Thermodynamic optimization of a staged supercritical CO₂ system for high-purity ‎bioactive separation from coriander seeds

Abstract

This study aims to optimize the thermodynamic behavior and separation performance of a staged supercritical CO₂ (scCO₂) extraction system, using coriander seeds as a model matrix for high-purity essential oil recovery. A sequential cooling–compression strategy first liquefied CO₂ at 25 °C by pressurization above its saturation pressure (≈ 64–65 bar at 25 °C; operated ∼ 70 bar), and then brought the stream above the critical point (P > 73.8 bar, T > 31.1 °C), enabling controlled gas→liquid→supercritical transitions and reducing process irreversibility. A Box–Behnken response surface design evaluated the effects of pump pressure ((100, 150, 200) bar), extraction temperature ((35, 40, 45) °C), and extraction time ((30, 60, 90) min) on yield and composition. Optimal conditions (200 bar, 43 °C, 83 min) produced 5.53 wt% oil with 79.1 % ± 1.6 % linalool (wt%), representing enhanced selectivity and terpene purity. Integrated energy–exergy (2E) analysis identified the liquid-CO₂ pump as the dominant source of irreversibility (42 % of total exergy destruction at the optimum). Reducing discharge-pressure transients by stabilizing the pump near 150 bar decreased exergy destruction by 14 %, while the extractor heating unit operated at 32.6 % energy and 8.0 % exergy efficiency. Overall process efficiencies were 32 % (energy) and 27 % (exergy), with a specific energy demand of 0.62 kWh/kg oil, comparable to best-practice scCO₂ operations. Engineering the phase-transition pathway—rather than relying on extreme conditions—thus improves compound selectivity and lowers energy use, and the staged architecture is readily scalable for bioactive purification.