Thermal Kinetic Study Research Articles

Precise Immobilization Strategy Combined with Rational Design to Improve β-Agarase Stability.

Recently, the orientational immobilization of enzymes has attracted extensive attention. In this study, we report the development of a strategy combined with rational design to achieve precise site-specific covalent immobilization of β-agarase. We first rationally screened six surface sites that can be mutated to cysteine by combining molecular dynamics simulation and energy calculation. Site-specific immobilization was successfully achieved by Michael addition reaction of mutant enzymes and maleimide-modified magnetic nanoparticles (MAL-MNPs). The enzyme activity retention rate of R66C-MAL-MNPs and K588C-MAL-MNPs was greater than 96%. The thermal deactivation kinetics study revealed that the site-specific immobilization strategy significantly improved the thermal stability of Aga50D, resulting in a substantial increase in its antidenaturation activity at elevated temperatures, and the highest t1/2 of the immobilized mutant enzymes was increased by an impressive 21.25-fold at 40 °C. The immobilized mutant enzymes also showed significantly enhanced tolerance to metal ions and organic reagents. For instance, all of the immobilized enzymes maintained over 90% of their enzymatic activity in the 50% (v/v) acetone/water solution. The present work may pave the way for the design of precisely immobilized enzymes, which can help promote green manufacturing.

Physico-chemical and Biological Studies of Some Metal Complexes with Fluorinated Chloramphenicol Derivative

Abstract Due to the prevalence of FF, its complexes with (CoII, NiII, and CuII) were prepared, characterized, and the effect of these metal ions on the biological effectiveness of FF was studied. Elemental analysis; IR and 1H-NMR were used to determine the structures and mode of bonding, TGA, and DSC techniques were used to make thermal analysis for the prepared complexes. TGA was used to study the mechanisms of the thermal decomposition for florfenicol complexes. The prepared complexes are thermally stable and started to decompose after 200οC. Broido’s method was used to determine the activation energy for the prepared compounds, while thermal transitions and kinetic studies were carried out by differential scanning calorimetry technique (DSC). The antimicrobial activity of the complexes of florfenicol with different concentrations (0.005, 0.01, 0.02 μg/mL) was examined by the agar prolixity technique against common human pathogenic Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). Comparatively, Nickel and Copper complexes showed a higher zone of inhibition against the tested pathogens. The antibiotic complexes were more active than the ligand itself for some breeds.

Thermal stability, preformulation, and kinetic degradation studies for gestrinone

AbstractGestrinone is an active pharmaceutical ingredient used in the treatment of endometriosis as capsules, with ongoing evaluation for intravaginal administration, while also having been studied for its potential antitumoral effects. The purpose of this study was to determine the compatibility of gestrinone with four excipients used in the development of solid pharmaceutical formulations (α-lactose monohydrate, magnesium stearate, starch, and talc) and to obtain a fully characterized thermoanalytical profile of gestrinone with the help of kinetic analysis. Preformulation studies were carried out on 1:1 mass/mass binary mixtures between gestrinone and each excipient by instrumental screening under ambient conditions using ATR-FTIR spectroscopy investigations, and later by studying the effect of thermal treatment over the samples (TG/DTG/DSC). The obtained results suggest that under ambient conditions, no chemical interactions take place between the active pharmaceutical ingredient and selected excipients, whereas under thermal stress incompatibilities are observed in all systems. The mechanism of decomposition was preliminary evaluated by the ASTM E698 and later completed by the isoconversional methods of Friedman, Kissinger–Akahira–Sunose, and Flynn–Wall–Ozawa, which suggest similar mean activation energies. The mechanism of decomposition was elucidated in the last part of the study, by employing the modified NPK method. This method suggests that gestrinone is thermally degraded by the contribution of two individual processes, both consisting of superimposed physical transformations and chemical degradations.

Characterization and optimization of waste Cucurbita maxima moschata lashes for biomass composite applications

