Fractional distillation of algae based hydrothermal liquefaction biocrude for co-processing: changes in the properties, storage stability, and miscibility with diesel

Abstract

Hydrothermal liquefaction (HTL) biocrude is a promising source of energy with potential for co-processing with conventional fuels or as a drop-in fuel. However, it needs upgrading to reduce heteroatoms (e.g., N, S, O), improve physical properties, stability, and miscibility with hydrocarbons. Distillation is a conventional physical upgrading method that has not been studied extensively for biocrude using an industry-accepted procedure on a large scale. In this study, an algae-based biocrude was distilled into four fractions using ASTM D2892 standard method: Fraction 1 (<100°C), Fraction 2 (100-175 °C), Fraction 3 (175-275 °C), and Fraction 4 (275-350 °C). The column has 15 theoretical stages, so it is realistic for large scale production. Algae-based biocrude is rich in nitrogen and sulphur content, which causes NOx and SOx emissions contribute to acid rain and soot formation, poisons the upgrading catalysts. Distillation decreased the nitrogen content of all fractions by 18.1 – 91.0%, and a similar reduction in sulphur (up to 71.2%) and oxygen content (up to 15.2%) was also observed in the heavy fractions. Fractional distillation reduced the viscosity and density of biocrude fractions making the fractionated fuel more similar to diesel, which increases the potential for applications either in co-processing or as a drop-in fuel for diesel engines. Stability tests for ten weeks’ storage in three different conditions (4 ℃, 15-33 ℃ and 43 ℃) revealed distillate fractions were far more stable in terms of chemical structure, viscosity, and higher heating value. Miscibility and blending stability tests showed that the miscibility of the distillates mixture (DistMix) was greatly improved due to the reduction in heteroatoms. In addition, the blend was stable after one-month in storage, which all assists potential for co-processing.