Near-Critical CO2-Assisted Liquefaction-Extraction of Biomass and Wastes to Fuels and Value-Added Products

Abstract

With growing need for sustainable carbon neutral liquid fuels, and low-grade feedstocks such as lignocellulosic biomass, and municipal solid wastes offer sufficient potential via thermochemical conversion. But, existing thermochemical means are limited in feed flexibility, and scalability, require significant processing (energy and costs) of the intermediates. Bio-oil/biocrude intermediate from fast-pyrolysis and hydrothermal techniques is impeded with issues of stability and oxygen content, along with hydrotreating viability. To address these issues, we investigated a novel pathway of near-critical CO2-assisted Integrated liquefaction-extraction (NILE) technology in conceptual aspects for conversion of various biomass and municipal solid wastes into high-quality biocrude with high compatibility for co-hydrotreating with traditional fossil crude for liquid fuel needs in power and transportation sectors. Using supercritical CO2 for dewatering wet feedstocks, for liquefaction and extraction for lighter biocrude has produced biocrude with lower oxygen content by 50%, lowered metal content by 90%, stable viscosity, low acidity, and good aging stability compared to that produced from hydrothermal liquefaction along with higher hydrotreating and co-hydrotreating compatibility. Hydrotreating of the biocrude extract from sCO2 extraction also was feasible with no detected coke deposition, oxygen content of 1% and catalyst deactivation. The validation and capabilities of the NILE concept urges for its further development to obtain sustainable liquid fuels with lower GHG emissions and costs.