This paper examines the use of organic co-solvent (n-heptane, toluene and anisole, up to 10 wt.%) in the hydrothermal
liquefaction of macroalgal biomass as a means of achieving in situ fractionation of the biocrude product
according to polarity. The filamentous freshwater macroalga Oedogonium was grown under nutrient-depleted
conditions to achieve a low nitrogen content, 1.1 wt.% N. Its hydrothermal liquefaction in a continuous pilot
plant reactor (300–350 °C, 3–5min and2–5 wt.% loadings) yielded up to 25 wt.% (dry ash-free basis, daf) extractable
biocrude. More severe conditions led to biocrudes in higher yields, with reduced oxygen and slightly increased
nitrogen contents, and with lower viscosity. The presence of co-solvents had little effect on the total
biocrude yield but gave rise to in situ separation of the biocrude into distinct fractions associated with the organic
phase (designated solvent oil) and the aqueous phase (designated DCM oil). The amount of solvent oil produced
exceeded the amount that could be extracted at room temperature, by that solvent, from the product mixture obtained
in the absence of co-solvent. The relative proportions and properties of the solvent and DCM fractions varied
with the polarity of the co-solvent. Anisole co-solvent dissolved nearly all the biocrude and the resulting
viscous oil was similar to that obtained without co-solvent. On the other hand, solvent oil produced with n-heptane
(~7.4wt.% daf yield, or ~37% of the total biocrude) had significantly reduced levels of nitrogen (1.1wt.%) and
oxygen (12.5 wt.%) and possessed relatively low viscosity. Toluene co-solvent HTL produced a solvent oil with
intermediate yield and properties. Co-solvent HTL offers a simple and effective means of fractionating HTL
biocrude on the basis of polarity. A non-polar co-solvent such as n-heptane produces an enhanced product fraction
more suitable for hydrotreating than the mixed product obtained without co-solvent.
This paper examines the use of organic co-solvent (n-heptane, toluene and anisole, up to 10 wt.%) in the hydrothermalliquefaction of macroalgal biomass as a means of achieving in situ fractionation of the biocrude productaccording to polarity. The filamentous freshwater macroalga Oedogonium was grown under nutrient-depletedconditions to achieve a low nitrogen content, 1.1 wt.% N. Its hydrothermal liquefaction in a continuous pilotplant reactor (300–350 °C, 3–5min and2–5 wt.% loadings) yielded up to 25 wt.% (dry ash-free basis, daf) extractablebiocrude. More severe conditions led to biocrudes in higher yields, with reduced oxygen and slightly increasednitrogen contents, and with lower viscosity. The presence of co-solvents had little effect on the totalbiocrude yield but gave rise to in situ separation of the biocrude into distinct fractions associated with the organicphase (designated solvent oil) and the aqueous phase (designated DCM oil). The amount of solvent oil producedexceeded the amount that could be extracted at room temperature, by that solvent, from the product mixture obtainedin the absence of co-solvent. The relative proportions and properties of the solvent and DCM fractions variedwith the polarity of the co-solvent. Anisole co-solvent dissolved nearly all the biocrude and the resultingviscous oil was similar to that obtained without co-solvent. On the other hand, solvent oil produced with n-heptane(~7.4wt.% daf yield, or ~37% of the total biocrude) had significantly reduced levels of nitrogen (1.1wt.%) andoxygen (12.5 wt.%) and possessed relatively low viscosity. Toluene co-solvent HTL produced a solvent oil withintermediate yield and properties. Co-solvent HTL offers a simple and effective means of fractionating HTLbiocrude on the basis of polarity. A non-polar co-solvent such as n-heptane produces an enhanced product fractionmore suitable for hydrotreating than the mixed product obtained without co-solvent.
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