Coats-Redfern Integral Method Research Articles

Effects of Algal Biomass Blending on Coal Decomposition Behaviour and Kinetics at Intermediate Pyrolysis Regimes

Co-pyrolysis of coal with biomass is becoming a popular method of reducing the net carbon dioxide emissions associated with the process. In present work, the pyrolysis of coal and algae was studied using thermogravimetric methods and the kinetics were analyzed using the Coats-Redfern integral method. The kinetics were evaluated for 1st and 2nd order reaction models. The effect brought by blending coal with algae on kinetics was studied via the analysis of pyrolysis of different coal-algae blends. The results revealed that the pyrolysis of coal and algae follows 2nd and 1st order kinetics with activation energy evaluated in the range 213.4-241.8 and 108.9-122.8 kJ/mol, respectively. It was observed that for coal-algae blending of 20-40% algae, intermediate pyrolysis, typical heating rates of 50-200 ºC/min was characterized by two distinct stages (ignoring the drying stage) that correspond to the individual decomposition of algae and coal. However, there was an evidence of coal-algae interactions during co-pyrolysis, which made the kinetics of the two distinct stages not to correspond to the kinetics of the individual materials.

Transformation of nitrogen, sulfur and chlorine during waste tire pyrolysis

The transformation of N/S/Cl during pyrolysis of waste tire were investigated by Thermogravimetry-Mass Spectrum (TG-MS) and flow tube furnace reactor. The pyrolysis of waste tire included four stages, i.e., dehydration below 200 ℃, decomposition of tire additives at 200∼300 ℃, degradation of natural rubber at 300∼420 ℃, and cracking of synthetic rubber at 420∼500 ℃. The activation energy Eα were calculated according to the Coats-Redfern integral method, ca. 154.72∼158.23 and 200.46∼231.58 kJ/mol for degradation of natural rubber and synthetic rubber, respectively. Most of nitrogen (60.32∼67.78 wt.%), sulfur (56.73∼62.38 wt.%), and chlorine (58.60∼64.92 wt.%) were remained in the pyrolytic char. For the pyrolytic oil composition, expect for alkanes, alkenes, aromatic hydrocarbons, and oxygenates, the S-containing disulfide and sulfurous acid ester, N-containing quinoline and pyrimidine diamine, and Cl-containing silane, dichlorododecylmethyl- were detected. The nitrogen, sulfur, and chlorine in pyrolytic gas had diverse types. The N-containing pollutants mainly derived from inorganic ammonium and heterocyclic-N. NH3 had a wide releasing temperature range, while NO, HCN, and HNCO were mainly generated at 300∼600 °C. The C–S and -SH radicals mainly contributed to S-containing pollutants, i.e., H2S, COS, CS2, SO2, CH3SH, and C6H5SH. The Cl-containing pollutants exhibited dominant release within the temperature range of 300∼600 °C. Overall, higher heating rate promoted gas emissions, especially for NO, HCN, CH3SH, and HCl. This article provides basic knowledge on hazardous N/S/Cl transformation in solid char, liquid oil, and gas during pyrolysis of waste tire that will provide valuable information for future control technologies of pollutants emission.

A thermogravimetric assessment of the tri-combustion process for coal, biomass and polyethylene

Thermogravimetric analysis (TGA) was applied to evaluate the combustion behaviour of combining three feedstocks coal, biomass and polyethylene as a tri-fuel for various blend ratios. The feed materials assessed were bituminous coal (BC), anthracite coal (AC), camphor wood (CW), wheat straw (WS) and polyethylene-terephthalate (PET). The kinetic parameters of the tri-fuel blends were assessed using a Coats-Redfern integral method. The kinetic analysis indicates that the tri-fuel combustion mechanisms follow the diffusion model (D1 & D4) and can be separated in to three distinct stages. TGA analysis demonstrated that an increase in the blend ratio of biomass (CW/WS) and plastic (PET) enhances the combustion properties with respect to lowering the ignition (Ti) and burnout (Th) temperatures, along with an increase in the combustion stability indices (Cs/Csi). This enhancement of the combustion behaviour is more evident for the lower volatile anthracite coal tri-fuel blends. As the blend ratio of the anthracite coal is lowered the overall hydrocarbon-volatile content is increased as a function of increasing the biomass and plastic blend ratios. Laboratory scale analytical analysis of blending biomass, plastic with either bituminous coal or anthracite coal demonstrates a synergistic influence which is observed to benefit the overall combustion behaviour (enhanced mass loss rate and burnout). However, further investigation of tri-fuel blending streams assessing the combustion performance (Ti, Th, Ci, Csi, Ea, flue gas emissions and ash chemistry) is required at pilot and plant scale.

