Energy potential and thermogravimetric study of pyrolysis kinetics of biomass wastes

The use of agricultural wastes for energy conversion has been widely studied as renewable and carbon neutral energy sources. This paper aims to evaluate the energetic potential of six agricultural wastes—sugarcane bagasse, bean pods, corn stover, pineapple crown leaves, white cotton and natural coloured cotton stalks, through their characterization and pyrolysis kinetic study. The energetic potential of biomasses was evaluated by ultimate and proximate analysis, higher heating value (HHV), apparent density, and kinetic parameters of conversion and apparent activation energy (E_a) determined by Model-Free kinetics though thermogravimetric analysis data. The results indicate energetic density for dry basis biomasses, such as moisture content less than 7%, volatiles higher than 77% and moderate ash content. The HHVs were higher for the biomass with low O:C ratio. The E_a values increased with increasing O:C ratio and were also influenced by the biomass ash content. Among the studied biomasses, PCL are less explored for energy application, although the results confirm its potential for application in thermochemical processes such as pyrolysis or combustion.

     

Kinetic analysis of co-pyrolysis of cellulose and polypropylene

The present research work focuses on understanding the kinetics and mechanism of co-pyrolysis of cellulose, a major constituent of biomass, and polypropylene (PP) that is abundantly present in waste plastics. Co-pyrolysis of cellulose and PP of different compositions, viz., 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 (mass%/mass%), was carried out in a thermogravimetric analyzer at various heating rates from 5 to 180 K min^?1. The kinetics of slow to medium heating rate pyrolysis was analyzed using first Kissinger and Kissinger–Akahira–Sunose techniques. Cellulose and PP decomposition occurred in two distinct temperature regimes, viz., 575–650 and 675–775 K, respectively. However, apparent activation energies of thermal decomposition of the mixtures clearly indicated the presence of interaction between cellulose and PP. The presence of cellulose in the mixture decreased the apparent activation energy of PP decomposition from 210 to 120 kJ mol^?1, while the presence of PP did not affect the apparent activation energy of cellulose decomposition (E _a = 158 ± 3 kJ mol^?1). A significant decrease in apparent activation energy was observed in the conversion regime corresponding to the completion of cellulose pyrolysis and beginning of PP pyrolysis. Differential scanning calorimetry data clearly showed the shift of exothermic char formation to higher temperatures with PP incorporation in the mixture. The presence of PP also resulted in reduction of final char content. Based on the above analyses, a new interaction step that involves a bimolecular reaction of activated PP with volatiles from cellulose pyrolysis to form interaction products and char is proposed, and the rate limiting steps for char formation are clearly identified.     

Characterization and comparative study of pyrolysis kinetics of the rice husk and the elephant grass

A comparative evaluation of different biomasses allows the choice that presents the best potential as fuel for energy production. The knowledge of the thermal and kinetics parameters of the biomass in the process of thermal conversion is fundamental as their chemical and physical characterization. Various methodologies have been developed for the determination of kinetic parameters as apparent activation energy and reaction order from the thermogravimetric analysis. In this work, the apparent activation energy needed to break the bonds of hemicelluloses and cellulose of rice husk and elephant grass during the thermal conversion was evaluated according to the kinetics models of Flynn and Wall and Model Free Kinetics developed by Vyazovkin. The biomass elephant grass and rice husk were characterized for moisture, ash and volatile matter by ASTM E871, ASTM E1755, ASTM E872, respectively, and fixed carbon by difference. The percentage of carbon, hydrogen, nitrogen, and oxygen were determined by ultimate analysis. The elephant grass showed to be more suitable for production of bio-oil through pyrolysis due to the higher percentage of volatile, less ash content and less energy required to break the bonds of hemicellulose and cellulose than rice husk in the thermal conversion process.     

