Reaction Mechanism Of Pyrolysis Research Articles

Chemical insight into thermal degradation, chemical kinetics, and thermodynamics behavior of sewage sludge through thermogravimetry and Fourier transform infrared analysis

Pyrolysis emerges as a promising path for sewage sludge (SS) management and value creation by producing compounds with enhanced utility. This study focuses on a comprehensive analysis of the thermal decomposition of SS using thermogravimetric analysis (TGA) and Fourier transform infrared spectrometry (FTIR). The TGA and FTIR were employed to evaluate the pyrolysis behavior, kinetics, and characteristics during pyrolysis of SS. The process revealed three distinct stages: 1st stage ranged between 30–185 °C with the removal of moisture, 2nd stage saw devolatilization of SS in the range of 185–595 °C, and the 3rd stage was mainly the formation of char in the temperature range of 595–900 °C. Pyrolysis kinetics, reaction mechanisms, and thermodynamic properties were extensively investigated at three different heating rates of 10, 20, and 30 °C /min. It was observed that with the temperature rise, the decomposition rate also increased rapidly, notably for the heating rate of 30 °C/min. Using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Tang methods, activation energies for SS pyrolysis were estimated for α in the range of 0.2–0.85, and the average value for that range was found to be 84.72, 92.29, 91.99, and 91.76 kJ/mol, respectively for different iso-conversional methods. The chemical kinetics analysis through Coats-Redfern methods identified that 3-D diffusion-reaction mechanisms have the highest coefficient of determination among the other models. Criado z-master plot emphasizes the prevalence of Avrami-Erofeev (A4) as the bestsuited reaction model in combination with α, providing a detailed examination that illuminates the complex processes and mechanisms inherent in the pyrolysis of sewage sludge.

Rapid pyrolysis mechanism and product distribution of coal model compounds containing typical C–O bonds

The structure and reactivity of coal is the core problem of coal chemistry, and solving it at the molecular level has been an international unsolved problem. The chemical similarity-based coal chemistry group elevates the study from the macroscopic to the molecular level. However, the previous free radical mechanism lacks experimental confirmation and theoretical computational support. Here, the pyrolysis products of model compounds are first utilized to predict pyrolysis. The hydrogen-donating solvent is then used as a radical trap to confirm the reaction. Subsequently, density functional theory calculations are utilized to aid in the validation. Finally, family components are utilized to demonstrate the universality of the free radical mechanism of coal pyrolysis. This work combines radical trapping with quantum chemical calculations to analyze the radical reaction mechanism of coal pyrolysis in depth at the molecular level. This will provide a theoretical basis for coal pyrolysis and clean and efficient utilization.

Pyrolysis of macadamia nut peel using multicomponent Gaussian kinetic modeling and ANN analysis

The physicochemical properties of macadamia nut peel (MNP) were explored based on pyrolysis characteristics, kinetics, thermodynamic parameters, reaction mechanism, and artificial neural network (ANN) application to evaluate its suitability and potential for pyrolytic conversion into bioenergy products. Pyrolysis experiments of MNP were performed using a thermogravimetric analyzer in a nitrogen atmosphere. The thermal degradation process of MNP can be successfully modeled into pseudo hemicellulose (PS–H1), cellulose (PS–C2), and lignin (PS-L3) using a multicomponent Gaussian kinetic model with high correlation coefficient (R2 > 0.99). The average apparent activation energy was 179.28 kJ/mol for PS-H1, 192.31 kJ/mol for PS-C2, and 129.42 kJ/mol for PS-L3 using Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink, and Tang four model-free methods. Master plots method was used to determine the reaction mechanism models of three pseudo components, and the pyrolysis progress can be described well using order-based and nucleation mechanism models. The thermal degradation behaviors of MNP were predicted using artificial neural network, and the best artificial neural network prediction model was ANN (3*15*1). Based on the physicochemical properties, pyrolysis characteristics, kinetics, thermodynamic parameters, reaction mechanism and ANN prediction model, MNP is suitable for pyrolytic conversion into bioenergy products.

