Single Kinetic Model Research Articles

Determining reaction rate parameters for an energetic material through inverse multi-scale analysis of shock-to-detonation transition

ABSTRACT In multi-scale predictive models of shock-to-detonation transition (SDT), microstructure-aware burn models are employed to connect meso-scale dynamics with macro-scale energy release. Meso-scale calculations of hotspot ignition and growth rely on chemical reaction rates expressed in Arrhenius forms. However, even for well-studied energetic materials such as HMX, the reaction time scales and pathways provided by available reaction kinetic schemes vary widely. Uncertainties in reaction rate parameters can amplify to produce large uncertainties in predicted initiation envelopes (James curves or Pop-plots). To better pin down reaction rate parameters for HMX, we perform an inverse analysis to extract the rate constants in an Arrhenius model (assuming a single reaction global kinetics model) that best predicts an experimentally obtained criticality envelope. Interestingly, the estimated global kinetic scheme is shown to conform to the well-known Henson 1-equation model. To establish the validity of the inverse analysis, we further carry out a forward analysis using the determined rate law and demonstrate good predictions of SDT for a different class of pressed HMX material. While the inverse analysis has been applied herein to HMX, the paper presents a general route to arrive at global kinetics models that can be applied to a wide class of EM species.

Degradation of the novel herbicide tiafenacil in aqueous solution: Kinetics, various influencing factors, hydrolysis products identification, and toxicity assessment

As new pesticides are continually introduced into agricultural systems, understanding their environmental behavior and potential toxicity effects is crucial for effective risk assessment. This study utilized QuEChERS and UPLC-QTOF-MS/MS techniques to analyze Tiafenacil (TFA) and its six hydrolysis products (HP1 to HP6) in water, marking the first comprehensive report on these degradation products. Calibration curves demonstrated strong linearity (R2 ≥ 0.9903) across concentrations ranging from 0.02 to 3.50 mg L−1. TFA's hydrolysis followed single first-order kinetic (SFOK) model, with rapid degradation observed under alkaline and high-temperature conditions, resulting in half-lives ranging from 0.22 to 84.82 days. The ECOSAR model predicts that TFA's hydrolysis products exhibit acute and chronic toxicity to fish, Daphnia, and green algae. Additionally, hydrolysis products HP1, HP5, and HP6 were detected in irrigation water from citrus orchards, posing higher predicted toxicity risks to fish and green algae. This highlights the necessity for further risk assessments considering transformation products. Overall, this study enhances our understanding of TFA's environmental fate and supports its safe agricultural application and monitoring practices.

Effective degradation of azo dyes by ABTS (2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) mediated laccase. Kinetic studies

Laccases are enzymes with low substrate specificity that in certain cases require the presence of a mediator in order to work properly. Therefore, this paper investigated the degradation of Orange G, Ponceau 4 R and Methyl Red in the presence of laccase isolated from Trametes versicolor and laccase-ABTS system. Laccase, in high concentration, was able to oxidize only Orange G and Ponceau 4 R, with a degree of decolorization less than 10 % in 20 min. In the presence of laccase-ABTS system, the reaction is much faster, and at least 40 % of dyes were degraded in 15 min. A kinetic model accounting for enzymatic oxidation of all dyes, including a step for enzyme operational inactivation, was proposed. This study proves that we can use a single kinetic model for the oxidation of all dyes in the laccase-ABTS system.

A Mathematical Logistic Model Describes Both Global CO2 Emissions and its Accumulation in the Atmosphere

A single kinetic model, of a logistic nature, is able to describe two different phenomena: the global emission of CO2 due to the combustion of fossil fuels and the observed accumulation of CO2 in the atmosphere. Unexpectedly, the analysis of the experimental data clearly shows that the two rates of emission and accumulation are almost exactly in phase and differ by a constant factor. The fraction of CO2 that accumulates in the atmosphere is constantly equal to 65% of the emissions. The same percentage also applies to the rate of change of the two phenomena, i.e., the accelerations.

