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Abstract: For decades a particular interest has been devoted to the enhancement of adsorption processes by means of activated carbons (AC) pore size tailoring. In the present study, an original textural modification route is presented and applied to a commercial AC. It is composed of cyclic treatments of mild-oxidation at 250°C under air followed by a carbonization step under nitrogen. This technique provides series of homologous adsorbents of similar surface chemistry and gradual increase in mean pore size and microporous volume. Comparing the raw material and the modified adsorbent after 12 cycles, a ratio of about two is reached for these two parameters representative of their microtexture. The corresponding performances of the elaborated adsorbents are compared in the case of CO2 storage. According to the amount of CO2 cycled per unit of column volume, the optimal extend in textural modification is found to depend strongly on the temperature–pressure working ranges. At low temperature level as 273K, the storage capacity is found to be enhanced for all considered loading pressure levels within the range of 1–3MPa. At higher working temperature as 333K, the enhancement is severely reduced but still observed for the highest loading pressure level and very first oxidative cycles. [Copyright &y& Elsevier]

Abstract: Composite materials made of expanded natural graphite (ENG) matrix in which activated carbon has been elaborated, present high thermal conductivity (up to 30Wm−1 K−1) compared to conventional activated carbon bed (0.15–0.5Wm−1 K−1). In a first part [D. Menard, X. Py, N. Mazet, Activated carbon monolith of high thermal conductivity for adsorption processes improvement. Part A. Adsorption step, Chem. Eng. Process., 44 (2005) 1029–1038], the experimental adsorption of pure and diluted CO2 has been presented for both the composite and a commercial granular bed for comparison. In the present part, thermal regenerations of the two adsorptive beds by peripheral heating are presented. The conductive composite leads to reduced regeneration time and to the production of concentrated gaseous streams of the adsorbate. The experimental data have been used for numerical model validation which is used for the estimation of the materials performances in larger column scale. [Copyright &y& Elsevier]

Abstract: Due to the low thermal conductivity of conventional beds of granular adsorbents (0.15–0.5Wm−1 K−1), performances of gas separation as well as gas storage processes are usually strongly inhibited by the induced adsorptive thermal effects. A monolithic composite of intensified overall thermal conductivity (10Wm−1 K−1), made of activated carbon (AC) in situ elaborated within a consolidated expanded natural graphite (CENG) matrix has been experimentally tested under both conditions of non-isothermal and non-adiabatic CO2 adsorption. Heat transfer intensification and process performances improvements for the conventional saturation step is described in terms of induced local temperature increases, adsorbate breakthrough and sorption capacity. Experimental conductive packing achievements are compared to those of a conventional packed bed of commercial TA70 granular activated carbon. [Copyright &y& Elsevier]

Abstract: Two complementary wearing off cycling methods based on an initial wet oxidation in a sodium hypochlorite solution or an initial dry oxidation under air, both followed by a thermal pyrolysis under nitrogen, have been applied to a same carbon molecular sieve to study its gradual pore structure modifications. The changes in microporous properties resulting from these cycles were studied by N2 physisorption at 77K and analyzed by using the Dubinin–Radushkevich equation. The observed textural behaviour is different from those usually observed using conventional activation processes. The surface complexes created on the surface of carbon by each NaOCl oxidation were characterized by temperature-programmed desorption (TG-TPD-MS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Corresponding surface functional species have been identified and quantified. Each of the two methods leads to the formation of two distinct microporous domains developed on the obtained modified CMS series. The gradual mean pore size values of one of those domains are common to the two series while the others are much more enlarged by the oxygen than by the NaOCl treatments. Therefore, the two methods lead to complementary data allowing experimental differentiation of the different porosities encountered in activated carbons. Such series of materials of common origin and surface chemistry but different gradual textural properties are of great interest for activated carbons structural studies as well as for characterization technique improvements. [Copyright &y& Elsevier]

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]

Activated-carbon pore size tailoring is usually achieved by pore size reduction, pore size widening or more rarely by direct activation. Successive widening cycles composed of an initial molecular oxygen sorption step, followed by a carbonization step under nitrogen, have been applied to three different materials in order to study their gradual pore size modifications. For years, the whole microporosity obtained after several cycles is known to present better pore size distribution than those inherited from conventional activations. Moreover, as shown in the present paper, the gradual obtained microporosities cover a wide and valuable range of porous textures highly dependent on the initial material origin and initial activation. Gradual mean pore size evolutions of 1 or 2 A˚ per cycle were observed linked to a simultaneous increase in microporous specific volume in the case of pitch-based and coconut activated carbons, respectively. Comparatively, the microporous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature. [Copyright &y& Elsevier]

Abstract: A new method for setting the porous particle overall density is proposed. The apparent density of the particle including the solid matter as well as the different internal porosities (from microporous to macroporous pore size ranges) is currently needed for industrial applications as gas storage, heterogeneous catalysis… The technique proposed is based on the principle own immersion fluid applied to a granular medium consisting of extremely fine particles playing the role of non-wetting liquid. Here are presented the restrictive theoretical and experimental conditions, which have to be fulfilled by any granular medium before applying this principle. The conventional technique of mercury porosimetry has been used to characterize apparent grain density and validate the obtained results. The technique has been calibrated to be used with particles, which exhibit a different density, size, shape, and surface roughness. In a second part, the proposed method has been applied to a crop of materials including modified activated carbons previously obtained by oxidative transient treatments. The corresponding change in microporous properties has been studied by N2 physisorption at 77K. Moreover, the size ranges of the particle over which each technique leads to efficient measurements have been identified. [ABSTRACT FROM AUTHOR]