Sabino R. Moinelo

Application of extrography for characterization of coal tar and petroleum pitches

Extrography has been used for fractionation of coal tar and petroleum pitches into six fractions of increasing polarity by a given sequence of solvents. Sample recovery, composition of the fractions and reproducibility of separation into distinct classes of compounds were determined. The results of several samples show the efficiency of extrography for the characterization of pitches of different origin. FT-i.r. and gas chromatography were used to evaluate the separation. Extrography is a rapid, simple and reproducible technique for the characterization of pitch materials.

Mass spectrometric characterization of polynuclear aromatic nitrogen compounds in coal tar pitches separated by extrography

Abstract Extrography is a rapid technique for fractionating relatively large quantities of coal tar and petroleum pitches. Mass spectrometry (m.s.) and gas chromatography (g.c.)-m.s. have confirmed that the technique separates non-basic heterocyclic nitrogen compounds from aza bases in coal tar pitches. However, the nitrogen-containing fractions also contain higher molecular weight (MW) polynuclear aromatic compounds. Azabenzopyrenes are the major low-MW bases present. A range of mixed heterocyclic compounds were identified, including basic quinones.

Solid state 13C NMR and high temperature 1H NMR determination of bulk structural properties for mesophase-containing semi-cokes prepared from coal tar pitch

A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ 1H NMR and optical microscopy with extremely close agreement being obtained between the two techniques. Quantitative solid state 13C NMR measurements using the single pulse excitation technique indicated that the extent of anisotropy in the pitch is a function of the condensation of the aromatic structure, where isotropic pitches contain 5–6 rings on average, assuming pericondensation, which increases to 9–10 rings for the fully converted mesophase pitches. Characterisation of the pyridine-solubles (PS) and insolubles (PI) from the pitches confirmed that development of mesophase in the coal tar pitch is limited by the loss of low molecular mass compounds, in that the PS contain 5–6 rings throughout the series while the PI, even in largely the initial isotropic state, are as condensed as in the anisotropic pitches.

Influence of weathering process on the flotation response of coal

Abstract The floatability of a Spanish coal from a seam (Adolfa) which is simultaneously surface mined (ASM) and underground mined (AUM) has been studied. The mineral composition of AUM and ASM coal samples, as well as changes in both mineral and organic constituents due to chemical weathering, were characterized by X-ray diffraction, i.r. and Mossbauer spectroscopies and X-ray fluorescence spectrometry. The effect of pH and surface charge on the floatability of AUM and ASM samples was investigated. The formation of humic substances in the surface of ASM coal and the presence of Fe(III) species in its mineral matter, both a consequence of weathering, together with the high content of mineral impurities (especially aluminosilicates) provide an explanation for the flotation behaviour of this coal. Basic pHs that led to humic acids dissolution and to iron(III) hydroxide precipitate desorption from the surface improved ASM coal floatability up to values similar to those obtained with unoxidized AUM coal. The formation of humic acids-mineral impurities complexes at basic pHs renders clay particles hydrophobic. As a consequence, the improvement of ASM coal floatability at pHs higher than neutral was accompanied by a low ash rejection. Mineral impurities had a large influence on the surface charge of ASM coal.

Fractionation of coal-derived liquids by extrography

Abstract After a study of the influence of degree of activity of silica gel and sample-adsorbent ratio on the fractionation of a coal extract by extrography, several samples of coal-derived liquids were separated into six fractions of increasing polarity by a given sequence of eluents. The content and composition of the fractions, the recovery of the samples and the reproducibility of the fractionation were determined. Separations were evaluated by means of several chromatographic and spectroscopic methods. The method is a simple, reproducible and relatively fast preparative method for the fractionation of coal liquids.

Characterisation of pitch by HPLC

SummaryA new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.

Characterization of coal tars produced under different carbonization conditions by FT-i.r. spectroscopy and extrography

Abstract Coal tars produced by carbonization of wet charges of one coal blend on industrial and semi-industrial scales with different mean flue temperatures and from a preheated charge of the same blend were studied. These tars were characterized by FT-i.r. and 1 H n.m.r. spectroscopy in addition to the standard analytical methods. They were also separated by extrography into fractions differing in chemical functionality, which were examined by FT-i.r. spectroscopy and g.c.-m.s., Differences were mainly observed in the proportions of polynuclear aromatic hydrocarbons and nitrogen-containing heteroaromatics. The information can be used as an indicator of the severity of thermal cracking during tar formation in a coke oven.

Mesophase from a coal tar pitch: a Raman spectroscopy study

Raman spectroscopy has been utilised to detect changes in the structural order accompanying the process of mesophase spherules preparation. A coal tar pitch was selected as the precursor and it was carbonised under the appropriate conditions to produce a discrete amount of anisotropic material present almost completely in the form of spherules. These anisotropic spherules were concentrated by partial removal of the isotropic phase by hot filtration. The analysis by Raman spectroscopy confirmed an increase of the graphene-like orientation from the original coal tar pitch to the final anisotropic concentrate, with the carbonisation semicoke presenting an intermediate behaviour. The results indicate that Raman spectroscopy can be employed to monitor the process of production of mesophase spherules from coal tar pitches by studying the degree of structural order of the resultant product.

Utilization of flash chromatography for the fractionation of coal derived liquids

SummaryThe suitability of flash chromatography for the fractionation of coal liquids in compound classes has been studied. TLC data obtained from standards were used for establishing the sequence, composition and volume of eluents in order to collect the main components of coal liquids in six fractions of increasing polarity. The method was tested by the fractionation of a SCG coal extract and separations were evaluated by TLC, SEC, and IR and NMR spectroscopy.

Study of the composition of tars produced from blends of coal and polyethylene wastes using high-performance liquid chromatography

Tars produced at semi-industrial scale in a coke oven of 6 x 10(3) kg capacity were used to investigate the effect of using polyethylene waste as an additive in the carbonization process with coal. The polyethylene wastes used were low-density polyethylene from the agriculture greenhouses and high-density polyethylene from domestic sources. The high-performance liquid chromatography analysis of the soluble fractions in toluene and carbon disulfide, using two polystyrene-divinylbenzene columns and a mixture of dichloromethane-methanol as a mobile phase, provides useful information on the composition of tars and their derived pitches in terms of the substitution and molecular topology of polynuclear aromatic compounds (PACs). Differences in composition of tars produced with polyethylene waste at 1% (w/w) have been found to be negligible, while a higher amount of the waste (3%, w/w) promoted the formation of peri-condensed PACs at the expense of the substituted cata-condensed PACs. This behaviour is due to more extensive secondary reactions of tar precursors via dealkylation and aromatic condensation taking place during the carbonization process as a consequence of a more viscous co-carbonizing system. Changes in tar composition caused by this amount of polyethylene waste addition were comparable to those promoted by an increase in the carbonization temperature at semi-industrial and industrial ovens and by the coal preheating before the carbonization process. The characteristic features in tar composition were also found for the derived pitches from tars obtained with the polyethylene waste addition.