Combined techniques for revealing the mechanism beneath the inhibition effects of pectin on gluten digestibility using static in vitro gastro-duodenal protocols

In the current study, how pectin retards the digestibility of wheat gluten was investigated using a static in vitro gastric-duodenal model. The degree of protein hydrolysis was estimated using the o-phthaldialdehyde method, while the in vitro digestograms were mathematically fitted using a single first-order kinetics model. Peptides' profile, free amino acids compositions, gluten-pectin interactions and their effects on enzymatic activities of proteolytic enzymes as well as on the gluten secondary structures under digestive conditions were studied using combined techniques. Results showed that pectin could retard gluten digestibility through 1). preferential absorption to insoluble gluten aggregates by electrostatic interactions; 2). increasing the helix and reducing the β-sheet content of the solubilized gluten protein fractions in terms of their secondary molecular structures; 3). reducing pepsin activity by forming negatively charged pectin-gluten mixtures which then interacted with the positively charged pepsin molecules. The deeper insight into gluten-pectin interactions and their influences on gluten digestibility under gastrointestinal conditions provides important clues for developing effective forms of dietary fiber to improve the nutritional benefits of plant protein in individuals.

A Mathematical Logistic Model Describes Both Global CO2 Emissions and its Accumulation in the Atmosphere

A single kinetic model, of a logistic nature, is able to describe two different phenomena: the global emission of CO2 due to the combustion of fossil fuels and the observed accumulation of CO2 in the atmosphere. Unexpectedly, the analysis of the experimental data clearly shows that the two rates of emission and accumulation are almost exactly in phase and differ by a constant factor. The fraction of CO2 that accumulates in the atmosphere is constantly equal to 65% of the emissions. The same percentage also applies to the rate of change of the two phenomena, i.e., the accelerations.

The particle sizes of milled wheat fractions affect the in vitro starch digestibility and quality parameters of wire-cut cookies made thereof.

Slow digestion of starch is linked to various health benefits. The impact of wheat particle size on in vitro starch digestibility and quality of wire-cut cookies was here evaluated by including four soft wheat fractions [i.e. flour (average diameter, 83 μm), fine farina (643 μm), coarse farina (999 μm) and bran (1036 μm)] in the recipe. The susceptibility of starch in these fractions to in vitro digestion decreased with increasing particle size, resulting in a 76% lower digestion rate for coarse farina than for flour as found with the single first-order kinetic model. Starch was protected from hydrolysis likely due to delayed diffusion of pancreatic α-amylase through the intact farina cell walls. When 20-65% starch in flour for the control cookie recipe was substituted with the same percentages in fine and coarse farina, the starch digestion rate decreased when substitution levels increased. A 62% lower digestion rate was found at 65% substitution with coarse farina. Cell wall intactness was largely preserved in the cookies and most of the starch appeared as ungelatinised granules. Further, the cookie spread ratio during baking was 48% and 33% higher and the cookies were 63% and 57% less hard than control cookies when made with 65% fine farina and 65% coarse farina, respectively. The relatively low specific surface area of large wheat particles resulted in low water absorption and less dense packing. In conclusion, encapsulation of starch by intact cell walls in coarse wheat fractions makes them promising ingredients when developing starchy food products for controlled energy release.

Study on the reduction of Fe2O3 pellets by CO-CO2 and H2-H2O: Reaction kinetics and pore network model

