systems (Bio-CCS) is a novel concept aiming at reducing CO2 emissions, pointing to a short-term need to increase the use of non-conventional biomasses. The main objective of this experimental research is to characterize the behavior of two agro-waste biomasses under oxy-co-firing conditions, as concerns fuel conversion and NO formation, compared to the use of typical raw pine wood. The effect of replacing CO2 with H2O in the firing atmosphere is also sought. Two different biomass shares in the blends, 20 % and 50 %, are selected. The experiments are conducted in a lab-scale entrained flow reactor for two O2 concentrations (21 % and 35 %) and four H2O concentrations (0 %, 10 %, 25 %, 40 %). Some operating conditions are kept the same to enable the comparisons: mean residence time (3 s), initial reactor temperature (1000 °C) and oxygen excess (1.25). New results have been obtained from the experiments, optimizing burnout degrees and reducing NO levels. Minimum differences in conversions are detected for the 35 % O2 cases when the agro-biomasses replace the pine wood: less than 0.7 and 1.1 percentage points. Burnout degrees are maximized when 25 % CO2 is replaced with H2O in most cases, with maximum values in the range 97.3–97.7 %. The higher the agro-biomasses share in the blend, the higher the N-fuel to NO conversion, consistent with their larger nitrogen contents. Significant decreases of NO are detected when CO2 is replaced with H2O, with maximum reductions of 17.6 %. The extent of these NO reductions shows a clear dependence on the volatiles-to-char ratios for the fired blends: the higher the ratio, the lower the decrease. For the largest steam additions (40 %), the NO depleting effect caused by H2O is partially compensated with the enhancement of the N-volatiles oxidation, limiting the NO reductions to 1.7–7.3 % compared to the dry atmospheres.

Exothermic Reaction in the Cleaning of Wastewater by a Fe2O3/Coconut Shell Activated Carbon/H2O2 Heterogeneous Fenton-like System

Energy utilization in wastewater degradation has important implications for sustainability; however, efficient multiphase Fenton-like catalysts are still needed. In this study, a heterogeneous Fe2O3/coconut shell activated carbon (CSAC) Fenton-like catalyst was prepared and evaluated with respect to degradation performance and exothermic reaction for the treatment of organic wastewater. Fe2O3@CSAC retained the porous morphology of CSAS, and Fe2O3 was uniformly loaded on the surface of CSAS. In the reaction system, the degradation rate of wastewater was higher and a large amount of heat was released; therefore, it could be applied to the energy recovery from wastewater source heat pump technology. The degradation rate of 300 mL of o-phenylenediamine solution with a concentration of 0.04 mol·L−1 was 89.0% under 0.25 mol·L−1 H2O2, 532 g·L−1 Fe2O3@CSAC, pH 7.1, and an initial reaction temperature of 30 °C, elevated to 7.9 °C. These findings clearly demonstrate the degradation performance and exothermic laws of the Fe2O3@CSAC/H2O2 multiphase Fenton-like system.

Recovery of sulphur dioxide by converter dust synergistic coke decomposition of phosphogypsum

To further improve the decomposition ratio and sulfur dioxide mass yield of coke-reduced solid waste phosphogypsum (PG), converter dust (CD) is proposed as a novel additive. The effects of raw material ratio, time and temperature for roasting on the decomposition process of PG were inspected by simulation calculations and fluidized bed experiments. It turns out that the optimized reaction conditions are Fe3O4/Ca of 0.6, C/Ca of 0.4 at 1100 °C for 24 min, under which the PG decomposition ratio and SO2 mass yield are 99.56 % and 97.64 %, respectively. The addition of CD is able to reduce the initial reaction temperature from 975 °C to 914 °C, and promote the release of SO2. Kinetic analysis shows the mechanistic equation for this process is obtained as G(α) = [−ln(1 − α)]3/2, indicating that the decomposition reaction mechanism is a crystal nucleation and growth-controlled process. The chemical mechanism of the process is that coke and Fe3O4 in the CD convert CaSO4 to the intermediate CaS, and Fe3O4 is oxidized to Fe2O3. Then CaS and CaSO4 continue to react with Fe2O3 to form Ca2Fe2O5 and SO2. The presence of Fe2O3 accelerations the rate of CaS and CaSO4 roasting reaction and lowers the reaction temperature. Meanwhile, the self-decomposition of PG also produces CaO and SO2. Finally, a process for SO2 recovery from CD synergized with coke decomposition of PG is proposed.