Effect of KMnO4 on catalytic combustion performance of semi-coke

AbstractThe effect of KMnO4 on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric analysis. When 6 wt% KMnO4 was added, the ignition temperature of semi-coke was the lowest. The apparent activation energy of semi-coke with different addition amount of KMnO4 was calculated by Coats–Redfern integration method, the apparent activation energy of semi-coke during combustion reaction first decreased and then increased with increase in KMnO4. When 6 wt% KMnO4 is added, the apparent activation energy is minimal. The apparent activation energy of semi-coke with 2 wt% KMnO4 added at different conversion rates was calculated using Flynn–Wall–Ozawa integration method. The results show that the apparent activation energy of semi-coke combustion decreases with the increase of conversion.

Reaction characteristics and kinetics of the low-temperature oxidation and weight gain of coal

ABSTRACT The study of coal oxidation and weight gain at low temperatures is helpful in understanding the spontaneous combustion of coal and its mechanisms. In this study, we comprehensively investigated the low-temperature oxidation properties and the oxygen adsorption weight gain kinetics of Chinese Shenhua subbituminous coal (SH). Using thermogravimetric experiments with various particle sizes, heating rates, and coal ranks, the oxygen adsorption mass gain stages of coal oxidation at low temperatures were investigated. According to the results of these experiments, as the particle size of SH coal decreased, the dry cracking temperature (T1) decreased, the ignition temperature (T2) changed slightly, the weight gain increased, and the spontaneous combustion tendency increased. The three-dimensional diffusion model (Zhuralev-Lesokin-Tempelman) (D5) is suitable for SH coal samples with different particle sizes. A higher heating rate is not conducive to the formation of carbon-oxygen complexes. The D5 model can also be used to fit the kinetics of the SH coal samples at 5 K/min, 10 K/min, and 30 K/min. Unlike the SH coal samples, the Shengli lignite (SL) and Tavan Tolgoi anthracite (TT) samples fit the three-dimensional diffusion model (Jander) (D3). Based on the fitting results of the Achar differential method and the Coats-Redfern integral method, the activation energy E of the low-temperature oxidation weight gain of the coal samples decreases with decreasing coal particle size and with increasing oxidation rate and coal rank.

Determination of some optoelectrical and thermodynamic parameters of β-lithium ammonium sulphate crystals

β-Lithium ammonium sulphate single crystals were grown by slow evaporation solution growth technique. The X-ray diffraction analysis shows that the crystals have an orthorhombic crystal structure with P21cn space group. From the UV–visible spectroscopy, the high transmittance and low reflectance nature of grown crystals was observed. The various optoelectrical parameters like refractive index, extinction coefficient, optical conductivity, electronic polarizability, optical electronegativity and optical band gap were evaluated from the optical transmittance and reflectance data. The Clausius–Mossotti equation and band gap approach were used to calculate the electronic polarizability. The dispersion constants were calculated using Wemple–DiDomenico model and Cauchy dispersion relation. Optical and chemical hardness has been also discussed in terms of polarizability and band gap of the crystals. Some basic thermodynamical variables were also calculated from the thermal analysis. To calculate the activation energy for the decomposition step in these crystals, the Coats–Redfern integral method was used.

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H2PO4 −). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40 °C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350 °C and 350–565 °C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526 °C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.

Pyrolysis kinetics of ZrP-containing aliphatic waterborne polyurethane-based intumescent coating for flame-retarding plywood

The effect of zirconium phosphate (ZrP) on the fire resistance of aliphatic waterborne polyurethane (AWP)-based intumescent flame retardant coatings (IFRCs) has been preliminarily investigated by quantitative analysis including the cone calorimeter and pyrolysis kinetics of ZrP-containing AWP-based coating, respectively. It determines that an appropriate dosage (1 wt%) of ZrP in the AWP-based coating constitutes an improved fire resistance, evidenced by the fire growth index decreased from 0.49 to 0.32 kW m−2·s-1, and the risen fire performance index of 0.55 s m−2 kW-1 from 0.41 s m−2 kW-1. Because of the heat sink (Zr(HPO4)2⋅H2O→ZrP2O7) and catalytic charring of ZrP, the ZrP-containing AWP-based coating exhibits an enhanced flame resistance, evidenced by the formation of double-layer char residues. Furthermore, it clarifies that the 3D Jander model (n=2) mainly governs the whole pyrolysis process of the coating by modified Coats-Redfern integral method, the doped ZrP mainly makes the Eα of 310∼370 ℃ climb from 187.85 kJ mol-1 to 210.79 kJ mol-1, and the Eα during 95∼200 °C increases from 24.96 kJ mol-1 for S0 to 42.63 kJ mol-1. It provides a quantitative analysis of the flame-retarding mechanism of organic-inorganic hybrid coatings firstly.

