Thermal decomposition behavior of tobacco stem Part II: Kinetic analysis

As a continuation of the previous study on the thermal degradation behavior of tobacco stem, this work is focused on the kinetics of pyrolytic decomposition. Thermogravimetric analysis of tobacco stem samples was conducted under nitrogen atmosphere at different heating rates of 5, 10, 15, and 20°C/min at a temperature range of 25–1,000°C. The kinetic parameters, such as activation energy, pre-exponential factor, and reaction order, were determined by applying the Coats–Redfern method for the main pyrolysis occurred in the second zone by means of the decomposition of hemicellulose, cellulose, and lignin at a temperature range 180–540°C. In addition, the activation energy was calculated using various degradation models, including Kissinger, Friedman (FR), Flynn–Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS). The average activation energy of tobacco stem was calculated to be 150.40, 230.76, 216.97, and 218.56 kJ/mol by the Kissinger, FR, FWO, and KAS models, respectively.     

Experimental study on pyrolysis characteristic of coking coal from Ningdong coalfield

The thermal decomposition of coal was the essential step of many reactions, thus it was widespread concerned. In order to investigate the behaviors and kinetics of coal pyrolysis, coal samples which obtained from Ningdong coalfield of China were pyrolyzed with a tubular furnace in argon atmosphere at the heating rate of 5 K min^?1. The primary gaseous products including CH₄, H₂, N₂, CO, CO₂, C₂H₄ and C₂H₆ were quantified using a gas chromatogram. It can be seen that with the temperature increasing, the yields of H₂ and CO increased, while the others decreased. In order to produce possibly much tar, the optimal temperature was 923 K. The characteristic of pyrolysis kinetics was determined by thermo gravimetric analysis measurement. The Coats–Redfern and Flynn–Wall–Ozawa methods was used to obtain kinetic parameters. The activation energy range of 50–200 kJ mol^?1 was determined.     

Exploitation of Pongamia glabra deoiled cake for alternate energy: Physico-chemical characterization and thermogravimetric studies

Utilization of agro-wastes for biofuel generation has been accepted as one of the feasible means for curbing down mankind’s dependence on conventional petro fuels. In this regard, the present investigation aims to understand the properties of Pongamia glabra deoiled cake (a byproduct of the biodiesel production process) for biofuel production. The deoiled cake was investigated for its physico-chemical characteristics by Bomb calorimetry, TG analysis (10, 20, and 40° min^–1), CHN analysis, and Fourier transform infrared spectroscopy. The proximate composition was calculated using standard ASTM methodology. The temperature characteristics, activation energy, pre-exponential factor, and reaction order for the active pyrolysis zone of the species under investigation have been provided for the respective heating rates using Arrhenius, Coats–Redfern, and Flynn–Wall–Ozawa methods. The findings suggest feasibility of liquid fuel production from Pongamia glabra deoiled cake via thermochemical conversion.     

Kinetics of the thermal decomposition of Eucommia ulmoides Oliver leaves and its fermentation products

The pyrolysis characteristics of Eucommia ulmoides Oliver leaves untreated and treated by biological fermentation were investigated using thermogravimetric analysis. The derivative thermogravimetry curves, kinetic characteristics, and activation energy of the samples were significantly different from other biomass. The average activation energies (253.40 and 268.77 kJ/mol, 257.71, and 270.82 kJ/mol) were close almost similar to that obtained from Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods and were higher due to the presence of gutta-percha. Meanwhile, the decomposition and kinetic characteristics could be changed by fermentation technology. Besides, Coats–Redfern revealed that second-order model (f(α) = (1–α)²) could be used to better describe the decomposition mechanism of these samples.     

Carbonization of Eight Bamboo Species of Northeast India

Abstract

Eight bamboo species of northeast India were carbonized in a laboratory-scale fixed bed reactor at temperature ranging from 300°C to 600°C with a heating rate of 5°C/min, and their mass balance experiments of decomposition products were done at 600°C. At this temperature, the yields of charcoal, tar, gas, and condensable liquid ranged from 23.35–28.25%, 6.46–8.85%, 6.93–10.05%, and 51.98–57.96%, respectively. Fixed carbon content of the charcoal samples varied from 62.10–67.52% indicating their suitability only for domestic use or as a fuel for gasification and not for metallurgical use.     

