Leo J. Lynch’s research while affiliated with Tohoku University and other places

Proton magnetic resonance thermal analysis was applied to clarify the thermal behavior of a pale lithotype fraction of Bacchus Marsh brown coal (Victoria in Australia). Isothermal measurements at temperatures 400 - 450°C revealed three main components: two mobile components and one rigid component. The two mobile components could be distinguished by their rates of decrease mainly due to volatilization, but not by their signal lifetimes in solid echo NMR. The rate constants and activation energies were evaluated for the interconversion processes among these components. From the kinetic data, a model for the pyrolysis of this brown coal was proposed.

The proton magnetic resonance thermal analysis (PMRTA) method has been applied to the reaction of a bituminous coal with elemental sulfur (S8). From the non-isothermal PMRTA data including mobile and rigid hydrogen fractions, it is revealed that the dehydrogenation reactions are accelerated by S8 at temperature above 250 °C. The dehydrogenation reactions accompanied a decrease in mobile hydrogen and fusibility, resulting in an increase in the proportion of hydrogen that is rigid.

The solid-echo signal decays of 1H-NMR of four pitches were measured in-situ during the heat treatmentemploying proton-magnetic resonance thermal analysis (PMRTA). The pitches became mobile (long T2) in thetemperature region 400-700K. The mobility of coal tar pitch and Ashland 240 petroleum pitch, which exhibit sphericalmesophase and flow optical texture, was confirmed to be kept till 750K. On the other hand, aliphatic-and sulfur-richpetroleum pitches, which exhibit the mosaic optical texture, lost their mobility at temperature below 750K, indicatingthat they are thermally unstable. The thermal instability of these pitches could be due to their relatively high contentsof aliphatic groups and sulfur. The PMRTA pyrograms afford useful information about the mesophase formation.

Procedures are outlined by which the thermoplastic properties of coal blends - fluidity, as measured by Gieseler plastometry, and extent of fusion, as measured by proton magnetic resonance thermal analysis (PMRTA) - can be predicted from those of their component coals on the assumption that the thermoplastic properties of the blend are the appropriately weighted average of the properties of the component coals at every temperature. Account is taken of the influence of inert material on measured fluidity in the Gieseler plastometry model and thus the model can be applied to blends which have inert material added. The extent to which the observed thermoplastic behaviour of a blend deviates from these linear models is in principle a measure of any interactive effects that occur. Blends involving four Australian bituminous coals of different rank and fusibility were prepared so that the effect of a wide range of thermoplastic behaviour of the component coals on blend properties could be more clearly delineated. The coals and their blends were characterised by Gieseler plastometry and PMRTA. The maximum fluidity and PMRTA maximum fusion of the blends of coals of different rank were predicted by the models to be less than the weighted average of the component coals, and generally agreed with observation. The fluidity and fusibility of blends containing the higher rank, high fluidity coal and the two lower rank coals were significantly greater than expected by the model which is interpreted as evidence of an interactive effect between these coals that increases the fusibility of blends formed from them.

Proton magnetic resonance thermal analysis (p.m.r.t.a.) was used to monitor the pyrolysis behaviour of a variety of coals, their mixtures with four different addivites, and each of the additives alone. A model was developed to quantify the effects of small quantities of an additive on the thermoplastic and other molecular properties of coal, by measuring the difference in behaviour of the mixture from that predicted assuming no interactions between the coal and additive. This model was used to define a solvation index, which was used in turn to estimate the capacity of an additive to destabilize or ‘solvate’ the molecular structure of coals. It was found that 1.(1) pitches — both coal-tar and petroleum-derived — ‘solvate’ bituminous coals at temperatures significantly below the coal fusion or ‘softening’ temperature but do not solvate subbituminous or brown coals;2.(2) this capacity to solvate bituminous coals is shared by the two other aromatic additives tested — decacyclene and p-quaterphenyl; and3.(3) the rates of coking of both pitch and decacyclene are greatly increased when they are co-pyrolysed with low-rank coals, this enhancement decreasing with increasing rank of the coal.

The applications of in situ electron spin resonance (ESR) and NMR spectroscopic methods to study thermally induced transformations of coals and related materials are addressed. Brief background statements are given on the underlying principles, and the focus is on the particular methodologies developed at Hokkaido University and CSIRO during the past decade. Designs of both high-temperature and high-temperature—high-pressure ESR and NMR probes and spectrometer configurations for their use are outlined. The high-temperature in situ ESR technique is illustrated by its application to Argonne Premium coals. Applications of NMR techniques to derive chemical-shift information on coal and pitch materials during pyrolysis and liquefaction processes, and techniques that monitor molecular dynamics during pyrolysis are presented. Monitoring molecular dynamics is demonstrated to be an effective method of thermal analysis.

The proton nuclear magnetic resonance (H-1 NMR) properties of both untreated and acetylated samples of a brown, a subbituminous, and a bituminous coal have been measured during heating between 30 and 600-degrees-C in order to evaluate the role of polar interactions involving hydroxyl groups in providing conformational stability to the molecular structure of coals. The acetylated brown coal and, to a lesser extent, the acetylated subbituminous coal exhibit a greater degree of molecular mobility than the corresponding untreated coals at temperatures below 250-degrees-C, consistent with a minor but significant role of hydroxyl group bonding in the conformational stability of the molecular structure of the untreated coals. At higher temperature all three acetylated coals were found to be significantly less fusible than the corresponding untreated coals. This is attributed to thermal decomposition of the labile acetyl groups to free radicals which then form covalent cross-links. IR measurements of the heat treatment residues of the acetylated coals confirm the loss of acetyl groups and their reduced pyridine extractability is consistent with the formation of cross-links at these temperatures.

This chapter presents an investigation of coal–water molecular interactions. In a study described in the chapter, crushed samples of Australian coal were prepared with equilibrium water content between 0 and 25% (wt/wt). 1H NMR transverse relaxation signals of each specimen were measured using solid echo pulse sequence at regular intervals during a temperature cycle from 310 to 210 K and back to 310 K. The adsorption/desorption isotherm was determined at 298 K by allowing samples to equilibrate at seven different relative humidities for one month. Also, duplicate predried samples were monitored for four weeks by regular weighing for their uptake of water in an atmosphere of 100% rh at 293 K. The equilibrium adsorption/desorption isotherm showed little hysteresis, and the approach to saturation was not asymptotic so that an estimate of 12.4% for the saturation water content (SWC) was obtained with good precision. The uptake at 100% rh was rapid at first, but at least 200 min were required for equilibrium to be closely approximated. There was a significant difference between the two samples tested, and the SWC estimates obtained were 14.5% and 13.0%—both greater than the isotherm estimate.