Toshimasa Takanohashi

Characterization of the extracts and residues from CS2-N-methyl-2-pyrrolidinone mixed solvent extraction

Abstract The extracts and residues obtained by extraction of five bituminous coals with CS 2 -N-methyl-2-pyrrolidinone mixed solvent (1:1 by volume) were characterized at room temperature. The extraction yields were 31.1–63.0% (daf) and the extracts were fractionated into acetone soluble (AS), acetone insoluble-pyridine soluble (PS) and pyridine insoluble-mixed solvent soluble (MS) fractions. The MS fraction, which was the heaviest fraction examined, had higher values of % oxygen, f a , molecular weight and spin concentration than the corresponding AS and PS fractions, but a similar degree of aromatic condensation. The quantities of volatile matter (daf) in the residues were similar or slightly less than those in the extracts.

Effects of additives and oxygen on extraction yield with cs2-NMP mixed solvent for argonne premium coal samples

Abstract Addition of tetracyanoethylene or p -phenylenediamine to CS 2 -NMP mixed solvent markedly increased the extraction yield for Upper Freeport coal (86 wt% C). The presence of atmospheric oxygen during extraction decreased the yield. The pyridine-insoluble fraction of the extract was most affected. No such large effects were observed for other coals. The mechanisms responsible are discussed.

Structural Relaxation Behaviors of Three Different Asphaltenes Using MD Calculations

Abstract For asphaltene obtained from vacuum residues of three different kinds of crude oils (Khafji, Maya, and Iranian-Light), the energy-minimum conformation calculated by molecular mechanics–dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are the most stable conformation. Changes of aggregated structures by heating or solvent treatment were investigated by using the molecular dynamics calculation. For Khafji and Iranian-Light asphaltenes, the simulation showed that the aggregated structure was dissociated at 673K, while for Maya asphaltene the dissociation behavior was not observed, showing that Maya asphaltene seems difficult to be dissociated by heating, compared to other asphaltenes. In contrast, the simulation of relaxation of the Maya aggregates in quinoline showed that at 573K a part of aggregates was dissociated more easily than Khafji and Iranian-Light asphaltenes. These results above suggest that the effects of heating and solvent treatment on the structural relaxation of asphaltene aggregates can be different.

Sorption behaviors of methanol vapor by coal extracts and residues

Abstract Four Argonne coal samples (Pocahontas No.3, Upper Freeport, Illinois No.6, and Beulah-Zap coal) were extracted with a carbon disulfide–N-methyl-2-pyrrolidinone (CS2–NMP) mixed solvent at room temperature. To clarify the nature of the coal–methanol interaction, the mechanism of sorption, and the micropore and bulk structure of each coal fraction, sorption of methanol vapor by the extract fractions and residues was investigated using an automatic vapor adsorption apparatus. The sorption behavior of the residues with the low extraction yields was similar to that of the raw coals, regardless of rank. In contrast, the sorption for residues with the high extraction yields greatly increased compared to the raw coals, which suggests that more microporosity was formed by the extraction. For all fractions examined, experimental values were fit by the Langmuir–Henry dual-mode sorption model, which suggests that methanol sorption by the coal fractions can be explained by the adsorption on the surface described by a Langmuir isotherm and penetration (dissolution) into the bulk described by Henrys law. The Henrys dissolution constant, kD, was found to be similar in magnitude for both the extract fractions and residue from Upper Freeport coal, in agreement with the results of methanol swelling.

Molecular Dynamics Simulation of Structural Relaxation of Asphaltene Aggregates

Abstract For asphaltene obtained from vacuum residue of Khafji crude oil, the energy-minimum conformation calculated by molecular mechanics–dynamics simulations showed that aggregated structures of asphaltene molecules through noncovalent interactions are more stable. Changes induced in aggregated structures by pretreatment with solvents were investigated using molecular dynamics calculations. The simulation showed that in quinolin at 573 K, some staking interactions could be disrupted, while, in 1-methylnaphthalene it was not observed. Autoclave experiments showed that the coke yield after pyrolysis at 713 K was decreased when the asphaltene was pretreated with quinoline at 573 K for 1 h, compared to the yield without the pretreatment. While, in the case of pretreatment in 1-methylnaphthalene, the coke yield did not change significantly. The simulations results above can be related to the difference in coke yield between two solvents; in quinoline some aromatic–aromatic stacking interactions could be disrupted and mobility of molecules was increased. This resulted in prevention of the asphaltenes from polymerizing, as in condensation reactions among aromatic rings. Consequently, the coke yield after the pretreatment with quinoline was decreased.

Irreversible structural changes in coals during heating

A differential scanning calorimetry (DSC) study on the extraction residues of coals giving different extraction yields (which were prepared by changing the solvent composition of a carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent extraction) was carried out. For the residues from Upper Freeport coal (APCS-1) with extraction yields lower than 30 wt % (daf), an endothermic peak similar to that given by the raw coal was observed around 350 °C. This endothermic peak disappeared on the second and third scans, indicating that the peak is due to irreversible structural changes in coals. For the residues from the high extraction yield experiments, the peak was not observed up to 400 °C, even during the first scan. The reason for these endothermic peaks was discussed from the relationship among the extraction, swelling, and structural changes of coals.

