Richard Sakurovs

Interactions between coking coals and plastics during co-pyrolysis

Blends of three Australian coking coals and polypropylene, polystyrene, polyacrylonitrile and polyphenylene sulfide were prepared and the extent to which the blends fused on heating was monitored using proton magnetic resonance thermal analysis in order to identify interactions between them that could affect their fluidity. Different plastics had different effects. Polystyrene strongly reduced the fluidity of all of the coals, confirming previous findings. Polypropylene did not affect the fluidity of the two coking coals of lower rank. Polyphenylene sulfide reduced the fluidity of the coals at temperatures near the solidification temperature of the coals, and polyacrylonitrile appeared to increase the fluidity of the coals at temperatures near the softening temperature of the coals. The very different effects different plastics have on coal fluidity show that the interaction between plastics and coals must be carefully examined before plastics are added to coking coal blends.

The molecular basis of coal thermoplasticity

The molecular mobility of a range of Australian bituminous coals during heating and pyrolysis to 875 K has been studied by proton nuclear magnetic resonance (1H n.m.r.) thermal analysis. Mobility acquired at lower temperatures is correlated with both exinite content and HC ratio. Mobility occurring at higher temperatures is assessed to involve aromatic structures and is identified with the onset of coal thermoplasticity. The transient nature of the thermoplastic event is explained in terms of three partly overlapping processes: 1. 1. a physical mobilization of aromatic-rich structures; 2. 2. a rate-limiting thermochemical decomposition of the molecular structure to form reactive highly-aromatic molecular units in the residue; and 3. 3. after a critical level of decomposition has been reached, there is a rapid condensation of the residual units to produce a rigid semi-coke.

1H n.m.r. evidence to support the host/guest model of brown coals

The proposal that low rank coals consist of a two-component molecular structure has been investigated by in situ1H n.m.r. measurements during heating (to 875 K) of a suite of Australian and New Zealand brown coals, a set of Morwell brown coal lithotypes, and extracts and extract residues of some of these coals. The variation in behaviour of the coals during heating and pyrolysis, although significant, was not particularly sensitive to lithotype ranking, but showed a strong correlation with atomic H/C ratio. The extracts were found to be fully mobilized in the temperature range 470–700 K whereas the residues essentially remained rigid molecular lattices throughout heating and pyrolysis. This behaviour was independent of the lithotype and H/C ratio of the source coal. The higher H/C ratios of the extracts compared with the residue materials allow these observations to be explained (to a first approximation) in terms of the host/guest hypothesis whereby the coals are composed of extract (guest) and residue (host) materials in differing proportions.

Direct evidence that the thermoplastic properties of blends are modified by interactions between the component coals

Abstract A number of Australian coking coals were blended and their behaviour during carbonization was examined using proton magnetic resonance thermal analysis (PMRTA) to measure the degree to which the fusion behaviour of blends was affected by interactions between the component coals. Most blends examined showed evidence of interactions. Both significant positive and negative interactions (degree of fusion of the blend respectively greater and less than expected if the coals had acted independently) were observed. When interactions occurred between two coals, the temperature at which the interaction was greatest was independent of the proportion of the coal components in the blend, but the magnitude of the interaction was found to be proportional to x (1 − x ), where x is the proportion of one component in the blend. The interaction between coals is suggested to be mediated by interchange of volatile material.

Moisture-Induced Swelling of Coal

The gas-induced swelling behavior of coal is important when considering CO2 sequestration into coal seams or enhanced coalbed methane applications, but coals may also swell in the presence of moisture, or shrink on drying. In this paper we examine the moisture-swelling properties of coals from Australia and elsewhere. Results on the moisture uptake and corresponding swelling measurements are presented for 15 coals of various ranks (sub-bituminous and bituminous) at 22°C and atmospheric pressure. Measurements were made by exposing sample blocks of coal (nominally 30 × 10 × 10 mm) to relative humidities ranging from 0% to 97%. A selection of coals was also fully saturated in water. Moisture uptake at 97% relative humidity (RH) ranged from about 2.5% to more than 16% db. Maximum linear strain associated with the moisture sorption (measured at 97% RH) varied from about 0.2% to 1.3%, with lower rank coals showing the most swelling. In all cases, swelling was greater in the direction perpendicular to the bedding plane. These results correspond to volumetric swelling of about 0.5% to around 5%. Although exhibiting significant expansion, all of the samples returned to their original dimensions upon drying. Volumetric moisture sorption and the amount of swelling induced were found to be strongly correlated by a single linear expression that held for all of the coals examined. It was further found that the volume of the water adsorbed was linearly related to the pore space within the coal, however, at 97% relative humidity, only about 60% of the available pore space is occupied by water. Exposure to liquid water allowed the pores to completely fill; although for the lowest rank coals, the volume of water absorbed appeared to be slightly more than the corresponding pore volume. Despite the additional water uptake, immersion in water did not produce further swelling beyond that induced at 97% relative humidity.

Proton magnetic resonance thermal analysis of a brown coal: effects of ion-exchanged metals

Abstract Four versions of a Yallourn brown coal, each distinguished by the form of its carboxyl groups (acidic or cation-exchanged with Na, Ca or Ba), were subjected to proton magnetic resonance thermal analysis from 25 to 575°C. Analysis of the profiles of two second-moment parameters, calculated from the transverse relaxation signals of each coal, indicates the following: (1) Upon heating, cation-exchanged coals attain a lower extent of fusion (i.e. they are more rigid structures) than the acid-form coal—the two divalent cations Ba and Ca having a greater effect on fusion reduction than the monovalent cation Na. (2) The matrix densities of the coals follow the order: acid-form

Direct observations on the interaction of coals with pitches and organic compounds during co-pyrolysis

Abstract 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; and 3. (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.

Oxidation studies of high fluidity coals

Abstract Highly fluid fresh bituminous coals were oxidised and four techniques (cross-link measurement, chloroform extraction, proton magnetic resonance thermal analysis (PMRTA) and FT-i.r. diffuse reflectance spectroscopy) were used to correlate Gieseler fluidity changes with chemical differences between the fresh and oxidised samples. The oxidised samples were found to have a depleted concentration of aliphatic CH bonds. During slow heating through the plastic temperature range, they developed less molecular mobility, and generated smaller amounts of chloroform extracts but underwent cross-link formation to the same extent and at the same rate as the fresh samples. The addition of a radical stabiliser greatly inhibited fluidity loss and restored fluidity to some oxidised samples. The results suggest that for Geiseler fluidity development, the capping of radicals derived from the coal structure during heating is a far more important factor than variations in cross-link formation.

The rheological behavior during carbonization of iodine-treated coal tar pitch

Abstract Changes of rheological properties, especially thermal fusibility, during carbonization processes of iodine-treated coal tar pitches have been investigated by TG–Mass, viscometer and proton nuclear magnetic resonance thermal analysis. It was found that iodine could exist in two distinct forms in coal tar pitch (CTP). Introduced iodine molecules, about 30 wt% against the CTP, formed charge-transfer complexes with the CTP molecules. These charge-transfer complexes decompose at temperature above 200°C to form HI and free radicals, which promote cross-linkage and reduce the resolidification temperature of CTP by two hundred degrees. Additional iodine (at levels of greater than 30 wt%) could be eliminated by ethanol and be weakly bound to the CTP. Over extended periods of time at 100°C, latter form of iodine increases the softening temperature and viscosity of the CTP, possibly by acting as an oxidant. The combination of the two effects explains how iodine is so effective as a stabilizer of CTP.

The prediction of the fusibility of coal blends

Abstract 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.