Search Results (104)

This work presents a one-dimensional (1D) model for simulating the behavior of an FCC riser reactor processing bio-oil. The FCC riser is modeled as a plug-flow reactor, where the bio-oil feed undergoes vaporization followed by catalytic cracking reactions. The bio-oil droplets are represented using a Lagrangian framework, which accounts for their movement and evaporation within the gas-solid flow field, enabling the assessment of droplet size impact on reactor performance. The cracking reactions are modeled using a four-lumped kinetic scheme, representing the conversion of bio-oil into gasoline, kerosene, gas, and coke. The resulting set of ordinary differential equations is solved using a stiff, second- to third-order solver. The simulation results are validated against experimental data from a full-scale FCC unit, demonstrating good agreement in terms of product yields. The findings indicate that heat exchange by radiation is negligible and that the Buchanan correlation best represents the heat transfer between the droplets and the catalyst particles/gas phase. Another significant observation is that droplet size, across a wide range, does not significantly affect conversion rates due to the bio-oil’s high vaporization heat. The proposed reduced-order model provides valuable insights into optimizing FCC riser reactors for bio-oil processing while avoiding the high computational costs of 3D CFD simulations. The model can be applied across multiple applications, provided the chemical reaction mechanism is known. Compared to full models such as CFD, this approach can reduce computational costs by thousands of computing hours. Full article

This article aimed to incorporate the coordinated construction of classifiers to develop a model for predicting the pyrolysis of loose biomass. For the purposes of application, the ground form of pine cone was used to perform the thermogravimetric analysis at heating rates of 5, 10, and 15 °C∙min⁻¹. The supervised machine learning technique was considered to estimate the kinetic parameters associated with the thermal decomposition of the material. Here, the integral as well as differential form of the isoconversional method was used along with the Kissinger method for the maximum reaction rate determination. Python (version 3.13.2), along with PyCharm (2024.3.3) as an integrated development environment (IDE), was used to develop code for the given problem. The TG model obtained through the boosting technique provided the best fitting for the experimental dataset of raw pine cone, with the root squared error varying from ±1.82 × 10⁻³ to ±1.84 × 10⁻³, whereas it was in the range of ±1.78 × 10⁻³ to ±1.83 × 10⁻³ for processed pine cone. Similarly, the activation energies derived through the trained models of Friedman, OFW, and KAS were 176 kJ-mol⁻¹, 151.60 kJ-mol⁻¹, and 142.04 kJ-mol⁻¹, respectively, for raw pine cone. It was seen that the boosting technique did not provide a reasonable fit if the number of features was increased in the kinetic models. This happened owing to an inability to maintain a tradeoff between variance and bias. Moreover, the multiclassification in pyrolysis kinetics through the proposed scheme was not able to capture the distribution pattern of target values of the differential method. With the increase in the heating rates, the noise level in the predicted model was also relatively increased. Full article

This study systematically investigates the dynamic evolution of chemical regimes in pulsed coaxial dielectric barrier discharge (DBD) plasma under atmospheric pressure using mass spectrometry. An innovative real-time mass spectrometric monitoring methodology was established, enabling the dynamic tracking of the formation and consumption processes of key reactive species such as ozone (O₃) and nitrogen oxides (NO_x). Energy density was the critical parameter governing the evolution of gaseous chemical components, with a quantitative elucidation of the regulatory mechanisms of air flow rate and control voltage on plasma chemical regime transition kinetics. Experimental results revealed significant parametric correlations: Under a constant control voltage of 140 V, increasing the gas flow rate from 0.5 to 5.5 L/min prolonged the transition duration from O₃-NO_x coexistence regime to a NO_x-dominant regime from 408 s to 1210 s. Conversely, at a fixed flow rate of 3.5 L/min, elevating the control voltage from 120 V to 140 V accelerated this transition, reducing the required time from 2367 s to 718 s. Parametric sensitivity analysis demonstrated that control voltage exerts approximately 3.3 times greater influence on transition kinetics than flow rate variation. Through comprehensive analysis of the formation and consumption mechanisms of N, O, O₃, and NO_x species, we established a complete plasma chemical reaction network. This scheme provides fundamental insights into reaction pathways while offering practical optimization strategies for DBD systems. For aerospace applications, this work holds particular significance by demonstrating that the identified control parameters can be directly applied to plasma-assisted treatment of propellant wastewater at launch sites, where the efficient removal of nitrogen-containing pollutants is crucial. These findings advance both the fundamental understanding of atmospheric-pressure plasma chemistry and the engineering applications of plasma-based environmental remediation technologies in aerospace operations. Full article

