Probable Mechanism Function Research Articles

Oxidation mechanism and kinetics of TiB2 submicron powders in air

AbstractHigh‐activity TiB2 submicron powders were synthesized via microwave‐assisted carbothermal reduction, and their oxidation behavior at 550°C–1000°C for 0.5–1.5 h in air atmosphere was carried out by the isothermal oxidation test. The phase composition and microstructure evolution of the oxidation products were performed by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). It was established that TiB2 submicron powders had been significantly oxidized at 550°C, and the oxidation products were TiO2 and B2O3. Hexagonal plate‐like TiB2 grains had been completely disappeared, and fragmented into uniform nano‐scale spherical TiO2 particles after being oxidized at 1000°C for 1 h, accompanied by the violent evaporation of B2O3 products at temperatures above 1000°C. In addition, the corresponding oxidation kinetics was investigated by using a non‐isothermal thermogravimetric (TG)–differential scanning calorimetry (DSC) technique. The results showed that the Mample power law (n = 1) was the most probable mechanism function, and the oxidation activation energy E of TiB2 submicron powders was 640.58 kJ/mol.

Comprehensive Understanding of the Heavy Oil Combustion Process: Reaction Behavior, Kinetic Triplet, and Mechanism Implication.

In this work, thermo-oxidative behavior, kinetic triplet, and free radical mechanism of ultraheavy oil during an in situ combustion (ISC) process were systematically surveyed via multiple thermal analysis techniques (TG/DTG/DSC/PDSC), model-free methods, and related mathematical simulation. First, specific mass loss, exothermic intensity, and corresponding temperature intervals were respectively determined in low-/high-temperature oxidation (LTO/HTO) regions. In addition, the comparison of atmospheric/pressurized differential scanning calorimetry (DSC/PDSC) experiments indicated that the pressurized conditions could obviously strengthen the oxidation progress with more heat emission. Then two model-free methods were contrastively employed for PDSC data to calculate LTO and HTO activation energy variations with the conversion rate. Moreover, the acceleratory rate model for LTO and the Sestak-Berggren model for HTO were accordingly picked as the most probable mechanism functions, which were later used to determine the simulated curves. Then, the simulations of α-T and dα/dT-T curves were respectively attained using Friedman equation in MATLAB software and contrasted with experimental data to validate the accuracy of the yielded kinetic triplet and forecast the combustion behavior. Further, the evolution pathways of the underlying oxidation mechanism was illustrated. This study updates the understanding of the nonisothermal combustion process, contributing to the subsequent numerical simulation and feasible investigation for in situ combustion implementation to enhance heavy oil recovery.

Thermal dehydration kinetics of 4CaO·5B2O3·7H2O with different phases and morphologies

α-4CaO·5B2O3·7H2O (sheet-like structure) and three polymorphs of β-4CaO·5B2O3·7H2O (flower-like, succulent plant-like and book-like structure) were prepared by hydrothermal method, and characterized by XRD, FTIR, TG-DTA-DTG, SEM. The activation energies (Ea) of the two-step thermal dehydration of 4CaO·5B2O3·7H2O with different morphologies and phases were calculated by Kissinger-Akahira-Sunoes (KAS) method. The most probable mechanism function of the two-step dehydration reaction was determined by Coats-Redfern (CR) method, and the average pre-exponential factor (A) of the two-step thermal dehydration of the sample was calculated. The results showed that the thermal dehydration of 4CaO·5B2O3·7H2O was divided into two steps. The activation energy of thermal dehydration reaction was affected by the phase, morphology and particle size. The activation energies of the two-step thermal dehydration of β-4CaO·5B2O3·7H2O(flower-like, succulent plant-like and book-like structure) all decrease in turn, which is consistent with the change trend of particle size. The average pre-exponential factor of the first-step thermal dehydration of all samples is smaller than that of the second-step thermal dehydration. The mechanism functions of the first-step and second-step thermal dehydration stages are Jander equation [1-(1-α)1/3]2 and Z-L-T equation [(1-α)−1/3-1]2, respectively, which belong to three-dimensional diffusion. The three-dimensional diffusion process of the two-step thermal dehydration was analyzed and explained.

