Transport of Penetrants in the Macromolecular Structure of Coals Ii. Effect of Porous Structure on Pyridine Transport Mechanisms

Barr-Howell, Barbara D.; Peppas, Nikolaos A.; Winslow, Douglas N.

doi:10.1080/00986448608911338

Cited by 18 publications

(9 citation statements)

References 8 publications

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“…Often, there has been interest in diffusing organic solvents into coal, as in direct liquefaction or as part of some pretreatment step. As a result, over the past decade there have been a number of studies of the factors that influence diffusion in solid coals. − The cited studies have been mostly concerned with transport of organic solvents. Others have been concerned with the transport of gases, such as methane, but these are not considered here.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Solvent Swelling and Diffusion Processes in Coals

Otake

Suuberg

1997

Energy Fuels

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The rates of solvent swelling of the Argonne Premium Sample coals have been measured in various organic solvents at various temperatures. The results show that the extents of swelling, when experiments are carried out in liquid solvents, are independent of the temperature, within the temperature range studied here (10−60 °C). Thermodynamically, this requires that equilibrium swelling should occur with a near-zero enthalpy, as generally required for absence of a temperature effect on equilibrium. This conclusion is consistent with a number of other recently published results. The rates of swelling of the coals do not correlate with rank. The nature of the swelling process varies from relaxation controlled to Fickian diffusion controlled. The activation energies for the kinetics of swelling are consistent with other recently published values, but again, a correlation with rank could not be substantiated. The activation energies all fall in the range from 20 to 60 kJ/mol, suggesting that the activation barrier may be associated with the breakage of internal electron donor−acceptor (e.g., hydrogen bonding) interactions. Thermal pretreatment of some of the coals to 350 °C had significant effects on their swelling behaviors. The effect was generally to increase the rate of swelling, and in some cases, the extent of swelling. The activation energies for swelling were, however, unaffected. This is interpreted as consistent with the hypothesis that the activation energy barrier is determined by donor−acceptor interactions which are unaffected by pretreatment but that other thermally dissociable coal−coal interactions may serve to stiffen its structure.

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Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Solvent Swelling and Diffusion Processes in Coals

Otake

Suuberg

1997

Energy Fuels

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“…Diffusion limitations are of concern virtually in all aspects of coal utilization. Over the past decade there have been numerous studies about the factors that influence diffusion. − These studies have been mostly concerned with the transport of solvent through coals based on the packed-bed measurements. The diffusion of solvent into coals, which governs their swelling, has been noted by all workers to be highly non-Fickian in nature.…”

Section: Resultsmentioning

confidence: 99%

“…Qualitative studies have been published by Shibaoka et al and Brenner. , Quantitative studies have been also reported by Larsen and Lee, who investigated the effect of solvent-swelling on diffusion rates in two kinds of bituminous coals and found that the rate of diffusion of maleic anhydride into the coals was independent of the degree of swelling of the coals. Dynamic penetrant transport in coal particles, chunks, or thin sections has been performed using pyridine and a number of amines. − Some effort has been directed toward elucidation of the mechanism of vapor or liquid transport in the macromolecular structure of coal.…”

Section: Introductionmentioning

confidence: 99%

Statistical Distribution Characteristics of Pyridine Transport in Coal Particles and a Series of New Phenomenological Models for Overshoot and Nonovershoot Solvent Swelling of Coal Particles

et al. 1999

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In this study, the solvent-swelling processes of coal particles of Zao Zhuang coal and Taiheiyo coal were investigated using a novel orthogonal microscopy image analysis technique proposed recently by our laboratory. The overshoot swelling and slow-climbing swelling are characteristic of Zao Zhuang coal and Taiheiyo coal particles in pyridine at ambient temperature, respectively. Super-Case II diffusion is dominant in Zao Zhuang coal particles and anomalous diffusion in Taiheiyo coal. The present study shows that the slow-climbing-type solvent-swelling processes of Taiheiyo coal particles can be described using the semiempirical model proposed by Ritger and Peppas. However, overall solvent-swelling processes with an overshoot feature in many coals could not be simulated well by the model. In addition, we observed that both the diffusion mechanism exponent n and proportionality constant k in the model for the two coals have characteristic statistical distributions. The distributions of n and k for Zao Zhuang coal are normal, and those of Taiheiyo coal are doubly exponential. On the basis of these observations, the connotation of the parameters, k and n, in the Ritger and Peppas model was expanded in view of a statistical distribution. On the other hand, based on the analysis of swelling features of Zao Zhuang coal particles in pyridine at ambient temperature, a series of new phenomenological models, a second-order system with a unit-step forcing function in nature, was used to describe the solvent-swelling processes of Zao Zhuang coal particles with or without overshoot features. The simulated overall processes of the coal particles using the new models agree very well with the measured ones and suggest that the viscoelastic properties of pyridine-dilated Zao Zhuang coal, the main features of solvent-swelling and/or solvent transport of the coal particles, can be well characterized by second-order system with the denominator τ2 s 2 + 2ζτs + 1 and a unit-step forcing function (1/s).

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“…(I), where the transport mechanism deviates from Fickian diffusion to anomalous transport as the carbon content increases. The magnitude for the relaxation times fall down to 8.5 x 10-7 s-t. Ritger and Peppas (1987a) found relaxation constants between 0.5 x 10-5 and 3 x 10-5 s-t for the diffusion of high activity pyridine vapors into PSOC coals, and Barr-Howell et al (1986) found relaxation constants between 24.0 x 10-5 and 3.4 x 10-6 S-I for the diffusion of pyridine vapors (penetrant activity 0.04-0.20) into coals. The characteristic relaxation time is the reciprocal of these values and it is of the order of 10 6 s. Swelling studies as a function of carbon content in coals treated thermally at 35°C, showed that the initial diffusion rates and the equilibrium uptakes of pyridine, DMF and chloroform into PSOC coals increase with the average molecular weight between crossJinks.…”

Section: Determination Of Penetrant Diffusion Coefficients and Relaxamentioning

confidence: 99%

“…The molecular weight between crosslinks in coal as a function of carbon content was previously investigated by Lucht (1983) and Barr-Howell et al (1986). They used a modified Gaussian network equation to analyze their swelling studies and to determine values for the average molecular weight between crosslinks, Me> the number of repeating units between crosslinks, and the average molecular weight of the repeating unit.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Temperature Treatment on Penetrant Transport in Coal

Olivares

Peppas

1992

Chemical Engineering Communications

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The macromolecular structure of coals thermally treated at 35"C, lOO"C and 150"Cwas investigated by dynamic penetrant transport in thin coal sections. The effects of temperalure, carbon content in coal, and penetrant type on the transport mechanism were investigated. Dynamic swelling studies showed that penetrant transport into coal is a function of the average molecular weight between crosslinks, Me-The penetrant transport mechanism at low activity IS Fickian diffusion. The transport mechanismdeviates from Fickian diffusion to anomalous transport, when the carbon content in coal and penetrant activity increase. Variations of the diffusion coefficients and relaxation constants were determined using a diffusion/relaxation coupled model.

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Transport of Penetrants in the Macromolecular Structure of Coals Ii. Effect of Porous Structure on Pyridine Transport Mechanisms

Cited by 18 publications

References 8 publications

Temperature Dependence of Solvent Swelling and Diffusion Processes in Coals

Temperature Dependence of Solvent Swelling and Diffusion Processes in Coals

Statistical Distribution Characteristics of Pyridine Transport in Coal Particles and a Series of New Phenomenological Models for Overshoot and Nonovershoot Solvent Swelling of Coal Particles

The Effect of Temperature Treatment on Penetrant Transport in Coal

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