Combustion Behavior of Cellulose Ester Fibrous Bundles from Used Cigarette Filters: Kinetic Analysis Study.

This study is focused on the detailed examination of the combustion properties and kinetic analysis of a cellulose acetate fibrous bundle (CAFB), separated from used cigarette filters. It was shown that the faster rate of CAFB heating allows a large amount of heat to be supplied to a combustion system in the initial stages, where the increase in heating rate has a positive response to ignition behavior. The best combustion stability of CAFB is achieved at the lowest heating rate. Through the use of different kinetic methods, it was shown that combustion takes place through two series of consecutive reaction steps and one independent single-step reaction. By optimizing the kinetic parameters within the proposed reaction models, it was found that the steps related to the generation of levoglucosenone (LGO) (by catalytic dehydration of levoglucosan (LG)) and acrolein (by breakdown of glycerol during CAFB burning-which was carried out through glycerol adsorption on a TiO2 surface in a the developed dehydration mechanism) represent rate-controlling steps, which are strongly controlled by applied heating rate. Isothermal predictions have shown that CAFB manifests very good long-term stability at 60 °C (which corresponds to storage in a sea shipping container), while at 200 °C, it shows a sudden loss in thermal stability, which is related to the physical properties of the sample.

Upcycling of the Used Cigarette Butt Filters through Pyrolysis Process: Detailed Kinetic Mechanism with Bio-Char Characterization.

Thermo-chemical conversion via the pyrolysis of cigarette butt (CB) filters was successfully valorized and upcycled in the pre-carbonization and carbonization stages. The pre-carbonization stage (devolatilization) of the precursor material (cellulose acetate filter, r-CAcF) was analyzed by micro-scale experiments under non-isothermal conditions using TG-DTG-DTA and DSC techniques. The results of a detailed kinetic study showed that the decomposition of r-CAcF takes place via complex mechanisms, including consecutive reaction steps and two single-step reactions. Consecutive stages include the α-transition referred to as a cellulose polymorphic transformation (cellulose I → II) through crystallization mechanism changes, where a more thermodynamically ordered system was obtained. It was found that the transformation rate of cellulose I → II ('cellulose regeneration') is strongly affected by the presence of alkali metals and the deacetylation process. Two single-step reactions showed significant overlapping behavior, which involves a nucleation-controlled scission mechanism (producing levoglucosan, gaseous products, and abundant radicals) and hydrolytic decomposition of cellulose by catalytic cleavage of glycosidic bonds with the presence of an acidic catalyst. A macro-scale experiment showed that the operating temperature and heating rate had the most notable effects on the total surface area of the manufactured carbon. A substantial degree of mesoporosity with a median pore radius of 3.1695 nm was identified. The presence of macroporosity on the carbon surface and acidic surface functional groups was observed.

Thermal characteristics and combustion reactivity of coronavirus face masks using TG-DTG-MS analysis.

The presented paper deals with the influence of the heating rate on combustion characteristics (reactivity and reactivity evaluation, ignition index (D i), burnout index (D f), the combustion performance index (S), and the combustion stability index (R W)) of the protective coronavirus face masks. Two types of commonly used face masks in different state (new and exploited) were investigated by TG-DTG analysis in an air atmosphere, directly coupled with mass spectrometry (MS). Based on the experimental results, the impact of ultimate and proximate analysis data on the evolved gas analysis (EGA) was discussed. Also, the derived values from thermo-analytical (TA) data were compared with the literature reports, related to individual constitutive face mask materials. According to the performed research, it was established that different maximal reaction rate values at various heating rates indicate the complex nature of coronavirus face mask thermo-oxidative degradation, which is stimulated with carbon oxidation reactions and volatile matter (VM) release. By detailed analysis of obtained TG-DTG profiles, it was established that process takes place through the multiple-step reaction pathways, due to many vigorous radical reactions, causes by polymers degradation. The performed research was done to evaluate the possible utilization of coronavirus waste to energy production and sustainable pandemic environmental risk reduction.

Thermo-Analytical and Compatibility Study with Mechanistic Explanation of Degradation Kinetics of Ambroxol Hydrochloride Tablets under Non-Isothermal Conditions.

