Thermochemical Kinetics Research Articles

Thermochemical conversion characteristics and kinetics of Cu- and Mn-contaminated biomass using a continuous pyrolysis-combustion method

Thermochemical conversion characteristics and kinetics of Cu- and Mn-contaminated biomass using a continuous pyrolysis-combustion method

Thermo-chemical conversion kinetics of cannabinoid acids in hemp (Cannabis sativa L.) using pressurized liquid extraction

Cannabinoid decarboxylation via thermo-chemical conversion has the potential to reduce the cannabinoid degradation and evaporation due to short reaction time and use of water as the solvent. When combined with pressurized liquid extraction (PLE), thermo-chemical conversion can be performed as the first stage in the extraction procedure. PLE utilizes a closed system at elevated temperatures and pressure to increase the solvation power, which contributes to decreased viscosity and increased diffusion rate. With this new in-extraction decarboxylation approach there remain variables that need full understanding before up scaling from bench top to pilot or commercial scale. Herein, the thermo-chemical decarboxylation kinetics was studied for industrial hemp via PLE at different temperatures (80–160 °C) and reaction times (1–90 min). The reaction was found to be pseudo-first order. Model verification on CBD and CBG resulted in acceptable results; however, an anomaly in the minor cannabinoids suggests that cannabinoid concentration may influence model kinetics.

Noise-induced pattern evolution in thermochemical kinetics

Noise-induced pattern evolution in thermochemical kinetics

Thermo-Chemo-Mechanical Modeling of Residual Stress in Unidirectional Carbon Fiber-Reinforced Polymers during Manufacture.

The application of carbon fiber-reinforced composite materials in marine engineering is growing steadily. The mechanical properties of unbonded flexible risers using composite tensile armor wire are highly valued. However, the curing process generates a certain amount of internal residual stress. We present a detailed analysis of epoxy resin laminates to assess the impact of thermal, chemical, and mechanical effects on the curing stress and strain. An empirical model that correlates temperature and degree of cure was developed to precisely fit the elastic modulus data of the curing resin. The chemical kinetics of the epoxy resin system was characterized using differential scanning calorimetry (DSC), while the tensile relaxation modulus was determined through a dynamic mechanical analysis. The viscoelastic model was calibrated using the elastic modulus data of the cured resin combining temperature and degree of the curing (thermochemical kinetics) responses. Based on the principle of time-temperature superposition, the displacement factor and relaxation behavior of the material were also accurately captured by employing the same principle of time-temperature superposition. Utilizing the empirical model for degree of cure and modulus, we predicted micro-curing-induced strains in cured composite materials, which were then validated with experimental observations.

Insights into pyrolysis of ginger via TG-FTIR and Py-GC/MS analyses: Thermochemical behaviors, kinetics, evolved gas, and products

One of the key leverages for lessening the heavy reliance on fossil fuels is the conversion of non-food biomass into bioenergy and high value-added products. This study aimed to quantify the bioenergetic, emission, and biochar performances of ginger (Zb) pyrolysis. The main pyrolysis stage of Zb occurred in the range of 127–540 °C, releasing gaseous products, primarily CO2, in significant quantities between 200–600 °C. The dominant pyrolysis products were CO functional groups, accounting for 52.18–62.68% of the total. As the temperature rose, the primary pyrolysis products transitioned from ketones to benzene and its derivatives. Through the application of three model-free and three model-fitting methods, the most suitable mechanism identified for the main pyrolysis stage (0.2 < conversion degree < 0.7) was the three-dimensional diffusion (spherically symmetric) function, serving as an internal diffusion mechanism. Results of this study provide impactful and actionable insights into control over the generation of bioenergy potential, gas emissions, and value-added products via the Zb pyrolysis.

Thermochemical Characterization and Kinetics of Biomass, Municipal Plastic Waste, and Coal Blends and Their Potential for Energy Generation via Gasification

Thermochemical Characterization and Kinetics of Biomass, Municipal Plastic Waste, and Coal Blends and Their Potential for Energy Generation via Gasification

Short-range screened density matrix functional for proper descriptions of thermochemistry, thermochemical kinetics, nonbonded interactions, and singlet diradicals.

