Exothermic Conditions Research Articles

Mechanisms of CO and CO2 Production during the Low-Temperature Oxidation of Coal: Molecular Simulations and Experimental Research

The spontaneous combustion of coal caused by oxidation often leads to catastrophic fires. However, the understanding of oxidized carbon gas as a predictor of coal’s spontaneous combustion is still in its infancy. To better study the characteristics of CO2 and CO generation during low-temperature coal oxidation, the chemical reactions and activation energies during the formation of oxidized carbon gases within coal molecules were investigated using the molecular simulation method, and the reaction characteristics at different temperatures were determined. In addition, TG was used to experimentally analyze the variations in coal weight, exothermic conditions, and gas generation patterns. The results show that the low-temperature oxidation process consists of four different phases, each of which is characterized by unique CO and CO2 generation. The results of this study are important for the prevention and prediction of the spontaneous combustion of coal.

Modeling of diesel particulate filter temperature dynamics during exotherm using neural networks

Diesel Particulate Filter (DPF) in the diesel engine exhaust stream needs frequent regeneration (exotherm) to remove captured particulate matter (PM, or soot) without damaging to the porous DPF structure by controlling the peak temperatures and temperature gradients across the DPF. In this study, temperature distribution in a DPF is measured at 42 strategic locations in the test DPF under various regeneration conditions of exhaust flow rates, regeneration temperatures and soot loads. Then a data-based model with feed-forward neural network architecture is designed to model the thermal gradients and temperature dynamics of the DPF during the regeneration process. The neural network feature vector selection, network architecture, hyperparameter calibration process, measured data preprocessing, and experimental data acquisition procedure are evaluated. Over 7,400 experimental data points at various regeneration temperatures, flow rates and soot loads are used in training and validating the neural network model. It is found that the neural network model can accurately predict the 42 DPF bed temperatures simultaneously at different locations, and the time series analysis of both model-predicted and experimentally measured temperatures shows a good correlation. This indicates that the currently developed neural network model can provide spatial distribution of temperature in the DPF, and comprehend the nonlinearity of the temperature dynamics due to DPF soot load at exothermic conditions. These results demonstrate that the data-based model has capability in predicting thermal gradients within a DPF, aiding in determining a safer DPF regeneration strategy, onboard diagnostics and DPF development.

Development of a novel tailored ion-imprinted polymer for recovery of lithium and strontium from reverse osmosis concentrated brine

This study aims to prepare ion-imprinted polymer (IIP) with the benefit of a metal-based sorbent, which is fabricated to selectively adsorb lithium (Li+) from aqueous solutions, and in an attempt to remove strontium (Sr2+). The adsorption processes were carried out at different pH values, initial concentrations, and temperatures, to optimize the experimental conditions, with the use of response surface methodology (RSM). The seawater reverse osmosis (SWRO) brine was physically and chemically characterized, and the physicochemical characterization of the prepared IIP before and after adsorption was also performed using different spectroscopic methods. The adsorption capacity for Li+ and Sr2+ from SWRO brine was evaluated, and the reusability of IIP was investigated using adsorption–desorption cycles. The results showed that the IIP was efficient to remove Li+ but not Sr2+, and it follows Freundlich adsorption isotherms models. The analysis revealed a significant concentration of minerals in the brine sample It also revealed a low concentration of trace metals, like Ba (0.16 mg/L), Zn (0.845 mg/L), Fe (1.31 mg/L), Cu (1.165 mg/L), Pb (1.505 mg/L), and V (3.88 mg/L), except Li and Sr which shows a higher concentration of 43.32 mg/L and 16.93 mg/L respectively. pH 10 was selected to be the optimum pH for the adsorption isotherm experiments, as it was the highest efficient pH to adsorb Li+ and Sr2+. The thermodynamics study revealed that the adsorption of Li+ on the IIP favored exothermic conditions. It was noticed that the maximum adsorption capacity (Qm) was increased as the temperature rise from 714.3 mg/g at 25 °C to 2500 mg/g at 45 °C. The Li+ desorption results show that 94.03% − 94.71% of the ions were recovered, while the Sr2+ desorption results show that 96.35% − 96.56% of the ions were recovered. The efficiency of IIP to adsorb lithium and strontium from brine shows that the adsorption removal% of Li+ was between 84.21% and 84.68%, while the adsorption removal% of Sr2+ was between 3.83% and 10%. The cost analysis for IIP preparation was 2 USD/g.

