Advancing Process Intensification with High-Frequency Ultrasound: A Mini-Review of Applications in Biofuel Production and Beyond

High-frequency ultrasound (HFU) is an ultrasound technology with a frequency higher than 1000 kHz. It has become increasingly recognized as an emerging process intensification technology in various fields, such as biofuel production, carbon dioxide absorption, and wastewater treatment. HFU is seen as a potential intensifier technology for biofuel production, as its mechanisms, such as cavitational phenomena, microstreaming, and fountain formation, can benefit biofuel production. Previous research has shown that HFU can decrease the reaction time required for biofuel production, aid in lipid extraction, increase carbon dioxide absorption rates, and be effective in destroying pathogens in wastewater treatment. However, despite the potential benefits, there are limited reports on the use of HFU technology for biofuel production, which has led to uncertainties and constraints in its industrial deployment. These constraints include equipment design, economic analysis, and safety concerns, which require further in-depth analysis. Despite these limitations, previous studies have shown promising results for the incorporation of HFU into various fields due to its unique characteristics and mechanisms. This paper presents a review of the theory and application of HFU for process intensification, with a focus on its potential for biofuel production. It also provides recommendations for the further exploration of the technology to overcome industrial deployment obstacles.