Life Cycle Environmental Evaluation of Alternative Solvents Used in Lipid ExtractionRThe Case of Algae Biodiesel

Lipid extraction is regarded as a major bottleneck inan industrial-scaleproduction of algae biodiesel because of the use of hazardous solventsand energy-intensive operations for cell disruption and solvent recovery.This study uses life cycle assessment (LCA) to evaluate the environmentalimpacts and primary energy demand (PED) of algae biodiesel productionfrom "cradle to grave", focusing for the first timeon alternative solvents used for lipid extraction and to identifyopportunities for process design improvements. Limonene, ethyl tert-butyl ether (ETBE), and cyclohexane are investigatedalongside the benchmark solvent, hexane. The ReCiPe method is usedto estimate 18 midpoint environmental impacts of "the productionand combustion of 1 MJ of algae biodiesel". Results show thatthe climate change (CC) and PED of algae biodiesel range from 94 to101 g CO2 eq./MJ and 1.59 to 1.65 MJ/MJ, with hexane havingthe lowest CC and PED and limonene the highest. Lipid extraction isidentified as the main hotspot in downstream processing due to thehigh energy consumption for cell disruption (i.e., high-pressure homogenization)and solvent recovery. The use of an acid pretreatment for cell disruptionprior to lipid extraction reduces 11 out of 18 environmental impactsand PED of algae biodiesel for all solvents, including hexane. Overall,this study highlights the critical role of lipid extraction in algaebiodiesel production and the need for improvements in solvents andprocess design. Moreover, the findings provide valuable insights thatcan be applied to improve the environmental sustainability of otherextraction applications. Thispaper evaluates the environmental sustainability ofalgae biodiesel production using alternative solvents for lipid extraction.