Derek G. Mills

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.

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.

NEW CHROMATOGRAPHIC METHODS FOR ASPHALT ANALYSIS

ABSTRACT New methods in the analysis of asphalt by size exclusion chromatography (SEC) and supercritical fluid chromatography (SFC) are described. The evaporative analyser and viscometric detectors provide a more nearly universal response in SEC than does the UV detector; a number of alternatives to polystyrene as retention volume calibration standards were investigated. SFC permitted simulated distillation at much lower temperatures than in GC, with closer correspondence to actual distillation behaviour

On a possible role for electrochemical oxidation in coal liquefaction

Abstract The feasibility of coal conversion via electrochemical liquefaction has been investigated. Because of the complicating presence of inorganic materials in coals, humic acids extracted from lignites have been used as model substrates. Considerable reductions in molecular mass, as revealed by size exclusion chromatography, were achieved by anodic oxidation at 1.7 V for slurries in acid, and more especially for solutions in alkali. NMR spectroscopy of methylated humic acids before and after oxidation suggests cleavage of ether linkages between aromatic clusters, with generation of carboxyl groups.

Rapid analysis of coal-derived oils for polycyclic aromatic compounds by differential pulse voltammetry

Abstract The application of differential-pulse voltammetry (DPV) as an inexpensive and rapid screening procedure in the analysis of potentially hazardous polycyclic aromatic compounds (PAC) in coal processing emissions has been investigated. Reductive-mode DPV at the hanging mercury drop electrode offers advantages over electrochemical oxidation. A unique tabulation of reductive mode half-wave potentials ( E 1 2 ) was established for model compounds, and used to show that individual substances (e.g. pyrene in process solvents; various carcinogenic PAC) or specific compound types (diaromatics, polyaromatics) may be identified in coal-derived liquids. Graphs of differential pulse current against concentration were linear, so that quantitative analysis by calibration or standard addition was readily achieved. The DPV method is sensitive, rapid and discriminating and no complex clean-up procedure is necessary. However, more compositional information is available after separation by column chromatography, although the electrochemical method employed here did not allow liquid chromatography with online detection.

Defining the parameters of coal beneficiation by chemical and electrochemical oxidation

Abstract An investigation is reported of chemical and electrochemical oxidation of coal as a potential route to coal liquids and other derived products. Mild oxidation with a number of reagents gave high molecular mass (MM) material in addition to carboxylic acid derivatives of mono- and polycyclic aromatic compounds. Coal acids could be precursors for cheap resins. Sodium dichromate gave fragments with MM appropriate for use as liquid fuels after decarboxylation; anodic oxidation of dissolved coal derived material is more controllable, however, and avoids the problems of spent reagent.

Electrochemical identification of aromatic structures containing basic nitrogen in coal-derived liquids

Abstract Differential pulse voltammetry at the hanging mercury drop electrode is used to determine the reduction potentials, E 1 2 , of the aromatic structures containing a basic nitrogen substituent in the asphaltene fractions of coal derived liquids. In comparison with PAH, the substitution of a nitrogen atom alters E 1 2 so that reduction occurs at less negative potentials. Comparisons of the voltammograms obtained from nitrogen rich and total asphaltene fractions show that the basic fractions are nitrogen analogues of the hydrocarbon structures found in the original asphaltenes.

Analysis of methylated humic acids from fossil fuels by size exclusion chromatography and NMR

Molecular Mass (MM) distributions in humic acids from peat and two lignites have been investigated by high performance size-exclusion chromatography (SEC) after methylation and found to be in the range approximately 300 to more than 5000, with number average NM(Mn) near 800. Values of Mn determined by SEC were in good agreement with those from vapour pressure osmotery. High field13C NMR spectra of the methylated humic acids are extremely well resolved, and indicate that the samples are significantly different, despite their similar elemental compositions and MM distributions.

The chemical nature of material released from coal-derived asphaltenes by reprecipitation and cyclohexane extraction

Abstract The yields and chemical nature of n-pentane solubles released from three coal-extract asphaltenes by reprecipitation with n-pentane and cyclohexane extraction have been investigated. With increasing concentration of n-pentane solubles in the original coal liquid, the yield of oils obtained by reprecipitation increases, as also does the tendency for their structures to resemble those of the original n-pentane solubles. No alkanes below C40 were released from the asphaltenes by extraction with cyclohexane and therefore the long alkyl chains (10% of the total carbon in the lignite asphaltenes) must be bound to aromatic, carboxyl or heteroatomic groups.

Diffusion coefficients for a series of n-alkanes in two polar solvents

The diffusion coefficients for an homologous series of ca. 20 n-alkanes from ethane to octacosane have been measured in dilute solution in propan-2-ol and tetrahydrofuran at 300 K and atmospheric pressure using the Taylor dispersion technique with an accuracy of 3–5 % for most systems. The diffusion results are discussed in terms of the hydrodynamic theory of diffusion, in view of the relevance to diffusion-controlled reactions in polymerisation kinetics.