Exothermic Heat Research Articles

Multi-objective optimal configuration of CCHP system containing hybrid electric-hydrogen energy storage system

In order to cope with the increasing energy demand and achieve the “double carbon “goal of China’s 14th Five-Year Plan,” combined with hydrogen energy storage technology, it has the characteristics of zero pollution, high efficiency and rich source. In the context of reducing energy consumption and the vigorous development of hydrogen energy storage technology, a multi-objective optimization configuration model with economy, energy consumption index and carbon emission index is proposed, which takes into account the working characteristics of the hydrogen energy storage system, and the exothermic heat release from the electrolysis tanks and fuel cells when they are working to provide the loads with an additional heat source of the Combined Cooling, Heating and Power (CCHP) system, to reduce energy consumption and carbon emission. Finally, taking a region as an example, a multi-objective optimization algorithm based on decomposition is used to solve the model, so as to obtain a series of alternatives with better optimization effect. At the same time, the two-way projection method based on interval intuitionistic fuzzy information is used to make decisions, and the scheme that optimizes the economy, energy consumption index and carbon emission index is obtained, which verifies the feasibility of the system proposed in this paper.

Synthesis and thermal behavior of acrylonitrile/guanidine crotonate copolymer for carbon fiber precursor

AbstractThe thermal oxidation stabilization of polyacrylonitrile (PAN) copolymer is a highly exothermic process. It significantly impacts the quality of the finished PAN‐based carbon fiber, which is often addressed by adding appropriate comonomers. This paper synthesized guanidine crotonate (GCA) as a comonomer and copolymerized with acrylonitrile (AN) to prepare P(AN‐GCA). DSC analysis revealed that when compared to PAN and P(AN‐CA) copolymers, the initial exothermic temperature, maximum exothermic heat flux, and heat flux of P(AN‐GCA) copolymer were greatly reduced. FT‐IR spectroscopy showed that the degree of pre‐oxidation increased with the increasing comonomer GCA content, indicating that the addition of comonomer GCA could promote PAN pre‐oxidation cyclization and improve the copolymer's degree of pre‐oxidation. The activation energies of PAN and P(AN‐GCA) were 160 and 126 KJ/mol, respectively. It was shown that the addition of GCA could effectively reduce the activation energy of the cyclization reaction of the polymer while simultaneously promoting it. TGA analysis shows that the introduction of GCA improves the copolymer's thermal stability, and the yield at 800°C is more than 54%, which is at least 19% higher than PAN homopolymer. P(AN‐GCA) has the potential to be carbon fiber precursor.

Porous Monolithic Perovskite Structures for High-Temperature Thermochemical Heat Storage in Concentrated Solar Power (CSP) Plants and Renewable Electrification of Industrial Processes

A novel approach towards thermal energy storage of surplus renewable energy (RE) is introduced via a hybrid thermochemical/sensible heat storage concept implemented with the aid of porous structures made of redox metal oxides, capable of reversible reduction/oxidation upon heating/cooling in direct contact with air, accompanied, respectively, by endothermic/ exothermic heat effects and demonstrating fully reversible dimensional changes under cyclic operation. The proposed modular storage units can be heated during the day to a level exceeding the metal oxide’s reduction onset temperature either by hot air streams from air-operated Concentrated Solar Power (CSP) tower plants or via surplus/cheap RE-electricity from photovoltaics, wind, or other renewable sources (“charging”/energy storage step). When this RE sources become non-available or upon demand, the fully charged system can transfer its energy to a controlled airflow that passes through the porous oxide block and initiates the exothermic oxidation of the reduced metal oxide. Thus, a hot air stream is produced which can be used to provide electricity or exploitable heat for industrial processes. The present work elaborates on the operating principles and the potential application of this concept and reports progress in the preparation and shaping of reticulated porous ceramics (RPCs also known as “ceramic foams”) from CaMnO3-based perovskite compositions and their preliminary testing with respect to cyclic reduction-oxidation.