Dehydration kinetics and thermodynamics of ZrO(NO3)2-doped Ca(OH)2 for chemical heat storage

Long-term heat storage provides an efficient way to utilize solar energy. Hydroxides are potential candidates for this purpose by dehydration-hydration. In this study, we investigated the effect of doping calcium hydroxide with ZrO(NO3)2 on the thermodynamic and kinetic performance for heat storage. ZrO(NO3)2 improved the heat-storage performance of calcium hydroxide and significantly decreased the dehydration temperature. Differential scanning calorimetry and thermogravimetric data indicated that both the dehydration rate and heat-storage capacity of Ca(OH)2 at 310 °C notably increased by doping with ZrO(NO3)2. The Coats–Redfern integral method and Archar–Brindley–Sharp–Wendworth differential method were used to calculate the pre-exponential factor and the activation energy. The activation energy of the dehydration reaction decreased from 176 to 130 kJ/mol by doping with 10 wt% ZrO(NO3)2 (ZrO(NO3)2-Ca(OH)2-x composite, x = 10). The dehydration-mechanism functions for both the ZrO(NO3)2-Ca(OH)2-10 composite and pure Ca(OH)2 were determined to be the same. The kinetic control equation of the ZrO(NO3)2-Ca(OH)2-x composites was derived and tested. The cycling stability for heat storage was investigated. The results showed that these composites are promising materials for long-term heat storage.

Efficient pyrolysis of ginkgo biloba leaf residue and pharmaceutical sludge (mixture) with high production of clean energy: Process optimization by particle swarm optimization and gradient boosting decision tree algorithm

Production of sustainable clean energy can be achieved by co-pyrolysis of agricultural residues and wastewater sludge. Herein, non-additive thermal behaviour of co-pyrolysis of pharmaceutical sludge and ginkgo biloba leaf residues was investigated. Synergistic effect of co-pyrolysis was not obvious at elevated temperatures. Further, kinetics of co-pyrolysis was studied by fitting Coats-Redfern integration method to thermogravimetric (TG) curve. The change of heat and mass transfer in the reactor caused the change of dynamic parameters. Moreover, hybrid particle swarm optimization and gradient boosting decision tree (PSO–GBDT) algorithm was designed to boost the energy production at full-scale pyrolysis plant by monitoring TG curves. PSO–GBDT model well predicts mass loss rate of the mixture at different heating rates confirming that co-pyrolysis of PS and GBLR can results in high energy production by increasing PS pyrolysis. Designing PSO–GBDT model help to reduced waste production by resourceful treatment of waste in to energy.

Investigation on the Explosion and Combustion of Various Carbon–Starch Blended Dust

AbstractThe effect of different carbon allotropes on the explosion and combustion of potato‐starch dust is preliminarily investigated by modified Hartmann tube and cone calorimeter (CC), using expandable graphite (EG), naturally flaky graphite, vermicular graphite, and carbon black as the dust suppressants, respectively. The results show that the maximum explosion pressure (Pmax) decreases from 0.66 to 0.39 MPa and the peak heat release rate reduces from 31.45 to13.64 kW·m−2 for the EG‐starch blended dust, due to the physically shielding effect of the fluffy and charring layer. It clarifies that the combustion of starch is mainly governed by Zhuralev–Lesokin–Tempelman 3D diffusion calculated by the modified Coats–Redfern integral method; the carbonaceous materials block the pyrolysis and migration of volatiles, leading to a decrease in DTGmax. It establishes a comprehensive method to evaluate the explosion and combustion of organic combustible dust, combining the CC with combustion kinetics effectively.