Understanding cellulose pyrolysis via ab initio deep learning potential field

Comprehensive and dynamic studies of cellulose pyrolysis reaction mechanisms are crucial in designing experiments and processes with enhanced safety, efficiency, and sustainability. The details of the pyrolysis mechanism are not readily available from experiments but can be better described via molecular dynamics (MD) simulations. However, the large size of cellulose molecules challenges accurate ab initio MD simulations, while existing reactive force field parameters lack precision. In this work, precise ab initio deep learning potentials field (DPLF) are developed and applied in MD simulations to facilitate the study of cellulose pyrolysis mechanisms. The formation mechanism and production rate of both valuable and greenhouse products from cellulose at temperatures larger than 1073 K are comprehensively described. This study underscores the critical role of advanced simulation techniques, particularly DLPF, in achieving efficient and accurate understanding of cellulose pyrolysis mechanisms, thus promoting wider industrial applications.

Study on the Influence of Porous Gel on Coal Pyrolysis Performance Based on Experiments and Molecular Simulation

ABSTRACT Studying the kinetics of pyrolysis in pure coals and mixed coals (coals treated with porous gel) holds immense significance in effectively preventing and controlling the spontaneous combustion occurrences in coal. Firstly, porous gel materials were prepared based on physical mixing and chemical crosslinking reaction. Then, based on the thermogravimetric analysis method, the pyrolysis mechanism of porous gel in coal was studied using Flynn-Wall-Ozawa(FWO), Kissinger-Akahira-Sunose(KAS) and Coats Redfern models. Determine the mechanism of coal pyrolysis reaction using the Reaxx FF MD reaction mechanics model. Finally, the inhibition mechanism of porous gel on coal is analyzed through leading temperature rise experiment. The main reaction mechanisms of coal pyrolysis are the diffusion model in the low-conversion-rate range (D4), the R2 and R3 in the high-conversion-rate range, and the Avrami erofeev model (A2, A3). The molecular simulation results indicate that increasing the heating rate can accelerate the rate of coke cracking.

In-situ reaction mechanism of vacuum pyrolysis for extracting valuable materials from waste excess biological sludge

The large amount of biomass components contained in waste excess biological sludge make it a highly potential energy provider. The effective separation of organic and inorganic substances in waste biological sludge is crucial for the resource reuse of sludge. In this study, the vacuum pyrolysis technology has been developed to treat waste excess biological sludge. The product yields were 51.53 wt% residue, 48.47 wt% pyrolysis oil, and pyrolysis gas, respectively. Thermogravimetric analysis showed that at 10, 20, and 30 K∙min−1, the E value slightly changed from 11.02 to 12.08 kJ∙mol−1, with corresponding A values of 0.24, 0.46, and 0.74, respectively. High heating rate leads to an increase in reaction rate, but is not conducive to the effective separation of organic compounds. Based on in-situ analysis of vacuum temperature changes, FTIR and XRD indicate that organic functional groups fracture regularly, but inorganic substances do not show significant changes. XPS elemental flow analysis shows that P and S are enriched in residue after reaction, and Mg and Zn may enter the pyrolysis oil and gas. We also studied quality balance and cost evaluation. The total cost of pure air pyrolysis for 1 m3 dry sludge is approximately $143.375. In summary, the practical application of sludge vacuum pyrolysis technology still faces significant challenges, and this study provides support for improving understanding of the vacuum pyrolysis process of waste excess biological sludge.

Effect of microwave pretreatment on pyrolysis of chili straw: thermodynamics, activation energy, and solid reaction mechanism.

In this work, chili straw (CS) was pretreated by microwave at 250 W, 406 W, 567 W, and 700 W. The pyrolysis characteristics, kinetics, thermodynamic parameters, and solid reaction mechanism were investigated. The maximum weight loss rate increases from - 24.72%/°C at P0 to - 28.01%/°C at P700 after microwave pretreatment, and the residual mass decreases from 31.81 at P0 to 26.71% at P700. In addition, microwave pretreatment leads to a decrease in activation energy, ∆H, and ∆G at the end of the pyrolysis (α > 0.7). The solid reaction mechanism of CS pyrolysis is revealed by the Z-master plots method, with un-pretreated CS conforming to P2, D4, F3/2, and F3, respectively. Microwave pretreatment changes the solid reaction mechanism mainly in the third stage, when α = 0.8, the mechanism function changes from f(α) = (1 - α)3 at P0 to f(α) = (1 - α) at P700, and the number of reaction order is reduced, which is profitable for CS pyrolysis.