Fixed-Bed Pyrolysis of Hazelnut (Corylus Avellana L.) Bagasse: Influence of Pyrolysis Parameters on Product Yields

Fixed-bed slow pyrolysis experiments have been conducted on a sample of hazelnut bagasse to determine particularly the effects of pyrolysis temperature, heating rate, particle size and sweep gas flow rate on the pyrolysis product yields. The temperature of pyrolysis, heating rate, particle size and sweep gas flow rate were varied in the ranges 350–550° C, 10 and 50° C/min, 0.224–1.800 mm and 50–200 cm³/min, respectively. Under the various pyrolysis conditions applied in the experimental studies, the obtained char, liquid, and gas yield values ranged between 26 and 35 wt%, 23 and 34.40 wt%, and 25 and 32 wt%, respectively. The maximum biooil yield of 34.40% was obtained at the final pyrolysis temperature of 500°C, with a heating rate of 10° C/min, particle size range of 0.425–0.600 mm and a sweep gas flow rate of 150 cm³/min.     

Production of Solid Fuel from Ipomoea carnea Wood

Abstract

Ipomoea carnea woody stems were pyrolyzed in a laboratory-scale reactor in the temperatures ranging from 350° to 600°C and at constant heating rate of 5°C/min. Yield, density, ash content, volatile matter, fixed carbon content and calorific value of the charcoal samples produced were evaluated. Charcoal yield ranged from 24.23% to 37.89 wt% and calorific value varied from 17.29 to 33.47 MJ/Kg. Conversion of charcoal fines to solid fuel improved combustion quality. Mass balance experiments of pyrolytic decomposition products of I. carnea yielded much higher percentages of non-condensable liquid (59.2–61.8 wt%) as compared to those of tar (4.2–4.8 wt%) and gas (7.3–8.2 wt%) fractions.     

Thermo-oxidative characterization and kinetics of tar sands

In this research, non-isothermal kinetics and thermal analysis of Gerçü? tar sand sample is studied by DSC (differential scanning calorimeter) and TG/DTG (thermogravimetry). Experiments were performed using three different mesh size (20-35, 35-50 and >50) of sample. Differential scanning calorimeter (DSC) curves revealed three reaction regions in the temperature range of 20-600 °C. On the other hand, thermogravimetry (TG/DTG) curves of tar sand samples at different particle sizes demonstrated three stages of weight loss. Two different kinetic models (Coats & Redfern and Arrhenius) were used to determine the kinetic parameters of the samples and it was observed that the average activation energy values were between 17.5 and 26.6 kJ/mol, for reaction region-II and 126.2-160.1 kJ/mol for reaction region-III, respectively. In order to see the contribution of each region to the overall reactivity of the tar sand sample, weighted mean apparent activation energy of the samples are also determined.     

Determination and comparison of combustion kinetics parameters of agricultural biomass from olive trees

Thermogravimetric curves in air, measured for the different types of agricultural residues from olive trees (leaves, pruning and wood) at different heating rates (5, 10, 20, 40, 100 K/min), are subjected to kinetic evaluation by model-based and model-free methods. It is shown that the combustion process in the samples analyzed can be divided into three stages: water removal, roasting phase and char decomposition. At every stage, the activated energy varies with the mass conversion for the kinetic models considered. Its value was determined by the model-free methods, of which Flynn–Wall– Ozawa and Kissinger–Akahira–Sunose were the most appropriate for this purpose and resulted in similar values of activated energy. Once the activation energy was determined, the order of the reactions and the frequency factors of each stage were calculated by means of the Coats–Redfern model-based method in order to complete the determination of the kinetic triplet. From the results obtained, it was deduced that the most feasible reaction order was one.     

NaNH2–NaBH4 hydrogen storage composite materials synthesized via liquid phase ball-milling: Influence of Co–Ni–B catalyst on the dehydrogenation performances

The composite NaNH₂–NaBH₄ (2/1 molar rate) doped with different amount Co–Ni–B catalyst was synthesized via liquid phase ball-milling method in the cyclohexane agent. The composition evolution and dehydrogenation performance of the as-prepared sample were characterized by means of XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy) and TG–DTA–MS (Thermogravimetric–differential thermal analysis–mass spectroscopy) measurements, respectively; and the activation energies were calculated by the Achar differential and Coats–Redfern integral method. The composite NaNH₂–NaBH₄ (2/1) with 5 wt% Co–Ni–B catalyst (the sample C5) generated Na₃(NH₂)₂BH₄ successfully after the liquid phase ball-milling. Due to the interaction between functional groups of NaNH₂–NaBH₄ (2/1) with catalyst, Co–Ni–B catalyst not only benefits improving the thermodynamical performance, that is, the initial dehydrogenation temperature is as low as 200 °C and the weight percentage of hydrogen is about 5.05 wt% obtained from TG–DTA-MS curves; but also promoting the kinetics property that the activation energy of the major dehydrogenation stage is only 68.2 kJ mol^?1. Furthermore, it is revealed that the kinetics mechanism of the dehydrogenation performance depends on the synthesis methods and adding catalyst.     

