E. Broniek

Adsorption of H2S or SO2 on an activated carbon cloth modified by ammonia treatment

The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 8C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 8C or with ammonia/steam at 800 8C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption–regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process.

Exfoliation and textural modification of anthracites

Abstract Two anthracites (La Mure, France and Hongay, Vietnam) have been exfoliated after intercalation in a perchloric and nitric acid solution followed by a thermal shock treatment. The anthracites are extensively exfoliated as shown by scanning electron microscopy, and this treatment is responsible for a significant development of mesoporosity and a great increase of specific surface area. Hongay anthracite was then steam activated, and specific surface areas of 1200 m2/g have been obtained with a well developed mesoporous texture. Moreover, after exfoliation, the anthracite reactivity with water vapour during steam activation is increased by a factor of 3. This shows that anthracites may be an important source of raw materials for the production of active carbons with a large pore size distribution.

Following changes in the porous texture of Nomex-derived activated carbon fibres with the molecular probe technique

A series of Nomex-derived activated carbon fibres (ACFs) activated to different burn-offs (BOs) together with two series derived from the previous ACFs through chemical vapour deposition (CVD) treatments were used as adsorbents. The adsorption of molecules of different size, namely, dichloromethane, benzene, cyclohexane and carbon tetrachloride was used to monitor the textural evolution of microporous carbon fibres owing to these treatments. The analysis of the results showed that carbon deposit has taken place mainly at the entrance of the pores rather than in the interior. The information obtained about the porous structure and the molecular sieve behaviour of the samples in the different series was also useful for establishing the possible uses of these materials: thus, the obtained ACFs could be used for adsorbing volatile organic compounds (VOCs) in the field of environmental control while CVD-treated ACFs could be used as adsorbents for gas separations. In particular, the combined use of CH2Cl2 and C6H6 could be used to determine whether an adsorbent is a good carbon molecular sieve (CMS) for CO2/CH4 separation.

Porosity development in steam activated chars from mixtures of coal tar pitch with graphite-FeCl3 intercalation compounds

The effect of addition of the iron graphite intercalation compound (GIC-FeCl3) to coal tar pitch, used as a carbon precursor, on the porosity development in the resulting steam activated chars, was studied. Different conditions of chars preparation have been considered. Benzene (298 K), nitrogen (77 K), carbon dioxide (298 K) and water (298 K) sorption measurements were taken as basis for the porosity evaluation. The changes in the development of pores of different categories, caused by added amounts of GIC-FeCl3 to coal tar pitch, temperature of carbonization and activation, and the degree of activation, are discussed.

Effect of iron enrichment with GIC or FeCl3 on the pore structure and reactivity of coking coal

The effect of a Lewis acid addition to a coking coal on the porosity and reactivity towards steam of the resulting iron enriched coal chars are studied. GIC (FeCl3 graphite intercalation compound) or free FeCl3 are used as iron containing additives. Coal iron enrichment was performed using either directly FeCl3 in vapour phase, or by mixing of coal and additives in decaline or by common grinding of coal and additives under argon. Iron enriched coals were carbonized at 750°C (heating rate = 5°C min) and activation made with pure steam at 800°C to a burn-off off of 50 wt%. The pore structures of coal chars before and after activation were evaluated on the basis of CO2 and C6H6 sorption at 25°C. A significant development of the microporosity is observed in the iron enriched char before activation and its steam reactivity is also increased. After activation, BET surface area values are increased in presence of iron, and porosity is mainly microporous.

Graphitization, intercalation, and exfoliation of cokes and anthracites: a comparative study

Abstract In this work, we will compare the ability to graphitize of two petroleum cokes, isotropic and anisotropic, and of two varieties of anthracites, in order to understand their subsequent ability to give exfoliated carbons. Both series of derived materials obtained by heat treatment (1500–2600 °C) of these four precursors are compared after the action of an excess of mixture containing water, perchloric acid, and nitric acid, which were used to obtain exfoliated graphite from very small particles. The intermediate products are shock heated to induce the thermal decomposition of the perchloric acid present either in the microtexture or in the graphitic structure. This ultimate treatment gave exfoliated materials, the specific surface of which strongly depends on the nature of the raw material, its ability to graphitize.

Pore structure and reactivity of chars obtained by pyrolysis of coking coals containing MoCl5

Three coking coals were pyrolysed in the presence of the Lewis acid MoCl 5 under an inert atmosphere at a final temperature of 750°C, the ultimate aim of this work being the elaboration of active carbon supported catalysts for use in hydrodenitrogenation reactions. The values of the parameters characterizing the porous structure of the chars before and after steam activation were determined using CO 2 and C 6 H 6 sorption measurements at 25°C. Char from the lowest rank coal had the most developed ultramicroporosity (pore width < 0.4 nm) and the presence of MoCl 5 in the precursor does not seem to exert much influence. In the case of the higher rank coals, a significant development of the ultramicroporosity was observed in the molybdenum enriched chars before activation and their reactivity toward steam was increased. After steam activation, the structure of the activated chars was mainly microporous, but a significant development of the mesoporosity was observed.

Development of Porosity in Steam Activated Brown Coal Chars Obtained in Different Conditions of Pyrolysis

Abstract Two demineralized brown coals-a humodetrinitic and a humotelinitic coal-were subjected to pyrolysis at heating rates of 5°C/min and 1000°C/s. The influence of the petrographic composition of the coals and of the heating rate during pyrolysis on the reactivity and development of porosity in the non-activated and steam activated chars has been studied. A slightly better development of porosity was obtained for samples from the humotelinitic than from the humodetrinitic coal. The higher heating rate during pyrolysis caused an increase in reactivity accompanied by a very strong development of macroporosity. For a series of steam activated chars from compressed (225 MPa) humodetrinitic coal samples, adsorption of probe molecules (nitrogen, benzene, cyclohexane, n-heptane and n-nonane) was performed. For different burn-offs of the chars, the fractal dimensions were calculated. Differential enthalpies of nitrogen adsorption have been determined.