A kinetic modeling study of ethylene pyrolysis

2000 ◽  
Vol 78 (1) ◽  
pp. 16-25 ◽  
Author(s):  
John M Roscoe ◽  
Alain R Bossard ◽  
Margaret H Back
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Temperature Dependence ◽  
Key Words ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Preexponential Factor ◽  
Isomerization Reaction ◽  
Experimental Measurements ◽  
Experimental Conditions

A kinetic model is presented for the pyrolysis of ethylene at pressures ranging from 0.8 to 27 kPa and temperatures from 774 to 1023 K. The model is based on experimental measurements of C2H2, C2H6, C3H6, 1-C4H8, and 1,3-C4H6. In this temperature range the reaction is initiated by the disproportionation of C2H4 and the observed products result from reactions of the C2H3 and C2H5 radicals produced in this process. The C2H2 and 1,3-C4H6 result from reactions of C2H3 while C2H6, C3H6, and 1-C4H8 result from reactions of C2H5. C2H2 is produced exclusively by the decomposition of the C2H3 radical. This process is in its falloff region throughout the range of experimental conditions examined and the yield of C2H2 provides a measure of the degree of falloff. The production of 1,3-C4H6 is controlled by the reaction C4H7 –> C4H6 + H. The rate constants for this reaction were independent of pressure and are given as a function of temperature by k = 2.2 × 1013 exp (-19.6 × 103/T). Production of C2H6 is controlled by the reaction C2H5 + C2H4 –> C2H6 + C2H3. The rate constant for this reaction is given as a function of temperature by k = 5.83 × 1011 exp (-14.6 × 103/T). C3H6 is produced by decomposition of 2-C4H9 and is controlled kinetically by the isomerization reaction 1-C4H9 –> 2-C4H9. The temperature dependence of the rate constants obtained for this reaction leads to a preexponential factor of approximately 3 × 1016 and an activation energy of approximately 200 kJ mol-1. The yield of 1-C4H8 is controlled by 1-C4H9 –> 1-C4H8 + H. The rate constants for this reaction were independent of pressure and are given as a function of temperature by k = 2.97 × 1012 exp (-17.1 × 103/T). Key words: kinetic modeling, ethylene pyrolysis.

Temperature Dependence of Disproportionation–Combination Ratios for Alkyl Radicals in Liquid Methane

1971 ◽  
Vol 49 (17) ◽  
pp. 2861-2867 ◽  
Author(s):  
Hugh A. Gillis
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Transition States ◽  
Alkyl Radicals ◽  
Liquid Methane ◽  
Ethyl Radicals

The ratios of rate constants for disproportionation to combination have been measured for ethyl radicals and for i-propyl radicals in liquid methane between −181 and −94 °C. The radicals were generated by γ-radiolysis of dilute methane solutions of ethylene-d4 or propylene-d6. The activation energy for combination was found to exceed that for disproportionation by 290 ± 30 cal mol−1 for ethyl radicals and by 255 ± 25 cal mol−1 for i-propyl radicals. In both cases the disproportionation—combination ratio in the liquid, extrapolated to room temperature, is greater than that in the gas phase by a factor of about 2.5. These results are interpreted as indicating that disproportionation and combination reactions proceed by way of different transition states.

scholarly journals Kinetics of pyrolysis of wood biomass under isothermal conditions

2019 ◽  
Vol 64 (3) ◽  
pp. 321-331 ◽  
Author(s):  
M. V. Malko ◽  
S. V. Vasilevich
Keyword(s):  
Activation Energy ◽  
Raw Materials ◽  
Preexponential Factor ◽  
Woody Biomass ◽  
Experimental Conditions ◽  
Exponential Factor ◽  
Energy Value ◽  
Series Of Experiments ◽  
Static Conditions ◽  
Kinetics Of

The paper discusses the results of a kinetic study of the pyrolysis of woody biomass (ordinary oak wood – Quercus robur) under static conditions at temperatures of 673, 773 and 873 K. In experiments, biomass samples weighing about 1.4 g were kept in a heating furnace for a certain period, after which their residual weight was measured and the degree of decomposition achieved was determined. A total of 7 series of experiments were performed: two series each at temperatures of 673 and 873 K and three series at a temperature of 773 K. The obtained results were analyzed in the framework of a single-stage chemical reaction (one-step global model), leading to a loss of the initial mass. It was established that from the phenomenological point of view, the pyrolysis of woody biomass under experimental conditions corresponds to the sigmoidal reaction model by Avarami–Erofeev with an exponent n ranging from 0.508 to 0.985. The use of the results of the first series of experiments led to an activation energy value of 57.2 kJ/mol and a pre-exponential factor value of 38 s–1. The other series of experiments gave an activation energy value of 64.9 kJ/mol and a preexponential factor value of 130 s–1. It is shown that the use of these values of the activation energy and the preexponential factor leads to agreement of the calculated values of the degree of decomposition of the studied biomass samples with the experimental ones in the range of values of the degree of decomposition from 0 to 1. The data presented in this work contribute to a more complete understanding of the kinetics of pyrolysis of biomass, which is necessary for the development of effective equipment for the thermochemical processing of vegetable raw materials.