Effect of lighter constituents on the solubility of heavy constituents of coals

Zao Zhuang, Shin-Yubari and Upper Freeport bituminous coals were extracted with a carbon disulfide/N-methyl-2-pyrrolidinone (CS2/NMP) mixed solvent at room temperature. Extracts were further fractionated with acetone to give acetone-soluble (AS) and acetone-insoluble (AI) fractions; the AI fraction was further extracted with pyridine to give pyridine-soluble (PS) and pyridine insoluble (PI) fractions. Despite the fact that they were part of the whole solute in the original extract, the PI fractions from all coals were only partially soluble in the mixed solvent. Combination of the AS and PS, which are lighter fractions than the PI, from the parent coal with the respective PI fraction greatly enhanced the solubility of PI in the mixed solvent. In addition, the solubility in mixed solvent of the PI fraction from Zao Zhuang coal was increased by addition of AS and PS fractions from Miike, Shin-Yubari, and Illinois No. 6 coals; the amount of enhanced solubility in comparison with the solubility of PI alone depended on the coal fraction used, i.e. AS and PS. In general, the enhancement caused by PS fractions was greater than that by AS fractions. The mechanism of solubility enhancement of the heavy constituent (PI fraction) by the addition of lighter constituents (AS and/or PS) is discussed, from the viewpoint of differences in the chemical structures of the constituents, i.e. AS, PS and PI fractions.

Effect of maceral composition on the extraction of bituminous coals with carbon disulphide-N-methyl-2-pyrrolidinone mixed solvent at room temperature

The residues obtained from the extraction with carbon disulphide-N-methyl-2-pyrrolidinone mixed solvent at room temperature were optically examined and their maceral composition was determined. At low extraction yields, below 30 wt% (daf), a significant amount of semifusinite and pseudovitrinite were extracted. The solvents penetrated the vitrinite particles, softening and extracting them. Pseudovitrinite, an intermediate component between vitrinite and semifusinite, was fragmented like the vitrinite by the penetration of the solvents. Semifusinite was also fragmented and extracted. Fusinite, macrinite, and micrinite were hardly extracted with the mixed solvent. Above 50 wt% (daf) extraction yield, vitrinite was preferentially extracted, but even at 74.1 wt% (daf) extraction yield, some vitrinite components remained in the residue.

Temperature-variable dynamic viscoelastic measurements for coal blends of coking coal with slightly coking coal

Thermoplasticity for coal blends of Goonyella high-coking coal and Witbank slightly coking coal was evaluated by dynamic viscoelastic technique using a temperature-variable rheometer. As the weight ratio of Witbank coal in the blend increases, the thermoplasticity at a heating rate of 3 °C/min apparently decreased, compared to that for Goonyella coking coal alone. In the case of 30 wt.% Witbank coal, it still showed a sufficient thermoplasticity to form coke. In contrast, for the 50:50 blend, its thermoplasticity significantly decreased and was almost the same as Witbank coal alone, indicating that Witbank coal has any negative effect for thermoplasticity of the blends with Goonyella coal. However, when the 50:50 blend was rapidly heated (80 °C/min), the thermoplasticity was found to be enhanced greatly, compared to calculated one. Therefore, rapid heating is suggested to be effective to convert such blends into good coke, and this measurement technique was found to be useful to evaluate thermoplasticity of coals and blends under rapid heating as well as slow heating. The dependence of heating rate on thermoplasticity of coking coal was also investigated. As the heating rate increased, the maximum fluidity greatly increased and its temperature shifted to a higher value, while no significant changes in softening temperatures were observed.

Molecular simulation of relaxation behaviors of coal-aggregated structures

Abstract Upper Freeport coal (Argonne Premium Coal Sample, APCS 1) was extracted and fractionated with a carbon disulfide/ N -methyl-2-pyrrolidinone mixed solvent, acetone and pyridine at room temperature, and three extract fractions were obtained: acetone-soluble (AS), acetone-insoluble–pyridine-soluble (PS) and pyridine-insoluble (PI) fractions. A molecular dynamics (MD) computer simulation method was used to study the structural relaxation behaviors of the fractions during heating. The calculation was carried out at 373–773 K in order to see changes in various properties by heat. For the PS and PI fractions, the temperature at which the average volume of unit cell discontinuously changed was observed. The DSC thermograms of PS and PI showed a reversible endothermic peak at 610–710 and 650–710 K, respectively, corresponding to the temperature ranges in which the structural relaxation was estimated by the simulation. The simulation suggests that the endothermic peak is the result of physical relaxation of the aggregated structures through dissociation of nonbonded interactions.