Parallel Reaction Scheme Research Articles

Experimental and numerical investigation on the combustion behavior of densified wood: Differences among wood species and impact of char oxidation

Densified wood (DW) is a novel structural material with promissing application potential in construction industry due to its excellent mechanical performance. However, it could also be a disastrous fuel contributing to the development of fires. This work experimentally and numerically investigated the combustion behavior of DW. The differences among wood species (fir, pine and oak) and their char oxidation impacts are emphasized. The experimental results indicate that DW has a 44.7 K lower pyrolysis peak temperature on average, a 32.2 % lower peak mass loss rate, and a 8 % higher residual mass ratio than natural wood (NW) in N2 due to the delignification process. The hemicellulose and cellulose pyrolysis are endothermic in N2 but exothermic in air. Wood pyrolysis has an additional char oxidation reaction in air. The higher density of DW leads to longer times for ignition and flaming combustion. DW presents a higher heat release rate and average 4.7 MJ kg−1 higher effective heat of combustion of char. Two parallel pyrolysis reaction schemes based on ambiance are proposed, which well-predict the microscale characterizations but fail to represent the combustion behavior. An optimized mode was developed by adding a continuous char oxidation reaction to the N2 reaction scheme, which best predicts the combustion behaviors.

A Study of Parallel and Competitive Reaction Schemes in Kinetic Modeling of Plastic Pyrolysis.

Pyrolysis is a technology capable of harnessing energy from challenging-to-recycle plastics, thus mitigating the necessity for incineration or landfill disposal. To optimize the plastic pyrolysis process, reliable models for product yield prediction are imperative. This study endeavors to determine the suitability of lumped models, a widely used approach for modeling biomass and coal pyrolysis, in accurately estimating product yields in the context of plastic pyrolysis. To address this question, three lumped models with parallel and competitive reaction mechanisms were compared and fitted to experimental data collected across a broad temperature range. The aim is to identify which models can elucidate the most appropriate reaction pathway for the plastic pyrolysis process. The first model in this study assesses whether the commonly employed wood pyrolysis kinetic models can effectively fit the experimental data from plastic pyrolysis. Subsequently, the final two models introduce additional reactions into the pyrolysis process, prompting the authors to investigate the necessity of these supplementary reaction pathways for accurately predicting plastic pyrolysis outcomes. This investigation seeks to pinpoint the essential terms and discern which ones may be safely omitted from the models. The results of the study reveal that the model incorporating secondary tar reactions with gas, tar, and char is the most precise in predicting the products of plastic pyrolysis, surpassing all other combinations evaluated in this research.

TG-FTIR-MS and Py-GC/MS study on the pyrolysis characteristics and gas evolution behavior of forest duff

Temperate and boreal duff layers are well-distributed in forests and swamps across North America, Europe, and Asia. Despite its abundance, forest duff remains predominantly a fire load or forest redundancy rather than being developed as a biofuel. This study analyzed the pyrolysis characteristics and gas evolution behavior of forest duff at different heating rates and pyrolysis temperatures by coupling technique TG-FTIR-MS and Py-GC/MS. The pyrolysis behavior of forest duff was modeled by a parallel reaction scheme encompassing water evaporation and hemicellulose, cellulose, and lignin degradation. The calculated decomposition temperature ranges of hemicellulose, cellulose, and lignin were 180–400 °C, 220–540 °C, and 200–800 °C, respectively. The temperature zones for the primary mass conversion were 200–500 °C, from which the main functional groups and volatile products were C-O-C, CO, -CnH2n+1, -OH, and non-condensable gases (CO2, CO, and CH4). The carbohydrate and ketone yields peaked at 288 °C, whereas the maximum acid and ester yields were at 320 °C. The yields of furans, phenols, and aromatics increased with pyrolysis temperature, peaking at 622 °C. This study elucidates the influence of the heating rate and pyrolysis temperature on the selectivity of bioenergy and value-added chemicals from forest duff pyrolysis.

Comparison of parallel and in-series reaction schemes for kinetic modeling of VGO hydrocracking

An analysis of the reaction pathways developed during the hydrocracking of vacuum gas oil (VGO) was carried out using kinetic models based on parallel and in-series reaction schemes. A methodology that considers diverse crucial factors was applied for the estimation of kinetic parameters based on experimental data reported for VGO hydrocracking using a Ni-Mo-F3.6/ASA-Al2O3 catalyst in a temperature range of 380–410 °C and 10 mPa. The results of a kinetic model that considers parallel reaction pathways presented a better fit than kinetic parameters reported in the literature. While, models based on in-series reaction schemes indicated that some reaction pathways present considerable values of the kinetic coefficients. Every set of kinetic parameters was analyzed by sensitivity analysis, parity plot, and residual analysis to ensure that these values are the most suitable for the experimental data and reaction scheme used. Each kinetic model presented an adequate fit with the experimental data, obtaining values of AAE less than 5 %.