The pyrolysis process of wood biomass samples under isothermal experimental conditions—energy density considerations: application of the distributed apparent activation energy model with a mixture of distribution functions

This work deals with the isothermal pyrolysis of Pine and Beech wood samples and kinetic studies, using the thermo-analytical technique, at five different operating temperatures. Pyrolysis processes were investigated by using the distributed apparent activation energy model, which involves the complex mixture of different continuous distribution functions. It was found that decomposition processes of wood pseudo-components take place in different conversion areas during entire pyrolyses, whereby these areas, as well as the changes in apparent activation energy (E _a) values, are not the same for softwood and hardwood samples. Bulk density (Bden) and energy density (ED) considerations have shown that both biomass samples suffer from low Bden and ED values. It was concluded that pyrolysis can be used as a means of decreasing transportation costs of wood biomass materials, thus increasing energy density. The “pseudo” kinetic compensation effect was identified, which arises from kinetic model variation and wood species variation. In the current extensive study, it was concluded that primary pyrolysis refers to decomposition reactions of any of three major constituents of the considered wood samples. Also, it was established that primary reactions may proceed in parallel with simultaneous decomposition of lignin, hemicelluloses and cellulose in the different regions of wood samples, depending on the operating temperature. It was established that endothermic effects dominate, which are characterized with devolatilization and formation of volatile products. It has been suggested that the endothermic behavior that arises from pyrolyses of considered samples may indicate the endothermic depolymerization sequence of cellulose structures.     

Reducing end-group of cellulose as a reactive site for thermal discoloration

Thermal discoloration of cellulose (Avicel PH-101 and Whatman No. 42 filter paper) was studied in N₂ at 160-280 °C with glycerol-treated and NaBH₄-reduced samples, to understand the role of the reducing end. Thermal discoloration of glycerol-treated Avicel PH-101, in which some of the reducing ends were converted into glycosides (non-reducing ends), was suppressed compared with the original cellulose, and the level of suppression was directly related to the extent of glycosylation of the reducing ends. The stabilization efficiency of glycerol-treated Whatman No. 42 filter paper suggested that the reducing ends newly formed by reduction of the degree of polymerization (DP) (to about 200) during heat treatment contributed to the discoloration. The important role of the reducing ends in thermal discoloration was supported by the stabilization of Avicel PH-101 by reduction with NaBH₄ (giving a reducing end content that was 2% of that of the original cellulose). Thermally induced discoloration was also inhibited by heating cellulose in suspension in the polyether tetraethyleneglycol dimethylether, which has been reported to inhibit the thermal degradation of reducing sugars.     

On the thermal degradation of cellulose in cotton fibers

Thermal decomposition of cellulose has been widely studied for the past several years. It has been reported that the source of cellulose and its composition greatly affect its pyrolysis. One of the most widely used analytical tools for the study of cellulose pyrolysis is thermogravimetric (TG) analysis. Several model-fitting methods have been employed to study cellulose pyrolysis kinetics. An alternative to the model-fitting approach is the so-called model-free method developed by Vyazovkin. This isoconversional technique calculates the activation energy as a function of the degree of the conversion. In this article, the pyrolysis of cellulose in cotton fibers compared to microcrystalline cellulose (Avicel, PH 105) was investigated. TG curves were acquired as a function of the heating rates (4, 5, 8, 10, and 16 °C min^?1) and the model-free method was used to analyze the data. Activation energies of cotton fibers and Avicel were obtained, and compared to the data reported in the literature. In addition, models for isothermal decomposition were calculated and compared with experimental data at the same temperature.     

Thermogravimetric analysis of lignocellulosic and microalgae biomasses and their blends during combustion

Thermogravimetric analysis was used to study and compare the combustion of different blends of corn bioresidues with sunflower, rape and algae bioresidues. Non-isothermal thermogravimetric data were used to obtain the combustion kinetics of these bioresidues. This paper reports on the application of the Vyazovkin and Ozawa–Flynn–Wall isoconversional methods for the evaluation of kinetic parameters (energy activation, pre-exponential factor and order of reaction) for the combustion of the biomasses studied. Differences were found in the TG curves in accordance with the proximate analysis results for the cellulose, hemicellulose and lignin content of biomasses. The activation energy obtained from combustion (E ~ 151.6 kJ mol^?1) was lower than that from the blends (similar values were obtained for corn–sunflower, E ~ 160.5 kJ mol^?1 and corn–rape, E ~ 156.9 kJ mol^?1) whereas the activation energy obtained from the microalgae was higher (E ~ 171.5 kJ mol^?1). Both the Vyazovkin and Ozawa–Flynn–Wall methods yielded similar results.     