МЕХАНОАКТИВАЦІЯ ПОРТЛАНДЦЕМЕНТУ ТА ЇЇ ВПЛИВ НА ВЛАСТИВОСТІ БУДІВЕЛЬНИХ КОМПОЗИЦІЙ РІЗНОГО ПРИЗНАЧЕННЯ

The issues considered in the article are related to determining the effect of mechanical activation on the properties of cement-water compositions and building mortars based on them. The activation of cement in combination with the use of ground quartz sand and the superplasticizer Relaxol-Super PC is relevant for this study. The amount of quartz sand was adjusted in the range from 0 to 40% of the cement mass, and the superplasticizer (0,15 – 1,5%) of the binder mass. The use of this technology ensures acceleration of cement hydration processes, maintaining the required level of composition mobility with a lower consumption of mixing water, and intensification of exothermic heating. The presented experimental data made it possible to evaluate the effect of the binder activation period and the superplasticizer consumption on the flow of the aqueous cement-containing composition. It was found that the main contribution to the decrease in the water-solid ratio (provided that equiviscous compositions are obtained) is achieved by activating the cement-containing composition for 180 sec. with the addition of 1,5% superplasticizing additive. The water-solid ratio decreases by more than 50%. A further increase in the amount of plasticizer has low efficiency and has little effect on decreasing the water-solid ratio. Activation in combination with reduced water hardening of the cement-water composition contributes to both an increase in the heating intensity and an increase in its maximum temperature. After activation, the maximum temperature increased by 5-11% compared to the non-activated cement-water composition. The peak of the exothermic reaction for the mechanically activated cement-water composition occurs 3 hours earlier compared to the non-activated mixture. The increase in the strength of the mortar on mechanically activated cement with the addition of a superplasticizing additive reached 71% compared to the control.

INFLUENCE OF MECHANICAL ACTIVATION ON THE PROPERTIES OF CEMENT-WATER COMPOSITIONS WITH THE ADDITION OF GROUND LIMESTONE

The paper considers the issue related to determining the effect of mechanical activation of a mineral binder on the properties of both hardening and hardened cement-water compositions. The mechanical activation of cement in combination with the consumption of ground limestone, the amount of which was adjusted in the range from 0 to 40 % of the cement mass, is relevant for this study. The effect of mechanical chemical activation of Portland cement only and Portland cement with the addition of 20 and 40 % ground limestone on changing the water-solid ratio of equiviscous compositions was studied. It was shown that mechanical and chemical activation of a cement-water composition has a positive effect on reducing the W/S ratio of equiviscous compositions from 0.42 (no activation) to 0.38 (activation period 180 sec). The obtained experimental results indicate the presence of an induction period of heating of the cement paste both on Portland cement not subject to mechanical activation (this period is approximately 6 hours from the moment of interaction of cement with water) and on Portland cement subject to mechanical activation. In this case, the induction period was no more than 2 hours. Joint mechanical activation of an aqueous mixture of Portland cement and ground limestone ensures acceleration of the hydration processes of the binder, which is confirmed by the intensification of the exothermic heating of the filled cement-mixing compositions. The positive role of mechanical activation is also reflected in the acceleration of the thickening rate of the compositions, which was recorded by the kinetics of the decrease in the diameter of their spread over time. The positive role of mechanical activation in reducing the effective viscosity of cement-containing compositions is confirmed, which ensures a decrease in their water-solid ratio by an average of ‒ 8 ... 10 %. A positive effect of mechanochemical activation of Portland cement with the addition of ground limestone on the strength of cement stone at the age of 3 days has been revealed. Experimental studies indicate that only due to mechanical activation the strength of samples made of cement stone with the addition of ground limestone can be increased by almost 25...30 %.