Pyrolysis characteristics and kinetic reaction parameters estimation of sassafras wood via thermogravimetric modeling calculation coupled with hybrid optimization methodology

The thermokinetics of sassafras wood pyrolysis were studied via thermogravimetric inverse modeling. Model-free combined with model-fitting methods were used to explore the optimal kinetics. Results indicate the obtained averaged activation energy and pre-exponential factor are 215.12 kJ/mol and 8.65 × 1017s−1, while the reaction model in charge is g(α) = [-ln(1-α)]1/3. In the following, Kissinger-based K–K method was adopted to separate the single reaction kinetics for each pseudo components. The analysis of K–K method provided the basis of the search range for each kinetic parameters. Finally, a new optimization algorithm was put forward, and the multi parallel reactions scheme incorporated into the Grey Wolf Optimization coupled with the Least Squared Fitting procedure was adopted to perform the optimization. The predicted MLR curves based on the simultaneously optimized kinetic parameters fit well with the experimental data not only at heating rates of 10, 20 and 30 K/min, but also at 5 and 40 K/min which were not used in the optimization. Such results indicated the excellent applicability of the optimized parameters and efficiency of the hybrid optimization procedure. Results from the present work could be a guidance for further biomass pyrolysis evaluation under more complex practical scenarios.

Thermal behavior and kinetic analysis of torrefied coconut fiber pyrolysis

The present work discusses the effect of mild torrefaction on coconut fiber pyrolysis kinetics. Firstly, it was evaluated by statistical experimental design (473–523 K, 15–45 min) in the fixed bed reactor. The results showed a reduction of volatile matter content and atomic ratios of hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C), and an increase in heating values. Secondly, the thermal decomposition was quantified by thermogravimetric analysis, in which the hemicellulose fraction was partially removed after torrefaction. Thirdly, the activation energy was determined by two isoconversional methods (single-step reaction) obtaining a variation from 184 to 238 kJ/mol. Fourthly, the kinetics of thermal decomposition of the torrefied sample was well-described (average deviation <3%) by three independent parallel reactions scheme assuming first-order reactions with activation energies of 99.5, 203.2 and 45.4 kJ/mol for hemicellulose, cellulose, and lignin, respectively. Finally, these kinetic parameters remained constant at different heating rates, providing more reliable information, which can be used to model the pyrolysis of coconut fiber in future works.

Devolatilization of Lippia origanoides bagasse. A kinetic study

Biomass is one of the most promising renewable energy sources; however, there is a lack of knowledge about the fuel properties of several biomasses. Lippia origanoides bagasse is a residue from the essential oil extraction process that could be used as fuel for the same process. With the aim of contributing to the knowledge of the fuel properties of that residual biomass, in this work, we carried out a kinetic study of its devolatilization using the Friedman method and the Independent Parallel Reactions Scheme. The results were verified by comparing the calculated and measured conversion curves. Although both methods show good agreement with the experimental results, the parallel reactions scheme provides a more detailed description of the process. The results are similar to those reported for other biomasses used as solid fuels, which indicates that the studied biomass could be a potential fuel for solid combustion systems.

Linear-Rate Reactions for the Thermal Devolatilization of Wheat Straw Based on Pseudo-Components

Thermogravimetric curves are measured in the nitrogen of wheat straw heated up to 773 K with rates between 5–20 K/min. A five-step (or component) parallel reaction scheme was developed for the interpretation of the weight loss characteristics, which makes use of the lumped volatile products based on the volatiles released by the pseudo-macrocomponents. The volumetric rates show the usual Arrhenius dependence on temperature and a linear dependence on the mass fraction of the lumped volatile products. The wheat straw devolatilization mechanism consists of a single step for pseud-ocellulose (activation energies of about 180 kJ/mol) and two steps for the pseudohemicellulose, also including extractives, (activation energies of about 101 and 136 kJ/mol) and pseudo-lignin (activation energies of 189 and 126 kJ/mol). For the first two pseudo-macrocomponents, the activation energies were lower than those obtained through a similar approach for beech wood, owing to the much higher content of alkalis acting as catalysts for the decomposition reactions. These occur at lower temperatures and show an enhanced overlap between the pseudo-components.