Effect of Er(NO3)3 content on the thermal decomposition kinetics of kaolinite

This study investigated the thermal decomposition process of kaolinite mixed with different Er(NO3)3 contents by means of a comprehensive thermal analysis (TG-DTG). HTXRD, SEM-EDS, TEM, AFM and 27Al MAS NMR analyses were used; the activation energy, controlling mechanism function and pre-exponential factor of the thermal decomposition kinetics for kaolinite were obtained through the Coats-Redfern integral and Achar differential methods; and the Ozawa method was used to verify the activation energy. The results showed that as the Er(NO3)3 content increased, the controlling mechanism function of the thermal decomposition kinetics of kaolinite transformed from chemical reaction model F3 to F2, whereas the activation energy and pre-exponential factors decreased rapidly before stabilizing. The corresponding temperature at the maximum reaction rate decreased significantly as the Er(NO3)3 content increased for higher heating rates (≥25 °C·min−1), promoting the thermal decomposition reaction of kaolinite. The 27Al MAS NMR spectra indicated that increasing the Er(NO3)3 content accelerated the transformation of A1VI to AlV as part of the thermal decomposition reaction of kaolinite. Er(NO3)3 in the sample was first converted to ErONO3 and was then dispersed evenly as Er2O3 nanoparticles.

Comprehensive Kinetic Study on the Pyrolysis and Combustion Behaviours of Five Oil Palm Biomass by Thermogravimetric-Mass Spectrometry (TG-MS) Analyses

Thermochemical conversion process is one of the most promising routes to harness the potential of oil palm biomass as renewable energy alternative in Malaysia. Despite this potential, there is a lack of comprehensive study that characterises the complete spectrum of oil palm biomass. In this work, thermogravimetric-mass spectrometry (TG-MS) results of five oil palm biomass, i.e., oil palm trunk (OPT), palm kernel shell (PKS), oil palm frond (OPF), mesocarp fibre (MF) and empty fruit bunch (EFB), in pyrolysis and combustion conditions are presented and analysed. Kinetic studies on the TG data of these biomass were performed using Coats–Redfern integral method and Sestak–Berggren function to determine the activation energy and the reaction mechanism at different thermal decomposition stages. Pyrolysis of hemicellulose, cellulose, and lignin occurs at 140–331, 235–435, and 380–600 °C, respectively, while combustion of hemicellulose, cellulose, and lignin took place at 140–313, 225–395, and 372–600 °C, respectively. The activation energy was the highest for cellulose decomposition in both pyrolysis and combustion cases. Phase boundary reaction dominated during hemicellulose and cellulose decompositions, while nucleation dominated during lignin decomposition and char oxidation. MS results show that majority of the gases came out between 250 and 600 °C, mainly from CH4 and H2O in pyrolysis case and from CH4, CO2 and H2O in combustion case. Other than these major gases, NO, NO2 and SO2 were also generated although in much lower proportion compared to these gases. Based on TG-MS results, the best potential application for each biomass was also identified where OPT and OPF are suggested for gasification and fermentation, PKS for bio-char production and combustion, MF for bio-oil production, combustion, and bio-char production and EFB for bio-oil and bio-char production.

Comparative studies of structure, thermal decomposition mechanism and thermodynamic parameters of two kinds of silk fibroin films

The silk fibroin films from Chinese and Thai silkworms were prepared by a new method of calcium chloride-formic acid system. The films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. The morphological, molecular conformation and thermal stability of the material and the thermal decomposition mechanism were obtained as well as the kinetic parameters (activation energy E , pre-exponential factor A ) and thermodynamic parameters (Δ H ≠, Δ G ≠ and Δ S ≠), and a compare research were performed. The results showed that the structure of silk fibroin film under 1.5 wt% concentration system mainly appeared β -sheet, and the membrane structure under 3.0 wt% concentration system was dominated by random coils or α -helix; At the different heating rate, the decomposition temperature, activation energy and activation enthalpy of 3.0 wt% concentration system were all lower than those of 1.5 wt%, and the latter has better thermal stability than the former. Under the same concentration, the β -sheet content of Thai silk fibroin film is slightly higher than that of China and it had better thermal stability. It was found by Achar differential method and Coats-Redfern integration method that the thermal decomposition process of silk fibroin film follows the cylindrical symmetry (two-dimensional diffusion) mechanism at 464~ 594 K.

