Pyrolysis is a promising method for the recovery of waste printed circuit boards (WPCBs), but few researches have noticed the influence of in-situ metals. This study conducted a series of comparisons ...between metal-free leftover pieces (LP) and intact boards (IB), including pyrolysis characteristics, volatile emission, kinetics, and thermodynamic parameters. The thermo-gravimetry (TG) analyses indicated that both the samples presented predominant mass loss in narrow temperature intervals, and characteristic pyrolysis temperatures of IB were approximately 15 °C lower than those of LP. Dominant constituents in evolved gases were detected by Fourier-transform infrared spectrometry as CO2, phenol, bromophenol, ethers, ketones, and aldehydes, and metals accelerated the generation of light hydrocarbons and aromatic compounds. The activation energy and thermodynamic parameters were calculated and compared, and the results verified the presence of in-situ metals led to a lower energy barrier and higher reaction extent. Moreover, conversion behaviors of Cu, Fe, Sn, and Pb manifested the formation of metal bromides and implied the reduction of brominated volatiles. The obtained results confirmed the catalytic effect of in-situ metals on PCBs pyrolysis and their bromine fixation abilities. This study contributes to fundamental knowledge that can be used to guide the pyrolysis of WPCBs.
•Systematic comparisons were conducted between WPCBs with and without metals.•Characteristic pyrolysis temperatures of IB were ~15 °C lower than those of LP.•In-situ metals catalyze WPCBs pyrolysis by altering the mechanism and decreasing Eα.•The formation of metal bromides reduced the generation of brominated volatiles.•Remaining in-situ metals in WPCBs was beneficial for pyrolysis.
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•Waste IHS was used as feedstock to produce biochar.•First detailed investigation on non-isothermal pyrolysis kinetics of IHS.•The reaction mechanism model of IHS pyrolysis was ...reconstructed.•The TPR model well described the pyrolysis process of IHS.
The evaluation of pyrolysis kinetics for waste industrial hemp stem (IHS) is essential to achieve the high-value utilization of agricultural waste. In present study, firstly, non-isothermal pyrolysis experiments of IHS were performed at different heating rates using a thermogravimetric analyzer. Then, the kinetic triplets (apparent activation energy, pre-exponential factor, and reaction mechanism) of the three pseudo components for IHS (hemicellulose, cellulose, and lignin) were determined by a three-parallel-reaction model. Moreover, the pyrolysis products were also characterized via FTIR and SEM. The results showed that the apparent activation energies of hemicellulose, cellulose and lignin were 86.523, 113.257 and 197.961 kJ/mol, respectively; the pre-exponential factors were 6.887 × 107, 8.179 × 109 and 1.801 × 1015 s−1, respectively; and the reaction mechanism functions were f(α) = α1.35629(1-α)0.34832-ln(1-α)−1.20128, f(α) = α3.42900(1-α)0.01288-ln(1-α)-2.84445, f(α) = α0.68738(1-α)3.09313-ln(1-α)-1.58522, respectively. The release temperature for volatile products of IHS pyrolysis was mainly between 440 and 840 K. IHS as an agricultural waste is a suitable feedstock to produce renewable energy.
The compositional distribution of pyrolysis products is related to the molecular structure of coal and pyrolysis parameters. In this study, gaseous products generated from the pyrolysis of two ...low-rank coals were analyzed by an online home-built infrared detection system. The effect of heating rate and temperature on compositional distribution was considered and evaluated. Fourier transform infrared (FTIR), gas chromatograph/mass spectrometry (GC/MS), and Orbitrap-MS were employed to analyze other pyrolysis products such as raw coals, chars, and tars. In the pyrolysis process, oxygen-containing compounds in coal were the first species to participate in pyrolysis reactions. With the enhancement of temperature, the content of aromatic hydrocarbons showed an increasing trend, and the contents of aliphatic hydrocarbons and oxygenates decreased. In the four major pyrolysis gases, the yield of H2 was the highest and the lowest for CO2. In addition, dynamic curves of the main pyrolysis gas were obtained, and the activation energies of pyrolysis gases were calculated by Ozawa-Flynn-Wall’s (OFW) method. The possible generation pathways of gaseous products were proposed.
•Online infrared device was used to study the release behavior of pyrolysis gas.•The transformation path of pyrolysis products is proposed.•The effect of secondary reaction on the product was investigated.
