Hydrothermal liquefaction of Caulerpa sertularioides: Optimized biocrude production and characterization with pretreatment techniques
Ziba Borazjani, Reza Azin, Shahriar Osfouri, Rahim Karami, Eric M. Kennedy, Michael Stockenhuber
Abstract
Hydrothermal liquefaction (HTL) is presented as an eco-friendly method for producing biocrude from algal biomass, specifically macroalgae, which are abundant resources but often overlooked for biofuel production. This research aimed to create sustainable fuel from macroalgae and explored HTL product yields alongside ultrasonic and microwave pretreatments. Focusing on the green macroalga Caulerpa sertularioides in a batch reactor, the study used response surface methodology to analyze operational parameters like temperature (250–350 °C), pressure (50–150 bar), and feedstock concentration (3–10 wt%). Optimal conditions were identified at 350 °C, 150 bar, and 9.75 wt% feed concentration, achieving a biocrude yield of 22.15 wt%. The biocrude showed a high heating value of 39.17 MJ/kg with energy recovery at 73.19 %. Predominantly consisting of complex cyclic compounds such as acids and ketones, about 35.79 % of biocrude components have boiling points similar to standard diesel oil. However, an upgrading process is necessary due to the high oxygen content. Pretreatment using microwave and ultrasonication at 350 °C did not enhance biocrude yield. • The RSM with the CCD was used to optimize operation parameters of HTL from green macroalgae. • The maximum biocrude yield of 22.15 wt% was obtained at 350 °C, 150 bar, and 9.75 wt% feed concentration. • The major compounds of biocrude were cyclic compounds such as acids, n-containing heterocyclic compounds, and ketones. • The energy recovery peaked at 73.19 %, and the highest HHV of 39.17 MJ/kg was reached at 300 °C and 184 bar. • Ultrasonic and microwave pretreatments reduced solid and biocrude yields while increasing the aqueous phase yields.