Thermogravimetric investigation of the pyrolysis of pitch materials. A compensation effect and variation in kinetic parameters with heating rate

Thermogravimetric measurements of weight loss accompanying the pyrolysis of four pitches have been made over a range of linear heating rates. For three of the samples, the data at each heating rate could be described by an integral and a differential method of analysis, assuming a simple order function for f(α), with the result that the apparent activation energy increased with heating rate. The data for all four samples could also be satisfactorily described by the Ozawa or Friedman multiple heating rate methods, and these resulted in apparent activation energies (E_a) which increased with the value of β at which they were determined. It is suggested that this tendency for the apparent activation energy to increase, as the temperature is raised, is due to a change in the relative importance of the different reactions which lead to weight loss in this system. The apparent kinetic parameters all fall on a common compensation plot which is used to explain the relative magnitude of E_a values from Ozawa and Doyle methods of analysis. The higher values of E_a from Friedman than from Ozawa analyses are also explained.     

The pyrolysis characteristics of moso bamboo

In the research, thermogravimetry (TG), a combination of thermogravimetry and Fourier transform infrared spectrometer (TG–FTIR) and X-ray diffraction (XRD) were used to investigate pyrolysis characteristics of moso bamboo (Phyllostachys pubescens). The Flynn–Wall–Ozawa and Coats–Redfern (modified) methods were used to determine the apparent activation energy (E_a). The TG curve indicated that the pyrolysis process of moso bamboo included three steps and the main pyrolysis occurred in the second steps with temperature range from 450 K to 650 K and over 68.69% mass was degraded. TG–FTIR analysis showed that the main pyrolysis products included absorbed water (H₂O), methane gas (CH₄), carbon dioxide (CO₂), acids and aldehydes, ammonia gas (NH₃), etc. XRD analysis expressed that the index and width crystallinity of moso bamboo gradually increased from 273 K to 538 K and cellulose gradually degraded from amorphous region to crystalline region. The E_a values of moso bamboo increased with conversion rate increase from 10 to 70. The E_a values were, respectively 153.37–198.55 kJ/mol and 152.14–197.87 kJ/mol based on Flynn–Wall–Ozawa and Coats–Redfern (modified) methods. The information was very helpful and significant to design manufacturing process of bio-energy, made from moso bamboo, using gasification or pyrolysis methods.     

The role of microstructure in the pyrolysis of polypropylene. A preliminary study on the syndiotactic stereoisomer

The pyrolysis of two syndiotactic polypropylene samples with different molar mass and microstructure has been studied by means of TGA. The volatiles evolved have been analysed as a whole by mass spectrometry. The relative content of the different low mass alkenes, alkanes and dienes provides a fingerprint which has been used to asses the similarity of the mechanism. The changes in the apparent E_a with conversion have been shown by means of the Friedman’s method.The results show that, even though the chemical pattern is identical in both samples, important differences in the E_a trends are found. Such disparity in the energy requirements for the pyrolysis to take place can be reasonably attributed to the different microstructure of the samples.     

Application of isoconversional calculation procedure to non-isothermal kinetics study

The kinetics of thermal decomposition of NH₄CuPO₄·H₂O was studied using isoconversional calculation procedure. The iterative isoconversional procedure was applied to estimate the apparent activation energy E _a; the values of apparent activation energies associated with the first stage (dehydration), the second stage (deamination), and the third stage(condensation) for the thermal decomposition of NH₄CuPO₄·H₂O were determined to be 117.7 ± 7.7, 167.9 ± 8.4, and 217.6 ± 45.5 kJ mol^?1, respectively, which demonstrate that the third stage is a kinetically complex process, and the first and second stages are single-step kinetic processes and can be described by a unique kinetic triplet [E _a, A, g(α)]. A new modified method of the multiple rate iso-temperature was used to define the most probable mechanism g(α) of the two stages; and reliability of the used method for the determination of the kinetic mechanism were tested by the comparison between experimental plot and model results for every heating rate. The results show that the mechanism functions of the two stages are reliable. The pre-exponential factor A of the two stages was obtained on the basis of E _a and g(α). Besides, the thermodynamic parameters (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of the two stages were also calculated.     

