Helena Wachowska

Oxidation studies on coking coal related to weathering. 4. Oxygen linkages influencing the dilatometric properties and the effect of cleavage of ether linkages

Abstract Samples of a vitrinite concentrate of Balmer 10, medium-volatile bituminous coal (433) and high-volatile Moss 3 coal (535) were oxidized in air at 85°C for four days to partially destroy the swelling characteristics as measured by the Ruhr dilatometer. Similar samples were oxidized at 100°C for three days to completely destroy the swelling properties. These artificially weathered coals were then treated with reagents to remove peroxides, keto and aldehyde groups. The hydroxyl groups were also blocked to prevent condensation reactions. The result of the removal of these functional groups and the blocking of the hydroxyl groups had little influence in restoring the swelling properties. This suggested that the swelling properties were largely destroyed by ether-type cross-links which form at low temperature. The cleavage of these ether linkages in the Balmer coal using potassium in tetrahydrofuran resulted in the lowering of the melting point and a large increase in dilatation. The values of these properties after cleavage were essentially the same for the fresh and oxidized coal indicating that no significant amount of polymerization through carbon-carbon bond formation occurred during the low-temperatureoxidation step. Indications were obtained that the large increase in dilatation after cleavage was due to steam formation resulting from condensation reactions occurring at the temperature of the dilatation measurements. After the cleavage of the ether linkages, the dilatation could be reduced by blocking the hydroxyl groups or removing water by heat treatment under vacuum.

X-ray photoelectron spectroscopy study of oxidized coals with different sulphur content

The aim of the study reported was to determine the effect of oxidation on the surface composition of coal as studied by X-ray photoelectron spectroscopy (XPS) method. Five coals characterized by a different degree of coalification and different amounts of sulphur were subject to oxidation with peroxyacetic acid (PAA). The process of oxidation was carried out for coal samples demineralised by the Radmacher method. Carbon, oxygen, sulphur and nitrogen peaks were registered and analysed. The effect of oxidation depended on coal rank. In case of S 2p, three or four peaks were found for the oxidized samples, corresponding to tiophene, sulphoxides (Ph 2 -SO type), sulphonic acids and in some cases, more oxidized forms of sulphur, possibly inorganic sulphates. The surface sulphur content increased upon oxidation. A possible reason could be the mobility of the S-containing species.

Active carbons prepared by chemical activation of plum stones and their application in removal of NO2

A technology of obtaining active carbon from plum stones by chemical activation with KOH is described. The effect of carbonisation temperature as well as activation procedure on the textural parameters, acid-base character of the surface and sorption properties of active carbons has been checked. The sorption properties of the activated carbons obtained were characterised by determination of nitrogen dioxide adsorption in dry and wet conditions. The final products were microporous activated carbons of well-developed surface area varying from 2174 to 3228 m(2)/g and pore volume from 1.09 to 1.61 cm(3)/g, showing different acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the carbonisation and activation procedure for plum stones can produce activated carbons with high capacity of nitrogen dioxide, reaching to 67 and 42 mg NO(2)/g in dry and wet conditions, respectively. The results of our study have also shown that the adsorption ability of carbonaceous sorbents depends both on the method of preparation as well as on the textural parameters and acid-base properties of their surface.

Ammoxidation of brown coals for supercapacitors

The paper reports results of a study on the use of active carbon from ammoxidated brown coal as electrode material for supercapacitors. The raw coal was subjected to demineralisation and ammoxidation by a mixture of ammonia and air, then it was carbonised and activated by steam or carbon dioxide. The electrochemical properties of carbons were determined by galvanostatic and potentiodynamic methods for water electrolytes. The best capacitance parameters of ca. 220 F/g in acidic and ca. 140 F/g in alkaline conditions were obtained for active carbon containing from 2 to 3 wt.% of nitrogen.

Microbial desulfurization of coal with Thiobacillus ferrooxidans bacteria

Abstract Microbial desulfurization of Polish flame coal, characterized by high total concentration of sulfur and a high concentration of pyrite sulfur, was studied. The optimum conditions of the process were established. When using Thiobacillus ferrooxidans bacteria, the best results were obtained with desulfurization carried out on coal samples making 2.4 wt% of the extraction mixture at the initial concentration of ferrous ions of 15 g dm −3 and for a process duration of seven days. Since desulfurization of coal mainly involves oxidation of the pyrite, a kinetic model of Fe 2+ oxidation by Thiobacillus ferrooxidans bacteria was proposed. The process was found to be described well by the equation derived for autocatalytic reaction of the first-order, both towards the inorganic substrate (Fe 2+ ) and the biocatalyst (protein). The rate constants and induction times of Fe 2+ oxidation and protein growth were determined for different temperatures, pH values and initial concentrations of Fe 2+ . The highest rate constant and the shortest induction time were obtained for 35°C and the initial Fe 2+ concentration of 3 g Fe 2+ dm −3 . No effect of pH changes, in a range 2.0–3.0, on the kinetics of the process was noted.

