Masaharu Nishioka

Evidence for the associated structure of bituminous coal

Abstract Previous studies have shown that coal swelling is not reversible and highly dependent on coal concentration in a solvent. This rules out the conventional coal structural model of a covalently cross-linked three-dimensional network. Many coal molecules may be physically associated by relatively strong intra- and intermolecular interactions. Coal swelling in selected solvents was examined for fractionated samples of two high volatile C bituminous coals to investigate the role of physical associations in coal structure. The dependence of coal concentration on swelling in tetrahydrofuran and toluene was similar for pyridine soluble and insoluble fractions. Solvent swelling of pyridine solubles was smaller than that of pyridine insolubles. Pyridine extract was mixed with iodine and further fractionated into pyridine soluble and insoluble fractions. The swelling ratio of the pyridine solubles was much smaller than that of the pyridine insolubles. The difference between swelling with toluene and with tetrahydrofuran was larger for pyridine insolubles than for pyridine solubles. All these results indicate that significant portions of coal molecules are not a three-dimensional network, but are physically associated.

Molecular mobility of high-volatile bituminous coals accompanying drying

Abstract Pyridine-extractability, solvent swelling and free swelling index of selected high-volatile bituminous coals decreased upon drying under vacuum at 80–120 °C overnight. The temperature necessary to induce these changes varied among the coals. This behaviour was attributed to molecular association caused by molecular mobility after and/or during the removal of volatile matter such as water. The following mechanism is proposed. Molecules in the raw coals are partly blocked by hydrogen bonds. Water and functional groups such as ue5f8COOH and ue5f8OH are partly incorporated into these hydrogen bonds. During the drying step, the blocked water and presumably CO 2 are eliminated, a glass transition temperature is locally lowered, and coal molecules can move and form a more stable and associated state.

The associative nature of lower rank coal

Abstract Initial volumetric swelling in tetrahydrofuran of pyridine-unextracted parts from subbituminous coal and lignite showed no dependence of their concentration, and was smaller than that of their pyridine extracts. These results are opposite to those obtained from high volatile bituminous coals and coincide with predictions for the cross-linked network model of coal. However, when ionic forces in these coals were reduced by acid washing or O-alkylation, these coals showed the same associative nature as did high volatile bituminous coals. Swelling kinetics were analysed on the basis of associative equilibria controlled by the ionic forces. It was concluded that solvation of the ionic forces was the rate determining step of volumetric swelling of lower rank coal rather than solvent diffusion into the coal, although diffusion has been proposed to be the most important factor in swelling.

Dependence of solvent swelling on coal concentration

Abstract Volumetric solvent swelling of coal is highly dependent on coal concentration, and is significantly enhanced at low concentration. This indicates that associated coal complexes dissociate at low concentration. The dependence of coal concentration on solvent swelling can be expressed by an empirical equation when the concentration is low. The intrinsic swelling ratio, which is independent of the concentration, has been introduced. Solvent swelling approaches a given (saturated) value when the concentration becomes high. The conventionally observed swelling is usually this saturated value. Associative equilibria observed through this swelling imply that significant portions (far more than is generally believed) of coal molecules are physically associated.

Irreversibility of solvent swelling of bituminous coals

Abstract Solvent-induced swelling has been used to characterize the macromolecular nature of bituminous coal. It is necessary to prove the reversibility of coal swelling in order to apply the statistical theory of rubber elasticity. Although such reversibility has been reported, there is little reliable evidence for it. The conventional procedure of volumetric swelling was used to investigate the reversibility of coal swelling. Irreversibility of solvent swelling was observed. Two different ranks of coal showed distinctly different irreversibility which was consistent with the results of solvent extractability.

Isolation of aliphatic sulfur compounds in a crude oil by a non-reactive procedure

Abstract Ligand exchange chromatography using CuCl 2 has been developed for the isolation of aliphatic sulfur compounds in fossil fuels. The procedure is simple and non-reactive. Aliphatic sulfur compounds form stronger ligands with CuCl 2 , because of their higher nucleophilicity, than do aromatic sulphur compounds. After the isolation of aliphatic sulfur compounds from a crude oil, they were identified by gas chromatography and mass spectrometry, including tert -butyl disulfide.

Mechanism of coal solubilization by high temperature soaking: Investigation by extractability after soaking under various conditions

Abstract Solvent swelling has previously been examined for coal samples obtained by soaking in toluene at 200 and 350 °C. The result has implied that associative equilibrium is the major factor for large disintegration of coal in high temperature soaking. A systematic study using actual coal liquids was carried out to further investigate the proposition. Although it was very difficult to differentiate chemical and physical phenomena in soaking at 300 to 400 °C, all results obtained under various conditions could be rationalized by associative equilibria. Significant physical dissolution by high temperature soaking of coal was consistent with the associated molecular nature of coal.

Strong interactions between selected compounds and coal

Abstract Interactions between coal and a coal liquid and also between coal and various standard compounds were investigated. The mixtures were soaked in cyclohexane under nitrogen at 25, 200 and 350 °C for 2 h, and recoveries of the coal liquid and standard compounds were determined by solvent extraction. Nearly 100% of neutral compounds were recovered after the treatment. However, weakly acidic aromatics containing a hydroxyl group and basic aromatics containing nitrogen were seelectively adsorbed on coal even at 25 °C, and complete recovery with tetrahydrofuran and pyridine was difficult. The adsorption of weakly acidic compounds was stronger than that of basic compounds. The adsorption became stronger when the mixtures were soaked at higher temperatures. Similar results were also observed for the coal liquid.