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1.
A very low-pressure pyrolysis (VLPP) apparatus has been constructed and shown to yield kinetic data consistent with other VLPP systems. The technique has been applied to the pyrolysis of cyclobutyl cyanide over the temperature range of 833–1203°K. The reaction was found to proceed via a single pathway to yield ethylene and vinyl cyanide. If A∞ is based on previous high-pressure data for this reaction and for cyclobutane pyrolysis, then RRKM theory calculations show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by where θ=2.303 RT in kcal/mole. If A∞ is adjusted relative to the more recent parameters for cyclobutane pyrolysis suggested by VLPP studies, then the Arrhenius expression becomes The cyano group reduces the activation energy for cyclobutane pyrolysis by 6±1 kcal/mole, and on the basis of a biradical mechanism this value may be attributed to the cyano stabilization energy. 相似文献
2.
The very low-pressure pyrolysis (VLPP) technique has been applied to the pyrolysis of di- t-amyl peroxide (DTAP) over the temperature range 523-633°K. VLPP yields a low-pressure rate constant, kuni The conversion of kuni to k∞ which must be made to calculate the Arrhenius parameters, is accomplished via the RRKM theory. The transition state model used in the RRKM calculations was based on a transition state model which accurately reproduced the VLPP data for di- t-butyl peroxide for which the Arrhenius parameters are well known. For the decomposition of DTAP it was found that log k∞(300°K) = 15.8 - 36.4/θ, where θ = 2.303 RT, in kcal/mole, and the units of k∞, are sec ?1. 相似文献
3.
A pyrolysis–gas chromatographic technique for measuring the amount of hydrogen chloride released during the high temperature pyrolysis of poly(vinyl chloride) resins, plastisols, copolymers and compounds containing inert fillers has been developed. The technique, which is also applicable to the analysis of chlorinated polyethylene and chlorinated poly(vinyl chloride), is based on the use of a standard precursor of HCl, poly(vinyl chloride) homopolymer. The analysis has been successfully used to measure the degree of in situ absorption of HCl during pyrolysis by certain basic fillers [K 2CO 3, CaCO 3, CaO, MgO, Al(OH) 3, Na 2CO 3, Al 2O 3 and LiOH] dispersed in a poly(vinyl chloride)– o-dioctyl phthalate matrix. Combustion of a number of combustion residues (chloride determination) revealed that the amount of HCl absorbed by the basic filler was independent of the method of degradation (pyrolysis or combustion). Flammability measurements of those matrices having the same composition indicate that in situ absorption of HCl during combustion has little effect on the overall flammability of these materials. 相似文献
4.
The very low-pressure (VLPP) technique was used to study the pyrolysis of azoethane (AE), azoisopropane (AIP), and 2,2′-azoisobutane (AIB). The low pressure rate constants were related to the high-pressure Arrhenius parameters by means of the RRKM theory. This procedure in itself does not yield an unambiguous set of parameters. However, thermochemical and kinetic arguments are given which support the following values of log k∞ for the pyrolysis of AE, AIP, and AIB, respectively: 16.4–49.7/θ 16.6–47.9/θ, and 16.4–42.8/θ, where θ = 2.303 RT in kcal/mole. The flow dependence of kuni was used to estimate the collisional efficiencies of the azo compounds relative to the wall. 相似文献
5.
Polyurethanes derived from xylylene diisocyanates and trans-1,4-cyclohexanedimethanol were thermally degraded by using the techniques of thermogravimetry and pyrolysis at atmospheric pressure. Quantitative determination of the pyrolysis products such as CO 2, diamine, olefin, and starting diol showed that these polyurethanes follow the typical mechanism of degradation via dissociation into starting diol and diisocyanate. Kinetic parameters for the overall degradation reaction were determined using four different methods. The results showed the influence of the experimental technique used when making a comparison of the thermal stability of polymers, as determined by the kinetic parameters of the degradation reactions. 相似文献
6.
The thermal unimolecular decomposition of hex-1-ene has been investigated over the temperature range of 915–1153 K using the technique of very low-pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C 3?C 4 fission and retro-ene elimination, with the latter dominant at low temperatures and the former at high temperatures. This behavior results in an isokinetic temperature of 1035 K under VLPP conditions (both reactions in the unimolecular falloff regime). RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log k1 (sec ?1) = (12.6 ± 0.2) -(57.7 ± 1.5)/θ for retro-ene reaction, and log k2 (sec ?1) = (15.9 ± 0.2) - (70.8 ± 1.0)/θ for C-C fission, where θ = 2.303 RT kcal/mol. The A factors were assigned from the results of a recent shock-tube study of the decomposition in the high-pressure regime, and the activation energies were found by matching the RRKM calculations to the VLPP data. The parameters for C-C fission are consistent with the known thermochemistry of n-propyl and allyl radicals. A clear measure of the importance of the molecular pathway in the decomposition of a mono-olefin has been obtained. 相似文献
7.
