from kerogen extracted from two Moroccan oil shales (from Timahdit and Tarfaya)
were oxidized in air. The oxidations were studied by isothermal thermogravimetry.
Several kinetic models for mechanisms of the reactions were tested to fit
the experimental data. Oxidation of the residual carbon derived from Timahdit
oil shale followed a two-third order reaction with an activation energy of
58.5 kJ mol–1, whilst that from Tarfaya oil
shale was a half order reaction with activation energy of 64.1 kJ mol–1.
Thermal analysis has been used to determine the impact of heating on the decomposition reaction of two Moroccan oil shales
between ambient temperature and 500C. During pyrolysis of raw oil shale, the residual organic matter (residual carbon) obtained
for both shales depends on the heating rate (5 to 40C min-1). Three stages characterize the overall process: the concentration of carbonaceous residue decreases with increase of heating
rate, become stable around 12C min-1 and continue to decrease at higher heating rates. Activation energies were determined using the Coats-Redfern method. Results
show a change in the reaction mechanism at around 350C. Below this temperature, the activation energy was 41.3 kJ mol-1 for the decomposition of Timahdit, and 40.5 kJ mol-1 for Tarfaya shale. Above this temperature the respective values are 64.3 and 61.3 kJ mol-1. The reactivity of Timahdit and Tarfaya oil shale residual carbon prepared at 12C min-1 was subject to a dynamic air atmosphere to determine their thermal behaviour. Residual carbon obtained from Tarfaya oil shale
is shown to be more reactive than that obtained from Timahdit oil shale.
Organic matter evolution and kinetics of combustion of Tarfaya and Timahdit oil shales have been examined by thermogravimetry (TG) and by differential thermal analysis (DTA). An agreement is observed between both techniques where it was found that combustion of organic matter occurs in two steps. Kissinger's method applied on experimental results gives an activation energy of the same magnitude for the first step of both oil shales (103 kJ mol–1) whereas the second is 148 kJ mol–1 for Timahdit and 118 kJ mol–1 for Tarfaya.The changes in specific surface area during thermal combustion of Timahdit and Tarfaya oil shales have been studied by thermogravimetric gas sorption balance and correlated with experimental results obtained on TG/DTA in air. For Timahdit oil shale oxidation products, specific surface areas calculated from nitrogen adsorption data shows a slight increase during the temperature domain of 280 to 430°C and after this temperature, they increase sharply. However, data obtained with Tarfaya oil shales shows a significant increase at the temperature of maximum oxidation of the first stage of combustion of organic matter.
The gasification with carbon dioxide of residual carbons prepared from Timahdit and Tarfaya oil shale kerogens has been studied
by thermal analysis techniques (TG and DTA) under heating rates varying from 5 to 48C min-1. The reactions obey first order kinetics. Activation energies have been calculated by several methods, such as Kissinger,
Chen-Nuttall and Coats-Redfern methods, and are broadly comparable with literature data for similar carbons.
Authors:L. Vincent, S. Connolly, F. Dolan, P. Willcocks, and S. Jayaweera
The fracture toughness of blends
of polypropylene terephthalate (PPT) with polyethylene terephthalate (PET)
and polybutylene terephthalate (PBT) were investigated. Binary blends were
prepared comprising 10:90, 30:70, 50:50, 70:30 and 90:10 mass/mass%. The fracture
toughness was determined for each blend using the essential work of fracture
(EWF) method and thin film double edge notched tension (DENT) specimens. The
specific essential work of fracture, we,
values obtained for blends of PET/PPT ranged from 27.33 to 37.38 kJ m–2
whilst PBT/PPT blends yielded values ranging from 41.78 to 64.23 kJ m–2.
Differential scanning calorimetry (DSC) was employed to assess whether or
not crystallinity levels influence the mechanical properties evaluated. The
fracture toughness of PPT deteriorated with PET incorporation. However, high
we values exceeding that of pure PPT were obtained for PBT/PPT blends across
the composition range studied.
Authors:E. Robens, P. Klobes, D. Balköse, S. Amarasiri, and A. Jayaweera
A short survey is given on mass units and recommendations on the proper use of the notations mass and weight.Whereas mass
is an inertial physical quantity in classical mechanics, weight is a force due to the gravitational field and depending on
the geographic situation.