Combustion Characteristics, Kinetics, and Thermodynamics of Pine Wood Through Thermogravimetric Analysis.

The thermal conversion of woody biomass is increasingly critical for the development of the energy processing technologies and fire safety engineering. The combustion characteristics, kinetics, and thermodynamics of pine wood were characterized through a thermogravimetric analyzer in the air atmosphere. There were two apparent peaks in the derivative TG curves for pine wood. The combustion process of pine wood was divided into two stages. Therein, the first stage occurring in the conversion degree range of 0-0.6 may be considered a one-step reaction. It was easier for pine wood to decompose under air than under nitrogen. Moreover, the first stage of pine wood combustion may be characterized by the diffusion model g(α) = [1 - (1 - α)1/3]2. The kinetic modeling showed a good agreement between the predicted and experimental conversion degree curves. In addition, the high comprehensive combustion index of pine wood at 10 K min-1 (6.73 × 10-7 %2 min-2 K-3) showed its great potential for bioenergy generation. Besides, both the value of ΔH and ΔS exhibited similar patterns with the activation energy value versus conversion degree, while the ΔG value almost remained at a positive constant with conversion degree. The average ΔH, ΔG, and ΔS value was nearly equal under different heating rates.

Kinetics, Thermodynamics, and Volatile Products of Camphorwood Pyrolysis in Inert Atmosphere.

The kinetics, thermodynamics, and volatile products of camphorwood pyrolysis were investigated via thermogravimetry coupled with Fourier transform infrared (FTIR) spectroscopy at multiple heating rates. The kinetic triplets and thermodynamic parameters were estimated via model free combined with the model-fitting approach. The results showed that the pyrolysis of camphorwood in the conversion rate range from 0 to 0.85 might be considered as one-step process. The mean value of the activation energy and pre-exponential factor was 192.63 kJ/mol and 2.38 × 1013 s-1, respectively. The pyrolysis process (0 ≤ α ≤ 0.85) can be described by the three-dimensional diffusion model g(α) = [(1-α)-1/3 - 1]2. Furthermore, the predicted curves of the conversion rate α showed good agreement with the experimental curves. The values of ΔH, ΔG, and ΔS varied little with α and remained positive. In addition, the major gas products released from the camphorwood waste pyrolysis were H2O, methane, CO2, CO, C=O, O-H, C-O-C, and NH3, whose concentration in the order from highest to lowest was C=O > CO2 > O-H > H2O > methane > NH3 > C-O-C > CO. The main conclusions in the present study can provide guidance for the design and optimization of industrial reactor and selection of target biofuels or chemical raw materials.

Comparative Pyrolysis Characteristics and Kinetics of Typical Hardwood in Inert and Oxygenous Atmosphere.

Combustion (pyrolysis with oxygen) and pyrolysis without oxygen are two potential methods to convert wood into biofuels or biochemicals. To evaluate which is preponderant to convert wood into biofuels or biochemicals and provide guidance for optimization of product yield, the pyrolysis characteristics and kinetics of typical hardwood (black walnut) are comparatively investigated in nitrogen and air employing thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). Two model-free methods including Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) method are applied to obtain the kinetic parameters, and a model-fitting method called Coats-Redfern (CR) method is employed to estimate the reaction mechanism. The black walnut pyrolysis in nitrogen may be divided into two stages with the threshold of conversion rate α = 0.4, but that in air may be separated into three stages with the thresholds of α = 0.25 and 0.7. The reaction mechanism for pyrolysis in nitrogen may be assumed random nucleation and its subsequent growth, but that in air may be assumed random nucleation and its subsequent growth followed by chemical reaction. The average activation energy and natural logarithm of pre-exponential factor for the whole pyrolysis process in nitrogen and air are 211.59 and 187.73 kJ/mol and 32.33 and 28.36 min-1, respectively.

Pyrolysis Characteristics and Reaction Mechanisms of Pine Needles.