Thermal dehydration kinetics of SrB6O10·5H2O with different morphologies

The globular-like, sheet-like, coral-like SrB6O10·5H2O was prepared by hydrothermal method, and characterized by X-ray powder diffractometer(XRD), thermogravimetry(TG), differential thermal analysis(DTA), scanning electron microscopy(SEM). The activation energy of the thermal dehydration of SrB6O10·5H2O with different morphologies was calculated by Ozawa-Flynn-Wall (OFW) method. The most probable mechanism function of the dehydration reaction was determined by master-plots method, and the average pre-exponential factor of the thermal dehydration of the sample was calculated. The results show that the thermal dehydration of SrB6O10·5H2O is divided into two steps. The activation energy of thermal dehydration reaction is affected by the morphology and size. The activation energy of SrB6O10·5H2O in the first step of thermal dehydration is close, while there is a significant difference in the activation energy value of SrB6O10·5H2O in the second step of thermal dehydration. The order of activation energy, as well as the order of the average pre-exponential factor, is consistent with the size order of the constituent units of the sample microstructure. The first-step thermal dehydration mechanism functions of SrB6O10·5H2O (globular-like, sheet-like, coral-like) are all [-ln(1-α)]3, which belongs to random nucleation and growth, and the second-step thermal dehydration mechanism functions are α2(one-dimensional diffusion), α+(1-α)·ln(1-α) (two-dimensional diffusion), and [-ln(1-α)]3 (random nucleation and growth), the reasons for the difference of their two-step mechanistic functions are analyzed.

The effect of N2/CO2 blend ratios on the pyrolysis and combustion behaviors of coal particles: Kinetic and thermodynamic analyses

The aim of this work is to investigate the impact of various CO2/N2 ratios on coal pyrolysis and combustion properties and to provide theoretical guidance for better preventing and controlling coal spontaneous combustion in the goaf. The dynamic pyrolysis and combustion characteristics of DX coal were analyzed by using a thermal gravimetric analyzer (TGA) in a constant oxygen atmosphere with different CO2/N2 blend ratios. The Málek method combining Coats-Redfern and Achar methods was used to determine the most probable mechanism functions. CO2 containing atmospheres increased characteristic temperatures, burnout rate, maximum mass loss rate and comprehensive combustion performance index compared to O2/N2 atmospheres. In stages I-III, a lower apparent activation energy was observed in O2/CO2 atmospheres. Apparent activation energy and enthalpy changes showed upward trends in the reaction stage (I→III→IV), whereas Gibbs free energy change and entropy change decreased. The dynamic pyrolysis and combustion of DX coal necessitated increased energy in environment with a CO2/N2 ratio of 4:6, revealing the optimal inhibitory effect on DX coal with this particular ratio.

Detailed investigation on the oxidation behavior and kinetic triplet of tight oil via TG-DSC-PDSC analyses

It remains some barriers for continental tight oils to enhance oil recovery owing to low or ultra-low permeability in China. Whether low temperature combustion mode (or deflagration fracturing) could be employed to expand the fracture, is an interesting but debatable topic in consideration of the not well-understood oxidation behavior and kinetic mechanism for the tight oil. This study initiated a comprehensive characterization on the oxidation behavior and kinetic triplet for the Mahu tight oil via the combination of atmospheric and pressurized thermal analyses (TG/DTG, DSC/DDSC, PDSC) and unconventional Popescu method. Threshold, peak, and end temperatures were shifted to higher temperature ranges following lower cumulative heat emission (from 13.21 to 9.15 kJ·g−1) with the heating rate increment from 5 to 15 K·min−1. Inversely, a more thorough oxidation process with higher cumulative heat releases (8.69 kJ·g−1 for LTO, 4.48 kJ·g−1 for HTO) was presented under elevated pressure condition. In order to elucidate the latent reaction mechanism, seven sequential temperature subzones were divided to acquire the most probable mechanism function G(α) and corresponding kinetic parameters. The results indicated that, owing to the high reservoir pressure, generated enormous heat in LTO stage had a significant acceleration to initiate and sustain the low temperature combustion process, which in some degree was conducive to update and expand the understanding of the low temperature in-situ combustion mode of air injection in low permeability and tight oil reservoirs via fracturing reservoir matrix.

Analysis on the thermal decomposition kinetics and storage period of biomass-based lycorine galanthamine.