4,5-Difluoro-1,3-dioxolan-2-one as a film-forming additive improves the cycling and thermal stability of SiO/C anode Li-ion batteries

SiO/C is currently considered the most favorable anode material for high-energy-density lithium-ion batteries (LIBs). Nevertheless, its potential applications are constrained because of its inherent capacity decay and thermal safety concerns engendered by its volumetric expansion during extended cycling periods. The present study investigated the effectiveness of 4,5-difluoro-1,3-dioxolane-2-one (DFEC) as a film-forming additive to augment the safety and electrochemical efficacy of LIBs. A blank electrolyte (BE) was used as a control. Electrochemical test and characterization results revealed that the capacity retention rate of a battery containing the DFEC additive improved significantly; specifically, it increased from 45.23% (for a battery with the BE) to 73.14%. DFEC also increased the quantity of LiF components on the anode surface, resulting in the formation of a robust and stable solid electrolyte interphase film, which enhanced the battery’s cycling stability. Differential scanning calorimetry, thermogravimetric analysis, and thermokinetic analysis revealed that DFEC inhibited exothermic reactions between the electrolyte and the lithiated anode. Notably, the initial reaction temperature for the electrolyte slowly transitioned from 232.17 to 238.67 °C. The apparent activation energy increased from 439.56 to 506.995 kJ/mol. This study presents a practical approach for the development of safe, high-energy-density batteries by incorporating DFEC as a film-forming additive.

Synthesis of high‐quality vanadium nitride particles by one‐step vacuum carbothermal reduction–nitridation method: Theoretical and experimental study

AbstractOwing to its high hardness, favorable stability, and good electrical performance, vanadium nitride (VN) has been extensively used as an alloy additive, an electrode material, a ceramic material, and a catalyst. However, traditional VN synthesis methods require high temperatures and long soaking times. In this study, high‐quality VN particles were prepared from V2O3 powder at a lower temperature and shorter soaking time by a one‐step vacuum carbothermal reduction–nitridation (VCRN) method. Thermodynamic and kinetic analyses elucidated the mechanism of this process. Thermodynamic analysis showed that vacuum was conducive to the carbothermal reduction of V2O3, reducing the initial reaction temperature, and the main reaction path was V2O3→VO→VxCy(VC/ V2C/ V8C7/ V6C5)→VN. Kinetic results indicated that the one‐step VCRN method was a gas–solid reaction. Within the temperature range of 1373–1473 K, the rate‐determining step was controlled by the carbothermal reduction–nitridation reaction, combination control of the reduction–nitridation reaction and the interlayer diffusion, and interlayer diffusion control of N2 during the different reaction processes. High‐quality VN particles obtained at a temperature of 1473 K, pressure of 300 Pa, and soaking time of 3 h were characterized by X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and particle size distributions. The O and N contents, measured by an O/N analyzer, were 0.85% and 19%, respectively, and the C content, measured by a C/S analyzer, was 0.92%. These analyses indicate that high‐quality VN can be obtained by a one‐step VCRN method.

Functionalized magnetic chitosan-based adsorbent for efficient tetracycline removal: Deep investigation of adsorption behaviors and mechanisms

