Establishment and performance of a plug-flow continuous hydrothermal reactor for biocrude oil production

It is critical important for continuous production of biocrude oil and scale-up of hydrothermal liquefaction (HTL) technology. Pickering emulsion associated with solid (e.g. ash, char etc.) content is currently identified as a challenge for products recovery. Here, we investigated the continuous biocrude oil production from Spirulina sp., swine manure wastewater-fed Chlorella sp., and biogas wastewater-fed Chlorella sp. with quite different ash content ranging from 5.85% to 26.9%. The continuous reactions were evaluated at 300 °C with a flow rate of 45 mL·min⁻¹ and a solid content of 18%. All the samples were converted into biocrude oil without obvious clogging issues. Subsequent analysis proves the feasibility of steady continuous HTL operation regarding the product yields, nutrients recovery, energy recovery as well as biocrude oil properties. The highest biocrude oil yield (42.3%, dw) was obtained with Spirulina sp. while the highest energy recovery (68.6%) and carbon recovery (59.7%) of biocrude oil were obtained from swine manure wastewater-fed Chlorella sp. Results reveal that higher ash content related to Pickering emulsion led to lower biocrude oil recovery rate. Further studies should focus on addressing the issue, especially for large-scale continuous HTL products separation system.