C(2)-H isotopic exchange in coordinated imidazoles revisited. The case of the [Co(NH3)5ImH]3+ ion

1999 ◽  
Vol 77 (2) ◽  
pp. 178-181 ◽  
Author(s):  
Charles R Clark ◽  
Allan G Blackman ◽  
M Ross Grimmett ◽  
Akbar Mobinikhaledi
Keyword(s):  
Metal Complex ◽  
Temperature Dependence ◽  
Key Words ◽  
Rate Constant ◽  
Rate Constants ◽  
Isotopic Exchange ◽  
Ionization Constant ◽  
Ionization Constants ◽  
First Order ◽  
Acid Ionization

The temperature dependence of the acid ionization constants of [Co(NH3)5ImH]3+ in H2O (I = 1.0 M (NaClO4)): pKa (°C) = 10.10 ± 0.04 (25.0), 9.92 ± 0.03 (30.0), 9.82 ± 0.02 (35.0), 9.62 ± 0.03 (40.0), and [Co(ND3)5ImD]3+ in D2O (I = 0.35 M (NaClO4)): pKa (°C) = 10.58 ± 0.06 (25.0), 9.46 ± 0.08 (60.0) is reported. Observed first-order rate constants for H/D exchange at C-2 in [Co(ND3)5ImD]3+ over the pD range 8.08-11.20 (60.0°C, I = 0.35 M (NaClO4)) follow an equation of the form: kobs = kODKw/(aD+ + Ka)γ±, with kOD (0.27 ± 0.06 M-1 s-1) corresponding to the rate constant for OD--catalyzed abstraction of H-2 in [Co(ND3)5ImD]3+, and Ka ((2.8 ± 0.7) × 10-10 M, pKa = 9.55 ± 0.13) to the acid ionization constant of this species. No evidence was found for a pathway to H/D exchange in the imidazolate moiety of [Co(ND3)5Im]2+.Key words: kinetics, H/D-exchange, imidazole, metal complex.

PHOTO-INITIATED REACTIONS OF THIOLS AND OLEFINS: II. THE ADDITION OF METHANETHIOL TO UNCONJUGATED OLEFINS

1964 ◽  
Vol 42 (10) ◽  
pp. 2250-2255 ◽  
Author(s):  
D. M. Graham ◽  
R. L. Mieville ◽  
R. H. Pallen ◽  
C. Sivertz
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Addition Product ◽  
Isomerization Reaction ◽  
Ethylene Propylene ◽  
Intermittent Illumination ◽  
Competing Reactions

Kinetic studies have been made of the addition of methanethiol to ethylene, propylene, and butene-2. The results obtained are consistent with the mechanism postulated for the isomerization reaction (1). The overall activation energy was found to be negative and could be explained in terms of two competing reactions of the adduct radical: thermal decomposition leading to [Formula: see text] and olefin and dehydrogenation of thiol yielding addition product. Only the ratio of the rate constants for these two reactions could be determined. The method of intermittent illumination was used to evaluate the termination rate constant for the combination of two [Formula: see text] radicals which was found to be (2.5 ± 0.7) × 1010 l mole−1 s−1.

Article

1999 ◽  
Vol 77 (11) ◽  
pp. 1728-1733
Author(s):  
RED McClung ◽  
T T Nakashima ◽  
H Yamamoto ◽  
G Kotovych
Keyword(s):  
Density Matrix ◽  
Key Words ◽  
Rate Constants ◽  
Water Exchange ◽  
Experimental Measurements ◽  
Spin Lock ◽  
Solvent Water ◽  
Ph Values ◽  
Product Operator ◽  
Theoretical Predictions

A product operator description of the nuclei in an ensemble of molecules undergoing intermolecular exchange during the spin-lock period of TOCSY is presented. Experimental measurements of the transfer of magnetization from the CH2 protons in N-acetylglycine to the solvent water protons, via exchange of the NH proton with water protons during the spin-lock period in TOCSY, are shown to be in agreement with theoretical predictions at lower pH values (7.85-9.54) where the rate constants for NH-water exchange are known. Measurements at higher pH (up to 11.03) indicate that the highest rate constant for exchange that can be determined by this technique is τA-1 ~ 4000 s-1.Key words: product operator, density matrix, intermolecular exchange, TOCSY, NMR.

Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I

1959 ◽  
Vol 32 (1) ◽  
pp. 128-138 ◽  
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Temperature Dependence ◽  
Induction Period ◽  
Rate Constants ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
First Order ◽  
The One ◽  
Limiting Value

Abstract The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.

