Reaction Mechanism Of Pyrolysis Research Articles

Competing reactions limit levoglucosan yield during fast pyrolysis of cellulose

Efforts to understand the reaction mechanisms of cellulose pyrolysis have been stymied by short reaction times and difficulties in probing the condensed phase of cellulose intermediate products.

Elucidation of Pyrolysis Reaction Mechanism inside Wood Pellet

Elucidation of Pyrolysis Reaction Mechanism inside Wood Pellet

Pyrolytic behavior of coal-related model compounds connected with C–C bridged linkages by in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry

Coal pyrolysis is generally considered to initiate by cleavage of weak covalent bonds bridged between aromatic rings. The C–C covalent bonds are predominant bridged linkages among the framework of coal, which have a critical influence on coal pyrolysis reaction but lack of direct online observation. Five representative coal-related model compounds containing C–C bridged bonds, polypropylene (PP), polyvinylpyrrolidone (PVP), poly-4-vinylpyridine (P4VP), polystyrene (PS) and poly-4-vinylphenol, were selected to pyrolyze in an in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry (Py-VUV-PIMS). The soft ionized mass spectral detection can provide product distribution and evolved information of original products and intermediates, which are the key evidence to understand the initiation, recombination and reaction routes during pyrolysis process. Online analysis of pyrolysis reaction was found to be priority with cracking of C–C bond in the five polymer samples, and homologous free radicals and original products, which mainly include monomers, dimers and their alkyl and alkenyl radicals, were detected. The results reveal the cleavage temperature of C–C covalent bond is deeply related to its chemical environment, and obvious conjugation effect and steric effect for the bridged linkage were observed. In addition, the effect of hydrogen bond was also observed during the pyrolysis of model compounds containing hydroxyl groups, and intramolecular or intermolecular hydrogen bonding reduced the temperature at which C–C bridged bonds break. The analogous fracture mode and pyrolysis behavior of coal-related model compounds, which are beneficial to understand the reaction route and mechanism of coal pyrolysis, were discussed based on the experimental observations and theoretical calculation.

Kinetic analysis and modeling of coal pyrolysis with model-free methods

Knowledge about the rate of coal pyrolysis is of great importance because it exerts remarkable effect on its thermal conversions such as combustion, gasification and liquefaction. Different approaches can be used to obtain the kinetics of coal pyrolysis, the simplest are empirical and global kinetics, where Arrhenius expression is used to correlate the mass loss with temperature. This work conducted pyrolysis of a lignite and a bituminite at various heating rates with a thermo-gravimetric analyzer (TGA). Thermogravimetry coupled with mass spectroscopy (TG-MS), solid state 13C Cross Polarization/ Magic Angle Spinning nuclear magnetic resonance (13C CP/MAS NMR) and Raman analyses were also conducted to correlate the structural characteristics and pyrolysis behavior of the coals. Kinetic analysis was performed by using three model-free methods including Distributed Activation Energy model (DAEM), Ozawa-Flynn-Wall (OFW) and Friedman method. Kinetic modeling was also performed based on the DAEM model with multiple Gaussian sub-distributions of activation energy. The results show that DAEM, OFW and Friedman methods are almost equally effective for analyzing activation energy, which gradually increases with the extent of pyrolysis. Pyrolysis of both the coals can be divided into three stages corresponding to the reactions of various covalent bonds. Three-Gaussian distributed activation energy model (DAEM-G3) is applicable to describing pyrolysis of both coals. The well-matched modeling results with the experimental data over the entire temperature range indicate the validity of DAEM-G3 model in studying and understanding the reaction mechanism of coal pyrolysis.

A comprehensive kinetics study on non-isothermal pyrolysis of kerogen from Green River oil shale

Fundamentally understanding the pyrolysis kinetics of kerogen is of prime scientific and industrial importance. Herein, bitumen- and carbonates-free kerogen sample is prepared through Soxhlet extraction followed by decarbonation of Green River oil shale, and its pyrolysis is studied by non-isothermal thermogravimetric analysis. The systematic analyses show that both the Popescu and master plots methods are not applicable to describe the kerogen pyrolysis process due to the changed reaction model and the varied activation energy over certain conversion range, respectively, while the piecewise non-linear least squares analysis is identified as an effective method to discriminate the most probable kinetic model from commonly used 15 reaction models based on four solid-state pyrolysis mechanisms. Two-stage reaction model, i.e., F1 at the early stage and F2 at the later one, is proposed to well describe the kerogen pyrolysis process, which demonstrates a wide applicability owing to their insensitivities on the heating rate and estimation methods of the activation energies. The methodology revealed here could be applicable to determine other solid-state pyrolysis kinetics and reaction mechanism.

