E. Alain

Some aspects of carbonization of mixtures containing coal tar pitch and graphite FeCl3 compounds

Abstract Pyrolysis of coal tar pitch has been carried out with new added species: a first-stage FeCl 3 graphite intercalation compound (GIC). Small particles of graphite were used (average diameter ≈ 5 μm) with the aim of obtaining a good distribution of the particles within the pitch matrix. Contrary to many works described in the literature, FeCl 3 intercalation in such small particles does not need stringent conditions for first-stage synthesis. Many hk0 reflexions of the FeCl 3 lattice are observed by X-ray diffraction; the incommensurability of the two macromolecular lattices (graphite and intercalated FeCl 3 ) is well characterized. The coal tar pitch-GIC mixture (4% in volume) presents a good distribution of the particles, as confirmed by scanning electronic microscopy (SEM). X-ray measurements show that the GIC particles are not deintercalated during the thermal treatment of mixing. Pyrolysis was carried out at 550°C with a heating rate equal to 20°C/min. The green coke yield obtained after this treatment is higher than in the case of a pure coal tar pitch pyrolysis, and new species containing iron are characterized in the green coke matrix. A partial diffusion of this element out of GIC particles occurs during the thermal treatment, and the released iron is reduced to oxidation degrees 2 and 0.

Pyrolysis of coal tar pitch and its mixtures with a graphite-FeCl3 intercalated compound. Influence of heating rate and GIC concentration

Abstract The influence of heating rate upon pyrolysis of coal tar pitch (CTP) and mixtures of coal tar pitch plus first-stage FeCl 3 -graphite intercalated compounds (CTP-GIC) has been studied. In the two cases, the smaller the heating rate (from 20 to 0.5°C min −1 ), the higher the green coke yield. The presence of FeCl 3 in GIC, present in the CTP, also provokes an increase of the green coke yield by a significant value: in analogy to literature results with other kinds of added species, GIC certainly favours hydrogen evolution at lower temperatures and provokes more polycondensation reactions. Different concentrations of first-stage GIC (2–8 wt%) have been used, and pyrolyses were carried out from 550 to 750°C. Green cokes were characterized by elemental analyses, X-ray diffraction and scanning electron microscopy. Beyond the different iron species (FeS, FeCl 2 and α-Fe), the α-Fe phase is maximum when the CTP is mixed with 8 wt% GIC and pyrolysis is carried out up to 750°C. The thermal behaviour of C 7 FeCl 3 GIC under the same heat treatment conditions has also been studied: from ambient temperature to 500°C, the quantities of Fe and Cl decrease gradually and the ratio Cl/Fe becomes equal to 2. At 750°C, all the iron chloride is desorbed out of the GIC. In the case of the CTP-GIC mixture treated under the same experimental conditions, a great part of the iron is desorbed out of the graphite and is present in the resulting green coke.

Carbonization of mixtures of coal tar pitch and graphite FeCl3 compounds. A Mössbauer study

Mixtures of coal tar pitch (CTP) and first-stage FeCl3-graphite intercalation compounds (GIC) have been synthesized with different GIC concentrations, then pyrolysed at different final temperatures and at several heating rates. Mossbauer spectroscopy has been used to characterize the iron states after these thermal treatments. The initial GIC is characterized by a typical singlet of highspin Fe(III) and we have studied the thermal stability of the GIC under nitrogen flow by X-ray measurements: FeCl3 is progressively reduced to FeCl2 and reduction is complete at 500 °C. At 750 °C, all iron has been removed from the graphene layers. n nAfter pyrolysis of the CTP and GIC mixture, different phases are identified in the resulting green-coke: metallic iron (α-Fe), which is present in greater quantities at high GIC concentrations and at higher pyrolysis temperatures, ferrous chloride, iron sulfide (FeS, troilite), nonstoichiometric Fe1−χS (pyrrhotite), and a not-well-determined fourth phase that could be austenitic iron (γ-Fe). n nAfter steam activation of the green-coke at 750 °C, most of the iron is oxidized into magnetite as confirmed by X-ray measurements and Mossbauer spectroscopy.

