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Despite the extensive use of 129Xe NMR for characterization of high surface-to-volume porous solids, particularly zeolites, this method has not been widely used to explore the properties of microporous carbon materials. In this study, commercial amorphous carbons of different origin (produced from different precursors) and a series of activated carbons obtained by successive cyclic air oxidation/pyrolysis treatments of a single precursor were examined. Models of 129Xe chemical shift as a function of local Xe density, mean pore size, and temperature are discussed. The virial coefficient arising from binary xenon collisions, σXe-Xe, varied linearly with the mean pore size given by N2 adsorption analysis; σXe-Xe appeared to be a better probe of the mean pore size than the chemical shift extrapolated to zero pressure, σS. [ABSTRACT FROM AUTHOR]

For centuries, activated-carbons are widely used adsorbents the nanomorphology of which is still badly understood. Nevertheless, recent advances in the characterization of their microporosities and in their carbonaceous structures lead to experimental evidences in a common frame shared by those materials. By plotting their mean pore size calculated using the D.R. method vs. their corresponding specific microporous volume, activated carbons made from various precursors and activated by different conventional methods gather themselves according to three linear domains. In the same representation, activated carbons submitted to transient oxidative treatments lead also to linear behaviour but with very higher slopes. In the present study, simple geometrical models of porosity based on a BSU packing approach are proposed and tested on KOH and CO2 activated pitches and on a modified commercial coconut activated carbon. The conventional activation processes seem to concern mainly the slit-like porosity potentially available between adjacent BSU faces while transient oxidative treatments concern mainly a star-like porosity potentially available between the edges of adjacent BSU. As the proposed model could be unsuitable for other kinds of activated carbons, it will be tested on other materials for generalization. [Copyright &y& Elsevier]

A new highly thermally conductive composite material made of activated carbon in-situ activated within a consolidated expanded natural graphite (CENG) matrix is developed in the specific case of gas separation processes. According to the particular chosen testing case of CO2/N2 mixture, the microporous characteristics of the adsorbent fraction have been selected and the various properties of the whole material studied. Activated carbon effective densities, overall thermal conductivities and external heat transfer coefficients up to 650 kg×m−3, 32 W×m−1×K−1 and 3000 W×m−2×K−1 were obtained, respectively. Two macroscopic external shapes were realized, namely a corrugated-sheets static mixer and a multi-axial-diffuser cylindrical monolith which will be further tested in a pilot equipment for comparison with conventional adsorbents. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]