In this paper, 5 % sodium hydroxide solution, mixed 20 % acetic acid and 5 % sodium chlorite solution, and 5 % silane coupling agent solution were successively used to soak the waste pumpkin (Cucurbita maxima moschata) lashes. Subsequently, FTIR, XRD, thermogravimetric analysis and other experimental methods were used to comprehensively characterize the properties of the discarded pumpkin lashes. On this basis, this work prepared cement mortar specimens with unadulterated pumpkin lashes, adulterated raw pumpkin lashes, and adulterated modified pumpkin lashes, and their residual mechanical properties were investigated after exposure to elevated temperatures. The experimental results indicate that the chemical modification utilized in this paper can increase the cellulose content of pumpkin lashes as well as reduce the proportion of amorphous components, and thus, improve the tensile strength, crystallinity index, grain size, thermal stability, and surface roughness of the samples. Meanwhile, the chemical treatment process can effectively reduce the water absorption and density of pumpkin lashes. The calculation outcomes of our thermal kinetics study showed that the apparent activation energies corresponding to the main pyrolysis stage of the treated pumpkin lashes were significantly enhanced. The one-dimensional diffusion model and the second-order model could better characterize the pyrolytic mechanism of the raw pumpkin lashes, while the mechanism was closer to the third-order model because of the chemical modification. Finally, the addition of chemically modified pumpkin lashes reduced the mass loss rate of cement mortar specimens at elevated temperatures while clearly increasing the residual strength of the specimens at 300 and 400 °C compared to those with referential pumpkin lashes.

Chemical Kinetics and Thermal Properties of Ablator Pyrolysis Products During Atmospheric Entry

Legacy and modern-day ablation codes typically assume equilibrium pyrolysis gas chemistry. Yet, experimental data suggest that speciation from resin decomposition is far from equilibrium. A thermal and chemical kinetic study was performed on pyrolysis gas advection through a porous char, using the Theoretical Ablative Composite for Open Testing (TACOT) as a demonstrator material. The finite-element tool SIERRA/Aria simulated the ablation of TACOT under various conditions. Temperature and phenolic decomposition rates generated from Aria were applied as inputs to a simulated network of perfectly stirred reactors (PSRs) in the chemical solver Cantera. A high-fidelity combustion mechanism computed the gas composition and thermal properties of the advecting pyrolyzate. The results indicate that pyrolysis gases do not rapidly achieve chemical equilibrium while traveling through the simulated material. Instead, a highly chemically reactive zone exists in the ablator between 1400 and 2500 K, wherein the modeled pyrolysis gases transition from a chemically frozen state to chemical equilibrium. These finite-rate results demonstrate a significant departure in computed pyrolysis gas properties from those derived from equilibrium solvers. Under the same conditions, finite-rate-derived gas is estimated to provide up to 50% less heat absorption than equilibrium-derived gas. This discrepancy suggests that nonequilibrium pyrolysis gas chemistry could substantially impact ablator material response models.

High-temperature oxidation behaviours of rare earth-based pyrochlore structured A2B2O7/yttria-stabilized zirconia thermal barrier coatings

Addressing the challenge of cost-effectively synthesizing stable thermal barrier coating materials has been a significant hurdle. This study describes the bulk synthesis of stannate-based pyrochlore compounds, specifically erbium tin oxide (Er2Sn2O7) and yttrium tin oxide (Y2Sn2O7). These synthesized pyrochlore oxides and commercially available yttria-stabilized zirconia (YSZ) were coated onto nickel super alloy. The coated specimens were subjected to thermal oxidation kinetics studies at 900 ± 5°C for 200 h, and alterations in physico-chemical characteristics, modifications in surface morphology, and variations in the composition of thermal barrier coating (TBCs) before and after exposure to oxidation conditions were evaluated. Oxidation kinetics results demonstrate that Er2Sn2O7 pyrochlore oxide has better performance than other Y2Sn2O7 and commercial YSZ TBC materials in high-temperature thermal barrier systems.

Co-pyrolysis of real-world plastics polystyrene, polypropylene and low-density polyethylene, its thermal behaviour and kinetic studies

Co-pyrolysis of real-world plastics polystyrene, polypropylene and low-density polyethylene, its thermal behaviour and kinetic studies

Exploring the interaction between 1,4-butanediol and acid phosphatase using spectroscopic techniques and molecular modeling studies

The functional characteristics of enzymes greatly rely on their stability, which is a vital factor to be considered when utilizing these biomolecules in industrial settings. This study investigated the effects of 1,4-butanediol (BD) on the structure and activity of acid phosphatase (AP). To this end, an array of analytical techniques, such as circular dichroism (CD), thermal stability analysis, kinetic studies, fluorescence spectroscopy, molecular docking, and molecular dynamics (MD) simulations, were employed to elucidate the impact of BD on AP. The data gathered indicated that BD has a positive effect on enhancing the stability of AP. BD demonstrated its capability to bind to AP, leading to the quenching of AP's inherent fluorescence through the static quenching mechanism. The binding process was spontaneous, with van der Waals forces and hydrogen bonding serving as the primary interactions between BD and AP. The formation of the complex was also validated via UV–Vis. According to CD studies, the presence of BD induced alternations in the structure of AP. Further, docking studies showed the favored binding site of BD within the structure of AP. Besides, the kinetic parameters showed that BD could act as an activator for AP.

