Design and operation of an inexpensive, laboratory-scale, continuous hydrothermal liquefaction reactor for the conversion of microalgae produced during wastewater treatment

Recently, much research has been published on the hydrothermal liquefaction (HTL) of microalgae to form bio-crude, which can be further upgraded into sustainable 3rd generation biofuels. However, most of these studies have been conducted in batch reactors, which are not fully applicable to large-scale industrial production. In this investigation an inexpensive laboratory scale continuous flow system was designed and tested for the liquefaction of microalgae produced during wastewater treatment. The system was operated at a range of temperatures (300 °C – 340 °C) and flow rates (3 – 7 ml min-1), with the feed being delivered using high pressure N2 rather than a mechanical pump. The design incorporated the in-situ collection of solids through a double tube design. The algae was processed at 5 wt% and the results were compared to those from a batch reactor operated at equivalent conditions. By combining high heating rates with extended reaction times, the continuous system was able to yield significantly enhanced bio-crude yields compared to the batch system. This demonstrates the need for inexpensive continuous processing in the lab, to aid in scale up decision making.