State-of-the-art conceptual design of supercritical carbon dioxide as a green technology involved in bioresource conversion processes

Biomass can be converted into various chemicals, materials, and biofuels through different chemical and biological technologies. In recent years, applications of supercritical carbon dioxide (SC-CO2) in biomass conversion processes are drawing growing attention due to its non-toxic nature and satisfactory physical properties. Several works have reviewed the performance of SC-CO2 in these processes, but the mechanism and relevant potential are rarely concerned. In fact, the mechanisms vary for different applications of SC-CO2, and insights into mechanisms contribute to the development of efficient biomass conversion processes based on SC-CO2 technology. It is widely accepted that operation parameters including temperature, pressure, co-solvent, and treatment time could affect the performance of SC-CO2 on biomass, leading to their physic-chemical property changes. Previous studies proved that the changes are likely to significantly affect the downstream bioenergy recovery and overall economic performance. Accordingly, this review provides a comprehensive review of (i) Mechanisms for different applications of SC-CO2 for extraction, drying, pretreatment and acting as reaction medium, (ii) State-of-the-art applications of SC-CO2 involved biomass utilization processes, (iii) impacts on the physiochemical properties and bioenergy recovery of raw materials after SC-CO2 treatment, (iv) economic analysis of SC-CO2 technology, (v) future outlook for SC-CO2 applications.