Multi-angle research on the performance of self-foaming filling materials and analysis of engineering applications

Utilizing self-foaming filling material to fill the hollow area is an effective way to settle the issues of low rate and poor effect of filling and roofing in the large stope. There are fewer studies related to the expansion rate, hydration exotherm and strength properties of self-foaming fillers in mines. Based on this, this paper investigates the expansion characteristics, hydration exothermic characteristics and compressive strength characteristics of the self-foaming filler under different cement-tailings ratios (1:4, 1:6, 1:8), reveals the hydration reaction mechanism of the material and its microscopic characteristics through XRD, TG and SEM tests, and evaluates the application effect and economy of the self-foaming filler in practical engineering with the background of Mashong Iron Ore Mine. The main findings are as follows: (1) The volumetric expansion of self-foaming filling material can be divided into the initial stage Ⅰ (0–1.5 h), the rapid reaction stage Ⅱ (1.5–8 h) and the stabilization stage, and as the cement-tailings ratio grows, the expansion rate of the filling body increases, and the expansion rate of the filling material with 1:4 ratio is as high as 20.4 %. (2) The hydration process of a self-foaming filled body does not contain induction and acceleration stages; under the same conditions, the self-foaming filled body has more exothermic heat of hydration than that of a self-foaming filled body by about 50 J/g, and the bigger the cement-tailings ratio, the bigger the hydration exothermic rate and exothermic quantity. (3) The compressive strength of self-foaming filler is inferior to the strength of conventional filler, the higher the cement-tailings ratio, the greater the degree of hydration, the more hydration products are produced, and the greater the compressive strength. (4) The bigger the ratio of gray sand, the greater the proportion of macropores and the actual engineering of self-foaming filling materials to catch the top rate of up to 98 %, directly saving the total cost of 11.6 %. The above research results can offer theoretical support and scientific guidance for the utilization of spontaneous foam materials to fill the goaf and control the roof rate, temperature, and strength of the stope.

The Effect of CO on the Exothermic Characteristics of Low-Temperature Oxidation in Coal

ABSTRACT In recent years, abnormally high concentrations of CO gas have often been detected in goaf areas of coal mines in China, which have posed a serious threat to safe production in coal mines and the life and safety of underground personnel. The effect of CO on the exothermic characteristics of low-temperature oxidation in coal was studied by analyzing the exothermic characteristics, heat release, oxidation stages, and activation energy of coal at different CO concentrations using a C600 microcalorimeter. The experimental results indicated that CO promoted the coal oxidation at low temperature, but inhibited it after reaching 144°C. When the CO concentration is 30%, the exothermic characteristics of coal in low-temperature oxidation adsorption stage were significantly affected, with the heat flow value decreased by 27.0% and the initial exothermic temperature point moved forward by 3.9 K. In the later stage of the oxidation reaction, the heat release of coal was linearly negatively correlated with CO concentration. The higher the concentration, the lower the heat release. These findings contribute to understanding the combustion mechanism of coal in high-concentration CO atmosphere and provide valuable insights for designing and optimizing coal utilization technologies.

Exploring the effect of self-combustion gangue powder particle distribution on rheological behavior and hydration mechanism in cement-based systems

Solid waste-based mineral admixtures are widely employed as a partial replacement for Portland cement due to their superior performance and minimal carbon and environmental footprint. This study involves the production of self-combustion gangue powder (SCGP) with varying particle sizes achieved through crushing, screening, and grinding. The SCGP is subsequently blended with cement to form a self-combustion gangue powder-cement (SCGP-C) system with diverse particle size distribution. Rheological tests and hydration exothermic tests were conducted to investigate the rheological behavior and degree of hydration of the SCGP-C mixed system. The results show that SCGP enhances the plastic viscosity and thixotropy of the mixed slurry. However, when a finer SCGP (d50=1.36 μm) was used to replace 15 % of the cement for the same mass, the yield stress and rheological index of the slurry were reduced by 28.1 % and 15.4 % respectively compared to the control group, while the closed-packing of the SCGP-C system was obtained. When the cement was replaced by 15 % SCGP (mass substitution), the yield stresses of finer and coarser SCGP (d50=18.24 μm) and pure cement slurries were increased by 289.1 %, 67.3 %, and 29.2 %, respectively, at T=60 min compared to T=0 min. This suggests that the fineness of SCGP has a greater effect on the yield stresses of mixed slurries over time. Mixed slurries with different finenesses of SCGP all prolonged the hydration induction period and reduced the total exothermic heat of hydration. Incorporating 15 % finer SCGP extended the induction period of the mixed slurry by 27 min and increased the peak value of the main hydration curve. Appropriate incorporation of SCGP helps to improve the fluidity and early strength of mortar in the SCGP-C system and promotes the physical filling effect and the positive role of SCGP volcanic ash in the cement system.

