Pyrolysis Reaction Kinetics Research Articles

Catalytic and non-catalytic reactions of methane pyrolysis for hydrogen production in screening and electromagnetic levitation reactors using computational fluid dynamics

Molten metal (MM)-based methane (CH4) pyrolysis is a promising technology for clean hydrogen production with a minimal carbon footprint. Electromagnetic levitation (EMLR) and screening reactors (SR) were used to investigate the intrinsic catalytic reaction kinetics of MM-based CH4 pyrolysis. Heterogeneous catalytic reactions in the SR and EMLR occurred on the surfaces of the MM crucible and droplet, respectively. However, a homogenous non-catalytic reaction may occur just above the surface because the CH4 gas is preheated by the high-temperature MM. This study presents three-dimensional (3D) computational fluid dynamics (CFD) model coupled with chemical reactions to assess the extent to which non-catalytic reactions intervene in CH4 pyrolysis in both the SR and EMLR, which is difficult to measure experimentally. The CFD model validated against experimental data revealed that the non-catalytic reaction accounted for 4.0 % of CH4 pyrolysis in the CH4-Ni0.27Bi0.73 SR at 1045 °C, whereas it represented 0.02 % in the CH4-Sn EMLR at 1021 °C. This result highlights that the EMLR is suitable for studying the intrinsic catalytic reaction kinetics of MM-based CH4 pyrolysis because the non-catalytic reaction occurs to a lesser extent.

An experimental and modeling study on pyrolysis reaction kinetics of oxygenated biofuel blended with aviation kerosene RP-3

Blending the renewable oxygenated biofuels with conventional fossil fuels is one of the feasible approaches to achieve carbon-neutral in the aviation industry, while there is very limited research available on the fundamental reaction characteristics of blended fuels. The primary objective of the present study is to conduct experimental investigations on the pyrolysis and oxidative pyrolysis reaction kinetics of oxygenated biofuels blended with China aviation kerosene RP-3 and establish a kinetic model. Pyrolysis experiments were conducted in a flow reactor at atmospheric pressure and temperature of 1130 K for blended fuels (methyl butanoate blended with RP-3, and n-butanol with RP-3) to examine fuel reactivity and formation of critical intermediates. The introduction of alternative oxygenated biofuel to the conventional hydrocarbon fuel RP-3 leads to the generation of CO during the pyrolysis reactions, as well as the reduced formation of olefin products. Notably, the CO yield from pyrolysis reactions of the blended fuel is increasing almost linearly with the concentrations of added oxygenated biofuels. A Two-Step Reaction Scheme (TSRS) modeling approach was extended for describing the reaction kinetics of oxygenated biofuels. TSRS models for methyl butanoate and n-butanol were constructed and merged with the HyChem model of RP-3 to complete the blended fuel model. Results show that the blended model predicts well the evolution of key intermediates with time, demonstrating the applicability of the model based on the two-stage characteristics of high-temperature reaction kinetics for describing the pyrolysis reactions of oxygenated fuels and hydrocarbon fuels.

Modeling of a heat-integrated biomass downdraft gasifier: Influence of feed moisture and air flow

A model for a heat-integrated biomass downdraft gasifier is developed and used to study the influence of changes in biomass moisture content and gasifier air flow. This one-dimensional steady-state model accounts for pyrolysis, combustion and gasification reaction kinetics as well as transport phenomena occurring within the gasifier and heat integration system. The gasifier is divided into four zones for solving the ordinary differential equations (ODEs), because each zone has different geometry for the reactor or heating system. The material and energy balance ODEs are solved as a boundary value problem (BVP), ensuring that conditions for the producer gas at the bottom of the reactor match the conditions of the countercurrent annulus gas, which is used for heating. The model also accounts for the preheating of the biomass using exhaust gas from an associated engine used to generate electricity from the producer gas. The model predicts the process gas temperature, flow rate and composition and was validated using two experimental runs with different control inputs. The model predictions show good agreement with the data. Simulations with the highest feed moisture result in lower reactor temperatures and simulations with the highest air flow result in the highest reactor temperatures.

