**2.12 Solvent extraction**

Solvent extraction is a relatively modern technology used in the extraction of products from its substrates (**Figure 7**). By choosing a solvent that best dissolves the wanted product, this process usually results in higher yields when compared with other methods. The separation is quick and efficient and most of the solvent can be reused. Extraction of oils via this technology is a common application in the industry, normally used after mechanical extraction. Hexane is the most used solvent, but ethanol and isopropanol have also been proposed as alternative options. The Soxhlet extractor is often the preferred method for lipid extraction due to the simplicity of operation, relative safety, and ease of replicating results on an industrial scale [76]. From research, organic solvents such as chloroform, ethanol, and hexane were found to produce the best results when performing lipid extraction from microalgae. Solvent mixtures were also observed to yield better results

**Figure 7.** *Example scheme of solvent extraction technology.*

than mono-solvent extractions, with a 50/50 mixture of chloroform and ethanol leading to 11.76% lipid extracts. As a mono-solvent, chloroform resulted in the highest quantity of lipids extracted at 10.78% with 3 h showing the best extraction efficiency [77]. Solvent extraction also has the potential to be integrated with other processes like supercritical extraction or pyrolysis in order to produce higher value chemicals from bio-oils [78, 79].