Pyrolysis/combustion potential and heavy metal risk of oily sludge and derived products in industrial scale

Pyrolysis of oily sludge (OS) has been widely applied for harmless disposal in industrial scale with the benefits of high removal and recovery efficiency of total petroleum hydrocarbons (TPHs). However, seldom research focuses on the evaluation of solid products from industrial apparatus. This paper devoted to evaluate the TPHs removal effect and optimizing directions of this technique by assessing the pyrolysis/combustion potential and environmental risk of OS and derived products, including fly ash (FA) and pyrolysis residue (PR). Unexpectedly, FA and PR still carried trace TPHs, ca. 0.27 and 0.24 wt%, which should arise attention. In comparison, the maximum weight losses of combustion for these solid samples were all higher than that of pyrolysis at the same final temperature, ca. 600 °C. Oxygen-rich atmosphere promoted decomposition of deposited coke and degradation of TPHs, especially heavy fractions. Therefore, these products had a certain potential for combustion utilization. Although the total weight losses of FA and PR were similar with that of OS, the comprehensive combustion characteristic index and combustion stability index of OS were much higher than those of FA and PR, indicating TPHs were more inclined to be burned that coke and dissociated metal compounds. Higher heating rate caused an increasing trend of these indexes. The thermal decomposition kinetics study based on the most probable mechanism function showed that FA and PR followed the mechanism of random nucleation and subsequent nucleation growth. The wastewater produced during gas washing was measured that contained large amounts of organics and harmful elements, which should be properly treated before emitted. Heavy metals are the dominant sources of environmental risks of solid products. Pb and Cu in FA and PR showed higher leaching concentrations and posed severer environmental risk than those in OS, which originated from accumulation effect. However, Cr, Ni, and Zn became more stable and safer after thermal pyrolysis/desorption treatment. These information on solid products and wastewater from industrial OS pyrolysis reminds future work to concern on the final disposal of the output of the whole technique.

Thermal decomposition behavior and kinetic study of nitrocellulose in presence of ternary nanothermites with different oxidizers

Nanothermites have recently attracted a great deal of interest in both military and civilian domains owing to their capability of igniting or exploding and releasing a significant quantity of heat via a redox reaction. In this study, three ternary nanothermites, which contain MgAl alloy as fuel and different metal oxides (MXOY = CuO, NiO, TiO2) as oxidizers, were prepared through the arrested reactive milling technique. These metastable intermolecular composites were introduced to nitrocellulose (NC), using a fast solution drying technique, to assess their catalytic behavior. The as-obtained energetic composites, namely, NC/MgAl-MXOY, were scrutinized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The ignition delay time of NC/MgAl-MXOY composite films was also determined, and the results revealed the positive effect of the introduction of nanothermite through the decrease of its value compared to pure NC. Using the isoconversional kinetic analysis, the Arrhenius parameters associated with the thermal decomposition of the as-obtained NC/MgAl-MXOY energetic composites films were also evaluated. The findings indicated that the choice of the oxidizer within the nanothermite composition significantly influences the decomposition behavior of the NC/MgAl-MXOY energetic composites. Based on the obtained results, the MgAl-CuO nanothermite provides better performance than MgAl-NiO and MgAl-TiO2 nanoparticles.

Thermal stability, thermodynamics and kinetic study of (R)-(–)-phenylephrine hydrochloride in nitrogen and air environments

Thermal stability, thermodynamics and kinetic study of (R)-(–)-phenylephrine hydrochloride in nitrogen and air environments

Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy Sensitivity to the Thermal Decay of Bone Collagen.

The analysis of collagen stability is of interest in forensics, archaeology, and molecular paleontology. Collagen decay rates are often measured by thermal kinetic studies that employ liquid chromatography mass spectrometry (LC-MS) to assay collagen quantities. However, these kinetic studies generally focus on measuring the decreasing levels of collagen instead of an exact molecular concentration of each sample. Thus, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy can offer a simpler and less expensive alternative to LC-MS. The application of a new protocol to determine decreasing amounts of bone collagen in artificially decayed porcine and bovine bone was assessed. The protocol uses a forensic application of ATR FT-IR spectroscopy on size-restricted bone powder from three uniformly high temperature conditions. Also, for the first time, collagen-specific second-harmonic generation (SHG) imaging was also applied to artificially aged bone to add an independent, qualitative perspective to parallel FT-IR assessments. SHG images and ATR FT-IR spectra together reveal the same orderly bone collagen decay as found in previous thermal kinetic studies. Resulting Arrhenius plots with r2 values > 0.95 suggest that the ATR FT-IR-based protocol has potential as a precise and simple tool for measuring bone collagen decay rates. The results are significant for applications of thermal kinetic studies, and our protocol can serve as an inexpensive, precise, and pragmatic means of evaluating bone collagen stability within an array of conditions.