Comparative effect of ionic liquids pretreatment on thermogravimetric kinetics of crude oil palm biomass for possible sustainable exploitation

Crude oil palm biomass (OPB) residue is an important source of lignocellulose and could be transformed into biofuels through thermochemical conversion for heat and power in CHP plants or act as sustainable reinforcement in the biocomposite industry. Effective pretreatment is an essential task for the utilization of waste biomass for bioenergy and biomaterials. The comparative effect of two ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and 1-ethyl-3-methylimidazolium diethylphosphate ([emim[dep]), on OPB pyrolysis kinetic and thermodynamic parameters was studied using thermogravimetric analysis (TGA) coupled with Coats-Redfern integral method. The OPB residue was pretreated with ILs [bmim][Cl] and [emim][dep] under mild processing conditions of 90 °C for 3 h and was also subjected to three other conventional pretreatment methods called dilute acid, alkaline, and hot compressed water to better understand and compare the performance of ILs for pretreatment of lignocellulosic OPB. Results reveal that ILs pretreatment was superior in terms of delignification of OPB and produced the cellulose-rich fiber with 48.2% and 41.2% cellulose compared to cellulose fraction of 26.4% for the untreated sample. The values of apparent activation energies were found to be 81.8, 90.9, 92.0, 84.9, 83.8, and 93.5 kJ/mol for untreated, [bmim][Cl], [emim][dep], dilute acid, base, and hot compressed water pretreatments respectively. Further calculation of thermodynamic parameters led to the change in Gibb's free energy (ΔG°) values of 188.9, 208.0, 210.9, 219.1, 217.4 and 217.1, kJ/mol for untreated, [bmim][Cl], [emim][dep], dilute acid, base, and hot compressed water pretreatments respectively. The higher change in entropy (ΔS°) values of ILs-pretreated fibers compared to the untreated one showed that dissolution and regeneration from ILs solution had unlocked the complex 3D structure of lignocellulose, resulting in increased disorder. The results plainly revealed that ILs-based pretreatment could be a promising and environmentally benign technology for efficient utilization of agricultural residues in the fields of biofuels and biocomposite materials.

Synergistic effect on co-pyrolysis of rice husk and sewage sludge by thermal behavior, kinetics, thermodynamic parameters and artificial neural network

This study investigates the thermal decomposition, thermodynamic and kinetic behavior of rice-husk (R), sewage sludge (S) and their blends during co-pyrolysis using thermogravimetric analysis at a constant heating rate of 20 °C/min. Coats-Redfern integral method is applied to mass loss data by employing seventeen models of five major reaction mechanisms to calculate the kinetics and thermodynamic parameters. Two temperature regions: I (200–400 °C) and II (400–600 °C) are identified and best fitted with different models. Among all models, diffusion models show high activation energy with higher R2(0.99) of rice husk (66.27–82.77 kJ/mol), sewage sludge (52.01–68.01 kJ/mol) and subsequent blends (45.10–65.81 kJ/mol) for region I and for rice husk (7.31–25.84 kJ/mol), sewage sludge (1.85–16.23 kJ/mol) and blends (4.95–16.32 kJ/mol) for region II, respectively. Thermodynamic parameters are calculated using kinetics data to assess the co-pyrolysis process enthalpy, Gibbs-free energy, and change in entropy. Artificial neural network (ANN) models are developed and employed on co-pyrolysis thermal decomposition data to study the reaction mechanism by calculating Mean Absolute Error (MAE), Root Mean Square Error (RMSE) and coefficient of determination (R2). The co-pyrolysis results from a thermal behavior and kinetics perspective are promising and the process is viable to recover organic materials more efficiently.

Towards oxy-steam combustion: The effect of increasing the steam concentration on coal reactivity

Oxy-steam combustion and devolatilization performance of three different coals (anthracite, blend of bituminous coals and low-rank coal) was studied in a thermobalance with a water vapour furnace under variable steam concentrations (0, 20, 40 and 70 vol% H2O) in N2 and CO2. Two oxygen concentrations were used during the combustion tests (20 and 30 vol%). Devolatilization behaviour was similar under N2 and CO2 atmosphere and increasing steam concentration did not affect significantly the observed reactivity and the reaction temperature range. Replacing CO2 with 20 vol% H2O during combustion tests produced a decrease in ignition and burnout temperatures. When H2O content increased to 40 and 70 vol%, this effect was only found with high-rank anthracite. Maximum mass loss rates for the low-rank coal with high volatile content were up to four times higher than with the other two coals. During direct oxidation experiments, DTG curves of anthracite and the coal blend showed a double peak, corresponding to devolatilization and oxidation reactions. This allowed determining independent kinetic parameters (Ea and A) for both stages. An only DTG peak was detected with the low-rank coal since devolatilization and oxidation reactions took place simultaneously owing to its high reactivity. Devolatilization and oxidation kinetics followed a first-order reaction using the Coats-Redfern integral method. Significant differences were not observed between the activation energies of the three coals when comparing conventional (N2), oxy-fuel (CO2) and oxy-steam conditions (70 vol% H2O in CO2), although Ea values were higher for the devolatilization stage than for the oxidation process.

