Upgrading of low-rank coal and biomass utilizing mild solvent treatment at around 350°C

The authors have been proposing methods to dewater, and fractionate coal by using the sequential thermal solvent extraction. They have recently showed that the degradative extraction at around 350°C using a non-polar solvent such as 1-methylnaphthalene under 10 MPa is effective to recover several fractions having similar chemical and physical properties from a wide range of low-rank coals. In this paper the applicability of the method to much lower grade carbonaceous resources is examined. Two biomasses, cellulose, lignite, a peat and four low rank coals, and mixed samples of biomass and two coals were treated by 1-methylnaphthalene at 350°C to upgrade and to fractionate the raw materials into several fractions having similar chemical and physical properties. The extracted fractions, Solubles and Deposits, were very close to each other in elemental composition, chemical structure, molecular weight distribution, pyrolysis behavior, and softening/melting behavior. Thus, the proposed degradative solvent extraction method was found to be effective to convert low grade carbonaceous resources into solid fuels having higher heating values and significantly upgraded compounds having similar chemical and physical properties.