Mechanisms and effects of ultrasound-assisted supercritical CO2 extraction

Background: Supercritical CO2 (SC-CO2) extraction is a novel technology, with numerous advantages over conventional extraction methods, such as improved kinetics, extract quality, and environmental sustainability. Nevertheless, low yield and high cost relative to conventional extraction methods limit its industrial practicality. Ultrasound assistance may be useful in addressing some of these limitations, although it simultaneously affects multiple aspects of SC-CO2 extraction. An understanding of these effects is useful to harness ultrasound to address current limitations of SC-CO2 extraction. Scope and approach: In this review the mechanisms of ultrasound assistance are considered in the context of supercritical CO2. These mechanisms are further analyzed to describe the effects of ultrasound on extraction kinetics and to determine the effects of ultrasound under different operating conditions. Ultimately, an understanding of these factors provides a basis to observe the effects of ultrasound on the accuracy of mathematical modelling and the commercialization potential of ultrasound-assisted SC-CO2 extraction. Key findings and conclusions: While there is a promising outlook for ultrasound-assisted SC-CO2 extraction, its benefits are not universal across all extraction conditions. Particularly, its effects are lessened when the substrate particle size is optimized. Ultrasound may also increase temperature, leading to reduced extraction efficiency. While preliminary results in some research work indicate that high-power ultrasound for a short duration is effective, future work should continue to address optimal ultrasound operating parameters. Despite notable reductions in the accuracy of mathematical modelling, due to ultrasound, some adapted models have achieved comparable accuracy. To limit the challenges of a coupled ultrasonic SC-CO2 process, a hyphenated process may also be suitable.