Modeling of biomass pyrolysis kinetics using sequential multi-step reaction model

Simultaneous thermal analysis (TGA-DSC) of biomass pyrolysis was conducted to understand the kinetics and energy requirements of biomass pyrolysis. DSC results revealed the energy requirement to heat biomass samples to pyrolysis temperature with contributions from both sensible enthalpy changes along with reaction enthalpy change required to break their chemical bonds. The information obtained was used to determine theoretical energy efficiency of biomass pyrolysis, which was found to be in the range of 86–95%, depending on the sample analyzed, with pinewood providing efficiency of ∼95%. The TGA results were used for inverse modeling of pyrolysis kinetics of various biomass feedstocks that varied in their source of origin. Sequential multi-step pyrolysis model was explored to understand its capability in representing the global pyrolysis reaction of lignocellulosic wastes since they are carbon neutral and can produce clean and sustainable energy to potentially replace the existing fossil fuel resources with minimal change in existing energy consumption infrastructure. Inverse modeling, by fitting with respect to thermogravimetric analysis (TGA), was carried out using global minimization in an elite multi-objective genetic algorithm and with appropriate choice on the number of reaction steps. Biomass/bio-wastes investigated were cardboard, dry-paper waste, pinewood, rice husk and chicken manure. Cellulose was also investigated as a baseline standard sample. The char formation selectivity of the components involved in biomass was obtained from this model and found similar values for most of the biomasses. A set of ∼48%, 65% and ∼70% charring tendencies (based on vi values) was common among paper, pinewood, cardboard. The α-cellulose decomposition also provided the 70% charring reaction suggesting its role in these biomasses. The obtained multi-step kinetic parameters are considered essential to develop simplified reaction mechanism of biomass gasification and pyrolysis for computational fluid dynamics (CFD) models, which can help in the design of energy efficient and feedstock flexible reactors for sustainable energy production from wastes.

Thermal degradation of typical plastics under high heating rate conditions by TG-FTIR: Pyrolysis behaviors and kinetic analysis

Pyrolysis of plastics has gained more attention recently due to the advantages of environmental protection and energy conversion. In this study, low-density polyethylene (LDPE), polypropylene (PP) and polyvinyl chloride (PVC) were studied under high heating rate conditions to investigate pyrolysis behaviors and find the most suitable kinetic reaction mechanisms. The TG and DTG curves for LDPE were similar to those for PP, but different from those for PVC. It was found that high heating rate led to the shifting of initial, end and peak temperatures to higher values. The FTIR results showed the main products of LDPE and PP were alkanes and alkenes, and the major products of PVC were HCl, alkenes and a small number of aromatic compounds. A comparative study of model-free methods like Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) and Friedman method were discussed to calculate activation energy. Kinetic reaction mechanisms were predicted by using model-fitting methods including Coats-Redfern and Criado method. The pyrolysis reaction mechanism of LDPE was summarized as contracting sphere model, PP was summarized as contracting cylinder model, whereas that of PVC was concluded that two-dimension nucleation for the first stage and three-dimension diffusion (Jander) for the second stage.

Water catalyzed pyrolysis of oxygen functional groups of coal: A density functional theory investigation

The pyrolysis mechanism of carboxylic and hydroxyl groups which are present in the coal has been investigated with the help of density functional theory calculations. The role of water in the pyrolysis reaction mechanisms has also been investigated by the calculation of activation energy barriers. The activation energy barriers for the water mediated reactions are less when compared to thermal pyrolysis process. The results show the significant decrease in the energy barriers for decarboxylation reactions than the hydroxyl groups in the presence of water. Therefore, water can significantly decrease the oxygen content in the non-coking coals with high content of carboxylic groups.

Utilisation of a waste biomass, walnut shells, to produce bio-products via pyrolysis: investigation using ISO-conversional and neural network methods

This study was conducted to investigate the kinetic, thermodynamics and the reaction mechanism of pyrolysis of native walnut shells of Kashmir, India. Thermal degradation experiments were performed at three heating rates of 10, 25, and 50 K min−1 to calculate the kinetic and thermodynamic parameters, using iso-conversional Kissinger-Akahira-Sunrose (KAS) and Ozawa-Flynn-Wall (OFW) models. The reaction mechanism was predicted by applying Coats-Redfern (CR) method. Moreover, an artificial neural network (ANN) simulation was used to obtain best fit points after comparing the experimental data with the predicted data points. Average activation energy was calculated from the thermogravimetric study was found to be in the range of 146.03–148.89 kJ mol−1, while the Gibbs free energy (ΔG) value for walnut shells was found to be ~180 kJ mol−1. The most appropriate degradation mechanism was found to be based on diffusion and chemical reaction for the temperature range under study. The broad characterisation along with the values of thermodynamic parameters show that the walnut shells can be used as an economical as well as eco-friendly bio-energy feed-stock for pyrolysis. The reaction mechanism of thermal degradation of walnut shells was found to be consisting of two broader zones based on conversion achieved, zone I (0.2 ≤ α ≤ 0.4) and zone II (0.4 ≤ α ≤ 0.8).