Common one-electron reduced density matrix (1-RDM) functionals that depend on Coulomb and exchange-only integrals tend to underestimate dynamic correlation, preventing reduced density matrix functional theory (RDMFT) from achieving comparable accuracy to density functional theory in main-group thermochemistry and thermochemical kinetics. The recently developed ωP22 functional introduces a semi-local density functional to screen the erroneous short-range portion of 1-RDM functionals without double-counting correlation, potentially providing a better treatment of dynamic correlation around equilibrium geometries. Herein, we systematically evaluate the performance of this functional model, which consists of two parameters, on main-group thermochemistry, thermochemical kinetics, nonbonded interactions, and more. Tests on atomization energies, vibrational frequencies, and reaction barriers reveal that the ωP22 functional model can reliably predict properties at equilibrium and slightly away from equilibrium geometries. In particular, it outperforms commonly used density functionals in the prediction of reaction barriers, nonbonded interactions, and singlet diradicals, thus enhancing the predictive power of RDMFT for routine calculations of thermochemistry and thermochemical kinetics around equilibrium geometries. Further development is needed in the future to refine short- and long-range approximations in the functional model in order to achieve an excellent description of properties both near and far from equilibrium geometries.

Mars2020 Entry Shock Layer Thermochemical Kinetics Examined by Megahertz-Rate Laser Absorption Spectroscopy

A mid-infrared laser absorption diagnostic was deployed to examine the evolution of thermophysical properties across a simulated Mars2020 shock layer in the Electric Arc Shock Tube (EAST) facility at NASA Ames. Rapid laser tuning techniques using bias-tee circuitry enabled quantitative temperature and number density measurements of CO2 and CO with microsecond resolution over a shock velocity range of 1.30–3.75 km/s. Two interband cascade lasers were utilized at 4.17 and 4.19 μm to resolve rovibrational CO2 lines spanning across J′′=58 to J′′=140 in the asymmetric stretch fundamental bands. In test cases with enough energy to dissociate CO2, a quantum cascade laser scanned multiple transitions of the CO fundamental bands near 4.98 μm. The results are compared to the Data Parallel Line Relaxation (DPLR) code and Lagrange shock tube analysis (LASTA) simulations of the shock layer. A numerical simulation of the compressible boundary layer is used to account for measurement sensitivities to this flow feature in the EAST facility. Temperature and species transients are compared to multiple chemical kinetic models. The laser absorption data presented in this work can be used to refine the models used to simulate the aerothermal environment encountered during Mars entry.

Thermochemical behavior and kinetics study of algae pyrolysis using iron oxide catalyst

AbstractThe shift in emphasis from fossil fuel‐derived energy to waste‐to‐energy technologies has widened the possibility for environmentally sustainable methods such as pyrolysis. Algae collected from local sources that grow in wastewater using atmospheric CO2 is a potential feedstock for pyrolysis. Thus, the work focuses on studying the pyrolysis reaction of macroalgae sourced from regional sources in the presence of Fe2O3 catalyst using the thermogravimetric analysis, followed by kinetic analysis using iso‐conversional methods of Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink methods, and model free Kissinger method. The kinetic model was developed using master plot method. XRD analysis of the Fe2O3 catalyst confirms the presence of the maghemite and hematite phases in the sample. Based on the conversion profile, DTG trend, and kinetic parameter variation, the overall pyrolysis process can be divided into three different stages of dissociation reactions. The apparent activation energy calculated from different models varies in the range: stage I (∼268 kJ/mol), stage II (∼261 kJ/mol), and stage III (∼328 kJ/mol), respectively. Master plot analysis of the kinetic data confirms the best fit of the nucleation model (A2) to experimental data in stage II. Further, the thermodynamic properties of the reaction, such as change in enthalpy (ΔH), change in Gibbs free energy (ΔG), and change in entropy (ΔS) range between 206 and 405 kJ/mol, 189 and 651 kJ/mol, −450 and 27 J/mol/K, respectively, corroborates the complexity of the reaction. Kinetics and thermodynamic property analysis of complex reactions like pyrolysis is essential for pilot plant design.