The steel industry contributes to creating an environmentally friendly society by providing high-quality steel and working to develop low-carbon processes. Using hydrogen produced from renewable energy to replace part of coke in blast furnaces is one of the measures to reduce fossil carbon dioxide emissions in the process of steelmaking. In this paper, a series of reduction experiments of Fe2O3 pellets at different temperatures were carried out under three conditions of hydrogen-rich in blast furnace. The variation law between reduction degree and apparent activation energy was calculated. The result shows that when the reduction degree reaches 11% and 70%, the apparent activation energy reaches the peak, which are 38.9 kJ/mol and 19.5 kJ/mol, respectively. This suggests that the reduction process is affected by two or more mechanisms. Then, on the basis of the typical single interface reaction kinetics model, the multistep reduction kinetics model of hydrogen-rich reduction Fe2O3 pellets was established. In addition, based on the results of industrial computerized tomography (CT) analysis, the three-dimensional pore network model and velocity model of Fe2O3 pellets after reduction were established. The coupling relationship between the fractal dimension of pellet pores and reduction atmosphere was studied by introducing fractal theory. Under hydrogen-rich reduction condition, the volume fractal dimension of pore structure of Fe2O3 pellets increases from 2.41 to 2.58. Therefore, the pore structure formed by hydrogen-rich reduction is conducive to the diffusion of reducing gas in the pellet, so as to improve the reduction degree of pellet.

Kinetic modeling and experiments on removal of COD/nutrients from dairy effluent using chlorella and co-culture.

A sustainable and cost-effective approach of waste water management is biological treatment for reducing organic carbon, nitrate, and phosphate content. Co-culturing of algae with bacteria in wastewater leads to higher biomass yield and improvement in COD/nutrients removal compared to the single strain counterparts. In this study, a mathematical modeling framework is proposed to predict the dynamic behavior of microbial co-culture in dairy waste water. Initially, the model has been developed to predict the biomass growth and COD/nutrients removal with discrete cultures (algae and bacteria). As an extension of the single strain kinetic model, Lotka-Volterra model was formulated to explore the symbiotic relationship between algae and bacteria in a co-culture and the impact of the interactions on the COD/nutrients removal efficiency and growth dynamics. Supporting experiments were carried out in 6 parallel sets (3 sets with triplicates) with standalone algae (Chlorella vulgaris, CV), bacteria (activated sludge), and co-culture in real-time dairy liquid effluent in lab flasks and predicted values from modeling were validated against experimental findings. Statistical analysis confirms reasonably good agreement between the model predictions and experimental findings indicating a positive synergistic effect of the algae-bacterial co-culture on COD removal.

Molecular Latent Space Simulators for Distributed and Multimolecular Trajectories.

All atom molecular dynamics (MD) simulations offer a powerful tool for molecular modeling, but the short time steps required for numerical stability of the integrator place many interesting molecular events out of reach of unbiased simulations. The popular and powerful Markov state modeling (MSM) approach can extend these time scales by stitching together multiple short discontinuous trajectories into a single long-time kinetic model but necessitates a configurational coarse-graining of the phase space that entails a loss of spatial and temporal resolution and an exponential increase in complexity for multimolecular systems. Latent space simulators (LSS) present an alternative formalism that employs a dynamical, as opposed to configurational, coarse graining comprising three back-to-back learning problems to (i) identify the molecular system's slowest dynamical processes, (ii) propagate the microscopic system dynamics within this slow subspace, and (iii) generatively reconstruct the trajectory of the system within the molecular phase space. A trained LSS model can generate temporally and spatially continuous synthetic molecular trajectories at orders of magnitude lower cost than MD to improve sampling of rare transition events and metastable states to reduce statistical uncertainties in thermodynamic and kinetic observables. In this work, we extend the LSS formalism to short discontinuous training trajectories generated by distributed computing and to multimolecular systems without incurring exponential scaling in computational cost. First, we develop a distributed LSS model over thousands of short simulations of a 264-residue proteolysis-targeting chimera (PROTAC) complex to generate ultralong continuous trajectories that identify metastable states and collective variables to inform PROTAC therapeutic design and optimization. Second, we develop a multimolecular LSS architecture to generate physically realistic ultralong trajectories of DNA oligomers that can undergo both duplex hybridization and hairpin folding. These trajectories retain thermodynamic and kinetic characteristics of the training data while providing increased precision of folding populations and time scales across simulation temperature and ion concentration.

