Hydrothermal processing of high-lipid biomass to fuels

Abstract

High-lipid algae are potential sources of biofuels. Lipids in this biomass provide a straightforward chemical route to hydrocarbon-based high energy-density fuels needed for diesel and jet engines. However, current schemes for producing these biofuels require large amounts of energy and solvents to recover the oil. The feedstocks have dilute concentrations (1 wt% or less) in aqueous media, and must be dewatered significantly to form biofuels. A hydrothermal environment, utilizing a highpressure, high-temperature, water-based medium, is well-suited for processing these dilute biomass feedstocks. Conversion of high-lipid model feedstocks to bio-crude oils was investigated over temperatures from 250 to 350 C and a wide range of reaction times (from minutes to several hours). Temperature and pressure controlled batch reactions were performed on Isochrysis sp., and T. Weissflogii. Chemical analysis was performed to give a detailed characterization of the products, including fatty acid conversion and oil yields. Product analysis was thorough enough to be used for simulation of the hydrothermal process. These results were used to fit a model for lipid reactions in hydrothermal systems. Life cycle assessment (LCA) of the algal hydrothermal process was performed for comparison to conventional algal biofuel production techniques. Extraction and conversion to fuels had similar energy inputs for either hydrothermal or extracted oil.