Influence of donor amount in the hydrogen-transfer liquefaction of Australian brown coal

Effects of tetrahydrofluoranthene (4HFL) concentration on the product composition in the liquefaction of an Australian brown coal at 450 °C were studied, using a coal-solvent weight ratio of 1:3 under low nitrogen pressure to optimize the conditions. Pure 4HFL solvent liquefied the coal very rapidly, a longer reaction time markedly increasing the yield of gaseous product as well as the total yield of oil and asphaltenes. Although a reduction in the 4HFL content of the solvent reduced the rates of liquefaction for both gas and liquid products, 4HFL contents of 75 and 50 mol% provided more favourable product compositions (high yield, > 80% of oil plus asphaltenes and low yields of preasphaltenes and gaseous products). In liquefaction of the deashed coal with 75 % 4HFL, the product composition was further improved by using a shorter reaction time. Several roles of donors in the liquefaction process are proposed to explain the product composition and rate of liquefaction.