Nanosized Zn–Sn metal composite oxide: a new anode material for Li ion battery

Abstract

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g^?1, and the first charge specific capacity is up to 903 mAh g^?1 for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.     

Conversion of hydrogen/carbon dioxide into formic acid and methanol over Cu/CuCr2O4 catalyst

Cu/CuCr₂O₄ catalysts were prepared by impregnation method at various calcination temperatures (300, 400, and 500 °C) and then reduced in H₂ stream. The aggregated particles and decreasing surface area/pore volumes of the deactivated catalysts during HCOOH and CH₃OH formations were also observed. Particularly, the EXAFS data showed that first shells of Cu atoms transforms from Cu–O to Cu–Cu after catalytic reactions, their bond distances and coordination numbers are quite different, respectively. It revealed that metallic Cu atoms are one of the important active species over catalyst surface at different reaction temperatures having many unoccupied binding sites for HCOOH and CH₃OH formations. Additionally, the optimal calcination temperature for Cu/CuCr₂O₄ catalysts was demonstrated at 400 °C that attributed to its strongest acidity and basicity. The catalytic reactions in the duration of HCOOH and CH₃OH preparation were proposed that were composed of HCOOH formation, CH₃OH formation, and CH₃OH decomposition happening at CuCr₂O₄, Cu, and CuO active sites, respectively. The highest CO₂ conversion (14.6%), HCOOH selectivity/yield (87.8/12.8%), and TON/TOF values (4.19/0.84) were obtained at 140 °C and 30 bar in 5 h, respectively. Optimal rate constant (2.57 × 10^?2 min^?1) and activation energy (16.24 kJ mol^?1) of HCOOH formation were evaluated by pseudo first-order model and Arrhenius equation, respectively.     

Hot deformation behaviour of niobium in temperature range 700–1500°C

Abstract

Niobium was hot deformed in vacuum in uniaxial compression to a true strain of 0·6 in the temperature range of 700–1500°C and the strain rate range of 10^?3–10 s^?1. Strain rate sensitivity was calculated from the compression tests data and mapped out in contour plots with the aim to optimise the hot workability of niobium. The domain of hot workability was identified in the temperature range of 1200–1500°C and strain rate range of 10^?2–1 s^?1. In this domain the strain rate sensitivity was ～0·15, the stress exponent 7·5 and the activation energy 246 kJ mol^?1. Microstructure of the deformed samples showed features of dynamic recrystallisation within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. Compared to a previous study on Nb–1Zr–0·1C alloy, Nb showed a lower flow stress and an optimum hot working domain at lower temperatures.     

Liquefaction of palm kernel shell to bio-oil using sub- and supercritical water: An overall kinetic study

Palm kernel shell was liquefied using sub- and supercritical water at 330–390 °C and 25 MPa for different reaction times. The overall kinetics of the liquefaction based on the conversion of biomass was analyzed using kinetic equation adopted from the literature, and the kinetic parameters were estimated from the evaluation of the kinetic equation. In this study, the rate constant (k) increased from 0.43 to 0.49 s^?1 with reaction temperature from 330 to 390 °C. The relationship of rate constant (k) and temperature agreed reasonably well with the Arrhenius equation. The activation energy (E) and pre-exponential factor (A) values for the liquefaction process were estimated to be 6.70 kJ/mol and 1.65 s^?1, respectively. In addition, the experimental bio-oil yields with respect to reaction time were well-fitted using the modified Reverchon-Sesti Osseo equation.     

A weighted average global process model based on two−stage kinetic scheme for biomass combustion

This research study combustion kinetics of four biomass samples in China, red pine (Pinus tabulaeformis), corn straw (hybrid corn Zheng Dan-958), Bermuda grass and bamboo (Phyllostachys heterocycla var), using thermogravimetric analysis (TGA). Three stages of combustion process are identified as water evaporation, removal and combustion of volatile matters and combustion of char. Thermal kinetic parameters of each sample are calculated by using 1st order Coats–Redfern method based on the TGA data. It is found that the activation energy of the global process is in the range of 53.6–65.2 kJ mol⁻¹ with a poor linear correlation. The experimental data are then used to develop a two−stage reaction kinetic scheme with low temperature region (2nd stage) and high temperature region (3rd stage). The activation energy of the second stage is in the range of 123.5–140.5 kJ mol⁻¹, and that of the third stage was in the range of 59.4–93.4 kJ mol⁻¹, both of which were based on the 1st order Coats–Redfern method. Because the global process of actual combustion is different from the TGA, a modified weighted average model is proposed based on the two−stage reaction kinetic scheme. According to the modified model, the kinetic parameters of the global process for actual combustion are calculated and are all found a little smaller than that of the 2nd stages. That will benefit for the combustion simulation and the design of facility of biomass fuel.     