Pyrolysis and autoignition behaviors of oriented strand board under power-law radiation

This contribution addresses a multi-component high order parallel reaction scheme developed for pyrolysis of Oriented Strand Board (OSB), a typical engineered wood product, and its application in estimating autoignition behaviors under power-law heat flux (HF). Thermogravimetric analysis tests were conducted first to parameterize the pyrolysis model by model fitting method. Subsequently, gram-scale autoignition experiments, using five power-law HFs, were implemented in a newly designed apparatus. Thermodynamics of OSB were determined by inverse modelling combining an improved numerical model and the measured surface temperatures and mass loss rates under a moderate HF. The extrapolation capability of the developed model was verified by simulating the remaining experimental measurements at alternative heating scenarios. Both critical temperature and critical mass flux were employed in predicting autoignition times. The results show that the developed pyrolysis model accurately captures the measured mass and mass loss rate collected in TGA tests. Meanwhile, relatively good agreement was found between the simulated and measured surface temperatures and mass loss rates in bench-scale tests despite some minor divergence due to the observed cracks of generated char layer. Furthermore, the uncertainties of the attained kinetic and thermodynamic parameters were quantitatively evaluated by parametric study.

Catalytic oxidation of α-substituted cyclohexanone with steric hindrance to 6-oxohexanoic acid involved during the total synthesis of (+)-biotin

A homogeneous catalyst system FeCl3/DMSO was developed to catalyze α-substituted cyclohexanone to corresponding 6-oxohexanoic acid, an important intermediate involved during the synthesis of (+)-biotin. A highly efficient oxidation with 95.3 % of conversion and 88.0 % of selectivity was achieved using oxygen as the oxidant, which shows great advantage over the traditional peroxide method from industrial aspects. The detailed reaction process was evaluated to determine the parallel reactions scheme consisted by two oxidative reactions and one chlorination reaction. The [Fe(DMSO)4Cl2]Cl complex detected by UV–vis and FT-IR spectrometer was proposed as the active component during the catalytic process. The control experiments, capture of important intermediates, and kinetic study were performed, which showed the oxidation proceeded via the combination of ionic and radical pathway. The FeCl3/DMSO can be recycled with minor yield loss.

Performance comparison of WO3/SiO2 to ZSM-5 and γ-Al2O3 in the catalytic dehydration of methanol

The performance of ZSM-5, γ-Al2O3 and WO3/SiO2 catalysts for the dehydration of methanol was studied in a fixed bed reactor over a temperature range of 150 to 450 °C and at atmospheric pressure. A parallel reaction scheme for dehydration of methanol to dimethyl ether and methane was proposed for the WO3/SiO2 catalyst, and kinetic parameters for the two reactions were identified. The WO3/SiO2 catalyst was less active than both ZSM-5 and γ-Al2O3 for dehydration. At temperatures above 400 °C, experimental data indicated that WO3/SiO2 could be producing heavier hydrocarbons than the other catalysts. The gas product for γ-Al2O3 and WO3/SiO2 also contained ethylene and methane whereas the gas product for ZSM-5 contained propane and propylene. At higher temperatures ZSM-5 produced gasoline range hydrocarbons but a similar product was absent from all experiments conducted using the WO3/SiO2 and γ-Al2O3 catalysts. It has been shown that WO3/SiO2 can function as a methanol dehydration catalyst for the synthesis of dimethyl ether.

Coconut fiber pyrolysis decomposition kinetics applying single- and multi-step reaction models

This work aims to evaluate the thermal decomposition kinetics of coconut fiber in a thermogravimetric analyzer using four heating rates (5−20 °C/min) in nitrogen atmosphere. Three decomposition stages were identified (dehydration, pyrolysis, and carbonization) and the pyrolysis kinetic was performed considering two reaction models (single- and multi-step). In the first model, the apparent activation energy (94.5–210.8 kJ/mol) was determined using five isoconversional methods, and the reaction model representative was the three-dimensional diffusion model, f(α) = (3/2) (1-α)2/3 [1 - (1-α)1/3]−1, obtained using the master plots method. Through the linearization method of the conversion rate equation, the global activation energy found was 129.8 kJ/mol and the pre-exponential factor (log A) was 18.8 1/s. Due to the complexity of the biomass decomposition, the second model, three independent parallel reactions scheme (IPRS), was applied to describe each pseudo-component (hemicellulose, cellulose, and lignin). It was possible to obtain activation energies from 79.1–196.3 kJ/mol, pre-exponential factors (log A) from 3.1–15.0 1/s, volatilized fractions from 0.3 to 0.5, considering 1st and 2nd reaction orders. Finally, the modeling of conversions and conversion rates of both approaches was in a good agreement with the experimental data, however, the second model proved accuracy in describing the coconut fiber pyrolysis.