Effects of FeCl3 (intercalated or not in graphite) on the pyrolysis of coal or coal tar pitch

Addition of iron chloride to coal tar pitch or coal before carbonization speeds up mesophase growth and increases the yield of an iron loaded microporous char. After steam activation a mesoporous activated carbon with specific adsorbents properties can be obtained. Iron oxide (magnetite) at the internal surface of the carbon plays the role of a basic centre for the catalytic oxidation of polluting gas. The present work deals with the effect on the pyrolysis and activation processes of the mode of introduction of FeCl3-either free or intercalated in graphite (GIC)—in coal tar pitch (CTP), in coking coal itself, or in a mixture of coal and CTP. Lewis acid effects on oil, methane, dihydrogen and carbon monoxide evolution could be correlated with those on mesophase growth, on char yield and on the properties of the steam activated chars. The study shows that free FeCl3 loading can be advantageously used to prepare cheap adsorbents.

Pyrolysis of coal tar pitch mixed in the presence of a graphite intercalation compound : a kinetic study

Abstract A kinetic study has been carried out to determine the influence of the addition of first stage FeCl 3 -graphite intercalation compound (GIC) to coal tar pitch (CTP) on the formation and the development of the mesophase. The mesophase formation was followed by the determination of the tetrahydrofuran insoluble fraction (THFI) of the solid residues, which were further characterized by polarized light microscopy. The presence of the Lewis acid (desorbed from the graphite layers) has a great influence during the mesophase spherule formation and development. The activation energy of the formation and the development of the mesophase (E a ) is equal to 159 and 204 kJ/mol in the case of the CTP-GIC 8% mixture and the CTP respectively. This corresponds to a decrease of 22% of E a when the CTP is mixed with the GIC. The authors want to highlight the difficulties and mainly the limitations of the method used to calculate this activation energy by THFI measurements. However, we assume that the mesophase formation and growth rates are accelerated in the presence of compounds such as GIC for two reasons: the absence of QI particles on the surface of the mesophase spherules and the catalytic activity of the Lewis acid.

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.

A thermodesorption study of first stage graphite FeCl3 intercalation compounds

Abstract With the aim of synthesizing carbonaceous materials with specific adsorbent properties obtained from the pyrolysis of mixtures of coal tar pitch (CTP) and FeCl 3 graphite intercalation compounds (GIC), we present a study of the thermodesorption of first stage FeCl 3 GIC. These GICs were synthesized in a two temperature reactor with several kinds of graphites characterized by different granulometry and crystallinity (one a monocrystalline graphite and the others, polycrystalline). During heating under an inert atmosphere, FeCl 3 is decomposed into FeCl 2 and partially sublimed. At 500 °C, second stage FeCl 2 GIC reflections are observed on X-ray diffractograms, and at 750 °C, all iron and chlorine are desorbed out of the graphene layers in polycrystalline graphite, whereas monocrystalline graphite always contains some amount of iron and chlorine. Thermogravimetric evolution has been followed using a McBain balance. FeCl 3 desorption mainly occurs between 350 and 550 °C, and is more quantitative in the case of polycrystalline materials. The graphite granulometry significantly influences the desorption level, and the higher the heating rate, the greater the FeCl 3 desorption.

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.

Effect of graphite or FeCl3-graphite intercalation compounds on the mesophase development in coal tar pitch

Abstract The influence of the addition of first stage FeCl3-graphite intercalated compounds (GIC) or pristine graphite to coal tar pitch (CTP) upon the formation and the development of mesophase has been studied at 400, 430 and 450 °C. Differences in the final samples were principally observed and studied via polarized light microscopic examinations of partially carbonized portions of the green-cokes. The insolubility was also investigated. The addition of pristine graphite to CTP inhibits the development of the mesophase: its presence generates a physical barrier which hinders the mobility and the coalescence of mesophase spherules. In the case of the addition of GIC to the CTP, the Lewis acid FeCl3 desorbed out of the graphene layers plays the role of a catalyst during the early stages of the mixture carbonization, by enhancing the rate of formation of the mesophase.