Jacek Machnikowski

The characterization of coal macerals by diffuse reflectance infrared spectroscopy

Abstract Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0–91.5%C) using a centrifugal float–sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH 2 , and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CH ar /CH al ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CH ar /CH al and reflectance is observed up to vitrinite R 0 value of 1.80%. For all macerals, the ratio CH ar /CC increases with reflectance, but at different rates. Structural parameters CH ar /CH al and CH ar /CC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank.

Effect of polymeric additives to coal tar pitch on carbonization behaviour and optical texture of resultant cokes

Abstract Homogeneous compositions of coal tar pitch with 10% addition of various polymers were prepared under relatively mild conditions. The effect of a polymer on properties of composition and yield and optical texture of resultant semi-coke was assessed. There was no correlation between softening point or toluene insoluble content and carbonization yield. The addition of cumarone-indene resin, polystyrene, poly(ethylene-terephthalate), polypropylene and polysaccharide resulted in an increase in carbonization yield by 5–3%. Pitch-polymer compositions gave semi-coke of less homogeneous optical texture compared to parent coal tar pitch coke. Poly(vinyl chloride) was the only polymer which clearly improved the development of anisotropy on carbonization. The addition of polypropylene, polysaccharide and butadiene–styrene copolymer contributed to the deterioration of the optical texture.

Characterization of the surface properties of nitrogen-enriched carbons by inverse gas chromatography methods

Abstract The characterization of the surface properties of carbonaceous materials by inverse gas chromatography (IGC) techniques is described. The cokes investigated were produced by the co-pyrolysis of a coal-tar pitch (CTP) with different amounts of polyacrylonitrile (PAN) as a possible method to synthesize carbonaceous materials enriched in nitrogen. IGC at infinite dilution and LSER (linear solvation energy relationship) techniques were used to determine the physical and chemical surface properties of the cokes. In general, the surface free energy of adsorption is due to both dispersive and specific interactions. The dispersive component of the surface free energy was determined using n-alkane probes. For the specific component, which is primarily due to acid–base interactions, different polar probes were used. The LSER method was applied to improve our understanding of the adsorption process in terms of molecular interactions. We show that, to characterize dispersive interactions using n-alkanes, the LSER and IGC methods are equivalent. On the other hand, with both methods we find that all the samples present acidic and basic characteristics. However, the sensitivity of the LSER method does not allow us to discriminate between the three samples in terms of specific interactions.

Modification of coking behaviour of coal blends by plasticizing additives

Abstract Commercial coal-tar pitch (CTP) and pitch-like residue (RP)—a waste by-product of coking plants—were used as an additive to two coal blends in metallurgical coke production. The additives were characterized in terms of chemical composition, solvent analysis, 1 H NMR spectroscopy, extrographic fractionation, hydrogen transfer properties, thermogravimetric analysis and plastic properties. Both the thermal behaviour and hydrogen transfer properties of the additives are crucial for the coal plastic phase modification during co-carbonization. CTP improves the coking properties of coal blend, i.e. coking and swelling abilities, dilation and fluidity, whereas RP leads only to a fluidity enhancement. This is reflected in different yields, anisotropic carbon, microstrength and reactivity to carbon dioxide of the cokes produced at two different laboratory scales. The beneficial effect of the additives on the metallurgical coke quality not only depends on the properties of the additives themselves, but also the coking properties of the coal blend to which the plasticizing agent was added is a critical factor.

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m2/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.