The unimolecular decomposition of 3,3-dimethylbut-1-yne has been investigated over the temperature range of 933°-1182°K using the technique of very low-pressure pyrolysis (VLPP). The primary process is C? C bond fission yielding the resonance stabilized dimethylpropargyl radical. Application of RRKM theory shows that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log ( k/sec ?1) = (15.8 ± 0.3) - (70.8 ± 1.5)/θ where θ = 2.303 RT kcal/mol. The activation energy leads to DH0[(CH 3) 2C(CCH)? CH 3] = 70.7 ± 1.5, θ H0f((CH 3) 2?CCH, g) = 61.5 ± 2.0, and DH0[(CH 3) 2C(CCH)? H] = 81.0 ± 2.3, all in kcal/mol at 298°K. The stabilization energy of the dimethylpropargyl radical has been found to be 11.0±2.5 kcal/mol. 相似文献
8.
The rate of the inhibited pyrolysis of pentachloroethane was studiedover the temperature range of 820 to 865°K using the toluene-carrier technique in a stirred-flow reactor. The pyrolysis rate was found to be first order in reactant, and the rate constant is described by k=10 11.6±0.7 exp [(?48,200±2600)/ RT] sec ?1. An increase by a factor of 6.6 in the surface/volume of the reactor had a negligible effect on the rate. This observation, in addition to a reevaluation of earlier kinetic data for the pyrolysis of pentachloroethane, lead to the following conclusions concerning the pyrolysis mechanism. The initiation and termination as well as the propagation reactions were homogeneous, the termination involved both Cl and C 2Cl 5 radicals (crosstermination), and autocatalysis was caused by interaction between chlorine and pentachloroethane rather than by dissociation of molecular chlorine. 相似文献
9.
Impregnation techniques for corundum ( S
BET = 0.5 m 2/g) as a support for Ni catalysts for C 3–C 4 alkane pyrolysis into catalytic filamentous carbon (CFC) are compared. The effects of the following factors on the uniformity
of the active component (Ni) deposition on the inert support and on the CFC yield (g CFC)/(g Ni) are reported: (1) pH of the
nickel nitrate solution, (2) presence of aluminum(III) nitrate in the solution, (3) addition of viscosifying agents (glycerol,
glucose, sucrose) to the solution, (4) catalyst calcination conditions before pyrolysis, and (5) catalyst drying technique.
The surface morphology of the Ni catalysts and of the carbon deposits resulting from the catalytic pyrolysis of C 3–C 4 alkanes in the presence of hydrogen has been investigated by scanning electron microscopy. The optimum way of preparing the
supported Ni catalysts is by carrying out the incipient wetness impregnation of corundum with a nickel nitrate solution (0.05–0.1
mol/l) containing glycerol (20–25 vol %), drying the product in a microwave oven, and burning away the glycerol before alkane
pyrolysis. 相似文献
10.
The homogeneous gas-phase thermal decomposition kinetics of germane have been measured in a single-pulse shock tube between 950 and 1060 K at pressures around 4000 torr. The initial decomposition is GeH 4 → GeH 2 + H 2 in its pressure-dependent regime, with log k = 13.83 ± 0.78 – 50,750 ± 3570 cal/2.303 RT. RRKM calculations suggest that the high-pressure Arrhenius parameters are log k GeH 4(M → ∞) = 15.5 – 54,300 cal/2.303 RT. Extrapolations to static system pyrolysis conditions ( T ~ 600 K, P ~ 200 torr) give homogeneous reaction rates which are much slower than those observed, hence the static system pyrolysis of germane must be predominantly heterogeneous. Shock-initiated pyrolysis reaction stoichiometry is 2 mol H 2 per mole GeH 4, suggesting that the subsequent decomposition of germylene is essentially quantitative. Investigations of the hydrogen product yields for pyrolysis of GeD 4 in øCH 3 further indicate that the germylene decomposition reaction is mainly GeH 2 → H 2 + Ge, but that a small amount of reaction to H atoms may also occur. 相似文献
11.
The homogeneous gas-phase decomposition kinetics of silane has been investigated using the single-pulse shock tube comparative rate technique ( T = 1035–1184?K, Ptotal ≈? 4000 Torr). The initial reaction of the decomposition SiH 4 \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document} SiH 2 + H 2 is a unimolecular process in its pressure fall-off regime with experimental Arrhenius parameters of log k1 (sec ?1) = 13.33 ± 0.28–52,700 ± 1400/2.303 RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM-pressure fall-off calculations for four different transition-state models are reported, and good agreement with all the data is obtained with a model whose high-pressure parameters are log A1 (sec ?1) = 15.5, E1(∞) = 56.9 kcal, and Δ E0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH 2 → (Si 2H 4)* → (SiH 3SiH)* → Si 2H 2 + H 2. The mechanism of H ? D exchange absorbed in the pyrolysis of SiD 4-hydrocarbon systems is also discussed. 相似文献
12.