Choice of Inversion Time for Arterial Spin Labeling MRI in the U.S. POINTER Lifestyle Intervention Trial

AbstractBackgroundThe U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER) is a 2‐year randomized controlled trial to evaluate the effect of lifestyle interventions in older adults (60‐79 years). The POINTER Imaging ancillary study is collecting Arterial Spin Labeling (ASL) MRI data to map cerebral blood flow (CBF) and evaluate the effect of interventions in the perfusion imaging biomarker. The optimization of timing parameters is essential for robust and efficient acquisition of ASL MRI.MethodA subset (n=83; F/M=51/32; age=69.0±5.5) of POINTER Imaging participants at two imaging sites underwent two ASL MRI scans during the same baseline session. Two 3D Pulsed ASL were obtained with TI1 of 790ms and TI2 values of 2000ms or 2750ms, which provide the delay times (between labeling and imaging) of 1210ms or 1960ms. ASL images were quantified into a physiological unit of CBF, ml/100g/min, using a single compartment kinetic model. CBF maps from two scans were normalized into a standard space and a voxel‐wise paired t‐test was performed after site variations were harmonized and covariates (age and sex) were adjusted. The age and sex effects in the difference of CBF values between two scans were also examined using linear regression. To control false positives, clusters smaller than 41ml were removed based on a simulation with α=0.05.ResultThe CBF values in ASL MRI rely on the timing of image acquisition: only a fraction of label bolus arrives in the tissue with a short delay while images suffer from low signal due to the magnetization decay with a long delay. Figure 1 shows the regions that require a long delay time (red) or a short delay (blue). The difference in CBF is proportional to arterial transit time (ATT) and the analysis shows females have shorter ATT mainly in the peri‐Sylvian region (Figure 2). No cluster survived correction in the analysis of the aging effect.ConclusionThe acquisition of two CBF maps not only offers optimization of acquisition timing but provides an additional perfusion parameter, arterial transit time, which may be a potential biomarker of cerebrovascular pathophysiology.

Reclamation of aqueous waste solutions polluted with pharmaceutical and pesticide residues by biological-photocatalytic (solar) coupling in situ for agricultural reuse

This work focuses on the detoxification of aqueous waste solutions polluted with 24 emerging pollutants (13 pharmaceuticals and 11 pesticides) using a coupled biological-photocatalytic facility under natural sunlight for use in crop irrigation. The polluted wastewater (urban, agricultural, and industrial) processed by conventional wastewater treatment plants is in some cases insufficient to reach the degree of purity required. This concern is of particular interest, especially in areas where a low rainfall pattern provides insufficient water resources to meet the demands caused by agriculture, which requires increased reuse of wastewater effluents. For this purpose, polluted water was first subjected to biological treatment followed by a photocatalytic process using the tandem TiO2/Na2S2O8. Residues of pharmaceuticals and pesticides were isolated by solid phase extraction (SPE) and analysed by HPLC-QqQ-MS2. A notorious removal of pharmaceuticals was observed after biological treatment (average removal = 78%), except for diclofenac (31%) and carbamazepine (1%). In a contrary way, biodegradation of pesticides was inconspicuous (average removal = 48%) due to their recalcitrant properties. However, all compounds were rapidly degraded during the photocatalytic treatment because the fluence (H) required to obtain 90% degradation (H90) was<470 kJ m−2 for the most persistent pollutant (terbuthylazine). Single first order kinetic model satisfactorily explained the photooxidation of all micropollutants. Therefore, solar heterogeneous photocatalysis is presented as a promising technology to be incorporated as a tertiary process in wastewater treatment plants to remove biorecalcitrant pollutants. This implementation could be interesting especially in arid and semi-arid areas characterised by water scarcity but receiving many hours of sunshine per year, where a high percentage of reclaimed water is used for crop irrigation.