Practical synthesis of diaryliodonium(iii) triflates using ArI(OAc)2/TfOH/MeCN reaction system

Diaryliodonium(iii) triflates were synthesized in a safe manner by the reaction of aryliodine(iii) diacetates ArI(OAc)2 with triflic acid (TfOH) in MeCN under mild exothermic conditions. This method provides access to a variety of diaryliodonium(iii) triflates, including derivatives with two different aryl substituents, with high purity.

Electrochemical and Dynamic Characterization of a 6-Cell Solid Oxide Cells Stack in Steam Electrolysis and Steam and Carbon Dioxide Co-Electrolysis

High temperature steam electrolysis and co-electrolysis of steam and carbon dioxide for hydrogen and syngas production is gaining attention for its potential to play a key role in the production of renewable fuels and for long-term energy storage. Unlocking a longer lifetime and lower costs for these systems is required if they are to be widely deployed. In this work, we consider a 6-cell Solid Oxide Cell (SOC) short-stack, manufactured by SOLIDpower S.p.a. (Italy), that has been installed and tested at UC Irvine. The short-stack is installed in a test bench that maintains the operating temperature in a controlled range of 650-850°C, via an electric furnace. The cells are characterized by an 8 mol% Y2O3 stabilized Zirconia (YSZ) electrolyte (8 ± 2 μm) supported on a conventional porous Ni/YSZ anode electrode (240 ± 20 μm). The cathode electrode is comprised of a composite of metallic perovskite Sr-doped LaMnO3 (LSM) and oxide-ion electrolyte YSZ (40 ± 10 μm). The active area of each cell is 80 cm2.The aim of the study is the experimental characterization of the short-stack via electrochemical and dynamic techniques to: i) characterize stack performance in steady-state; ii) investigate single cell degradation and interdependencies between adjacent cell operating conditions to determine stack degradation; and iii) determine characteristic time responses of thermal, fluid-dynamic and electrochemical phenomena. The experiments are conducted for both steam electrolysis and co-electrolysis of steam and carbon dioxide. The experimental electrochemical methods employed include chronopotentiometry, electrochemical impedance spectroscopy and current interrupt. Moreover, fluid-dynamic step response and thermal ramp dynamic response of the stack are evaluated to achieve a better understanding of the effect of an operating control system on local fuel starvation and local temperature hot spot regions, which are possible contributors to increased degradation.Preliminary results show unequal degradation rates for the six cells under thermal cycles (which put stack under continuous switching between exothermic and endothermic operating modes). The unequal degradation rates of the cells were investigated and are possibly related to unequal flow distribution within the stack. Degradation rates were below 1% for thirty consecutive thermal cycles for operation in steam electrolysis. Responses that included fluid-dynamic step step changes allowed determination of the fluid-dynamic and thermal time constants associated with preheating flows introduced to the stack of the order of 200 to 300 seconds, depending on the step size. The evaluation of the fluid-dynamic and thermal response allowed decoupling of the thermal capacitance of the stack and that associated with the furnace and piping, via an equivalent circuit model approach. This has led to an ability to estimate the amount of heat produced by the stack when operating in exothermic conditions and the absorbed heat from the furnace when operating in endothermic (sub-thermoneutral voltage) conditions. Figure 1

Grain Structure Formation in Ni3Al Intermetallic Compound Synthesized Under High-Temperature and Pressure Conditions

The paper presents theoretical and experimental results of studying the grain structure formation of the Ni3Al intermetallic compound produced by self-propagating high-temperature synthesis (SHS) under the pressure and volume exothermic reaction conditions, in a stoichiometric powder mixture. It is shown that the grain size in the SHS-produced intermetallic compound depends on both the preliminary load on the powder mixture and the SHS product deformation during its crystallization. It is found that the increased pressure on the initial powder mixture reduces the grain size in the bulk of the SHS-produced intermetallic compound, whereas its deformation provides a manifold decrease of the grain size at a simultaneous averaging of its distribution in the bulk of the SHS product obtained under pressure.

