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Heats of chemisorption ofn-Aliphatic alcohols on α-Al2O3 at 25–200°C
A thermokinetic study
Abstract
A differential microcalorimeter (E. Calvet) was used to study the processes of adsorption of five aliphatic alcohols (C1-C5) on α-Al2O3 at 25, 50, 100, 150 and 200°C. In particular, the importance of the thermokinetic study of the chemisorption of such alcohols
at different experimental temperatures was demonstrated, with regard to the variations in the thermokinetic parameters (tmax, t1/2 and t0) and the evolution of the alcohol vapor pressure on the adsorbent during the adsorption process. It was concluded that:
a)
all the heat emission peaks of alcohol adsorption have the same rounded shape at 25°C;
b)
on passing from methanol to 1-pentanol, the area of the adsorption peaks increases as the chain length or molecular weight
increases;
c)
on passing from 25 to 200°C, the shape of the adsorption peaks becomes more pointed.
The adsorption of benzene at room temperature onα-Fe2O3 and onγ-Al2O3 powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.
Interactions between paper and adsorbed molecules
A preliminary study and some experimental results
Abstract
We have studied the geometry and energy involved in the interactions between adsorbed molecules and paper substrate, over a wide range of partial pressures. A two-dimensional virial equation of state was employed to evaluate the extent of interactions by the compressibility factor (Z). Data of H-bonded molecules (water and butan-1-ol) and of more weakly interacting ones (n-decane and dioxane) were selected from the literature. At low surface coverage, the compressibility factor Z exceeds 1, showing a deviation from ideality due to interactions, and reaches a maximum at a value close to the BET monolayer. As preliminary results we have measured by means of a differential microcalorimeter (Calvet) at 25‡C the energy of interactions of water andn-heptane vapor on chromatographic grade Whatman paper. At very low coverage, the differential heats of adsorption of water on paper are higher than those ofn-heptane adsorption on paper: 114 kJ mol−1 > 77 kJ mol−1. During the whole process of adsorption, in the first case, the specific interaction predominates, while in the second non-specific interactions predominate i.e. the dispersion or Van der Waals forces.
Heat of chemisorption of 1-propanol on α-Al2O3 at 25–200°C
A microcalorimetric study
Abstract
We have studied by means of differential microcalorimetry the adsorption process of 1-propanol on α-Al2O3 at the temperatures of 25, 50, 100, 150 and 200°C, respectively. Both amounts of adsorbed alcohol and heats released decrease as the temperature of adsorption increases. At very low coverage, the high value of differential heat shows a strong irreversible chemisorption on active sites (Lewis acid sites) (qdiff>200 kJ·mol−1). Moreover, we carried out some thermokinetic investigations on heat emission peaks at different coverage degree (different equilibrium pressure of 1-propanol vapour as a function of time) and at different temperatures of adsorption, at same coverage.
The glass transition temperatures,T g, and thermal effects of polymerization,ΔH, have been determined for five epoxy adhesives of unknown composition. From the trendsΔH vs./t cure it has been possible to attain a phenomenological kinetic order of the polymerization rate at 100° through an iterative calculation procedure. For most of the investigated adhesives there are reasons (double peak of polymerization and doubleT g signal) to assume that they are graft copolymers.
Abstract
The authors studied the ignifugation and the kinetic of thermal degradation of the Styrene-Butadiene copolymer with an intumescent system Ammonium polyphosphate-Pentaerythrinol-Melamine. For that, they used the thermogravimetric and oxygen index techniques. The best formulation of intumescent system which can give the optimum results is proposed.
