Author: Josh Schmidt
Date/Time: November 24th, 2025 at 10am EST
Location: EGR-2162
Committee Members:
- Dr. Ashwani Gupta, Chair
- Dr. Peter Sandborn
- Dr. Bao Yang
Title of Thesis: Combined Liquefaction and Extraction of Biocrude Using Supercritical Carbon Dioxide
Abstract: The reliance on finite petroleum reserves, coupled with ever-increasing global energy demands, necessitates a concerted effort to develop sustainable liquid fuels. Given the inherent energy density advantage of liquid hydrocarbons, combustion engines will remain integral to the transportation sector for decades. This underscores the importance of advancing research into the liquefaction and extraction of biocrude from renewable feedstocks. However, scaling existing thermochemical processes is hampered by significant challenges concerning product separation, solvent recovery, and overall economic viability. This thesis seeks to address these issues by investigating the innovative application of supercritical carbon dioxide (sCO2) in a combined liquefaction and extraction system utilizing pinewood, an abundant lignocellulosic biomass resource. The experimental work utilized a novel integrated system for process intensification operated in the ranges of 250–350 °C and 200-300 bar. Feeding biomass between vessels at high-pressure was investigated using a mechanical feeder. It was found that the combined process is limited by the extraction reaction, therefore rapid parameter screening was done via batch reactor setups. Critical process parameters investigated included temperature, CO2 density, co-solvent, residence time, and the biomass-to-CO2 ratio. Representative biocrude samples were analyzed using Gas Chromatography-Mass Spectrometry (GCMS). The analysis focused on identifying the presence and relative ratios of various detectable product species, including alkanes, esters, alcohols, and phenols. The results confirmed that the biocrude derived from pinewood was rich in phenolic derivatives and aromatic hydrocarbons, characteristic products of lignin decomposition. To address liquefaction yield, this study demonstrated the effectiveness of a cosolvent system. A water and ethanol (50/50 wt%) cosolvent was introduced at a 5:1 combined solvent-to-biomass ratio. This improved yield from under 20% when only sCO2 to above 60%, along with improved biomass conversion. This experimental work demonstrates that the integrated sCO2 system, with the implementation of a polar cosolvent blend, offers a promising, scalable pathway to produce high-quality biocrude from lignocellulosic sources, directly supporting the long-term objective of offsetting petroleum dependency in the energy sector.