Ambroxol hydrochloride (AMB), used as a broncho secretolytic and an expectorant drug, is a semi-synthetic derivative of vasicine obtained from the Indian shrub Adhatoda vasica. It is a metabolic product of bromhexine. The paper provides comprehensive and detailed research on ambroxol hydrochloride, gives information on thermal stability, the mechanism of AMB degradation, and data of practical interest for optimization of formulation that contains AMB as an active compound. Investigation on pure AMB and in commercial formulation Flavamed® tablet (FT), which contains AMB as an active compound, was performed systematically using thermal and spectroscopic methods, along with a sophisticated and practical statistical approach. AMB proved to be a heat-stable and humidity-sensitive drug. For its successful formulation, special attention should be addressed to excipients since it was found that polyvinyl pyrrolidone and Mg stearate affect the thermal stability of AMB. At the same time, lactose monohydrate contributes to faster degradation of AMB and change in decomposition mechanism. It was found that the n-th order kinetic model mechanistically best describes the decomposition process of pure AMB and in Flavamed® tablets.

Model-free and model-based analysis of thermo-oxidative response of wolfberries: A new developed mechanistic scheme.

Thermally accelerated oxidative degradation of wolfberry pulp was kinetically monitored using model-free and model-based approaches. Kinetic calculations were performed based on simultaneous thermal analysis measurements in an air at four different heating rates. From kinetic analysis, new developed mechanistic scheme which is responsible for wolfberries anti-oxidative behavior was proposed. It was found that thermo-oxidative process proceeds through multiplestep mechanism including sum of two independent reaction sets, via consecutive and competitive steps. It was established that rutoside degradation pathway to flavonol through hydrolysis reaction is rate-determining step of considered process. Furthermore, it was found that key flavonol compound degraded by competitive reactions mechanism forming such kinetic branches, which lead to compounds responsible for wolfberries antioxidant activity. It was established that flavonol oxidative cleavage reaction and oxidative polymerization are main chemical routes which are very important in a complex antioxidant mechanism for scavenging free radicals in wolfberries oxidative stress response.

Comparative pyrolysis kinetics of various biomasses based on model-free and DAEM approaches improved with numerical optimization procedure.

The pyrolysis process of various types of biomass (agricultural and wood by-products) in non-isothermal conditions using simultaneous thermal analyses (STA) was investigated. Devolatilization kinetics was implemented through combined application of model-free methods and DAEM (distributed activation energy model) using Gaussian distribution functions of activation energies. Results obtained were used in the curve prediction of the rate of mass loss against temperature at various heating rates by numerical optimization. The possible calculation of biomass samples behavior under pyrolytic conditions as the summation of their pseudo-components, hemicelluloses, cellulose, and lignin is also explored. The differences between experimental and calculated data are less than 3.20% offering a quality test of applicability of proposed model on the kinetic studies of a wide range of biomass samples. It seems that the most physically realistic model is the decomposition of biomass in three reactions, depending on the composition of the biomass regarding hemicelluloses, cellulose, and lignin. Kinetic model applied here may serve as a starting point to build more complex models capable of describing the thermal behavior of plant materials during thermochemical processing.

New insights in dehydration stress behavior of two maize hybrids using advanced distributed reactivity model (DRM). Responses to the impact of 24-epibrassinolide.

Proposed distributed reactivity model of dehydration for seedling parts of two various maize hybrids (ZP434, ZP704) was established. Dehydration stresses were induced thermally, which is also accompanied by response of hybrids to heat stress. It was found that an increased value of activation energy counterparts within radicle dehydration of ZP434, with a high concentration of 24-epibrassinolide (24-EBL) at elevated operating temperatures, probably causes activation of diffusion mechanisms in cutin network and may increases likelihood of formation of free volumes, large enough to accommodate diffusing molecule. Many small random effects were detected and can be correlated with micro-disturbing in a space filled with water caused by thermal gradients, increasing capillary phenomena, and which can induce thermo-capillary migration. The influence of seedling content of various sugars and minerals on dehydration was also examined. Estimated distributed reactivity models indicate a dependence of reactivity on structural arrangements, due to present interactions between water molecules and chemical species within the plant.