As global ageing deepens and galanthamine is the preferred clinical drug for the treatment of mild to moderate Alzheimer's disease, it will be valuable to examine the behaviour and mechanism of galanthamine's thermal decomposition for its quality control, formulation process, evaluation of thermal stability, and expiry date in production. In order to study the pyrolysis of galanthamine hydrobromide with nitrogen as the carrier gas, a thermogravimetric-differential thermogravimetric technique (TG-DTG) was applied at a temperature rise rate of 10Kmin-1 and a volume flow rate of 35mLmin-1. The apparent activation energy E a and the prefactor A (E a = 224.45kJmol-1 and lnA = 47.40) of the thermal decomposition reaction of galanthamine hydrobromide were calculated according to the multiple heating rate method (Kissinger and Ozawa) and the single heating rate method (Coats-Redfern and Achar), and the most probable mechanism function was derived, and then the storage period was inferred from E a and E. A three-dimensional diffusion mechanism was suggested to control the thermal decomposition of galanthamine hydrobromide in accordance with the Jander equation, random nucleation and subsequent growth control, corresponding to the Mample one-way rule and the Avrami-Erofeev equation. As a result, the thermal decomposition temperature of galanthamine hydrobromide gradually increased with the rate of temperature rise. From Gaussian simulations and thermogravimetric data, galanthamine hydrobromide decomposed at the first stage (518.25-560.75K) to release H2O, at the second stage (563.25-650.75K) to generate CO, CO2, NH3 and other gases, and finally at the third stage (653.25-843.25K) to release CO2. After 843.25K, the residual molecular skeleton is cleaved to release CO2 and H2O. According to the E a and A presenting in the first stage of thermal decomposition, it is assumed that the storage life of galanthamine hydrobromide at room temperature 298.15K is 4-5years.

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.

Mechanism and kinetics for chlorination roasting of copper smelting slag

An efficient process based on chlorination roasting with CaCl2 was proposed to recover zinc from copper smelting slag. The reaction mechanism and the kinetics of the chlorination process were investigated by thermodynamic calculation, thermogravimetry and differential scanning calorimetry (TG−DSC) analysis and X-ray diffraction (XRD) methods. The results demonstrated that the temperatures of oxidative decomposition of CaCl2 and chlorination of all Zn-containing phases were above 774.3 and 825 °C, respectively. The chlorination roasting process was divided into four stages: precipitation of adsorbed water, extraction of crystallized water, oxidation of Fe-containing phases, and chlorination volatilization of zinc. The average apparent activation energies of the iron oxidation and zinc chlorination were 101.70 and 84.4 kJ/mol, respectively. The most probable mechanism function for the iron oxidation process was the Avrami−Erofeev model (n=2). Zinc chlorination followed the shrinking unreacted core model, and the chemical reaction was the rate-controlling step.

Insights into a co-precursor driven solid-state thermal reaction of ferrocene carboxaldehyde leading to hematite nanomaterial: a reaction kinetic study.

Thermal decomposition of a mixture of ferrocene carboxaldehyde and oxalic acid dihydrate in O2 atmosphere produced rod-like hematite nanomaterial. The decomposition reaction was complex as evident from the overlapped multistep reaction steps in the non-isothermal thermogravimetry (TG) profiles obtained in the 300-700 K range. A peak deconvolution method was applied to separate the overlapped reaction steps. The multistep TG profiles were successfully deconvoluted, which showed that the decomposition occurs in six individual steps. However, it was found that only the last three reaction steps were responsible for the production of hematite. To estimate the activation energy values for these thermal reactions, six model-free integral isoconversional methods were used. The activation energy value significantly depends on the extent of conversion in each step; however, the nature of its dependence significantly different for each step. The most probable stepwise reaction mechanism functions for the solid-state reactions were obtained using the master plot method. The reaction mechanism was found to be different for different steps. Utilizing the activation energy and reaction mechanism function, the reaction rates of decomposition for each step were determined. To substantiate the validity of the assumed kinetic models, the experimental conversion curves were compared with the constructed ones, and the agreement was quite reasonable. The conversion-dependent thermodynamic parameters were obtained utilising the estimated kinetic parameters. Role of the co-precursor in the thermal reaction of the precursor was plausibly revealed. The present study describes how the use of a co-precursor significantly enhances the thermal decomposition of the precursor, how hematite nanomaterials can be synthesized from a co-precursor driven solid state reaction at low temperatures, and how the kinetic calculations facilitate the understanding of the solid-state reaction process. This study proposes the use of a suitable combination of precursor and co-precursor for solid-state thermal synthesis of iron-based nanoparticles using organo-iron compounds as precursor and also illustrates the effective application of the thermal analysis technique to understand the decomposition reaction.

