Production of Biocrude from Biomass by Acidic Subcritical Water Followed by Alkaline Supercritical Water Two-Step Liquefaction

Increased demand in transportation fuels, environmental concerns, and depletion of fossil fuels require the development of efficient conversion technologies for second-generation biofuels. The main objective of this work is to efficiently liquefy biomass into energy-dense biocrude. A novel two-step process is proposed in which acidic subcritical water followed by alkaline supercritical water media are utilized for the liquefaction. The concept is tested with switchgrass. The first step is carried out at 200 degrees C in acidic subcritical water to liquefy hemicelluloses to biocrude while avoiding the repolymerization reactions that would otherwise produce char. In the second step, the remaining unliquefied biomass (biomass-H) is subjected to supercritical water at 380 degrees C with Ca(OH)(2) as catalyst for minimizing the formation of char, enhancing lignin solubilization and therefore increasing liquefaction of the remaining polysaccharides toward biocrude. The proposed two-step liquefaction produces a significantly higher amount of biocrude, as compared to the traditional one-step process. The yield of biocrude from the proposed process is 40% on mass basis and 67% on energy basis of the feedstock biomass.