Biopolymeric degradation of jute sticks under pyrolytic thermal stresses

For the first time pyrolytic degradation of biopolymers and multi-pseudo component of jute sticks (JS) was executed through thermogravimetric analysis. Gaussian deconvolution of first order derivative have been registered in the current manuscript to find individual signals related to each pseudo component (hemicellulose, cellulose and lignin) in biomaterial. The JS characteristics, pyrolysis reaction kinetics, reaction mechanism and nature of the volatile compounds released were examined by various analytical instruments and methods, such as elemental analyzer, FTIR, AAS, TGA, GC-MS and kinetics models. The average activation energy values for JS 243.77, 234.05, 246.61, 246.74 and 260.03 kJ.mol−1 when OFW, KAS, STM, TANG and Friedman models, respectively, were used for analysis. Thermodynamic parameters (ΔH, ΔS, and ΔG) of different component of JS were also evaluated and discussed in the current context. Z(α) analysis has shown that the experimental curves have followed Avrami- Erofeyev (A2, A3, A4), power-law (P2), geometric (R2, R3), diffusional (D1, D2, D3) and reaction (F1) curves according to Criado’s master plots, indicating complex nature of pyrolysis process. Finally, it was confirmed that alcohols are major pyrolysates, followed by hydrocarbon and benzene among all other components released during pyrolysis action of JS. The finding of the study contributes to the potential of jute stick as a raw material for bioenergy and renewable chemical production. It also proves to be useful in the design and optimization of JS-based thermochemical degradation processes.

Recovery of enhanced gasoline-range fuel from catalytic pyrolysis of waste polypropylene: Effect of heating rate, temperature, and catalyst on reaction kinetics, products yield, and compositions

The present study focuses on the recovery of superior-quality pyrolytic oil (PO) from the pyrolysis of waste polypropylene (WPP). The optimum heating rate, temperature and catalyst dosing were identified from experimental pyrolysis runs in a batch pyrolyzer. The thermal pyrolysis at 550 0C at 20 0C/min produced 83.5% PO, the maximum yield. The activated zeolite and kaolin catalyst prepared from the low-cost natural zeolite and kaolin clay were used for catalytic pyrolysis. The specific surface areas were determined to be 16.45 and 13.62 m2/g, with pore sizes 18.5 and 20.6 nm for zeolite and kaolin, respectively. The catalytic dosing of 12% zeolite and 10% kaolin was found to be the most optimum towards maximum PO yield. The FTIR and GC-MS analysis provided the qualitative and quantitative identification of various hydrocarbons (HCs) in PO. The HCs were classified as diesel-range (DHC) and gasoline-range (GHC) based on the carbon numbers. The catalyst zeolite and kaolin enhanced the yield of GHC components in PO by 6.45 and 7.7%, respectively. The catalyst considerably reduced the density, viscosity and improved the flash and pour points of PO. Finally, the reaction mechanism and reaction kinetics of pyrolysis reaction were determined from thermogravimetric data obtained under identical reaction conditions as in batch pyrolyzer. A shift of the reaction mechanism with lower activation energy was identified in the presence of a catalyst. The detailed characterization of gaseous products and solid residues were also performed.

