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PTAC. This is caused by the fact that anhydride is more reactive than carboxylic acids of PTAC in their reaction with epoxy group. Though PTAC decreases the overall activation energy, this advantage is found to be offset by a larger decrease in

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Abstract  

A phenomenological approach was used to characterize the cure processes of epoxy resins (a diglycidyl ether of bisphenol A and its modifier CTBN) from dynamic experiments by DSC. Various kinetic parameters were obtained by using a modified Avrami expression. The resulting overall activation energies for the two systems agreed very well with the published data in the whole cure temperature range. In contrast with the isothermal results and the general dynamic models, a change in the exponent and the non-linear temperature dependence of the rate constant were also observed.

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The extraction of iodine and bromine under various conditions from their saturated aqueous solutions by CCl4, C6H6 and o-xylene has been studied. The data obtained from the experiments carried out at various temperatures, for H2O(I2)−CCl4 and H2O(I2)−C6H6 systems, exhibit an Arrhenius behaviour. The overall activation energy calculated for the extraction in the H2O(I2)−CCl4 system, 650±50 cal·mol−1 is lower than that of H2O(I2)−C6H6, 3600±300 cal·mol−1. The use of the solubility parameter for the interpretation of the data in the extraction of iodine is investigated. The data obtained in multiple extractions are treated by using the analogy between extraction and radioactive decay. The half number of extraction for each system is determined. The complex curves obtained in the H2O(I2)−CCl4 and H2O(I2) −Br2)−CCl4 systems are resolved into two components.

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The overall activation energy of the thermal degradation of polyisobutylene has been measured using factor-jump thermogravimetry to be 206±1 kJ/mole over the range 365 to 405° in N2 at 800 mm Hg pressure and flowing at 4 mm/s over the sample. This is consistent with some values reported for thermal degradation in vacuum and in solution. In 5 mm Hg of N2, an apparent activation energy of 218±2 kJ/mole was found, and in vacuum the apparent activation energy is 238±13 kJ/mole. Troublesome bubbling made the vacuum values difficult to measure. Substitution of reasonable values for the activation energies of initiation,E i, termination,E t, and the activation energy,E a, for vacuum degradation in the equationE a=E i/2E d-E t/2 yields an activation energy Ed=84 kJ/mole for the unzipping reaction. This equation presupposes a degradation mechanism of random initiation, unzipping, and bimolecular termination. Substitution of reasonable values for the heat of polymerization, ΔH, in the definition ΔH=E pe d suggests that the activation energy of the polymerization reaction at 375° is approximately 30 kJ/mole.

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The thermal decomposition of polytetrafluoroethylene (TFE, Teflon), high and low density polyethylene (HDP and LDP), Delrin Acetal (DA), AVCO Phenolic Fiberglass (APFG), and carbon phenolic (CP), were studied by a thermogravimetric technique which utilized a constant heating rate. Loss in sample weight was recorded as a function of time or temperature from room temperature to approximately 700°. Reaction orders were established from logarithmic rate versus temperature plots. Arrhenius frequency factors and overall activation energies were determined from computerized integrations of the appropriate rate equations in which the results were treated on the basis of first-order reaction mechanisms for specific temperature regions. Zero-order mechanisms were estimated by the usual graphical methods.

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The high concentrations of hydrogen sulfide found in many oil and gas fields is thought to arise from the oxidation of petroleum hydrocarbons by sulfate—a reaction that reduces the value of the resource. This review, undertaken in order to better understand the geochemistry of TSR reaction in oil field sediments, covers the relevant information on thermochemical sulfate reduction (TSR) to 1991. The theoretical and experimental aspects of TSR reactions (including sulfur and carbon isotope studies) are reviewed and their significance to the geochemical system discussed. The present review agrees with previous suggestions that biochemical reduction of sulfate dominates in sedimentary environments below 120°C, and supports the possibility that reactive sulfur species will oxidize certain organic molecules at meaningful rates in geochemically reasonable reaction periods at temperatures above 175°C. We conclude that under typical petroleum reservoir reaction conditions, both elemental sulfur and polysulfides are capable of oxidizing some organic molecules under basic conditions. But that sulfate alone will not react unless lower oxidation state sulfur is present. The possible interaction of low-valence-state sulfur with sulfate to form TSR active oxidants is examined. both H2S and SO 4 2− are required for the formation of active polysufide reductants (e.g. thiosulfate or polythionates) in TSR systems. Such intermediates can serve to lower the overall activation energy of the oxidation of hydrocarbons by sulfate via thermal generation of sulfur radicals that can function as TSR active oxidants in many oil field sediments. We suggest that some proposed chemical mechanisms for TSR need to be experimentally verified and the results re-interpreted with respect to TSR relations in geologic systems.

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segmental and translational diffusion and so decreases rapidly with conversion. Assuming that at low conversion the activation energy for termination is nearly zero, the overall activation energy for a photo-polymerization reaction would be given by: 6

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determined using both integral and differential isoconversional methods. The overall activation energy was also evaluated from the temperature dependence of the induction period. Results and discussion Under linear heating

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