Indian coal pyrolysis behaviour and kinetics study using covalent bond information

Coal pyrolysis is a critical step of coal thermal conversion, impacting the downstream utilisation of coal, such as combustion and gasification. The understanding of this complex process plays a crucial role to predict the products, operation optimisation and reactor design. Indian coals typically have 25–52% (as received) ash yields. There is little knowledge about the pyrolysis kinetics of Indian high-ash coals, which are widely used in Indian power plants. In this work, five Indian thermal coals were investigated using thermogravimetric analysis (TGA) at heating rates varying from 278 to 773 K/min to provide pyrolysis kinetic data. The common single reaction kinetic model (Friedman) was used to analyse the pyrolysis behaviour of the coals and estimate the kinetic parameters. The activation energies ranged from 428.78 to 520 kJ/mol. Six Gaussian functions were used to analyse the DTG curves, each presenting a group of covalent bonds. The variation of pyrolysis behaviour is highly correlated to the distribution of aliphatic and aromatic carbon structures in the coal. The activation energy of coal pyrolysis can be estimated using the chemical bonds information obtained from the curve-fitting results of the DTG curve.

Aggregation Kinetics of Polysorbate 80/m-Cresol Solutions: A Small-Angle Neutron Scattering Study.

Polysorbate 80 (PS80), a nonionic surfactant used in pharmaceutical formulation, is known to be incompatible with m-cresol, an antimicrobial agent for multi-dose injectable formulations. This incompatibility results in increased turbidity caused by micelle aggregation progressing over weeks or longer, where storage temperature, ionic strength, and component concentration influence the aggregation kinetics. Small-angle neutron scattering (SANS) analysis of PS80/m-cresol solutions over a pharmaceutically relevant concentration range of each component reveals the cause of aggregation, the coalescence mechanism, and aggregate structure. PS80 solutions containing m-cresol concentrations below ≈2.0 mg/mL and above ≈4.5 mg/mL are kinetically stable and do not aggregate over a 50 h period. At 5 mg/mL of m-cresol, the mixture forms a kinetically stable microemulsion phase, despite being well below the aqueous solubility limit of m-cresol. Solutions containing intermediate m-cresol concentrations (2.0-4.5 mg/mL) are unstable, resulting in aggregation, coalescence, and eventual phase separation. In unstable solutions, two stages of aggregate growth (nucleation and power-law growth) are observed at m-cresol concentrations at or below ≈3.6 mg/mL. At higher m-cresol concentrations, aggregates experience a third stage of exponential growth. A single kinetic model is developed to explain the stages of aggregate growth observed in both kinetic mechanisms. This work establishes the phase diagram of PS80/m-cresol solution stability and identifies component concentrations necessary for producing stable formulations.

Total-Body PET Multiparametric Imaging of Cancer Using a Voxelwise Strategy of Compartmental Modeling.

Quantitative dynamic PET with compartmental modeling has the potential to enable multiparametric imaging and more accurate quantification than static PET imaging. Conventional methods for parametric imaging commonly use a single kinetic model for all image voxels and neglect the heterogeneity of physiologic models, which can work well for single-organ parametric imaging but may significantly compromise total-body parametric imaging on a scanner with a long axial field of view. In this paper, we evaluate the necessity of voxelwise compartmental modeling strategies, including time delay correction (TDC) and model selection, for total-body multiparametric imaging. Methods: Ten subjects (5 patients with metastatic cancer and 5 healthy volunteers) were scanned on a total-body PET/CT system after injection of 370 MBq of 18F-FDG. Dynamic data were acquired for 60 min. Total-body parametric imaging was performed using 2 approaches. One was the conventional method that uses a single irreversible 2-tissue-compartment model with and without TDC. The second approach selects the best kinetic model from 3 candidate models for individual voxels. The differences between the 2 approaches were evaluated for parametric imaging of microkinetic parameters and the 18F-FDG net influx rate, KiResults: TDC had a nonnegligible effect on kinetic quantification of various organs and lesions. The effect was larger in lesions with a higher blood volume. Parametric imaging of Ki with the standard 2-tissue-compartment model introduced vascular-region artifacts, which were overcome by the voxelwise model selection strategy. Conclusion: The time delay and appropriate kinetic model vary in different organs and lesions. Modeling of the time delay of the blood input function and model selection improved total-body multiparametric imaging.