Biosynthesis of Metal Nanoparticles from Leaves of Ficus palmata and Evaluation of Their Anti-inflammatory and Anti-diabetic Activities.

Metal nanoparticles (AgNPs and ZnONPs) were synthesized using a green methodology with the green leaves extract of the Bedu (Ficus palmata) tree as a reducing agent and the support of natural fibers. The synthesized AgNPs and ZnONPs were characterized by several techniques, including ultraviolet-visible spectral analysis, powder X-ray diffraction crystal analysis, scanning electron microscopy, EDAX, transmission electron microscopy, and Fourier transform infrared spectroscopy, which confirmed that the synthesized particles are in the nano range (1-100 nm), i.e., 30 nm for AgNPs with polydispersity and a spherical shape, whereas the average size of synthesized ZnONPs is 34 nm and they seem to exhibit a distorted spherical shape. The results of thermogravimetric analysis confirmed a weight loss of 18.02% for AgNPs under exothermic conditions due to the desorption of water, and ZnONPs show weight loss between 265 and 500 °C. Both synthesized MNPs are highly thermally stable. Anti-inflammatory and anti-diabetic studies of metal NPs have been evaluated. The AgNPs and ZnONPs of F. palmata leaves showed remarkably highly potent activity for respective strains. In vitro anti-diabetic activity was found for inhibition of α-amylases and α-glucosidases by synthesized silver nanoparticles.

Enthalpy changes during pyrolysis of biomass: Interpretation of intraparticle gas sampling

The results of birch wood pyrolysis are presented providing details on the gas, liquid and char mass production rates as a function of temperature from 25 °C to 500 °C. Quantitative measurements, using a Kr tracer, were taken from the center of a sphere sample enabling insight into the product gas formation profiles over the same temperature range. A unique calculation methodology was developed to combine data from TG measurements, quantitative GC measurements of the gaseous chemical species and ultimate analysis of the char product enabling the elucidation of the energetics of the pyrolysis process as a function of temperature. Precise calculations based on the measurements of gas, liquid and char production rates demonstrated the pyrolysis of birch wood transitions from endothermic to exothermic conditions at 280 °C. The reactions maintain an exothermic character until 480 °C then return to an endothermic nature at 500 °C. Changes in gas, char and liquid elemental compositions, plotted as a Van Krevelen diagram, indicated as temperature increases char and liquids trend toward lower O/C and H/C ratios. However, the gaseous H/C decreased slightly from 1.7 to 1.45 yet the O/C increased dramatically from 0.3 to 2.0.

Maturity testing of 3D printing concrete with inert microfiller

The 3D Printing of cement composites is one of the fastest developing technologies of modern concrete. The 3D printing involves concretes with high amounts of microfillers. The study analyses the influence of curing conditions on the development of strength of concretes applicable in 3D printing. Ten mixes were tested in the study. In the studied cases cement constituted to 50% of the mass, while microfillers such as lime stone powder, kaolin, quartz powder and sand (up to 2 mm) constituted to the rest of the mass. Samples were cured for 7 days in exothermic conditions at 5°C, 20°C, 35°C. Standard mortar samples of 4x4x16 cm and cylinders with 46.5 mm and height of 35 mm that simulate the printed 3D path were made. The compressive strength was tested after 12h, 24h, 48h, 72h, 168 h and 28 days. Based on the acquired results the temperature development function was formulated and activation energy was determined. The results showed that the proposed method is useful in evaluation of printed concrete curing. It can be also used to determine the time of loading the wall which can speed up the process of constructing while maintaining degree of safety.