Kinetic parameters of pyrolysis reaction were important data for simulations of thermal conversion processes of biomass. This study aimed to develop a proper kinetics investigation method for the ...pyrolysis reaction. Here, a quasi-single reaction of pyrolysis was assumed to simplify the reactions. The model comparison among three favorite model-free methods including Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose and Friedman methods, was considered. From TGA results of three biomasses, i.e., corn cob, Napier grass, and sugarcane top and leaves, they indicated that using parameters values via Friedman method in a conversion range of 0.1–0.6 could give conversion curves mostly in good agreement with experimental results when deriving them in a polynomial order of 2 (quadratic) regression model and using a reaction order of 3. Another purpose of the study was to investigate effect of mixing different biomasses on kinetics of pyrolysis reaction by plotting the parameters in a ternary diagram of tri-component biomass which was mixture of the herein biomasses. The diagram indicated that mixtures with more high-hemicellulose biomass (like corn cob) would show less activation energy in a temperature range of 220–315 °C. While mixtures with more high-cellulose biomass (like sugarcane top and leaves) would show less activation energy in a temperature range of 315–400 °C.
Considering the extensive application of wood materials in the construction and manufacturing, waste wood has potential of converting into new natural energy sources. In this study, cypress, pine and ...fir woods commonly used in China, as well as old samples for above each species (more than 200 years old) have been used to study the aging and species effects on their thermal stability and combustion models. To obtain the kinetic triplets of the pyrolysis process, all samples have been heated in a nitrogen atmosphere with heating rates of 5, 10, 15, and 20 K min−1. The kinetics parameters of pyrolysis throughout the conversion process were then calculated using isoconversional method, Coats-Redfern (CR), and masterplots methods. The reconstructed theoretical models have been then adjusted using the accommodation functions. The results of this study contribute to an increased understanding of the fire mechanism of waste woods, and implications concerning to provide scientific theoretical guidance for its feasibility as a new energy fuel more efficiently.
Corn residues are an important source of bioenergy. Due to their highly diverse lignocellulosic structures, the hydrochar produced from microwave-assisted carbonization of different corn residues may ...have distinct fuel properties and pyrolysis kinetics. This study comprehensively investigated the effect of processing temperature on the basic fuel properties of hydrochar and examined the pyrolysis behavior of hydrochar as a precursor through kinetic analysis. The results indicate that the fuel quality of corn straw hydrochar prepared by microwave-assisted hydrothermal carbonization at 230 °C was significantly improved over that of its feedstock, with a higher heating value of approximately 20.7 MJ/kg. Hydrochar prepared by microwave-assisted hydrothermal carbonization of corn cob at 230 °C presents noticeable environmental advantages because it contains the lowest ash and nitrogen contents (0.5% and 0.5%, respectively) and lower sulfur content (0.05%). Moreover, regarding the kinetic modeling, the Doyle and Coats-Redfern models, which are both first-order and single-step kinetic models, were identified as satisfactory in interpreting the key pyrolysis kinetic parameters. Additionally, the microwave-assisted hydrothermal process increased the apparent activation energy of hydrochar due to the increase in crystallinity and the increase in the number of CC and CO bonds.
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•Fuel properties of microwave hydrochar from different corn residues are compared.•Pyrolysis kinetic analysis based on Doyle and Coats-Redfern models is performed.•Higher heating values of hydrochar produced from corn straw reached 20.7 MJ/kg.•First-order and single-step kinetic models are suitable for the pyrolysis of corn residues.•Corn cob showed the lowest activation energy, which could ease its carbonization.
Biomass pyrolysis is a fundamental thermochemical conversion process that is of both industrial and ecological importance. From designing and operating industrial biomass conversion systems to ...modeling the spread of wildfires, an understanding of solid state pyrolysis kinetics is imperative. A critical review of kinetic models and mathematical approximations currently employed in solid state thermal analysis is provided. Isoconversional and model-fitting methods for estimating kinetic parameters are comparatively evaluated. The thermal decomposition of biomass proceeds via a very complex set of competitive and concurrent reactions and thus the exact mechanism for biomass pyrolysis remains a mystery. The pernicious persistence of substantial variations in kinetic rate data for solids irrespective of the kinetic model employed has exposed serious divisions within the thermal analysis community and also caused the broader scientific and industrial community to question the relevancy and applicability of all kinetic data obtained from heterogeneous reactions. Many factors can influence the kinetic parameters, including process conditions, heat and mass transfer limitations, physical and chemical heterogeneity of the sample, and systematic errors. An analysis of thermal decomposition data obtained from two agricultural residues, nutshells and sugarcane bagasse, reveals the inherent difficulty and risks involved in modeling heterogeneous reaction systems.