As removal performance of tetracyclines in traditional wastewater treatment plants cannot satisfy the increasingly strict discharge requirements, developing an efficient approach to overcome this problem is quite urgent. Herein, a novel functionalized magnetic chitosan-based adsorbent (Fe3O4@CAA) with core-shell structure and unique magnetic responsiveness was facilely prepared by ultrasound-initiated radical grafting copolymerization and cross-link reaction. The as-prepared Fe3O4@CAA was fully characterized with TEM, SEM, BET, FTIR, TGA, XRD, VSM, and served as an efficient adsorbent for tetracycline hydrochloride (TCH) removal. Adsorption behaviors of TCH by Fe3O4@CAA were deeply evaluated at different adsorption time, initial TCH concentration, reaction temperature, solution pH, and background pollutant concentration. Results showed that Fe3O4@CAA presented a more competitive adsorption capacity of 325.04 mg g−1 compared with Fe3O4@CS and other reported adsorbent, due to the introduction of more active adsorption sites by abundant functional groups, including amino groups, hydroxyl groups, and sulfonic acid groups. After saturated adsorption, TCH loaded Fe3O4@CAA was easily collected by magnetic separation, and recycled after acid pickling. Fe3O4@CAA was successfully reused in five adsorption-desorption cycles, without obvious adsorption capacity loss. In binary pollutant systems, inorganic cations and Pb(II) restrained TCH adsorption by competitive effect, while proper amount of Cu(II) promoted TCH adsorption by bridge effect. FTIR and XPS analyses revealed that the adsorption mechanism of TCH by Fe3O4@CAA mainly included electrostatic interaction and hydrogen bonding, and Cu(II) could play a “mediator” role to form a strong Cu(II)-TCH complex to enhance TCH removal performance. This study provides an effective strategy for the design of magnetic chitosan-based adsorbents and valuable guidance for the removal of tetracyclines from wastewater.

Estimation and testing of single-step oxidation reactions for hydrogen and methane in low-oxygen, elevated pressure conditions

Advanced combustion concepts, such as moderate or intense low-oxygen dilution (MILD) combustion, offer a reduction in NOx emissions and increased thermal efficiency. MILD is characterised by low-oxygen, high-temperature conditions, where finite-rate chemistry effects are significant. Modelling this regime using reduced or single-step chemistry remains a challenge in part due to the finite-rate chemistry. This work proposes a generalised method for assigning Arrhenius coefficients of a single-step reaction using the outputs of a detailed mechanism. Assigning the typical chemical conservation equation to a progress variable, activation energy and pre-exponential factor for an Arrhenius kinetics global reaction are determined for hydrogen and methane across a number of conditions, with the proposed method extended to n-heptane as well. The temperature exponent in the modified Arrhenius equation is determined by minimising the ignition delay error between detailed and single-step simulations. Functional forms of each coefficient are calculated from a multivariate regression, dependent on initial temperature, pressure, and oxidant mole fraction. The predicted mechanisms are compared against the detailed kinetics in closed homogeneous batch reactors, with comparisons for hydrogen extended to both laminar opposed flow diffusion flames, and computational fluid dynamics (CFD) simulations. Ignition delay and equilibrium temperature are both well predicted for all three fuels in the batch reactors. Notably, the negative temperature coefficient behaviour of n-heptane is successfully recreated with the single-step mechanism. Temperature and heat release of hydrogen flames are well captured in both opposed flow laminar flames, and in turbulent CFD simulations. The computational time was also significantly reduced through the single-step mechanisms, resulting in ∼100 times reduction in compute time for CFD simulations. The function form of the Arrhenius coefficients shows promise for extension outside of the ranges and fuels analysed herein, and presents interesting phenomena for exploring how initial reactant temperature and pressure influence the effective activation energy of an oxidation process.

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

Highly efficient removal of tetracycline and methyl violet 2B from aqueous solution using the bimetallic FeZn-ZIFs catalyst

Abstract Residual antibiotics and organic dyes in wastewater have gained the current challenge all over the world because of their toxicity to humans and the environment. In this study, the bimetallic porous FeZn-ZIFs materials were successfully prepared under mild conditions at room temperature and atmospheric pressure and characterized by various techniques. The FeZn-ZIFs were used as a heterogeneous catalyst to remove tetracycline antibiotics (TC) and methyl violet 2B dyes (MV) in an aqueous solution by activating peroxymonosulfate (PMS) and peroxydisulfate (PDS), respectively. The catalytic activity of FeZn-ZIFs towards TC and MV under different oxidant dosages, the catalyst dosage, the initial pollutant concentration, contact time, and reaction temperature were optimized. The results indicated that FeZn-ZIFs was an efficient catalyst for removing TC and MV based on advanced oxidant processes, having a removal capacity of 92% at TC concentration of 50 mg·L−1 and 95% MV concentration of 20 mg·L−1. More importantly, this bimetallic catalyst was identified the superior structural stability when the removal efficiency of TC and MV was maintained at approximately 90% after five cycles. In short, the FeZn-ZIFs and PMS/PDS system exhibited a promising application prospect for antibiotic and dye-containing wastewater treatment.