Vulcanization of Elastomers. 21. Vulcanization of Natural Rubber with Thiuram Disulfides. VI

1959 ◽  
Vol 32 (2) ◽  
pp. 566-576
Author(s):  
Walter Scheele ◽  
Klaus Hummel
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Temperature Dependence ◽  
Sulfur Content ◽  
Rate Constants ◽  
Order Reaction ◽  
First Order Reaction ◽  
Kcal Mole ◽  
First Order ◽  
Limiting Value

Abstract Bound sulfur in a pure thiuram vulcanizate increases relatively rapidly at first at all temperatures, reaches a poorly defined maximum at about 27 to 30%, independent of temperature, and then recedes slightly to reach a limiting value of 25% also independent of temperature, based on the original thiuram disulfide. The rise in sulfur content at the start points to a temperature-independent limiting value of 33%. It is shown that the combination of sulfur in this region initially follows a first order reaction, and goes at the same rate as the reduction in concentration of thiuram disulfide. It can be seen from the above that sulfur may be combined in thiuram vulcanization without simultaneous crosslinking. The dithiocarbamate formation increases rapidly in the region of longer vulcanization times, after the maximum in bound sulfur has been reached, without further combination of sulfur with the vulcanizate. The rate constants for thiuram decrease, for dithiocarbamate increase and for sulfur combination were calculated. The temperature dependence of each of these reactions has practically the same activation energy, 23 kcal/mole. The bound sulfur content of the vulcanizates in pure thiuram vulcanizations is no criterion of the state of vulcanization.

Thermooxidative degradation and its kinetics of natural rubber coagulated by microwave radiation

2012 ◽  
Vol 32 (8-9) ◽  
pp. 511-517 ◽  
Author(s):  
Lu-Sheng Liao ◽  
Jian-He Liao ◽  
Yi-Min Li ◽  
Yong-Ping Chen ◽  
Yan-Fang Zhao ◽  
...  
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Natural Rubber ◽  
Microwave Radiation ◽  
Preexponential Factor ◽  
Degradation Process ◽  
Main Stage ◽  
Thermooxidative Degradation ◽  
Mean Values ◽  
One Step

Abstract The thermooxidative degradation of natural rubber (NR) coagulated by microwave radiation (NR-m) was investigated by thermogravimetry (TG) analysis, and compared with NR coagulated by acid (NR-a). It was found that the degradation process is not a one-step reaction, the main degradation process occurs at 300–400ºC, and the equilibrium degradation temperatures of NR-m are higher than those of NR-a. Different methods were used to find the most probable kinetic model and the Arrhenius para­meters (activation energy E and preexponential factor A) for the main stage of thermooxidative degradation of NR-m. The results show that the values of E and A, obtained from the Coats-Redfern method, are highly variable with the kinetic model chosen and the heating rate (β), and the apparent activation energy (E0) when β approaches zero for the Dn type kinetic model is in the range of 96.7–106.4 kJ ∙ mol-1. The mean values of E, calculated by the Friedman and Flynn-Wall-Ozawa (FWO) methods, are 113.8 and 83.3 kJ ∙ mol-1, respectively, suggesting E in the range of 83.3–113.8 kJ ∙ mol-1. Comparison of these two ranges indicates the most probable kinetic model to be Dn type kinetic models, corresponding to a diffusion-controlled mechanism.

scholarly journals KINETIKA DAN SELEKTIFITAS SISTIM TRANSPOR Cu(II) ANTAR FASA MELALUI TEKNIK MEMBRAN CAIR FASA RUAH DENGAN MENGGUNAKAN OKSIN SEBAGAI ZAT PEMBAWA

2015 ◽  
Vol 4 (1) ◽  
pp. 63
Author(s):  
Refinel ◽  
Zaharasmi ◽  
Olly Norita Tetra
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Optimum Condition ◽  
Transport System ◽  
Rate Constants ◽  
Phase Extraction ◽  
Membrane Phase ◽  
First Order ◽  
Stirring Rate ◽  
Source Phase

  ABSTRACTThe effect of addition oleat acid 1.575 × 10-4M into membrane phase had been employed at the optimum condition of Cu(II) transport by the composition Cu(II) 3.15 × 10-4M as source phase with pH 3, oxine 17.5 × 10-4M dissolved into chloroform as membrane phase, H2SO4 0.15 M as receiving phase, stirring rate was 340 rpm. The result of the research showed increase in effectivity of transport Cu(II) interphase from 6 hours to 3 hours with the rate constants into membrane phase extraction (k1) 0.0454 minute-1, the stripping (k2) 0.0364 minute-1 at the temperature of 301°K and activation energy (Ea) 51.147 Kj/mol. The reaction was identified by means of kinetic model involving two consecutive irreversible first order. The selectivity of Cu(II) transport system analyzed to mixed Cu(II) ion with Cd(II), Co(II), Ni(II), Mg(II), Ca(II) and Sr(II) ions in pairing system or totaly system in 1 : 1 comparison. The measurement was performed to each ions that was transported receiving phase and the remains in resource phase by using SSA model Alfa-4. The result of research showed that Cu(II) was selective enough transported.  Keywords: Kinetic transportation, Cu(II) ions, oxine, oleat acid, selectivity   

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