Distribution of apparent activation energy counterparts during thermo - And thermo-oxidative degradation of Aronia melanocarpa (black chokeberry).

Kinetics of degradation for Aronia melanocarpa fresh fruits in argon and air atmospheres were investigated. The investigation was based on probability distributions of apparent activation energy of counterparts (εa). Isoconversional analysis results indicated that the degradation process in an inert atmosphere was governed by decomposition reactions of esterified compounds. Also, based on same kinetics approach, it was assumed that in an air atmosphere, the primary compound in degradation pathways could be anthocyanins, which undergo rapid chemical reactions. A new model of reactivity demonstrated that, under inert atmospheres, expectation values for εa occured at levels of statistical probability. These values corresponded to decomposition processes in which polyphenolic compounds might be involved. εa values obeyed laws of binomial distribution. It was established that, for thermo-oxidative degradation, Poisson distribution represented a very successful approximation for εa values where there was additional mechanistic complexity and the binomial distribution was no longer valid.

Kinetic modeling of native Cassava starch thermo-oxidative degradation using Weibull and Weibull-derived models.

A new approach in kinetic modeling of thermo-oxidative degradation process of starch granules extracted from the Cassava roots was developed. Based on the thermoanalytical measurements, three reaction stages were detected. Using Weibull and Weibull-derived (inverse) models, it was found that the first two reaction stages could be described with the change of apparent activation energy (Ea) on conversion fraction (α(T)) (using "Model-free" analysis). It was found that first reaction stage, which involves dehydration and evaporation of lower molecular mass fractions, can be described with an inverse Weibull model. This model with its distribution of Ea values and derived distribution parameters includes the occurrence of three-dimensional diffusion mechanism. The second reaction stage is very complex, and it was found to contain the system of simultaneous reactions (where depolymerization occurs), and can be described with standard Weibull model. Identified statistical model with its distribution of Ea values and derived distribution parameters includes the kinetic model that gives the variable reaction order values. Based on the established models, shelf-life studies for first two stages were carried out. Shelf-life testing has shown that optimal dehydration time is achieved by a programmed heating at medium heating rate, whereas optimal time of degradation is achieved at highest heating rate.

Kinetic and thermodynamic analysis of Creosote degradation process under isothermal experimental conditions.

Isothermal degradation process of commercial Creosote was analyzed by the thermogravimetric (TG) technique in a nitrogen atmosphere, at four different operating temperatures (230, 250, 270 and 290°C). The kinetic triplet [Ea , A and f(α)] and the thermodynamic parameters (ΔH (≠), ΔS (≠)and ΔG (≠)) for investigated Creosote samples were calculated. It was found that two-parameter autocatalytic Sesták-Berggren (SB) kinetic model best describes the process, but in the form of accommodation function with phenomenological character. Applying the multiplicative factor, the true value of activation energy (E (true) a ) was calculated. The experimental density distribution function of the apparent activation energy values was evaluated from isoconversional kinetic analysis. Based of the characteristic shape of distribution curve, it was concluded that the isothermal degradation of Creosote represents a complex physico-chemical process, given the chemical structure of the studied system. It is assumed that the considered process probably includes primary and secondary (autocatalytic) pyrolysis reactions, together with various decomposition reactions and radicals recombination pathways. The objective of the presented work is the proof of principle of the pyrolysis-based thermo-chemical conversion technologies for the production of value-added chemicals from the complex organic compounds, which even include chemical contaminants (such as PAHs). Also, the present work allows us that by using a unified kinetic approach we can obtain a significant physico-chemical characteristics of the tested system, which can then be used in the procedure for the separation of organics from creosote-treated woods and creosote-contaminated soils. The significance of this research is to identify the global kinetic behavior of some target contaminant compounds for pyrolysis, which are primarily PAHs.

Thermal characterization and detailed kinetic analysis of Cassava starch thermo-oxidative degradation.

