Organic solvent extraction-assisted catalytic hydrothermal liquefaction of algae to bio-oil

Abstract

In this paper, we report our investigation into a two-step method of transformation of algae to bio-oil. Elemental analysis, gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy were used to analyze bio-oil. First, organic solvent Soxhlet extraction and reflux extraction were used in the algal extraction step. Ethanol was proven to be the best solvent, and the addition of MgSO₄ could transform acids to esters. In MgSO₄ extraction oil, the yield of hexadecanoic acid ethyl ester was as high as 48.40%. Then, the residual algae powders through the catalytic hydrothermal liquefaction process were converted to bio-oil. Commercialized noble metal catalysts Pd/C, Pt/C, Ru/C and Rh/C combined with Pd/HZSM-5 were used in the second step. Rh/C performed the best in the catalytic hydrothermal liquefaction process, and the highest bio-oil yield of 50.98% and HHV of 30.67 MJ kg⁻¹ were achieved. The oil yield through two steps was higher than that by a direct decomposition step. Also, the two-step method could achieve a higher energy conversion ratio of 85.61% and total energy of 81.09 kJ.