Filtration in coal liquefaction.: 2. Relation between digestion conditions and filtration rate

In systems for the liquefaction of coal by solvent extraction, removal of the undissolved solids from the liquefaction products is a fundemental part of the process. For separation of solids by filtration to be economically viable, it is essential to achieve high filtration rates. The influence of the extraction conditions, temperature, residence time and coal feed size, on the rate of filtration has been investigated. It has been shown that the rate of filtration is sensitive to the presence of a gel-like intermediate formed during the dissolution of the coal. The formation of this intermediate imposes limitations on the choice of digestion conditions, in particular the coal feed size. However, by inducing polymerization, the gel can be stabilized, thus allowing significantly improved filtration rates to be achieved.