Life Cycle Environmental Evaluation of Alternative Solvents Used in Lipid Extraction─The Case of Algae Biodiesel

Lipid extraction is regarded as a major bottleneck in an industrial-scale production of algae biodiesel because of the use of hazardous solvents and energy-intensive operations for cell disruption and solvent recovery. This study uses life cycle assessment (LCA) to evaluate the environmental impacts and primary energy demand (PED) of algae biodiesel production from "cradle to grave", focusing for the first time on alternative solvents used for lipid extraction and to identify opportunities for process design improvements. Limonene, ethyl tert-butyl ether (ETBE), and cyclohexane are investigated alongside the benchmark solvent, hexane. The ReCiPe method is used to estimate 18 midpoint environmental impacts of "the production and combustion of 1 MJ of algae biodiesel". Results show that the climate change (CC) and PED of algae biodiesel range from 94 to 101 g CO2 eq./MJ and 1.59 to 1.65 MJ/MJ, with hexane having the lowest CC and PED and limonene the highest. Lipid extraction is identified as the main hotspot in downstream processing due to the high energy consumption for cell disruption (i.e., high-pressure homogenization) and solvent recovery. The use of an acid pretreatment for cell disruption prior to lipid extraction reduces 11 out of 18 environmental impacts and PED of algae biodiesel for all solvents, including hexane. Overall, this study highlights the critical role of lipid extraction in algae biodiesel production and the need for improvements in solvents and process design. Moreover, the findings provide valuable insights that can be applied to improve the environmental sustainability of other extraction applications.