Preparation, characterization, thermal behavior and decomposition kinetics of new high-nitrogen energetic salts based on 3-amino-5-hydrazinopyrazole

Three novel energetic salts (2, 3, and 4) based on 3-amino-5-hydrazinopyrazole were synthesized and were fully characterized. The corresponding thermal and kinetic behaviors were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) for the first time. Accurate kinetic models based on the analysis were selected to describe the decomposition by applying an isoconversional methods and nonlinear regressions to data of DSC and the most probable mechanism function of decomposition for salts 2–4 were obtained. Their physicochemical properties, such as densities, heat of formation, detonation performances and mechanical sensitivities acquired from experimental measurements or theoretical calculations were investigated. The results show that the strong hydrogen bond interactions make energetic salts have high densities and good detonation properties while maintaining reasonable mechanical sensitivities. The energetic salts 2–4 show superior detonation performance than TNT or exhibit comparable detonation parameters with RDX while having more insensitive mechanical sensitivities and higher nitrogen contents. These properties provide them as promising energetic materials.

Theoretical analysis and experimental verification of thermal decomposition mechanism of CuSe

Experiments on the thermal decomposition of CuSe were carried out by using a thermogravimetric analyzer (TGA) at different heating rates. The kinetic parameters and mechanisms were discussed based on model-free and model-based analyses. The decomposition rate and decomposition behavior of CuSe were investigated by using a vacuum thermogravimetric furnace. The results showed that the R3 model was identified as the most probable mechanism function under the present experimental conditions. The average values of activation energy and the pre-exponential factor were 12.344 J/mol and 0.152 s-1, respectively. The actual decomposition rate of CuSe was found to be 0.0030 g/(cm2·min).

Mechanochemical effect of spontaneous combustion of sulfide ore

Spontaneous combustion of sulfide ore is a typical disaster in mining, which can cause a series of environmental and safety problems. In order to reveal the mechanical activation’s influence on the spontaneous combustion of sulfide ore during the mining process, the changes in the microstructure of sulfide minerals and their spontaneous combustion kinetics before and after activation were studied in this paper. The most probable mechanism function, apparent activation energy, and pre-exponential factor were derived using the Malek and Friedman methods, respectively. The results showed that mechanical activation leads to aggregation of mineral particles, defect generation in crystals, reduction in crystallize size, and increase in lattice distortion rate, which result in samples more actively. In the process of oxidation and spontaneous combustion, the main products were Fe2O3 and SO2 gas. And the mechanochemical effect will cause the reaction rate to become faster and lead the reaction to move toward low temperature. The mechanochemical effect will also lead to chemical reactions at low temperatures, causing some ore samples to be oxidized without changing the samples’ reaction mechanism functions. After mechanical force, the average apparent activation energy decreased by 26.27 kJ/mol, 32.73 kJ/mol, 27.01 kJ/mol, and 35.30 kJ/mol, respectively, and the sample’s spontaneous combustion tendency increased. In addition, ore samples’ active surface and grain boundary area increased under the mechanical forces, the lattice was distorted and dislocated, and a sub-stable amorphous phase was formed. In this process, the mechanical energy was partially converted into energy storage in the solid material, significantly increasing reactivity.

