Techno-economic and Environmental Analysis of Algae Biodiesel Production via Lipid Extraction Using Alternative Solvents

Lipid extraction and biodiesel production from algae biomass rely on volatile organic solvents obtained from fossil resources such as hexane, whose use involves high energy consumption for recovery and negative environmental impacts due to their volatile and hazardous nature. This study presents a techno-economic and environmental analysis of using alternative lipid extraction solvents in algae biodiesel production in an effort to understand how they may affect the performance of the process. Lipid recovery (LR), minimum biodiesel selling price (MBSP), solvent intensity (SI), energy intensity (EI), and water consumption (WC) are considered here as performance indicators at process and downstream processing levels. The studied solvents are limonene, ethyl tert-butyl ether (ETBE), and cyclohexane, which were screened in a previous study by the authors, and hexane for reference. The assessment is carried out using data sourced from the literature (upstream processing), while downstream processing data is generated in this study using the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) method and process simulation tools in the absence of experimental data for the solvents. The results indicate that while there is no single candidate solvent that outperforms hexane in every criteria considered here, ETBE and limonene are promising alternative solvents for lipid extraction and should be explored further. For example, ETBE presented the highest LR (95.5%) and lowest MBSP (8.58 $/US gal), while limonene has a SI that is 35% lower than hexane. In terms of EI and WC, ETBE is the best performing solvent after hexane with a 4% difference. The MBSP of ETBE is still around 3.5 times the selling price of fossil diesel, and further efforts to improving the economic viability of algae biodiesel production are still needed. Besides from decreasing algae biomass costs (upstream processing), other improvement opportunities worth exploring in downstream processing includes alternative cell disruption technologies, as this is the most energy intensive stage in lipid extraction. While the use of biobased and less hazardous solvents can help improve the environmental performance of downstream processing in algae biodiesel production, it is recommended that their environmental impacts are quantified on a life cycle basis, i.e., solvent production and disposal.