Highly sensitive real-time microwave sensor for detection of organic liquid solvents in an oleic phase

Accurately determining the concentration of organic solvents in an oleic phase is essential for various industrial applications, including enhanced oil recovery. Popular detection methods, like chromatographic and distillation-based approaches, suffer from sample processing-induced solvent loss. There is a lack of standard methods for detecting solvents in produced fluid streams during solvent-aided oil recovery. We propose a novel sensing approach for solvent monitoring using planar microwave sensors. The proposed sensor consists of a chipless tag-reader pair communicating wirelessly using electromagnetic coupling. The sensor has a high sensitivity response to variations in permittivity at various solvent concentrations, which is reflected in the resonance-frequency spectrum. To maximize repeatability response of sensor, the sensor is integrated into a plastic container to form a sensing probe that can be used as an on-site in-line instrument. The experiments were conducted using four solvents, including n-pentane, n-hexane, n-heptane, and ethyl acetate. The results demonstrated that when solvent concentration changes from zero to 20 wt%, the frequency shift of resonance peak changes by 2.71, 2.01, 1.66, and 2.10 MHz for the examined solvents, respectively, indicating an exceptional capability of real-time monitoring for measuring solvents in oleic phase. The proposed approach offers the potential for applying planar microwave sensors to detect organic solvents in industrial processes.