S.P. Marinov

Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide

Simultaneous pyrolysis and gasification of biomass samples of different origin is performed in a flow of steam or in a mixture of steam and carbon dioxide. Wastes from birch wood, olive stones, bag ...

Low rank coals sulphur functionality study by AP-TPR/TPO coupled with MS and potentiometric detection and by XPS

Abstract Atmospheric pressure-temperature programmed reduction (AP-TPR) and X-ray photoelectron spectroscopy (XPS) techniques were applied to low rank coals sulphur study. Coal samples were pyrolysed in a flow of water vapor (WV). It was demonstrated that this treatment influenced mainly aliphatic sulphur. Samples were characterised by two methods and data were interpreted within the limits of the techniques. XPS measurements registered sulphur 2p spectra with two main signals for organic and inorganic sulphur compounds. The AP-TPR set-up, with potentiometric detection of the formed H2S as S2− using an ion selective Ag2S-electrode, gives quantitative data about the presence of different sulphur species. The AP-TPR equipment on-line coupled with a mass spectrometer (MS) gives extra qualitative information about different reductive and oxidative organic sulphur forms. Using MS not only H2S but also SO2, COS, CS2, and all other volatile sulphur and organic compounds can be monitored, giving more information for the initial presence of the different sulphur forms and to the mechanisms involved in the pyrolytic process. This AP-TPR-MS experiment is subsequently followed by AP-TPO-MS measurement (in an oxidated atmosphere) to study sulphur presence in the residue (tar and char) in the reactor. Comparing all these AP-TPR profiles results in a better assignment of the different signals to specific sulphur functionalities.

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.

The composition of lignite humic acids

Abstract Humic acids from lignite deposits in Bulgaria were characterized with respect to the concentration of oxygen-containing functional groups. The following ranges were determined, in mequiv g −1 : total acidity 5.1–6.8; carboxylic groups 3.5–4.5; phenolic OH groups 1.6–2.3; ketone groups 1.0–2.0; quinone groups 1.0–1.3; and methoxyl groups 0.3–1.3. Yields of high- and low-molecular fractions were monitored by g.p.c. on Sephadex G-50. The molecular mass for the lower molecular fraction was ~ 4000u. On the basis of the elemental composition, molecular mass and distribution of oxygen in functional groups, a concept for lignite humic acid structure was developed.

Emission of oxygen, sulphur and nitrogen containing heterocyclic polyaromatic compounds from lignite combustion

Abstract Maritza–East Bulgarian lignite was burnt in an atmospheric fluidised bed pilot plant, laboratory scale, at conditions close to the real ones used in power generation (850 °C, 3% oxygen excess, limestone with ratio Ca/S=3.25) in order to analyse in a qualitative way the polycyclic aromatic compounds (PAC) emissions. The samples studied were collected by flowing an aliquot of the combustion gases through a sampling system, consisting of cyclones, nylon and teflon filters and an XAD-2 resin. Before sample analysis by gas chromatography with mass spectrometry detection (GC-MS), ligand exchange chromatography on PdCl 2 impregnated silicagel was used to separate PAC with different heteroatoms, concretely, oxygen (O-PAC), sulphur (S-PAC) and nitrogen (N-PAC) of the polycyclic aromatic hydrocarbon (PAH) fraction. For all samples studied, the highest PAC emissions were due to compounds containing three and four aromatic rings in their structure. The O-PAC constituted carbonyl-containing compounds Z(O)=−18 to −22, with carbon numbers n =13–17; anthraquinones, Z(O 2 )=−20, n =14 and 15, phenols, phenanthroaldehyde, and furans, Z(O)=−22, n =16, where concentration of quinones far predominated. A peculiar group of C 19 –C 23 alkylbenzones, with a maximum at C 20 –C 21 , was found as well. Dibenzothiophenes, phenanthrothiophene and benzonaphthothiophenes, Z(S)=−16 to −20, were the major constituents of the S-PAC, while the N-PAC were determined at trace levels.

Aliphatic biomarkers from Miocene lignites desulphurization

Lignites of the Thracian basin, the main coal potential of Bulgaria have been subjected to an extensive study, as their high sulphur content (3–7%) creates ecological problems during combustion. The aim of the present study was to examine the effect of desulphurization (three techniques, i.e. hydrothermal, t-BuONa and n-BuLi/TMEDA treatments) on biomarkers assemblage, as sulphur bridge cleavage could release covalently attached species or trapped molecules. Results of the chromatographic analysis of the aliphatic portions of the chloroform extracts from initial and treated lignites have pointed out that during desulphurization treatments coal organic matter was rearranged and smaller fragments became soluble. Some peculiarities were registered: alkane fraction of Maritza-Iztok treated by t-BuONa was strongly dominated by “even” carbon numbered n-alkanes, n-C16, n-C18 and n-C20; in products of Elhovo lignite desulphurized by n-BuLi/TMEDA alkyl cyclopentanes were tentatively identified. After n-BuLi/TMEDA desulphurization, hopane distribution was largely affected in the case of the Maritza-Iztok sample: the higher homologues and ββ dominance from C29 to C31 hopanes have disappeared; “geo hopanes” prevailance was registered;—18α(H)-oleanane, 25-nor-17α(H)21β(H)-hopane, C29, and a suite of “non-hopanoid” C30 triterpanes were observed. Our data have demonstrated the negligible steric protection of macromolecular structure in the case of low rank coals as far as covalently-bound species were characterized by higher degree of maturation compared to the easily extractable species.

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.

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.

Molecular mass distribution of modified coal extract

Abstract The chloroform soluble portion of dimethylacetamide extract from a subbituminous coal was subjected to different types of chemical modification i.e. reduction, reductive alkylation, non-reductive alkylation, ‘ionic’ oxidation with subsequent alkylation, etc. The products of the reactions were studied by spectral and Chromatographic methods. An increase in molecular mass, prevailing over degradation, was registered by gel permeation chromatography (g.p.c.) analysis.