A Precise Prediction of the Chemical and Thermal Shrinkage during Curing of an Epoxy Resin.

A precise prediction of the cure-induced shrinkage of an epoxy resin is performed using a finite element simulation procedure for the material behaviour. A series of experiments investigating the cure shrinkage of the resin system has shown a variation in the measured cure-induced strains. The observed variation results from the thermal history during the pre-cure. A proposed complex thermal expansion model and a conventional chemical shrinkage model are utilised to predict the cure shrinkage observed with finite element simulations. The thermal expansion model is fitted to measured data and considers material effects such as the glass transition temperature and the evolution of the expansion with the degree of cure. The simulations accurately capture the exothermal heat release from the resin and the cure-induced strains across various temperature profiles. The simulations follow the experimentally observed behaviour. The simulation predictions achieve good accuracy with 2-6% discrepancy compared with the experimentally measured shrinkage over a wide range of cure profiles. Demonstrating that the proposed complex thermal expansion model affects the potential to minimise the shrinkage of the studied epoxy resin. A recommendation of material parameters necessary to accurately determine cure shrinkage is listed. These parameters are required to predict cure shrinkage, allow for possible minimisation, and optimise cure profiles for the investigated resin system. Furthermore, in a study where the resin movement is restrained and therefore able to build up residual stresses, these parameters can describe the cure contribution of the residual stresses in a component.

Investigating how oxygen levels and particle size impact the thermodynamics of low temperature coal oxidation: A case study using weakly caking coal

Oxygen concentration and particle size play critical roles in the combustion of coal. Notably, the low temperature oxidation stage is considered pivotal for coal spontaneous combustion (CSC). In this study, we examined the exothermic oxidation of low-temperature weakly caking coal. We used a C80 microcalorimeter to assess the impact of different oxygen concentrations and particle sizes. For weakly caking coal during low-temperature oxidation, the heat flow (HF) curve decreases as oxygen concentration drops. The characteristic temperature increases, and the HF curve shows a noticeable lag. Under identical external conditions, decreasing the particle size of coal results in a reduced minimum floating coal thickness, lowers the oxygen concentration needed for CSC, increases the upper-limit of air leakage intensity, and makes the coal more susceptible to CSC. Reducing the particle size significantly increases the exothermic heat release during low-temperature oxidation, leading to a higher risk of CSC. These research results not only deepen the understanding of the law of coal spontaneous combustion, but also provide a scientific basis for improving the technical level of coal spontaneous combustion fire prevention and control.

Improving the pozzolanic reactivity of recycled powders from retired wind turbine blades by removing the polymer phase through thermal treatment

By 2050, the world will accumulate a substantial 43.4 million tons of waste wind turbine blades. Utilizing the powder from grinding these waste blades as a new supplementary cementitious material (SCM) presents an optimal recycling solution and resource utilization. The powder primarily consists of both organic (polymer resin) and inorganic (glass fiber) phases. It is essential to remove the polymer phase to achieve improved pozzolanic reactivity of the glass phase. This removal was achieved through thermal treatment in this study. Based on thermogravimetric (TG) analysis, polymer removal temperatures were set at 550 °C, 600 °C, 700 °C, and 800 °C. The optimal temperature was identified as 550 °C for the highest activity in the alkaline solution. The impact of polymer removal on pozzolanic reactivity was analyzed through various tests including paste flowability, exothermic heat flow, compressive and flexural strength, mercury intrusion porosimeter (MIP), TG, and scanning electron microscope (SEM). For paste sample with 30 % replacement ratio, the experimental results show that, the removal of polymer phase is beneficial in achieving a 0.46-h shorter hydration induction period, 9.4 % higher flowability, 10 % less pore volume at 90 days, and 20 % higher compressive strength. This study confirms that the pozzolanic reactivity of recycled powders from retired wind turbine blades can be improved by removing the polymer phase, making the recycled powder a potential SCM. This research is crucial for developing a new recycling route for waste wind turbine blades.