The conversion of n-hexane into its isomers is highly relevant in the petroleum refining industry due to its contribution to improving gasoline quality by increasing the octane number. This study presents a comparative analysis of eight reaction schemes for the C₆ series isomerization process. It was demonstrated that incorporating rigorous chemical equilibrium information, based on experimental data, yields virtually identical results across all schemes, enabling a detailed analysis. Five schemes were taken from the literature, two were modified to ensure linear independence, and one was proposed in this study under the same criteria. It was confirmed that using linearly independent schemes reduces the number of reactions without affecting model accuracy, facilitating its numerical solution. Each scheme was evaluated using simulations under industrial conditions with a kinetic model that includes 16 reactions. The results show predictions with average errors of 1.44% in reactor outlet temperature and 3.25% in molar flow rates. The kinetic constants for each reaction of the C6 series were generalized, ensuring their invariability regardless of the scheme used, allowing for their application to different schemes and eliminating the need for individualized tuning of the isomerization reactors in the process under study. Full article

Cu₂O, a narrow-bandgap semiconductor with visible light absorption capabilities, faces limitations in photocatalytic applications due to photocorrosion from hole self-oxidation and insufficient light absorption. In this work, a series of novel spherical Cu₂O/FePO₄ Z-scheme heterojunctions were successfully synthesized via self-assembly to overcome these challenges. The photocurrent, electrical impedance spectroscopy (EIS), and photoluminescence (PL) tests showed that Cu₂O/1.5FePO₄ (CF1.5) had excellent electron hole separation efficiency. Subsequently, photocatalytic degradation was utilized as a probing technique to further confirm the above conclusions, with the kinetic reaction constants of CF1.5 being 2.46 and 11.23 times higher than those of Cu₂O and FePO₄, respectively. After five cycles of experiments and XPS analysis, it was found that the content of Cu(I) in CF1.5 did not significantly decrease after the reaction, indicating that it has superior anti-photocorrosion performance compared to single Cu₂O, which is also due to the establishment of a Z-scheme heterojunction. Systematic studies using radical scavenging experiments and ESR tests identified ·OH and ·O₂⁻ as the main active species involved in photocatalysis. The formation of a Z-scheme heterojunction not only enhances the photocatalytic activity of the CF1.5 composite but also effectively suppresses the photocorrosion of Cu₂O, thereby offering a promising approach for enhancing anti-photocorrosion of Cu₂O. Full article

The literature devoted to the issue of a forced modified Van der Pol–Duffing oscillator with asymmetric potential is a major and varied way to represent nonlinear dissipative chemical dynamics. It is known that this model is based on the real reaction–kinetic scheme. In this paper, we suggest a novel class of oscillators that are appealing to users due to their numerous free parameters and asymmetric potential. The rationale for this is because an expanded model is put out that enables the investigation of both classical and more recent models that have been reported in the literature at a “higher energy level”. We present a few specific modules for examining these oscillators’ behavior. A much broader Web-based application for scientific computing will incorporate this as a key component. Probabilistic construction to offer possible control over the oscillations is also considered. Full article

Triplet–triplet transfer photochemical reactions are essential in many biological, chemical, and photonic applications. Here, the Pd-octaethylporphyrin sensitizer along with triplet–triplet annihilator (TTA) active 9,10-diphenylantracenes (DPA) and the related substituted variants in low concentrations were examined. A full experimental approach is presented for finding the necessary rate parameters with statistical standard deviation parameters. This was achieved by solving the pertinent non-analytical kinetic differential equation and fitting it to the experimental time-resolved photoluminescence of both slow fluorescence and sensitizer phosphorescence. The efficiency of the triplet–triplet energy transfer rate was found to be around 90% in THF but only around 75% in toluene. This appears to follow from the shorter lifetime of the sensitizer triplet in toluene. Moreover, the TTA transfer rate was on average more than 40% in THF toluene whereas a considerably lower value around 20–30% was found for toluene. This originated in an order of magnitude higher solvent quenching rate using toluene, based on the analysis of the delayed fluorescence decay traces. These are also higher than the statistically expected 1/9 TTA efficiency but in accordance with recent results in the literature, that attributed these high values to an inverse intersystem crossing process. In addition, quantum chemical calculations were carried out to reveal the pertinent excited triplet molecular orbitals of the lowest triplet excited state for a series of substituted DPAs, in comparison with the singlet ground state. Conclusively, these states distribute mainly in an anthracene ring in all compounds being in the range 1.64–1.65 eV above the ground state. The TTA efficiency was found to vary depending on the DPA annihilator substitution scheme and found to be smaller in THF. This is likely because the molecular framework over which the T1 excited molecular orbitals distribute is less sensitive for a longer lifetime of the annihilator triplet state. Full article

