Simultaneous culture and hydrocarbon recovery from Botryococcus braunii with squalane as a solvent

Abstract This study aimed to examine a novel milking process for hydrocarbon recovery from the green microalga Botryococcus braunii with squalane as a solvent. Squalane is a hydrogenated derivative of squalene, one of the hydrocarbon components produced by B. braunii (Race B), and it is considered harmless to the alga. First, we conducted comparative experiments with previously reported organic solvents, followed by two-phase culture experiments to assess the feasibility of long-term culture and extraction. Solvent comparison revealed that squalane can effectively recover hydrocarbons while maintaining high cell viability, particularly in a modified medium supplemented with 0.5% sodium chloride. In a two-phase culture system with squalane as the upper phase, simultaneous hydrocarbon extraction and algal culture were achieved, providing a hydrocarbon recovery rate of 45.1% without compromising photosynthetic activity. Furthermore, the total hydrocarbon production increased by 19.5% compared to that under the control conditions. When unsaturated long-chain hydrocarbons are used as biofuels, hydrogenation followed by cracking is typically necessary. The proposed process, in which the hydrogenated hydrocarbon product itself is employed as the solvent, may reduce the energy input required by eliminating the need for fractional distillation between the solvent and the target product. Future research should aim to develop a practical process by verifying the reuse of botryococcane—the hydrogenated form of the main hydrocarbon produced by B. braunii —as a solvent.