Transition metal complexes supported by ONNN/ONNS bis-bidentate benzoxazine Schiff base: Synthesis, characterization, geometry optimization and non-isothermal kinetic parameters

Thiophene nucleus has shown various biological activities like antibacterial, analgesic, antitumor, anti-inflammatory and used as building blocks for synthesis of agrochemicals. It has applications as metal chelating agents and in the development of insecticides. Due to excellent chelation, studies on metal chelates with Schiff bases of thiophene nucleus have received good attention.In the present study, the complexes of Co (II), Ni (II), Cu (II) and Zn (II) with Schiff base 3-(2-(thiophen-2-yl methylene) hydrazinyl)-2H-benzo [b] [1,4] oxazin-2-one (TM-HBO) derived from Thiophene-2-carboxaldehyde and 3-Hydrazino-1,4-benzoxazine-2-one (HBO) have been synthesized. The ligand acts as bis-bidentate ONNN/ONNS donor.The characterization of the ligand was done by LC-MS, IR, 1H NMR and electronic spectral studies. Characterization of the complexes was done by elemental analysis, molar conductivity studies, magnetic susceptibility studies, thermal studies, IR, electronic, ESR spectral studies etc. The geometrical structures have been found to be octahedral and square planar/octahedral. Degradation pattern of the compounds is shown by thermal studies.Thermal stabilities of Co (II), Ni (II), Cu (II) and Zn (II) complexes of TM-HBO were calculated by TGA analysis. The Kinetic parameters-energy of activation (Ea), enthalpy (ΔH), entropy (ΔS) and free energy changes (ΔG) have been determined by thermogravimetric data. Coats-Redfern integration method with thirteen kinetic models was used to calculate the kinetic and thermodynamic parameters for the degradation of all the complexes.The stability of the ligand and Cu (II) complex were obtained from their molecular orbital structures from which the quantum chemical parameters were calculated using the HOMO-LUMO energies.

Prediction of combustion activation energy of NaOH/KOH catalyzed straw pyrolytic carbon based on machine learning

Abstract Wheat straw, corn straw and sorghum straw were used as raw materials. KOH and NaOH were used as catalysts to prepare straw pyrolytic carbon (SPC) and the characteristics of combustion activation energy (AE) were analyzed by thermogravimetric analysis. The distributed modified Coats-Redfern integration method was used to compute the distributed AE. The predictive models of combustion AE based on Linear Regression (LR), Support Vector Regression (SVR) and Random Forest Regression (RFR) were proposed and compared. The results showed the AE variation trend of three kinds of SPCNaOH, SPCKOH and SPCNa-KOH were basically the same and obviously decreased. In the LR model, degree value was 2 and R2 reached 0.8531. In the SVR model, the kernel function was Polynomial, C = 3000, degree = 4, coef0 = 0.3 and R2 reached 0.9048. In the RFR model, the n_estimators value was 400 and R2 reached 0.9834. Compared with the LR and SVR model, the RFR model was more suitable for the AE prediction of alkali-catalyzed SPC.

Pyrolysis of high ash sewage sludge: Kinetics and thermodynamic analysis using Coats-Redfern method

Abstract This study aims to investigate the thermo-kinetics of high-ash sewage sludge using thermogravimetric analysis. Sewage sludge was dried, pulverized and heated non-isothermally from 25 to 800 °C at different heating rates (5, 10 and 20 °C/min) in N2 atmosphere. TG and DTG results indicate that the sewage sludge pyrolysis may be divided into three stages. Coats-Redfern integral method was applied in the 2nd and 3rd stage to estimate the activation energy and pre-exponential factor from mass loss data using five major reaction mechanisms. The low-temperature stable components (LTSC) of the sewage sludge degraded in the temperature regime of 250–450 °C while high-temperature stable components (HTSC) decomposed in the temperature range of 450–700 °C. According to the results, first-order reaction model (F1) showed higher Ea with better R2 for all heating rates. D3, N1, and S1 produced higher Ea at higher heating rates for LTSC pyrolysis and lower Ea with the increase of heating rates for HTSC pyrolysis. All models showed positive ΔH except F1.5. Among all models, Diffusion (D1, D2, D3) and phase interfacial models (S1, S2) showed higher ΔG as compared to reaction, nucleation, and power-law models in section I and section II.