Experimental evidence is presented for a unimolecular gas-phase Wagner-Meerwein shift in neopentyl chloride pyrolysis. In the decomposition of α,α-neopentyl chloride- d2 at 445°C, maximally inhibited by cyclohexene, the initial products were isotopically pure 2-methyl-1-butene- d2 and 2-methyl-2-butene- d1. Rearrangement, accompanied by loss of either α- or γ-hydrogen in the formation of hydrogen chloride, is consistent with an incipient ion-pair type of transition state. The cyclohexene maximally inhibited pyrolysis of neopentyl chloride was also examined over the temperature range 424–478°C and Arrhenius parameters of E, 258.7 kJ/mole and log A/sec ?1, 13.78, were determined. 相似文献
13.
The decomposition of neopentane was studied using the very-low-pressure pyrolysis (VLPP) technique at temperatures from 1000 to 1260 K. The derived Arrhenius parameters are consistent with δ Hf0( t-butyl) = 8.4 kcal/mol. Using the above A factor, data on the decomposition of tetramethyltin yield DH0(Sn(CH 3) 3 - CH 3) = 69 ± 2 kcal/mol. 相似文献
14.
A technique has been developed to study cellulose pyrolysis by in situ visualization of cellulose transformation in a quartz capillary under a microscope using a CCD camera monitoring system and Raman spectroscopy. The processes and temperature of cellulose transformation during pyrolysis reaction can be observed directly. In situ visualization of reaction revealed that how oil is generated and expulsed concurrently from cellulose during pyrolysis. The in situ visualization result is the first direct evidence to show cellulose pyrolysis transformation. Pyrolysis characteristics were investigated under a highly purified N 2 atmosphere using a thermogravimetric analyzer from room temperature to 500 °C at the heating rate of 5 °C/min. The results showed that three stages appeared in this thermal degradation process. Kinetic parameters in terms of apparent activation energy and pre-exponential factor were determined. 相似文献
15.
The behaviour of gibberellic acid (GA 3) under electron impact and chemical ionization conditions has been examined. The tendency of GA 3 to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi-allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule. 相似文献
16.
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 (Ea) 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 Ea 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. 相似文献
17.
The unimolecular decomposition of but-1-yne has been investigated over the temperature range of 1052° – 1152°K using the technique of very low-pressure pyrolysis (VLPP). The primary process is C? C bond fission yielding methyl and propargyl radicals. Application of RRKM theory shows that the experimental rate constants are consistent with the highpressure Arrhenius parameters given by where θ = 2.303 RT kcal/mol. The parameters are in good agreement with estimates based on shock-tube studies. The activation energy, combined with thermochemical data, leads to DH°[HCCCH 2? CH 3] = 76.0, Δ H(HCC?CH 2,g) = 81.4, and DH° [HCCCH 2? H] = 89.2, all in kcal/mol at 300°K. The stabilization energy of the propargyl radical SE° (HCC?CH 2) has been found to be 8.8 kcal/mol. Recent result for the shock-tube pyrolysis of some alkynes have been analyzed and shown to yield values for the heat of formation and stabilization energy of the propargyl radical in excellent agreement with the present work. From a consideration of all results it is recommended that Δ H(HCC?CH 2,g) = 81.5±1.0, DH[HCCCH 2? H] = 89.3 ± 1.0, and SE° (HCC?CH 2) = 8.7±1.0 kcal/mol. 相似文献
18.
Cyclic sulfoness containing structural elements such as aromtic rings, heteroatoms. functional groups, and further SO 2-groups as ring members decompose on heating with cleavage of SO 2 and formation of a new C? C bond. In the last decade this “sulfone pyrolysis” has been expanded into a generally applicable method even allowing the synthesis of sterically strianed medium-membered and multi-membered cyclic and polycyclic systems containing aromatic ring. By the pyrolysis of sulfones which are only unilateally activated by benzyl moieties, aromatic systms can be bridged by ? (CH 2) n chains of any desired length. In addition, ? (CH 2)? chains can be split off together with two SO 2 molecules, with recombination of the remaining centers, resulting in ring contraction by four to n atoms. However, sulfone pyrolysis is of importance not only as a ring-contraction method but as a crucial final step in the synthesis of multi-membered hydrocarbon cycles, e.g. of the phane type. 相似文献
20.
Combining the spray pyrolysis and the sol–gel techniques gives the possibility to produce Fluorine doped Tin oxide (SnO 2:F) thin films. Transparent conducting SnO 2:F thin films have been deposited on glass substrates by the spray pyrolysis technique. This technique for the fabrication of SnO 2:F filmsby combining sol–gel process and the spray pyrolysis technique ispresented in this paper. The Sol–gel precursors have been successfully prepared using SnCl 2·5H 2O and (Ac)F 3. The structural, electrical, and optical properties of these films were investigated. The high resolution transmission electron microscopy (HRTEM) and selected area diffraction (SAD) patterns of SnO 2:F films show that the gel films lead to a tetragonal structure. The X‐ray diffraction pattern of the films deposited at substrate temperature 530° , the orientation of the films was predominantly [110]. In addition, the surface chemical components were also examined by X‐ray photoelectron spectroscopy (XPS) showing the SnO 2:F deposited with the atomic concentration ratios Sn/F 1.82:1. The minimum sheet resistance was 50 Ω and average transmission in the visible wavelength range of 300 to 800 nm was 87.25%. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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