The study is focussed on the experimental investigation of fine coal pyrolysis in TGA reactor. The non-isothermal pyrolysis experiment is conducted at three different heating rates (20,30 and ...40 °C/min) in Nitrogen ambience. The highest experimental temperature was maintained at 950 °C. The mass loss profile shows that higher heating rate favours the higher conversion as compared to low heating rate but the final conversion on the given time span is lower in the case of higher heating rate. The reaction kinetics is estimated using Iso-conversional method. activation energy varies from the range of 31.41 kJ/mol to 50.42 kJ/mol. Also, the pre-exponential factor value varies in the range of 1.05 × 106 to 1.4 × 107 min−1. The average pre-exponential factor was calculated from the average energy of activation found by model-free method. The value of pre-exponential factor is found to be A0 = 5.52 × 1010 min−1.
This study aimed to clarify the catalytic characteristic and hydrogen supply of spent bleaching clay (SBC) in the pyrolysis of corncob lignin. The effects of lignin doping ratio (0%, 25%, 50%, 75%, ...and 100%) and pyrolysis temperature (450 ℃, 550 ℃, and 650 ℃) on pyrolysis products were evaluated. The results of the kinetic analysis showed that when the lignin doping ratio was 75%, the activation energy was 51.753 kJ·mol−1, which was lower than that achieved in lignin-only pyrolysis. When the lignin doping ratio was 75% (550 ℃), the relative content of P-type phenols (methoxy-free phenols) was 23.08%, which reflected an increase of 34.23% relative to the theoretical value. Corncob lignin and SBC produced favorable synergistic effects during co-pyrolysis, which promoted the production of P-type phenols (synergistic effect reached 134.44%) and aromatic hydrocarbons (synergistic effect reached 36.98%) and the inhibition of various oxygenated compounds. Concurrently, the mechanism of the synergy between lignin and SBC during co-pyrolysis was proposed based on the experimental results. This study could provide basic research and theoretical reference for the resource utilization of lignin and SBC waste.
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•SBC was not only a hydrogen donor but also a catalyst during co-pyrolysis.•SBC promoted demethoxy and decarbonylation reactions during co-pyrolysis.•The highest promoting synergistic effect of hydroxy phenols during co-pyrolysis was 134.44%.•The possible co-pyrolysis synergistic mechanism of lignin with SBC was proposed.
The waste corncob-based lignin (AL) treated by alkali was applied as feedstock to prepared activated carbon (AC) for the methylene blue (MB) adsorption. To explore the pyrolysis mechanism of ALs, the ...pyrolysis kinetics were discussed by the methods of Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) equations at different heating rates, which are widely applied in the determination of dynamic parameters with reduction of the errors of multi-step dynamics. In the process of preparing lignin-based activated carbon (LC), the relationship between pyrolysis condition and structure of LCs was systematically investigated. The maximum specific surface area of LCs reached 1215.83 m2/g with high the mesoporous proportion (77.3%) at optimal activation conditions including activation temperature (550 °C), activation duration (120 min) and phosphoric acid concentration (50%). For the adsorption of methylene blue (MB) solution, the fitted kinetic model was in accordance with the pseudo-second-order kinetic model. The adsorption capacity of MB could achieve as high as 493.28 mg/g (± 5 mg/g), and the highest removal rate of MB could reach 99.0% (± 0.2%) during the secondary adsorption process. This work offers a prospective proposal to provide theoretical reference for producing LC based on pyrolysis of alkaline lignin, and utilize the LC as potential adsorbent in the dyeing wastewater treatment.
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•The pyrolysis mechanism of lignin at different heating rates were investigated.•The maximum SSA of lignin activated carbon (LC) reached 1216 m2/g.•The structure and adsorptivity of LC were systematically elucidated.•The maximum adsorption capacity of LC to methylene blue (MB) reached 493.28 mg/g.•The highest removal rate of MB reached 99% during the secondary adsorption process.
