Lazarin Lazarov

Direct preparation of ionic potassium—coal adducts

Abstract The possibility for a direct preparation of ionic potassium—coal adduct is shown, from finely ground low-volatile bituminous coal (89.2% C) and metallic potassium with stirring at 120 °C and a vacuum of 13 mPa. The treatment of the adduct dispersed in THF with CH 3 l results in reductive methylation of the coal, similar to that of the ‘coal anion’, obtained in THF during its interaction with potassium—naphthalene.

Ash agglomeration during fluidized bed gasification of high sulphur content lignites

Abstract Intensive ash agglomeration has hampered the fluidized bed gasification of lignites from the Elhovo deposit (Bulgaria) containing 5.9 wt% sulphur in the dry state. Samples of slag and agglomerates from the pilot plant have been examined by means of chemical, X-ray analysis, IR spectroscopy and scanning electron microscopy. Pyrrhotite (FeS) and wustite (FeO) have been established in the agglomerates, where junctions between ash particles have been found to consist of magnetite, spinel and garnet grains. The chemical reactions leading to garnet formation have been studied. Centres of sintering and centres of melting during the ash agglomeration process have been distinguished. The pyrite product, an eutectic of FeS and FeO melting at 924°C, is assumed to be responsible for the cessation of lignite gasification with steam and air under pressure at a bed temperature of 930°C.

Structural study of coals by means of directly-prepared potassium-coal adducts☆

Abstract Directly-prepared potassium adducts (PA) of different rank coals and of an anthracite are studied by X-ray diffraction and e.s.r.-spectroscopy. The reactivity of the PAs towards butyl iodide and methanol are also examined. Complete disruption of the lamellar coal structure (i.e. disappearance of the 002 line in the X-ray diffraction patterns) is observed after reaction with potassium. E.s.r.-spectroscopic parameters are not substantially changed by the potassium except for coals with C, 85–90 wt%, for which the concentration of paramagnetic centres is significantly increased. These coals are also capable of significant butylation and reduction (thus becoming soluble). A correlation between the number of unpaired electrons and the number of alkyl groups introduced is established. Anthracite is not capable of butylation or reduction in this manner. With all coals (including anthracite) the layer stacking indicated by the 002 diffraction line is partially recovered after the treatment of the PA with butyl iodide or alcohol. Also, the diffraction intensities in the γ-band region are increased depending on the degree of the butylation or reduction occurred. The results are interpreted with respect to the similarity of PA of different rank coals with the intercalation compounds of graphite and with the ionic adducts of polycyclic aromatic hydrocarbons with alkali metals.

E.s.r. spectrometric study of directly prepared potassium-coal adducts

Abstract E.s.r. spectral parameters (concentrations of paramagnetic centres, g values and linewidths) of two vitrains of different rank (C, 89.2 and 75.8 wt%) and of their potassium adducts prepared by a direct method, as well as of the reductively alkylated high-rank vitrain are reported. The potassium adduct of the high-rank vitrain is characterized by the accumulation of a rather high concentration of unpaired electrons, 7.7 spins per 100 C atoms (a 120-fold enhancement). With the adduct of the low-rank vitrain the concentration is 0.14 spins per 100 C atoms (a 17-fold enhancement). The adduct of the low-rank vitrain is negligibly alkylated by alkyl halides in THF, unlike the adduct of the high-rank vitrain which can be significantly alkylated. The g values and linewidths of the spectra of the vitrains and the corresponding potassium adducts are very similar. The experimental results are interpreted mainly with respect to the formation of ionic potassium-coal adducts of coals of different rank and their alkylation.

Reductive alkylation of a phenanthrene—formaldehyde resin

Abstract A model insoluble oxygen-free phenanthrene—formaldehyde resin has been reductively alkylated by means of potassium—naphthalene in THF and subsequent treatment with alkyl halide. The extractability of the resultant alkylated products by benzene reaches 50% and depends on the size of the groups introduced. The polydispersity of the benzene-soluble portions and the presence of methyl groups in them indicate that decomposition processes are taking place at the methylene bridges as well. Mainly on the basis of n.m.r. analysis of the benzene-soluble fraction of a reductively trimethylsilylated resin, quantitative information about the silylation and decomposition processes was derived. The results obtained are of interest to the study of reductive alkylation of coals.

