Ronald Liotta

Oxidative weathering of Illinois No.6 coal

The exposure of freshly-mined Illinois No.6 bituminous coal (Monterey Mine No.1) to atmospheric oxygen at ambient conditions resulted in a slow oxidation reaction which appeared to be complete within two months to produce an oxidized coal product with ≈26% more organically bound oxygen than the fresh coal. An oxygen functional group analysis was performed to determine the carboxylic acid, hydroxyl and ether group content of the coal before, during and after the reaction. Infrared analysis showed no carbonyl production; however, ether functionality was being produced. O-methylation reactions which employed isotopically labelled methyl groups (both C-13 and deuterium) were used to identify and quantify O-H and CO2H sites in the weathering coal samples. It was found that these acidic groups were not the products of oxidative weathering. Essentially all of the chemically incorporated oxygen eventually formed ether linkages. In a related study on this coal, hydroperoxide was detected as a transient intermediate in the early stages of the oxidation. A mechanism is proposed which involves the simultaneous formation under mild temperatures of a hydroperoxide and a carbon radical that undergoes a radical displacement producing the ether product directly. Solvent swelling studies revealed that these ethers act as cross-linking agents in the coal structure. The more highly cross-linked coal structure that resulted from weathering was responsible for the destruction of the plastic properties of this bituminous coal.

Selective alkylation of acidic hydroxyl groups in coal

Abstract The organic molecules which make up coal are held together not only by covalent bonds, but also by a substantial network of hydrogen bonds as well as certain other weak intermolecular associations, which together are called the secondary structure. It is believed that acidic hydroxyl groups are responsible for most of the secondary structure. These attractive forces have been diminished traditionally by solvent swelling the coal, then permanently removed by selective silylation or acetylation of the polar functionalities. A new selective alkylation procedure has been developed which converts polar hydroxyls into relatively non-polar ethers and esters, and has been successfully tested on a bituminous and sub-bituminous coal. This selective O-alkylation proceeds rapidly under very mild conditions and renders the coal essentially free from its secondary structure.

Coal Science: Basic Research Opportunities

More fundamental knowledge of coal (knowledge of its structure and its behavior during conversion processes) is essential before we can generate new technologies necessary for the efficient use of coal in the future. Herein are suggested specific basic research opportunities in the areas of coal characterization, gasification, combustion, and liquefaction, along with an assessment of the impact such research programs could have. Critical characterization needs include qualitative and quantitative determination of the chemical forms of carbon, oxygen, nitrogen, and sulfur and reliable methods for the measurement of surface area, pore volume, and weight-average molecular weights. Mechanistic studies aimed at increasing understanding of the thermal breakdown of the functionalities in coal, the behavior of coal in the presence of molecular and donor hydrogen environments, and carbon gasification and hydrocarbon synthesis reactions starting from carbon monoxide and hydrogen will lay the scientific foundation for the development of new processes for converting coal into clean usable fuels and chemicals.

Caustic oxidation as a pretreatment to high pressure bituminous coal gasification

Abstract Illinois No. 6 bituminous coal, which had been pretreated with potassium hydroxide, could not be efficiently gasified at the high pressure of 3.5 MPa in a fluidized-bed gasifier. The same feedstock performed well at a much lower operating pressure. However, at the high pressure the pyrolysed coal swelled significantly. The resulting low bed density produced a small carbon inventory in the gasifier. In addition, the coal char was very friable and large quantities of fine particulate material were entrained by the product gas. To prevent the swelling the coal was initially oxidized. A way was discovered to selectively convert the coal bitumen to humic acid, a substance that is rich in carboxylic acid groups. A direct correlation was found between the humic acids carboxylate content and the swelling characteristics of the pyrolysed coal. The char bulk density was greatest when the humate carboxylic acid group content was maximized. It appears that when the coal was fed to the hot gasifier, these carboxylic acids decarboxylated and produced radical centres. The crosslinks that resulted from these radicals formed relatively stable carbon-carbon bridges, and this was sufficient to prevent the pyrolytic swelling.