Risk Based Design of Allyl Chloride Production Plant

The necessity to identify and quantify the risks for men and the environment, but also the excessive consumption of resources and energy related to the process plants has led to the formulation of analytical methods capable of assessing the reliability and availability of these systems in order to optimize their operation. Integrated Dynamic Decision Analysis (T.D.D.A.), in particular, represents a tool for the modeling of the process plants based on dynamic event trees able to describe the system both as logic concatenation of events and probabilistic coherence. This approach was used for reviewing the design of a plant for the production of allyl chloride by chlorination of propylene in exothermic conditions. This paper aims at building an objective and documented reference for the decision making about the design altrenatives to be adopted for risk minimization

Impact of Gas-Phase Reactions on SOFC Systems Operating on Diesel and Biomass-Derived Fuels

The use of diesel fuel to power a solid oxide fuel cell (SOFC) presents several challenges. A major issue is deposit formation in either the external reformer, the anode channel, or within the SOFC anode itself. These deposits are generally poly-aromatic hydrocarbons (PAHs) produced either by gas-phase pyrolysis of the fuel or by catalytic reactions. In this report we describe n-hexane and ethylene pyrolysis experiments under conditions relevant to reformer or SOFC operation (τ=~1s, T=550~900°C, P~0.8 atm) to explore the potential for gas-phase reactions to produce deposit precursors. N-hexane is very reactive under these conditions and forms significant amounts of olefins (mainly ethylene) which can lead to deposits. The ethylene experiments also demonstrated that higher molecular weight species (deposit precursors) are rapidly formed. Under autothermal reforming conditions, such pyrolytic reactions are possible upstream of the catalyst bed if the fuel, air, and steam streams are not fully mixed. If part of the fuel does not mix with the oxidizer it will simply pyrolyze. At the same time, the remaining fuel fraction mixes with the entire oxidant inlet and thus creates higher local oxidant to fuel ratios than expected. Reaction of this leaner mixture can lead to temperature overshoots as more CO2 is formed. We have used a validated detailed kinetic model for ethane to explore the impact of incomplete fuel mixing on reforming performance. If only half the fuel mixes with the oxidants, this approach predicts formation of ethylene in the pyrolysis zone and excess CO2 with associated very high temperatures in the oxidation zone. This case could result in both excessive deposit formation as well as potential thermal damage to the downstream catalyst. On the other hand, assuming perfect fuel mixing under exothermic ATR conditions (τ=~1s, Ti=800°C, S/C=1.25, O/C=1.4), the gas phase reactions alone are sufficient to drive the system to equilibrium (no olefins or methane formed) due to the substantial increase in temperature. These results demonstrate the necessity for complete mixing of the fuel stream with the oxidant streams to limit both olefin production (and subsequent deposit formation) as well as the temperature overshoots. The model predictions for ethane as fuel suggest that the temperature should be kept below 500oC and the residence time in the mixing region should be minimized to avoid these undesired gas reactions. Since actual diesel fuel is expected to be even more reactive than ethane, the impact of gas-phase reactions is expected to be even greater than predicted in this study.

Influence of thermal effects on buoyancy-driven convection around autocatalytic chemical fronts propagating horizontally

The spatiotemporal dynamics of vertical autocatalytic fronts traveling horizontally in thin solution layers closed to the air can be influenced by buoyancy-driven convection induced by density gradients across the front. We perform here a combined experimental and theoretical study of the competition between solutal and thermal effects on such convection. Experimentally, we focus on the antagonistic chlorite-tetrathionate reaction for which solutal and thermal contributions to the density jump across the front have opposite signs. We show that in isothermal conditions the heavier products sink below the lighter reactants, providing an asymptotic constant finger shape deformation of the front by convection. When thermal effects are present, the hotter products, on the contrary, climb above the reactants for strongly exothermic conditions. These various observations as well as the influence of the relative weight of the solutal and thermal effects and of the thickness of the solution layer on the dynamics are discussed in terms of a two-dimensional reaction-diffusion-convection model parametrized by a solutal R(C) and a thermal R(T) Rayleigh number.

