Study on the thermal kinetics and microscopic characteristics of oxidized coal

Revealing the characteristics of spontaneous combustion and re-combustion of oxidized coal is of great significance for the coal fire prevention and control. Synchronous Thermal Analyzer (STA) and Fourier Transform Infrared Spectrometer (FTIR) were used to measure the thermal kinetics and microscopic characteristics of coal samples with different oxidation degrees (unoxidized, 100 ℃, 200 ℃ and 300 ℃ oxidized coal). It is found that the characteristic temperatures decrease first and then increase with the increasing degree of oxidation. The ignition temperature of 100 ℃-O coal (oxidized at 100 ℃ for 6 h) is relatively the lowest at 334.1 ℃. Pyrolysis and gas-phase combustion reactions dominate the weight loss process, while solid-phase combustion reactions are relatively minor. The gas-phase combustion ratio of 100 ℃-O coal is the highest at 68.56%. With the deepening of coal oxidation degree, the relative content of aliphatic hydrocarbons and hydroxyl groups gradually decreases, while that of oxygen-containing functional groups (C-O, C = O, COOH, etc.) increases first and then decreases, reaching the highest value of 42.2% at 100 ℃. Moreover, the 100 ℃-O coal has the minimum temperature at the point of maximum exothermic power of 378.5 ℃, the highest exothermic power of -53.09 mW/mg and the maximum enthalpy of -18,579 J/g. All results show that 100 ℃-O coal has the highest risk of spontaneous combustion than the other three coal samples. This suggests that there is a maximum point of spontaneous combustion risk in the range of pre-oxidization temperatures of oxidized coal.

Thermal, dielectric, mechanical and structural behavior of 2-amino 4-methylpyridinium 4-nitrophenolate 4-nitrophenol bulk single crystal

Applications in both science and industry have received increased attention as a result of bulk single crystals with particular orientations. However, due to the instability of organic crystals at high temperatures and stress, there is an interest in growing good-quality bulk single crystals with stable thermal and mechanical properties. Here, the 2-amino 4-methylpyridinium 4-nitrophenolate 4-nitrophenol (2A4MPPP) crystal was prepared employing a single-wall ampoule and the vertical Bridgman technique. Structure and functional groups were determined by XRD, NMR, and FTIR studies. More importantly, detailed thermal and kinetic properties such as activation energy, frequency factor, rate constant, and Avrami exponent are discussed. The mechanical stability and dielectric studies are also demonstrated for the title compound. According to the single crystal XRD investigation, 2A4MPPP is a member of the orthorhombic crystal system with the Pna21 space group. Through the TGA and DTA analyses, it was confirmed that the compound starts to melt at 98 °C and complete melting occurs at 103.3 °C. The dielectric experiments reveal the crystal's poor dielectric constant and high-frequency dielectric loss. Vickers microhardness investigations show that grown 2A4MPPP belongs to the soft materials group. As a result of these findings, the 2A4MPPP crystal should be well suited for usage in thermomechanical, microelectronic, optical communications, and nonlinear optical applications.

Thermal stability of extracted lignin from novel millet husk crop residue

Recent alarming tones regarding the environment and energy crises have resulted in an emergent need for the utilization of bio-based materials. The current study aims to experimentally investigate the thermal kinetics and pyrolysis behavior of lignin extracted from novel barnyard millet husk (L-BMH) and finger millet husk (L-FMH) crop residue. The characterization techniques FTIR, SEM, XRD, and EDX were employed. TGA was performed to assess the thermal, pyrolysis, and kinetic behavior using Friedman kinetic model. The average lignin yield was obtained as 16.25 % (L-FMH) and 21.31 % (L-BMH). The average activation energy (E_a) was recorded as 179.91-227.67 kJ mol^-1 for L-FMH while 158.50-274.46 kJ mol^-1 for L-BMH in the conversion range of 0.2-0.8. The higher heating value (HHV) was found to be 19.80 ± 0.09 MJ kg^-1 (L-FMH) and 19.65 ± 0.03 MJ kg^-1 (L-BMH). The results create a possibility for the valorization of extracted lignin in polymer composites as potential bio-based flame retardant in polymer composites.

Thermal decomposition kinetics of Prosopis juliflora charcoal briquette using thermogravimetric analysis

In the current study, the energy potential of Prosopis juliflora charcoal briquette sample was assessed using thermogravimetric analysis at heating rates 10 °C/min, 15 °C/min, and 20 °C/min under nitrogen atmosphere. The thermogravimetric study showed that the thermal devolatilization of the briquette sample occurred in four principal stages. The major degradation of the sample occurred in the fourth stage indicating that the significant mass loss occurred due to the fixed carbon that was abundant in the briquette sample. The activation energy was determined by employing five different model-free methods. The average activation energy attained for the briquette sample by Kissinger-Akahira-Sunose method, Flynn-Wall-Ozawa method, Tang method, Starink method, and Friedman method was 83.55 kJ/mol, 91.60 kJ/mol, 79.91 kJ/mol, 80.06 kJ/mol, and 96.74 kJ/mol, respectively. The frequency factor obtained in the study ranged between 1.42 × 10³ and 6.23 × 10⁷ min^-1. The contracting sphere model was found to be closely related to the reaction model obtained for charcoal briquettes. The lower activation energy and frequency factor indicated rapid thermal degradation of the charcoal briquettes. The estimated thermodynamic parameters indicated that the thermal degradation process was endothermic in nature.