The kinetic models analyses of hydrogenated natural rubber during non‐isothermal degradation process

AbstractHydrogenated natural rubber (HNR) was prepared by diimide reduction of natural rubber (NR) latex and characterized by FT‐IR, 1H NMR and TG‐DTG. The thermal degradation kinetic models of HNR were studied under a nitrogen atmosphere by TG‐DTG. Achar and Coats–Redfern methods were used to study the non‐isothermal kinetics models change during the thermal degradation process of NR after hydrogenation. The results indicated that HNR with 34.69% and 63.74% hydrogenation degree were prepared. A one‐stage pyrolysis pathway could be observed from all the TGA curves which were shifted to higher degradation temperatures with the rise of saturation degree. The similar activation energies obtained by both Coats–Redfern and Achar methods confirmed that the kinetics calculation was accurate. The results showed the best‐fit models of the samples with the highest regression coefficient values (R2 > 0.90) were chemical reaction models. The reaction order was three (N3) in NR case and the corresponding mechanism functions were g(α) = [(1‐α)−2–1]/2, f(α) = (1‐α)3. The reaction order was two (N2) when it came to HNR with hydrogenation degree of 34.69%. The most probable mechanism functions were g(α) = (1‐α)−1–1, f(α) = (1‐α)2. As the degree of hydrogenation increased to 63.74%, the reaction order best‐fit changed to one (N1) which was proved to be the same as the ethylene‐propylene diene rubber samples. And the mechanism functions were g(α) = −ln(1‐α), f(α) = 1‐α. The thermal degradation models of polymers was closely related to the structure. And the structure effects affected the degradation behavior as well as the thermal properties of polymers.

Thermal stability and non‐isothermal kinetics of poly(ethyl cyanoacrylate) nanofibers

AbstractA thermogravimetric study of poly(ethyl cyanoacrylate) nanofibers was carried out at five heating rates with a linear increase in the temperature in a nitrogen atmosphere. The data provided by the thermogravimetric study were used to evaluate the kinetics of the degradation process using three isoconversional methods. Considering that the kinetic parameters of the process depend on the reaction mechanism, various approaches were applied in order to determine the most probable mechanism function. In this respect, the mechanism of thermal degradation of poly(ethyl cyanoacrylate) is a phase boundary reaction with cylindrical symmetry (F0.5 function) as demonstrated by the z(α) master plots method, iso‐temperature method and isoconversional method. On their basis, the values of the kinetic triplet (Ea, A and the shape of the most appropriate f(α) function) of the process were obtained, and subsequently the thermodynamic functions of the activated complex formation were calculated. The thermal stability of the polymer was predicted according to the integral procedure decomposition temperature. © 2022 Society of Chemical Industry.

Thermal hazard and mechanism study of 5-(4-Pyridyl)tetrazolate (H4-PTZ)

Thermal decomposition experiment of 5-(4-Pyridyl)tetrazolate (H4-PTZ) was carried out. The heat flow curve and reaction rate data under different heating rates were obtained. The characteristic parameters were obtained. The apparent activation energy for each individual reaction was calculated by applying different methods. On this basis, Malek method was used to predict the most probable mechanism function of thermal decomposition reaction of H4-PTZ. The thermal safety parameters, including self-accelerating decomposition temperature, hot spot fire temperature and thermal explosion critical temperature were predicted also. The activation enthalpy, activation entropy, and activation Gibbs free energy of H4-PTZ are calculated. Gaussian16 program was used to optimize the molecular structure, search the transition state and calculate the intrinsic reaction coordinates of H4-PTZ. The most probable decomposition path of H4-PTZ was found, and the activation energy calculated by experiment was compared with that calculated by theory.

Study on pressurized isothermal pyrolysis characteristics of low-rank coal in a pressurized micro-fluidized bed reaction analyzer

In order to investigate the pressurized isothermal pyrolysis characteristics of coal, the effect of pressure on gas release characteristics and the kinetics of pressurized isothermal pyrolysis are explored for the first time in a pressurized micro-fluidized bed reaction analyzer (P-MFBRA). This work finds that the yields of CO2, CO, CH4, and H2 increases with temperature and pressure. The difference in the order of gas-releasing reduces as temperature and pressure rises, but that of gas-ending first decreases and then increases with pressure. The most probable mechanism functions of CO2, CO and CH4 change from shrinking core model to homogeneous model at 1 MPa, 0.8 MPa and 0.5 MPa, respectively, showing that reaction is controlled by chemistry under low pressure but affected by diffusion effect with elevating pressure. The rate constant and activation energy (Ea) of each gas appear an increasing-decreasing tendency and the difference between Ea of each gas reduces with pressure. Compared with non-isothermal experiments, the Ea (20.8–475 kJ mol−1) and pre-exponential factor in P-MFBRA are less than those (70–150 kJ mol−1) in the pressurized thermogravimetric analyzer (P-TGA), indicating P-MFBRA can effectively reduce the diffusion inhibition, and the kinetics obtained is close to the reaction in industrial fluidized bed reactor.

