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 the catalyst under the H2 pressure of as low as 2.0 MPa (at room temperature). Then, 62.1 wt % of RS soluble and 56.8 wt % of LY soluble were converted to the liquid fraction (oil), excluding H2O. The oxygen contents of the oils produced from the two-stage liquefactions of RS and LY were as low as 2.2 and 3.9 wt %, respectively, much lower than those from the direct liquefaction of the raw materials (single-stage liquefaction). Furthermore, both the amount of CO2 emitted and the amount of H2 consumed during the two-stage liquefaction were much less than those of the single-stage liquefaction. Thus, it was shown that combining the degradative solvent extraction method and the liquefaction of the soluble is a promising method to produce high-quality liquid fuel from low-rank coals and/or biomass wastes.

Preparation of activated carbon nanofibers using degradative solvent extraction products obtained from low-rank coal and their utilization in supercapacitors

“…Moreover, Soluble can be used for producing high-quality liquid fuels. 25 Residues have better performance in combustion and gasication 26,27 and are a precursor for activated carbon preparation. 28 High ash contents in carbon nanobers lead to leakage current and self-discharge and have a bad inuence on the cycling performance.…”

Direct liquefaction techniques on lignite coal: A review

“…Lignite together with renewable biomasses such as oils, lipids, and lignin is a promising bio-resource for generating fuel and chemicals via pyrolysis and liquefaction [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Lignite can produce a high number of liquefied products via direct liquefaction [13].…”

“…Lignite can produce a high number of liquefied products via direct liquefaction [13]. The enormous reserves of lignite coals can be converted into transportation fuel via the direct liquefaction process of coal to overcome the deficiency of petroleum oil [14]. Thus, the macromolecular structure of lignite can be decomposed effectively into relatively small molecular-weight liquid compounds by applying the catalytic liquefaction process in the presence of catalysts that can increase the yield of the low molecular-weight fractions [15].…”

“…Pre-treatment by various methods has been found to be beneficial. The degradative solvent extraction method can be employed to upgrade various types of low-ranking coal, including lignite [14], while thermal degradation of lignite at a high temperature can produce various organic products [21b]. Briefly, we summarized related review papers in Table 1 to obtain more knowledge on lignite and coal, their structures, pyrolysis, gasification, drying, distributions, liquefaction, etc.…”

Liquefaction of lignite with a Ru/C catalyst in supercritical ethanol

“…However, high moisture content materials such as microalgae and lignite pose challenges for direct liquefaction. [3][4][5] A feedstock drying procedure is commonly required, which increases cost dramatically.…”