Experimentally Implementing the Linear Nonisothermal Equation for Simultaneously Obtaining D- and z-Values of Salmonella Senftenberg in Skim Milk with a Differential Scanning Calorimeter

ABSTRACT

For bacteria with log-linear thermal inactivation kinetics in food, D-values are obtained in multiple isothermal inactivation experiments at different temperatures, and the z-value is obtained from these D-values. In a previous work, the cumulative lethality integral was mathematically solved in closed form when temperature in the food increased linearly with time. The solution revealed that each nonisothermal experiment could yield both D- and z-values, eliminating the need for getting multiple D-values to get a z-value. The present study reports on the first experimental implementation of this method of obtaining D- and z-values for Salmonella Senftenberg suspended in skim milk for which a differential scanning calorimeter (DSC) provided the required constant heating rate. The resulting D- and z-values were compared with those obtained from an isothermal method with capillary tubes. No significant differences in z-values were found between the two methods. The D-values also agreed but only after correcting the nonisothermal value for temperature lag in the DSC caused by the large sample size required. A 5 K/min heating rate was used in this comparison. Other rates were also investigated: 1, 3, 7.5, and 10 K/min. Although D- and z-values should be independent of DSC heating rate, heating rates of 1 and 10 K/min yielded values that were significantly different from the others; therefore, these rates cannot be recommended for use in this nonisothermal method.

HIGHLIGHTS

Thermo-chemical potential of solid waste seed biomass obtained from plant Phoenix dactylifera and Aegle marmelos L. Fruit core cell

The present study explores thermo-chemical potential of two biomasses namely; Phoenix dactylifera seed (PDS) and Aegle marmelos L core (AMP). These biomasses contain high amount of cellulose and exhibit heating value of 3-18 MJ/kg. The thermal kinetic of both the biomasses have been extensively studied using thermogravimetric analysis (TGA) at four different heating rates 5, 10, 15, and 20 °C/min. Kinetic analysis was carried out using three model-free techniques including Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Starink. The average activation energy has been found to be 173.75, 172.94 and 170.71 kJ/mol, for PDS whereas 170.26, 167.24 and 164.80 kJ/mol, for AMP analyzed through KAS, FWO and Starink methods, respectively. Further, among all these models, the Starink model exhibits better result for the biofuels potential point of view.

Experimental and theoretical study on thermal kinetics and reactive mechanism of nitrocellulose pyrolysis by traditional multi kinetics and modeling reconstruction

Nitrocellulose (NC) has been applied in many fields of daily life and military industry, but its instability brings large danger during storage and usage, which greatly limits its application. In this study, decomposition behavior and reaction model of NC were explored. To obtain its kinetic triplets during decomposition, NC samples were heated in nitrogen atmosphere with different heating rates of 5, 10, 15, 20 °C min^-1, respectively. A 3-th order reaction model was obtained by model fitting methods. Meanwhile, the relationship between activation energy and conversion was obtained by multi isoconversional methods, including KAS, FR, FWO, and Advanced Vyazovkin methods. Then the reaction model was reconstructed by introducing adjustment functions with result of an expression of f(α) = 19.38193α^1.41177(1-α)^4.60503.

Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods

There is a great interest in natural yellow colorants due to warnings issued about certain yellow food colorings of synthetic origin. However, no comparative studies have been reported of their thermal stability. For this reason, the thermal stabilities of six natural yellow colorants used in foods--lutein, riboflavin, curcumin, ß-carotene, gardenia yellow and Opuntia betaxanthins--were studied in simple solutions over a temperature range 30-90 °C. Spectral properties and visual color were investigated during 6 h of heat treatment. Visual color was monitored from the CIEL*a*b* parameters. The remaining absorbance at maximum wavelength and the total color difference were used to quantify color degradation. The rate of color degradation increased as the temperature rose. The results showed that the thermal degradation of the colorants followed a first-order reaction kinetics. The reaction rate constants and half-life periods were determined as being central to understanding the color degradation kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. Activation energies ranged from 3.2 kJmol(-1) (lutein) to 43.7 kJmol(-1) (Opuntia betaxanthins). ß-carotene and lutein exhibited high thermal stability, while betaxanthins and riboflavin degraded rapidly as temperature increased. Gardenia yellow and curcumin were in an intermediate position.

Effect of leaching with 5-6 N H2SO4 on thermal kinetics of rice husk during pure silica recovery

Rice husk is a potential source for renewable energy and silica. To extract the maximum amount of silica, usually the rice husk is treated with strong acids that burn the organic part leaving behind a black residue. In this research, sulfuric acid is used as an oxidizing agent. Efforts are focused to find out more about the behavior of acid-treated rice husk by using thermal exposure, and results are compared with results for raw rice husk which is thermally exposed but not acid treated. Reaction ratio of rice husk combustion and energy of activation were calculated using the thermogravimetric data. Acid treatment was found influential in initiating degradation earlier compared to raw husk and an overall increase in value of activation energy was observed when heating rate was increased.