Experimental investigation on CO2 desorption kinetics from MDEA + PZ and comparison with MDEA/MDEA + DEA aqueous solutions with thermo‐gravimetric analysis method

AbstractThe carbon dioxide discharged from fossil fuels combustion products is considered as a major contributor to global warming. The current investigation aimed at CO2 desorption kinetics in 3.25 mol L–1 methyldiethanolamine (MDEA)–0.1 mol L–1 piperazine (PZ) rich amine aqueous solution with thermo‐gravimetric analysis (TGA) method under different heating rates of 2.5, 5, 10, and 20 °C min–1. The kinetics parameters were determined by comparison of 40 mechanism functions with thermal analysis kinetic method. The average activation energy E was 59.16 kJ mol–1, preexponential factor A was 5.54 × 108, and the most probable mechanism function was G(α) = [–ln(1 – α)]3/2. In addition, the kinetic parameters of CO2 desorption process from three rich amine aqueous solutions (MDEA, MDEA + diethanolamine(DEA), MDEA + PZ) were compared and the influence of kinetic parameters was further discussed. The desorption rate models of three rich amine aqueous solutions were established and desorption rates were well predicted. The order of desorption rate inferred from desorption rate model was MDEA > MDEA + DEA > MDEA + PZ. The results indicated that TGA combined with thermal analysis kinetics was an effective and quick method with high accuracy, easy operation, and good repeatability for screening absorbents preliminarily in laboratory. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Kinetic study and modeling on the regeneration of Li4SiO4-based sorbents for high-temperature CO2 capture

Li4SiO4 is acknowledged as a promising sorbent candidate in high-temperature CO2 adsorption. However, reaction kinetics for the regeneration process of Li4SiO4, especially its dependence on CO2 pressure is lack of understanding. This work designed and carried out a series of isothermal tests on the regeneration of pure Li4SiO4 and K-Li4SiO4 under CO2 partial pressure of 0–0.5 atm and temperature of 625–725 °C. For the first time, the expression of (Peq − PCO2)n is introduced into the regeneration rate equation so as to reveal its dependence on CO2 pressure. The reaction order (n) is found to grade according to the value of (Peq − PCO2), and the apparent activation energy is calculated as 284.42 kJ•mol−1 and 146.31 kJ•mol−1 for the regeneration of Li4SiO4 and K-Li4SiO4, respectively. Furthermore, this work proposes that power law model with m = 4/3 is the most probable mechanism function for the regeneration of Li4SiO4-based sorbents.

Kinetic analysis and reaction mechanism of p-alkoxybenzyl alcohol ([4-(hydroxymethyl)phenoxymethyl]polystyrene) resin pyrolysis: Revealing new information on thermal stability

This study provides new information on the thermal stability and kinetics of pyrolysis of commonly used resins in solid-phase peptide synthesis. Pyrolysis process of 4-benzyloxybenzyl alcohol resin was monitored by simultaneous TGA-DTG measurements in a nitrogen atmosphere, at four different heating rates (5, 10, 20 and 30 K min−1). Kinetic computations included the model-free (isoconversional) and model-based methods for reliable estimation of kinetic parameters and the mechanism of investigated process. Based on the findings from applied methods, the pyrolysis process can be described by three reaction steps, where one of them encompasses the consecutive reactions. The first step (n-th order reaction, referred to Fn) is attributed to the random scission of the main chain in PS (polystyrene) solid support, where polymer radicals were formed. The second step proceeds through homolytic cleavage path of ether linkage of the resin (by the first-order reaction, referred to F1) and then via phenoxy radical (semiquinone) formation which is converted into the benzoquinone through a dehydrogenation (by autocatalysis reaction, referred to Cnm). Finally, the third step (referred to Fn reaction) was characterized by depolymerization mechanism, which takes place at higher temperatures (T > 385 °C). With determined kinetic parameters and the most probable mechanism functions, the model agrees excellently with experimental data. By applying the obtained kinetic results, isothermal life-time prediction was also performed.