Experimental and theoretical study of heat and mass transfer in a continuous, vertical and coaxial pyrolysis reactor for high porosity biochar production

The development of a high porosity biochar production facility to meet an industrial need requires a detailed knowledge of the thermochemical phenomena of pyrolysis. The main challenge of this work is the production of biochar with a high porosity in large quantities, and producing a residual gas that can be used for drying biomass. Two complementary tools have been here developed and operated: a patented prototype and a designing numerical model. The model was developed in parallel with tests on the prototype and a characterisation phase of the various materials involved in the pyrolysis process in order to increase the correspondence between numerical model and experimental results. The model is used to predict, depending on the geometry chosen, the temperature in the pyrolysis zone, the heating rate and residence time corresponding to the applied biomass flow rate, as well as the biochar and gas mass yields.This study demonstrated the ability of the experimental plant to produce a high porosity biochar with a specific surface of 200m2.g-1 in the best case and a constant carbon content around 90% on dry basis due to the separation of the partial oxidation and pyrolysis zones. Following a material characterisation phase and a customisation of the parameters of the Arrhenius formalism adapted to pine bark, the numerical model shows a strong correspondence in terms of temperatures, biochar yield and thermochemical kinetics with the experimental observations from the prototype.

Canards Oscillations, Noise-Induced Splitting of Cycles and Transition to Chaos in Thermochemical Kinetics

We study how noise generates complex oscillatory regimes in the nonlinear thermochemical kinetics. In this study, the basic mathematical Zeldovich–Semenov model is used as a deterministic skeleton. We investigate the stochastic version of this model that takes into account multiplicative random fluctuations of temperature. In our study, we use direct numerical simulation of stochastic solutions with the subsequent statistical analysis of probability densities and Lyapunov exponents. In the parametric zone of Canard cycles, qualitative effects caused by random noise are identified and investigated. Stochastic P-bifurcations corresponding to noise-induced splitting of Canard oscillations are parametrically described. It is shown that such P-bifurcations are associated with splitting of both amplitudes and frequencies. Studying stochastic D-bifurcations, we localized the rather narrow parameter zone where transitions from order to chaos occur.

Performance improvement of a solar volumetric reactor with passive thermal management under different solar radiation conditions

To alleviate the effect of solar radiation fluctuation on the solar volumetric reactor, phase change material (PCM) is applied to buffer the temperature vibration and improve the stability of thermochemical reactions. In this work, we analyzed the heat flow and distribution characteristics of the conventional double-walled volumetric reactor filled with PCMs (SVR1). We then proposed a novel solar volumetric reactor design (SVR2) to solve the problems of local high temperature, slow charging-discharging rate, and fluctuating methane conversion in various radiation conditions. The heat and mass transfer model coupled with thermochemical reaction kinetics was established to compare the performance of SVR1 and SVR2 under steady state, heat charging-discharging mode, and actual solar radiation fluctuation, respectively. The results show that compared to SVR1, the maximum temperature of SVR2 decreases by 106.3 K, and the minimum methane conversion rate increases from 77.4% to 93.6% under natural solar radiation fluctuation.

Design of a multi-inlet solar thermochemical reactor for steam methane reforming with improved performance

Reactor structure design plays an important role in the performance of solar-thermal methane reforming reactors. Based on a conventional preheating reactor, this study proposed a cylindrical solar methane reforming reactor with multiple inlets to vary the temperature field distribution, which improved the temperature of the reaction region in the reactor, thereby improving the reactor performance. A multi-physical model that considers mass, momentum, species, energy conservation, as well as thermochemical reaction kinetics of methane reforming, was applied to numerically investigate the reactor performance and analyze the factors that affect performance improvement. It was found that compared with a conventional preheating reactor, the proposed cylindrical reactor with inner and external inlets for gas feeding enhanced heat recovery from the exhausted gas and provided a more suitable temperature field for the reaction in the reactor. Under different operating conditions, the methane conversion in the cylindrical reactor with multi-inlet increased by 9.5% to 19.1%, and the hydrogen production was enhanced by 12.1% to 40.3% in comparison with the conventional design, even though the total reaction catalyst volume was reduced.

