Hydrothermal Liquefaction of Chlorella pyrenoidosa in Water and Ethanol

Abstract

This study aimed at converting low lipid content microalgae (Chlorella pyrenoidosa) to biofuels via hydrothermal liquefaction (HTL). In this article, ethanol was introduced as a solvent for the HTL process. The products of the HTL process were separated into gas, residue, bio-crude, and volatile components. The effects of using ethanol as the solvent are discussed in detail and compared with the traditional HTL process. Preliminary results showed that HTL with ethanol, compared with using water as the solvent, resulted in higher bio-crude yield (51.1%) with better thermal stability (95% acetone soluble after drying at 105°C), along with lower gas and residue yields (1.4% and 14.2%, respectively). The effects of operating parameters, including feedstock load ratio, solid load ratio, and initial pressure, on processing pressures and product yields were investigated. Experimental results indicated that HTL with a high feedstock load ratio increased the residue yield. Compared with water, ethanol was more suitable for HTL under high solid load ratio conditions. HTL of Chlorella pyrenoidosa with water as the solvent was fairly insensitive to the investigated processing parameters within the measuring ranges. Yields of bio-crude, gas, and residue had average values of 40.5% ±1.7%, 6.3% ±0.7%, and 20.8% ±2.9%, respectively.