Dynamic variations of dissolved organic matter from treated wastewater effluent in the receiving water: Photo- and bio-degradation kinetics and its environmental implications

Dissolved effluent organic matter (dEfOM) from wastewater treatment plants (WWTPs) is bound to encounter photo- and bio-degradation as discharged into the receiving water body. However, the comprehensive variations of dEfOM by photo- and bio-degradation are not well unveiled because of its compositional heterogeneity. In this work, dissolved organic carbon (DOC) concentrations, UV–Vis and fluorescent spectra combined with fluorescence regional integration (FRI) analysis were used to investigate the changes in bulk dEfOM and its fluorescent components during photo- and bio-degradation processes in the receiving water body. Results showed that 48.49%–69.62% of the discharged dEfOM was decomposed by ultra violet (UV)-irradiation and indigenous microbes, while the others (33%–45%) were recalcitrant and stable in the receiving water body. Specifically, the photo- and bio-degradation of chromophoric, fluorescent dEfOM and its components were found to follow the single or double exponential kinetic model, and the differences in photo- and bio-degradability of each components shifted its composition. Furthermore, results of bio-degradation after UV-irradiated dEfOM indicated that there was overlapping of photo- and bio-degradable fractions in dEfOM, and photoreactions could improve the self-production of natural organic matter in the receiving water body. These results could improve the understanding the fate of discharged dEfOM in the receiving water body, and we proposed some cost-effective strategies for discharging WWTPs effluent.

Towards a general kinetic model for the thermal oxidation of epoxy-diamine networks. Effect of the molecular mobility around the glass transition temperature

The kinetic model previously established for describing the thermal oxidation of polymethylenic substrates has been successfully generalized to a series of six epoxy-diamine networks (EPO-DA) characterized by very different glass transition temperatures. This model is derived from the so-called “closed-loop” mechanistic scheme which consists in a radical chain reaction initiated by the decomposition of hydroperoxides and propagating via the C-H bonds located in α of heteroatoms (N and O). The numerous model parameters were determined by applying a “step by step” procedure combining experiment and simulation. On the one hand, oxygen transport properties (i.e. coefficients of oxygen diffusion and solubility) were estimated from a compilation of literature data. On the other hand, rate constants and formation yields were determined by inverse solving method from the measurements of oxygen consumption and carbonyl build-up performed on six different EPO-DA networks between 25 and 200 °C and between 0.16 and 20 bars of oxygen partial pressure in our laboratory or in the literature. It was found that the molecular mobility mainly affects the rate constants of the elementary reactions involving the reactive species in the lowest concentration, i.e. peroxy radicals. In fact, the rate constant k6 of the apparent termination of peroxy radicals is reduced by about five orders of magnitude when passing from rubbery to glassy state due to the freezing of large amplitude cooperative molecular movements. In contrast, the rate constant k3 of the propagation of oxidation, involving peroxy radicals but also the polymer substrate, is only changed by one order of magnitude around the glass transition temperature. The introduction of the effect of molecular mobility into the Arrhenius laws of k6 and k3 allows building master curves and finally, proposing a single kinetic model for the whole family of EPO-DA networks.

Understanding How the Rate of C-H Bond Cleavage Affects Formate Oxidation Catalysis by a Mo-Dependent Formate Dehydrogenase.