Impact of stellar flares on the chemical composition and transmission spectra of gaseous exoplanets orbiting M dwarfs

Context. Stellar flares of active M dwarfs can affect the atmospheric composition of close-orbiting gas giants, and can result in time-dependent transmission spectra. Aims. We aim to examine the impact of a variety of flares, differing in energy, duration, and occurrence frequency, on the composition and transmission spectra of close-orbiting, tidally locked gaseous planets with climates dominated by equatorial superrotation. Methods. We used a series of pseudo-2D photo- and thermochemical kinetics models, which take advection by the equatorial jet stream into account, to simulate the neutral molecular composition of a gaseous planet (Teff = 800 K) that orbits a M dwarf during artificially constructed flare events. We then computed transmission spectra for the evening and morning limb. Results. We find that the upper regions (i.e. below 10 μbar) of the dayside and evening limb are heavily depleted in CH4 and NH3 up to several days after a flare event with a total radiative energy of 2 × 1033 erg. Molar fractions of C2H2 and HCN are enhanced up to a factor three on the nightside and morning limb after day-to-nightside advection of photodissociated CH4 and NH3. Methane depletion reduces transit depths by 100–300 parts per million (ppm) on the evening limb and C2H2 production increases the 14 μm feature up to 350 ppm on the morning limb. We find that repeated flaring drives the atmosphere to a composition that differs from its pre-flare distribution and that this translates to a permanent modification of the transmission spectrum. Conclusions. We show that single high-energy flares can affect the atmospheres of close-orbiting gas giants up to several days after the flare event, during which their transmission spectra are altered by several hundred ppm. Repeated flaring has important implications for future retrieval analyses of exoplanets around active stars, as the atmospheric composition and resulting spectral signatures substantially differ from models that do not include flaring.

Analysis of deterministic and stochastic oscillatory regimes in nonlinear thermochemical kinetics

In this paper, we analyze mechanisms of generation of complex oscillatory regimes in thermochemical reactors. In this study, a mathematical model of the continuous stirred tank reactor (CSTR) is used. Various scenarios of transitions between equilibrium and oscillatory regimes (quasiharmonic and spiking) are studied, and corresponding local and global bifurcations are discussed. It is shown how inevitably present weak noise in the temperature of CSTR can generate complex mixed‐mode oscillatory regimes in parameter ranges where the unforced initial deterministic model exhibits a stable equilibrium as an attractor. In the study of such noise‐induced excitement, direct numerical simulation and a new mathematical technique based on the stochastic sensitivity and confidence domain method are effectively used.

Highly efficient solar-driven CO2 reforming of methane via concave foam reactors

Solar-driven CO2 reforming of methane into value-added syngas is promising to solve global climate change and energy crisis problems simultaneously. However, there remains a large gap between currently reported solar-to-fuel efficiency and the theoretical limit. Here, we proposed an alternative way to enhance solar-driven CO2 reforming of methane performances by shaping foam reactors into concave geometries. By coupling solar radiation transport, fluid-solid coupling heat transfer, thermochemical kinetics, non-isothermal flow and mass transfer, a numerical analysis model is built. For the uniform planar reactor, multi-parameter optimization of porosity, pore diameter, and reactor length is conducted through a multi-island genetic algorithm, and the optimized solar-to-fuel efficiency achieves as high as 50.4%. By shaping planar foam reactors into parabolic concave geometries, the solar-to-fuel efficiency further increases 53.3%, the efficiency is increased by 21.97% compared with the reactor without multi-parameter optimization. This superior performance can be attributed to more uniform and appropriate temperature distribution, which makes major reactant components react within a higher temperature range above 1000 K. This work provides alternative routes for designing high-performance porous foam reactors and achieving highly efficient solar-driven CO2 reforming of methane.

Co-pyrolysis and co-combustion of orange peel and biomass blends: Kinetics, thermodynamic, and ANN application

Co-pyrolysis and co-combustion of orange peel, oil palm shell, and empty fruit bunch biomass with and without blends were investigated in a thermogravimetric analyzer (TGA) at 5, 10, 15, and 20 °C/min heating rate. The kinetic parameters were calculated using the model-free and model-fitting methods. Results showed that blending altered the thermogravimetry (TG) and derivative thermogravimetry (DTG) profiles and indicated the existence of multiple reactions. Biomass blends showed a strong synergetic effect, specifically during the char formation. The average activation energy was a function of conversion degree, and the values for the biomass blends were 82–120 kJ/mol compared to their parent biomass (64–111 kJ/mol). The trained artificial neural network model predicted the TG profiles of biomass blends with high R2 values (≥0.9), but the prediction accuracy was relatively poor for DTG profiles (≤0.8). Overall, mixing orange peel waste and oil palm biomass altered the thermo-chemical behavior and kinetics, which could develop a new dimension for future studies.