The structure and catalytic activity of Pd monolayers versus single Pd atoms were studied for the reverse water–gas shift reaction (rWGSR) at the anatase (101) and (001) facets for which Pd flat fragments have been observed experimentally. Thermodynamic and partial kinetic analyses of five steps of the rWGSR scheme were considered on the two facets. The projected density of states for the d-orbitals of single Pd atoms of the (101) facet of a-TiO₂ are compared to the ones for Pd atoms in both monolayers at (101) and (001) facets to interpret the different activity of Pd. The low activity of single Pd atoms is probably related to the (001) facet, while a Pd monolayer participates at the (101) facet due to its heterogeneity induced by the support. Full article

This study investigated the fast pyrolysis of biomass in fluidized-bed reactors using computational fluid dynamics (CFD) with an Eulerian multifluid approach. A detailed analysis was conducted on the influence of various modeling parameters, including hydrodynamic models, heat transfer correlations, and chemical kinetics, on the product yield. The simulation framework integrated 2D and 3D geometrical setups, with numerical experiments performed using OpenFOAM v11 and ANSYS Fluent v18.1 for cross-validation. While yield predictions exhibited limited sensitivity to drag and thermal models (with differences of less than 3% across configurations and computational codes), the results underline the paramount role of chemical kinetics in determining the distribution of bio-oil (TAR), biochar (CHAR), and syngas (GAS). Simplified kinetic schemes consistently underestimated TAR yields by up to 20% and overestimated CHAR and GAS yields compared to experimental data (which is shown for different biomass compositions and different operating conditions) and can be significantly improved by redefining the reaction scheme. Refined kinetic parameters improved TAR yield predictions to within 5% of experimental values while reducing discrepancies in GAS and CHAR outputs. These findings underscore the necessity of precise kinetic modeling to enhance the predictive accuracy of pyrolysis simulations. Full article

Accurate and selective monitoring of thiamine levels in multivitamin supplements is essential for preventing deficiencies and ensuring product quality. To achieve this, a Förster resonance energy transfer (FRET) system using carbon dots (CDs) as energy donors and citrate-stabilized silver nanoparticles (AgNPs) as energy acceptors was developed. The aqueous synthesis of AgNPs using microwave irradiation was optimized to obtain efficient plasmonic nanoparticles for FRET applications, targeting maximal absorbance intensity, stability, and wavelength alignment. Using a central composite orthogonal design (CCOD), the optimal conditions were identified as a 12.5 min microwave reaction time, a Ag molar ratio of 0.72, and a pH of 8.28. The FRET sensing scheme was applied for thiamine determination, where the vitamin’s presence impaired the FRET process, restoring CDs’ photoluminescence (PL) emission in a concentration-dependent manner. To mitigate interference from other vitamins, PL kinetic data and excitation–emission matrix (EEM) data were analyzed using unfolded partial least-squares (U-PLS) with the subsequent application of the residual bilinearization technique (RBL), achieving high sensitivity and specificity for thiamine detection. This method demonstrated its accuracy and robustness by attaining a determination coefficient (R²) of 0.952 and a relative error of prediction (REP%) of 11%. This novel method offers highly sensitive and interference-free thiamine detection, with significant potential for a wide range of analytical applications. Full article

Thermal decomposition (pyrolysis) of coal bottom ash (collected after lignite combustion in coal-fired power plant TEKO-B, Republic of Serbia) was investigated, using the simultaneous TG-DTG techniques in an inert atmosphere, at various heating rates. By using the XRD technique, it was found that the sample (CBA-TB) contains a large amount of anorthite, muscovite, and silica, as well as periclase and hematite, but in a smaller amount. Using a model-free kinetic approach, the complex nature of the process was successfully resolved. Thermodynamic analysis showed that the sample is characterized by dissociation reactions, which are endothermic with positive activation entropy changes, where spontaneity is achieved at high reaction temperatures. The model-based method showed the existence of a complex reaction scheme that includes two consecutive reaction steps and one single-step reaction, described by a variety of reaction models as nucleation/growth phase boundary-controlled, the second/n-th order chemical, and autocatalytic mechanisms. It was established that an anorthite I1 phase breakdown reaction into the incongruent melting product (CaO·Al₂O₃·2SiO₂) represents the rate-controlling step. Autocatalytic behavior is reflected through chromium-incorporated SiO₂ catalyst reaction, which leads to the formation of chromium(II) oxo-species. These catalytic centers are important in ethylene polymerization for converting light olefin gases into hydrocarbons. Adiabatic T_D24 prediction simulations of the process were also carried out. Based on safety analysis through validated kinetic parameters, it was concluded that the tested sample exhibits high thermal stability. Applied thermal treatment was successful in promoting positive changes in the physicochemical characteristics of starting material, enabling beneficial end-use of final products and reduction of potential environmental risks. Full article