A highly stabilized–inhibited nitric acid/ferric nitrate-based solder stripping solution

The effect of ammonium sulfamate and benzotriazole on the prevention of exothermic conditions, the evolution of toxic NO x gases and the reduction of copper attack during solder stripping were studied. The effect of these additives on the rate of temperature rise for solutions treating 63Sn37Pb solder alloy and pure copper were investigated. Weight loss analysis was also performed in order to evaluate the rate of copper etching in various compositions. Scanning electron microscopy was employed to investigate the nature of the attack on the copper surface. In order to identify the role of ammonium sulfamate and benzotriazole on the stripping process, anodic polarization measurements were performed for the copper electrodes. The results revealed that ammonium sulfamate is capable of eliminating the reduction of nitric acid and the evolution of toxic NO x gases, can prevent excessive temperature rise, and can inhibit the rate of copper etching. On the other hand, benzotriazole is capable of providing a mirror bright copper surface after the solder stripping. Simultaneous addition of ammonium sulfamate and benzotriazole to the stripping solution led to a unique solder stripping composition which is substantially secure in terms of the temperature rise, evolution of toxic NO x gases and copper attack.

HARMONIC ANALYSIS AND MODELLING OF ANNUAL SOIL TEMPERATURE VARIATIONS

Harmoni c analysi s using se ries is applied to th e annual variation s of so il tem pe rature From th esurface down to I III depth. TIle fir st harmo nic alon e expla ins about 99% of the variation .II is also shO\\TI th at heat conduction is nor valid in a soil med iuIIIunder exothermic conditions. especially in th euppermost layer of abom 20 em. as neither the thermal properties. exp ressed by the damping depth (D), nor th e meansoil temperature (nremai n constant with depth . and th e am plitude ofoscilla tio n (.4:) does nOI vary strictly expcnen rially.Thi s is as sumed to be con sider ably reduced soil moisture of thi s in compari son with deeper layers,Finally. cons truction of a mod el to predict mon thly or ten-d ay period mean soil temper atures is based' onwr-at h e r vari ab les (difference between precipitation and pan evaporation), providing an ind ex for the soil moisturede ficit and an est imate of D. and overcomes the difficulties of ch angi ng T and A: with depth.

Non-isothermal effects in a single pellet diffusion reactor

A theoretical analysis of an adiabatic non-isothermal single-pellet diffusion reactor shows that non-isothermal effects can alter the value of the centerplane concentration. Deviation from isothermal behavior is significant under exothermic conditions where multiplicity of solutions can lead to reactor instabilities or falsification of reaction parameters. Conversely, it is shown that the internal isothermal model is a good approximation to detect non-isothermal pellet behavior from centerplane concentration measurements.

Energetics and growth of L929 cell under exothermic conditions

Growth studies of mouse L cells have been concluded at elevated temperatures. The energy of activation is −90 425 cal for the range 37 ° to 40 °C as compared with 16 799 cal for that immediately below the optimal 37 °C. The implication of a negative activation energy and the retardation of cellular activities under exothermic conditions are discussed in terms of bioenergetics.

Energy Transfer from Differentiation in a Diferential Pressure System under Non-Equilibrium Conditions

A model is presented which relates the differentia] pressures in a dynamic system to the ensuing differentiation and temperature differences progressing under non-equilibrium conditions. A method is developed for subdividing the heat of formation of silicates among the constituent oxides, in order to trace recrystallization under shearing stress, leaving a residual depleted mass deposited under endothermic conditions in one area and a contemporaneously developed enriched mass formed under exothermic conditions in the adjacent lew-pressure area. The mobile material is shown to create the thermal gradient against which it migrates. The "stability" of a crystal is considered in relation to the proportional ΔH values of the constituent oxides, recrystallization being related to the threshold energy values for the weakest bonded oxides. The relative affinities that oxides have in different crystal structures are interpreted as a measure of the "internal stress" in a crystal, and the varying response of the individual oxides to an activation causes recrystallization and accounts for incongruent melting phenomena and a sequence in the release of mobilized constituents. The migrating material is considered to transfer its energy of activation from the point of departure to the point of final deposition. The changes in temperature in both areas are interpreted as the results of this process.