Study on pyrolysis behavior of municipal sludge based on TG-FTIR-MS

Sludge pyrolysis, as a new sludge disposal technology, can realize the reduction and resource utilization of municipal sludge. Based on TG-FTIR-MS technology, pyrolysis behaviors such as pyrolysis reaction kinetics, pyrolysis product composition and other pyrolysis behaviors of four common municipal sludges (SD, NJ, CS, TJ) at different pyrolysis rates were investigated in this paper, and the migration and transformation of nitrogen elements in municipal sludge were analyzed. The results showed that the pyrolysis of municipal sludge was mainly divided into three stages: dewatering (below 160 °C), volatile decomposition (160–550 °C), and carbonization stage (550–900 °C). The activation energies of the four sludge pyrolysis stages were 189.75 kJ/mol, 138.13 kJ/mol, 300.76 kJ/mol, and 237.83 kJ/mol, respectively. It was found that the sludge pyrolysis stage followed the stochastic nucleation and subsequent growth mechanism through the study of SD and CS sludge. The pyrolysis gaseous product content was affected by the rate of heating and pyrolysis temperature. Moderate temperatures (400–550 °C) favored complete sludge decomposition. Sludge is more likely to decompose in a narrow temperature range at higher heating rates, and increasing the heating rate accelerates sludge decomposition. The nitrogenous compounds in sludge are mainly pyrrole nitrogen, protein nitrogen, and pyridine nitrogen. During sludge pyrolysis, the nitrogenous compounds decompose and precipitate in the form of heterocyclic nitrogen (pyridine, pyrrole), and release small molecules of nitrogenous compounds (NH3, HCN, HCNO). The experimental results can provide a reference for the disposal of municipal sludge by pyrolysis.

Study on the Pyrolysis Characteristics of Tobacco Stems Under Different Steam Explosion Pressures

Thermal weight loss behavior of tobacco stems is the key to studying the chemical properties of tobacco stalks. In this research, four steam explosion pressure gradients with three heating rates were investigated for the pyrolysis characteristics of tobacco stems. Three methods were employed to analyze pyrolysis reaction kinetics. The results showed that pyrolysis of tobacco stems consists of three phases: dehydration, degradation, and carbonization. The influence of steam explosion pressure on the thermal stability of tobacco stems was as follows: 0.5 MPa > 0.2 MPa > 0.8 MPa > block sample > 1.1 MPa. The pyrolysis of tobacco stems followed the first-order reaction kinetics equation, and the pyrolysis experiments fit the Kissinger equation, Tang equation, and Hu-Gao-Zhang equation well. The experimental results provide a reference for research on the subject of pyrolysis of tobacco stems.

Effect of pyrolysis reaction kinetics modified by adding inorganics on flame spread of cellulose

The influence of pyrolysis reaction parameters on the flame spread rate over a thin cellulose strip was examined for varying additive amounts of an inorganic compound (K2CO3). The increase in the mass fraction of K2CO3 in the sample causes a decrease in the flame spread rate. Above 1.8% in K2CO3, the flame experiences extinction and smoldering occurs. The results of kinetic analysis reveal that the rate of pyrolysis reaction rate is decreased with the increase of K2CO3. To elucidate the decrease in the flame spread rate by the suppression of the pyrolysis reactions, the influence of the change of the flame temperature by various pyrolysis gas compositions or the pyrolysis reaction rate on the flame spread rate is examined theoretically. With regard to the temperature effect, the estimated adiabatic flame temperature decreases weakly with the increase of the K2CO3, which implies a weak contribution of the flame temperature to the flame spread rate. The results of theoretical analysis reveal that the reduction of the flame spread rate comes from the suppression of the pyrolysis reactions by adding K2CO3.

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.

Effect of pressure on the pyrolysis and gasification mechanism of corn stovers from kinetics

In the exploration of the mechanism of corn stovers pyrolysis and gasification, the kinetic parameters is of great significance for regulating the production of target products. Although the kinetic calculations of corn stovers pyrolysis gasification have been reported, the study of kinetics under high pressure and supercritical conditions is still very limited. Therefore, the effect of pressure on the kinetics of corn stovers pyrolysis and gasification reaction was investigated through experiments of atmospheric pressure, high pressure thermogravimetry and supercritical water gasification (SCWG). Different kinetic calculation models were used. It was found that an increase in pressure would increase the activation energy value and inhibit the generation of gas products, but at the same time it would also promote the interaction between gas components and samples. Through this research, this work can provide scientific and technological references for the mechanism of pyrolysis gasification under pressure and the regulation of target products.