Pyrolysis has been considered as a promising method to utilize biomass by thermal cracking for energy or feedstock. In order to provide guidance for thermochemical process management of pine needle utilization by pyrolysis, the pyrolysis kinetics and reaction mechanism of one typical pine needle are investigated employing thermogravimetric analysis in nitrogen in the present study. Multi kinetics methods including model-free method and model-fitting method are adopted. Results indicate that one peak and three shoulders occur in the reaction rate curves. The maximum reaction rates decrease with the increasing of heating rates, and the average reaction rate of the whole process is 0.0021 K-1. The pyrolysis process of pine needles in nitrogen may be divided into four stages in the conversion rate range of 0~0.1, 0.1~0.5, 0.5~0.75, and 0.75~1, which may be mainly resulted by the reaction of the extractives, hemicellulose, cellulose, and lignin, respectively. The reaction mechanisms of stages I, II, and III may be regarded as random nucleation and nuclei growth, but the reaction mechanism of stage IV may be chemical reaction. The average value of activation energy and logarithm of the pre-exponential factor for the whole pyrolysis process is 215.99 kJ mol-1 and 38.75 min-1, respectively.

Preparation and Surface Properties Study of Novel Fluorine-Containing Methacrylate Polymers for Coating.

A new structural fluorine-containing methacrylate monomer CH2=C(CH3)COOC⁻(CF3)2CF2CF2CF3 (5) was synthesized derived from perfluoro-2-methyl-2-pentene (D2). A homopolymer of 5 and copolymers of 5 and methacrylate with different alkyl chain length (chain length n = 1, 2, 4, 6, 8, 12, 18) were obtained. These new fluorinated acrylate polymers showed excellent water and oil repellency. The contact angle of the films of the homopolymer and part of the copolymers were similar with the corresponding polymers prepared from CH2=CHC(O)OCH(C3F7)(CF(CF3)2), but greater than that of the C6F13(CF3)CHOC(O)CH=CH2 homopolymer. The structure-property relationship research indicated that the copolymers' hydrophobicity decreased first and then increased with the increase of alkyl chain length. Td of all the polymers were greater than 220 °C and Tg fluctuated within the range of -51~103.8 °C. Contact angle and Tg could be adjusted by controlling the feed ratio of monomer to meet the requirements of technical indicators in the practical applications. The outstanding liquid repellency and thermal stability make monomer 5 a promising alternative to perfluorinated long-chain fluorosurfactants.

Potassium Nitraminofurazan Derivatives: Potential Green Primary Explosives with High Energy and Comparable Low Friction Sensitivities.

Lead-based primary explosives were widely applied in military and civilian ammunition, which have subsequently caused serious environmental and health-related problems. Therefore, the development of green alternatives for the lead-based primary explosives has been one of the major focuses in the field of energetic materials. Four potassium salts based on nitraminofurazan have been easily synthesized and show excellent comprehensive performances. Among them, potassium 3-dinitromethyl-4-nitraminofurazan (K2 DNMNAF, 1) showed better thermal stability (Td : 281.4 °C), higher density (2.174 g cm-3 ), and lower friction sensitivities (72 N) than that of potassium 4,5-bis(dinitromethyl)furoxanate (K2 BDNMF, Td : 218.3 °C, density: 2.130 g cm-3 , FS: 5 N, P: 27.3 GPa, vD : 7759 m s-1 ); furthermore, it displayed comparable detonation performances (P: 27.2 GPa, vD : 7758 m s-1 ). The promising properties of these salts make this kind of material a competitive alternative to lead azide as a primary explosive.

Novel dinitromethyl-featured polynitro energetic salts.

A unique and facile method was developed to synthesize a new class of energetic salts based on 2-amino-1,1,5,5-tetranitro-4-oxo-3-aza-pentene. All the salts were fully characterized by NMR (1H and 13C), IR spectroscopy and elemental analysis. Furthermore, the crystal structure of the guanidinium salt (5) was determined by single-crystal X-ray diffraction. The differential scanning calorimetry (DSC) results showed that the decomposition temperatures of these salts were between 126.2 °C (10) and 148.8 °C (9). The densities of these salts lie in the range of 1.745 (8) to 1.880 (4) g cm-3. Their impact sensitivities and friction sensitivities were measured to be in the range of 1-16 J and 48-84 N, respectively. All the salts exhibited promising detonation performances (detonation pressure: 28.6 to 34.3 GPa; detonation velocity: 8037 to 8674 m s-1), and the detonation performances of salt 4 were comparable to those of RDX.

