Production of Heavy Oils with High Caloric Values by Direct Liquefaction of Woody Biomass in Sub/Near-critical Water

TLDR

Direct liquefaction of Jack pine sawdust in sub/near‑critical water (280–380 °C) was performed with and without alkaline‑earth or iron‑based catalysts. The process produced heavy oils with 30–35 MJ/kg and water‑soluble oils with 19–25 MJ/kg, with maximum yields (up to 45 % heavy oil and 65 % total oil) achieved at 280–340 °C; alkaline‑earth and iron catalysts improved heavy‑oil production while promoting gas and water at higher temperatures, and GC/MS analysis revealed the oils are rich in carboxylic acids, phenolics, and long‑chain alkanes.

Abstract

Direct liquefaction of a woody biomass (Jack pine sawdust) in sub/near-critical water without and with catalysts (alkaline earth and iron ions) has been investigated at temperatures of 280–380 °C. Heavy oils with a high caloric value of 30–35 MJ/kg (much greater than that of the crude wood sample used) were obtained, along with water soluble oils with a caloric value of 19–25 MJ/kg. The yields of heavy oil and total oil products tended to maximize in the temperature range of 280–340 °C for all the liquefaction operations regardless of the presence of a catalyst or the type of catalyst. All the catalysts tested, i.e., Ca(OH)2, Ba(OH)2, and FeSO4, were found effective for enhancing the formation of heavy oil products at 280–340 °C, while they significantly promoted the formation of gas and water at >340 °C. The yield of heavy oil in the operation at 300 °C for 30 min was improved significantly from around 30% without catalyst to greater than 45% by Ba(OH)2. The maximum yield of total oil products reached 51% in the operation without catalyst, while it increased to about 65% with Ca(OH)2 at 300 °C. The GC/MS measurements for the heavy oil products revealed that the oils contain mainly carboxylic acids, phenolic compounds and derivatives, and long-chain alkanes.