Adsorption behavior of vanadium(V) by supported imidazolium-based difunctionalized ionic liquid

This study reports the functionalization of imidazolium-based ionic liquids (ILs) anions to synthesize novel supported imidazolium-based difunctionalized ILs (SIBD-ILs). Polystyrene [1-butyl-3-methylimidazolium][bis(2-ethylhexyl)phosphate] (PS[C4mim][D2EHP]) was used as an adsorbent to separate and enrich vanadium from vanadium-containing solutions. The effects of parameters such as the initial pH, liquid-solid ratio (L/S), reaction time, and reaction temperature on V(V) adsorption behavior were investigated. The adsorption capacity of 283.63 mg/g was reached under optimal conditions. V(V) adsorbed on PS[C4mim][D2EHP] was effectively desorbed using 3 mol/L NaOH solution and regenerated PS[C4mim][D2EHP]. After 10 adsorption-desorption cycles, the adsorption capacity was maintained at 95.36% of the initial value. The selective adsorption property of PS[C4mim][D2EHP] was studied in vanadium solutions containing Fe(III) and Al(III) ions. At pH = 2.0, the separation coefficients of towards Fe(III) and Al(III) were the highest, 62.05 and 38.69, respectively. The adsorption process of PS[C4mim][D2EHP] for V(V) conformed to Freundlich and pseudo-second-order kinetic models. SIBD-ILs were characterized by Fourier transform infrared, X-ray Photoelectron Spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results showed that PS[C4mim][D2EHP] was successfully prepared, and PS[C4mim][D2EHP] mainly adsorbed vanadium by ion association.

Thermal decomposition characteristics and spontaneous combustion phenomenon of emulsion explosive containing FeS2 impurity

AbstractIn the process of pyrite blasting mining, emulsion explosives in blast holes can sometimes spontaneously detonate prematurely. In order to reveal its accidental explosion mechanism, the effects of different content of FeS2 impurity on the thermal decomposition characteristics and thermal spontaneous combustion parameters of emulsion explosives were studied in detail. The experimental results of thermal analysis showed that pure emulsion explosive had a strong stability, but when it was doped with FeS2 impurity, its initial temperature of thermal decomposition reaction reduced and the decomposition rate accelerated. With the increase of FeS2 impurity content, the average activation energy of emulsion explosives decomposition decreased from 110.84 to 63.78 kJ/mol, resulting in an increasing risk of thermal runaway. The results of thermal spontaneous combustion experiments showed that FeS2 impurity would significantly shorten the ignition delay period and combustion flame duration of emulsion explosive, and increase the combustion flame temperature. With the increase of FeS2 impurity content in emulsion explosive, the ignition delay period and the duration of the flame continued to decrease and increase, respectively, and the maximum average temperature of the flame showed a trend of rising at first and then decreasing. The research results were of great significance to the accident identification of emulsion explosive accidental explosion in pyrite blasting operations.

Heterogeneous activation of peroxymonosulfate by recyclable magnetic CuO/Fe3O4 nanosheets for efficient degradation of organic pollutants