Pyrolysis kinetics study of biomass waste using Shuffled Complex Evolution algorithm

To better understand the biomass waste pyrolysis, a series of thermogravimetric experiments of basswood waste was performed at various heating rates in an inert atmosphere. Two model-free methods including Flynn-Wall-Ozawa (FWO) and Kissinger-Akahria-Sunose (KAS) and one model-fitting method named Coats-Redfern (CR) coupling Shuffled Complex Evolution (SCE) method were used in this work. The pyrolysis behaviors of hemicellulose and cellulose are responsible for the shoulder peak and the main peak. The evolution of activation energy supports the pyrolysis process divided into two regions. The 3D diffusion-Jander model (D3) can be used to describe the pyrolysis process of basswood waste. The optimized kinetic parameters estimated by the SCE algorithm coupled with a three-component parallel reaction scheme. The predicted values match the experimental data well, which shows that the optimized kinetic parameters are potentially promising in evaluating the biomass waste pyrolysis.

Thermal Analysis and Cone Calorimeter Study of Engineered Wood with an Emphasis on Fire Modelling

Engineered wood products (EWPs) are a group of materials having a very similar chemical composition but having different and non-uniform thermo-physical properties throughout their thickness. Such materials present a significant challenge from the pyrolysis modelling point of view. The main focus of the paper is to study and compare the differences between six EWPs—oriented strand board (OSB), plywood, particle board (PB), low-density (LDF), medium-density (MDF) and high-density (HDF) fibreboard—in terms of their pyrolysis and burning behaviour. Vertical density profiles (VDPs), thermal degradation behaviour, and burning behaviour were studied and compared. There is a considerable need for a consistent and systematic approach in estimating pyrolysis model complexity and model input parameters. A systematic method to determine the minimum level of the EWPs decomposition model complexity to reproduce the thermal degradation behaviour as measured using thermogravimetric analysis and using the set of parallel reactions was applied. EWPs were found to have similar thermal decomposition onset and range. Maximal decomposition rates were within 25%. OSB, PB, LDF and HDF decomposition can be modelled using three-step parallel reactions scheme, MDF using four parallel reactions. A set of parallel reactions cannot describe the thermal degradation behaviour of plywood. Cone calorimeter tests at heat flux levels of 20 kW/m2, 50 kW/m2 and $$80\, \hbox {kW}/\hbox {m}^{2}$$ revealed that influence of the different thermo-physical properties on time to ignition and time to peak heat release rate (HRR) is not significant except LDF and HDF due to their very different density. Peak HRR varies between EWPs, which is attributed primarily to charring and different thermo-physical properties of the EWPs char. EWPs gas phase combustion parameters for the fire models were derived.

Influence of torrefaction on the pyrolysis of energy cane

This work aims to study the influence of torrefaction on the energetic properties and thermal decomposition kinetics of energy cane Saccharum spontaneum. An experimental planning (473–533 K, 15–45 min) was realized, and the best conditions were 503 K and 45 min with mass yield above 70%, which led to the decrease in volatile matter and oxygen contents (15%) and the increase of 14.5% in the heating value. The thermogravimetric analysis (heating rates of 5, 10 and 15 K min−1) under inert atmosphere was used for the application of the independent parallel reactions scheme in the multistep model. The activation energies found were 111, 119, 197 and 51 kJ mol−1 for both raw and torrefied biomasses related to extractive, hemicellulose, cellulose, and lignin, respectively. Then, this approach provided reliable kinetic models capable of describing the thermal decomposition for both raw and torrefied samples (deviation < 3%).

Kinetic Analysis of Digestate Slow Pyrolysis with the Application of the Master-Plots Method and Independent Parallel Reactions Scheme.

