Impact of time on yield and properties of biocrude during downstream processing of product mixture derived from hydrothermal liquefaction of microalga

This paper is a study on effects of separation procedures on yield and characteristics of biocrude derived from hydrothermal liquefaction (HTL) of Tetraselmis sp. microalgae. The algae was grown and cultivated in outdoor open raceway ponds. The HTL experiments were performed using 1 l custom built high pressure–temperature reactor with inbuilt magnetic stirrer. HTL experimental studies were conducted at reaction temperature of 350 °C and 15 min holding time using alga solids loading of 16 w/v%. HTL product mixture diluted with dichloromethane (ratio 1:1) was allowed to stand for 1 h, 3 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h and 15 h at room temperature. The result showed that varying stand times for product mixture separation influenced yields in biocrude, solid residue and dissolved aqueous solids. Biocrude yields were in the range of 30 wt% to 56 wt% characterised with higher heating value of ~ 35 to 37 MJ/kg and hydrogen to carbon atomic ratios of 1.56 to 1.95. Maximum yield of biocrude was obtained after 9 h stand time for product mixture and dichloromethane (PM–DCM) mixture. Although, varying PM–DCM mixture stand times showed variation in product yields, there was no clear trend in distribution of elemental contents. Majority of alkali metals distributed in aqueous phase and solid residue, which could be used as nutrients, an alternative to conventional fertiliser.