Mechanism and kinetics of thermal degradation of insulating materials developed from cellulose fiber and fire retardants

The mechanism and kinetics of thermal degradation of materials developed from cellulose fiber and synergetic fire retardant or expandable graphite have been investigated using thermogravimetric analysis. The model-free methods such as Kissinger–Akahira–Sunose (KAS), Friedman, and Flynn–Wall–Ozawa (FWO) were applied to measure apparent activation energy (E_α). The increased E_α indicated a greater thermal stability because of the formation of a thermally stable char, and the decreased E_α after the increasing region related to the catalytic reaction of the fire retardants, which revealed that the pyrolysis of fire retardant-containing cellulosic materials through more complex and multi-step kinetics. The Friedman method can be considered as the best method to evaluate the E_α of fire-retarded cellulose thermal insulation compared with the KAS and FWO methods. A master-plots method such as the Criado method was used to determine the possible degradation mechanisms. The degradation of cellulose thermal insulation without a fire retardant is governed by a D3 diffusion process when the conversion value is below 0.6, but the materials containing synergetic fire retardant and expandable graphite fire retardant may have a complicated reaction mechanism that fits several proposed theoretical models in different conversion ranges. Gases released during the thermal degradation were identified by pyrolysis–gas chromatography/mass spectrometry. Fire retardants could catalyze the dehydration of cellulosic thermal insulating materials at a lower temperature and facilitate the generation of furfural and levoglucosenone, thus promoting the formation of char. These results provide useful information to understand the pyrolysis and fire retardancy mechanism of fire-retarded cellulose thermal insulation.

     

Determination of the kinetic parameters for the electrothermal atomization of gold with and without chemical modifiers

The effect of various experimental parameters and the presence of chemical modifiers on the atomization kinetics of gold have been investigated. The dissipation process of the atomic vapour is also studied and the diffusion parameters calculated in the absence and in the presence of chemical modifiers. The chemical modifiers studied are ascorbic acid, rhenium, palladium and rhodium. In the absence of chemical modifiers, a two-precursor atomization mechanism is observed in distinctive different temperature regions. When a long pyrolysis step and low masses of gold are employed, an atomization from dispersed particles with low E_a value is observed in the low temperature region (LT region). At high masses of gold, a fractional order atomization from gold agglomerates with high, mass-dependent, E_a values, approaching the heat of vaporization, ΔH_vap, is observed in the high temperature region (HT region). In the presence of ascorbic acid, a high E_a value is obtained in the LT region, suggesting a fast atomization from surface particles at the active sites produced by the pyrolysis of ascorbic acid and a low E_a value is obtained in the HT region, with first-order kinetics, which indicates a desorption process through the micropores of the amorphous carbon residue of ascorbic acid. In the presence of 5 μg Re, a two-precursor mechanism is also found, with a high E_a value in the LT region, suggesting vaporization from small clusters, and a low E_a value in the HT region with a first-order kinetics, indicating vaporization of disperse particles from the graphite surface. In the presence of 0.1–1 μg Pd, a two-precursor mechanism is also observed. The first process, in the LT region, has a low E_a value, which indicates vaporization of disperse particles from the available free active sites of the graphite surface. The second process, in the HT region, begins at the appearance temperature of Pd and shows a high E_a value and first-order kinetics, which means that release of gold atoms occurs only after the vaporization of Pd has begun. In the presence of Rh, a mass-dependent E_a value is found in the LT region, suggesting atomization from gold clusters. However, in the HT region, the generation of atomic vapour of Au is kinetically controlled by the release of the Rh modifier.     

Thermogravimetry of the thermal degradation of Japanese lacquer (urushi) films

The kinetics of the thermal degradation of Japanese lacquer (urushi) films in N₂ and in air were studied by means of thermogravimetry (TG). Thermogravimetric and derivative thermogravimetric curves indicated that the degradation occurred in three stages. The atmosphere influenced the apparent activation energies (E _a) of the three degradation stages. The activation energies (E _a) for the first stage in N₂ and air, obtained from the TG curve, were 19.12 and 10.19 kcal mol^?1, respectively, and the corresponding pre-exponential factors (A) were 6.18 × 10⁵ and 1.24 × 10² min^?1 for 1-year-old urushi films.     

The investigation of methyl phenyl silicone resin/epoxy resin using epoxy-polysiloxane as compatibilizer

Styrene–butadiene rubber was subjected to long-term thermal aging treatment at 80 °C with aging period up to 180 days. The degradation kinetics of the aged sample was analyzed by thermogravimetric analysis. Multiple heating rate experiments were carried out in nonisothermal conditions and three isoconversional model-free methods (Friedman; Kissinger–Akahira–Sunose; Li and Tang methods) were employed. The results showed that the temperature for 5 % mass loss increased, whereas the maximum mass loss temperature decreased after aging. Activation energies (E _a) derived from the three methods were found to be dependent on conversion degree (α). E _a increased with increasing α in the whole range of conversion for samples aged for 0, 60, and 120 days, while the aged samples displayed higher E _a values. However, samples aged for 180 days showed declining E _a versus α. The changes on the degradation kinetics were associated with the modification on the chemical structure after thermal aging.     