Benefits of Range-Separated Hybrid and Double-Hybrid Functionals for a Large and Diverse Data Set of Reaction Energies and Barrier Heights.

To better understand the thermochemical kinetics and mechanism of a specific chemical reaction, an accurate estimation of barrier heights (forward and reverse) and reaction energies is vital. Because of the large size of reactants and transition state structures involved in real-life mechanistic studies (e.g., enzymatically catalyzed reactions), density functional theory remains the workhorse for such calculations. In this paper, we have assessed the performance of 91 density functionals for modeling the reaction energies and barrier heights on a large and chemically diverse data set (BH9) composed of 449 organic chemistry reactions. We have shown that range-separated hybrid functionals perform better than the global hybrids for BH9 barrier heights and reaction energies. Except for the PBE-based range-separated nonempirical double hybrids, range separation of the exchange term helps improve the performance for barrier heights and reaction energies. The 16-parameter Berkeley double hybrid, ωB97M(2), performs remarkably well for both properties. However, our minimally empirical range-separated double hybrid functionals offer marginally better accuracy than ωB97M(2) for BH9 barrier heights and reaction energies.

A mini-chemical scheme with net reactions for 3D general circulation models

Context. Growing evidence has indicated that the global composition distribution plays an indisputable role in interpreting observational data. Three-dimensional general circulation models (GCMs) with a reliable treatment of chemistry and clouds are particularly crucial in preparing for upcoming observations. In attempts to achieve 3D chemistry-climate modeling, the challenge mainly lies in the expensive computing power required for treating a large number of chemical species and reactions. Aims. Motivated by the need for a robust and computationally efficient chemical scheme, we devise a mini-chemical network with a minimal number of species and reactions for H2-dominated atmospheres. Methods. We apply a novel technique to simplify the chemical network from a full kinetics model, VULCAN, by replacing a large number of intermediate reactions with net reactions. The number of chemical species is cut down from 67 to 12, with the major species of thermal and observational importance retained, including H2O, CH4, CO, CO2, C2H2, NH3, and HCN. The size of the total reactions is also greatly reduced, from ~800 to 20. We validated the mini-chemical scheme by verifying the temporal evolution and benchmarking the predicted compositions in four exoplanet atmospheres (GJ 1214b, GJ 436b, HD 189733b, and HD 209458b) against the full kinetics of VULCAN. Results. The mini-network reproduces the chemical timescales and composition distributions of the full kinetics well within an order of magnitude for the major species in the pressure range of 1 bar–0.1 mbar across various metallicities and carbon-to-oxygen (C/O) ratios. Conclusions. We have developed and validated a mini-chemical scheme using net reactions to significantly simplify a large chemical network. The small scale of the mini-chemical scheme permits simple use and fast computation, which is optimal for implementation in a 3D GCM or a retrieval framework. We focus on the thermochemical kinetics of net reactions in this paper and address photochemistry in a follow-up paper.

Study of co-pyrolysis kinetics, synergetic effects, and thermodynamics of coal and biomass blends

ABSTRACT The present work investigates the thermochemical conversion characteristics, reaction kinetics, and thermodynamic behavior of coal and biomass (Rice husk (RH)) blend pyrolysis in a TG reactor. Three different proportions of biomass (75, 50, and 25%) are blended with sub-bituminous Indian coal for the co-pyrolysis study. Pure coal and pure RH pyrolysis is characterized by three reaction stages, whereas the blended sample shows a four-stage thermal degradation reaction. A significant synergy is not found in the present study. Model-free techniques (FWO, KAS, and Starnik) are used to estimate the activation energy for various blending mixtures of the feed samples. The activation energy obtained for the equal mass ratio of coal and RH using the KAS, FWO, and Starnik methods is 61.45, 76.58, and 75.54 kJ/mol, respectively. The reaction order for coal: RH blend 25:75, 50:50, and 75:25 is estimated to be 4, 2.4, and 1.3, respectively. The favorable activation energy (Eα ) is found for the blending mixture of 50% coal and 50% RH. The positive value of ΔH indicates the endothermic nature of pyrolysis. The positive and negative values of ΔS indicate the complexity and nonspontaneous nature of coal and biomass blend pyrolysis. The average Entropy (ΔS) for an increasing % of coal is decreasing and the value comes to negative for 75% coal, indicating that thermal equilibrium is favorable for a higher % of coal.