Two-Stage Conversion of Low-Rank Coal or Biomass into Liquid Fuel under Mild Conditions

Abstract

The authors have recently proposed a novel degradative solvent extraction method that upgrades and fractionates various types of low-rank coals or biomass wastes into several different molecular weight fractions at around 350 °C. The lowest molecular weight fraction that was recovered as solid (termed soluble) by the yield of 19.4–71.7 wt % on a carbon basis had unique and almost raw-material-independent properties: almost free from ash and moisture, average molecular weight of around 300, carbon content of as high as 81.5–84.8 wt %, and oxygen content of as low as 6.5–12.1 wt %. In this work, the combination of the proposed extraction method and the liquefaction of the soluble under mild conditions was investigated as a two-stage liquefaction method to produce liquid fuel. A rice straw (RS) and a brown coal (LY) were extracted by the proposed extraction method to produce solubles by the yields of 31.5 and 21.7 wt %, respectively. The solubles produced were then liquefied at 400 °C using FeOOH/sulfur as t...