Norman Taylor

Molecular mass calibration in size-exclusion chromatography of coal derivatives

A number of procedures have been investigated for the calibration of a size-exclusion chromatography (s.e.c.) column in the determination of molecular mass (MM) distributions of coal derivatives. The behaviour of narrow fractions of coal extracts in the MM range 200–3000 was compared with a variety of the more generally available calibration standards. Calibration with preparative s.e.c. subfractions of materials similar to those under study has been recommended. Polystyrene standards are satisfactory, however, for MM < 1000, but above this range other polymer standards should be sought. Universal and molar volume calibration do not apply to coal-derived materials.

p-Doped high spin polymers1

High spin polymers have been created from p-doping of networked polyaryl and polyarylamine polymers which were synthesized using the Pd0 mediated coupling reaction of aryl di- and tri-bromides with aryl bis- and tris-boronic acids. The doping procedures produce polyradical polycations in which (in the limit of 100% doping) each spin is coextensive in its spatial distribution with three neighbouring spins. Magnetic susceptibility studies show the expected ferromagnetic spin-coupling. In this respect the best of these systems is the polymer obtained by the Pd0 mediated coupling of 1,3-dibromo-5-tetradecylbenzene with tris(4-boronic acid-2-hexyloxyphenyl)amine which was subsequently p-doped with NO+BF4– . A Brillouin function fit to the field dependence of the magnetization of this doped polymer at 2 K corresponds to an average spin S of 5/2. The best levels of doping achieved so far are about 15% of the theoretical maximum. These are sufficient to demonstrate the genuine high-spin nature of these polymers but are well short of the ca. 70% percolation limit needed for bulk superparamagnetic or ferromagnetic behaviour. The low doping levels are attributed to steric rather than coulombic effects.

Evaporative analyser as a mass detector in the size-exclusion chromatography of coal extracts

Abstract The applicability of the evaporative analyser in the size-exclusion chromatography (SEC) of coal derivatives has been explored. The detector, in which the intensity is measured for the light scattered from the finely divided solute particles resulting from evaporation of droplets of chromatographic eluate, is mass responsive, sensitive, and linear for both narrow and gross coal-extract fractions. For molecular masses above 300 the mass response is almost uniform, and there are considerable advantages over the detectors commonly used in SEC. Application to lower molecular mass coal materials is limited by the evaporation of solute along with solvent in the detector.

Ferromagnetic spin-coupling 4,4″-through metaterphenyl: models for high-spin polymers

Model diradical dications have been synthesised which have the 4,4″-through metaterphenyl spin-coupling pathway found in arylamine high-spin polymers. In the model triplet diradical dication derived by a two-electron oxidation of N,N,N″,N″-tetrakis(4-tert-butyl-2-methoxyphenyl)-3,3″-dimethoxy[1,1′;3′,1″]terphenyl-4,4″-diamine the separation between the triplet and singlet states was found to be 0.083 kcal mol−1. This value is close to that predicted on the basis that the energy difference should be proportional to the product of the spin densities in the ‘common’ ring (the ring in which the two spin densities overlap). This is an important principle in the design of new high-spin polymers.

Variation of coal extract structure with molecular mass

Abstract Asphaltenes and benzene-insolubles, and their methylated counterparts, of high-yield supercritical gas (SCG) and hydrogen donor solvent (HDS) extracts have been separated by size exclusion chromatography (SEC) on cross-linked polystyrene microspheres so as to investigate the variation in coal extract structure with molecular mass (MM). Narrow SEC fractions have been obtained which have been subjected to elemental, molecular mass (MM), functional group, n.m.r. and voltammetric analyses. The analytical results revealed that the M M range of the solvent fractions was 300 to ≈3000. With increasing MM the following trends were observed: aromaticity decreased, but the degree of condensation of aromatic nuclei did not vary significantly; the size of aliphatic substituents increased; and phenolic hydroxyl content decreased for SCG extract fractions but, in contrast, increased for HDS extract fractions. These variations about averages are considerable and demonstrate that caution is necessary in making use of analytical results for gross fractions. Solubility in benzene of coal extracts results from low MM or from low polarity for higher MM materials.