The solid fraction obtained by mechanical separation of digestate from anaerobic digestion plants is an attractive feedstock for the pyrolysis process. Especially in the case of digestate obtained from biogas plants fed with energy crops, this can be considered a lignin rich residue. The aim of this study is to investigate the pyrolytic kinetic characteristics of solid digestate. The Starink model-free method has been used for the kinetic analysis of the pyrolysis process. The average Activation Energy value is about 204.1 kJ/mol, with a standard deviation of 25 kJ/mol, which corresponds to the 12% of the average value. The activation energy decreased along with the conversion degree. The variation range of the activation energy is about 99 kJ/mol, this means that the average value cannot be used to statistically represent the whole reaction. The Master-plots method was used for the determination of the kinetic model, obtaining that n-order was the most probable one. On the other hand, the process cannot be modeled with a single-step reaction. For this reason it has been used an independent parallel reactions scheme to model the complete process.

A further study of pyrolysis of carbon fibre-epoxy composite from hydrogen tank: Search optimization for kinetic parameters via a Shuffled Complex Evolution.

The study of hydrogen fuel cell vehicles is currently one of the popular research topics. However, a vital issue for hydrogen fuel cell vehicles is the hydrogen tank safety when hydrogen tank catch fires. In this paper, the carbon fibre-epoxy composite from hydrogen tank was investigated by thermogravimetric analysis. Thermogravimetric experiments were carried out at three heating rates (20, 30 and 40 K/min) in a nitrogen atmosphere. A two-step parallel reaction scheme was developed for the decomposition of the carbon-fibre epoxy composite based on the K-K method and previous studies. The kinetic reaction scheme was coupled to Shuffled Complex Evolution (SCE) method to obtain optimized kinetic parameters. The predicted values using the optimized kinetic parameters show a good agreement with the experimental data, which shows the potential promising application of the reaction scheme and optimized kinetic parameters of the carbon-fibre epoxy composite.

2D to 3D solvent mediated transformation of a photoreactive lanthanum MOF: a case of three parallel photo-cycloaddition reactions

Irradiation of the 3D MOF [La2(hex)3(H2O)4]3H2O, obtained upon dehydration of the layered compound [La2(hex)3(H2O)6]9H2O, gives two [2 + 2] and one [4 + 4] photocycloaddition reactions occurring in the parallel reaction scheme.

Kinetic Study on the Pyrolysis of Medium Density Fiberboard: Effects of Secondary Charring Reactions

The reaction models employed in the kinetic studies of biomass pyrolysis generally do not include the secondary charring reactions. The aim of this work is to propose an applicable kinetic model to characterize the pyrolysis mechanism of medium density fiberboard (MDF) and to evaluate the effects of secondary charring reactions on estimated products yields. The kinetic study for pyrolysis of MDF was performed by a thermogravimetric analyzer over a heating rate range from 10 to 40 °C/min in a nitrogen atmosphere. Four stages related to the degradation of resin, hemicellulose, cellulose, and lignin could be distinguished from the thermogravimetric analyses (TGA). Based on the four components and multi-component parallel reaction scheme, a kinetic model considering secondary charring reactions was proposed. A comparison model was also provided. An efficient optimization algorithm, differential evolution (DE), was coupled with the two models to determine the kinetic parameters. Comparisons of the results of the two models to experiment showed that the mass fraction (TG) and mass loss rate (DTG) calculated by the model considering secondary charring reactions were in better agreement with the experimental data. Furthermore, higher product yields than the experimental values will be obtained if secondary charring reactions were not considered in the kinetic study of MDF pyrolysis. On the contrary, with the consideration of secondary charring reactions, the estimated product yield had little error with the experimental data.

Drying and thermal decomposition kinetics of sugarcane straw by nonisothermal thermogravimetric analysis

This work aims the study of the drying (25 ± 3 °C–150 °C) and thermal decomposition (150–900 °C) of sugarcane straw kinetics in inert and oxidative atmospheres by nonisothermal thermogravimetry (TG) analysis using heating rates of 2.5, 5 and 10 °C/min. The drying kinetic analysis was carried out using five models, Lewis, Page, Henderson and Pabis, Midilli and Logaritmic, obtaining the activation energy of 1.25 kJ/mol, in which the Page’s model showed to be the most accurate description for both atmospheres. The thermal decomposition kinetics was analyzed through three consecutive reactions scheme, obtaining activation energies of 130, 200 and 56 kJ/mol as well as 200, 350 and 100 kJ/mol for both atmospheres, respectively. The consecutive reaction scheme allowed an excellent agreement between experimental and modeled data, providing a quality of fit similar than the obtained with independent parallel reactions scheme.