Detailed kinetic analysis of Cassava starch thermo-oxidative degradation was performed, using thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) at four different heating rates. It was found that degradation process is very complex, as identified through continuous change of apparent activation energy with degree of degradation. It was established that process proceeds through three main degradation stages with one additional sub-stage attached to the second degradation stage, which was detected by appearance of "shoulder" on DTG curves. It was found that most important degradation stage can be described by "lumped" model, which implies that free radicals simultaneously attack both linear and branched molecular forms of the starch. This is characterized by an unusually high value of obtained reaction order (n=3.49). Application of nonlinear least squares method was confirmed the reliability of evaluated kinetic parameters and function of reaction mechanism, which were derived on the basis of other kinetic methods.

Tritium concentration analysis in atmospheric precipitation in Serbia.

Tritium activity concentration were monitored in monthly precipitation at five locations in Serbia (Meteorological Station of Belgrade at Zeleno Brdo, Vinca Institute of Nuclear Sciences, Smederevska Palanka, Kraljevo and Nis) over 2005, using electrolytic enrichment and liquid scintillation counting. The obtained concentrations ranged from 3.36 to 127.02 TU. The activity values obtained in samples collected at Zeleno Brdo were lower or close to the minimum detectable activity (MDA), which has a value of 3.36 TU. Significantly higher tritium levels were obtained in samples collected in Vinca Institute of Nuclear Sciences compared with samples from the other investigated locations. Amount of precipitation were also recorded. A good linear correlation (r = 0.75) for Zeleno Brdo and VINS between their tritium activity was obtained. It was found that the value of the symmetrical index n (which indicates the magnitude of tritium content changes with time (months) through its second derivative) is the highest for Vinca Institute of Nuclear Sciences compared to other locations, which is in accordance with the fact that the highest concentrations of tritium were obtained in the samples from the cited place.

The comparative kinetic analysis of Acetocell and Lignoboost® lignin pyrolysis: the estimation of the distributed reactivity models.

The non-isothermal pyrolysis kinetics of Acetocell (the organosolv) and Lignoboost® (kraft) lignins, in an inert atmosphere, have been studied by thermogravimetric analysis. Using isoconversional analysis, it was concluded that the apparent activation energy for all lignins strongly depends on conversion, showing that the pyrolysis of lignins is not a single chemical process. It was identified that the pyrolysis process of Acetocell and Lignoboost® lignin takes place over three reaction steps, which was confirmed by appearance of the corresponding isokinetic relationships (IKR). It was found that major pyrolysis stage of both lignins is characterized by stilbene pyrolysis reactions, which were subsequently followed by decomposition reactions of products derived from the stilbene pyrolytic process. It was concluded that non-isothermal pyrolysis of Acetocell and Lignoboost® lignins can be best described by n-th (n>1) reaction order kinetics, using the Weibull mixture model (as distributed reactivity model) with alternating shape parameters.

Thermal stability and nonisothermal kinetics of Folnak degradation process.

AIM: The purpose of this article is to investigate the thermal stability and nonisothermal kinetics of Folnak drug degradation process using different thermoanalytical techniques. METHODS: The nonisothermal degradation of Folnak powder samples was investigated by simultaneous thermogravimetry-differential thermal analysis, in the temperature range from ambient to 810 degrees C. RESULTS: It was found that the degradation proceeds through five reaction stages, which include the dehydration, the melting process of excipients, the decomposition of folic acid, corn starch, and saccharose. The presence of compounds such as excipients increases the thermal stability of the drug and some kind of solid-solid and/or solid-gas interaction occurs. CONCLUSION: It was concluded that the main degradation stage of Folnak sample represents the decomposition of folic acid. It was established that the folic acid decomposition cannot be explained by simple reaction order model (n = 1) but with the complex reaction mechanism that includes higher reaction orders (n > 1). The isothermal predictions of the folic acid decomposition at four different temperatures (T(iso) = 180 degrees C, 200 degrees C, 220 degrees C, and 260 degrees C) were established. It was concluded that the shapes of conversion curves at lower temperatures (180-200 degrees C) were similar, whereas they became more complex with further temperature increase because of the complexity of the decomposition reaction.