Design and performance verification of a fast-reaction thermogravimetric analyzer

Ca(OH)2/CaO fluidized thermochemical heat storage can provide considerable heat storage power, and is a promising large-scale energy storage technology. Owing to the limitations of existing gas–solid reaction kinetics research equipment, there is a lack of Ca(OH)2/CaO reaction kinetics research under fluidization conditions, with a lack of reliable reference data for the design and operation of fluidized bed reactors. In response to the above-mentioned problem, and through our research, we developed a fast-reaction thermogravimetric analyzer to provide samples with excellent heat and mass transfer conditions close to fluidization. The fast-reaction thermogravimetric analyzer enables the reaction of Ca(OH)2 to mainly take place under isothermal conditions by rapidly moving the high-temperature reactor, as well as inputting purge gas at a high flow rate to provide excellent mass transfer conditions for the sample, while obtaining real-time and reliable mass data for thermal analysis kinetics studies. Through an in-depth performance verification, the apparent activation energy of char combustion in a TGA (144.82 kJ/mol), fast-reaction thermogravimetric analyzer (88.32 kJ/mol), and fluidized bed reactor (47.23 kJ/mol) were obtained by the model-free method (iso-conversional). The comparison of data proved that the fast-reaction thermogravimetric analyzer could obtain kinetic parameters similar to a fluidized bed reactor, which was also verified using other materials. Therefore, the fast-reaction thermogravimetric analyzer developed in this study can provide a new solution for studying the reaction kinetics of fluidized thermochemical heat storage for Ca(OH)2/CaO, in addition to acting as a reliable reference for the design and operation of fluidized bed reactors.

Thermal kinetics study on the conversion of β-MoO3 to α-MoO3; A molybdenite concentrate derivative as a catalyst

Herein, thermal decomposition kinetics of molybdic acid (MA) obtained from the leaching of molybdenite concentrate are extensively studied as a precursor for the preparation of molybdenum trioxide (MoO3). The thermal kinetics equation of the reaction suggests that the precursor (MA, H2MoO4.H2O) is converted to β-MoO3 and then to α-MoO3 due to the heating process, giving rise to a transformation temperature of 260-320°C, the average activation energy of about 26.53 ± 0.02 kJ/mol, and a pre-exponential factor of 107 1/min for the transformation of β-MoO3 to α-MoO3. Moreover, differential scanning calorimetry reveals that the volume diffusion mechanism controls the crystallization reaction, leading to the decomposition of MA. Our results indicate that Johnson-Mehl-Avrami (JMA) kinetics with nucleation and three-dimensional growth mechanism can model the experimental data with acceptable accuracy. The catalytic attributes of the stable β-MoO3/α-MoO3 compound provided an efficiency of over 89 % for the oxidation process of methanol to formaldehyde.

Thermal, flammability and iso-conversional multiple heating rate kinetic studies of impregnated poplar wood veneers

Thermal, flammability and iso-conversional multiple heating rate kinetic studies of impregnated poplar wood veneers

Thermal behavior and kinetic study on the co-pyrolysis of biomass with polymer waste

Thermal behavior and kinetic study on the co-pyrolysis of biomass with polymer waste

Radio frequency inactivation of E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 in black pepper (piper nigrum) kernels: Thermal inactivation kinetic study and quality evaluation

In recent years, E. coli O157: H7 and Salmonella Typhimurium outbreaks in black peppers have caused intestinal diseases among human being, which calls for emergence of pasteurization processes for black pepper. Radio frequency (RF) energy has the potential of pasteurizing low moisture spices within a short time. In this study, thermal inactivation kinetics studies of E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 on black pepper kernels were conducted, respectively. Then, RF inactivation experiments were conducted on inoculated black pepper kernels to achieve the required lethality. Results showed the number of log reduction for E. coli O157: H7 was > 6 log CFU/g after 7.0 min when heating to 90 °C in RF. Meanwhile, Salmonella Typhimurium ATCC 14028 reached > 6 log CFU/g reduction after 8.0 min RF heating and reaching 100 °C. From the quality point of view, the residual amount of Caryophyllene, 3-Carene, d-Limonene, β-Pinene in black pepper after RF pasteurization was 0.0060, 0.0038, 0.0034, 0.0016 mg/g, respectively. Comparatively, after steam pasteurization, Caryophyllene, 3-Carene, d-Limonene, β-Pinene content in black pepper was 0.0043, 0.0023, 0.0020, 0.0009 mg/g, respectively. Compared with steam heating, flavor substances in black pepper were better retained after RF heating. Thus, RF heating could effectively inactivate E. coli O157: H7 and Salmonella Typhimurium ATCC 14028 without significant influence on the quality of black pepper kernels.