Comprehensive evaluation of various pyrolysis reaction mechanisms for pyrolysis process simulation

In recent years, an acceleration of global warming and various environmental pollution problems has been observed due to the increase in energy demand. Biomass, which has several advantages over more typical sources, is very popular as a green energy source. This study focuses on process modeling and analysis of biomass fast pyrolysis. The fast pyrolysis reaction mechanisms, proposed by previous researchers, are applied to the modeling of a fast pyrolysis reactor. This process analysis is performed according to operating conditions such as the reaction temperature, residence time, type of biomass and reactor type. To evaluate these results, the results of the process analysis of other researchers and the GC/MS (gas chromatograph-mass spectrometry) data of fast pyrolysis experiment are compared.

Pyrolysis study of waste phenolic fibre-reinforced plastic by thermogravimetry/Fourier transform infrared/mass spectrometry analysis

Pyrolysis is considered to be a promising method to dispose waste plastics by thermal cracking into chemicals. Previous studies focus on pyrolysis recycling of waste thermoplastics. The pyrolysis of waste thermosetting plastics, which may be different from that of waste thermoplastics, receives little attention. In order to provide guidance for reactor design and thermo-chemical process management for the pyrolysis recycling of waste thermosetting plastics, the pyrolysis kinetics, volatile products and reaction mechanisms of one typical waste thermosetting plastics namely phenolic fibre-reinforced plastic (phenolic FRP) are studied in the present study. Thermogravimetric analysis (TGA), in situ Fourier transform infrared (FTIR) and online TGA-FTIR-mass spectra (MS) analyses are employed. Results indicate that the pyrolysis of waste phenolic FRP in inert atmosphere may be divided into two stages with the threshold conversion rate of 0.2. The average values of activation energy in the first, second and whole pyrolysis process were 174.66 kJ/mol, 233.62 kJ/mol and 223.22 kJ/mol, respectively. The crosslinking between phenol derivatives and breakage of branched chain may result in the occurrence of the first stage, while the occurrence of the second stage may be due to the breakage of chain backbone and oxidation of methylene and hydroxymethyl. Four kinds of gases including H2O, alcohols, aliphatic compounds and carboxylic acids mainly constitute the volatile products in the first stage. The volatile products in the second stage mainly consist of CO, CO2, carboxylic acids and aromatic compounds. The amount of the volatile products in the second stage is much larger than that in the first stage. The maximum amount of these seven gases in the order of most to least is CO2 > CO > alcohols > carboxylic acids > aliphatic compounds > water vapour > aromatic compounds. It may be better to recover the waste phenolic FRP for valuable gases either as fuel or chemical feedstock in the first stage than the second stage.

Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional (2D) numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.

Evolved gas analysis of cassava (Manihot esculenta) industrial waste

Introduction: The pyrolysis of agro-industrial waste is an alternative to produce second-generation liquid fuels.Objective: Determine the kinetics in the pyrolysis process of cassava industrial waste as well as of evolved product formation.Methodology: Pyrolysis of waste from cassava starch processing was studied via thermogravimetric analysis coupled to mass spectrometry. Thermogravimetric data were adjusted to the distributed activation energy model with one pseudo-component.Results: Pyrolysis of samples heated at ramps below 30 K/min showed kinetics parameters with different values from the ones obtained for the samples heated at ramps above 50 K/min. This suggests a change in the pyrolysis reaction mechanism linked to heating rate. The kinetic parameters obtained in this work are in agreement with values reported for other biomass in literature. From the evolved gases, 23 m/z signals were identified with enough signal/noise ratio. Mass spectrometry signals were also adjusted with the distributed activation energy model using the kinetic parameters obtained from thermogravimetric data.Conclusions: Satisfactory results were achieved with the DAEM model with one pseudo component for most of m/z ratio. The lack of adjustment in some m/z ratio can be attributed to secondary reactions in the gas phase.