In this work, recyclable magnetic CuO/Fe3O4 nanosheetswere successfully synthesized via a simple continuous precipitation method, which can effectively activate peroxymonosulfate (PMS) to decompose organic pollutants. The properties of CuO/Fe3O4 nanosheets were measured by a series of characterization techniques. CuO/Fe3O4 composites showed highly effectiveness for PMS activation to degrade methyl blue (MB), and several influencing factors were investigated, such as initial pH, catalyst dosage, PMS concentration and reaction temperature. Although CuO/Fe3O4/PMS system exhibited effectiveness for MB degradation in a wide pH range, the natural pH value was the best. The increase in reaction temperature is favorable for MB degradation, and the activation energy was calculated as 40.34 kJ/mol. Quenching experiments and electron spin resonance (ESR) analysis proved that OH, SO4- and 1O2 were generated in the CuO/Fe3O4/PMS system, and SO4- and 1O2 played the dominant role. Moreover, CuO/Fe3O4 remained good activity and stability after being recycled five times. In addition, the complete degradation of methylene orange (MO) and tetracycline hydrochloride (TC), and MB degradation in tap water and lake water further confirmed the wide applicability of the CuO/Fe3O4/PMS system. These results exhibited that CuO/Fe3O4/PMS system has great advantages of high removal efficiency, reusability and wide applicability, demonstrating its potential environmental application in the treatment of organic wastewater.

Chemical reactions in poly(acrylonitrile-co-itaconic acid) during stabilization as revealed by solid-state NMR spectroscopy and 13C isotope labeling

Understanding and controlling chemical reactions of atactic-Poly(acrylonitrile) (PAN) and its copolymer during thermal heat-treatment under air are critical subjects to produce PAN-based carbon-fibers. Copolymerization of PAN with itaconic acid (IA) monomers effectively lowers initial chemical reaction temperature and thus promote chemical reactions during stabilization. In this work, detailed chemical structure of PAN and poly(acrylonitrile-co-itaconic acid) (PAI) stabilized under air atmosphere were studied by combined use of solid-state (ss) NMR spectroscopy and 13C isotope labeling. By applying 13C–13C INADEQUATE and fully relaxed 13C DPMAS NMR spectra, it was elucidated that 2% cyclized structure can be initially formed in PAI during stabilization. Moreover, five elemental reactions including cyclization, aromatization, oxidization, dehydrogenation, and intermolecular cross-linking were identified and corresponding structures were quantitatively analyzed in both PAN and PAI as a function of stabilization temperature. It was revealed that all the reactions concertedly occur in PAN in the narrow temperature range (290–340 °C). For PAI, it was demonstrated that cyclization and aromatization are dominant in the low temperature range (180–270 °C, regime I), dehydrogenation and intermolecular cross linking are promoted in the high temperature range (270–340 °C, regime II), and oxidization occurs across two regimes. The sensitivity enhanced ssNMR study not only provides fundamental understanding of the chemical reactions in PAN and PAI during stabilization but also guide ones to potentially control the stabilized structures from one dimensional structure to two dimensional one for PAI by choosing a proper temperature and time.

Investigation of the adsorption and degradation of metronidazole residues in agricultural wastewater by nanocomposite based on nZVI on MXene

Metronidazole is a widely used antibiotic with powerful antimicrobial properties, but its presence in water can be detrimental to aquatic life and human health. To address this issue, we developed a novel composite material, zero-valent iron nanoparticles on alkalized Ti3C2Tx nanoflakes (NZVI/Ti3C2Tx), using an in-situ growth technique, aiming to efficiently adsorb and degrade metronidazole from aqueous solutions. The incorporation of Ti3C2Tx in NZVI/Ti3C2Tx resulted in enhanced dispersion, stability, and reactivity of NZVI. Our study demonstrated that NZVI/Ti3C2Tx exhibited the highest metronidazole removal efficiency (95.80%) within just 10 min of reaction time, outperforming NZVI and Ti3C2Tx alone. To optimize the removal process, we investigated the influence of various parameters on the degradation of metronidazole by NZVI/Ti3C2Tx, including the NZVI/Ti3C2Tx ratio, initial metronidazole concentration, pH, and reaction temperature. The highest removal rate was achieved with an NZVI/Ti3C2Tx ratio of 2:1 after 90 min of reaction time. As the initial concentration and pH of metronidazole increased, the removal efficiency decreased, while higher reaction temperatures improved the removal efficiency. Kinetic studies revealed that the degradation of metronidazole by NZVI/Ti3C2Tx followed a modified second-order parameter pseudo-first-order kinetic model, highlighting the effective reduction reaction. The unique properties of MXene nanosheets and NZVI synergistically contributed to the enhanced removal performance, with NZVI/Ti3C2Tx acting as an efficient adsorbent and reducing agent. Uur findings demonstrate the potential of the NZVI/Ti3C2Tx nanocomposite as an efficient and eco-friendly approach for the removal of metronidazole from agricultural wastewater. The combination of NZVI and Ti3C2Tx offers enhanced removal efficiency and stability, making it a promising material for water purification and environmental applications.

