THE FILTRATION OF COAL SOLUTIONS

Special Research Report SR-26 The object of this work was to find conditions for the efficient filtration of the undissolved matter resulting from the dispersion of coal in coal tar oils, for the purpose of obtaining a homogeneous coal solution which might be useful, especially in the field of coal hydrogenation. Filtrations of solutions of coal in various solvents were carried out under a variety of conditions. The results showed that the pre-filtration temperature and time of heating of the solutions, and their amount and concentration, had a bearing on the manner in which the solution filtered. Filtration also depended on the filter aid and the manner in which it was used. The best filtrations were achieved by stirring a diatomaceous earth into the coal solution prior to filtration th•rough a fiber-glass cloth. The data indicated that in a 10 per cent mixture of coal in topped creosote oil, 86 per cent of the coal was dispereed at 400°C., and could be efficiently filtered. The filtrate showed a 95 per cent removal of the mineral matter of the coal. It was also found that pressurization aided filtration, if the pressure was not so great that it compressed the filter cake, thus slowing filtration. Also, there was an intermediate temperature which gave the best filtration. This temperature was one at which the solution was neither too viscous due to low temperature, nor too viscous due to the longer heating time necessary to attain a higher temperature.