Water assisted liquefaction of lignocellulose biomass by ReaxFF based molecular dynamic simulations

ReaxFF based molecular dynamics (MD) simulation provides opportunities for fundamentally understanding pyrolysis of lignocellulose biomass through precisely controlled reaction conditions and monitoring of reaction evolution processes. Despite demonstration of simulating the pyrolysis process of dry lignocellulose, MD investigation of this process assisted by water is yet to be performed. This is important considering that hydrothermal liquefaction could be promising to concentrate the energy of biocrude yielded from lignocellulose biomass. In this paper, roles of water on the pyrolysis process of the lignocellulose were investigated by ReaxFF MD simulation. In the simulation, both dry cellulose and lignin systems as well as their systems containing 33% and 66% water by weight were studied at a temperature range of 1250–2000 K at a time scale of 6 ns. Products were characterized by studying their phases, H/C, O/C ratios, and their higher heating values (HHV) that are used to evaluate their value as fuels. Time evolutions of water and other chemical products were investigated to determine the role of water in the reactions and to reveal the reaction mechanism. Compared with dry systems, pyrolysis of the cellulose in presence of water shows several interesting trends, including enhanced breakdown of the cellulose polymer, increased oxygenation of the products, and shift of the final products from char to oil. In contrast, lignin remains largely unaffected by water, and simulation has reproduced experimental results of lignin char formation at elevated temperature in liquefaction. Moreover, it is found that the temperature plays an important role in the reactions. As temperature increases the water’s oxygenating effects in the cellulose is decreased. These theoretical results provide solid evidence for unveiling the reaction mechanism of biomass pyrolysis, offering useful guidance for processing wet biomass to liquid fuels.

Theoretical study of the furfuryl benzoate and furfuryl acetate pyrolysis

AbstractIn the present work, the pyrolysis reaction mechanism of both furfuryl benzoate and furfuryl acetate was evaluated at the M06/6‐311++g(d,p) level. The uncommon methylenecyclobutenone compound and either the benzoic or the acetic acid were determined as the products of a multistep process consisting in two [3 + 3] rearrangements and a subsequent hydrogen α‐elimination step, through a cyclic 5‐membered transition state (TS), being the latter the rate‐limiting step for both reactants. Furthermore, a deeper analysis on the basis of the reaction force formalism showed that the TS is formed in two stages: The first one is characterized by the weakening of the C─O bond, and the second one is where the H atom is transferred from the C atom to its nearest O atom. The H─O bond formation was determined to contribute the most to the electronic activity occurring during the TS formation as suggested by a reaction electronic flux analysis. Accordingly, natural bond orbital calculations showed that the most significant changes occur in the charge distribution of the O and H atoms. Finally, a negligible effect of the substituting group on the reaction was determined since similar activation energies were obtained for the pyrolysis of furfuryl benzoate and furfuryl acetate; however, a minor difference was evidenced in the reaction force results. In this sense, the structural contribution to the activation energy is larger than the electronic one for the furfuryl benzoate reaction, , whereas the opposite is observed for the furfuryl acetate reaction, .

Pyrolysis, kinetics analysis, thermodynamics parameters and reaction mechanism of Typha latifolia to evaluate its bioenergy potential

This work was focused on understanding the pyrolysis of Typha latifolia. Kinetics, thermodynamics parameters and pyrolysis reaction mechanism were studied using thermogravimetric data. Based on activation energies and conversion points, two regions of pyrolysis were established. Region-I occurred between the conversion rate 0.1–0.4 with peak temperatures 538K, 555K, 556K at the heating rates of 10Kmin−1, 30Kmin−1, and 50Kmin−1, respectively. Similarly, the Region-II occurred between 0.4 and 0.8 with peak temperatures of 606K, 621K, 623K at same heating rates. The best model was diffusion mechanism in Region-I. In Region-II, the reaction order was shown to be 2nd and 3rd. The values of activation energy calculated using FWO and KAS methods (134–204kJmol−1) remained same in both regions reflecting that the best reaction mechanism was predicted. Kinetics and thermodynamic parameters including E, ΔH, ΔS, ΔG shown that T. latifolia biomass is a remarkable feedstock for bioenergy.

