Pore entry effects in the solvent-induced swelling of low-rank coals

The swelling of a low-rank coal under the influence of various solvents is examined and results compared with those for a similar coal in briquetted from. Results are interpreted in terms of the effects of briquetting on pore structure.     

A rapid and convenient method for measuring the swelling of coals by solvents

The volumetric swelling procedure developed by Liotta was applied to a pair of coals using 10 solvents. The results were compared with the results of gravimetric swelling experiments. Good straight-line correlations having slopes of 0.93 (Bruceton coal) and 1.01 (III. No. 6 coal) were observed. The much more rapid and convenient volumetric swelling procedure gives the same results as the gravimetric procedure. Additionally, no correction for pore volume is necessary with the volumetric procedure. From plots of the gravimetric vs. volumetric swells, the accessbile pore volumes of the coals can be determined. They are 21% and 15% for Bruceton and III. No. 6 coals, respectively.     

Displacement of retained pyridine by aqueous tetrahydrofuran from Illinois No. 6 coals

It has been found that repetitive washing of an Illinois No. 6 vitrain and O-methylated Illinois No. 6 vitrain containing 10.7 and 7.9 wt% pyridine, respectively, with a 5% (v/v) tetrahydrofuran in water solution followed by vacuum drying at 110 °C (18 h) effectively removes all of the retained pyridine. Experiments with ¹⁴C-labelled THF establish that tetrahydrofuran is not retained under these conditions in significant amounts (< 1.2% by weight) by either of the two coals. Furthermore, the difference in weight before and after the extraction agrees well with the amount of pyridine initially present indicating only small (< 5%) losses of coal during this process. Plots of per cent pyridine released versus vol% THF are consistent with a displacement mechanism in which THF penetrates the coal matrix and replaces the adsorbed pyridine.     

Influence of the oxygen content of low-rank coals on the development of porosity during carbonization

The development of porosity in the course of carbonization of a flame coal, original and pre-oxidized, was studied by means of the adsorption of benzene and carbon dioxide. The results were compared with corresponding data for cokes from a xylitic brown coal. The influence of coal oxygen content on the formation of coke porosity and its thermal dependence is discussed.     

Contributions of the crosslinked and noncrosslinked moieties to the solvent-induced swelling of brown coals

A suite of brown coals from different sources was examined for solvent-induced swelling in two forms: oven-dried whole coal and pyridine-extraced coal. This enabled the swelling to be resolved into the component due to imbibition of solvent by the crosslinked part and the component due to the non-crosslinked part.     

Solvent swelling behavior of Permian-aged South African vitrinite-rich and inertinite-rich coals

Two South African coals similar in rank and age, but different in maceral composition, were studied using solvent swelling. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were evaluated for swelling extent and swelling rate using N-methylpyrrolidone (NMP) and CS₂/NMP. A stop-motion videography method was developed to study individual particle swelling behavior. This method allowed observation of overshoot and climbing-type swelling, as well as swelling kinetics. Single-particle swelling experiments showed that both coals exhibited overshoot-type and climbing-type swelling. The inertinite-rich coal swelled much faster (in both solvents) than the vitrinite-rich coal. The swelling in CS₂/NMP was faster for both coals. Kinetic parameters showed that solvent swelling was governed by relaxation (super-Case II relaxation) of the coal structure. X-ray computed tomography was conducted over a 50 h swelling period in NMP for single particles of each coal. Anisotropic swelling was observed in all the particles (swelling greater perpendicular to the bedding plane than parallel to it). The subtle changes in molecular structure, fine structural and physical differences resulted in significant differences in solvent swelling behavior.     

Low-temperature air oxidation of caking coals. 2. Effect on swelling and softening properties

Three highly swelling bituminous coals (< 75 um > 63 um size) were pre-oxidized to various levels of weight gain and then their plastic properties monitored during carbonization. Additions of relatively small amounts of oxygen (<1–2% by wt) cause marked changes in swelling and softening properties. In general, oxidation causes: substantial reductions in volume changes, increases in softening and dilation temperatures, and a slight reduction in resolidification temperatures. For coals which exhibit high fluidities, slight oxidation results in an increase in expansion prior to destruction of swelling properties. For a given level of weight gain, reduction in plastic behaviour of a coal becomes more severe as the temperature of pre-oxidation is increased. Weathering studies indicate that exposure of an hvA bituminous coal to moist air at ambient temperature has more effect on subsequent swelling and softening properties than exposure to dry air. Fine coal particles stored for extended periods of time in atmospheres with even slight oxygen concentrations show definite signs of weathering. The plastic properties of an oxidized coal may be partially resotred by grinding to expose new surface.     

Hydrogenolysis products of pyridine extract of a Japanese lignite

Petroleum ether insoluble fractions of a pyridine extract of a Japanese lignite were pyrolysed with tetralin. The chain length of alkyl groups bonded to aromatic rings and the average chemical structure of aromatic compounds in the lignite were obtained from analyses of hydrogenolysis products. Gas Chromatographic analyses of fractions eluted by cyclohexane showed the presence of C₁₅ to C₃₄ straight-chain alkanes. The chemical structures of the other fractions were analysed quantitatively by a combination of ¹³C and ¹H n.m.r. The unit structure of petroleum ether insoluble fractions in the lignite consists of one to three aromatic rings with straight-chain alkyl groups, some of which are about 25–30 carbon atoms long.     