Combined Methane Pyrolysis and Solid Carbon Gasification for Electrified CO2-Free Hydrogen and Syngas Production

The coupling of methane pyrolysis with the gasification of a solid carbon byproduct provides CO2-free hydrogen and hydrogen-rich syngas, eliminating the conundrum of carbon utilization. Firstly, the various types of carbon that are known to result during the pyrolysis process and their dependencies on the reaction conditions for catalytic and noncatalytic systems are summarized. The synchronization of the reactions’ kinetics is considered to be of paramount importance for efficient performance. This translates to the necessity of finding suitable reaction conditions, carbon reactivities, and catalysts that might enable control over competing reactions through the manipulation of the reaction rates. As a consequence, the reaction kinetics of methane pyrolysis is then emphasized, followed by the particularities of carbon deposition and the kinetics of carbon gasification. Given the urgency in finding suitable solutions for decarbonizing the energy sector and the limited information on the gasification of pyrolytic carbon, more research is needed and encouraged in this area. In order to provide CO2-free hydrogen production, the reaction heat should also be provided without CO2. Electrification is one of the solutions, provided that low-carbon sources are used to generate the electricity. Power-to-heat, i.e., where electricity is used for heating, represents the first step for the chemical industry.

Pyrolysis behavior of bastnaesite in an air environment: Thermodynamics, phase transition and kinetics

BackgroundOxidation roasting is an eco-friendly pre-treatment process that is utilized before leaching bastnaesite concentrate, and it is currently the main process for pretreating bastnaesite concentrate in China. Despite this, there is still a lack of systematic and detailed studies on the pyrolysis behavior of bastnaesite concentrate in an air environment. MethodsThe reaction thermodynamics, pyrolysis characteristics, phase transition and kinetics of bastnaesite pyrolysis in air were studied in detail by thermogravimetric and mass spectrometric, in-situ X-ray diffraction, and advanced kinetic parameter analysis method recommended by ICTAC. Significant findingsCe7O12, CeF3, and CO2 were the primary pyrolysis products of bastnaesite in the air. Spontaneous reactions dominated during the process, and the oxidation of pyrolysis products released heat. Bastnaesite pyrolysis initially occurred within the temperature range of 400°C to 500°C, with higher temperatures facilitating easier pyrolysis. The non-isothermal pyrolysis kinetic triplets for bastnaesite concentrate in the air were determined, which included activation energy (Eα) of 161.52 kJ/mol, pre-exponential factor (lnA) of 26.70 s−1, and appropriate kinetic mechanism of random nucleation and growth model (n=3/2–2).

Analysis and prediction model of the minimum explosion concentration of plastic dust in gaseous fuel environments

Polyethylene dust and polypropene dust were selected to measure the minimum explosion concentration in three kinds of gaseous fuel environments. The results show that the MEC of polyethylene dust with higher apparent activation energy decreased more significantly, and the plastic dust showed higher explosion sensitivity for the gaseous fuel with high combustion heat. The explosion mechanism for plastic dust in gaseous fuel environments was proposed with the global reaction kinetics of plastic pyrolysis, and it suggests that the gaseous fuels reduce the apparent activation energy of plastic dust and provide additional heat for the plastic dust explosion. A corresponding prediction model for the minimum explosion concentration of plastic dust was established. The new model has good applicability for the data obtained in this work and the data in the previous reference.

Pyrolysis Characteristics and Determination of Kinetic and Thermodynamic Parameters of Raw and Torrefied Chinese Fir.