Initial Products and Reaction Mechanisms for Fast Pyrolysis of Synthetic G‐Lignin Oligomers with β‐O‐4 Linkages via On‐Line Mass Spectrometry and Quantum Chemical Calculations

AbstractThe products of fast pyrolysis that first leave the hot pyrolysis surface were identified for three G‐lignin model compounds, a trimer, a tetramer and a synthetic polymer, all containing β‐O‐4 linkages, by using a very fast heating pyrolysis probe coupled with a linear quadrupole ion trap mass spectrometer or a linear quadrupole ion trap coupled with an orbitrap detector. High‐resolution measurements were used to determine the elemental compositions of the deprotonated pyrolysis products. Their structures were examined using collision‐activated dissociation experiments and via comparison to the dissociation reactions of ionized authentic compounds. The initial pyrolysis products for all model compounds range from monomers to tetramers. Even for the polymer, no products larger than tetramers were observed. None of the products were radicals. The observed trimers and tetramers were formed directly from the intact model compounds rather than from repolymerization of initially formed monomers. Both the observed product distributions and quantum chemical calculations suggest that the mechanism(s) of the major reactions occurring under the conditions employed here are Maccoll and/or retro‐ene eliminations rather than radical reactions. Based on a comparison of the behavior of the smaller β‐O‐4 model compounds to the synthetic β‐O‐4 lignin polymer, the smaller model compounds appear to be good surrogates for further studies of the mechanisms of fast pyrolysis of lignin.

Numerical Study of Flow and Heat Transfer of n-Decane with Pyrolysis and Pyrolytic Coking under Supercritical Pressures

Pyrolysis and pyrolytic coking of hydrocarbon fuel have significant influences on the regenerative cooling process. In this article, a three-dimensional (3D) model is developed for numerically investigating the flow and heat transfer of pyrolytically reacted n-decane with pyrolytic coking in the engine cooling tube under supercritical pressure. The one-step global pyrolytic reaction mechanism and the kinetic coking model are incorporated into the numerical model to simulate the pyrolysis and pyrolytic coking process of n-decane. The numerical method is validated based on the good agreement between the current predictions and the experimental data. Numerical studies of the characteristics of pyrolysis and surface coking rate at the start time under various outer wall heat fluxes from 1.2 to 1.8 MW/m2 have been conducted under 5 MPa. Results reveal that heat flux has huge effects on the pyrolytic reaction and the distribution of pyrolytic coking rate. In order to better understand the complicated unsteady p...

Pyrolysis characteristics and kinetic modeling of Artemisia apiacea by thermogravimetric analysis

Chinese herbal medicine plays an important role in disease treatment and world medicine market. Its fire safety, especially pyrolysis in storage deserves more attentions due to low bulk density. As an herbal medicine representative and malarial drug, Artemisia apiacea pyrolysis was investigated based on thermogravimetric analysis in an inert atmosphere at different heating rate from 10 to 50 K min−1. Two model-free methods of Kissinger–Akahria–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were employed to estimate pyrolysis activation energy. A model-fitting method called Coats–Redfern (CR) was used to predict the reaction mechanism for pyrolysis of Artemisia apiacea stem and leaf. For stem, a single peak can be observed at a range from 584 to 604 K, while two shoulders and a single peak exist for leaf. With increasing the conversion rate, activation energy of stem pyrolysis increases but leaf pyrolysis activation energy first decreases, then increases and lastly decays. So the cellulose plays a significant role in stem pyrolysis, while hemicellulose, cellulose and lignin together do in leaf pyrolysis. Correspondingly, the average values of activation energy were also estimated for both stem and leaf by three above methods. The diffusion-Valensi model or diffusion-Ginstling model can be used to describe stem reaction mechanism. Furthermore, a detailed pseudo-mechanistic model serves for leaf reaction mechanism.

Technical Progress and the Prospect of Low‐Rank Coal Pyrolysis in China

AbstractChina possesses an amazing variety of low‐rank coal (LRC) resources. The developed strategies for the large‐scale use of coal resources in China suggest that achieving the grading effective conversion and utilization of LRC by mid–low‐temperature coal‐pyrolysis technologies can maximize LRC resources. On the basis of investigations on and the analysis of coal‐pyrolysis technologies, a comprehensive overview of the LRC pyrolysis technologies in recent years is described in this review. The technologies include square‐retort pyrolysis technology, upgraded square‐retort pyrolysis technology, solid‐heat‐carrier pyrolysis technology, belt‐type‐furnace pyrolysis technology, and rotary‐kiln pyrolysis technology. Focusing on the technical characteristics with analysis and comparison of different LRC pyrolysis technologies, we summarize the main problems in the development of pyrolysis processes, namely, dust separation of coal tar, wastewater treatment, and incomplete pyrolysis reaction mechanisms. Moreover, suitable methods for the rational and efficient utilization of LRC resources are discussed to achieve the sustainable development of pyrolysis technologies based on optimizing pyrolysis reactors and developing deep‐processing multigeneration technologies.