Soxhlet extraction is a distillative extraction method that uses a chemical solvent and the extraction unit is equipped with a heated solvent reflux mechanism. These days, Soxhlet extraction is very widely used in chemical laboratories for extraction of a variety of materials (chemical, biological, and polymeric), where the desired compound has a limited solubility in a chosen solvent. Interestingly, the original Soxhlet extraction process was invented in 1879 by Franz von Soxhlet for the extraction of a lipid from a solid material [37].

Oils are extracted from the algae via repeated washing, or percolation, with an organic solvent such as hexane or petroleum ether, under hot reflux in a specially designed glassware setup equipped with a condenser, a dis­tillation path, a siphon arm, a thimble, and a distillation pot [35]. Soxhlet extraction is meant to be a laboratory process for a small-scale operation, but it is very useful for initial technology development. The extraction process is usually slow, taking an hour to several days, depending upon the specifics of the extraction process conditions as well as the specific solvent chosen for the extraction. The energy efficiency per unit mass of product yield is inevitably very low.