Coupled Electrochemical-Thermal Runaway Model of Lithium-Ion Cells Operating Under High Ambient Temperatures

The risk of thermal runaway (TR) in high energy density Lithium-ion batteries (LIBs), which may initiate at around 90 °C, is a critical safety concern, particularly in regions where summer temperatures can reach nearly 50 °C. While multiple exothermic reactions that cause TR and modeled using Arrhenius equations lead to good predictions in controlled oven tests, their use in practical applications is questionable as these do not consider internal electrochemical processes that cause temperature rise and trigger exothermic reactions. Further, limited literature focuses on coupling electrochemical thermal models with exothermic reactions. This study demonstrates a method to couple the electrochemical and thermal runaway models for a commercial cylindrical Lithium-ion cell. The proposed model averages pseudo-2D electrochemical heat and couples it to a two-dimensional, axisymmetric heat transfer model of 18650-type Lithium-ion cell. The jellyroll structure is approximated as a homogeneous and anisotropic domain for electrochemical and exothermic heating. Simulations are performed through several, uninterrupted charge-discharge cycles at different ambient temperatures and C-rates. We show that while cycling rate is critical in instigating and accelerating TR, parameters like ambient temperature, particle radii and initial electrolyte concentration also play a role in determining the core temperature and its rate of growth in the cell.

Eco-friendly low-carbon manganese ferroalloy production for cleaner steel technologies

Global steel production, a major contributor to anthropogenic carbon dioxide, heavily relies on manganese, a key ingredient that significantly impacts the carbon footprint during the production of high-carbon ferromanganese. A single-step generation of low-carbon ferromanganese (LC-FeMn) from manganese ore in an electric arc furnace (EAF) was investigated. The theoretical and experimental investigations helped to balance the required and supplied energy. The process sustainability was predicted based on the enthalpy of the reaction. Pre-reduction of manganese ore decreased energy consumption in the smelting process and saved raw materials costs. The simulation studies revealed a significant effect of lime and silica on the slag-metal equilibrium. It further confirmed the best-reducing condition with the basicity 1.5–1.77 by smelting tests in EAF. Experimental results showed an optimal charge mixture comprising appropriate ratios of ore:SiMn:lime ratio, producing a standard-grade product. Simultaneous melting and smelting sensibly used the exothermic heat, consuming 410–880 kWh/ton, much lower than the international benchmark, i.e. approximately 2000 kWh/ton. The characterization of resulting slags corroborated the advantages of the manganese ore pre-reduction on the energy and reductant consumption, alloy grade, and slag characteristics. The present study's findings can potentially contribute to the ongoing low-carbon initiatives of steel.

Effect of perturbations on dantrolene - A DFT treatise

Dantrolene and an isomer of dantrolene which is obtained by a pair of centric perturbations (carbon to nitrogen replacement in N-N=CH moiety) are considered within the constraints of density functional theory at the level of B3LYP/6-31++G(d,p). Dantrolene is a skeletal muscle relaxant which interferes with the release of calcium ion from the sarcoplasmic reticulum. Both of the isomeric structures of present interest have exothermic heat of formation values and favorable Gibbs free energy of formation values. They are electronically stable as well. The perturbation results in a more exothermic and more favorable isomer than dantrolene. It is also electronically more stable than the parent structure. Various quantum chemical data have been collected and discussed including IR and UV-VIS spectra.

Three-dimensional CFD analysis of PHWR exposed core under postulated severe accident condition

