The Effect of Reagent Access on the Reactivity of Coals

The aim of the present report is to measure the diffusion coefficients at temperatures about 20-27 °C, the activation energies of diffusion, and to determine the type of transport mechanism of diffusion of pyridine in macromolecular structure of Turkish Elbistan lignite (C: 53.0 wt %, dmmf). The raw coal sample was demineralized with HCl and HF by standard methods. The raw and demineralized coal samples were extracted with pyridine. Pyridine uptake of the coal samples was recorded at temperatures 20-27 °C in an adiabatic setup until a constant weight was attained. The extent of swelling of original and treated coal samples in pyridine were measured. Pyridine extraction created a fraction of enlarged particle size due to irreversible solvent swelling. The diffusion coefficients were measured from the slope of graphs of M t /M ∞ versus t 1/2 . The diffusion of pyridine in the raw coal seemed to be less, compared to those of the treated coal samples. Extraction of the raw coal with pyridine extended the pyridine diffusion in the coal very little. The formation of new carboxylic acid groups in acid-washed samples enhanced diffusion of pyridine. In all of the samples the diffusion constants increased linearly with an increase in the temperature. The greater diffusion coefficients are encountered with the coal samples which swelled more in pyridine. It seemed that the diffusion coefficients increased with swelling and acid washings as a result of structural variations decreasing the activation energy of diffusion of the solvent to the coal. The transport mechanism of pyridine in the macromolecular coal network of Elbistan lignite was not relaxation controlled. The diffusion of pyridine in the low rank Elbistan lignite obeyed generally Fickian mechanism or an intermediate case of Fickian-anomalous mechanism.

Section: Introductionmentioning

confidence: 99%

Diffusion of Solvents in Coals: 1. Measurement of Diffusion Coefficients of Pyridine in Elbistan Lignite

Seferinoğlu

Yürüm

2000

“…In addition, it was found that the retention times for probes in ILC are similar to those found for IGC of coal surfaces . If the injected probes are interacting with bulk coal forces then it is expected that the retention times for diffusion of probes into the glassy coal would be extremely long …”

Section: Introductionmentioning

confidence: 70%

Surface Thermodynamics for Polar Adsorbates on Wyodak Coals

Glass

Wenger

1998

Adsorption enthalpies have been measured for polar molecules interacting with Wyodak coal. All of the polar adsorbates studied, including organic bases and 1-propanol, interact more strongly than predicted based on a model that includes van der Waals forces only. After the van der Waals component is subtracted from the total adsorption heat, the specific adsorption heat for each polar molecule on Wyodak coal is ∼1-4 kcal/mol more exothermic than its value on Illinois No. 6 coal. On alkylated Wyodak coal, the adsorption heats for organic bases are ∼1-3 kcal/mol as well. The adsorption heats for organic bases on alkylated Wyodak coal decrease in exothermicity by g5.0 kcal/mol, an amount that is similar to the specific hydrogen-bond interaction for each base with Illinois No. 6 coal. In contrast, 1-propanol's adsorption heat decreases by only ∼2 kcal/mol after alkylating the coal and 1-propanol's specific adsorption heat on alkylated Wyodak coal (6.8 kcal/mol) is the same as its specific adsorption heat on Illinois No. 6 coal. These results demonstrate that in addition to the van der Waals force, polar molecules experience two other forces on Wyodak coal, a ∼1-3 kcal/mol nonspecific dipole-induced dipole force and a g5.0 kcal/mol specific hydrogen-bond force. Organic bases lose their hydrogen-bond force but retain their nonspecific dipole-induced dipole force while 1-propanol loses its dipole-induced dipole force but retains its specific hydrogen-bond force after alkylating Wyodak coal. This interpretation of the data sugests that different modes exist on Wyodak coal for hydrogen bonding to 1-propanol than for hydrogen bonding to organic bases.

“…The rates of many reactions of coals are limited by the rate of diffusion of a reacting molecule into the coal . To understand reactions of coals and especially to design methods for carrying out coal reactions it is necessary to know the limitations that limited diffusion places on reactions of coals.…”

Section: Introductionmentioning

confidence: 99%

Steric Effects on Diffusion into Bituminous Coals

Larsen

Lee

2005

Self Cite

The reactions of maleic anhydride, cis-maleate esters, and acetylenedicarboxylate esters with Pittsburgh No. 8 or Illinois No. 6 coal using o-xylene or o-dichlorobenzene solvent are diffusion controlled. Diffusion is Fickian in all cases. The measured activation energies are between 5.4 and 7.6 kcal/mol. Diffusion rates decrease slowly with increasing alkyl chain length and sharply with branching. Diffusion rates are slightly faster with o-xylene than when o-dichlorobenzene is used.