Spanish Low Rank Coal Research Articles

Novel carbon based catalysts for the reduction of NO: Influence of support precursors and active phase loading

Carbon-supported catalysts in the form of powder, briquettes and monolitos have been prepared. Powder and briquette samples have been obtained using a Spanish low-rank coal as raw material for carbon support through a pyrolysis process whereas monoliths were prepared by coating cordierite monoliths with a blend of two polymers. Vanadium was chosen as active element and impregnated by equilibrium adsorption from 1 to 8 wt% on the surface of as-prepared supports. All samples were tested in the selective catalytic reduction of NO with NH 3 as reducing agent at low temperature (150 °C), demonstrating a considerable efficiency which was enhanced mainly by oxidation treatments and an increase of vanadium loading up to vanadium agglomerates formation. The nature of carbon precursor determines the porosity development and surface chemistry of supports, what results in a different dispersion and fixation of active phase. An enhancement of NO efficiency is achieved by increasing microporosity and the amount of surface oxygen groups in pyrolysed coal whereas in polymer blend, mesoporosity and just a certain amount of surface oxygen groups should be promoted. An excess in vanadium loading decreases NO reduction efficiency because of a pore blockage and the formation of vanadium agglomeration what makes to expose a lower vanadium surface to the reactants.

Co-pyrolysis of a mineral waste oil/coal slurry in a continuous-mode fluidized bed reactor

The main objective of this paper is to study the co-pyrolysis of a Spanish low rank coal and a mineral waste oil (MWO) slurry. The goal is to process the coal, handling it as a slurry by using a waste as the fluid component of the slurry in a continuous-mode preparative scale pyrolysis unit. It has been shown that a MWO/coal slurry can be successfully processed in a pulsed feeding fluidized bed reactor. Liquid and gases fractions have been analysed for organic products and metals. High yields of valuable light olefins such as ethylene and propylene and light aromatics as benzene, toluene, xylene and naphthalene derivatives have been obtained. The results show that both quantity and quality of gases and liquids obtained are significantly improved in relation to those obtained from coal. Special attention has been paid to the fate of metals contained in the MWO/coal slurries and their distribution into the co-pyrolysis products. In particular, the distribution of six metals (Cd, Ni, Pb, Cu, Cr, V) has been studied. The data show that metals under study are totally or partially trapped in the char formed during co-pyrolysis. This way the contents of Pb, Cu, V and Ni in the pyrolysis products leaving the reactor is substantially lower than in the feeding what will facilitate the obtention of valuable products.

96/03516 Thermal behavior of sulfur forms in Spanish low-rank coals

96/03516 Thermal behavior of sulfur forms in Spanish low-rank coals

Characterization of common lignite, xylitic lignite and pyropissite varieties of low-rank coals

The chemical characteristics of the organic and mineral constituents of common lignite, xylitic lignite and pyropissite varieties of Spanish low-rank coals were studied. Chemical analyses showed distinct differences in the H and O contents of xylitic lignite and pyropissite: the former is particularly rich in O and poor in H, whereas the reverse is true for the latter. FT-i.r. spectroscopy showed that the organic matter of xylitic lignite contains abundant hydroxyl and ether groups whereas pyropissite is rich in acid/ester and methylene groups. Mineral matter was characterized by X-ray diffraction and FT-i.r. spectroscopy of low-temperature ash. The main minerals found were kaolinite and quartz; illite was detected only in pyropissite. Ca is present in form of carboxylate salts which react during low-temperature ashing with sulfur and nitrogen oxides, leading to formation of sulfate and nitrate artefacts; these species produced the strongest peaks in the X-ray diffractograms and FT-i.r. spectra of all varieties. Aluminium, relatively abundant in xylitic lignite, is probably organic in origin. In addition to nine major and minor inorganic elements, 13 trace elements were analysed by X-ray fluorescence spectrometry. These trace elements do not exhibit a specific association with any of the lignite varieties and their concentrations cannot be used as distinguishing characteristics. In contrast, the chemical characteristics of the organic component allow the three coal varieties to be differentiated clearly.

