The chemistry of the alkali-induced solubilisation of coal

by Shoko, Lay.

This thesis outlines a study carried out to understand the effects of coal dissolution variables. Several parameters that are thought to have a direct influence on the degree of coal dissolution in organic solvents were investigated by means of a series of experiments. The work done constitutes part of the research being carried out for the PBMR Company, whose aim is to synthesise nuclear-grade graphite from coal-based materials. To enhance the efficiency of the process, it was necessary to gain a clear-cut understanding of the parameters that affect the process. The work carried in this project was divided into two sections. The first section involved the solubilisation of coal in polar aprotic organic solvents with the addition of a small amount of alkali. In this section as well, many parameters that influence the process were investigated. The second section involved the use of various analytical techniques to obtain information on the composition of coal extracts. The conclusions reached were as follows: • An alkali is required for the solubilisation of coal to occur in polar organic solvents. This also gives an overall high extraction percentage of ~ 92%. • In pure dimethylformamide (DMF), the sodium hyroxide (NaOH) does not go into solution but on the addition of coal, the NaOH goes into solution. iii University of Pretoria etd, Shoko L (2006) • The characteristic smell of the Refcoal solution confirms the presence of dimethylamine, although the titration results show otherwise. • The texture of the alkali used in the extraction affects the rate and degree of extraction. Finely ground alkali gives a faster dissolution rate, as well as a high extraction percentage. • • There is no hydrolysis of solvent during the extraction of coal. The concentration of the alkali used in the extraction process affects the degree to which coal can be extracted. • The use of a strong alkali increases the rate at which coal can be dissolved in the solvent. • Temperature does not affect the degree of extraction, as shown by the closeness of the extractions done at different temperatures. Also, external factors, such as oxidation and weathering of coal, have little effect on the extent of extraction. • Coal characterization techniques provide information about the composition of coal extracts. The coals used in this process consisted of aliphatic and aromatic compounds. iv University of Pretoria etd, Shoko L (2006)