Transition from fossil-derived fuels to sustainable energy sources requires upgrading routes that minimize dependence on externally supplied hydrogen. In this study, we investigate the hydroprocessing of acid oils using supercritical ethanol as an active reaction medium and renewable in situ hydrogen donor. Above its critical point (240 °C, 63 atm), ethanol enhances mass transfer, solubilization of fatty acids, and hydrogen availability, enabling efficient hydrogenation and hydrodeoxygenation (HDO) without external H2. A cost-effective Ni/beta zeolite catalyst was employed using oleic acid as a model compound and acidulated soybean oil soapstock as a real waste-derived feedstock. Reaction temperature, time, and catalyst loading were systematically evaluated. Near-complete conversion of fatty acids (~100%) and significant deoxygenation were achieved, with a relative hydrocarbon content of 58% at 340 °C, 8 wt% catalyst, and 6 h reaction time, evaluated through normalized GC-MS peak areas. Catalyst loading was identified as the most influential parameter. The results demonstrated that supercritical ethanol acts not only as a solvent but as a key promoter of hydrogen-assisted upgrading, intensifying hydrodeoxygenation reactions while eliminating the need for external hydrogen. This integrated supercritical process offers a sustainable pathway for hydrocarbon production based on low-cost catalysts, renewable alcohols, and waste-derived feedstocks.
The growing use of dry hopping in craft brewing generates substantial amounts of spent hops containing commercially valuable bitter acids and flavonoids. This study evaluates heat pump drying (HPD), conventional drying (CD), and freeze-drying as pretreatments for supercritical fluid extraction (SFE) of bioactive compounds from dry-hopping spent hops, assessing the preservation of bitter acids, xanthohumol, phenolics, antioxidant activity, and color. HPD at 50 °C showed performance comparable to freeze-drying while reducing processing time from 48 h to 120 min, preserving 76% of total phenolics and maintaining high levels of α-acids, β-acids, and xanthohumol. Based on these results, HPD-dried spent hops were selected for subsequent SFE. The effects of temperature (40–80 °C), pressure (15–25 MPa), and ethanol-to-solid mass ratio (0–4:1, w/w) on the recovery of α-acids, β-acids, and xanthohumol were investigated using an experimental design. Temperature and cosolvent ratio were the main factors affecting extraction performance, while ethanol addition proved essential for xanthohumol recovery. Multi-response optimization identified 80 °C, 25 MPa, and a cosolvent mass ratio of 4:1 as the optimal condition, yielding 7.0 g 100 g⁻¹ of α-acids, 3.4 g 100 g⁻¹ of β-acids, and 0.39 g 100 g⁻¹ of xanthohumol. UHPLC-QTOF-MS/MS analysis confirmed the presence of bitter acids and bioactive prenylated flavonoids, including xanthohumol, isoxanthohumol, 6-prenylnaringenin, and 8-prenylnaringenin. Overall, coupling HPD at 50 °C with optimized SFE offers a promising strategy for spent hop valorization, enabling the recovery of bioactive compounds with potential applications in the brewing, food, and pharmaceutical industries.
Conventional experimental diagnostic methods fail to capture the multiphase flow features of in supercritical water circulating fluidized beds (SCWCFBs) owing to extremely high-temperature and high-pressure operating environments. Accordingly, this study quantitatively investigates cluster hydrodynamics in an SCWCFB riser using a three-dimensional two-fluid model coupled with an energy minimization multiscale drag model validated using experimental pressure drop data. The effects of the superficial velocity, solid circulation rate, temperature, and pressure on cluster characteristics are also examined. The results show that the cluster number ranges from 10 to 60, increasing axially from the lower to the upper section, and radially from the tube center to the wall. The clusters have equivalent diameters of 3 mm to 6 mm (7–16 times the particle diameter), with the preferential vertical alignment confirmed by aspect ratios > 1. The average upward cluster velocity is 0.04 m·s−1 to 0.16 m·s−1. A key new finding is the identification of a distinct low-velocity recirculation zone at the radial positions of 9 mm to 11 mm. Higher superficial velocity and pressure reduce the cluster count and size, whereas a higher circulation rate and temperature promote cluster formation and growth. These quantitative results provide hydrodynamic support for designing and optimizing SCWCFB reactors.
