Effect of acetone as a solvent and supercritical CO2 extraction on liquid products from near-critical liquefaction of pinewood

Abstract

Biomass conversion to biocrude and further to biofuels has potential to alleviate U.S. energy dependency while making use of existing and robust liquid carbonaceous fuels infrastructure. One proposed method for biomass conversion is the Near-critical Integrated Liquefaction Extraction (NILE) using supercritical CO₂ (ScCO₂). The process aims to improve biocrude properties than other traditional processes while also reducing energy consumption by utilization of ScCO₂. Acetone can theoretically be used in conjunction with the NILE process as a solvent or co-solvent with supercritical CO₂. This investigation attempted to understand the impact of acetone addition to improve liquid yields from the biomass conversion process with specific emphasis on the suitability of acetone to act as a solvent or co-solvent along with the effectiveness of ScCO₂ extraction as a liquid yield recovery method towards direct separation of better quality biocrude. Liquefaction of pinewood was carried out in the presence of acetone at a 2:1 solvent to biomass mass ratio, at 300 °C for a total heating time of 45 min. The results showed that acetone increased the liquid yields, and it may be due to the result of acetone reacting rather than acting as a solvent. Additionally, the presence of solvents was found to play a critical role in determining the composition of the liquid. ScCO₂ extraction of biocrude directly from liquefaction product slurry was demonstrated along with recycled CO₂ operation. Compared to conventional acetone extraction, ScCO₂ extraction at 330 bar and 100 °C was found to dewater the biocrude by almost half, lower (almost half) the phenolic acid number (PhAN), along with increased H/C ratio of the extracted biocrude.