The Nature of the Aggregated Structure of Upper Freeport Coal

Abstract

Data for the sorption and interaction of alcohols with the coal suggested Upper Freeport coal has a large number of micropores into which relatively bulky reagents could diffuse only marginally; micropores may be molecular voids in the aggregated. The irreversible structural relaxation observed on differential scanning calorimeter (DSC) thermograms at 350 °C is probably very similar in nature to that caused by extraction with highly efficient mixed solvents such as carbon disulfide/N-methyl pyrrolidinone (CS 2 /NMP). Upper Freeport coal must be greatly relaxed (swollen) before solvents have access. A molecular dynamics simulation of relaxation at several temperatures was carried out on a model structure for the aggregated coal. A large change in the volume of the model structure was found between 350 °C and 400 °C, the region in which the irreversible peak was observed in the DSC thermograms. Moreover, in agreement with the experimental results, the structural changes caused by "heating" in the simulation were not reversible. These results suggested that irreversible structural relaxation caused by heating is the result of thermal stabilization of the strained structure of the raw coal.

The role of volatiles and coal structural variation in coal methane adsorption

“…7b). The newly created pore spaces become the physical diffusion sites that contribute to the enhancement of methane adsorption capacity [30,31]. This is consistent with data from Bae et al [23], who indicated that volatiles produce energy barriers that prevent adsorbed molecules from passing through the pores.…”

“…The alignment of these structures generates the coal's aggregate, crystal structure. The aggregation states reflect the stability of the carbonaceous coal matrix [30,31]. Chemically, coal consists of three-dimensional, cross-linked macromolecule networks [32].…”

“…The aggregated coal structure has been investigated using chemical methods. Takanohashi et al [30,31] prepared coal samples with different aggregation states by extracting Argonne premium coal with a solvent composed of carbon disulfide, N-methyl-2-pyrrolidinone (CS 2 -NMP), acetone, and pyridine. They found that the adsorption capacity of the solvent-extracted coal was enhanced due to newly developed pores in these less aggregated structures.…”

Development of Continuous Solvent Extraction Processes for Coal Derived Carbon Products

“…Research by Takanohashi differed in that it concluded coal was a large aggregate, and Takanohashi proposed different mechanisms for describing coal dissolution. 26 Thus, Takanohashi's research suggested that coal is solubilized without breaking covalent bonds.…”

The dissolution and swelling of bituminous coal in N-methyl-pyrrolidone

“…Research by Takanohasi differed in that it concluded coal was a large aggregate, and Takaanohashi proposed different mechanisms for describing coal dissolution 14 . Takanohashi's research suggested that coal is solubilized without breaking covalent bonds16 .The most common model of solvent extraction treated extraction in terms of the electron donor and acceptor interactions in the solvent coal system24 . This model assumed that donor-acceptor bonds in coal were responsible for binding together the macromolecular network and the extractable carbonaceous materials that filled the pores of the network24 .…”