Energy & Fuels, Vol.19, No.1, 200-207, 2005
Comparison of temperature conditions in direct liquefaction of selected low-rank coals
The direct liquefaction of one lignitic and two subbituminous coals was studied in laboratory-scale microautoclave reactors. The principal focus of this work was to investigate the effects of three strategies for employing temperature: single-staged liquefaction at one temperature; temperature-staged liquefaction involving rapid heat-up between low- and high-temperature reaction stages; and temperature-programmed liquefaction, with slow heat-up between stages. Both the temperature-staged and temperature-programmed conditions are advantageous relative to the single-staged reaction, particularly for coals that are less easily converted. The benefits of using temperature-staging or programming appear to derive from both physical and chemical processes related to the catalyst and solvent, such as allowing more time for the catalyst precursor to transform into an active form and enhancing solvent-coal interactions. For a highly reactive coal, single-stage conditions appear to be sufficient. In single-stage reactions without solvent or catalyst, or with nonreactive solvent, the conversion of these three coals is related to their organic sulfur content.