A comprehensive study of facemasks pyrolysis using Py-GC/MS, kinetic analysis and ANN modeling

The thermo-kinetics of pyrolysis and product distribution of facemasks, as a blend of filter layers were explored in this study. Pyrolysis products were studied using Py-GC/MS at 550 °C for 30 s, resulting in predominantly aliphatic hydrocarbons (82.6%): alkanes (34.5%) and alkenes (48.1%). Notable gaseous products identified include propene, 2-methyl pentane, and 2,3-dimethyl-1-pentene, while the dominant species among the cycloalkanes were 1,2,3,5-tetraisopropylcyclohexane and 1,3,5-trimethylcyclohexane. Furthermore, we developed a chemical reaction mechanism to describe the main products formed during pyrolysis. Besides, the activation energy was predicted using model-free methods namely FR (214.2 kJ/mol), KAS (200.5 kJ/mol), and FWO (200.6 kJ/mol), as a function of conversion. The Coats – Redfern (CR) model-fitting method revealed that the pyrolysis reaction mechanism within the temperature range of 400 – 550 °C (pyrolysis active zone) belonged to one-dimensional diffusion and contracting cylinder model. The reliability of these results was further affirmed using the Criado method, showing agreement between the experimental and theoretical master plots. The thermodynamic parameters for facemask degradation indicated an endothermic process (ΔH = 205.5 kJ/mol, ΔG = 182.4 kJ/mol, and ΔS = 0.03 kJ/mol·K). To predict weight loss during facemask pyrolysis, we developed an artificial neural network (ANN) model that considered heating rate and temperature as inputs. The most efficient model structure involved an ANN with 2 input layers (2 neurons each), 2 hidden layers (each with 10 neurons), and an output layer (1 neuron). This study is crucial for advancing our understanding of the theoretical aspects of polymeric waste pyrolysis.

Kinetic reaction mechanism of lignocellulosic biomass oxidative pyrolysis based on combined kinetics

The kinetics knowledge of lignocellulosic biomass decomposition is essential to develop efficient thermochemical conversion technology. However, the simplification of reaction mechanisms in existing oxidative pyrolysis studies largely compromises the application of kinetic models. To explore more exact kinetic parameters and reaction mechanism of lignocellulosic biomass oxidative pyrolysis, an updated oxidative pyrolysis kinetic model (seven-step reaction combined kinetics model) coupled with an optimization algorithm is proposed. Based on a series of thermogravimetric experiments in an air atmosphere, the extra oxidative pyrolysis kinetic parameters are obtained by the Shuffled Complex Evolution method. The proposed kinetic model is validated based on the degradation process of each component (hemicellulose, cellulose, and lignin). Furthermore, the obtained kinetic parameters are applied to predict the oxidative pyrolysis behavior, and the predicted mass loss rate is in good agreement with the experimental data. Eventually, according to the key combined kinetics parameters, it is found that the oxidative pyrolysis mechanisms of hemicellulose, cellulose, and lignin correspond to the power law, nucleation & growth, and chemical reaction order, respectively, while the combustion of char corresponds to the reaction order mechanism.

Characterization of pyrolysis behavior for rigid polyurethane foam wastes with different densities through TGA-FTIR-DSC-MCC and Hill Climbing Optimization methods