Hydrogen-transfer ability of extrographic fractions of coal-tar pitch

Coal-tar pitch was fractionated using extrography into classes of compounds of similar functionality and molecular weight. Hydrogen acceptor and donor abilities of the whole pitch and its extrographic fractions were evaluated by reaction at 360°C with tetralin and anthracene, respectively, and related to structural characteristics by elemental analysis, VPO, 1H NMR and HPLC. Hydrogen acceptor ability (HAA) of the fractions increases markedly with the elution depth. There is a good correlation between HAA and the total oxygen content in the fraction. On the other hand, all extrographic fractions show comparable relatively low hydrogen donor abilities (HDA) in the initial period of reaction with anthracene due to a similar content of hydroaromatic rings and methylene bridges. On further treatment, F2 and F4 are differentiated by a stronger HDA than other fractions. Among the fractions, only in F2 the hydrogen donor ability outweighs over hydrogen acceptor ability. The opposite situation is observed for F5, F6 and F7. In the case of F3 and F4, a comparable amount of hydrogen is transferred from tetralin to fraction and from fraction to anthracene. There is no straight correlation between the observed hydrogen transfer behaviour of fraction and its ability to develop an anisotropic texture in carbonization product. Possible contribution of various fractions to the creation of optical texture of pitch coke is discussed.

Guanidine, amitrole and imidazole as nitrogen dopants for the synthesis of N-graphenes

Three N-containing organic compounds – guanidine, amitrole (3-amino-1,2,4-triazole) and imidazole were selected and evaluated as new nitrogen dopants for the preparation of N-graphene. A graphene oxide aqueous dispersion was subjected to hydrothermal treatment at 180 °C for 8 h in the presence of the selected N-compounds. The nitrogen contents in the resultant N-graphenes were as high as 13.4 at%, which is among the highest reported for graphene materials. The X-ray photoelectron spectroscopy revealed that pyridinic nitrogen was predominant in all of the N-graphenes, accounting for up to 47% of the total nitrogen content. Deoxygenation of graphene oxide under hydrothermal conditions was also improved through the use of the N-compounds. Possible reaction mechanisms between graphene oxide and each N-compound are proposed.

Kinetics and mechanism of carbonization of QI free products from gas-coking coal hydrogenation—I: The structure and carbonization behavior of pitches produced by the coal hydrogenation at 420°C AND 455°C

Abstract The structure and carbonization behavior of the pitches from the products of gas-coking coal hydrogenation performed at 420°C and 455°C in a continuous bench scale unit were estimated. The pitches, prepared as residues from vacuum distillation of purified hydrogenation products, were characterized y elemental analysis, solvent fractionation, IR and 1H NMR spectroscopy. The mesophase formation on isothermal carbonization at 450°C and the optical texture of resultant semicokes were studied by polarized-light optical microscopy. The most pronounced effect of hydrogenation temperature rise was an increase in asphaltene content at the expense of preasphaltenes and a decrease of heteroatom content and reactivity of resultant pitch. This alteration of pitch nature resulted in distinctly different carbonization behavior of both materials. The transformation of the low temperature (420°C) hydrogenation pitch occurred at a high rate leading to the coke of small size optical texture. The high temperature (455°C) hydrogenation pitch produced on carbonization large, easily deformable anisotropic units, and the optical texture of resultant semicoke was comparable to that observed in the cokes from petroleum pitch or QI free coal tar pitch.

Tailoring micro-mesoporosity in activated carbon fibers to enhance SO2 catalytic oxidation

Enhanced SO2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mesoporous structure in the fibers. This architecture is obtained via metal catalytic activation of the fibers with a novel precursor, cobalt naphthenate, which contrary to other precursors, also enhances spinnability and carbon fiber yield. In the SO2 oxidation, it is demonstrated that the combination of micropores and large mesopores is the main factor for an enhanced catalytic activity which is superior to that observed in other similar microporous activated carbon fibers. This provides an alternative way for the development of a new generation of catalytic material.

Structural characterization of residues from supercritical gas extraction of brown coal

Abstract Residues from supercritical gas extraction of brown coal with toluene and butanol were studied by proximate and ultimate analyses, optical microscopy and X-ray diffractometry. The type of solvent appeared to have a decisive influence on the yield, properties and structure of the residues produced in the range 380–440 °C. The residues from extraction with toluene had a microstructure and structural ordering similar to those of the raw coal. Extraction with butanol gave caked and optically anisotropic residues with a relatively high degree of structural ordering.