Metal-dependent formate dehydrogenases (FDHs) catalyze the reversible conversion of formate into CO2, a proton, and two electrons. Kinetic studies of FDHs provide key insights into their mechanism of catalysis, relevant as a guide for the development of efficient electrocatalysts for formate oxidation as well as for CO2 capture and utilization. Here, we identify and explain the kinetic isotope effect (KIE) observed for the oxidation of formate and deuterioformate by the Mo-containing FDH from Escherichia coli using three different techniques: steady-state solution kinetic assays, protein film electrochemistry (PFE), and pre-steady-state stopped-flow methods. For each technique, the Mo center of FDH is reoxidized at a different rate following formate oxidation, significantly affecting the observed kinetic behavior and providing three different viewpoints on the KIE. Steady-state turnover in solution, using an artificial electron acceptor, is kinetically limited by diffusional intermolecular electron transfer, masking the KIE. In contrast, interfacial electron transfer in PFE is fast, lifting the electron-transfer rate limitation and manifesting a KIE of 2.44. Pre-steady-state analyses using stopped-flow spectroscopy revealed a KIE of 3 that can be assigned to the C–H bond cleavage step during formate oxidation. We formalize our understanding of FDH catalysis by fitting all the data to a single kinetic model, recreating the condition-dependent shift in rate-limitation of FDH catalysis between active-site chemical catalysis and regenerative electron transfer. Furthermore, our model predicts the steady-state and time-dependent concentrations of catalytic intermediates, providing a valuable framework for the design of future mechanistic experiments.

Study of pyrolysis kinetics and characterization using TG-FTIR, GC, and BET using high ash Indian sub-bituminous coal

ABSTRACT In the present investigation pyrolysis of high ash Indian coal is performed in N2 ambiance using thermo-gravimetric analyzer under non-isothermal heating condition. The presence of various functional groups in low-grade high ash sub-bituminous coal is characterized by an FTIR analyzer. The absorbance spectra are categorized into four distinct zones, and functional groups are detected by the technique of curve-fitting. The evolved volatiles are analyzed by in-line Fourier Transform Infrared Spectrometry (FTIR) to identify the presence of various gaseous species (H2O, CO2, CO, COS) during thermal degradation of coal. Three different kinetic models – single reaction kinetic model (SRKM), single reaction and the distributed activation energy model (DAEM) are employed to estimate the activation energy and pre-exponential factor. Further, the single reaction model is extended with a multi-stage kinetic model (MKM) at various temperature ranges to evaluate the kinetic constants and is found to fit the experimental findings well. The evolution of CO2 and CH4 significantly depends upon the presence of the carboxylic group and aliphatic chains in low-grade coal. The quantification of evolved volatiles is also performed in Gas Chromatographic (GC) Analyzer, and the results confirm the presence of individual gaseous species as detected in the FTIR analyzer. The residual char obtained at a higher heating rate during pyrolysis exhibits a gradual rise in the BET surface area, resulting in the formation of more porous char.

Adsorption phenomenon and kinetic mechanisms of Hg0 and HgCl2 by innovative composite sulfurized activated carbons

This study investigated the adsorption phenomenon and kinetic mechanisms of Hg0 and HgCl2 onto innovative composite sulfurized powdered activated carbons (PACs). The physiochemical properties of PACs were analyzed by energy dispersive spectrometer (EDS), specific surface area analyzer (SSAA), X-ray diffraction spectroscopy (XRD), and Fourier-transform infrared spectroscopy (FTIR). A two-stage adsorption phenomenon was observed and further fitted by Fick’s diffusion model, linear driving force approximate model (LDFA model), pseudo second order kinetic model (PSOKM), and Elovich model, respectively, to explore the kinetic mechanisms by two stages. Additionally, the resistances of external film diffusion and interior diffusion of the adsorption were explored as well. Finally, the isothermal equilibriums of the adsorption of Hg0 and HgCl2 were simulated by Langmuir and Temkin models, respectively. This study revealed that the adsorption of Hg0 or HgCl2 on the composite sulfurized PACs was attributed to chemisorption and favorable at elevated temperatures. The fitting level of single kinetic model was not high enough because the kinetic mechanisms for the two-stage adsorption process were different. Additionally, the kinetic mechanism for the adsorption in the same stage varied with different PACs due to the variation of the physiochemical properties of PACs. Finally, the results of both kinetic and thermodynamic simulations showed that the chemisorption of Hg0 or HgCl2 onto the composite sulfurized PACs can be simulated by Langmuir adsorption model.