Pyrolysis technology is one of the most effective thermal treatment methods recycling rigid polyurethane foam (RPUF) waste. To optimize pyrolysis recovery efficiency, quantifying the pyrolysis reaction kinetics and the heat required for the thermal treatment process is critical. This work focuses on establishing a systematic methodology to quantify pyrolysis reaction kinetics and thermodynamics for RPUF waste. RPUF waste with two different densities (RPUFρ100 and RPUFρ45) were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) under anaerobic atmosphere to measure mass and heat flow information. The obtained data were inversely analyzed using a numerical framework known as ThermaKin2Ds. Pyrolysis reaction mechanisms with four and three consecutive first-order reactions were developed to reproduce the TGA data for RPUFρ100 and RPUFρ45, respectively. The Hill Climbing Optimization Algorithm was employed to adjust the reaction kinetics for an improved agreement between the ThermaKin2Ds-reproduced and experimental data. Based on the heat flow data from DSC tests, the specific heat capacity of each condensed-phase component was determined by using the inverse modeling method. Additionally, the micro-scale combustion calorimeter was used to generate the heat release data that served as the target data for inversely determining the heats of complete combustion, hc, of each pyrolyzate. The established pyrolysis reaction models was further validated by predicting the TGA results collected under different external heating conditions. Subsequently, the generated combustion-inhibiting gases (CO2) and combustion-promoting gases (olefins, alkanes, carboxylic acids, etc.) were characterized through TGA coupled with Fourier-transform infrared spectroscopy (TG-FTIR). This allowed us to elucidate the gas-phase combustion phenomena observed in MCC experiments. This work provides a core set of parameters for optimizing the thermal treatment conditions of RPUF waste.

Pyrolysis and combustion reaction mechanisms of methyl palmitate with ReaxFF-MD method

As a substitute for fossil fuel, methyl palmitate (C17H34O2) has important scientific and practical significance to study its pyrolysis and combustion mechanism. In this paper, the ReaxFF-MD method is used to research the reaction mechanism and main products of C17H34O2. The effects of temperature and O2 on the decomposition, main products and reaction paths of C17H34O2 are analyzed to determine its reaction mechanism. The results show that the reaction activation energies of C17H34O2 in pyrolysis and combustion are 201.76 kJ/mol and 139.07 kJ/mol, respectively. The effect of temperature on C17H34O2 is greater than O2 on C17H34O2 at higher temperature. The basic reaction paths for the initial decomposition of C17H34O2 is that the CC, CO, and CH bonds are broken into smaller intermediates. In addition, the detailed distribution and generation paths of the main products C2H4, H2, H2O, CH2O, and so on are depicted to construct the reaction mechanism of C17H34O2.

Experimental and theoretical study of cyclopropanated fuel exo,exo-Tetracyclo[3.3.1.02,4.06,8]nonane pyrolysis in a jet-stirred reactor

Exo,exo-Tetracyclo[3.3.1.02,4.06,8]nonane (exo-TCN), a kind of cyclopropanated fuel with high tension three-membered ring, which has the characteristics of high density, high net heat of combustion and good low-temperature performance, is a potential high-energy-density liquid fuel. To deeply understand its combustion behavior, and lay a foundation for practical application, detailed experimental and theoretical study is necessary. The pyrolysis of exo-TCN was investigated in a jet-stirred reactor at a temperature range of 500–1010 K under atmospheric pressure with a residence time of 2 s. 54 products and intermediates ranging from m/z = 2–204 were identified and quantified by synchrotron vacuum ultraviolet photoionization mass spectrometry and online gas chromatography, the major products were hydrogen, ethylene, benzene, methane, propene, toluene and styrene. The potential energy surfaces of exo-TCN unimolecular decomposition reactions were calculated by quantum chemistry at CBS-QB3 level. It is found that the pyrolysis of exo-TCN experiences three stages. In the first stage, exo-TCN isomerizes into Tricyclo[3.3.1.02,4]non-6-ene (TCN-6) by ring expansion of the three-membered ring. In the second stage, TCN-6 generates two main isomers through ring expansion reactions, and decomposes into pyrolysis products. The third stage is the secondary reaction of the intermediate products. Finally, combined with the experimental results and theoretical calculation, the possible reaction mechanism of exo-TCN pyrolysis was proposed, and the related reaction rate constants were calculated.