Torrefaction influences the structural and physicochemical properties of biomass, thus further altering its thermal degradation behavior. In this study, the pyrolysis characteristics, reaction kinetics, and thermodynamic parameters of raw and torrefied Chinese fir (CF) were investigated. The torrefaction was conducted at 220 °C (mild) and 280 °C (severe), the pyrolysis was performed from ambient temperature to 600 °C, and four different heating rates (i.e., 5, 15, 25, and 35 °C/min) were adopted. The activation energy for pyrolysis was estimated by adopting three isoconversional methods. The master-plot method was employed to analyze the reaction mechanism. Furthermore, thermodynamic parameters, i.e., the enthalpy change (ΔH), Gibbs free energy change (ΔG), and entropy change (ΔS), were calculated. The average activation energy increased with the torrefaction temperature, whose values estimated by using different methods ranged from 88.57 to 97.70, from 121.04 to 126.35, and from 167.51 to 179.74 kJ/mol for raw, mildly, and severely torrefied CF samples, respectively. A compensation effect between the activation energy and pre-exponential factor was observed for all samples. The degradation process was characterized as endothermic, involving the formation of activated complexes and requiring extra energy for torrefied samples.

On the intrinsic reaction kinetics of polypropylene pyrolysis

On the intrinsic reaction kinetics of polypropylene pyrolysis

Assessing pyrolysis performance and product evolution of various medical wastes based on model-free and TG-FTIR-MS methods

The COVID-19 pandemic has caused a substantial rise in the amount of medical waste, posing additional hurdles in waste management. Disposing of this waste properly is essential to curb transmission of the diseases. The pyrolysis reaction kinetics, synergistic interactions, and pyrolysis gas release behavior of typical constituents of medical waste (MW): syringe (SY), medical gloves (MG), cotton swab sticks (CS), and their blends were examined by utilizing advanced analytical techniques including TG, TG-FTIR, TG-MS, and kinetic models (Friedman, KAS). The experiments were conducted using a wide range of heating rates, namely 10, 20, 30, and 40 °C⋅min−1. The pyrolysis reactions were mainly endothermic, with main stages ranging from 352.0–480.0 °C, from 381.0–511.0 °C, from 200.0–404.5 °C, 336.6–509.9 °C, 375.4–477.6 °C, 384.0–500.9 °C, for SY, MG, CS, SY5MG5, SY7CS3, and MG7CS3, respectively. According to the KAS method, the average activation energies for the mono-pyrolysis of SY, MG, and CS were determined as 240.8, 226.1, and 147.5 kJ⋅mol−1 respectively. Interestingly, during the pyrolysis of blends such as SY5MG5, SY7CS3, and MG7CS3, the activation energies decreased to 177.2, 159.9, and 149.1 kJ⋅mol−1 respectively. Notably, the experimental activation energy values (Eexp) obtained during the co-pyrolysis were significantly lower than the calculated values (Ecal), revealing an apparent synergistic effect during the pyrolysis of various MW blends. The pyrolysis process of MW blends resulted in the release of significant volatile components, including CH4, CO, C3H6, CO2, C2H5OH, C4H8, C5H8, C6H6, C6H14, C7H8, and C8H10. The specific composition of these volatile components varied depending on the types of waste present in the blends.

Kinetic analysis and pyrolysis behavior of pine needles by TG-FTIR and Py-GC/MS

The pyrolysis performances and reaction kinetics of pine needles (PN) were investigated by integrating thermogravimetric analysis, Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography/mass spectrometry. The average activation energy of PN was estimated to be 183.2 kJ/mol by Kissinger Akahira Sunose (KAS) and 183.8 kJ/mol by Flynn Wall Ozawa (FWO), respectively at heating rates of 10, 20, and 40 °C/min. The pyrolysis of PN was found to be more efficient at the lower heating rates, while increased heating rates promoted the reaction. Using the King-Kai (K-K) method, the activation energies of hemicellulose, cellulose, and lignin were calculated to be 156, 165, and 172 kJ/mol, respectively. The descending order of evolving gases and functional groups from PN was found to be CO2, C=C, C=O, H2O, CH4, and CO. The main pyrolytic by-products identified were hydrocarbons, phenols, alcohols, ketones, and aldehydes. The determination of kinetic parameters provides fundamental information for predicting the rates at which chemical reactions occur. This study demonstrates the potential of PN as a suitable source for bioenergy.

