Solid-liquid extraction

Solid-liquid extraction is a separation process in which a substance is separated from a solid matrix by dissolving the substance in a suitable solvent. In a second step, the solid and liquid phase (the extract), are then separated, e.g. by filtration. A well-known example of solid-liquid extraction is the extraction of flavourings from coffee powder during coffee brewing.

Solid-liquid extraction is a separation process in which a substance is separated from a solid matrix by dissolving the substance in a suitable solvent. In a second step, the solid and liquid phase (the extract), are then separated, e.g. by filtration. A well-known example of solid-liquid extraction is the extraction of flavourings from coffee powder during coffee brewing.

Important parameters to consider:

• Solvent: The substance should be easily soluble in the solvent used for extraction. It is also advantageous if it also extracts few accompanying substances, i.e. it should dissolve the substance as selectively as possible.
• Temperature and pressure: The temperature during the extraction process influences the solubility of the substance in the solvent. As a rule, solubility is increased at higher temperatures. Pressure only plays an indirect role when extracting in closed vessels at temperatures above the boiling point.
• Time: Longer extraction times improve the yield. However, an equilibrium is reached after a certain time.
• Surface area: The largest possible surface area of the solid sample facilitates the transition to the liquid phase and thus ensures better yields and shorter extraction times. In practice, powders are generally used, so this aspect is of secondary importance.
• Stirring: Stirring during the extraction process ensures that the dissolved substances are quickly removed from the boundary layer between the solid and liquid. The extraction process is faster and more efficient.