New insight into the oxidation of propene at elevated pressure

Comprehensive experimental and kinetic studies of propene (C3H6) oxidation were conducted by using a jet-stirred reactor at 12.0 atm within 725–1020 K under both fuel-lean (Φ = 0.5) and fuel-rich (Φ = 3.0) conditions. Molecular species concentration profiles were obtained by using online gas chromatography and gas chromatography-mass spectrometry, including CO, CO2, CH4, C2H4, C2H6, A-C3H4, C3H8, 1,3-C4H6, 1-C4H8, nC4H10, CH3CHO, C2H3CHO, CH3COCH3, C3H6O1-2 CH3CH2CHO, and C6H6. Sixteen products and intermediates including light hydrocarbons, oxygenated and aromatic species were identified and quantified. Based on Aramco Mech 3.0 and previous works, the rate coefficients of some key elementary reactions were updated, and a detailed kinetic reaction model was developed with reasonable predictions involving 587 and 3037 reactions. Rate-of-production analysis indicates the four main pathways for high-pressure oxidation of C3H6, namely hydrogen atom abstraction reactions, OH addition reactions, H atom addition reactions, and the formation of C3H6O1-2. Sensitivity analysis reveals that H2O2(+M) <=> 2OH(+M) and the H-abstraction of C3H6 by OH radicals are the most promoting and inhibiting reactions for C3H6 consumption, respectively. The benzene formation during C3H6 oxidation was analyzed, mainly generated by the C1 + C5 channel and consumed by OH addition. It was found that increasing pressure can decrease the initial reaction temperature and increase the conversion of C3H6. The importance of addition and hydrogen abstraction reactions in the oxidation of C3H6 was identified by analyzing the pressure effect. To confirm its validity, the proposed kinetic model could be used to the previous literature data, including JSR oxidation at around 1 atm and ignition delay times for C3H6. These experimental and modeling efforts provide a basis for gaining a more comprehensive insight into the oxidation of propene.

Numerical investigations on hydrothermal flame characteristics of water-cooled hydrothermal burner

Abstract Supercritical hydrothermal combustion, as a quick homogeneous oxidizing process, offers a promising treatment option for industrial wastewater. This paper established a computational fluid dynamics model of a water-cooled hydrothermal combustion burner to investigate the thermal flame characteristics. The effects of the fuel mass flow rate, fuel concentration, initial reactor temperature, reaction pressure, and oxidant temperature on the thermal combustion ignition were revealed. The results indicate that the fuel concentration (from 10 wt% to 60 wt%) and initial reactor temperature (from 623 to 773 K) had less effect on the ignition temperature. In contrast, the ignition temperature increases by 398 K with increasing fuel mass flow rate (from 24 kg h−1 to 1080 kg h−1). As the oxygen temperature increases (from 273 to 673 K), the ignition temperature gradually decreases to 573 K and then increases. An increase in reaction pressure can facilitate a decrease in ignition temperature to a certain extent, and the optimal reaction pressure is 25 MPa. This study provides a vital reference for a hydrothermal burner’s scale-up design and ignition operation.