Comprehensive Kinetic Study of PET Pyrolysis Using TGA.

The pyrolysis of polyethylene terephthalate (PET) is a well-known process for producing high fuel value. This paper aims to study the kinetics of PET pyrolysis reactions at 4 different heating rates (2, 5, 10, and 20 K min-1) using thermogravimetric analysis (TGA) data. TGA data show only one kinetic reaction within the temperature ranges of 650 to 750 K. Five different model-free models, namely, the Freidman (FR), Flynn-Wall-Qzawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK), and distributed activation energy model (DAEM), were fitted to the experimental data to obtain the activation energy (Ea) and the pre-exponential factor (A0) of the reaction kinetics. The Coats-Redfern (CR) model equation was fitted with the help of master plot (Criado's) to identify the most convenient reaction mechanism for this system. Ea's values were determined by the application of the five aforementioned models and were found to possess an average value of 212 kJ mol-1. The mechanism of PET pyrolysis reaction was best described by first-order reaction kinetics; this was confirmed by the compensation. Further thermodynamic parameter analysis indicated that the reaction was endothermic in nature.

Effect of biomass components’ interaction on the pyrolysis reaction kinetics and small-molecule product release characteristics

The first step in uncovering pyrolysis interaction is to understand the pyrolysis reaction kinetics and small-molecule product release mechanisms of biomass components. Therefore, the cross-coupled thermal decomposition properties, gaseous product release characteristics, and functional group evolution of cellulose, hemicellulose, and lignin were investigated. The reaction activation energy is shown to be lower in co-pyrolysis, and there exist optimal mixing ratios where they favor each other's thermal breakdown. When the cellulose ratio was low, dehydration reactions, as well as the cyclization and condensation processes of open-chain hexoses and pentoses, were stimulated, but these processes were hindered when the cellulose level was high. Mixing with lignin aids in the opening of cellulose rings. However, at lower lignin levels, the dehydration, demethylation, decarboxylation, and decarbonylation processes were largely hindered, and these reactions were only stimulated at greater lignin content. The pyrolysis reaction kinetics, as well as product composition and distribution, may be altered by adjusting the composition ratio of biomass. This research helps to better understand the biomass pyrolysis interaction.

Investigation of tobacco straw pyrolysis: Three-parallel Gaussian reaction modeling, products analysis and ANN application

The pyrolysis behaviors, reaction kinetics, thermodynamic parameters, and reaction mechanism models of tobacco straw (TOS) were determined using a three-parallel Gaussian reaction model. The apparent activation energies for the pyrolysis of pseudo cellulose (P1-HE), hemicellulose (P2-CE) and lignin (P3-LI) pyrolysis were determined using the Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink, Tang, and Distributed Activation Energy Model model-free methods. The average apparent activation energies for P1-HE, P2-CE, and P3-LI were 153.67, 178.53, and 190.45 kJ/mol, respectively. The pyrolysis process was well described by the dimensional, order, diffusional, and power law reaction mechanism models. Twelve types of pyrolysis products, including benzenes, acids, phenols, furans, indoles, pyridines, hydrocarbons, pyrroles, ketones, alcohols, quinolines, and aldehydes, were identified as the main pyrolysis products. Combining Raman and SEM analyses, pyrolyzed biochar at 800 °C was suitable as a catalyst or catalyst carrier. An artificial neural network (ANN) was utilized to predict the thermal degradation behaviors of TOS pyrolysis, and the hyperparameters of the activation function were optimized. The best ANN model structure was ANN (5 *11 *1). This study provided theoretical and practical guidance for further rational utilization of TOS waste.