Development of a Continuous Liquid-Liquid Extraction of Salicylic Acid with Integrated Membrane Separation

The transition from traditional batch processing to flow has been a key topic in the pharmaceutical and specialty chemicals fields. In many cases, flow operation has advantages over batch in terms of control, safety, and cost. However, the implementation of flow presents different challenges including workforce training, motivating the development of a hands-on training course on the fundamentals of heat transfer, mixing, separation, microreactor assembly in flow chemistry. The work presented focuses on building an efficient flow system for the extraction of salicylic acid. Salicylic acid is an important chemical in the pharmaceutical and cosmetics industries due to its anti-inflammatory and antibacterial properties. It is also the main chemical used in the production of acetylsalicylic acid (ASA); a common over-the-counter medication known as Aspirin. The consumption of free salicylic acid is toxic to humans. Therefore, it is important to ensure that there is no residual salicylic acid in drugs such as Aspirin. In this work, batch extractions have been conducted in different solvent systems to compare their performance. Then the best-performing solvent system was used in a flow system equipped with a static mixer to enhance extraction and a liquid/liquid membrane separator. The concentration of salicylic acid was measured by taking advantage of the reaction between salicylic acid and Fe3+ to produce a violet complex ion that can be detected at 512 nm using spectrophotometry. Compared to batch, flow extractions took less time and were more efficient. In flow extractions, the addition of the static mixer enhanced mixing and showed better extraction. The static mixer enhances interfacial mixing by maximizing contact between the oil and water phases.