Effect of cleavage of ether linkages on physicochemical properties of coals

Abstract Coals of different rank were treated with naphthalene anion in tetrahydrofuran. It was found that, as in the case of coal of 87.8% C (daf), large amounts of unreactive oxygen bonds, possibly of the ether type, were cleaved. Cleavage of these ether linkages led to a lowering of the melting point and, in some types of coals, to a large increase in dilatation and a substantial increase in Gieseler fluidity.

Oxidation of demineralized coal and coal free of pyrite examined by EPR spectroscopy

The influence of oxidation on complex paramagnetic centres system of demineralized coal and coal free of pyrite was compared. Polish orthocoking coal with a carbon content of 87.8 wt% was studied. This coal was oxidized with nitric acid (HNO3), peroxyacetic acid (PAA) and in O2/Na2CO3 system. Multi-component structure of X-band EPR spectra of the coal samples was numerically analysed. The lineshape and the parameters of the component lines: linewidths and g-factors, were determined. Concentrations of paramagnetic centres were measured. The three groups of paramagnetic centres belonging to different molecular units were found in the studied samples. They were responsible for broad Gauss (DBpp: 0.49 ‐ 0.84 mT), broad Lorentz 1 (DBpp: 0.18 ‐ 0.35 mT), and narrow Lorentz 3 (DBpp: 0.04‐ 0.08 mT) EPR lines. Properties of paramagnetic centres of the simple molecular units with broad Gauss and Lorentz 1 lines were changed during demineralization of coal and after pyrite removing from coal. g-Values of Gauss and Lorentz 1 lines increased, Lorentz 1 lines were broadened and concentrations of paramagnetic centres with Lorentz 1 lines increased. Oxidation of both demineralized coal and coal free of pyrite with nitric acid led to the highest decrease of the concentration of paramagnetic centres with Gauss lines, narrowing of these lines and increase of g-factor. The higher effects of oxidation on paramagnetic centres responsible for broad lines were observed for coal free of pyrite. Paramagnetic centres with narrow Lorentz 3 lines belonging to multi-ring aromatic units in demineralized coal and coal free of pyrite were not susceptible for oxidation. q 2002 Elsevier Science Ltd. All rights reserved.

AP-TPR study of sulphur in coals subjected to mild oxidation. Part 1. Demineralised coals

Abstract Five samples of coal characterised by different degree of coalification and different content of sulphur have been subjected to oxidation in the dry phase and in aqueous media in order to determine the effect of oxidation on the sulphur groups. The transformations were studied by the classical chemical methods and by atmospheric pressure–temperature programmed reduction. It has been shown that the greatest changes in sulphur groups occurs in the case of the oxidation with HNO3 and peroxyacetic acid, while the air oxidation and the oxidation in the O2/Na2CO3 system is much less effective. The oxidation leads to formation of sulphoxides, sulphones and sulphonic acids. The non-thiophene groups have been found much more susceptible to oxidation than the thiophene ones.

Chemical structure of coals as indicated by reductive alkylation

Abstract Reduction with potassium in tetrahydrofuran in the presence of naphthalene, and alkylation of the ‘coal anion’, were applied to coals of different rank. The reduction reaction alone increases the dissolution of the coals in benzene only to a very small extent. However, the reduction process in conjunction with alkylation of the ‘coal anion’ leads to products readily soluble in benzene. The solubilization of alkylated coals depends on the type of coal, the degree of its substitution with alkyl groups, and the length of the substituent alkyl chain. The number-average molecular weights of benzene extracts from the lowest-rank coal ranged from 500 to 800, whereas the higher-rank coals consist essentially of structural units characterized by number-average molecular weights ranging from 1300 to 2000.

Chemical structure of coal macerals in Balmer 10 coal and fusinite from Illinois coal as indicated by reductive alkylation

Abstract A Canadian Cretaceous coking coal from the Balmer 10 seam, Fernie, British Columbia, was separated by sink-and-float methods into vitrinite and a semifusinite-rich fraction. A portion of the vitrinite fraction was oxidized in air at 100 °C for 72 h to destroy the coking properties. The fresh vitrinite, oxidized vitrinite, and semifusinite of the Balmer coal, and the fusinite from Illinois coal, were each subjected to the reductive alkylation procedure of Sternberg, to cleave the ether linkages and octylate the products. The oxygen functional groups before and after ether cleavage were determined, as were the extractabilities by benzene of the octylated products. Thus the molecular weights of the benzenesoluble fractions of the octylated cleavage products were: fresh vitrinite 1930, oxidized vitrinite 1830, and fusinite 1490. The molecular-weight distribution of the octylated cleavage products was estimated by volatility analysis, which demonstrated the presence of much lower-molecular-weight material. Dilatation analysis of fresh and oxidized vitrinite showed that after cleavage of the ether linkages with potassium in tetrahydrofuran, the two could be brought to the same state. The dilatation behaviour of semifusinite after cleavage of the ether links and octylation showed only contraction, whereas the oxidized vitrinite treated in a similar manner exhibited a large dilatation.