Electrochemical oxidation of coals: Voltammetry and mass spectrometry

Abstract The anodic oxidation of sulphuric acid slurries of lignite, bituminous, and anthracite coals; a high-yield extract of coal; and carbon black, has been investigated voltammetrically and with simultaneous m.s. monitoring of evolved gases. The previously reported evolution of carbon dioxide at very low voltages was shown to be chemically released from minerals. The low rank coals and the asphaltite did show considerable electrochemical activity near to 1.0–1.2 V, mainly from the conversion of leached ferrous ion to the ferric form. Further activity near 1.4–1.5 V arose from the oxidation to CO2 of leached organic matter. For well-washed low rank coals, the coal extract and the anthracite, CO2 release was only observed at high (>2.8V) anode voltages, with simultaneous release of oxygen. Electrochemical gasification of coal via anodic oxidation of macromolecules at low voltages did not occur.

Characterization of petroleum feedstocks for coal-oil co-processing

Abstract Point-of-Ayr coal was co-processed with five different petroleum residues under a variety of conditions in tubing bombs. In addition, a number of petroleum sub-fractions and hydrotreated fractions were co-processed with the coal to assess the influence of the various structural types on extraction yield. Feedstocks and liquid products were subjected to chemical fractionation followed by ultimate analysis, size exclusion chromatography and 1H nuclear magnetic resonance. Detailed analysis of the hydrotreated fractions indicates that under low severity conditions the aliphatic side chains are removed from the aromatics, whilst at higher severities this is followed by condensation of the aromatic units. Reasonable extraction yields were only obtained with the three most aromatic petroleum feedstocks and the most severely hydrotreated feeds. Coal extraction was found to correlate with the amount of pentane-insoluble aromatics in the solvent. The high yields obtained from experiments using anthracene oil as a third component indicate that the petroleum feedstocks contain significant amounts of hydrogen donors.

New technique for the electrochemical analysis of coal-derived materials

A new method of electrochemical analysis has been developed for polycyclic aromatic and heterocyclic structures in coal-derived liquids: electroactive species are adsorbed on hard, planar mercury electrodes, which can then be transferred to aqueous electrolytes for electrochemical studies. Previously obtained tabulations of reduction potentials for a wide range of model aromatic and heterocyclic compounds have been revised and extended for comparison with potentials observed for coal-derived liquids. Redox potentials for single compounds did not differ systematically from those measured for mixtures. Different structures with similar redox potentials could be distinguished by variations in adsorption potentials. A further means of distinguishing nitrogen compounds from hydrocarbons was afforded by the forms of the electrode adsorption isotherms and their different adsorption-time behaviour. A quantitative analytical method for mixtures was developed from measurements of the charge passed in reducing the adsorbed layer, using fluorimetry to measure the concentrations of dilute solutions, and the relation between the molecular structure and the apparent number of electrons transferred during reduction was investigated. A wide variety of representative coal-derived liquids was investigated; the principal aromatic groups present were identified and quantitative estimates were made of their concentration.

Quantification of organic sulphur containing functional groups for coal conversion processes

Abstract An improved and automated temperature programmed reduction (TPR) apparatus has been applied to the study of sulphur functional groups in model compounds, coals and coal derived products. Experiments were performed in two independent laboratories and showed good reproducibility. A set of sulphur containing model compounds representing the types of functional groups believed to be present in coal were studied and were found to exhibit characteristic H 2 S evolution profiles. Quantitative conversion was observed for the model compounds. To gain a better understanding of the processes involved cysteine was the subject of a detailed kinetic study. Samples from a coal liquefaction process were investigated and the changes in sulphur functional group distributions rationalised in terms of the processing conditions.

Identification of aromatic systems by differential pulse voltammetry in the study of the hydropyrolysis of pyrene and coal asphaltenes

Abstract Differential pulse voltammetry at the hanging mercury drop electrode has proved effective in determining the identity of the aromatic structures present in the complex mixtures resulting from the hydropyrolysis of pyrene and coal-derived asphaltenes. Voltammetric results are consistent with g.c.-m.s. analyses for low molecular mass fractions, and the method is also applicable to asphaltenes.