A three-dimensional steady-state thermal–hydraulic analyses of a large sized Pressurized Heavy Water Reactors (PHWRs) with varying levels of exposure is carried out for degraded core heat transfer assessment and presented in this paper. Low-frequency postulated severe accident without mitigating actions leads to exposure of fuel channels in PHWRs. Such exposure of fuel channels leads to their heat-up, governed by interdependent heat transfer mechanisms such as radiation, convection and conduction heat transfer and thermo-chemical interactions among the core constituents. In order to understand such complex behavior and plan the severe accident management guidelines, numerical analyses of the exposed core are of necessary. This paper illustrates the influence of the temperature and velocity profiles vis-à-vis different regions of the exposed core on the fuel channel heat-up. The interesting interdependency of convection and radiation heat transfer on fuel channel heat-up is reported. The dominance of convection heat transfer is observed for initial exposures of the fuel channels. However, the advanced stages of fuel channel exposures are observed to be dominated by radiation heat transfer. Intriguingly, it is observed that the convective cooling of exposed fuel channels by steam flow is counter-acted by exothermic heat generation from Zircaloy-made calandria tube surface and steam interaction. This leads to supplemental power addition for fuel channel heat-up. Moreover, it is interesting to note that the heat-up of fuel channels is restricted to central regions of the exposed core due to degraded steam cooling and higher-powered fuel channels. It is worth noting that fuel channel disassembly is observed in the advanced levels of fuel channel exposures. Moreover, fuel channel length equivalent to nearly 7–8 fuel bundle lengths undergo disassembly depending upon the fuel channel elevation and location in the core. The calandria vault water is observed to undergo film boiling at the onset of fuel channel disassembly.

An in-situ study of the interaction mechanism between xanthate and unactivated/Cu-activated sphalerite surfaces at solid–liquid interfaces

The mechanism of surface hydration and xanthate adsorption in the flotation of unactivated/Cu-activated sphalerite is still controversial. Therefore, a study combining in-situ measurement and quantum simulation is employed to investigate the interaction mechanism of ethyl xanthate (EX) and butyl xanthate (BX) on the fully hydrated, unactivated/Cu-activated sphalerite surfaces at solid–liquid interfaces. Density functional based on tight-binding (DFTB+) and molecular dynamics (MD) results suggest that the Cu-activated surface is hydrophobic with the first layer of water being distributed more disorderly on it. This is due to the difficulty of the lone pair electrons of water to interact with Cu. On the unactivated surface, water adsorption is more favorable than xanthates, hence, water molecules are physically adsorbed on it. Whereas the interaction of EX/BX with the hydrated, activated surface is chemisorption. The higher reactivity of Cu+ d orbitals to form π-backbonds with xanthate and the orbital symmetry matching of the Cu dyz orbitals and xanthate pz orbitals contribute to these results. Microcalorimetric results also demonstrate that copper activation enhances the exothermic heat and reaction rate, facilitating the interaction of EX/BX with sphalerite. These are consistent with the flotation and quartz crystal microbalance with dissipation (QCM-D) results.

The influence and mechanism analysis of aluminum sulfate as an environmentally friendly early strength agent on the properties of cement-based materials

Environmentally friendly chemical admixtures are becoming important in the cement industry. The research objective of this paper is to use aluminum sulfate as an early-strengthening agent to achieve the goals of a large increase in early strength and a reduction in CO2 emissions. The experimental design was as follows: The macroscopic properties and microscopic characteristics of aluminum sulfate were experimentally investigated on five different replacement ratios of 0%, 1%, 2%, 3%, and 4% paste specimens of cement at different ages. The results show that (1) AS4 demonstrated a notable enhancement in early strength, while AS2 and AS3 contributed to increased late-stage strength. Over time, the Ultrasonic Pulse Velocity (UPV) of all samples exhibited a steady rise. Additionally, aluminum sulfate was found to reduce the electrical resistivity of the samples. (2) aluminum sulfate increased the rate of exothermic heat release of samples at induction and acceleration phases, advanced the accumulated heat was high in the samples with high aluminum sulfate content, and the accumulated heat was strongly correlated with the compressive strength. FT-IR and XRD results show that aluminum sulfate promoted the formation of AFt while depleting the CH content, and the TGA results show the content of bound water in the samples increased from Day 1 to Day 28, which had a positive effect on the compressive strength. UHR-SEM results show that increasing aluminum sulfate substitution results in the formation of a denser microstructure. (3) for all the various mixtures, AS2 has the lowest CO2 emissions per unit strength.

Thermal decomposition characteristics of BHT and its peroxide (BHTOOH).