Numerical simulation of nano-aluminum ignition in oxygen and steam environments

The ignition characteristics of nano-aluminum (nano-Al) in oxygen and steam environments were numerically studied in this work. A detailed kinetic mechanism of nano-Al combustion was developed, and the effects of initial reaction temperature, ignition pressure, the phase of reactant, and the ratio of O2 and H2O in the oxidizer on the oxidation performance of aluminum (Al) were analyzed in detail. Numerical results show that increasing the initial temperature promotes the ignition of liquid-phase Al, while the promotion is not significant for gas-phase Al ignition. The oxidation of liquid-phase Al is significantly slower than that of gas-phase Al, and the phase transition reaction of liquid-phase Al exhibits a typical endothermic process, which results in a temperature drop before ignition. The increase of initial reaction pressure can accelerate the consumption of both liquid-phase Al and gas-phase Al in the ignition process. The oxidizability of O2 is much larger than that of H2O, and the oxidation of Al becomes slower by adding H2O in the oxidizer. The rate of production (ROP) was performed to deeply realize the reaction pathways of Al consumption and main products formation. The reaction Al + O2 = AlO + O is the key reaction pathway in the Al-O2 ignition process, while the reaction Al + H2O = AlOH + O plays a more important role in the Al-H2O ignition process. In the all ignition cases, Al2O2 is a key intermediate species since it is the main precursor of gaseous Al2O3, and liquid-phase Al2O3 formed by the phase transition reaction of gaseous Al2O3 is the dominant final product.

Kinetics study of the selective hydrogenation of furfural to furfuryl alcohol over CuAl2O4 spinel catalyst

The catalytic hydrogenation of furfural is an important process that produce value-added furfural derivatives, especially furfuryl alcohol. In this work, the kinetics of the catalytic furfural hydrogenation over copper aluminate spinel (CuAl2O4) was studied in a batch-type reactor under various reaction parameters including the stirring speed, initial furfural concentration, H2 pressure, and reaction temperature. The CuAl2O4 catalyst showed excellent performance in furfuryl alcohol production as the furfural conversion could reach 100% and the furfuryl alcohol yield was >98%. The furfural concentration and the reaction temperature were found to significantly impact on the reaction rate, while other parameters showed less contributions leading to a flexible operation window. It was determined that the reaction rate expression followed the equation r = kCfurfural0.335 with the apparent activation energy of 44.6 kJ/mol. The developed kinetic model for hydrogenation of furfural to furfuryl alcohol were in good agreement with the experimental results. The kinetic model presented here could be useful for process design and scale-up of the hydrogenation reactor in the industrial application.

Introducing metal oxide as solid oxygen carrier for energy release enhancement of boron suspension fuel

Boron (B) suspension fuel is a novel high-density fuel for aerospace propulsion. However, it suffers from significant incomplete energy release of B during combustion, which seriously restricts its practical application. This study focuses on the key causes of this problem, insufficient oxygen supply, and proposes to introduce metal oxides (MOx) as solid oxygen carriers to form B-MOx and replace pure B to enhance the energy release characteristics of B suspension fuel. TG-DSC analysis is conducted to sort out CuO as the optimal additive for B oxidation enhancement and its enhancement mechanism is analyzed with thermal equilibrium calculation. It was found that CuO could generate active O atoms through two-step reduction, thus achieving efficient oxygen supply for B and reduce its initial reaction temperature from 810 °C to 661.7 °C with an optimal B-CuO ratio of 1:1. CO2 laser ignition experiment and combustion residue analysis are conducted to analyze the combustion characteristics of B-CuO/JP-10 suspension fuel. Compared with original B/JP-10 suspension fuel, B-CuO/JP-10 suspension fuel presents much higher combustion intensity with local explosion after ignition, and a second stage of intensive energy release is realized with the reignition and explosion of solid agglomerate. The oxidation of JP-10 and B are enhanced with no incomplete oxidation product found in the residue. The enhancement mechanism of CuO on B suspension fuel is proposed including the generation of active radical, efficient internal oxygen supply and enhanced external oxygen supply.

Effect of particle size on initial reaction temperature of Ti and Zr powders

In order to study the effect of particle size on the initial reaction temperature of reactive metal powders, thermogravimetric analysis- differential scanning calorimetry (TG-DSC) experiments and hot plate combustion tests were performed on Zr and Ti powders with an average particle size of 13±2, 25±5, 48±3, 75±5, 150±10 μm. Differential scanning calorimetry (DSC) results show that the initial reaction temperature of the metal powder with smaller particle size is lower. The heat flow rate and reaction rate are negatively correlated to the particle size. The hot plate combustion test shows that the initial reaction temperature of the metal powder increased with the increasing particle size. The heating rate also has a certain influence on the initial reaction temperature of the reactive metal powder. The initial reaction temperature is lower with a faster heating rate, for Ti and Zr particles of this study.