Pyrolysis characteristics and reaction mechanism of intumescent fire-retardant coating with thermogravimetry/Fourier transform infrared analysis

A research of intumescent fire-retardant coating (IFRC) pyrolysis characteristics and reaction mechanism was conducted by thermogravimetric analysis coupled with Fourier transform infrared spectrometry analysis at various heating rates. The results demonstrate that the pyrolysis process of IFRC could be separated into two stages. In stage I, which occurs within the temperature range of 300–800 K, there is a mass loss of 8.5 %. The main gases released during this stage are NH3 and CH4. Moving on to stage II, which takes place within the temperature range of 800–1200 K, there is a significant mass loss of 42.9 %. The main gases released during this stage are CO2 and H2O. Through the use of FTIR spectra, the production amount of main four components ranked as follows: CO2 > H2O > CH4 > NH3. Especially, the reaction expressions were further speculated and proposed. Subsequently, the two aforementioned stages were utilized based on both model-free and model-fitting methods to ascertain the possible reaction mechanism.

Pyrolysis kinetics and thermodynamic behavior of pseudo components of raw and torrefied maple wood

ABSTRACT In this work, pyrolysis kinetics and thermodynamic behavior of pseudo components (PCs) of raw and torrefied maple wood (MW) were studied. The MW torrefaction experiments were conducted at 240°C and the pyrolysis process was performed under three distinct heating rates. Through the deconvolution procedure, three PCs, i.e. pseudo-hemicellulose (PC-HC), pseudo-cellulose (PC-CL), and pseudo-lignin (PC-LG), were identified. The activation energy (E α ) of PCs were evaluated using the Starink method, and the pyrolysis reaction mechanisms were analyzed using the Criado’s master plot method. Furthermore, three thermodynamic parameters were also calculated and discussed. Results showed that after torrefaction, the PC-HC content dropped from 47.30% to 7.90%, while the PC-CL and PC-LG contents increased from 33.67% to 55.72% and from 19.03% to 36.38%, respectively. The average E α of raw MW PC-HC, PC-CL and PC-LG were 114.56, 117.12 and 116.02 kJ/mol, respectively, whereas they were 92.86, 103.82 and 159.26 kJ/mol for torrefied PCs, respectively. The master plot results suggested that the pyrolysis of MW PCs involved different order-based models. In addition, the thermodynamic analysis revealed that the torrefied PC-HC required slightly less heat energy during pyrolysis. All these observations can be conducive to better understand the pyrolysis mechanisms of raw and torrefied MW PCs.

Thermal degradation properties, kinetic, thermodynamic and reaction mechanism of pyrolysis of biomass shells: pistachio, almond, walnut and hazelnut as bioenergy potential

Thermal degradation properties, kinetic, thermodynamic and reaction mechanism of pyrolysis of biomass shells: pistachio, almond, walnut and hazelnut as bioenergy potential

Stepped pyrolysis: A novel approach for enhanced adsorbency and carbon in Pigeon pea stalk char

This article introduces a novel technique, stepped pyrolysis, for thermal degradation of biomass. The differential thermogram (DTG) of pigeon pea stalk was deconvoluted into their intrinsic bioconstituents and these deconvoluted peaks were used to decide the different stages or steps to finalize the thermal protocol to be executed for stepped pyrolysis. The stepped pyrolysis and traditional pyrolysis of pigeon pea stalk were conducted and the characterisation of outputs was done. The obtained result for the char produced by the stepped pyrolysis method showed a reduction of 5% in the volatile matter and an increment of 5% in fixed carbon content, over the product of traditional pyrolysis. The stepped pyrolysis increased the iodine number by 17% while reducing the methylene blue values by 31% as compared to the traditional pyrolysis. A significant reduction in activation energy by 21% for FWO, 18% for KAS, and 26% for Starink methods were recorded for stepped, over traditional pyrolysis. The pyrolysis reaction mechanism of stepped and traditional pyrolysis methods followed the second-order (F2) and two-dimensional diffusion model (D2). The stepped pyrolysis method produced a better quality product with more micropores and carbon-rich char than the traditional method.

