Process design enhancement of a pilot-scale supercritical-CO2 extraction plant for efficient recovery of wheat germ bioactives

Supercritical carbon dioxide (SC-CO2) extraction is a promising green alternative to conventional solvent-based processes, though its industrial implementation is often hindered by operational instability and high operational costs. This study presents the process optimization of a pilot-scale SC-CO2 extraction unit (50 L) aimed at improving start-up reliability, pressure stability, and energy efficiency. Wheat germ was used as a model agro-industrial by-product. The volumetric efficiency of the dosing pump was increased through the thermodynamic design and installation of a dedicated CO2 subcooler, ensuring stable liquid feeding conditions. Pressure fluctuations inside the extractor were significantly reduced by re-tuning a pneumatically actuated back-pressure valve, resulting in improved control of solvent density and enhanced process reproducibility. Extraction tests conducted at 260 bar and 40–60 °C (CO2 density 800–900 kg·m⁻³) showed that extraction kinetics and yield were strongly influenced by CO2 density under the investigated conditions, with a maximum oil recovery of 6.9 wt%. Analytical characterization confirmed the preservation of polyunsaturated fatty acids (determined as FAMEs) and α-tocopherol (∼2 mg·g−1 extract). Energy analysis demonstrated that the optimized SC-CO2 process requires energy input amount comparable with conventional hexane extraction. These results provide practical guidelines for the scale-up of stable and energy-efficient SC-CO2 extraction systems.