2,6-Di-tert-butyl-4-methylphenol (BHT) is an excellent antioxidant that is easily oxidized to 2,6-di-tert-butyl-4-hydroperoxyl-4-methyl-2,5-cyclohexadienone (BHTOOH). For the safety of BHT production and usage, it is meaningful to study the thermal stability and decomposition properties of BHT and BHTOOH. In this paper, the thermal decomposition properties of BHT and BHTOOH were compared by the mini closed pressure vessel test (MCPVT) and differential scanning calorimetry (DSC). Their kinetics of thermal decomposition were studied using thermogravimetric analysis (TGA). The thermal decomposition products of BHT and BHTOOH were analyzed by gas chromatography-mass spectrometry (GC-MS). The results show that there was no significant change in temperature pressure when BHT was warmed up under a nitrogen atmosphere, indicating that BHT was stable within 400K. The thermal decomposition reaction of BHTOOH was rapid with an initial reaction temperature of 375.2K. The initial exothermic temperature (Ti) and heat release (QDSC) of DSC were 384.9K and 865.0Jg-1, respectively. The apparent activation energies (Ea) for the thermal decomposition reactions of BHT and BHTOOH calculated by the Kissinger method were 151.8kJmol-1 and 66.07kJmol-1, respectively. The main decomposition products of BHT were isobutene and 2-tert-butyl-4-methylphenol. The thermal decomposition products of BHTOOH included BHT, 2,6-di-tert-butyl-4-ethylphenol, 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 4,4'-(1,2-ethanediyl) bis [2,6-bis (1,1-dimethylethyl) phenol, etc. Based on the thermal decomposition behavior and products, the reaction pathway has been described. These results indicate that BHT is a potential thermal hazard during production, storage and application. For the safety of the chemical industry, the oxidation of BHT should be avoided.

Combustion Behaviors, Kinetics, and Thermodynamics of Naturally Decomposed and Torrefied Northern Red Oak (Quercus rubra) Forest Logging Residue

Torrefaction and combustion have been applied to naturally decomposed red oak logging residues. The results indicated that four-year natural decomposition would lower the energy density of red oak from 20.14 to 18.85 MJ/kg. Torrefaction reduced the O/C and H/C ratios but improved the energy yield values. Two combustion stages were observed for all samples, and no hemicellulose derivative thermogravimetric peak appeared for torrefied samples. The differential scanning calorimetry exothermic heat flow increased after torrefaction. In addition, the Kissinger–Akahira–Sunose average activation energy of untorrefied samples decreased in the first stage (from 157.77 to 149.52 KJ/mol), while it increased in the second stage (from 131.32 to 181.83 KJ/mol). The ∆H, ∆G, and ∆S values of all samples decreased in the first stage, while they increased when the conversion rate was greater than 0.5 for torrefied samples. These findings can aid in a better understanding of the fuel performance of torrefied and untorrefied naturally decomposed red oak logging residues.

Early age reaction, rheological properties, and environment impact of NaOH-activated fly ash mixtures at ambient environment

To improve the performance of NaOH alkali-activated fly ash (AAFA) cured at ambient temperature, silica fume (SF) and metakaolin (MK) were utilized as partial replacements for fly ash (FA). Subsequently, the rheology, compressive strength, and environmental impact of these mixtures were examined. Besides, the geopolymerisation mechanisms were studied by Isothermal calorimetry, LF-NMR, XRD, TGA, and FTIR tests. The results show that the rheological properties of all mixtures conform to the Bingham model. Both SF and MK can improve the rheological properties of FA-based geopolymer pastes by increasing exothermic heat and shortening T2 relaxation time. MK could enhance geopolymerisation by decreasing the Si/Al ratio, thus promoting the precipitation of aluminosilicate gel. However, it is difficult for the SiO2 in SF to geopolymerize under ambient temperature. As a result, MK improves the compressive strength of FA-based geopolymer, while SF hinders the development of strength. The environmental impact assessment shows that the carbon emissions of the developed FA/SF/MK geopolymer pastes are much lower than those of OPC. Production of NaOH FA geopolymers at ambient temperature without the addition of high-carbon footprint Na2SiO3 contributes to the industrialization of green low-carbon FA geopolymers.