Pyrolysis characteristics, reaction mechanisms and gas emission of organic fireproof plugging materials by TG-FTIR-MS

Pyrolysis characteristics, reaction mechanisms and gas emission of organic fireproof plugging materials by TG-FTIR-MS

Investigations into extra-heavy crude oil pyrolysis under non-isothermal conditions: thermal characteristics, kinetics, and thermodynamic parameters

This study comprehensively investigated the pyrolysis characteristics, kinetics, and thermodynamic parameters of extra-heavy oil through thermogravimetry (TG) experiments. The TG results revealed a two-stage pyrolysis process, consisting of light-temperature pyrolysis (LTP) and high-temperature pyrolysis (HTP), in which the HTP was the primary mass loss interval, contributing roughly 53.5% of mass loss from 370 to 500 °C. The pyrolysis kinetics were obtained using Ozawa-Flynn-Wall (OFW) and Friedman methods. The results revealed that the main pyrolysis reaction mechanism shifted from volatilization to thermal cracking while the conversion degree exceeded 0.35. The thermodynamic parameters, including enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS), were also calculated. The thermodynamic features showed that the pyrolysis process absorbed large amounts of energy to change the main reaction mechanism in the range of α = 0.4–0.6, and altered from an organized to a disordered state due to the disruption of intramolecular structure induced by the formation of coke while the conversion degree exceeded 0.6. These findings have the potential to offer a thorough comprehension of the pyrolysis mechanism of extra-heavy oil.

Comprehensive investigation on fast pyrolysis of waste Lotus shells to produce valuable products: Pyrolysis characteristics, reaction mechanism and economic analysis

Lotus shells (LS) represent an abundant, underutilized renewable resource with significant potential for producing bio-based fuels and chemicals. Pyrolysis emerges as an effective means to maximize the value derived from LS waste. This study assessed the behavior, kinetics of LS pyrolysis for bioenergy production through thermogravimetric analysis (TGA), model-free and model methods. The product distribution resulting from LS fast pyrolysis and the physicochemical properties of the derived products were comprehensively investigated. A plausible reaction mechanism for LS pyrolysis was proposed, followed by an estimation of the associated costs for bioenergy production through pyrolysis. The activation energy (Eα) for LS calculated through Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman (FR) methods was 197.36 kJ/mol, 193.66 kJ/mol, and 197.16 kJ/mol, respectively. The kinetic reaction model for LS pyrolysis was represented by the equation f(α) = α−26.59(1-α)12.35[-ln(1-α)]−27.26, indicating the dominance of a diffusion model and nucleation mechanism in the LS pyrolysis process. Notably, the fast pyrolysis bio-oil derived from LS mainly comprised phenols (34.73 % at 300 °C), acids (42.33 % at 600 °C), and nitrogenous compounds (27.40 % at 800 °C), and the gaseous products primarily consisted of H2, CH4, CxHy, CO, and CO2. Biochar derived from LS exhibited abundant functional groups and mesoporous structure, and its moderate C/N ratio and low H/C ratio indicated potential for soil remediation. Furthermore, the high heating value (21.55–27.01 MJ/kg) of LS biochar exceeded that of Zhaotong lignite, demonstrating its favorable combustion characteristics. This study lays the theoretical foundation for the efficient treatment and high-value utilization of Lotus shells.

Effects of pressure and heating rate on coal pyrolysis: A study in simulated underground coal gasification

Underground coal gasification (UCG) is a promising technology which in-situ converts coal into fuel gases through controlled chemical reactions. In order to precisely control coal pyrolysis and increase the char yield, it is vital to understand the influences of operating factors such as heating rate and pressure, on coal pyrolysis. In this study, the effects of heating rate and pressure on the char formation of bituminous coal pyrolysis are investigated. The reaction mechanism of coal pyrolysis and the solid-state kinetic model are firstly reviewed. Subsequently, thermal experiments are conducted to study the effects of heating rate and pressure on coal pyrolysis characteristics. Moreover, the connection between the dominant coal pyrolysis reaction type and corresponding solid-state kinetic model is revealed. An empirical model of coal pyrolysis rate, pressure, and heating rate is also developed, which can be used to quantitatively predict pyrolysis rates under varying heating rate and pressure conditions. The results show that the optimal heating rate for char generation is at around 10 °C/min. On the other hand, when the pressure exceeds 2 MPa, it will enhance the char production by obstructing the physical release of volatiles and has insignificant impact on the reaction type. This study contributes to our understanding of the coal pyrolysis mechanism, and the proposed empirical model can provide valuable insights for optimizing operating parameters during UCG process.