Preparation of ammonium nitrate-based solid composite propellants supplemented with polyurethane/nitrocellulose blends binder and their thermal decomposition behavior

To improve the performance of solid composite propellants (SCPs) supplemented with ammonium nitrate (AN) as an oxidizer, the incorporation of energetic ingredients such as explosives, energetic binders or catalysts is a common effective approach. For this purpose, polyurethane (PU), a typical inert binder, was mixed with nitrocellulose (NC) as an energetic polymer. Numerous composite solid propellant compositions based on AN and NC-modified polyurethane binder with different NC ratios were prepared. The prepared formulations were characterized using Fourier transform infrared spectroscopy (FTIR), RAMAN spectroscopy, X-ray diffraction (XRD), electron densimetry, thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). A kinetic study was then performed using the iterative Kissinger-Akahira-Sunose (It-KAS), Flynn-Wall-Ozawa (It-FWO), and non-linear Vyazovkin integral with compensation effect (VYA/CE) methods. The theoretical performances, such as theoretical specific impulse, adiabatic flame temperature, and ideal exhaust gaseous species, were also determined using the NASA Lewis Code, Chemical Equilibrium with Application (CEA). Spectroscopic examinations revealed the existence of NC and full polymerization of PU in the prepared propellants. According to density tests, the density of the propellant increases as the nitrocellulose component increases. According to the thermal analysis and kinetics study, the increase in NC content catalyzed the thermal decomposition of the AN-based composite solid propellants. Based on the theoretical study, increasing the amount of NC in the propellant increased the specific impulse and, as a result, the overall performance.

Design of laccase–metal–organic framework hybrid constructs for biocatalytic removal of textile dyes

This study aims to present a simple and effective carrier matrix to immobilize laccase as opposed to complex and tedious immobilization processes and also to use it in the removal of textile dyes. For this purpose, Cobalt (Co) and Copper (Cu) based metal-organic frameworks (MOFs) were prepared and laccase was immobilized on two different MOFs via encapsulation. The characterization outcomes showed that laccase was well immobilized into MOF supports. Optimum pH and temperature were found for Lac/Co-MOF (pH 4.5 at 50 °C) and Lac/Cu-MOF (pH 5.0 at 50 °C). The Km (0.03 mM) and Vmax (97.4 μmol/min) values of Lac/Cu-MOF were lower than those of Lac/Co-MOF (Km = 0.13 mM, Vmax = 230.7 μmol/min). The immobilized laccases showed good reusability as well as improved resistance to temperature denaturation and high storage stability. For instance, the Lac/Co-MOF and Lac/Cu-MOF retained more than 58% activity after 4 weeks of storage at room temperature. Meanwhile, Lac/Co-MOF and Lac/Cu-MOF maintained 56.5% and 55.8% of their initial activity, respectively, after 12 reuse cycles. Moreover, thermal deactivation kinetic studies of immobilized laccases displayed lower k value, higher t1/2, and enhancement of thermodynamic parameters, which means better thermostability. Finally, the decolorization activities for the Lac/Co-MOF were 78% and 61% at the 5th cycle for Reactive Blue 171 and Reactive Blue 198, respectively. In conclusion, it can be inferred that the MOFs are more sustainable and beneficial support for laccase immobilization and they can be efficient for removing textile dyes from industrial wastes.

Comparative Studies on Thermal Decompositions of Dinitropyrazole-Based Energetic Materials.

Dinitropyrazole is an important structure for the design and synthesis of energetic materials. In this work, we reported the first comparative thermal studies of two representative dinitropyrazole-based energetic materials, 4-amino-3,5-dinitropyrazole (LLM-116) and its novel trimer derivative (LLM-226). Both the experimental and theoretical results proved the active aromatic N-H moiety would cause incredible variations in the physicochemical characteristics of the obtained energetic materials. Thermal behaviors and kinetic studies of the two related dinitropyrazole-based energetic structures showed that impressive thermal stabilization could be achieved after the trimerization, but also would result in a less concentrated heat-release process. Detailed analysis of condensed-phase systems and the gaseous products during the thermal decomposition processes, and simulation studies based on ReaxFF force field, indicated that the ring opening of LLM-116 was triggered by hydrogen transfer of the active aromatic N-H moiety. In contrast, the initial decomposition of LLM-226 was caused by the rupture of carbon-nitrogen bonds at the diazo moiety.