| Modelling of solvent extraction was studied using 1,2,3,4--tetrahydronaphtalene (tetralin) and Poplar coal (lignite). A kinetic model was developed taking into account temperature, mass transfer limitations and dominating events (physical or chemical) during coal liquefaction. It was found there is no influence of coal particle size (53 -- 1000mum) and coal to solvent ratio (1:2 -- 1:8) on the extraction yield. After 15 minutes or longer extraction time, two regions were identified, physical and chemical dissolution. The physical dissolution is dominant at low temperatures and chemical dissolution is dominant at high temperatures.;Physical and chemical dissolution were modelled using separate terms. The term for physical dissolution employed a limiting concentration and was of the form Cs--physical(1 -- e-kpt ). The term for chemical dissolution also included a limiting concentration and was of the form (Cs--reactive -- Cs--physical )(1 -- e-krt ). The description of chemical dissolution was further refined to predict the coal soluble, coal insoluble and light fraction. |