Bio-oil Production from an Oilseed By-product: Fixed-bed Pyrolysis of Olive Cake

Abstract

A study of pyrolysis of olive cake at the temperature range from 400°C to 700°C has been carried out. The experiments were performed in a laboratory scale tubular reactor under nitrogen atmosphere. The yields of derived gases, liquids, and char were determined in relation to pyrolysis temperature and sweeping gas flow rates, at heating rates of about 300°C min^?1. As the pyrolysis temperature was increased, the percentage mass of char decreased whilst gas product increased. The oil products increased to a maximum value of ～39.4 wt% of dry ash free biomass at a pyrolysis temperature of about 550°C in a nitrogen atmosphere with flow rate of 100 mL min^?1 and with a heating rate of 300°C min^?1. Results showed that the bio-oil obtained under the optimum conditions is a useful substitute for fossil fuels or chemicals.     

桦甸油页岩燃烧性能的热分析研究

利用热重分析仪在非等温条件下对桦甸油页岩进行了燃烧试验。考察了粒径、升温速率、样品种类等因素对油页岩燃烧特性的影响。采用积分法（C-R法）获得了油页岩的燃烧动力学参数。结果表明，油页岩的燃烧性能随着其挥发分含量的增大而变好，且在燃烧过程中油页岩的表现活化能变化很大，对于不同的燃烧温度范围可用不同的反应级数来描述，在燃烧前期反应级数为1级，而燃烧后期反应级数为3．5级。     

Chemical energy storage by the reaction cycle CuO/Cu2O

The cyclic decomposition of cupric oxide followed by the oxidation of cuprous oxide in air was studied, in order to investigate the potential use of this reaction cycle for chemical energy storage. Isothermal and non-isothermal thermogravimetric method was used to study the kinetics of these reactions. The activation energy of the forward reaction (decomposition) is 313.0 kJ mol^?1 in the temperature range 760–910°C, while that for the backward reaction is 76.5 kJ mol^?1 in the temperature range 400–500°C. The reaction reactivity was found to be essentially unchanged for up to 20 cycles. This was explained as due to the swelling of the CuO particles and the development of a highly porous structure on repeated cycling.     

Combustion characteristics of Turkish lignites at oxygen-enriched and oxy-fuel combustion conditions

Combustion and oxy-fuel combustion characteristics of two Turkish lignites (Orhaneli and Soma) were investigated by Thermogravimetric Analysis (TGA) method. Experiments were carried out under oxygen-enriched air and oxy-fuel combustion conditions with 21, 30, 40% oxygen concentrations. Three heating rates of 5, 10, and 20 °C/min were considered and the isoconversional kinetic methods of FWO, KAS, and Friedman were employed to estimate activation energies. The uncertainty assessment in obtaining the activation energy values was also considered. The obtained results indicated that the combustion of volatiles at both air and oxy-fuel conditions were approximately identical. However, at air combustion conditions, the decomposition of CaCO₃ took place at temperatures above 700 °C. This decomposition process was independent of the oxygen concentration and took place when the temperature reached to a certain threshold. The decomposition of CaCO₃ did not accomplish in oxy-fuel conditions as far as the temperature was higher than 900 °C. Combustion in oxy-fuel conditions had higher activation energy values comparing to conventional combustion atmosphere. The activation energy values were approximately unchanged at the start of combustion regardless of oxygen concentration or combustion atmosphere at about 165 kJ/mol and 150 kJ/mol for Orhaneli and Soma lignites, respectively. The apparent activation energies were higher at elevated oxygen concentrations. The uncertainties values related to FWO method were lower than KAS and Friedman methods. The calculated average uncertainty values were found to be at the range of 5–15% for most of the cases.     

Synthesis of SnO2 nanorods and hollow spheres and their electrochemical properties as anode materials for lithium ion batteries

Abstract

SnO₂ nanorods and hollow spheres were conducted via a surfactant assisted hydrothermal reaction with the hydrothermal temperature. The crystalline structure and morphologies of the as prepared samples were characterised by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the products are hollow spheres with diameters of approximately 400–800 nm and shell thicknesses of 60–70 nm via hydrothermal treating at 160°C for 42 h and rod-like nanostructures with diameters of ～30 nm and lengths of 100–300 nm via hydrothermal treating at 200°C for 42 h respectively. The as prepared samples were used as anode materials for lithium ion battery, whose charge–discharge properties and cycle performance were examined. The results show that the initial discharge capacities of SnO₂ hollow spheres and SnO₂ nanorods samples are 1303 and 1426 mA h g^?1 at 0·2C rate, and still retain charge capacities of 518 and 578 mA h g^?1 respectively. Its good cycling behaviour and charge capacities make it a promising cathode material for advanced electrochemical devices for lithium ion batteries.