This work presents a comprehensive model for lignocellulosic biomass pyrolysis, addressing kinetics, energy balances, and gas product composition with the aim of its application in wood combustion. The model consists of a two-stage global mechanism in which biomass initially reacts into tar, char, and light gases (non-condensable gases), which is followed by tar reacting into light gases and char. Experimental data from the literature are employed for determining Arrhenius kinetic parameters and key energy parameters, like tar and char heating values and the specific enthalpy of primary and secondary reactions. A methodology is introduced to derive correlations, allowing the model’s application to diverse biomass types. This work introduces several novel approaches. Firstly, a pyrolysis model that determines the composition of light gases by solving mass, species, and energy balances is developed, limiting the use of correlations from the literature only for tar and char elemental composition. The mass rate of light gases, tar, and char being produced is also determined. Secondly, kinetic parameters for primary and secondary reactions are determined following a Shafizadeh and Chin scheme but with a modified Arrhenius form dependent on $T^n$, significantly enhancing the accuracy of product composition prediction. Additionally, correlations for the enthalpies of reactions, both primary and secondary, are determined as a function of pyrolysis temperature. Primary reactions exhibit an overall endothermic behavior, while secondary reactions exhibit an overall exothermic behavior. Finally, the model is validated using cases reported in the literature, and results for light gases composition are presented. Full article

Due to growing interest in providing and storing sufficient renewable energies, energy generation from biomass is becoming increasingly important. Biomass gasification represents the process of converting biomass into hydrogen-rich syngas. A one-dimensional kinetic reactor model was developed to simulate biomass gasification processes as an alternative to cost-intensive experiments. The presented model stands out as it contains the additional value of universal use with different biomass types and a more comprehensive application due to its integration into the DWSIM process simulator. The model consists of mass and energy balances based on the kinetics of selected reactions. Two different reactor schemes are simulated: (1) a fixed bed reactor and (2) a fluidized bed reactor. The operating mode can be set as isothermal or non-isothermal. The model was programmed using Python and integrated into DWSIM. Depending on incoming mass flows (biomass, oxygen, steam), biomass type, reactor type, reactor dimensions, temperature, and pressure, the model predicts the mass flows of char, tar, hydrogen, carbon monoxide, carbon dioxide, methane, and water. Comparison with experimental data from the literature validates the results gained from our model. Full article

Hydrogen generation by photocatalytic water-splitting holds great promise for addressing the serious global energy and environmental crises, and has recently received significant attention from researchers. In this work, a method of assembling GeC/MXY (M = Zr, Hf; X, Y = S, Se) heterojunctions (HJs) by combining GeC and MXY monolayers (MLs) to construct direct Z-scheme photocatalytic systems is proposed. Based on first-principles calculations, we found that all the GeC/MXY HJs are stable van der Waals (vdW) HJs with indirect bandgaps. These HJs possess small bandgaps and exhibit strong light-absorption ability across a wide range. Furthermore, the built-in electric field (BIEF) around the heterointerface can accelerate photoinduced carrier separation. More interestingly, the suitable band edges of GeC/MXY HJs ensure sufficient kinetic potential to spontaneously accomplish water redox reactions under light irradiation. Overall, the strong light-harvesting ability, wide light-absorption range, small bandgaps, large heterointerfacial BIEFs, suitable band alignments, and carrier migration paths render GeC/MXY HJs highly efficient photocatalysts for overall water decomposition. Full article

The FitzHugh–Nagumo model has been used empirically to model certain types of neuronal activities. It is also a non-linear dynamical system applicable to chemical kinetics, population dynamics, epidemiology and pattern formation. In the literature, many approaches have been proposed to study its dynamics. In this paper, initially, we have employed cutting-edge tools from discrete dynamics for discretization and fixed points. It has been proven that an exact discrete scheme exists for this paradigm. This project also considers the phase space and integral surfaces of these evolutionary equations. In addition, it carries out a thorough symmetry analysis of this reaction diffusion system to find equivalent systems. Moreover, steady-state solutions are obtained using ansatzes for traveling wave solutions. The existence of infinite traveling wave solutions has also been proven. Yet again, this investigation establishes the potential of symmetry methods to unravel non-linearity. Finally, singular perturbation theory has been employed to obtain analytical approximations and to study stability in different parameter regimes. Full article