Structural analysis of a bituminous coal vitrinite by NaH pretreatment and n.m.r. spectroscopy

A bituminous coal vitrinite (82.3%C, daf) was treated with NaH in decalin under 3 MPa hydrogen pressure at 300 °C for 6 h. The reacted vitrinite was fractionated according to its solubility in decalin, methanol, tetrahydrofuran and pyridine. The THF-soluble, but decalin- and methanol-insoluble fraction was sub-fractionated by gel permeation chromatography (g.p.c.). The fractions were characterized by elemental and phenolic group analysis, and by DD-TOSS technique for solid state 13C n.m.r. spectral editing with CHn discrimination. Average molecular mass measurements and FT 1H and 13C n.m.r. spectroscopy were also applied to the soluble fractions. Important atomic ratios and parameters, describing the average aromatic structural units of the fractions, were derived. The behaviour of various model compounds under the NaH treatment conditions was also tested. This treatment led to the removal of sulphur and 80% of the oxygen content in the vitrinite (the diarylether oxygen and substantial parts of heterocyclic and phenolic oxygen undergo reductive splitting off). Data indicate that the hydrocarbon skeleton structure of the vitrinite was preserved to a great extent in the decalin- and methanol-insoluble fractions. These fractions showed slightly lower aromaticity, (HC)al ratio and degree of aromatic substitution as compared with the initial vitrinite. They had rather diverse CH ratios, but the average number of aromatic unit rings varied within 1.8–3.4.

Oxidation of ionic potassium-coal adducts

Abstract The behaviour of potassium-graphite intercalation compounds (GIC) and directly prepared potassium-coal adducts (PCA) was studied during their oxidation by oxygen. The reactions were carried out in dry state or after dispersion in a solvating medium. The reaction rate in THF was found to be higher. E.s.r. data showed that the KO 2 produced in the oxidation process was in the form of a complex in the interlayer space of graphite or inserted between the parallel layers of condensed aromatic nuclei in the case of coal adducts. This state of KO 2 explains the fact that its e.s.r. signal was registered at room temperature. This work revealed an approach for the mild oxidation of PCA with a view to structural investigation of solubilized coal.

Reactions of a bituminous coal with metal chlorides in carbon tetrachloride

Abstract The interaction of a bituminous coal (87.2% C) with several metal chlorides in carbon tetrachloride was studied using the conditions under which graphite forms intercalation compounds. Adducts with SbCl5, AlCl3, FeCl3 and MoCl5 were isolated by filtration and washing with carbon tetrachloride. Atomic ratios versus coal carbon are as follows: C10.0SbCl7.4; C6.2AlCl4.1; C6.3FeCl3.3; and C11.3MoCl3.8. X-ray diffraction patterns of the adducts show no 002-band, the latter being partially recovered after extraction with diluted hydrochloric acid. The g-value of the e.s.r. signal of the coal vitrain shows a characteristic increase because of adduct formation with SbCl5 and AlCl3 and is reversible by hydrolysis extraction. The results obtained indicate that the bonding with SbCl5 and AlCl3 is mainly due to formation of chloro-complexes and with FeCl3 and MoCl5 — to formation of organo-metal complexes.

Malthenes from solubilization of low rank coal by methanol/sodium hydroxide treatment

Abstract The possibility of O-methylation occurring during the treatment of low rank coals with methanol/sodium hydroxide is evaluated. Chemical and spectral data of malthene fractions confirm unequivocally the presence of methoxyl groups. Their content was found to correlate with the efficiency of treatment. Formation of methyl esters after saponification of ester bridges in lignites is also probable. Reactions of O-alkylation contribute to stabilization through methylation of reactive intermediate species formed after cleavage of ether or ester linkages in coal organic matter, thus improving solubilization.

Thermochemical transformation of the quinoline-soluble portion of coal tar pitch

Abstract The quinoline-soluble portion of coal tar pitch and products of its carbonization at 250, 350 and 450°C were subjected to chemical study. The structural transformations were followed by extraction and chemical and number-average analyses. The samples under study, i.e. asphaltenes + preasphaltenes and carboids, were non-reductively alkylated in the system n-BuLi-BuI. The modification improved the solubility, owing to addition of 6–7 butyl groups per 100 carbon atoms. The alkylation procedure was considered mild, in so far as it affected only the ‘acidic’ centres in the pitch and did not alter the condensed aromatic systems. A set of structural parameters was calculated. Chemical transformations for carbonization temperatures > 350°C were established as an abrupt increase in carboid content, an increase in aromaticity and degree of condensation of the aromatic structures, intense cleavage of ether bridges, their replacement by phenolic OH groups, and further rearrangement of oxygen in cyclic form.