Structural rank parameters of Spanish low rank coals and their influence on pyrolysis yields

In this paper some structural characteristics of a series of Spanish coals are reported and their influence on the behaviour of coal during slow pyrolysis is studied. Nine Spanish low rank coals ranging from brown coal to sub-bituminous were characterized by proximate and ultimate analyses, maceral composition, Fourier transform infrared spectroscopy (FT-IR) and solid state 13C nuclear magnetic resonance spectroscopy (CP/MAS 13C NMR). Apparent aromaticities, ( f a), varied from 0.43 to 0.61. The aromaticity correlated well with fixed carbon and with the mean reflectance of the samples. All coals exhibited a large content of methylene structures and a high degree of aromatic substitution. From spectroscopic data some structural parameters such as the H ar/H al and the H aru/C ar ratios were estimated. Pyrolysis of samples was carried out at 600°C under slow heating conditions (7°C/min). Attempts were made to establish several relationships between product yields and parameters derived from coal analyses, and spectroscopic data. Tar yields seem to decrease with increasing O/C atomic ratio of coals and increase with the vitrinite content of samples. The negative influence on tar formation of the crosslinking capacity of coals, evaluated from the pyrolysis water and the CO 2 released, was observed. A significant reduction of organic sulphur in char was achieved at 600°C, indicating that in low rank coals this sulphur form is very sensitive to temperature.

Relationship between liquefaction yields and characteristics of different rank coals

Three Spanish low rank coals, including a brown lignite, a black lignite and a subbituminous coal, and a German bituminous coal were liquefied for 1 h in a stirred autoclave with tetralin. The influence of temperature on conversion was studied from 300 to 475°C observing retrogressive reactions at T > 450°C. A study of the influence of rank on liquefaction has been made, finding an increase in conversion as rank decreases. A comparison of these results with those of others investigators is presented. Linear correlations between liquefaction yields and H/C ratios and volatile matter are established.

Influence of cross-linking on tar formation during pyrolysis of low-rank coals

In this paper the pyrolysis behaviour of two Spanish low-rank coal in the 275–600° C range is studied. Gases evolved from pyrolysis were analyzed by on-line Fourier transform infrared spectroscopy (EGA-FTIR) and gas chromatography and the changes in the macromolecular structure of coal by a solvent swelling technique. The studied coals cross-link very early and the differences found in their tar yields can be explained in terms of cross-linking reactions. Cross-linking of chars correlates with the evolution of CO 2 and pyrolysis water and the extent of the cross-linking reactions is related to the coal's initial content of labile functional groups, namely carboxyl and hydroxyl groups.

Data on low rank coal liquefaction from DRIFT analysis

A Spanish low rank coal was hydrogenated without solvent in the presence of a molybdenum catalyst. The asphaltenes and derived residues were analysed to obtain an understanding of the behaviour of the coal under hydrogenation conditions and the influence of a previous extraction with chloroform, as well as reaction time and temperature, on the structure of the products obtained. Under the reaction conditions used, with tubing bomb reactors and an initial hydrogen pressure of 7 MPa, the data obtained for this coal show that an increase in temperature from 350 to 400 °C, and of reaction time from 5 to 60 min gives, in general, lower content of organic matter in the residues. The two variables have opposing effects on the aromatic content of the asphaltenes. Increasing reaction time reduces the aromaticity, whereas increasing the temperature will increase aromaticity. Prior extraction of the low molecular weight chloroform-soluble compounds increased conversion, and resulted in asphaltenes with higher content of aromatic- and oxygen-containing groups.

