Emmanuel Daguerre

Composites of expanded natural graphite and in situ prepared activated carbons

Abstract Activated carbons present very low thermal conductivity (0.2 W m −1 K −1 ) responsible for severe thermal limitations inducing low overall adsorption and desorption kinetics as well as secondary reaction products or hazards in industrial applications. The in situ activation of various precursors within a consolidated expanded natural graphite matrix led to composites of high thermal conductivities (from 1 to 32 W m −1 K −1 ) and high effective adsorbent level (80 wt.%). Preparation protocols adapted to the different precursors and activation agents are proposed and a wide range of microporous characteristics (from molecular sieve to super-adsorbent) was obtained.

Activated carbons prepared from thermally and chemically treated petroleum and coal tar pitches

Abstract Petroleum and coal tar pitches have been treated thermally at 400°C and 470°C, extracted with toluene and subsequently activated with CO2 at 900°C. With one exception, the development of the micropore widths and volumes in the resulting carbons follows the trend observed for carbons based essentially on precursors of vegetable origin. On the other hand, petroleum pitch treated at 400°C leads to an active carbon which follows the pattern observed for cokes, semi-cokes and pyrolyzed tyres. It is suggested that the difference between the two types of active carbons is due to the large amount of compounds with low molecular weight left in the petroleum pitch after thermal soaking.

Microporosity of activated carbons produced from heat-treated and fractionated pitches

Activated carbons with degrees of burn-off ranging from 12 wt.% to 60 wt.% have been prepared from toluene-insoluble (T.I.) fractions of a heat-treated A240 petroleum pitch. After toluene fractionation, the resulting pitches have been stabilized, carbonized and then activated using carbon dioxide at 1173 K. Characterization by high pressure carbon dioxide adsorption has been performed in order to determine the properties of activated carbons and to evaluate their performances for adsorption refrigerating machines. Microporous properties are influenced by pitch composition resulting from toluene fractionation and residual γ-resins inhibit the microporosity development. Due to their high microporous volume, activated carbons prepared from extensively γ-resins extracted pitches appear appropriate for cooling applications.

Alpha-relaxation of an isotropic petroleum pitch: A controlled stress and strain oscillatory rheometry study

Abstract Oscillatory measurements under controlled stress and controlled strain have been performed on the Ashland A240 isotropic petroleum pitch using a cone/plate rheometer. The storage and loss components of the modulus of rigidity have been analysed by means of time-temperature superposition coupled with the Williams, Landel and Ferry (WLF) procedure. Loss modulus results obtained under controlled stress are in good agreement with those previously published on the same material but using a plate/plate geometry (Turpin et al., Carbon, 1994, 32, 225). The temperature-dependence of the storage modulus presents a three decades α-relaxation step at Tga = 114 °C followed by a corresponding 11 units peak of tan (δ) at Tδ = 124 °C. Such a-relaxation has been extensively studied for amorphous polymers and other glassy materials within the glass transition temperature range but, up to now, has not yet been studied for pitches. Characteristic relaxation time τga similar to τmol has been calculated within the investigated experimental temperature range and correlated by the Tammann-Vogel-Fulcher (TVF) equation. The corresponding TVF parameters are within the same order of magnitude of those encountered in amorphous polymers. A detailed analysis of the applicability of the WLF method is presented. Same values for the storage and loss modulus shift factors are obtained at low temperature up to Tδ. At higher temperature, storage modulus shift factor presents a change of regime and a strong deviation from loss shift factor. Therefore, with respect to the α-relaxation phenomenon, the applicability of the WLF procedure to an isotropic pitch is only possible at a temperature below Tδ.