Determination of carboxyl groups in low-rank coals

The determination of carboxyl groups in low-rank coals by exchange with barium chloride-triethanolamine reagent is re-examined. The difference in carboxyl contents calculated from the barium content of the exchanged coal, and the amount of acid used to extract the barium, is discussed. Reliable carboxyl contents are obtained providing the latter procedure is used.     

Comments on the reactivity of low-rank coals in liquefaction

This communication discusses the subject of the relative reactivities of low-rank and bituminous coals in liquefaction. Accounts given by several researchers have provided seemingly contradictory results. An explanation is presented to reconcile these opposing views.     

Determination of the kinetics of diffusion in coals by solvent swelling techniques

A simple technique has been developed for measuring the kinetics of solvent diffusion in coals at various temperatures. The technique is based on a well-known method for measuring the volumetric swelling of coals by solvents. Several coals have been examined in both pyridine and tetrahydrofuran, at temperatures between 298 and 332 K. The diffusion follows the well-established case II rate law at ambient temperatures, implying that the processes are controlled by relaxation in the coal network structure. As temperatures are increased, the process becomes more Fickian in nature. The activation energies for the diffusion-relaxation processes are in the range 31 to 82 kJ mol⁻¹.     

Model for drying during fluidized-bed combustion of wet low-rank coals

An unsteady state heat conduction model with a convective boundary condition is proposed for the drying of low-rank, high-porosity coals, such as lignites, during fluidized-bed combustion. The drying front is assumed to be the receding surface of a wet core. The solution technique for this moving boundary problem is based on the heat balance integral approach with immobilization of the moving boundary by a change in space variable. The governing cubic equation describing the drying curve in dimensionless form may be solved easily by the Newton—Raphson method. The model predictions are compared with experimental data for Mississippi lignite with excellent agreement. A correlation for estimation of total drying time is proposed. The temperature profiles obtained may be used for the study of the coupled drying and devolatilization in fluidized-bed combustors. The profiles could also be of importance in the study of formation of fissures/cracks in lignites subjected to intense heating conditions encountered during fluidized-bed combustion.     

依兰煤溶胀特性的初步研究

针对依兰煤的溶胀特性进行了初步研究，考察了不同试剂、温度、时间、粒度和浓度等因素对依兰煤溶胀度的影响，并对溶胀煤进行了激光粒度分析和扫描电镜分析。     

新疆伊犁煤溶胀行为的研究

本文研究了新疆伊犁煤在甲苯、甲醇、四氢呋喃（THF）、N-甲基吡咯烷酮（NMP）和陆梁原油不同溶剂下的溶胀行为,考察了煤预处理温度、不同溶剂、煤／溶剂体积比、溶胀时间对煤溶胀度的影响。结果表明：经过110℃真空干燥预处理煤样的溶胀度大于经过50℃真空干燥预处理煤样的溶胀度;相同条件下,NMP的溶胀度最大;煤／溶剂体积比越大,煤的溶胀度越小;溶胀24h煤样的溶胀度同溶胀60h煤样的溶胀度变化不大。     

Depolymerization of coals in hot pyridine or phenol

Experimental evidence is presented that suggests cleavage of bonds by solvent attack is a possible contributing mechanism for coal depolymerization.     

溶胀技术在煤科学中的研究进展

综述了煤溶胀技术的研究进展,着重从溶胀机理、煤溶胀度的影响因素、煤中氢键与溶胀率关系、溶胀动力学及溶胀煤的表征分析等几个方面论述了溶胀技术在煤科学中的研究进展。     

Carbonization of coals to produce anisotropic cokes. 1. Modifying activities of some additives in the co-carbonization of low-rank coals

Using low-rank coals, the modifying activities of some petroleum, coal tar and aromatic hydrocarbon additives have been examined to find procedures for their utilization in the preparation of blast furnace coke. Petroleum pitch, especially after hydrogenation, exhibited excellent modifying activity even with non-fusible coals. In contrast, the activity of coal tar was very limited with such coals. The napththenic component, revealed by n.m.r. of the additives, appears to be important in the co-carbonization by inducing fusibility and anisotropic development in such coals. Co-carbonization to recover the dehydrogenated additives was attempted. However, there was no development of the anisotropy in the resultant coke by dissolution of the coal particles although the coal particles were firmly fixed in the matrix. Acid-refluxing treatment of non-fusible coals was found to enhance their modification susceptibility, indicating that some of the acid-soluble mineral matter is important in the thermal depolymerization or fusion process of the coal.     

Mechanism of swelling and extraction and coal structure

An attempt is made to develop a comprehensive model of coal structure based on results of various experiments involving extraction and swelling of a coal by solvents. These are described in terms of electron-donor and electron-acceptor characteristics, of mass spectrometric analysis of coal extracts, of pulse ¹H n.m.r. measurements of mobilities of coal components, porosity measurements. The theory of coal swelling cannot be adapted from the theory of polymer swelling.