Size exclusion chromatography of pyrolysis and hydropyrolysis tars from Spanish low rank coal

The molecular weight distributions of tars obtained from a Spanish lignite by pyrolysis and hydropyrolysis at 500–700 °C have been determined by size exclusion chromatography (SEC) using tar fractions as calibration standards. Two peaks, at 400–500 amu and 250–280 amu were observed in the chromatograms of all the tars studied, but their relative intensities varied with the pyrolysis temperature and atmosphere. The variations appear to be related to thermal cracking at higher temperatures.

Sulphur removal from Spanish low rank coals by acid-catalyzed depolymerization

Reduction in the sulphur content of three Spanish high sulphur low rank coals by acid depolymerization has been studied. The results indicate that the depolymerization removes part of the pyritic sulphur as well as organic sulphur. Generally, between 50 and 75% of THF solubles were obtained with this process. The sulphur content decreased near 80% in some cases. Under applied reaction conditions, the total decrease of sulphur attained similar values for all the treated coals, in spite of their different ash content and sulphur forms. The degree of removal of the different sulphur forms, mainly pyritic and organic, depends on the coal. Sulphates are in most cases removed above 80%, whereas pyrite removal varies between 25 and 70%. A pre-extraction of coals has not a clearly defined role in the removal of the various sulphur forms. Depending on the coal and on the solvent, the results of the various may be opposite. In general, the pre-extraction increases the yields in extracts after the depolymerization, and decreases the total sulphur content of the coals on average with respect the sulphur content of the obtained products.

Sulphur evolution in mild conversion of a Spanish low rank coal

The removal and distribution of sulphur in products derived from acid catalysed depolymerization and dry hydroliquefaction of a Spanish low rank coal with a high sulphur content have been studied. A decrease of 75% in net overall sulphur content is attempted by depolymerization and hydrogenation for 15 min at 350 °C. With increasing hydrogenation yields, the sulphur content of extracts decreases from 4.4 to 1.8, while in residues it increases from 5.1 to 6.2%. The same is observed for depolymerized products, which would indicate the progressive desulphurization of organic sulphur functionalities present in the coal matrix. A previous extraction of the coal with non-specific solvents such as chloroform, isopropanol and THF has a variable effect on the yields and sulphur removal in the depolymerization process. In the case of hydroliquefaction, the pre-extraction significantly increases the H 2S production, and therefore the yields of chloroform solubles.

Characterization of pentane-solubles from low rank coal extract

The structural characterization by FT-i.r. and 1H n.m.r. spectroscopy of the pentane-soluble fraction of a toluene extract from a Spanish low rank coal has been performed. The pentane-solubles have been fractionated on deactivated SiO 2 by sequential elution with hexane, benzene and tetrahydrofuran. The structural parameters calculated for these fractions indicate branched and cyclic alkanes on the aromatic units, and the number of aromatic rings and rings containing ring-joining methylene and heteroatoms appears to be between 1 and 5. Benzene and THF eluates showed the presence of hydroxyl and carbonyl groups. A comparison with the pentane-solubles from BF 3-phenol depolymerized lignite was made to evaluate the influence of this process on the nature of the soluble products. The pentane solubles of lignite extract have a more aliphatic and less polar character than the same fraction of chemically depolymerized lignite, which contains a maximum of four aliphatic carbon atoms in the average molecule of its benzene and tetrahydrofuran eluates.

Hydropyrolysis of a spanish lignite

Hydropyrolysis (Hypy) of a Spanish low rank coal in a preparative fixed bed reactor yields much more tar than pyrolysis (Py). The external hydrogen incorporated in the gas, tar and water yields is less than the total hydrogen incorporated in the products, as a result of more efficient extraction of hydrogen from char in a H 2 atmosphere. The higher devolatilization rate in He and H 2 occur at the same temperature, which coincides with an exothermic peak. These results show that the Hypy rate of low rank coals is controlled by the initiation steps of thermal decomposition, with the hydrogen in the role of stabilizing the primary radicals and allowing them to escape as volatile matter.