Total Synthesis of Gelsedilam by Means of a Thiol-Mediated Diastereoselective Conjugate Addition-Aldol Reaction.

The total synthesis of gelsedilam, which features a highly diastereoselective thiol conjugate addition-intramolecular aldol reaction to install the strained and caged [3.2.2] bridged ring system and highly efficient NiCl2 /NaBH4 -mediated four-step transformation in one-pot to construct its five-membered lactam ring is reported. The synthesis requires only 18 linear steps from the known compounds, providing useful strategies for the construction of the intricate ring system in the synthesis of related gelsedine-type alkaloids.

Density functional theory study of C2F5I synthesis over activated carbon catalyst.

Quantum chemistry calculations based on the density functional theory (DFT) are carried out to investigate the reaction mechanism of C2F5I synthesis catalyzed by activated carbon. The possible adsorption configurations of fluorocarbon intermediates are analyzed carefully. Also, the related transition states and reaction pathway are analyzed. According to calculation, firstly, the dehydrofluorination of C2HF5, as the rate-determining step, is catalyzed by the carboxyl acid groups. Secondly, the tetrafluoroethylidene radicals disproportionate on graphite (001) surface instead of rearrangement or dimerization. Next, the fluorine abstractions between fluorocarbon intermediates over graphite (001) surfaces proceed successfully. Finally, the desorbed pentafluoroethyl abstracts iodine atom from molecular iodine spontaneously to afford C2F5I. In adition, our calculations reveal that the carbon deposit in experiment is caused by the fluorine abstraction from fluoroethinyl. The suggested mechanism corresponds with our calculations and available experiments.

Enantioselective direct Mannich reactions of cyclic ß-ketoesters catalyzed by chiral phosphine via a novel dual-reagent catalysis.

A combination of an amino acid derived chiral phosphine catalyst and methyl acrylate efficiently catalyzed the direct Mannich reaction of cyclic ß-ketoesters and N-Boc-aldimines. The dual-reagent catalysis was presumed to function through the formation of a zwitterion, which catalyzed the reaction with excellent stereocontrol via a hydrogen-bonding assisted chiral ion-pair pathway.

CF3I synthesis catalyzed by activated carbon: a density functional theory study.

A revised reaction mechanism of CF3I synthesis catalyzed by activated carbon is investigated with quantum chemistry methods using density functional theory (DFT). The adsorption configurations of possible intermediates are carefully examined. The reaction pathway and related transition states are also analyzed. According to our calculations, first, the dehydrofluorination of CHF3 is catalyzed by -COOH groups, which possesses the highest barrier and is accordingly identified as the rate-determining step. Second, the difluorocarbene disproportionation over graphite (001) surface proceeds instead of dimerization. The next reaction steps involving the association of fluoromethine and trifluoromethyl, the fluorine abstractions between intermediates and the iodine abstractions by the desorbed CF3 and CF2CF3 from molecular iodine are also feasible over graphite (001) surfaces. It is also found that the coke deposition in experiments is due to the fluorine abstraction from fluoromethine. This revised mechanism is in agreement with available experimental data and our theoretical computations.

[Study on thermal decompositon properties of hexafluoropropane clean gaseous fire-extinguishing agent].

The thermal decomposition properties of hexafluoropropane clean gaseous fire-extinguishing agent were studied in tubular reactor from 500 to 750 degrees C and the decomposed gas was characterized by gas chromatography(GC), Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). Hydrogen fluoride was detected after the decomposed gas was analyzed by pH testing, while pentafluoropropylene was found by GC-MS. The results showed that hydrogen fluoride eliminated from hexafluoropropane was the main reaction, while pentafluoropropylene was the primary product during hexafluoropropane decomposition under high temperature. GC and FTIR results indicated that the reaction temperatures had significant effects on the thermal decomposition of hexafluoropropane. Haxafluropropane was steady at 500 degrees C, whereas started to decompose weakly at 600 degrees C. The degree of the thermal decomposition of hexafluoropropane was enhanced with the temperature increase. And hexafluoropropane underwent intense decompositon at 750 degrees C. FTIR can be used as a new method to study extinguishing mechanism of fluorine-containing fire extinguishing agent online.