Application of iso-temperature method of multiple rate to kinetic analysis

A new method of the multiple rate iso-temperature was used to define the most probable mechanism g(α) of a reaction; the iterative iso-conversional procedure has been employed to estimate apparent activation energy E _a, the pre-exponential factor A was obtained on the basis of E _a and g(α). In this new method, the thermal analysis kinetics triplet of dehydration of calcium oxalate monohydrate is determined, which apparent activation energy E _a is 82.83 kJ mol^-1, pre-exponential factor A is 1.142·10⁵-1.235·10⁵ s^-1, the most probable mechanism belongs to phase boundary reaction R_n with integral form g(α)=1-(1-α)ⁿ and differential form f(α)=n(1-α)^1-(1/n), where accommodation factor n=2.40-1.40.     

A comprehensive assessment on degradation of multi-walled carbon nanotube-reinforced EMA nanocomposites

Thermal degradation kinetics of MWNT-reinforced EMA-based nanocomposites having different methyl acrylate (MA) contents (by % mass) ranging from 9 to 30% have been monitored. Kissinger and Flynn?CWall?COzawa methods for evaluating non-isothermal degradation of polymers have been examined. Overall, the thermal stabilities of the nanocomposites are the function of amount of MWNTs loading and their state of dispersion that depends on the MA content of respective EMAs. Composite samples exhibit higher activation energy (E _a) than the neat EMAs but the E _as of the composites diminish with increased MA contents of the matrices. TG-Mass spectrometry has been used to identify the volatile products resulting from thermal degradation of composites, and a promising mechanism has been proposed over different range of temperatures of degradation. It is proposed that the side-group scission of methoxycarbonyl group initiates thermal decomposition following combination of chain end and random chain scission reactions, ensuing pseudo second-order kinetics.     

Thermosetting polymers from epoxy resin and a Nickel catalyst of diethylenetriamine

The kinetics and mechanism of cure reaction of DGEBA using a chelate of Ni(II) with diethylenetriamine (dien), Ni(dien)₂I_2, as a curing agent was studied by DSC. TG curve of the complex curing agent showed mass loss in two region of temperature: 200–320 and 450–550 °C. Dynamic DSC measurements showed only one exothermic peak with a maximum about 250 °C depending on the heating rate. According to the methods of KAS and Ozawa–Flynn–Wall the values of E _a were 92.5 and 96.2 kJ/mol, respectively. The isoconversional kinetic analysis in whole range of conversion, α = 0.02–0.95, showed small changes in the E _a values in the region of α = 0.04–0.6 and most likely represent some average values (E _a = 110 kJ/mol) between the values of E _a of non-autocatalyzed and autocatalyzed reactions. Using the sole dependence of E _a on α, the time required to reach fully cured materials under isothermal conditions were also predicted and compared with the experimental results.     

Special Chapter Dedicated to the Memory of Prof. St. Bretsznajder

This study investigates the most appropriate conditions to perform the proximate analysis (moisture, volatile matter, fixed carbon, and ash) of biomasses by thermogravimetry, focusing on providing better distinction for quantification of volatile and fixed carbon components. It was found, using a series of thermogravimetric methodologies, that heating rate and particle size are important factors to be taken into account, whereas temperature and carrier gas (type and flow rate) are critical to enable the proper quantification of volatiles and fixed carbon. In this case, the best condition was achieved by applying 600 °C and CO₂ as carrier gas (instead of N₂). It is the highlight of the proposal method regarding the conditions often applied for this purpose. Furthermore, this method has proved to be advantageous in three important aspects: A single measurement is enough for quantification of all properties, it can be performed in a short time (1 h 27 min) in comparison with methods performed in a muffle furnace, and it can be applied for different kinds of biomasses, from lignocellulosic to residues. The procedure of validation demonstrated the low uncertainty of the data obtained by this method and the low propagation of uncertainty when they were applied for the prediction of the high heating value of the related biomasses, which supports its applicability as an alternative to biomass characterization.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.